817
FXUS02 KWBC 221845
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
244 PM EDT TUE SEP 22 2009
VALID 12Z FRI SEP 25 2009 - 12Z TUE SEP 29 2009
PRELIMINARY UPDATE...
THE FRONTS AND PRESSURES FOR DAYS 3 THROUGH 7 WERE UPDATED USING A
BLEND OF THE 00Z/22 ECMWF AND 00Z/22 EC ENSEMBLE MEAN...WITH
GREATER WEIGHT ALLOTTED TO THE MEAN LATER IN THE PERIOD TO ADDRESS
THE UNCERTAINTIES IN SYNOPTIC DETAIL INHERENT TO THAT TIME RANGE.
NOW THAT THE BIG UPPER LOW HAS NESTLED INTO A HOME IN THE PLAINS
STATES...ITS EJECTION IS MORE STRAIGHTFORWARD. THE BEHAVIOR OF
THE NORTHERN STREAM IS THE MOST CONTENTIOUS ASPECT OF THE
FORECAST...WITH AT LEAST TWO MAIN SLUGS OF ENERGY DETERMINING THE
LOW LEVEL FORCING ALONG THE CANADIAN BORDER AFTER DAY 5. BECAUSE
IT TENDS TO VERIFY BETTER...USED THE ECMWF...WHICH DEPICTS A
SMALLER...MORE INTENSE LOW TRACKING FARTHER SOUTH THAN THE
GFS...GEM GLOBAL...AND UKMET MODELS...THOUGH THE INCORPORATION OF
ITS ENSEMBLE MEAN INTO THE MANUAL BLEND IS AN INTENTIONAL HEDGE
TOWARD THOSE SOLUTIONS.
FINAL...
THE 12Z/22 GUIDANCE CAME IN RATHER VIGOROUS WITH THE VERY
SHORTWAVE THAT THE 00Z/22 ECMWF WAS EMPHASIZING CROSSING THE GREAT
LAKES DAY 6...BUT THE DEPTH AND LATITUDE ARE STILL UP FOR GRABS
WITH THE CYCLONE. WHILE NOT OUT OF THE QUESTION...SOME OF THE
MODELS ARE DEPICTING AN EVENT THAT APPROACHES 4 STANDARD
DEVIATIONS FROM THE MEAN OVER THE REGION. THE BLEND USED IN THE
PRELIMINARY UPDATE STILL SEEMS LIKE A SENSIBLE ONE...AND WITH THE
EJECTION OF THE PLAINS LOW ON TRACK...SAW NO COMPELLING REASON TO
MAKE CHANGES FOR THE FINAL ISSUANCE.
CISCO
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