667
FXUS02 KWBC 281846
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
246 PM EDT MON OCT 28 2024
VALID 12Z THU OCT 31 2024 - 12Z MON NOV 04 2024
..GENERAL OVERVIEW
AN INITIALLY ENERGETIC UPPER TROUGH AND MODERATE SURFACE LOW WILL
LIFT NORTHEASTWARD FROM THE MIDWEST THROUGH THE NORTHEAST
THURSDAY/FRIDAY OVERTOP A WARM AMBIENT UPPER RIDGE OVER THE
EASTERN-SOUTHEASTERN U.S.. AN ASSOCIATED COLD FRONT WILL SWING
THROUGH THE EAST-CENTRAL TO EASTERN U.S. TO FOCUS LINGERING SHOWERS
AND THUNDERSTORMS AND USHER IN MODERATING POST-FRONTAL HIGH
PRESSURE. THE TRAILING PORTION OF THE FRONT IS FORECAST TO
SLOW/DISSIPATE, BUT REMAIN A CONVECTIVE FOCUS TO EMINATE OUT FROM
THE SOUTH-CENTRAL U.S. WITH RETURN FLOW. MEANWHILE UPSTREAM, ROBUST
PACIFIC UPPER TROUGH ENERGY DIGS SHARPLY INTO AN UNSETTLED WEST,
WITH MODERATE RAINS AND SOME ELEVATION SNOWS OVER THE NORTHWEST,
AND MORE SPOTTY ACTIVITY FURTHER INLAND AND DOWN THE COAST ACROSS
CALIFORNIA. THIS PATTERN MAY LEAD TO CLOSED TROUGH/LOW DEVELOPMENT
NEAR SOUTHERN CALIFORNIA/BAJA. WARM AND AMPLIFIED SUBTROPICAL
RIDGING OVER THE SOUTHEAST LOOK TO REMAIN IN PLACE THROUGH THE
PERIOD.
..GUIDANCE/PREDICTABILITY ASSESSMENT
DETERMINISTIC GUIDANCE IS IN GOOD AGREEMENT FOR THE EARLY PART OF
THE PERIOD (LATE WEEK/EARLY WEEKEND) DEPICTING AN INITIAL UPPER-
LEVEL SHORTWAVE OVER THE MIDWEST PASSING OVER THE EAST COAST BY
SATURDAY. UPPER-LEVEL RIDGING WILL BUILD NORTHWARD IN ITS WAKE
AHEAD OF UPSTREAM ENERGIES SIGNIFICANTLY DEEPENING AN UPPER-LEVEL
TROUGH OVER THE WEST. THE MAIN UNCERTAINTY IS IN THE LATTER PART OF
THE PERIOD EARLY NEXT WEEK WITH RESPECT TO THE FINER DETAILS ON
THE EVOLUTION OF THE UPPER-TROUGH OVER THE WEST AS WELL AS THE
DEGREE OF AMPLIFICATION/STRENGTH OF THE EASTERN UPPER-LEVEL RIDGE
AND DISPLACEMENT OF NORTHERN STREAM FLOW. THE DETERMINISTIC AND
ENSEMBLE GUIDANCE DIFFER ON HOW UPSTREAM ENERGIES DIGGING SOUTHWARD
IN THE WEST MAY LEAD TO THE DEVELOPMENT OF A DEEP CLOSED LOW OVER
THE BAJA/NORTHWEST MEXICO. THE PAST FEW RUNS OF THE GFS THROUGH 00Z
HAVE SHOWN A BIT MORE AMPLIFIED PATTERN WITH A SHARPENING UPPER-
TROUGH AND NORTHWARD BUILDING RIDGE TO THE EAST, WHILE THE ECMWF
DEPICTS THE DEVELOPMENT OF THIS CLOSED CUT-OFF LOW OVER BAJA MEXICO
WITH A STRONG BUT LESS AMPLIFIED AREA OF HIGH PRESSURE TO THE
EAST. THE 06Z GFS DID TREND SLIGHTLY CLOSER TO THE MORE RECENT RUNS
OF THE ECMWF, SUGGESTING THE DEVELOPMENT OF A WEAKER CLOSED LOW
THAT DOES NOT CUTOFF FROM THE MEAN FLOW, BEFORE THE 12Z TRENDED
BACK TO SHOWING VARYING NORTHERN/SOUTHERN STREAM ENERGIES WITHIN
THE BROAD TROUGH BUT NO TREND TO DEVELOP A CLOSED LOW ON THE
SOUTHERN END. MOST OF THE GUIDANCE IN THE SUITE OF AI MODELS FROM
THE EC ACTUALLY TEND TO FAVOR THE PATTERN SHOWN IN THE GFS. THE
GEFS/ECENS ENSEMBLE MEANS ARE REMARKABLY SIMILAR IN PLACEMENT WITH
A DEEP UPPER TROUGH WHILE THE CMC ENSEMBLE MEAN DEVELOPS A CLOSED
LOW MORE SIMILAR TO THE ECMWF. THE CMC ENSEMBLE IS ALSO LESS
AMPLIFIED WITH THE RIDGING OVER THE EAST COMPARED TO THE GEFS/ECENS
AND CONTINUES MORE ZONAL FLOW OVER THE NORTHERN TIER OF THE
COUNTRY.
THE UPDATED WPC FORECAST USES A COMPOSITE BLEND OF THE
DETERMINISTIC GUIDANCE THROUGH THE EARLY TO MID-PERIOD GIVEN GOOD
AGREEMENT. OPTED TO INCLUDE A CONTRIBUTION FROM THE ECENS AND GEFS
MEANS FOR THE LATTER PART OF THE PERIOD WHICH, WHEN THE GFS REMAINS
INCLUDED, DOES NOT OFFER AS MUCH DETAIL OVER THE BAJA/NORTHWEST
MEXICO, BUT RATHER A COMPROMISE SOLUTION GIVEN UNCERTAINTIES IN THE
EVOLUTION AND LACK OF SUPPORT FROM THE EC AI GUIDANCE. WHILE THE
LINGERING UNCERTAINTIES DON'T HAVE A SIGNIFICANT EFFECT ON THE
BROAD OVERALL PATTERN THAT WILL FAVOR COOLER TEMPERATURES IN THE
WEST, WARMER TEMPERATURES IN THE EAST, AND HEAVY PRECIPITATION
CHANCES WHERE THE UPPER-JET/SURFACE FRONTAL SYSTEMS REMAIN IN PLACE
OVER THE CENTER OF THE COUNTRY, VARYING EVOLUTIONS/EMBEDDED ENERGY
TIMING SPECIFICALLY OVER THE WEST SHOW LARGER DISCREPANCIES IN
PRECIPITATION CHANCES. FOR THE QPF FORECAST, THE MEANS WERE RELIED
ON MORE SIGNIFICANTLY IN THE WEST COMPARED TO CENTRAL PORTIONS OF
THE COUNTRY.
..WEATHER/HAZARDS HIGHLIGHTS
AHEAD OF A SHARPENING FRONT, A LONG FETCH OF RETURN FLOW FROM THE
GULF OF MEXICO APPEARS TO INITIATE AND SUPPORT A LINGERING THREAT
OF MODERATE TO HEAVY RAIN OVER THE LOWER MISSISSIPPI VALLEY AND
VICINITY ALONG WITH A POSSIBLE SEVERE WEATHER THREAT HOLDING INTO
THURSDAY. MAINTAINED A WPC EXCESSIVE RAINFALL OUTLOOK MARGINAL RISK
FOR THIS AREA, THOUGH THE ANTECEDENT CONDITIONS ARE QUITE DRY AND
MOST OF THE RAIN WILL HOPEFULLY BE BENEFICIAL.
THE TRAILING PORTION OF THE FRONT IS THEN FORECAST TO STALL OVER
THE SOUTHERN PLAINS WHERE MODERATE TO HEAVY RAINFALL COULD
REDEVELOP WITH EJECTING IMPULSES AND INSTABILITIES. ACCORDINGLY, A
WPC ERO MARGINAL RISK HAS BEEN INTRODUCED OVER THE SOUTHERN HIGH
PLAINS TO ADDRESS POTENTIAL. EXPECT ACTIVITY TO EXPAND AND FOCUS
ALONG A NORTHEAST-SOUTHWEST AXIS AHEAD OF ADDITIONAL FRONTAL
BOUNDARIES SUNDAY AND INTO EARLY NEXT WEEK AS ROBUST UPPER
TROUGH/CLOSED LOW ENERGY DIGS UPSTREAM INTO THE WEST COAST TO RE-
AMPLIFY THE FLOW OVER THE LOWER 48 AND VICINITY. MULTIPLE DAYS OF
SOUTHERLY, MOIST GULF FLOW LOOK TO INCREASE THE CHANCES OF MORE
WIDESPREAD, HEAVY RAINFALL WITH FLOODING CONCERNS DESPITE DRY
ANTECEDENT CONDITIONS, ESPECIALLY OVER THE CENTRAL/SOUTHERN PLAINS
INTO THE MIDDLE MISSISSIPPI VALLEY.
PRECIPITATION ASSOCIATED WITH THE NEXT PACIFIC SYSTEM AND LONG-
FETCH MOISTURE IS FORECAST TO RE-FOCUS INTO THE WEST COAST LATER IN
THE WEEK AND INTO NEXT WEEKEND, WITH HIGH-ELEVATION SNOW REACHING
INTO THE NORTHERN ROCKIES AND MODEST RAINS REACHING DOWN THROUGH
CALIFORNIA. HERE, RAINFALL COULD BE HEAVIER (PER RECENT ECMWF AIFS
TRENDS) SHOULD A SLOWER/STRONGER SOLUTION VERIFY. REGARDLESS, THE
COLD FRONTAL SURGE AND POSSIBLE CLOSED LOW DEVELOPMENT AT THE
SOUTHERN BASE OF THE MAIN UPPER TROUGH WILL BRING IN COOLER
TEMPERATURES TO MUCH OF THE WEST TO WEST-CENTRAL U.S.. SOME
LINGERING FROST/FREEZE CONCERNS WILL REMAIN FOR SOUTHERN AREAS THAT
HAVE YET TO REACH FREEZING THIS SEASON.
UPPER RIDGING TOGETHER WITH A PRE-FRONTAL LONG FETCH OF STRONG AND
GUSTY SOUTHERLY WINDS WILL TRANSPORT WARMTH FROM THE SOUTH THROUGH
THE NORTHEAST THURSDAY BEFORE MODERATING INTO THE WEEKEND POST-
FRONTAL PASSAGE. TEMPERATURES WILL RETURN TO ABOVE AVERAGE EARLY
NEXT WEEK.
PUTNAM/SCHICHTEL
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 (QPF), EXCESSIVE RAINFALL
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:
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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