Texas winter wx thread#5 - big changes on the way eventually

[Tireman4]

Thank you so so much Wxman57. Your calmness and explanations do help. So this is not a trend, rather a flip flop? Or will you have to look at the next runs?

[cctxhurricanewatcher]

I'm more sure about the first GFS error (leeside low holding back Arctic air) than the 2nd error (trough not moving across the cold air early next week). It is possible that there will be no post-frontal precip. However, I do know that the GFS and the old MRF had a difficult time in the 3-5 day time frame before such an event.

It did that right before the 2004 Christmas snow down here.

[wxman57]

I'm more sure about the first GFS error (leeside low holding back Arctic air) than the 2nd error (trough not moving across the cold air early next week). It is possible that there will be no post-frontal precip. However, I do know that the GFS and the old MRF had a difficult time in the 3-5 day time frame before such an event.

It did that right before the 2004 Christmas snow down here.

Yes, it did absolutely great with the 2004 Christmas storm from 16 days out until 4-6 days before the event then it got lost. This time frame always gave the MRF (and now the GFS) fits. But it doesn't do much to increase my confidence in any ice storm in Texas.

[southerngale]

I'm more sure about the first GFS error (leeside low holding back Arctic air) than the 2nd error (trough not moving across the cold air early next week). It is possible that there will be no post-frontal precip. However, I do know that the GFS and the old MRF had a difficult time in the 3-5 day time frame before such an event.

It did that right before the 2004 Christmas snow down here.

Yes, it did absolutely great with the 2004 Christmas storm from 16 days out until 4-6 days before the event then it got lost. This time frame always gave the MRF (and now the GFS) fits. But it doesn't do much to increase my confidence in any ice storm in Texas.

While you said it wasn't probable, but merely possible last night, you did talk about a potential historic event. Do you still feel the same as yesterday, or has confidence gone down (or up)?

[cctxhurricanewatcher]

I'm more sure about the first GFS error (leeside low holding back Arctic air) than the 2nd error (trough not moving across the cold air early next week). It is possible that there will be no post-frontal precip. However, I do know that the GFS and the old MRF had a difficult time in the 3-5 day time frame before such an event.

It did that right before the 2004 Christmas snow down here.

Yes, it did absolutely great with the 2004 Christmas storm from 16 days out until 4-6 days before the event then it got lost. This time frame always gave the MRF (and now the GFS) fits. But it doesn't do much to increase my confidence in any ice storm in Texas.

I don't care really if we get any precip or not out of this. At the risk of allienating the tropical plant lovers on this thread, I'd really like a good freeze to help get rid of bugs and fungus in my yard. If I have to re-plant my tropical stuff, oh well. One day it will take a hit from cold or hurricane, I rather it be cold.

Speaking of tropical storms, a prolonged period of cold like is being advertised around here will do wonders at cooling of the coastal waters. So unlike past years where the water has been above normal way before the start of 'cane season, perhaps this year it will take time to warm them up.? Here's hoping we have a cooler than normal spring too.

[aggiecutter]

Bastardi just said it is possible the system could phase as it comes out early next week. If that were to happen, the eastern parts of central and north Texas would have a major winter storm.

[HouTXmetro]

The system could phase? Can you explain what that means, and what it means for SE Texas?

[Johnny]

And what exactly is the definition of 'phase'?

[AggieSpirit]

Hey... how disastrous would a solid inch of rainfall at below freezing temperatures be for the DFW area? Has DFW ever faced such a disaster?

[jasons2k]

I just went to Teas Nursery to get some freeze protection spray. The gardener there said he was more concerned with this situation than with one in many years. He said the Queen Palms, Norfolk Pines, etc., are in danger of getting wiped-out.

At the risk is alienating cold-lovers, palm trees - especially mature ones, are not cheap. Some species cost in the thousands and can't simply be replaced

[wxman57]

A little more detailed analysis of GFS/MRF issues with Arctic air that I posted on the KHOU forum just now:

I'm not surprised that the 12Z GFS has done a major flip-flop. The GFS (formerly the old MRF) has a long history of making critical errors with this type of weather pattern. Often, the GFS/MRF does quite well in the long-range (8-16 days) then loses touch with reality in the mid-range (3-7 days). Finally, if gigures out what's going to happen the day or two before a major Arctic front.

I'll discuss some of the errors to watch out for.

1. Error number one usually involves the prediction of a lee-side low either in eastern Colorado or NE New Mexico. The GFS will develop this low and hold back the Arctic air until the low kicks out. Generally such a low doesn't develop. Today's 12Z GFS developed that low, and that's why it is so slow in driving the front south through Texas on Saturday.

2. A second common problem is the handling of post-frontal waves/trofs. In many cases, the GFS will erroneously drive the energy southwest and off the west U.S. coast (as it did on the 12Z run today). This leads to a dry post-frontal forecast. With no trof moving through Texas over the cold air, there's no winter weather threat. Usually, the GFS is wrong with such a prediction. Other models like the new NOGAPS show the trof heading right for Texas on Monday as opposed to cutting off a closed low near CA:

https://www.fnmoc.navy.mil/products/WXM ... .namer.gif

The 12Z Canadian also moves the trof into Texas on Monday and Tuesday rather than off the west U.S. coast:

http://weatheroffice.ec.gc.ca/data/mode ... 12_144.jpg

3. Another quite common error with Arctic fronts is that the GFS tries to move the Arctic air out way too soon once it's firmly-entrenched in the region. I'd say this happens in over 90-95% of Arctic fronts. It seems to be making that error on the last 12Z run.

4. And the final common error I can think of at the moment is that the GFS will typically move the Arctic too far east too early instead of driving it straight south lee of the Rockies.

That's about all I can think of. Far as I can see, the 12Z GFS is making most of the above-mentioned errors. Will be interesting to see if the 12Z European brings that secondary trof across Texas early next week or if it, too, cuts off the low over CA and drives it offshore. I bet it will match the NOGAPS and Canadian runs and move the trof east, making the GFS the outlier. But the GFS divergence does nothing to increase my confidence in next week's ice storm threat. I'd rather see all the models in agreement.

[Portastorm]

And what exactly is the definition of 'phase'?

I'll defer the "phase" definition to the likes of our pro mets ... but my understanding in this reference is that all of the low pressure energy essentially coalesces into one strong low pressure system ... or a vigorous and large storm system.

[Yankeegirl]

The local FOX news this morning also mentinoned the sleet word as well.... Still a very interesting event in the works...

[Johnny]

Roger that Portastorm.

[jasons2k]

Yes, phasing is the merging of two systems (or sometimes applies to the Jet Stream) and a good explanation can be found about 1/2 way down this page:

http://philadelphiaweather.blogspot.com ... coast.html

[wxman57]

I see that the 12Z European is in. It continues the forecast of the disturbance moving across the Gulf Coast with the Arctic air in place early next week. So the GFS is the only model saying different now. That's a sign that the GFS was lost at 12Z. This increaes my confidence of an ice storm across central and SE TX next week a bit. For now, I'd say a 60-70% chance that there will be enough icing to cause travel problems and a 20-30% shot of a storm that could cause tree damage and power interruptions.

[GeneratorPower]

wxman57, one more time, how about points to the east? I.E., north Alabama, North Mississippi?

[wxman57]

wxman57, one more time, how about points to the east? I.E., north Alabama, North Mississippi?

You're still under the gun, too, in Huntsville. The path of any ice storm would extend from San Antonio/Austin ENE across east-central TX, central LA, and northern MS/AL. Probably lesser ice amounts farther east due to the onset of precipitation and cold air being later.

[Yankeegirl]

I see that the 12Z European is in. It continues the forecast of the disturbance moving across the Gulf Coast with the Arctic air in place early next week. So the GFS is the only model saying different now. That's a sign that the GFS was lost at 12Z. This increaes my confidence of an ice storm across central and SE TX next week a bit. For now, I'd say a 60-70% chance that there will be enough icing to cause travel problems and a 20-30% shot of a storm that could cause tree damage and power interruptions.

This makes me nervous... Looks like this is going to happen this time... At least you dont have the numbers too high for damage, but as for travel... Im staying put!!!

[LaBreeze]

So what exactly are we looking at for the coastal communities of SW LA?