000 FXUS64 KHUN 041959 AFDHUN AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE HUNTSVILLE AL 259 PM CDT FRI JUL 4 2008 .DISCUSSION... MAIN FCST FOCUS FOR THE SHORT TERM REVOLVES AROUND THE OBVIOUS POTENTIAL FOR ONGOING CONVECTION TONIGHT...WHERE AND WHEN. HAVE WEIGHED FCST HEAVILY TOWARDS LATEST RADAR/SAT TRENDS...WHICH SUGGEST LARGE SCALE CONVECTIVE DEVELOPMENT CONTINUING FROM THE CENTRAL TN VALLEY WWRD TOWARDS THE MID-MISS VALLEY. CONSIDERING MOVEMENT OF ACTIVITY WILL GENERALLY BE E-SE PER CORFIDI VECTOR/MID-LVL STEERING ANALYSIS...MUCH OF THE ONGOING ACTIVITY TO OUR WEST SHOULD PRIMARILY AFFECT THE SOUTHERN HALF OF THE HUN CWFA. ANOTHER AREA OF CONVECTION WHICH IS ALREADY INITIATING IN THE LOWER OH VALLEY IS AHEAD OF AN UPR-LVL SHORT WAVE WHICH WILL MOVE QUICKLY EWRD AHEAD OF THE MAIN SHORT WAVE IMPULSE STILL FURTHER NW. RIGHT NOW...AM EXPECTING THE BULK OF THIS ACTIVITY TO PASS BY TO OUR NORTH...BUT COULDN'T RULE OUT THE SRN FLANK OF THIS SPREADING INTO OUR NERN AREAS LATER THIS EVENING. FOR NOW...HAVE PAINTED A NW TO SE GRADIENT W/RESPECT TO POPS WITH SLIGHTLY HIGHER VALUES IN THE SE PER THE REASONING ABOVE. THE RESULT IS LIKELY POPS FOR THE SERN HALF OF THE AREA...WITH CHANCE POPS NWRN HALF. OF COURSE...THIS TYPE OF CONVECTION ALONG WEAKLY DEFINED BOUNDARIES ALWAYS PRESENTS A LARGE DEGREE OF UNCERTAINTY...SO FURTHER UPDATES TO THE FCST MAY BE NECESSARY LATER THIS EVENING. ESSENTIALLY...I WOULD LIKE TO EXPRESS LOW TO MODERATE CONFIDENCE IN THE FCST FOR TONIGHT WHICH IS THE UNFORTUNATE CONSEQUENCE IN THESE CASES. CONSIDERING THE HOLIDAY AT HAND AND THE ABUNDANCE OF OUTDOOR ACTIVITIES TONIGHT...FEEL IT NECESSARY TO SPECIFY THE WX THREATS...WHICH AS STATED IN PREV FCSTS WILL STILL CONSIST OF STRONG WIND GUSTS AND FREQ LIGHTNING. ANOTHER SHORT WAVE NOTED ON WATER VAPOR IMAGERY IS GIVING RISE TO CONVECTION IN PORTIONS OF AR/OK THIS AFTN. AS THIS PIVOTS EWRD...THIS MAY PRESENT CONVECTIVE OPPORTUNITY ESPECIALLY FOR WRN/SRN PORTIONS OF THE AREA LATER TONIGHT...BUT FEEL THAT MOST OF THIS ACTIVITY MAY ACTUALLY SHIFT TO OUR SOUTH. NEVERTHELESS...SOME UNCERTAINTY REMAINS REGARDING EXACT TIMING/MOVEMENT OF THIS CONVECTION...SO IT WILL BE IMPORTANT TO PAY ATTENTION TO ANY FURTHER UPDATES LATER THIS EVENING. FOR SATURDAY...FEEL THAT THE MAIN FOCUS FOR CONVECTION WILL SHIFT TO OUR SOUTH AND NORTHEAST WITH SEPARATE LOW-LVL CONFLUENT BOUNDARIES NOTED IN STRMLINE PROGS. THIS IS LIKELY DUE TO THE EFFECTS OF THE STALLED FRONT TO OUR NORTH...AND CONVERGENCE TO THE SOUTH ALONG THE EDGE OF THE OUTFLOW BOUNDARY FROM OVERNIGHT CONVECTION. ANYWAY...THINK THAT CHANCES FOR CONVECTION WILL DECREASE A LITTLE TOMORROW NOW...AND HAVE LEFT CHANCE POPS IN FOR ALL AREAS AND TAILORED TO SHOW HIGHER VALUES IN THE EAST...WHERE BETTER THERMODYNAMICS WILL EXIST. FOR SUNDAY...MAIN UPR LEVEL SHORT WAVE WILL TRAVERSE THE REGION...WITH MUCH OF THE DIFFERENTIAL PVA ACTUALLY OCCURRING DURING THE MORNING HOURS TO EARLY AFTN...PER THE BEST TIMING AVAILABLE NOW. THIS MAY HELP ALLEVIATE ANY SIG THREAT FOR WIDESPREAD ACTIVITY WHICH WOULDN'T BE BAD IF WE DIDN'T NEED THE RAIN. NEVERTHELESS...HAVE KEPT IN CHANCE POPS BUT HAVE SKEWED TO SHOW HIGHER VALUES (40S) IN THE EAST...WITH NEAR 30S IN THE WEST. SO FOR NOW...WOULD EXPECT THE BULK OF ANY ACTIVITY THAT DEVELOPS ON SUNDAY TO BE IN THE EAST. MON THROUGH FRIDAY...EXPECTING ISOLD/SCTRD PRIMARILY AFTN/EVENING CONVECTION EACH DAY THROUGH THIS PERIOD. LONGER RANGE GUIDANCE IS SUGGESTING LOW AMPLITUDE TROUGHING IN THE EAST AROUND MID/LATE WEEK. TELECONNECTION PATTERNS ARE FAVORING A RIDGING PATTERN BEGINNING IN THE ERN CONUS BY LATE IN THE WEEK. SO...AM A LITTLE RELUCTANT TO FOLLOW ANY GUIDANCE NOW THAT WOULD SUGGEST OTHERWISE. GFS ENSEMBLES ARE RATHER SPLIT BUT SOME ARE CERTAINLY INDICATING A VERY QUICK BUT SUBTLE TROUGH PASSING THROUGH THE ERN CONUS ~WED-THU. THIS MAY REPRESENT THE LAST VESTIGES OF SHORT WAVE ENERGY PASSING AROUND THE LARGER SCALE TROUGH THAT HAS DOMINATED ERN NORTH AMERICA AS OF LATE...JUST BEFORE THE PATTERN MAKES A SHIFT TO WRN CONUS TROUGH/ERN CONUS RIDGE PATTERN. THUS...CHANCES FOR SHRA/TSRA MAY BE HIGHER ON WED/THUR AS COMPARED TO EARLIER IN THE WEEK. BUT...COUNTING ON A SLIGHTLY SLOWER EVOLUTION OF EVENTS WHICH IS USUALLY A SAFE BET THIS TIME OF YEAR MAY PUT ANY WEAKENING TROUGH THROUGH THE TN VALLEY LATE WEEK...WITH RIDGING BUILDING IN AND A RETURN TO TYPICAL HOT SUMMER WEATHER BEYOND THAT. && .AVIATION... CONVECTION DEVELOPING RAPIDLY ACROSS NWRN AL/NERN MS IS PRESENTING SOME CHALLENGES TO SAY THE LEAST FOR KHSV/KMSL TAFS. TAFS WILL DISPLAY BEST TIMING ATTAINABLE ATTM REGARDING TSRA ONSET AT BOTH LOCATIONS. HAVE ONLY LOWERED VIS TO MVFR AT BOTH LOCATIONS (3-4SM) BECAUSE CONVECTIVE HEAVY PRECIP WILL GENERALLY BE OF SHORT DURATION...WITH LONGER PERIOD MOD/LGT RAIN AND ASSOC BR BEING MORE REPRESENTATIVE. SO...ANY LOWER VIS EXPERIENCED BC OF HEAVY RAIN SHOULD BE LESS THAN ~15 MINS WITH ANY STORMS. HAVE KEPT VCTS IN AT KMSL THROUGH 00Z...THEN REMOVED BUT APPENDED CB TO LOW CLOUD LAYER AFTER THAT TO SUGGEST ONGOING THREAT. BUT NOT CONFIDENT ENOUGH TO PUT IN ACTUAL TIMING OF CONVECTION AT THIS POINT. FOR KHSV...HAVE LEFT IN VCTS UNTIL 0400...GIVEN BACKBUILDING TENDENCY ON RADAR/SAT SUGGESTS CONVECTION MAY LINGER IN NORTH CENTRAL/NERN AL LONGER. ALSO...HAVE INCLUDED MENTION OF LIGHT FOG FOR NOW WITH MVFR VIS AFTER 09Z AT EACH LOCATION BC OF PRECIP EXPECTED TODAY. HOWEVER...IF PRECIP AMOUNTS/DURATION BECOME STRONGER/LONGER LIVED THEN THESE MAY NEED TO BE LOWERED IN LATER TAFS. && .PRELIMINARY POINT TEMPS/POPS... HUNTSVILLE 68 87 69 88 / 60 50 30 40 SHOALS 68 87 68 88 / 50 40 30 30 CULLMAN 68 86 69 87 / 60 50 30 40 FAYETTEVILLE 67 86 68 86 / 50 50 30 40 ALBERTVILLE 68 86 69 88 / 60 50 30 40 FORT PAYNE 65 85 67 88 / 60 50 30 40 && .HUN WATCHES/WARNINGS/ADVISORIES... AL...NONE. TN...NONE. && $$ FCST AND AVIATION...KDW