HPC Alaska 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 

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

VALID 12Z FRI MAY 25 2012 - 12Z TUE MAY 29 2012

THE UPPER PATTERN OVER ALASKA DURING THE EXTENDED PERIOD WILL BE
DOMINATED A FAIRLY FAST/ZONAL FLOW BTWN 40-40N...WITH A COUPLE
SHORTWAVE H5 TROUGHS NORTH OF THE JET AXIS PROGRESSING W-E THROUGH
A BROAD LONGWAVE TROUGH. IN TERMS OF THE MODELS...THERE WAS FAIRLY
GOOD AGREEMENT AND RUN-TO-RUN CONTINUITY WITH THE 00/12Z
OPERATIONAL UKMET AND ECMWF RUNS...AND COMPARED MUCH BETTER WITH
THE 00Z ECENS MEAN ON DAYS 4-5 WITH RESPECT TO THE SLOWER H5 LOW
PROGRESSION OVER THE WRN ALEUTIANS. THE GFS/CMC AND THUS NAEFS
MEANWHILE REMAINED FASTER. MEANWHILE...THE 00-12Z OPERATIONAL
MODELS SHOW NOTABLY MORE SPREAD BY DAYS 6-8...INCLUDING THE
ECMWF...WHICH AGAIN NOTED FAIRLY POOR RUN-TO-RUN CONSISTENCY OVER
THE PAST 3-4 RUNS. THEREFORE...THE PREDICTABILITY OF THE PATTERN
AFTER DAYS 4-5 AGAIN SUGGESTS A BIT LESS THAN AVERAGE CONFIDENCE.
LEANED TOWARD THE ECENS MEAN TOWARD THE END OF THE MEDIUM RANGE
PERIOD AS A RESULT.

INITIAL LOW AROUND 50N SOUTH OF THE PENINSULA AT 12Z 5/25 LIFTS NE
ACROSS THE GULF AND INTO SE AK BY DAY 5-6. TOWARD THE END OF THE
PERIOD...THE UPPER PATTERN WOULD FAVOR A PSEUDO REX-BLOCKING SETUP
WITH THE H5 LOW OVER SE AK AND THE AMPLIFIED...W-E ORIENTED RIDGE
AND THICKNESS AXIS N ACROSS INTERIOR AK. MEANWHILE...AGAIN GIVING
MORE WEIGHT TO THE 00Z ECENS MEAN...THE LATEST HPC FORECAST
DEPICTS A DEEPENING TROUGH OVER THE BERING SEA DROPPING S ACROSS
THE ALEUTIANS BY DAY 8.

HURLEY