779
FXUS02 KWBC 221829
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
229 PM EDT FRI SEP 22 2023
VALID 12Z MON SEP 25 2023 - 12Z FRI SEP 29 2023
..OVERVIEW
THE PATTERN FEATURES AN UPPER TROUGH MOVING INTO THE WEST AND A
DOWNSTREAM OMEGA BLOCK EVOLVING INTO A REX-LIKE BLOCK ACROSS THE
EASTERN PORTION OF NORTH AMERICA AND THE ADJACENT NORTHWEST
ATLANTIC.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
A BLOCKY PATTERN WILL START THE FORECAST PERIOD WITH RIDGING
PRESENT SOUTH OF HUDSON BAY WHILE SHORTWAVE ENERGY OVER THE
CENTRAL U.S. WEAKENS AS IT MOVES SOUTH/EAST. MEANWHILE, FORECAST
GUIDANCE IS IN REALLY GOOD AGREEMENT WITH THE APPROACHING OF A
STRONGER, EARLY SEASON STORM SYSTEM / SHORTWAVE ENERGY INTO THE
PACIFIC NORTHWEST BEGINNING LATE THIS WEEKEND THROUGH NEXT WEEK,
WITH A COUPLE STRONGER EMBEDDED SHORTWAVES EXPECTED TO MOVE
ONSHORE. THE GREATEST MODEL UNCERTAINTY WAS TOWARD THE END OF THE
FORECAST PERIOD, WHERE WEAK TROUGHING OVER THE GREAT LAKES AND
EASTERN U.S. MAY EVENTUALLY BECOME CUT-OFF FROM MAIN UPPER FLOW
PATTERN OVER THE MID-ATLANTIC REGION. A LINGERING TROUGH AND
POSSIBLE SURFACE LOW DEVELOPMENT OFF THE COAST MAY BRING AN
UNSETTLED PERIOD OF WEATHER TO THE REGION LATE IN THE WEEK INTO
NEXT WEEKEND. THERE IS LOWER CONFIDENCE AND PREDICTABILITY WITH
THE MAIN SYNOPTIC FEATURES AND ANY SENSIBLE WEATHER IMPACTS, BUT
THE TRENDS FROM THE 00Z TO 12Z GUIDANCE SUGGEST SOME SORT OF
WEATHER FEATURE WILL LIKELY BE PRESENT. THE WPC BLEND LARGELY
FOLLOWED A NEAR EQUAL WEIGHT OF THE LATEST DETERMINISTIC GUIDANCE
INITIALLY THEN INCREASINGLY INCLUDED THE ECENS AND GEFS MEANS BY
DAY 6 TO ACCOUNT FOR GREATER MODEL UNCERTAINTY AND LOWER
CONFIDENCE, PARTICULARLY FOR THE EASTERN U.S.
..WEATHER/HAZARDS HIGHLIGHTS
AN EARLY SEASON STORM SYSTEM WILL BRING UNSETTLED AND ACTIVE
WEATHER TO THE PACIFIC NORTHWEST BEGINNING LATE THIS WEEKEND AND
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 INTO NORTHERN CALIFORNIA/SOUTHWEST
OREGON WHERE SOME LOCALIZED FLOODING MAY BE POSSIBLE WITH
REPEATING ROUNDS OF MODERATE RAINFALL, PARTICULAR IN BURN
AREAS/BURN SCARS NEAR THE WESTERN BORDER OF CA/OR MONDAY INTO
EARLY TUESDAY. A SLOW MOVING, FADING FRONT MOVING INTO THE
SOUTHERN PLAINS AND EVENTUALLY THE WESTERN GULF COAST REGION MAY
ACT AS THE FOCUS FOR SOME AREAS OF EXCESSIVE RAINFALL AT TIME,
PARTICULARLY ACROSS PORTIONS OF SOUTH-CENTRAL TO SOUTHEAST TEXAS
AND PORTIONS OF THE LOWER MISSISSIPPI VALLEY.
ACROSS THE EAST COAST, PARTICULARLY MID-ATLANTIC REGION, THERE
REMAINS CONSIDERABLE UNCERTAINTY HOW THE UPPER LEVEL PATTERN
EVOLVES AND ANY ASSOCIATED SURFACE FEATURES THAT ARE ABLE TO TAP
INTO ATLANTIC MOISTURE. COMPARED TO THE PREVIOUS CYCLE, THERE WAS
AN INCREASE IN THE PRECIPITATION CHANCES AND QPF BUT THERE REMAINS
MANY QUESTIONS AND OVERALL CONFIDENCE IS FAIRLY LOW FOR ANY AREAS
OF HEAVY RAINFALL.
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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