499
FXUS02 KWBC 230544
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
144 AM EDT SAT SEP 23 2023
VALID 12Z TUE SEP 26 2023 - 12Z SAT SEP 30 2023
..OVERVIEW
THE PATTERN FEATURES AN AMPLIFYING UPPER TROUGH MOVING INTO THE
WEST AND A DOWNSTREAM REX-LIKE BLOCK ACROSS THE EASTERN PORTION OF
NORTH AMERICA AND THE ADJACENT NORTHWEST ATLANTIC.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE GUIDANCE SHOWED REASONABLE AGREEMENT FROM TUESDAY INTO
THURSDAY. THEREAFTER, BOTH THE 12Z ECMWF AND 12Z CANADIAN
SIGNIFICANTLY DIVERGED WITH THE EXPECTED AMPLIFIED TROUGH SEEN IN
THE 18Z GFS/12Z NAEFS MEAN/12Z ECMWF ENSEMBLE MEAN. THE ECMWF WAS
ALSO AMPLIFIED, JUST FARTHER WEST, WHILE THE CANADIAN SIMPLY
FLATTENED OUT THE MID-LEVEL FLOW. THE INITIAL BLEND FOR THE
PRESSURES, 500 HPA HEIGHTS, FRONTS, QPF, AND WINDS WAS A
COMPROMISE OF THE 12Z ECMWF, 12Z UKMET, 12Z CANADIAN, AND 18Z GFS.
AFTER THURSDAY MORNING, THE BLEND SIMPLIFIED TO A 12Z NAEFS
MEAN/12Z ECMWF ENSEMBLE MEAN/18Z GFS COMPROMISE. THE REMAINDER OF
THE GRIDS WERE MORE HEAVILY WEIGHTED ON THE 01Z NBM.
..WEATHER/HAZARDS HIGHLIGHTS
AN EARLY SEASON STORM SYSTEM WILL BRING UNSETTLED AND ACTIVE
WEATHER TO THE PACIFIC NORTHWEST THROUGH EARLY NEXT WEEK. A FEW
ROUNDS OF HEAVIER PRECIPITATION ARE LIKELY, FAVORED FOR THE
COASTAL REGIONS AND UPSLOPE AREAS OF THE WASHINGTON AND OREGON
CASCADES. AN AMPLIFYING TROUGH MOVING THROUGH THE SOUTHEAST WILL
REINFORCE THE POLAR FRONT ACROSS FL AND THE GULF OF MEXICO. THE
DEGREE AND COVERAGE OF HEAVY RAINFALL IN AND NEAR THE SOUTHEAST
NEAR AND AHEAD OF THE UPPER TROUGH REMAINS A QUESTION MARK IN THE
GUIDANCE, WHICH PRECLUDED ANY EXCESSIVE RISK AREAS FOR MID NEXT
WEEK AT THIS TIME. THIS CAN BE REEVALUATED ON FUTURE SHIFTS.
TEMPERATURES SHOULD BE MOST ABOVE AVERAGE ACROSS PORTIONS OF THE
PLAINS/MIDWEST -- MORESO ON OVERNIGHT LOWS -- AND BELOW AVERAGE
ACROSS PORTIONS OF THE MID-ATLANTIC STATES AND WEST, WHICH WILL BE
MOST NOTICEABLE FOR DAYTIME HIGHS.
ROTH/TAYLOR
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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