897
FXUS02 KWBC 011844
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
144 PM EST FRI DEC 01 2023
VALID 12Z MON DEC 04 2023 - 12Z FRI DEC 08 2023
...HEAVY RAIN EXPECTED FOR THE PACIFIC NORTHWEST WITH MULTIPLE
ATMOSPHERIC RIVER EVENTS NEXT WEEK...
..SYNOPTIC OVERVIEW
THE MAIN THEME GOING INTO THE FIRST HALF OF NEXT WEEK WILL BE A
STRONG PACIFIC JET STREAM THAT WILL BE ACCOMPANIED BY A SERIES OF
ATMOSPHERIC RIVER EVENTS, WITH HEAVY RAINFALL EXPECTED FOR THE
PACIFIC NORTHWEST. A BUILDING UPPER RIDGE AXIS IS EXPECTED ACROSS
THE INTERMOUNTAIN WEST AND THEN ACROSS THE PLAINS GOING INTO THE
MIDDLE OF THE WEEK WITH WELL ABOVE AVERAGE TEMPERATURES EXPECTED.
MEANWHILE, A BROAD UPPER TROUGH WILL LIKELY BE IN PLACE FROM THE
GREAT LAKES TO THE EAST COAST, WITH A DEPARTING STORM SYSTEM ON
MONDAY, FOLLOWED BY A SASKATCHEWAN SCREAMER (A VARIANT OF THE
ALBERTA CLIPPER) CROSSING THE UPPER MIDWEST AND REACHING THE OHIO
VALLEY THROUGH WEDNESDAY WITH SOME SNOW SHOWERS ACCOMPANYING IT.
A MORE ZONAL FLOW PATTERN ALOFT LIKELY RESUMES AFTER THIS SYSTEM
EXITS THE EAST COAST.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
LATEST MODEL GUIDANCE REMAINS IN RELATIVELY GOOD MODEL AGREEMENT
AT MID-LARGER SCALES TO START NEXT WEEK AND HAS GOOD ENSEMBLE
SUPPORT, ALTHOUGH THE 00 UTC UKMET SEEMED A BIT OUT OF ALIGNMENT
WITH MODEL CONSENSUS. A MODEL COMPOSITE TENDS TO MITIGATE SMALLER
SCALE VARIANCES CONSISTENT WITH PREDICTABILITY. THIS GENERALLY
SEEMS IN LINE WITH THE NATIONAL BLEND OF MODELS GUIDANCE AND WPC
PRODUCT CONTINUITY. GUIDANCE IS STILL SOLIDIFIED ON THE BUILDING
RIDGE OVER THE CENTRAL U.S. THROUGH MIDWEEK, BEFORE TRANSITIONING
MORE TO A ZONAL FLOW TYPE PATTERN BY THURSDAY AND FRIDAY. MODEL
UNCERTAINTIES ARE MORE APPARENT BY THE END OF THE WEEK, AND OF THE
MODELS AND FOR MORE DETAIL, THE 00 UTC ECMWF REMAINED MOST IN LINE
WITH GEFS/ECMWF ENSEMBLE MEANS INTO THESE LONGER TIME FRAMES.
ACCORDINGLY OPTED TO BLEND THIS ECMWF WITH THE GEFS/ECMWF ENSEMBLE
MEAN DURING THE LESS CERTAIN PATTERN TRANSITION.
..WEATHER/HAZARDS HIGHLIGHTS
OUT WEST, PRECIPITATION WILL BE ONGOING ON MONDAY, WITH A SERIES
OF ATMOSPHERIC RIVERS INTO THE NORTHWEST LASTING INTO THE MIDDLE
OF THE WEEK, WITH RISING CREEKS AND RIVER LEVELS EXPECTED. GIVEN
ENHANCED RAINFALL DURING THE WEEKEND, THE SOILS WILL BE MORE
VULNERABLE AND THUS THE POTENTIAL FOR GREATER RUN-OFF AND
FLOODING. SNOW LEVELS ARE INITIALLY EXPECTED TO BE RATHER HIGH,
AND THEREFORE WESTERN FACING SLOPES OF THE CASCADES MAY BE SUBJECT
TO AN ADDITIONAL RISK OF FLOODING DUE TO SNOW MELT. ACCORDINGLY,
COORDINATED THE ISSUANCE OF A SLIGHT RISK AREA FOR WESTERN SLOPES
OF THE WASHINGTON CASCADES FOR MONDAY, SHIFTING A BIT SOUTHWARD
FOR TUESDAY. ALSO, GIVEN A STRONGER MODEL SIGNAL FOR TERRAIN
ENHANCED 3-6 INCH RAINFALL TOTALS ON MONDAY-MONDAY NIGHT ACROSS
THE OLYMPIC PENINSULA, A SLIGHT RISK IS WARRANTED FOR THE DAY 4
EXCESSIVE RAINFALL OUTLOOK FOR THIS AREA. WITH THE ATMOSPHERIC
RIVER FOCUS MOST LIKELY SHIFTING A BIT MORE SOUTH INTO OREGON ON
TUESDAY, A MARGINAL RISK WAS ALSO WARRANTED FOR THE DAY 5 OUTLOOK
FOR WESTERN OREGON INTO THE CASCADES AND OLYMPICS.
FARTHER INLAND ACROSS NORTHERN PORTIONS OF THE INTERMOUNTAIN WEST
AND ROCKIES, SOME MODERATELY HEAVY SNOW IS EXPECTED INTO NEXT
MIDWEEK WITH THE PASSAGE OF THE NEXT ORGANIZED SYSTEM. HEAVY SNOW
IS ALSO EXPECTED FOR NEW ENGLAND INTO MONDAY WITH THE ORGANIZING
COASTAL LOW NEARBY, WITH MAINE LIKELY TO HAVE THE GREATEST IMPACTS
WITH WRAP-BACK FLOW AND UPPER SUPPORT. SOME UPSLOPE SNOW SHOWERS
ARE ALSO LIKELY FOR THE HIGHER ELEVATIONS OF THE CENTRAL
APPALACHIANS GOING INTO MIDWEEK AS THE NEXT LOW PRESSURE SYSTEM
PASSES BY.
IN TERMS OF TEMPERATURES, MUCH OF THE CENTRAL AND NORTHERN PLAINS
WILL ENJOY LATE SEASON WARMTH WITH HIGHS POSSIBLY 20-30 DEGREES
ABOVE EARLY DECEMBER AVERAGES FROM NORTHEAST COLORADO TO THE
CANADIAN BORDER ON WEDNESDAY AND INTO THURSDAY, WITH SOME RECORD
HIGHS WITHIN THE REALM OF POSSIBILITY. THE SAME IS EXPECTED TO
HOLD TRUE WITH OVERNIGHT LOWS AS WELL ACROSS MUCH OF THE CENTRAL
AND WESTERN U.S., WITH THE GREATEST POSITIVE ANOMALIES ACROSS
MONTANA AND THE DAKOTAS. CONDITIONS SHOULD BE CLOSE TO SEASONAL
AVERAGES FOR THE EASTERN U.S. FOR MUCH OF THE WEEK WITH NO MAJOR
ARCTIC AIR INTRUSIONS EXPECTED.
HAMRICK/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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