139
FXUS02 KWBC 270731
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
331 AM EDT TUE MAY 27 2025
VALID 12Z FRI MAY 30 2025 - 12Z TUE JUN 03 2025
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODELS AND ENSEMBLES CONTINUE TO SHOW A REASONABLY SIMILAR MEDIUM
RANGE LARGER SCALE PATTERN EVOLUTION OVER THE LOWER 48 AND
VICINITY. HOWEVER, COMPLEX SYSTEM AND STREAM PHASING INTERACTIONS
HAVE AGAIN LED TO AN INCREASE IN SMALLER SCALE VARIANCES,
ESPECIALLY EMINATING FROM ENERGY TRANSFERS FROM A NORTH-CENTRAL
U.S./MIDWEST CLOSED LOW TO AN UPPER TROUGH OVER THE EAST. FORECAST
SPREAD REMAINS GREATER THAN NORMAL FOR THESE SYSTEMS FROM THE
START OF THIS FORECAST PERIOD ONWARD. ACCORDINGLY, FAVOR A MORE
COMPATIBLE 18 UTC GEFS AND 12 UTC ECMWF/CANADIAN ENSEMBLE MEANS
BLEND THAT TENDS TO MITIGATE SMALLER SCALE DIFFERENCES CONSISTENT
WITH INDIVIDUAL SYSTEM PREDICTABILITY. WPC PRODUCT CONTINUITY IS
DECENTLY MAINTAINED WITH THIS STRATEGY, WITH A SOLUTION IN LINE
WITH A COMPOSITE OF LATEST 00 UTC GUIDANCE.
..WEATHER/HAZARDS HIGHLIGHTS
THE PATTERN WILL BE IN TRANSITION INTO LATER THIS WEEK INTO THE
WEEKEND AS A SERIES OF LEAD DIGGING SHORTWAVES AND SECONDARY
SYSTEMS IN MULTIPLE STREAMS ACT TO CARVE OUT A COOLING AND
WET/UNSETTLING AMPLIFIED UPPER TROUGH OVER THE EAST AS A TRAILING
AND RAINFALL FOCUSING FRONT WORKS OFFSHORE THE SOUTH INTO THE GULF.
THE BULK OF UPPER TROUGH ENERGY LIFTS OUT INTO NEXT WEEK, BUT WITH
UPSTREAM ENERGIES STILL DIGGING UPSTREAM TO CARVE OUT A RENEWED BUT
LESS ENERGETIC UPPER TROUGH POSITION OVER THE EAST.
A MAIN SURFACE LOW WILL LIFT OVER EASTERN CANADA FRIDAY INTO THE
WEEKEND, WHILE FRONTAL AND SECONDARY BOUNDARIES TRAIL DOWN OVER THE
EAST, THE SOUTH AND INTO THE GULF TO FOCUS LINGERING AND WAVE
ENHANCING SHOWERS AND THUNDERSTORMS LOCALLY. THE WPC DAY 4/FRIDAY
EXCESSIVE RAINFALL OUTLOOK SHOWS A MARGINAL THREAT AREA FROM THE
EAST-CENTRAL GULF COAST AND NORTH-CENTRAL FLORIDA UP THROUGH THE
CAROLINAS, BUT GUIDANCE FOCUS UNCERTAIN THERE AND POTENTIALLY UP
INTO THE CENTRAL MID-ATLANTIC TO MONITOR. ADDITIONAL ENHANCED
RAINFALL IS EXPECTED TO REJUEVENATE INTO THE WEEKEND FROM THE
NORTHERN MID-ATLANTIC/APPALACHIANS THROUGH THE NORTHEAST GIVEN
RENEWED NORTHERN STREAM UPPER TROUGH SUPPORT.
MEANWHILE, UPPER RIDGING WILL PREVAIL OVER MUCH OF A WARMED WEST
INTO THE WEEKEND AS A SOUTHERN STREAM CLOSED LOW SLOWLY WORKS
TOWARD THE SOUTHWEST. HOWEVER, AMPLE NORTHERN STREAM EASTERN
PACIFIC UPPER TROUGH AMPLIFICATION AND SOUTHEASTWARD APPROACH INTO
THIS WEEKEND AND SUBSEQUENT STEADY INLAND PROGRESSION BREACH INTO
THE WEST, ALONG WITH THE EJECTION OF THE LEAD SOUTHERN STREAM
CLOSED SYSTEM, WILL ACT TO PROVIDE RELIEF FROM THE HEAT OVER THE
WEST WITH THE BUILDING OF MUCH MORE UNSETTLED AND INCREASINGLY
WIDESPREAD WET FLOW PATTERN SPREADING INCREASINGLY INLAND AND DOWNSTREAM
TO THE INTERMOUNTAIN WEST AND ESPECIALLY THE NORTHERN ROCKIES.
IN THE WEST, A BUILDING UPPER RIDGE WILL LEAD TO AN EXPANDING AREA
OF HEAT FROM THE INTERMOUNTAIN WEST INTO THE WEST COAST STATES
THIS WEEK INTO THE WEEKEND, WITH TEMPERATURES RISING UPWARDS TO 10
TO 20 DEGREES ABOVE NORMAL. THIS IN PARTICULAR MAY LEAD TO A
HAZARDOUS HEAT FOCUS FOR THE CALIFORNIA CENTRAL VALLEY INTO DESERT
SOUTHWEST LATE WEEK/WEEKEND. ABOVE NORMAL TEMPERATURES CLOSER TO
10-15 DEGREES ABOVE NORMAL SHOULD EXPAND TO THE NORTH-CENTRAL U.S.
AS THE PERIOD PROGRESSES.
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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