FXUS64 KHUN 140232 AFDHUN AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE HUNTSVILLE AL 932 PM CDT MON OCT 13 2014 .UPDATE... REMOVED LAUDERDALE/COLBERT/LAWRENCE/FRANKLIN AL COUNTIES FROM TORNADO WATCH...ALSO CANCELLED WIND ADVISORY. REST OF THE FCST PARAMETERS HAS NOT BEEN CHANGED ATTM. && .DISCUSSION... LINE OF STRONG TO OCCASIONALLY SEVERE STORMS EXTENDED FROM LIMESTONE COUNTY TO WRN MORGAN AND INTO WRN CULLMAN COUNTY. THIS LINE OF STORMS WILL CONTINUE TO SLOWLY MOVE ACROSS THE REST OF THE CWA THIS EVENING. THE THREAT OF SEVERE WX IS ALSO BEGINNING TO DIMINISH...HOWEVER WITH 50 KT 8H WINDS AND GOOD LOW LEVEL SHEAR...STILL CANT RULE OUT A FEW SEVERE STORMS WITH DAMAGING WINDS OR A BRIEF TORNADO. BETWEEN MIDNIGHT AND 2 AM...IT LOOKS LIKE THE THREAT OF SEVERE WX WILL END. WENT AHEAD AND CANCELLED THE WIND ADVISORY AS SFC WINDS WERE ALSO DIMINISHING...BUT WIND GUSTS ARND 25 MPH WILL STILL BE POSSIBLE FOR THE OVERNIGHT HOURS. AFTER MIDNIGHT EXPECT TO TRANSITION FROM DAMAGING WINDS TO MORE OF A HVY RAIN EVENT...THUS WILL KEEP THE FLASH FLOOD WATCH GOING. 07 && .AVIATION... /ISSUED 647 PM CDT MON OCT 13 2014/ FOR 00Z TAFS...A LINE OF SHRA/TSRA ALONG THE AL/MS BORDER HAS WEAKEN CONSIDERABLY ATTM. HOWEVER THERE COULD BE SOME MORE STORM REDEVELOPMENT LATER THIS EVENING DUE TO A 50 KT LLJ AHEAD OF THE LINE OF STORMS. THE ACTUAL SFC CDFNT WAS STILL ACROSS WRN AR. THUS WILL KEEP TSRA IN TAFS THRU 04Z/05Z. AFTER 05Z WILL KEEP SHRA IN TAFS AS THE CDFNT CONTINUES TO SLOWLY MOVE TOWARDS THE TN VALLEY OVERNIGHT. THE CDFNT WILL PASS THRU KMSL ARND 12Z AND KHSV BY 14Z. HOWEVER WINDS BEHIND THE CDFNT WILL STILL BE FROM THE SW. PCPN WILL TAPER OFF BY 21Z/22Z ACROSS THE TAF SITES...HOWEVER MORE WRAP ARND SHOWERS WILL BE POSSIBLE AFTER 00Z TUESDAY NIGHT. 07 && .PREV DISCUSSION... /ISSUED 342 PM CDT MON OCT 13 2014/ THE TIMING OF THE APPROACHING QLCS HAS DEFINITELY BEEN DIFFICULT TO PREDICT OVER THE PAST FEW DAYS, BUT IT APPEARS THAT HRRR/RAP/WRF HAVE A BETTER HANDLE WITH THIS SEVERE QLCS AND THE DEEP CONVECTION TO THE SOUTH. WIND SHEAR HAS INCREASED THROUGHOUT THE DAY WITH MODEST INSTABILITY OBSERVED ON MORNING SOUNDINGS. MORE SPECIFIC ON THE WIND SHEAR EXPECTED THIS AFTERNOON AND EARLY THIS EVENING, 0-3 KM SRH IS BETWEEN 200-300 M2/S2 WITH HIGHER VALUES TONIGHT (500-600 M2/S2 BY 01-06Z), WHILE BULK SHEAR (0-6 KM) INCREASES TO 40-60 KTS- GRADUALLY SPREADING EAST OVERNIGHT. THE HIGHEST VALUES ARE LOCATED OVER NW AL INITIALLY. THE INCREASE IN WIND SHEAR IS LIKELY DUE IN PART TO THE ORIENTATION OF THE TROUGH AS IT MOVES EAST AS IT APPEARS THE SOUTHERN FLANK PUSHES NORTHEAST AND BECOMES NEGATIVELY TILTED ACROSS E LA/W MS BTWN 01-07Z. THIS MAY ALSO HAVE THE EFFECT OF ACCELERATING THE LINE EASTWARD IN ADDITION TO INCREASING/MAINTAINING THE STRONG WIND SHEAR. THE STRONG WINDS INDUCED BY THE APPROACHING SYSTEM HAS ALSO NECESSITATED KEEPING THE WIND ADVISORY IN EFFECT FOR SUSTAINED WINDS RISING BETWEEN 15-25 MPH AND GUSTS UP TO 35 MPH LIKELY. REGARDING INSTABILITY, THE MODEL PROGS THE HIGHEST INSTABILITY TO OCCUR DURING PEAK HEATING THIS AFTERNOON AND EVENING WITH MUCAPES RISING CLOSE TO 2000 J/KG BEFORE FALLING OFF OVERNIGHT. THE STRONG LLJ (40-50 KTS FROM THE SOUTH) IN CONJUNCTION WITH A SCATTERED TO BROKEN CLOUD DECK ACROSS THE AREA HAS ALREADY RESULTED IN A WARM/MOIST ENVIRONMENT AND UNSTABLE ENVIRONMENT ACROSS THE TN VALLEY. THIS UNSTABLE ENVIRONMENT WILL ALSO PLAY A PART IN SUSTAINING DEEP CONVECTION THROUGH THIS AFTERNOON AND THIS EVENING. HOWEVER, DESPITE THE DECREASE IN SENSIBLE HEATING/INSTABILITY, ELEVATED INSTABILITY AND THE ALREADY STRONGLY SHEARED ENVIRONMENT WILL STILL TRANSLATE TO A HIGH LIKELIHOOD FOR DAMAGING WING GUSTS AND TORNADOES ALONG THE QLCS TONIGHT. THOUGH THE FRONT IS LAGGING BEHIND THIS QLCS, EXPECTING IT TO BEGIN MOVING RAPIDLY THIS EVENING AND TONIGHT IMPACTING THE TN VALLEY BTWN 07-12Z EARLY TUESDAY MORNING. AN ADDITIONAL CONSIDERATION IS THAT DUE TO THE HEAVY RAINFALL WE HAVE RECEIVED OVER THE PAST FEW DAYS AND WITH THE ADDITIONAL 2-3 INCHES EXPECTED, THE AREA IS RIPE FOR FLASH FLOODING WHICH COULD BE ESPECIALLY DANGEROUS DURING THE OVERNIGHT PERIOD. THUS, THE FLASH FLOOD WATCH HAS BEEN RETAINED THROUGH THE OVERNIGHT. AS A RESULT OF THIS CURRENT ANALYSIS AND MODEL PROGS, HAVE MADE SOME ADJUSTMENTS TO THE TIMING AND PASSAGE OF THE SUPERCELLS/CLUSTERS AND QLCS AND MAINTAINED THE THREATS SEVERE WORDING THROUGH THIS EVENING AND OVERNIGHT. RIGHT NOW, THE SUPERCELLS/CLUSTERS FROM THE SOUTH SHOULD IMPACT PORTIONS OF NORTH ALABAMA BETWEEN 5-8PM. THEN, THE QLCS/SQUALL LINE SHOULD IMPACT NORTHWEST ALABAMA BY 5-9PM, INTERSTATE 65 CORRIDOR BY 8PM-1AM, AND NORTHEAST ALABAMA BY 1AM-5AM. ONCE THE FROPA OCCURS, SOME POST-FRONTAL SHOWERS/STORMS ARE POSSIBLE BUT SHOULD QUICKLY DIMINISH IN INTENSITY. DID KEEP SHOWERS IN THE FORECAST FOR TUESDAY AND TUESDAY NIGHT BEHIND THE FRONT MAINLY DUE TO THE SOUTHERN FLANK OF THE TROUGH BECOMING QUASI-CUTOFF FROM THE PREVAILING FLOW AND SPINNING OVER THE MID MS AND OH RIVER VALLEYS. KEPT MOSTLY CLOUDY CONDITIONS FOR MOST OF THE DAY ON TUESDAY WITH MUCH COOLER DAYTIME HIGHS (UPPER 60S) DUE TO THIS SCENARIO. OVERNIGHT LOWS ON TUESDAY NIGHT WILL THEN BE NOTICEABLY COOLER IN THE 40S. OTHERWISE, A COMPLETE CLEARING MAY NOT OCCUR UNTIL WEDNESDAY AND THEN DRY AND CLOSE TO SEASONABLE TEMPERATURES SHOULD OCCUR THROUGH FRIDAY. THERE IS EVIDENCE OF A REINFORCING COLD FRONT ON FRIDAY NIGHT INTO SATURDAY WHICH SHOULD BE A DRY FRONT BUT THERE IS SOME INDICATION THAT ENOUGH MOISTURE MAY RESULT IN SOME SHOWER ACTIVITY BUT DID NOT MAKE ANY ADJUSTMENTS TO THAT FORECAST AT THIS TIME. SL.77 && .HUN WATCHES/WARNINGS/ADVISORIES... AL...FLASH FLOOD WATCH THROUGH TUESDAY AFTERNOON FOR ALZ001>010-016. TN...FLASH FLOOD WATCH THROUGH TUESDAY AFTERNOON FOR TNZ076-096-097. && $$ FOR MORE INFORMATION PLEASE VISIT OUR WEBSITE AT WEATHER.GOV/HUNTSVILLE.
Posted on: Tue, 14 Oct 2014 02:38:14 +0000
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