147
FXUS02 KWBC 091859
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
258 PM EDT MON OCT 09 2023
VALID 12Z THU OCT 12 2023 - 12Z MON OCT 16 2023
...MID-LATE WEEK EXCESSIVE RAIN THREAT FOR THE MIDWEST/GREAT LAKES
TO NORTHEAST AS WELL AS THE SOUTHEAST...
..OVERVIEW
GUIDANCE STILL OFFERS A STRONG SIGNAL THAT A LEADING CLOSED UPPER
LOW WILL SHIFT SLOWLY EASTWARD ACROSS EASTERN CANADA LATE WEEK AND
EASE UNSETTLED CONDITIONS UNDER/AROUND THIS AMPLIFIED FEATURE AWAY
FROM THE NORTHEAST. MEANWHILE, ANOTHER DYNAMIC UPPER TROUGH/CLOSED
LOW AND SURFACE LOW/FRONTAL SYSTEM WILL WORK OUT FROM THE WEST TO
FAVOR ENHANCED MOUNTAIN SNOWS FOR THE NORTHERN/CENTRAL ROCKIES AND
EVEN INTO THE BLACK HILLS AND PERHAPS THE LOWER ELEVATIONS OF
NEBRASKA THURSDAY. THIS POTENT AND WELL-ORGANIZED UPPER SYSTEM
WILL THEN STEADILY TRACK FROM THE PLAINS TO THE NORTHEAST FRIDAY
THROUGH NEXT WEEKEND. THIS WILL FOSTER ENHANCED PRECIPITATION
CHANCES TO SPREAD IN EARNEST FROM THE CENTRAL U.S./MIDWEST THROUGH
THE NORTHEAST AS INFLOW MOISTURE INCREASES AHEAD OF DEEP
CYCLOGENESIS. TO THE SOUTH, A FRONTAL BOUNDARY ENHANCED WITH
TROPICAL MOISTURE WILL LIFT THROUGH THE GULF OF MEXICO TO INCREASE
HEAVY PRECIPITATION CHANCES ACROSS THE CENTRAL GULF COAST AND
FLORIDA/SOUTHEAST INTO LATER THIS WEEK BEFORE LIFTING OFF THE EAST
COAST. NEXT UPSTREAM, THE SLOW TRANSLATION OF AN AMPLIFIED AND
COMPLEX EASTERN PACIFIC UPPER/SURFACE SYSTEM MAY RENEW WET FLOW
INTO THE PACIFIC NORTHWEST INTO EARLY NEXT WEEK.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
AS THE LEADING UPPER LOW LIFTS AWAY FROM THE CONUS, THE MAIN
CONCERN WILL BE FOR THE NEXT UPPER AND SURFACE LOWS COMING OUT OF
THE WEST TRACKING EAST THROUGH LATE WEEK/WEEKEND. THERE IS GOOD
AGREEMENT FOR THIS SYSTEM TO EXIST. GUIDANCE DOES DIFFER IN THE
DETAILS OF THE PLACEMENT OF THE SURFACE LOW; THESE DIFFERENCES ARE
SOMEWHAT SMALL IN TERMS OF POSITION BUT CREATE NOTABLE DIFFERENCES
IN THE QPF. THIS FORECAST CYCLE SLOWED THE SURFACE LOW AND THE
ASSOCIATED FRONTAL SYSTEM A BIT THROUGH THURSDAY-FRIDAY, WITH THE
QPF TRACK ALSO SLOWING COMPARED TO CONTINUITY AND THE 13Z NBM
STARTING POINT, AS IT INCORPORATED THE SLOWER ECMWF AND CMC. THE
NEWER 12Z MODELS SUPPORT THIS AS WELL, WITH A PRETTY PERSISTENT
ECMWF LOW POSITION AND THE 12Z GFS/GEFS MEAN LOWS TRENDING WEST A
BIT THROUGH FRIDAY.
BY THE WEEKEND INTO EARLY NEXT WEEK, THE 00Z CMC DIFFERED IN TERMS
OF THE EVOLUTION OF THE UPPER LOW (SPLITS IT WITH SOME HELD BACK
IN THE NORTHERN PLAINS AND SOME MOVING EAST, UNLIKE OTHER
GUIDANCE), SO IT WAS NOT FAVORED. THE SURFACE LOW ENDS UP WITH
SOME VARIABILITY IN MODEL/ENSEMBLE GUIDANCE ESPECIALLY AS IT
SHIFTS INTO THE WESTERN ATLANTIC EARLY NEXT WEEK. THEN FARTHER
WEST, RIDGING IS LIKELY ACROSS THE INTERIOR WEST UP INTO CENTRAL
CANADA, WHILE ENERGY MAY ENTER THE NORTHWEST FROM THE EASTERN
PACIFIC. THE STRENGTH OF THIS ENERGY AND THE ONSHORE FLOW AND
TROUGHING IT BRINGS IS STILL IN QUESTION, WITH THE GFS LESS
AMPLIFIED COMPARED TO OTHER GUIDANCE. GIVEN THESE CONSIDERATIONS
FOR THIS TIMEFRAME, PREFERRED A BLEND OF THE 06Z GFS AND GEFS MEAN
AND 00Z ECMWF AND EC MEAN.
..WEATHER/HAZARDS HIGHLIGHTS
DYNAMIC UPPER TROUGH/HEIGHT FALLS AND SURFACE SYSTEM PASSAGE
ACROSS THE WEST INTO THURSDAY WILL FAVOR A SWATH OF AUTUMN
MOUNTAIN SNOWS THAT COULD BE HEAVY ACROSS THE NORTHERN/CENTRAL
ROCKIES, WITH SOME FARTHER EAST INTO THE HIGH PLAINS POSSIBLE.
MEANWHILE DOWNSTREAM, PRECIPITATION CHANCES WILL EXPAND EAST AS
THIS MAIN SYSTEM WORKS INCREASINGLY INTO THE CENTRAL U.S. BY LATER
WEEK. DEEP CYCLOGENESIS AND WRAPPING ANOMALOUS MOISTURE INTO A
LEADING WARM FRONT LIFTING THROUGH THE EAST-CENTRAL U.S. WILL
SHIFT FOCUS FOR EMERGING HEAVY RAINS FROM THE NORTH-CENTRAL PLAINS
THROUGH THE MIDWEST/GREAT LAKES. WHILE LONGER DURATION RAINS AND
AMBIENT RELATIVELY DRY SOILS MAY PARTIALLY LIMIT IMPACT, THE WPC
DAY 4/THURSDAY AND DAY 5/FRIDAY EXCESSIVE RAINFALL OUTLOOKS (EROS)
SHOW MARGINAL AND SLIGHT RISK AREAS FROM THE NORTH-CENTRAL
PLAINS/MIDWEST/GREAT LAKES GIVEN POTENTIAL FOR TRAINING AND MODEL
AND ENSEMBLE SIGNALS FOR SOME HIGHER RAIN TOTALS. RISK AREAS WERE
NOT CHANGED TOO FUNDAMENTALLY IN THIS UPDATE, BUT ADJUSTED TO SHOW
THE SLOWER TREND OF THE QPF AXIS. MEANWHILE, A SEPARATE FRONT
MEANDERING THROUGH THE GULF OF MEXICO AND THE FLORIDA PENINSULA
COULD BRING A THREAT FOR HEAVY RAINFALL TO THE SOUTHEAST THURSDAY
INTO FRIDAY. THIS MAY BE AIDED BY AN AREA OF LOW PRESSURE IN THE
GULF OF MEXICO THAT IS NOW BEING MONITORED BY NHC AND POSSIBLE
EASTERN PACIFIC REMNANT TROPICAL MOISTURE. ERO DAY 4/5 MARGINAL
RISK AREAS SHIFT OUT FROM THE CENTRAL GULF COAST TO THE SOUTHEAST.
THE WARM FRONT LIFTING LATE WEEK MAY INCREASE THE AREAL COVERAGE
OF CONVECTION THERE AS INSTABILITY TREKS FARTHER INLAND. THESE TWO
MAIN SYSTEMS MAY INCREASINGLY INTERACT TO SOME DEGREE TO SPREAD
ENHANCED RAINFALL AND RUNOFF ISSUES POSSIBLE ACROSS THE
EAST/NORTHEAST THIS WEEKEND WITH COASTAL LOW DEVELOPMENT/DEEPENING
AS A MARITIME RISK. WIDESPREAD ENHANCED WINDS ARE POSSIBLE ON THE
BACKSIDE OF THE LOW FIRST IN THE PLAINS AND TRACKING EASTWARD INTO
THE ATLANTIC. THE SYSTEM'S COLD FRONT WILL ALSO SPREAD COOLER THAN
AVERAGE TEMPERATURES FROM WEST TO EAST ACROSS THE LOWER 48, WITH A
FIRST FROST/FREEZE OF THE FALL SEASON POSSIBLE IN THE CENTRAL
PLAINS.
TATE/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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page