224
FXUS02 KWBC 050700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 AM EDT THU OCT 05 2023
VALID 12Z SUN OCT 08 2023 - 12Z THU OCT 12 2023
..OVERVIEW
AS THE MEDIUM RANGE PERIOD BEGINS SUNDAY, WHAT IS CURRENTLY
TROPICAL STORM PHILIPPE IS FORECAST TO BE POST-TROPICAL BY THEN,
AND ITS ENERGY WILL BECOME ABSORBED INTO A REASONABLY DEEP UPPER
LOW THAT LOOKS TO MEANDER BETWEEN THE GREAT LAKES AND JAMES BAY
THROUGH MUCH OF THE WEEK. THE HEAVIEST PRECIPITATION FROM THIS
FEATURE IS PHASING INTO THE SHORT RANGE PERIOD NOW, BUT SOME RAIN
COULD LINGER INTO EARLY NEXT WEEK UNDERNEATH THE UPPER LOW, WITH
LAKE EFFECT ENHANCEMENT LIKELY. FARTHER WEST, INITIALLY DRY
CONDITIONS UNDER AN UPPER RIDGE WILL GIVE WAY TO A TROUGH AND
FRONTAL SYSTEM, INCREASING PRECIPITATION CHANCES FIRST FOR THE
PACIFIC NORTHWEST BY MONDAY WITH SOME LOCALLY HEAVY RAIN POSSIBLE,
AND SPREADING EAST AS NEXT WEEK PROGRESSES.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE REMAINS GENERALLY AGREEABLE REGARDING THE OVERALL
PATTERN THROUGH THE EARLY PART OF NEXT WEEK, THOUGH SOME
DIFFERENCES REMAIN WITH THE EXACT INTERACTIONS OF PHILIPPE AND THE
UPPER/SURFACE LOWS EARLY IN THE PERIOD. BY MONDAY IT IS ALL
EXPECTED TO HAVE MERGED AND THE PLACEMENT OF THE FEATURES BECOME A
LITTLE MORE CLEAR. THE 12Z UKMET THOUGH LOOKED TO BE TOO FAR
NORTHEAST OF CONSENSUS WITH THE CENTER OF THE UPPER LOW ESPECIALLY
BY DAY 5/TUESDAY, AND WAS AGGRESSIVE WITH SOME SHORTWAVES AROUND
THE SOUTHERN SIDE OF THE LOW THAT OTHER MODELS HAD MORE MERGED
INTO THE TROUGH ITSELF. FAVORED A BLEND OF THE 18Z GFS/12Z ECMWF
AND A LESSER COMPONENT OF THE 12Z CMC EARLY IN THE PERIOD INSTEAD.
THIS FORECAST BLEND ALSO WORKED FOR THE RIDGE TO THE WEST AND THE
EASTERN PACIFIC TO NORTHWEST TROUGH.
BY TUESDAY AND BEYOND, SOME GREATER DIFFERENCES ARISE WITH THE
WESTERN TROUGH. GFS RUNS HAVE BEEN PERSISTENTLY ON THE LESS
AMPLIFIED SIDE WITH THE TROUGH, FOR SOME INITIALLY MINOR TIMING
DIFFERENCES OF THE COLD FRONT. THE EVOLUTION OF THE TROUGHING AND
ENERGY BECOME MORE QUESTIONABLE GOING FORWARD INTO WEDNESDAY AND
THURSDAY. GFS AND GEFS RUNS PROGRESS THE TROUGH EASTWARD MORE
QUICKLY THAN THE ECMWF SUITE THAT DIGS IT INTO THE WEST. THE CMC
SUITE SEEMS MORE LIKE THE ECMWF, ESPECIALLY THE CMC MEAN, THOUGH
THE DETAILS VARY WITH THE DETERMINISTIC RUNS. GIVEN TYPICAL MODEL
BIASES, FAVORED THE SLOWER EC-TYPE SOLUTIONS TO SOME EXTENT FOR
THE MASS FIELDS AND THE QPF BLENDS. DID THINK THE 12Z ECMWF MAY
HAVE DUG TOO DEEPLY BY DAY 7/THURSDAY AS IT FORMS AN EMBEDDED
UPPER LOW, AND THE NEWER 00Z RUN DID HAVE THE LOW A BIT FARTHER
EAST. SOMEWHERE CLOSE TO THE 12Z EC MEAN SEEMED LIKE THE BEST
POSITION FOR THE TROUGH. ANOTHER POTENTIAL WRINKLE LATE IN THE
FORECAST PERIOD IS FOR SOUTHERN STREAM ENERGY POSSIBLY ORIGINATING
FROM AN EASTERN PACIFIC TROPICAL SYSTEM TO TRACK INTO MEXICO INTO
INTO THE SOUTHWEST/SOUTH TEXAS, WHICH COULD MERGE INTO THE LARGER
PATTERN BUT THIS REMAINS HIGHLY UNCERTAIN AT THIS TIME. WITH THE
GROWING DIFFERENCES IN THE MODEL GUIDANCE, ESPECIALLY THE
DETERMINISTIC RUNS, RAMPED UP THE PROPORTION OF ENSEMBLE MEANS IN
THE FORECAST BLEND TO OVER HALF BY DAY 7, ESPECIALLY FAVORING THE
ECENS MEAN.
..WEATHER/HAZARDS HIGHLIGHTS
THE EXCESSIVE RAINFALL THREATS IN THE NORTHEAST WILL END BY BY
SUNDAY AS THE LOWS AND ASSOCIATED FRONTS PIVOT. HOWEVER, SHOWERS
ARE LIKELY TO LINGER UNDERNEATH THE UPPER LOW THROUGH MUCH OF THE
WEEK, WITH ENHANCED RAIN AMOUNTS POSSIBLE DOWNWIND OF THE GREAT
LAKES. A FEW SHOWERS MAY BE POSSIBLE ACROSS THE CENTRAL/NORTHERN
APPALACHIANS AS WELL WITH UPSLOPE FLOW.
FARTHER WEST, SUNDAY LOOKS TO BE A MOSTLY DRY DAY ACROSS THE CONUS
ASIDE FROM LIMITED SHOWERS IN THE SOUTHWEST AND THE FLORIDA
PENINSULA. BY MONDAY THOUGH, TROUGHING AND A COLD FRONT
APPROACHING AND ENTERING THE PACIFIC NORTHWEST SHOULD LEAD TO
INCREASING RAIN CHANCES THERE. SOME RELATIVELY HEAVY RAIN RATES
ARE POSSIBLE DUE TO A MODERATE TO STRONG ATMOSPHERIC RIVER TAKING
AIM AT THE THE PACIFIC NORTHWEST AND A COUPLED JET ALOFT PROVIDING
SUPPORT FOR ASCENT, ALONG WITH PERHAPS SOME INSTABILITY. UPSLOPE
AREAS OF THE COASTAL MOUNTAIN RANGES, OLYMPICS, AND CASCADES COULD
SEE HIGHER RAIN TOTALS. BUT RECENT DRY CONDITIONS AND IT BEING
THIS EARLY IN THE WET SEASON MAY MEAN NOT MANY FLOODING ISSUES
ARISE FROM THIS RAIN, SO DECIDED AGAINST ANY MARGINAL RISK AREA IN
THE EXCESSIVE RAINFALL OUTLOOK AT THIS TIME. PRECIPITATION CHANCES
WILL SPREAD EASTWARD TUESDAY AND WEDNESDAY INTO THE ROCKIES AND
LIKELY INTO THE CENTRAL U.S. WEDNESDAY AND THURSDAY, BUT WITH
UNCERTAINTY IN THE DETAILS. MEANWHILE FRONTS OVER FLORIDA SHOULD
PROVIDE A FOCUS FOR RAIN AND THUNDERSTORMS, WITH RAIN TOTALS
INCREASING ESPECIALLY BY MIDWEEK.
COOLER THAN NORMAL TEMPERATURES ARE LIKELY EARLY IN THE WEEK
UNDERNEATH THE UPPER TROUGH IN THE EAST-CENTRAL TO EASTERN U.S.
THE COOLEST ANOMALIES (AROUND 10-15F BELOW NORMAL) FOR LOWS ARE
FORECAST ACROSS THE SOUTHEAST, WHILE BELOW AVERAGE HIGHS BY 15-20F
LOOK TO FOCUS ACROSS THE GREAT LAKES/OHIO VALLEY/CENTRAL
APPALACHIANS. TEMPERATURES SHOULD GRADUALLY MODERATE CLOSER TO
NORMAL AS THE WEEK PROGRESSES, LASTING THE LONGEST WHERE THE
STUBBORN UPPER LOW REMAINS OVERHEAD. MEANWHILE, THE WEST WILL SEE
ABOVE AVERAGE TEMPERATURES EARLY IN THE WEEK, WHICH WILL GET
PUSHED INTO THE CENTRAL U.S. THROUGH THE WORKWEEK AS THE RIDGE
OVERHEAD TRACKS EASTWARD AND GIVES WAY TO TROUGHING IN THE WEST
THAT FLIPS TEMPERATURES TO BELOW AVERAGE (ESPECIALLY IN TERMS OF
HIGHS) BY TUESDAY-THURSDAY.
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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