784
FXUS02 KWBC 230700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 AM EST THU NOV 23 2023
VALID 12Z SUN NOV 26 2023 - 12Z THU NOV 30 2023
..OVERVIEW
AN UPPER RIDGE INITIALLY EXTENDING FROM THE EASTERN PACIFIC INTO
NORTHWESTERN NORTH AMERICA AS OF SUNDAY WILL SUPPORT A FAIRLY DEEP
MEAN TROUGH OVER THE EASTERN HALF OF CANADA AND THE LOWER 48.
WHILE RIDGING OVER CANADA SHOULD REMAIN FAIRLY STABLE THROUGH THE
PERIOD, GUIDANCE SHOWS MORE INLAND PROGRESSION AND GRADUAL
WEAKENING OF THE RIDGE OVER THE WESTERN U.S. FOLLOWED BY THE
ARRIVAL OF A MODEST TROUGH WITH AN OPENING UPPER LOW. MEANWHILE,
MODELS/ENSEMBLES ARE STILL HAVING DIFFICULTY IN RESOLVING THE
EVENTUAL CHARACTER OF WEAK ELONGATED ENERGY OVER THE SOUTHWESTERN
U.S. AT THE START OF NEXT WEEK. THIS PATTERN EVOLUTION SHOULD KEEP
A MAJORITY OF THE LOWER 48 ON THE DRY SIDE. THE MAIN
PRECIPITATION AREAS OF INTEREST WILL BE OVER PARTS OF THE GULF
COAST STATES WITH A WAVE ON SUNDAY, NEW ENGLAND WITH A BRIEF
PERIOD OF SOME POTENTIALLY ENHANCED ACTIVITY IN ASSOCIATION WITH A
COMPACT WAVE BRUSHING THE REGION AROUND MONDAY, AND THE GREAT
LAKES WHERE LAKE EFFECT SNOW WILL BE POSSIBLE OVER MULTIPLE DAYS.
ALSO SOME LIGHT PRECIPITATION COULD REACH THE WEST COAST TOWARD
MIDWEEK WITH THE ARRIVAL OF THE WEAKENING PACIFIC FEATURE.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
BASED ON GUIDANCE THROUGH THE 12Z/18Z CYCLES, THE PREFERRED
SOLUTION STARTED WITH A BLEND OF MOSTLY 18Z-12Z GFS/12Z ECMWF WITH
A SMALL CONTRIBUTION OF THE 12Z CMC FOR DAYS 3-4 SUNDAY-MONDAY AND
THEN TRANSITIONED TOWARD A DAY 7 BLEND CONSISTING OF EVEN WEIGHT
AMONG THE 12Z GFS/18Z GEFS MEAN AND 12Z ECMWF/ECENS MEAN. AS OF
THE TIME OF FORECAST PREPARATION, THE GFS/ECMWF AND THEIR MEANS
HAD GENERALLY BEEN THE MOST CONSISTENT AND IN THE SLIGHT MAJORITY
FOR THE TRACK AND TIMING OF THE COMPACT WAVE FORECAST TO DEVELOP
OFFSHORE THE CAROLINAS ON SUNDAY AND TRACK SLIGHTLY OFFSHORE THE
NEW ENGLAND COAST AS STRONG UPSTREAM TROUGHING APPROACHES. RECENT
UKMET RUNS AND SPORADIC CMC RUNS (INCLUDING THE NEW 00Z VERSION)
HAVE BEEN SHOWING A MORE COASTAL TRACK. LATEST TRENDS ARE
INCREASING POTENTIAL FOR THE WESTERN SIDE OF THE SPREAD AS THE NEW
00Z GFS HAS JOINED THE UKMET/CMC WHILE THE 00Z ECMWF HAS MADE A
SUBTLE WESTWARD NUDGE. MEANWHILE ANOTHER VIGOROUS WAVE SHOULD
BRUSH THE UPPER GREAT LAKES SUNDAY-SUNDAY NIGHT AND ULTIMATELY
MERGE WITH THE COASTAL WAVE TO THE NORTH OF MAINE. BEHIND THESE
SYSTEMS, THERE IS STILL SOME AMBIGUITY OVER SURFACE FRONTS/WAVES,
REFLECTIVE OF SHORTWAVE DETAIL UNCERTAINTIES. AT LEAST THE FAVORED
BLEND WAS ABLE TO MAINTAIN SOME DEGREE OF CONTINUITY WITH THE
THEME OF A GENERAL AREA OF LOW PRESSURE (ONE OR TWO DISTINCT
WAVES) REACHING THE UPPER MIDWEST/GREAT LAKES BY DAY 6 WEDNESDAY.
TRAILING NORTHERN TIER DETAILS BY THE END OF THE PERIOD COME DOWN
TO ORIENTATION OF FLOW ALOFT, WITH THE 18Z GFS BEING MOST
PRONOUNCED IN BRINGING UPPER RIDGING INTO THE CENTRAL U.S. IN
CONTRAST TO THE 12Z ECMWF'S MORE PERSISTENT CYCLONIC FLOW. THE
ENSEMBLE MEANS ARE GENERALLY BETWEEN THESE EXTREMES AND THE NEW
00Z GFS HAS ADJUSTED SOMEWHAT SLOWER WITH THE NORTHERN TIER PART
OF THE UPPER RIDGE. OVER THE WEST, THE UKMET HAS GENERALLY BEEN
THE LEAST AGREEABLE SOLUTION WITH HOW ITS SOUTHWEST ENERGY
EVOLVES, HOLDING ONTO AN UPPER LOW LONGER THAN OTHER GUIDANCE,
THOUGH NOW THE NEW 00Z ECMWF HAS ADJUSTED THAT WAY. THE WEAKENING
EAST PACIFIC TROUGH/UPPER LOW HAS BEEN INCREMENTALLY TRENDING
TOWARD BETTER CLUSTERING THOUGH SOME SPREAD REMAINS. THE NEW 00Z
CMC BECOMES A FAST EXTREME WITH UPSTREAM ENERGY BY NEXT THURSDAY.
..WEATHER/HAZARDS HIGHLIGHTS
A WAVE NEAR THE GULF COAST ON SUNDAY MAY PRODUCE AREAS OF RAINFALL
WITH VARYING INTENSITY ON SUNDAY, WHILE A SEPARATE WAVE DEVELOPING
OFF THE CAROLINAS AND LIFTING NORTHWARD MAY BRING SOME LOCALLY
ENHANCED PRECIPITATION TO THE NORTHERN MID-ATLANTIC COAST AND NEW
ENGLAND SUNDAY INTO MONDAY. SNOW WILL BE POSSIBLE OVER INTERIOR
NEW ENGLAND, ESPECIALLY IN HIGHER ELEVATIONS. SPECIFICS ARE STILL
SUBJECT TO ADJUSTMENT BASED ON THE EXACT SURFACE LOW TRACK. WITH A
RELATIVE LACK OF INSTABILITY, CURRENTLY EXPECT RAINFALL OVER THE
ABOVE AREAS NOT TO BE SUFFICIENTLY INTENSE TO WARRANT ANY RISK
AREAS IN THE DAYS 4-5 EXCESSIVE RAINFALL OUTLOOKS. COLD FLOW
BEHIND A FRONT CROSSING THE GREAT LAKES AROUND MONDAY WILL LIKELY
SUPPORT AREAS OF LAKE EFFECT SNOW THAT MAY PERSIST THROUGH AT
LEAST MIDWEEK. SOME LIGHT PRECIPITATION, MOSTLY RAIN, MAY REACH
THE CENTRAL-NORTHERN PARTS OF THE WEST COAST BY MIDWEEK WITH THE
MODEST AND WEAKENING SYSTEM APPROACHING THE REGION AT THAT TIME.
THE START OF THE PERIOD ON SUNDAY WILL SEE MOSTLY BELOW NORMAL
TEMPERATURES OVER THE LOWER 48 WITH DECENT COVERAGE OF HIGHS
10-15F BELOW CLIMATOLOGY FROM THE GREAT BASIN INTO THE
CENTRAL-SOUTHERN PLAINS. AS UPPER TROUGHING BECOMES MORE FOCUSED
OVER THE EASTERN U.S. AFTER THE WEEKEND, EXPECT THE COLDEST HIGHS
VERSUS NORMAL TO PROGRESS EASTWARD WHILE THE WESTERN/CENTRAL PARTS
OF THE COUNTRY MODERATE. FAR SOUTHERN TEXAS SHOULD SEE THE CHILLY
CONDITIONS INTO MIDWEEK THOUGH. ALSO, FROM LATE WEEKEND INTO
EARLY NEXT WEEK BRISK WINDS WILL MAKE IT FEEL COLDER OVER THE
SOUTHWESTERN U.S. AND VICINITY. TOWARD THE EAST COAST SOMEWHAT
BELOW NORMAL HIGHS WILL LIKELY PERSIST INTO NEXT THURSDAY. ON THE
OTHER HAND, THE NORTHERN PLAINS WILL START OUT JUST SLIGHTLY BELOW
NORMAL FOR HIGHS ON SUNDAY (WITH ABOVE NORMAL LOWS) AND THEN TREND
ABOVE NORMAL FOR MAX/MIN READINGS BY TUESDAY-THURSDAY. THE UPPER
RIDGE DRIFTING INTO THE NORTHWEST EARLY NEXT WEEK SHOULD PROMOTE
SLIGHTLY ABOVE NORMAL HIGHS NEAR THE CENTRAL/NORTHERN WEST COAST
BEFORE A TREND TOWARD NORMAL AS THE RIDGE WEAKENS.
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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