FXUS64 KHUN 070956
AFDHUN
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HUNTSVILLE AL
355 AM CST MON DEC 7 2009
.DISCUSSION...
AN UNSETTLED WEATHER PERIOD AWAITS THE TENNESSEE VALLEY THIS WEEK.
ANALYSIS OF 00Z UPPER AIR DATA REVEALED LARGE SCALE TROUGHING
EXTENDING FROM NE CANADA TO OREGON...WITH AN OTHERWISE ZONAL FLOW
OVER THE REMAINDER OF THE LOWER-48. AN APPROACHING MID LEVEL SYSTEM
IN THIS FLOW HAS BROUGHT SOME LIGHT RAINS ACROSS PARTS OF NW AL AND
MIDDLE TENNESSEE SO FAR THIS MORNING. A RATHER DRY LOWER LEVEL AND
COOLING OF THE PRECIP AS IT FALLS MAY PRODUCE A FEW ICE PELLETS...
ESPECIALLY OVER TENNESSEE AND OUR HIGHER ELEVATED ALABAMA TERRAIN.
NO PROBLEMS ARE ANTICIPATED AT THIS TIME. MORE LIGHT RAIN WAS NOTED
VIA REGIONAL RADAR APPROACHING FROM MISSISSIPPI.
GIVEN THE DRY AIR OVER THE REGION AND THE LIGHT/SPARSE CHARACTER OF
THE RAIN HAS LEAD TO A REDUCTION OF RAIN CHANCES FOR LOCATIONS EAST
OF NW ALABAMA. THE RAIN SHOULD WIND DOWN DURING THE AFTERNOON AS
THIS SYSTEM EXITS STAGE RIGHT. THE FIRST HALF OF TONIGHT FOR THE
VALLEY SHOULD BE DRY.
IN THE MEANWHILE...A SIGNIFICANT SYSTEM WILL SPIN UP OVER SOUTH
CENTRAL CALIFORNIA AND THE GREAT BASIN TODAY. AS ITS UPPER
REFLECTION HEADS EAST...IT WILL GENERATE A SURFACE LOW EAST OF THE
COLORADO ROCKIES TONIGHT (AFTER CREATING SIGNIFICANT SNOWS OUT
THERE). THIS DEVELOPING LOW WILL HELP DRAW PLENTY OF GULF MOISTURE
INLAND...AND SET THE STAGE FOR A WET...STORMY TUESDAY.
BOTH THE NAM/GFS INCREASE 850MB WINDS INTO THE 50-70KT RANGE BY
TUESDAY EVENING...WITH CORRESPONDING 0-3KM HELICITIES GOING OFF THE
CHART... EXCEEDING 1000M/S PER THE NAM AND 500M/S THE GFS. STABILITY
AND THERMODYNAMIC NUMBERS HOWEVER DO NOT REALLY BECOME UNSTABLE...AS
LOWER LEVEL INSTABILITY DOES NOT GET WELL ESTABLISHED. WITH THAT IN
MIND...HAVE INTRODUCED ISOLATED THUNDER TUESDAY AFTERNOON...AND A
CHANCE OF THUNDER WITH THE MAXIMUM SHEAR TUESDAY NIGHT. THE VERY
HIGH SHEAR COULD LEAD TO STRONG...POSSIBLY DAMAGING WINDS. BREEZY TO
WINDY CONDITIONS ARE OTHERWISE IN THE FORECAST...ESPECIALLY FOR
TUESDAY EVENING. TEMPERATURE CHANGES WITH THE SYSTEM PASSING MAY
LEAD TO GRAVITY WAVE OR WAKE LOW TYPE WINDS. A MORE CERTAIN ITEM
WITH THIS SYSTEM WILL BE RAINS. SOME LOCALLY HEAVY RAINFALL MAY
PRODUCE PONDING OF WATER. WITH MOST OF THE DECIDUOUS VEGETATION
BEING DORMANT...CANNOT RULE OUT STREAM/RIVER LEVEL RISES ESPECIALLY
AFTER THE EVENT.
DRY WEATHER SHOULD RETURN FOR THE MIDDLE OF THE WEEK AS COLD HIGH
PRESSURE BUILDS INTO THE REGION. THE GFS MAY BE TOO COLD FOR THE
LATER HALF OF THE WEEK COMPARED TO THE WARMER ECMWF. HAVE TRENDED
SOMEWHAT COLDER BUT NOT TO THE GFS.
ANOTHER CHANCE OF RAIN RETURNS FOR FRIDAY AS ANOTHER SYSTEM NEARS
THE REGION. THE GFS WAS FASTER AND WETTER WITH THIS THAN THE ECMWF
WHICH WAS ABOUT A DAY DELAYED. HAVE NOTED RAIN FOR FRIDAY AND
SATURDAY...WITH RAIN OR SNOW FOR FRIDAY NIGHT...GIVEN LOW TEMPS WILL
FLIRT WITH THE FREEZING POINT. THE UPCOMING WEEKEND AT THIS TIME
LOOKS DRY BUT COLD.
&&
.AVIATION... /06Z ISSUANCE/
HIGH CLOUDS ARE MOVING OUT...AND MID CLOUDS ARE MOVING IN. CIGS WILL
CONTINUE TO LOWER...AND BE BORDERLINE MVFR BY DAYBREAK AT KMSL...AND
BY NOON AT KHSV...AS -RA MOVES IN. HAVE REMOVED THE MVFR VISBYS
THOUGH AS PCPN IS EXPECTED TO BE LIGHT. ONE FORECAST MODEL IS
SHOWING QUITE LOW CIGS AT KMSL AFTER THE RAIN MOVES OUT. CANNOT RULE
THIS OUT...SO WILL KEEP MVFR CIGS THERE FOR THE LAST 9 HOURS OF THE
FCST.
&&
.PRELIMINARY POINT TEMPS/POPS...
HUNTSVILLE 47 42 58 52 58 / 40 20 100 100 20
SHOALS 47 42 59 50 56 / 60 40 100 100 20
VINEMONT 48 42 57 53 59 / 40 20 100 100 20
FAYETTEVILLE 45 40 56 50 56 / 40 20 100 100 20
ALBERTVILLE 47 42 56 53 56 / 40 20 100 100 30
FORT PAYNE 49 40 55 51 57 / 40 20 100 100 30
&&
.HUN WATCHES/WARNINGS/ADVISORIES...
AL...NONE.
TN...NONE.
&&
$$
DISCUSSION...RSB
AVIATION...JE/23
