953
FXUS02 KWBC 010659
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
258 AM EDT WED NOV 1 2023
VALID 12Z SAT NOV 4 2023 - 12Z WED NOV 8 2023
..SYNOPTIC OVERVIEW
THE AMPLIFIED UPPER LEVEL PATTERN DURING THE SHORT RANGE FORECAST
PERIOD IS FORECAST TO EVOLVE INTO A MORE QUASI-ZONAL FLOW ACROSS
THE CONTINENTAL U.S. GOING INTO THE WEEKEND, WITH BROAD CYCLONIC
FLOW ALOFT OVER SOUTHERN CANADA. SHORTWAVE PERTURBATIONS
ORIGINATING FROM A LARGE UPPER LEVEL GYRE OVER THE NORTHEASTERN
PACIFIC WILL QUICKLY TRACK EASTWARD, AND THE TROUGH THAT DEVELOPS
ACROSS THE PLAINS BY MONDAY WILL LIKELY SPUR SURFACE CYCLOGENESIS
ACROSS THE OHIO VALLEY AND GREAT LAKES REGION BY TUESDAY, AND THEN
REACHING THE EAST COAST BY WEDNESDAY. UNSETTLED CONDITIONS ARE
EXPECTED TO CONTINUE ACROSS THE PACIFIC NORTHWEST WITH MULTIPLE
ROUNDS OF RAINFALL.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
WITH THE TRANSITION TO A MORE ZONAL UPPER LEVEL FLOW PATTERN AND
THE RELATIVELY FAST PROGRESSION OF INDIVIDUAL SHORTWAVES, THERE IS
TYPICALLY A REDUCTION IN FORECAST CONFIDENCE AND THIS HOLDS TRUE
IN THIS CASE. MODELS HAVE STRUGGLED WITH LOW AND FRONTAL
PLACEMENT WITH THE STORM SYSTEM APPROACHING THE PACIFIC NORTHWEST
ON SATURDAY, AND EARLIER RUNS OF THE ECMWF HAVE APPEARED DISPLACED
TO THE EAST OF THE MODEL CONSENSUS, SO LITTLE IN THE WAY OF ECMWF
WAS USED DURING THE WEEKEND TIME PERIOD. HOWEVER, THE 00Z ECMWF
IS IN MUCH BETTER AGREEMENT HERE. LOOKING AHEAD TO EARLY-MID NEXT
WEEK, THE GFS IS QUITE FAST WITH TAKING THE SURFACE LOW ACROSS NEW
ENGLAND AND THEN OFFSHORE, AND WELL AHEAD OF ITS OWN ENSEMBLE
MEANS, SO THE GFS WAS NOT FAVORED BY THIS TIME. TO ACCOUNT FOR
THE UNCERTAINTIES IN THE MODEL GUIDANCE, ABOUT 25% OF THE PREVIOUS
WPC PRESSURES WAS INCORPORATED FOR DAYS 3 THROUGH 6, AND ENSEMBLE
MEANS WERE GRADUALLY INCREASED, AND BY NEXT WEDNESDAY UP TO 70% OF
THE MEANS WERE USED.
..WEATHER/HAZARDS HIGHLIGHTS
SIGNIFICANT RAINFALL HAZARDS ARE NOT EXPECTED FOR MOST OF THE
CONTINENTAL U.S. THROUGH NEXT WEEKEND. SIMILAR TO THE PAST FEW
DAYS, THE ONLY REGION WHERE THERE WILL BE A RISK OF EXCESSIVE
RAINFALL LEADING TO POTENTIAL FLOODING CONCERNS WILL BE IN THE
COASTAL RANGES OF THE PACIFIC NORTHWEST WITH THE ENHANCED ONSHORE
FLOW THAT WILL CONTINUE INTO THE WEEKEND. THERE IS A MARGINAL
RISK OF EXCESSIVE RAINFALL PLANNED ON DAY 4 (SATURDAY) FROM
NORTHWESTERN CALIFORNIA TO THE OREGON CASCADES AND COASTAL RANGES.
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. LOOKING AHEAD TO DAY 5 (SUNDAY), ADDITIONAL
MODERATE TO HEAVY RAIN IS LIKELY FOR AREAS SLIGHTLY FARTHER NORTH
AS ANOTHER POTENTIAL ATMOSPHERIC RIVER EVENT DEVELOPS WITH 1-2
INCHES OF ADDITIONAL RAINFALL DURING THAT TIME PERIOD. ACROSS THE
EASTERN U.S., WIDESPREAD LIGHT TO MODERATE RAIN WILL LIKELY
DEVELOP FROM THE MIDWEST TO THE OHIO VALLEY AND GREAT LAKES REGION
AS THE NEXT LOW PRESSURE SYSTEM GETS BETTER ORGANIZED, AND THIS
RAINFALL SHOULD REACH THE EAST COAST BY LATE TUESDAY INTO
WEDNESDAY.
TEMPERATURES WILL CONTINUE A SLOW WARMING TREND OVER THE WEEKEND
AS THE AIRMASS MODIFIES ACROSS THE EASTERN U.S. AND READINGS
RETURN TO NEAR SEASONAL AVERAGES. SOME SLIGHTLY ABOVE AVERAGE
TEMPERATURES ARE LIKELY BY MONDAY ACROSS A LARGE PORTION OF THE
CENTRAL AND EASTERN U.S. AHEAD OF THE NEXT FRONT, AND THEN COOLING
BACK DOWN BY MID-WEEK. 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, WITH THE COLDEST WEATHER OVER NORTHERN NORTH
DAKOTA.
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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