717
FXUS02 KWBC 281941
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
340 PM EDT WED JUN 28 2023
VALID 12Z SAT JUL 01 2023 - 12Z WED JUL 05 2023
...MAJOR HEATWAVE EXPANDS FROM TEXAS THROUGH THE MID-LOWER
MISSISSIPPI VALLEY AND SOUTHEAST...
..HEATWAVE DEVELOPS OVER DESERT SOUTHWEST
...EXCESSIVE RAINFALL THREAT FOCUS FROM THE OHIO VALLEY THROUGH
THE NORTHEAST THIS WEEKEND...
...PATTERN OVERVIEW AND GUIDANCE EVALUATION/PREDICTABILITY
ASSESSMENT...
THE MEDIUM RANGE PERIOD (SAT JULY 1 - WED JULY 5) BEGINS IN THE
MIDDLE OF AN OVERALL PATTERN CHANGE AWAY FROM THE BLOCKY FLOW THAT
HAS BEEN IN PLACE FOR MUCH OF JUNE. THE STUBBORN UPPER-LEVEL
RIDGE/CLOSED HIGH OVER NORTHERN MEXICO/THE SOUTH-CENTRAL CONUS IS
FORECAST TO SHIFT EASTWARD OVER THE SOUTHEAST AND WEAKEN TO START
JULY. AN UPPER-LEVEL WAVE WILL FOLLOW OVER THE PLAINS AS A RIDGE
BUILDS OVER CALIFORNIA AND THE GREAT BASIN. THE WAVE IS EXPECTED
TO LIFT NORTHEASTWARD TOWARDS THE EAST COAST AS THE OVERALL FLOW
TRANSITIONS A BIT MORE ZONAL, ESPECIALLY ACROSS THE SOUTHERN TIER,
AS MORE AGGRESSIVE UPPER-LEVEL ACTIVITY LIFTS NORTHWARD OVER
SOUTHERN CANADA AND THE NORTHERN TIER IN A MORE SUMMER-LIKE
PATTERN. AN UPPER-LEVEL TROUGH LOOKS TO DROP SOUTHEASTWARD ACROSS
WESTERN CANADA TOWARDS THE NORTHERN TIER AND WILL HELP TO DRIVE
ANOTHER SYSTEM SOUTHWARD OVER THE MIDWEST/PLAINS IN THE MID- TO
LATE PERIOD. SOME SOUTHERN STREAM ENERGY MAY LINGER OVER THE
SOUTH-CENTRAL CONUS/SOUTHEAST AS WELL AS ANOTHER WEAK WAVE MOVING
OVER CALIFORNIA. THE MODEL GUIDANCE IS IN GENERALLY GOOD AGREEMENT
WITH DECENT RUN-TO-RUN CONTINUITY SHOWN BETWEEN THE ECMWF/GFS. THE
MOST NOTABLE DIFFERENCES ARE RELATED TO THE TIMING/STRENGTH OF THE
DISCUSSED WAVES, THOUGH THE MORE SUBTLE NATURE OF THE FLOW MAKES
PREDICTABILITY AT THE LONGER RANGES MORE DIFFICULT, REGARDLESS. IN
TERMS OF TRENDS, THE WAVE OVER CALIFORNIA HAS BEEN SHIFTING WEAKER
IN THE LATEST RUNS OF THE ECMWF/GFS AND THE LATTER SYSTEM DROPPING
SOUTH FROM CANADA HAS SLOWED.
GIVEN THE GOOD AGREEMENT IN THE GUIDANCE, A GENERAL DETERMINISTIC
MODEL BLEND OF THE 00Z ECMWF/CMC/UKMET AND 06Z GFS WORKS WELL FOR
THE WPC MEDIUM RANGE PRODUCT SUITE DURING THE EARLY TO
MID-FORECAST PERIOD, AND FOLLOWS CONTINUITY FROM THE PRIOR
FORECAST. A SHIFT TOWARDS A CONTRIBUTION FROM THE 00Z GEFS/ECENS
MEANS IS USED FOR THE END OF THE PERIOD AS THE FORECAST-TIME
LIMITED UKMET CONTRIBUTION ENDS AND UNCERTAINTY WITH RESPECT TO
THE DETAILS IN LATTER WAVES GROWS. DESPITE GENERAL RUN-TO-RUN
CONTINUITY IN THE GUIDANCE ON THE LARGE-SCALE, THERE DOES REMAIN
SOME NOTABLE UNCERTAINTY WITH AREAL COVERAGE OF QPF EARLY IN THE
PERIOD.
..WEATHER/HAZARDS HIGHLIGHTS
THE MAIN EJECTION OF UPPER TROUGH ENERGIES OUT FROM THE
ROCKIES/CENTRAL PLAINS INTO THE HOLIDAY WEEKEND IS EXPECTED TO
FOCUS SHOWERS AND STRONG TO SEVERE STORM CHANCES ALONG A FRONTAL
SYSTEM FROM THE CENTRAL PLAINS THROUGH THE MID-MISSISSIPPI AND
OHIO/TENNESSEE VALLEYS TO THE APPALACHIANS/NORTHERN
MID-ATLANTIC/NORTHEAST ALONG WITH A THREAT FOR LOCALLY HEAVY
RAINFALL AND RUNOFF ISSUES. "MARGINAL RISKS" OF EXCESSIVE RAINFALL
ARE IN EFFECT FOR THE DAY 4/5 EXCESSIVE RAINFALL OUTLOOKS GIVEN
INSTABILITY/MOISTURE POOLING AND POTENTIAL FOR REPEAT/TRAINING OF
CELLS ALONG THE FRONTAL SYSTEM AND AHEAD OF THE DEEPENING WAVE.
ANTECEDENT RAINFALL AND ADDITIONAL INFLUENCE FROM NORTHERN STREAM
ENERGY ARE ALSO IN THE MIX. A "SLIGHT RISK" AREA IS OUTLINED FOR
PORTIONS OF THE MIDDLE MISSISSIPPI TO LOWER OHIO VALLEY FOR DAY
4/SATURDAY GIVEN HIGH POOLED PRECIPITABLE WATER VALUES AND OVERLAP
OF HIGHER QPF TOTALS/ENSEMBLE PROBABILITIES. A NOTED BIT OF
UNCERTAINTY REMAINS WITH THE TIMING/LOCATION/PROGRESSION OF
POTENTIALLY ORGANIZED CONVECTION WHICH MAY LEAD TO ADDITIONAL
AREAL ADJUSTMENTS OF THE RISKS. THE OVERALL CONVECTION AND HEAVY
RAIN FOCUS SHOULD SHIFT SOUTHEAST AND BECOME LESS ORGANIZED INTO
EARLY NEXT WEEK WITH WAVE AND TRAILING FRONT PROGRESSION AND
EVENTUAL STALLING. PRECIPITATION CHANCES WILL INCREASE ACROSS THE
CENTRAL/NORTHERN PLAINS AND THE UPPER MIDWEST TUESDAY/WEDNESDAY
AHEAD OF THE NEXT FRONTAL SYSTEM DROPPING SOUTH FROM CANADA.
EXCESSIVE HEAT TO START THE WEEKEND FROM SOUTHERN/SOUTHEAST TEXAS
INTO THE LOWER MISSISSIPPI VALLEY AND SOUTHEAST/FLORIDA WILL
BRIEFLY EXPAND NORTHEASTWARD INTO THE CAROLINAS THROUGH MONDAY
BEFORE A GENERAL DOWNWARD TREND TOWARDS SUMMER AVERAGES OUTSIDE OF
SOUTH TEXAS. THE HEAT WILL BE OPPRESSIVE WITH WIDESPREAD HIGH
TEMPERATURES IN THE MID-90S TO LOW 100S WHICH, WHEN COMBINED WITH
THE HUMIDITY, WILL LEAD TO HEAT INDICES IN THE 110-115 DEGREE
RANGE, LOCALLY EVEN A BIT HIGHER. EXCESSIVE SUMMER HEAT WILL ALSO
OVERSPREAD PORTIONS OF THE WEST THIS WEEKEND, WITH THE CENTRAL
CALIFORNIA VALLEYS SEEING HIGHS OF 105-110 DEGREES, UPWARDS OF
10-15 DEGREES ABOVE AVERAGE. THE DESERT SOUTHWEST WILL EXPERIENCE
A NOTABLE HEATING THIS WEEKEND AS WELL WITH MAX TEMPS 5 TO 10
DEGREES ABOVE AVERAGE WHICH MEANS LOW TO MID 110S FOR THESE HOT
ENVIRONS SOUTH FROM LAS VEGAS AND WEST FROM PHOENIX. ELSEWHERE,
ABOVE AVERAGE HIGH TEMPERATURES IN THE UPPER 80S TO MID 90S ALONG
THE NORTHERN TIER OF THE CENTRAL U.S. THIS WEEKEND WILL SHIFT
EASTWARD INTO THE UPPER MIDWEST/GREAT LAKES REGION AHEAD OF A COLD
FRONT, WHICH WILL BRING MUCH COOLER TEMPERATURES IN THE 70S TO
PORTIONS OF THE CENTRAL/NORTHERN HIGH PLAINS FOR THE JULY 4
HOLIDAY.
PUTNAM/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
HAZARDS:
- FLOODING POSSIBLE ACROSS PORTIONS OF THE NORTHERN PLAINS.
- HAZARDOUS HEAT ACROSS PORTIONS OF CALIFORNIA, FRI-SUN, JUN
30-JUL 2.
- HAZARDOUS HEAT ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY,
THE TENNESSEE VALLEY, THE
MID-ATLANTIC, THE SOUTHERN APPALACHIANS, THE SOUTHEAST, AND THE
SOUTHERN PLAINS, FRI-TUE, JUN
30-JUL 4.
- HAZARDOUS HEAT ACROSS PORTIONS OF THE CENTRAL AND SOUTHERN
PLAINS, THE LOWER AND MIDDLE
MISSISSIPPI VALLEY, THE TENNESSEE VALLEY, THE SOUTHERN
APPALACHIANS, AND THE OHIO VALLEY, FRI, JUN
30.
- HAZARDOUS HEAT ACROSS PORTIONS OF THE LOWER AND MIDDLE
MISSISSIPPI VALLEY, THE TENNESSEE VALLEY,
THE MID-ATLANTIC, THE SOUTHERN APPALACHIANS, THE SOUTHEAST, THE
SOUTHERN PLAINS, AND THE OHIO
VALLEY, FRI-SAT, JUN 30-JUL 1.
- HEAVY RAIN ACROSS PORTIONS OF MAINLAND ALASKA, SUN-MON, JUL
2-JUL 3.
- HEAVY RAIN ACROSS PORTIONS OF MAINLAND ALASKA, FRI, JUN 30.
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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