December: Warm Days & Cool-Foggy Nights To End 2011

[srainhoutx]

The front is nearing the Hill Country at this hour. Our clouds have lingered, but we should see some clearing overnight before those clouds racing S and E from the Permian Basin drape the Lone Star State tomorrow...

[srainhoutx]

18Z 4km NAM suggested snowfall...through 60 hours...

[sleetstorm]

I was gazing at the drought monitor earlier today and saw that the recent rainfall has done some good in several parts of this state. What are the signs that drought may or could come back with retribution next month and all throughout next year?

[srainhoutx]

The HPC suggesting a Euro/Canadian blend via the 00Z solutions. The overall theme has been to slow things down a bit and to keep precip gong into Saturday night/early Sunday morning. That trend would tend to not bode well for the Hill Country into the Metroplex. It does appear the H5 low may be a tad further S into Old Mexico than guidance had suggested, so we'll see what future runs do with handling this evolving situation. Stay Tuned!

[srainhoutx]

I thought some would find this discussion from San Angelo informative regarding all the complexities that go into forecasting snow in Texas. It is not a simple or easy process...

SHORT TERM...
A HAND ANALYSIS OF THE 00Z RAOB DATA SHOWED THE CLOSED MID LEVEL
CYCLONE OVER THE FOUR CORNERS REGION HAD CONTINUED A GENERAL
SOUTHWARD MOTION OF THE LAST 12 HRS WITH A STRONG SUBTROPICAL JET
DEVELOPING OVER THE SOUTHERN PLAINS. THE H85 FREEZING LINE HAD
DROPPED SOUTH TO NEAR A KMAF TO KFSM LINE WITH STRONG H7
BAROCLINICITY OVER THE CWA. YESTERDAY/S COLD FRONT IS WELL SOUTH OF
THE AREA AND WE WILL WILL CONTINUE TO SEE SURFACE COLD ADVECTION
THROUGHOUT THE DAY UNDER NORTHEAST WINDS OF 10-15 MPH. STRONG
VERTICAL MOTION WAS NOTED OVER NM PER THE WATER VAPOR LOOP
SUGGESTING STRONG DYNAMICS DOWNSTREAM OF THIS CYCLONE. SKIES WILL
REMAIN GENERALLY OVERCAST THROUGHOUT THE DAY SO TEMPS WILL STRUGGLE
TO CLIMB OUT OF THE 30S THIS AFTERNOON. I THINK THE SOUTHEAST 1/3 OF
THE CWA WILL BREAK 40 DEGREES TODAY BUT THE REMAINDER OF THE AREA
SHOULD RANGE FROM 35-39 DEGREES. I REMOVED MENTION OF PRECIP FOR
THIS AFTERNOON ACROSS THE WESTERN TIER GIVEN THE DRY BOUNDARY LAYER
AND SLOWER EASTWARD PROGRESSION OF THE UPPER LEVEL FORCING.
HOWEVER...WE COULD SEE SOME BRIEF PATCHY DRIZZLE FROM TIME TO TIME.

TONIGHT IS WHEN THINGS SHOULD BEGIN TO GET INTERESTING. THE
SUBTROPICAL JET IS PROGGED TO BECOME ORIENTED FROM WEST TX THROUGH
SOUTHERN MO OVERNIGHT. THIS WILL PUT THE CWA UNDER THE DIRECT
THERMAL CIRCULATION IN THE RIGHT ENTRANCE REGION OF THE JET. THE
CORRESPONDING INCREASE IN ISENTROPIC ASCENT WILL HELP MOISTEN THE
COLUMN. WARM ADVECTION NOTED BY THE VEERING WIND PROFILE ALSO
SUGGEST INCREASING MESOSCALE LIFT BUT MID LEVEL FRONTOGENESIS
APPEARS TO BE LACKING GIVEN THE PLACEMENT OF THE UPPER CIRCULATION.
STRONG H5-H3 Q-VECTOR CONVERGENCE WILL APPROACH THE AREA WITH THE
STRONGEST FORCING DELAYED UNTIL SATURDAY. ALL THAT SAID...PRECIP
CHANCES WILL BE ON THE INCREASE ASSUMING ADEQUATE MOISTURE. THE BIG
QUESTION IS PRECIP TYPE AND HOW MUCH.

THE MOISTURE IN THE DENDRITIC GROWTH ZONE IS NOT AS GOOD AS I WOULD
LIKE TO SEE. BUFR SOUNDINGS INDICATE SATURATION BY 06Z TONIGHT TO
AROUND -10C WHEREAS THE DESIRED TEMPERATURE IS -12C AND COLDER...
ESPECIALLY ACROSS THE NORTHWEST HALF OF THE AREA. BAUMGARDT /1999/
SHOWED THAT SATURATION AT -10C CORRESPONDED TO A 60 PERCENT CHANCE
OF ICE CRYSTALS BEING PRESENT WITH -15C CORRESPONDING TO A 90
PERCENT CHANCE. THIS IS ALL THEORY OF COURSE AND NOT A PERFECT
SYSTEM. MANY OF OUR ICE NUCLEI COME FROM THE KAOLINITE /CLAY/ FAMILY
WHICH ARE ACTIVATED AT -8C AND COLDER. THUS...WHILE NOT OPTIMAL...I
DO ANTICIPATE SOME ICE BEING PRESENT IN THE COLUMN DESPITE THE LESS
THAN DESIRABLE SOUNDINGS. THIS SHOULD RESULT IN MAINLY SNOW ACROSS
THE NORTHWEST ONE OF THE FORECAST AREA...OR ROUGHLY NORTH OF A LINE
FROM OZONA...TO SAN ANGELO...TO CROSS PLAINS. A TRANSITION BAND OF
MIXED PRECIP IS EXPECTED FROM SONORA TO BROWNWOOD WITH ALL RAIN
ANTICIPATED OVER THE NORTHWEST HILL COUNTRY. SNOW ACCUMULATIONS ARE
EXPECTED TO BE LIGHT THROUGH 12Z SATURDAY OWING TO WEAKER FORCING
ALTHOUGH QUASI ISOTHERMAL PROFILES JUST BELOW 0C WILL PROVIDE AN
ENHANCED OPPORTUNITY FOR GROWTH OF SNOWFLAKES BY AGGREGATION. WILL
ALSO HAVE TO WATCH FOR THE POTENTIAL FOR SOME MIXED FREEZING PRECIP
IN AREAS WHERE SUFFICIENT ICE CRYSTALS ARE NOT AVAILABLE FOR
NUCLEATION...NAMELY ACROSS THE CENTRAL AND SOUTHEAST COUNTIES.

[srainhoutx]

SHORT RANGE FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
358 AM EST FRI DEC 23 2011

VALID 12Z FRI DEC 23 2011 - 12Z SUN DEC 25 2011

...MAJORITY OF RAIN/SNOW TO EXIT THE NORTHEAST EARLY THIS
MORNING...FOLLOWED BY COLDER TEMPERATURES DOWN INTO THE CENTRAL
APPALACHIANS...

...ADDITIONAL MODERATE SNOW ACCUMULATIONS ACROSS NEW MEXICO INTO
WEST TEXAS ALONG WITH ANOMALOUS COLD...

AN AREA OF LOW PRESSURE WILL BRISKLY EXIT NORTHEASTWARD FROM THE
NORTHERN MID-ATLANTIC THIS MORNING WHICH WILL BRING AN END TO
AREAS OF MODERATE RAIN AND SNOW CURRENTLY FALLING IN THE
NORTHEAST. MAINLY LIGHT SNOW ACCUMULATIONS ARE EXPECTED FOR
NORTHERN NEW YORK AND NEW ENGLAND BY THIS AFTERNOON...BEFORE
PRECIPITATION TAPERS OFF TO LIGHT SNOW SHOWERS FOR THE REMAINDER
OF TODAY. A TEMPORARY BLAST OF COLD TEMPERATURES WILL IMPACT NEW
ENGLAND TODAY AND ESPECIALLY SATURDAY...WHEN PORTIONS OF MAINE
WILL ONLY GET UP INTO THE TEENS FOR HIGH TEMPERATURES. FARTHER
WEST...A WEAK UPPER LEVEL DISTURBANCE WILL REACH THE UPPER GREAT
LAKES LATER TODAY BRINGING LIGHT SNOW SHOWERS TO THE UPPER
MISSISSIPPI VALLEY...WITH PRECIPITATION TAPERING OFF BY SATURDAY
MORNING. ACCUMULATIONS ARE EXPECTED TO BE LIGHT...FOLLOWED BY
WARMER TEMPERATURES TOWARD THE LATTER HALF OF THE WEEKEND.

ACROSS THE SOUTH CENTRAL U.S....AN UPPER LEVEL LOW DIGGING DOWN
THROUGH ARIZONA EARLY THIS MORNING WILL SLOWLY MIGRATE ALONG THE
U.S.-MEXICAN BORDER...BEFORE TAKING A TRACK INTO WEST TEXAS BY
SUNDAY MORNING. THIS SYSTEM WILL ENSURE TEMPERATURES REMAIN
ATYPICALLY COLD FROM NEW MEXICO INTO TEXAS THROUGH SATURDAY ALONG
WITH ACCUMULATING SNOW. WINTER STORM WARNINGS ARE CURRENTLY IN
PLACE ACROSS MUCH OF NEW MEXICO...ESPECIALLY INTO THE HIGHER
TERRAIN...ALONG WITH WINTER WEATHER ADVISORIES AND WINTER STORM
WATCHES INTO WEST TEXAS IN ANTICIPATION OF THIS EVENT. THE HIGHEST
ACCUMULATIONS ARE FORECAST INTO SOUTHERN/CENTRAL PORTIONS OF THE
NEW MEXICAN HIGHER TERRAIN WHICH WILL BEGIN TO WIND DOWN TONIGHT
AS SNOW MOVES INTO WEST TEXAS AS THE UPPER LOW EDGES EASTWARD.
MOSTLY LIGHT TO LOCALLY MODERATE SNOWFALL IS EXPECTED INTO WEST
TEXAS AS FAR SOUTH AS BIG BEND NATIONAL PARK. FARTHER
EAST...OVERRUNNING FLOW FROM THE GULF WILL BRING MOISTURE ACROSS
THE COLD AIR IN TEXAS LEADING TO LIGHT RAIN. AS THE UPPER LOW
MOVES INTO TEXAS...RAIN SHOULD PICK UP...WITH A FOCUS NEAR THE
GULF FROM EAST TEXAS INTO LOUISIANA.

THE NORTHWEST WILL SEE A SERIES OF STORM SYSTEMS WHICH WILL FOCUS
THEIR ENERGY INTO BRITISH COLUMBIA OVER THE NEXT COUPLE OF DAYS.
NORTHWEST WASHINGTON AND THE NORTHERN CASCADES WILL SEE RAIN AND
HIGHER ELEVATION SNOW WITH THE OLYMPICS LIKELY SEEING THE GREATEST
TOTALS THROUGH SATURDAY.

[srainhoutx]

The 12Z WRF/NMM suggests a close call for the Metroplex regarding any wintry mischief chances. Further W in Midland/Odessa and San Angelo things do look a bit different with some accumulation possible. That model also suggests a coastal low/trough S of Galveston late Christmas Eve into Christmas morning with over running precip.

[srainhoutx]

A new wrinkle appears in the WRF/NMM. Now that guidance suggests a stalling of the upper low over NW Texas as additional upper level energy hangs back into Old Mexico. That model also slows the progression of the coastal low/trough S of Galveston for about 6-12 hours.

[MontgomeryCoWx]

Maybe its just me, but I really feel someone in Central/West Tx is really going to get a nice storm out of this....

Thinking someone could see 4-6 inches west DFW. Wouldn't be surprised to see DFW see an inch if the track is beneficial.

[JackCruz]

[wxman57]

Are Austin and Dallas really in the same predicament as far as snow potential tomorrow? Let's take a closer look. First, Dallas.

Here's a GFS-based meteogram for DFW with 2m temp, dew point and 850mb temp plotted. Note that surface temps remain well above freezing through the precip period. However, as the precip ends, the 850mb temp is predicted to finally drop to 32F or lower. This would indicate that any snow that does fall would not stick to the ground.



Now let's take a look at the vertical profile in a little more detail. The graphic below is a GFS model sounding for DFW valid 21Z tomorrow (3pm). Note something interesting. The precipitation (where the red and green lines are close together) occurs in sub-freezing air as the precip is ending. However, below the precip, the air is above freezing from about 6000ft down to the surface. This would suggest that the precip develops/forms as snow and falls through an above-freezing layer down to the surface. Since the sounding is not necessarily taking into consideration cooling due to melting snowflakes/evaporating rain in the above-freezing layer, it is possible that the lower 6000 ft could be a little cooler than the sounding indicates, allowing some snowflakes to reach the ground.

However, I don't think the surface temps will be cold enough to allow any falling snowflakes to hang around long.



Is Austin in the same boat? Not hardly. Look at the meteogram below. Surface and 850mb temps well above freezing through the whole precip event.



What about aloft where the precip forms? Sorry, the predicted vertical profile is above freezing where the precip forms, quite different from Dallas:



Note that the 12Z NAM is quite similar to the GFS profile for Austin. It's actually a bit warmer than the 6Z GFS in the lower 5000 ft during the precip tomorrow. This strongly suggests cold rain with no chance of snow in Austin. Can't completely 100% rule out a stray snowflake there in Austin as the precip ends, but only if all the models are wrong about the upper air profile.

[redneckweather]

Great break down wxman. I appreciate you taking the time to put that together.

[jasons2k]

I'm very excited about our rain chances - looks like another good event for us

This kind of weather is perfect for me - a little chilly, but not freezing cold. Great for the holidays

[srainhoutx]

I agree that we need to take what we can get in the rainfall department. Once this storm exits, we look to return to a more typical La Nina pattern. The 12Z GFS finally got a clue and slowed the progression of the upper low. The 12Z Canadian would bring some nice beneficial rains to our lakes before we dry out...

[perk]

I'm very excited about our rain chances - looks like another good event for us

This kind of weather is perfect for me - a little chilly, but not freezing cold. Great for the holidays

My kind of weather too,especially for a football Saturday.

[srainhoutx]

A snowy day near El Paso International Airport...

[srainhoutx]

Guidance has come into agreement suggesting the upper low will slowly eject from near El Paso ENE to near Wichita Falls and meander for about 12-24 hour before sweeping NE. The 12Z Euro also suggests the same solution and is in agreement with other guidance suggesting showers/light rain may linger into Christmas day.

[srainhoutx]

HPC says 12Z Euro it is via their model diagnostics discussion...

...SHORTWAVE TROUGH CROSSING THE NORTHWEST AND PLAINS SUN-MON...
...CLOSED LOW OVER ARIZONA/NEW MEXICO...

PREFERENCE: 12Z ECMWF

MODEL FORECASTS ARE LARGELY SIMILAR UNTIL THE TROUGH CROSSING THE
NORTHWEST ENTERS THE PLAINS...BY WHICH TIME THE 00Z ECMWF BECOMES
MORE AMPLIFIED AND EJECTS THE LOW FROM THE SOUTHWEST FASTER THAN
MOST OTHER GUIDANCE...INCLUDING THE NAM/GFS AND ITS OWN ENSEMBLE
MEAN. THUS...THE 00Z ECMWF SOLUTION IS DISCOUNTED. AMONG THE
REMAINING SOLUTIONS...THE GFS IS SLIGHTLY FASTER THAN THE NAM BUT
HAS TRENDED SLOWER...AND GIVEN ITS FAST BIAS AT LONGER
RANGES...ITS SOLUTION MAY STILL BE TOO FAST. MEANWHILE...THE NEW
UKMET HAS TRENDED CONSIDERABLY SLOWER AND IS EVEN SLOWER THAN THE
NAM...AND GIVEN A PROPENSITY FOR LOWER LATITUDINAL CLOSED LOWS TO
EJECT MORE SLOWLY OVER SUBSEQUENT RUNS...A SOLUTION NOT UNLIKE THE
UKMET ALOFT SEEMS QUITE REASONABLE...ALTHOUGH ITS PMSL SOLUTION
NEAR THE GULF OF MEXICO LIES NEAR THE DEEP EDGE OF THE GUIDANCE
WHICH THE MODEL HAS A PROPENSITY TO DO AT LONGER TIME FRAMES.

FINALLY...THE 12Z ECMWF HAS TRENDED MUCH SLOWER AND IS NOW IN
PHASE WITH THE SLOWER NAM/UKMET. HOWEVER...ITS SOLUTION IS NOT AS
DEEP AT THE SURFACE AS THE UKMET...NOR AS COLD AS THE NAM...WHICH
LEAVES THE UKMET AND NAM NEAR THE OUTER EDGES OF THE GUIDANCE.
THUS...THROUGH A PROCESS OF ELIMINATION THE FINAL PREFERENCE IS
FOR THE 12Z ECMWF.

CONFIDENCE: LESS THAN AVERAGE

[singlemom]

Great break down wxman. I appreciate you taking the time to put that together.

Hear! Hear! Just a word of thanks to you, 'Srain, Jeff, and *all* the great pros (and other wise guys\girls) who take the time to keep it honest; break it down; put up with our whining; post all the graphics (obviously from some super secret collection of sites in Area 51); give timely info so that we can prepare and otherwise do what you guys\girls do to make this one amazing source for weather info. If we haven't said it enough, "thanks!"

[srainhoutx]

Midland/Odessa issues Winter Weather Advisory for areas mainly N of I-10. 1-4 inch amounts expected. Winter Storm Warning remains in effect for higher elevations further N.