Southern Plains Next Week

#1 Postby **jeff** » Fri Dec 17, 2004 11:40 am

Guidance has sped up the arcitc invasion to reach N TX by the evening hours on Tuesday and then deep into the Gulf by Wed. This may be about 12 hours fast given the pattern setup and the expected surface low formation over the TX panhandle which could hold up the air until it moves E. However, once that happens bombs away with very chilly air heading for the Gulf. Temps. will be cold, probably some of the coldest air we have seen in several years, but likley not as cold as 1989 or 1983 at least here in TX and LA. The outbreak is supported by -15 to -10 dm height anomolies over the eastern 2/3rds of the US around Christmas Eve. Confidence in the cold air is fairly high.

Note: I think the GFS guidance is running about 10-15 degrees too warm for highs behind the front and about 5 degrees too warm on lows. Dirunal ranges will be very small with a low level cold stratus deck in place over TX and LA.

Now to the much discussed winter weather event:

The GFS guidance likes the idea of a coastal trough and surface low in the western GOM on the 24th. There is also a decent short wave trough seen in the mean flow over SE CO heading SSE within the mean overall flow. The sub-tropical jet appears to phase with the polar jet near the S TX coast late on the 24th. GFS guidance supports freezing and frozen precip. developing over S TX on the 24th and spreading NE into SE TX and LA late on the 24th and the 25th. P-type is IP and ZR on the model run with what appears to be more warm advection above the surface than indicated yesterday. However the short wave dropping down from the NW may be all snow over a larger part of the state into LA. The main concern I have ight now is moisture availibility as the current guidance is showing little QPF and POP chances of only 30-45% from SE TX into LA. However, guidance did not grasp yesterday's rain event until it was about 24 hours away and under did rainfall amounts.

To be short and to the point, it will be getting much colder in TX and LA next week, and there is an above average chance of winter precip around the Christmas Holiday.

JL

Johnny · #2 Postby **Johnny** » Fri Dec 17, 2004 12:08 pm

Jeff, I appreciate the insight and I enjoy reading your discussions. Since we are now talking pretty heavy about the possibility of wintry precip. chances here in Southeast, Texas.....I'd be perfectly fine with no accumulations. A 20 minute flurry of snow would suit me just fine on Christmas Eve or Christmas morning. That would be very nice. Again, thanks for the input....keep 'em coming.

#3 Postby **Portastorm** » Fri Dec 17, 2004 12:15 pm

Good report and insights Jeff. Thanks!

#4 Postby **jeff** » Fri Dec 17, 2004 5:37 pm

First PNS statements (NWS San Angelo) being released about next weeks cold air outbreak. Guidance is too warm folks with this event and could easily be undercut by 5-10 degrees (maybe more) on the highs and about 5 degrees on the lows. Probably will not get above freezing for a good part of TX and LA from the 24th to the 27th.

Frozen precip. possibilities remain, but moisture availibility is looking scant. Details will become more clear on this as the event draws closer.

Jeff L

#5 Postby **Portastorm** » Fri Dec 17, 2004 6:19 pm

Jeff, it seems like each run of the GFS today has progressively sped up the Arctic front as well as appear colder and colder. Is that your take?

I'll be curious to see the 12Z Euro run tonight.

And yes, I give kudos to San Angelo NWS for the heads up. Credit given where credit is due. Good work folks!

#6 Postby **jeff** » Fri Dec 17, 2004 7:32 pm

Portastorm wrote:Jeff, it seems like each run of the GFS today has progressively sped up the Arctic front as well as appear colder and colder. Is that your take?

I'll be curious to see the 12Z Euro run tonight.

And yes, I give kudos to San Angelo NWS for the heads up. Credit given where credit is due. Good work folks!

Yes the model is speeding up the event, but it is actually going back to what it forecast 3-4 days ago with the cold blast happening around the 22-23. As I stated before the GFS tends to lock on things at 14-16 days flip flop between 13 and 7 days and then trend back to the 16 day solution with 7 days of the event. The GFS has been forecasting this outbreak for a while now (10-14 days) with varying intensities.

#7 Postby **jeff** » Fri Dec 17, 2004 8:01 pm

Just check RAOB from Northern Russia and northern Alaska:

Chokurdah: -37 C
Tiksi: -38 C
Olenek: -51 C

Northern Alaska

Point Barrow: -23.3 C

There is out arctic air mass.

#8 Postby **wx247** » Fri Dec 17, 2004 8:12 pm

I get cold just reading those numbers.

Jeff... how significant do you think this frozen event will be?

#9 Postby **jeff** » Fri Dec 17, 2004 8:49 pm

wx247 wrote:I get cold just reading those numbers.

Jeff... how significant do you think this frozen event will be?

It will be a cold blast, but probably not as bad as 1989 or 1983. We will have to see how much comes down from the north and how strong the ridge is compared to what the models are forecasting.

AggieSpirit · #10 Postby **AggieSpirit** » Fri Dec 17, 2004 10:01 pm

Any setup like the 1983 event where nearly 300 hours passed in parts of Texas where the mercury did not get above 32?

Thanks, and WHOOP!
BEAT THE HELL OUTTA UT! (Yes, U.T.)

#11 Postby **Portastorm** » Sat Dec 18, 2004 8:13 am

The cold game is on, the big question now is precip.

Don't know about the rest of the Lone Star State but I am at a loss to understand why our NWS guys in Austin/San Antonio are forecasting highs in the 40s and lows in the 20s on Friday. Every model guidance I have seen this (Sat) morning is WAY WAY colder than that. Maybe they're following the GFS MOS numbers, I dunno.

The GFS unrealistically blows the Arctic airmass out next weekend, confirming Jeff what you've said about the flip-flopping between days 7-13. This airmass will be much harder to dislodge as it won't be a typical shallow Arctic airmass.

And the Euro shows a real deep, sharp through moving through Texas around Christmas. Raises the precip question, of course.

Wow, this is going to be fun (I think)!

Jagno · #12 Postby **Jagno** » Sat Dec 18, 2004 10:55 am

Portastorm; I'm in SW LA and by looking at our forecast showing lows in the mid 30's and highs in the upper 50's I'm confused as well. There has been no mention of hard freezes let alone snow at all. What happened? :?:

#13 Postby **Portastorm** » Sat Dec 18, 2004 12:10 pm

Jagno wrote:Portastorm; I'm in SW LA and by looking at our forecast showing lows in the mid 30's and highs in the upper 50's I'm confused as well. There has been no mention of hard freezes let alone snow at all. What happened?

Jagno, I wouldn't get too bummed yet. I bet those numbers drop in the forecast issued in 48 hours. GFS runs today and the reliable Euro show a trend toward colder, colder, colder.

#14 Postby **jeff** » Sat Dec 18, 2004 12:16 pm

Guidance has trended warmer with the cold air outbreak this week and also has a much shorter duration as ridging develops over the west and a more zonal flow returns to the lower 48. This is a big change from yesterday and the last several runs for that fact. I would like to see at least 3-4 more runs confirm this before buying into the warmer solution.

As for precip. over the south, moisture is looking really scant so maybe a few flurries. This is another point that will change many times over the next 2-4 days.

#15 Postby **CaptinCrunch** » Sat Dec 18, 2004 12:44 pm

Jeff,

I agree with you on more model runs to confirm a warming trend, how ever as of right now I don't buy the current models. If you look at my other post you will that I think this artic front will be colder than forecasted and have reason to beleive that this may be the trend for the rest of the winter with west coast blocking setting up and artic pools dropping south. As for wintery precip the NWS here in Ft Worth is in agreement with the NWS out of Norman OK on a slight chance of freezing drizzel and light snow here Thursday night and another chance after Christmas if the cold air holds.

If you have the time please read my "North Texas Winter Outlook" and tell me what you think.

#16 Postby **jeff** » Sat Dec 18, 2004 2:23 pm

12Z data from GFS is in and it has come back in line with its previuos forecast. It is back to light snow for SE TX and LA on the 24th with some light acc. possible. It is showing about .15 of liquid inches of snow. However given the profile its rain on the 24th is questionable as the entire column is frozen from the surface up.

Last nights run was just a bad run, it is now back in line with previous thinking. Cheer up southern folks the hopes are still alive.

Southern Plains Next Week

Southern Plains Next Week

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