712
FXUS02 KWBC 270654
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
253 AM EDT FRI OCT 27 2023
VALID 12Z MON OCT 30 2023 - 12Z FRI NOV 3 2023
***MAJOR PATTERN CHANGE TO RESULT IN ABRUPTLY COLDER CONDITIONS
COMPARED TO THE RECENT SEPTEMBER-LIKE WARMTH ACROSS MUCH OF THE
SOUTHERN U.S.***
..SYNOPTIC OVERVIEW
A MAJOR PATTERN CHANGE WILL CONTINUE TO BE IN PROGRESS ACROSS MUCH
OF THE CENTRAL AND EASTERN PORTIONS OF THE NATION AS A STRONG COLD
FRONT HERALDS THE ARRIVAL OF THE COLDEST AIRMASS THUS FAR THIS
SEASON. THIS FRONT SHOULD CLEAR THE SOUTHEAST U.S. COAST BY
TUESDAY MORNING, AND THEN CLEAR THE FLORIDA PENINSULA BY LATE
WEDNESDAY, WITH A STRONG SURFACE HIGH BUILDING IN BEHIND THE
FRONT. A COUPLE OF REINFORCING UPPER TROUGHS AND SURFACE COLD
FRONTS WILL GIVE THIS COLDER AIRMASS SOME STAYING POWER ACROSS
MUCH OF THE CENTRAL AND EASTERN STATES, WITH PERHAPS THE FIRST
NOTABLE LAKE EFFECT SNOW EVENT OF THE SEASON. THE AIRMASS SHOULD
GRADUALLY MODIFY SOME GOING INTO THE END OF NEXT WEEK, AND A
PACIFIC STORM SYSTEM APPROACHING THE NORTHWESTERN COAST WILL
INCREASE THE PROSPECTS FOR RAIN AND MOUNTAIN SNOW TO CLOSE OUT THE
WORK WEEK.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE 00Z MODEL GUIDANCE SUITE IS IN GOOD OVERALL SYNOPTIC SCALE
AGREEMENT FOR THE BEGINNING OF THE WEEK, AND HAVE COME INTO BETTER
FOCUS WITH A POTENT NORTHERN STREAM SHORTWAVE DROPPING SOUTH FROM
NORTHERN CANADA FOR THE MIDDLE OF THE WEEK. THIS FEATURE WILL
DETERMINE THE EXTENT OF ANY COASTAL LOW CYCLOGENESIS OFF THE NEW
ENGLAND COAST, AND THE CONSENSUS RIGHT NOW IS FOR THE LOW TO
DEVELOP FAR ENOUGH OFFSHORE TO KEEP THE HEAVIEST PRECIPITATION
AWAY FROM NEW ENGLAND, BUT THIS WILL CONTINUE TO BE MONITORED FOR
FUTURE TRENDS. RIGHT NOW, THE GFS REMAINS THE MOST PROGRESSIVE
AND WEAKEST WITH THIS FEATURE, WHILST THE NON-NCEP GUIDANCE FAVORS
A STRONGER SYSTEM. FOR THE PACIFIC STORM SYSTEM MOVING IN LATE
WEEK, THE GFS IS THE MOST PROGRESSIVE WITH THE TROUGH, AND THE 12Z
ECENS SLOWER, WITH THE GEFS MEAN REPRESENTING A REASONABLE
COMPROMISE. A MORE ZONAL FLOW PATTERN IS LIKELY ACROSS THE NATION
BY FRIDAY, AND THE GREATEST MODEL SPREAD IS ACROSS THE
INTERMOUNTAIN WEST AND THE NORTHERN ROCKIES AS THE TROUGH MOVES
INLAND. THEREFORE, THE ENSEMBLE MEANS ACCOUNTED FOR ABOUT HALF OF
THE MODEL BLEND GOING INTO NEXT FRIDAY.
..WEATHER/HAZARDS HIGHLIGHTS
IN CONTRAST TO THE HEAVY RAINFALL EXPECTED IN THE SHORT RANGE
FORECAST PERIOD ACROSS THE SOUTH-CENTRAL U.S., THE EXTENDED
FORECAST GOING INTO EARLY NEXT WEEK FEATURES A RETURN TO QUIETER
CONDITIONS IN TERMS OF RAINFALL ACROSS THE ENTIRE COUNTRY. THE
RAINFALL EXPECTED ALONG AND BEHIND THE STRONG COLD FRONT IS
FORECAST TO BECOME LIGHTER FROM TEXAS TO THE MID-ATLANTIC, AND
SHOULD BE BELOW THE THRESHOLDS OF ANY EXCESSIVE RAINFALL
HEADLINES. THERE MAY BE SOME LOCATIONS THAT GET 0.5 TO 1 INCH OF
RAINFALL ON MONDAY ACROSS PARTS OF TEXAS, BUT MOST AREAS AFFECTED
SHOULD BE UNDER HALF AN INCH.
DEPENDING ON THE POTENTIAL EVOLUTION OF AN OFFSHORE LOW AROUND
MIDWEEK, SOME MOISTURE IS EXPECTED TO BE ADVECTED INLAND ACROSS
PORTIONS OF THE NORTHEAST U.S., WITH RAIN FOR THE BIG CITIES AND
PERHAPS SOME SNOW FOR THE HIGHER INLAND TERRAIN. LAKE EFFECT SNOW
COULD ALSO MAKE HEADLINES FROM MICHIGAN TO UPSTATE NEW YORK AS A
STRONG SURGE OF COLD AIR ADVECTION RUSHES ACROSS THE WARMER LAKE
WATERS, WITH SEVERAL INCHES OF ACCUMULATION FOR SOME AREAS.
LOOKING AHEAD TO THE END OF THE WEEK, SHOWERS AND MOUNTAIN SNOW IS
LIKELY TO MAKE A RETURN FROM NORTHWESTERN CALIFORNIA TO WESTERN
WASHINGTON, WITH SOME OF THIS MOISTURE REACHING THE NORTHERN
ROCKIES BY LATE FRIDAY.
A TEMPERATURE DICHOTOMY WILL EXIST ACROSS THE EASTERN U.S. ON
MONDAY WITH WARM AND HUMID CONDITIONS ACROSS THE SOUTHEAST STATES
AHEAD OF THE FRONT WITH HIGHS WELL INTO THE 80S, AND MUCH COLDER
FROM TEXAS TO THE OHIO VALLEY WHERE HIGHS WILL STRUGGLE TO REACH
50 DEGREES IN MANY CASES. THE COLD AIRMASS THEN ENGULFS ALL OF
THE CENTRAL AND EASTERN U.S., WITH THE EXCEPTION OF THE FLORIDA
PENINSULA, BY TUESDAY. WIDESPREAD ANOMALIES ON THE ORDER OF 15 TO
25 DEGREES BELOW AVERAGE FOR THIS TIME OF YEAR ARE EXPECTED,
PERHAPS SETTING SOME DAILY RECORD LOWS. THE FIRST FROST/FREEZE OF
THE SEASON IS EXPECTED FOR A VAST EXPANSE OF THE SOUTH-CENTRAL
U.S. AND ACROSS MUCH OF THE MID-ATLANTIC GOING INTO THE MIDDLE OF
THE WEEK. THIS AIRMASS SHOULD THEN MODIFY GOING INTO THE END OF
THE WEEK AS A MORE ZONAL FLOW PATTERN EVOLVES.
HAMRICK
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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