Texas/New Mexico/Louisiana/Mexico Obs And Discussion Thread Part 5

[DFWWeather]

The 768 hour monthly of the ECMWF has Arctic air returning to the CONUS big time toward the end of December into New Year's. That would be about the right time from the stratospheric warming episode over the pole last week.

[aggiegeog]

Keep a close eye on the closed upper low for next week. Should produce good rain and depending on upper air temps snow for a good part of the state. Until late this month our cold will come from above not the Arctic.

[Quixotic1]

Keep a close eye on the closed upper low for next week. Should produce good rain and depending on upper air temps snow for a good part of the state. Until late this month our cold will come from above not the Arctic.

Agree with this.  We had a couple of storms in Mar of 2008 where it was 70 the day before and 60 the day after.  The storms were powerful and cold enough to produce heavy snow with little or no low level cold air to work with.  DFW only got an inch on the last one but parts just to the NW got 9 inches with lightning and thunder.    

[bubba hotep]

Keep a close eye on the closed upper low for next week. Should produce good rain and depending on upper air temps snow for a good part of the state. Until late this month our cold will come from above not the Arctic.

This system might have a surprise for some in Texas but it won't be the last. It looks like a stretch of unsettled weather for the second half of December. I especially like the early Christmas week window for Texas snow lovers.

[1900hurricane]

The chances of heavy rain also look pretty good with this system, which is what I'm personally looking forward to. There may also be a chance for some strong storms with the cold air aloft from the system, but low level instability will be a big question mark, as is common this time of year. Directional shear is also often fairly poor with closed lows like this, but I'll be happy with craploads of rain in the absence of severe weather. These things have a tendency to be fairly prolific rain makers. Any winter precip that may occur beneath/just on the backside of the energy aloft would just be icing on the cake for me.

[aggiegeog]

Agree with this.  We had a couple of storms in Mar of 2008 where it was 70 the day before and 60 the day after.  The storms were powerful and cold enough to produce heavy snow with little or no low level cold air to work with.  DFW only got an inch on the last one but parts just to the NW got 9 inches with lightning and thunder.    

 

The one I remember the best was Dec 10, 2008 in College Station on the last day of finals at A&M for that fall semester, I was up all night finishing up a big paper and upon finishing it it started snowing on the way back to my dorm and snowed most of the morning if I remember correctly. Prob got a couple inches on campus. The setup seems like it could be similar to this one.

[1900hurricane]

Just issued:

 

[Srain]

There is still some spread within the ensemble mean via the Euro and GEFS. While there is some similarities to the November 21-22 event, the pattern is a bit different with less in the way of cold air. That said these pesky 5H lows tend to be a forecasting nightmare at this range and until the system nears California late week into the weekend as it enters the RAOB network, expect changes. It is noteworthy that this is likely the beginning of a very active parade of southern stream storms that will bring us into the Christmas/New Year timeframe with progressive colder air building in with each storm system. This +PDO/+PNA regime is going to be interesting to watch unfold.

 

[bubba hotep]

For those of you bummed out by the new Euro weeklies, well there is this:

 

[1900hurricane]

From EWX this afternoon:

 

.LONG TERM (WEDNESDAY THROUGH MONDAY)...
THE RETURN OF RETURN FLOW WILL BEGIN WEDNESDAY MORNING. WHICH WILL
BEGIN A MULTI DAY PROCESS OF MOISTENING THE ATMOSPHERE. A SERIES
OF WEAK SHORTWAVES...ONE ORIGINATING FROM THE SOUTHERN CALIFORNIA
COAST AND ANOTHER FROM NORTH DAKOTA...WILL INTERACT TO FORM A
QUAZI TROUGH AXIS OVER CENTRAL TEXAS LATE WEDNESDAY NIGHT AND
THURSDAY MORNING. THIS SHOULD COUPLE WITH THE MORE MOIST
ENVIRONMENT FOR SOME LIGHT SHOWER ACTIVITY PRETTY MUCH EACH DAY
THROUGH THE BEGINNING OF THE WEEKEND. THE WARMEST DAY LOOKS LIKE
SATURDAY WITH HIGHS REACHING THE MID 70S IN OUR SOUTHERN COUNTIES.
THE RIDGE AXIS WILL BE OVERTOP CENTRAL TEXAS AND AT ITS MOST
AMPLIFIED...JUST IN ADVANCE OF A MUCH MORE SIGNIFICANT UPPER LEVEL
SYSTEM PROGGED TO BEGIN IMPACTING THE STATE SUNDAY.

REGARDING THAT SYSTEM...CONSIDERING PREVIOUS RUNS WERE SO STARKLY
DIFFERENT FROM RUN TO RUN AND BETWEEN EACH SYNOPTIC MODEL...IT IS
QUITE SURPRISING HOW MUCH AGREEMENT EXISTS IN THE LONG RANGE
MODELS WITH THE 12Z RUNS. BOTH ARE SHOWING A STRONGLY AMPLIFIED
UPPER LEVEL LOW EVOLVING FROM THE MIDDLE CALIFORNIA COAST TO THE
SOUTHERN ROCKY MTNS. THIS LOW BECOMES CUT OFF AS IT ENTERS THE
STATE AND ALSO BECOMES SLIGHTLY NEGATIVELY TILTED. THIS RESULTS IN
WELL AGREED UPON PVA AND HEIGHT FALLS OVER WEST CENTRAL TEXAS AND
NORTHERN HILL COUNTRY BY LATE SUNDAY AFTERNOON. IN THE UPPER
LEVELS...MODERATE 250MB DIVERGENCE DEVELOPS AS IN BOTH
MODELS...MORE IMPRESSIVELY IN THE EURO...OVER EAST AND NORTHEAST
TEXAS SUNDAY EVENING.

LOWER IN THE ATMOSPHERE...A 40-45KT LLJ IS BEING SHOWN IN BOTH
MODELS TO DEVELOP BY 18Z SUNDAY...EFFICIENTLY ADVECTING LOW LEVEL
MOISTURE ACROSS MUCH OF THE EASTERN HALF OF THE STATE. AT THE
SFC...A MODERATELY UNSTABLE AIR MASS...AT LEAST FOR
DECEMBER...WILL BE IN PLACE WITH LI VALUES IN THE -2 TO -4 RANGE
ON FORECAST SOUNDINGS AND SFC BASED CAPES AT 800-1000 J/KG UP AND
DOWN THE I35 CORRIDOR UP TO JUST SOUTH OF DALLAS. PWAT VALUES ARE
OVER AN INCH AS WELL.

BASICALLY...CONFIDENCE HAS INCREASED QUITE A BIT FROM PREVIOUS
DAYS ON THIS SYSTEM WITH BOTH MODELS BEING IN SUCH GOOD AGREEMENT.
BASED OFF THE PARAMETERS ADVERTISED...A STRONG AND POTENTIALLY
SEVERE THUNDERSTORM SITUATION COULD DEVELOP SUNDAY AFTERNOON AND
EVENING...MAINLY FOR THE NORTHERN AND EASTERN HALF OF OUR CWA. DO
THINK HEAVY RAIN IS THE THREAT WITH THE MOST CONFIDENCE BUT THE
SYSTEM COULD CONTAIN DAMAGING WINDS AS WELL. WOULD LIKE TO SEE
BETTER LAPSE RATES IN THE SOUNDINGS FOR HAIL POTENTIAL BUT THAT
THREAT COULD EVOLVE WITH MORE RESOLUTION IN THE SHORT TERM MODELS.

[Nairobi]

ECMWF operational progging only 1/3 inch of rain for Austin Sunday and Monday but 6/10 for this Thursday and Friday.

http://www.yr.no/place/United_States/Texas/Austin/long.html

GFS 12/10 0Z operational progging 1/2 inch of rain for Austin Sunday and Monday and 1/4 inch of rain for this Thursday and Friday.

http://wxweb.meteostar.com/sample/sample.shtml?text=katt

[Nairobi]

The 12/10 0Z parallel GPS operational predicted temperature anomalies for the Yukon, often a source for cold air for Texas, during the next 10 days shows repeated influxes of warm anomalies. The cold stuff stays over northwest Alaska and eastern Siberia (but not right on the Bering Sea coast).

From this morning's KEWX forecast discussion:

THE LATEST ROUND OF MEDIUM RANGE MODEL GUIDANCE CONTINUES TO SHOW THE ABOVE MENTIONED UPPER LEVEL SYSTEM WILL MOVE FARTHER NORTH OF OUR REGION THIS WEEKEND. WE DO EXPECT A CHANCE OF RAIN WITH THIS SYSTEM ON SUNDAY... BUT THE BETTER OPPORTUNITY FOR RAINFALL IS EXPECTED TO REMAIN ACROSS NORTH TEXAS. FOR NOW...WE/LL MENTION 30-50% PRECIPITATION CHANCES FOR AREAS GENERALLY NORTH OF I-10. IF LATER MODEL RUNS REMAIN CONSISTENT...THE BETTER RAIN CHANCES WOULD LIKELY NEED TO BE SHIFTED FARTHER NORTH. WE SHOULD SEE A QUICK END TO PRECIPITATION BY MONDAY AS DRIER AIR AND COOLER TEMPERATURES BEHIND A PACIFIC COLD FRONT SPREAD INTO THE REGION. THE DRY AND COOL WEATHER WILL CONTINUE THROUGH TUESDAY.

From this morning's KSJT forecast discussion:

The next upper level trough/low will be across the Intermountain West late Saturday, then move across the Southern/Central Plains on Sunday. The 00Z ECMWF is farther north in the track of the low, which results in less precipitation across West Central Texas than the GFS solution. Even the GFS solution would keep the best PoPs across mainly our eastern and northern counties. For now, very minor changes were made to PoPs, with the best PoPs across the eastern and northern half of the forecast area.

[1900hurricane]

Not real enthused with model trends. The system is trending further north and the current nor'easter is going to mess with moisture return too.

 

[bubba hotep]

I am digging the look of the 12z Euro at D10. I've been high on the possible Christmas week setup for a while now and that system moving into California is right on time.

[Nairobi]

ECMWF 500 mb prog:

[Srain]

Briefing from Jeff that was sent out late last evening:


Fairly mild and tranquil pattern since before Thanksgiving will begin to undergo changes over the next 5-10 days.

Zonal upper air pattern of late will begin to undergo amplification as current “intense” western US storm system begins to buckle the upper air pattern. This system will move across the SW US on Friday and eject into the central plains late this weekend sending a Pacific cold front across TX. Main energy and dynamics will pass well north of SE TX, but combination of increasing moisture and incoming cold front will likely result in a round of showers and thunderstorms from midday Sunday into midday Monday. Not looking at severe weather with best dynamics northward toward OK. Will have to watch for winds shifting to the SW in the mid levels which can dry slot this area and really cut back on rainfall potential. Given the best forcing will be well to the north, only expecting modest rainfall amounts of generally less than an inch. This is also a classic case of where the best rain chances tend to be across the northern portions of the region.  

Of bigger interest is the apparent change in the storm track following this first “ lead” storm. Southern branch jet stream appears to become the increasingly dominant weather maker leading up toward Christmas and even into early 2015. A secondary storm system will follow the first “late weekend” storm by the mid to end of next week and likely progress much further southward yielding a more active weather event for TX. Additionally, long range model guidance with support from their ensemble means indicate cold air will make a return into the US near/just before Christmas with an active southern storm track continuing. Would like to see a little more support for this pattern change before jumping fully on board with a colder and wetter regime starting next week and lasting into early January 2015, but this would be supported by warm phase ENSO (El Nino) conditions in the Pacific. While current water temperatures in the Nino regions are near or above the required thresholds, other indicators are still not fully suggesting El Nino conditions. There remains a 65% chance of El Nino conditions early in 2015 and while “official” warm phase ENSO may not be in place, the atmospheric response appears to be favoring what one would likely see in such a warm phase.

[Nairobi]

Per ECMWF operational, 500 mb closed low digging southeast at 216 and 240 hours with slight weakening:

Parallel GFS operational at 240 hours is faster and slightly weaker but progs widespread light rain and snow for the state with a weak coastal low taking shape in deep south Texas:

[Portastorm]

Classic set up in Nino-esque Texas winters with an upper level low crossing the state and shearing out to some degree and a coastal low developing.  Seen it many times.