Area Forecast Discussion
Issued by NWS Huntsville, AL

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000
FXUS64 KHUN 220318 AAB
AFDHUN

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE HUNTSVILLE AL
918 PM CST SUN DEC 21 2014

.UPDATE...
REMOVED PRECIP MENTION THIS EVENING ALL AREAS...BUT LEFT IT IN FOR
OUR EASTERN ZONES FOR THE OVERNIGHT.

&&

.DISCUSSION...
AN EXTENSION OF THE SUBTROPICAL JET CONTINUED TO MOVE IN A SW-NE
FASHION OVER THE FORECAST AREA...WITH WINDS IN THE 130-140KT RANGE
AROUND 35KFT UP. UNDER THE JET...LOWER LEVEL STRATUS HAS RETURNED AS
LOWER LEVEL WINDS BECOME MORE SE. THE EDGE OF THOSE CLOUDS HAVE
COVERED ALL OF THE FORECAST AREA EXCEPT FAR NW ALABAMA. WELL TO OUR
SOUTH...A WEAK WAVE NEAR THE GULF COAST HAD SHOWERS ASSOCIATED WITH
IT...EXTENDING FROM SOUTH OF THE MISSISSIPPI DELTA TO SW GEORGIA.

NEW OUTPUT FROM THE NAM/RAP INDICATED THAT LOWER LEVEL MOISTURE
SHOULD SLOWLY RETURN TO THE AREA DURING THE OVERNIGHT. HOWEVER...
AMOUNTS OF IT SHOULD REMAIN ON THE SLIM SIDE...WHICH WILL KEEP RAIN
CHANCES TEMPERED. AS SUCH...HAVE REMOVED IT FROM THE FORECAST FOR THE
REST OF EVENING AREAWIDE. BUT HAVE LEFT IT IN (AS A SLIGHT CHANCE OF
RAIN/DRIZZLE) FOR OUR EASTERN AREAS. ISENTROPIC UPGLIDE AND TERRAIN
WILL BRING BETTER ODDS FOR RAIN AFFECTING THOSE AREAS. BETTER RAIN
CHANCES ARE EXPECTED LATER TOMORROW...AND ESPECIALLY ON TUE...AS A
STRONGER SYSTEM MOVES IN FROM THE SW. OTHER MAIN PARAMETERS...AKA
TEMPS/DEWPOINTS/WINDS/SKY COVER WERE LEFT AS IS. A SOLSTICE STARTING
THE WINTER SEASON EARLIER OCCURRED AT 503 PM.

RSB

&&

.AVIATION...
/ISSUED 543 PM CST SUN DEC 21 2014/
FOR 00Z TAFS...
STRATUS...MAINLY ABOVE MVFR THRESHOLD CONTINUED ACROSS THE AREA. A
WEAK SYSTEM FORMING TO OUR SOUTH AND MOVING TOWARD THE MID ATLANTIC
WILL RESULT IN CIGS BECOMING MVFR THIS EVENING...WITH IFR CIGS LIKELY
BEFORE DAYBREAK MON. ALONG WITH LOWER CIGS...LIGHT DRIZZLE SHOULD
MOVE ACROSS THE AREA AFTER SUNRISE. LATEST MODEL TRENDS CONTINUE TO
KEEP THE BULK OF THE PRECIP ASSOCIATED WITH THIS SOUTHERN SYSTEM
MAINLY EAST/SOUTH OF THIS AREA. ANOTHER SYSTEM NEARING FROM THE WEST
COULD BRING RAIN CHANCES VERY LATE IN THE FORECAST FOR KMSL.

RSB

&&

.PREV DISCUSSION...
/ISSUED 145 PM CST SUN DEC 21 2014/
LOW CLOUDS CONTINUE TO SPREAD TO THE NW THIS AFTERNOON AS LOW LEVEL
FLOW TURNS SELY. THE MOISTENING WILL PERSIST TONIGHT WHICH SHOULD
LEAD TO PATCHY DRIZZLE DEVELOPMENT AND PERHAPS SOME -RA IN OUR SERN
COUNTIES. HOWEVER, RAINFALL DOES NOT APPEAR AS LIKELY AS THE
SHORTWAVE CROSSING THE MS RIVER WILL DEPART RAPIDLY.

ADDITIONAL SHORTWAVES QUICKLY FOLLOW BEHIND AS EARLY AS MONDAY WHICH
SHOULD INSTIGATE A FEW SHRA, MAINLY DURING THE AFTERNOON AS LARGE-
SCALE SOUTHERLY FLOW INCREASES OVER THE REGION. FEW CHANGES WERE MADE
TO MONDAY NIGHT THROUGH TUESDAY NIGHT. THE MODELS ARE A BIT SLOWER
WITH THE CYCLOGENESIS AND FRONTAL PROGRESSION THRU OUR AREA. A CAD
WILL CONTINUE TO SLOW THE PROGRESSION OF SURFACE BASED MOISTURE INTO
OUR EASTERN COUNTIES, ESPECIALLY IF THE SFC LOW DEVELOPMENT IS SLOWER
AND STRONGER THAN INDICATED. HOWEVER, THE RRQ UPPER JET DIVERGENCE
AND RESULTANT LLJ WILL BRING GOOD MOISTURE TRANSPORT/ADVECTION AT
925-850MB LAYER INTO THE REGION. EVENTUALLY, SFC FLOW WILL VEER TO A
SOUTHERLY DIRECTION BY TUESDAY EVENING. ALL THIS POINTS TO A
FAVORABLE SITUATION FOR PROLONGED BANDS OF SHOWERS/TSTMS AND POSSIBLE
ECHO TRAINING DUE TO A HIGHLY UNDIRECTIONAL WIND PROFILE IN MID TO
UPPER LEVELS. RAINFALL TOTALS OF 2-3 INCHES ARE LIKELY IN SOME
LOCATIONS. THIS COULD ELEVATE A FEW CREEKS AND STREAMS IN THE AREA,
BUT AM NOT EXPECTING FLASH FLOODING ATTM. MID LEVEL LAPSE RATES ARE
RATHER MARGINAL TO SUPPORT MUCH CAPE, AND THUS RESULTANT SHERBE
VALUES ARE PROGGED TO STAY BELOW 1 UNIT IN OUR AREA GIVING A LOWER
CONCERN OF SIGNIFICANT HSLC SEVERE CONVECTION.

WINDY CONDITIONS ARE STILL ANTICIPATED ON WEDNESDAY BEHIND THE COLD
FRONT AS MEDIUM RANGE MODELS CONTINUE TO INDICATE POTENTIAL
BOMBOGENESIS TUE NIGHT THRU WED NIGHT. THE GOOD NEWS IS, THE PRESSURE
GRADIENT RELAXES RAPIDLY BY WEDNESDAY NIGHT IN THE TN VALLEY. WE HAVE
KEPT A BRIEF MIX OF SNOW SHOWERS WITH THE RAIN SHOWERS WEDNESDAY
EVENING IN OUR SRN TN AND NERN AL COUNTIES, BUT THIS REMAINS LOW
CONFIDENCE AT BEST WITH PRONOUNCED DRY AIR ADVECTION AND SUBSIDENCE
IN PLACE ABOVE THE -5C ISOTHERM LEVEL. IT WILL BE DIFFICULT TO
GENERATE ICE CRYSTALS IN THIS SITUATION.

WILL FOLLOW BLENDS CLOSELY D5-7. CHRISTMAS DAY LOOKS LIKE A SUNNY
AND CALM WEATHER DAY AS A HIGH PRESSURE RIDGE SKIRTS THRU BETWEEN
SYSTEMS. THE NEXT COLD FRONT IS HANDLED DIFFERENTLY BY THE GFS AND
ECMWF, SO PLAN TO HOLD ONTO LOW CHC POPS THRU D6. THEN UNCERTAINTY
IS TOO HIGH TO VENTURE OUT WITH PRECIP AT DAY 7.

AK

&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...NONE.
TN...NONE.
&&

$$

FOR MORE INFORMATION PLEASE VISIT OUR WEBSITE
AT WEATHER.GOV/HUNTSVILLE.


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