Snow to Impact Denver with Most Areas Seeing 3-6″ and a Few Seeing 6-12″

Just a quick forecast today.

Storm Timing (snowfall amounts below)-
Rain showers are expected to develop around the Denver metro area around noon and will continue through the afternoon. They are expected to increase in coverage between 5-6pm and change over to snow in the early evening. Snow will continue to fall until early afternoon Saturday.

Snowfall Amounts-
Most areas around Denver and the surrounding suburbs will see 3-6″ of snow by the time everything is done. Lower amounts will be on the north side of town and higher amounts will be to the south and west. Northerly wind will sling moisture onto the Palmer Divide and that will result in the possibility of snow amounts 4-8″ for Highlands Ranch, southern Aurora, and parts of southern Littleton. 6-12″ (possibly higher in small areas) in possible in Castle Rock, Monument, parts of Parker.

I’ll update as new information comes out! Have a great Friday!


UPDATE 1 [12:45]: The National Weather Service has issues a Winter Storm Warning effective until 6pm on Saturday.


The National Weather Service in Denver has issued a Winter Storm
Warning, which is in effect from 6 PM this evening to 6 PM MDT
Saturday. The Winter Weather Advisory is no longer in effect.

* TIMING...Rain and snow showers late this afternoon will change
  to all snow during the early evening. Periods of heavy snow are
  likely during the night. Lighter snow will continue on Saturday
  but road conditions should be improving.

* SNOW ACCUMULATIONS...6 to 12 inches. The heaviest amounts will
  likely be in the southern part of the Denver metro area.

* WIND/VISIBILITY...North winds 15 to 25 mph east of Interstate
  25. Visibility may be reduced to a half mile or less in the
  heavier snow showers tonight.

* IMPACTS...Wet snow may accumulate on already leafed out trees,
  resulting in broken tree limbs and scattered power outages. Some
  roads will become snow and slush covered tonight during the
  heavier snow showers. Road conditions should improve during the
  day Saturday.


A Winter Storm Warning means significant amounts of snow are
expected or occurring. This could make travel hazardous. Residents
are encouraged to check road conditions before you travel and be
prepared for winter travel conditions. Also monitor snow
accumulation on trees and be prepared for possible power outages.

A Bit of Snow and Frigid Temperatures this Weekend


Edit: Holy moly! Way more snow than expected! The model runs late last night did a bit better with snow totals, but they still underproduced. We’ve been dry lately so I can’t argue with some extra snow.

After a bit of moderate weather over the last few days, we’re heading into another arctic air outbreak that will bring us some snowfall along the front range and low temperatures in below zero with pretty severe wind chills. So, if you’re embarking on a journey away from your home to buy Christmas presents, go to the Broncos game, or just down the street to get groceries, be prepared for slippery conditions and very cold temperatures!

Today’s forecast will be broken into the following sections-

  1. Current Conditions
  2. Storm System Timing
  3. Expected Low Temperatures
  4. Expected Snow Totals
  5. Summary

Current Conditions


Large drop in temperature at Marshall, Colorado at ~14:00UTC, which is 7:00am MST. A cold front passage caused the drop and the continuing decrease.

As you can see in the plot above, we experienced a powerful cold front at 7am that dropped temperatures around the metro area 20°F in the course of about thirty minutes. Along with the cold front came some intense winds that are gusting up to 25mph at the airport and are causing wind chill temperatures that hover right around zero. Currently there aren’t a lot of clouds hovering overhead and there aren’t any snowflakes to be be seen… yet.

Storm System Timing

Obviously, we’ve already started down the path of our winter storm with the cold front that passed through earlier this morning. As we continue through the day, our sunny skies will change to that familiar grey that means snow is on its way. Sunset is currently looking to be the time when cloud cover and chance for snowfall really increases. Snowfall around Denver will begin this evening and will continue through tomorrow morning. The frigid temperatures, however, will be sticking around all weekend until we return to highs in the 40s on Monday.

Expected Low Temperatures


Expected low temperatures across the region on Saturday night

Low temperatures are expected to be between 0°F and -5°F for most of the metro area tonight with wind chills that could reach as low as -20°F. Saturday night is expected to be a few degrees colder, but winds are expected to be lighter which means wind chills should remain roughly the same. At this point in time, it looks like our low temperatures will be a few degrees warmer than the record lows for the metro area but there’s always a possibility that will change. Regardless of whether they’re record-breaking or not, please keep your pets inside, dress in layers, and have an emergency kit in your car with a blanket. It doesn’t pay to gamble with these cold temperatures!

Expected Snow Totals

This storm is shaping up to be similar to the last arctic storm that we had which means that we’re looking at 1-3″ for most areas (I know, it’s not thrilling). Denver and the immediately surrounding cities should expect 1-3″ while areas to the south and west can expect 2-4″. Contrary to popular belief, lower temperatures do not mean more snow. In fact, it’s the opposite. Cold air cannot hold as much moisture as warm air and so we get small accumulations with arctic storm systems. This is also why we get lots of snow from our spring blizzards, the warmer air can hold more moisture and dump it on us!

Regardless of how much snow we get, it could be very icy on the roads tomorrow.


Snow will start this evening and will continue through Saturday morning with accumulations for most areas around 1-4″. Temperatures will continue to fall over the next two days and many areas will see below-zero temperatures tonight and Saturday night. Wind chills will be extreme and could be as low as -20°F overnight, which means that precautions should be taken if you need to go outside. These severe low temperatures will continue through Sunday, but 40s will return on Monday.

Thanks for reading! Let me know if you have any questions!


Warmer Temperatures for Denver, Feet of Snow in the Mountains

A brief Denver update, but the main purpose of this is to describe the return of snow, beautiful-beautiful-large-amounts-of-snow, to the forecast for the mountains.

Denver Current Conditions and Near Future Forecast

It is still very cold outside and temperatures will only reach the upper teens and low 20s today around the metro area. Overnight we had a low temperature of -8°F in Denver with a wind chill value -25°F when our winds reached a maximum of 8kts (~9mph) at 11pm at the official Denver weather station at DIA. Luckily, the wind died down as the night progressed and, while the temperatures remained low, the wind chill became less of a factor. Right now, Denver is sitting at roughly 5°F and we should reach highs in the upper teens and low 20s.

Our recent cold snap comes to an end tomorrow when temperatures will climb into the mid-40s and will be around 50°F on Saturday. We will have another slight chance at some light snowfall on Sunday morning as another weak storm system moves through Denver, but accumulations won’t add up to much. While temperatures will again drop next week, they will be close to seasonal temps and will be in the 30s and 40s.

Mountain Snow Forecast

This is the main reason that I decided to make a post today. Break out the skis and wax the board! Great shredding is coming our way! I did a quick overview, described a couple regional forecasts, and a brief word of caution. Check it out!

It finally looks like big precipitation amounts will be coming to the mountains. Current models have loads of moisture coming from the Pacific and impacting most of the western US with the Colorado mountains getting up to five FEET of snow in some areas over the next two weeks. In fact, some areas of northwestern Colorado are expecting over 60″ of snowfall in the next seven days! Overall, most areas along I-70 are looking at 18-36″, but it’s possible that we could see up to four feet of new snow on the taller peaks in that time.


Total snowfall from today through 6pm MST December 22nd, 2016. Notice the 51.7″ amount near Routt County in Northwestern Colorado.

Regional Mountain Forecasts

Medicine Bow/Routt National Forests Including Steamboat Springs

It looks like the Northwestern part of Colorado will be getting the best snow over the last two weeks . Below if a graphic that shows the Quantitative Precipitation Forecast (liquid precipitation in inches) as well as the expected snow totals for the GEFS, CMCE, and NAEFS models. If this forecast were to verify, over five feet of snow will fall in the next seven days! THAT’S “WEEK” SINGULAR! Steamboat Springs and Rabbit Ears Pass are starting to sound pretty good, aren’t they?


Forecasted QPF and snowfall amounts for Medicine Bow/Routt National Forests over the next week. Thanks to the University of Utah for the graphic.

I-70 Corridor

The I-70 corridor is not going to see the same insane amount of snowfall over the next week that Steamboat will. However, there will still be plenty of snowfall over the next week and even more over the next two weeks (3-4 feet expected through the 22nd). Right now, this area is looking at roughly 18-24″ of snow over the next week depending on where you’re targeting on the forecast map. As an example, Vail Pass is expecting upwards of 24″ of snow over the next week while areas slightly to the east are expecting closer to 18″. Still, that’s some great snow when the earlier part of the season had been very dry.


Forecasted QPF and snowfall amounts for Vail Pass over the next week. Thanks to the University of Utah for the graphic.

A Word of Caution

We are all aware that models fluctuate frequently and these totals are anything but set in stone. However, to see this amount of precipitation in the forecast does give me hope and, at the very least, we should see some good snowfall over the next two weeks. Will it be five feet in a week? That’s hard to say, but multiple models are liking the chances of big snow from the next few storms. We’ll have to wait and see, but the mountains could just be an amazing place to be over the next few weeks!

Thanks for reading!


Final Forecast- Timing, Snow Totals, and Temperatures for the December 6th Snow Storm

I’ve been keeping a close eye on this storm for quite a while leading up to today. The promise of snow and possibility of below zero temperatures after a summer that was seemingly endless filled me with endless amounts of excitement. Then again, I’m a winter person and I love cold weather, your feelings about this storm system may vary. Regardless of whether you’re excited about the cold and snowy weather, it has arrived and will make things treacherous over the next 24 hours!

Today’s forecast will be broken into the following sections-

  1. Current Conditions
  2. Storm System Timing
  3. Expected low temperatures (possibly record-breaking)
  4. Expected Snow Totals
  5. Summary

Current Conditions


Visible satellite image 9:15 MST December 6th, 2016

The front range has clear skies and that has contributed to low temperatures in the low teens and even around 10°F over night.In fact, most areas are still hovering right around the 10°F mark currently, but negative temperatures lie just to our north in Wyoming and they will make their way down here by tomorrow tonight. Cloud cover is positioned over the western part of the state and, as this storm system makes its way from west to east, the front range will eventually become cloudy later this morning and afternoon as well.

Storm System Timing

Obviously this system has already started to come through the state with our big drop in temperatures over the last 24 hours and high winds last night (that reached 75mph at the NCAR Mesa Lab!). The snow associated with this storm system should start making its way  into the metro area late-afternoon around 5-6pm and will continue through most of the day tomorrow. Initially, snowfall rates will be light but should start picking up intensity around rush hour this evening. The heaviest snowfall rates should occur late tonight between 9pm and midnight while light snow and flurries will continue through much of tomorrow.

Expected low temperatures (possibly record-breaking)


Forecast Temperatures at 5am MST December 08, 2016

The real story with this storm won’t be the snow totals, but the dangerously low temperatures that we’ll encounter tomorrow night (and tonight to a lesser degree). Lows around the Denver metro area are expected to dip down below zero and will be between -5°F and -10°F for most areas with wind chills that could be between -15°F and -20°F on Wednesday night. Tonight, we’ll still be cold with temperatures in the single digits and wind chills possibly below zero, but the clouds will help keep some heat near the ground whereas tomorrow night, they will not. These are dangerous temperatures and should not be taken lightly. Make sure to keep your pets inside and dress warm and in layers if you have to go outside. Also, make sure that you have an emergency kit in your car that includes a blanket. It will only take 30 minutes to incur frostbite on exposed skin in these temperatures!

Expected Snow Totals


Global Forecast System (GFS) 12Z run Snowfall Totals through 8pm MST December 7th, 2016

I’m expecting 2-5″ for most areas around the front range with slightly higher amounts of 3-6″ along the foothills and more as you venture into the mountains. Bear in mind that this is 2-5″ of snow by Wednesday night. This has been a particularly challenging forecast because of the cold temperatures that will be associated with the snowfall.

Cold temperatures mean that we can get more snowfall accumulation from similar amounts of water. As an example, think of the champagne powder that falls in the mountains. It’s light, fluffy, and very “dry” snow which allows it to move easily and create those brilliant powder clouds that shoot over your head when skiing or snowboarding. By comparison, think about spring storm snowfall. It’s wet, heavy, and incredibly difficult to shovel when it accumulates on your sidewalk.

It all comes down to what is known as the snow to liquid ratio (SLR), which gives a certain amount of snow accumulation per inch of liquid water in the atmosphere. Generally we use a 10:1 ratio which means that we get 10″ of snow to 1″ of water that falls. However, spring storms can be as low as 6:1 or 8:1 and very cold winter storms can be as high as 20:1 or 30:1. For this storm, I’m expecting a SLR of approximately 20:1 due to the low temperatures. This means that we’ll see light and fluffy snow out of this storm and it won’t have a ton of moisture (easy shoveling!). Colorado needs all the precipitation that it can get!


Snow will arrive in town early this afternoon and will continue through Wednesday afternoon. While 3-6″ of snow are expected in most areas, the real hazard will be the dangerously low temperatures in single digits tonight and below zero tomorrow night. Snowfall rates will be most intense over night tonight, but light snowfall will continue through tomorrow and will make commutes slippery and dangerous. Again, make sure that you have an emergency kit in your car and stay warm, friends!

Thanks for reading! Feel free to comment or ask any questions!


Brief Outlook- Bitter Cold and Snow for Denver


Temperature at the National Center for Research Winter Weather Test Site in Marshall, Colorado (Just south of Boulder)- December 05, 2016

Edit: Ignore the (C) on the y-axis of the plot. It’s actually in Fahrenheit but the axis title didn’t chance.

Denver and the surrounding regions have already started to cool off dramatically after the passage of a cold front earlier that has caused temperatures to drop ~14°F in the last few hours. We’re still about 10°F warmer than tomorrow’s expected high temperature of 28°F which means that we still have a lot of cooling off to do tonight. In fact, we’re going to be dropping into the low teens this evening. A Winter Weather Advisory has been issued by the National Weather Service and can be found below.

Winter Weather Advisory-








As we edge closer to the storm system that will impact us tomorrow and Wednesday, some things are clear and others are still a bit fuzzy. What we know is that we will see a pretty drastic change to our weather that has been relatively mild over the last few days and we’ll wind up with frigid temperatures and snow arriving in Denver tomorrow afternoon and continuing through Wednesday. However, we still don’t know just how much snow we’ll actually be getting. There is a bit of disagreement between models, but the overall consensus is that it’s looking like 2-4″ of snow for most areas around Denver that will fall primarily between late afternoon/evening tomorrow through Wednesday morning. Snowfall will be relatively light, but heavier areas in the foothills, mountains, and to the east of Denver are expected.

A more comprehensive forecast will be available tomorrow morning so make sure to check back!

Thanks for reading!


Denver Parade of Lights 2016 Forecast


A joyful family enjoys their local Christmas Parade in Hohman, IL. Through an unprecedented  string of good luck earlier in the month, the father had received a “major award” and their son was recruited to help with the rigorous decryption of important messages. (1940, colorized)

Tonight’s the night! The 2016 Denver Parade of Lights will march past the Denver City and County Building and through the streets of Downtown Denver. First-nighters, packed earmuff-to-earmuff, will jostle in wonderment before a golden, tinkling display of mechanized, electronic joy!

Floats, marching bands, and all sorts of wild acts will fill the streets of Denver to the delight of children and adults-who’ve-had-too-much-hot-chocolate-and-Peppermint-Schnapps alike! However, what will the weather be and what will I need to wear if my Schnapps doesn’t keep me warm enough?! Don’t worry! I’ve got you covered.

Parade Tonight

Tonight’s parade and festivities will definitely be cold as will tomorrow night as well. We’ll be sitting around 26°F when the parade kicks off at 8pm and by the time it ends at its last point around 9 or 10pm, we’ll be around 21°F with wind chills as low as 17°F. Now, bear in mind that these are wind chills for all of Denver and that the winds are really amplified by the tall buildings downtown which means that the temperatures could feel another 5° colder. Some light snow is also possible late this afternoon and early this evening which means road surfaces could be wet or icy. Make  sure that you plan ahead and give yourself extra time, if needed.

Parade Tomorrow

With an earlier start and a sunny day ahead of it, temperatures at the kickoff of the parade tomorrow should be about 10° warmer than they will be tonight at 36°F and a balmy (in comparison) 30°F at the end of the parade. With that being said, there is a higher chance of wind chills tomorrow that could make the forecasted temperatures feel about 5° colder than reality. Tomorrow’s ramp up to the parade promises to be drier as well with sunny skies to get rid of any moisture left on the concrete and asphalt surfaces. It should make for easier watching with the ability to sit on the sidewalk for the kiddies.


A young boy fulfills his dream of speaking with Santa about his love of football only to realize, after the conversation, that his real desire is weaponry.


Overall, it will be cold for either parade and they both will require bundling up and hand warmers. However, the parade at 6pm tomorrow looks to be a little warmer and, more importantly, drier. We all know how hard it is to stay warm if you’re wet and it will be downright impossible if you’re wet and temperatures are in the 20s and 30s. So, if warmer weather is a factor for your voyage to the parade, tomorrow might be the best route. If you’re like me and enjoy pretending that you’re lost in a arctic wasteland and the only salvation is the soft glow of electric sex gleaming in the… ok, that Christmas Story quote doesn’t work here. Let’s try that again. If you’re like me and enjoy pretending that you’re lost in a arctic wasteland and the only salvation is the soft glow of electric lights and the anxious anticipation of seeing Santa in his sleigh, Friday might be right up your alley.

Thanks for reading! As always, feel free to ask questions and I’ll answer as quickly as possible.


First Snowfall Forecast

The day of infinite glory is upon us! Our first snowfall of the 2016/2017 winter is falling in a few places along the front range. The mountains will be getting their fair share of the white fluffy stuff as well as they get some much neededermahgerd relief from the incredibly dry and record-breaking hot weather of the last month.

Assuming that the forecast isn’t completely wrong, we will have our first measurable snowfall of the season just four days before we would have broken the record for the latest first snowfall in Denver history. While this storm isn’t going to dump feet of snow or have you on the couch for days drinking hot cocoa and watching Netflix (it might, who am I to tell you what to do with your life), it is going to give us much needed moisture. For many of us though, this storm is not about the moisture in an increasingly dry year, it gives us  some peace of mind that winter has not forgotten us. It’s a simple reminder that we are, indeed, marching forward towards the holidays, skiing and riding the mountains, winter breaks from school, and that we’re not just stuck eternally in an endless late summer. How sweet it is!

Anyway, this is going to look like a fairly normal forecast and will be broken down into these categories-

  1. Current Conditions
  2. Storm System Timing
  3. Expected Accumulations
  4. Summary (If you don’t want the specifics, skip to this one!)


Current Conditions

Yesterday afternoon we experienced a cold front coming through the area that has kept our temperatures falling for about 12 hours now. Current temperatures are in the mid-30s around the front range and humidity has increased steadily. Yesterday’s cold front brought plenty of cloud cover as we can currently see blanketing the metro area in a wonderful sheet of grey this morning. Snow and rain have just barely started making their way onto the front range and can be seen on the radar image below. Right now we can see plenty of snowfall in the mountains and, although there is some green in areas like Longmont, Westminster, and to the west of Boulder, that is most likely radar noise and not actually rainfall.


Radar Image: 10:00am MST Nov 11, 2016 — Blue signifies snow and green signifies rain, darker colors means heavier snow/rain.

Storm System Timing

The latest model runs show rain and snowfall beginning around town at approximately 11am MST. Initial thoughts were that we were going to get a period of rain followed by a longer period of snowfall that would last until roughly midnight. However, with the cooler temperatures around the metro area, it’s looking like the switch from rain to snowfall should happen sooner rather than later and there’s a good possibility that light snow will be falling in time for the evening rush hour commute. The snow still looks to finish off right around midnight and cloud cover should be clearing out shortly thereafter. I’m so happy to be able to say this… be prepared for very cold temperatures tonight. Most of the front range will be down into the teens and low twenties. Don’t be caught unprepared!

Expected Accumulations

Right now we’re right on par with what we’ve been expecting over the last few days, 1-2″ for the Denver area, 2-4″ for areas south and west along the foothills, and 3-6″ at most mountain locations along the I-70 corridor. There is a possibility for some higher amounts on the high mountain peaks like Echo Mountain, Breckenridge, and Vail, but it isn’t going to effect much down here. Keep in mind that despite the snowfall accumulation predictions, we might not actually see that much laying on the ground because the ground temperature is exceedingly warm from our record breaking temperatures. You will still probably see some accumulation on patio furniture and things of that nature (Don’t tell Kyle Clark), but it won’t be on everything.

You might notice that on the snowfall map there is a lot more snow out east, this is not a glitch. The northeastern plains of Colorado are expecting more snow than the Denver metro area. Make sure that you are prepared for poor driving conditions if you are headed out that way!


Expected snowfall amounts from this storm


This storm has already brought us cooler temperatures and they will continue to stay low today and will be downright frightful tonight with lows in the teens and low 20s.  Snowfall beginning soon will bring 1-2″ for most areas and 3-4″ for a lucky few. Other than wet roads, there shouldn’t be much impact from this storm system today. However, tomorrow 3bbf5610b9b464b562e30cfddc491f39morning could yield a few icy conditions after roads have cooled a bit and remained wet overnight. My best advice for this storm is to enjoy it. We’re a week away from Thanksgiving and are FINALLY getting cold weather!

In my opinion, there has been a lot to make just about anyone anxious lately and the holidays are coming up which can make people even more anxious. That’s why I can’t stress this enough. Even if you don’t like winter, take a page out of Linus’ book and go catch snowflakes on your tongue! It keeps you hydrated and is a great way to remind yourself that life isn’t all about nonsensical bickering!


Thanks for reading! I hope you enjoyed the forecast.


Five Day Forecast Sept 26th, 2016


Beaver Run in Breckenridge Sept 25th, 2017     Photo Credit: Megan Schwartz

Another new product today! I’ll be doing brief weekly weather write-ups on Sundays and/or Mondays for those that wanted something to be posted on a more regular basis. These will be known as “Five Day Forecasts” and will actually include an outlook for the foreseeable future past five days as well. Let me know if there’s anything that you’d like to see in them and I’ll do my best to accommodate your request!

It’s definitely cold outside this morning as temperatures hover in the 40s for most of the state and fresh snow that fell over the weekend blankets the highest mountain peaks. We are certainly living up to the Autumn season after the first official day of meteorological Fall occurred last Thursday the 22nd. A brief respite from cooler temperatures will come again this week, but will transition into cooler temperatures this weekend and early next week. However, our temperatures continue to be above the daily averages this year and we won’t see any big cool downs in the foreseeable future.

Next Five Days

Today- Abundant sun will help us see highs in the mid-70s around town today before cooling down to the mid-40s tonight under clear skies.

Tomorrow (Tuesday)- After a day of recovery from cool temperatures on Monday, highs for the Denver Metro area will be in the upper 70s and low 80s with a few stray clouds. Low temperatures at night will reflect the slight warming trend and will be in the low 50s.

Wednesday- Very similar to Tuesday with highs in the upper 70s and low 80s, mostly clear skies, and lows around 50 degrees.

Thursday- A few more clouds will build into the region as our next small weather system begins to arrive in Colorado. Highs will again be in the upper 70s and low 80s and our overnight lows will be in the mid-50s.

Friday- A low pressure system entering the state will make its way to the eastern plains and will bring a small chance of rain and thunderstorms with it. We’ll see an increase in clouds over Thursday and will have highs that are a few degrees cooler in the mid to upper 70s.


Extended Forecast

This upcoming weekend we’ll see another cool down similar to the one that we had this past Saturday and Sunday, but with one notable difference. Based off of the current model runs, the next storm system that comes into the state on Thursday will intensify on the eastern plains until it continues on its path on Monday. However, there is indication of a second storm system that will immediately follow the first one! Between these two systems, we could be looking at a few light rainy days from Saturday through Tuesday of next week. One thing is certain, we are beginning to see weather patterns that are indicative of active fall and winter weather rather than the ones that produce our boring summer weather!


As always, let me know how I can improve these posts and if you’d like me to cover anything specific.

Thanks for reading!


Denver’s Autumn and Winter Outlook

It’s no secret that the hot and sweaty dog days of summer are over. There’s fresh snow on the mountain tops, grey skies, and even a few changing leaves around town. Over the last few days we’ve noticed a big dip in temperatures around the Rocky Mountain region and we’re beginning to enter a period with seasonally average temperatures, which is a nice departure from what has become the hottest year on record across the globe. However, we seem to have returned to 90° temperatures after having similar cool downs in the last two months. So, there are some real questions


I70 Eastbound Near Frisco on September 16th, 2016

as far as weather cooler temperatures will continue and, realistically, what Fall and Winter will have in store for us.

Let’s dive into these questions, but first, we’ll examine how seasonal forecasts are made, their strengths and shortcomings. As always, I’m going to break this into sections. If you want to skip the science-y stuff and go right to the forecast! No problem, just skip ahead.


  1. Climate and Weather Models
  2. The Farmer’s Almanac
  3. El Nino/La Nina Impacts on Colorado Weather
  4. Fall and Winter Forecasts


Before we continue, something important to note is that climate and weather are NOT the same thing. Weather is short term, smaller in scale and much more erratic. Climate is long term, larger in scale (think all of Earth) and follows trends.

Climate and Weather Models

Trade offs, trade offs, trade offs! It’s no secret that we are not very good at predicting the weather far in advance, but few people actually know why it’s so difficult. It’s comes down to trade offs between length of prediction (how far into the future we’re forecasting) and the size of the area we’re trying to predict. Why? Why does this trade off exist? We’re going to start with something that I saw from my professor, Dr. Sam Ng, multiple times when I was in school. Get out the bongos and get ready to snap your fingers because it’s a poem! Yes, that’s right, a poem by Lewis Fry Richardson who actually changed it from someone else’s poem, but that doesn’t matter.


WRF Model of Hurricane Sandy

“Big whirls have little whirls,
That feed on their velocity;
And little whirls have lesser whirls,
And so on to viscosity.”

Ok, I know what you’re thinking, “This poem sucks”, and you’re not wrong, it does. However, it perfectly describes our current issue with weather and climate modeling. When we talk about the atmosphere we see interactions everywhere. We see the transport of temperature, moisture, soil, gases, mass, aerosols, etc. These motions don’t exist only at large planetary scales, they shrink down to be infinitely small. They also exist in three dimensions that can interact with each other! That’s a “duh!” statement, but we have to make sure that we’re on the same page. Each parameter of the environment has its own unique set of governing equations in addition to the overall equations that describe the motion and evolution of the atmosphere and current computational power isn’t enough to get long range forecasts on small scales that can predict snowfall on a neighborhood by neighborhood basis. Hence, why there are so many botched forecasts.

For example, the NCAR supercomputers that we use to run the Weather Research and Forecasting (WRF pronounced warff) model can compute 5.34 quadrillion calculations per second and yet, they are still extremely limited in their processing abilities for detailed models.

It all comes down to grid spacing within the model structure. Our most detailed operational model, the High Resolution Rapid Refresh (HRRR), operates at 3km grid spacing and forecasts out to 24 hours in the future. It is generally assumed that, in order to resolve a weather feature, three grid points are needed. This means that our most detailed model can only resolve features that are bigger than approximately 5.5 miles. Now 5.5 miles sounds small,  but it could mean the difference between the model predicting that downtown Denver will get hit and then only the areas west of Wadsworth seeing snow and Denver not getting any. Sound familiar from last year when the foothills and southern areas got snow and Denver saw almost nothing?


HRRR Model Forecast Vs. Observed Storm System- Good but not perfect

Due to its high resolution, the HRRR can only realistically be run for short forecasts in the future before it becomes computationally expensive/problematic. It is very reliable for short term forecasts and detail in small areas, but it comes at the cost of only being short term. By comparison, our climate models do very well with long range forecasting, but at the price of detail. We can accurately predict future climate patterns, but we won’t be able to have the fine details of individual weather systems and rainfall/snowfall. So, there’s that trade-off mentioned earlier. We can either use all our processing power on looking far into the future or we have to focus it on looking at very small areas. We can’t do both.


Now, this is assuming that all the data that we have pumped into these models is absolutely perfect and, you know what? It’s just not. We do a fairly good job of making measurements of the atmosphere and feeding it into the models, but the instrumentation sites are sparse and have limitations and that can create problems. Imagine an errant temperature measurement propagating forward in space and time every five minutes for thirty days! SCARY! Overall, our long range (climate) models and very short range (weather) models perform well. It’s those intermediate models that tend to have issues. So, when we are asked what the future holds and what the models are saying about seasonal weather in a particular region, it’s not as straight forward as it sounds.

The Farmer’s Almanac

For some reason, people LOVE the forecasts presented by the Farmer’s Almanac. I’m not entirely sure whether it’s due to nostalgia, good marketing, or maybe people just like to say “almanac”. It is kind of fun to say. Sounds a bit like a french pastry. “I’ll have two croissants and a raspberry almanac!” Anyway, the Farmer’s Almanac really isn’t any more reliable that any other forecast out there (maybe AccuWeather’s 90 day forecast) and its approach to forecasting weather is fairly common sense. They don’t havefarmers-almanac_0 a gypsy fortune teller tied to a weather tower or anything.

According to their webpage-

“We derive our weather forecasts from a secret formula that was devised by the founder of this Almanac, Robert B. Thomas, in 1792. Thomas believed that weather on Earth was influenced by sunspots, which are magnetic storms on the surface of the Sun.”

Apart from the rest of their “secret formula”, which I’m fairly sure is just a fancy way of saying “climatology”, sunspots can be an indicator of weather patterns. EVERYTHING in our atmosphere is driven by solar radiation. Without it, we’re not evaporating water for clouds, temperatures would remain constant and fronts wouldn’t exist (neither would high and low pressure centers), nothing would be happening. So, when a sunspot appears and releases increased amounts of solar radiation, chances are high that we’re going to see additional warming. This is a gross oversimplification of the processes involved, but it conveys the point.

Now, there’s another possible explanation for the love of The Farmer’s Almanac and that’s what’s known as confirmation bias. Many people swear that it’s the only accurate source for weather and, after hearing that enough, others start to believe it and will look for ways (intentionally and unintentionally) to show that it is right. So, when it nails a forecast, everyone praises the Farmer’s Almanac like they did with the “Polar Vortex” outbreaks. However, when Boston had its record breaking snowfall in the 2014/2015 winter, the Almanac had failed to predict it and no one paid attention to it. A prime example of confirmation bias where you only search for data that supports what you already believe. Realistically, it is a good source of rough estimates, but it’s no better than any other source at predicting weather.

As a side note, the Polar Vortex really doesn’t travel into America. Al Roker is an idiot. The Polar Vortex is named for the region that it circles which is…. the north pole. What Al Roker was referring to was an Arctic Cold Front which brings very cold arctic air southward.

El Nino/La Nina Impacts on Colorado Weather


Higher than normal sea-surface temperatures (yellow and red) west of South America during the 1997 El Nino

This is something that needs to be touched on from time to time to remind, even myself, to be aware that there are problems with attributing Denver’s weather to ENSO (El Nino Southern Oscillation). Briefly, increased sea surface temperatures that extend westward for northern South America are classified as El Nino years. Conversely, La Nina years are times with cooler sea surface temperatures. Most often we hear people attribute big snow storms to one or the other.

“This 34 inch blizzard is awesome! I knew El Nino would come through!”

However, looking at the impacts of El Nino or La Nina on a single weather event in Denver isn’t realistic. In fact, there is almost a perfect 50/50 split of Denver’s largest blizzards between El Nino and La Nina years. That’s not to say that it doesn’t effect the weather. It effects weather patterns in a big way and can bring differences in temperature and moisture to different areas, but as far as Denver is concerned, there has never really been a correlation drawn between the ENSO cycle and our weather. This means that all those “We’re transitioning into a La Nina year so we can expect _______!” statements simply aren’t true.

Fall and Winter Forecasts

Over the last week, we’ve seen an extended period of 60 and 70 degree temperatures around the Denver metro area. While a resurgence of mid-80s temperatures will occur this weekend and into the beginning of next week, it looks like our 90 degree days are behind us as we will again see 70s late next week. The current models are showing a typical cool down over the next few weeks and seasonal high temperatures, but they’re also showing almost no precipitation at all. Unfortunately, that looks like a trend that will continue all winter.


Probabilities of higher or lower temperatures from October to December. Orange and reds are above average, blues are below average temperatures.


Probabilites of increased or decreased precipitation. Greens are above average, yellows are below average.

Right now, Denver is looking at a warmer than average winter according to the latest model runs and, unfortunately, that includes the Rocky Mountains as well. The figures above show increased temperature across most of the USA and an equal chance (EC) for above or below normal precipitation. One area of concern is that even if we get plenty of snowfall in the mountains, the warmer temperatures will ensure that it melts off faster and that our water supply is lower come summer. If the current observable trends are any indication, we could be entering into another drought stage later this winter and spring but only time will tell. So, from a climate/seasonal perspective, more of the same. Record breaking heat and drought over much of the United States.

As far as Denver is concerned, it looks like we’ll be warmer than average through all of winter based off of the latest models and information. How much snow or rain we’ll get has yet to be seen, but a wet winter isn’t looking particularly promising.

As always, if you have any questions, feel free to ask here or on Facebook and I’ll get back to you!

Thanks for reading!


Denver’s July Weather and June Summary

June Summary

June finished up with a total of 1.62 inches of rain, which is .36 inches below normal. The average temperature was 70.8 degrees F, which is 3.4 degrees above normal. I find the precipitation number to be a bit misleading since the official Denver station is at DIA. The airport only recorded a trace of rain while downtown got pounded by a strong thunderstorm on the 28th. Finishing up the month 3.4 degrees above average is pretty significant, but not enough to get in the top 5 warmest June’s. 12 days were above 90 degrees with 98 as the hottest temperature recorded.

July Climatology

July is Denver’s hottest month on average with normal highs in the upper 80’s and low 90’s, and average low’s around 60. July tallies 2.16 inches of rain on average, almost a full inch less than June! (With .61 inches of rain already recorded on the 1st of this month, we’re already 1/4th the way there!) The typical day consists of a warm sunny morning, and hot early afternoons followed by afternoon clouds and showers, more so towards the end of the month when the North American Monsoon kicks in. The North American Monsoon is a seasonal change in the upper level patterns. The subtropical ridge, which has clockwise flow around it, is usually centered just to our east or south brining moist air all the way from the Gulf of Mexico. This is moisture in the upper levels, which usually translates to high-based thunderstorms that don’t provide a whole lot of rain, and can be wildfire starters. Cool fronts from the north can slip in cooling things off about 10 degrees and helping to spark some storms.

July 2016 Outlook

Looking at patterns that could affect our monthly weather, one major player is the ENSO oscillation (El Nino and La Nina) over the tropical Pacific Ocean. Summer effects are less so than other seasons, but there is still some correlation. In years transitioning from an El Nino to a La Nina as we likely are this year, July was slightly warmer and wetter than average (Figures 1, 2). The average upper level pattern during those years had a ridge centered just to our south, bringing the usual monsoonal moisture our way (Figure 3). There are other oscillations that can alter long-term weather patterns such as the Pacific North American Oscillation, but those patterns don’t have a whole lot of correlation to our weather in July. Current CFS model runs show a general trough to our west and in our area during the second week of the month indicating normal to slightly cooler temperatures. The subtropical high is shown to build back in during the second half of the month leading to warm temperatures and some monsoonal flow. The Climate Prediction Center is calling for a slightly warm and dry first half of the month, and a warm second half with near average precip.

Enjoy the weather!


(Figure 1) Temperature Anomalies in Celsius, warm colors are above average temperatures, cool colors below normal.


(Figure 2) Precipitation anomalies in mm per day. Blue colors indicate above average precip.


(Figure 3) Average 500mb Heights with clockwise flow around the High pressure center