195
FXUS02 KWBC 281846
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
245 PM EDT WED OCT 28 2009
VALID 12Z SAT OCT 31 2009 - 12Z WED NOV 04 2009
CONSENSUS OF TODAYS MODEL GUIDANCE SHOWS A PROGRESSIVE AND
DEAMPLIFYING PATTERN OVER NOAM DURING THE NEXT 5 DAYS. THE HUGE
TROF DIGGING INTO THE WEST IN THE SHORT RANGE WILL SPLIT... THEN
THE SRN PORTION OF THE SPLIT WILL BE ABSORBED BY THE NRN BRANCH OF
THE WESTERLIES OVER THE ST LAWRENCE SEAWAY BY EARLY NEXT WEEK. A
WEAK TROF MAY REPLACE THE RIDGE SOMEWHERE OVER FAR ERN NOAM EARLY
NEXT WEEK....BUT CONFIDENCE IN THIS TROF IS BELOW AVERAGE. OUR
CONFIDENCE LEVEL IS EVEN LOWER OVER THE NERN PACIFIC DAYS 6-7
WHERE VERY HIGH ENSEMBLE SPREAD DEVELOPS.
THE MAIN FORECAST PROBLEM OF THE DAY FOCUSES ON THE
DEAMPLIFICATION OF THE INITIAL STRONG HIGHS IN THE WRN ATLANTIC
AND ERN PACIFIC...AND THE TREND FOR MORE PROGRESSIVE AND
DEAMPLIFYING UPSTREAM FLOW TO COME INTO NOAM FROM THE PACIFIC. IN
THE TRANSITION PERIOD FRI-SAT FROM A HIGHLY AMPLIFIED WRN TROF TO
MORE ZONAL FLOW ACROSS THE NWRN STATES...DETERMINISTIC MODELS
GENERALLY SPLIT OFF THE SRN END OF THE ROCKIES TROF INTO ANOTHER
CLOSED UPPER SYS CROSSING THE S CENTRAL PLAINS FOR SAT DAY 3.
MODEL ENSEMBLE MEANS ARE WEAKER WITH THIS CLOSED SYS DAYS 3-4 THAN
THEIR DETERMINISTIC COUNTERPARTS. BY DAY 5 THEY HAVE ABSORBED ITS
REMNANTS INTO THE MAIN POLAR WESTERLIES OVER THE CANADIAN
MARITIMES.
12Z/28 MODELS SHOW THE LATEST 12Z/28 GFS CONSISTENT WITH ITS
00Z/28 CONTINUITY WITH THE SRN PLAINS DAY 3 CLOSED LOW...BUT ON
THE SLOW SIDE OF THE ENVELOPE OF MODEL SOLUTIONS COMPARED THE THE
12Z/28 UKMET AND CANADIAN. THE SLOWER 12Z/28 GFS SOLUTION IS
SOMEWHAT FAVORED BY THE INITIAL VERY HIGH AMPLITUDE IN THE ERN
PACIFIC BUT THE FASTER CANADIAN/UKMET SOLUTIONS ARE CONSISTENT
WITH THE RAPIDLY DEAMPLIFYING LONGWAVE PATTERN. OUR UPDATED PRELIM
BLEND OF 30% DETERMINISTIC ECMWF AND 70% ECMWF ENSEMBLE MEAN FROM
00Z/28 IS ABOUT A THIRD OF THE WAY BETWEEN THE SLOWER GFS AND THE
FASTER SOLUTIONS OF THE CANADIAN/UKMET. THIS SEEMED AS GOOD A
PLACE TO BE AS ANY...HENCE WE LEFT OUR EARLIER GRAPHICS UNCHANGED.
HOWEVER THE NEW ECMWF CAME IN A BIT FASTER WITH THIS EJECTING SRN
PLAINS SYS DAY 4 THAN OUR FINAL GRAPHICS...SO THERE IS STILL
MODERATE UNCERTAINTY WITH ITS TIMING.
THE MAIN SENSIBLE WEATHER HIGHLIGHTS WILL BE DOMINATED BY THE EWD
PROGRESSION OF A COLD FRONT AND ITS ATTENDANT OPENING UP UPPER LOW
EJECTING OUT OF THE SRN PLAINS DAYS 3-4. PRECIP WILL BECOME LESS
ORGANIZED ON ITS EWD TREK AS THE ASSOCIATED UPPER SUPPORT WEAKENS.
THE APPALACHIANS WILL WRING OUT SOME MODERATE AMOUNTS FROM THE
FRONT WITH LIGHTER QPF E OF THE MOUNTAINS. ONCE THIS COLD FRONT
CLEARS THE COAST...EXPECT VERY QUIET CONDITIONS OVER MOST OF THE
COUNTRY AS GULF MOISTURE SHOULD BE SHUT OFF AND UPPER DYNAMICS
SHOULD BE MARGINAL. PERIODS OF LIGHT QPF MAY AFFECT THE
OROGRAPHICALLY FAVORED AREAS OF WA/OR FROM FAST MOVING POORLY
DEFINED SHORTWAVES...ALTHOUGH SURFACE RIDGE CONDITIONS WILL
PREVAIL OVER THE PACIFIC NW.
FLOOD
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page