HPC Extended Forecast Discussion

Hydrometeorological Prediction Center

Table of HPC Discussions
Forecast Discussion	QPF Forecast Discussion	Alaska Extended Discussion
Short Range Discussion	Excessive Rain Discussion	Caribbean Discussion
Extended Range Discussion	Probabilistic Snow Discussion	Model Diagnostic Discussion

EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
148 PM EDT MON MAY 21 2012

VALID 12Z THU MAY 24 2012 - 12Z MON MAY 28 2012


PRELIMINARY UPDATE...

USED AN EVEN BLEND OF THE 00Z/21 ECMWF AND ECENS MEAN TO UPDATE
THE PRELIMINARY FRONTS AND PRESSURES FOR DAY 3...SWITCHING TO JUST
THE ECENS MEAN BY EARLY DAY 5 TO MITIGATE THE MODEL SPREAD IN THE
POSITIONS AND INTENSITIES OF THE MAJOR SYNOPTIC CYCLONES AFFECTING
CENTRAL NORTH AMERICA.  THE ECMWF IS A SLOW...INTENSE OUTLIER WITH
THE STORM OVER EASTERN CANADA LATE DAY 4 INTO DAY 5...WITH THE
ECENS MEAN AND PARTICULARLY THE GEFS MEAN OFF TO THE
RACES...APPROACHING LABRADOR IN THE CASE OF THE LATTER.  THE NEXT
LOW TO AFFECT THE NORTHERN TIER OF THE UNITED STATES LATER IN THE
PERIOD IS REASONABLY REPRESENTED BY THE ECENS MEAN...AGAIN
CONSIDERING THE SPREAD SEEN AMONG THE VARIOUS DETERMINISTIC MODELS.


FINAL...

MADE ONLY COSMETIC CHANGES TO THE UPDATE PACKAGE FOR THE FINAL
ISSUANCE.  THE MANUAL PROGS ARE FASTER THAN THE ECMWF WITH THE
SYSTEM OVER SOUTH CENTRAL CANADA DAY 4...AND SLOWER THAN THE GFS
AND GEFS MEAN.  THE UKMET...AND PARTICULARLY THE GEM
GLOBAL...CORRELATE WELL WITH THE FINAL FORECAST OVER THAT REGION. 
THE GEM GLOBAL AND UKMET ALSO CLUSTER WELL WITH THE SYSTEM
CROSSING THE NORTHERN TIER OF STATES DAY 6...ADDING CONFIDENCE TO
THE MANUAL BLEND.


CISCO