FXUS63 KPAH 280509
AFDPAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PADUCAH KY
1109 PM CST FRI NOV 27 2009

.UPDATE...
UPDATED FOR 06Z AVIATION FORECAST DISCUSSION.

&&

.SHORT TERM... /TONIGHT THROUGH MONDAY/ 
MAIN CONCERN IN THIS TIME FRAME ARE FRONTAL PASSAGE AND POPS
SUNDAY INTO MONDAY.

THE 12Z MODELS HAVE COME INTO LINE WITH THE SYNOPTIC PATTERN. THEY 
ALL LEAVE A CUT OFF LOW OVER THE SOUTHWEST...LEAVING ONLY THE 
PROGRESSIVE NORTHERN STREAM PORTION OF THE TROUGH TO EFFECT OUR 
AREA. IT WILL BASICALLY LOOK LIKE A CLIPPER SYSTEM.

THE 12Z MODELS HAVE ALSO COME INTO DECENT AGREEMENT IN FRONTAL 
TIMING...BRINGING IT INTO THE AREA LATE SUNDAY AFTERNOON...AND 
PUSHING IT THROUGH THE AREA BY MIDNIGHT SUNDAY NIGHT. THE MAIN 
ISSUES NOW ARE HOW FAR NORTH AND WEST THE PRECIPITATION SHIELD WILL 
DEVELOP...AND HOW MUCH QPF THERE WILL BE.

WITH THE CLIPPER APPROACHING THE AREA FROM THE NORTHWEST...THE 
LOW-LEVEL FLOW WILL NOT INCREASE DRAMATICALLY...AND THEREFORE THE 
MOISTURE RETURN WILL BE QUITE WEAK. IN ADDITION...THE PRIMARY 
FORCING MECHANISM WILL BE FRONTOGENETICAL IN NATURE...SO LITTLE 
REASON TO EXPECT MEASURABLE PRECIPITATION AHEAD OF THE FRONT. 

WITH THE PROGRESSIVE SYSTEM...THE LIFT WILL BE RATHER SHORT-LIVED AT 
ANY ONE LOCATION. LACKLUSTER MOISTURE RETURN AND RATHER BRIEF 
LIFT...POINT TOWARD A LOW QPF EVENT...WITH THE BEST CHANCES FOR 
SIGNIFICANT PRECIPITATION IN THE SOUTHEAST PORTIONS OF THE AREA.

KEPT THE CATEGORICAL POPS OVER THE SOUTHEAST HALF OF THE AREA...WITH 
LIKELY POPS NORTHWEST...BUT WOULD NOT BE SURPRISED IF KMVN GETS A 
TRACE OR NOTHING OUT OF THIS SYSTEM. HPC QPF IS FAR TOO GREAT. I CUT 
IT IN HALF AND STILL HAVE A THIRD OF AN INCH OVER MUCH OF WEST 
KENTUCKY. MAY HAVE SOME LINGERING LIGHT RAIN IN THE FAR SOUTHEAST 
BEYOND 12Z MONDAY...SO KEPT A SLIGHT CHANCE DOWN THERE MONDAY 
MORNING.

IN THE MEANTIME...SOUTHERLY SURFACE WINDS HAVE ALREADY DEVELOPED AND 
THE WARM UP IS STILL EXPECTED FOR SATURDAY.

.LONG TERM... /MONDAY NIGHT THROUGH FRIDAY/
AFTER THE RAIN MOVES EAST OF THE AREA ON MONDAY...HIGH PRESSURE WILL 
TAKE HOLD MONDAY NIGHT AND TUESDAY. WITH MAINLY CLEAR SKIES... 
TEMPERATURES WILL WARM INTO THE UPPER 40S AND LOWER 50S DURING THE 
DAY...WITH LOWS IN THE UPPER 20S AND LOWER 30S AT NIGHT.

BY TUESDAY NIGHT AND WEDNESDAY...AN UPPER LEVEL LOW OVER THE 
SOUTHWEST WILL TRANSITION TO AN OPEN WAVE AS IT PROGRESSES EASTWARD 
INTO THE LOWER MISSISSIPPI VALLEY BY 12Z WEDNESDAY...THEN THE MID 
ATLANTIC STATES BY 12Z THURSDAY. WHILE THE BEST MOISTURE AND LIFT 
WITH THIS SYSTEM IS INDICATED TO OUR SOUTH... THE ECMWF AND GFS 
STILL KEEP THE IMMEDIATE FORECAST AREA ON THE NORTHERN FRINGE OF ANY 
PRECIPITATION CHANCES. AS A RESULT...WE MAINTAINED LOW CHANCE POPS 
OVER THE ENTIRE REGION WEDNESDAY AND WEDNESDAY NIGHT. ALSO ADDED 
SLIGHT RAIN CHANCES FOR THURSDAY GIVEN THE POTENTIAL SLOW DEPARTURE 
OF ANY WRAP-AROUND MOISTURE.

HEADING INTO WEEK/S END...SUBSTANTIAL DIFFERENCES DEVELOP AMONG THE 
GFS AND ECMWF REGARDING THE AMOUNT OF COOLING THAT WILL TAKE PLACE. 
BOTH THE 26/12Z AND 27/00Z ECMWF OPERATIONAL RUNS DEPICTED THE 
SOUTHWARD MIGRATION OF A DEEP CYCLONIC VORTEX INTO THE UPPER 
MIDWEST...WITH MID LEVEL FLOW STRAIGHT FROM CANADA. WHILE A COUPLE 
OF THE 00Z AND 12Z GFS ENSEMBLE MEMBERS HAVE ALSO HINTED AT THIS 
SCENARIO...THE GFS OVERALL IS KEEPING THE POLAR VORTEX AT BAY OVER 
EASTERN CANADA. THIS STILL RESULTS IN AN INFLUX OF COLD AIR...BUT 
NOT NEARLY TO THE DEGREE INDICATED BY THE 26/12Z AND 27/00Z ECMWF. 
THE LATEST 27/12Z OPERATIONAL ECMWF IS ALSO NOT AS AGGRESSIVE WITH 
THE SOUTHWARD DRIFT OF THE VORTEX. ALL THIS SAID...HPC/S RELIANCE ON 
THE ECMWF ENSEMBLE MEAN SEEMS A GOOD WAY TO GO FOR NOW...AND THIS IS 
REFLECTED IN OUR TEMPERATURE FORECAST DAYS 6 AND 7.

&&

.AVIATION...
THE TAFS BOIL DOWN TO A WIND FORECAST...AS SKIES WILL
BE CLEAR FOR THE MOST PART. HIGH PRESSURE HAS BEEN STEADILY
MOVING SOUTHEAST OF THE AREA AND IS NOW CENTERED OVER CENTRAL
KENTUCKY/MIDDLE TENNESSEE AND DOWN INTO THE GULF COAST STATES.
LIGHT AND VARIABLE WINDS LATE TONIGHT WILL BECOME SOUTHERLY BY
SATURDAY MORNING AT 10-11KTS. WINDS WILL STAY UP DURING THE
EVENING HOURS AS THE GRADIENT REMAINS TIGHT AHEAD OF A COLD FRONT
TO OUR WEST. OTHER THAN SOME HIGH CLOUDS MOVING INTO THE
AREA...THE WEATHER WILL BE QUIET FOR SATURDAY EVENING.

&&

.PAH WATCHES/WARNINGS/ADVISORIES...
KY...NONE.
MO...NONE.
IL...NONE.
IN...NONE.
&&

$$