FXUS64 KHUN 112149
AFDHUN
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HUNTSVILLE AL
349 PM CST FRI DEC 11 2009
.DISCUSSION...
ACTIVE WX PATTERN TO GET GOING AGAIN EARLY SAT FOR THE TN VALLEY.
THE PRIMARY FOCUS FOR THE SHORT TERM INVOLVES CHANCES FOR LGT WINTRY
PRECIP AT THE ONSET OF PRECIPITATION ON SAT MORNING...AND RAINFALL
AMOUNTS FROM SAT THROUGH SUN. MORE ON THAT BELOW. THE LONG TERM
PORTION OF THE FCST WILL MAINLY BE DEALING WITH ANOTHER FRONTAL
PASSAGE FOR MON NIGHT.
OTHERWISE...THE LATEST ANALYSIS SHOWS A DEVELOPING SFC LOW IN THE
WRN GULF OF MEX...EAST OF BROWNSVILLE...AND SFC HIGH PRESSURE
PUSHING EWRD INTO THE SRN APPS. VERY DRY AIR CONTINUED TO BE
FUNNELED INTO THE REGION AROUND THE SFC HIGH...WITH DEW POINT TEMPS
IN THE SINGLE DIGITS AND TEENS AROUND THE AREA. ALOFT...A CIRRUS
CANOPY WAS STREAMING NEWD ACROSS THE AREA...HELPING TO KEEP TEMPS
SUPPRESSED THIS AFTN...WITH VALUES MAINLY ARND THE UPR 30S.
SHORT TERM (TONIGHT THROUGH SUNDAY)...
DEFINITELY A CHALLENGING FCST FOR THE SHORT TERM...MAINLY INVOLVING
CHANCES FOR LGT WINTRY PRECIP ON SAT MORNING. SUCCESSIVE MODEL RUNS
HAVE GENERALLY BEEN COMING IN DRIER AND WARMER FOR THE SAT MORNING
PERIOD. HOWEVER...THE 12Z GFS DID BUCK THIS TREND...REVERTING BACK
TO A SLIGHTLY FASTER/WETTER SCENARIO. GIVEN THAT MODELS ARE
GENERALLY TOO SLOW WITH REGARDS TO OVERRUNNING PRECIPITATION
SITUATIONS...MY FCST HAS HEDGED TOWARDS A SLIGHTLY FASTER (ABOUT 3
HOURS) SOLN THAN MODEL AVERAGES SUGGEST. WITH ISENTROPIC PROGS/BUFR
SOUNDINGS SUGGESTING SUFFICIENT LIFT/SATURATION FOR LGT PRECIP
BEGINNING BY ABOUT 16-19Z...HAVE ELECTED TO PUSH THAT UP A FEW
HOURS. STILL...AT THIS POINT...LIFT IS NOT EXPECTED TO BE STRONG
AT THE ONSET...AND VERY DRY NEAR SFC AIR WILL CONTINUE TO BE
PUSHED INTO THE AREA AROUND THE SFC RIDGE.
SO...THE QUESTION IS...WHEN WILL PRECIP ALOFT MANAGE TO REACH THE
SFC. GIVEN THE TENDENCY FOR SLEET TO SURVIVE THESE SHORT TRIPS
THROUGH DRY LAYERS...THINK THAT IT MAY BE SLIGHTLY FAVORED AT THE
ONSET IN OUR SWRN AREAS...GENERALLY FROM MARSHALL THROUGH COLBERT
COUNTIES SOUTHWARD. WAA ALOFT WILL BECOME ROBUST OVERNIGHT...WITH
WET-BULB TEMPS GRADUALLY CLIMBING ABOVE ABOUT 2-3C BY THE TIME OF
PRECIP ONSET. THUS...SNOW DOESN'T LOOK LIKELY AT THIS POINT. AS FAR
AS SFC TEMPS ARE CONCERNED...ALTHOUGH SFC WINDS WILL GRADUALLY BE
INCREASING TO ABOUT 5-10 MPH BY DAYBREAK HELPING TO DEEPEN
MIXING...PRECIP FALLING INTO THE DRY NEAR SFC LYR WILL ACT TO KEEP
TEMPS SUPPRESSED...AND MAY EVEN HELP THEM TO CONTINUE TO DECREASE
TOWARDS DAYBREAK. EARLY MORNING LOWS SHOULD MANAGE TO FALL INTO THE
UPR 20S IN OUR NERN AREAS...TO THE LOW 30S IN THE SOUTHWEST.
ALTHOUGH INSOLATION WILL BE RELATIVELY WEAK TMRW...WITH THE AID OF
MOISTURE ADVECTION AND MIXING...TEMPS SHOULD GRADUALLY CLIMB TO
ABOVE FREEZING STARTING IN THE SW AND SPREADING NEWD DURING THE
MORNING. ANY BAND OF LGT PRECIP THAT MANAGES TO REACH THE SFC WILL
LIKEWISE MOVE NEWD...WITH THE POSSIBILITY FOR LGT SLEET OR FRZ RAIN
NORTH OF THE TN RIVER ARND 14-16Z AND IN OUR TN COUNTIES ARND
15-17Z. BY ABOUT 15-17Z HOWEVER...MOST AREAS SHOULD BE ABOVE
FREEZING...BUT ISOLD AREAS MAY REMAIN AT OR JUST BELOW FREEZING.
SO...THE FCST WILL CONTINUE TO INCLUDE MENTION OF FRZ RAIN IN OUR
NRN AREAS THROUGH 18Z...BUT THIS IS LIKELY TO BE EARLY IN THE
PERIOD...WITH A GRADUAL CHANGEOVER TO LGT RAIN.
OKAY...WITH ALL OF THIS BEING SAID...ITS IMPORTANT TO STRESS THAT
THIS IS STILL A LOW TO MDT CONFIDENCE SCENARIO. IT DOESN'T LOOK
LIKELY (EMPHASIS LIKELY) THAT PRECIP WILL REACH THE SFC UNTIL LATE
IN THE MORNING OR THE EARLY AFTN. BY THAT TIME...MOST IF NOT ALL
AREAS SHOULD BE ABOVE FREEZING. THUS...PRECIP CHANCES IN THE MORNING
ARE STILL RATHER SMALL. IN ADDITION...GROUND TEMPS AS MONITORED FROM
MANY SITES ARND THE AREA ARE ARND 40F. SO...NOT EXPECTING ANY
ACCUMULATIONS DUE TO ICE ON THE GROUND. BUT...COULDN'T RULE OUT A
BRIEF PROBLEM WITH ICY PATCHES DEVELOPING ON ELEVATED
ROADWAYS/SURFACES.
TEMPS WILL BE SLOW TO CLIMB ON SAT...WITH HIGHS ONLY TOPPING OUT IN
THE LOW/MID 40S...AND THAT MAY BE OPTIMISTIC. WITH RAIN CONTINUING
TO INCREASE AND SERLY WINDS AROUND 10-15 MPH...A RAW DAY IS EXPECTED
FOR ANY OUTDOOR EVENTS.
RAIN WILL CONTINUE INTO SAT NIGHT AS AN UPR WAVE CROSSES THE REGION.
THE WETTER NAM SOLN WAS DISCOUNTED SOMEWHAT AS THE UPR WAVE LOOKS
MORE LIKE A SPURIOUS FEATURE AT THIS POINT. NEVERTHELESS...AROUND AN
INCH OF PRECIP COULD FALL...ESPECIALLY IN SERN AL FROM SAT THROUGH
SUN MORNING. WILL LEAVE TEMPS ON THE COOL SIDE FOR SUN AS LOW CLOUDS
AND -RA/DZ MAY LINGER ACROSS THE AREA.
LONG TERM (SUNDAY NIGHT THROUGH THURSDAY)...
FCST FOCUS IN THE LONG TERM CENTERS ARND FRONTAL PASSAGE FOR LATE
MON NIGHT. RELATIVELY STRONG MODEL CONSENSUS CONTINUES FOR THE
TIMING OF THE FRONTAL PASSAGE...DUE ARND 06-12Z TUES MORNING.
ELEVATED INSTABILITY MAY BE PRESENT...SO WILL LEAVE IN MENTION OF
ISOLD -TSRA. OTHERWISE...THIS COULD BE A QUICK BURST OF HEAVY RAIN
AS PW VALUES CLIMB TO ABOUT 1.5 INCHES. BUFR SOUNDINGS INDICATE
PARCELS MAY BECOME BRIEFLY SFC BASED JUST ALONG THE FRONT. ALTHOUGH
SHEAR/INSTABILITY ARE STILL MARGINAL...WILL CONTINUE TO HAVE TO
WATCH THIS ONE.
FCST COORDINATION WAS CONDUCTED WITH BIRMINGHAM...PEACHTREE
CITY...THANKS!
&&
.PRELIMINARY POINT TEMPS/POPS...
HUNTSVILLE 28 41 41 53 46 / 10 90 100 50 10
SHOALS 29 43 42 54 47 / 10 90 100 40 10
VINEMONT 29 41 41 53 48 / 10 100 100 50 10
FAYETTEVILLE 27 44 40 51 45 / 10 90 100 50 10
ALBERTVILLE 29 43 40 51 46 / 10 90 100 50 10
FORT PAYNE 26 43 38 52 43 / 10 90 100 50 10
&&
.HUN WATCHES/WARNINGS/ADVISORIES...
AL...RED FLAG WARNING UNTIL 5 PM CST THIS AFTERNOON FOR THE FOLLOWING
ZONES: COLBERT...CULLMAN...DEKALB...FRANKLIN AL...JACKSON...
LAUDERDALE...LAWRENCE...LIMESTONE...MADISON...MARSHALL...
MORGAN.
TN...NONE.
&&
$$
KDW
