Area Forecast Discussion
Issued by NWS Huntsville, AL

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000
FXUS64 KHUN 302024
AFDHUN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HUNTSVILLE AL
324 PM CDT SAT MAY 30 2015

.SYNOPSIS...

WEAKLY AMPLIFIED SHORTWAVE TROUGHS PREVAIL FROM THE PLAINS TO
MS/OH/TN VALLEYS TODAY WITH MORE AMPLIFICATION IN THE UPPER FLOW
LATER THIS WEEK. ONE OF THESE SHORTWAVE TROUGHS MOVING ACROSS THE
LOWER/MID MS RIVER VALLEY TOWARDS THE OH RIVER VALLEY HAS BROUGHT
STRONG TO MARGINALLY SEVERE THUNDERSTORMS OVER THOSE REGIONS. IN
ADDITION, THUNDERSTORMS HAVE BEEN DEVELOPING ACROSS THE TN VALLEY ON
THE E/SE FRINGE OF THIS SHORTWAVE TROUGH. WITH STRONG INSOLATION AND
MODERATE INSTABILITY ASSOCIATED WITH THE PREVAILING MARITIME TROPICAL
AIRMASS, MARGINALLY SEVERE THUNDERSTORMS WILL REMAIN POSSIBLE UNTIL
AFTER SUNSET TODAY, ESPECIALLY OVER NW AL.

SL.77

&&

.DISCUSSION...

AS MENTIONED ABOVE, THE PRIMARY LIFTING MECHANISMS FOR DEEP
CONVECTIVE DISCRETE AND MULTI-CELL CLUSTERS IS A SLOW MOVING MID-
LEVEL SHORTWAVE TROUGH OVER THE OZARKS/W TN. AS THIS SHORTWAVE TROUGH
APPROACHES FOR TONIGHT, THUNDERSTORMS WILL BE POSSIBLE ESPECIALLY
OVER NW AL (AT LEAST INITIALLY). THE WESTERN FLANK OF A RIDGE
(CENTERED OVER THE WESTERN ATLANTIC) CURRENTLY RETREATING FROM THE
SOUTHEAST IS ACTUALLY PREVENTING A FURTHER SPREAD EASTWARD IN
THUNDERSTORM DEVELOPMENT. HOWEVER, AS THE SHORTWAVE TROUGH LIFTS NE,
SOME THUNDERSTORM ACTIVITY IS POSSIBLE FURTHER EAST AFTER 06Z. THEY
WILL BE MORE DISCRETE AND SCATTERED IN NATURE DUE TO THE LIGHT WIND
SHEAR PROFILES, WITH MAINLY MICROBURST INDUCED GUSTY WINDS UP TO 30-
40 MPH THE PRIMARY THREAT WITH ANY STORMS.

THIS SHORTWAVE TROUGH WILL SHIFT NORTHEAST OVERNIGHT AS IT IMPACTS
THE SLOWLY RETREATING RIDGE. IT SHEARS APART LATER TONIGHT INTO
TOMORROW AS A POLAR SHORTWAVE TROUGH OVER CANADA MERGES WITH THE
NORTHERN FLANK OF SHEARED TROUGH. ADDITIONALLY, AS THE SHEARED TROUGH
SLOWLY SHIFTS NE, THE ACCOMPANYING SFC LOW WILL RACE NE AND THE SEWWD
PROGRESSION IN A SFC COLD FRONT LOCATED OVER THE CORN BELT REGION
WILL GRADUALLY INCREASE. BY TOMORROW, THE SFC FRONT IS FORECAST TO BE
LOCATED FROM FAR SE TX NEWWD TO W TN AND OH RIVER VALLEY. MUCAPES
(0-3 KM) WILL RISE TO 1000-2000 J/KG BY SUN AFTERNOON ESPECIALLY WITH
BREAKS IN THE CLOUD COVER. THE FRONT SHOULD BECOME THE FOCUS FOR
STORM DEVELOPMENT WHICH WITH THE WEAK STEERING FLOW (SE 15-20 KTS)
ALOFT SHOULD MEAN STORMS THAT DEVELOP SHOULD MOVE FROM NW MS/CENTRAL
AL TOWARDS N AL/S MIDDLE TN.

THIS IS WHERE THE FORECAST IS RATHER CHALLENGING IN TERMS OF
THUNDERSTORM CHANCES AS DIFF VORTICITY ADVECTION FROM THE SOUTHERN
FLANK OF THE SHEARED TROUGH IS SHOWN BY SOME MODEL RUNS CLOSING OFF
OVER THE LOWER MS RIVER VALLEY AMPLIFIED RIDGE BUILDS OVER S PLAINS.
THE MED RANGE MODELS ARE NOW ALL SHOWING THIS FEATURE DESPITE EARLIER
RUNS OF THE ECMWF/CMC DEPICTING MORE OF AN OPEN WAVE. THE CLOSED WARM
CORE LOW SCENARIO BEGINS ON MONDAY WITH ECMWF STALLING THIS
MEANDERING FEATURE OVER W AL/E MS BY TUESDAY/WEDNESDAY. IF THIS
SOLUTION VERIFIES, IT WILL MEAN A RATHER COMPLEX SCENARIO OF
THUNDERSTORMS DEVELOPING DURING THE DAY EACH DAY FOLLOWED BY BREAKS
IN THE ACTIVITY THAT ARE DIFFICULT TO TIME AT THIS POINT. AS A
RESULT, THERE COULD BE WIDE VARIATIONS IN FORECAST POP/WX OVER COMING
DAYS AS DETAILS EMERGE WITH THIS SCENARIO. THE ECMWF EVEN SHOWS THE
POSSIBILITY OF A SMALL REX BLOCK SETTING UP OVER THE SOUTHEAST. SO
FOR NOW WILL KEEP THE BLENDED FORECAST OF THUNDERSTORMS GOING THROUGH
PRETTY MUCH THE ENTIRE FORECAST. IN ADDITION, KEPT DAYTIME
TEMPERATURES CLOSE TO NORMAL (OR JUST BELOW NORMAL) FOR THIS TIME OF
YEAR.

SL.77

&&

.AVIATION...
/ISSUED 1133 AM CDT SAT MAY 30 2015/
FOR 18Z TAFS... SCT SHRA AND TSRA WILL OCCUR EARLY THIS AFTN IN NWRN
AL, WHICH MAY IMPACT KMSL AND KHSV. THUS FAR, LIGHTNING HAS BEEN
QUITE LIMITED, SO HAVE ONLY INCLUDED VCSH AT BOTH SITES. AMDS MAY BE
NECESSARY DEPENDING ON CELL TRENDS. OTHERWISE, VFR CONDS ARE FORECAST
THRU SUNDAY MORNING.

AK

&&

.PRELIMINARY POINT TEMPS/POPS...
HUNTSVILLE    66  83  65  83 /  50  60  40  40
SHOALS        66  81  63  80 /  50  60  30  40
VINEMONT      66  83  64  81 /  40  60  40  50
FAYETTEVILLE  65  81  62  80 /  50  60  40  40
ALBERTVILLE   65  83  63  82 /  40  60  50  50
FORT PAYNE    65  83  63  81 /  40  60  50  50

&&

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

$$

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



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