Area Forecast Discussion
Issued by NWS Austin/San Antonio, TX

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FXUS64 KEWX 250552 AAA
AFDEWX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE AUSTIN/SAN ANTONIO TX
1152 PM CST WED DEC 24 2014

.AVIATION.../06Z TAF CYCLE/
VFR PREVAILS THIS EVENING AND WILL CONTINUE OVERNIGHT AND THROUGH
MUCH OF THURSDAY. MAIN CONCERNS CONTINUE TO BE ELEVATED SURFACE
WINDS AND RETURN OF MVFR CONDITIONS BY EARLY FRIDAY MORNING.
SOUTHERLY SURFACE WINDS FOR KAUS/KSAT/SSF WILL BE SUSTAINED 15-20
KT WITH WIND GUSTS UP TO 25-30 KT 25/17-23Z. WINDS WILL DECREASE
TO NEAR 10 KT OVERNIGHT BUT ADDITIONAL MOISTURE FROM THE SOUTH
WILL AID A STRATUS/FOG DEVELOPMENT. HAVE DELAYED MVFR CIGS FOR 30
HR TAF SITES TILL 26/11Z GIVEN LOW/MEDIUM CONFIDENCE AS 5 KT
SURFACE WIND MAY HAMPER FULL FOG DEVELOPMENT WITH STRATUS CIGS
BEING THE MAIN CULPRIT FOR MVFR. IF WINDS DECREASE ANY FURTHER,
WILL NEED TO MONITOR FOR GREATER FOG COVERAGE WEST OF ANY STRATUS
DECK ACROSS HILL COUNTRY TOWARDS RIO VALLEY. /ALLEN/

&&

.PREV DISCUSSION... /ISSUED 748 PM CST WED DEC 24 2014/

UPDATE...
SPENT A DECENT AMOUNT OF TIME ATTEMPTING TO ADD SOME PRECISION TO
THE MIN T GRID AND THE POTENTIAL FOR A FREEZE FOR VAL VERDE
COUNTY. A VERY GOOD RADIATIONAL COOLING SET UP WILL BE IN PLACE
FOR THE EDWARDS PLATEAU AND FARTHER NORTH INTO THE HILL COUNTRY.
WITH WIND FIELDS VERY LIGHT TONIGHT...EXPECT TEMPS TO DROP RATHER
RAPIDLY AND FASTER AT LOCATIONS WITH CALM WINDS. AT FIRST
GLANCE...WOULD THINK THAT MIN TEMPS SHOULD DROP BELOW GUIDANCE.
HOWEVER...MODEL SOUNDINGS ARE INDICATING A VERY STRONG NEAR
SURFACE INVERSION SETTING UP LATE IN THE NIGHT THAT WOULD RESULT
IN HIGHER ELEVATION LOCATIONS LIKE THE ESCARPMENT TO ACTUALLY STAY
A FEW DEGREES ABOVE THE VALLEY AREAS. NOT SURE IF THAT OUTCOME
WILL ACTUALLY PLAY OUT...SO WENT STAYED WITH THE THINKING OF
ESCARPMENT LOCATIONS FALLING TO 32 OR BELOW AND A FEW DEGREES
WARMER OFF THE PLATEAU.

ADDITIONALLY...NEW GUIDANCE IS SUGGESTED TOMORROW AFTERNOONS WIND
POTENTIAL WILL BE HIGHER THAN PREVIOUSLY THOUGHT. TEND TO AGREE
WITH THE AMPING UP OF WIND GRIDS DUE TO THE TIGHTENING SURFACE
PRESSURE GRADIENT ASSOCIATED WITH A SOUTHWARD MOVING SURFACE LOW
FROM THE LEE OF THE ROCKIES. THEREFORE RAMPED UP WINDS TO 15-20 KT
SUSTAINED IN THE AFTERNOON WITH WIND GUST POTENTIAL UP TO UPPER 20
KT RANGE.

PREV DISCUSSION... /ISSUED 308 PM CST WED DEC 24 2014/

SHORT TERM (TONIGHT THROUGH THURSDAY NIGHT)...
IT HAS BEEN AWHILE SINCE WE HAD A NICE DAY WITH ABUNDANT SUNSHINE
WHICH IS NICE FOR ANYONE DOING SOME LAST MINUTE SHOPPING.
TEMPERATURES ARE IN THE 50S WITH BREEZY NORTHWEST WINDS AT THE
SURFACE. THE SURFACE HIGH WILL SHIFT EAST OF THE AREA THIS EVENING
AND OVERNIGHT AND WE SHOULD SEE SOUTHERLY WINDS RETURN TO THE AREA
FROM WEST TO EAST OVERNIGHT. HOWEVER...WITH LIGHT WINDS...CLEAR
SKIES AND DEWPOINTS IN THE 20S...MANY LOCATIONS WILL BE ABLE TO
DROP TO OR BELOW FREEZING TONIGHT. IT WILL DEFINITELY FEEL LIKE
CHRISTMAS MORNING WHEN YOU WAKE UP. VAL VERDE COUNTY HAS NOT HAD A
FREEZE WARNING VERIFY SO FAR THIS WINTER AND THE NORTHERN PORTIONS
OF THE COUNTY WILL LIKELY BE NEAR FREEZING. WILL OPT NOT TO ISSUE
A WARNING AT THIS TIME AS DEL RIO AND THE EASTERN PORTIONS OF THE
COUNTY SHOULD BE AROUND 33 DEGREES. IF TEMPERATURES LOOK TO BE A
BIT COLDER TONIGHT WHEN THE EVENING SHIFT DOES A FORECAST
UPDATE...THEN THEY MAY NEED TO PUT ONE OUT. WILL ISSUE AN SPS TO
COVER THE THREAT. NEVERTHELESS...ALL RESIDENTS OF SOUTH-CENTRAL
TEXAS SHOULD PROTECT SENSITIVE VEGETATION TONIGHT.

WITH THE SOUTHERLY FLOW...TEMPERATURES WILL MODERATE CHRISTMAS DAY
WITH HIGHS REACHING THE UPPER 50S TO UPPER 60S. CLEAR SKIES CAN BE
EXPECTED AS WELL. LOWS THURSDAY NIGHT WILL BE MUCH WARMER THAN
TONIGHT WITH THE CONTINUED SOUTH FLOW...RANGING FROM LOWER 40S TO
NEAR 50 DEGREES. SHOULD SEE A RETURN OF LOW CLOUDS AIDED BY THE
RETURN OF THE LOW-LEVEL JET.

LONG TERM (FRIDAY THROUGH WEDNESDAY)...
LOW LEVEL FLOW WILL CONTINUE TO INCREASE FRIDAY WITH 25 TO 35
KNOTS EXPECTED AT 850 MB. AT THE SAME TIME...THE NEXT STRONG
TROUGH WILL BE MOVING INTO THE FOUR CORNERS REGION. THE COMBINED
LOW-LEVEL ASCENT WITH THE FORCING APPROACHING FROM THE WEST SHOULD
ALLOW A FEW SHOWERS TO DEVELOP FRIDAY AFTERNOON...MAINLY IN THE
EASTERN ZONES WHERE THE LOW-LEVEL JET WILL BE STRONGEST.

THE TROUGH WILL ELONGATE BY FRIDAY NIGHT...INTO SATURDAY MORNING
AS IT MOVES NEAR THE PLAINS. A STRONG COLD FRONT ASSOCIATED WITH
THIS DEEP TROUGH WILL PUSH THROUGH THE AREA SATURDAY MORNING AND
WILL DROP TEMPERATURES BACK INTO THE 50S FOR HIGHS SUNDAY AND LOWS
IN THE 30S/40S. RAIN CHANCES ASSOCIATED WITH THE FRONT WILL BE
BEST ACROSS THE EAST WHERE THE BEST LOW-LEVEL FLOW AND MOISTURE
REMAINS IN PLACE. MODELS ARE ALSO IN FAIRLY GOOD AGREEMENT WITH
BRINGING IN AN IMPULSE OF ENERGY LEFT BEHIND BY THE MAIN TROUGH
INTO THE AREA SATURDAY NIGHT AND SUNDAY. THIS COULD LEAD TO
LINGERING CHANCES OF RAIN FOR THE WEEKEND DEPENDING ON HOW MUCH
MOISTURE REMAINS.

NOW FOR THE MOST INTERESTING PART OF THE FORECAST. AS THIS TROUGH
MOVES OUT SUNDAY...THE NEXT STORM SYSTEM WILL BE TAKING SHAPE
ACROSS THE NORTHWEST CONUS SUNDAY EVENING. A VERY AMPLIFIED RIDGE
AXIS WILL BE EXTENDED OFF THE WESTERN CONUS...NORTH INTO THE
CANADA/ALASKA BORDER WITH 500 HEIGHTS NEAR 570DM REACHING 60 DEGREES
NORTH. THIS IS A STANDARDIZED ANOMALY OF ABOUT ABOUT 3 STANDARD
DEVIATIONS ABOVE NORMAL FOR THAT REGION. TO THE EAST OF THIS RIDGE
AXIS A VERY DEEP TROUGH AXIS IS ABLE TO THEN DIG SOUTHWEST WITH THE
MAIN RIDGE AXIS ORIENTED FROM NEAR NORTH DAKOTA BACK INTO ARIZONA
MONDAY EVENING. THIS UPPER PATTERN IS TYPICALLY KNOWN FOR BRINGING
COLD ARCTIC AIRMASSES INTO TEXAS. MODELS ARE FORECASTING THE SURFACE
HIGH BEHIND THE ASSOCIATED COLD FRONT TO ENTER THE CONUS NEAR
MONTANA SUNDAY. SURFACE HIGHS WHICH ENTER IN THIS REGION ARE KNOWN
TO BE FAVORABLE FOR THE COLDEST AIRMASSES FOR THE SOUTHERN PLAINS.
THIS IS MOSTLY DUE TO COLD AIR DAMMING WHICH OCCURS AS THE COLD
AIRMASS MOVES SOUTH ON THE LEE SIDE OF THE ROCKIES. AS THE HIGH
CIRCULATION DROPS SOUTH...EAST WINDS ON THE SOUTHERN PERIPHERY GET
BLOCKED BY THE TERRAIN AND THE COLD AIR IS ALLOWED TO POOL AND
COLLECT AS THE HIGH MOVES SOUTH. THIS ALLOWS THE AIR TO BECOME MORE
DENSE WHICH EQUATES TO COLDER AIR. IT WILL BE INTERESTING TO SEE HOW
THIS SYSTEM PLAYS OUT...BUT MODELS TEND TO BE TOO WARM WITH
TEMPERATURES WITH THIS PATTERN BY THE TIME THE COLD AIR MAKES IT
INTO TEXAS. ANOTHER INTERESTING PIECE TO THIS PUZZLE IS MODELS ARE
IN FAIRLY GOOD AGREEMENT THAT A PIECE OF THE TROUGH WILL MOVE
THROUGH THE AREA SOMETIME NEXT WEEK AFTER THE COLD AIR MAKES IT.
THERE ARE TIMING AND STRENGTH DISCREPANCIES BETWEEN THE MEDIUM-RANGE
GUIDANCE AND THIS IS LIKELY TO BE THE CASE FOR THE NEXT SEVERAL
DAYS. HOWEVER...MODELS THEN DO AGREE ON ENOUGH MOISTURE FOR PRECIP
WITH THE SYSTEM. THE QUESTION THEN TURNS TO HOW TO CONVEY THE
POSSIBILITY OF WINTER PRECIP IN THE OFFICIAL FORECAST FOR DAY 7. FOR
NOW...WILL MENTION A RAIN OR FREEZING RAIN MIX FOR THE HILL COUNTRY
TUESDAY NIGHT. THIS IS A GOOD START BECAUSE THERE ARE SOME TIMING
AND STRENGTH DIFFERENCES WITH THE TROUGH AS IT MOVES THROUGH THE
REGION. THERE IS THE POTENTIAL THAT THE AIR MASS WILL COLDER THAN
WHAT THE GFS IS SUGGESTING...SIMILAR TO THE ECMWF SOLUTION FOR
TEMPS. THIS BEARS WATCHING AS THE FORECAST IS LIKELY TO CHANGE ONE
WAY OR THE OTHER AS THE NEXT WEEK PROGRESSES.

HAMPSHIRE

&&

.PRELIMINARY POINT TEMPS/POPS...
AUSTIN CAMP MABRY              54  33  62  51  68 /   0   0   0  -   10
AUSTIN BERGSTROM INTL AIRPORT  55  31  62  48  69 /   0   0   0  -   10
NEW BRAUNFELS MUNI AIRPORT     57  33  63  50  70 /   0   0   0  -   10
BURNET MUNI AIRPORT            52  31  59  48  65 /   0   0   0  -   10
DEL RIO INTL AIRPORT           58  33  63  43  65 /   0   0   0   0   0
GEORGETOWN MUNI AIRPORT        54  33  60  50  67 /   0   0   0  -   10
HONDO MUNI AIRPORT             57  31  64  44  69 /   0   0   0  -   10
SAN MARCOS MUNI AIRPORT        56  31  63  49  70 /   0   0   0  -   10
LA GRANGE - FAYETTE REGIONAL   56  34  64  51  71 /   0   0   0  10  20
SAN ANTONIO INTL AIRPORT       57  34  63  50  69 /   0   0   0  -   10
STINSON MUNI AIRPORT           57  34  64  49  71 /   0   0   0  -   10

&&

.EWX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

MESOSCALE/AVIATION...15
SYNOPTIC/GRIDS...03





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