516
FXUS02 KWBC 040659
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
158 AM EST MON DEC 4 2023
VALID 12Z THU DEC 7 2023 - 12Z MON DEC 11 2023
..PATTERN OVERVIEW
THE RIDGE AXIS THAT WILL BE IN PLACE ACROSS THE NORTH-CENTRAL U.S.
MID-WEEK IS EXPECTED TO FLATTEN OUT BY THURSDAY WHILE A RIDGE THEN
BUILDS ACROSS THE EASTERN U.S. TO CLOSE OUT THE WEEK. PACIFIC
SHORTWAVE ENERGY REACHING THE WEST COAST THURSDAY NIGHT WILL HELP
BUILD AN UPPER TROUGH ACROSS THE WESTERN U.S. FRIDAY AND INTO
SATURDAY, AND THIS WILL THEN EJECT EASTWARD ACROSS THE PLAINS AND
SPUR SURFACE CYCLOGENESIS OVER THE WEEKEND ACROSS THE CENTRAL
PLAINS. THIS WILL LIKELY RESULT IN A WELL ORGANIZED STORM SYSTEM
TRACKING NORTHEAST TOWARDS THE OHIO VALLEY AND GREAT LAKES, WITH
INCREASING RAIN AND STORM CHANCES AHEAD OF THE COLD FRONT, AND
WINTRY PRECIPITATION NORTHWEST OF THE SURFACE LOW.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE 00Z MODEL GUIDANCE SUITE IS IN GOOD OVERALL AGREEMENT FOR THE
END OF THE WEEK, AND A GENERAL MODEL COMPROMISE WORKS WELL AS A
STARTING POINT IN THE FORECAST PROCESS. THERE WERE SOME
DIFFERENCES WITH THE CMC REGARDING THE NORTHWESTERN PLACEMENT OF
THE SURFACE LOW CROSSING NEAR THE U.S./CANADIAN BORDER, SO THAT
MODEL WAS WEIGHTED SLIGHTLY LESS THAN THE BETTER CLUSTERED
GFS/ECMWF/UKMET. IN TERMS OF THE DEVELOPING CENTRAL-EASTERN U.S.
STORM SYSTEM, THE GUIDANCE HAS COME INTO BETTER AGREEMENT ON THE
TIMING OF THE LOW AND THE TRAILING COLD FRONT, IN CONTRAST TO
YESTERDAY WHEN THERE WERE STILL MAJOR RUN-TO-RUN VARIATIONS. THE
ECMWF HAS TRENDED MORE TO THE WEST WITH THE 00Z RUN WITH THE MAIN
LOW, AND A TRIPLE POINT LOW CLOSER TO WHERE THE GFS/CMC HAVE THEIR
MAIN LOWS. IN ANY CASE, THERE WILL LIKELY BE A SUB-1000MB SURFACE
LOW TRACKING SOUTHWEST TO NORTHEAST ACROSS THE EASTERN U.S. ON
SUNDAY AND EVEN STRONGER INTO MONDAY. ENSEMBLE MEANS ACCOUNTED
FOR UP TO 50% OF THE FORECAST BY NEXT MONDAY.
..WEATHER/HAZARDS HIGHLIGHTS
THE NEXT ROUND OF RAINFALL FOR THE PACIFIC NORTHWEST IS EXPECTED
TO BE CONSIDERABLY LIGHTER ON THURSDAY COMPARED TO THE ONGOING
ATMOSPHERIC RIVER EVENT IN THE SHORT RANGE FORECAST PERIOD, AND
ALTHOUGH SOME PORTIONS OF THE OREGON COASTAL RANGES MAY GET AN
ADDITIONAL INCH OF RAIN, IT DOES NOT APPEAR THE INTENSITY NOR THE
OVERALL TOTALS ARE CURRENTLY HIGH ENOUGH TO MERIT ANY EXCESSIVE
RAINFALL CONCERNS, ALTHOUGH LOCAL RIVERS MAY STILL BE RUNNING
HIGH. EVEN LESS PRECIPITATION IS EXPECTED HERE ON FRIDAY, BEFORE
THE NEXT ROUND OF PACIFIC MOISTURE ADVECTS INLAND NEXT WEEKEND.
THE DEVELOPING WESTERN U.S. TROUGH BY THE END OF THE WEEK IS
EXPECTED TO RESULT IN MOISTURE ADVECTING INLAND ACROSS THE
INTERMOUNTAIN WEST AND THE ROCKIES, WITH WIDESPREAD MODERATE TO
LOCALLY HEAVY SNOW FOR THE HIGHER ELEVATIONS. THERE MAY ALSO BE
SOME SNOW FOR ADJACENT PORTIONS OF THE WESTERN HIGH PLAINS AS THE
LOW EXITS THE ROCKIES. FARTHER SOUTH IN THE WARM SECTOR OF THE
DEVELOPING SURFACE LOW, INCREASING COVERAGE OF SHOWERS AND
THUNDERSTORMS CAN BE EXPECTED FROM THE CENTRAL GULF COAST TO THE
OHIO VALLEY, ALONG WITH BREEZY TO WINDY CONDITIONS. THIS STORM
SYSTEM SHOULD THEN REACH THE EAST COAST BY LATE SUNDAY INTO MONDAY
WITH WIDESPREAD RAIN FROM THE MID-ATLANTIC TO NEW ENGLAND, WITH
SOME SNOW BEHIND THE SYSTEM ACROSS THE CENTRAL AND NORTHERN
APPALACHIANS.
PLEASANTLY MILD CONDITIONS FOR EARLY DECEMBER ARE EXPECTED FROM
THE CENTRAL PLAINS TO THE DAKOTAS AND MONTANA ON THURSDAY, WITH
TEMPERATURES RUNNING 15 TO 30 DEGREES ABOVE AVERAGE IN MANY CASES.
THE MILD CONDITIONS THEN REACH THE MIDWEST BY FRIDAY AND MUCH OF
THE EASTERN U.S. FOR THE WEEKEND WITH WIDESPREAD 10-20 DEGREE
ABOVE AVERAGE TEMPERATURES LIKELY, WITH GRADUALLY COOLING
TEMPERATURES ACROSS THE PLAINS. COLDER WEATHER ENVELOPS MUCH OF
THE INTERIOR WEST AND ROCKIES BY THE WEEKEND IN RESPONSE TO THE
UPPER TROUGH/LOW.
HAMRICK
ADDITIONAL 3-7 DAY HAZARD INFORMATION CAN BE FOUND ON THE WPC
MEDIUM RANGE HAZARDS OUTLOOK CHART AT:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,
QUANTITATIVE PRECIPITATION FORECAST, EXCESSIVE RAINFALL OUTLOOK,
WINTER WEATHER OUTLOOK PROBABILITIES, HEAT INDICES AND KEY
MESSAGES ARE AT:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST500_WBG.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST_WBG_CONUS.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/5KM_GRIDS/5KM_GRIDSBODY.HTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/DAY4-7.SHTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=ERO
HTTPS://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=OVW
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