116
FXUS02 KWBC 240655
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
155 AM EST FRI NOV 24 2023
VALID 12Z MON NOV 27 2023 - 12Z FRI DEC 01 2023
..OVERVIEW
UPPER TROUGHING WILL GENERALLY DOMINATE THE PATTERN OVER PARTS OF
THE CENTRAL AND EASTERN U.S. THROUGH MUCH OF NEXT WEEK, WITH SOME
EMBEDDED SHORTWAVES AND FRONTAL SYSTEMS. A WESTERN ATLANTIC
SURFACE LOW ON MONDAY SHOULD QUICKLY TRACK THROUGH/CLOSE TO MAINE
WITH SOME MODERATE TO LOCALLY HEAVY PRECIPITATION LIKELY ACROSS
NEW ENGLAND. BEHIND THIS, FAVORABLE WESTERLY FLOW AND CHILLY
CONDITIONS SETS THE STAGE FOR ENHANCED LAKE EFFECT SNOWS THROUGH
AT LEAST THE FIRST HALF OF THE WEEK. AN INITIAL RIDGE OVER THE
WESTERN U.S. TO START THE WEEK SHOULD BE REPLACED BY MEAN
TROUGHING AS A COUPLE OF SHORTWAVES SLIDE THROUGH, WITH A POSSIBLE
STRONGER ONE REACHING THE SOUTHWEST BY THE END OF THE WEEK
PROMOTING SOME RIDGE BUILDING DOWNSTREAM ACROSS THE GULF
COAST/SOUTHEAST. WITH THE EXCEPTION OF THE GREAT LAKES, THE
WEATHER FORECAST ACROSS THE CONUS LOOKS FAIRLY QUIET FOR THE
ENTIRE MEDIUM RANGE PERIOD.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
ON THE LARGE SCALE, THERE IS MODEST AGREEMENT IN THE PRESENCE OF
MAINTAINED TROUGHING ACROSS THE EASTERN U.S., BUT A LOT OF SPREAD
IN THE DETAILS OF INDIVIDUAL SHORTWAVES ROUNDING THE BASE OF THE
TROUGH. THIS AFFECTS FRONTAL AND SURFACE WAVE POSITIONS MID TO
LATER IN THE WEEK, WITH MORE UNCERTAINTY THAN DESIRED. THERE IS
ALSO GROWING UNCERTAINTY OUT WEST WITH THE SMALLER SCALE PLACEMENT
OF ENERGY MOVING INTO THE REGION, THROUGH THERE IS A LITTLE BIT
BETTER CONSENSUS ON SOME DEEPENING OF A TROUGH OVER THE SOUTHWEST
LATER IN THE WEEK. GIVEN ABOVE AVERAGE DISAGREEMENT, FELT
INTRODUCING THE ENSEMBLE MEANS INTO THE WPC FORECAST BLEND AS
EARLY AS DAY 3/MONDAY WAS PRUDENT IN AN ATTEMPT TO SMOOTH THESE
DIFFERENCES OUT. WAS ABLE TO USE SOME COMPONENT OF THE GFS/ECMWF
FOR SOME ADDED SYSTEM DEFINITION, AS THESE WERE THE OPERATIONAL
MODELS CLOSEST TO THAT OF THE ENSEMBLE MEANS. GRADUALLY INCREASED
THE PERCENTAGE OF ENSEMBLE MEANS IN THE OVERALL BLEND FROM 20 TO
60% THROUGHOUT THE WEEK. FOR THE MOST PART, THIS MAINTAINED FAIRLY
GOOD CONTINUITY WITH THE PREVIOUS WPC FORECAST. IN TERMS OF QPF,
OR LACK THERE OF, THE ONLY MAJOR CHANGE FROM THE NBM WAS TO
INCREASE QUITE A BIT QPF IN THE GREAT LAKES GIVEN THE LOW BIAS IT
TYPICALLY HAS WITH LAKE EFFECT PRECIPITATION.
..WEATHER/HAZARDS HIGHLIGHTS
A SURFACE LOW JUST OFF THE MID-ATLANTIC COAST ON MONDAY LOOKS TO
TRACK NORTHWARD NEAR OR OVER NEW ENGLAND. THIS COULD SPREAD SOME
MODERATE TO LOCALLY HEAVY PRECIPITATION INTO PARTS OF NEW ENGLAND,
BUT WITH A GENERAL LACK OF INSTABILITY AND HIGHLY ANOMALOUS
MOISTURE COMBINED WITH HOW FAST IT WILL BE MOVING, PROBABILITIES
FOR ANY ADVERSE FLOODING/FLASH FLOODING IMPACTS ARE LESS THAN THE
THRESHOLD FOR EVEN A MARGINAL RISK ON THE DAY 4/MONDAY EXCESSIVE
RAINFALL OUTLOOK. IN THE HIGHER TERRAIN OF NORTHERN NEW ENGLAND,
THIS PRECIPITATION SHOULD FALL AS SNOW. BEHIND THIS SYSTEM,
FAVORABLE WESTERLY COLD FLOW OVER THE STILL RELATIVELY WARM GREAT
LAKES SHOULD PROMOTE A PERIOD OF ACCUMULATING LAKE EFFECT SNOW
ESPECIALLY DOWNWIND OF LAKES ERIE AND ONTARIO ON MONDAY-TUESDAY.
MODELS ARE COMING INTO BETTER AGREEMENT ON A FAVORABLE LAKE EFFECT
EVENT, BUT STILL WITH PLENTY OF UNCERTAINTY IN THE AMOUNTS AND
EXACTLY WHERE THE HEAVIEST SNOWBANDS COULD SET UP. PROBABILITIES
IN THE DAY 4 WINTER WEATHER OUTLOOK WERE INCREASED FROM THE
PREVIOUS WPC SHIFT TO SHOW THIS POTENTIAL. LAKE EFFECT SNOW WILL
BE POSSIBLE DEEPER INTO NEXT WEEK AS WELL BUT WITH LIKELY LIGHTER
AMOUNTS. ELSEWHERE ACROSS THE COUNTRY, CONDITIONS LOOK MOSTLY DRY
THROUGH NEXT WEEK THOUGH SOME LIGHT PRECIPITATION MAY ACCOMPANY A
SHORTWAVE INTO THE WEST AROUND MID WEEK. PRECIPITATION CHANCES
ALONG THE GULF COAST REGION MAY BEGIN TO INCREASE AGAIN BY LATE
WEEK AS A WARM FRONT LIFTS NORTHWARD THROUGH THE GULF OF MEXICO.
MUCH OF THE LOWER 48 SHOULD SEE NEAR TO BELOW NORMAL TEMPERATURES
ESPECIALLY DURING THE FIRST HALF OF NEXT WEEK. DECENT COVERAGE OF
HIGHS AND LOWS 10-15F BELOW CLIMATOLOGY CAN BE EXPECTED FROM THE
GREAT BASIN INTO THE CENTRAL/SOUTHERN PLAINS EARLY IN THE WEEK,
SHIFTING INTO THE EASTERN U.S. TUESDAY-WEDNESDAY WHILE THE
WEST-CENTRAL U.S. BEGIN TO SLIGHTLY MODERATE BACK TOWARDS NORMAL.
AN EXCEPTION TO THE BELOW AVERAGE TEMPERATURES MAY BE ACROSS THE
NORTHERN PLAINS, WHERE BY TUESDAY AND BEYOND LOWS IN THE 20S AND
HIGHS IN THE 40S ARE EXPECTED, WHICH ARE AROUND 5-15F ABOVE
NORMAL. LOWS OF A FEW DEGREES ABOVE AVERAGE AND HIGHS NEAR AVERAGE
IN FLORIDA ON MONDAY ARE LIKELY TO COOL TUESDAY AND BEYOND AFTER A
FRONTAL PASSAGE.
SANTORELLI
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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page