333
FXUS02 KWBC 270646
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
246 AM EDT TUE JUN 27 2023
VALID 12Z FRI JUN 30 2023 - 12Z TUE JUL 04 2023
...MAJOR HEATWAVE EXPANDS FROM TEXAS THROUGH THE MID-LOWER
MISSISSIPPI VALLEY BEFORE PIVOTING TO SOUTHEAST INTO THIS
WEEKEND...
..HEATWAVE DEVELOPS OVER DESERT SOUTHWEST BY THIS WEEKEND
...EXCESSIVE RAINFALL THREAT FOR THE CENTRAL PLAINS, MIDWEST AND
NORTHEAST LATE WEEK INTO THE HOLIDAY WEEKEND...
..OVERVIEW WITH GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE WPC MEDIUM RANGE PRODUCT SUITE WAS PRIMARILY DERIVED FROM A
BLEND OF BEST CLUSTERED MID-LARGER SCALE GUIDANCE FROM THE 18 UTC
GFS/GEFS MEAN AND 12 UTC ECMWF/ECMWF ENSEMBLE MEAN ALONG WITH THE
01 UTC NATIONAL BLEND OF MODELS. APPLIED MOST BLEND WEIGHTING TO
THE HIGHER RESOLUTION MODELS DAYS 3/4 (FRIDAY/SATURDAY) FOR BETTER
DETAIL IN A PERIOD OF SEEMINGLY ABOVE NORMAL PREDICTABILITY.
TRANSITIONED MOST BLEND WEIGHTING TO THE ENSEMBLE MEANS BY JULY
4TH AMID SLOWLY GROWING FORECAST SPREAD. OVERALL, WPC PRODUCT
CONTINUITY IS WELL MAINTAINED IN THIS MANNER WITH THE BLENDING
PROCESS TENDING TO MITIGATE SMALLER SCALE GUIDANCE DIFFERENCES
CONSISTENT WITH INDIVIDUAL SYSTEM PREDICTABILITY. LATEST 00 UTC
GUIDANCE IS MORE IN LINE WITH THIS WPC PREFERRED SOLUTION NOW THAT
THE CANADIAN AND UKMET HAVE BOTH STRONGLY TRENDED TO A MORE
AMPLIFIED/LESS PROGRESSIVE WESTERN CANADIAN UPPER TROUGH/SURFACE
SYSTEM BY THE HOLIDAY WEEKEND.
..WEATHER/HAZARDS HIGHLIGHTS
A MAIN EJECTION OF UPPER TROUGH ENERGIES OUT FROM THE WEST/ROCKIES
IS EXPECTED TO SPAWN SCATTERED SHOWERS AND STRONG TO SEVERE STORM
CHANCES OUT FROM THE CENTRAL PLAINS TO THE MID-MISSISSIPPI AND
LOWER OHIO VALLEY ALONG WITH A THREAT FOR LOCALLY HEAVY RAINFALL
AND RUNOFF ISSUES INTO FRIDAY. A "MARGINAL RISK" OF EXCESSIVE
RAINFALL IS PLANNED GIVEN HEIGHT FALLS/INSTABILITY AND POTENTIAL
FOR REPEAT/TRAINING OF CELLS MAINLY ALONG/NORTH OF A DEVELOPING
WAVE AND LEADING WARM FRONT. THIS WAVE SHIFTS EAST SATURDAY WITH
THE WARM FRONT AND SOUTHWESTWARD TRAILING COLD FRONT, WARRANTING
AN OVERLAP/EXPANSION OF A "MARGINAL RISK" AREA FROM THE
MID-MISSISSIPPI/OHIO VALLEYS THROUGH THE NORTHEAST GIVEN WET SOILS
AND ADDITIONAL NORTHERN STREAM ENERGY. THE PATTERN WILL LIKELY
WARRANT FUTURE ISSUANCE OF "SLIGHT RISK" AREAS AND BUMPED UP QPF
GIVEN POOLED HIGH PWS WITH ADVENT OF A STRONGER LOCAL GUIDANCE
SIGNAL FOCUS CLOSER TO THE EVENT. THE OVERALL HEAVY RAIN FOCUS
WILL SHIFTS EAST AND SOUTHEAST AND BECOME LESS ORGANIZED LATER
WEEKEND INTO EARLY NEXT WEEK WITH WAVE AND TRAILING FRONT
PROGRESSION THEN EVENTUAL FRONTAL STALLING AND RETURN.
EXCESSIVE HEAT WILL CONTINUE TO PLAGUE THE SOUTHERN PLAINS AND
EXPAND NORTH AND EAST THIS WEEKEND TO PORTIONS OF THE CENTRAL
PLAINS AND THE MID-LOWER MISSISSIPPI VALLEY. THE HEAT WILL BE
OPPRESSIVE WITH WIDESPREAD HIGH TEMPERATURES EXCEEDING 100 DEGREES
AND HEAT INDICES AS HIGH AS 120 DEGREES. HEAT INDICES MAY EVEN
EXCEED 120 DEGREES IN SOME LOCATIONS IN SOUTH TEXAS. TENS OF HIGH
TEMPERATURE RECORDS ARE IN DANGER OF BEING BROKEN DURING THIS
SIGNIFICANT HEAT WAVE. THE DESERT SOUTHWEST WILL ALSO EXPERIENCE A
NOTABLE HEATING THIS WEEKEND WITH MAX TEMPS 5 TO 10 DEGREES ABOVE
NORMAL WHICH MEANS 110 TO 115 DEGREES MAX TEMPS FOR THESE HOT
ENVIRONS SOUTH FROM LAS VEGAS AND WEST FROM PHOENIX.
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, EXPERIMENTAL EXCESSIVE RAINFALL
OUTLOOK, WINTER WEATHER OUTLOOK PROBABILITIES, HEAT INDICES AND
KEY MESSAGES ARE AT:
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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