FXUS64 KHUN 040935
AFDHUN
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HUNTSVILLE AL
335 AM CST FRI DEC 4 2009
.DISCUSSION...
LATEST WATER VAPOR IMAGERY AND RUC ANALYSIS SHOWS VERY HIGH
AMPLITUDE FLOW AT THE MID LEVELS WITH DUE SOUTH FLOW ACROSS THE
ROCKY MOUNTAINS AS A BROAD/DEEP TROUGH CONTINUES TO DIG ACROSS THE
CENTRAL CONUS AND INTO TEXAS. OVER THE NEXT 24 HOURS...THE SHORTWAVE
ABOUT TO ROUND THE BASE OF THE TROUGH WILL MERGE WITH A DEVELOPING
WAVE IN THE GOMEX...EVENTUALLY SENDING A SURFACE CYCLONE ACROSS THE
NORTHERN GOMEX...THROUGH FLORIDA...AND INTO THE OBX REGION BY
MID-WEEKEND. MEANWHILE AND CLOSER TO HOME...LATEST IR SATELLITE AND
METARS SHOW A STRATUS DECK STILL PREVAILS ACROSS THE TENNESSEE
VALLEY...WITH HIGH CLOUDS STREAMING INTO THE AREA FROM THE
SOUTHWEST. WITH A SURFACE HIGH SITTING OVER THE CENTRAL
PLAINS...NORTHWEST FLOW CONTINUES AT THE SURFACE...WITH DEWPOINTS IN
THE 20S /AND EVEN INTO THE TEENS/ JUST TO THE NORTHWEST OF THE CWFA.
MAIN STORY FOR THE SHORT TERM CONTINUES TO CENTER ON SNOW CHANCES
TONIGHT INTO SATURDAY MORNING ACROSS THE AREA AS THE UPPER TROUGH
KICKS IN AND MOISTURE ASSOCIATED WITH THE GOMEX CYCLONE
SKIRTS THE AREA. AT THIS TIME YESTERDAY...THERE WAS PRETTY GOOD
MODEL AGREEMENT BETWEEN THE 21Z/03Z SREF AND THE 00Z RUNS OF THE
NAM/GFS. UNFORTUNATELY...CANNOT SAY THE SAME THIS MORNING. A QUICK
LOOK AT THE GUIDANCE POP VALUES AT CHATTANOOGA ILLUSTRATES THIS
DISCREPANCY...WITH THE MAV SUGGESTING A 12HR POP OF 37...COMPARED TO
THE MOISTURE LADEN MET AT A WHOPPING 89.
THERMAL PROFILES AMONG THE NAM/GFS/SREF ARE SIMILAR TO EACH OTHER
AT MSL AND HSV...BUT CLEARLY THERE ARE SIGNIFICANT DIFFERENCES IN
HOW MUCH MOISTURE IS INGESTED INTO THE REGION. GIVEN THE VERY DRY
AIR JUST UPSTREAM OF HERE...ALONG WITH A RELATIVELY DRY FETCH AT THE
MIDLEVELS...HAVE A HARD TIME BELIEVING WE WILL SATURATE AS QUICKLY
/AND AS MUCH/ AS THE NAM...SO HAVE TRENDED THIS FORECAST TOWARD THE
GFS...WHICH IS SUPPORTED BY THE 21Z AND 03Z SREFS ALONG WITH HPC.
BUFR SOUNDINGS AT MSL SHOW A PALTRY AMOUNT OF MOISTURE IN NORTHWEST
ALABAMA...SO HAVE REDUCED PRECIPITATION CHANCES IN THAT
REGION...WITH ONLY FLURRIES MENTIONED ALONG THE NATCHEZ TRACE. CROSS
SECTIONS THROUGH THE CWFA ILLUSTRATE SUBSIDENCE /PER H7 OMEGA
FIELDS/ UNTIL ABOUT THE I-65 CORRIDOR...SO GENERALLY KEPT COUNTIES
WEST OF THE INTERSTATE IN THE SLIGHT CHANCE RANGE...WITH SNOW CHANCES
REACHING ABOUT 50/50 TOWARD THE ALABAMA/GEORGIA BORDER.
OF COURSE THERE ARE ALWAYS CAVEATS TO WINTER WEATHER FORECASTING IN
THE TENNESSEE VALLEY AND GIVEN THE BREADTH OF THE UPPER TROUGH IN
CONJUNCTION WITH UPSLOPE FLOW...LOCATIONS IN THE
OROGRAPHICALLY-FAVORED NORTHEAST SUCH AS SEWANEE...LOOKOUT
MOUNTAIN...AND SAND MOUNTAIN MAY WELL SEE OVER AN INCH OF SNOW
TONIGHT...PERHAPS TWO IF EVEN A LITTLE BIT OF THE NAM-ADVERTISED
MOISTURE PANS OUT. NOW THAT SAID...GIVEN THE 2-IN/4-IN SUBTERRANEAN
THERMAL PROFILES /IN THE UPPER 40S/...ANY SNOW THAT FALLS WILL
QUICKLY MELT AND SHOULD NOT CAUSE LINGERING HAZARDOUS DRIVING
CONDITIONS ON AREA ROADWAYS.
PREVIOUS SHIFT OPTED TO RAISE AWARENESS OF THE POSSIBLE WINTER
WEATHER CONDITIONS WITH A SPECIAL WEATHER STATEMENT AND WILL
CONTINUE TO UTILIZE THIS...ALONG WITH THE HAZARDOUS WEATHER OUTLOOK
TO ENHANCE FORECAST VISIBILITY DURING THIS RATHER UNCERTAIN EVENT.
NOW FOR THE REMAINDER OF THE FORECAST PACKAGE. EXPECT A GRADUAL WARM
UP IN TEMPERATURES SUNDAY AND INTO THE NEW WORK WEEK AS MID LEVEL
FLOW BECOMES MORE ZONAL. A SHORTWAVE MOVING NORTH OF THE CWFA WILL
LEND TO PRECIPITATION CHANCES EARLY IN THE WEEK...WITH A LARGER
CYCLONE BARRELING INTO THE TENNESSEE VALLEY ON TUESDAY NIGHT/EARLY
WEDNESDAY. WITH INCREASING CONFIDENCE IN THE MIDWEEK EVENT GIVEN
GOOD RUN/RUN CONTINUITY IN GLOBAL MODELS...INCREASED RAIN CHANCES ON
TUESDAY NIGHT INTO THE LIKELY CATEGORY...AND ALSO ADDED ISOLATED
THUNDER INTO THE FORECAST AS A 60KT+ H85 JET PUNCHES INTO THE
REGION. DRY POST FRONTAL CONDITIONS ARE EXPECTED TO ROUND OUT THE
WORK WEEK.
&&
.PRELIMINARY POINT TEMPS/POPS...
HUNTSVILLE 44 30 42 24 50 / 0 30 20 0 0
SHOALS 43 28 44 23 51 / 0 20 10 0 0
VINEMONT 44 29 40 25 49 / 0 30 20 0 0
FAYETTEVILLE 43 29 38 24 49 / 0 30 20 0 0
ALBERTVILLE 45 30 39 24 49 / 0 50 30 0 0
FORT PAYNE 47 33 40 23 51 / 0 50 40 0 0
&&
.HUN WATCHES/WARNINGS/ADVISORIES...
AL...NONE.
TN...NONE.
&&
$$
JLL
