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000
FXUS64 KSJT 252330
AFDSJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN ANGELO TX
630 PM CDT SAT MAY 25 2013

.DISCUSSION...

EXPECT STRATUS TO BRING MVFR CEILINGS BACK TO WEST CENTRAL TEXAS
DURING THE NEXT 6 HOURS. AVIATION BELOW HAS DETAILS.

&&

.AVIATION...

MODELS DATA INDICATE STRATUS WILL RETURN TO WEST CENTRAL TEXAS
TONIGHT AND PERSIST UNTIL AROUND NOON TOMORROW. THE LATEST RUC 925
MB RELATIVE HUMIDITY AND WIND FIELD DATA INDICATE STRATUS WILL
RETURN TO WEST CENTRAL TEXAS...FROM THE EAST AND
SOUTHEAST...BEGINNING AROUND 03Z. BY 06Z TONIGHT...PLAN FOR MVFR
CEILINGS TO DOMINATE WEST CENTRAL TEXAS. MOS GUIDANCE DATA FROM
THE GFS INDICATE MVFR CEILINGS AROUND 1500 FEET ABOVE GROUND LEVEL
AT ALL 5 TERMINALS. THE NAM BASED GUIDANCE IS MORE AGGRESSIVE AND
PREDICTS IFR CEILINGS AROUND 700 FEET ABOVE GROUND LEVEL. I
DECIDED TO CONTINUE WITH A FORECAST FAVORING THE GFS
SOLUTION...MAINLY BASED ON PERSISTENCE. AS WAS THE CASE
TODAY...LOOK FOR VFR CEILINGS TO RETURN TO WEST CENTRAL TEXAS
AROUND NOON TOMORROW.

HUBER

&&

.PREV DISCUSSION... /ISSUED 501 PM CDT SAT MAY 25 2013/

UPDATE...
FORECAST IS BEING UPDATED FOR POPS...QPF AND SKY CONDITION.  SEE
DISCUSSION.

DISCUSSION...
SCATTERED SHOWERS WHICH WERE OVER THE EASTERN THIRD OF WEST CENTRAL
TEXAS EARLIER TODAY HAVE SINCE MOVED OUT OF THE AREA OR DISSIPATED.
RADAR LATE THIS AFTERNOON SHOWS NO ADDITIONAL SHOWER OR THUNDERSTORM
DEVELOPMENT...BUT A SLIGHT CHANCE REMAINS GIVEN THE MOIST AND
UNSTABLE AIRMASS STILL IN PLACE. WITH THE UPPER TROUGH AXIS MOVING
FARTHER AWAY FROM OUR AREA AND ACROSS EAST TEXAS...AND WITH THE
CONVECTIVE ACTIVITY DIURNALLY DRIVEN...EXPECT THE RAIN CHANCE IN
WEST CENTRAL TEXAS TO END BY OR BEFORE 9 PM. HAVE ADJUSTED THE
21Z-00Z WEATHER GRID TO REFLECT THE AFOREMENTIONED TRENDS...AND HAVE
ENDED THE RAIN CHANCE AFTER 02Z. THE GFS AND NAM BOTH SUGGEST LOW
CLOUD DEVELOPMENT NORTHWEST INTO OUR AREA LATE TONIGHT AND EARLY
SUNDAY MORNING...IN MOIST SOUTHEASTERLY BOUNDARY LAYER FLOW. HAVE
ADJUSTED THE SKY CONDITION GRIDS TO REFLECT THIS SCENARIO WITH
INCREASING CLOUDINESS TOWARD MORNING...TO ROUGHLY THE INTERSTATE 20
CORRIDOR. EXPECT THE LOW CLOUD FIELD TO ERODE BY MID TO LATE SUNDAY
MORNING. HAVE ALSO MADE DOWNWARD ADJUSTMENTS TO THE QPF GRIDS FROM
21Z-00Z. WITH LOW CONFIDENCE IN MEASURABLE PRECIPITATION OCCURRING
TONIGHT...HAVE DROPPED THE QPF GRIDS TO ZERO. UPDATED FORECAST
PRODUCTS WILL BE OUT SHORTLY.

PREV DISCUSSION... /ISSUED 341 PM CDT SAT MAY 25 2013/

SHORT TERM...
EARLY THIS AFTERNOON...UPPER TROUGH AXIS IS LOCATED JUST EAST OF
THE FORECAST AREA WITH ASSOCIATED RAINFALL AND THUNDERSTORMS
OCCURRING FROM THE CENTRAL TEXAS GULF COAST NORTH OVER MUCH OF
EAST TEXAS. WITH THE CLOSE PROXIMITY OF THE UPPER LOW TO OUR
CWA...WILL MAINTAIN A SLIGHT CHANCE OF SHOWERS AND ISOLATED
THUNDERSTORMS THROUGH THE NIGHT. AS THE UPPER TROUGH CONTINUES TO
MOVE EAST DURING THE DAY TOMORROW...AN UPPER RIDGE WILL BUILD OVER
THE OUR AREA FROM THE WEST...BRINGING AN END TO OUR RAINFALL
CHANCES. AFTER SUNDAY MORNING LOWS GENERALLY IN THE MID 60S...
AFTERNOON HIGHS ON SUNDAY WILL BE WARMER THAN TODAY...LOWER 90S VS
LOW TO MID 80S.

15

LONG TERM...
THE LONG TERM PORTION OF THE FORECAST WILL BE HIGHLIGHTED BY
PERSISTENT STRONG SOUTHERLY FLOW...OVERNIGHT AND MORNING
STRATUS...AND MIDWEEK PRECIPITATION CHANCES.

THE WEST COAST TROUGH IS PROGGED TO DEEPEN EARLY NEXT WEEK AS THE
SHORTWAVE TROUGH CURRENTLY LOCATED SOUTH OF THE ALEUTIANS MOVES
INTO THE PACNW. WE WILL SEE INCREASING SOUTHWEST FLOW ALOFT WHICH
WILL BOTH ENHANCE THE ELEVATED MIX LAYER /EML/ AND SUPPORT LEE
CYCLOGENESIS. THE LATTER WILL PROVIDE BRISK SOUTH WINDS THROUGHOUT
THE DURATION OF THE FORECAST PERIOD...WITH DAYTIME WIND SPEEDS OF
15-25 MPH AREAWIDE. A STRONG NOCTURNAL LOW LEVEL JET WILL KEEP
GUSTS IN THE FORECAST DURING THE OVERNIGHT HOURS WITH THE
STRONGEST WINDS FOUND ACROSS THE CONCHO VALLEY AND BIG COUNTRY.
THESE SOUTH WINDS WILL PROVIDE A STEADY STREAM OF GULF MOISTURE
INTO THE AREA...KEEPING DEWPOINTS GENERALLY IN THE LOWER 60S AND
PUSHING OVERNIGHT LOWS INTO THE UPPER 60S AND LOWER 70S THROUGH
THE WEEK. THESE BREEZY CONDITIONS MAY BE TEMPORARILY INTERRUPTED
BY CONVECTIVE OUTFLOW BUT I WILL GET MORE INTO THAT IN A BIT.

I EXPECT DRY CONDITIONS THROUGH MONDAY...ALTHOUGH SOME DIURNAL
CONVECTION TO OUR WEST MAY TRY TO SNEAK INTO THE WESTERN ZONES
MONDAY EVENING. THAT SAID...THE STEERING FLOW WILL KEEP THE BEST
CHANCES TO OUR NORTH AND WEST. OTHERWISE...THE CAP LOOKS TO HOLD
AND KEEP A LID ON THE CONVECTIVE POTENTIAL. TEMPS ON MONDAY ARE
EXPECTED TO RANGE FROM THE UPPER 80S TO LOWER 90S ACROSS MOST OF
WEST CENTRAL TX.

PRECIPITATION STILL DO NOT LOOK ALL THAT PROMISING ON TUESDAY DUE
TO THE STRENGTH OF THE EML. THAT SAID...I DID INCLUDE A SLIGHT
CHANCE OF THUNDERSTORMS GENERALLY WEST OF A SONORA...TO WINTERS...
TO HASKELL LINE TO ACCOUNT FOR THE EASTWARD DRIFT ON CONVECTION
OVER WEST TX. THE BEST RAIN CHANCES APPEAR TO OCCUR ON WEDNESDAY.
THE MEDIUM RANGE GUIDANCE IS DEPICTING A NEGATIVELY TILTED
SHORTWAVE TROUGH EJECTING INTO THE SOUTHERN PLAINS BY WEDNESDAY
AFTERNOON. THEY DO DIFFER IN THE LOCATION OF THE STRONGEST
FORCING...WITH THE GFS FAVORING THE CENTRAL HIGH PLAINS AND THE
ECMWF LOOKING FARTHER SOUTH TOWARD WEST TX. EITHER WAY...SYNOPTIC
SCALE FORCING WILL WORK ON THE EML...LIFTING AND COOLING THE LAYER
TO ERODE THE CAP. THE BIGGEST QUESTION IS HOW FAR SOUTH THIS
ASCENT REACHES. THE SEVERE POTENTIAL WILL EXIST GIVEN THE STEEP
MID LEVEL LAPSE RATES...STRONG INSTABILITY AND MORE THAN ADEQUATE
DEEP LAYER SHEAR. THE BIG QUESTION /AS IS USUALLY THE CASE/ IS THE
CAP.

THUNDERSTORM CHANCES LINGER ON THURSDAY BUT THE STRONGEST FORCING
LOOKS TO MOVE EAST BY THURSDAY. MODEL CONSENSUS SHOWS A DEEP...
BROAD TROUGH OVER THE WESTERN 2/3 OF THE CONUS WITH STRONG WEST
SOUTHWEST FLOW OVER WEST TX. WE MAY BEGIN TO SEE THE DRYLINE DRY
TO MIX EAST LATE IN THE PERIOD BUT THE EML LOOKS TO TAKE OVER WITH
THE CAP STRENGTHENING AND TEMPS WARMING BACK INTO THE LOW/MID 90S.
WE COULD BE LOOKING AT A PATTERN CHANCE BY THE LATTER HALF OF THE
WEEKEND WITH THE DEEP WESTERN TROUGH BEING REPLACED BY A SPLIT
FLOW REGIME.

JOHNSON

&&

.PRELIMINARY POINT TEMPS/POPS...
ABILENE  68  91  69  91  68 /  20  10   5   5  10
SAN ANGELO  68  91  69  92  70 /  20  10   5   5  10
JUNCTION  66  91  69  88  71 /  20  10   5   5   5

&&

.SJT WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

HUBER