975
FXUS02 KWBC 020629
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
229 AM EDT MON SEP 2 2024
VALID 12Z THU SEP 05 2024 - 12Z MON SEP 09 2024
...HAZARDOUS HEAT LIKELY LATE WEEK ACROSS PARTS OF THE SOUTHWEST
AND CALIFORNIA WITH HEAVY RAINFALL THREATS ACROSS THE LOWER
MISSISSIPPI VALLEY TO THE SOUTHEAST...
..OVERVIEW
UPPER RIDGING WILL BUILD OVER THE WEST DURING THE PERIOD, WITH
HEAT THREATS FOR PARTS OF THE SOUTHWEST INTO CALIFORNIA.
DOWNSTREAM, AN AMPLIFIED RIDGE AND EVENTUAL CLOSED LOW WILL DIG
INTO THE EASTERN THIRD OF THE NATION WITHIN AN INCREASINGLY BLOCKY
LATE PERIOD REGIME. MEANWHILE, WEAK ENERGY NEAR THE GULF COAST
INTERACTING WITH A PERSISTENT SURFACE BOUNDARY SHOULD PROVIDE FOCUS
FOR HEAVY RAINFALL THAT SHIFTS FROM THE LOWER MISSISSIPPI
VALLEY/GULF COAST INTO THE SOUTHEAST AND EAST COAST LATE THIS WEEK.
WEATHER ACROSS THE NATION SHOULD BE VERY QUIET BY SUNDAY AND
BEYOND.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODELS AND ENSEMBLES SHOW FAIRLY GOOD AGREEMENT THROUGH MUCH OF
THE PERIOD ON AN INCREASINGLY AMPLIFIED AND BLOCKY UPPER FLOW
PATTERN ACROSS THE LOWER 48. THE GREATEST AREA OF UNCERTAINTY
REMAINS SURROUNDING THE DEEP TROUGH/CLOSED LOW NEAR THE GREAT LAKES
THAT SHOULD SLOWLY LIFT NORTH AND TIMING OF THE ASSOCIATED FRONT
INTO THE NORTHEAST. THE CMC REMAINS DISPLACED SLIGHTLY SOUTH OF THE
GFS/ECMWF AND THE ENSEMBLE MEANS WITH THE CLOSED LOW. TIMING
UNCERTAINTIES ALSO SURROUND AN ADDITIONAL SHORTWAVE ENTERING THE
NORTHWEST EARLY NEXT WEEK.
THE WPC FORECAST USED A BLEND OF THE DETERMINISTIC GUIDANCE FOR
THE FIRST HALF OF THE PERIOD, INCREASING TO AN EQUAL MIX OF
DETERMINISTIC (GFS AND ECMWF) AND ENSEMBLE MEANS BY THE LATE PERIOD
TO SMOOTH OUT SOME OF THE DIFFERENCES.
..WEATHER/HAZARDS HIGHLIGHTS
THE MAIN HEAVY RAINFALL FOCUS DURING THE PERIOD WILL BE ACROSS THE
SOUTH AS SHORTWAVE ENERGY MOVES INLAND FROM THE WESTERN GULF AND A
SURFACE FRONT LINGERS ALONG/NEAR THE COAST. PRECIPITATION COVERAGE
AND TOTALS REMAIN UNCERTAIN, BUT THE OVERALL DYNAMICS AND
ANOMALOUS MOISTURE SUPPORT A HEAVY TO EXCESSIVE RAINFALL THREAT
WHICH SLOWLY SHIFTS ACROSS THE DEEP SOUTH. THE DAY 4 EXCESSIVE
RAINFALL OUTLOOK (COVERING THURSDAY-THURSDAY NIGHT) SHOWS A BROAD
MARGINAL RISK ACROSS THE LOWER MISSISSIPPI VALLEY INTO THE LOWER
TENNESSEE VALLEY AND PARTS OF THE SOUTHEAST. AN EMBEDDED SLIGHT
RISK WAS ADDED NEAR THE COAST FROM SOUTHEAST LOUISIANA TO THE FAR
WESTERN FLORIDA PANHANDLE WHERE MODELS SHOW OVERLAP IN HEAVY QPF
FROM THE SHORT RANGE INTO THE MEDIUM RANGE PERIOD. THE OVERALL
THREAT SHIFTS EAST ON FRIDAY INTO THE SOUTHEAST AND NORTHWARD
TOWARDS THE MID-ATLANTIC AS A WEAK AREA OF LOW PRESSURE LIFTS UP
THE COAST. THIS IS COVERED BY A LARGE MARGINAL RISK ON THE DAY 5
ERO, WHERE AND EMBEDDED SLIGHT MAY BE NEEDED IN FUTURE ISSUANCES
ONCE MODELS SHOW BETTER CONSISTENCY. WRAP BACK MOISTURE AND
RAINFALL SHOULD CONTINUE ACROSS THE NORTHEAST ON SATURDAY ON THE
BACKSIDE OF THE CYCLONE, BUT OTHERWISE RAINFALL SHOULD CLEAR THE
EAST COAST. BY SUNDAY AND BEYOND, MUCH OF THE COUNTRY LOOKS QUIET
AND DRY.
INCREASING HEAT AND ABOVE NORMAL TEMPERATURES ARE EXPECTED ACROSS
MUCH OF THE WEST, WITH MODERATE TO MAJOR HEATRISK THREATS ACROSS
THE SOUTHWEST AND CENTRAL VALLEYS OF CALIFORNIA THROUGH AT LEAST
FRIDAY. A MUCH COOLER AIRMASS WILL FILTER EASTWARD FROM THE
NORTHERN PLAINS AND GREAT LAKES INTO THE EAST THIS WEEKEND AND
EARLY NEXT WEEK, WITH DAYTIME HIGHS 10 TO 20 DEGREES BELOW NORMAL.
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 (QPF), EXCESSIVE RAINFALL
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:
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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