113
FXUS02 KWBC 181909
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
209 PM EST SAT NOV 18 2023
VALID 12Z TUE NOV 21 2023 - 12Z SAT NOV 25 2023
..PATTERN OVERVIEW
CONFIDENCE REMAINS FAIR AT BEST GIVEN THAT THE LATEST RUNS OF
GUIDANCE CONTINUE TO DIVERGE ON THE TRACK AND EVOLUTION OF THE
SYSTEM EXPECTED TO TRACK NORTHEASTWARD FROM THE MISSISSIPPI VALLEY
FROM TUESDAY ONWARD, SPREADING A BROAD AREA OF PRECIPITATION OVER
THE EAST JUST AHEAD OF THE THANKSGIVING HOLIDAY. ADDITIONALLY,
THERE IS POTENTIAL FOR TRAILING WAVINESS DUE TO ANY CENTRAL U.S.
INTO NORTHWESTERN MEXICO TROUGH ENERGY THAT MAY HAPPEN TO
CONSOLIDATE AND THEN EJECT EASTWARD/NORTHEASTWARD. A SHORTWAVE
TROUGH IS DEPICTED TO ENTER THE PACIFIC NORTHWEST BY THE LATER
PERIODS AND IN COMBINATION WITH SOUTHERN CANADA/NORTHERN TIER U.S.
FLOW SHOULD YIELD A MEAN TROUGH WITH AN AXIS EXTENDING
SOUTHWESTWARD FROM THE NORTHERN PLAINS/UPPER MIDWEST. TEMPERATURES
WILL BE VARIABLE LEADING UP TO THANKSGIVING BUT THERE WILL BE A
GENERAL COLDER TREND SPREADING SOUTH THROUGH THE CENTER OF THE
COUNTRY.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE LATEST GUIDANCE HAS CONTINUED TO FAVOR A NORTHWARD SHIFT WITH
AN UPPER TROUGH/LOW PASSING NORTH OF THE GREAT LAKES WITH A WEAKER
LOW PRESSURE OVER THE EASTERN U.S. THE PLACEMENT OF SCATTERED TO
WIDESPREAD PRECIPITATION ACROSS THE EASTERN U.S. CONTINUES TO VARY
FROM THE MID-ATLANTIC TO NORTHERN NEW ENGLAND. THE RESULTANT
PRECIPITATION WILL LIKELY BE BENEFICIAL TO PORTIONS OF THE
SOUTHEAST AND MID-ATLANTIC WHERE CONDITIONS HAVE BEEN DRIER OF
LATE.
THE GFS PERSISTS IN DEVELOPING A SECONDARY SURFACE SYSTEM ACROSS
THE CENTRAL U.S. AS DIGGING NORTHERN ENERGY EXTENDS THE TROUGH
FURTHER SOUTHWEST INTO THE SOUTHERN ROCKIES/SOUTHWEST... THE UKMET
IS TRENDING TOWARD THAT SOLUTION AS WELL. BOTH WERE DEEMED
EXTREMES AND WERE NOT UTILIZED FOR THIS FORECAST. SOLUTIONS
CONTINUE TO VARY FOR THE UPPER TROUGH MOVING INTO THE WEST, WITH
MINIMAL CONFIDENCE IN ANY SPECIFIC SOLUTION BY LATE IN THE PERIOD.
THIS LACK OF CONFIDENCE APPLIES TO THE SURFACE PATTERN FARTHER
EAST, WITH CONSECUTIVE OPERATIONAL RUNS VARYING CONSIDERABLY BY
NEXT SATURDAY.
GIVEN NO APPRECIABLE IMPROVEMENT IN THE GUIDANCE, THE WPC BLEND
MAINTAINED CONTINUITY BY USING EQUAL WEIGHTS OF THE PAST TWO
CYCLES OF THE ECWMF, GEFS MEANS AND THE EC/CMC ENSEMBLE MEANS.
..WEATHER/HAZARDS HIGHLIGHTS
A BROAD AREA OF PRECIPITATION IS EXPECTED TO AFFECT THE EASTERN
U.S. TUESDAY INTO WEDNESDAY WITH SOME POSSIBLE ADVERSE EFFECTS ON
HOLIDAY TRAVEL. DURING THE PERIOD COVERED BY THE DAYS 4-5
EXCESSIVE RAINFALL OUTLOOKS (TUESDAY THROUGH WEDNESDAY NIGHT), THE
BEST POTENTIAL FOR HEAVIEST RAINFALL SHOULD EXTEND FROM NEAR THE
CENTRAL GULF COAST NORTHEASTWARD THROUGH THE MID-ATLANTIC AND
PARTS OF SOUTHERN/EASTERN NEW ENGLAND. THE NEW DAY 4 OUTLOOK
MAINTAINS THE PRIOR MARGINAL RISK, WITH A MODEST ADJUSTMENTS NEAR
THE SOUTHEAST AND CENTRAL APPALACHIANS. INITIALLY DRY SOIL
CONDITIONS SHOULD TEMPER RUNOFF ISSUES SOMEWHAT WITHIN MOST OF THE
MARGINAL RISK AREA, BUT STILL EXPECT SOME LOCATIONS WHERE DRAINAGE
IS IMPAIRED (DUE TO URBANIZATION/LEAVES/ETC) TO HAVE SOME
SENSITIVITY TO PERIODS OF HEAVIER RAIN. THE DAY 5 MARGINAL RISK
AREA OVER EASTERN NEW ENGLAND, WITH THE MOST LIKELY FORECAST
SCENARIO HAVING A FRONTAL WAVE PROMOTING A PERIOD OF STRONG
ONSHORE FLOW AHEAD OF IT TO ENHANCE RAINFALL TOTALS. AS WITH
AREAS TO THE SOUTH THE PRIOR DAY, RELATIVELY DRY GROUND CONDITIONS
MAY HELP TO MITIGATE RUNOFF ISSUES TO SOME DEGREE BUT LOCALIZED
SENSITIVITY MAY STILL EXIST.
ELSEWHERE, SNOW WILL BE POSSIBLE OVER PARTS OF INTERIOR NEW
ENGLAND AT THE START OF THE TUESDAY-WEDNESDAY EVENT. A PERIOD OF
LAKE EFFECT SNOW WILL BE POSSIBLE AFTER SYSTEM PASSAGE, WITH
DURATION AND TOTALS DEPENDENT ON HOW QUICKLY THE SYSTEMS LIFTS
AWAY. WINDS SHOULD BE BRISK BEHIND THE SYSTEM BUT NOT AS STRONG
AS THEY WOULD HAVE BEEN BASED ON SOME EARLIER FORECASTS OF A
STRONGER GREAT LAKES INTO CANADA STORM. WITH VERY UNCERTAIN
DETAILS, ONE OR MORE WAVES COULD PRODUCE ADDITIONAL AREAS OF
RAINFALL ACROSS THE SOUTHERN/EASTERN U.S. AFTER MIDWEEK. OVER THE
WEST, A SYSTEM MOVING INTO THE REGION LATE IN THE WEEK MAY BRING
MOSTLY LIGHT TOTALS ACROSS NORTHERN AREAS, POSSIBLY EXTENDING INTO
THE PLAINS BY FRIDAY. THERE IS SOME POTENTIAL FOR LOCALLY HEAVIER
SNOWFALL IN PARTS OF THE NORTHERN ROCKIES AROUND THANKSGIVING, BUT
STILL WITH A LOT OF UNCERTAINTY IN THE DETAILS.
THE MOST PROMINENT TEMPERATURE ANOMALIES DURING THE PERIOD WILL BE
WITH COLDER AIR DROPPING SOUTH THROUGH THE PLAINS/EASTERN SLOPES
OF THE ROCKIES AROUND NEXT FRIDAY-SATURDAY, WITH AN EXPANDING AREA
OF HIGHS 10-15F BELOW NORMAL. OTHERWISE, MODERATELY BELOW NORMAL
READINGS WILL PROGRESS EASTWARD THROUGH THE SOUTHERN TIER AND
EASTERN U.S. FROM TUESDAY INTO THANKSGIVING, WHILE AN INITIAL
UPPER RIDGE OVER THE WEST WILL SUPPORT ABOVE NORMAL TEMPERATURES
INTO MIDWEEK BEFORE A GRADUAL COOLING TREND.
CAMPBELL/RAUSCH
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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