Southern Plains winter wx thread (2008-2009)

[Extremeweatherguy]

Well I never saw any snow here today, but there were plenty of cool virga clouds and a few rain drops from time to time. According to the news, there were a few sleet and snow reports received this evening around OKC, but they all happened to occur somewhere other than my immediate area of town.

Hopefully we can get a more substantial winter weather threat soon!

[Extremeweatherguy]

The 00z GFS run looks slightly colder for the plains next week. Previous GFS runs were trying to shunt the cold air well north and east, only bringing us a glancing blow. The 00z run is a little different though. It shows a stronger high pressure system, and pushes the canadian air mass a bit further south into the plains. Take a look at the comparison between the 12z and 00z for next Wednesday night...

12z GFS run = http://www.nco.ncep.noaa.gov/pmb/nwprod ... p_090l.gif

00z GFS run = http://www.nco.ncep.noaa.gov/pmb/nwprod ... p_078l.gif

The 12z run had all of Oklahoma in the >0C 850mb zone, while the 00z has most of the state in the <0C 850mb zone.

And here is the comparison for Thursday afternoon...

12z GFS run = http://www.nco.ncep.noaa.gov/pmb/nwprod ... p_102l.gif

00z GFS run = http://www.nco.ncep.noaa.gov/pmb/nwprod ... p_090l.gif

Tonight's 00z is once again much cooler, showing the sub-0C 850mb temperatures extending much further south and west.

[Portastorm]

The 0z GFS doesn't look all that impressive over the next 15 days, unfortunately ... but I am not putting much stock into that. This model has been widely variable in the longer range. One would like to see a little more consistency.

The 0z Euro, however, looks rather chilly at about 216 hours ... check out the deep, cold trough over the Southern Plains!

[Extremeweatherguy]

Yeah, the GFS has been all over the place in the long range. The 00z was warm, while the newest 6z is cold and snowy. It is very hard to trust that model at all beyond 180 hours. The ECMWF definitely caught my attention though. With a better track record in the long range than the GFS, it is certainly interesting to see it showing such a nice scenario for next week. The setup it depicts at 216 hours would be a great one for southern plains winter weather events.

[Ed Mahmoud]

Yeah, the GFS has been all over the place in the long range. The 00z was warm, while the newest 6z is cold and snowy. It is very hard to trust that model at all beyond 180 hours. The ECMWF definitely caught my attention though. With a better track record in the long range than the GFS, it is certainly interesting to see it showing such a nice scenario for next week. The setup it depicts at 216 hours would be a great one for southern plains winter weather events.

Good for cold, not sure about snow, it looks like Texas and Oklahoma would be on the downward motion side of the jet shortly after the cold air arrived. Might get lucky for a brief period of freezing/frozen as precip ends, especially under the upper low, but probably nothing that cancels school.




Best case, especially for Texas, is a sub-tropical jet from the Pacific running over a fairly shallow cold wedge. If the cold wedge is shallow enough, and South and Southeast low level flow can over-run it, even better.

About 5 years ago, during a significant DFW area ice storm, down here in Houston, it was raw, with a stiff North wind, and low 40sF. But low clouds were streaking from South to North towards Dallas, the bases about the level of the top of the Williams Tower, maybe 1000 feet. Even though we didn't get wintry wx here, it was still exciting to see an ice storm from the inside, as it were.

[Extremeweatherguy]

The 12z GFS run looks very wintry for next week, showing multiple winter weather threats into the southern plains. If this can become a trend for a few more runs, then I might have to start getting excited.

[Valkhorn]

The winter GFS is a different beast than the late summer one.

Why?

Different patterns throw different models for different loops.

What I typically have seen in the past six years with the GFS in the winter is that it has trouble seeing past one or two cold fronts or eastern troughs. Everything beyond that is hazy and can swing either way. Plus, a lot of troughs (like the one I'm currently in) wasn't really progged until about 150 hours away. It wasn't really consistent until about 100 hours or less.

Do we all remember the runs where a low developed in the southwest? That's an error that happens in the GFS when it can't figure out what to do with the pattern. When you see that, it's usually going to be a bad run. Think about it, how many lows just break away from the jet and sit southeast of TX for a week?

The reason I don't completely buy the latest GFS is that it takes an enormous amount of cold air (0F in the panhandle of Texas and just doesn't let it move on. It just sits there until it modifies. That's going to be extremely rare in a pattern with a very active southern jet and a pretty progressive pattern.

What the GFS is seeing is a trend toward colder and perhaps a decent arctic outbreak, but it doesn't know how cold or where to put it so it just sits it there. With the long range GFS, the trend is your friend. Wait for it to do similar things over and over before jumping on it. If it keeps a trough for only two runs and replaces it with a ridge - it's too much uncertainty. However it has been seriously developing a very cold patch of air near the Canadian border over the last few days in the 10-15 day time frame, so I'd say that it could be seeing whats developing there but the details are not going to be there within a week from it happening.

[Portastorm]

Points well taken on the GFS runs ... I'm just giggling now over the 12z GFS run and the Accuwx snowcover map derived from it. By Dec. 15th-ish, the map shows snowcover in Texas from about Tyler down south to College Station and back west through Austin out to about Fredericksburg. Ooo-eee, wouldn't that be something??!!

But for now, I'll take it with a grain of salt.

[Ed Mahmoud]

Valkhorn, Joe Bastardi frequently rags on the GFS, although it seems as good as any other model in the short range. The loss of resolution at 180 hours from about 35 km^2 to 80 km^2 on a model that already has to have a somewhat coarse resolution to be a global model and go out for more than a few days means anything beyond 7 days is very shaky. Bastardi thinks it doesn't handle the transfer of heat between the tropics and the mid-latitudes, and has trouble concentrating energy in developing storms, and has shown examples of the GFS showing a series of weak storms developing rather than one strong one.

Bastardi is not a modeler, and I'm not a met, so I don't know how valid that is. I do know the GFS has only about two thirds of the vertical resolution the Euro has, so I'm not surprised that shallow, dense, cold air masses are frequently underforecast by the GFS.


At any rate, a 15 day snowpack map from the GFS is the equivalent to a GFS major hurricane two weeks away approaching the Bahamas. It might be on to something, but more often than not, it isn't.


I will say, as a positive sign, the 12Z individual GFS ensemble members,as a whole, seem to show the 540 dm thickness line spending a fair amount of time in the Southern Plains and Deep South.

[Ed Mahmoud]

Euro shows an impressive Nor'Easter on the East Coast mid next week, but generally in the longer range mostly zonal flow over the Plains.



ETA- The Penn State Euro, which shows 850 mb freezing line and 540 dm thickness line, only goes to Day 7, so I can't tell whether the Nor-Easter with 850 mb winds in excess of 30 m/s (over 60 knots) would be rain or snow on the coast, but it is December now, and it looks like the surface low (hard to tell in 1 day time steps) will pass near/Southeast of the 40º/70º benchmark, so potentially the first Big City snow of 2008.

[hriverajr]

One thing I am noticing.. finally is a pretty good building of pressures in Alaska that began yesterday, Earlier last week when people were talking cold.. I was thinking where are the pressure rises to bring the air south. Yes you had building pressures in The lower 48 but all that brought down was mostly local recycled air.

[vbhoutex]

One thing I am noticing.. finally is a pretty good building of pressures in Alaska that began yesterday, Earlier last week when people were talking cold.. I was thinking where are the pressure rises to bring the air south. Yes you had building pressures in The lower 48 but all that brought down was mostly local recycled air.

That will help with the delivery of the colder air, but until we have some snow pack in the plains any arctic air that makes it south to OK, TX, Etc. will be severely modified by the still warm uncovered ground.

[hriverajr]

True but at least I see something.. and it is getting pretty chilly up there... -29 F at one spot. The old rule was cold in Alaska with high pressure meant Texas had a shot at some cold weather. No need for models there.. hehe..

[iorange55]

I am certainly no expert on Weather, so I'm sure someone will set me straight on this. But I'm sure there has been plenty of times where we got some really cold weather here in Texas without a decent snow pack to the north. It just seems like some people count a little too much on the snow pack. I'm not saying it doesn't help, I'm just saying it's not like we have to have it.

[vbhoutex]

Nor did I say we have to have it. What I said is that the temperatures will be severely modified compared to at a time when there is snowpack. To me a true arctic outbreak that affects us here in the deep Southern plains or Texas coastal areas normally brings in temperatures far below normal for an extended period of time and that does not usually happen, at least not as far south as Houston, unless there is a pretty good snowpack to our north and there is almost none all the way to Canada.

[vbhoutex]

True but at least I see something.. and it is getting pretty chilly up there... -29 F at one spot. The old rule was cold in Alaska with high pressure meant Texas had a shot at some cold weather. No need for models there.. hehe..

You got that right!! Now if those temps were about 20ºf colder I would really be starting to get somewhat excited, even without snow pack.

[Johnny]

Does anyone have any data about how much snow pack was to out north during the arctic outbreak before x-mas in 1989?

[vbhoutex]

Does anyone have any data about how much snow pack was to out north during the arctic outbreak before x-mas in 1989?

That would be interesting to know. Is there a place that has archives of sat pics or other depictions like that from that far back?

[Ed Mahmoud]

True but at least I see something.. and it is getting pretty chilly up there... -29 F at one spot. The old rule was cold in Alaska with high pressure meant Texas had a shot at some cold weather. No need for models there.. hehe..

1036 mb and -30º C at Tanana, AK


No idea where that is, but the chapped lip problem must be severe.


Even colder in Bettles.

[Extremeweatherguy]

The 00z GFS continues to show a massive push of arctic air entering the picture by mid month...

288 hrs - http://www.nco.ncep.noaa.gov/pmb/nwprod ... n_288l.gif

300 hrs - http://www.nco.ncep.noaa.gov/pmb/nwprod ... n_300l.gif

324 hrs - http://www.nco.ncep.noaa.gov/pmb/nwprod ... n_324l.gif

348 hrs - http://www.nco.ncep.noaa.gov/pmb/nwprod ... n_348l.gif

372 hrs - http://www.nco.ncep.noaa.gov/pmb/nwprod ... n_372l.gif

This is still wayyy out there, but the GFS has to eventually be correct one of these times, right? lol.

BTW: That -10C line represents temperatures below 14˚F! If tonight's GFS run plays out, then Oklahoma is in for some COLD mornings come mid December with low temperatures likely bottoming out in the single digits.