205
FXUS01 KWBC 280817
PMDSPD
SHORT RANGE FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
417 AM EDT MON SEP 28 2009
VALID 12Z MON SEP 28 2009 - 00Z WED SEP 30 2009
A VERY DYNAMIC UPPER PATTERN HAS SET UP ACROSS THE NATION WITH A
PAIR OF STRONG SYSTEMS AFFECTING THE WESTERN U.S. AND NORTHEASTERN
STATES...RESPECTIVELY. WHILE THE MOST ACTIVE WEATHER WILL RESIDE
ACROSS THESE REGIONS...A DOME OF HIGH PRESSURE ACROSS THE CENTRAL
STATES WILL DOMINATE AND WILL SLOWLY EDGE EASTWARD TOWARD THE
MISSISSIPPI RIVER VALLEY BY TUESDAY EVENING. THIS HIGHLY AMPLIFIED
UPPER-LEVEL FLOW WILL BRING SOME STRONG FRONTAL PASSAGES ALLOWING
FOR COOL...DRY AIR TO FUNNEL IN THE WAKE.
ACCORDING TO THE LATEST SURFACE OBSERVATIONS...A FRONTAL BOUNDARY
WAS CURRENTLY PUSHING THROUGH THE OHIO RIVER VALLEY AND BACK
THROUGH THE ARKLATEX...AND AGAINST THE HIGH TERRAIN OVER THE
CENTRAL ROCKIES. THIS FRONTAL SYSTEM WILL CONTINUE TO BRING A
THREAT FOR GUSTY WINDS AS A TIGHT PRESSURE GRADIENT REMAINS IN
PLACE. IN ADDITION TO THE CHANGING TEMPERATURES AND
HUMIDITY...PRECIPITATION IS ALSO A THREAT...ESPECIALLY CLOSER TO
THE GREAT LAKES REGION. THIS DELINEATES THE AREA OF STRONGEST
UPPER-LEVEL FORCING IN RESPONSE TO THE STRONG LOW CENTER ALOFT
MOVING THROUGH. THIS PROGRESSIVE BOUNDARY WILL REACH THE WESTERN
ATLANTIC BY TUESDAY MORNING WITH ITS EFFECTS EVEN PUSHING INTO THE
NORTHERN GULF OF MEXICO AT THIS TIME. TUESDAY WILL MARK A CHILLY
DAY ACROSS MUCH OF EASTERN THIRD OF THE NATION WITH HIGHS ONLY IN
THE 50S AND 60S WITH SLIGHTLY WARMER CONDITIONS FARTHER SOUTH. THE
FLOW BEHIND THE COLD FRONT WILL BE FAVORABLE FOR LAKE EFFECT RAIN
SHOWERS ACROSS ALL OF THE MAJOR GREAT LAKES THROUGH MUCH OF
TUESDAY.
AS A STRONGER UPPER TROUGH PUSHES INTO THE PACIFIC NORTHWEST LATE
MONDAY...CONDITIONS WILL SLOWLY BEGIN TO DETERIORATE AS THE SYSTEM
MOVES ONSHORE. WHILE PRECIPITATION WILL GENERALLY REMAIN ON THE
LIGHTER SIDE...SCATTERED RAIN SHOWERS WILL BE IN THE FORECAST
ACROSS MUCH OF THE PACIFIC NORTHWEST WITH EVEN A MIXTURE OF RAIN
AND SNOW OVER SOME OF THE HIGHER PEAKS. HOWEVER...MUCH OF THE
COLDEST AIR ALOFT SHOULD REMAIN NORTH OF THE U.S./CANADIAN BORDER
ALLOWING FOR MUCH OF THE SNOWFALL TO REMAIN UP THERE. AS THE
SURFACE PRESSURES BEGIN TO FALL WITH THIS SYSTEM...WINDS WILL PICK
UP ACROSS THE GREAT BASIN ALLOWING FOR DRY AND WINDY CONDITIONS TO
PREVAIL. THIS WILL ASSIST IN AN INCREASED FIRE DANGER OVER THE
CENTRAL GREAT BASIN AND EVENTUALLY DOWN INTO THE DESERT SOUTHWEST
TOWARD THE MIDDLE TO END OF THE WEEK.
RUBIN-OSTER
GRAPHICS AVAILABLE AT WWW.HPC.NCEP.NOAA.GOV
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