FXUS64 KSJT 150526 AAC
AFDSJT
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE SAN ANGELO TX
1126 PM CST MON DEC 14 2009
.DISCUSSION...
SEE AVIATION SECTION.
&&
.AVIATION...
PREVIOUS THINKING ON THE AVIATION FORECAST REMAINS THE SAME. IN
THE WAKE OF THE COLD FRONTAL PASSAGE...NORTH-NORTHEAST WINDS WILL
INCREASE OVERNIGHT AND INTO THE EARLY MORNING HOURS OF TUESDAY
ACROSS WEST CENTRAL TEXAS IN THE PRESSURE RISE FIELD...AS A STRONG
SURFACE HIGH MOVES SOUTHEAST INTO THE CENTRAL PLAINS. LOW CLOUDS
WILL DEVELOP AND EXPAND WESTWARD ACROSS ROUGHLY THE SOUTHERN THIRD
OF WEST CENTRAL TEXAS OVERNIGHT. EXPECT THE CEILINGS TO BE
GENERALLY IN THE MVFR CATEGORY. THE LOW CLOUDS WILL ERODE LATER
FRIDAY MORNING AS DRIER AIR INFILTRATES THE REGION FROM THE
NORTHEAST.
&&
.PREV DISCUSSION... /ISSUED 834 PM CST MON DEC 14 2009/
UPDATE...
LATEST SATELLITE AND METAR DATA INDICATE THE COLD FRONT IS SLOWLY
PUSH SOUTH ACROSS OUR COUNTIES. SURFACE WINDS ARE CURRENTLY NORTH
BEHIND THE FRONT AT AROUND 10 TO 15 MPH. SOUTH OF THE
FRONT...WINDS ARE MAINLY LIGHT AND VARIABLE. BASED ON PROGRESS
OVER THE LAST COUPLE HOURS...THE FRONT SHOULD BE NEAR INTERSTATE
10 AROUND MIDNIGHT. ALSO...IR SATELLITE LOOP INDICATES UPPER-LEVEL
MOISTURE IS MOVING ACROSS THE NORTHWESTERN HALF OF TEXAS FROM THE
SOUTHWEST. ELSEWHERE ACROSS TEXAS...STRATUS DOMINATES. SO...I JUST
COMPLETED ADJUSTMENTS TO SEVERAL OF THE GRIDS FIELDS FOR THE
REMAINDER OF THE TONIGHT PERIOD TO BRING THEM IN LINE WITH CURRENT
CONDITIONS. RECENT ZONE PRODUCT REFLECTS THESE ADJUSTMENTS. AS FOR
OVERNIGHT TEMPERATURES...THEY LOOK ON TRACK. THUS...NO CHANGES
THERE.
23/HUBER
PREV DISCUSSION... /ISSUED 600 PM CST MON DEC 14 2009/
DISCUSSION...
SEE AVIATION SECTION.
AVIATION...
COLD FRONT...WHICH IS POSITIONED ROUGHLY ALONG INTERSTATE 20 IN
THE SOUTHERN BIG COUNTRY EARLY THIS EVENING...WILL PUSH SOUTH
ACROSS THE REST OF WEST CENTRAL TEXAS THROUGH LATE EVENING AND
EARLY TONIGHT. GUSTY NORTH-NORTHEAST WINDS ARE EXPECTED AFTER
MIDNIGHT AND INTO THE EARLY MORNING HOURS OF TUESDAY ACROSS
WEST CENTRAL TEXAS IN THE PRESSURE RISE FIELD...AS A STRONG
SURFACE HIGH MOVES SOUTHEAST INTO THE CENTRAL PLAINS. LOW CLOUDS
WILL DEVELOP AND EXPAND WESTWARD ACROSS ROUGHLY THE SOUTHERN THIRD
OF WEST CENTRAL TEXAS TONIGHT. EXPECT THE CEILINGS TO BE GENERALLY
IN THE MVFR CATEGORY. THE LOW CLOUDS WILL ERODE LATER FRIDAY
MORNING AS DRIER AIR INFILTRATES THE REGION FROM THE NORTHEAST.
PREV DISCUSSION... /ISSUED 336 PM CST MON DEC 14 2009/
SHORT TERM...
THE MAIN FORECAST CHALLENGE WILL BE TEMPS WITH THE ARCTIC FRONT THAT
WILL ARRIVE TONIGHT.
CURRENT SFC ANALYSIS SHOWS THE ARCTIC FRONT CURRENTLY MOVING SOUTH
ACROSS OKLAHOMA AS OF 1 PM. A PRE-FRONTAL WIND SHIFT IS NOTED AHEAD
OF THE FRONT...CAUSING WINDS TO SHIFT TO THE NORTHEAST. THIS WIND
SHIFT WILL ARRIVE LATER TODAY INTO THIS EVENING FOLLOWED BY THE REAL
PUSH OF COLDER AIR TOWARD MORNING. LOWS TONIGHT WILL BE VERY
TRICKY...MAINLY ACROSS THE SOUTH...WHERE THE POOL OF LOW LVL
MOISTURE RESIDES. THERE WILL LIKELY BE SOME LOW CLOUDS ACROSS MY
SOUTHERN COUNTIES AFTER MIDNIGHT AND THIS MAY KEEP TEMPS UP SOME. A
WAVE OVER AZ CURRENTLY WILL BASICALLY SPLIT IN TWO AS IT HEADS
EAST...WITH THE NORTHERN PART SHEARING OUT OVER THE TX PANHANDLE AND
THE SOUTHERN PART DIVING DOWN INTO MEXICO. THE LIFT FROM THIS SYSTEM
WILL BASICALLY DETERIORATE AS THE TROUGH AXIS MOVES ACROSS WEST
CENTRAL TX EARLY TUESDAY. THERE WILL BE SOME MID CLOUDINESS WITH
MODEL TIME HEIGHT PLOTS SHOWING HIGHER LEVELS OF RH AT 600MB AND
HIGHER AND FAIRLY DRY BELOW THAT. I WILL THEREFORE KEEP THE FORECAST
DRY.
SKIES WILL CLEAR BY THE END OF THE DAY AS THE SOUTHERN PIECE OF
ENERGY DIVES DOWN INTO MEXICO AND THE COLUMN DRIES OUT. HIGHS ON
TUESDAY HAVE BEEN THE MAIN CHALLENGE FOR SEVERAL DAYS AND IT IS NO
DIFFERENT TODAY. LOOKING AT CURRENT OBS ACROSS OKLAHOMA BEHIND THE
FRONT AND COMPARING IT TO THE NAM12 2M TEMPS...IT DOES APPEAR THAT
THE NAM IS UNDERDONE ON THE STRENGTH OF THE COLD AIR AS ONE MIGHT
SUSPECT. THE NAM HAS A HIGH OF 48 AT ABI AND 53 AT SJT
TOMORROW...BUT WITH STRONG COLD ADVECTION AND MID LEVEL CLOUD COVER
I WILL BE UNDERCUTTING THIS BY 5 TO 10 DEGREES AND STAYING CLOSER TO
THE GOING FORECAST. THIS ALSO AGREES WELL WITH THE ECMWF
TEMPS...WHICH APPEAR TO BE DOING BETTER SO FAR.
LACY
LONG TERM...
ALL THE MODELS ARE CONSISTENT IN STRETCHING THE MID-LEVEL TROUGH
DEEP INTO MEXICO BY WEDNESDAY MORNING WITH THE 12Z NAM FORMING A
CLOSED LOW WELL SOUTH OF THE 12Z GFS AND THE 12Z ECMWF. THE PRIOR
RUN OF THE ECMWF FAVORED THE LESS PROGRESSIVE NAM. THE NAM KEEPS
ANY ASSOCIATED PRECIP WELL SOUTH AND EAST OF THE FORECAST AREA AS
THE UPPER LOW TRACKS EAST FROM CENTRAL MEXICO ACROSS DEEP SOUTH
TEXAS THROUGH THURSDAY. THE ECMWF PRODUCES A SLIGHT CHANCE OF
MOISTURE OVERNIGHT TUESDAY INTO WEDNESDAY MORNING AS THE LOW
TRACKS EAST FROM THE BIG BEND REGION ACROSS THE MIDDLE RIO GRANDE
VALLEY...WILL KEEP WITH THE MORE CONSISTENT DRIER NAM FOR THIS
FORECAST RUN.
WEDNESDAY MORNING WILL BE THE COLDEST POST-FRONTAL MORNING WITH
TEMPERATURES IN THE 20S AREA WIDE. WILL SEE AFTERNOON
TEMPERATURES WARM INTO THE 60S BY THURSDAY BEFORE THE NEXT FRONT
MOVES THROUGH THE AREA ON FRIDAY. MODELS ARE ESSENTIALLY OUT OF
PHASE TOWARD THE END OF THE EXTENDED WITH THE GFS FORMING A
CLOSED LOW OVER THE SOUTHWESTERN STATES WITH ASSOCIATED MOISTURE
TRACKING OVER THE FORECAST AREA...AND THE ECMWF BUILDING A DRY
RIDGE OVER THE SOUTHWESTERN STATES. WILL KEEP THE INHERITED DRY
FORECAST THROUGH THE EXTENDED FOR THIS FORECAST RUN UNTIL MORE
CONSISTENCY DEVELOPS BETWEEN THE MODELS.
&&
.PRELIMINARY POINT TEMPS/POPS...
ABILENE 29 40 25 53 35 / 10 10 0 0 0
SAN ANGELO 33 45 26 54 35 / 10 10 0 0 0
JUNCTION 39 48 29 53 33 / 10 10 0 10 0
&&
.SJT WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
