348
FXUS01 KWBC 240834
PMDSPD
SHORT RANGE FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
434 AM EDT SAT OCT 24 2009
VALID 12Z SAT OCT 24 2009 - 00Z MON OCT 26 2009
AT UPPER LEVELS...AN EXPANSIVE TROUGH WILL COVER MUCH OF THE
UNITED STATES...WHILE A PAIR OF CLOSED HIGHS WILL RESIDE OVER EACH
OCEANIC BASIN. IN THIS REGIME...SYSTEMS SWINGING THROUGH THE GULF
OF ALASKA WILL DESCEND SOUTHEASTWARD INTO WESTERN CANADA AND
EVENTUALLY INTO THE PACIFIC NORTHWEST AND UPPER INTERMOUNTAIN
WEST. THIS IS EXPECTED TO HOLD TRUE INTO MONDAY AS THE PATTERN IS
FORECAST TO HOLD STEADY BEFORE UNCERTAINTY LURKS INTO NEXT WEEK.
AN AMPLIFIED UPPER TROUGH CURRENTLY MOVING THROUGH THE UPPER GREAT
LAKES IS CARRYING A SHARP FRONTAL BOUNDARY THROUGH THE OHIO VALLEY
SPREADING COOLER AND DRIER AIR BEHIND IT WITH AN ACCOMPANIED
THREAT OF WIDESPREAD RAINFALL. AS THE SURFACE COLD FRONT MOVES
THROUGH THE MID-ATLANTIC REGION...AN AXIS OF HEAVIER SHOWERS AND
THUNDERSTORMS IS FORECAST TO DEVELOP JUST IN ADVANCE OF THIS
BOUNDARY. MOIST LOW-LEVELS ALONG WITH STRONG WIND SHEAR WILL
ENHANCE THE SEVERE WEATHER POTENTIAL ACROSS THE MID-ATLANTIC ON
SATURDAY BEFORE THE SYSTEM EVENTUALLY EDGES OFFSHORE BY LATE
SATURDAY NIGHT. BY SUNDAY...A SURFACE DOME OF HIGH PRESSURE WILL
SETTLE IN ACROSS THE EAST COAST WHICH WILL BRING GOOD WEATHER FOR
THOSE VIEWING FALL FOLIAGE. AN EXCEPTION TO THIS PLEASANT WEATHER
OVER THE EAST WILL BE SOUTH FLORIDA WHERE THE FRONTAL BOUNDARY IS
EXPECTED TO SLOW IN FORWARD SPEED AND KEEP CONDITIONS UNSETTLED
FOR SUNDAY.
SEVERAL DISTURBANCES DROPPING SOUTHEASTWARD INTO THE NORTHERN
ROCKIES AND EVENTUALLY INTO THE PLAINS IS SPREADING SCATTERED
PRECIPITATION TO THE REGION. WHILE NOT HEAVY IN INTENSITY...THE
COVERAGE WILL BE WIDESPREAD WITH SNOW SHOWERS EXPECTED ACROSS THE
HIGHER ELEVATIONS. SNOW LEVELS ARE NOT EXPECTED TO DROP
SIGNIFICANTLY AS THE COLDEST AIR SHOULD REMAIN NORTH OF THE
U.S./CANADIAN BORDER. THIS QUICK-MOVING WEATHER SYSTEM WILL
DESCEND SOUTHWARD AND REACH THE SOUTHERN PLAINS BY LATE SUNDAY
BRINGING SCATTERED SHOWERS AND THUNDERSTORMS TO THE REGION. IN THE
WAKE OF THIS DISTURBANCE...HIGH TEMPERATURES WILL DROP BACK INTO
THE 60S BY EARLY NEXT WEEK AS HIGH PRESSURE BEGINS TO DOMINATE.
BY THE LATTER HALF OF THE WEEKEND..THE PACIFIC NORTHWEST CAN
EXPECT CONDITIONS TO DETERIORATE BY SUNDAY EVENING AS THE NEXT
PACIFIC SYSTEM LURKS NEARBY. A 3O TO 40 MPH WESTERLY FLOW ALONG
THE COASTLINE WILL BRING AN ABUNDANCE OF MOISTURE INLAND WHICH
WILL BE USED TO PRODUCE MODERATE TO HEAVY PRECIPITATION ACROSS THE
REGION. AS USUAL...THE MOST CONCENTRATED AXIS OF RAIN AND SNOW
WILL BE ALONG THE WINDWARD-FACING TERRAIN AS OROGRAPHIC EFFECTS
COME TO PLAY. THIS HIGHLY PROGRESSIVE SYSTEM IS EXPECTED TO IMPACT
THE INTERMOUNTAIN WEST BY AS EARLY AS MONDAY MORNING.
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