Texas winter wx thread (2009-2010)

[srainhoutx]

We are about six days out. The GFS usually starts flip flopping in this range as it struggles with colder airmasses. Even the ECMWF is known to struggle in the medium ranges. What many look at concerning guidance is trends. Remember that there is far more involved than a numerical computer model in longer range forecasting. Reading the AFD's just issued from WFO forecasters across TX the differences and struggles of guidance is discussed at length and will likely change as we see the system get closer. Keep on eye on Western Canada.

EDIT to add guidance differences between 12 GFS and EC...(very large spead in the Operational Guidance)...

http://www.met.sjsu.edu/weather/models/ ... c-ani.html

[Portastorm]

The 12z GFS is looking a lot more like the 0z Euro next week and beyond. Very cold looking with some possible winter precip events.

http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/gfs/12/fpc.shtml

I dont follow.
I see some cold in the long range, but a warmer drier front in about 6 days than the model was showing yesterday. And no winter precip
sigh....

Once you get past 3-5 days the operational GFS should only be used for general trends not specifics. It's much better to use the EURO or the Ensembles when looking in the long range. Speaking of long term trends, all the models are strongly suggesting a trough in the central and southern US from the first through mid December. This favors cyclogenesis in the GOM, and it's just a matter of time before one of these systems meshes with cold air that will becoming down from the north. Who will get what can only be determined once you get to within a couple days of the storm.

Well said snow and ice.

Mypoint is, cheezy, if the 12z GFS and 0z Euro are close to correct, we'll have a huge cold trough over the southern Plains. That will dump unseasonably cold air on top of us and we'll have a subtropical jetstream either over us or just to our south and any perturbation in the atmosphere will have the potential to create precipitation. It's a pattern conducive to winter weather in the southern Plains.

[iorange55]

Wow the 18z does not look good at all. I know the models flip flop, so thats what i'm hoping for. Hopefully this is not a trend.

[wxgirl69]

Wow the 18z does not look good at all. I know the models flip flop, so thats what i'm hoping for. Hopefully this is not a trend.

When you say it does not look good at all. Are you talking about it being to cold or warm?

[cheezyWXguy]

Wow the 18z does not look good at all. I know the models flip flop, so thats what i'm hoping for. Hopefully this is not a trend.

When you say it does not look good at all. Are you talking about it being to cold or warm?

warm

[wxgirl69]

Wow the 18z does not look good at all. I know the models flip flop, so thats what i'm hoping for. Hopefully this is not a trend.

When you say it does not look good at all. Are you talking about it being to cold or warm?

warm

Well bummer... I know nothing is set in stone. But, darn those models....

[gboudx]

Larry Cosgrove still talking about some possible snow for Dallas.

Discussion
(Relevant Graphics Follow The Text)

Much of the Thanksgiving four day weekend will be very nice around Houston, courtesy of an impressive surface high pressure that bridges down from the Great Lakes into Texas. Since the anticyclone is associated with a polar air mass, it may well be that low temperatures for Thursday and Friday will be quite chilly. But latitude and lots of sunshine will start to warm the atmosphere, and as the ridge pulls eastward the flow of air will turn off of the Gulf of Mexico on Saturday. With warm and humid back in the forecast, therein lies the undoing of our weekend condition on November 29.

Even though the latest GFS model output lost the storm threat for Sunday and Monday, I am fairly confident that a high-yield precipitation threat will advance into Texas from the lower Front Range late in the coming weekend. The linkage with the subtropical jet stream and boost from a Kelvin wave nearing the International Dateline will give the disturbance great potential to drop very heavy rain and thunder while also channeling some much colder air. The freeze line is expected to drop as far south as Matamoras Mexico, and it is entirely possible that locations such as Dallas TX and Shreveport LA could see a touch of snow before the low pressure system makes its run fro the eastern Great Lakes.

It can be said with some certainty (a rarity in weather forecasting, I know....) that most of the medium range and longer term forecast for Houston, and indeed much of the U.S., will be colder than normal. There is now good agreement among the numerical models on a strong Rex signature forming over Alaska and northwestern Canada, with the net effect of setting up drainage of cPk and cA regimes into the nation mainly east of the Continental Divide. Since the subtropical jet stream is so active and lodged to our south and east, we may have to confront the possibility of a more important winter precipitation episode in Texas at some point during the first half of December. And while normally snow or ice is a rarity, just remember what happened last December 11!

[iorange55]

Well the 0z looks better than the 18z thats for sure. I still hope they go back to what they were showing yesterday, though. Still looks like we'll have cold enough temps, and maybe some precip hanging around. It might not be as much as previous thought, but i'd take anything after last "winter"




Edit: Anything looks better than the 18z*

[vbhoutex]

One thing I have not seen mentioned in any of the discussions about the cold headed our way is how much it may modify. IIRC(I really need to check), there is not a whole lot of snow cover between Texas and the Canadian border. Leaves a lot of room for the extremely cold temps that some think may be coming to modify substantially before arriving in Texas. I'm not saying that it won't get cold, but I wonder how really cold it will get initially.

[srainhoutx]

Very true David. Modified Canadian Air, but the trend is to see more of these type fronts coming down. I like to think of it as a stair stepping process. The trend is stepping down (cooler) over time. And more chances to add the "snow cover" to our N.

Lubbock offered a "hint" at the end of their AFD this morning...snipet..

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LUBBOCK TX
417 AM CST WED NOV 25 2009



ALTHOUGH A MOOT POINT THIS FAR OUT...THERE IS A SURPRISING AMOUNT
OF AGREEMENT BETWEEN THE MODELS THAT AN ARCTIC AIRMASS WILL BECOME
DISLODGED EARLY NEXT WEEK AND BEGIN MOTORING SOUTH INTO THE
CENTRAL AND POSSIBLY SOUTHERN GREAT PLAINS BY MIDWEEK.

[iorange55]

Dallas NWS seem sure of themselves

ASSOCIATED COLD FRONT WILL REACH NORTHWESTERN NORTH TEXAS SUNDAY
MORNING...WITH THE ECMWF AND GFS AGREEING FAIRLY WELL ON FRONTAL
TIMING. FAIRLY COOL AIR WILL STREAM IN...BUT THIS IS NOT ARCTIC
AIR AND RAIN IS THE PRECIP TYPE EXPECTED. ATMOSPHERE DRIES OUT
MONDAY EVENING...SO BY THE TIME IT WOULD BE COLD ENOUGH FOR ANY
WINTER PRECIPITATION IT WILL BE TOO DRY TO PRODUCE ANY. THIS IS
TYPICAL OF TEXAS COLD FRONTS...SO THIS IS NOT AN EXCEPTION.

AFTER MONDAY BOTH MODELS KEEP NORTH TEXAS IN DRY WESTERLY FLOW SO
NO MORE PRECIP EXPECTED THROUGH DAY 7.



&&

Hope they're wrong.

[srainhoutx]

Yet Austin mentions for the first time the possibility...

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE AUSTIN/SAN ANTONIO TX
408 AM CST WED NOV 25 2009

.DISCUSSION...
CURRENT SAT ANALYSIS SHOWS TEXAS UNDER CLEAR SKIES AT THE BOTTOM
OF A BROAD...FLAT UPPER AIR TROF. HIGH PRESSURE AT THE SFC IS
CENTERED AROUND SAN ANGELO. THE CLEAR SKIES COMBINED WITH LIGHT
WINDS ARE PRODUCING EXCELLENT RADIATIONAL COOLING. TEMPS ARE
RUNNING GENERALLY 15 TO 25 DEGREES LOWER THAN YESTERDAY. SO...WE
WILL SEE A CHILLY START TO THE DAY. IN THE SHORT TERM HIGH
PRESSURE WILL DRIFT ACROSS FROM WEST TO EAST THROUGH THE END OF
THE WEEK. THIS WILL MEAN COOL MORNINGS AND WARM AFTERNOONS.

GFS AND ECMWF ARE IN GOOD AGREEMENT THAT BY SAT SFC HIGH WILL MOVE
EAST OF THE STATE AND LOW LEVEL FLOW WILL TURN AROUND TO SE
BRINGING A RETURN OF GULF MOISTURE. THIS WILL MEAN A SLIGHT CHANCE
FOR STREAMER SHOWERS ACROSS THE EASTERN COUNTIES SAT NIGHT. SUN AND
MON THE NEXT COLD FRONT WILL PASS THROUGH THE AREA BRINGING A
BETTER CHANCE FOR RAIN TO THE CWA. SUN THERE WILL BE A CHANCE FOR
THUNDERSTORMS AND MODERATE RAIN. THIS SYSTEM WILL ALSO BRING COLD
AIR. THE GFS IS SHOWING A CHANCE FOR SOME WINTER PRECIP OVER THE
HILL COUNTRY MON MORNING/AFTERNOON ON THE BACK EDGE OF THE SYSTEM.
TIMING OF PRECIP AND COLD AIR IS NOT CERTAIN AT THIS TIME...SO
HAVE NOT INCLUDED ANY MENTION IN FORECAST. WE WILL HAVE TO
CONTINUE TO MONITOR THE SITUATION THROUGH THE WEEK.

[Portastorm]

Interesting to see that the 0z Euro paints a colder picture for the southern Plains/Texas next week than the 0z GFS. Here are a few comparisons from the 500mb charts.

Euro at 192 hrs:


GFS at 192 hrs:


Euro at 240 hrs:


GFS at 240 hrs:

[srainhoutx]

HPC mentioning the modified Arctic Airmass later next week in the Morning Prelim Disco...

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
859 AM EST WED NOV 25 2009

VALID 12Z SUN NOV 29 2009 - 12Z WED DEC 02 2009





THE UPDATED PRELIM GRAPHICS KEPT THE SAME GENERAL IDEAS OF THE
EARLY PRELIM BUT SUBSTITUTED THE NEW 00Z/25 ECENS MEAN FOR THE
OLDER CORRESPONDING 12Z/24 MEAN. OUR BLEND WAS 70% DETERMINISTIC
ECMWF EARLY IN THE PERIOD BUT TAPERED OFF TO 70% ECMWF ENSEMBLE
MEAN TOWARDS THE END OF THE PERIOD.


DESPITE BIG CONTINUITY CHANGES IN ITS LAST TWO RUNS FOR THE MIDDLE
OF NEXT WEEK...THE EUROPEAN CENTRE GUIDANCE STILL LOOKS MORE
STABLE THAN THE OTHER GLOBAL NUMERICAL MODELS...INCLUDING THE GFS
AND GEM GLOBAL...WITH THE HANDLING OF THE UPCOMING PATTERN. THE
MAIN FORECAST PROBLEM....FOR TUE-WED DAYS 6-7...APPEARS TO BE THE
POSSIBLE SPLITTING OF A TROF CROSSING THE MS RIVER INTO NRN AND
SRN STREAM PIECES OF ENERGY. THIS SPLITTING IS COMPLICATED BY A
THIRD SHOT OF ENERGY DROPPING INTO THE NRN ROCKIES AT THAT TIME
WITH ITS OWN POTENTIAL FOR SPLITTING INTO TWO PARTS. IT WAS
SOMEWHAT ENCOURAGING TO SEE THE NEW 00Z GFS PARALLEL RUN
SUPPORTING THE 00Z ECMWF WITH A POSITIVE TILT SPLITTING TROF
SCENARIO TUE DAY 6 VERSUS THE REGULAR GFS DEEP ONE PIECE SYS OVER
THE ERN CONUS. HOWEVER THE 06Z/25 PARALLEL RUN EVOLVED A WHOLE
DIFFERENT SCENARIO BY DAY 6 CREATING TWO CUTOFF LOWS FROM THE
SPLIT OFF SRN END OF THE NRN ROCKIES TROF AS WELL AS THAT OF THE
ERN CONUS TROF. THAT WILD 06Z GFS PARALLEL SOLUTION HAD NO SUPPORT
FROM THE 00Z/25 ENSEMBLE SPAGHETTI PLOTS...WHILE THE SPLITTING
SOLUTION OF THE 00Z DETERMINISTIC ECMWF HAS GOOD SUPPORT FROM
ECMWF/CANADIAN ENSEMBLE MEMBERS AND EVEN A FEW GFS ENSEMBLE
MEMBERS. BEHIND THAT SYSTEM...ALL THE MODELS SHOW AN INVASION OF
AT LEAST MODIFIED ARCTIC AIR OVER THE NORTHERN PLAINS LATE DAY 7
AND JUST BEYOND THIS FORECAST PERIOD...THE FIRST SUCH OUTBREAK IN
SEVERAL WEEKS.

CISCO/FLOOD

[snow and ice]

The EURO 8-10 day means looks very cold. Check out that blocking over the top.
http://www.meteo.psu.edu/~gadomski/ECMW ... tcomp.html

[Portastorm]

Usually a good idea when we get into this season to see what our friends at NWSFOs in Oklahoma are saying. Seems like they have an eye to the north later next week as well as Lubbock's comments this morning.

From Tulsa:
SIGNIFICANT COLD ON THE WEATHER HORIZON ABOUT THIS
TIME NEXT WEEK AS A MAJOR LEAGUE RIDGE BUILDS NEAR
THE WEST COAST..AND EQUALLY IMPRESSIVE TROUGH TAKES
SHAPE OVER THE MIDDLE OF THE COUNTRY.


From Norman:
AFTER ANOTHER PERIOD OF MILD WEATHER AROUND THE MIDDLE OF NEXT
WEEK... BOTH THE GFS AND ECMWF PULL A RATHER COLD CANADIAN AIRMASS
SOUTH INTO THE SOUTHERN PLAINS... PROBABLY COLDER THAN ANY WE HAVE
SEEN SO FAR THIS SEASON. BUT... THAT IS BEYOND THE RANGE OF THIS
FORECAST.

[mysterymachinebl]

Dallas NWS seem sure of themselves

ASSOCIATED COLD FRONT WILL REACH NORTHWESTERN NORTH TEXAS SUNDAY
MORNING...WITH THE ECMWF AND GFS AGREEING FAIRLY WELL ON FRONTAL
TIMING. FAIRLY COOL AIR WILL STREAM IN...BUT THIS IS NOT ARCTIC
AIR AND RAIN IS THE PRECIP TYPE EXPECTED. ATMOSPHERE DRIES OUT
MONDAY EVENING...SO BY THE TIME IT WOULD BE COLD ENOUGH FOR ANY
WINTER PRECIPITATION IT WILL BE TOO DRY TO PRODUCE ANY. THIS IS
TYPICAL OF TEXAS COLD FRONTS...SO THIS IS NOT AN EXCEPTION.

AFTER MONDAY BOTH MODELS KEEP NORTH TEXAS IN DRY WESTERLY FLOW SO
NO MORE PRECIP EXPECTED THROUGH DAY 7.



&&

Hope they're wrong.

Me too! They have switched from yesterday evening's forecast of showing a high in the low 60's on Tuesday to a high in the upper '40s now. So, things can change!

[srainhoutx]

A quick look at the 12 GFS will likely perk some ears. Got to love the models. Cold Core Low over Central TX moving slowly E on Monday night through Wedneday.

[Portastorm]

A quick look at the 12 GFS will likely perk some ears. Got to love the models. Cold Core Low over Central TX moving slowly E on Monday night through Wedneday.

Holy cow!! That run is amazing. You aren't kidding srainhoutx! Yeah, it would spell some wintry precip for at least parts of Texas for sure! It's a little questionable though how it holds back the upper low over west Texas while developing a surface low in the NW Gulf. My guess is that if this 12z run were to verify, that a line from San Angelo to Waco to Texarkana and parts to the north and northwest of that would be possible seeing ice or snow. Probably ice as the atmospheric profile doesn't look cold enough to support snow except under the upper low. But yeah ... what a conversation-starter this run is!

[srainhoutx]

Maybe wxman57 will post some thoughts although he mainly posts in the Tropical areas. I know he has posted in the "local Forum".