089
FXUS02 KWBC 051830
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
229 PM 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 ON THE OVERALL PATTERN
THROUGH ESPECIALLY THE FIRST HALF OF THE PERIOD. THERE ARE SOME
DIFFERENCES IN THE DETAILS OF THE UPPER LOW OVER THE
NORTHEAST/SOUTHEAST CANADA AND PARTICULARLY WITH EXACT
INTERACTIONS OF PHILIPPE INTO THIS SYSTEM. THE 00Z UKMET CONTINUED
TO BE DISPLACED MORE NORTHEAST OF THE CONCENSUS OF THE CENTER OF
THE LOW BY DAY 5/TUESDAY, BUT THE 12Z RUN (AVAILABLE AFTER
FORECAST GENERATION TIME) SEEMS TO HAVE ADJUSTED CLOSER TO
CONSENSUS. THE WPC FORECAST FOR TODAY FAVORED A BLEND OF THE CMC,
GFS, AND ECMWF FOR THIS SYSTEM.
BY TUESDAY AND BEYOND, SOME GREATER DIFFERENCES ARISE WITH THE
WESTERN TROUGH. GFS RUNS HAVE BEEN PERSISTENTLY A LITTLE LESS
AMPLIFIED BUT ALSO QUICKER TO PROGRESS THE TROUGHING EASTWARD THAN
THE ECMWF AND CMC WHICH DIG IT INTO THE WEST/CENTRAL U.S. MORE.
ENSEMBLE MEANS GENERALLY FOLLOW THEIR RESPECTIVE DETERMINISTIC
RUNS, BUT THERE REMAINS A LOT OF UNCERTAINTY IN THE INDIVIDUAL
ENSEMBLE MEMBERS. THE 00Z ECMWF MAY BE A LITTLE TOO DEEP AS IT
FORMS AN EMBEDDED CLOSED UPPER LOW, BUT RECENT CMC RUNS ARE
TRENDING IN THAT DIRECTION TOO. ALSO SOME UNCERTAINTY LATE IN THE
FORECAST PERIOD FOR SOUTHERN STREAM ENERGY POSSIBLY ORIGINATING
FROM AN EASTERN PACIFIC TROPICAL SYSTEM TO TRACK INTO MEXICO AND
THEN MAYBE SOUTH TEXAS/THE GULF, WHICH COULD MERGE INTO THE LARGER
PATTERN ENHANCING RAINFALL TOTALS ACROSS THE GULF/GULF
COAST/FLORIDA AROUND THE MIDDLE OF NEXT WEEK. WITH THE GROWING
DIFFERENCES IN THE DETERMINISTIC GUIDANCE THE SECOND HALF OF THE
PERIOD, INCREASED USAGE OF THE ENSEMBLE MEANS INTO THE BLEND DAYS
6 AND 7.
..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 INCREASING HEAVY
RAIN CHANCES BY MIDWEEK AND EVEN MORE SO IF AIDED BY ANY SORT OF
TROPICAL MOISTURE.
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 BY 15-20F LOOK TO FOCUS ACROSS THE GREAT
LAKES/OHIO VALLEY/CENTRAL APPALACHIANS, WHERE SOME LOCATIONS COULD
SEE THE FIRST FROST/FREEZE FOR THE SEASON. 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.
SANTORELLI/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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