418 
FXUS64 KHUN 152345 AAA
AFDHUN

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE HUNTSVILLE AL
645 PM CDT FRI MAR 15 2013

.UPDATE...
FOR 00Z TAFS 

&& 

.DISCUSSION...
/ISSUED 454 PM CDT FRI MAR 15 2013/
PRIMARY FORECAST CHALLENGES CENTER AROUND POTENTIAL CHANCES FOR 
PRECIP LATE SAT NIGHT AND AGAIN MONDAY MORNING...AND RESOLVING STORM 
CHARACTERISTICS AND TIMING WITH THE COLD FRONT FOR MONDAY NIGHT. 
ADJUSTMENTS TO THE PREVIOUS FORECAST WERE GENERALLY SMALL. 
ALTHOUGH...SLIGHT CHANCES FOR THUNDER WERE REMOVED FOR SUNDAY. 
DETAILS FOLLOW BELOW. 

A LOW PRESSURE SYSTEM TRACKING ALONG A BAROCLINIC FRONT STRETCHING 
ACROSS THE CENTRAL GREAT PLAINS AND OH VALLEY REGION WILL CONTINUE 
TO MOVE GENERALLY EWRD OVERNIGHT. A SLIGHT NORTHERLY COMPONENT IN 
GEOSTROPHIC FLOW WILL PUSH THE FRONT SLOWLY TOWARDS THE TN VALLEY 
REGION THROUGH SAT NIGHT. IN THE MEANTIME...MID/HIGH CLOUDS IN 
ASSOC/W UPLIFT INDUCED BY A MID/UPR SHORT WAVE WILL CONTINUE TO 
DRIFT INTO THE REGION OVERNIGHT. FOR THOSE TRYING TO GET A VIEW OF 
COMET PANSTARRS...YOU MAY BE STRUGGLING A BIT TO SEE THROUGH THIN 
HIGH CIRRUS TONIGHT. OTHERWISE...TEMPS HAVE RISEN SEVERAL DEGREES 
HIGHER TODAY THAN MOS DEPICTIONS AND WITH BOUNDARY LYR WINDS ARND
7-10 KTS AND MID/HIGH CLOUDS BLOCKING SOME IR...TEMPS WERE INCREASED
A LITTLE ABOVE SUGGESTED MOS FOR TONIGHT.

THE ADDITION OF MORE MID/HIGH CLOUDS FOR SAT WILL CURTAIL SOME 
SENSIBLE HEATING...HOWEVER WILL CONTINUE TO TREND ABOVE MOS WITH 
ROBUST WAA ONGOING. AFTN TEMPS SHOULD TOP OUT IN THE 70S FOR MOST 
AREAS. IF CLOUDS ARE THINNER THAN EXPECTED...AN 80 DEGREE TEMP IS 
NOT OUT OF THE QUESTION MAINLY FOR NW PARTS OF ALABAMA. BREEZY 
CONDITIONS WILL LIKELY AGAIN EXIST...WITH SW WINDS ARND 15 KTS AND 
GUSTS ARND 20 KTS POSSIBLE. 

THE AFORE-MENTIONED SFC FRONT WILL PUSH SOUTHWARD TOWARDS THE 
AREA...POTENTIALLY REACHING NEAR THE AL/TN BORDER BY 00-06Z. WEAK 
SHORT WAVE MAXIMA MOVING EWRD IN THE INCREASINGLY ZONAL FLOW ALOFT 
MAY INDUCE SUFFICIENT ISENTROPIC LIFT OVHD TO GENERATE SOME -SHRA 
ACTIVITY SAT NIGHT AND SUN MORNING IN THE NORTH. SUFFICIENT 
SATURATION ALOFT MAY ONLY ALLOW FOR -SHRA IN THE FAR NORTHERN TIER 
COUNTIES IN AL AND OUR TN COUNTIES DURING THIS PERIOD. THIS WILL 
ULTIMATELY DEPEND ON THE LOCATION OF THE STALLED FRONTAL BOUNDARY AS 
WELL...WHICH MAY END UP STALLING A LITTLE FURTHER NORTH IN TN. 
THUS...ONLY 20 PCT POPS WERE INCLUDED IN FCST.

MID/HIGH CLOUDS MAY BE SUFFICIENT AGAIN TO BLOCK SOME INSOLATION FOR 
SUNDAY...THUS TEMPS ARE CURRENTLY FCST TO BE ARND LOW/MID 70S. 
HOWEVER...IF CLOUDS DO NOT MANIFEST AS CURRENTLY THOUGHT...THEN 
CURRENT FCST TEMPS ARE PROBABLY ABOUT 5-8 DEGREES TOO LOW. CHANCES 
FOR PRECIP FOR SUNDAY AFTERNOON WERE REMOVED WITH GLOBAL MODEL 
EVIDENCE SUGGESTING THE FRONT TO OUR NORTH WILL BEGIN TO PUSH BACK 
TO THE NORTH AS A WARM FRONT...AND ISENTROPIC LIFT WILL ESSENTIALLY 
COME TO AN END ACROSS THE AREA.

A MORE ORGANIZED UPR WAVE IS LIKELY TO MOVE ACROSS THE AREA EMBEDDED 
IN W-SW FLOW ALOFT AND INDUCE MORE SHOWERS FOR SUNDAY NIGHT INTO 
MONDAY MORNING. WITH ROBUST WARM/MOIST ADVECTION ALOFT...ELEVATED 
INSTABILITY MAY BE SUFFICIENT TO PRODUCE A FEW TSTMS. 

A LINE OF STRONG TO SEVERE THUNDERSTORMS IS POSSIBLE FOR LATE MONDAY 
AFTN THROUGH MONDAY EVENING AHEAD OF A COLD FRONT. SB CAPE VALUES 
MAY EXCEED 1500 J/KG ACROSS THE AREA...CONCURRENT WITH ABOUT 25 KTS 
OF SHEAR IN THE 0-1KM LAYER. OVERALL...LARGE HAIL APPEARS TO BE THE 
MAIN STRONG/SEVERE TSTM THREAT AT THIS TIME. HOWEVER...THE SHEAR AND 
LOW LCL HEIGHTS (PERHAPS <1KM) MAY BE SUFFICIENT TO ALLOW FOR SOME 
STORM ORGANIZATION AND PERHAPS A FEW BRIEF TORNADOES. FOR NOW...THE 
HWO PRODUCT ADDRESSES MAINLY THE HIGHER CONFIDENCE THREAT (HAIL). 
THE STORMS WILL MOVE ACROSS THE AREA...QUICKLY EXITING BY TUESDAY 
MORNING.

TEMPS WILL FALL MODESTLY BEHIND THE COLD FRONT WITH NEAR ZONAL UPR 
FLOW ESTABLISHED ACROSS THE CONUS BY MIDWEEK. ANOTHER QUICK-MOVING 
SYSTEM IS EXPECTED TO MOVE ACROSS THE INTERIOR SOUTH FROM WED NIGHT 
THROUGH FRIDAY. THIS STORM SYSTEM IS LIKELY TO TAKE A MORE SOUTHERLY 
TRACK...WITH LIMITED INSTABILITY FOR OUR AREA AND THUS WILL 
NECESSITATE ONLY A FCST OF SHRA AT THIS TIME. 

KDW

&&

.AVIATION...
FOR 00Z TAFS... 

VFR CONDITIONS ARE EXPECTED TO CONTINUE FOR THE NEXT 24 HOURS ACROSS
N AL/S MIDDLE TN. LLWS WILL BE LIKELY ACROSS THE AREA BTWN 00-14Z DUE
TO STRONG SW WINDS JUST ABOVE THE SURFACE (015-018 KFT) AND WEAKER
WINDS AT THE SFC. SFC WINDS WILL THEN INCREASE AFTER 14Z TO 12-15 KTS
GUSTING TO 20 KTS.

SL.77

&&

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

$$ 

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AT WEATHER.GOV/HUNTSVILLE.