113
FXUS02 KWBC 011812
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
212 PM EDT SUN SEP 1 2024
VALID 12Z WED SEP 04 2024 - 12Z SUN SEP 08 2024
..OVERVIEW
AN UPPER RIDGE OVER THE SOUTHERN TIER TO START THE PERIOD WILL
STRENGTHEN OVER THE WEST MID TO LATE WEEK AS A SHORTWAVE SHIFTS
INTO THE NORTHERN PLAINS. THIS LOOKS TO INTERACT WITH ENERGY
DROPPING OUT OF CANADA TO PRODUCE A FAIRLY AMPLIFIED TROUGH OVER
THE GREAT LAKES, MOVING INTO THE NORTHEAST NEXT WEEKEND. THIS
SHOULD PUSH A MEAN BOUNDARY THROUGH THE NORTHERN TIER DURING THE
PERIOD. MEANWHILE, EMBEDDED ENERGY WITHIN THE LARGER SCALE UPPER
RIDGE AND A PERSISTENT SURFACE BOUNDARY DRAPED NEAR THE GULF COAST
SHOULD PROVIDE FOCUS FOR HEAVY RAINFALL THAT SHIFTS SLOWLY FROM THE
LOWER MISSISSIPPI VALLEY/GULF COAST INTO THE SOUTHEAST AND
POSSIBLY POINTS NORTH.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODELS ARE SLOWLY CONSOLIDATING AROUND A SPLIT FLOW PATTERN OVER
EASTERN NORTH AMERICA TOWARD THE END OF THE WEEK. THE OPERATIONAL
GFS HAS TRENDED SLOWER AND CLOSER IN LINE WITH THE REST OF THE
GUIDANCE WITH RESPECT TO THE MID-LEVEL TROUGH PROPAGATING THROUGH
THE GREAT LAKES AND MIDWEST LATE WEEK. THE OPERATIONAL CANADIAN
CONTINUES TO BE FASTER AND MORE AMPLIFIED THAN THE REST OF THE
GUIDANCE. IN TERMS OF QPF, THE GFS SUITE HAS INCREASED SIGNALS FOR
HEAVY RAINFALL OVER THE LOWER MISSISSIPPI/TENNESSEE VALLEY ON
WEDNESDAY. THE ENSEMBLE MEANS APPEAR TO SIGNAL SIMILARLY.
A GENERAL MODEL BLEND CONSISTING OF THE 00Z EC/CMC/UKMET AND 06Z
GFS WERE UTILIZED THROUGH DAY 4 WITH THE EC AND GFS FAVORED. BY DAY
5 THE 00Z ECE AND 06Z GEFS ARE INTRODUCED AT THE EXPENSE OF THE
00Z UKMET, WHICH IS REMOVED FROM THE BLEND. THE DETERMINISTIC GFS
IS REPLACED WITH THE 00Z CANADIAN ENSEMBLE MEAN ON DAY 6, WHILE
THE GEFS AND ECE ARE FAVORED IN THE BLEND THROUGH DAY 7.
..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
WITH SLOW-MOVING STORMS. THIS IS COVERED BY FAIRLY BROAD MARGINAL
RISKS ON THE DAYS 4 AND 5 EROS (COVERING WEDNESDAY TO THURSDAY
NIGHT), WITH A FOCUS FOR A POSSIBLE EVENTUAL SLIGHT UPGRADE ACROSS
THE GULF COAST AND/OR FARTHER INLAND ACROSS PORTIONS OF THE LOWER
MISSISSIPPI/TENNESSE VALLEY ON WEDNESDAY AND THURSDAY. LATER, THE
LINGERING FRONTAL BOUNDARY ACROSS THE SOUTH WILL PROMOTE ADDITIONAL
RAIN AND LOCALLY HEAVY DOWNPOURS WITH AMOUNTS AND LOCATIONS STILL
VERY UNCERTAIN, BUT THE TREND IS FOR INCREASED RAIN TOTALS ALONG
THE GULF COAST AND INTO PARTS OF THE SOUTHEAST. BY THE WEEKEND,
SOME MOISTURE MAY SPREAD INTO THE OHIO VALLEY AND/OR EASTERN
SEABOARD. MEANWHILE, SOME LIGHT TO MODEST PRECIPITATION SHOULD
ACCOMPANY A SHORTWAVE MOVING THROUGH THE INTERIOR WEST, AND RAIN
CHANCES COULD SPREAD INTO THE NORTHERN PLAINS AND MIDWEST/GREAT
LAKES LATER NEXT WEEK ALONG AND AHEAD OF THE NORTHERN FRONT.
INCREASING HEAT IS EXPECTED ACROSS MUCH OF THE WEST, WITH MODERATE
TO MAJOR HEATRISK THREATS ACROSS THE SOUTHWEST AND CENTRAL VALLEYS
OF CALIFORNIA. ELSEWHERE, FROM THE CENTRAL U.S. INTO THE EAST,
TEMPERATURES WILL BE BELOW OR NEAR NORMAL AS SYSTEMS MOVE THROUGH.
KEBEDE/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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