369
FXUS02 KWBC 281904
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
303 PM EDT WED MAY 28 2008
VALID 12Z SAT MAY 31 2008 - 12Z WED JUN 04 2008
..FINAL MEDIUM RANGE DISCUSSION
..LARGE SCALE CONSIDERATIONS
A SPLIT FLOW...RIDGE-ATOP-A-TROF PATTERN OVER THE ERN PACIFIC
SHOULD GRADUALLY MOVE INTO WRN NORTH AMERICA WHILE A MODEST MEAN
TROF PERSISTS CLOSE TO THE EAST COAST. BETWEEN THESE TWO FEATURES
WE FIND A RIDGE ANCHORED VICINITY OF THE PLAINS. THERE IS
UNCERTAINTY OVER HOW BIG A CHUNK OF ENERGY WILL COME ASHORE OUT OF
THE UPPER TROF OFF THE CA COAST INTO THE WEST EARLY NEXT WEEK.
EVEN BEFORE THAT MAIN CHUNK OF ENERGY COMES IN...THERE WILL BE
SMALLER SCALE IMPULSES SHEARING OUT OF THE MAIN TROF OFF THE CA
COAST INTO THE NWRN STATES SAT-MON.
THE UPDATED FINAL SURFACE GRAPHICS WERE UNCHANGED FROM THE UPDATED
PRELIMS OVER THE CONUS.
THE 12Z/28 GFS BEGINS TO DEVIATE FROM PREFERRED CONTINUITY BY DAY
5...APPEARING TO BRING TOO MUCH ENERGY OUT OF A TROF OFF THE W
COAST INTO THE NRN PORTIONS OF THE ROCKIES/PLAINS BY TUE DAY
6...INTO THE CREST OF A MEAN LONGWAVE RIDGE POSITION. THE LATEST
GFS IS JUST A LITTLE FASTER WITH THIS SHORTWAVE THAN THE REJECTED
00Z/28 ECMWF WAS IN OUR EARLIER PRELIMS. WHILE THE 12Z/28
CANADIAN/UKMET MODELS SEEM TO OFFER A MORE REASONABLE SOLUTION TO
THE CA TROF DAYS 5-6 AS IT SLIDES INTO THE SWRN STATES....THE NW
CONUS WILL BE AN AREA OF UNCERTAINTY DAYS 5-6...AS THE NEW 12Z/28
ECMWF IS FOLLOWING MORE OF THE IDEA OF THE NEW 12Z/28 GFS AND ITS
OLD 00Z/28 RUN. HPC IS FOLLOWING A CONSENSUS APPROACH OVER THE
ENTIRE CONUS THAT MAINTAINS THE BEST CONSISTENCY AND LEANS AWAY
FROM MORE EXTREME IDEAS OF GUIDANCE.
...REGIONAL HIGHLIGHTS
..PLAINS/EAST
TYPICAL FOR THIS OF YEAR...FRONTAL CONVECTIVE ACTIVITY AND
ASSOCIATED MESOSCALE ACTIVITY WILL BE LARGELY DEFINED BY THE SRN
EDGE OF THE POLAR WESTERLIES. ONE BOUNDARY AND ITS ACTIVITY WILL
SINK S INTO THE SRN STATES SUN-MON. ACTIVITY SHOULD WEAKEN ON THIS
OLD DECAYING BOUNDARY THE FIRST HALF OF NEXT WEEK AND BE REPLACED
BY REDEVELOPMENT ON A NEW BOUNDARY FORMING FARTHER N. HIT AND MISS
TOTALS ARE EXPECTED EXCEPT FOR HEAVY AMOUNTS VCNTY OF MORE
ORGANIZED MCS ACTIVITY.
..TROPICS
WE ARE WATCHING A BROAD DISTURBED WEATHER OVER CENTRAL AMERICA FOR
SIGNS OF TROPICAL DEVELOPMENT. MODELS KEEP A BROAD AREA OF
CYCLONIC CURVATURE AND LOW PRESSURE FROM THE CARIBBEAN SEA
WESTWARD ACROSS CENTRAL AMERICA TO THE WEST COAST OF MEXICO THIS
NEXT WEEK BUT ARE IN NO HURRY TO CONVERGE ON A DEVELOPMENT. THE
06Z/28 GFS FINALLY GETS A SYS GOING E OF YUCATAN AT THE VERY END
OF THIS MEDIUM RANGE PERIOD.
..WEST
PERIODS OF SHOWERS WILL BE DIFFICULT TO TIME ACROSS INTERIOR
PORTIONS OF THE NWRN STATES AS PIECES OF ENERGY SHEAR OUT OF A
MEAN TROF ALONG THE W COAST. BELOW 40 DEGREES LATITUDE...EXPECT
DRY AND WARM WEATHER. UPPER FEATURES S OF 40N NOT EXPECTED TO FIND
ENOUGH MOISTURE TO WRING OUT SHOWERS.
FLOOD
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