778
FXUS02 KWBC 211844
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
143 PM EST TUE NOV 21 2023
VALID 12Z FRI NOV 24 2023 - 12Z TUE NOV 28 2023
..PATTERN OVERVIEW
THE MEDIUM RANGE PERIOD (FRIDAY NOVEMBER 24 TO TUESDAY NOVEMBER
28) WILL FEATURE A BROAD, AMPLIFIED MEAN TROUGH EXTENDING FROM
CANADA INTO THE LOWER 48 WHILE A PERSISTENT UPPER RIDGE REMAINS IN
PLACE OVER THE EASTERN PACIFIC AND NORTHWESTERN NORTH AMERICA. AN
INITIAL WESTERN U.S. UPPER TROUGH WITH AN EMBEDDED CLOSED LOW 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 MAY
CONTRIBUTE TO WAVINESS FROM THE GULF OF MEXICO INTO THE WESTERN
ATLANTIC THAT COULD CAUSE AFFECT PARTS OF THE EAST COAST NEXT
WEEK. SNOW AND COLD TEMPERATURES OVER THE CENTRAL ROCKIES/HIGH
PLAINS WILL BE A PROMINENT WEATHER STORY LATE THIS WEEK, BUT THERE
IS LESS CONFIDENCE IN SPECIFICS OF PRECIPITATION COVERAGE AND
AMOUNTS ON A DAY-TO-DAY BASIS FARTHER EASTWARD.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE IS IN GOOD AGREEMENT ON THE OVERALL PATTERN;
HOWEVER, THERE ARE DIFFERENCES IN SOME OF THE SMALLER SCALE
DETAILS THAT COULD AFFECT SENSIBLE WEATHER. MODELS CONTINUE TO
SHOW THE SYSTEM DEVELOPING IN THE GULF/ATLANTIC OVER THE WEEKEND
REMAINING FAIRLY WEAK AND OFFSHORE OF THE EAST COAST THROUGH EARLY
NEXT WEEK THEN TRACKING INTO THE CANADIAN MARITIMES. LATEST
GUIDANCE SUGGESTS THE LOW PRESSURE CENTER MAY TRACK SLIGHTLY
CLOSER TO CAPE HATTERAS THAN THE PREVIOUS FORECAST, WHICH WOULD
ALLOW FOR INCREASED PRECIPITATION CHANCES IN COASTAL NORTH
CAROLINA. GUIDANCE ALSO CONTINUES TO SHOW SEVERAL UPPER WAVES AND
SURFACE FRONTAL SYSTEMS DROPPING SOUTH FROM CANADA WITH SLIGHT
DIFFERENCES IN POSITION AND TIMING. THE ECMWF IS FASTER AND
STRONGER WITH THE WAVE LATE IN THE PERIOD, BRINGING A FRONTAL
SYSTEM INTO THE UPPER MIDWEST ON TUESDAY, WHILE THE GFS AND CMC
ARE SLOWER AND WEAKER WITH THIS FEATURE.
THE AFTERNOON FORECAST STARTED WITH A BLEND OF THE 06Z GFS/00Z
ECMWF AND LESSER WEIGHT OF THE 00Z CMC/UKMET EARLY IN THE PERIOD
AND THEN GRADUALLY INCREASED 06Z GEFS/00Z ECENS MEAN WEIGHT
MID-LATE PERIOD TO COME TO A SOLUTION CLOSE TO THE MODEL 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 LATE THIS WEEKEND INTO EARLY NEXT WEEK 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. WITH MODEL GUIDANCE SHIFTING
SLIGHTLY EAST WITH THE OFFSHORE LOW, PRECIPITATION CHANCES HAVE
INCREASED SLIGHTLY FOR COASTAL NORTH CAROLINA OVER THE WEEKEND.
THIS COASTAL SYSTEM IS THEN FORECAST TO TRACK TOWARDS THE CANADIAN
MARITIMES AND COULD BRING PRECIPITATION TO THE NORTHEAST.
CURRENTLY THERE IS NO SUFFICIENTLY COHERENT SIGNALS FOR ORGANIZED
HEAVY RAINFALL TO WARRANT ANY RISK 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 COLD MORNING LOWS AND BREEZY
WINDS MAY BRING NOTICEABLY COLD WIND CHILLS TO VALLEY LOCATIONS
SUCH AS LAS VEGAS. A DECENT PORTION OF THE PLAINS MAY SEE A
SUFFICIENT WARM UP 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/DOLAN
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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