Issued by NWS San Angelo, TX
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000 FXUS64 KSJT 230346 AFDSJT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SAN ANGELO TX 946 PM CST SUN NOV 22 2009 .UPDATE... WILL LOWER TEMPERATURES IN THE CONCHO VALLEY AND N EDWARDS PLATEAU TONIGHT. && .DISCUSSION... WITH WEAK MOISTURE RETURN AND LIGHT WINDS WILL LOWER TEMPERATURES INTO THE MID 30S FROM CONCHO VALLEY SOUTHWARD TONIGHT. && .PREV DISCUSSION... /ISSUED 525 PM CST SUN NOV 22 2009/ DISCUSSION... SEE BELOW FOR THE 00Z AVIATION DISCUSSION. AVIATION... AS HAS BEEN THE CASE FOR THE PAST COUPLE OF NIGHTS...A TRICKY FORECAST LIES AHEAD FOR TONIGHT. THE LATEST 18Z NAM FORECASTS A DRIER BOUNDARY LAYER FOR THE OVERNIGHT AS COMPARED TO PREVIOUS NIGHTS...AND THE NAM BUFKIT SOUNDINGS SHOW A VERY SHALLOW LAYER OF MOISTURE NEAR THE SFC. AS A RESULT...I`M NOT AS CONFIDENT THAT THERE WILL BE WIDESPREAD STRATUS DEVELOPMENT AND INSTEAD WILL FORECAST SOME LIGHT MVFR GROUND FOG. I CAN`T RULE OUT A BRIEF PERIOD OF IFR VSBYS BUT CONFIDENCE IS NOT HIGH ENOUGH THIS FAR OUT TO INCLUDE IT IN THE TAFS. LACY PREV DISCUSSION... /ISSUED 256 PM CST SUN NOV 22 2009/ SHORT TERM... ANOTHER PLEASANT DAY ACROSS WEST CENTRAL TEXAS....WITH CLEAR SKIES AND AFTERNOON HIGHS IN THE UPPER 60S TO LOW 70S ACROSS MUCH OF WEST CENTRAL TEXAS. SOUTHERLY WINDS HAS ALLOWED FOR SOME MOISTURE RETURN. LATEST WATER VAPOR IMAGERY SHOWS AN UPPER LEVEL TROUGH ACROSS THE CENTRAL PLAINS AND THIS TROUGH WILL CONTINUE TO PUSH EAST WITH A TRAILING COLD FRONT.EXPECT CLEAR SKIES AGAIN TONIGHT BUT THIS COMBINED WITH INCREASED PRESSURE GRADIENT AND MOISTURE THINK TONIGHTS OVERNIGHT LOWS WILL BE WARMER THAN THE PAST COUPLE OF NIGHTS...WITH OVERNIGHT LOWS IN THE UPPER 30S TO MID 40S...WHICH IS STILL A FEW DEGREES COOLER THAN GUIDANCE. LOOKING AT BUFKIT AND LATEST NAMBFR SOUNDINGS HAVE ADDED THE MENTION OF PATCHY FOG FOR EARLY MONDAY MORNING ACROSS THE CONCHO VALLEY ...HEARTLAND AND SOUTHWARD. THE MOISTURE APPEARS TO BE TOO SHALLOW TO MAKE IT PAST THE HILLS OF THE BIG COUNTRY. FOR MONDAY...THE COLD FRONT ISN`T EXPECTED TO MOVE ACROSS WEST CENTRAL TEXAS UNTIL LATE MONDAY EVENING INTO TUESDAY MORNING...BUT AHEAD OF THE FRONT COMPRESSIONAL HEATING WILL RESULT IN THE WARMER TEMPERATURES MONDAY AFTERNOON WITH AFTERNOON HIGHS WARMING UP TO THE MID TO UPPER 70S ACROSS WEST CENTRAL TEXAS. LONG TERM... BY MONDAY EVENING...A SIGNIFICANT COLD FRONT IS EXPECTED TO BE DRIVING SOUTH THROUGH THE SOUTH PLAINS OF TEXAS. THIS COLD FRONT WILL MOVE THROUGH THE WEST CENTRAL TEXAS AREA MONDAY NIGHT INTO TUESDAY MORNING. LOW LEVEL MOISTURE WILL BE DRAWN NORTHWARD AHEAD OF THE FRONT. HOWEVER...MOISTURE IS STILL EXPECTED TO BE FAIRLY SHALLOW ALONG THE FRONT AS IT MOVES THROUGH...ARGUING AGAINST RAISING POPS IN OUR AREA AND SUGGESTING THAN ANY PRECIP WE SEE ALONG THE FRONT WILL BE FAIRLY LIGHT. THEREFORE...HAVE KEPT ONLY SLIGHT CHANCE POPS IN WITH ONLY LIGHT PRECIP WORDING. WITH THE MOISTURE PILING UP SOMEWHAT AHEAD OF THE FRONT FOR AREAS SOUTH OF INTERSTATE 20...WE MAY SEE SOME FOG DEVELOP MONDAY NIGHT OUT AHEAD OF THE FRONT. HOWEVER...MODELS DO SHOW ENOUGH WIND AHEAD OF THE FRONT AT THIS TIME TO HOLD OFF ON ANY MENTION FOR NOW. COOLER TEMPERATURES WILL FOLLOW THE FRONT FOR TUESDAY AND TUESDAY NIGHT. MANY AREAS WILL ONCE AGAIN BE CLOSE TO FREEZING TUESDAY NIGHT AND WEDNESDAY NIGHT...ALTHOUGH WE WILL SEE TEMPERATURES REBOUND INTO THE MID AND UPPER 60S ON WEDNESDAY FROM THE UPPER 50S TO LOWER 60S TUESDAY. AS A TROUGH REMAINS IN PLACE OVER THE GREAT LAKES REGION THROUGH THE END OF THE WEEK...SFC RIDGING WILL BE REINFORCED ACROSS THE MID AND LOWER MISSISSIPPI VALLEY. WEST CENTRAL TEXAS WILL BE ON THE WESTERN EDGE OF THE SFC RIDGING...SO MAIN EFFECTS WILL BE EASTERLY SFC FLOW. FORECAST IS EXPECTED TO REMAIN GENERALLY DRY WITH SEASONAL VALUES FOR TEMPERATURES THROUGH THE REST OF THE FORECAST. HOWEVER...LARGE MODEL DISCREPANCIES BETWEEN THE GFS AND ECMWF DEVELOP LATE IN THE EXTENDED PERIOD. THE ECMWF DEVELOPS A CLOSED LOW OVER THE DESERT SOUTHWEST...WHILE THE GFS JUST HAS NORTHWEST FLOW ACROSS THE WESTERN U.S. AND TEXAS. WILL ONLY INCREASE POP VALUES TO 10 TO 14 PERCENT FOR THE TIME PERIOD AND WAIT FOR MODELS TO COME TO BETTER AGREEMENT BEFORE ADDING ANY PRECIP TO THE FORECAST. && .PRELIMINARY POINT TEMPS/POPS... ABILENE 43 77 43 62 34 / 0 0 10 10 0 SAN ANGELO 35 79 43 61 32 / 0 0 10 10 0 JUNCTION 40 75 45 67 30 / 0 0 20 20 0 && .SJT WATCHES/WARNINGS/ADVISORIES... NONE. && $$ 99/04
