438
FXUS01 KWBC 182006
PMDSPD
SHORT RANGE FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
405 PM EDT FRI SEP 18 2009
VALID 00Z SAT SEP 19 2009 - 12Z SUN SEP 20 2009
A PAIR OF CUT-OFF LOWS...ONE ACROSS THE FOUR CORNERS REGION WITH
THE OTHER ACROSS THE LOWER MISSISSIPPI VALLEY...WILL FINALLY
EVACUATE THESE LOCATIONS ALLOWING FOR SLOW IMPROVEMENT IN THE
WEATHER CONDITIONS. BOTH OF THESE AREAS OF LOW PRESSURE ALOFT WILL
GRADUALLY DISSIPATE AFTER BEING MAINSTAY FEATURES FOR NEARLY THE
WHOLE WEEK. WHILE MUCH OF THE PRECIPITATION WILL COME TO AN END
ACROSS THE FOUR CORNERS REGION...SCATTERED SHOWERS AND
THUNDERSTORMS WILL REMAIN IN THE FORECAST OVER MUCH OF THE
SOUTHEASTERN QUARTER OF THE U.S. THROUGH THE WEEKEND. A FRONTAL
BOUNDARY LINGERING ACROSS THE TENNESSEE RIVER VALLEY WILL ALLOW A
MILD AND MOIST AIR MASS TO STAY IN PLACE. ALTHOUGH THE
THUNDERSTORM ACTIVITY WILL GENERALLY BE SCATTERED IN
NATURE...PRECIPITATION WILL BE A POSSIBILITY AND MAY AFFECT AREAS
THAT WILL BE PRONE FOR FLOODING. IN PARTICULAR...THIS INCLUDES
NORTHERN MISSISSIPPI AND STRETCHING NORTHWARD INTO WESTERN
TENNESSEE. BY SATURDAY EVENING AND INTO SUNDAY...THE SWATH OF
PRECIPITATION SHOULD SLOWLY EXPAND NORTHWARD INTO THE UPPER GREAT
LAKES AND OHIO RIVER VALLEY AS A SERIES OF WEAK IMPULSES ALOFT
SWING THROUGH THE REGION.
WHILE MUCH OF THE STRONGEST JET ENERGY HAS BEEN CONFINED TO
CANADA...THE NEXT TROUGH APPROACHING THE PACIFIC NORTHWEST SHOULD
HELP BRING A SHOT OF COOLER AIR TO PORTIONS OF THE NORTHWESTERN
U.S. BY SUNDAY. MUCH OF THIS DISTURBANCE REMAINS WELL OFFSHORE
OVER THE GULF OF ALASKA...BUT WILL QUICKLY PUSH INLAND BRINGING
COOLER TEMPERATURES ACCOMPANIED BY A CHANCE OF RAINFALL. THE
ASSOCIATED FRONTAL BOUNDARY IS FORECAST TO PUSH ONSHORE EARLY
SATURDAY MORNING...WITH AN INCREASE IN THE ONSHORE FLOW HELPING
PRODUCE MODERATE TO HEAVY RAINFALL ALONG THE COASTAL RANGES OF
WASHINGTON AND BRITISH COLUMBIA. AS THE SYSTEM EDGES
EASTWARD...THE PRECIPITATION SHOULD BECOME MORE SCATTERED IN
NATURE EAST OF THE CASCADES AS IS TYPICAL WITH MANY PACIFIC
STORMS. SIGNIFICANT CHANGES WILL BE IN STORE ACROSS THIS REGION
WITH TEMPERATURES PLUMMETING OVER 20 TO 25 DEGREES BY SUNDAY
ACROSS THE NORTHERN ROCKIES. HIGHS BY THE END OF THE WEEKEND WILL
REMAIN IN THE 60S AFTER ONCE BEING IN THE 80S THIS WEEK.
A COOL DOME OF HIGH PRESSURE WILL SETTLE IN ACROSS NORTHEASTERN
U.S. ALLOWING FOR TRANQUIL CONDITIONS TO PERSIST FOR THE WEEKEND.
AFTER A BRIEF SHOT OF SHOWER ACTIVITY THIS EVENING OVER THE NEW
ENGLAND STATES...EXPECT PLEASANT WEATHER TO PREVAIL. AS THE SKIES
CLEAR AND WINDS CALM...FORECAST LOWS ON SATURDAY NIGHT WILL EASILY
PLUMMET DOWN TO THE MID TO UPPER 30S ACROSS THE INTERIOR NORTHEAST
WITH 40S CLOSER TO THE METROPOLITAN AREAS.
RUBIN-OSTER
GRAPHICS AVAILABLE AT WWW.HPC.NCEP.NOAA.GOV
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