108
FXUS01 KWBC 300835
PMDSPD
SHORT RANGE FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
434 AM EDT TUE SEP 30 2008
VALID 12Z TUE SEP 30 2008 - 00Z THU OCT 02 2008
THE OVERALL WEATHER PATTERN ACROSS THE UNITED STATES WILL BE
HIGHLY AMPLIFIED WITH A LARGE CLOSED LOW OVER THE GREAT LAKES AND
A RIDGE STRENGTHENING OVER THE INTERMOUNTAIN WEST. COOLER AIR HAS
ALREADY BEGUN TO SPILL IN ACROSS THE NORTHERN TIER STATES WHERE
OVERNIGHT TEMPERATURES HAVE APPROACHED THE FREEZING MARK ACROSS
THE NORTHERN PLAINS. AS THE COLD AIR MOVES TOWARD THE SOUTH AND
EAST...CHILLY WEATHER WILL BEGIN TO AFFECT THE UPPER MIDWEST WITH
HIGHS STRUGGLING TO GET OUT OF THE UPPER 40S TO LOWER 50S ON
TUESDAY. THIS FIRST SIGNIFICANT SHOT OF COLD AIR WILL SURGE AS FAR
SOUTH AS THE GULF COAST STATES WHERE THE SURFACE BOUNDARY WILL
CROSS THE REGION BY LATE IN THE DAY ON TUESDAY. A NOTICEABLE
CHANGE IN THE SENSIBLE WEATHER WILL TAKE PLACE ACROSS THE GULF
COAST WHERE MUCH DRIER AIR WILL FILL IN FROM THE NORTH WHICH WILL
SIGNIFICANTLY REDUCE THE RELATIVE HUMIDITY ALONG THE COASTLINE. IN
TERMS OF PRECIPITATION...MUCH OF THE FOCUS FOR RAINFALL WILL
RESIDE WELL TO THE NORTH...CLOSER TO THE CORE OF THE UPPER-LEVEL
CYCLONE. SHOWERS AND THUNDERSTORMS WILL FIRE IN CLOSE PROXIMITY TO
THE COLD FRONT ACROSS A MAJORITY OF THE NORTHEASTERN QUARTER OF
THE NATION. CONDITIONS SHOULD BE FAIRLY OVERCAST ACROSS MUCH OF
THE REGION AS SEVERAL UPPER-LEVEL DISTURBANCES WILL RIDE AROUND
THE CLOSED LOW OVER THE GREAT LAKES. THE CLOUDY SKIES COMBINED
WITH THE COOL...CANADIAN AIR MASS SETTLING IN PLACE SHOULD
RESTRICT DAYTIME TEMPERATURES TO THE 60S BY MIDWEEK.
THE SOUTHERN PORTION OF FLORIDA WILL START OFF SOGGY AS A SURFACE
BOUNDARY WILL LINGER OVER THE REGION ON TUESDAY. THE COMBINATION
OF CONVERGENCE CREATED BY THE STATIONARY BOUNDARY...AND A LARGE
PLUME OF MOISTURE STREAMING IN FROM EASTERN GULF OF MEXICO WILL
SET THE STAGES FOR MODERATE TO HEAVY SHOWERS AND THUNDERSTORMS.
CONDITIONS WILL SLOWLY IMPROVE BY THE FOLLOWING DAY AS THE FRONT
EVENTUALLY MOVES TOWARD THE BAHAMAS. SOME SCATTERED THUNDERSTORMS
MAY STILL LINGER ACROSS EXTREME SOUTHERN FLORIDA ON WEDNESDAY AS A
MOIST ONSHORE FLOW WILL COMBINE WITH WARMING SURFACE TEMPERATURES
TO SPAWN AREAS OF THUNDERSTORMS.
ACROSS THE WESTERN HALF OF THE NATION...A STRENGTHENING
UPPER-LEVEL RIDGE WILL DOMINATE THE WEATHER THROUGH THE MIDDLE OF
THE WEEK. STRONG SUBSIDENCE WILL WARM UP THE INTERMOUNTAIN WEST
INTO THE UPPER 70S TO LOWER 80S DURING THE NEXT COUPLE OF DAYS.
THIS MARKS AT LEAST A 15 DEGREE DEPARTURE FROM THE NORMAL HIGHS
EXPECTED IN LATE SEPTEMBER/EARLY OCTOBER. WHILE MUCH OF THE REGION
WILL STAY DRY THROUGH THE NEXT 60 HOURS...DAYTIME HEATING WILL
HELP SPAWN ISOLATED THUNDERSTORMS ACROSS THE FAVORED HIGH TERRAIN
OF WEST. MUCH OF THIS THUNDERSTORM ACTIVITY SHOULD DIE DOWN BY
NIGHTFALL AFTER THE LOSS OF SURFACE HEATING.
RUBIN-OSTER
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