Prognostic Meteorological Discussion
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000
FXUS02 KWBC 201600
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1059 AM EST MON NOV 20 2017

VALID 12Z THU NOV 23 2017 - 12Z MON NOV 27 2017

...RECORDS HIGHS ACROSS THE SW/WRN US AND PROLONGED HEAVY
RAIN/SNOW OVER THE NWRN US...


...OVERVIEW...

THE GENERAL PATTERN SETUP FOR THE NEXT WEEK ENTAILS A TROUGH OVER
THE GULF OF ALASKA/PACIFIC OCEAN... A RIDGE OVER THE WEST AND A
TROUGH OVER THE EAST. MUCH OF THE PACIFIC NORTHWEST WILL REMAIN IN
AN ACTIVE, PROLONGED WET PERIOD WITH COOLER TEMPERATURES... AS
WILL THE GREAT LAKES REGION AND THE NORTHEAST. A VAST MAJORITY OF
SOUTHERN CALIFORNIA, THE DESERT SOUTHWEST, SOUTHERN ROCKIES AND
SOUTHERN PLAINS WILL BE DRY WITH ABOVE NORMAL TEMPERATURES. SOME
LOCATIONS ARE PROGGED TO REACH OR EXCEED PRIOR TEMPERATURE
RECORDS, PRIMARILY FOR LOCATIONS IN THE SOUTHWEST. THE CENTRAL
U.S. WILL BEGIN WITH ABOVE AVERAGE TEMPERATURES BUT WILL HAVE A
COOLING TREND THROUGH THE WEEKEND. ADDITIONAL WET WEATHER IS
LIKELY OVER FLORIDA ASTRIDE A SLOWLY MOVING AND WAVY FRONTAL
BOUNDARY.


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

OVERALL THE DETERMINISTIC MODELS/ENSEMBLE MEANS ARE IN AGREEMENT
WITH THE LARGE-SCALE SETUP; HOWEVER, WITH PERSISTENT DIFFERENCES
IN TIMING AND AMPLITUDE. THE INITIAL CONSENSUS WAS BASED ON THE
00Z ECWMF/CMC/CONTINUITY AND 06Z GFS... WITH INCREASED WEIGHTING
OF THE ENSEMBLE MEANS TOWARD THE END OF THE FORECAST PERIOD.
CONFIDENCE OF PREDICTABILITY IS ON THE LOW END OF AVERAGE.


...WEATHER HIGHLIGHTS...

HEAVY DAILY RAINS AND LOCALLY HEAVY ELEVATION SNOWS WILL PERSIST
OVER THE NORTHWESTERN STATES THIS WEEK. UPPER RIDGING WILL SUPPORT
WELL-ABOVE AVERAGE TEMPERATURES IN THE SOUTHWEST AND SOUTHERN
CALIFORNIA TO THE INTERMOUNTAIN WEST/ROCKY STATES. SOME RECORD
HIGHS/LOWS ARE LIKELY. MILD TEMPERATURES WILL EXTEND EASTWARD
THROUGH THE PLAINS AHEAD OF A COLD FRONT THURSDAY AND FRIDAY.
COOLER TEMPERATURES WILL FILTER IN THIS WEEKEND AFTER THE FRONTAL
PASSAGE. THERE IS A GOOD CHANCE FOR APPRECIABLE PRECIPITATION
ALONG THE GULF/SOUTHEAST US COAST... ESPECIALLY FL... AS LOW
PRESSURE CENTERS MEANDER ALONG A SLOW MOVING FRONT. RAIN AND SNOW
WILL IS EXPECTED FOR THE GREAT LAKES REGION WITH POTENT NORTHERN
STREAM CLIPPER PASSAGES AND POST-SYSTEM LAKE EFFECT.


...THANKSGIVING FORECAST...

PRECIPITATION WILL CONCENTRATE FROM THE PACIFIC NORTHWEST SOUTH TO
NORTHERN CALIFORNIA... AND EASTWARD INTO NORTHERN
ROCKIES...INCLUDING HIGHER ELEVATION SNOWS. MODEST PRECIPITATION
IS ALSO POSSIBLE ACROSS THE GREAT LAKES WITH LEAD CLIPPER PASSAGE.
ORGANIZED RAIN IS POSSIBLE OVER CENTRAL AND SOUTHERN FLORIDA AND
THE COASTAL SOUTHEAST DEPENDING ON HOW THE SURFACE SYSTEMS EVOLVE.
HIGHEST RECORD HIGH TEMPERATURES ARE LIKELY IN THE SOUTHWEST WITH
80S AND SOME 90S. PHOENIX HAS THE CHANCE OF RECORDING THEIR LATEST
90 DEGREE DAY SO LATE IN THE YEAR (RECORD IS NOV 15 1999)
INCLUDING THEIR WARMEST THANKSGIVING DAY (RECORD IS 87 ON NOV 23
1950 AND NOV 27 2014 - THANKS TO THE PHOENIX NWS OFFICE FOR THE
CLIMATE/RECORD INFORMATION). COOLER 30S/40S IN THE UPPER
MIDWEST/GREAT LAKES/NORTHEAST/MID-ATLANTIC ARE LIKELY BY NEXT
WEEKEND BEHIND THE FRONT.

CAMPBELL


$$




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