402
FXUS02 KWBC 071820
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
218 PM EDT MON JUL 07 2008
VALID 12Z THU JUL 10 2008 - 12Z MON JUL 14 2008
THE GENERAL FLOW PATTERN FEATURES A SERIES OF UPPER CYCLONES WITH
THEIR MEAN CENTER SHIFTING FROM CENTRAL CANADA TO HUDSON BAY BY
LATE IN THE PERIOD. WHEN THE INFLUENCE OF THIS GYRE IS COUPLED
WITH A DEEP CYCLONE OVER THE ALEUTIANS WITH NO SIGNIFICANT
POSITIVE ANOMALY ACROSS WESTERN CANADA...THE MAIN BELT OF THE
WESTERLIES IS FORCED TO REMAIN RELATIVELY ZONAL NEAR THE 45TH
PARALLEL. THE MODELS AGREE WITH THESE IDEAS...BUT AS USUAL DIFFER
REGARDING THE DETAILS.
THE MODELS ARE IN GOOD AGREEMENT LATE THIS WEEK REGARDING THE
DETAILS OF THE FORECAST...SO USED THE 00Z ECMWF FOR THE PRESSURES
THURSDAY INTO FRIDAY DUE TO ITS TYPICALLY BETTER VERIFICATION ON
DAYS 3 AND 4. HOWEVER...THE SITUATION CHANGES BY THIS WEEKEND.
THE 06Z GFS AND 00Z ECMWF REMAIN MORE PROGRESSIVE THAN THEIR MOST
RECENT ENSEMBLE MEANS WITH THE LONG WAVE TROUGH CROSSING SOUTHERN
AND EASTERN CANADA. THE 12Z GFS AND 12Z CANADIAN GENERALLY
MAINTAINED CONTINUITY...LEADING TO NO REAL CHANGE IN THE MODEL
SPREAD. SINCE THE 00Z CANADIAN IS CLOSER TO THE VARIOUS MEANS
FROM THIS WEEKEND ONWARD...WE USED A 00Z CANADIAN/NCEP ENSEMBLE
MEAN COMPROMISE FOR THE PRESSURES DURING THAT TIME FRAME WHICH
KEPT GOOD CONTINUITY. THE 00Z GFS /ALTHOUGH A BIT TOO DEEP WITH
THE CYCLONE NEAR THE US AND CANADIAN BORDER SATURDAY MORNING/ IS A
REASONABLE ALTERNATIVE FOR MANY AREAS OF THE COUNTRY.
SOUTHWEST/COLORADO/NEW MEXICO...
MONSOON CONDITIONS ARE EXPECTED THIS PERIOD AS AN INVERTED TROUGH
IN THE MID AND UPPER LEVELS RETROGRADES ACROSS NORTHERN MEXICO TO
THE SOUTH OF THE SUBTROPICAL RIDGE...SKIMMING THE DESERT
SOUTHWEST. BOTH THE CANADIAN MODEL AND THE HPC DAY 4-5 QPF
ANTICIPATE ROBUST RAINFALL PRIMARY ACROSS ARIZONA IN THE MOGOLLON
RIM AS THE UPPER LEVEL SYSTEM TRANSITS SOUTHERN ARIZONA. LOCAL
AMOUNTS OF 3-5 INCHES ARE POSSIBLE...PRIMARILY NEAR AND
WEST/DOWNWIND OF THE ARIZONA MOUNTAINS.
GREAT LAKES...
A FRONTAL BOUNDARY WILL WAVER ACROSS THE REGION AS A SURFACE
CYCLONE SCOOTS ACROSS SOUTHERN CANADA. THE BULK OF THE
PRECIPITATION IS EXPECTED ACROSS MICHIGAN WHERE THE FRONTAL
BOUNDARY LINGERS THE LONGEST. LOCAL RAINFALL AMOUNTS OF 5 INCHES
ARE POSSIBLE HERE DURING THE MEDIUM RANGE PERIOD.
MID-MISSISSIPPI VALLEY INTO THE CAROLINAS...
INITIALLY...A FRONTAL BOUNDARY DEGENERATES INTO A SHEAR LINE...BUT
REMAINS A FOCUS FOR THUNDERSTORM ACTIVITY IN A MOISTURE-RICH AIR
MASS. LATE IN THE PERIOD...ANOTHER COLD FRONT DROPS INTO THE
CAROLINAS...WHICH SHOULD LEAD TO RENEWED RAINS LATE THIS WEEKEND.
LOCAL AMOUNTS OF 5 INCHES OR MORE ARE POSSIBLE ACROSS THIS REGION
DURING THE MEDIUM RANGE PERIOD.
ROTH
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