364
FXUS01 KWBC 152027
PMDSPD
SHORT RANGE FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
427 PM EDT TUE SEP 15 2009
VALID 00Z WED SEP 16 2009 - 12Z THU SEP 17 2009
A PAIR OF CUT-OFF UPPER LOW CENTERS WILL PROVIDE A FOCUS FOR A
MAJORITY OF THE RAINFALL THIS WEEK. IN PARTICULAR...THE MORE
POTENT OF THE TWO HAS BEEN STUCK IN PLACE FOR DAYS ACROSS THE
LOWER MISSISSIPPI VALLEY AS THE STRONGEST JET ENERGY REMAINS
CONFINED WELL TO THE NORTH ACROSS CANADA. CONSEQUENTLY...MANY OF
THE FEATURES ACROSS THE SOUTHERN HALF OF THE U.S. HAVE REMAINED
STAGNANT IN NATURE. AS THE LOW CENTER CONTINUES TO SPIN IN
PLACE...MOISTURE WILL RISE NORTHWARD FROM THE GULF OF MEXICO AND
HELP PROVIDE THE MEANS FOR PERSISTENT MODERATE TO HEAVY SHOWERS
AND THUNDERSTORMS ACROSS MUCH OF THE SOUTHERN STATES.
FURTHERMORE...EARLIER RAINS HAVE BROUGHT PORTIONS OF THE ARKLATEX
TO NEAR FLOODING CONDITIONS. AS MORE RAINFALL REMAINS IN THE
FORECAST...SUCH LOCATIONS CAN EXPECT FLOODING TO BE A DISTINCT
POSSIBILITY...ESPECIALLY ACROSS MUCH OF ARKANSAS. THROUGH THURSDAY
EVENING...THE UPPER LOW RESPONSIBLE FOR THIS EXCESSIVE RAINFALL IS
FORECAST TO MEANDER ACROSS THE REGION WITH LITTLE TO NO CHANGE IN
THE AXIS OF HEAVIER RAINS.
ANOTHER STALLED UPPER LOW POSITIONED ACROSS THE FOUR CORNERS
REGION WILL ALSO BE A FOCUS FOR WIDESPREAD PRECIPITATION THROUGH
THE MIDDLE OF THE WEEK. RAINFALL AMOUNTS WILL NOT BE AS NEARLY AS
HIGH AS THOSE ACROSS THE SOUTHERN U.S. GIVEN LESS FAVORABLE
MOISTURE PROFILES. HOWEVER...SCATTERED SHOWERS AND THUNDERSTORMS
WILL REMAIN IN THE FORECAST IN RESPONSE TO THIS LOW CENTER ALOFT
WITH TERRAIN EFFECTS BRINGING LOCALLY HEAVIER RAINFALL. LOCATIONS
IMPACTED WILL INCLUDE THE FOUR CORNERS REGION AND EXTENDING INTO
THE CENTRAL ROCKIES THROUGH THURSDAY.
LOOKING TO THE NORTH...A MUCH MORE PROGRESSIVE SET OF WEATHER
SYSTEMS WILL IMPACT THE NORTHERN HALF OF THE NATION THIS WEEK. THE
MOST NOTEWORTHY OF THESE SYSTEMS IS ONE THAT IS CURRENTLY
APPROACHING THE PACIFIC NORTHWEST. BEFORE THE FRONTAL BOUNDARY
SWINGS ONSHORE MIDDAY WEDNESDAY...A STEADY PLUME OF PACIFIC
MOISTURE WILL INTERACT WITH THIS SYSTEM HELPING PRODUCE WIDESPREAD
RAIN SHOWERS FROM THE PACIFIC NORTHWEST NORTHWARD INTO WESTERN
BRITISH COLUMBIA. THE HEAVIEST PRECIPITATION SHOULD BE CONFINED TO
THE COASTAL RANGES WHERE OROGRAPHIC EFFECTS WILL ENHANCE AMOUNTS.
BY THURSDAY MORNING...THIS FAST-MOVING BOUNDARY WILL REACH THE
UPPER INTERMOUNTAIN WEST AND BACK THROUGH THE CENTRAL GREAT BASIN.
ACROSS THE NORTHEAST...AN EXPANSIVE DOME OF HIGH PRESSURE AT THE
SURFACE WILL BRING COOL...AUTUMNAL CONDITIONS TO THE REGION. THE
EFFECTS WILL BE ESPECIALLY NOTICEABLE AT NIGHT ACROSS THE INTERIOR
NORTHEAST WITH NUMEROUS LOWS APPROACHING THE FREEZING MARK THE
NEXT COUPLE OF NIGHTS.
RUBIN-OSTER
GRAPHICS AVAILABLE AT WWW.HPC.NCEP.NOAA.GOV
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