Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 191111
AFDPAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PADUCAH KY
611 AM CDT TUE MAY 19 2015

.SHORT TERM...(TODAY THROUGH THURSDAY NIGHT)
ISSUED AT 327 AM CDT TUE MAY 19 2015

THE SHORT TERM STARTS OFF FRESH IN THE WAKE OF THE COLD FRONTAL
PASSAGE THROUGH THE WFO PAH FORECAST AREA. SHORTWAVE RIDGING
(SURFACE AND ALOFT) AND WEAK COLD/DRY AIR ADVECTION WILL DOMINATE
THROUGH AT LEAST NOON ON WEDNESDAY...BEFORE THE FLOW BECOMES
ZONAL IN ADVANCE OF A LOW AMPLITUDE SHORTWAVE IN THE UPPER
MIDWEST/GREAT LAKES REGION.

THE IMPRESSED BAROCLINIC ZONE GENERATES A SHARPER AGEOSTROPHIC
RESPONSE IN LOW LOW LEVEL FLOW OVER WESTERN SECTIONS OF THE LOWER
MISSISSIPPI VALLEY. THIS IN TURN, DEVELOPS AN INVERTED TROUGH (00Z
TUE GFS) OR SHARPENING SURFACE LOW (00Z TUE ECWMF) OVER AR/S MO BY
SUNSET WEDNESDAY.

UP TO THIS POINT, HAVE FAIRLY GOOD CONFIDENCE IN
THE FORECAST. HOWEVER, THERE ARE SUBTLE TIMING DIFFERENCES IN
RETURN SPEED OF THESE FEATURES AND THE ATTENDANT
MOISTURE/INSTABILITY ASSOCIATED WITH IT. USUALLY THE GFS IS MORE
AGGRESSIVE WITH MASS/INSTABILITY FIELDS, BUT WITH THIS SYSTEM, THE
RETURN OF THE PRECIPITATION IS DELAYED BY NEARLY 12 HOURS AS
COMPARED WITH THE ECMWF. WITH THIS IN MIND, TRENDED SLOWER AND
WEAKER WITH MOISTURE RETURN (MAINLY ISENTROPIC) FOR WEDNESDAY AND
WEDNESDAY NIGHT. THIS WILL PUT THE GREATEST CHANCES FOR
PRECIPITATION IN PLACE FOR LATE WEDNESDAY INTO THE EARLY OVERNIGHT
HOURS ON THURSDAY MORNING.

DRY CONDITIONS RETURN FOR THE REMAINDER OF THE PERIOD OF RIDGINGDEVELOPS
BACK IN THE PLAINS AHEAD OF A DEEPENING WEST COAST LOW.

UTILIZED AN ECMWF/GFS BLEND IN ADDITION TO THE BLENDED SHORT TERM
BACKGROUND GUIDANCE FOR THE MAIN SENSIBLE WEATHER ELEMENTS IN THIS
FORECAST PERIOD.

.LONG TERM...(FRIDAY THROUGH MONDAY)
ISSUED AT 327 AM CDT TUE MAY 19 2015

AVERAGE TO ABOVE AVERAGE FORECAST CONFIDENCE IN THE LONG TERM WITH
MODELS COMING INTO SOMEWHAT BETTER AGREEMENT.

AT THE BEGINNING OF THE LONG TERM PERIOD THE REGION WILL BE UNDER
ZONAL FLOW ALOFT WITH HIGH PRESSURE AT THE SURFACE CENTERED OVER THE
AREA. THIS SCENARIO SHOULD KEEP THE REGION DRY WITH BELOW NORMAL
TEMPERATURES FRIDAY AND FRIDAY NIGHT.

AS A STORM SYSTEM LIFTS NORTHEAST ACROSS THE CENTRAL PLAINS ON
SATURDAY...PRECIPITATION CHANCES MAY MAKE THEIR WAY INTO OUR FAR
WESTERN COUNTIES. MODELS ARE STILL SHOWING H5 RIDGING DEVELOPING
OVER THE AREA SO EASTWARD PROGRESS OF MOISTURE AND PRECIPITATION
EXPECTED TO BE SLOW.

SATURDAY NIGHT THE GFS KEEPS THE AXIS OF THE H5 RIDGE OVER THE AREA
WHILE THE ECMWF BEGINS TO FLATTEN THE RIDGE AND MOVE IT SLIGHTLY
EASTWARD. IF THE ECMWF PANS OUT...PRECIPITATION CHANCES MAY SHIFT
EASTWARD...JUST NOT SURE HOW FAR. IF THE GFS SOLUTION VERIFIES
PRECIPITATION CHANCES WILL BE SLIM AT BEST.

ON SUNDAY THE GFS FINALLY BEGINS TO SHIFT THE RIDGE AXIS EASTWARD SO
PRECIPITATION CHANCES SHOULD EXPAND ACROSS THE REGION. AS A SECOND
SYSTEM LIFTS NORTHEAST ACROSS THE PLAINS SUNDAY NIGHT INTO
MONDAY...WITH THE ABSENCE OF THE RIDGE...PRECIPITATION CHANCES
SHOULD INCREASE THROUGH THE PERIOD.

TEMPERATURES STARTING OFF THE PERIOD NEAR NORMAL SHOULD GRADUALLY
WARM TO ABOVE NORMAL READINGS BY THE END OF THE PERIOD.


&&

.AVIATION...
ISSUED AT 611 AM CDT TUE MAY 19 2015

VFR CONDITIONS TO DOMINATE ALL OF THE WFO PAH TAF SITES WITH THIS
FORECAST PACKAGE. MAIN DELINIATION FOR AVIATION FORECAST WAS FOR
THE INTRODUCTION OF CIRRUS AND MEAN WIND DIRECTION CHANGE WITH
TIME.

&&

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

$$

SHORT TERM...SMITH
LONG TERM...JP
AVIATION...SMITH



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