689
FXUS02 KWBC 210701
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 AM EST TUE NOV 21 2023
VALID 12Z FRI NOV 24 2023 - 12Z TUE NOV 28 2023
..PATTERN OVERVIEW
THE MODELS AND ENSEMBLE MEANS GENERALLY SUGGEST A TREND TOWARD A
BROADER AND MORE AMPLIFIED MEAN TROUGH EXTENDING FROM CANADA INTO
THE LOWER 48 GOING FROM LATE THIS WEEK INTO EARLY NEXT WEEK,
SUPPORTED BY A PERSISTENT UPPER RIDGE OVER THE EASTERN PACIFIC AND
NORTHWESTERN NORTH AMERICA. AS THIS EVOLUTION DEVELOPS, AN
INITIAL WESTERN U.S. UPPER TROUGH WITH EMBEDDED LOW AS OF FRIDAY
WILL OPEN UP BY THE WEEKEND, WITH SOME OF THE ENERGY POTENTIALLY
PHASING WITH NORTHERN STREAM FLOW WHILE WEAKER RESIDUAL TROUGHING
EXTENDS THROUGH THE SOUTHWEST. NORTHERN STREAM SHORTWAVES AND THE
EJECTING WESTERN ENERGY WILL SUPPORT ONE OR MORE WAVES/FRONTAL
SYSTEMS EAST OF THE ROCKIES WHILE SOUTHERN TIER ENERGY COULD ALSO
CONTRIBUTE TO WAVINESS FROM THE GULF OF MEXICO INTO WESTERN
ATLANTIC WITH UNCERTAIN EFFECTS ALONG THE EAST COAST. SNOW AND
COLD TEMPERATURES OVER THE CENTRAL ROCKIES/HIGH PLAINS WILL BE A
PROMINENT WEATHER STORY LATE THIS WEEK, LESS CONFIDENCE IN
SPECIFICS OF PRECIPITATION COVERAGE AND AMOUNTS ON A DAY-TO-DAY
BASIS FARTHER EASTWARD.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
AS HAS BEEN THE CASE RECENTLY, GUIDANCE CONTINUES TO SHOW VARIOUS
IMPORTANT DETAIL DIFFERENCES WITHIN THE MORE AGREEABLE LARGE SCALE
EVOLUTION. AFTER A LOT OF VARIABILITY/TRENDING IN THE PAST DAY OR
SO, THERE IS AN IMPROVING CONSENSUS THAT WHATEVER GULF/ATLANTIC
WAVINESS EXISTS LATE WEEK INTO EARLY SUNDAY DUE TO SOUTHERN TIER
SHORTWAVE ENERGY SHOULD BE FAIRLY WEAK AND A WAYS OFFSHORE (MINUS
THE 12Z ECMWF THAT WAS CLOSE TO NORTH CAROLINA). HOWEVER RIGHT
AFTER THAT TIME SOLUTIONS AT THE SURFACE BEGIN TO DIVERGE MORE AS
THE EJECTING WESTERN ENERGY AND NORTHERN STREAM TROUGHING APPROACH
(POTENTIALLY SUPPORTING A SEPARATE WAVE/FRONTAL SYSTEM). THE 00Z
GFS HAS REVERTED TO A SUPPRESSED AND WELL OFFSHORE TRACK, IN
CONTRAST TO 12Z/18Z RUNS THAT HAD A MORE NORTH-NORTHEAST TRACK,
WITH THE 12Z ECMWF AND NEW 00Z CMC JUST FAR ENOUGH OFFSHORE LIKELY
TO HAVE MODEST INFLUENCE ON THE EAST COAST. ENSEMBLE MEMBERS
CONTINUE TO EXHIBIT ENOUGH SPREAD TO KEEP THE MEANS VERY
ILL-DEFINED. MEANWHILE GUIDANCE CONTINUES TO SHOW ONE OR MORE
WAVES/FRONTAL SYSTEMS DROPPING SOUTH FROM CANADA DURING THE PERIOD
BUT WITH TYPICAL DIFFERENCES AND VARIABILITY. THE MOST COMMON
CLUSTER SHOWS A FRONT REACHING THE NORTHERN TIER BY SUNDAY,
FOLLOWED BY ANOTHER POTENTIAL WAVE AROUND TUESDAY (ECMWF/CMC RUNS
AND THEIR MEANS; GFS RUNS SHOWING HIGHER PRESSURES AT THAT TIME
WITH THE GEFS MEAN ILL-DEFINED). FINALLY, MODEL/ENSEMBLE
SPAGHETTI PLOTS GET QUITE MESSY ACROSS THE EASTERN PACIFIC INTO
WESTERN U.S. EARLY NEXT WEEK AS SOLUTIONS INCREASINGLY DIFFER ON
THE DISTRIBUTION OF ENERGY WITHIN A TROUGH BETWEEN ALASKA AND
HAWAI'I AND DOWNSTREAM EFFECTS ON THE RIDGE NEARING THE WEST COAST
PLUS THE DOWNSTREAM DETAILS. A BLENDED SOLUTION CLOSEST TO THE
MEANS LOOKS BEST THERE, BETWEEN THE 12Z ECMWF'S UPPER LOW OVER
NORTHERN BAJA CALIFORNIA BY EARLY TUESDAY AND SOME GFS RUNS/NEW
00Z CMC THAT BRING MORE SIGNIFICANT HEIGHT RISES INTO THE WEST.
THE UPDATED FORECAST STARTED WITH A BLEND OF THE 18Z GFS/12Z ECMWF
AND LESSER WEIGHT OF THE 12Z CMC/UKMET EARLY IN THE PERIOD AND
THEN GRADUALLY INCREASED 18Z GEFS/12Z ECENS MEAN WEIGHT MID-LATE
PERIOD TO YIELD A HALF MODEL/HALF MEAN MIX BY DAY 7 TUESDAY. BY
THAT TIME, MORE PRONOUNCED DIFFERENCES IN OPERATIONAL RUNS OVER
THE WEST OFFSET TO KEEP THE FORECAST CLOSER TO THE MEANS.
..WEATHER/HAZARDS HIGHLIGHTS
SNOW OVER THE CENTRAL ROCKIES AND HIGH PLAINS (INCLUDING LOWER
ELEVATIONS) SHOULD CONTINUE AT LEAST INTO FRIDAY WITH SOME LOCALLY
ENHANCED TOTALS POSSIBLE. EXPECT THE SNOW TO TREND LIGHTER AND
MORE SCATTERED AS THE INITIAL UPPER LOW OVER THE WEST OPENS UP AND
PROGRESSES EASTWARD. SOME PRECIPITATION (SNOW NORTH, RAIN SOUTH)
MAY CONTINUE INTO THE CENTRAL/EASTERN U.S. ALONG A FRONT BUT MOST
SHOULD BE FAIRLY LIGHT. ONE OR MORE PERIODS OF LAKE EFFECT SNOW
WILL BE POSSIBLE AS WELL, UNDER BROADENING CHILLY CYCLONIC FLOW
ALOFT. RECENT FORECASTS HAVE BEEN QUITE VARIABLE FOR HOW MUCH
PRECIPITATION MAY OCCUR ACROSS PARTS OF THE SOUTHERN/EASTERN U.S.,
WITH LATEST TRENDS TENDING TO KEEP COVERAGE FAIRLY LOW. HOWEVER
THERE ARE SOME MIXED SIGNALS ABOUT A POTENTIAL BRIEF PERIOD OF
RELATIVELY HEAVIER RAINFALL ACROSS PARTS OF FLORIDA LATE THIS
WEEK, WITH MINOR POSSIBILITIES OF OTHER PARTS OF THE GULF
COAST/EAST COAST GETTING BRUSHED WITH MEANINGFUL PRECIPITATION AT
SOME POINT DURING THE PERIOD. CURRENTLY THERE NO SUFFICIENTLY
COHERENT SIGNALS FOR ORGANIZED HEAVY RAINFALL TO WARRANT ANY
EXCESSIVE RAINFALL AREAS ON THE DAY 4 AND DAY 5 EXCESSIVE RAINFALL
OUTLOOKS.
MOST OF THE COUNTRY WILL LIKELY SEE NEAR TO BELOW NORMAL HIGH
TEMPERATURES FROM LATE THIS WEEK INTO EARLY NEXT WEEK. COLDEST
READINGS VERSUS CLIMATOLOGY SHOULD BE OVER THE CENTRAL HIGH PLAINS
AND VICINITY FRIDAY-SATURDAY WITH HIGHS GENERALLY 15-25F BELOW
NORMAL. LOW TEMPERATURES WILL BE LESS EXTREME BUT PARTS OF TEXAS
MAY EXPERIENCE SOME FROST/FREEZE CONDITIONS FOR THE FIRST TIME
THIS SEASON AND THE COMBINATION OF MORNING LOWS AND BREEZY
CONDITIONS MAY BRING NOTICEABLY COLD WIND CHILLS TO VALLEY
LOCATIONS SUCH AS LAS VEGAS. A DECENT PORTION OF THE PLAINS MAY
SEE A SUFFICIENT WARMUP TO BRING HIGHS WITHIN A FEW DEGREES ON
EITHER SIDE OF NORMAL BY NEXT TUESDAY. THE IMMEDIATE
CENTRAL-NORTHERN WEST COAST SHOULD BE AN EXCEPTION TO THE CHILLY
THEME, WITH EAST PACIFIC UPPER RIDGING CLOSE ENOUGH TO KEEP HIGHS
A LITTLE ABOVE NORMAL.
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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