419
FXUS01 KWBC 202052
PMDSPD
SHORT RANGE FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
451 PM EDT SUN SEP 20 2009
VALID 00Z MON SEP 21 2009 - 12Z TUE SEP 22 2009
AS THE START OF AUTUMN NEARS...A SURGE OF COOL...CANADIAN AIR WILL
DROP SOUTHWARD AND BEGIN AFFECTING MUCH OF THE INTERMOUNTAIN WEST
AND INTO THE PLAINS BY THIS EVENING AND INTO MONDAY. A FRONTAL
BOUNDARY CURRENTLY SURGING SOUTH AND EAST THROUGH THE NORTHERN
HIGH PLAINS AND BACK ACROSS THE CENTRAL ROCKIES WILL BRING A MUCH
COOLER AIR MASS WITH IT. THE PRIMARY EFFECTS WITH THIS FRONTAL
SYSTEM WILL INITIALLY BE THE THE COLDER WEATHER...BUT LIGHT TO
MODERATE RAIN SHOWERS ARE ALSO POSSIBLE UPON FRONTAL PASSAGE. AS
THE SYSTEM BEGINS TO INTERCEPT A RICH PLUME OF GULF MOISTURE
ACROSS THE PLAINS...HEAVIER SHOWERS AND THUNDERSTORMS ARE EXPECTED
TO DEVELOP ALONG THE FRONT BY MONDAY AFTERNOON OVER THE CENTRAL
PLAINS AND EVENTUALLY SPREADING INTO THE ARKLATEX BY THE FOLLOWING
MORNING. IN THE WAKE OF THIS STRONG BOUNDARY...A COLD DOME OF
SURFACE HIGH PRESSURE WILL FILL IN ACROSS THE INTERMOUNTAIN WEST
BRINGING A CHILLY START TO NEXT WEEK. IN FACT...HIGHS ON MONDAY
WILL STRUGGLE TO PUSH ABOVE THE MID 50S ACROSS THE NORTHERN AND
CENTRAL ROCKIES WITH LOW TEMPERATURES THAT NIGHT APPROACHING THE
FREEZING MARK. ACCOMPANYING THE COLDER TEMPERATURES IS A CHANCE
FOR MEASURABLE SNOW ACROSS THE HIGHER PEAKS OF THE CENTRAL AND
NORTHERN ROCKIES.
A COMPLEX OF SHOWERS AND THUNDERSTORMS CURRENTLY EXTENDING FROM
THE UPPER GREAT LAKES AND OHIO RIVER VALLEY SOUTHWARD TO THE
CENTRAL GULF COAST WILL SHOW VERY GRADUAL MOVEMENT TO THE EAST
DURING THE NEXT 48 HOURS. ITS SLUGGISH MOTION IS PRIMARILY DUE TO
ITS POSITION SANDWICHED BETWEEN THE DEEPENING SYSTEM ACROSS THE
ROCKIES AND THE RIDGE OVER THE WESTERN ATLANTIC. THE PRECIPITATION
SHOULD REMAIN SCATTERED IN NATURE WITH POCKETS OF HEAVIER RAINFALL
AS THE COMPLEX EDGES SLOWLY TO THE EAST. BY LATE MONDAY
NIGHT...CONDITIONS WILL BEGIN TO DETERIORATE ACROSS THE
MID-ATLANTIC REGION AS THE AREA OF HIGH PRESSURE MOVES OFFSHORE.
AS THE SURFACE RIDGE BUILDS ACROSS THE INTERMOUNTAIN
WEST...CONDITIONS WILL BECOME RIPE FOR SANTA WINDS TO DEVELOP. IN
ANTICIPATION OF THE HOT...DRY...AND WINDY CONDITIONS...SOME
FORECAST OFFICES ALONG THE WEST COAST HAVE ISSUES RED FLAG
WARNINGS. HIGH TEMPERATURES THE NEXT COUPLE OF DAYS WILL REACH THE
90S AND 100S ACROSS THE INTERIOR VALLEYS WITH SLIGHTLY COOLER
WEATHER NEAR THE COASTLINE. IN ADDITION TO THE HEAT...THE FIRE
DANGER WILL BE ON THE INCREASE AS ADVERTISED BY THE LATEST STORM
PREDICTION CENTER FIRE WEATHER OUTLOOK.
RUBIN-OSTER
GRAPHICS AVAILABLE AT WWW.HPC.NCEP.NOAA.GOV
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