356
FXUS02 KWBC 301856
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
154 PM EST THU NOV 30 2023
VALID 12Z SUN DEC 03 2023 - 12Z THU DEC 07 2023
...A SERIES OF PACIFIC SYSTEMS WILL FOCUS ATMOSPHERIC RIVERS TO
FUEL A WET PATTERN OVER THE NORTHWEST TO INCLUDE HEAVY RAIN AND
INLAND HEAVY SNOW THREATS...
...INLAND AND COASTAL SYSTEMS TO SUPPORT A HEAVY SNOW THREAT FOR
THE NORTHEAST NORTHERN TIER AND VICINITY SUNDAY/MONDAY...
..OVERVIEW
IT REMAINS THE CASE THAT AN AMPLIFIED AND ACTIVE WEATHER PATTERN
IS EXPECTED TO CONTINUE INTO THE MEDIUM RANGE PERIOD, ESPECIALLY
ACROSS THE WESTERN U.S. AS A SERIES OF ATMOSPHERIC RIVERS IMPACTS
THE REGION RAISING CONCERNS FOR HEAVY RAINFALL FOR
WASHINGTON/OREGON COASTAL AREAS AND FAVORABLE WESTERN FACING
SLOPES OF THE CASCADES, WITH HEAVY SNOW FOR PARTS OF THE NORTHERN
INTERMOUNTAIN WEST/ROCKIES. DOWNSTREAM, AN AMPLIFIED TROUGH
PERIODICALLY REINFORCED BY SHORTWAVE ENERGY, WILL SLIDE FROM THE
CENTRAL U.S. INTO THE EAST SUNDAY-MONDAY, WITH A SECOND MAIN
SHORTWAVE ACROSS THE NORTH-CENTRAL U.S. TO THE NORTHEAST MID-NEXT
WEEK. IN BETWEEN THIS TROUGH AND THE NEXT SYSTEM OUT OF THE EAST
PACIFIC, A STRONG RIDGE LOOKS TO BUILD INITIALLY OVER THE WEST ON
TUESDAY, MOVING INTO THE PLAINS WEDNESDAY-THURSDAY BRINGING WELL
ABOVE NORMAL TEMPERATURES, ESPECIALLY ACROSS THE NORTHERN AND
CENTRAL PLAINS.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
GUIDANCE STILL SHOWS PRETTY GOOD AGREEMENT ACROSS THE BOARD WITH
THE OVERALL PATTERN EVOLUTION AND LARGER SCALE FEATURES, BUT
PLENTY OF EMBEDDED SYSTEM TIMING/AMPITUDE VARIABILITY TO VARY LESS
CERTAIN LOCAL WEATHER FOCI. OUT WEST, MODELS AGREE ON THE PRESENCE
OF MULTIPLE ARS DURING THE PERIOD (THE FIRST ON SUNDAY, AND THE
NEXT MOVING IN LATE MONDAY/EARLY TUESDAY) IN A VERY WET PROTRACTED
PATTERN, BUT STILL WITH SOME UNCERTAINTY IN THE AR
TIMING/STRENGTH/DURATION AND IN THE DETAILS AND EXACT LOCATIONS OF
MAXIMUM QPF. CONTINUING TO FEEL THE NBM IS SLIGHTLY TOO WET WITH
QPF VOLUMETRICALLY, SO THE WPC FORECAST TEMPERED THAT DOWN SOME
USING DETERMINISTIC GUIDANCE TO ACCOUNT FOR THE LINGERING
UNCERTAINTIES. IN THE MIDWEST AND THE EAST, RUN TO RUN VARIABILITY
AND TIMING OF INDIVIDUAL SHORTWAVES THIS WEEKEND/EARLY NEXT WEEK
STILL TRANSLATES TO EVEN SOME REGIONAL SENSIBLE
WEATHER/PRECIPITATION UNCERTAINTIES.
OVERALL, A COMPOSITE BLEND OF BEST CLUSTERED GUIDANCE FROM THE 06
UTC GFS/GEFS AND 00 UTC CANADIAN/ECMWF/ECMWF ENSEMBLE MEAN ALONG
WITH THE 13 UTC NATIONAL BLEND OF MODELS AND WPC CONTINUITY SEEMED
TO PROVIDE A SOLID FORECAST BASIS THROUGH MEDIUM RANGE TIME SCALES
WITH SMALLER SCALE VARIANCES SEEMINGLY DECENTLY MITIGATED
CONSISTENT WITH PREDICTABILITY. LATEST 12 UTC GUIDANCE OFFERS
OVERALL FAVORABLE TRENDS, BUT DOES SHOW A MORE AMPLIFIED UPPER
FLOW PATTERN DAYS 5-7.
..WEATHER/HAZARDS HIGHLIGHTS
OUT WEST, PRECIPITATION WILL BE ONGOING AS THIS FORECAST PERIOD
BEGINS SUNDAY, WITH A SERIES OF ATMOSPHERIC RIVERS INTO THE
NORTHWEST CONTINUING WELL INTO NEXT WEEK, WITH GROWING TOTALS AND
IMPACTS POSSIBLE. SOME MODEST RAINFALL TOTALS ARE LIKELY ALONG THE
COAST WITH BOTH EVENTS SUNDAY AND AGAIN LATE MONDAY-WEDNESDAY.
WITH HEAVY RAIN ALSO IN THE FORECAST DURING THE SHORT RANGE, THE
SOILS AND RIVERS MAY BE PRIMED INCREASING THE RISK FOR FLOODING
AND FLASH FLOODING. SNOW LEVELS WITH BOTH SYSTEMS WILL BE VERY
HIGH SO ESPECIALLY WESTERN FACING SLOPES OF THE CASCADES MAY BE
SUBJECT TO AN ADDITIONAL RISK OF FLOODING DUE TO SNOW MELT AS ANY
ACCUMULATING SNOW WILL BE CONFINED TO THE VERY HIGHEST PEAKS (OR
FARTHER INLAND). GIVEN THIS, A MARGINAL RISK FOR EXCESSIVE
RAINFALL WAS INCLUDED ON THE DAY 4 AND 5 EROS ACROSS THIS REGION.
IT IS POSSIBLE A SLIGHT RISK WILL BE NEEDED IN SUBSEQUENT UPDATES
OF THE ERO, BUT AT THIS POINT THERE WAS STILL ENOUGH UNCERTAINTY
TO PRECLUDE THAT. FARTHER INLAND ACROSS NORTHERN PORTIONS OF THE
INTERMOUNTAIN WEST AND ROCKIES, BURSTS OF HEAVY SNOW ARE MOST
LIKELY INTO SUNDAY, AND POSSIBLY AGAIN INTO NEXT MIDWEEK WITH
PASSAGE OF THE NEXT BEST ORGANIZED SYSTEM.
DOWNSTREAM, EJECTING SHORTWAVE ENERGY AND A LEADING/WAVY FRONTAL
SYSTEM MAY CONTINUE TO SUPPORT RAINFALL INTO SUNDAY AND MONDAY
ACROSS THE SOUTHEAST, WITH MUCH OF THE EASTERN U.S. ALSO LOOKING
UNSETTLED THROUGH NEXT WEEK WITH HIGHER UNCERTAINTY ON
PRECIPITATION AMOUNTS GIVEN SHORTWAVE DIFFERENCES. HOWEVER, THE
APPROACH AND PASSAGE OF SEVERAL SHORTWAVES AND ADVANCE OF AN
AMPLIFIED MAIN UPPER TROUGH SHOULD SPAWN SEVERAL WAVY FRONTS TO
FOCUS ACTIVITY. SOME OF THE PRECIPITATION COULD BE IN THE FORM OF
SNOW ACROSS PARTS OF THE GREAT LAKES AND NORTHEAST. FAVORED
TERRAIN OF NORTHERN NEW YORK/NEW ENGLAND MAY BEST FOCUS A
PLOWABLE/HEAVY SNOWFALL THREAT GIVEN LONGEVITY OF THE PATTERN AND
COLD AIR AVAILABILITY LATER WEEKEND INTO EARLY NEXT WEEK.
THROUGH SUNDAY, TEMPERATURES ACROSS THE EAST MAY BE MODERATELY
ABOVE NORMAL, WITH SLIGHTLY BELOW NORMAL TEMPERATURES ACROSS THE
INTERIOR SOUTHWEST. THE WESTERN U.S. SHOULD TREND WARMER WITH TIME
AND ESPECIALLY BY NEXT TUESDAY-THURSDAY IN THE NORTHERN HIGH
PLAINS/PLAINS WHERE DAYTIME HIGHS COULD BE 15 TO 25 DEGREES ABOVE
NORMAL. MEANWHILE, THE EASTERN U.S. SHOULD TREND BACK TOWARDS
NORMAL/SLIGHTLY COOLER THAN NORMAL NEXT WEEK AS REINFORCED
TROUGHING AFFECTS THE AREA.
SANTORELLI/SCHICHTEL
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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