136
FXUS02 KWBC 261837
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
237 PM 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 THIS
WEEKEND AND INTO EARLY NEXT WEEK...
..OVERVIEW
AN ENERGETIC UPPER LEVEL LOW/TROUGH WILL TRAVERSE SOUTHERN CANADA
AND 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 THROUGH PORTIONS OF THE NORTHEAST/MID-ATLANTIC BACK
THROUGH THE EAST-CENTRAL U.S. INTO THE SOUTH-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. MOISTURE FEEDING AROUND THE
WESTERN PERIPHERY OF THIS RIDGE ALSO OFFERS A WET PERIOD FOR THE
SOUTHERN ROCKIES STATES. 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 A MULTI-DAY
PERIOD FAVORABLE FOR HEAVY CONVECTIVE RAINS TO PARTS OF THE UPPER
MIDWEST, PARTICULARLY FOR MONDAY INTO TUESDAY WITH SLOW PROGRESSION.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL AND ENSEMBLE FORECAST SPREAD HOLDS MUCH LOWER THAN NORMAL
THROUGH MEDIUM RANGE TIME SCALES IN A PATTERN WITH ABOVE AVERAGE
PREDICTABILITY FOR MASS FIELDS AND SENSIBLE WEATHER/HAZARDS. THE
WPC PRODUCT SUITE WAS PRIMARILY DERIVED FROM A BLEND OF THE 06 UTC
GFS/GEFS MEAN AND 00 UTC ECMWF/CANADIAN/ECMWF ENSEMBLE MEAN ALONG
WITH THE COMPATIBLE 13 UTC NATIONAL BLEND OF MODELS AND WPC
CONTINUITY, ALBEIT WITH MORE BLEND WEIGHTING APPLIED TO THE MODELS
FOR BETTER DETAIL SATURDAY-MONDAY WHEN SHORTWAVE TIMING ISSUES ARE
MOST MANAGEABLE. A SIMILAR BLEND OF LATEST 12 UTC GUIDANCE REMAINS
IN LINE OVERALL FOR MOST WEATHER ASPECTS.
..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 FOR THE EASTERN MID-ATLANTIC/CAROLINAS.
ANOTHER ROUND OF HEAVY RAIN IS FORECAST TO IMPACT PARTS OF THE
NORTHERN PLAINS AND UPPER MIDWEST AND VICINITY 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 FOR 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/SCHICHTEL
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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