710
FXUS02 KWBC 260648
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
248 AM EDT WED JUN 26 2024
VALID 12Z SAT JUN 29 2024 - 12Z WED JUL 03 2024
...HAZARDOUS HEAT THREATS TO FOCUS ACROSS PARTS OF THE SOUTH NEXT
WEEKEND AND INTO EARLY NEXT WEEK...
..OVERVIEW
AN UPPER LEVEL LOW/TROUGH WILL TRAVERSE THE NORTHERN TIER OF THE
NATION AND PUSH A SURFACE FRONTAL SYSTEM ACROSS PARTS OF THE GREAT
LAKES AND EASTERN U.S. THIS WEEKEND. THIS SYSTEM MAY BRING A THREAT
OF AT LEAST LOCALLY HEAVY RAINFALL FROM PORTIONS OF THE
NORTHEAST/MID-ATLANTIC BACK INTO THE CENTRAL PLAINS. MEANWHILE, AN
UPPER LEVEL RIDGE WILL BUILD OVER THE SOUTH AND SOUTHEAST THROUGH
EARLY NEXT WEEK, AND THERE WILL BE AN INCREASED THREAT FOR
HAZARDOUS HEAT FOR THESE AREAS UNDER THE RIDGE THROUGH MUCH OF THE
MEDIUM RANGE PERIOD. A SECOND UPPER LEVEL LOW/TROUGH WILL MOVE INTO
THE NORTHWEST LATE THIS WEEKEND AND PUSH TOWARDS THE UPPER MIDWEST
EARLY NEXT WEEK. THIS SYSTEM WILL LIKELY BRING ANOTHER ROUND OF
HEAVY RAINFALL TO PARTS OF THE UPPER MIDWEST BY MONDAY.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE LATEST MODEL GUIDANCE CONTINUES TO SHOW ABOVE AVERAGE
AGREEMENT ON THE OVERALL PROGRESSIVE NORTHERN STREAM PATTERN. THERE
ARE SOME LINGERING DETAIL DIFFERENCES IN TIMING AND STRENGTH OF
THE SHORTWAVES, WHICH MAY HAVE IMPACTS ON SENSIBLE WEATHER/QPF, BUT
THESE DETAILS COULD TAKE UNTIL THE SHORT RANGE TO FULLY RESOLVE.
LATE IN THE PERIOD, THE 12Z/JUN 25 CMC SEEMED OVERALL TOO FLAT WITH
THE NORTHERN STREAM FLOW COMPARED TO THE BETTER CONSENSUS OF
GUIDANCE. OTHERWISE, MODELS CONTINUE TO SUGGEST ANOMALOUS SUMMER
RIDGING CENTERED OVER THE SOUTHERN PLAINS THROUGH MUCH OF THE
PERIOD, BUT ALSO EXTENDED EASTWARD INTO THE SOUTHEAST AND
PERIODICALLY NORTHWARD INTO THE CENTRAL PLAINS/MIDWEST. SOME
RIDGING MAY TRY TO BUILD BACK IN OVER THE WEST LATE PERIOD AS WELL.
GIVEN THE OVERALL GOOD AGREEMENT IN THE GUIDANCE, AT LEAST ON THE
LARGE SCALE, A GENERAL MODEL COMPROMISE (INCORPORATING ENSEMBLE
MEANS LATER IN THE PERIOD) SHOULD SUFFICE FOR THE MEDIUM RANGE
PERIOD.
..WEATHER/HAZARDS HIGHLIGHTS
AS THE FRONTAL SYSTEM INITIALLY OVER THE GREAT LAKES PROGRESSES
EAST BY SATURDAY, PRECIPITATION CHANCES WILL SPREAD INTO THE
EASTERN U.S. AND BACK INTO THE CENTRAL PLAINS. MODEL GUIDANCE SHOWS
SOME SIGNAL FOR HEAVIER RAINS ACROSS PORTIONS OF THE NORTHEAST,
BUT THE PROGRESSIVE NATURE OF THE FRONT SHOULD LIMIT THE OVERALL
FLASH FLOOD THREAT. THE DAY 4/SATURDAY EXCESSIVE RAINFALL OUTLOOK
SHOWS JUST A ELONGATED MARGINAL RISK FROM THE NORTHEAST BACK INTO
THE CENTRAL PLAINS/SOUTHWEST. A WEAK SURFACE LOW AND SLOWING OF THE
FRONT THROUGH THE MID-ATLANTIC ON SUNDAY COULD CONTRIBUTE TO
HEAVIER RAIN POTENTIAL ACROSS THAT REGION AND SO A MARGINAL RISK IS
HIGHLIGHTED ON THE DAY 5 ERO ACROSS SOUTHEAST VIRGINIA AND EASTERN
NORTH CAROLINA.
ANOTHER ROUND OF HEAVY RAIN IS FORECAST TO IMPACT PARTS OF THE
NORTHERN PLAINS AND UPPER MIDWEST MONDAY INTO TUESDAY AS A SECOND
UPPER LEVEL LOW/TROUGH MOVES ACROSS THE NORTHERN TIER. THIS SYSTEM
WILL REQUIRE CLOSE MONITORING GIVEN RECENT AND FORECAST HEAVY RAIN,
WHICH COULD CAUSE NEW FLOODING ISSUES AND EXACERBATE ANY ONGOING
FLOODING.
MONSOONAL TYPE FLOW INTO THE SOUTHWEST WILL CONTINUE THE DAILY
THREAT FOR SHOWERS AND STORMS THROUGH MUCH OF THE PERIOD. MARGINAL
RISKS ARE IN PLACE ACROSS PARTS OF ARIZONA AND NEW MEXICO FOR THE
DAYS 4 AND 5 ERO. DAILY PRECIPITATION CHANCES WILL ALSO PERSIST IN
THE SOUTHEAST/FLORIDA AS ABOVE NORMAL MOISTURE LINGERS OVER THE
REGION.
HAZARDOUS HEAT POTENTIAL WILL FOCUS ACROSS THE SOUTH AND SOUTHEAST
UNDERNEATH A PERSISTENT UPPER RIDGE THROUGH THE WEEKEND INTO EARLY
NEXT WEEK. SEVERAL DAYS OF ABOVE NORMAL TEMPERATURES (BOTH DAYTIME
HIGHS AND NIGHTTIME LOWS) ARE FORECAST FROM THE CENTRAL AND
SOUTHERN PLAINS EASTWARDS, EXPANDING WITH TIME INTO PARTS OF THE
MIDWEST AND MID-ATLANTIC BY MID NEXT WEEK. THE NORTHERN TIER STATES
SHOULD BE NEAR OR BELOW NORMAL WITH SYSTEM PASSAGES, AND SOME
ABOVE NORMAL TEMPERATURES MAY BUILD BACK INTO PARTS OF CALIFORNIA
AND NEVADA NEXT WEDNESDAY.
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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