Prognostic Meteorological Discussion
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FXUS02 KWBC 200700
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
159 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...

IT REMAINS THE CASE THAT STRONG UPPER HIGHS NEAR SAN DIEGO AND THE
DAVIS STRAIT BETWEEN FAR NERN CANADA AND GREENLAND CONTINUES TO
FAVOR ERN US TROUGHING AND COOLER THAN AVERAGE TEMPERATURES.
RECORD WARM TEMPERATURES ARE LIKELY FOR PARTS OF THE SOUTHWEST AND
SRN CA INTO THE INTERMOUNTAIN WEST/ROCKY STATES...BUT WEST TO
SOUTHWESTERLY FLOW INTO THE PACIFIC NORTHWEST WILL MAINTAIN A
PROLONGED WET PATTERN. ADDITIONAL WET WEATHER IS LIKELY OVER
FLORIDA ASTRIDE A SLOWLY MOVING AND WAVY FRONTAL BOUNDARY. THE
MIDDLE PART OF THE COUNTRY IS EXPECTED TO BE RATHER DRY AND MILD
TO START BUT TRENDING COOLER BY THE WEEKEND.


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

MODELS/ENSEMBLES ARE IN GOOD AGREEMENT ON THE LARGE SCALE PATTERN
BUT DIFFER ON SOME TIMING/AMPLITUDE DETAILS. FORECAST SPREAD AND
UNCERTAINTY IS SLOWLY DECREASING...BUT REMAINS HIGHER THAN
AVERAGE. THE WPC PRODUCT SUITE WAS MAINLY DERIVED FROM THE 12 UTC
ECMWF ENSEMBLE MEAN TO MAINTAIN MAX WPC CONTINUITY...BUT INCLUDED
SMALLER INPUTS FROM THE LARGER SCALE ALOFT COMPATABLE BUT HIGHLY
RUN TO RUN VARIABLE WITH LOWER ATMOSPHERIC PARAMETERS 18 UTC
GFS/GEFS AND 12 UTC ECMWF. THIS ADDED A BIT MORE DETAIL CONSISTENT
WITH BELOW NORMAL PREDICTABILITY.


...WEATHER HIGHLIGHTS...

HEAVY DAILY RAINS AND LOCALLY HEAVY ELEVATION SNOWS WILL PERSIST
OVER THE NWRN US THIS WEEK. UPPER RIDGING WILL SUPPORT WELL ABOVE
AVERAGE TEMPERATURES IN THE SOUTHWEST AND SRN CA 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 THU/FRI WITH COOLER TEMPERATURE TO FOLLOW
HEADING INTO THE WEEKEND. THERE IS A GOOD CHANCE FOR APPRECIABLE
PRECIPITATION ALONG THE GULF/SERN US COAST...ESPECIALLY FL...AS
LOW PRESSURE CENTERS MEANDER ALONG A SLOW MOVING FRONT.
MEANWHILE...EXPECT SOME ORGANIZED RAIN/SNOW AROUND THE GREAT LAKES
WITH POTENT NRN STREAM CLIPPER PASSAGES AND POST-SYSTEM LAKE
EFFECT.


...THANKSGIVING FORECAST...

PRECIPITATION WILL CONCENTRATE FROM THE PACIFIC NORTHWEST INTO NRN
CA AS WELL AS NRN ID/WRN MT/NW WY...INCLUDING HIGHER ELEVATION
SNOWS. MODEST PRECIPITATION IS ALSO POSSIBLE ACROSS THE GREAT
LAKES WITH LEAD CLIPPER PASSAGE. ORGANIZED RAIN IS POSSIBLE OVER
CENTRAL AND SRN FL AND THE COASTAL SOUTHEAST DEPENDING ON HOW THE
SURFACE SYSTEMS EVOLVE. HIGHEST RECORD HIGH TEMPS 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.

SCHICHTEL/FRACASSO


$$




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