730
FXUS02 KWBC 310657
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
256 AM EDT TUE OCT 31 2023
VALID 12Z FRI NOV 3 2023 - 12Z TUE NOV 7 2023
..SYNOPTIC OVERVIEW
AN EXPANSIVE SURFACE HIGH WILL CONTINUE TO ENCOMPASS MUCH OF THE
EASTERN U.S. FOR THE END OF THE WEEK, WITH THE HIGH SLOWLY MOVING
OFFSHORE OVER THE WEEKEND. THIS AIRMASS WILL SLOWLY MODERATE
AFTER THE WIDESPREAD FROST AND FREEZE CONDITIONS EARLIER IN THE
WEEK. HOWEVER, COLD TEMPERATURES WILL HAVE STAYING POWER FOR THE
NORTHERN PLAINS AND UPPER MIDWEST THROUGH EARLY NEXT WEEK. A
STORM SYSTEM MOVING INLAND ACROSS THE PACIFIC NORTHWEST AND
NORTHERN ROCKIES IS EXPECTED TO INCREASE PRECIPITATION ACROSS
THESE AREAS FOR THE END OF THE WEEK, AND THEN A RENEWED SURGE OF
MOISTURE FOLLOWING THAT AS A SECOND STORM SYSTEM APPROACHES THE
REGION. AN ORGANIZED LOW PRESSURE SYSTEM IS EXPECTED TO DEVELOP
ACROSS THE OHIO VALLEY AND GREAT LAKES REGION BY NEXT TUESDAY.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
MODEL AGREEMENT IS GENERALLY GOOD ACROSS THE CENTRAL/EASTERN U.S.
EARLY IN THE PERIOD, BUT THERE ARE SOME DIFFERENCES NOTED ACROSS
THE EASTERN PACIFIC BY FRIDAY AND THEN ACROSS THE ROCKIES AND
WESTERN HIGH PLAINS GOING INTO SATURDAY REGARDING THE EVENTUAL
AMPLITUDE OF THE TROUGH THAT DEVELOPS. THE OVERALL PATTERN
TRANSITIONS TO A MUCH MORE ZONAL FLOW, AND THESE SITUATIONS TEND
TO HAVE LOWER OVERALL FORECAST CONFIDENCE REGARDING SHORTWAVE
SPECIFICS, AND THIS HOLDS TRUE GOING INTO THE SUNDAY THROUGH
TUESDAY TIME PERIOD WITH LIMITED CONFIDENCE IN ANY PARTICULAR
MODEL RUN. IT APPEARS THE GFS IS TOO STRONG WITH THE FIRST
SHORTWAVE CROSSING THE OHIO VALLEY ON SUNDAY COMPARED TO THE MODEL
CONSENSUS, WHEREAS THE ECMWF APPEARS TOO WEAK. LOOKING AHEAD TO
EARLY NEXT WEEK, THERE IS A SLIGHTLY BETTER SIGNAL FOR THE SECOND
AND POTENTIALLY STRONGER LOW PRESSURE SYSTEM ACROSS THE OHIO
VALLEY AND GREAT LAKES REGION, BUT STILL SIGNIFICANT MODEL SPREAD
ON ITS LOCATION AND MAGNITUDE. ENSEMBLE MEANS ACCOUNTED FOR 60%
OF THE FORECAST BLEND BY NEXT TUESDAY.
..WEATHER/HAZARDS HIGHLIGHTS
SIGNIFICANT RAINFALL HAZARDS ARE NOT EXPECTED FOR MOST OF THE
CONTINENTAL U.S. THROUGH SATURDAY. THE ONLY REGION WHERE THERE
WILL BE A RISK OF EXCESSIVE RAINFALL LEADING TO FLOODING CONCERNS
WILL BE IN THE PACIFIC NORTHWEST WITH THE ENHANCED ONSHORE FLOW
THAT WILL UNFOLD LATE THIS WEEK AND ALSO INTO SATURDAY. THERE IS
A MARGINAL RISK OF EXCESSIVE RAINFALL PLANNED ON DAY 5 (SATURDAY)
FROM NORTHWESTERN CALIFORNIA TO THE OLYMPIC PENINSULA IN
WASHINGTON. LOCALLY HEAVIER RAINFALL ON THE WEST FACING SLOPES
MAY JUST BE ENOUGH TO CAUSE SOME MINOR FLOODING CONCERNS,
ESPECIALLY IN URBAN AND BURN SCAR AREAS. THERE SHOULD BE ENOUGH
OF A LULL ON DAY 4 TO AVOID HAVING A MARGINAL RISK AT THIS TIME.
LOOKING BEYOND SATURDAY, ADDITIONAL MODERATE TO HEAVY RAIN IS
LIKELY FOR THESE SAME AREAS AS ANOTHER POTENTIAL ATMOSPHERIC RIVER
EVENT DEVELOPS WITH A FEW INCHES OF ADDITIONAL RAINFALL DURING THE
SUNDAY-MONDAY TIME PERIOD. SHOWERS WILL LIKELY ALSO INCREASE IN
COVERAGE ACROSS PORTIONS OF THE OHIO VALLEY AND GREAT LAKES REGION
AS THE NEXT LOW PRESSURE SYSTEM GETS BETTER ORGANIZED.
TEMPERATURES WILL START OFF COLD FRIDAY MORNING ACROSS MUCH OF THE
CENTRAL AND EASTERN U.S. WITH A SLOW WARMING TREND ENSUING OVER
THE WEEKEND AS THE AIRMASS CONTINUES TO MODIFY. PLEASANTLY MILD
CONDITIONS WILL ALSO RETURN TO THE ROCKIES AND ADJACENT PORTIONS
OF THE CENTRAL AND SOUTHERN PLAINS THIS WEEKEND. HOWEVER, IT
SHOULD CONTINUE TO REMAIN QUITE CHILLY FOR PARTS OF THE NORTHERN
PLAINS AND UPPER MIDWEST WITH HIGHS GENERALLY RANGING FROM THE
UPPER 20S TO LOWER 40S IN MOST CASES.
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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