915
FXUS02 KWBC 061828
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
227 PM EDT FRI OCT 06 2023
VALID 12Z MON OCT 09 2023 - 12Z FRI OCT 13 2023
...INCREASING HEAVY RAIN THREATS FOR THE MIDWEST AND GULF
COAST/NORTHERN FLORIDA BY MID TO LATE NEXT WEEK...
..OVERVIEW
A DEEP UPPER LEVEL LOW IS FORECAST TO PARK ITSELF OVER
SOUTHEASTERN CANADA AND THE GREAT LAKES AND CHURN IN PLACE THROUGH
MOST OF NEXT WEEK. A NEARLY STATIONARY SURFACE LOW WILL CREATE
PRECIPITATION CHANCES NEAR THE GREAT LAKES EARLY IN THE WEEK WITH
SOME LAKE EFFECT ENHANCEMENT POSSIBLE. IN THE WEST, A TROUGH WILL
MOVE ONSHORE EARLY IN THE WEEK DIVING THROUGH THE WEST WITH SOME
CHANCE FOR CLOSED UPPER LOW DEVELOPMENT OVER THE ROCKIES AROUND
THURSDAY. THIS FEATURE WILL DRIVE A SURFACE FRONTAL SYSTEM EAST
ACROSS THE COUNTRY THROUGH THE WEEK. PRECIPITATION CHANCES WILL BE
GREATEST ON MONDAY AND TUESDAY IN THE PACIFIC NORTHWEST WHERE
LOCALLY HEAVY RAINFALL MAY BE POSSIBLE, THEN PRECIPITATION WILL
SPREAD INTO THE CENTRAL U.S. MIDWEEK AND TO THE EAST COAST BY
FRIDAY. A FRONTAL BOUNDARY LIFTING THROUGH THE GULF AND FLORIDA
WILL INCREASE PRECIPITATION CHANCES ACROSS FLORIDA/THE GULF COAST
AS WELL BY MID TO LATER IN THE WEEK.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE IS IN GOOD ENOUGH AGREEMENT MONDAY-WEDNESDAY ON THE
OVERALL PATTERN ACROSS THE CONUS TO USE A EQUAL BLEND OF THE
LATEST DETERMINISTIC GUIDANCE. AFTER WEDNESDAY, UNCERTAINTY
INCREASES AS THE WESTERN TROUGH DIVES ACROSS THE INTERMOUNTAIN
WEST (SOUTH OF A BLOCKY UPPER HIGH OVER CENTRAL CANADA) AND
ATTEMPTS TO CLOSE OFF AN UPPER LOW OVER THE ROCKIES WHICH
PROGRESSES INTO THE CENTRAL PLAINS. THERE IS STILL A LOT OF RUN TO
RUN VARIABILITY IN THE DETAILS OF THIS, BUT MODELS HAVE BEEN
TRENDING MORE TOWARDS THE PRESENCE OF THIS FEATURE THE PAST FEW
RUNS. THE ENSEMBLE MEANS OFFER A GOOD MIDDLE GROUND SOLUTION, BUT
THE 06Z GEFS MEAN WAS NOTABLY FASTER THAN THE REST OF THE GUIDANCE
WITH THE SURFACE LOW NEXT FRIDAY WELL ON THE EASTERN EDGE OF THE
GUIDANCE ENVELOPE. THE WPC BLEND FOR DAYS 6-7/THURSDAY-FRIDAY USED
A BLEND OF THE DETERMINISTIC GFS, ECMWF, AND CMC ALONG WITH THE
ECENS MEAN LATE IN THE PERIOD WHICH OFFERED GOOD CONTINUITY WITH
THE PREVIOUS WPC FORECAST AS WELL.
..WEATHER/HAZARDS HIGHLIGHTS
THE THREAT FOR EXCESSIVE RAINFALL IS FORECAST TO REMAIN LOW MONDAY
AND TUESDAY. THE ONLY AREA OF CONCERN IS THE PACIFIC NORTHWEST
WHERE MOISTURE WILL STREAM ONSHORE AHEAD OF AN APPROACHING FRONTAL
SYSTEM. LOCALLY HEAVY TO POSSIBLY EXCESSIVE RAINFALL WILL BE
POSSIBLE AT TIMES DUE TO THE COMBINATION OF SURFACE LIFT AND UPPER
LEVEL DYNAMIC SUPPORT FOR ASCENT, AND UPSLOPE AREAS OF THE COASTAL
MOUNTAIN RANGES, OLYMPICS, AND CASCADES WILL LIKELY SEE THE
HIGHEST RAINFALL TOTALS. A MARGINAL RISK OF EXCESSIVE RAINFALL
AREA WAS CONSIDERED, BUT WAS NOT INTRODUCED FOR EITHER DAY AT THIS
TIME BECAUSE THE SYSTEM SEEMS QUITE PROGRESSIVE, A STRETCH OF DRY
WEATHER WILL PRECEDE THIS EVENT, AND IT IS EARLY IN THE WET
SEASON. THESE FACTORS WILL ALL LIMIT THE FLASH FLOOD POTENTIAL.
MUCH OF THE PACIFIC NORTHWEST IS STILL EXPERIENCING DROUGHT
CONDITIONS, SO MUCH OF THIS RAINFALL COULD BE MORE BENEFICIAL THAN
HAZARDOUS.
PRECIPITATION CHANCES WILL EXPAND EAST THROUGHOUT THE WEEK AS A
FRONTAL SYSTEM MOVES ACROSS THE NATION, REACHING THE CENTRAL U.S.
BY AROUND MIDWEEK. A WARM FRONT LIFTING THROUGH THE EAST-CENTRAL
U.S. WILL PROVIDE FOCUS FOR POSSIBLY HEAVY RAIN FROM THE CENTRAL
PLAINS INTO THE MIDWEST WEDNESDAY-FRIDAY. MEANWHILE, A SEPARATE
WARM FRONT LIFTING THROUGH THE GULF OF MEXICO AND THE FLORIDA
PENINSULA BRINGS A THREAT FOR HEAVY RAINFALL TO MAINLY THE FLORIDA
PANHANDLE AND NORTHERN FLORIDA STARTING WEDNESDAY. THIS MAY BE
AIDED BY AN AREA OF LOW PRESSURE IN THE GULF OF MEXICO AND
POSSIBLE REMNANT TROPICAL MOISTURE.
TEMPERATURES WILL BE COOLER THAN NORMAL DURING THE FIRST HALF OF
NEXT WEEK FROM THE MIDWEST TO THE NORTHEAST UNDERNEATH THE UPPER
LOW. HIGH TEMPERATURES ARE FORECAST TO BE 10-15 DEGREES BELOW
AVERAGE, AND OVERNIGHT LOWS WILL BE COLD ENOUGH FOR FROST TO FORM
IN PARTS OF THE UPPER MIDWEST AND GREAT LAKES REGION. ABOVE
AVERAGE TEMPERATURES ARE FORECAST TO START THE WEEK ACROSS MUCH OF
THE CENTRAL U.S. AND THE WEST, BUT TEMPERATURES WILL DROP THROUGH
MIDWEEK AS THE FRONTAL SYSTEM MOVES THROUGH.
SANTORELLI
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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