377
FXUS02 KWBC 091930
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
229 PM EST THU NOV 09 2023
VALID 12Z SUN NOV 12 2023 - 12Z THU NOV 16 2023
...MOISTURE DIRECTED INTO CALIFORNIA COULD LEAD TO HEAVY RAIN AND
SNOW TUESDAY-THURSDAY...
..OVERVIEW
GUIDANCE GENERALLY SHOWS THE UPPER PATTERN TRANSITIONING FROM
FAIRLY LOW AMPLITUDE MEAN FLOW WITH PROGRESSIVE SHORTWAVES TOWARD
A MORE AMPLIFIED REGIME CONSISTING OF A DEEP EASTERN PACIFIC
TROUGH, A BROAD RIDGE ALIGNED OVER THE CENTRAL U.S., AND A TROUGH
REACHING THE WESTERN ATLANTIC. THIS EVOLUTION WILL FAVOR DRY
WEATHER OVER A MAJORITY OF THE LOWER 48 AND A TREND TO WELL ABOVE
NORMAL TEMPERATURES OVER THE NORTHERN TWO-THIRDS OF THE CENTRAL
U.S. INTO MIDWEST. THE MOST LIKELY AREAS OF PRECIPITATION FOCUS
DURING THE PERIOD WILL BE ALONG THE WEST COAST, WITH GRADUALLY
INCREASING COVERAGE AND INTENSITY AHEAD OF THE AMPLIFYING PACIFIC
TROUGH THAT SHOULD EVENTUALLY DIRECT AN ATMOSPHERIC RIVER INTO
CALIFORNIA IN PARTICULAR, AND ACROSS THE SOUTHERN TIER/GULF COAST
STATES WHERE MOISTURE SHOULD OVERRUN A SLOW-MOVING FRONT OVER THE
GULF OF MEXICO. A SOUTHERN STREAM SHORTWAVE/UPPER LOW EJECTING
FROM NORTHWESTERN MEXICO AFTER SUNDAY SHOULD CONTRIBUTE TO THIS
ACTIVITY, WITH THE REGION TRENDING WETTER OVER THE PAST DAY. ALONG
THE EASTERN SEABOARD, ONE OR MORE SHORTWAVES PUSHING THROUGH THE
NORTHERN TIER OF THE COUNTRY EARLY NEXT WEEK AND FORMING THE
MIDWEEK ATLANTIC TROUGH WILL LEAD TO COOLER THAN AVERAGE
TEMPERATURES BEFORE A MODERATING TREND AS THE WEEK PROGRESSES.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
GUIDANCE INDICATES THE MEDIUM-RANGE PERIOD WILL FEATURE AMPLIFYING
MEAN LONG-WAVE RIDGING IN THE NORTHERN STREAM, SHIFTING WEST TO
EAST ACROSS THE CONUS, AS A SOUTHERN STREAM SHORTWAVE PASSES
ACROSS THE SOUTH AND A DEEP TROUGH DIGS SOUTHWARD OFF THE WEST
COAST. RECENT RUNS OF THE GFS AND ECMWF HAVE SHOWN TIMING AND
STRENGTH DIFFERENCES WITH AN INITIAL SHORTWAVE OVER THE UPPER
MIDWEST AND THE EMBEDDED SOUTHERN STREAM WAVE OVER NORTHWESTERN
MEXICO BENEATH RIDGING OVER THE WESTERN U.S. HOWEVER, THE MOST
RECENT 00Z/06Z RUNS HAVE AT LEAST CONVERGED TOWARDS A SIMILAR
SOLUTION EVEN AS CONFIDENCE REMAINS A BIT LOW GIVEN THE RUN-TO-RUN
VARIABILITY. THE NORTHERN WAVE SHOULD SHIFT EASTWARD THROUGH THE
EARLY-MID PERIOD AS A SUBSEQUENT SURFACE SYSTEM TRAVERSES THE
UPPER GREAT LAKES/NORTHEAST, WHILE THE SOUTHERN WAVE PASSES SLOWLY
OVER THE SOUTH-CENTRAL AND THEN SOUTHEASTERN U.S. HELPING TO
ENCOURAGE RAINFALL CHANCES NORTH OF A QUASI-STATIONARY BOUNDARY IN
THE GULF. ALL OF THE GUIDANCE LOOKS AGREEABLE ON THE NORTHERN WAVE
EVOLUTION WHILE THE 12Z CMC DIFFERS IN STRENGTH/PHASE WITH THE
SOUTHERN WAVE. THE 00Z ECENS MEAN ALSO OFFERS SUPPORT FOR THE
CLUSTERED DETERMINISTIC SOLUTIONS OF THE SOUTHERN WAVE WHILE THE
GEFS MEAN NOTABLY LACKS ANY SIGNAL ENTIRELY. ON A BROADER SCALE,
THE 00Z CMC/ECMWF ARE MORE AMPLIFIED WITH THE EXPANDING LONGWAVE
RIDGING OVER THE WESTERN THEN CENTRAL U.S., AS RECENT RUNS OF THE
GFS HAVE BEEN SHIFTING LESS AMPLIFIED, THOUGH REVERSE A BIT WITH
THE 06Z RUN.
ATTENTION IN THE MID-LATE PERIOD TURNS TO THE WEST COAST AS ENERGY
OVER THE NORTHEASTERN PACIFIC DROPS SOUTHWARD WITH CONTINUED
NOTABLE RUN-TO-RUN DIFFERENCES WITH REGARDS TO ALL ASPECTS OF THE
SYSTEM EVOLUTION, INCLUDING TIMING OF EMBEDDED SHORTWAVE ENERGY,
CLOSED/OPEN WAVE, AND PHASING AS THE MEAN TROUGHING EITHER PUSHES
CLOSER TOWARDS OR LINGERS OFF THE WEST COAST. THIS WILL CONTINUE
TO HAVE IMPACTS ON SUBSEQUENT PRECIPITATION CHANCES. THE 00Z/06Z
ECMWF/CMC/GFS HAVE A GENERAL CONSENSUS EARLY ON WITH A SLOW
SOUTHWARD PROGRESSION AS AN INITIAL SURGE OF UPPER-LEVEL ENERGY
FROM THE NORTHEASTERN PACIFIC DROPS SOUTHWARD OFF THE WEST COAST,
WHILE THE 00Z UKMET HAS A STRONGER CLOSED LOW IN COMPARISON.
LATER, THE ECMWF HAS BEEN FASTER AND MORE AGGRESSIVE WITH THIS
FIRST WAVE OF UPPER-LEVEL ENERGY, DEEPENING TROUGHING ALONG
SOUTHERN CALIFORNIA, WHILE THE MEAN TROUGH AXIS IN THE GFS/CMC
LINGERS FURTHER OFF THE COAST. THERE ARE ALSO SUBSEQUENT
DIFFERENCES ACROSS THE GUIDANCE WITH RESPECT TO ADDITIONAL SURGES
OF ENERGY DROPPING SOUTHWARD, WITH THE 00Z ECMWF INDICATING A
SECONDARY WAVE WILL REINFORCE TROUGHING OFF THE WEST COAST WHILE
THIS ENERGY REMAINS TO THE NORTH IN THE MOST RECENT 06Z RUN OF THE
GFS. THE 06Z GFS ALSO TRENDS BACK TOWARDS A CLOSED LOW CUTTING OFF
AND LINGERING FURTHER OFF THE WEST COAST GIVEN THE LACK OF
REINFORCING ENERGY DROPPING SOUTHWARD, AND THE 12Z GFS UPDATE
CONTINUED THIS TREND. THE 00Z ECENS MEAN OFFERS A GENERAL
COMPROMISE BETWEEN SOLUTIONS IN TERMS OF THE AXIS OF MEAN
TROUGHING. THE 00Z GEFS MEAN IS SIMILAR HERE AS WELL, THOUGH THE
LACK OF AGREEMENT FURTHER EAST WITH THE SOUTHERN STREAM WAVE
COMPLICATES FINDING A BROAD GENERAL CONSENSUS.
THE UPDATED WPC FORECAST BLEND FEATURES A COMPOSITE OF THE
DETERMINISTIC GUIDANCE EARLY IN THE PERIOD GIVEN GOOD OVERALL
AGREEMENT WITH RESPECT TO ALL SYSTEMS. THE CONTRIBUTION FROM THE
UKMET IS REMOVED BY THE MID-PERIOD AS THE EVOLUTION OF THE WESTERN
SYSTEM DIVERGES, WITH A STEADILY INCREASING CONTRIBUTION FROM THE
ECENS MEAN GIVEN ITS FIT WITHIN THE DETERMINISTIC SOLUTIONS WITH
RESPECT TO BOTH THE SOUTHERN STREAM WAVE AND THE WESTERN SYSTEM.
VARIABLE CONTRIBUTION REDUCTIONS ARE MADE WITH THE OTHER
DETERMINISTIC GUIDANCE DEPENDING ON THEIR DIVERGENCE FROM ECENS
MEAN AS A COMPROMISE SOLUTION, AND A LOWER CONTRIBUTION FROM THE
GEFS MEAN IS INCLUDED DUE TO DIFFERENCES WITH RESPECT TO THE
SOUTHERN WAVE, WHICH NOW APPEARS TO LINGER OVER THE SOUTHEASTERN
U.S. LONGER THAN PRIOR FORECASTS. GIVEN THE NOTED RUN-TO-RUN
VARIABILITY OPTED TO ALSO INCLUDE A BIT OF CONTINUITY MID-LATE
PERIOD.
..WEATHER/HAZARDS HIGHLIGHTS
MOISTURE OVERRUNNING THE COLD FRONT THAT IS FORECAST TO STALL OVER
THE NORTHWESTERN GULF (BUT TRACK A BIT MORE PROGRESSIVELY THROUGH
FLORIDA) WILL LEAD TO SOME RAIN ACROSS THE SOUTH-CENTRAL TO
SOUTHEASTERN QUADRANT OF THE U.S. CONTINUING INTO NEXT WEEK. THE
HIGHEST RAINFALL TOTALS ARE LIKELY TO SHIFT FROM SOUTHERN TEXAS
SUNDAY EASTWARD ALONG THE CENTRAL GULF COAST MONDAY-TUESDAY AND
POTENTIALLY EVEN INTO THE SOUTHEAST/FLORIDA BY LATER NEXT WEEK,
WITH EASTERN PACIFIC AND GULF MOISTURE COMBINING. NOT MUCH
INSTABILITY WILL BE IN PLACE THROUGH EARLY NEXT WEEK SINCE THE
REGION WILL BE IN A POST-FRONTAL AIRMASS, SO RAIN RATES SHOULD NOT
BE TOO HIGH. BY MONDAY THOUGH, THERE MAY BE MORE SUPPORT FOR
CONVECTION FROM TEXAS INTO THE LOWER MISSISSIPPI VALLEY AS
MID-UPPER LEVEL ENERGY APPROACHES AND POSSIBLY INCREASES
INSTABILITY, AND THE POTENTIAL FOR HEAVIER RAIN TOTALS HAS TRENDED
UPWARD AS THE GUIDANCE INDICATES THIS MID-UPPER ENERGY MAY BE
STRONGER AND TRACK SLOWER OVER THE REGION. SOME OF THE
DETERMINISTIC GUIDANCE HAS BECOME PARTICULARLY AGGRESSIVE WTIH
RAINFALL TOTALS ALONG THE CENTRAL GULF COAST AROUND MONDAY.
HOWEVER, WITH THE HEAVIEST RAINFALL EXPECTED TO REMAIN ALONG THE
GULF COAST, AND ANTECEDENT CONDITIONS ALREADY VERY DRY, THE RISK
FOR FLASH FLOODING SHOULD REMAIN VERY LOW UNLESS THERE IS A
SUBSTANTIAL INCREASE IN FORECAST TOTALS, AND NO AREAS ARE
DELINEATED IN THE EXCESSIVE RAINFALL OUTLOOK FOR SUNDAY AND MONDAY.
ROUNDS OF FRONTAL SYSTEMS AND SHORTWAVES PUSHING THROUGH THE
NORTHWEST WILL MAINTAIN PRECIPITATION CHANCES ACROSS THE PACIFIC
NORTHWEST AND THE NORTHERN ROCKIES THROUGH EARLY NEXT WEEK.
MODERATE TO HEAVY AMOUNTS MAY BE DIRECTED INTO THE NORTHERN PARTS
OF THE OLYMPICS AND CASCADES, WITH LOWER ELEVATION RAIN AND HIGHER
ELEVATION SNOW. STARTING MONDAY AND ESPECIALLY BY
TUESDAY-THURSDAY, UPPER TROUGHING WILL DEEPEN OVER THE EASTERN
PACIFIC AND DIRECT MOISTURE PLUMES/ATMOSPHERIC RIVERS INTO THE
WEST, ESPECIALLY CALIFORNIA. EXPECT HEAVY LOWER ELEVATION RAIN AND
HIGHER ELEVATION SNOW. WHILE CONFIDENCE IS SOMEWHAT ABOVE AVERAGE
IN A PERIOD OF ENHANCED PRECIPITATION ASSOCIATED WITH THE OVERALL
UPPER TROUGH, IT IS MUCH LOWER IN TERMS OF SPECIFICS (TIMING,
COVERAGE, AMOUNTS OVER PARTICULAR LOCATIONS) DUE TO MODEL SPREAD
AND VARIABILITY OF INDIVIDUAL SHORTWAVE ENERGIES.
ON SUNDAY, MUCH OF THE EAST WILL BE UNDER A POST-FRONTAL COOL HIGH
PRESSURE SYSTEM, WITH TEMPERATURES NEAR TO BELOW AVERAGE, BUT
WARMING CLOSER TO NORMAL TUESDAY-WEDNESDAY AND PERHAPS REACHING
ABOVE NORMAL BY THURSDAY. THE EXCEPTION WILL BE THE FLORIDA
PENINSULA, WITH HIGHS WELL INTO THE 80S ON SUNDAY MODERATING
GRADUALLY CLOSER TO NORMAL AFTER THE COLD FRONT PRESSES THROUGH.
AS UPPER RIDGING BUILDS ACROSS THE NORTH-CENTRAL U.S. EARLY NEXT
WEEK, ABOVE NORMAL TEMPERATURES BY AROUND 10-20F WILL OVERSPREAD
THE CENTRAL AND NORTHERN PLAINS INTO THE MIDWEST, WITH ABOVE
AVERAGE POCKETS EXTENDING BACK INTO THE ROCKIES AND GREAT BASIN AS
WELL. MEANWHILE, BELOW NORMAL HIGHS ARE EXPECTED IN THE
SOUTH-CENTRAL U.S. EARLY NEXT WEEK WITH LOWER HEIGHTS OVERHEAD AND
CLOUDS AND RAIN POSSIBLE, BEFORE MODERATING MIDWEEK.
PUTNAM/TATE
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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