538
FXUS02 KWBC 071851
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
250 PM EDT SAT OCT 07 2023
VALID 12Z TUE OCT 10 2023 - 12Z SAT OCT 14 2023
...INCREASING HEAVY RAIN THREATS FOR THE MIDWEST AND GULF
COAST/NORTHERN FLORIDA BY MID TO LATE NEXT WEEK...
..OVERVIEW
IT REMAINS THE CASE THAT 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 WITH SOME INDICATIONS IT MAY
BEGIN TO PUSH EAST LATER IN THE WEEK. A NEARLY STATIONARY SURFACE
LOW WILL CREATE PRECIPITATION CHANCES NEAR THE GREAT LAKES EARLY
IN THE WEEK WITH SOME LAKE EFFECT ENHANCEMENT POSSIBLE. OUT WEST,
A TROUGH WILL MOVE ONSHORE EARLY IN THE WEEK DIVING THROUGH THE
WEST WITH POSSIBLE 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 INTO TUESDAY IN THE PACIFIC NORTHWEST WHERE
LOCALLY HEAVY DOWNPOURS MAY BE POSSIBLE, THEN PRECIPITATION WILL
SPREAD INTO THE CENTRAL U.S. MIDWEEK AND TO THE EAST
COAST/NORTHEAST BY FRIDAY. A FRONTAL BOUNDARY WITH DEEPENED
TROPICAL MOISTURE LIFTING THROUGH THE GULF AND FLORIDA WILL
INCREASE PRECIPITATION CHANCES ACROSS FLORIDA/THE GULF COAST THEN
SOUTHEAST AS WELL BY MID TO LATER IN THE WEEK BEFORE LIFTING UP
THE EAST COAST.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
MODEL AND ENSEMBLE SOLUTIONS REMAIN OVERALL WELL CLUSTERED WITH
THE LARGE SCALE PATTERN THROUGH ABOUT THURSDAY AND A GENERAL
DETERMINISTIC MODEL BLEND WORKED WELL. THERE CONTINUES TO BE A
TREND TOWARDS A DEFINITIVE CLOSED LOW DEVELOPING OVER THE ROCKIES
AROUND WEDNESDAY MOVING INTO THE PLAINS/MIDWEST LATE WEEK. LATEST
MODEL RUNS OFFER ADDITIONAL UNCERTAINTIES WITH WHETHER THIS LOW
PHASES WITH THE BIGGER LOW OVER SOUTHEAST CANADA OR REMAINS A
SEPARATE FEATURE. THROUGH THE 00Z/06Z MODEL RUNS, BOTH THE ECMWF
AND CMC (ALONG WITH THE ECENS MEAN) SUGGEST THESE FEATURES STAY
SEPARATE AND THE NEW MIDWEST UPPER LOW SIMPLY PUSHES THE SOUTHEAST
CANADIAN LOW TO THE EAST. THE GFS/GEFS SEEMED ALONE IN SUGGESTING
A MUCH SLOWER/MORE NORTHWARD PROGRESSION OF THIS LOW, BUT WAS MORE
CONSISTENT WITH WPC CONTINUITY. GFS WAS ALSO MUCH TOO FAST WITH
THE SURFACE SYSTEM THROUGH THE EAST COMPARED TO THE BETTER
CONSENSUS. A BLEND TOWARDS THE ECMWF, CMC, AND ECENS MEAN LATE
PERIOD BROKE WPC CONTINUITY IN SOME WAYS, BUT THE NEW 12Z GFS
(AVAILABLE AFTER FORECAST GENERATION TIME) DID COME IN MUCH BETTER
AGREEMENT WITH THE ECMWF AND CMC WHICH INCREASES CONFIDENCE IN
THIS SHIFT. ALSO SOME TIMING DIFFERENCES IN THE NEXT TROUGH AS IT
REACHES THE WEST COAST NEXT FRIDAY-SATURDAY.
..WEATHER/HAZARDS HIGHLIGHTS
THE THREAT FOR EXCESSIVE RAINFALL IS FORECAST TO REMAIN LOW
TUESDAY. HOWEVER, MOISTURE WORKING INTO THE PACIFIC NORTHWEST
AHEAD OF AN APPROACHING FRONTAL SYSTEM WILL COMBINE WITH UPPER
LEVEL DYNAMIC SUPPORT AND TERRAIN UPSLOPE TO ENHANCE RAINFALL FOR
THE COASTAL MOUNTAIN RANGES, OLYMPICS, AND CASCADES THAT WILL
LIKELY SEE THE HIGHEST RAINFALL TOTALS. A MARGINAL RISK OF
EXCESSIVE RAINFALL WAS NOT INTRODUCED AS THE SYSTEM SEEMS
PROGRESSIVE AND MUCH OF THE PACIFIC NORTHWEST HAS LINGERING
DROUGHT CONDITIONS, SO MUCH OF THIS RAINFALL COULD BE MORE
BENEFICIAL THAN HAZARDOUS. HIGHER ELEVATIONS FROM THE CASCADES
THROUGH THE NORTHERN ROCKIES WILL SEE SNOW WITH UPPER
TROUGH/HEIGHT FALL APPROACH AND PASSAGE.
PRECIPITATION CHANCES WILL EXPAND EAST THROUGHOUT THE WEEK AS A
FRONTAL SYSTEM MOVES ACROSS THE NATION, REACHING THE CENTRAL U.S.
BY AROUND MIDWEEK. DEEP CYCLOGENESIS AND WRAPPING MOISTURE INTO A
LEADING WARM FRONT LIFTING THROUGH THE EAST-CENTRAL U.S. WILL
SHIFT FOCUS FOR POSSIBLY HEAVY RAIN FROM THE CENTRAL PLAINS
THROUGH THE MIDWEST INTO WEDNESDAY. THE WPC DAY 5 EXCESSIVE
RAINFALL OUTLOOK (ERO) SHOWS A MARGINAL RISK OVER THE MID-MS
VALLEY GIVEN RISK FOR TRAINING AND GROWING MODEL AND ENSEMBLE
SIGNALS. GUIDANCE SUGGESTS THIS HEAVY RAINFALL AREA WILL LIKELY
EXPAND THURSDAY ACROSS THE MIDWEST WITH CONTINUED SYSTEM
DEVELOPMENT AND TRACK/INFLOW AND A POSSIBLY HEAVY TO EXCESSIVE
RAINFALL THREAT. MEANWHILE WELL SOUTH, A SEPARATE WARM FRONT
LIFTING THROUGH THE GULF OF MEXICO AND THE FLORIDA PENINSULA
BRINGS A THREAT FOR HEAVY RAINFALL FROM THE CENTRAL GULF COAST TO
THE SOUTHEAST WEDNESDAY/THURSDAY. THIS MAY BE AIDED BY AN AREA OF
LOW PRESSURE IN THE GULF OF MEXICO AND POSSIBLE REMNANT TROPICAL
MOISTURE TO BE MONITORED IN THE COMING DAYS. LATEST MODEL GUIDANCE
PROMPTED A MARGINAL RISK BEING INTRODUCED BY THE DAY 5/WEDNESDAY
ERO FROM THE CENTRAL GULF COAST TO THE FLORIDA PENINSULA, WITH
THIS RISK LIKELY TO CONTINUE INTO THURSDAY AS WELL. THESE TWO MAIN
SYSTEMS MAY INCREASINGLY INTERACT TO SPREAD ENHANCED RAINFALL AND
RUNOFF ISSUES POSSIBLE ACROSS THE EAST/NORTHEAST FRIDAY INTO
SATURDAY, WITH WIDESPREAD ENHANCED BACKSIDE WINDS AND POST-FRONTAL
FALLING AUTUMN TEMPERATURES.
SANTORELLI/SCHICHTEL
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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