664
FXUS01 KWBC 162030
PMDSPD
SHORT RANGE FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
429 PM EDT WED SEP 16 2009
VALID 00Z THU SEP 17 2009 - 12Z FRI SEP 18 2009
A HIGHLY AMPLIFIED UPPER PATTERN WILL REMAIN WELL TO THE NORTH
ACROSS CANADA. MEANWHILE...A PAIR OF STAGNANT FEATURES ARE
EXPECTED TO KEEP PRECIPITATION IN THE FORECAST ACROSS PORTIONS OF
THE SOUTHERN HALF OF THE NATION. THE MOST NOTEWORTHY OF THE TWO IS
THE CUT-OFF LOW WHICH CONTINUES TO MEANDER ACROSS THE LOWER
MISSISSIPPI VALLEY. AS THE LOW CENTER SITS IN PLACE...A STEADY
PLUME OF GULF MOISTURE WILL RISE NORTHWARD INTO THE DEEP SOUTH
ALLOWING FOR A CONCENTRATED AXIS OF MODERATE TO HEAVY SHOWERS AND
THUNDERSTORMS ACROSS THE REGION. THE BEST CHANCE FOR HEAVIER
PRECIPITATION WILL REMAIN IN CLOSE PROXIMITY TO THE ARKLATEX WHERE
THE LOW PRESSURE CENTER RESIDES. DUE TO EARLIER RAINFALL ALONG
WITH A RISK FOR FURTHER ACCUMULATIONS THE NEXT 24 TO 48
HOURS...FLASH FLOOD WARNINGS AND FLOOD WATCHES HAVE BEEN PUT INTO
EFFECT ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY AND
STRETCHING INTO THE WESTERN TENNESSEE VALLEY.
ANOTHER FEATURE WHICH WILL BE QUASI-STATIONARY IN NATURE IS A WEAK
UPPER LOW WHICH IS POSITIONED ACROSS THE FOUR CORNERS REGION.
ALTHOUGH RAINFALL AMOUNTS WILL NOT BE AS IMPRESSIVE AS ITS
COUNTERPART OVER THE SOUTHERN U.S...LOCALLY HEAVIER PRECIPITATION
IS FORECAST ACROSS THE FAVORED TERRAIN OF THE SOUTHERN ROCKIES.
GIVEN LITTLE MOVEMENT IN THE STEERING FLOW OVER THE REGION...THE
SWATH OF PRECIPITATION WILL NOT SHOW MUCH CHANGE THROUGH THE END
OF THE WORK WEEK WITH RAINFALL EXPECTED ACROSS MUCH OF NEW MEXICO
AND EDGING NORTHWARD INTO COLORADO.
WITHIN THE AMPLIFIED NORTHERN STREAM OF THE JET...AN ACTIVE
PATTERN WILL BE FEATURED AS A SERIES OF PROGRESSIVE WEATHER
SYSTEMS PUSH EASTWARD. THE FIRST OF THESE FRONTAL SYSTEMS HAS
ALREADY MOVED ONSHORE DROPPING LIGHT TO MODERATE RAINFALL TO THE
PACIFIC NORTHWEST AND UP INTO WESTERN CANADA. AS IS TYPICAL WITH
PACIFIC SYSTEMS...THE HEAVIEST PRECIPITATION HAS BEEN CONFINED TO
THE WINDWARD SIDE OF THE TERRAIN WHERE UPSLOPE EFFECTS COME INTO
PLAY. CONDITIONS WILL BECOME QUIET FOR THE NEXT COUPLE OF DAYS
UNTIL THE NEXT UPPER TROUGH DROPS INTO THE NORTHWESTERN U.S. BY
LATE FRIDAY NIGHT AND INTO THE WEEKEND.
AS A STRONG UPPER RIDGE DEVELOPS ACROSS CENTRAL CANADA...AN AREA
OF TROUGHING IS ALSO FORECAST ACROSS EASTERN CANADA WITH ITS
EFFECTS SPREADING DOWN INTO THE NORTHEASTERN U.S. WHILE
PRECIPITATION WILL NOT BE MUCH OF AN ISSUE UNTIL FRIDAY
MORNING...COOLER TEMPERATURES WILL PREVAIL THE NEXT COUPLE OF DAYS
WITH HIGHS ONLY IN THE 60S. IN ADDITION...UNDERNEATH A LARGE AREA
OF SURFACE HIGH PRESSURE...TEMPERATURES TONIGHT WILL APPROACH THE
FREEZING MARK ACROSS THE INTERIOR NORTHEAST.
RUBIN-OSTER
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