688
FXUS02 KWBC 081900
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
159 PM EST WED NOV 08 2023
VALID 12Z SAT NOV 11 2023 - 12Z WED NOV 15 2023
..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 THE
REGION, 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. SOUTHERN TEXAS MAY SEE THE HIGHEST RAINFALL TOTALS
DURING THE PERIOD BUT THERE IS STILL CONSIDERABLE UNCERTAINTY WITH
HOW MUCH RAIN FALLS ONSHORE VERSUS OFFSHORE AND HOW MUCH
INSTABILITY WILL BE IN PLACE TO ENHANCE RAIN RATES. ALONG THE
EASTERN SEABOARD, ONE OR MORE SHORTWAVES PUSHING THROUGH THE
NORTHERN TIER OF THE COUNTRY THIS WEEKEND INTO EARLY NEXT WEEK AND
FORMING THE MIDWEEK ATLANTIC TROUGH WILL LEAD TO COOLER THAN
AVERAGE TEMPERATURES BEFORE A MODERATING TREND NEXT
TUESDAY-WEDNESDAY.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
OVER THE WEST COAST AND EASTERN PACIFIC, MODELS AND ENSEMBLES HAVE
BEEN SHOWING A STRONG SIGNAL FOR AMPLIFIED TROUGHING TO DEVELOP
WITH A CORRESPONDING INCREASE OF PRECIPITATION OVER THE WESTERN
U.S. AND IN PARTICULAR CALIFORNIA TOWARD MIDWEEK. HOWEVER THERE
HAS BEEN QUITE A BIT OF SPREAD AND RUN-TO-RUN VARIABILITY FOR
DETAILS WITHIN THE OVERALL TROUGH, THUS LIMITING CONFIDENCE IN
SPECIFICS OF PRECIPITATION TIMING/COVERAGE/AMOUNTS. IN GENERAL THE
ECMWF AND SOME ECMWF ENSEMBLES HAVE BEEN FASTEST TO BRING LEADING
HEIGHT FALLS INTO THE WEST, INCLUDING ONE SHORTWAVE WHICH THE 00Z
ECMWF BRINGS INTO THE NORTHWEST AROUND LATE MONDAY-TUESDAY AND
FARTHER SOUTH AHEAD OF THE LARGER SCALE TROUGH (AND IN PARTICULAR
ITS OPENING UPPER LOW NEARING CALIFORNIA EARLY NEXT WEDNESDAY).
RECENT SLOWER TREND FOR HEIGHT FALLS/QPF ARRIVAL AMONG CONSECUTIVE
OPERATIONAL ECMWF RUNS, ALONG WITH THE MAJORITY OF
GFS/GEFS/CMC/CMCENS GUIDANCE BEING SLOWER THAN THE ECMWF, WOULD
ARGUE FOR SOME DEGREE OF COMPROMISE AT THE VERY LEAST.
PREDICTABILITY TENDS TO DECREASE BY 6-7 DAYS OUT FOR DETAILS OF
HOW EMBEDDED UPPER LOW(S) AND UPSTREAM ENERGY MAY ULTIMATELY
INTERACT. A BLEND APPROACH BY THAT TIME DEPICTS THE BEST POTENTIAL
(ON A RELATIVE BASIS) FOR AN EMBEDDED LOW TO BE OFFSHORE THE
PACIFIC NORTHWEST. THE NEW 12Z ECMWF HAS TRENDED SLOWER WITH
LEADING HEIGHT FALLS FOR BOTH ASPECTS OF THE FORECAST DESCRIBED
ABOVE.
THERE IS A MODERATE DEGREE OF SPREAD FOR DETAILS OF THE UPPER
LOW/TROUGH EJECTING OUT OF NORTHWESTERN MEXICO AND INTO THE
SOUTHERN PLAINS, WITH THE 00Z ECMWF/12Z UKMET LEANING ON THE
FASTER SIDE RELATIVE TO THE GFS/12Z CMC. CONFIDENCE IN SPECIFICS
WOULD TEND TO DECREASE AS THE FEATURE BECOMES EMBEDDED
WITHIN/UNDERNEATH THE LARGER SCALE UPPER RIDGE BUILDING OVER THE
CENTRAL U.S. THESE DIFFERENCES CONTRIBUTE TO EVEN MORE SPREAD FOR
QPF DETAILS ACROSS THE FAR SOUTHERN TIER THAN WHAT MIGHT BE
SUGGESTED BY THE COMPARISONS ALOFT. ECMWF RUNS HAVE BEEN
PARTICULARLY HEAVY ALONG AND INLAND FROM THE GULF COAST WHILE THE
GFS IS MOST SUPPRESSED WITH THE MOISTURE. THE CMC (HEAVIER OVER
SOUTHERN TEXAS) AND UKMET (SOME ENHANCED TOTALS NEAR THE CENTRAL
GULF COAST) OFFER VARYING INTERMEDIATE IDEAS.
THE DETAILS CONTINUE TO BE VARIABLE FOR PIECES OF SHORTWAVE ENERGY
TRACKING ACROSS THE NORTHERN TIER AND THEN REACHING INTO THE
EASTERN U.S./WESTERN ATLANTIC. SPLIT FLOW OVER THE GREAT LAKES
AROUND SUNDAY COMPLICATES MATTERS TOO, WITH VARIATIONS IN MODELS
WITH WHERE THE TROUGHING FARTHER SOUTH IN THE MIDWEST SPLITS WITH
RIDGING FARTHER NORTH INTO SOUTHERN CANADA. OPERATIONAL MODEL RUNS
THROUGH THE 00Z/06Z CYCLES (USED FOR THE UPDATED FORECAST) PLUS
THE NEW 12Z CYCLE SEEM TO BE WAFFLING WITH RESPECT TO OVERALL
TROUGH AMPLITUDE NEAR THE EAST COAST, FAVORING A MULTI-MODEL AND
EVENTUALLY MODEL/ENSEMBLE MEAN BLEND.
THE WPC FORECAST CONTINUED THE APPROACH OF TRANSITIONING FROM A
MULTI-MODEL DETERMINISTIC BLEND (06Z GFS AND 00Z ECMWF/CMC/UKMET)
EARLY IN THE PERIOD TOWARD A MIX OF MODELS AND MEANS (06Z GEFS AND
00Z ECENS) TO DOWNPLAY SOME OF THE LESS CONFIDENT INDIVIDUAL MODEL
DIFFERENCES WHILE CAPTURING THE OVERALL PATTERN.
..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. FOR THE WEEKEND INTO EARLY NEXT
WEEK. THE HIGHEST RAINFALL TOTALS ARE LIKELY TO BE OVER SOUTHERN
TEXAS NEAR A MEANDERING SURFACE LOW ALONG THE FRONT, WITH EASTERN
PACIFIC AND GULF MOISTURE COMBINING. NOT MUCH INSTABILITY IS
LIKELY TO BE IN PLACE SINCE THIS WILL BE AFTER THE FRONTAL
PASSAGE, SO RAIN RATES SHOULD NOT BE TOO HIGH. THERE IS ALSO
CONSIDERABLE UNCERTAINTY WITH HOW MUCH RAIN SPREADS INLAND, WITH
RAIN TOTALS MAXIMIZED OVER THE GULF. THUS THROUGH THE WEEKEND,
THERE ARE NO FLASH FLOODING RISK AREAS DELINEATED IN THE EXCESSIVE
RAINFALL OUTLOOK. INTO MONDAY AND BEYOND THOUGH, THERE MAY BE MORE
SUPPORT FOR CONVECTION FROM TEXAS INTO THE LOWER MISSISSIPPI
VALLEY AS MID-UPPER LEVEL ENERGY APPROACHES, BUT MODEL GUIDANCE
CONTINUES TO DIVERGE SIGNIFICANTLY FOR SPECIFICS. THIS POTENTIAL
RAINFALL EVENT WILL CONTINUE TO BE MONITORED.
ROUNDS OF FRONTAL SYSTEMS AND SHORTWAVES PUSHING THROUGH THE
NORTHWEST WILL MAINTAIN PRECIPITATION CHANCES ACROSS THE PACIFIC
NORTHWEST AND THE NORTHERN ROCKIES OVER THE WEEKEND. MODERATE TO
HEAVY AMOUNTS ARE LIKELY TO 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-WEDNESDAY, 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 FOR INDIVIDUAL COMPONENTS OF THE TROUGH.
ON SATURDAY, MOST OF THE LOWER 48 WILL BE UNDER A POST-FRONTAL
COOL HIGH PRESSURE SYSTEM, WITH TEMPERATURES NEAR TO BELOW
AVERAGE. THE EXCEPTION WILL BE THE FLORIDA PENINSULA, WITH HIGHS
WELL INTO THE 80S WHICH WILL ACTUALLY BE CLOSE TO DAILY RECORDS.
TEMPERATURES OVER FLORIDA SHOULD GRADUALLY MODERATE TO NEAR NORMAL
EARLY NEXT WEEK AS 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 SOME ABOVE
AVERAGE POCKETS EXTENDING BACK INTO THE GREAT BASIN AS WELL.
MEANWHILE BELOW NORMAL HIGHS SHOULD LINGER IN THE SOUTH-CENTRAL
U.S. WITH LOWER HEIGHTS OVERHEAD AND CLOUDS AND RAIN POSSIBLE, AND
INTERESTINGLY LEAD TO SIMILAR HIGHS FROM TEXAS ALL THE WAY NORTH
TO SOUTH DAKOTA OR SO (IN THE UPPER 50S AND 60S). NEAR TO COOLER
THAN NORMAL TEMPERATURES OVER THE EASTERN SEABOARD THIS WEEKEND
SHOULD GRADUALLY MODERATE THROUGH THE EARLY PART OF NEXT WEEK.
RAUSCH/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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