000
FXUS64 KSJT 200856
AFDSJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN ANGELO TX
356 AM CDT MON MAY 20 2013

.SHORT TERM...
DRYLINE WILL AGAIN MOVE EAST OF A SONORA...SAN ANGELO...ABILENE...
THROCKMORTON LINE BY LATE AFTERNOON. SIGNIFICANT INSTABILITY
WILL AGAIN EXIST EAST OF THE DRYLINE...WHERE GFS AND NAM GFS
MODELS GIVE SB CAPES FROM 2500 TO 3500 J/KG...ALONG WITH 0 TO 6 KM
BULK SHEARS OF 35 TO 40 KTS. IF STORMS DO DEVELOP...CAN EXPECT
THEM TO BECOME SEVERE. CONDITIONS ARE SIMILAR TO YESTERDAY. WHILE
STORMS DID NOT DEVELOP YESTERDAY...THERE WAS A TCU FIELD IN THE
LATE AFTERNOON. WENT CLOSE TO GFS AND NAM MOS TEMPERATURES FOR
TODAY AND TONIGHT... WHICH ARE NEAR PERSISTENCE VALUES.

04

.LONG TERM...
POTENTIALLY SEVERE CONVECTION REMAINS IN THE FORECAST FOR TUESDAY
AFTERNOON AND EVENING WITH UNSEASONABLY WARM TEMPERATURES LIKELY
TO PERSIST THROUGH THE WEEKEND.

A WEAK COLD FRONT WILL MAKE ITS WAY SOUTH ACROSS THE BIG COUNTRY
EARLY TUESDAY AND IS EXPECTED TO STALL OVER THE SOUTHEAST
ZONES...PROVIDING A FOCUS FOR AFTERNOON AND EVENING THUNDERSTORMS.
BEHIND THIS COLD FRONT...TEMPERATURES WILL STILL BE SLIGHTLY
ABOVE NORMAL /UPPER 80S/ BUT WILL BE A GOOD 10 DEGREES COOLER THAN
WHAT IS EXPECTED FOR TODAY. AHEAD OF THE FRONT...DEEP MOISTURE AND
TEMPERATURES IN THE MID 90S WILL RESULT IN STRONG DESTABILIZATION
OF THE AIRMASS. GFS/NAM MLCAPE VALUES ARE PROGGED TO RANGE BETWEEN
3500-4000 J/KG ACROSS THE SOUTHEAST QUADRANT OF THE CWA. GIVEN THE
0-6KM SHEAR VALUES EXCEEDING 40 KTS...THE POTENTIAL FOR
SUPERCELLULAR CONVECTION IS HIGH. WEAK BOUNDARY LAYER WINDS NEAR
THE QUASI STATIONARY FRONT WILL YIELD WEAK LOW LEVEL SHEAR
PARAMETERS WHICH WILL LIMIT /BUT NOT PRECLUDE/ THE TORNADO
POTENTIAL. EXPECT HAIL LARGER THAN GOLF BALLS /POTENTIALLY LARGER
THAN GOLF BALLS/ WITH THE STRONGEST STORMS...GENERALLY SOUTH AND
EAST OF A LINE FROM SONORA...TO EDEN...TO BROWNWOOD. STORMS WILL
PERSIST IN THE EVENING HOURS BUT SHOULD TREND DOWN IN INTENSITY
SHORTLY AFTER SUNSET.

THE CURRENT FORECAST IS DRY FOR WEDNESDAY. AMPLE INSTABILITY WILL
EXIST ACROSS THE AREA AS DEWPOINTS REMAIN QUITE HIGH GIVEN THE
LACK OF A DISCERNIBLE DRYLINE OVER THE AREA. HOWEVER...WE ARE
LACKING A LOW LEVEL FORCING MECHANISM. THAT SAID...I WOULD NOT
RULE OUT A FEW STORMS DEVELOPING SIMPLY DUE TO STRONG DIURNAL
HEATING. COVERAGE SHOULD BE VERY LIMITED AND WILL PRECLUDE MENTION
OF STORMS IN THE FORECAST AT THIS TIME ALTHOUGH A CONDITIONAL
SEVERE THREAT WILL EXIST. EXPECT AFTERNOON HIGHS IN THE MID 90S
WITH SOUTHEAST WINDS OF 10-15 MPH.

THURSDAY AND FRIDAY HAVE BEEN A FORECAST HEADACHE OWING TO THE
DIFFERENCES IN HANDLING OF DIURNAL CONVECTION ALONG THE SURFACE
TROUGH OVER WEST TX. I THINK THIS ACTIVITY WILL LIKELY DEVELOP
CLOSER TO THE TX/NM STATE LINE WHICH WOULD LIMIT ITS POTENTIAL TO
REACH OUR WESTERN BOUNDARY BEFORE DISSIPATING. ON FRIDAY...THE
TROUGH SHOULD BE SLIGHTLY FARTHER EAST SO I HAVE RETAINED /AND
EXPANDED/ THE SLIGHT CHANCE POPS FOR FRIDAY NIGHT. ALL OF THAT
SAID...SUBTLE SHORTWAVES ARE DIFFICULT TO TIME WHEN DEALING WITH
SOUTHWEST FLOW ALOFT AT DAYS 4-5. IF ANY WAVES DO EJECT ACROSS THE
REGION AND ARE COINCIDENT WITH PEAK HEATING...THIS WOULD LEND
TOWARD A MORE ROBUST CONVECTIVE ENVIRONMENT AND COULD YIELD AN MCS
OR TWO DURING THE EVENING HOURS. TEMPS ARE EXPECTED TO WARM INTO
THE 90S BOTH DAYS WITH OVERNIGHT LOWS GENERALLY IN THE UPPER 60S.

BY THE WEEKEND...THE MODELS ARE KEYING ON THE BUILDING SUBTROPICAL
RIDGE OVER THE SOUTHERN PLAINS. THIS WOULD DIRECT MOST OF THE
SYNOPTIC SCALE FORCING WELL NORTH OF THE AREA AND WOULD PROMOTE
THE DEVELOPMENT OF A CAPPING INVERSION VIA NORTHEASTWARD ADVECTION
OF THE ELEVATED MIXED LAYER. I HAVE A DRY FORECAST FOR THE WEEKEND
WITH TEMPS ONCE AGAIN IN THE 90S. THE MODELS ARE NOT SHOWING MUCH
OF A LOWER TROPOSPHERIC THERMAL RIDGE DEVELOPING BUT MY GUT SAYS
THAT WE COULD BE APPROACHING 100 DEGREES SATURDAY AND/OR SUNDAY.
WE WILL JUST HAVE TO WAIT AND SEE.

JOHNSON

&&

.FIRE WEATHER...
A DRYLINE WILL BE MOVING EAST OF A SONORA...SAN ANGELO...
ABILENE...THROCKMORTON LINE LATE THIS AFTERNOON. ELEVATED FIRE
WEATHER CONDITIONS ARE EXPECTED WEST OF THE DRYLINE IN THE BIG
COUNTRY AND CONCHO VALLEY...AS RH VALUES IN THE SINGLE DIGITS AND
TEENS COMBINE WITH SOUTHWEST 20 FOOT WINDS OF 10 TO 15 MPH.

04

&&

.PRELIMINARY POINT TEMPS/POPS...
ABILENE  99  68  88  65  94 /   5  20  20  20   5
SAN ANGELO 101  70  93  66  96 /   5  10  20  20   5
JUNCTION  96  70  94  69  93 /  20  20  30  40   5

&&

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

&&

$$

04/25