Texas Winter 2020-2021

[bubba hotep]

As someone who has been burned for decades now by “sure thing” model snowstorms, I’m trying one last time to inject a little balance into what has become an echo chamber for you DFW folks. This event (meaning ample snowfall for the Metroplex) is far from certain!

The setup is not simple. It’s complex. We’ll be dealing with an upper level low not fully sampled yet by US weather forecasting tools and the possibility of a coastal trough/low developing. What I have seen happen MANY times in Texas is that the upper low shears out as it crosses the state and transfers energy to the coastal trough/low. What happens then? QPF values further north get robbed of moisture and dreams and visions of multi-inch Metroplex snowfall are crushed. Hell, it wouldn’t surprise me in the least that all we get in Austin is cold rain, the heavy snow falls in West Texas and areas of north central and north Texas see minimal amounts of snow.

For the sake of you snow-starved Metroplexers, I hope you get buried with snow! But I worry about y’all getting so certain of an outcome which I think is far from certain. There’s nothing worse than being certain that Lucy won’t pull the football THIS TIME and then finding yourself on your backside because she did it again. For your mental health sake please try and temper those expectations, friends.

Also, we are getting into a funky range over the next 24hrs when globals seem to start struggling with precipitation placement but the event is still a bit far out for hi-res models to really pin down. It seems like we see this impacting forecast often here lately and don't be surprised to see qpf totals jump around pretty significantly between now and tomorrow afternoon. Today is a day to focus on the upper levels and not pay too much attention to smaller scale surface outputs.

[rwfromkansas]

Is the system getting better sampled yet? Still way out in the ocean not much closer.

[bubba hotep]

Is the system getting better sampled yet? Still way out in the ocean not much closer.

12z models were initialized with the system just offshore. So the balloons that go up this afternoon should fully sample it as it will be onshore later this morning.

[gboudx]

Here's Jeff Lindner's take:

A powerful winter storm will impact much of TX this weekend.

Main focus is on the Sunday-early Monday period as a powerful upper level storm system and coastal surface low move across the region bringing various weather types to the area.

Upper level trough currently just off the Oregon coast will move inland today and then drop SSE into the Great Basin on Saturday before ejecting eastward across TX on Sunday. As this trough approaches TX this weekend, coastal surface pressure will lower and a surface low will form in association with the strong ascent that will come to bear over coastal area on Sunday. This surface low will quickly deepen and move generally ENE/E from near Matagorda Bay on Sunday with strong winds developing over the coastal waters. The surface low will also push moisture NW into a deepening cold air mass associated with a cold front that forms under the upper level trough that will move across central and north Texas.

Set Up:
Incoming upstream air mass is not overly cold for this time of year and is more Canadian in origin than Arctic, in fact most of the area will likely remain above to well above freezing well into Sunday evening and it is the lowest few thousand feet of the air mass which is causing all the issues with the potential precipitation type over the area. It will likely be cold enough for snow to form in the higher levels of the atmosphere, but then melt as it falls through the warm layer near the surface. As the upper level cold pocket associated with the upper level trough moves closer to the area on Sunday evening, this warm layer in the lower atmosphere begins to shrink from the top toward the surface. The more this warm layer shrinks, the more snow aloft will begin to reach the ground and mix with rain or transition to snow. Strong lift can also help cool the column of air and some of the models are showing some mesoscale banding of the precipitation and strong precipitation bands which can help locally cool the air mass and allow snow to reach the ground and accumulate due to the increase in the precipitation rates and the pulls of the cold air toward the surface. One would also look for any near surface dry air that can be evaporated to help cool the lower atmosphere…this is looking unlikely in this event as much of the air column looks to become saturated on Sunday.

Forecast:
Think most of the area will start out as rain on Sunday morning and likely remain rain for much of the day. Track of the coastal surface low could result in some moderate to at times heavy rains across the coastal counties on Sunday afternoon and given the soggy grounds in place will need to watch for any run-off issues. As the air column begins to cool Sunday late afternoon into the evening rain will likely begin to mix with snow north of HWY 105 and then potentially become all snow by late evening. Between HWY 105 and I-10 rain could mix with snow late Sunday evening, but this area is much more marginal as it is just south of the track of the upper level cold pocket and south of I-10 expecting all precipitation to remain all rain.

North of HWY 105:
Transition to rain/snow mix then all snow Sunday evening. Some accumulation is possible especially on grassy surfaces and elevated surfaces. Accumulations will be strongly tied to snowfall rates…with heavier rates resulting in maybe a dusting to 1-2 inches of accumulation. Bridges and overpasses in this area may have some concerns late Sunday evening into Monday morning.

HWY 105 to I-10:
Rain/snow mix is possible Sunday evening. Accumulation at this time is not likely

South of I-10:
Precipitation is expected to remain all liquid

Confidence:
While there is increasing confidence, the exact locations of precipitation type, possible accumulations, and impacts remain on the lower side. Any slight deviation of the surface and upper level lows will result in differing forecast for the area and shifting of the current forecast lines. With the upper level system just now entering the upper air network along the US west coast and becoming sampled by this network, better data of this feature will be ingested into models runs later today and early Saturday to help increase forecast confidence.

Jeff Lindner
Director Hydrologic Operations Division/Meteorologist
Harris County Flood Control District

[Ralph's Weather]

The setup is not simple. It’s complex. We’ll be dealing with an upper level low not fully sampled yet by US weather forecasting tools and the possibility of a coastal trough/low developing. What I have seen happen MANY times in Texas is that the upper low shears out as it crosses the state and transfers energy to the coastal trough/low. What happens then? QPF values further north get robbed of moisture and dreams and visions of multi-inch Metroplex snowfall are crushed. Hell, it wouldn’t surprise me in the least that all we get in Austin is cold rain, the heavy snow falls in West Texas and areas of north central and north Texas see minimal amounts of snow.

Do you see this in the data or just climo? We are in the time frame where big issues like this typically are resolved by the models. I think we are down to exact track and where banding sets up.

[orangeblood]

I strongly feel like all the model guidance we have now (still early as system hasn’t moved ashore) is bugged when it comes to temps, which has significant impacts on accumulation amounts etc. With temps that cold aloft, and that much snow falling (12-24 hour period) it’s going to drag that cold air down to the surface, allowing cold air advection to take place keeping us around 32, or below for the entire event. Especially after sundown. (Mid to upper 20’s where snow is heaviest) We have seen this many times with previous events most notably feb 2010.

@orangeblood @Ntxw thoughts?

Yeah, lots of deja vu with this one...set up is very similar except cold air aloft seems colder this time around compared to 2010. The same model biases seem to still exist as they did back then! Although QPF amounts don't seem as high so at this time, I'd go with 50% of Feb 2010 event. 4-6 inch amounts across Metroplex maybe 8 on the southside of DFW

[dhweather]

Don't get your hopes up, this guy will inevitably appear.

[cheezyWXguy]

As someone who has been burned for decades now by “sure thing” model snowstorms, I’m trying one last time to inject a little balance into what has become an echo chamber for you DFW folks. This event (meaning ample snowfall for the Metroplex) is far from certain!

The setup is not simple. It’s complex. We’ll be dealing with an upper level low not fully sampled yet by US weather forecasting tools and the possibility of a coastal trough/low developing. What I have seen happen MANY times in Texas is that the upper low shears out as it crosses the state and transfers energy to the coastal trough/low. What happens then? QPF values further north get robbed of moisture and dreams and visions of multi-inch Metroplex snowfall are crushed. Hell, it wouldn’t surprise me in the least that all we get in Austin is cold rain, the heavy snow falls in West Texas and areas of north central and north Texas see minimal amounts of snow.

For the sake of you snow-starved Metroplexers, I hope you get buried with snow! But I worry about y’all getting so certain of an outcome which I think is far from certain. There’s nothing worse than being certain that Lucy won’t pull the football THIS TIME and then finding yourself on your backside because she did it again. For your mental health sake please try and temper those expectations, friends.

Also, we are getting into a funky range over the next 24hrs when globals seem to start struggling with precipitation placement but the event is still a bit far out for hi-res models to really pin down. It seems like we see this impacting forecast often here lately and don't be surprised to see qpf totals jump around pretty significantly between now and tomorrow afternoon. Today is a day to focus on the upper levels and not pay too much attention to smaller scale surface outputs.

I feel like we are seeing this now. Seeing the 12k NAM go from a nearly uniform shield of precip to these broken areas of precip as the event approaches, makes me think the model is getting within the range to attempt to resolve banding and small scale features, but isn’t within range to do it accurately.

[EnnisTx]

Wxman57?



https://lh3.googleusercontent.com/proxy/8tdPpfrNPAEIWKptWBwVje5cUNtviygnmBScVMyDV0c6qmFAR6q2-Sls9rYZtX0g17oLzShgGA0Knplhpz6tqJtrCbZSjj6RxoM-dic

Don't get your hopes up, this guy will inevitably appear.

[Portastorm]

The setup is not simple. It’s complex. We’ll be dealing with an upper level low not fully sampled yet by US weather forecasting tools and the possibility of a coastal trough/low developing. What I have seen happen MANY times in Texas is that the upper low shears out as it crosses the state and transfers energy to the coastal trough/low. What happens then? QPF values further north get robbed of moisture and dreams and visions of multi-inch Metroplex snowfall are crushed. Hell, it wouldn’t surprise me in the least that all we get in Austin is cold rain, the heavy snow falls in West Texas and areas of north central and north Texas see minimal amounts of snow.

Do you see this in the data or just climo? We are in the time frame where big issues like this typically are resolved by the models. I think we are down to exact track and where banding sets up.

I am speaking merely from an anecdotal, climatological perspective for Texas winter weather setups. But think of it this way ... if a surface low/coastal trough develops along the middle Texas coast which is what NWS is predicting, where is the upper low going to get its moisture from? It'll be raining pretty good in southeast Texas as a result of the surface low. There won't be as much Gulf moisture flowing into North Texas as a result. It's a distinct possibility.

And we're far from exact track of the upper low ... heck, did you see how the 12z NAM has shifted the bulk of the heavier precip further south again? We're getting the proverbial windshield-wiper effect. I won't feel confident about any forecast until tomorrow afternoon. And how many times have we seen Wxman57 tell us the same? Don't trust the models on specifics until you get to the 24-36 hour range. And yes, the short range, hi-res models will help a lot in this regard.

[gpsnowman]

https://lh3.googleusercontent.com/proxy/8tdPpfrNPAEIWKptWBwVje5cUNtviygnmBScVMyDV0c6qmFAR6q2-Sls9rYZtX0g17oLzShgGA0Knplhpz6tqJtrCbZSjj6RxoM-dic

Don't get your hopes up, this guy will inevitably appear.

Haha that gets me every time. Someone a couple years ago called it the "Margaret Hamilton".

[orangeblood]

Latest SREF coming in much more aggressive and further north with QPF amounts...

ARW


NMB


Mean

[Haris]

6z euro decent move S for us in CTX

[cheezyWXguy]

Latest SREF coming in much more aggressive and further north with QPF amounts...

ARW
https://images.weatherbell.com/model/sref-all-arw_c00/tx/total_snow_10to1/1610096400/1610409600-71euv3V8Cx0.png

NMB
https://images.weatherbell.com/model/sref-all-nmb_c00/tx/total_snow_10to1/1610096400/1610409600-aOqyS0RUAeg.png

Mean
https://images.weatherbell.com/model/sref-all-mean/tx/total_snow_10to1/1610096400/1610409600-WWoZUAvARec.png

Orangeblood, what are these models seeing that others like the nam and gfs aren’t?

[TropicalTundra]

Latest SREF coming in much more aggressive and further north with QPF amounts...

ARW


NMB


Mean

That ARW model is very unlikely. Goes from 7.5 inches in Coryell county to just half an inch in Bell county

[ztshanklin]

Latest SREF coming in much more aggressive and further north with QPF amounts...

ARW
https://images.weatherbell.com/model/sref-all-arw_c00/tx/total_snow_10to1/1610096400/1610409600-71euv3V8Cx0.png

Man, that bullseye's my parents in my hometown of Cleburne! Doesn't look too shabby for me in FW either

[bubba hotep]

The setup is not simple. It’s complex. We’ll be dealing with an upper level low not fully sampled yet by US weather forecasting tools and the possibility of a coastal trough/low developing. What I have seen happen MANY times in Texas is that the upper low shears out as it crosses the state and transfers energy to the coastal trough/low. What happens then? QPF values further north get robbed of moisture and dreams and visions of multi-inch Metroplex snowfall are crushed. Hell, it wouldn’t surprise me in the least that all we get in Austin is cold rain, the heavy snow falls in West Texas and areas of north central and north Texas see minimal amounts of snow.

Do you see this in the data or just climo? We are in the time frame where big issues like this typically are resolved by the models. I think we are down to exact track and where banding sets up.

12z 3k NAM shows this pretty clearly if you track the frontogenesis. There is a transition to the surface low as the system is moving across Central and Norh Texas. This appears to account for the decrease in qpf across NE DFW into NE Texas. However, this is at the very end of the run and will probably change in coming runs.

[orangeblood]

Latest SREF coming in much more aggressive and further north with QPF amounts...

ARW
https://images.weatherbell.com/model/sref-all-arw_c00/tx/total_snow_10to1/1610096400/1610409600-71euv3V8Cx0.png

NMB
https://images.weatherbell.com/model/sref-all-nmb_c00/tx/total_snow_10to1/1610096400/1610409600-aOqyS0RUAeg.png

Mean
https://images.weatherbell.com/model/sref-all-mean/tx/total_snow_10to1/1610096400/1610409600-WWoZUAvARec.png

Orangeblood, what are these models seeing that others like the nam and gfs aren’t?

As has been discussed previously...at this range, some deterministic models become unreliable particularly when you have a large scale event, such as this, where noisy variables/borderline temps are in play. I've found it to be useful in moderate to heavy precip events in the southern plains

[rwfromkansas]

If this misses DFW again or we only get a half inch, not sure I will ever be able to trust the models until it's a few hours before. I am concerned that the talk is switching to the surface low likely causing problems from it being a possibility yesterday. Previously it was supposed to help us, not hurt us... The shift in conversation here usually implies bad things.

[Ralph's Weather]

12z 3k NAM shows this pretty clearly if you track the frontogenesis. There is a transition to the surface low as the system is moving across Central and Norh Texas. This appears to account for the decrease in qpf across NE DFW into NE Texas. However, this is at the very end of the run and will probably change in coming runs.

Thanks for the reply, I haven't had a chance to study the morning models in detail. I will watch for it on future runs.