Hydrometeorological Prediction Center Forecast Discussion

Hydrometeorological Prediction Center

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
456 AM EDT TUE MAY 22 2012

VALID 12Z SAT MAY 26 2012 - 12Z TUE MAY 29 2012

THE WRN TROF-ERN RIDGE PATTERN FCST TO DEVELOP LATE THIS WEEK
SHOULD REACH MAXIMUM AMPLITUDE/STRENGTH DURING THE WEEKEND.  THEN
THE WRN TROF SHOULD BEGIN TO EJECT FROM THE WEST AS LOWER
AMPLITUDE NRN PAC FLOW ARRIVES... WITH THE ERN RIDGE ALSO
WEAKENING.  EXPECT A MEANINGFUL DECREASE IN PREDICTABILITY OF
DETAILS BY THE END OF THE PERIOD GIVEN THE TRANSITION TO FLATTER
MEAN FLOW WITH THE MAIN BAND OF WESTERLIES CONFINED TO THE NRN
HALF OF THE CONUS.

WITHIN THE WRN TROF THE 00Z GFS IS FASTER THAN OTHER GUIDANCE TO
KICK OUT THE EMBEDDED CLOSED LOW.  THE AMPLIFIED PATTERN AND FAST
TENDENCIES OF THE GFS FAVOR THE SLOWER MAJORITY THAT INCLUDES THE
ECMWF/UKMET/CANADIAN.  THE GEFS MEAN IS GENERALLY A COMPROMISE AND
LIKELY STILL A LITTLE TOO FAST.  WITH UPSTREAM FLOW MODEL/ENSEMBLE
SOLNS INCREASINGLY DIFFER ON THE SHRTWV DETAILS... THOUGH WHAT
CONSENSUS EXISTS SUGGESTS THE 00Z ECMWF MAY BE A LITTLE TOO QUICK
TO RAISE HGTS OVER THE WEST BY DAY 7 TUE.  FARTHER EWD... BY THE
LATTER HALF OF THE PERIOD THE 00Z ECMWF SHOWS LOWER SERN
CANADA/NERN CONUS HGTS ALOFT THAN OTHER SOLNS OR ECMWF
CONTINUITY... BRINGING THE MEAN SFC FRONTAL ZONE OVER THE EAST
WELL SWD OF CONSENSUS.  PREFERENCE FOR SLOWER EJECTION OF THE WRN
TROF/CLOSED LOW VERSUS THE GFS/GEFS MEAN YIELDS AN EMPHASIS ON THE
00Z ECMWF/12Z ECMWF MEAN FOR DAYS 3-5 FRI-SUN... WITH MINORITY
INCLUSION OF THE 12Z ECMWF ON DAY 3 TO ACCOUNT FOR GUIDANCE
SPREAD/CONTINUITY ADJUSTMENTS FOR THE SYSTEM FCST TO BE TO THE N
OF THE GRTLKS AS OF EARLY FRI.  LACK OF CONFIDENCE IN VARIOUS
ASPECTS OF THE 00Z ECMWF LATER IN THE PERIOD LEADS TO 70 PCT
WEIGHTING OF THE 12Z ECMWF MEAN BY DAYS 6-7 WITH THE GEFS MEAN
BECOMING SUFFICIENTLY PLAUSIBLE TO MERIT A 30 PCT COMPONENT IN THE
BLEND AT THAT TIME. 

RAUSCH