Area Forecast Discussion
Issued by NWS Huntsville, AL

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000
FXUS64 KHUN 252336 AAB
AFDHUN

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE HUNTSVILLE AL
636 PM CDT SAT APR 25 2015

.UPDATE...
FOR 00Z TAFS

&&

.MESOSCALE UPDATE...
/ISSUED 613 PM CDT SAT APR 25 2015/
HAVE UPDATED THE FORECAST SLIGHTLY FOR THIS EVENING BASED ON CURRENT
MESOSCALE TRENDS. CI/CS CANOPY HAS NOW EXITED SRN TN AND NWRN AL
LATE THIS AFTERNOON ALLOWING FOR SOME LATE DAY HEATING. A LOW LEVEL
MIXED LAYER HAS ESTABLISHED BEHIND THE CLOUDS ACROSS MIDDLE AND
WESTERN TN INTO AR AND NWRN MS. TEMPS HAVE WARMED IN THIS REGION
ALONG WITH DEW POINTS LOWERING INTO THE 50S. THIS HAS PRODUCED A WEAK
BOUNDARY WHERE SOME CU HAS DEVELOPED FROM NEAR NASHVILLE INTO NRN MS.
AHEAD OF THE BOUNDARY WHERE DEW POINTS REMAIN IN THE 60S WITH TEMPS
IN THE U70S-L80S, MLCAPE VALUES ARE IN THE 1000-1500 J/KG RANGE IN
NRN AL AND EASTERN MIDDLE TN AND EVEN HIGHER OVER MS. SUPERCELL
PARAMETERS (CAPE/SHEAR COMBO) ALL SUGGEST THE POTENTIAL IF DEEP
CONVECTION CAN DEVELOP. HOWEVER, CONVERGENCE WAS QUITE WEAK ALONG
THE BOUNDARY, SO DEVELOPMENT APPEARS TO BE UNLIKELY ALONG THIS
FEATURE AT LEAST INITIALLY. HOWEVER, CONVECTION CONTINUES TO
BACKBUILD ALONG THE OH RIVER ALONG THE KY/IL BORDER. THE HRRR AND RAP
HAVE SUGGESTED IN RECENT RUNS THAT THIS WILL PERSIST WITH CONVECTION
REACHING SRN MIDDLE TN AND NERN AL BETWEEN 04-07Z. IN FACT, THERE IS
SOME SUGGESTION THAT CONVERGENCE FROM OUTFLOW MAY IGNITE THE EXISTING
AFOREMENTIONED BOUNDARY. THUS, WE HAVE REARRANGED THE CHC POP
CONFIGURATION SLIGHTLY IN A NW-SE FASHION ACROSS SRN TN AND NERN AL
FOR THIS EVENING.

AK

&&

.PREV DISCUSSION...
/ISSUED 248 PM CDT SAT APR 25 2015/
THE 19Z SURFACE ANALYSIS INDICATED THAT THE WARM FRONT WAS EXTENDING
WEST TO EAST ACROSS SOUTHWEST THROUGH SOUTH CENTRAL KENTUCKY. SKIES
WERE GENERALLY CLOUDY ACROSS THE FORECAST AREA WITH TEMPS IN THE LOW
TO MID 70S. THE LAST SEVERAL RADAR IMAGES INDICATED THAT A LARGE AREA
OF SHOWERS/STORMS WERE MOVING EAST-NORTHEAST OUT OF SOUTHEAST
MISSISSIPPI INTO WEST CENTRAL ALABAMA. MOST OF THIS CONVECTION SHOULD
REMAIN GENERALLY SOUTH OF THE FORECAST AREA INTO THE EVENING
HOURS...BUT WILL STILL CARRY A SLIGHT CHANCE POP FOR THE EVENING DUE
TO VERY UNSTABLE CONDITIONS. THE CLOUD COVER OVER THE AREA HAS
LIMITED ANY SHRA/TSRA DEVELOPMENT THIS AFTERNOON...WITH FORECAST
SOUNDINGS CONTINUING TO INDICATE CAPE VALUES EXCEEDING 3300 J/KG AND
LIFTED INDICES APPROACHING -11. THE LACK OF A TRIGGERING MECHANISM
HAS BEEN THE KEY TO THE LACK OF STORM DEVELOPMENT.

THE SHORT TERM MODELS MOVE THE SURFACE LOW TO THE NORTH OF THE
FORECAST AREA IN THE LOWER OHIO VALLEY THROUGH WESTERN KENTUCKY BY
00Z TONIGHT INTO SOUTHWEST VIRGINIA BY 06Z TONIGHT. THE LOW LEVEL
WIND FLOW IS PROGGED BY THE MODELS TO GRADUALLY SHIFT AROUND TO
THE WEST AND THEN NORTHWEST OVERNIGHT...AS THE TRAILING COLD FRONT
MOVES THROUGH THE REGION. THE MODELS INDICATE THAT A SECONDARY COLD
FRONT WILL PUSH SOUTHWARD THROUGH THE AREA ON SUNDAY...FURTHER
PUSHING DRIER AIR INTO THE FORECAST AREA. HIGH PRESSURE IS PROGGED BY
THE MODELS TO BUILD SOUTHEAST INTO THE REGION THROUGH MONDAY AND INTO
TUESDAY. WILL KEEP TEMPS IN THE SHORT TERM PORTION OF THE FORECAST
SLIGHTLY BELOW NORMAL AND NEAR GUIDANCE VALUES.

BY 12Z TUESDAY...ANOTHER SOUTHERN STREAM SYSTEM...AN UPPER LEVEL AREA
OF LOW PRESSURE IN THE SOUTHERN PLAINS...IS EXPECTED TO SLOWLY EJECT
NORTHEAST TOWARD THE REGION. ONE INITIAL SHORT WAVE IS EXPECTED TO
MOVE THROUGH THE FORECAST AREA DURING THE DAY ON TUESDAY AND HAVE
CONTINUED TO KEEP IN CHANCE SHRA POPS. THE UPPER LOW IS FINALLY
EXPECTED TO MOVE EAST INTO NORTHWEST ALABAMA BY 00Z THURSDAY AND
SHOULD FINALLY DISSIPATE BY 12Z THURSDAY IN NORTH GEORGIA. WILL KEEP
IN CHANCE/SLIGHT CHANCE SHRA POPS DURING THE TUESDAY-EARLY THURSDAY
TIME FRAME. IN THE WAKE OF THIS UPPER LOW...HIGH PRESSURE WILL BUILD
SOUTHWARD THROUGH THE LOWER OHIO AND TENNESSEE VALLEY REGION THROUGH
SATURDAY...WITH NEARLY NORMAL TEMPS EXPECTED.

TT

&&

.AVIATION...
VFR CONDITIONS CURRENTLY PREVAILED ACROSS THE FORECAST AREA.
HOWEVER...A COLD FRONT ORIENTED WEST TO EAST ACROSS THE OHIO VALLEY
SHOULD CONTINUE SOUTHWARD...REACHING THE FORECAST AREA AROUND
MIDNIGHT. GIVEN NEW GUIDANCE...HAVE ADDED VCSH AND MVFR CIGS FOR THE
0400-0700Z TIME FRAME. TS FORMATION IS POSSIBLE...BUT CONFIDENCE NOT
HIGH ENOUGH FOR INCLUSION THIS ISSUANCE. SW WINDS AROUND 10KT SHOULD
BECOME NW TOWARDS MIDNIGHT. VFR WEATHER SHOULD RETURN BEFORE DAWN...
WITH 5-10KT NW WINDS FOR MUCH OF SUNDAY.

RSB

&&

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

$$

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



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