Possible Winter Storm in the south Sunday and Monday

[Lightning]

I am sure you all have heard about the possiblity of ice, snow and sleet across the deep south for Sunday and Monday. Why are these kind of weather events so tricky, complicated and difficult to forecast?

[TWCToday]

I am sure you all have heard about the possiblity of ice, snow and sleet across the deep south for Sunday and Monday. Why are these kind of weather events so tricky, complicated and difficult to forecast?

A large part of forecasting is based on computer models and analyses. There are several highly regarded models: GFS (American) ECMWF (European) and NAM. There are countless others that are considered less accurate but are used to compare to the main models. Most models are run four times a day. 0z, 6z, 12z, 18z. 0z and 12z models are typically more accurate because they contain the latest observations and balloon launch data from across the country. This year has been VERY tough for forecasters because there have been such HUGE changes in each model run with each model showing a different picture. The Euro might show 20in of snow at 0z then only 1in by 12z. There has been little model consistency this winter. To throw another headache in the system.... Forecasting events in the south is always extra tricky when you have to consider temperatures.

[phw115wvwx]

Here's the reason why forecasting winter storms is so difficult:  A difference of 50 miles in a storm's track can mean the difference between a foot of snow, a quarter inch of ice, or an inch of rain for your area.  Why?  It's because precipitation type is extremely sensitive to the temperature at the surface and aloft.  During one storm last month, I observed the snow suddenly changing over to all sleet, and the forecasters asked me to do a special balloon launch in the storm.  Just above the surface, my balloon revealed a layer no bigger than a thousand feet in depth where the temperature was above freezing.  The highest temperature I recorded in that little layer was just 33.5°F.  One degree can literally mean everything, which is why the storm track is so critical.

Now, try your luck forecasting a storm several days out in the future given how sensitive precipitation type is to the temperature and with how inconsistent the models can be.  The slightest details in the first 24 hours of a model solution can severely affect what the models show by days 3-7, so even the intensity and amount of moisture available for the storm can be highly uncertain.  Some of our models can barely even resolve that 50-mile difference that I mentioned previously.  The bottom line is that it's just not easy.

[toxictwister00]

It's amazing to see the swath of WSW (Winter Storm Watches) that extend from ARK to N/SC. NAM really wants to dump on I-20 a large area of 8-10 inches of snow from Brimingham to Atlanta to Athens and north. But that's only if the latest NAM run has it's way. Speaking of the NAM 00z run is running right now, I'm interested to see what it says. I plan on making a snow map tomorrow night (preliminary) and again Sunday (Final) on this storm, I'm gonna post it here and at other weather forum communities I'm apart of. One of our local mets said this evening to stock up for 2 or more days in case to prepare for the worst.

[WeatherWitness]

I'm going to be interested in seeing if we get anything from this storm. We're going to be on the very tail end of this, so I'm not sure, especially since TWC hasn't said anything about an impact on Texas. However, both TWC and the NWC and predicting a great chance (70-90 percent) of a wintry mix on Sunday and possible flurries later. Obviously, nothing big, but ANY type of wintry precipitation in Dallas is something to note.

It's going to be quite chilly though...we may be below freezing for a couple of days.

[gt1racerlHDl]

What if this stormed caused TWC to have another meltdown?

[TWCToday]

What if this stormed caused TWC to have another meltdown?

Ok....

[gt1racerlHDl]

Ok....

i was being sarcastic 

either way Maria Larosa did a NAM run and it projected 10.6" of snow and ice for Downtown Atlanta

[Localonthe8s]

It was bad sarcasm Alex and Dallas is projected to get around 4" of snow as well. It's been awhile since the Big D has seen flurries

[toxictwister00]

I'm watching this very closely, especially our temps. Seems like we'll be anywhere from the upper teens to low 20's tonight and the clouds are expected to move in late tomorrow morning. I don't want to jump the gun, but I can't see it getting to the upper 30's tomorrow if there's a lot of thick clouds around during the day. The best thing about this is about 90% of this will be all snow since the worst of it will be in the overnight hours. I keep looking at these huge snowfall totals that keep coming out on some of the models and all I can say is I think we warped back to the 70's and 80's because the last time we saw large swaths of 4-8, 8-10 10+ over areas of the South was during that era. We haven't had good snows like that since. It's been nearly a decade since we saw 6 inches. This is definitely going to be fun to watch for sure. Somebody is gonna get whacked hard.

[WeatherWitness]

...and Dallas is projected to get around 4" of snow as well. It's been awhile since the Big D has seen flurries

Wow, that's even more than I thought TWC is predicting a 100% chance of a wintry mix tomorrow; NWS is predicting rain changing to snow. Accumlations expected to be anywhere between 1 and 3 inches. Our high temperatures will be above freezing and the ground is pretty warm, though, so will we have to worry about ice?

And yes, the last time Dallas saw any snow was actually March 2010 (first day of spring, ironically). Can't forget our record-setting 12 inches of snow in February, either.

[Mr. Rainman]

The National Weather Service is calling for 3-6 inches in Chattanooga, with about a foot or more on higher elevations. Of course, we're still 48 hours out on that, so things may change. Lows are supposed to be treacherous throughout the week, though. One model (can't remember) called for lows of 10 in Chattanooga on Thursday, and a low of 1 in Knoxville. GEEZUS!

[toxictwister00]

According to the Memphis NWS, there is a chance of thundersnow there. So snowfall rates could be of excess of 2-3 inches an hour if that occurs which I believe is likely, there looks to be a lot of lift with the development of this storm atm.

EDIT: I forgot to mention this earlier, I was on my NBC affiliate's website and Cheryl Lemkee afternoon update video was forecasting 6-10 inches here. They must have gotten more confident in higher totals because Chris Holcomb was there this morning was saying the model run he showed that had a large area of 6-12 was overdone was thinking more in line with 5 inches, only higher totals in isolated spots.

WSB-TV (ABC) - Brad Nitz forecasting 4-7 inches, he said he was being "conservative" could be higher before mixing starts near the latter end. Also forecasting 1/4-1/2, this is the part that's alraming to me. Hopefully it'll end up being less ice. (This channel is also in "Storm Watch", can't remember the last time I saw that so that's saying something.)

WAGA-TV (FOX) - 5-7 inches

I don't know about the forecast from our CBS affilate

TWC - 4-6 inches Sunday Night, possibility of more accumulations Monday going by the LF.

[WeatherWitness]

This must be a fast-moving system. It has been sunny with not a cloud in the sky all day, and I now only see a few clouds in the sky as I look out the window. So, since we're supposed to get precip. tonight, the storm must be a very quick one.

Here are our latest forecasts:

WINTER STORM WATCH - in effect until Sunday evening

TWC

TONIGHT: A 70% chance of rain, becoming steady after midnight. Low 38.

SUNDAY: A 90% chance of wintry mix in the morning, changing to all snow by the afternoon. High 37. 2 to 4 inches expected.

SUNDAY NIGHT: Cloudy. No more precipitation expected.


NWS

TONIGHT: A 70% chance of rain before midnight, then rain and snow after midnight. Low 35.

SUNDAY: An 80% chance of snow, ending by noon. High 35 and falling. 2 to 4 inches expected.

SUNDAY NIGHT: Cloudy. No more precipitation expected.


For here, it's the timing of this storm rather than the snow accumulation that seems to be debatable.

[TWCToday]

Rather interesting setup. Have to two low pressure systems that will come together off the eastern seaboard. I am getting screwed