Area Forecast Discussion
Issued by NWS Paducah, KY

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000
FXUS63 KPAH 131922
AFDPAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PADUCAH KY
222 PM CDT MON APR 13 2015

.SHORT TERM...(THIS EVENING THROUGH WEDNESDAY NIGHT)
ISSUED AT 209 PM CDT MON APR 13 2015

WARM AIR ADVECTION SHOWERS OCCURRING ALONG/AHEAD OF FRONTAL
BOUNDARY NOW BISECTING PAH FA...WITH SOME POST FRONTAL RAIN AS
WELL. THERE HAVE BEEN A FEW STROKES OF THUNDER NEARBY BUT NOT
WITHIN FA RECENTLY. WILL CONTINUE TO MENTION IT BUT LIMITED
INSTABILITY MEANS IT WILL GET ONLY SLGT CHANCE MENTION AND ONLY
ALONG/AHEAD OF BOUNDARY. GFS DEVELOPS SURFACE WAVE AND LIFTS IT
ACROSS THE BOUNDARY/TN VALLEY TONIGHT. THIS WILL AMPLIFY THE PCPN
FIELD ACROSS MAINLY WKY TONIGHT...AS DRY AIR WORKS IN FROM THE
NORTH AND WEST WITH HIGH PRESSURE NUDGING INTO AND ACROSS THE
SOUTHERN GREAT LAKES. COULD SEE A HEALTHY 1-2" AVERAGE AREA OF
RAIN SPREAD ACROSS THE SOUTH AND EAST BY THE TIME IT DRAWS TO A
CLOSE TMRW MORNING. WINDS WILL PICK UP AS THE GRADIENT TIGHTENS
BETWEEN THE LOW TO THE SOUTHEAST AND THE HIGH TO THE
NORTH/WEST...WITH TEENS MPH AVERAGE NE WINDS GUSTING INTO THE 20S
MPH AT TIMES LATER TONIGHT-TMRW. THEY`LL START TO RELAX JUST A
LITTLE TMRW PM AS THE LOW MOVES OUT AND THE HIGH STRENGTHENS ITS
GRIP. THIS WILL ALLOW FOR A RELATIVE DRY PERIOD FROM MIDDAY
TUESDAY TIL WED...WHEN THE NEXT POP STARTS TO RAMP BACK UP LATER
WED INTO WED NIGHT...IN RESPONSE TO A DEVELOPING WET SWLY FLOW
ALOFT INDUCED BY SYNOPTIC SCALE TROFFING IN THE SOUTHERN PLAINS.

.LONG TERM...(THURSDAY THROUGH SUNDAY)
ISSUED AT 255 AM CDT MON APR 13 2015

THE EVOLUTION OF THE LATE WEEK WEATHER SYSTEMS HAS GONE FROM QUITE A
DYNAMIC, COLD CORE LOW SYSTEM IMPINGING ON THE WFO PAH FORECAST AREA
TO A MORE BENIGN WEATHER SYSTEM MOVING INTO NEXT WEEKEND. THAT IS
THE PERIL OF TRANSLATING CLOSED LOW SYSTEMS OVER THE EASTERN PACIFIC
AND MODIFYING THEM OVER A LAND MASS. TO THE CREDIT TO THE MEDIUM
RANGE GUIDANCE TRENDS, THESE SYSTEMS HAVE BEEN WEAKENED WITH TIME TO
A LESS DRAMATIC (AND SEVERE) VERSION.

WITH THAT SAID, THE BETTER INITIALIZING NUMERICAL MODEL GUIDANCE
WITH THE NORTHERN MEXICO/WESTERN TX LOW AND THE OFFSHORE LOW NEAR
THE PACIFIC NW/SOUTHWEST CANADA COASTLINE WERE BEST INITIALIZED BY
THE CANADIAN/NAM-WRF GUIDANCE, FOLLOWED BY THE DETERMINISTIC GFS.

THE CANADIAN AND GFS 00Z MONDAY DETERMINISTIC GUIDANCE WERE FAIRLY
SIMILAR IN THE LOCATION OF THE DEEP CLOSED LOW OVER THE FOUR CORNERS
REGION OF THE DESERT SOUTHWEST U.S. THROUGH 12Z (7 AM CDT)THURSDAY
TIME FRAME. BEYOND THAT TIME, THE GFS RECURVES THE UPPER LOW TOO FAR
NORTH, BRINGING HEIGHTS, THICKNESSES, AND INSTABILITY TOO FAR NORTH
AHEAD OF THIS LOW. IN ADDITION, THE DETERMINISTIC GFS PRECIPITATION
PARAMETERIZATION SCHEME WAS WAY TO AGGRESSIVE.

WITH THIS IN MIND, A BLEND, WEIGHTED TOWARD THE CANADIAN WAS USED
INTO NEXT WEEKEND, LEANING TOWARD A DRIER SOLUTION WITH TIME. THE
CANADIAN APPEARS TO KEEP THE NORTHERN STREAM A LITTLE MORE DOMINANT
THAN DEPICTED BY THE GFS, WHICH MAKES THE SOUTHERN STREAM (CLOSED
LOW) THE DOMINANT FEATURE WITH TIME. WITH THE ABSENCE OF CANADIAN
DATA NEXT WEEKEND, ATTEMPTED TO BLEND THE AVAILABLE GFS DATA TOWARD
THE CANADIAN WEATHER TRENDS. THE NORTHERN STREAM PHASES WITH AND
WEAKENS THE SOUTHERN STREAM CLOSED UPPER LOW INTO A SHARPER WAVE BY
THE END OF NEXT WEEKEND.

GIVEN THESE TRENDS, THE OVERALL POP/WEATHER FORECAST WITH THIS
PACKAGE IS LESS AGGRESSIVE THAN RECENT DAYS, WITH THE BEST CHANCES
OF RAIN MORE CLOSELY TIED TO THE SOUTHERN 1/3-1/4 OF THE WFO PAH
FORECAST AREA FOR THE MAJORITY OF THE FORECAST PERIOD.

THIS SHOULD ALLOW FOR SLIGHTLY WARMER MAX/MIN TEMPERATURES THAN
PREVIOUSLY FORECAST, BUT WITHIN TOLERANCE WITH PREVIOUS SOLUTIONS.

&&

.AVIATION...
ISSUED AT 209 PM CDT MON APR 13 2015

WIDESPREAD CIGS FROM LOW VFR TO MVFR WERE ASSOCIATED WITH A
FRONTAL BOUNDARY MAKING PASSAGE THIS PM AND RELATED RAIN
SHOWERS/ISOLD RISK OF THUNDERSTORMS. THESE DETERIORATED CONDITIONS
MAY INCLUDE TEMPORARY MVFR OR LOWER VSBYS RESTRICTIONS IN SHOWERS
THROUGH AT LEAST THE FIRST HALF OF TONIGHT/IF NOT MUCH OF THE
NIGHT. ULTIMATELY FROPA WILL ALLOW HIGH PRESSURE TO WORK IN FROM
THE NORTH AND WEST...MAINLY LATE TONIGHT-EARLY TMRW...EFFECTIVELY
ENDING POPS AND ALLOWING CIGS TO RECOVER BACK TO VFR RANGE FOR THE
REMAINDER OF THE PLANNING PERIOD. WINDS WILL STIFFEN AS THEY TURN
TO THE NE AFTER FROPA...WITH GUSTS INTO THE 20S KTS TONIGHT
POSSIBLE.

&&

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

&&

$$


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