Preliminary Forecasts
Issued by NWS

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FXUS02 KWNH 180653
PREEPD

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

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

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

A DYNAMIC LEAD MID-UPPER LEVEL TROUGH/HEIGHT FALLS PROGRESS FROM
THE UPPER MIDWEST THROUGH THE GREAT LAKES/NERN US TUE-WED WITHIN
NRN STREAM FLOW. THIS SUPPORTS A DEEPENED CLIPPER LOW TRACK AND
SWATH OF PCPN ALONG THE US/CANADIAN BORDER ALONG WITH A
REINFORCING COOLING SURGE AND A PERIOD OF LAKE EFFECT SNOWS IN THE
WAKE OF SYSTEM PASSAGE. SEVERAL LESS CERTAIN WEAKER PROGRESSIVE
SYSTEMS ARE SLATED TO FOLLOW LATER NEXT WEEK WITHIN THIS NRN
STREAM FLOW.

THE EXTENT OF DIGGING OF EMBEDDED SRN STREAM IMPULSES UNDERNEATH
TO THE LEE OF A BUILDING WARMING WRN US MID-UPPER LEVEL RIDGE
EARLY NEXT WEEK AND MID-LATER NEXT WEEK POTENTIAL SRN STREAM
TROUGH/LOW SEPARATION OVER THE GULF COAST REMAINS FURTHER
COMPLICATED BY POTENTIAL FOR NRN STREAM INTERACTION IN SOME
SOLUTIONS. FORECAST SPREAD AND UNCERTAINTY REMAINS ABOVE NORMAL
ALONG WITH MODEL RUN TO RUN VARIANCE. OF THE ENSEMBLES...PREFER
THE ECENS THAT SHOWS MORE FLOW SEPARATION AND WEATHER FOCUS THAN
THE GEFS/CANADIAN/NAEFS. THIS MATCHES WPC CONTINUITY AND FITS THE
OVERALL FLOW AMPLIFICATION UPSTREAM AS PER RECENT MODEL TRENDS.

MEANWHILE...CONTINUED INLAND FLOW OF PACIFIC IMPULSES FROM AN
AMPLIFIED OFFSHORE MID-UPPER LEVEL MEAN TROUGH PROLONGS A WET
PATTERN THAT INCLUDES ELEVATION SNOWS OVER THE NWRN US THROUGH THE
EXTENDED THANKSGIVING BREAK...ALBEIT WITH QUICKLY GROWING TIMING
UNCERTAINTY.

OVERALL...THE WPC MEDIUM RANGE PRODUCT SUITE WAS PRIMARILY DERIVED
FROM A BLEND OF THE 12 UTC GFS/ECMWF AND GEFS/ECMWF ENSEMBLES INTO
THANKSGIVING BEFORE TRANSITIONING TO AN ECMWF ENSEMBLE MEAN
CENTERED SOLUTION BY DAYS 6/7 (NEXT FRI-SAT) THAT MAINTAINS MAX
WPC CONTINUIY.


...WEATHER HIGHLIGHTS...

WET FLOW CONTINUES FOR THE PACIFIC NW WITH OCCASIONALLY HEAVY
DAILY RAINS AND LOCALLY HEAVY ELEVATION SNOWS. UPPER RIDGING WILL
SUPPORT ABOVE AVERAGE TEMPERATURES FROM THE SOUTHWEST THROUGH THE
SOUTHERN GREAT BASIN/ROCKIES AND PLAINS...BUT COOLER THAN AVERAGE
IN THE EASTERN US BEHIND A COLD FRONT. 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 PACIFIC NORTHWEST INTO NORTHERN
CALIFORNIA AS WELL AS NORTHERN IDAHO/WESTERN MONTANA/NW WYOMING.
ORGANIZED RAIN IS ALSO QUITE POSSIBLE ALONG THE GULF COAST FROM
TEXAS EASTWARD TO FLORIDA . RECORD HIGH TEMPS ARE POSSIBLE IN THE
SOUTHWEST WITH WIDESPREAD 80S AND SOME 90S.

SCHICHTEL

$$





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