256
FXUS02 KWBC 231900
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
159 PM EST THU NOV 23 2023
VALID 12Z SUN NOV 26 2023 - 12Z THU NOV 30 2023
..OVERVIEW
A BROADENING AND FAIRLY DEEP UPPER TROUGH WILL DOMINATE THE
PATTERN OVER THE CENTRAL AND EASTERN U.S. THROUGH MUCH OF NEXT
WEEK, WITH SOME EMBEDDED SHORTWAVES AND FRONTAL SYSTEMS. ONE
SURFACE LOW TRACKING NORTH THROUGH THE WESTERN ATLANTIC IS LIKELY
TO BRUSH THE NORTHEAST AROUND MONDAY AND ENHANCE PRECIPITATION
THERE, BEHIND WHICH WESTERLY FLOW AND CHILLY CONDITIONS WILL
PROMOTE LAKE EFFECT SNOW THROUGH THE FIRST HALF OF THE WEEK. THE
PATTERN IN THE WEST IS MORE COMPLEX AND UNCERTAIN, AS ENERGY COULD
LINGER OVER THE SOUTHWEST WHILE UPPER RIDGING BUILDS IN THE
NORTHWEST EARLY IN THE WEEK BUT THEN MODEL SPREAD INCREASES WITH
WHEN/HOW THESE FEATURES COULD INTERACT WITH AN UPSTREAM TROUGH
COMING THROUGH THE EASTERN PACIFIC. THIS OVERALL PATTERN SHOULD
LEAD TO RELATIVELY DRY AND COOL CONDITIONS ACROSS THE LOWER 48.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE IS REASONABLY AGREEABLE EARLY IN THE FORECAST
PERIOD SUNDAY-MONDAY AS ENERGY DIGGING THROUGH SOUTH-CENTRAL
CANADA CAUSES TROUGHING TO EXPAND ACROSS THE EAST-CENTRAL U.S. AND
RIDGING COMES INTO THE NORTHWEST. AT THE SURFACE, A NOR'EASTER
LOOKS TO TRACK QUICKLY NORTH THROUGH THE ATLANTIC WITH A PATH
TRENDING FARTHER WEST OVER THE PAST DAY, POTENTIALLY OVER EASTERN
PARTS OF NEW ENGLAND, WHICH WOULD INCREASE PRECIPITATION POTENTIAL
IN THE NORTHEAST. THE 12Z MODELS MAINTAIN THIS TRACK ALONG WITH A
SLIGHTLY SLOWER TREND IN THE NEWER 12Z GFS/ECMWF. AFTER THAT THE
DETAILS OF THE TROUGH GET MORE UNCERTAIN BASED PARTLY ON THE
PLACEMENT OF AN UPPER LOW WITHIN IT IN CANADA BY TUESDAY/DAY 5.
GFS RUNS HAVE BEEN FARTHEST EAST TOWARD THE ST. LAWRENCE RIVER
WITH THE CENTROID OF THE LOW LIKELY COMBINING WITH OTHER ENERGY,
WHILE THE CMC RUNS ARE WEST OF JAMES BAY. SHORTWAVES WITHIN THE
TROUGH SHOW A LOT OF VARIABILITY AND THIS AFFECTS THE FRONTAL AND
SURFACE WAVE POSITIONS TUESDAY-THURSDAY, FOR MORE UNCERTAINTY THAN
DESIRED.
SPEAKING OF UNCERTAINTY, MODEL SOLUTIONS CONTINUE TO VARY OVER THE
WEST FIRST WITH ENERGY PULLED WEST INTO THE SOUTHWEST U.S. AND
THEN HOW UPSTREAM PACIFIC ENERGY (IN THE FORM OF A CLOSED LOW THAT
OPENS UP AS IT PROGRESSES EAST) MAY INTERACT WITH IT. ECMWF RUNS
HAVE THE SOUTHWEST ENERGY TRACKING FAR ENOUGH WEST THAT IT
INTERACTS MORE WITH THE PACIFIC FEATURE BY AROUND TUESDAY COMPARED
TO OTHER GUIDANCE, THOUGH THE 12Z CMC HAS STARTED TRENDING IN THIS
DIRECTION. OVERALL THE RIDGE THAT BEGINS OVER THE NORTHWEST SHOULD
BE GRADUALLY WEAKENING AS IT PUSHES EAST WITH A MORE TROUGHY
PATTERN FOR THE WEST, BUT THE SPECIFICS ARE YET TO BE DETERMINED.
THE WPC FORECAST WAS BASED ON A BLEND OF THE 00Z/06Z GFS AND 00Z
ECMWF, CMC, AND UKMET EARLY IN THE PERIOD. INCREASED THE
PROPORTION OF THE GEFS AND EC ENSEMBLE MEANS AS THE PERIOD
PROGRESSED, AMID INCREASING SPREAD. ADDITIONALLY, INCREASED QPF IN
THE GREAT LAKES COMPARED TO THE NBM GIVEN THE LOW BIAS IT HAS WITH
LAKE EFFECT PRECIPITATION.
..WEATHER/HAZARDS HIGHLIGHTS
SOME MOISTURE MAY POOL NEAR A FRONTAL BOUNDARY AND WAVE OF LOW
PRESSURE NEAR THE GULF COAST ON SUNDAY FOR SOME SHOWER POTENTIAL
OVER THE GULF COAST STATES. MEANWHILE A SEPARATE LOW DEVELOPING
OFF THE CAROLINAS AND LIFTING NORTHWARD THROUGH THE WESTERN
ATLANTIC IS TRENDING TOWARD A TRACK CLOSER TO OR OVER NEW ENGLAND
AND IS LIKELY TO SPREAD SOME PRECIPITATION TO THE NORTHEAST. SNOW
IS POSSIBLE IN THE INTERIOR REGIONS AND ESPECIALLY IN THE HIGHER
ELEVATIONS. AREAS CLOSER TO THE COAST MAY SEE A BRIEF BOUT OF
HEAVY RAIN, AND TOTALS HAVE INCREASED FROM THE PREVIOUS FORECAST
GIVEN THE LOW TRACK. HOWEVER, THIS RAIN SHOULD BE MOVING QUICKLY
SO THE DAYS 4-5 EXCESSIVE RAINFALL OUTLOOKS REMAIN WITH NO RISK
AREAS. BEHIND THIS SYSTEM, COLD FLOW WILL SUPPORT AREAS OF LAKE
EFFECT SNOW THAT MAY PERSIST THROUGH AT LEAST MIDWEEK. GENERALLY
DRY CONDITIONS ARE LIKELY ELSEWHERE, WITH PERHAPS SOME LIGHT
PRECIPITATION PERHAPS COMING INTO THE WEST BY MIDWEEK AFTER A DRY
PERIOD AND SOME MOIST RETURN FLOW INTO THE GULF COAST AROUND
MIDWEEK AS WELL.
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. SLIGHTLY MODERATES. 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 EARLY NEXT
WEEK ARE LIKELY TO COOL TUESDAY AND BEYOND AFTER A FRONTAL
PASSAGE.
TATE
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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