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FXUS01 KWBC 190658
PMDSPD
SHORT RANGE FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
257 AM EDT SAT SEP 19 2009
VALID 12Z SAT SEP 19 2009 - 00Z MON SEP 21 2009
...WET AND UNSETTLED WEATHER TO IMPACT THE TENNESSEE AND OHIO
VALLEYS...
A DEEP LAYER CUT-OFF LOW PRESSURE SYSTEM OVER THE LOWER
MISSISSIPPI VALLEY IS EXPECTED TO GRADUALLY WEAKEN AND LIFT
NORTHWARD OVER THE WEEKEND WHICH WILL FINALLY ALLOW PORTIONS OF
THE GULF COAST STATES TO DRY OUT AFTER SEEING DAYS OF LOCALLY
HEAVY TO EXCESSIVE RAINFALL. HEAVY SHOWERS AND THUNDERSTORMS WILL
CONTINUE TO IMPACT PORTIONS OF THE TENNESSEE VALLEY...BUT BY THE
END OF THE WEEKEND THE HEAVIEST RAINFALL THREAT SHOULD BECOME
FOCUSED MORE ON THE OHIO VALLEY AND EVEN PARTS OF THE LOWER GREAT
LAKES REGION AS THE SYSTEM LIFTS NORTHWARD AHEAD OF A DEVELOPING
UPPER TROF OVER THE PLAINS. MUCH OF THIS MOISTURE SHOULD REMAIN
WEST OF THE APPALACHIANS THOUGH AS COOL HIGH PRESSURE IS EXPECTED
TO BUILD ACROSS THE NORTHEAST AND NOSE SOUTHWARD DOWN ACROSS THE
MID-ATLANTIC REGION. THIS SHOULD HELP KEEP MUCH OF THE EASTERN
SEABOARD DRY THROUGH THE PERIOD.
AN UPPER TROF AND AN ASSOCIATED COLD FRONT MEANWHILE WILL BE
PUSHING INLAND ACROSS THE PACIFIC NORTHWEST BY EARLY
SATURDAY...AND THEN INTO THE NORTHERN ROCKIES AND HIGH PLAINS BY
EARLY SUNDAY. INCREASED ONSHORE FLOW AND FORCING ASSOCIATED WITH
THE FRONTAL PASSAGE SHOULD FOSTER NUMEROUS SHOWERS FOR THE
TOPOGRAPHICALLY FAVORED CASCADES AND COASTAL RANGES OF WASHINGTON
AND OREGON...BUT THE PROGRESSIVE NATURE TO THIS SYSTEM SHOULD
ALLOW THE REGION TO DRY OUT BY SUNDAY. IN FACT...HIGH PRESSURE
SHOULD AGAIN HAVE FIRM CONTROL OF THE WEATHER ALONG THE WEST COAST
BY THE END OF THE WEEKEND ALONG WITH A WARMING TREND. TEMPERATURES
THOUGH WILL BE DROPPING ON THE OTHER HAND ACROSS THE NORTHERN
ROCKIES AND INTO THE HIGH PLAINS SUNDAY AND SUNDAY NIGHT AS THE
AFOREMENTIONED COLD FRONT CLEARS THE REGION. IN ADDITION TO
THIS...THE UPPER LEVEL TROF THAT IS INITIALLY DRIVING THE COLD
FRONT IS EXPECTED TO AMPLIFY RATHER SHARPLY OVER THE NORTHERN HIGH
PLAINS SUN NIGHT AND SO THIS WILL LIKELY DRIVE EVEN COLDER
TEMPERATURES SOUTHWARD AND IT CANNOT BE RULED OUT THAT SOME SNOW
COULD MIX IN WITH THE RAIN EXPECTED FOR THE HIGHER TERRAIN OF THE
ROCKIES. GIVEN THE STRONG DYNAMICS ASSOCIATED WITH THE UPPER
TROF...INCREASING COVERAGE AND INTENSITY OF SHOWERS AND
THUNDERSTORMS WILL BE EXPECTED IN TIME FOR THE REGION AND
ESPECIALLY INTO THE NORTHERN PLAINS SUNDAY NIGHT AND BY EARLY
MONDAY.
ORRISON
GRAPHICS AVAILABLE AT WWW.HPC.NCEP.NOAA.GOV
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