317
FXUS02 KWBC 310625
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
225 AM EDT SAT AUG 31 2024
VALID 12Z TUE SEP 03 2024 - 12Z SAT SEP 07 2024
..OVERVIEW
A FAIRLY PROGRESSIVE NORTHERN STREAM UPPER LEVEL PATTERN WILL BE
IN PLACE NEXT WEEK DURING THE MEDIUM RANGE PERIOD. ON THE LARGE
SCALE, UPPER RIDGING ACROSS THE SOUTHERN U.S. WILL EXPAND AND BUILD
INTO THE WEST AS SYSTEMS RIDE THE TOP OF THE RIDGE FROM WEST TO
EAST, EVENTUALLY BUILDING A DEEPENING TROUGH OVER THE GREAT LAKES
TO NORTHEAST MID TO LATE NEXT WEEK. THIS PATTERN SHOULD PUSH A
COUPLE OF FRONTAL BOUNDARIES INTO THE CENTRAL AND SOUTHEASTERN
U.S., WITH PERIODS OF STORMY WEATHER EXPECTED TO ACCOMPANY THEM.
MEANWHILE, EMBEDDED ENERGY WITHIN THE LARGER SCALE UPPER RIDGE AND
A PERSISTENT SURFACE TROUGH AND EMBEDDED WAVES NEAR THE GULF COAST
SHOULD PROVIDE FOCUS FOR HEAVY RAINFALL FROM TEXAS TO THE LOWER
MISSISSIPPI VALLEY AND GULF COAST.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODELS SHOW FAIRLY GOOD AGREEMENT ON THE OVERALL LARGE SCALE
PATTERN THROUGH MUCH OF NEXT WEEK, BUT THE TYPICAL DIFFERENCES IN
THE DETAILS OF INDIVIDUAL SYSTEMS CAUSE SOME NOTABLE DIFFERENCES IN
SENSIBLE WEATHER. ONE FEATURE OF NOTE IS SHORTWAVE ENERGY IN THE
SOUTHERN PLAINS OR SO THAT, ALONG WITH SURFACE TROUGHING AND FRONTS
IN THE VICINITY, WILL HELP FORCE CONVECTION IN TEXAS AND SPREADING
EASTWARD WITH TIME. MODELS MAY BE COMING MORE IN LINE WITH EACH
OTHER, BUT THERE IS STILL A CONSIDERABLE AMOUNT OF SPREAD. TO THE
NORTH, A SHORTWAVE OVER THE NORTHWEST WILL PHASE WITH A SHORTWAVE
THROUGH CENTRAL CANADA AS IT SHIFTS EAST, EVENTUALLY RESULTING IN A
DEEPENING TROUGH (OR CLOSED LOW) OVER/NEAR THE GREAT LAKES BY
FRIDAY. THERE ARE SOME TIMING DIFFERENCES BETWEEN THE GFS, ECMWF,
AND CANADIAN, BUT NOT ENOUGH CONFIDENCE TO THROW OUT ANY PARTICULAR
SOLUTION AT THIS TIME. THIS DOES HAVE IMPLICATIONS FOR TIMING OF
THE MAIN FRONTAL BOUNDARY THAT PUSHES FROM THE NORTH-CENTRAL U.S.
INTO THE EAST LATE PERIOD.
THE WPC FORECAST FOR TONIGHT USED A BLEND OF THE DETERMINISTIC
MODELS THE FIRST HALF OF THE PERIOD, TRANSITIONING TO JUST UNDER
HALF OF THE ENSEMBLE MEANS INTO THE BLEND AMIDST INCREASING LATE
PERIOD SPREAD.
..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 HIGHLY 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 TUESDAY TO WEDNESDAY
NIGHT), WITH A POSSIBLE FOCUS ACROSS THE GULF COAST AND FARTHER
INLAND ACROSS MUCH OF TEXAS TUESDAY, SPREADING EASTWARD WITH TIME
INTO THE LOWER MISSISSIPPI VALLEY. FOR MIDWEEK AND BEYOND, THE
LINGERING FRONTAL BOUNDARY ACROSS THE SOUTH WILL PROMOTE ADDITIONAL
RAIN AND LOCALLY HEAVY DOWNPOURS. AMOUNTS AND LOCATIONS REMAIN
VERY UNCERTAIN, BUT THE TREND IS FOR INCREASED RAIN TOTALS ALONG
THE GULF COAST AND INTO PARTS OF THE SOUTHEAST. EVENTUALLY BY LATE
WEEK, 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.
MODESTLY ABOVE NORMAL TEMPERATURES ACROSS THE NORTHERN PLAINS ON
TUESDAY SHOULD SHIFT EAST AND MODERATE. MEANWHILE, INCREASING HEAT
IS EXPECTED ACROSS MUCH OF THE WEST, WITH MODERATE TO MAJOR
HEATRISK THREATS ACROSS THE SOUTHWEST AND CENTRAL VALLEYS OF
CALIFORNIA. FROM THE SOUTHERN PLAINS TO THE MIDWEST AND THE EAST,
TEMPERATURES SHOULD BE NEAR OR BELOW NORMAL FOR THIS TIME OF THE
YEAR WITHIN A RATHER PLEASANT AIR MASS THROUGH MUCH OF NEXT WEEK.
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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