048
FXUS02 KWBC 191929
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
328 PM EDT SAT JUL 19 2008
VALID 12Z TUE JUL 22 2008 - 12Z SAT JUL 26 2008
..FINAL MEDIUM RANGE DISCUSSION
THE MEAN LONGWAVE PATTERN SHOWS A STRONG BLOCKING RIDGE OVER THE
WRN DAVIS STRAIT THAT IS FORECAST TO WEAKEN AFTER ABOUT 5
DAYS....WITH TROFS IN THE NE PACIFIC AND ALONG THE MID ATLANTIC
AND NEW ENG COASTS. AFTER 5 DAYS...THE PATTERN APPEARS TO BE IN
TRANSITION AS A NEW POS HEIGHT ANOMALY CENTER FORMS NEAR THE GRT
LAKES. ENSEMBLE SPREAD BECOMES RATHER HIGH ACROSS MOST OF
CANADA...ESPECIALLY ERN CANADA...AS THE OLD ANOMALY OVER THE WRN
DAVIS STRAIGHT WEAKENS AND AND THE NEW ONE BEGINS TO FORM JUST N
OF THE GRT LAKES.
THE NEW 12Z/19 GFS FOLLOWS CONTINUITY CONCERNING THE NERN CONUS
TROF WELL THRU WED DAY 4. BY THU DAY 5...IT BEGINS TO KICK OUT THE
MAIN PORTION OF THIS TROF WHILE LEAVING A PIECE BEHIND OVER NY
STATE. UPSTREAM...IT BECOMES ALMOST A DAY SLOWER THU WITH THE
NEXT CANADIAN SHORTWAVE...AND HAS GONE BACK TO HIGH AMPLITUDE IN
THE NE PACIFIC. I DO NOT TRUST THE CONTINUITY CHANGES OF THE NEW
12Z GFS FROM ITS PREVIOUS 06Z AND 00Z RUNS FROM THU DAY 5 ONWARD.
CONCERNING OTHER 12Z MODELS...THE NEW ECMWF IS THE SLOWEST AND
FARTHEST SW OF THE MODELS WITH THE NEN CONUS TROF/CLOSED LOW THU
DAY 5...WITH THE UKMET A CLOSE SECOND. THE CANADIAN AND GFS ARE
MOST AMPLIFIED IN THE NE PACIFIC DAY 5 WHILE THE ECMWF AND UKMET
SHOW LESS TROF S OF 50 DEGREES LATITUDE.
WITH MUCH SPREAD AMONG 12Z MODELS...I FEEL JUSTIFIED IN STICKING
WITH THE UPDATED PRELIM CONTINUITY OF AN 00Z/19 ECMWF/GEFS/EC ENS
BLEND...AS THE 12Z/19 GFS ENSEMBLE MEAN HAD VERY GOOD CONTINUITY
WITH ITS 06Z AND 00Z MEAN. A COMPARISON OF THE 00Z/19 ECMWF
ENSEMBLE MEAN WITH ITS CORRESPONDING 12Z/18 MEAN GAVE VERY GOOD
CONTINUITY...AS DID A COMPARISON OF THE NEW 06Z/19 GEFS ENSEMBLE
MEAN TO THE CORRESPONDING 00Z/19 MEAN. THE 06Z/19 GFS HAD TRENDED
FLATTER WITH THE FLOW ACROSS THE NE PACIFIC INTO CANADA THU DAY
5...SUPPORTING OUR EARLY PRELIM REASONING THAT THE ECMWF WAS TOO
DEEP AND PERSISTENT WITH ITS TROF OVER THE NE STATES/ST LAWRENCE
SEAWAY NEXT THU/FRI.
AT THIS TIME...HPC PREFERS OVERALL THE SLIGHTLY LESS AMPLIFIED
SIDE OF THE ENVELOPE OF MODEL AND ENSEMBLE SOLUTIONS WITH THE
500MB FLOW ACROSS NOAM WED-SAT DAYS 4-7. THE NE CONUS TROF ON DAY
5 MAY BE BRIEFLY MORE AMPLIFIED THAN THE ENSEMBLE MEANS WOULD
INDICATE.
..REGIONAL HIGHLIGHTS
.SW MONSOON AREA
A PERSISTENT UPPER HIGH CENTERED NE OF 4 CORNERS FAVORS THE
CONTINUANCE OF THE PRESENT ROBUST MONSOONAL PRECIP PATTERN OVER
AZ/NM/UT/CO FOR THE FORESEEABLE FUTURE. WITHIN THIS AREA SMALLER
DAY TO DAY CHANGES WILL BE HARDER TO PINPOINT...AS MODEL SMALL
SCALE UPPER AIR VORTS MAY BE CORRUPTED BY CONVECTIVE FEEDBACK.
..TX/LA GULF COAST
A STRONG SLUG OF TROPICAL MOISTURE NOW MOVING NW FROM THE
CARIBBEAN SEA WILL REACH S TX ON TUE...AND HANG AROUND LONG ENOUGH
TO BRING LOCALLY HEAVY DOWNPOURS THE NEXT 2 DAYS. THE SRN THIRD OF
TX WILL BEAR THE BRUNT OF THIS ONSLAUGHT OF TROPICAL MOISTURE.
WHILE THE MODEL ENSEMBLE MEANS SUGGEST MAX ACTIVITY AROUND WED OR
THU....LINGERING HIGH MOISTURE COULD FUEL SOME SHOWERS OVER FAR S
TX RIGHT INTO NEXT FRI OR SAT.
...STALLING OUT COLD FRONT TN VLY TO JUST OFF THE MID ATLANTIC AND
NEW ENG COASTS....
THIS FRONT AND ITS ASSOCIATED MESO-BOUNDARIES SHOULD BE A FOCUS
FOR CONVECTION THROUGHOUT THE MEDIUM RANGE PERIOD...AS WILL AS A
LEESIDE TROF SE OF THE APLCHNS OVER THE S ATLANTIC STATES.
CONVECTION WILL BE RATHER GENERAL ALONG AND S OF THE FRONT. SOME
BENEFICIAL RAINS ARE EXPECTED IN PORTIONS OF THE SE STATES THAT
STILL HAVE A LONG TERM DEFICIT OF RAINFALL. SOME LOCALLY EXCESSIVE
RAINS POSSIBLE WHERE CELL TRAINING OCCURS.
..NRN PLAINS/MID MS VLY
THE WRN END OF THE ABOVE MENTIONED FRONT WILL BECOME A FOCUS FOR
CONVECTION BY MIDWEEK AS WEAK RETURN FLOW MOVES NWD INTO THE
PLAINS. THE GFS AND ECMWF SUGGEST THAT WED/THU COULD BE THE MOST
ACTIVE DAYS AS SHORTWAVE ENERGY MOVES EWD THRU THE MEAN LONGWAVE
RIDGE OVER THE HIGH PLAINS. PORTIONS OF IA RECOVERING FROM RECENT
FLOODING COULD BE UNDER THE GUN FOR MORE LOCALLY EXCESSIVE
RAINFALL.
..TROPICAL FEATURES
OFF THE EAST COAST...T.S CRISTOBAL IS FCST TO BECOME ABSORBED INTO
THE LARGER SCALE AREA OF LOW PRESSURE OVER THE NORTHEAST SHORTLY
AFTER THE BEGINNING OF DAY 3 TUE. MEANWHILE THE LATEST TPC
GUIDANCE MOVES A SYS OUT OF THE CARIBBEAN TO 23N/93W BY DAY 3.
PLEASE REFER TO FUTURE BULLETINS FROM THE TPC CONCERNING THIS
TROPICAL SYS.
FLOOD
CLICK HERE TO GO TO PREVIOUS BULLETINS.
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