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FXUS01 KWBC 210852
PMDSPD
SHORT RANGE FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
351 AM EST SAT NOV 21 2009
VALID 12Z SAT NOV 21 2009 - 00Z MON NOV 23 2009
THE UPPER PATTERN ACROSS THE PACIFIC NORTHWEST IS NOT EXPECTED TO
CHANGE SIGNIFICANTLY THIS WEEKEND AS YET ANOTHER IN A SERIES OF
TROUGHS WILL IMPACT THE WESTERN U.S. THIS FIRST OF THESE SYSTEMS
HAS ALREADY PUSHED ONSHORE WITH ITS ASSOCIATED FRONTAL BOUNDARY
REACHING THE CENTRAL GREAT BASIN AND BACK THROUGH THE GOLDEN
STATE. MUCH OF THE HEAVIEST RAIN AND SNOW HAS ALREADY FALLEN WITH
MAINLY SCATTERED PRECIPITATION EXPECTED ACROSS THE FAVORED TERRAIN
OVER THE NORTHERN ROCKIES AND CENTRAL INTERMOUNTAIN WEST ON
SATURDAY. BY SATURDAY EVENING...ANOTHER UPPER DISTURBANCE WILL
SLAM INTO THE PACIFIC NORTHWEST BRINGING ANOTHER ROUND OF
PRECIPITATION. THE COASTAL REGIONS WILL RECEIVE A BRUNT OF THE
MODERATE RAIN AND SNOWFALL AS A 30 TO 40 MPH ONSHORE FLOW WILL
BRING AN ABUNDANCE OF PACIFIC MOISTURE INLAND...WHICH WILL THEN
INTERACT WITH THE COASTAL TOPOGRAPHY. ONCE THE FRONTAL SYSTEM
SURGES EASTWARD INTO INTERMOUNTAIN WEST BY MIDDAY SUNDAY...THE
PACIFIC AIR MASS WILL LOSE MUCH OF ITS MOISTURE AS IT CROSSES INTO
THE LEE OF THE CASCADES AND INTO THE CLIMATOLOGICAL RAIN SHADOW
AREA. AT THIS POINT...SCATTERED SNOW SHOWERS WILL REMAIN ACROSS
PORTIONS OF THE NORTHWESTERN QUADRANT OF THE NATION WITH THE
BETTER CHANCES FOR HEAVIER AMOUNTS ACROSS THE TETONS AND WASATCH.
THE OTHER MAJOR WEATHER SYSTEM THIS WEEKEND IS A DISTURBANCE WHICH
IS CURRENTLY MOVING ACROSS THE WESTERN GULF COAST. AS THE SURFACE
LOW CENTER EDGES EASTWARD WHILE CLOSELY PARALLELING THE IMMEDIATE
GULF COAST...SHOWERS AND THUNDERSTORMS WILL BREAK OUT ACROSS THE
DEEP SOUTH. MUCH OF THE HEAVIER BATCHES OF STORMS ARE FORECAST TO
RESIDE NEAR THIS SURFACE LOW. THEREFORE...HIGHER AMOUNTS OF
RAINFALL ARE EXPECTED TO MAINLY BE CONFINED TO THE COASTLINE. THIS
SYSTEM WILL THEN TAKE A NORTHWARD TURN AS IT NEARS THE SOUTHEAST
COAST WHERE IT WILL EVENTUALLY SPREAD RAIN SHOWERS INTO THE LOWER
MID-ATLANTIC BY LATE SUNDAY.
ACROSS THE MID-SECTION OF THE NATION...A WEAK FRONTAL BOUNDARY
WILL TREK ACROSS THE PLAINS ON SATURDAY WITH PRECIPITATION BEING A
MINIMAL IMPACT WITH THIS SYSTEM. GIVEN MEAGER MOISTURE CONTENT
ACROSS THE NORTHERN TIER...ONLY WIDELY SCATTERED RAIN SHOWERS CAN
BE EXPECTED ACROSS THE UPPER MIDWEST AND BACK THROUGH THE MIDDLE
MISSISSIPPI VALLEY FOR SUNDAY.
LOOKING EASTWARD...A LARGE SURFACE HIGH PRESSURE AREA ACROSS THE
NORTHEASTERN U.S. WILL BRING A QUIET WEEKEND WEATHER-WISE FROM THE
UPPER GREAT LAKES EASTWARD THROUGH THE MID-ATLANTIC AND UP INTO
THE NEW ENGLAND STATES. AN EXCEPTION TO THIS RULE WILL BE FOR THE
INTERIOR NORTHEAST WHICH CAN EXPECT LINGERING RAIN SHOWERS TO
BEGIN THE DAY ON SATURDAY.
RUBIN-OSTER
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