AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE HUNTSVILLE AL
648 AM CDT FRI OCT 30 2009
.UPDATE...FOR 12Z AVIATION DISCUSSION
&&
.AVIATION...
LLWS WILL REMAIN A CONCERN FOR ANOTHER FEW HOURS BEFORE MIXING
INCREASES SURFACE GUSTS AND NOSE OF STRONGEST LLJ SHIFTS NORTH. CIGS
EAST OF FRONT ARE CURRENTLY AOB 2KFT...AND WHILE THESE WILL ADVECT
TOWARD MSL/HSV THIS MORNING...DAYTIME HEATING SHOULD LIFT THEM TO
AROUND 2.5KFT UNTIL LOWER CIGS/VIS ARRIVE JUST AHEAD OF
FRONT...ALONG WITH SCATTERED SHRA. WHILE SOME INSTABILITY IS
ASSOCIATED WITH FRONT...TS COVERAGE WILL REMAIN ISOLATED...SO HAVE
HANDLED THIS WITH A CB GROUP ATTM. SOUTH/SOUTHEAST WINDS WILL REMAIN
GUSTY THROUGH THE DAY...AND WINDSHIFT TO THE NW WILL ACCOMPANY THE
FROPA...ALONG WITH MVFR/IFR RAIN SHOWERS THROUGH MUCH OF THE NIGHT.
&&
.PREV DISCUSSION.../ISSUED 430 AM CDT FRI OCT 30 2009/
ALL THE FORECAST CONCERNS FOR THE NEXT SEVEN DAYS ARE IN THE FIRST
36 HOURS AS A POTENT AND PATTERN-CHANGING STORM SYSTEM SLOWLY SWINGS
THROUGH THE SOUTHEASTERN STATES. TEMPERATURES THIS MORNING ARE IN
THE UNSEASONABLY WARM MID TO UPPER 60S...EVEN NEAR 70 ALONG THE
AL/MS BORDER. THE MOST MOISTURE-RICH AIR IS STILL WEST OF THE BORDER
WITH 70-PLUS DEWPOINTS.
SHORT TERM (TODAY THROUGH SATURDAY NIGHT)...
PCPN SHIELD...VIRTUALLY ALL ALONG/BEHIND THE COLD FRONT...WILL
STEADILY SPREAD EASTWARD TODAY. CURRENT TIMING BRINGS THE FRONT TO
PICKWICK DAM BY 4PM...THROUGH THE SHOALS BY 7PM...TO HUNTSVILLE BY
10PM...AND INTO GEORGIA BY 2 OR 3AM. FORECAST THINKING IS THAT A
DECAYING LINE OF TSTMS WILL ACCOMPANY THE FRONT AS IT MOVES IN...
AND THEREFORE WE COULD SEE STRONG TO SEVERE STORMS LATE THIS
AFTERNOON INTO EARLY EVENING. HIGHER RISK IS TO THE WEST OF THE
TENNESSEE VALLEY HOWEVER. MAIN THREAT WILL BE DAMAGING WINDS...WITH
FCST SOUNDINGS SHOWING 50 MPH AT 3-4KFT.
THERE WILL ALSO ALMOST CERTAINLY BE A QUICK SHOT OF VERY HEAVY
RAIN...FOLLOWED BY LIGHT TO MODERATE STEADY RAIN FOR THE REST OF THE
NIGHT. THIS IS UNLIKELY TO BE ENOUGH TO CAUSE FLASH FLOODING EXCEPT
PERHAPS ON A BRIEF AND ISOLATED BASIS. WORTH NOTING THOUGH THAT
PARTS OF NORTHWEST ALABAMA DID GET OVER AN INCH OF RAIN YESTERDAY...
AND SO THE FLOOD THREAT SHOULD NOT BE DISCOUNTED IN THE WESTERN FOUR
NORTH ALABAMA COUNTIES. COMMUTERS IN THE SHOALS SHOULD BE ALERT THIS
AFTERNOON SINCE THE FRONT WILL BE COMING IN DURING THE AFTN RUSH.
BACKING UP TO TODAY...WINDS ARE ALREADY RATHER BREEZY AND WILL GET
MORESO AS THE PRESSURE GRADIENT INCREASES BETWEEN HIGH PRESSURE TO
THE EAST AND THE APPROACHING SYSTEM. WILL NOT ISSUE A WIND ADVISORY
WITH THIS FORECAST PACKAGE...BUT IT WILL BE VERY CLOSE TO ADVISORY
CRITERIA AND ONE MAY BE REQUIRED LATER TODAY. AM ALMOST SURE WE WILL
REACH CRITERIA ON SOME OF THE RIDGETOPS...BUT THAT IS TOO ISOLATED
TO ISSUE AN ADVISORY. DRIVERS OF HIGH-PROFILE VEHICLES SHOULD USE
CAUTION...ESPECIALLY DRIVING OVER/ATOP MOUNTAINS TODAY.
GIVEN THE WARM START...HIGHS LOOK LIKELY TO RISE WELL INTO THE 70S
IN MOST AREAS...PERHAPS OVER 80...ESPECIALLY WEST. TEMPERATURES WILL
PLUMMET WITH THE FROPA...INTO THE MID 50S. THE SHOALS WILL PROBABLY
ALREADY BE CLOSE TO FORECAST LOWS BY SUNSET...AND THEN HOLD STEADY
WITH THE RAIN OVERNIGHT.
THE 00Z NAM WAS A HORRIBLE OUTLIER...AND THE 06Z NAM HAS COME BACK
IN LINE WITH EVERYTHING ELSE IN PUSHING THE RAIN OUT DURING THE DAY
ON SATURDAY. DEPENDING ON HOW QUICKLY THIS OCCURS...SOME TEMP
REBOUND COULD OCCUR...LETTING THE WEST HALF REACH 60 DEGREES. BUT
FOR MOST OF US...TEMPS WILL HOLD IN THE 50S ALL DAY.
THE STRONG UPPER LOW PUSHES THROUGH SATURDAY NIGHT...BUT THE BULK OF
THE MOISTURE WILL BE GONE. PERHAPS THERE COULD BE SOME DRIZZLE BUT
EVEN THAT LOOKS DOUBTFUL. SLIGHTLY MORE LIKELY WOULD BE SOME LIGHT
OROGRAPHIC-INDUCED PRECIP IN THE EASTERN COUNTIES...SO WILL KEEP A
SLIGHT CHANCE DURING THE EVENING HOURS THERE. OTHERWISE...SKIES WILL
BE CLEARING AND LOWS WILL DROP INTO THE LOWER 40S.
EXTENDED (SUNDAY THROUGH NEXT FRIDAY)...
SOMEWHAT INCREDIBLY...THE ENTIRE EXTENDED FORECAST LOOKS DRY. HIGH
PRESSURE WILL BE THE DOMINATING INFLUENCE FOR ALL OF NEXT WEEK...
EXCEPT FOR ONE OR TWO REINFORCING SHOTS OF COOLER AIR. ANY SFC
FEATURES THAT MOVE THROUGH WILL COME THROUGH WITH LITTLE MORE THAN A
FEW CLOUDS...AND NO RAIN. THE REINFORCING COOL AIR MASSES WILL ALLOW
BOTH HIGHS AND LOWS TO STAY PRETTY CLOSE TO NORMAL FOR EARLY
NOVEMBER...WITH HIGHS IN THE 60S AND LOWS IN THE UPPER 30S AND 40S.
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