Monday, December 02, 2013

Winter Storm Looking Likely


1:15 PM Monday update... I just wanted to update everyone with the newest model data.  The purpose is NOT to cause alarm, but raise awareness.  We really need everyone to pay attention to the forecast.  By no means is anything etched in stone.  This forecast can and will likely change.  I have no doubt the cold is coming, but precipitation types and placement can't be pinned down at this point.  

I really don't know where to begin?  This week is going to be complex, yet simple (forecasting) if we just follow what has happened in the past in these situations.  As I always tell you, this blog is not our official forecast.  I want to share with everyone what goes into making a forecast and discuss the possibilities. 

As I have said over the years and I'll always continue to say, arctic air is stronger and faster than what the models predict.  I can't think of a time when this isn't true.  A classic example is last Christmas.  The ice during the day was something I discussed here a couple days prior to the event.  That batch of arctic air... stronger and faster.  

Many of you know how much I LOVE snow, I DO NOT like ice.  I think our best case scanario in central Arkansas is sleet.  That does not adhere to power lines.  Freezing rain scares the you know what out of me.  That coats everything with a heavy layer of ice on trees, power lines, etc.  This is one of the big questions that STILL has to be answered for later this week... PRECIPITATION TYPE AND WHERE THIS SETS UP.  Confidence is very high that very cold air is coming and confidence is growing we'll have a few rounds of wintry weather.  I would even go far enough this far out to say winter storm watches will be issued.  As I said, the precipitation type is in question.  This is a shallow layer of cold air.  The deeper, the better.  This allows precip to fall as sleet and/or snow.  Knowing exactly where these precip boundaries set up will be impossible to predict this far out.  

I want to show you the European model this morning from weatherbell.com.  It has been remarkably consistent and actually shows where it thinks snow and ice is on the ground only by looking at temperature forecasts.  I'll explain below.

One more note to watch in all this.,,  Little Rock has not had an official temperature in the single digits since February of 1996.  That will have to be watched.  It is within the realm of possibilities by the beginning of next week.  Also, it's very possible many areas of the state will spend a few days below freezing.  This is the type of cold that can cause problems with pipes.  Think about that, pets and people!!!! Now onto the models


This is valid Thursday from noon to 6PM.  With ALL of these precipitation maps, it's showing you how much has fallen over the previous 6 hours.  The light blue line is the 35 degree line and the dark blue line is the freezing line.  By 6PM Thursday, it's COLD across much of the state.  HOWEVER, the subfreezing air is held up by the Ozarks.  That's very typical when dealing with shallow, cold air masses.  This is mainly sleet/freezing rain up there in the NW Thursday afternoon.
From 6PM to midnight Thursday, the freezing line is heading south and almost into the metro.  There's a heavy cold rain across the south.

From 6AM Friday to Noon Friday, this is where things get interesting in central and south Arkansas.  The freezing line is near Texarkana over to Warren up to Dumas.  Everyone north of it is cold enough for ice/snow.  Another wave of moisture should override that cold air and produce problems.
Fast forward to Saturday night and Sunday morning.  Another wave of moisture moves across the state and it could be heavy.  The freezing line is still across southern AR so most of this is frozen.  At this time, it's possible the cold air is deep enough for sleet/snow.
Now onto temperture forecasting.  This is valid at 6PM Thursday.  See the pinks covering up the Ozarks?  The model is doing a fantastic job seeing the terrain and bottling up the subfreezing air across far west central Arkansas into the Ozarks.  Remember, arctic air is shallow and the mountains there are tall enough to slow its progress south.  You can also clearly see the arctic boundary over LA into MS.
By Friday at noon, most of central and northern Arkansas is in the teens and 20s as that wave of additional moisture rides over the top.  Wind chill values are brutal at this point.
Now this is AMAZING in my weather geek opinion.  This is valid late Friday at 6PM.  The Euro actually sees where it thinks snow and ice is on the ground.  See the reds and purples in a band from eastern OK through the NW half of the state?  How do I know this just isn't cold air behind the front?  Look at SE Kansas.  It's warmer there than in Arkansas!  That would NOT make sense, UNLESS there's something frozen on the ground here.  Also, look at the River Valley near Clarksville.  See that area of somewhat warmer temperatures?  It's seeing less snow/ice cover there because the arctic air has a tough time getting there due to the mountains.  This is amazing stuff for a weather geek like me.  The model sees accumulating ice/snow all the way into the metro, but barely.  Will this and can this change?  ABSOLUTELY!
By Saturday morning, look at these lows!  Single digits north to teens and 20s central and south. BRRRRRRRRRRRRR.  Once again, you can see where the model thinks there is snow/ice cover.  There's even a swath through south Arkansas at this point.
By Tuesday morning, it's still COLD!  Lows in the single digits and teens across the state.  This cold air will have some "staying power"
In summary, PLEASE REMEMBER THIS BLOG IS NOT A FORECAST!!  We do base our forecasts on what the data tells us.  Here is what we do know... it's going to turn much colder with waves of moisture causing a wintry mix across the state.  Here's what still has to be answered: timing of each wave, precipitation type, and where it sets up exactly.

All I an say at this time is STAY TUNED.

7 comments:

J. Betnar said...

I've been watching this system since Thanksgiving Day, thinking please verify. The models just might have it! The GEM and GFS are dancing around each other, but now the GFS is looking more and more like the Euro. Just need the NAM to keep the forecasts conservative LOL.

ChristiJ said...

I love this post--I don't like watching videos so I really appreciate the pictures and explanations! Super interesting!

Cody Reno said...

Hey Todd,
I really appreciate all the weather data you guys put out for Arkansas. Seeing as this can be in only 4,096 characters I will split this message in half. Thought I might throw in a little help for people wondering what’s going to happen in the future via rain/freezing rain/sleet/snow totals. I’ll make it as simple as I can. Go to http://meteocentre.com/models/. Move your mouse over NWP models and for this example click on GFS. Then scroll down to meteograms-Prec and click on the checkmark. It should come up as Montreal, Canada. Click on the blue where it says USA then New York City should pop up. Click on the little arrow by New York City and 8 cities above should be Little Rock, Arkansas. This is the only station for the state so sorry about that. It should then show Rain Accum, Snow Accum, Ice Pellets (Sleet) Accum, and Freezing Rain Accum. All of this is measured in millimeters so to measure in inches just use your calculator and go with how many millimeters times .04 (roughly). There you will get your inches. The millimeters are on the left part and the dates are on the bottom of each graph (for example Dec06 is measured as December 6th 0z or in our time during standard daylight time it’s December 5th at 6 PM (Go back 6 hours in the winter months, 5 hours with daylight savings time.) Back up near the top of the page you will see where it says latest and that’s the latest model run. I would suggest using the 0z (Midnight) or the 12z (Noon) run as they have weather balloon soundings. To the right of that is precipitation. Click on that and standard should come up so click on that. This will show the Mean Sea Level Pressure. The one below that shows the Thickness pressure in which you always want to watch below the 540 line because it will usually be freezing precipitation. Below that is the 2m Temperature and Dew Point in Celsius. It should show on the left temperatures a little above 10 degrees Celsius which is 50 degrees Fahrenheit and temperatures near or below -10 degrees Celsius which is 14 degrees Fahrenheit. 0 degrees Celsius is 32 degrees Fahrenheit so that is what you should be looking for on the map. Below that is 850-hPA temperatures which is about 5000 feet up but unless you’re really into meteorology just ignore that one. The Precip. Accum. Is just a smaller and less detailed version of what the GFS thinks is going to happen. The Total Cloud Fraction pretty much speaks for itself in terms of the amount of clouds there will be in the sky according to the GFS. The 10m Wind Speed and Gusts are in kilometer per hour and 10 meters is over 32 feet high. To convert from Kilometer to MPH just use your calculator and go with how many Kilometer Per Hour times roughly .62 and you have your wind in miles per hour. Unless you’re really into meteorology don’t worry about the bottom 10 m Wind Barbs (Knots) because it’s basically showing you the wind direction and speed based on the notches on the bars. The next message will have instructions for the rest of Arkansas.

Cody Reno said...

Part 2: Remember, the website is meteocentre.com/models/gfs if you got lost from my last post. If you want to see more of the state of Arkansas in a map (all be it small) just go to NWP models on the top again and again click on GFS. Go down to the bottom and click on Accumulation-Types. It should start out as snow over North America. As I said earlier, I would strongly urge you to use the 0z (Midnight) or 12z (Noon) runs since they have weather balloon soundings. On top it will say the beginning hour and then to the right the ending hour. On the right ending hour click on the down arrow and 240h will be above it which means 240 hours or 10 days so click on that then click go. To change the precipitation type click on type near the top then click on freezing rain or ice pellets (sleet) and on the right once again the precipitation will be measured in millimeters. To convert to inches just use your calculator and go with how many millimeters you see over your area times .04 (roughly) and you’ll have your snow/freezing rain/sleet in inches. Finally, if you want to see what the Canadian model thinks then just click over on model on the left side of the page and click GEM-GLB. It should still be at 240 hours so you can compare the snow/freezing rain/sleet that the American GFS has VS the Canadian GEM model. I’m sure Todd will continue showing you the ECMWF (Euro) model since he has permission to so please watch his the closest since the best model in the business, the Euro, will be on there. Once again, please stay tuned to what Todd, The weatherninja Michael Hook, the rest of the TV weather teams across your viewing area and your local National Weather Service Office for more information on this upcoming winter storm. Thanks for reading and stay safe!

Gusty said...

Congrats to Will (just like last year's Christmas storm) for being the first to mention this on the blog. It's great that Todd allows others to mention the possibilities and then either verifies or dismisses them with his in depth detail and analysis.

Doug Dawson said...

I'm new to the blog and really appreciate the data and explanations associated with it. I too am a native of Arkansas and have always been weather keen, to the point of taking several courses in meteorology and oceanography. I first learned to analyze map data from school studies and from this lay-mans standpoint, I think you are spot on and I also agree on the possibility of colder temps. Regardless, it will be interesting! I'm stocking up on generator fuel and chili makings, bread and milk go without saying. Thanks again for this valuable forecasting tool.

Doug Dawson said...

I'm new to the blog and really appreciate the data and explanations associated with it. I too am a native of Arkansas and have always been weather keen, to the point of taking several courses in meteorology and oceanography. I first learned to analyze map data from school studies and from this lay-mans standpoint, I think you are spot on and I also agree on the possibility of colder temps. Regardless, it will be interesting! I'm stocking up on generator fuel and chili makings, bread and milk go without saying. Thanks again for this valuable forecasting tool.