419
FXUS02 KWBC 251918
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
317 PM EDT FRI JUL 25 2008
VALID 12Z MON JUL 28 2008 - 12Z FRI AUG 01 2008
..FINAL MEDIUM RANGE DISCUSSION
BIG-PICTURE MEDIUM RANGE GUIDANCE CONTINUES TO SUPPORT CONTINUITY
IN THE MEAN UPPER PATTERN...WHICH FEATURES A TROUGH OVER ERN
CANADA SWD TO THE MID ATLC AREA...A RIDGE DOMINATING THE SOUTHWEST
AND PLAINS...AND A TROUGH FROM THE GULF OF AK TO BRITISH COLUMBIA.
WHILE MODEL MEANS AGREE ON THE LONGWAVE PATTERN...THERE ARE BIG
DIFFERENCES IN THE WAY THEY ARE HANDLING THE SHORTWAVES MOVING
INTO BOTH OF THE LONGWAVE TROFS.
THE NEW 12Z/25 GFS SEEMS TO HAVE CAUGHT UP TO THE ECMWF WITH A
SHORTWAVE MOVING FROM THE NRN PLAINS TO NEW ENG NEXT TUE-THU DAYS
4-6. THE NEW 00Z/25 ECMWF ENSEMBLE MEAN HAD BEEN A BIT DEEPER THAN
ITS 12Z MEAN YESTERDAY WITH ITS MEAN TROF OVER ERN CANADA/THE NE
CONUS AROUND DAY 6...AND THE NEW 12Z GFS SEEMS TO BE SUPPORTING
THAT TREND. HOWEVER...WE STILL DO NOT TRUST ITS RUN TO RUN
CONTINUITY CHANGES UPSTREAM OF THAT AREA...ESPECIALLY IN THE NERN
PACIFIC/GULF OF ALASKA. THE 12Z/25 GFS/CANADIAN LOOK WAY TOO DEEP
WITH A TROF ALONG AND OFFSHORE THE PACIFIC NW
COAST...RESPECTIVELY...AROUND DAY 6. THE 12Z UKMET LOOKS MORE
REASONABLE IN THE WAY IT HANDLES THIS TROF AT THAT TIME
RANGE...CLOSER TO THE PATTERN SHOWN BY GFS/ECMWF ENSEMBLE MEANS.
SINCE THE DAY 5-7 PRELIM PROGS WAS COMPRISED OF 50% 00Z/25 ECMWF
MEAN...WE STILL JUDGE THAT THE CENTER OF THE ENVELOPE OF MODEL AND
ENSEMBLE SOLUTIONS IS THE SAFEST PLACE TO BE UNTIL THERE IS BETTER
AGREEMENT ON THE DETAILS OF SHORTWAVE TRAFFIC MOVING THRU THE
FLOW. THEREFORE I WILL NOT MAKE ANY MAJOR CHANGES FOR THE FINAL
FROM THE UPDATED PRELIM GRAPHICS.
...REGIONAL HIGHLIGHTS
...WAVY FRONT FROM THE NRN/CENTRAL PLAINS TO THE MID ATLANTIC
STATES...
THE ENSEMBLE SOLNS FAVOR A WAVY STNRY FRONTAL BNDRY EXTENDING FROM
THE CNTRL PLAINS TO THE OH VALLEY AND MID ATLC DURING MUCH OF THE
5-DAY PERIOD. A DESCRIPTION OF EXPECTED PCPN WILL ONLY BE AS
ACCURATE AS THE ACTUAL FRONT AND FRONTAL WAVES...AND CONVECTIVELY
GENERATED OUTFLOW BOUNDARIES TO ITS S. BELOW AVERAGE CONFIDENCE IN
THE DETAILS. THE FRONT WILL BE A GENERAL FOCUS FOR CONVECTION THRU
THE PERIOD. PCPN NEAR THE WRN PORTION OF THE FRONT OVER KS MAY BE
ENHANCED BY RESIDUAL MOISTURE FROM T.S. DOLLY.
..CENTRAL GULF COAST TO THE S ATLANTIC COAST INCLUDING FL
DIURNAL CONVECTION SHOULD FIRE UP MOST EVERY DAY WITH A SOMEWHAT
CLIMATOLOGICAL PRECIP MAXIMUM THRU THIS AREA. THE MAXIMUM THRU THE
S ATLANTIC COAST MAY BE ENHANCED BY CONVERGENCE E OF A
LEE-OF-THE-APLCHNS SURFACE TROF.
..MONSOONAL AREAS OF NM/AZ/CO
MOISTURE FROM THE REMNANTS OF TS DOLLY WILL FUEL CONVECTION IN THE
FAVORED MONSOONAL AREAS. ONCE THIS MOISTURE IS ESTABLISHED...THERE
IS NO MECHANISM IN SIGHT TO REMOVE IT...WITH A WEAK MEAN UPPER
HIGH CENTERED SOMEWHERE TO THE SE OF 4 CORNERS. THE EXAGGERATED
12Z GFS TROF ALONG THE W COAST DAY 6 SHOULD HAVE LITTLE OR NO
EFFECT. IF ANYTHING...WEAK PREFERRED GFS/ECMWF ENSEMBLE MEAN 500MB
RIDGING OVER CO/WY LATE NEXT WEEK WILL BECOME EVEN MORE FAVORABLE
FOR MONSOONAL ACTIVITY. WE SUSPECT THAT IN GENERAL...THE GFS AND
ECMWF MODELS APPEAR DEFICIENT IN THE WWD EXTENT OF THE MONSOONAL
PRECIP INTO AZ MOST OF THIS MEDIUM RANGE PERIOD.
..PACIFIC NW COAST
JUST ENOUGH HEIGHT FALLS ARE EXPECTED TO SUPPORT LIGHT PCPN
AMOUNTS OVER THE COASTAL AND CASCADE RANGES FROM CENTRAL OR NWD
WED DAY 5. GUIDANCE WAS IN REASONABLE AGREEMENT IN SUPPORTING A
STRENGTHENING THERMAL FIELD OVER THE NWRN STATES DAYS 3-5....AND
MAINTAINING THIS THERMAL GRADIENT DAYS INTO DAYS 6-7. DESPITE SOME
THICKNESS COOLING...FOLLOWING A SURFACE FRONT INTO THE NWRN STATES
MAY BE MORE PROBLEMATIC. ONE THING WE ARE HIGHLY CONFIDENT OF.
THAT IS...THE AMPLITUDE OF THE NEW 12Z GFS BRINGING A TROF INTO
THE PACIFIC NW THU DAY 6 IS QUITE OVERDONE.
FLOOD
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page