592
FXUS02 KWBC 241908
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
208 PM 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 NEW
ENGLAND WITH SOME MODERATE TO LOCALLY HEAVY PRECIPITATION LIKELY
THERE. 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 WEST 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, AND THEN PERHAPS SOME WET WEATHER ENTERING THE
SOUTH-CENTRAL U.S. BY THURSDAY, THE WEATHER FORECAST ACROSS THE
CONUS LOOKS FAIRLY QUIET FOR THE ENTIRE MEDIUM RANGE PERIOD.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
WHILE THE PATTERN ON THE SYNOPTIC SCALE SHOWING TROUGHING IN THE
EASTERN HALF OF THE U.S. THROUGH AT LEAST THE MIDDLE OF NEXT WEEK
IS IN GOOD AGREEMENT, THE DETAILS OF INDIVIDUAL SHORTWAVES
AFFECTING FRONTAL AND SURFACE WAVE POSITIONS STILL HAVE LOWER
CONFIDENCE THAN DESIRED. THE FIRST FORECAST CHALLENGE WITH THIS IS
THE TIMING AND PLACEMENT OF A NOR'EASTER AFFECTING NEW ENGLAND AT
THE START OF THE PERIOD MONDAY. MOST OF THE MODELS IN THE 00/06Z
CYCLE SPED UP THE SURFACE LOW A TAD, PUTTING IT OVER EASTERN
MASSACHUSETTS 12Z MONDAY. THE GFS RUNS, UKMET, AND MANY GEFS
MEMBERS ALL SHOWED THIS, WHILE THE CMC AND CMC ENSEMBLE WERE EVEN
A BIT FASTER, BUT THE ECMWF SUITE WAS A BIT SLOWER, ESPECIALLY THE
DETERMINISTIC 00Z EC. SINCE EVEN THE ECMWF-BASED MACHINE LEARNING
MODELS WERE FASTER THAN THE EC, THE WPC FORECAST FAVORED THE
FASTER TREND, MOST LIKE THE MIDDLE GROUND GFS/GEFS SOLUTIONS. THE
NEWER 12Z ECMWF IS FASTER THAN ITS 00Z RUN BUT STILL NOT QUITE AS
FAST AS OTHER GUIDANCE. THE LOW SHOULD TRACK QUICKLY INTO CANADA
MONDAY-TUESDAY. AFTER THAT THERE IS INCREASING UNCERTAINTY IN THE
DETAILS WITHIN THE TROUGH PATTERN.
MEANWHILE ACROSS THE WEST, FORTUNATELY MODELS HAVE CONVERGED
SOMEWHAT ON THE PATTERN, WITH SOUTHWEST U.S. ENERGY THAT WAS
COMPLICATING THE PATTERN APPEARING WEAKER NOW. SO THE TIMING OF
THE UPPER LOW TRACKING EAST FROM THE PACIFIC HAS IMPROVED THOUGH
THE GFS RUNS ARE FARTHER SOUTH THAN OTHER GUIDANCE, AND THEN
ESTABLISHES TROUGHING ACROSS THE WEST. BY THE LATTER PART OF THE
WEEK THOUGH, ADDITIONAL ENERGY COMING INTO THE WEST SHOWS
INCREASING SPREAD.
SIMILAR TO THE PREVIOUS SHIFT, USED A BLEND OF MAINLY
DETERMINISTIC MODELS EARLY IN THE FORECAST PERIOD BUT WITH SOME
ENSEMBLE MEAN COMPONENT TO SMOOTH OUT INDIVIDUAL MODEL
DIFFERENCES. GRADUALLY INCREASED THE PERCENTAGE OF ENSEMBLE MEANS
IN THE OVERALL BLEND TO HALF THROUGHOUT THE WEEK. FOR THE MOST
PART, THIS MAINTAINED FAIRLY GOOD CONTINUITY WITH THE PREVIOUS WPC
FORECAST, THOUGH SOME CHANGES IN FRONTS WERE MADE. IN TERMS OF
QPF, OR LACK THEREOF, 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 LOOKS TO TRACK NORTHWARD NEAR OR OVER NEW ENGLAND ON
MONDAY. THIS COULD SPREAD SOME MODERATE TO LOCALLY HEAVY
PRECIPITATION INTO PARTS OF NEW ENGLAND WITH A QUICK PUSH OF HEAVY
RAINFALL IN COASTAL AREAS, 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 GIVEN THE SMALL
SCALE OF THE HEAVY SNOWBANDS, MINOR SHIFTS IN LOCATION OF THE
BANDS WOULD PROVIDE CONSIDERABLY DIFFERENT CONDITIONS AND
ACCUMULATIONS OVER SLIGHTLY DIFFERENT AREAS. 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 MIDWEEK. PRECIPITATION CHANCES
ALONG THE GULF COAST REGION TO PERHAPS AS FAR NORTH AS THE MIDDLE
MISSISSIPPI VALLEY 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
THROUGH THE FIRST HALF OF NEXT WEEK. DECENT COVERAGE OF HIGHS AND
LOWS 10-15F BELOW CLIMATOLOGY CAN BE EXPECTED FROM THE FOUR
CORNERS STATES INTO THE CENTRAL/SOUTHERN PLAINS AND
MISSISSIPPI/OHIO VALLEYS ON MONDAY, SHIFTING INTO THE EASTERN U.S.
TUESDAY-WEDNESDAY WHILE THE WEST-CENTRAL U.S. MODERATES BACK
TOWARD NORMAL. HOWEVER, THE INTERIOR WEST LOOKS TO COOL BACK DOWN
DURING THE LATTER HALF OF THE WEEK DUE TO TROUGHING ALOFT. 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. BY THURSDAY AND ESPECIALLY FRIDAY, SOUTHERLY FLOW OFF THE
WARM GULF OF MEXICO LOOKS TO RAMP UP AND INCREASE TEMPERATURES,
ESPECIALLY LOWS, IN THE SOUTH-CENTRAL U.S. LOWS OF A FEW DEGREES
ABOVE AVERAGE AND HIGHS NEAR AVERAGE IN FLORIDA ON MONDAY ARE
LIKELY TO COOL TUESDAY-WEDNESDAY AFTER A FRONTAL PASSAGE, BEFORE
SLOWLY REBOUNDING.
TATE/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
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