257
FXUS02 KWBC 051931
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
330 PM EDT SAT SEP 05 2009
VALID 12Z TUE SEP 08 2009 - 12Z SAT SEP 12 2009
THE LONGWAVE PATTERN CONTINUES PROGRESSIVE AT LATITUDES HIGHER
THAN 45N THRU DAY 4. FROM DAY 5 ONWARD...MODELS AND ENSEMBLES SHOW
A LARGE INCREASE IN AMPLITUDE TO A TROF IN THE GULF OF ALASKA.
MODELS BEGIN TO RESPOND DIFFERENTLY TO THIS AMPLIFICATION IN THE
GULF OF ALASKA IN THE DOWNSTREAM SHORTWAVES OVER CANADA DAYS 5-7.
THIS GIVES US A SLIGHLTY LOWER THAN NORMAL CONFIDENCE LEVEL FOR
THE LATTER PART OF NEXT WEEK..
THE GFS 12Z/05 APPEARS TO BE TOO MUCH ON THE AMPLIFIED SIDE OF
THE ENVELOPE OF SOLUTIONS CONCERNING A NRN PLAINS TROF DAY 6-7.
HOWEVER...THE LATEST DAY 6 UKMET/ECMWF/CANADIAN ARE ALSO SHOWING
AN INCREASE IN AMPLITUDE IN THE SAME TROF..JUST A DAY OR SO BEHIND
THE GFS.
FINAL GRAPHICS STAYED WITH THE 50-50 06Z GFS/NAEFS BLEND USED IN
THE PRELIMS.
WE ARE STILL FORECASTING A PATTERN OF EASTERLY SURFACE FLOW
DEVELOPING OVER THE CAROLINAS AND MID ATLANTIC REGIONS DAYS 5-6.
THE COMPLEX PATTERN OF UPPER VORTICITY OVER THE SERN STATES STILL
LEADS TO AN UNCERTAIN FORECAST ALONG THE E COAST DAYS 5-7. THE
06Z/05 GFS AND 12Z/05 CANADIAN...BEING WESTERN OUTLIERS...WOULD
BRING SIGNIFICANT RAINFALL WELL INLAND INTO THE
PIEDMONT...HOWEVER...THE REMAINDER OF 12Z/05 MODEL GUIDANCE
SUGGESTS THAT WE SHOULD HOLD OFF ON BRINGING HEAVY PRECIP VERY FAR
INLAND THE LATTER PORTION OF NEXT WEEK. THE STRENGTH OF THE DEEP
LAYERED RIDGE CROSSING NEW ENG TO THE N WILL BE CRITICAL.
SCATTERED MONSOONAL CONVECTION IS EXPECTED TO CONTINUE THRU THE
PERIOD IN OAR SRN PORTIONS OF THE ROCKIES AND INTERMOUNTAIN
REGIONS. FARTHER N...DRIER AIR AND HEIGHT RISES SHOULD FOSTER A
DECREASE TO VERY WIDELY SCATTERED ACTIVITY FROM WED EVENING ONWARD
AS HEIGHTS RISE TO THE REAR OF A SHORTWAVE MOVING INTO THE NRN
PLAINS. SOME CONVECTION IS EXPECTED ALONG A FRONT IN THE CENTRAL
PORTION OF THE NATION.
FLOOD
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