FXUS63 KPAH 050307 AAB
AFDPAH
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PADUCAH KY
907 PM CST THU DEC 4 2008
.UPDATE...
UPDATED PUBLIC DISCUSSION FOR TONIGHT.
&&
.DISCUSSION...
COMPETING EFFECTS MAKING FOR AN UNPLEASANT FORECAST UPDATE THIS
EVENING. FIRST PROBLEM IS CLOUD COVER. 18Z MODELS WERE QUITE
ROBUST WITH MID/UPPER LEVEL CLOUD COVER OVERSPREADING THE ENTIRE
AREA THROUGH THE NIGHT...AND SATELLITE TRENDS INITIALLY SUPPORTED
THIS AS MID CLOUD DEVELOPED RAPIDLY EASTWARD JUST INTO WESTERN
COUNTIES OF SOUTHEAST MISSOURI EARLIER THIS EVENING.
HOWEVER...MOST RECENT IMAGERY HAS SLOWED THE EASTWARD PROGRESSION
OF THE MID CLOUDS...AND 00Z NAM HAS SIGNIFICANTLY DECREASED
EASTWARD EXTENT OF CLOUD COVER OVERNIGHT. IN ADDITION...LOWER
CLOUDS OVER SOUTHWEST INDIANA ARE EXPECTED TO CONTINUE DIVING
SOUTHEAST.
DECIDED TO INCREASE CLOUD COVER OVER THE ENTIRE AREA...AND EXPECT
MOST OF THE AREA TO HAVE A CEILING AT 12Z. TO GO ALONG WITH THIS
CHANGE...INCREASED LOW TEMPERATURES JUST A BIT IN THE SOUTH AND
WEST. MAIN PROBLEM FOR TEMPERATURES IS THAT OBSERVED WINDS HAVE
BEEN LIGHTER THAN EXPECTED...AND RADIATIONAL COOLING COULD ALLOW
READINGS TO TANK BEFORE THE CLOUDS ARRIVE OR WINDS PICK BACK UP
AGAIN. USED THE 00Z NAM T/TD/WIND DATA AS A GUIDE TO TWEAK OUT
HOURLY TRENDS THROUGH THE NIGHT.
&&
.DISCUSSION... /ISSUED 530 PM CST THU DEC 4 2008/
SHORT TERM.../TONIGHT THROUGH SATURDAY NIGHT/
COLD AIR WILL BE THE MAIN THEME FOR THE REST OF THE WORK WEEK...AS A
LARGE HIGH PRESSURE SYSTEM FROM CANADA DROPS SOUTH INTO THE CENTER
PART OF THE COUNTRY. WILL LIKELY SEE TEMPS TONIGHT FALL DOWN TO
NEAR 20 IN MOST LOCATIONS...AND MAY EVEN GET INTO THE TEENS SOME
AREAS IF HIGH CLOUDS DO NOT INTERFERE TOO MUCH. ALSO...WILL LIKELY
SEE DAY TIME TEMPS STRUGGLE TO GET ABOVE FREEZING FRI ALONG THE I 64
CORRIDOR.
ON SATURDAY...A QUICK CLIPPER SYSTEM WILL MOVE THROUGH THE GREAT
LAKES REGION...AND DRAG YET ANOTHER COLD FRONT DOWN THROUGH THE
AREA. FOR NOW...WILL GO WITH A SMALL CHANCE FOR A LITTLE LIGHT RAIN
OR SNOW ACROSS SOUTHWEST INDIANA AND A SMALL PART OF SOUTHEAST
ILLINOIS DURING THE DAY ON SATURDAY. GIVEN THE VERY LOW QPF
SUGGESTED BY THE SHORT RANGE ENSEMBLES...AS WELL AS THE LATEST
DETERMINISTIC RUNS OF THE GFS/ECMWF...THIS STILL LOOKS MORE LIKE A
TRACE EVENT. WARM UP WILL BE MODEST AND BRIEF AHEAD OF THE FRONT.
WILL LIKELY SEE TEMPS BACK DOWN IN THE 20 TO 25 DEGREE RANGE SAT
LATER SAT NIGHT.
LONG TERM.../SUNDAY THROUGH NEXT FRIDAY NIGHT/
FOR SUNDAY THROUGH MONDAY...THE DETERMINISTIC GFS IS IN PHASE WITH
THE SLOWER ECMWF SOLUTION...THEREFORE...I HAVE CONTINUED A DRIER
SOLUTION. WITH THIS IN MIND...LEANED MORE HEAVILY TO LOWER DEWPOINTS
THAN ADVERTISED BY THE GFS...AS ELY COMPONENT STILL FOCUSES DRY AIR
AT LOW LEVELS INTO THE WFO PAH FORECAST AREA. FOR MAX/MIN
TEMPERATURES...KEPT SOME CONTINUITY WITH EARLIER RUNS...BUT LOWERED
SUNDAY MAX TEMPS BY 1-2 DEGREES AND RAISED MAXES ON MONDAY 1-2
DEGREES AS SOUTHERLY WINDS AND WARM AIR ADVECTION MOVES INTO THE
AREA.
FOR MONDAY NIGHT THROUGH TUESDAY NIGHT...THIS PERIOD WILL SEE THE
GREATEST PRECIPITATION TYPE TRANSITION...MAINLY DURING THE DAY ON
TUESDAY AND TUESDAY NIGHT. LOW LEVEL TEMPERATURES AND DEWPOINTS
DIFFERENCES SHOULD KEEP WET BULB TEMPERATURES HIGH ENOUGH TO SUPPORT
RAIN THROUGH MOST OF THE NIGHT ON MONDAY. ON TUESDAY
AFTERNOON...UTILIZED DETERMINISTIC INFLUENCE FROM GFS IN FOR TOP
DOWN PRECIPITATION ALGORITHM APPLICATION...SINCE IT WAS NOT MUCH
DIFFERENT THAN STRAIGHT TEMPERATURE CONVERSION OF PRECIPITATION TYPE
FOR THAT PERIOD. IT IS AT THIS TIME...THAT AN INITIAL RAIN/SNOW MIX
WILL WORK ACROSS SERN MO/SRN IL/SWRN IN...AS COLD AIR IS ADVECTED IN
AND WORKS DOWN ALONG THE NORTHERN LIMB OF THE SURFACE LOW PRESSURE
SYSTEM IN THE LOWER MS VALLEY. BOTH THE GFS/ECMWF ARE AMAZINGLY
SIMILAR ON THE POSITION OF THIS LOW ON TUESDAY. COLD AIR ADVECTION
INFILTRATES THE LOW LEVELS SUFFICIENTLY LATE TUESDAY EVENING TO
SUPPORT A COMPLETE CHANGE TO SNOW OVER THE SERN MO FOOTHILLS AND
SOUTHWEST IL...BUT MOISTURE WILL ALSO BE LACKING TO SUPPORT MORE
THAN JUST A SMALL CHANCE OR SLIGHT CHANCE OF SNOW IN THESE AREAS.
THERE IS A LITTLE MORE ROBUST CHANCE FOR SNOW OVER SWRN IN AND
WESTERN KY IN THE PRE-DAWN HOURS OF WEDNESDAY...BUT FOR NOW...SNOW
AMOUNTS IN THIS AREA MAY ONLY AMOUNT TO A TRACE TO LOCALLY ONE TENTH
OF AN INCH AT MOST.
FOR WEDNESDAY AND WEDNESDAY NIGHT...THE GREATEST
DETERMINISTIC/ENSEMBLE MODEL UNCERTAINTY SHOWS UP DURING THIS TIME
PERIOD. THERE IS SOME POTENTIAL THAT MEASURABLE SNOW MAY BE POSSIBLE
ON WEDNESDAY...ESPECIALLY OVER WRN KY. BOTH THE 00Z THURSDAY ECMWF
AND 06/12Z THURSDAY GFS DETERMINISTIC RUNS SUGGEST MOISTURE/THERMAL
PROFILES FAVORABLE FOR SNOW. HOWEVER...TIMING...EVEN WITH HPC
GUIDANCE SUGGESTS HIGH VARIABILITY DURING THIS FORECAST PERIOD. SO
FOR NOW...WILL KEEP ONGOING DRY FORECAST IN PLACE FOR WEDNESDAY.
GIVEN THE PERSISTENCE FORECAST FOR WEDNESDAY...THE WEDNESDAY NIGHT
PERIOD MUST BE CONDITIONAL DRY AS WELL.
FINALLY...FOR THURSDAY THROUGH FRIDAY NIGHT...DRY FORECAST REMAINS
IN PLACE. THERE STILL MAY STILL BE A LOW PROBABILITY...TRACE SNOW
EVENT WITH THE PROGRESSIVE NWLY FLOW...BUT UNCERTAINTY REMAINS TOO
HIGH TO WARRANT A MENTION OF ANY PRECIPITATION AT ALL. LEANED CLOSER
TO ECMWF MAX/MIN TEMPERATURES...BUT COMPROMISED WITH GFS ON
WIND/DEWPOINTS DURING THIS TIME PERIOD.
AVIATION...
LARGE AREA OF MID LEVEL CLOUDS OVER THE PLAINS WILL MAKE EASTWARD
PROGRESS. EXPECT SCATTERED TO BROKEN CLOUDS WITH BASES AT OR ABOVE
10K FEET TO ARRIVE LATE THIS EVENING AT KCGI/KPAH. THE CLOUDS WILL
THEN BE SUPPRESSED SOUTH OF OUR REGION FRIDAY AFTERNOON. FOR
KEVV/KOWB...AREAS OF LOW CLOUDS ENTERING THE WABASH VALLEY AS OF 23Z
WILL PASS MOSTLY NORTHEAST OF THE TAF SITES. FORECAST MENTIONS A FEW
CLOUDS THERE TONIGHT. LIGHT NORTH WINDS WILL BECOME VARIABLE FRIDAY
AFTERNOON AS HIGH PRESSURE MOVES OVERHEAD.
&&
.AVIATION...
LARGE AREA OF MID LEVEL CLOUDS OVER THE PLAINS WILL MAKE EASTWARD
PROGRESS. EXPECT SCATTERED TO BROKEN CLOUDS WITH BASES AT OR ABOVE
10K FEET TO ARRIVE LATE THIS EVENING AT KCGI/KPAH. THE CLOUDS WILL
THEN BE SUPPRESSED SOUTH OF OUR REGION FRIDAY AFTERNOON. FOR
KEVV/KOWB...AREAS OF LOW CLOUDS ENTERING THE WABASH VALLEY AS OF 23Z
WILL PASS MOSTLY NORTHEAST OF THE TAF SITES. FORECAST MENTIONS A FEW
CLOUDS THERE TONIGHT. LIGHT NORTH WINDS WILL BECOME VARIABLE FRIDAY
AFTERNOON AS HIGH PRESSURE MOVES OVERHEAD.
&&
.PAH WATCHES/WARNINGS/ADVISORIES...
KY...NONE.
MO...NONE.
IL...NONE.
IN...NONE.
&&
$$
SHORT TERM...DRS/GM
LONG TERM....SMITH
AVIATION.....MY
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