070 FXUS64 KHUN 241120 AAA AFDHUN AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE HUNTSVILLE AL 620 AM CDT MON JUN 24 2013 .UPDATE... FOR 12Z TAFS && .DISCUSSION... /ISSUED 518 AM CDT MON JUN 24 2013/ CURRENT WATER VAPOR SATELLITE ANIMATION INDICATES THAT A BROAD/WEAK CYCLONIC FLOW ALOFT REMAINS IN PLACE ACROSS NORTHERN ALABAMA AND SOUTHERN MIDDLE TENNESSEE THIS MORNING -- AS THE REGION IS LOCATED BETWEEN A MID-LEVEL HIGH CENTERED OFF THE SOUTHEAST ATLANTIC COAST AND A SHORTWAVE TROUGH EXTENDING FROM THE LOWER OHIO VALLEY SOUTH- SOUTHWESTWARD INTO THE LOWER MISSISSIPPI VALLEY. OVER THE COURSE OF THE DAY...SHORT TERM NWP GUIDANCE SUGGESTS THAT THE EASTERN SEABOARD RIDGE WILL BEGIN TO RETROGRADE ACROSS FLORIDA/GEORGIA...WITH THE SHORTWAVE TROUGH EXPECTED TO ADVANCE EASTWARD ACROSS THE FORECAST AREA. ALTHOUGH THE STRONGEST LARGE SCALE FORCING FOR ASCENT WILL LIKELY OCCUR TO THE NORTH OF THE REGION...AT LEAST WIDELY SCATTERED CONVECTION IS EXPECTED TO DEVELOP AS WEAK LIFT OCCURS WITHIN THE INCREASINGLY MOIST AIRMASS /PWAT VALUES NOW IN THE 1.4-1.6 INCH RANGE/. WE ARE ONLY EXPECTING ACTIVITY TO BE ISOLATED/WIDELY SCATTERED AT MOST...BUT POPS WERE INCREASED A BIT ACROSS NORTHWEST ALABAMA -- WHERE AN OUTFLOW BOUNDARY MAY APPROACH FROM THE NORTHWEST AND SERVE AS A FOCUS FOR DEVELOPING CONVECTION. A LOW CHANCE OF SHOWERS/STORMS WAS RETAINED FOR MOST OF THE AREA THIS EVENING...AS STRENGTHENING NORTH/NORTHWEST FLOW ALOFT IN THE WAKE OF THE DEPARTING MID-LEVEL TROUGH AXIS MAY ALLOW LATE AFTERNOON CONVECTION ACROSS MIDDLE AND EASTERN TENNESSEE TO SPREAD SOUTHWARD INTO THE REGION. HAVE FORECASTED HIGH TEMPERATURES TODAY TO BE A DEGREE OR SO COOLER...WITH EXPECTATIONS OF THICKER MORNING CLOUD COVER AND MORE SHOWER/THUNDERSTORM ACTIVITY THIS AFTERNOON. LOWS TONIGHT WILL ONCE AGAIN BE AROUND 70 FOR MOST LOCATIONS. DURING THE PERIOD FROM TUESDAY THROUGH TUESDAY NIGHT...MODELS AGREE THAT THE MID-TROPOSPHERIC SUBTROPICAL RIDGE WILL CONTINUE TO RETROGRADE ALONG THE GULF COAST...AND BECOME CENTERED ACROSS NORTHERN SONORA/NORTHERN CHIHUAHUA BY TUESDAY EVENING. SEVERAL LOW AMPLITUDE 500-MB WAVES WILL ADVANCE EASTWARD ACROSS THE LOWER GREAT LAKES REGION DURING THIS PERIOD...BUT DEEP-LAYER FORCING ASSOCIATED WITH THESE FEATURES WILL BE VERY WEAK THIS FAR TO THE SOUTH. A LOW CHANCE FOR SHOWERS/STORMS WILL BE MAINTAINED ON TUESDAY AFTERNOON...BASED ON EXPECTATIONS OF AN EVEN MORE MOIST AIRMASS IN PLACE ACROSS THE LOCAL AREA...BUT THIS MAY EVEN BE TOO OPTIMISTIC. HOWEVER...SHOWER AND THUNDERSTORM CHANCES WILL INCREASE MORE SUBSTANTIALLY ON WEDNESDAY THE SUBTROPICAL RIDGE IS FORECAST TO INTENSIFY AND BUILD NORTHWARD INTO ARIZONA/NEW MEXICO -- INDUCING WEAK NORTHWEST FLOW ALOFT ACROSS THE TENNESSEE VALLEY. GLOBAL MODELS INDICATE THAT A STRONGER MID- LEVEL DISTURBANCE WILL DIG SOUTHEASTWARD ACROSS THE AREA ON WEDNESDAY...LEADING TO A HIGHER COVERAGE OF CONVECTION AND POTENTIALLY BRINGING A GREATER THREAT FOR STRONG STORMS AS MID-LEVEL NORTHWEST FLOW WILL INCREASE TO 20-25 KNOTS DURING THE AFTERNOON. MEDIUM RANGE GUIDANCE CONTINUES TO ADVERTISE A HIGHLY AMPLIFIED LONGWAVE PATTERN BECOMING ESTABLISHED ACROSS THE CONUS FOR THE REMINDER OF THE WEEK/UPCOMING WEEKEND...AS THE WESTERN U.S. RIDGE AMPLIFIES FURTHER AND BUILDS NORTHWARD INTO UTAH/COLORADO WHILE A STRONG UPPER CYCLONE DIGS SOUTHEASTWARD ACROSS ONTARIO AND THE GREAT LAKES. AN EVEN STRONGER MID-LEVEL SHORTWAVE WILL LIKELY IMPACT THE REGION ON THURSDAY/THURSDAY NIGHT...BRINGING ANOTHER ROUND OF SHOWERS AND STORMS. AFTER A BRIEF RESPITE ON FRIDAY...ANOTHER EVEN MORE ROBUST WAVE WILL BRING A MORE WIDESPREAD COMPLEX OF CONVECTION TO THE REGION ON FRIDAY NIGHT. DEEP-LAYER SHEAR AND INSTABILITY PARAMETERS INDICATE THAT EACH ROUND OF STORMS WILL HAVE THE CAPABILITY TO PRODUCE SEVERE WEATHER...WITH DAMAGING WINDS BEING THE PRIMARY HAZARD. THE PASSAGE OF A WEAK COLD FRONT WILL LIKELY END THE THREAT FOR SIGNIFICANT SHOWER/THUNDERSTORM ACTIVITY BY SATURDAY EVENING... BUT A SLIGHT CHANCE POP WILL BE RETAINED THROUGH THE END OF THE FORECAST PERIOD AS THE FRONT MAY STALL NEAR THE FORECAST AREA. AFTER WARMING INTO THE LOWER/MID 90S ON WEDNESDAY-FRIDAY...HIGHS WILL FALL BACK INTO THE UPPER 80S OVER THE WEEKEND...WITH LOWS DROPPING INTO THE MID 60S BY SATURDAY/SUNDAY. 70/DD && .AVIATION... FOR 12Z TAFS... MOIST SOUTHERLY FLOW JUST ABOVE THE SURFACE HAS LED TO THE DEVELOPMENT OF LOW CLOUD DECKS. CIGS ARE IN THE IFR AND MVFR RANGE DEPENDING ON THE LOCATION. AT THIS TIME, HAVE FORECASTED MVFR CONDS AT KHSV UNTIL 15Z. CIGS HAVE A LOWER CHC OF ARRIVING AT KMSL, SO HAVE GONE WITH A TEMPO GROUP THERE. ISOLATED TO SCATTERED TS ARE EXPECTED TO DEVELOP BY THIS AFTN. THE PROBS ARE TOO LOW TO INCLUDE AT EITHER TAF SITE ATTM. THE STRONGER STORMS WILL BE CAPABLE OF +RA, BRIEF GUSTY WINDS, AND FQT LIGHTNING STRIKES. AK && .HUN WATCHES/WARNINGS/ADVISORIES... AL...NONE. TN...NONE. && $$ FOR MORE INFORMATION PLEASE VISIT OUR WEBSITE AT WEATHER.GOV/HUNTSVILLE.