Texas/New Mexico/Louisiana/Mexico Obs And Discussion Thread Part 4

[Ed Lizard]

Bed time. Based on Euro AccuWx PPV text (No maps yet) Houston doesn't get much Christmas rain, but DFW is real close to significant Winter weather. Mind you, six hour increments with *previous* six hour precip doesn't tell how much precip when 2 meter, 850 mb temps and 1000-500 mb thicknesses would support snow. 850 mb cools faster than 2 meter, and gets colder, if there is any Winter precip, just a guess, rain to snow with little ice in between.

[bubba hotep]

Bed time. Based on Euro AccuWx PPV text (No maps yet) Houston doesn't get much Christmas rain, but DFW is real close to significant Winter weather. Mind you, six hour increments with *previous* six hour precip doesn't tell how much precip when 2 meter, 850 mb temps and 1000-500 mb thicknesses would support snow. 850 mb cools faster than 2 meter, and gets colder, if there is any Winter precip, just a guess, rain to snow with little ice in between.

Yes, the 00z Euro was a real nice step in the right direction for MBY. FWD is sounding more confident regarding snow on Christmas Day and they put MBY precariously close to the 1" - 2" zone I hope we see a bit of a S trend today b/c the dry slot would be uncomfortably close, if you blend the 00z Euro and 6z GFS.

[Srain]

E-mail from Jeff:

Powerful upper level storm system will bring widespread impacts to TX Christmas Morning.

Next upper level storm system to affect the state is currently diving down into the western US this morning and will begin to move eastward into TX tomorrow. At the surface low level warm air and moisture advection is underway across the state while to our north a shallow cold front is moving southward. Expect this shallow boundary to reach the area tonight and then stall between I-10 and the coast on Monday. Much more powerful system to be approaching from the west Monday night/ Tuesday AM. Southerly winds will continue to pump moisture into the area today into Monday even as the weak boundary stalls. Not expecting much rainfall in the warm air advection pattern with moisture mainly below 800mb.

Surface boundary begins to lift northward as a warm from late Monday as strong upper level system moves into TX. Do not think the warm front will move rapidly northward with developing rainfall north of the boundary helping to roughly maintain its position in the I-10 to HWY 105 corridor into Tuesday morning. Surface low pressure developing over EC TX early Tuesday will bring a punch of dry air eastward out of central TX in the form of a dry line. Powerful mid level jet will rotate through the base of the trough over the state with shear values on the order of 60kts and building instability in the warm sector south of the warm front between midnight and 1000am Tuesday. Expect numerous thunderstorms to develop after midnight to 300am Tuesday some of which will become severe.

A review of severe weather parameters for early Tuesday morning suggest a highly sheared low level environment with low level winds backed to the SE to ESE near the warm front veering to WSW in the mid levels. Both speed and directional shear will be in place over the area and expect storms that develop near and south of the warm front will have a tornado potential. There is some possibility that storms will go into a line along the advancing dry line during the morning hours with a damaging wind threat. We are still about 40-48 hours from the event and some fine tuning is likely on the warm frontal position and where the greatest severe threat will be found on Tuesday morning.

Note: Such strong storm systems in the winter time in the deep south and after dark can have some significant severe weather and tornadoes. Such tornadoes tend to occur in the early morning hours and result in higher fatalities than spring time tornadoes mainly because they occur when residents are asleep.

Dry line will punch rapidly through the area by noon on Tuesday with a quick drying of the air mass. Strong cold front will lag behind the dry line and cross the area in the late afternoon. Very strong winds will onset once again behind this boundary…although not likely as strong as last Thursday…still could see a few gust to 40mph. Temperatures will tumble from the 60’s/70’s prior to the front quickly into the 40’s behind the front. A band of snow will likely develop over N TX within the comma head portion of the upper level storm system. Some accumulation of snow will be possible from the DFW area NE into OK and AR on Christmas Evening and night. No snow is expected across SE TX as moisture will be scoured out of the area prior to the thermal column being cold enough for snow.

Strong winds Tuesday night and Wednesday morning should keep lows mainly near freezing north of US 59. Highs on Wednesday will struggle to reach 50 degrees under continued cold air advection. Surface high pressure will build over the area Wednesday night with mainly clear skies and light winds. With very low dewpoints (in the 20’s) should see a widespread freeze for all areas except the immediate coast. Even the urban heat areas may see a light freeze this time around. Colder locations could see lows in the mid 20’s for Thursday morning.

[bubba hotep]

FWD issued a multimedia briefing on the upcoming system.

MBY continues to be nervously between the 2" - 4" and the trace.... (images from the NOAA multimedia briefing)

I would love to lock in an inch or two but am still looking for some last minute jogs to the south.

and it looks like the 00z NAM is a bit south and maybe that will kick off a 00z trend

[Ed Lizard]

Backyard into Louisiana severe homerism...

And if the ground turns white from hail tomorrow, I'm claiming a White Christmas.

[bubba hotep]

12z GFS looks like it takes just enough of a south jog to get a little snow into MBY. Grasping at straws at this point

[Quixotic1]

12z GFS looks like it takes just enough of a south jog to get a little snow into MBY. Grasping at straws at this point

I'm in the "trace" zone. Good luck tomorrow. an 80 mile jog is nothing!

[bubba hotep]

GFS clown map changes from 6z to 12z, fun to look at but probably not worth much more than that. From Harris WeatherCaster™:

6z GFS

12z GFS

ETA: FWD afternoon update - they took MBY out of the 1" - 2" zone with the overnight packages but put us back in the game with this update!

[Quixotic1]

1-3" per wwa. i'll gladly take it.

[Ed Lizard]

Still glass eight full on accumulating hail producing a White Christmas.

[bubba hotep]

Some great Christmas Eve reading from FWD as they explain why a more southern track might be taking hold:

FXUS64 KFWD 250312

AFDFWD

AREA FORECAST DISCUSSION

NATIONAL WEATHER SERVICE FORT WORTH TX

912 PM CST MON DEC 24 2012

.UPDATE...

WE HAVE ANALYZED THE 00Z UPPER AIR DATA AND HAVE WATCHED THE

SURFACE OBS CLOSELY FOR SIGNS OF ANY DISCREPANCIES BETWEEN THEM

AND THE MODEL DATA. THE BIG THING THAT STANDS OUT ARE THAT THE

SURFACE LOW IN NORTHEAST NEW MEXICO AT 6PM WAS ABOUT 80 MILES

FARTHER SOUTH THAN ALL OF THE MODELS HAD FORECAST 24 HOURS AGO.

WHEN DEALING WITH A SWINGING/DIGGING UPPER LEVEL SYSTEM...THE

SURFACE PRESSURE PATTERN AND PRESSURE TENDENCIES OFFER ENORMOUS

CLUES ON THE FUTURE TRACK OF A POTENTIAL VORTICITY ANOMALY BEFORE

IT CLOSES OFF TO BECOME A FULL FLEDGED UPPER LOW. THE 3PM AND 6PM

SURFACE ANALYSIS SHOWED A LARGE REGION OF PRESSURE FALLS ACROSS

NEW MEXICO AND WEST TEXAS IN ADVANCE OF THE SYSTEM. GIVEN THE

ORIENTATION OF THE PRESSURE FALLS AND LOCATION OF THE SURFACE

LOW...IT CAN BE DETERMINED WITHOUT EVEN LOOKING AT A FORECAST

MODEL THAT THE UPPER LOW HAS NOT FINISHED DIGGING SOUTH. THE BIG

QUESTION IS HOW FAR SOUTH WILL THE UPPER LOW MAKE IT BEFORE IT

BEGINS TO SWING BACK TO THE NORTHEAST. AT THIS HOUR PRESSURE FALLS

CONTINUE IN THE REGION FROM LUBBOCK TO MIDLAND...WITH ANOTHER

PRESSURE FALL AREA DEVELOPING IN SOUTHEAST TEXAS. EXTRAPOLATING

SUGGESTS THE UPPER LOW WILL TRACK JUST SOUTH OF LUBBOCK BY SUNRISE

AND TO NEAR WACO BY SUNSET. AS THE LOW APPROACHES WACO...A WARM

FRONT WILL BE ORGANIZING OUT OF THE WEAK STATIONARY FRONT

CURRENTLY ANALYZED FROM SAN ANTONIO TO HOUSTON. BAROCLINIC QG

THEORY SUGGESTS THAT ONCE LOW LEVEL WARM ADVECTION BEGINS IN

EARNEST ACROSS SOUTHEAST TEXAS BY MORNING...IT WILL INDUCE HEIGHT

RISES TO THE SOUTHEAST OF OUR UPPER LOW WHICH WILL CAUSE THE LOW

TO CLOSE OFF AND FINISH DIGGING SOUTH...AND START ITS GRADUAL

TURN TO THE NORTHEAST. TOMORROW EVENING I WOULD EXPECT THE LOW TO

TRACK FROM NEAR WACO TO NEAR SHREVEPORT. IN SUMMARY THE USUAL

MEDIUM RANGE MODELS APPEAR TO BE A LITTLE TOO FAR NORTH WITH THE

TRACK OF THE UPPER LOW. OUR EXPECTATIONS FOR THE TRACK OF THE LOW

ALIGN WELL WITH THE RAP FORECAST WHICH IS TO THE SOUTH OF ALL

OTHER MODELS...SO WE WILL USE THE RAP HEAVILY.

OUR FORECAST HAS BEEN ON THE SOUTHERLY SIDE AND SNOWIER SIDE OF

THE MODEL GUIDANCE. SO ALTHOUGH WE ARE SEEING AN EVEN MORE

SOUTHERLY TRACK COME TO FRUITION...THIS DOES NOT NECESSARILY

MEAN THE FORECAST SNOW AMOUNTS NEED TO BE AMENDED MUCH. THIS IS IN

PART DUE TO THE DIFFICULTY IN GETTING THE COLDER/SUBFREEZING AIR

FARTHER SOUTH BEFORE THE PRECIPITATION ENDS. THE EXCEPTION IS THE

NORTHWEST ZONES WHERE THE MORE SOUTHERLY TRACK SUGGESTS MORE

PRECIP WILL FALL IN SUBFREEZING AIR. DUE TO THE TERRAIN EFFECTS

HERE...COLD AIR HAS AN EASY TIME GETTING INTO OUR NORTHWEST ZONES

WHEN WE HAVE A NORTH/NORTHEAST SURFACE WIND. HAVE EXPANDED THE

SNOW ADVISORY TO INCLUDE YOUNG/JACK/WISE COUNTIES...AND HAVE

INCREASED SNOW TOTALS TO THE 2-4 INCH RANGE FROM BOWIE TO SHERMAN.

THE NORTHEAST ZONES LIKELY WONT SWITCH TO SNOW UNTIL LATE

AFTERNOON...AS COLD AIR WILL HAVE TROUBLE MOVING IN AT THE SURFACE

DUE TO THE LEE SHADOW WARMING EFFECT OF THE OZARK PLATEAU. MOST OF

THE SNOW THAT OCCURS THERE WILL BE AFTER 6 PM AND WILL BE HIGHLY

DEPENDENT ON WHETHER MESOSCALE BANDING CAN SET UP IN THE WAKE OF

THE UPPER LOW. THE NEW NAM HAS FINALLY FORECAST SOME SIGNIFICANT

BANDING TO OCCUR...THUS WILL LEAVE THE ADVISORY ALONE IN THIS

AREA...BUT CONFIDENCE IS A LITTLE LOWER IN THE NORTHEAST ZONES FOR

2+ INCHES OF SNOW.

FARTHER TO THE SOUTH OF THE ADVISORY...FOR THE I-20 CORRIDOR AND

INCLUDING THE METROPLEX...THERE IS NOW HIGH CONFIDENCE THAT SNOW

WILL OCCUR. HOWEVER ALL INDICATIONS ARE THAT IT WILL STILL BE A

BRIEF 1-3 HOUR EVENT WITH NOT ENOUGH TIME TO GET ACCUMULATIONS

OVER AN INCH. IT MUST BE STRESSED THAT WITH TEMPERATURES FALLING

INTO THE 20S BY SUNSET...ANY APPRECIABLE MOISTURE REMAINING ON

BRIDGES...OVERPASSES AND EVEN SURFACE STREETS WILL LIKELY RE-

FREEZE INTO BLACK ICE. ALTHOUGH WE ARE USING 1+ INCH AS CRITERIA

FOR THE COUNTIES IN THE WINTER WEATHER ADVISORY AREA...WE MAY

EXPAND THE ADVISORY SOUTH INTO THE METROPLEX OVERNIGHT DUE SOLELY

TO TRAVEL IMPACTS.

FINALLY CONCERNING THE SEVERE WEATHER TREAT. WITH A MORE SOUTHERLY

TRACK OF THE UPPER LOW...THIS MEANS THERE IS LESS OF A CHANCE OF

THE WARM FRONT MAKING IT INTO THE SOUTHEAST CWA TONIGHT AS IT WILL

LIKELY STAY SOUTHEAST OF THE AREA. ELEVATED THUNDERSTORMS ARE

STILL EXPECTED TO RAPIDLY INCREASE IN COVERAGE AFTER 3 AM...WITH

ELEVATED INSTABILITY HIGH ENOUGH FOR A FEW SEVERE HAIL STORMS

SOUTH OF I-20. HAVE TONED DOWN THE DAMAGING WIND AND TORNADO

THREAT FROM OUR PRODUCTS...BUT WE WILL CONTINUE TO ADVERTISE HAIL

STORMS POSSIBLE LATE TONIGHT AND EARLY TOMORROW MORNING.

[bubba hotep]

Kids are in bed, plenty of beer in the fridge, and the clown maps keep getting more lol:

00z NAM

[David Reimer]

The RAP runs from the past few hours are making this situation look much more interesting snow-wise for North Texas.

[bubba hotep]

Heavy rain and hail to get the show started.

[Ed Lizard]

My usual source for RAP/HRRR goodies, not working, but I don't give up.

15-17Z looks interesting locally with 1 hour precip in area. Off 10Z RAP

[oldlogin]

Tornado watch

[bubba hotep]

Now we wait for changeover

[bubba hotep]

Merry Christmas all!

Even if we don't get any snow, it looks like we have gotten a good bit of very beneficial rainfall across most of the DFW area.

[Ed Lizard]

[bubba hotep]

Ugh, the waiting game Rain is starting to let up but we probably got 1.5 - 2+" here IMBY. The RAP continues to insist that the snow will get cranking here around 20z and then last 4 or 5 hours.

[Terpeast]

Wind direction shifted, screaming from the N/NW. Temps in the mid 40s, and starting to drop. (Location: Forney, TX)

I see a sharp cut off between 2-3" and a trace (or nothing) along I-20. Small shifts can make a huge difference.

[Terpeast]

RAP insists on potential for mesoscale banding (mod-heavy snows) from DFW to Terrell to Mt Pleasant. We shall see if that pans out, and if it does, then we could get bigger snows than currently predicted. If the band misses DFW-east just to the north, then trace or nothing.

[bubba hotep]

RAP insists on potential for mesoscale banding (mod-heavy snows) from DFW to Terrell to Mt Pleasant. We shall see if that pans out, and if it does, then we could get bigger snows than currently predicted. If the band misses DFW-east just to the north, then trace or nothing.

Yeah, this is going to be a nail biter, reminds me of my time back in the DC area and waiting for storms to get cranking.

ETA: Temps are finally starting to fall after holding steady all morning.

[DFWWeather]

Wichita Falls now under a Blizzard Warning!

Growing very concerned for significant icing on area roadways as temperatures drop to the teens tonight at DFW.

[bubba hotep]

Wichita Falls now under a Blizzard Warning!

Growing very concerned for significant icing on area roadways as temperatures drop to the teens tonight at DFW.

Temps are plummeting here as we wait for changeover

ETA: RAP is still insisting that snow will start cranking here around 20z

[bubba hotep]

MESOSCALE DISCUSSION 2213

NWS STORM PREDICTION CENTER NORMAN OK

0100 PM CST TUE DEC 25 2012

AREAS AFFECTED...N-CNTRL/NERN TX...SWRN AR...FAR NWRN LA...EXTREME

SERN OK

CONCERNING...HEAVY SNOW

VALID 251900Z - 260000Z

SUMMARY...RAIN WILL TRANSITION TO SNOW AFTER A BRIEF PERIOD OF

SLEET. HEAVY SNOW IS ANTICIPATED...WITH SNOWFALL RATES OF 1-1.5

IN/HR POSSIBLE...ESPECIALLY TO THE NORTH OF A LINE FROM THE DFW AREA

TO TEXARKANA.

DISCUSSION...MOISTURE TRANSPORT/ASCENT ACCOMPANYING THE WRN BRANCH

OF A BIFURCATED WARM CONVEYOR BELT AND COLD CONVEYOR BELT STRUCTURES

NEAR AND S OF THE RED RIVER WILL MAINTAIN PRECIPITATION INTO THE

EVENING FROM N-CNTRL TX EWD TO THE ARKLATEX REGION. AS DEEPER COLD

AIR ADVANCES INTO THE AREA ON THE BACKSIDE OF A LOWER-MS-VALLEY SFC

LOW...LOWER TROPOSPHERIC TEMPERATURE PROFILES WILL COOL. THIS WILL

SUPPORT A PHASE CHANGE TO SNOW FROM W TO E...THOUGH A BRIEF PERIOD

OF SLEET MAY OCCUR. PER OBSERVATIONAL DATA AND CONSENSUS AMONGST

SHORT-RANGE...HIGH-RESOLUTION WRF GUIDANCE...THE CHANGEOVER TO SNOW

WILL LIKELY OCCUR AROUND THE DFW METROPLEX TO S OF DURANT OK AROUND

20Z...WITH A CHANGEOVER TO SNOW LIKELY OCCURRING OVER THE ARKLATEX

REGION BETWEEN 22Z AND 00Z. BASED ON RECENT TRENDS IN THE TRACK OF

THE MID-LEVEL VORT MAX PER WATER VAPOR IMAGERY AND ZONE OF INFERRED

ASCENT...THE HIGHEST SNOWFALL RATES ARE EXPECTED N OF A LINE FROM

THE DFW AREA TO TEXARKANA...WHERE SNOWFALL RATES OF 1-1.5 IN/HR WILL

BE MOST LIKELY. THESE RATES WILL BE IN ASSOCIATION WITH A

W/E-ORIENTED LOW-TO-MID-LEVEL CONFLUENCE AXIS AT THE BASE OF

STRONGER UPWARD MOTION. RELATIVELY WEAKER ASCENT WILL SUPPORT

SOMEWHAT LOWER RATES FARTHER SOUTH.

..COHEN.. 12/25/2012

[Srain]

If the 12Z Euro is correct, we'll be dealing with another big Winter Storm beginning New Years Eve into New Years Day...

[bubba hotep]

If the 12Z Euro is correct, we'll be dealing with another big Winter Storm beginning New Years Eve into New Years Day...

Hmmm.... something to track. Maybe the rest of this week won't be so boring up at the office.

[bubba hotep]

Sleet is starting to mix in here

ETA: Full fledged winter mix now with flakes flying

[Terpeast]

Still rain in Forney. Snow should mix in here by 3 pm CST.