Texas/New Mexico/Louisiana/Mexico Obs And Discussion Thread Part 8

[aggiegeog]

Looks like the I-20 corridor of TX will see a classic snow storm Saturday through Monday. 

[cheese007]

6 hours ago, aggiegeog said:

Looks like the I-20 corridor of TX will see a classic snow storm Saturday through Monday. 

FWD thinks it more likely than not is exclusively a south of I-20 event:

But don`t buy those snowman kits just yet. The main uncertainty
is the track of the upper level low which will dictate the areas
that get snow and the ones that either are cloudy or rainy. As of
now there`s 2 general scenarios, both highlighted in the ensemble
data: a weaker upper low and a more northern track, and a stronger
low with a more southern track. The southern track seems to be the
more likely solution based on cluster analysis of the ensemble
members and the primary deterministic runs of the global models.
This track means that snow potential tapers off dramatically north
of I-20 with Central Texas seeing the higher totals. The weaker
northern solutions means more rain than snow across Central
Texas, with the higher snow totals along the I-20 corridor. But
it`s also worth nothing that a deeper and more southerly track
may also allow the upper low to swing northeast through East Texas
and bring snow northward Sunday evening. All said, it`s too early
to pick a forecast track solution and we will stick close to the
NBM blend. This will advertise the highest PoPs in the Central
Texas Sunday, tapering down to slight chance north of I-20. For
precipitation type, since the surface layer may need to be cooled
by precipitation, it may start out as rain early Sunday but should
transition to snow. Given the cold temps aloft, any areas that do
see sufficient precipitation should cool to near freezing and
accumulations would occur. We do not expect temps to get much
below freezing which will help keep roads more slushy than icy at
least through Sunday night. It`s too early to talk about
accumulation totals, but needless to say accumulations somewhere
in our CWA look like a good bet. Again, the worded forecast will
stay generic with precipitation type being advertised as a rain
and snow mix.

It's like someone built a snow shield over DFW or something

[aggiegeog]

I do think the best snow will be south of DFW, say Waxahachie to Palestine to Marshall. Thankfully this will be basically all snow for N and E TX. If 1" plus QPF verifies in these areas it will be wild, but even 0.5" QPF would make this one of the top snow events for these areas.

 

[aggiegeog]

Wow, looks like we could see a 1982 or even 2010 type event out of this. Models showing maxes around a foot south of I-20 and 3-6" along I-20 with around an inch along the Red River. There will likely be some impressive thundersnow which will drop snow at rates in excess of 2" per hour so even with above freezing surface temps accumulations could be hefty even on roads.

[Chinook]

Models are coming into better agreement with the storm system moving south from the Rockies into Texas. It is kind of strange to see this. Most of the time, when a model shows snow for Dallas, it doesn't really happen. Over the weekend, temperatures will be close to freezing around and south of I-20 with 850mb temps of possibly -2C to -4C. There are a variety of model solutions on snow totals, so this should be interesting to see how this turns out.

[raindancewx]

The GFS seems to be caving to the Euro a bit.

[Powerball]

8 hours ago, Chinook said:

Models are coming into better agreement with the storm system moving south from the Rockies into Texas. It is kind of strange to see this. Most of the time, when a model shows snow for Dallas, it doesn't really happen. Over the weekend, temperatures will be close to freezing around and south of I-20 with 850mb temps of possibly -2C to -4C. There are a variety of model solutions on snow totals, so this should be interesting to see how this turns out.

As good as things are looking, with the shortwave still way out in the middle of the ocean and several days out, it's best to keep expectations in check. If anything, I'm still worried about a miss just to the south. The 06z model runs and 12z NAM were definitely a step backwards.

But yes, this has the potential to be a big one. Probably as good of a setup as you can get for North/Central TX. 

[cheese007]

Given the past 6 years I'll believe it when I see it

[Powerball]

12z GFS has gone back towards a more suppressed look.

[DFWWeather]

As you know, we are in the longest stretch in Weather history of no significant snow or ice for DFW (~6 years). I very much like the pattern for Sunday for a potential winter storm, probably the best setup in years. Some of our best events come form such a 500mb pattern. However, I do see caveats. To bring this into perspective, the models have a had a cold bias at this time range all winter long. I still don't see a large reservoir of cold air to tap into, thus we will need to rely on the storm to manufacture its own cold air, much like the New Year's Eve storm. I am always skeptical on this type of winter storm as 9 times out of 10, it ends up as a cold rain. Assuming the models are correct in the their temperature forecasts, this may not be much of a problem with -25C air at 500mb with system itself. The models do show colder air at 850mb over our area anywhere from -2C to -8C (depending on the model). This translates roughly to 28 to 34 degrees at the surface during the event. Should clouds clear after and we do get some accumulating snow, then we could be dealing with some of the coldest temps so far this winter. This brings me to the next caveat which is the system itself and its eventual track.  It is still out over the water, thus any deviation from the modeled track or change in timing, could greatly effect our outcome. 12z NAM looks pretty good.

Speaking of cold air...I am also liking a transition to a colder period to close out the month. I think the potential is there to tap into some bona fide Arctic air. I am starting to see some of the models latch on to this idea. Perhaps this event will be the transition?

[aggiegeog]

1 hour ago, Powerball said:

12z GFS has gone back towards a more suppressed look.

06Z and 12Z GFS are just an example of the GFS's warm bias, they are 5-10 degrees warmer at the surface than other models otherwise the GFS is the same as the other models. We know we will have a strong upper low crossing the state Sunday with a cold air mass already in place. This upper low will generate a coastal low which will throw a lot of moisture into the path of the cold upper low. I am expecting a 150 mile wide swath of heavy snow across Texas generally along and south of I-20 though that swath could shift 50 miles north or 100 miles south. If you are in the core of the heavy swath though I don't see you missing out totally at this point. We are talking about a potential historic snow event for north Central and East Texas with 0.5-1.5" QPF in areas where the temperature profile suggests primarily a snow precip type.

[Powerball]

21 minutes ago, aggiegeog said:

06Z and 12Z GFS are just an example of the GFS's warm bias, they are 5-10 degrees warmer at the surface than other models otherwise the GFS is the same as the other models. We know we will have a strong upper low crossing the state Sunday with a cold air mass already in place. This upper low will generate a coastal low which will throw a lot of moisture into the path of the cold upper low. I am expecting a 150 mile wide swath of heavy snow across Texas generally along and south of I-20 though that swath could shift 50 miles north or 100 miles south. If you are in the core of the heavy swath though I don't see you missing out totally at this point. We are talking about a potential historic snow event for north Central and East Texas with 0.5-1.5" QPF in areas where the temperature profile suggests primarily a snow precip type.

I'm not even concerned about thermals. 

It's the storm's track and intensity I'm more worried about. 

Gonna need the trough to dig further than what the GFS shows, and for it to come through with at least a neutral tilt for any appreciable snows in the heart of DFW. With the dry air advecting in from the NE gradient around the arctic high, there's going to be a sharper northward cut off than the models are suggesting. 

The 00z GGEM's depiction was just about the best case scenario.

[aggiegeog]

10 minutes ago, Powerball said:

I'm not even concerned about thermals. 

It's the storm's track and intensity I'm more worried about. 

Gonna need the trough to dig further than what the GFS shows, and for it to come through with at least a neutral tilt for any appreciable snows in the heart of DFW. With the dry air advecting in from the NE gradient around the arctic high, there's going to be a sharper northward cut off than the models are suggesting. 

Good point and something to watch out for in DFW. I am not overly bullish on DFW and north. I am thinking Waxahachie, Corsicana, Athens, Tyler and Nacogdoches will be the sweet spot with amount tapering off quickly north of I-20 and areas to the south dealing with rain for some time. Below is the map I put together last night. I think it is still in decent shape though amounts may taper off even more sharply along and north of I-30.

[Powerball]

32 minutes ago, aggiegeog said:

Good point and something to watch out for in DFW. I am not overly bullish on DFW and north. I am thinking Waxahachie, Corsicana, Athens, Tyler and Nacogdoches will be the sweet spot with amount tapering off quickly north of I-20 and areas to the south dealing with rain for some time. Below is the map I put together last night. I think it is still in decent shape though amounts may taper off even more sharply along and north of I-30.

FWIW, I think those amounts are going to end up being low on the western part of your map.

[aggiegeog]

Just now, Powerball said:

FWIW, I think those amounts are going to end up being low on the western part of your map.

I could see that, I haven't focused hard on that area since my audience is generally DFW and E TX. I do think the area between Lubbock/Big Spring and east could see some good totals (likely will up that area to the 7" type range). My biggest question for now is the Amarillo to Wichita Falls area, do they stay in the 1-2" range. Deep East Texas is another tricky forecast as they will have 1-2" QPF but when will the change to all snow occur, the Lufkin to Jasper area could see anywhere from just a mix to 10" of snow.

[Chinook]

The NWS digital forecast is now showing 3-5" of snow west of Dallas (out to 00z Monday)-- this may increase as this forecast incorporates more hours.

Here is the late night Euro-- this is still a pretty large snow accumulation

[aggiegeog]

RGEM seems to be handling the convective nature of this event well even if the QPF may be overdone. Though around 1" QPF for a dynamic system with great moisture is clearly possible. I believe and there will be a number of areas that receive near or over 12" with the area between Hillsboro  and Nacodoches being the most likely stretch to see that. All models give this area between 0.5 and 1.5" QPF with temps supporting primarily snow.

Texas has been waiting 11 years for a Gulf surface low, potent upper low combo pumping moisture into an Arctic air mass.

[DFWWeather]

3 hours ago, aggiegeog said:

RGEM seems to be handling the convective nature of this event well even if the QPF may be overdone. Though around 1" QPF for a dynamic system with great moisture is clearly possible. I believe and there will be a number of areas that receive near or over 12" with the area between Hillsboro  and Nacodoches being the most likely stretch to see that. All models give this area between 0.5 and 1.5" QPF with temps supporting primarily snow.

Texas has been waiting 11 years for a Gulf surface low, potent upper low combo pumping moisture into an Arctic air mass.

First off, there is no Arctic air associated with the system on Sunday. Let's be clear on the source region of the airmass. This airmass did not originate in the Arctic circle or Siberia. It exhibits none of the properties of Arctic airmasses.  It is modified continental and Rocky mountain air. We are all excited by the snow and some impressive amounts are being forecasted by the models. However, none of that is taking into account the amount of snow that will be wasted to melting on impact. Many of the models surface temps are between 34 and 38 degrees (these may be warm given all the models H85 temps), including the NAM, during this event. If temps are being correctly modeled, It is going to be a fight to get accumulations with surface temperatures that warm. So to be realistic, I think your totals are a bit much. Even the NWS is not forecasting anything like that based from this morning AFD, thus this event may not even meet Winter Storm Warning criteria for the Metroplex. What happened in February of 2010 was extraordinary, and I would love to be wrong and it happen again, it just is not likely.

[aggiegeog]

6 minutes ago, DFWWeather said:

First off, there is no Arctic air associated with the system on Sunday. Let's be clear on the source region of the airmass. This airmass did not originate in the Arctic circle or Siberia. It exhibits none of the properties of Arctic airmasses.  It is modified continental and Rocky mountain air. We are all excited by the snow and some impressive amounts are being forecasted by the models. However, none of that is taking into account the amount of snow that will be wasted to melting on impact. Many of the models surface temps are between 34 and 38 degrees (these may be warm given all the models H85 temps), including the NAM, during this event. If temps are being correctly modeled, It is going to be a fight to get accumulations with surface temperatures that warm. So to be realistic, I think your totals are a bit much. Even the NWS is not forecasting anything like that based from this morning AFD, thus this event may not even meet Winter Storm Warning criteria for the Metroplex. What happened in February of 2010 was extraordinary, and I would love to be wrong and it happen again, it just is not likely.

Ok let's call it cold air then. True Arctic air would not support snow. I think its more likely we see temps dropping into the 20s under the heavy bands given the cold temps at 850 and even at 925. Daytime temps for North Central TX outside of the heavy bands will likely be 33 to 35 so there may be some melting. Under the heavy bands we are looking at >2"/hr rates with temps at or below freezing and ground temps not crazy warm given time of year and current cool temps. I am very confident in storm max totals being in the range of a foot or perhaps greater with widespread 6".

[DFWWeather]

15 minutes ago, aggiegeog said:

Ok let's call it cold air then. True Arctic air would not support snow. I think its more likely we see temps dropping into the 20s under the heavy bands given the cold temps at 850 and even at 925. Daytime temps for North Central TX outside of the heavy bands will likely be 33 to 35 so there may be some melting. Under the heavy bands we are looking at >2"/hr rates with temps at or below freezing and ground temps not crazy warm given time of year and current cool temps. I am very confident in storm max totals being in the range of a foot or perhaps greater with widespread 6".

I would agree with you given the impressive cold air aloft with this setup that surface temps should be colder. I would favor temps in the 28 to 32 range during the event with that kind of cold air aloft. I mean when was the last time you saw 528 thickness over DFW (forecast from 0z NAM) and an H85 temp of -7°C with a surface temp of 37°F? Something doesn't compute.  However, given the uncertainty still in this system, I would go with about half of what you are forecasting for right now. I think 2 to 6 looks reasonable, with heavier amounts likely south of I-20 in the Metroplex. However, if the surface temps verify colder, I would agree totals closer to what you have may not be out of the question.

[vwgrrc]

Both GFS and NAM 12z are showing the snow band skipping my area (Denton/Collin Ct). Not an expert here. But wish that's NOT the case for sure!

[cheese007]

FWD thinks the Dallas Snow Shield (TM) remains intact for this event. This lack of snowfall is getting increasingly absurd as time goes on

[aggiegeog]

Looks like QPF is similar on most models determining factor especially for us in E TX will be if it is 33 vs 35 Sunday afternoon. If we end up with the talked about but impossible to forecast convective band cooling then all bets are off and totals will pile up fast. Mid 30s would yield around a 6:1 ratio while low 30s would likely be closer to 8:1. In isolated convective bands we could talk about over 10:1.

[raindancewx]

The snow/precip shield has been trending west on the model runs. I think we'll get some snow in the city.

You can see the snow in NW NM on the 3 km-NAM now

It's gone way west on the GFS too -

The Euro has had some precip in the Rio Grande Valley for a while -

[cheese007]

DFW Snow Shield (TM). Never. Fails.

[vwgrrc]

44 minutes ago, cheese007 said:

DFW Snow Shield (TM). Never. Fails.

RGEM is still your friend

[aggiegeog]

Hi-Res models (MRRR and RAP) have the precip shield further north which gives DFW 3-6" with 6"+ to the west, south and east. Regional models (NAM and RGEM) are a touch south of the Hi-Res giving DFW 1-3".  I-20 may well be shut down Monday from Monroe to Midland with 4-8" along that whole stretch.

[aggiegeog]

21 hours ago, vwgrrc said:

 

22 hours ago, DFWWeather said:

 

Low of 24 here. These colder than expected temps this morning will help cool the ground for tomorrow.

[DFWWeather]

After looking at all the model data this morning. Nearly every model with the exception of the ECMWF shows Tarrant County meeting criteria, at least the southwestern portions of the county anywhere from 4 inches to 9 inches in that area (though this does not account for melting). SREF Member probabilistic guidance of Tarrant county receiving 6 inches of snow is greater than 50%. Some guidance has 4 inches plus as far north as DFW Airport. The ECMWF has shifted everything out west, and appears to be an outlier at this time. If the warmer temperatures verify, then it will be closer to being correct. Therefore, I would not be surprised if Tarrant County gets added to the watch and I fully expect the Watch to get upgraded to a Winter Storm Warning this afternoon. If the latest NAM and Canadian are correct then Dallas County, Ellis, Kaufman and Rockwall would likely need to be added. This does look to be a primarily south of I-20 event, thus the further southwest you are in the Metroplex south of I-20 the better your chances of seeing the most snow. There appears to be a rapid gradient to nothing north of I-30, particularly when you get into Denton and Collin counties.

[StormChazer]

1 hour ago, DFWWeather said:

After looking at all the model data this morning. Nearly every model with the exception of the ECMWF shows Tarrant County meeting criteria, at least the southwestern portions of the county anywhere from 4 inches to 9 inches in that area (though this does not account for melting). SREF Member probabilistic guidance of Tarrant county receiving 6 inches of snow is greater than 50%. Some guidance has 4 inches plus as far north as DFW Airport. The ECMWF has shifted everything out west, and appears to be an outlier at this time. If the warmer temperatures verify, then it will be closer to being correct. Therefore, I would not be surprised if Tarrant County gets added to the watch and I fully expect the Watch to get upgraded to a Winter Storm Warning this afternoon. If the latest NAM and Canadian are correct then Dallas County, Ellis, Kaufman and Rockwall would likely need to be added. This does look to be a primarily south of I-20 event, thus the further southwest you are in the Metroplex south of I-20 the better your chances of seeing the most snow. There appears to be a rapid gradient to nothing north of I-30, particularly when you get into Denton and Collin counties.

Popping I here to pretty much say this. Euro is an outlier, almost all the others show Dallas and Tarrant getting in on it too. 12Z HRRR shows the back end of the low coming though as well, setting up some moderate wrap around bands moving through DFW.

 

I think they’re very much undergoing it at this time.