332
FXUS02 KWBC 011858
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
258 PM EDT WED NOV 01 2023
VALID 12Z SAT NOV 04 2023 - 12Z WED NOV 08 2023
..SYNOPTIC OVERVIEW
MODELS AND ENSEMBLE MEANS SHOW THIS WEEK'S AMPLIFIED UPPER LEVEL
PATTERN EVOLVING INTO A MORE QUASI-ZONAL FLOW ACROSS THE
CONTINENTAL U.S. GOING INTO THE WEEKEND AND PERSISTING INTO NEXT
WEEK, WITH BROAD CYCLONIC FLOW ALOFT OVER SOUTHERN CANADA
DOWNSTREAM FROM A WESTERN CANADA RIDGE. MOIST FLOW TO THE SOUTH
OF A NORTHEAST PACIFIC MEAN UPPER LOW, POSSIBLY IN THE PROCESS OF
BEING REPLACED TOWARD THE MIDDLE OF NEXT WEEK, WILL LIKELY BRING
UNSETTLED CONDITIONS TO THE PACIFIC NORTHWEST WITH MULTIPLE ROUNDS
OF RAINFALL DURING THE PERIOD. EASTWARD PROGRESSION OF SHORTWAVES
EMBEDDED WITHIN THIS PACIFIC FLOW PLUS POTENTIAL INPUT FROM ENERGY
ON THE SOUTHERN PERIPHERY OF THE CANADIAN STREAM SHOULD SUPPORT
ONE OR MORE SURFACE WAVES/FRONTAL SYSTEMS WITH ASSOCIATED AREAS OF
PRECIPITATION OVER PARTS OF THE CENTRAL/EASTERN U.S. TYPICAL
DIFFICULTY OF RESOLVING SHORTWAVE DETAILS WITHIN THIS REGIME
LOWERS CONFIDENCE IN SPECIFICS OF SYSTEM EVOLUTION AND
CORRESPONDING SENSIBLE WEATHER OVER THE EASTERN HALF OF THE
COUNTRY BY NEXT WEEK.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
MODEL/ENSEMBLE SPREAD AND RUN-TO-RUN VARIABILITY OVER THE PAST
12-24 HOURS ARE HIGHLIGHTING THE CHALLENGE OF FORECASTING
IMPORTANT DETAILS WITHIN THE FORECAST LOW-AMPLITUDE FLOW REGIME.
THIS IS PARTICULARLY TRUE FOR THE SYSTEM WHICH THE MAJORITY OF
GUIDANCE HAS BEEN SHOWING OVER THE GREAT LAKES/OHIO VALLEY AS OF
EARLY TUESDAY AND CONTINUING EASTWARD THEREAFTER. 24 HOURS AGO
THERE WAS A FAIRLY STRONG GROUPING OF ECMWF/CMC RUNS AND
GEFS/ECENS/CMCENS MEANS RELATIVE TO THE FASTER GFS RUNS. 00Z/06Z
GUIDANCE DEVELOPED A SIGNIFICANT TIMING DIVERGENCE BY NEXT TUESDAY
AND ESPECIALLY WEDNESDAY, WITH THE CMC/CMCENS SLOWEST AND GFS
FASTEST. THERE WAS ALSO THE INTERESTING CONTRAST OF THE 00Z ECMWF
TRENDING FASTER FROM CONTINUITY AND ITS ENSEMBLE MEAN (AND THE NEW
12Z ECMWF REMAINS AT LEAST AS FAST) VERSUS THE LATEST GEFS MEANS
ADJUSTING A LITTLE SLOWER BY WEDNESDAY. THE 12Z GFS/CMC ADD MORE
INTRIGUE WITH OTHER POSSIBILITIES FOR SHORTWAVE INFLUENCE ON
FRONTAL WAVE DEVELOPMENT. PREFERENCE FOR THE UPDATED FORECAST
BASED ON 00Z/06Z SOLUTIONS WAS AN INTERMEDIATE APPROACH THAT
STAYED FAIRLY CLOSE TO CONTINUITY WHILE AWAITING MORE CONFIDENCE
IN ANY SIGNIFICANT CHANGES.
ELSEWHERE, WEAKER TRENDS IN THE GFS AND MORE SIGNALS IN OTHER
GUIDANCE HAVE YIELDED SOMEWHAT BETTER AGREEMENT FOR A MODEST WAVE
BRUSHING THE UPPER GREAT LAKES AROUND SUNDAY. HOWEVER THERE HAVE
BEEN SOME CHANGES IN DYNAMIC SUPPORT WITH MORE INFLUENCE FROM
SOUTHERN CANADA SHORTWAVE ENERGY COMPARED TO YESTERDAY. ECMWF
TRENDS HAVE IMPROVED GUIDANCE AGREEMENT WITH THE EASTERN PACIFIC
INTO PACIFIC NORTHWEST SURFACE EVOLUTION DURING THE WEEKEND.
THERE ARE STILL SOME DIFFERENCES WITH SURFACE DETAILS
MONDAY-WEDNESDAY BUT A BLEND APPROACH MAINTAINS GOOD CONTINUITY IN
PRINCIPLE. MODELS/MEANS GENERALLY SUGGEST THAT EASTERN PACIFIC
UPPER TROUGH ENERGY SHOULD PROGRESS INLAND NEXT WEDNESDAY. THE
12Z GFS APPEARS TO STRAY SOMEWHAT ON THE FAST SIDE AT THAT TIME.
FORECAST PREFERENCES LED TO STARTING WITH A 00Z/06Z OPERATIONAL
MODEL COMPOSITE EARLY IN THE PERIOD, FOLLOWED BY INCORPORATION OF
HALF OR MORE TOTAL WEIGHT OF WPC CONTINUITY AND THE 06Z GEFS/00Z
ECENS MEANS RELATIVE TO LINGERING INPUT FROM THE GFS/ECMWF/CMC.
..WEATHER/HAZARDS HIGHLIGHTS
MOST OF THE CONTINENTAL U.S. SHOULD NOT SEE ANY SIGNIFICANT
RAINFALL HAZARDS THROUGH THIS COMING 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. A MARGINAL RISK OF
EXCESSIVE RAINFALL HAS BEEN MAINTAINED 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. GUIDANCE IS ALSO SHOWING POTENTIAL FOR
ENHANCED RAINFALL OVER WESTERN IDAHO AND NORTHEASTERN OREGON BUT
FOR NOW THE HOURLY RAIN RATES DO NOT APPEAR TO BE HIGH ENOUGH TO
WARRANT A RISK AREA. LOOKING AHEAD TO DAY 5 (SUNDAY), ADDITIONAL
MODERATE TO HEAVY RAIN IS LIKELY FOR AREAS SLIGHTLY FARTHER NORTH
ALONG THE WEST COAST AS ANOTHER POTENTIAL ATMOSPHERIC RIVER EVENT
DEVELOPS WITH 1-2 INCHES OF ADDITIONAL RAINFALL DURING THAT TIME
PERIOD. EXPECT PRECIPITATION FROM THE PACIFIC NORTHWEST INTO THE
ROCKIES TO TREND LIGHTER BY THE MIDDLE OF NEXT WEEK. HIGHER
ELEVATIONS MAY SEE SOME SNOW THROUGH THE PERIOD.
ACROSS THE EASTERN HALF OF THE COUNTRY, A LEADING WEAK WAVE
BRUSHING THE GREAT LAKES AND ASSOCIATED FRONT MAY PRODUCE SOME
LIGHT PRECIPITATION OVER THE NORTHERN TIER, GREAT LAKES, AND
NORTHERN NEW ENGLAND DURING THE WEEKEND. A BETTER DEFINED SYSTEM
MAY BRING A BROADER AREA OF PRECIPITATION TO THE EASTERN HALF OF
THE COUNTRY DURING THE EARLY TO MIDDLE PART OF NEXT WEEK.
CONFIDENCE IS BELOW AVERAGE FOR THE COVERAGE/INTENSITY/TIMING OF
THIS PRECIPITATION DUE TO SIGNIFICANT GUIDANCE DIFFERENCES FOR
STRENGTH AND TIMING OF THE POTENTIAL PRIMARY SURFACE SYSTEM AS
WELL AS POSSIBLE WAVE DEVELOPMENT ALONG THE TRAILING FRONT.
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.
LOCATIONS ALONG AND NEAR THE CANADIAN BORDER MAY SEE SOME SNOW
DURING THE PERIOD WHILE RAIN WILL BE THE PREVAILING PRECIPITATION
TYPE ELSEWHERE.
TEMPERATURES WILL CONTINUE A SLOW WARMING TREND OVER THE EAST THIS
WEEKEND AS THE CURRENT CHILLY AIRMASS MODIFIES AND READINGS RETURN
TO NEAR SEASONAL AVERAGES. ABOVE AVERAGE TEMPERATURES WILL LIKELY
SPREAD ACROSS MUCH OF THE CENTRAL AND EASTERN U.S. EARLY NEXT
WEEK, AHEAD OF A FRONT REACHING THE PLAINS BY MONDAY. SOME HIGHS
MAY REACH 10-15F ABOVE NORMAL WITH SLIGHTLY HIGHER ANOMALIES
POSSIBLE FOR MORNING LOWS. EXPECT A COOLING TREND OVER MOST
LOCATIONS ASIDE FROM THE FAR SOUTHERN TIER BY TUESDAY-WEDNESDAY AS
THE FRONT PROGRESSES EASTWARD. PLEASANTLY MILD CONDITIONS WILL
ALSO RETURN TO THE ROCKIES AND ADJACENT PORTIONS OF THE CENTRAL
AND SOUTHERN PLAINS THIS WEEKEND. HOWEVER, QUITE CHILLY
CONDITIONS WILL PERSIST OVER PARTS OF THE NORTHERN PLAINS AND
UPPER MIDWEST WITH HIGHS OF 5-10F BELOW NORMAL, RANGING FROM THE
UPPER 20S TO LOWER 40S IN MOST CASES. THE COLDEST WEATHER SHOULD
BE OVER NORTHERN NORTH DAKOTA.
RAUSCH/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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