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Area Forecast Discussion

000
FXUS64 KHUN 241440 AAB
AFDHUN

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE HUNTSVILLE AL
940 AM CDT FRI OCT 24 2008

.UPDATE...BANDS OF LIGHT TO MODERATE SHOWERS CONTINUE TO MOVE
NORTHWARD ACROSS THE TN VALLEY THIS MORNING WITH THE PASSING COLD
FRONT BECOMING MORE DIFFUSE. THE FRONT LOOKS LIKE ITS GOING TO
HAVE A TOUGH TIME HOLDING TOGETHER MUCH LONGER ALTHOUGH A
PERSISTENT SELY MOISTURE FEED UNDERNEATH THE UPPER LOW SHOULD KEEP
THE RAIN GOING THROUGH AT LEAST THE AFTERNOON HRS. A WEDGE OF DRY
AIR THROUGH UNDERCUTTING THE LOW OVER THE LOWER MS VALLEY SHOULD
MAKE ITS WAY INTO THE TN VALLEY THIS EVENING BRINGING THE SHOWER
ACTIVITY TO AN END. WHILE THERE IS A BIT OF UPPER FORCING PRESENT
WITH THE UPPER LOW...THE LACK OF ANY SFC BASED AND/OR ELEVATED
INSTABILITY SHOULD LIMIT THE THREAT FOR ANY TSTMS THIS AFTERNOON.
OTHERWISE...WILL LEAVE CURRENT FORECAST PACKAGE IN TACT FOR NOW.
ONLY OTHER FACTOR TO CONSIDER OVERNIGHT WILL EITHER BE SOME
LINGERING LOW CLOUDS OR THE DEVELOPMENT OF SOME RADIATIONAL FOG.
WILL EVALUATE THIS FORECAST DILEMMA CLOSER TO THE ISSUANCE OF THE
AFTERNOON PACKAGE.
&&

.AVIATION...LARGE S-N BAND OF MODERATE RA/SHRA HAS ENTERED NW AL
INCLUDING KMSL. ADDITIONAL SMALLER BANDS HAVE DEVELOPED FURTHER
EAST AFFECTING KHSV. THESE RAIN BANDS WILL REMAIN PERSISTENT
THROUGH 18-20Z. PREVAILING MVFR CIGS/VSBY ARE ANTICIPATED...WITH
TEMPORARY PDS OF IFR CIGS/VSBY DUE TO HEAVIER SHRA. LLWS WILL
REMAIN A PROBLEM EARLY THIS MORNING AT KHSV WITH LIGHTER SFC FLOW
BENEATH SELY LOW LEVEL JET. STRONGER FLOW OF UP TO 55KT REMAINS
ABV 2KFT HOWEVER. FOR TONIGHT...WILL REMAIN PESSIMISTIC ON ANY
CLEARING...WITH IFR CIGS AND PERHAPS BR/DZ POSSIBLE. IF THE SKY
DOES CLEAR...DENSE FG WILL BECOME MORE OF AN ISSUE.
&&

.PREV DISCUSSION...

SHORT TERM...TODAY THROUGH SUNDAY NIGHT...RAINFALL SHOULD
INCREASE THROUGHOUT THE MORNING HOURS AS STRONGEST ISENTROPIC LIFT
MOVES OVER REGION BY 15-18Z. QPF ESTIMATES STILL INDICATE THE
POSSIBILITY OF RECEIVING 1-1.5 IN BEFORE THE CUTOFF LOW OPENS AND
LIFTS NE. WIND SHEAR IS STILL QUITE IMPRESSIVE. HOWEVER...MINIMAL
INSTABILITY SHOULD KEEP ANY T-STORMS NON-SEVERE. ELEVATED
INSTABILITY IS PRESENT DURING THE 15-18Z TIMEFRAME WHICH WOULD
ALLOW FOR SOME ISOLATED T-STORM ACTIVITY. CONVECTIVE BANDING COULD
RESULT IN HEAVY DOWNPOURS AT TIMES. WITH THE CLOUD COVER AND
RAINFALL...EXPECTING DAYTIME TEMPS TO HOLD IN THE UPPER 50S TO LOW
60S.

MOST OF THE MODERATE TO HEAVY RAINFALL SHOULD DECREASE BY 03-06Z
TONIGHT. HAVE LEFT CHANCE TO SLIGHT CHANCE POPS IN GRIDS WITH
GRADUAL TAPERING FROM WEST TO EAST FOR TONIGHT AS WRAPAROUND
MOISTURE DRIFTS NE.

RESIDUAL CLOUD COVER SHOULD RECEDE RAPIDLY ON SATURDAY AS THE TROUGH
EXITS. A SHORTWAVE RIDGE SHOULD BUILD BRIEFLY OVER THE AREA. TEMPS
SHOULD BE SOMEWHAT WARMER DURING THE DAY WITH INCREASED INSOLATION.
WITH THE COOLER AIR MASS IN PLACE AND A PARTLY CLOUDY SKY...TEMPS
SHOULD PLUNGE INTO THE LOW TO MID 40S. WITH AMPLE SUNSHINE IN PLACE
ON SUNDAY...TEMPS SHOULD WARM INTO THE MID TO UPPER 60S. THE
SHORTWAVE RIDGE SHOULD THEN GIVE WAY TO ZONAL FLOW AS A FAST
MOVING/DEEPENING TROUGH DIVES SE TOWARDS THE SE US.

LONG TERM...MONDAY THROUGH THURSDAY NIGHT...THE MEDIUM RANGE MODELS
DO AGREE THAT A TROUGH SHOULD DIVE RAPIDLY TOWARDS THE SE.
HOWEVER...TIMING AND DEPTH ARE DIFFERENT WITH GFS/ECMWF. ECMWF IS
SLOWER AND DEEPER WITH THE TROUGH AND MORE CONSISTENT RUN TO RUN.
THUS...HAVE CHOSEN THIS SOLUTION OF THE TROUGH AND SFC COLD FRONT
ENTERING THE TN VALLEY BY MONDAY MORNING. THICKNESSES DROP RAPIDLY
WITH FROPA. FOR EXAMPLE...850-700 HPA THICKNESS DECREASE FROM 1575M
TO 1515M BY MONDAY AFTERNOON. WITH THE STRONG NW FLOW ALOFT AND NEAR
SFC...NOT EXPECTING MUCH IN THE WAY OF MOISTURE RETURN PRIOR TO
PASSAGE OF TROUGH/FRONT. THUS...PRECIPITATION SHOULD BE NEGLIGIBLE.

TEMPS ON MONDAY SHOULD HOLD STEADY IN THE 50S AND FALL DURING THE
DAY WITH STRONG CAA ENVELOPING THE REGION WITH THE POLAR AIR
MASS...IF CURRENT SOLUTION HOLDS. CLOUD COVER SHOULD RECEDE ON
MONDAY ALLOWING TEMPS TO PLUMMET INTO THE LOW TO MID 30S. WILL
CONTINUE TO MONITOR AIR MASS PROGRESSION FOR FREEZING TEMPS ON
TUESDAY MORNING. WITH TEMPS IN THE 30S ON TUESDAY
MORNING...AFTERNOON TEMPS SHOULD NOT RISE HIGHER THAN THE MID TO
UPPER 50S.

NW FLOW ALOFT ASSOCIATED WITH A BUILDING RIDGE OVER THE WESTERN
STATES...SHOULD DOMINATE THE WEATHER PATTERN FOR THE REST OF THE
LONG TERM. A WARMING TREND SHOULD THEN START ON WEDNESDAY WITH
DAYTIME HIGHS RISING INTO THE 60S.
&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...NONE.
TN...NONE.
&&

$$

UPDATE...09
AVIATION...KULA
PREV DIS...77