425
FXUS64 KHUN 161052 AAA
AFDHUN
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE HUNTSVILLE AL
552 AM CDT WED OCT 16 2013
.UPDATE...
FOR 12Z TAFS
&&
.DISCUSSION...
/ISSUED 321 AM CDT WED OCT 16 2013/
THE 08Z SURFACE ANALYSIS INDICATED THAT THE COLD FRONT WAS SLOWLY
MOVING EAST AND EXTENDED SOUTHWEST FROM ACROSS WEST CENTRAL
INDIANA...TO NEAR PADUCAH KENTUCKY...THEN TO ALONG THE MISSISSIPPI
RIVER AND INTO NORTHWEST MISSISSIPPI. A LARGE AREA OF LIGHT TO
GENERALLY MODERATE RAINFALL WAS OCCURRING ALONG AND JUST AHEAD OF
THE COLD FRONT. IN THE SHORT TERM...THE PRECIPITATION AREA SHOULD
CONTINUE TO SLOWLY WORK ITS WAY EASTWARD THROUGH THE DAY AND SHOULD
OVERSPREAD THE FORECAST AREA TODAY. WILL CONTINUE WITH NEARLY
CATEGORICAL PRECIP CHANCES ACROSS THE FORECAST AREA FROM THE WEST TO
THE EAST THROUGH THE DAY. THE CLOUDS/PRECIP SHOULD HINDER TEMPS FROM
RISING MUCH ABOVE 70 DEGREES ACROSS THE FORECAST AREA...WHICH IS
GENERALLY ACCEPTED AS PER MODEL GUIDANCE. INSTABILITY WILL BE LIMITED
ALONG THE FRONTAL BOUNDARY...AND WILL ONLY CONTINUE WITH A TOKEN
SLIGHT CHANCE OF TSRA FOR MAINLY IN THE AFTERNOON HOURS.
THE MODELS ARE FAIRLY SIMILAR INVOLVING MOVING THE COLD FRONT INTO
NORTHWEST ALABAMA BY 00Z TONIGHT. WILL CONTINUE WITH AT LEAST LIKELY
POPS FOR MOST OF THE FORECAST AREA. THE PRECIP AREA SHOULD BEGIN TO
WORK ITS WAY EASTWARD OF NORTHWEST ALABAMA BY LATER THIS EVENING...SO
WILL GO CLOSER TO THE NAM PRECIP PROBABILITIES FOR TONIGHT FOR THE
SHOALS AREA. THE GFS/ECMWF MODELS ARE A LITTLE FASTER WITH THE
EASTWARD MOVEMENT OF THE COLD FRONT INTO THURSDAY...WHILE THE NAM
MODEL IS SLOWER. THE NAM MODEL INDICATES THAT A COUPLE OF VORT MAXES
ARE EXPECTED TO MOVE NORTHEAST ALONG THE FRONTAL BOUNDARY ON
WEDNESDAY NIGHT. HAVE DECIDED TO COMPROMISE BETWEEN THE SLOWER NAM
MODEL AND THE FASTER GFS/ECMWF MODELS INVOLVING THE DURATION OF THE
PRECIP ACROSS THE FORECAST AREA ON THURSDAY. HAVE KEPT IN A CHANCE OF
SHRA THROUGH AROUND 18Z ACROSS THE FORECAST AREA. WITH DRIER AIR AND
DECENT COLD ADVECTION EXPECTED TO MOVE INTO NORTHWEST ALABAMA BY
THURSDAY AFTERNOON...HAVE KEPT THE CURRENT PRECIP TIMING INVOLVING
ENDING SHRA CHANCES BY THURSDAY AFTERNOON IN NORTHWEST ALABAMA.
CONTINUED WITH JUST A SLIGHT CHANCE POP FOR MAINLY NORTHEAST ALABAMA
FOR THURSDAY AFTERNOON.
THE PROGRESSIVE UPPER TROUGH IS EXPECTED TO MOVE EASTWARD ACROSS THE
FORECAST AREA THROUGH FRIDAY...WITH SURFACE HIGH PRESSURE EXPECTED TO
SLIDE NORTHEAST OUT OF THE SOUTHERN PLAINS ON THURSDAY AFTERNOON...
ACROSS THE TENNESSEE AND OHIO VALLEYS ON FRIDAY...AND THEN TO THE MID
ATLANTIC COAST BY SATURDAY. BY FRIDAY...ANOTHER STRONG UPPER TROUGH
IS PROGGED BY THE MODELS TO PROGRESSIVELY MOVE SOUTHEAST THROUGH THE
UPPER PLAINS STATES...AND AFFECT THE LOWER OHIO VALLEY REGION BY
EARLY SATURDAY. ANOTHER SURFACE COLD FRONT IS EXPECTED TO MOVE EAST
INTO THE REGION BY SATURDAY...WITH A RETURNING CHANCE OF SHRA. THE
ECMWF MODEL DEPICTS MORE LOW LEVEL MOISTURE AND INTRUSION OF A
SOUTHERN STREAM LOW LEVEL JET...COMPARED TO THE WEAKER UPPER LEVEL
SUPPORT AND MOISTURE SHOWN BY THE GFS MODEL. HAVE DECIDED TO STAY
CLOSE OR SLIGHTLY BELOW GFS GUIDANCE TEMPS THROUGH MUCH OF THE
EXTENDED FORECAST PERIODS.
IN THE WAKE OF THIS COLD FRONT PASSING THROUGH THE FORECAST AREA ON
SATURDAY...SURFACE HIGH PRESSURE WILL MOVE EAST THROUGH THE LOWER
OHIO VALLEY FROM SUNDAY THROUGH MONDAY WITH SLIGHTLY BELOW NORMAL
TEMPS EXPECTED.
THE MODELS DIFFER BY TUESDAY INVOLVING THE NORTHEAST MOVEMENT OF A
SHORT WAVE AT 500 MILLIBARS OUT OF THE TEXAS/LOUISIANA AREA...INTO
CENTRAL ALABAMA. THE GFS MODEL INDICATES THAT MODERATE TO HEAVY
RAINFALL MAINLY SOUTH OF THE FORECAST AREA IS PROGGED TO MOVE EAST-
NORTHEAST THROUGH CENTRAL ALABAMA ON TUESDAY...COMPARED TO A DRIER
AND DELAYED ECMWF MODEL SOLUTION. FOR NOW...HAVE DECIDED TO AT LEAST
KEEP IN A SLIGHT CHANCE POP FOR SHRA ON TUESDAY DUE TO THE MODEL
DIFFERENCES.
TT
&&
.AVIATION...
FOR 12Z TAFS... SPOTTY SPRINKLES/-RA WILL CONTINUE IN THE KMSL/KHSV
AREA IN ADVANCE OF A LARGE AREA OF -RA/RA OVER NRN MS. THE MORE
CONTINUOUS RAINFALL WILL ARRIVE LATE THIS MORNING PRODUCING MVFR
CONDS AT KMSL BY AS EARLY AS 15-17Z. MVFR MAY HOLD OFF UNTIL THIS
AFTN AT KHSV, BUT THIS MAY NEED AMENDING. A NEARLY CONTINUOUS PERIOD
OF RA IS EXPECTED INTO TONIGHT UNTIL A COLD FRONT ARRIVES. CIGS AT
THAT TIME WILL LIKELY LOWER INTO THE IFR CATEGORY.
AK
&&
.HUN WATCHES/WARNINGS/ADVISORIES...
AL...NONE.
TN...NONE.
&&
$$
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AT WEATHER.GOV/HUNTSVILLE.