000 FXUS64 KHUN 221148 AAA AFDHUN AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE HUNTSVILLE AL 548 AM CST SUN NOV 22 2009 .UPDATE... FOR 12Z AVIATION. && .AVIATION... AN UPPER LOW WILL SWING ACROSS THE TN VALLEY TODAY AND CONTINUE TO BRING PATCHY -RA TO THE REGION. INITIALLY...EXPECTING VFR CONDITIONS THROUGH MOST OF THE MORNING HOURS. HOWEVER...UPSTREAM REGIONAL OBS AND MODEL DATA INDICATE MVFR CIGS LIKELY PUSHING IN BY 18Z...ALTHOUGH SPECIFIC TIMING DETAILS REMAIN UNCERTAIN. OTHERWISE...FORCING WILL REMAIN WEAK WITH -RA BECOMING PREDOM -DZ SHORTLY AFTER 23/00Z. EXPECTING DEVELOPMENT OF MVFR FOG AFTER 00Z AS WELL. && .DISCUSSION... /ISSUED 245 AM CST SUN NOV 22 2009/ DISCUSSION... THE LONG-AWAITED RAINFALL IS FINALLY MOVING INTO THE TENNESSEE VALLEY...AND WILL LEAD TO A RATHER WET SUNDAY OVER MUCH OF THE AREA. EARLY MORNING TEMPERATURES ARE IN THE 50S...AND IN MANY CASES... WARMER THAN THE EXPECTED DAYTIME HIGHS TODAY. THE INCOMING RAIN SHOULD HELP DROP TEMPS A FEW MORE DEGREES...BUT IF THAT DOES NOT HAPPEN...A FORECAST UPDATE WILL BE ISSUED AROUND 6 AM. SHORT TERM (TODAY THROUGH MONDAY)... ONE LOOK AT RADAR TELLS YOU THE STORY FOR TODAY...IT IS GOING TO RAIN...ESPECIALLY IN THE EASTERN COUNTIES THIS MORNING. THE MODELS ARE IN PRETTY GOOD AGREEMENT THAT A DEFORMATION ZONE OF PRECIP WILL DEVELOP ON THE NORTHWEST EDGE OF THE PRECIP SHIELD TODAY. IT HOPEFULLY GOES WITHOUT SAYING THAT THE MODELS ARE NOT GOOD ENOUGH TO PINPOINT WHERE THIS WILL DEVELOP...BUT THEY ALL ARE SHOWING SOMETHING OVER THE AREA TODAY. ASSUMING THIS DEFORMATION ZONE DOES DEVELOP...AREAS TO THE NORTH OF THAT WILL BE UNLIKELY TO SEE MUCH RAIN AT ALL. WITH THIS IN MIND...I AM CARRYING A SHARP POP GRADIENT FROM MID-CHANCE EXTREME NORTH AND WEST TO CATEGORICAL FROM HUNTSVILLE SOUTH AND EAST. TEMPERATURES ARE PROBABLY GOING TO FALL A BIT THIS MORNING AND HOLD STEADY THIS AFTERNOON AROUND 50. THE UPPER LOW WILL WEAKEN AND PULL AWAY THIS EVENING...TAKING MOST OF THE PRECIP WITH IT. HOWEVER...WEAK UPPER WAVES AND CONTINUED LOW-LEVEL MOISTURE ARE VERY LIKELY TO LEAD TO LOW CLOUDS...PATCHY FOG AND PATCHY DRIZZLE. COULD STILL SEE SOME MEASURABLE RAIN SHOWERS MAINLY FROM HUNTSVILLE EAST...BUT PRECIP WILL BE LIGHT. TEMPS WILL ONLY DROP A FEW DEGREES AT MOST. NOT SURE THOSE LOW-LEVEL CLOUDS ARE GOING ANYWHERE FOR MONDAY EITHER...ALONG WITH CONTINUED PATCHY FOG AND DRIZZLE...PERHAPS ALL DAY IN THE HIGHER ELEVATIONS. COULD STILL SEE PCPN HEAVY ENOUGH TO MEASURE IN THE HIGHER TERRAIN...SO WILL KEEP A SLIGHT CHANCE POP. I LOWERED HIGHS FOR MONDAY SIGNIFICANTLY FROM THE PREVIOUS FORECAST... AND GUT FEELING IS THAT I MAY NOT HAVE LOWERED THEM ENOUGH. EXTENDED (MONDAY NIGHT THROUGH NEXT SUNDAY)... WITH NOTHING TO SCOUR OUT THE MOISTURE...AREAS OF FOG ARE LIKELY MONDAY NIGHT...AND WITH LIGHT WINDS I WOULD NOT BE SURPRISED TO SEE WIDESPREAD DENSE FOG. FOR THOSE WHO LOOK AT MOS...I HAVE NO IDEA WHERE THE NAM MOS IS COMING UP WITH ITS LOWS FOR MONDAY NIGHT...OR THE 40 POPS IN CULLMAN. HAVE THROWN THAT OUT ENTIRELY...IT IS NOT EVEN SUPPORTED BY THE NAM ITSELF OR THE SREF ENSEMBLE SUITE. TUESDAY IS THE TRICKIEST DAY OF THE FORECAST. THE NAM SHOWS THE LOW CLOUDS STICKING AROUND...THE GFS BRINGS IN ENOUGH SOUTHERLY FLOW TO MIX THINGS OUT. HOWEVER...THE LIKELIHOOD OF HITTING THE GFS MOS HIGHS IN THE UPPER 60S IS...IN MY OPINION...LOW. I TOOK A 50/50 BLEND OF THE GFS MOS AND NAM MOS...TO TRY TO TREND TOWARD THE NAM SOLUTION. ALSO REMOVED THE PRECIP MENTION AS THE NEXT APPROACHING COLD FRONT HAS COME IN WITH SLOWER TIMING. THAT FRONT DOES PASS TUESDAY NIGHT BUT HAS ALMOST NO FORCING. COULD SQUEAK OUT A SHOWER...BUT IT IS NOT VERY LIKELY. THE AIRMASS BEHIND THIS FIRST FRONT IS NOT PARTICULARLY COLD BUT IT IS MUCH DRIER. A REINFORCING FRONT PASSES WEDNESDAY NIGHT...AND THAT ONE HAS THE COLD AIR. THERE MAY EVEN BE ANOTHER FRONT BEHIND THAT THURSDAY NIGHT. WITH THE DRIER AIRMASS IN PLACE...RAIN IS UNLIKELY BUT NOT ENTIRELY IMPOSSIBLE...ESPECIALLY IN SRN TN. WILL LEAVE DRY FOR NOW. HIGHS FRIDAY ARE UNLIKELY TO GO ABOVE 50...AND IT APPEARS FRIDAY NIGHT MAY BE OUR FIRST AREA-WIDE FREEZE. NEXT WEEKEND LOOKS DRY WITH TEMPS A COUPLE DEGREES BELOW NORMAL AS HIGH PRESSURE IS IN CONTROL. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...NONE. TN...NONE. && $$ AVIATION...KDW DISCUSSION...JE/23