478
FXUS02 KWBC 161931
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
330 PM EDT FRI OCT 16 2009
VALID 12Z MON OCT 19 2009 - 12Z FRI OCT 23 2009
MODELS ARE WEAKENING AN INITIAL BLOCK OVER THE BERING SEA AND
REPLACING IT WITH A MEAN LOW BY DAY 5. A FAIRLY VIGOROUS TROF
SHOULD EXTEND S OF THE MEAN LOW INTO THE MIDDLE LATITUDES OF THE
PACIFIC. A NEGATIVE HEIGHT ANOMALY BECOMES FAIRLY WELL ESTABLISHED
NEAR 45N/160W DURING THE MEDIUM RANGE PERIOD.
DOWNSTREAM OF THE MEAN NEGATIVE ANOMALY NEAR 45N/160W...A FLAT
MEAN RIDGE WILL BE FAVORED OVER WRN NOAM. THERE SHOULD BE ENOUGH
WESTERLY FLOW THRU THIS RIDGE THAT SEVERAL SHORT WAVES WILL RACE
THRU IT OVER THE NEXT WEEK. AS MEAN WESTERLIES INCREASE FROM THE
ERN PACIFIC INTO THE NWRN CONUS AND SWRN CANADA...THE DEEP COLD
TROF THAT IS BRINGING UNSEASONABLE COLD AND SN TO THE CENTRAL
APPALACHIANS WILL BE EJECTED BY UPSTREAM ENERGY MON. AS THIS
EJECTION OCCURS... MID LEVEL RIDGING WILL FOLLOW IN ITS
WAKE...ALONG WITH MODERATING TEMPS DAYS 4-5 OVER THE ERN CONUS.
FINAL GRAPHICS RETAINED THE PATTERNS THAT WE SENT OUT IN THE
UPDATED PRELIM GRAPHICS.
UPDATED PRELIM FRONTS HAD ATTEMPTED TO SIMPLIFY A COMPLEX SCENARIO
FOR DAYS 5-6 FROM THE PLAINS STATES TO THE APPALACHIANS CONCERNING
THE SPLITTING OF ENERGY WITHIN AN UPPER TROF CROSSING THAT PORTION
OF THE COUNTRY. AFTER VIEWING 12Z/16 DETERMINISTIC MODELS...A
BLEND OF THE 06Z/19 DETERMINISTIC GFS AND THE 00Z/19 GEFS ENSEMBLE
MEAN STILL APPEARS TO BE THE BEST GUIDANCE COMPROMISE INCLUDING
THE LATEST 00Z/16 ENSEMBLE SPAGHETTI PLOTS.
CONSENSUS OF 12Z/16 MODELS SUPPORTS OUR EARLIER REASONING...HENCE
NO MAJOR CHANGES WILL BE MADE TO THE UPDATED PRELIM GRAPHICS. THE
MAIN FORECAST DIFFICULTY REMAINS THE BEHAVIOR OF ENERGY THAT
MODELS BRING INTO NRN CA ON DAY 3. SUBSEQUENT TO THIS TIME.. THE
NEW GFS/UKMET RETAIN SOME ENERGY IN THE SRN PORTION OF THIS TROF
BUT EMPHASIZE A SRN CANADIAN STREAM MORE. THE NEW 12Z/16 CMC MODEL
HAS MORE SRN STREAM ENERGY THAN THE GFS/UKMET AND HINTS OF SOME
NRN STREAM ENERGY AS WELL. WE THINK THAT THE GFS/UKMET PLAY UP SRN
CANADIAN SHORTWAVE ENERGY TOO MUCH BY DAYS 6-7...MOVING MOST OF IT
ACROSS NEW ENG WHILE LEAVING TOO LITTLE BACK IN THE SRN STREAM. AS
A RESULT OF HAVING TOO LITTLE SRN STREAM ENERGY...THE GFS SEEMS
UNDERDONE IN SHOWING A SURFACE TROF DAY 7 APPROACHING THE SRN
APPALACHIANS.
THE 12Z/16 ECMWF IS INTERESTING. IT STARTS OFF LOOKING LIKE THE
CANADIAN DAYS 3-4 THEN CONSOLIDATES ENERGY INTO MORE OF A MIDDLE
SOLUTION OVER THE UPPER MIDWEST BY DAY 6 THAN EITHER THE NRN OR
SRN STREAM DOMINANT SOLUTIONS. THE 12Z/16 ECMWF SOLUTION SEEMS AS
LIKELY AS ANY. IN FACT IT HAS BETTER SUPPORT FROM TELECONNECTIONS
ON A WRN NOAM UPPER RIDGE THAN OTHER DETERMINISTIC MODEL
SOLUTIONS.
THE PRECIPITATION FORECAST FROM THE PLAINS TO THE APPALACHIANS
WILL WILL BE A LOW CONFIDENCE AFFAIR THAT WILL LARGELY BE A
FUNCTION OF HOW THE NRN CA TROF HOLDS TOGETHER AS IT REACHES THE
CENTRAL PORTION OF THE NATION. THE 12Z/16 ECMWF DEVELOPED A
FAIRLY WELL ORGANIZED AREA OF MODERATE TO HEAVY PRECIP IN THE E
CENTRAL PLAINS THEN DRIFTS IT EWD TO THE APPALACHIANS BY FRI DAY
7. A LESS ORGANIZED TROF SUCH AS OTHER MODELS ARE SHOWING WOULD OF
COURSE GENERATE A LESS WELL DEFINED PRECIP PATTERN CROSSING THE
ERN PORTION OF THE NATION. ENOUGH WESTERLIES ARE EXPECTED THRU THE
FLAT WRN NOAM LONGWAVE RIDGE TO BRING PERIODS OF MODERATE OR HEAVY
PRECIP TO THE COASTAL RANGES OF WA/OR WITH EACH PASSING SHORTWAVE.
FLOOD
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