Not Much Has Changed, 6-12″ for Denver and Possibly More for Areas West and South

Monday 2/1/2016 10:30 AM

Well, over the last few days we’ve gotten pretty deep into what will be happening today and tomorrow and the reasons for the snow that we’ll be experiencing. Today, I’m going to keep it short and sweet!

National Weather Service- Winter Storm Warning

A WINTER STORM WARNING FOR HEAVY SNOW MEANS SEVERE WINTER WEATHER
CONDITIONS ARE EXPECTED OR OCCURRING.  SIGNIFICANT AMOUNTS OF
SNOW ARE FORECAST THAT WILL MAKE TRAVEL DANGEROUS. ONLY TRAVEL IN
AN EMERGENCY. IF YOU MUST TRAVEL...KEEP AN EXTRA FLASHLIGHT...
FOOD...AND WATER IN YOUR VEHICLE IN CASE OF AN EMERGENCY.

Current Conditions

Screen Shot 2016-02-01 at 10.00.53 AM

Current Radar Reflectivity Showing Areas of Snowfall (Brighter Colors Mean Heavier Snow)

Currently, snow is starting to fill in the gaps around the front range and plains and the rates are starting to increase. Heavier bands of snow will begin to make make their home over the eastern foothills and eastern facing mountains slopes as well as along the Palmer Divide in areas like Castle Rock, Elizabeth, and The Pinery.

Forecast

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Current North American Model (NAM) Snowfall Accumulation Predictions

This latest progress by the storm signals what will be a very interesting next 24 hours. Not much has changed with the latest data on this storm. We’re still expecting 6-12″ totals for the Metro Denver area and 8-16″ amounts for the areas west of Wadsworth/US-287 and along the Palmer Divide. The snow is increasing in coverage and intensity currently and will continue to increase through the evening. Moderate to heavy snow rates will continue from early afternoon through early morning tomorrow. 3-6″ should fall around the metro area through this evening and 4-8″ will fall in that same time span along the foothills and Palmer Divide. Tonight and tomorrow morning will net another 3-6″ for the Denver Metro area and 4-8″ for those higher elevation areas. Consistent snow should end around noon tomorrow and snow showers will take its place. While high accumulations are unlikely during tomorrow afternoon’s snow showers, it might add another 1-2″ to our already existing snow.

Blizzard-like conditions will be possible at times with high gusting winds and low visibilities. Avoid all non-emergency travel as roads will be difficult or impossible to pass at times.

A quote from the National Weather Service-

"THOUGH THE MORNING COMMUTE WILL NOT BE TREACHEROUS...ROAD
  CONDITIONS WILL RAPIDLY DETERIORATE THIS AFTERNOON AS SNOW
  ACCUMULATES ON ROAD WAYS. EXPECT HAZARDOUS DRIVING
  CONDITIONS AND POSSIBLY VERY LONG DELAYS FOR THE EVENING
  COMMUTE."

"DON`T BE FOOLED BY THE LACK OF SNOW THIS MORNING. SNOW WILL
  INCREASE MID MORNING AND BY LATE MORNING SNOW WILL BE WIDESPREAD
  ACROSS THE AREA. SNOW WILL CONTINUE THROUGH THE AFTERNOON AND
  EVENING. ROADS CONDITIONS WILL DETERIORATE LATE THIS MORNING AND
  AFTERNOON. IF COMMUTING THIS MORNING...EXPECT MUCH WORSE
  CONDITIONS FOR YOUR RETURN TRIP HOME."

Impacts

Travel conditions will deteriorate as the day progresses. Roads will have increased congestion and will become more icy and snow-packed as the snow falls during the day. DIA has already cancelled many flights and more will likely be cancelled (including most flights from this afternoon through tomorrow morning). As for delayed or cancelled work tomorrow, a lot of that depends on how well snow removal services are performed. CDOT says that they’re ready for this storm and, if that is the case, there probably won’t be a ton of closures. If, however, snow does accumulate on road surfaces in significant amounts and it does not get cleared, cancellations and closures will become a real possibility.

Storm Advice

Snow will become more intense and accumulations will start rapidly adding up. If you are able to leave work early or work from home to avoid the evening rush hour, you are encouraged to do so. Once home, avoid all non-emergency travel while the storm is occurring as this will only congest roads and make the clearing of roads and emergency services more difficult (plus, who doesn’t want to stay inside with some Irish hot chocolate and watch some Netflix or game with big flakes falling?!).

If you can stay home today and tomorrow, that is the best option. You may do well driving on snow, but someone else may not and could pose the potential for an accident. Besides, wouldn’t you rather enjoy the snow from your living room and then venture out when it’s sunny again on Wednesday?!

Regardless of your plans, good luck out there and be safe in your travels!

You can get updates on the storm system with live monitoring as well as daily forecasts with the “My Weather Concierge” app! Forecasts every day from a real person (myself) as well as a “Request Custom Forecast” feature that allows you to get a custom forecast for your event, trip, or personal occasion from an actual Atmospheric Scientist/Meteorologist!

THANK YOU SO MUCH FOR READING! As always, feel free to comment or ask any questions below. I’d love to hear what you thought!

Cheers!

-Andrew

Blizzaster?! No, but Denver Will See Significant Snow!

Important Information Before thScreen Shot 2016-01-31 at 12.29.37 PMe Forecast-

The National Weather Service has issued a Winter Storm Warning for Denver and the
surrounding areas from 5pm today (1/31) through noon on Tuesday (2/2). As a good rule of thumb, travel with an emergency kit including food, water, a snow shovel (or kitty litter if you get stuck), and extra clothing. There will be large amounts of snow over the next 48 hours that could cause you to get stranded if you’re out.

From the NWS-

"A WINTER STORM WARNING FOR HEAVY SNOW MEANS SEVERE WINTER WEATHER
CONDITIONS ARE EXPECTED OR OCCURRING.  SIGNIFICANT AMOUNTS OF
SNOW ARE FORECAST THAT WILL MAKE TRAVEL DANGEROUS. ONLY TRAVEL IN
AN EMERGENCY. IF YOU MUST TRAVEL...KEEP AN EXTRA FLASHLIGHT...
FOOD...AND WATER IN YOUR VEHICLE IN CASE OF AN EMERGENCY."

A Quick Bone to Pick with the Media Hype-Train

As expected, the “B” word has been thrown around a lot over the last couple of days and it’s problematic (and a bit annoying) for more than one reason. To those of us who have experienced heavy snow in Colorado, the word “blizzard” evokes images of being snowed in for days, the shut down of businesses, and digging cars out waste deep snow. freesnow

Realistically, we don’t need the huge amount of snow to have a blizzard and a lot of people learned that hard lesson when the NWS put out a blizzard warning for Denver on November 17th and Denver wound up with only a couple inches of snow. That disappointment came as a result of a fundamental misunderstanding of what a weather phenomena is needed to declare a blizzard. According to the criteria below, the November 17th storm was a blizzard, it just didn’t include a lot of snow.

“To be a blizzard, a snow storm must have sustained winds or frequent gusts that are greater than or equal to 56 km/h (35 mph) with blowing or drifting snow which reduces visibility to 400 m or 0.25 miles or less and must last for a prolonged period of time—typically three hours or more.”

There will be a fundamental difference between the November 17th snow storm and the event that is going to start later this afternoon. This storm system will have much lower winds and that implies that, while this storm will will give us considerably more snow, it won’t technically be a blizzard.

survivedThe point of this seemingly random exercise is to point out the fact that buzz words tend
to get thrown around a lot during these events and, generally, it’s with disregard to their actual meanings. The word “blizzard” hypes people up and it generates more of that sweet sweet ad revenue that news outlets love. Want proof that it gets people all worked up? Head to your local grocery store today if you didn’t go shopping yesterday. It will be in complete chaos with Mad Max style brawls that break out over parking spaces or who gets the last turnip (looking at you Mario). This discussion is not to put news networks or weather anchors on trial, it’s to preach and apply the same logical approach that we take to the weather to the hype-train that so often mis-reports it. Networks generate money through viewership and the best way to create it is to over-hype something. So, the next time the apocalypse is announced on TV, whether or not it pertains to weather, take a step back and look at it logically (I have to do this a lot) and chances are high that it won’t be as big of a deal.

Anyway, enough of my ramblings. On with the forecast!

Storm to Arrive Earlier than Expected

Screen Shot 2016-01-31 at 11.26.43 AM

Simulated Radar Reflectivity over the Rocky Mountain Region Today (1/31) at 6pm

This storm appears just as anxious to get here as we are to see what it has in store for us. The latest data suggests that rather than starting tomorrow morning between 6-8am, we will be getting our first snow from the latest system today between 4-5pm. It will move in from the south initially and then build to the north along the I-25 corridor. While the storm will be coming into the area earlier, it will still stay through Tuesday and that’s really what’s going to give us our larger snow amounts. We aren’t expecting extremely heavy snow rates, but rather, a prolonged period of light to moderate rates with the heaviest snow falling tomorrow afternoon and evening. This provides positives and negatives as far as snow days go. If things start to shut down due to snow or your work is nice enough to keep everyone at home, it will be for longer. On the other hand, if people are able to keep up with clearing the snow as it falls, you might not get the snow day that you’re hoping for. Only time will tell.

The Forecast and Snow Totals

Screen Shot 2016-01-31 at 11.42.49 AM.png

It’s Gonna Get Cold!

Overall, not much has changed as far as what the models are predicting (that’s a good thing! It means they’re high in confidence). Every model run that has come in over the last 48 hours has an average of roughly 12″ for Denver and up to 20″ in the areas of higher terrain such as the eastern foothills and the Palmer Divide. The NAM’s snow forecast (pictured above) is still a bit low on it’s numbers, in my opinion. The other models seem to have a bit more snow, but the picture above gives an accurate illustration of the distribution of the snow totals. With model confidence fairly high in this system, I’m going to keep my forecast at 6-12″ for the Denver Metro area. As you can see from the map above, the northern metro area will get a it less with 5-10″, the west side and foothills will see 10-20″ (with higher amounts on high peaks), and the southern and eastern areas will see 7-14″ of snow. We will get one more good model run later tonight (around 10pm) and another tomorrow morning around (10am) and I will adjust the forecast as necessary after that.

So, for those of you waiting to crank that excitement to 11, you now have permission to go for it! ALL ABOARD THE HYPE-TRAIN!

Snowmaggedon or Snowverreaction? The Latest on Monday and Tuesday’s Snowstorm

Currently, one of the largest snowstorms in Denver history is bearing down on us! Roofs will collapse, flights will be cancelled, metro Denver will grindfrench toast to a halt, shelves will be barren without a single loaf of bread or gallon of milk, life as we know it will cease to exist! Or… maybe not.

There has been plenty of discrepancy between news and weather outlets regarding our latest chance for significant snowfall that will move into the area on Monday and give us some of that upslope precipitation that is a staple of Colorado. For days we’ve seen a guessing game from every authority on weather that has included every forecasted snowfall depth imaginable. Forecasts have ranged anywhere from 2″ to 36″ and seem to have no rhyme or reason to them other than the fact that everyone knows it will snow. All the shouting, over-hyping, and seemingly random forecasts come down to one criteria that I mentioned in my previous forecast, a blocking pattern. The million dollar question right now is; will the storm slow down and stay overhead long enough to really enhance our snowfall accumulations?

What Are The Models Saying?

Surprisingly, the weather models have held true to the position of this system with the exception of some very minor fluctuations. The low pressure center is continually located over the Texas and Oklahoma panhandles and there hasn’t been much uncertainty with it like there was in the November 17th storm when thousands of Denver-ites woke up to substantially less snow than they wanted. So, we’re off to a good start! We know that the low will create upslope winds for Denver and bring us deep moisture from the Gulf of Mexico! That’s the easy part.

Screen Shot 2016-01-30 at 10.17.05 AM

Low Pressure position at 8pm on Monday

Figuring out how long the low will hang out there is the hard part and for answers we have to look to the Hudson Bay. There’s another low pressure system that like to hang out around the Hudson and depending on its intensity and size, it can block other weather patterns to the west of it. The location and relationship of the two lows can be seen in the image below. The models have been having a harder time with resolving the Hudson Bay low and so we’re having a hard time figuring out just how long snow will hang out with us here in Denver. Realistically, for big snow we want a big block and, hence, a big and slow Hudson Low so that our system can stay in place and feed us that moisture. According to the last couple model runs, it does look like things have slowed down a bit and that’s why your local snow forecasts appear to be creeping up in amount.

Screen Shot 2016-01-30 at 10.30.18 AM

Temperature and Wind at 850 mb (if you look close, the USA is hiding in there)

The Final Word

Spinal_Tap_-_Up_to_Eleven

“This one goes to 11”

It looks like we are primed for a big snow event, but the overall accumulations have yet to be determined because they do fluctuate from run to run. I’m actually going to increase my previous forecast a bit and say that we’re looking at 6-12″ for most areas and possibly up to 18″ in some high elevation spots. Snow from this system should start mid-afternoon on Sunday increase in intensity during the night, then heavy snow will fall over night and into Monday morning before tapering off Tuesday afternoon. As you know, our ability to predict the weather greatly increases as we approach the start of the storm and that means that my forecast will likely change tomorrow and a little on Monday morning. If things don’t shift too dramatically, I will probably up my forecast once again, but that is far from a certainty. As I said in my previous post, measured excitement. If your excitement level was at a 5 before, I give you permission to move up to a 7, but no higher than a 7! If we get that blocking pattern and we’re sure about it by Monday morning… I’ll give you permission to go to 11, but not before then!

You can get updates on the storm system with live monitoring as well as daily forecasts with the “My Weather Concierge” app! Forecasts every day from a real person (myself) as well as a “Request Custom Forecast” feature that allows you to get a custom forecast for your event, trip, or personal occasion from an actual Atmospheric Scientist/Meteorologist!

THANK YOU SO MUCH FOR READING! As always, feel free to comment or ask any questions below. I’d love to hear what you thought!

 

Monday Night into Groundhog Day Snowstorm- Measured Excitement

It’s no secret that a big storm is brewing for the plains on Monday and Tuesday. That familiar excitement is floating through the air and the common buzz words like “blizzard”, “large winter storm”, and “f**king snowpocalypse” are beginning to pop up everywhere. OK, maybe not that last one, but it’ll start to appear around the beginning of the weekend if nothing in the weather system shifts too dramatically. For the most part, a lot of the excitement is justified based off of model output and the consistency with which it has shown the Denver Metro Area and Front Range getting significant snowfall. However, while I’m incredibly excited about the upcoming storm and its possibilities, we need to take a more measured and logical approach than the usual hype-train that everyone inevitably gets caught up in when there’s the chance for severe weather. Case in point; the November 17th snow storm where eveitswinterryone was calling for feet of snow up until the day before the event when the forecast actually showed that the majority of the snow would be to the south and east of Denver. The 24 hour forecast did verify pretty well and got a lot of the snowfall amounts correct, but everyone was already so hyped about feet of snow that when Denver got 2″ because rain had switched to snow too late and most of the moisture fell as liquid rather than solid, a mob of Metro area townspeople with pitchforks had formed ready to take off the heads of anyone who got more snow than they did.

While this next storm looks exciting (especially to me since I’ve been following it for about a week now) we’re going to pump the brakes a bit and take a rational look at it because I don’t have ratings and don’t need advertising money. That’s right, I’m only here for you because I love you…. or more importantly, because I love to talk weather! So, the forecast below will follow the standard format that some of you have become accustomed to; background on what it takes to give us a big storm, what is predicted to happen currently in the realm of computer models, and my predictions overall.

Why This Storm System Could Give Us Big Snowupslope

Anyone who has lived in Colorado for a while can tell you about the frequency with which the word “upslope” gets thrown around when winter weather is in the forecast, but a lot of people may still not know exactly what an “upslope” event refers to in meteorological terms. It’s pretty simple overall. An upslope event refers to winds during a storm that move from east to west that go up the slope of the mountains and lifts cool moist air that then turns to snow. It’s really a pretty simple concept and we get it several times a year. It’s Denver’s only real chance of heavy snowfall because of our unique topography with the mountains to the west that blocks a lot of our moisture and creates a rain shadow. Generally these upslope winds are created by a low pressure system that sits near southeast Colorado and flings the moisture against the mountains.

Snow accumulations from upslope storms can be attributed to three primary ingredients, wind speed and direction, atmospheric moisture content, and what meteorologists call “blocking patterns”. We already covered wind direction and wind speed is fairly self explanatory; as wind speed increases, the moisture being brought into the area also increases. Moisture content is a bit more complicated. When we look for big snowfall potential, we want as much moisture as possible through the depth of the atmosphere. For example, below we have two vertical profiles of the atmosphere in Denver where the red line is temperature and the green line is dew point. When the red and green lines are close to each other, there is a lot of moisture in the atmosphere and when they’re further apart, the atmosphere is drier.

On the left, we see today’s atmospheric moisture and winds (arrows on right hand side) which is dry until around 9km up when there is a bit of moisture that could lead to some cloudiness. On the right is the predicted atmospheric profile during the storm on Tuesday. Notice the temperature line and dewpoint line are stacked on top of each other predicting a very moist atmosphere through the lower 6km of the atmosphere and the winds are all heading towards the mountains for that upslope flow. For those that want heavy snow, you really like the right profile!

Finally, we need a blocking pattern for very heavy snowfall. A blocking pattern means that the weather in the US doesn’t change a lot during an extended period of time. This has led to a lot of our largest blizzards here in Colorado; the 2003 blizzard most notably. Unfortunately, it does not look like we will have a blocking pattern for this event, but that doesn’t mean that we can’t get significant snowfall!

So, two of the three parameters are lined up for Tueday’s storm. Not bad!

What Are The Models Saying?

Grooooooo

Storm Position at 5pm on Monday. Low pressure (white lines) centered over the Texas and Oklahoma Panhandles, Moisture/Dewpoint (brighter colors are more moisture) being funneled into the area from the Gulf of Mexico, Upslope Winds (Orange arrows- longer is higher speed)

Groundhogs

Same Map as before but with moisture replaced with Surface Liquid Water Equivalent Precipitation in inches. 1 inch of Liquid Water is approximately 10″ of snow.

We can see in the above maps that the models are predicting some good conditions to make this a heavy snowfall event. The one thing missing that would make this a truly epic storm system is a blocking pattern to keep it over Colorado and help the snow dump for longer, but currently the snowfall is looking pretty significant and that is consistent with what the models have been saying over the last week. Another thing that we need to be cautious about with this system is the position of that low pressure center. If the low moves at all in its position, we can see more or less snow. Possibly even no snow if it moves to a completely new region, but the models seem to like it over the panhandles so far which will really help us with upslope flow and moisture.

Below is the snowfall accumulation map for the storm from Ben Castellani at BoulderCast that I was graciously allowed to use! Make sure you check out Ben’s site if you live in or near Boulder. It’s a great resource. Obviously we’re seeing a pretty bold prediction out of the latest run of the Global Forecasting System (GFS) with 12-24″ of snowfall for the Front Range in the upcoming storm. Compared to most of the other model runs, this is a pretty big outlier but is a similar prediction (albeit a little high) to what we’ve seen for several days worth of model runs, but I would urge caution to anyone thinking that this a serious prediction. Again, leading up to the November 17th event we were seeing model predicted accumulations in Denver of anywhere from 1-4′ of snow and we only got a few inches. If the low ends up in a different spot than we’re predicting, we could see less snow. If the moisture isn’t as deep or plentiful as we’re expecting, we could see less snow. This is only what the current runs of the GFS are saying and, as we all know, the models aren’t perfect and weather is very unpredictable. Again, measured excitement.

BoulderCast_Snowfall

Forecast Precipitation Accumulation for Next Six Days Courtesy of Ben Castellani and BoulderCast

The Final Word

This storm is definitely exciting and isn’t anywhere close to something that we have seen in the last few months. I am more encouraged by this storm than I was during the November 17th storm. The low has a better shape to it and has the ability to bring us more moisture and, while we don’t have a block to keep it here, it does hang around for long enough to give us some significant snowfall. We obviously have plenty of time for this forecast to shift and snowfall amounts to change. In fact, one of the models is predicting that this won’t happen at all, but it seems to be in the minority amongst the 4 or 5 different models that I’ve looked at over the past few days. If we get to late Sunday night and Monday and we’re still looking confidently at 1-2 feet, we can start all the snowpocalypse stuff. But, for now, 4-8″ possibly more, possibly less, and measured excitement.

You can get updates on the storm system with live monitoring as well as daily forecasts with the “My Weather Concierge” app! Forecasts every day from a real person (myself) as well as a “Request Custom Forecast” feature that allows you to get a custom forecast for your event, trip, or personal occasion from an actual Atmospheric Scientist/Meteorologist!

THANK YOU SO MUCH FOR READING! As always, feel free to comment or ask any questions below. I’d love to hear what you thought!

Tonight’s Blizzard (11/16/2015) Could Bring Some Real Significant Snowfall to the Denver Metro Area

Good morning! I have good news for those of you that like winter weather and bad news for those of you that don’t. Denver is under a blizzard warning from tonight at 8pm through tomorrow at 2pm.

What’s a Blizzard Warning?

A blizzard consists of two criteria; *Winds have to be sustained or frequently gusting to at least 35 mph *Falling or blowing snow has to reduce visibility to less than 1/4 mile.

This means that if you can avoid traveling tonight and tomorrow morning, you absolutely should. Conditions will be horrible for travel and probably more problematic than it’s worth. If you have the ability to work from home. I highly recommend that you do.

The Forecast-

12Z NAM Predicted Snowfall

12Z NAM Predicted Snowfall

Storm Start and Duration: The storm should start around 6pm tonight as rain and will transition to snow around 8pm. The heaviest snow will fall between 8pm and 7am, but it won’t completely stop until early afternoon tomorrow.

Snow Accumulations: The last two model runs for the NAM, 4km, NAM, SREF, and GFS have changed the motion for this storm system. The most recent runs have shown that the system will stall for a short time and, therefore, will be able to sling more moisture at us. This has upped the snow totals from the most recent model runs. These snow accumulation totals will depend on a few factors including; when the rain changes to snow, and the temperature of the ground surface when that happens.

  • The southeast side of the metro area (southeast Aurora, Parker, Elizabeth, Palmer Divide region) will see accumulations of 18-24″.
  • Denver and immediate surrounding areas (Arvada, Littleton, Lakewood, Commerce City) will see snowfall accumulations between 8-16″
  • Boulder and surrounding areas (Broomfield, Erie, Louisville, Superior) will see accumulations of 6-12″
Low Pressure (Circle in Middle of Map) Forecast Position at 1pm Local Time Tuesday

Low Pressure (Circle in Middle of Map) Forecast Position at 1pm Local Time Tuesday

The bottom line-

We’ve seen how the models have shifted over the last few days and I’m a bit hesitant to put these accumulations out, but models do improve in accuracy the closer we get to a storm. The other thing that makes me trust these high numbers of snowfall is that they’re being predicted in all the models and not just in one or two. Travel should be avoided once things get going around 8pm. Make sure you have an emergency travel kit in your car if you need to leave. Air travel out of DIA will, more than likely, be cancelled until tomorrow afternoon so, if you have a flight between tonight and tomorrow afternoon, it will be a good idea to reschedule.

Also, it has come up a couple times in the other threads so, I’d like to mention it here. I do have an app and facebook page that I update once a day or more depending on how active the weather is at that time. The facebook page is called Denver Weather Prediction and the app is called My Weather Concierge and it’s has a one dollar per month subscription fee.

-Andrew

Next Week’s Possible Blizzard Forecast and Why It’s Hard to Predict Strong Winter Storms in Colorado

Hi guys, I wanted to do a quick forecast post for the upcoming storm system because I’ve already had quite a few questions about it on here and in a few other places. I will warn you, it’s long, but it’s definitely worth the read.

Current Model Forecast-

Predicted Snowfall Through Wednesday Morning

Predicted Snowfall Through Wednesday Morning (Click to enlarge)

Based off of the current model run, yes, we are supposed to see very heavy snow Monday Night through Thursday of next week. Snow predictions are currently 18-24″ for most of the urban corridor. If this verifies, it will be a true Colorado blizzard and you should buy all the milk and bread that you can immediately. I’m still not sure why only milk and bread. Does everyone make French Toast during blizzards and this is just something that I’ve never experienced? But, I digress.

Why the Current Forecast Can’t be Trusted and Weather Stations Seem to be Split on the Forecast-

Low Pressure Position 00Z GFS Run 11/13/15

Low Pressure Position 00Z GFS Run 11/13/15 (click to enlarge)

In order to bring Colorado these really intense and long snow storms, a lot of factors have to line up perfectly. This storm is no different. We need the low pressure to be in just the right place to produce the winds that sling moisture against the mountains and give us upslope blizzards. This critical position of the low is what makes these storm systems so difficult to predict for Denver. You can see the forecast low pressure for the storm system to the right. As it sits in this image (the blue circles on the Colorado/Kansas border), it’s in the perfect spot to give Denver a ton of snow, but when the new models runs are started, they incorporate current meteorological data which will make them adjust their diagnosis of the upcoming days. Most often, the change has to deal with the storm system position. So, if the low in the image is shifted because of new data, it can take the snow completely out of Denver.

These are the images in chronological order of accumulated snow predicted by the GFS model for the runs from yesterday morning through today. You’ll notice the first image shows 12+ inches of snow for the Denver Metro area. The next three runs had shifted the low pressure to the east which meant that Denver was getting only a couple inches of snow, if any. This type of oscillation in snowfall and system position happens a lot with winter storms and that is one of the main reasons that they’re so difficult to predict. This oscillation of position and Denver snowfall has been happening since I noticed this system over a week ago.WxCartoon_1414881038455_9409753_ver1.0_640_480

This uncertainty creates a problem with all forecasters. There is a chance of an epic snow storm, but the next model run could reveal that it is too far east to create good snow. So, it becomes, do you tell people about the storm system and run the risk of looking like and idiot when there’s only an inch of snow on the ground (this happened a couple times last winter) or do you call for a little snow and then wind up with feet? The answer to this question boils down to one factor; time.

Because the atmosphere is a chaotic system, trying to predict it far in advance is a nightmare for reasons similar to the one above, but as we get closer in time to when the event is supposed to happen, the forecast approves dramatically. So, the opposite of what I want to do is sprout off large storm totals only to have to redact them when we get closer and the model forecasts improve. Realistically, the models are pretty good at resolving systems 24-48 hours in advance so, I’ll be waiting until tomorrow night and/or Sunday to make any crazy predictions.

Your Wall of Text Blows and I Just Want a Quick Forecast-

Alright, here’s my forecast! Gun to my head, I’d say we will get some significant snow. The last four model runs have agreed on the position of the system and the European model that correctly made the forecast for Hurricane Sandy is on board with where the system will set up. With that being said, 72 hours prior to an event is an eternity in the forecast world. So, here’s my suggestion. Err on the side of caution. Get groceries and gas now so that if and/or when things line up and the news stations go ballistic, you won’t have to deal with the chaos that will be gas stations and grocery stores. If nothing happens, you got a couple errands out of the way early. When I’m not trying to be practical, I’m wishcasting the hell out of this storm, but only time will tell.

First Real Snowstorm Tonight for Denver and Eastern Colorado!

Well, it has finally happened. Denver is going to get its first real snowfall of the 2015 fall season which is great news for those of us that like the white and fluffy stuff and not so great of news for the ones that want another 6 months of summer and above average temperatures. All I can say is that I am ecstatic because, regardless of your view of cold weather, there’s actually some kind of interesting weather happening!

Okay, first things first. The National Weather Service has everything north of Colorado Springs under some type of winter weather related warning and since this is a weather page, I should probably start with the most pertinent information. So, here are the warnings (graphic from NWS Boulder)-

  • The Denver Metro area in under a Winter Weather Advisory.
  • The northern I-25 corridor is under a winter storm warning.
  • Areas east of Denver are under a Blizzard Warning

Ok, now that that’s out of the way, on to the forecast!

A cold front and intensifying low will move through Colorado over the next 24-36 hours. It will bring cooler temperatures, intense winds, and everyone’s favorite, snowfall. The system will then move to the northeast and leave the area tomorrow afternoon. So, it’s going to mean that all kinds of fun things will happen for us here in Denver.

Our precipitation will change from rain to snow around 8 or 9pm tonight and will intensify around midnight. Moderate snowfall will happen from midnight until roughly 6am and won’t completely end until late tomorrow morning so make sure that you leave early if you need to be anywhere in the morning.Snowfall totals for the metro area should be 2-4 inches in most places and should be highest to the southeast of the metro area. Northwest locations such as Boulder, Broomfield, and Longmont should see small accumulations of 1-2″. Far eastern Aurora, Centennial, and Parker as well as the Palmer Divide region will see 3-6 inches by morning.

Snowfall Accumulations around Colorado

Snowfall Accumulations around Colorado

Travel in the morning will be hazardous due to icy, slushy, and wet roads. This is especially true in eastern Colorado where blizzard warnings are in effect due to winds that could top 40 mph and heavy snowfall amounts. Give yourself plenty of extra time if you need to go somewhere.

El Nino and Denver’s Winter: Why it’s impossible to predict

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It’s been posted all over news and weather sites for months. It’s been referenced every time that an extreme or interesting weather event has happened. Some tv weather stations have gone as far as to add the adjective “Godzilla” to the the phrase (Which makes no sense to me. I mean really, Godzilla is the king of the Monsters, not some bs makeshift adjective to throw around to make yourself feel important. Don’t sully Godzilla’s good name because you need ratings, gees, but I digress). I’m speaking, of course, of the dreaded EL NINO which is Spanish for….. THE NINO! 

Yes, we are in the clutches of a dreaded El Nino, but what does it mean?! That’s an awfully big question so, I’m going to tackle it in parts below! (if you just want to get down to the nitty gritty Denver details, scroll down to the end)

What is El Nino?

El Nino is a warming of sea surface temperature along the equator to the East of Ecuador, Columbia, and Peru. Below is a map of sea surface temperature anomalies from today (Sept 17, 2015). These anomalies are departures from normal sea temperatures. Over the equator between South American and Indonesia, a belt of warm water can be seen, this is an indication of El Nino.

The warmer sea temperatures and corresponding rainfall from storms shift east towards Indonesia and the Philippines during these times. In addition to largely affecting South America’s fishing industry, El Nino impacts global weather patterns and can vary largely in intensity. The current El Nino is expected to be one of the strongest on record and has a 95% chance of continuing through fall and winter before gradually weakening in the spring of 2016.

Current Sea Surface Temperature Anomaly (Light Blue and Light Yellow are near normal)

Current Sea Surface Temperature Anomaly (Light Blue and Light Yellow are near normal) Click on image for high-res version

“How do you analyze impacts from El Nino?”

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Scales of Analysis

This is where things start to get tricky. As mentioned before, El Nino impacts global weather patterns, there is nothing to debate about that fact. However, when we try to narrow down impacts of El Nino to specific areas like Colorado or Denver, big issues arise in the accuracy of our forecasts. Meteorologists and Atmospheric Scientists use scales of motion to describe weather. We tend to start by looking at the big picture (Global Scale) and then zoom in a bit to an area roughly the size of the US or a continent (Synoptic Scale) followed by zooming in to a local scale such as the Denver Metro area (Meso Scale) and then, possibly, to a neighborhood or specific small area (Micro Scale).

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Water Vapor Image of US at 14:45Z Sep 17, 2015

When we look at El Nino, initially, it’s with a global perspective such as looking at the map of sea surface temperature anomaly above. Obviously, we know that we have a strong El Nino currently taking place and that it is affecting our global weather patterns. Now, we scale it down a bit more and look at the Synoptic scale which is approximately the size of the USA. We can see that El Nino does have some effect on the jet-steams (rivers of high wind speed at high altitudes) and on water vapor transportation, but the extent of these impacts are not known (we just haven’t had enough data and modelling to fully understand them). Now, below the synoptic (USA sized) scale, is when predictions and correlations between El Nino and local weather become very problematic. We know that the Synoptic-Scale weather and the Meso-Scale weather patterns are related and that they influence each other, but if we don’t know the extent of El Nino’s effects on the Synoptic-Scale, we certainly can’t make predictions about its impacts the Meso or Micro-scales. This is similar to the reasoscottyn why, even though there is no doubt that human caused climate change is real, scientists don’t have the ability to make significant predictions about the repercussions other than the fact that we will warm as a planet. WE. JUST. DON’T. HAVE. THE. (computing) POWER!!!! (But, that’s a discussion for another time)

“Yeah Yeah Yeah, but what does it mean for Colorado?”

Trying to predict what winter will hold for Colorado and, more specifically, Denver, when we’re still a couple months away is a very hard endeavor (let’s face it, sometimes we’re terrible at predicting it a few days away). Even with the loads of research that has been done on El Nino as well as the climatologies that have been done on Denver snow storms, we still don’t have a definitive answer to “Does El Nino mean that we will get more snow or a crazier winter?”.

Now, out of the top 10 largest blizzards to hit Colorado, four of them have been during El Nino years. Does that mean that the other 6 were La Nina years? For one of them, yes it was a La Nina year, but for the others we don’t have El Nino/La Nina records for them because they were prior to 1950. In fact, the 7 largest blizzards that do have El Nino/La Nina records, were all during El Nino years, but (and this is important) a sample size of seven events over 23 years of El Nino is NOT incredibly impressive or indicative of large Colorado blizzards being tied to El Nino.

THE BOTTOM LINE

The ultimate take-away from all of this is that we can’t base what our winter will be like on the current influence of the El Nino (Anyone that tells you that a weather event can be attributed to El Nino or climate change is an asshat). It really boils down to what the Synoptic and Meso-scale weather systems do once winter in underway. Could we wind up with an incredibly snowy winter? Yes. Could we have a normal winter? Yes. The Climate Prediction Center has put out it’s seasonal forecast and they have most of Colorado getting above average precipitation and I tend to agree with them based of the moist spring and summer we’ve had, but that can change very quickly. Even if we do have a wet summer it probably won’t be blizzard after blizzard after blizzard (I know, I’m just as disappointed as you). It will more than likely come in the form of an extra storm or two every month. Only time will tell and as soon as the fluffy stuff is in the forecast, I will start to be more brazen about forecasts (And more active on here. Late summer weather is BORING!). So, keep in touch and visit when possible and I will keep you updated!

Cheers!

-Andrew

Let me know what you think about this post! I would love to get some feedback on how it was to read and what you did/didn’t like about the content!

El Nino/Snow/Prediction Websites-

El Nino Discussion

El Nino and La Nina Years

Denver’s Historic Blizzards

Climate Prediction Center

When Severe Weather Strikes on Days Like Today, These are the Instruments We Use

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Weather forecasting has a unique balance of combining the past, present, and future in order to stay informed. Lots of data goes into making forecasts and monitoring current conditions in real time. So, what do we look at? On the average day we look through close to 110 weather maps to do the forecast for severe weather and that’s before we even start monitoring the current weather! As storms develop, a mixture of radar outputs, satellite output images, surface measurements, atmospheric profiles diagrams, and model outputs are monitored to watch storm evolution and track. 20150817_160927