Prognostic Meteorological Discussion
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000
FXUS02 KWBC 181552
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1052 AM EST SAT NOV 18 2017

VALID 12Z TUE NOV 21 2017 - 12Z SAT NOV 25 2017

...RECORDS HIGHS LIKELY IN THE SOUTHWEST LATER NEXT WEEK...


...OVERVIEW...

A VERY STRONG UPPER HIGH NEAR THE DAVIS STRAIT AND A SECONDARY
UPPER HIGH NEAR SOUTHERN CALIFORNIA WILL CONTINUE TO FAVOR
TROUGHING IN THE EASTERN CONUS NEXT WEEK. A LEAD SYSTEM WILL PUSH
THROUGH THE EAST ON TUESDAY AND OFF THE COAST ON WEDNESDAY EXCEPT
FOR FLORIDA WHERE THE FRONT WILL LINGER THROUGH THE WEEK. ANOTHER
SYSTEM WILL ENTER THE PACIFIC NORTHWEST BY THURSDAY/THANKSGIVING
AND MOVE EASTWARD THROUGH THE HIGH PLAINS ON FRIDAY AND INTO THE
GREAT LAKES NEXT SATURDAY.


...GUIDANCE/UNCERTAINTY PREFERENCES......

THE MODELS/ENSEMBLES REMAIN IN GOOD AGREEMENT ON THE LARGE SCALE
PATTERN BUT HAVE LINGERING ISSUES WITH THE DETAILS. THE 00Z UKMET
WAS STILL APART FROM THE BETTER CONSENSUS OF THE 00Z/06Z GFS AND
00Z ECMWF/CANADIAN AS IT REMAINED A BIT SLOWER THAN THE ENSEMBLES.
BASED THE FORECAST ON THAT LARGER CONSENSUS WITH INCREASED
ENSEMBLE WEIGHTING FOR THE LATER PERIODS.

00Z ECMWF MAY BE TOO AGGRESSIVE IN THE NORTHEAST BY LATE WEDNESDAY
NEAR NEW ENGLAND WITH A DEEPER SYSTEM THAN THE REST OF THE
GUIDANCE AS IT LIFTS NORTHWARD INTO NEW BRUNSWICK/NOVA SCOTIA
AROUND 00Z/23. ENSEMBLES CONTINUE TO WAVER ON HOW MUCH TO SEPARATE
THE FLOW OVER THE GULF OF MEXICO BY THE SAME TIME BUT DISMISSED
THE 06Z GFS FOR LIKELY BEING TOO QUICK AND RATHER FAVORED THE 00Z
GFS/ECMWF/CANADIAN THURSDAY AND THE ENSEMBLE MEANS THEREAFTER
(WITH THE ECMWF/CANADIAN CLOSEST) TO LINGER THE TROUGH OR WEAK
CLOSED LOW THROUGH SOUTHERN FLORIDA.

FARTHER WEST, TREND HAS BEEN TOWARD A STRONGER UPPER HIGH NEAR
SOUTHERN CALIFORNIA WHICH SHOULD PREVENT ANY SYSTEM FROM SLIDING
EASTWARD OUT OF THE EAST-CENTRAL PACIFIC AND KEEP A SURFACE FRONT
THROUGH NORTHERN CALIFORNIA FRI/SAT. NORTHEAST PACIFIC HAS BEEN
QUITE UNCERTAIN IN THE DETAILS EVEN IN THE SHORT RANGE BUT
ENSEMBLE AGREEMENT IS HIGH THAT ANOTHER TROUGH WILL DIG SOUTH OF
THE GULF OF ALASKA LATE NEXT WEEK.


...WEATHER HIGHLIGHTS...

WET FLOW CONTINUES FOR THE PACIFIC NW WITH OCCASIONALLY HEAVY
DAILY RAINS AND LOCALLY HEAVY ELEVATION SNOWS. UPPER RIDGING WILL
SUPPORT WELL ABOVE AVERAGE TEMPERATURES IN THE SOUTHWEST WHERE
RECORD HIGHS ARE LIKELY WED-SAT OVER PARTS OF CA/NV/AZ/UT. MILD
TEMPERATURES WILL EXTEND EASTWARD THROUGH THE CENTRAL/SOUTHERN
ROCKIES INTO PLAINS AHEAD OF A COLD FRONT THU/FRI. COOLER THAN
AVERAGE TEMPERATURES ARE EXPECTED IN THE EASTERN US BEHIND THE
INITIAL COLD FRONT WEDNESDAY. THERE IS A GOOD CHANCE FOR
APPRECIABLE PRECIPITATION ALONG THE GULF COAST AS LOW PRESSURE
MEANDERS ALONG A SLOW MOVING FRONT. EXPECT SOME RAIN/SNOW AROUND
THE GREAT LAKES BUT GENERALLY NO PRECIPITATION FROM THE SOUTHWEST
TO THE PLAINS AND MS VALLEY.


...THANKSGIVING FORECAST...

GENERALLY QUIET FOR MOST OF THE LOWER 48. PRECIPITATION WILL BE
MOST CONCENTRATED IN THE COASTAL PACIFIC NORTHWEST INTO NORTHERN
CALIFORNIA AS WELL AS NORTHERN IDAHO/WESTERN MONTANA/NW WYOMING.
RAIN IS ALSO QUITE POSSIBLE THROUGH FLORIDA AND THE COASTAL
SOUTHEAST DEPENDING ON HOW THE SURFACE SYSTEM EVOLVES. RECORD HIGH
TEMPS ARE POSSIBLE IN THE SOUTHWEST WITH WIDESPREAD 80S AND SOME
90S BUT COOLER 30S/40S IN THE UPPER MIDWEST/GREAT
LAKES/NORTHEAST/MID-ATLANTIC.


FRACASSO/SCHICHTEL


$$




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