January: Seasonal Temps To End The Month

[srainhoutx]

EWX (NWS San Antonio/Austin) expands their Winter Weather Advisories while chances of seeing anything other than a cold rain across SE Texas decreases.

URGENT - WINTER WEATHER MESSAGE
NATIONAL WEATHER SERVICE AUSTIN/SAN ANTONIO TX
333 PM CST THU JAN 3 2013

WINTER WEATHER ADVISORY FOR THE HILL COUNTRY AND EDWARDS PLATEAU
THIS EVENING THROUGH NOON FRIDAY...

.A MID TO UPPER LEVEL TROUGH OF LOW PRESSURE WILL MOVE OUT OF THE
SOUTHWESTERN UNITED STATES ACROSS CENTRAL TEXAS TONIGHT. WITH
COLD AIR IN PLACE IN THE LOWER LEVELS OF THE ATMOSPHERE THIS
SYSTEM WILL BRING RAIN AND SNOW TO THE AREA. EXPECT PRECIP TO
BEGIN AS A MIXTURE DURING THE EVENING AND CHANGE OVER TO SNOW
BY AROUND 10 PM AND CONTINUE OVERNIGHT. WARM AIR ADVECTION DURING
THE DAY FRIDAY WILL CHANGE PRECIPITATION OVER TO RAIN BY AROUND
NOON. BEFORE THE CHANGE EXPECT SNOW ACCUMULATION RANGING FROM A
DUSTING TO AROUND ONE INCH WITH A FEW SPOTS HAVING A BIT MORE.
THE HIGHER AMOUNTS WILL BE IN WESTERN VAL VERDE COUNTY.

TXZ183>186-040545-
/O.EXT.KEWX.WW.Y.0001.130104T0100Z-130104T1800Z/
VAL VERDE-EDWARDS-REAL-KERR-
INCLUDING THE CITIES OF...DEL RIO...ROCKSPRINGS...LEAKEY...
KERRVILLE
333 PM CST THU JAN 3 2013

...WINTER WEATHER ADVISORY NOW IN EFFECT FROM 7 PM THIS EVENING
TO NOON CST FRIDAY...

* TIMING...RAIN...SLEET AND SNOW WILL BEGIN THIS AFTERNOON AND
CHANGE TO SNOW LATE THIS EVENING.

* MAIN IMPACT...SNOW UP TO ONE INCH WILL MAKE DRIVING HAZARDOUS.

* OTHER IMPACTS...THERE IS SOME CHANCE THAT SNOW WILL BREAK OFF
WEAK TREE BRANCHES.


URGENT - WINTER WEATHER MESSAGE
NATIONAL WEATHER SERVICE AUSTIN/SAN ANTONIO TX
333 PM CST THU JAN 3 2013

WINTER WEATHER ADVISORY FOR THE HILL COUNTRY AND EDWARDS PLATEAU
THIS EVENING THROUGH NOON FRIDAY...

.A MID TO UPPER LEVEL TROUGH OF LOW PRESSURE WILL MOVE OUT OF THE
SOUTHWESTERN UNITED STATES ACROSS CENTRAL TEXAS TONIGHT. WITH
COLD AIR IN PLACE IN THE LOWER LEVELS OF THE ATMOSPHERE THIS
SYSTEM WILL BRING RAIN AND SNOW TO THE AREA. EXPECT PRECIP TO
BEGIN AS A MIXTURE DURING THE EVENING AND CHANGE OVER TO SNOW
BY AROUND 10 PM AND CONTINUE OVERNIGHT. WARM AIR ADVECTION DURING
THE DAY FRIDAY WILL CHANGE PRECIPITATION OVER TO RAIN BY AROUND
NOON. BEFORE THE CHANGE EXPECT SNOW ACCUMULATION RANGING FROM A
DUSTING TO AROUND ONE INCH WITH A FEW SPOTS HAVING A BIT MORE.
THE HIGHER AMOUNTS WILL BE IN WESTERN VAL VERDE COUNTY.

TXZ171-172-188-040545-
/O.EXB.KEWX.WW.Y.0001.130104T0100Z-130104T1800Z/
LLANO-BURNET-GILLESPIE-
INCLUDING THE CITIES OF...LLANO...BURNET...FREDERICKSBURG
333 PM CST THU JAN 3 2013

...WINTER WEATHER ADVISORY IN EFFECT FROM 7 PM THIS EVENING TO
NOON CST FRIDAY...

THE NATIONAL WEATHER SERVICE IN AUSTIN/SAN ANTONIO HAS ISSUED A
WINTER WEATHER ADVISORY FOR SNOW...WHICH IS IN EFFECT FROM 7 PM
THIS EVENING TO NOON CST FRIDAY.

* TIMING...RAIN...SLEET AND SNOW WILL BEGIN THIS EVENING AND
CHANGE TO SNOW LATE THIS EVENING.

* MAIN IMPACT...SNOW UP TO ONE INCH WILL MAKE DRIVING HAZARDOUS.

* OTHER IMPACTS...THERE IS SOME CHANCE THAT SNOW WILL BREAK OFF
WEAK TREE BRANCHES.

[srainhoutx]

RECORD EVENT REPORT
NATIONAL WEATHER SERVICE AUSTIN/SAN ANTONIO, TX
505 PM CST THU JAN 03 2013

...RECORD DAILY MAXIMUM TIE FOR THE AMOUNT OF ICE PELLETS OCCURRED
AT SAN ANTONIO...

A TRACE AMOUNT OF ICE PELLETS FELL AT THE SAN ANTONIO INTERNATIONAL
AIRPORT TODAY. THIS TIES THE PREVIOUS RECORD AMOUNT OF A TRACE OF ICE
PELLETS THAT FELL ON THIS DATE IN 1976.

[srainhoutx]

Starting to see some sleet reports coming in from Montgomery and Walker Counties, some of it rather heavy. Watching another batch of moisture heading ENE that may enter Western Harris/Waller Counties shortly...

[weatherrabbit]

sleeting light to moderately here in huntsville..

[tireman4]

Replaced my windshield wipers. Check. Coat is ready to be put on in the morning. Check. Having fun driving in sleet (if it comes down in the morning), check.

[srainhoutx]

From Nesdis:

SATELLITE PRECIPITATION ESTIMATES..DATE/TIME 01/04/13 0018Z
SATELLITE ANALYSIS BRANCH/NESDIS---NPPU---TEL.301-683-1404
LATEST DATA USED: GOES-13 2345Z JANKOT
.
LOCATION...TEXAS...
.
ATTN WFOS...EWX...SJT...MAF...EPZ...
ATTN RFCS...WGRFC...
.
EVENT...MOD TO HVY SNOWS SHAPING UP
.
SATELLITE ANALYSIS AND TRENDS...HIGHLY DIFFLUENT UPPER LEVEL PATTERN
EVIDENT IN LATEST WATER VAPOR IMAGERY WITH VORT ROTATING ACROSS N MEXICO
PROVIDING DYNAMICS NECESSARY TO INDUCE LIFT NEXT SEVERAL HOURS. MOISTURE
ADVECTION HAS SLOWLY BEEN ON THE INCREASE PER BLENDED TPW PRODUCT WITH
.4-.6" PWATS WRAPPING NW INTO DISCUSSION REGION. THIS LEVEL OF MOISTURE
NOT THAT IMPRESSIVE FOR THIS TIME OF YEAR...RUNNING 115-120% OF NORMAL.
MEANWHILE IR IMAGERY SHOWS A WEAK BAROCLINIC LEAF SIGNATURE DEVELOPING
OVER W TX/SE NM SUGGESTING HEAVIEST BAND OF PRECIP WOULD DEVELOP ALONG
A LINE FROM PRESIDIO ENE TO CROCKETT COUNTY. EXPECT RATES OF 1-2"/HR
IN BEST BANDS PROVIDING SEVERAL INCHES OF SNOW THROUGH 06Z. BEST RATES
SHOULD OCCUR IN UP-SLOPE FAVORED REGIONS W TX.
.
SHORT TERM OUTLOOK VALID 0030-0630Z...MEDIUM TO HIGH CONFIDENCE FACTOR
IN SHORT
TERM OUTLOOK...EXPECT MOD TO HEAVY SNOWS TO INCREASE OVER W TX AS VORT
CONTINUES TO SHIFT EAST WITH BEST OMEGAS MOVING ACROSS W TX. RATES
OF 1-2"/HR IS EXPECTED IN BEST BANDS WITH UPWARDS OF 4-8"+ POSSIBLE
THROUGH 6Z.

[Ptarmigan]

I'm not seeing any significant chance for snow in Houston over the next few weeks. Just a few sleet pellets mixed in with cold rain later today/tonight. Similar to what we saw yesterday. Long-term, the GFS is indicating some colder air moving out of Canada around the 14th. I'm not seeing any indications of "extreme cold" here, but maybe lows into the upper 20s across Houston (maybe mid 20s). Keep in mind that climatologically, the month we typically get the most snow is February. Can't rule out any snow here later this month, but I currently see no indications of it happening.

You are correct. February has most snowfall of any month in Houston going back to 1895. There have been 20 snowfall events in February. On average, February sees the highest amount of snow. However, January sees more measurable snow than in February. It is skewed because of the February 14-15, 1895 snow event.

Houston Snowfall Statistics (1895-2012)

Snowfall By Month (Includes Trace)
January: 13
Feburary: 20
March: 1
December: 10

Snowfall Average (Over Trace)
January
Mean: 1.23
Standard Deviation: 1.06
Heaviest: 3.00 on January 22, 1940
Over Trace Snowfall: 9

February
Mean: 3.69
Standard Deviation: 6.73
Heaviest: 20.00 on February 14-15, 1895
Over Trace Snowfall: 8

March (Yes, it snowed in March 1932)
Mean: 0.80
Standard Deviation: None
Heaviest: 0.80 on March 10, 1932
Over Trace Snowfall: 1

December
Mean: 1.40
Standard Deviation: 0.78
Heaviest: 2.50 on December 21-22, 1929
Over Trace Snowfall: 5

The ratio for snow to rain is 10 inch of snow is equivalent to 1 inch of rain. In Houston, the ratio for snow to rain is 7 inch of snow to 1 inch of rain. The lowest ratio is 1.05 inch of snow to 1 inch of rain on January 19, 1978 (0.40 inch of snow fell, while 0.38 inches of rain fell). The highest ratio is 12.73 inch of snow to 1 inch of rain on February 9, 1973 (1.40 inch of snow fell, while 0.11 inches of rain fell). That would be the closest that Houston saw powdery snow besides on December 22, 1989.

[Ptarmigan]

Possible Winter Weather Advisory for the northern portion of SE TX however of more concern is a possible severe weather and tornado event next week:

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
500 AM CST THU JAN 3 2013

.DISCUSSION...
AMAZING HOW THE FORECAST DATA CAN CHANGE IN 24 HRS. BUT AS IT
STANDS...HIGH PRESSURE AT THE SURFACE CONTINUES TO BUILD INTO N
TX. HIGH AND MID LEVEL CLOUDS CONTINUE TO MOVE OUT SO THERE MAY BE
SOME PEAKS OF SUNSHINE TODAY. HIGH CLOUDS MAY BE SLOW TO THIN OUT
TODAY WITH SW JET FLOW REMAINING OVER THE REGION. DO NOT THINK THE
AIR WILL HEAT UP MUCH WITH COLD ADVECTION SO WILL KEEP MAX TEMPS
IN THE UPPER 40S TODAY. CLOUD COVER SHOULD RETURN LATE THIS
AFTERNOON AS UPPER LOW DEVELOPS OVER S ROCKIES. UPPER LOW NOW OVER
BAJA MEXICO IS IN THE PROCESS OF SHEARING OUT WITH NEW UPPER LOW
FORMING OVER CENTRAL AND SOUTHERN ROCKIES. THE FIRST UPPER LOW
WILL BE THE FEATURE TO KEEP TRACK OF AS IT SHEARS OUT OVER TX.

SHORT RANGE MODELS ARE IN PRETTY GOOD AGREEMENT WITH THE BAJA
UPPER LOW MOVING INTO TX AROUND THE UPPER LOW FORMING OVER THE S
ROCKIES BY FRIDAY MORNING. THIS VORTICITY SUPPORTS INCREASED LARGE
SCALE ASCENT AND STRONG OMEGA OVER THE NORTHERN THIRD OF THE
FORECAST AREA. ISENTROPIC ANALYSIS DURING THIS TIME ALSO SUPPORTS
LIFT AT 290K AND 295K LEVELS. NAM CONTINUES TO SHOW BANDS OF
PRECIP FORMING OVER C TX AND MOVING INTO E TX DURING THE 12-18Z
FRI TIME FRAME. THERE DOES APPEAR TO BE INCREASED MID LEVEL
MOISTURE OVER THE REGION BUT A NOTICEABLE DRY LAYER BELOW 850MB.
LOOKING AT FORECAST SOUNDINGS FOR SEVERAL AREAS...IT LOOKS LIKE
RAIN/SLEET MIX WILL BE POSSIBLE PRIMARILY FOR AREAS NEAR A KCLL TO
KUTS LINE. SLEET MAY BE POSSIBLE AS FAR SOUTH AS A KATY TO TOMBALL
TO KINGWOOD LINE THROUGH HARRIS COUNTY BUT FORECAST SOUNDING FOR
KIAH SHOWS SOME ISSUES THAT NEED TO BE OVERCOME. MAINLY AREAS
NORTH OF KIAH HAVE ENOUGH MOISTURE AND WET BULBING TO OVERCOME
DRIER BOUNDARY LAYER. THIS MAY NOT BE THE CASE OVER THE HOUSTON
AREA SOUTHWARD. THERE SEEMS TO BE A WSW TO ENE ZONE BETWEEN KIAH
AND KCXO THAT WILL BE A TRANSITION AREA BETWEEN RAIN AND A
RAIN/SLEET MIX. NORTH OF A BRENHAM TO CONROE LINE COULD SEE A
SMALL TIME FRAME OF COMPLETELY SLEET AND PERHAPS SNOW BUT THIS
LARGELY DEPENDS ON MOISTURE...LIFT AND THERMODYANMICS ALL COMING
TOGETHER AT THE RIGHT TIME. IF THE NAM KEEPS UP ITS TREND FROM THE
00Z AND 06Z RUNS WITH COOLER TEMP PROFILES...MAY NEED TO MENTION
SNOW FOR THESE NORTHERN AREAS. AGAIN QUITE A FEW THINGS NEED TO
COME TOGETHER FOR THIS POSSIBILITY. FOR NOW WILL NOT MENTION ANY
SLEET/SNOW ACCUMULATIONS DUE TO UNCERTAINTY AND MIX WITH RAIN.
THIS MAY NEED TO BE EVALUATED WITH LATER FORECASTS AS QUITE
POSSIBLE THAT OVERPASSES AND ROADS COULD EXPERIENCE SOME SLIGHT
ICING SHOULD THERE BE MORE SLEET THAN RAIN. RAIN AMOUNTS LOOK TO
BE ON THE ORDER OF A FEW HUNDREDTHS TO A TENTH OF AN INCH. BUT
EVEN A COUPLE HUNDREDTHS OF AN INCH OF ICE COULD POSE PROBLEMS FOR
ROADS/OVERPASSES AND RESTRICT TRAVEL. AFTER 18Z FRI DO EXPECT A
TRANSITION TO ALL RAIN AS BOUNDARY LAYER WARMS. THE MAIN POINT IS
TO MONITOR FORECASTS FOR ANY UPDATES AND THE POSSIBILITY OF A
WINTER WEATEHR ADVISORY FOR THE NORTHERN THIRD OF THE FORECAST
AREA.
MAIN UPPER LOW OVER S ROCKIES DOES MOVE ACROSS THE S PLAINS AND N
TX FRI NIGHT INTO SAT MORNING. AGAIN ISENTROPIC LIFT WILL INCREASE
AND COMBINE WITH LARGE SCALE ASCENT OVER THE AREA FOR SOLID RAIN
CHANCES. FORECAST SOUNDINGS LOOK TOO WARM THIS TIME AROUND FOR
WINTERY PRECIP BUT THERE WILL STILL BE SOME CONCERN FOR SLEET
GIVEN THE LARGE AMOUNTS OF LARGE SCALE LIFT OVER THE REGION.
TROUGH AXIS WILL MOVE OUT SATURDAY BUT SOME LINGERING RAIN MAY
HOLD ON WITH DIVERGENCE FROM RIGHT ENTRANCE REGION OF JET BEING
OVER SE TX AND UPPER TX COAST.

TEMPS FINALLY MODERATE SUN/MON/TUE OF NEXT WEEK. THERE HAS BEEN
SOME DESCREPENCY BETWEEN THE GFS AND ECMWF REGARDING THE TIMING OF
THE NEXT UPPER LEVEL SYSTEM. THIS SYSTEM LOOKS QUITE STRONG WITH A
DEEP UPPER LOW DEVELOPING OVER W TX BY 12Z WED. THE ECMWF IS 6-12
HRS SLOWER THAN THE GFS WHICH IS TROUBLE SOME WITH REGARDS TO
SEVERE WEATHER. THIS TIMING DIFFERENCE WOULD ALLOW FOR MORE
MOISTURE AND INSTABILITY TO DEVELOP WITHIN A STRONGLY SHEARED
ENVIRONMENT. SEVERE WEATHER LOOKS TO BE A STRONG POSSIBILITY WITH
THIS SYSTEM SHOULD IT COME TO FRUITION. THE ENVIRONMENT WILL BE
SUPPORTIVE OF SUPERCELLS AND TORNADOES GIVEN THE COMBINATION OF
SHEAR AND INSTABILTY. AGAIN LOTS OF TIME FOR THE MODELS TO WORK
OUT DETAILS BUT THIS WILL BE A SYSTEM TO REALLY KEEP WATCH.

I know the atmosphere does not have a memory or care for statistics. Deja vu?

[srainhoutx]

I forgot to mention this earlier...NWS San Angelo upgraded their Western zones to a Winter Storm Warning for moderate to heavy snow tonight...

URGENT - WINTER WEATHER MESSAGE
NATIONAL WEATHER SERVICE SAN ANGELO TX
340 PM CST THU JAN 3 2013

...ACCUMULATING SNOW IS EXPECTED ACROSS THE CONCHO VALLEY...
NORTHERN EDWARDS PLATEAU...SOUTHERN BIG COUNTRY AND HEARTLAND
AREAS...

.A STRONG UPPER LEVEL STORM SYSTEM WILL APPROACH WEST TEXAS TODAY
AND MOVE ACROSS THE REGION ON FRIDAY. WITH THE APPROACH OF THIS
SYSTEM...PRECIPITATION IS EXPECTED TO DEVELOP THIS EVENING ACROSS
THE WESTERN CONCHO VALLEY AND INTO CROCKETT COUNTY. THE
PRECIPITATION COULD INITIALLY BEGIN AS A LIGHT MIX OF RAIN AND
SNOW...BUT WILL LIKELY CHANGE TO SNOW THIS EVENING. THE
PRECIPITATION WILL OVERSPREAD MOST OF WEST CENTRAL TEXAS
TONIGHT...AND WILL BE MOSTLY IN THE FORM OF SNOW ACROSS THE CONCHO
VALLEY AND BIG COUNTRY. A MIX OF RAIN AND SNOW IS POSSIBLE ACROSS
THE HEARTLAND AND NORTHWEST HILL COUNTRY...BEFORE CHANGING TO ALL
SNOW BY LATE TONIGHT. HAZARDOUS TRAVEL CONDITIONS ARE EXPECTED TO
DEVELOP WITH THE ACCUMULATING SNOWFALL AND TEMPERATURES DROPPING
BELOW FREEZING.

TXZ064-071-076-040600-
/O.UPG.KSJT.WW.Y.0001.000000T0000Z-130104T1200Z/
/O.NEW.KSJT.WS.W.0001.130103T2140Z-130104T1500Z/
STERLING-IRION-CROCKETT-
INCLUDING THE CITIES OF...STERLING CITY...MERTZON...OZONA
340 PM CST THU JAN 3 2013

...WINTER STORM WARNING IN EFFECT UNTIL 9 AM CST FRIDAY...

THE NATIONAL WEATHER SERVICE IN SAN ANGELO HAS ISSUED A WINTER
STORM WARNING FOR HEAVY SNOW...WHICH IS IN EFFECT UNTIL 9 AM CST
FRIDAY. THE WINTER WEATHER ADVISORY IS NO LONGER IN EFFECT.

* EVENT....MODERATE TO HEAVY SNOW.

* IMPACTS...SIGNIFICANT SNOW EXPECTED TO IMPACT THE AREA CAUSING
HAZARDOUS TRAVEL CONDITIONS. ROADS AND BRIDGES WILL BECOME SLICK
AND ICY.

* TIMING...THIS EVENING INTO FRIDAY MORNING.

* ACCUMULATIONS...4 TO 6 INCHES POSSIBLE MAINLY WEST OF A STERLING
CITY TO MERTZON TO OZONA LINE.

[C2G]

If I weren't working I'd take a road trip to the west. They'll have all that mega cool snow, while our area sees maybe a sleet pellet or two mixed with cold rain. Course Galveston County will probably just see cold light rain.

[srainhoutx]

As expected the warmer lower levels/surface temps have kept any frozen sleet/rain mix N of Houston, so no travel issues here. Further W, El Paso to Midland/Odessa and San Angelo or areas along and S of I-20 have received 2-4 inches of snow with some higher totals nearing 6+ in a few locations. Sleet reports continue across the San Antonio/Austin areas and there is likely some sleet/rain mix occurring near College Station down to Brenham and on E across Madisonville Huntsville and Lake Livingston.

All eyes turn W as another potent closed core upper low moves inland along the California Coast on Sunday setting the stage for our next best chance of rain and even storms, some likely severe. There remains some timing issues with the GFS being more progressive and shearing out that upper low, while the Euro keeps a closed core low tracking across Northern Mexico into Texas. Expect changes in the days ahead until this system enters the RAOB network on Sunday.

Following the mid week event, big changes are still indicated by the longer range guidance both operational and all the ensembles. A Long wave trough or a trough extending from Canada S into Mexico will usher in a very stormy and cold pattern across the West and Plains. Colder temps will extend well S into Mexico. Stay Tuned for further updates on that developing Weather Headline as we get closer and beyond the next Tuesday/Wednesday severe potential.

Euro Ensembles:

GEFS:

GGEM:

[Portastorm]

Numerous reports of sleet mixed with rain here in the Austin area for the past few hours, including at my house. Also seeing reports of sleet in NW San Antonio. Out in the Hill Country as of 6 a.m., snow was falling in Liberty Hill, Burnet, and Fredericksburg.

[srainhoutx]

Morning e-mail from Jeff:

Thus far only a few reports of sleet across the northern ½ of SE TX overnight as the sub cloud layer has been very dry and much of what is showing up on the radar is evaporating before reaching the ground.

Heavier mix of rain/sleet/snow has been confined to the Hill Country and SW TX since yesterday afternoon where best moisture and lift reside. Main question over the next 48 hours is how much rainfall will develop across SE TX. Coastal troughing is starting to take place along the lower TX coast as the main upper level low centered near El Paso this morning begins to move NE over the next 24 hours. A strong disturbance in the SW flow aloft over N MX will translate across the coastal bend of TX tonight into Saturday and this combined with increasing warm air advection and finally a reduction in the dry layer centered near 850mb should support a better chance of rain tonight into Saturday for mainly the coastal areas. Still not looking for much accumulation of rainfall…generally below .25 of an inch as what falls will be mainly in the form of light rain and drizzle. With thick cloud cover and period of rainfall expect little change in the temperatures today through Saturday with about a 5-8 degree change between the low and highs and most areas will stay locked in the 40’s.

Trough axis will finally move east of TX late Saturday into Sunday as this cold and cloudy pattern will finally break down. Skies will clear by early Sunday morning and expect temperatures on Sunday under sunny skies to reach the mid-upper 50’s.

Early next week another strong storm system will drop into the SW US and begin to move into the southern plains toward the Tuesday/Wednesday time period. GFS is by far the fast and most progressive with this feature while the ECMWF is slower, stronger and further south with the CMC nearly splitting the difference. Will lean toward the faster GFS solution as the southern stream pattern remains fairly progressive. This will bring warm air advection and a chance for showers back into the area by late Monday. Still much uncertainty in the surface features for Tuesday and the amount of moisture and instability which will be available at that time, but this system will need to be watched for a possible severe weather threat especially if the ECMWF model is correct.

[srainhoutx]

Nice little sleet event reported across our Northern zones of SE TX within the past 45 minutes.

[srainhoutx]

A very active pattern continues to develop across the West and Plains during the medium/long range. A potent close core low will move inland along the Pacific Coast on Sunday setting the stage for a myriad of potential high impact weather events. There are both higher elevation snow and even a severe potential involved with this feature. Looking ahead to late next week, the ensembles suggest heights build over Alaska and the EPO transitions to strongly negative setting the stage for a stormy and colder regime across the West and the Plains.




EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER COLLEGE PARK MD
940 AM EST FRI JAN 04 2013

VALID 12Z MON JAN 07 2013 - 12Z FRI JAN 11 2013

THE UPCOMING MEDIUM RANGE FORECAST CONTINUES TO FOCUS ON TWO
DOMINANT FEATURES ALOFT...A TROUGH OVER THE WEST AS OF EARLY MON
AND THEN EJECTING EWD THEREAFTER FOLLOWED BY A LARGER SCALE TROUGH
EXPECTED TO AMPLIFY INTO THE W-CENTRAL CONUS BY LATE NEXT WEEK.
INTERESTINGLY THERE IS GENERALLY GREATER SPREAD WITH DETAILS OF
THE INITIAL WRN TROUGH AND ASSOCIATED SENSIBLE WEATHER IMPACTS AS
THE FEATURE EJECTS OUT OF THE WEST...THAN WITH THE LATER-PERIOD
TROUGH THAT IN THE MEAN SHOULD SUPPORT A SURFACE FRONTAL SYSTEM
FROM THE GREAT LAKES SWWD INTO THE PLAINS BY DAY 7 FRI.

ALREADY AT THE START OF THE PERIOD THERE REMAINS SIGNIFICANT
DIFFERENCES FOR THE LEADING WRN TROUGH...WITH THESE DIFFS BECOMING
FURTHER MAGNIFIED WITH TIME. SOLUTIONS RANGE FROM THE PAST FEW
ECMWF RUNS THAT TRACK A SLOW CUTOFF LOW NEAR THE WRN US-MEXICO
BORDER AND THEN NEWD INTO THE PLAINS TO THE UKMET THAT HAS OFFERED
A MORE NRN STREAM PHASED/PROGRESSIVE TROUGH. IN VARYING WAYS MOST
RECENT GFS AND CANADIAN RUNS HAVE BEEN PROGRESSIVE...BUT THE
LATEST 06 UTC GFS HAS SLOWED DOWN. FROM A LONGER TERM PERSPECTIVE
ECMWF RUNS HAVE BEEN CONSISTENT WITH THEIR SEPARATED CLOSED LOW
ALBEIT WITH A MODESTLY FASTER TREND OVER THE PAST COUPLE OF
DAYS...WHILE A NUMBER OF GFS RUNS PRIOR TO 12 UTC YESTERDAY ALSO
HAD A SEPARATED CLOSED LOW. RECENT RUNS OF THE GEFS SHOWED SOME
FASTER TREND WITH THE SRN ENERGY...BUT NOT THE LATEST 00 UTC ECMWF
ENSEMBLE MEAN.

THAT 00 UTC ECMWF ENSEMBLE MEAN ALONG WITH THE COMPATABLE ECMWF
SEEMS TO CURRENTLY OFFER THE MOST APPEALING OPTION WITH GREATER
FLOW SEPARATION THAN THE ALTERNATE PROGRESSIVE CLUSTER OF
SOLUTIONS. HPC GUIDANCE HAS BEEN PRIMARILY DERIVED FROM A BLEND OF
THESE LESS PROGRESSIVE SOLUTIONS. THIS BLEND OFFERS GOOD HPC
CONTINUITY AND SEEMS A GOOD FIT WITH RECENT FLOW HISTORY. MORE
IMPORTANTLY...LATEST WATER VAPOR IMAGERY LOOPS ACROSS THE ERN PAC
SEEMS TO CLEARLY FAVOR AMPLIFICATION INCLUDING SRN STREAM CLOSED
LOW FORMATION AND THESE TYPES OF FEATURES ARE RARELY VERY
PROGRESSIVE. A LOOK AT ENSEMBLE PERTUBATIONS OVER THE FIRST 12-24
HOURS OF THE FORECAST CYCLE SHOWS ECMWF ENSEMBLE MEMBERS THAT ARE
SIGNIFICANTLY MORE AMPLIFIED THAN THOSE IN THE GEFS THAT SEEM IN
CONTRAST TO AFOREMENTIONED WATER VAPOR ANALYSIS.

ON THE OTHER HAND THERE IS BETTER THAN AVERAGE AGREEMENT WITH THE
TRAILING LARGER SCALE MID-UPPER LEVEL TROUGH FORECAST TO AMPLIFY
INTO THE WEST LATER NEXT WEEK. LATEST ENSEMBLE MEANS AND NOW EVEN
GFS/ECMWF RUNS SEEM TO PROVIDE A REASONABLE AND POTENT COMPOSITE
SOLUTION...BUT HPC HAS UTILIZED A ECMWF/ECMWF ENSEMBLE MEAN BLEND
TO BETTER FIT A RECENT GUIDANCE TREND TOWARD ENHANCED
AMPLIFICATION.

SCHICHTEL

[harpman]

Not sure what that would mean for those of us along the gulf coast. Perhaps you could elaborate?

[srainhoutx]

Not sure what that would mean for those of us along the gulf coast. Perhaps you could elaborate?

While we are still a ways out and things can and certainly does change daily as more data becomes available, the pattern suggested by the CPC Super Ensembles as well as a MWW Stratospheric Event (Mid Winter Warming) suggest a break down or split of the Polar Vortex. Think of the Polar Vortex as a very large and cold tornado if you will, situated over the Arctic. When we see these type events and a reversal of the normal westerly flow to that of easterly in the high latitudes, a cross Polar flow establishes and very cold air sinks S. While it remains to be seen if this event will lead to an Arctic Outbreak across the Western 2/3rd of North America, the longer range guidance is giving of some hints that we may be headed toward some significant cooling extending well S into Mexico and the Gulf. We will see.

[harpman]

Thanks again for your prompt response. I know this is primarily a Texas forum and I'm in New Orleans, but I do get a lot of information here!

[srainhoutx]

Thanks again for your prompt response. I know this is primarily a Texas forum and I'm in New Orleans, but I do get a lot of information here!

We have become a much more Regional Forum that covers New Mexico/Mexico/Oklahoma/Arkansas and Louisiana, harpman over the past several years. That was always the dream that those that came before such as Dan as well as the fine folks at KHOU had envisioned for our Community. Our members and those that read, post and participate stretch well beyond Texas. In fact we have members and followers from Coast to Coast, from Canada to the Caribbean.

[jasons2k]

Hi all - I've also been monitoring the developments for next week, wondering how this will all play out. As Ed mentioned above, the NWS offices are favoring the GFS over the Euro. In fact, here is what the NWS Houston stated yesterday:

" ATTM WILL NOT MAKE ANY CHANGES IN THE EXTENDED...BUT AM BEGINNING TO FAVOR THE GFS SOLUTION AS IT HAS BEEN VERIFYING BETTER IN THE RECENT PAST."

Whoa. Now wait a second. Rewind to last week and let's level-set. Remember the great debate over the Euro vs. the GFS? The GFS was showing a progressive pattern while the Euro was showing a cutoff low/trough hanging back after the cold front. Fast forward to today, and the low is still out near El Paso about to cross over Texas over the cold dome. IIRC correctly, this is NOT what the GFS was showing a week ago; it was indeed the Euro which had a better lock on this week's weather.

So, what am I missing? Why would the NWS say that?