aggiegeog

19 minutes ago, Stx_Thunder said:

 

Canadian always overdoes pretty much everything (including hurricanes), so I never rely on it. Mesoscale models also (except NAM for mainly surface temps in these polar/arctic air masses). 12z runs usually give the best insight overall, at least on globals (GFS, Euro).

Euro overdoes things to an extent (convective events/intensity also). Especially when the event is close, but never crazy most of the time. With tomorrow's event, I'm looking at GFS the most because it's been performing the best lately with these winter wx scenarios in this part of the country.

I'll take my chances with GFS. It keeps me at 32F through the whole event. Precip types just vary as warm nose builds then erodes.

No models besides the crazy Canadian are close to cold enough at initialization. Canadian is way too cold. Bizarre that all hi res models are initializing 4+ degrees warm right now. Most models have freeze line along I20 when it is actually south of Lufkin. 26 here in Lindale along I20 now. Some stations as low as 23 around East Texas.

5 minutes ago, Stx_Thunder said:

In winter wx forecasting, a +3 C LL layer can actually make a big difference in precip type at the surface. Even if it's below freezing at surface.

Today's 12z GFS has actually come in a little warmer at 850Mb around DFW because of the projected deep, large scale south-southeasterly over the eastern half of state (keyword: southeasterly) WAA flow until it cuts off there Thursday night. Showing even above 0 C spots now creeping into DFW. It's already been quite consistent on that the past several days on the 0 C area hovering over the area. So I'm confident it is not going to be all snow, daytime Thursday at least in DFW metro - southeast.

0z UA obs this evening even shows 850Mb temp is already right next to 0 C. And above freezing now north of Houston (3 C red dashed line). The LL warm-air advection regime has already started here in STX as I'm already seeing a fairly strong southeast flow near 30 knots on Brownsville VWP radar right now.

It can but that is but 3C is only on the warmest models. Some have the more like 1C or even 0C.

4 minutes ago, TXHawk88 said:

Temps are already 3-4 degrees cooler than modeled. Only projected to get down to 31 tonight but already at 28° here in North Grand Prairie near I-30. Significant cloudiness still looks to be an hour or 2 away. Not sure if it’s really going to have an effect, but that seems like a positive. 

27 in Lindale out north of Tyler, that is our forecasted low. DP of 22 so still some room to drop before clouds arrive.

We will soon see but nice to start a storm with cold ground. If we can get a solid layer of sleet to accumulate in the morning then that can insulate later precip from ground warmth even as surface temps may warm during the day. Also heavier precip can pull cold down and eliminate the slight warm nose.

45 minutes ago, canderson said:

I haven’t looked today but I imagine a warm nose is around the 500-800mb level which will flip a lot to sleet  N of 20 

Warm nose is expected to be very minor like max 3C around I20 and maybe only 1C depending on model. And those warm layers are shallow, generally less than 150mb. A decent amount of sleet for a long I20 but closer to I30 should be basically all snow. Some models show even I20 to be mainly snow profile.

Freeze line has sagged south of I20 already across Texas. 31 here in Lindale which is round 3 degrees lower than expected at this time. Not sure how much effect that has in the end but def can't hurt to have 12+ hours below freezing before onset even if onset warms things some. Models continue to ramp things up across N and NE TX.

Most schools have already closed around here.

9 minutes ago, TXHawk88 said:

Here is the 18Z HRRR, I can see this as a pretty reasonable solution. Most of the accumulation comes after 4pm tomorrow. If we are somehow able to cool the temps above quicker we could end up with a lot more. 

That does look really solid. 3-6" snow for DFW, 4-8" snow for I-30, 1-3" sleet/snow for I-20.

SHV expanded warning to include all of the former watch and added an advisory for counties south of I20. I see Advisories are now issued down to Del Rio for all of the Hill Country west of I-35.

FTW filling in their region with WWA now. I expect West Texas and SHV will fill in their regions shortly with WWAs.

Most Hi-Res models as well as RGEM indicating colder temps tomorrow. gonna be a close call on if just a rain/sleet mix tomorrow or all frozen with travel issues.

Around here key is the warm nose tomorrow 1C or 4C. Surface will be 32-35F so at 1C sleet is likely but at a warmer warm nose it could just be cold rain with some sleet. By sometime tomorrow night it should transition to snow or rain/snow2010 is still on the table with this event. 

Again this morning for the Tyler area, there is a massive range of outcomes from mostly rain with some mix to a foot of snow. As expected hires models show a colder profile. Again models print out 1-2" QPF area wide. I still do not see much freezing rain with this though there will be some. Areas where sleet is the main type are looking at 1-4" accumulations (say maybe areas from Hillsboro to Carthage up to maybe Tyler/Longview). A more even mix of sleet and snow would be like 4-8" (maybe Cleburne to Longview type areas). The main snow band will be a general 6-10" with some over a foot (thinking I-30 is a good bet).

Assuming we do get the 1 to 2" QPF and temps are at least partially supportive of frozen precip then amounts will be significant. Heck 0.5" QPF of sleet gets you to over an inch and I think that is certain at least east of I-35.

2 minutes ago, Powerball said:

Meanwhile, at first glance, 18z NAM is looking notably cooler...

There is a reason I have held off on updating my official forecast for the event. They do not have that option. They very well may be revising right back up tonight.

1 minute ago, Powerball said:

FWD is now only calling for 1-3" in the Metroplex with mixed precipitation, in their update that just came out...

Man I feel for them having to attempt to forecast this. SHV also lessening their amounts it seems.

Man, the data this afternoon is highlighting some extreme snow possibilities for NE TX. This is a wildly volatile setup.

Most of the model sites only plot snow or freezing rain. Have to interpret sleet in between. I believe so will see hefty sleet totals out of this. 1" QPF with a profile fluctuating near 0C could result in multi inch sleet.

4 minutes ago, Powerball said:

It was a no-win situation for them.

NWS, as standard practice, has to issue a Watch when we're no less than 48 hours away from the start of an event. This is to ensure sufficient notice is given to the general public to allow for storm preparation.

The guidance, as of last night at least, was still somewhat supportive of potential for warning criteria snowfall to being met (and in fairness, it's a low bar at 3").

My bigger bone to pick though is how the model verification will seemingly be so poor within 3-4 days.

 

 

agreed that it is wild that we are having this much model trouble within 48h of onset. RGEM has 2" QPF for DFW and NAM has basically 0" QPF. Other models in between but none go anywhere close to 0 for DFW. 06Z NAM fell in line with other models then 12Z just goes way off by itself. Super odd behavior even for the sometimes crazy NAM.

1 minute ago, vwgrrc said:

The thing I'm curious the most is that NWS is normally very conservative on issuing a Watch especially for DFW. They won't just take a few model runs and say it's gonna be a winter storm. What convinced them or is this gonna be a big bust fot them as well?

Yea its interesting for sure. SHV is even more conservative than FTW with these typically and they actually issued their watch before FTW. It seems that they are leaning on Euro heavily, I agree with that myself. I think the NAM is just being its wonky self, we are still in extended range for the NAM we have to remember. It is pretty clear that for DFW east we are looing at around 1" QPF with sub 35 temps. The question is mainly on when the SW trough and northern stream shortwave phase, I lean on Euro solution of this happening early. The earlier they phase the faster we get precip and the less the mid level WAA ahead of the storm. Also watching to see how much the Rockies high can press into the backside of this storm with cold air without shutting down precip.

Models this morning really want to hang a chunk of the trough back in the SW which is killing our event. I still think this has a good chance to revert back to previous solutions assuming we can get the trough to eject whole.

NWS has hoisted watches for N and NE TX. Solid snow for N and NE TX. Major ice and sleet with some snow for E TX.

16 minutes ago, vwgrrc said:

Yea. 18z GFS seems confirming that drier+warmer trend actually. ICON isn't the best but that NAM run looks really outlandish. This still has a chance to become a cold rain even for NTX looks like. 

I will disagree with it have a chance to become a rain event. We have a Arctic high pressing cold air into this storm and the storm starts below freezing in most places. All  rain is reserved for south of Austin to Lufkin and even along there it could well mix.

We are talking about a very wet storm, key for this forecast is nailing where the column stays sub 32F. For example my location is modelled for >1.5" QPF while the entire column rides within 2C of freezing the whole event from the surface to above 700mb. That would result in a constant fluctuation of precip types so could be talking a 1" elevated surface only ice storm, 3" plus sleet and snow mix or a foot of snow. Tiny variations in the atmosphere will make massive differences.

12 minutes ago, canderson said:

Fair enough - I've not looked closely at the thermals. I just always expect (and know from growing up there) a warm nose seems to always take over Tyler to Longview. 

That is for sure. My current thinking is that the new high over the Rockies will mitigate the WAA at least along and north of the I-20 corridor. Obviously this is E TX and WAA could win out.

Around here, I expect light snow Wed night. Intensity will increase while precip becomes more of a mix Thu. By Thu evening/night the trough nears cooling the mid levels for precip to go back to all snow. The snow should end Friday morning as the low passes to the east.

Something like >0.1" ice, 1" sleet and 2-3" snow for Tyler area. Maybe .1" ice, 1" sleet and 2" snow for Longview. I live north of I-20 so I am hoping mine leans even more in on mainly snow but gonna be a close call.