069
FXUS02 KWBC 051841
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
240 PM EDT MON OCT 05 2009
VALID 12Z THU OCT 08 2009 - 12Z MON OCT 12 2009
DIFFICULT TO JUSTIFY MAKING CONSIDERABLE CHANGES TO THE EARLIER
MEDIUM RANGE PACKAGE...WITH SOME 12Z GUIDANCE SUPPORTING PREVIOUS
MODEL PREFERENCES WHILE OTHER SOLUTIONS DO NOT. THIS COMES AS NO
SURPRISE HOWEVER...AS THE ANTICIPATED SHORTWAVE/LONGWAVE PATTERN
DURING THE MEDIUM RANGE PERIOD BEGINS AS A SPLIT-FLOW REGIME WITH
THE UPPER LOW OVER THE SOUTHWEST EXITING THE REGION...ALL WHILE
ADDITIONAL SHORTWAVE TROUGHS DEVELOP AND/OR ORIGINATE IN THE
HIGHLY UNCERTAIN NORTHERN STREAM OVER CANADA...WHICH THE MODELS
TYPICALLY HAVE A VERY DIFFICULT TIME PREDICTING MORE THAN A FEW
DAYS IN ADVANCE. THUS...THE FORECAST PHILOSOPHY IS ONE OF
PERSISTENCE...HEAVILY WEIGHTED TOWARD EARLIER PREFERENCES WHICH
CONSIDERED OVER 100 SOLUTIONS...AND NUDGED TOWARD 12Z
DETERMINISTIC CONSENSUS DAYS 3/4...WHERE IT EXISTED. DAYS 6/7 WERE
LEFT UNCHANGED. THE PREFERENCE IS FOR THE 00Z CANADIAN DAYS
3/4...WHICH IS SUPPORTED BY THE NEW GFS/GEFS MEAN...AND AN
APPROXIMATE 50/50 BLEND OF THE 00Z CANADIAN/00Z ECMWF ENSEMBLE
MEAN DAYS 6/7...WHICH IS VERY CLOSE TO THE 12Z GEFS MEAN.
WHILE THE PRECISE TIMING AND MAGNITUDE REMAIN UNCLEAR...ANTICIPATE
A SWATH OF HEAVY RAIN TO DEVELOP FROM PARTS OF THE OHIO VALLEY
INTO THE MIDWEST AND SOUTHERN PLAINS DAYS 3/4...WITH AMOUNTS
POSSIBLY EXCEEDING 5 INCHES LOCALLY...PARTICULARLY WITHIN VICINITY
OF MERGING FRONTAL BOUNDARIES OVER MO/AR/OK.
OTHERWISE...TEMPERATURES WILL REMAIN THE LARGEST FORECAST
CHALLENGE IN THE MEDIUM RANGE PERIOD...WITH THE LONGWAVE PATTERN
FAVORING PERIODIC SURGES AND REINFORCEMENT OF MODIFIED CANADIAN
AIR INFLUENCING THE NORTHERN ROCKIES/PLAINS/GREAT LAKES...WITH THE
AMPLIFIED SCENARIO FAVORING THE COLDER SIDE OF THE GUIDANCE...AND
LIKELY EVEN COLDER IN SOME AREAS.
JAMES
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page