540
FXUS02 KWBC 021959
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
357 PM EDT WED AUG 02 2023
VALID 12Z SAT AUG 05 2023 - 12Z WED AUG 09 2023
..HEATWAVE TO PERSIST OVER THE SOUTH
...EXCESSIVE RAIN/FLASH FLOOD THREAT TO FOCUS OVER THE NORTHERN
PLAINS INTO SATURDAY...
..OVERVIEW
IT REMAINS THE CASE THAT DEEPENED MONSOONAL MOISTURE AND UPPER
SYSTEM ENERGY WORKING THROUGH THE ROCKIES ON THE WESTERN TO
NORTHERN PERIPHERY OF AN AMPLIFIED UPPER RIDGE WILL FAVOR A SLOW
SHIFT OF A MAIN CONVECTIVE RAINFALL FOCUS INTO THE NORTH-CENTRAL
PLAINS. MEANWHILE, AMPLE NORTHERN STREAM UPPER TROUGHING FROM THE
CANADIAN PRAIRIES WILL DIG SOUTHEAST THROUGH THIS WEEKEND WHICH
ALONG WITH UPPER ENERGIES WORKING FROM THE ROCKIES INTO THE PLAINS
WILL ACT TO SUPPRESS THE CENTRAL CONUS UPPER RIDGE AXIS SOUTH TO
THE SOUTHERN TIER OF STATES WHERE ABOVE NORMAL
TEMPERATURES/HEATWAVES PERSIST. ANOMALOUSLY HOT WEATHER WILL ALSO
SPREAD BACK INTO THE DESERT SOUTHWEST.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
00/06Z GUIDANCE CAPTURED THE EVOLUTION OF THE SOUTHERN STREAM
RIDGE REASONABLY WELL DURING THE MEDIUM RANGE PERIOD. THE 06Z GFS
DIVERGED FROM THE REST OF THE GUIDANCE WHEN DEPICTING THE NORTHERN
STREAM TROUGHING THROUGH EARLY NEXT WEEK. THAT BEING SAID, THE GFS
HAD BETTER RUN-TO-RUN CONSISTENCY THAN THE ECMWF, THEREFORE OUR
GENERAL MODEL BLEND WAS WEIGHTED TOWARD THE 06 GFS THROUGH DAY 4.
THE GMB ALSO CONSISTED OF THE 00Z EC/CMC/UKMET. THE 06Z GEFS AND
00Z ECE WERE INTRODUCED ON DAY 5 WHILE THE 00Z UK WAS REMOVED DUE
TO ITS OVERAMPLIFICATION OF THE SHORTWAVE TROUGH OVER THE
MIDWEST/UPPER GREAT LAKES. THE DETERMINISTIC 00Z CMC WAS REPLACED
BY THE 00Z CMCE ON DAY 6 AND THE ENSEMBLES MAKE UP A MAJORITY OF
THE BLEND THROUGH THE END OF THE PERIOD. THE LAST SEVERAL RUNS OF
THE DETERMINISTIC GFS AND EC HAVE SIGNALLED A POTENTIALLY TROPICAL
CLOSED LOW IN THE EASTERN PACIFIC NEAR BAJA CALIFORNIA.
..WEATHER/HAZARDS HIGHLIGHTS
THE VERY WET PATTERN FOR THE NORTH-CENTRAL PLAINS WITH HEAVY
CONVECTIVE RAINS WILL PERSIST INTO SATURDAY BEFORE TRANSITIONING
AS THE UPPER RIDGE AXIS CENTERED OVER THE HIGH PLAINS
WEAKENS/SUPPRESSES SOUTH AND NORTHERN TIER FLOW SLOWLY BECOMES
MORE ZONAL BEFORE TRANSITIONING TO NORTHWESTERLY. DEEP MONSOONAL
MOISTURE AND SLOW MOVING/ORGANIZED EMBEDDED TO EFFICIENT CLOSED
ENERGIES ROUNDING THIS RIDGE WILL PRODUCE MORE HEAVY RAIN. A DAY 4
ERO SLIGHT RISK FOR EXCESSIVE RAINFALL HAS BEEN OUTLINED ACROSS
PARTS OF SOUTHEAST MONTANA AND THE DAKOTAS WHERE THE HIGHEST
ENSEMBLE PROBABILITIES INDICATE THE POTENTIAL FOR LOCALLY HEAVY
RAINFALL DESPITE LINGERING UNCERTAINTIES IN THE DETERMINISTIC
GUIDANCE ON MAX QPF PLACEMENT. THIS AREA IS ALSO EXPECTED TO HAVE
QUITE A BIT A HEAVY RAIN LEADING INTO THIS PERIOD TO SIGNIFICANTLY
WETTEN SOILS AND STREAMFLOWS. HOWEVER, IT IS POSSIBLE GIVEN
NOTABLE PW ANOMALIES 1.5-2 STANDARD DEVIATIONS ABOVE THE MEAN. THE
MORE ZONAL FLOW THAT DEVELOPS LATER SATURDAY/DAY 5 SHOULD ALLOW
THE REMAINING HEAVY RAIN FOCUS TO SLIDE TO THE UPPER MIDWEST AND
VICINITY WITH GENERAL LOCATION UNCERTAINTY AND LESS CURRENT
CONSENSUS ON HEAVIER RAINFALL AMOUNTS LEADING TO A ERO MARGINAL
RISK AREA.
THE ONGOING HEATWAVE SHOULD SETTLE A BIT SOUTH OVER THIS WEEKEND,
CLOSER TO THE SOUTHERN BORDER AND ALONG THE GULF COAST AS
UPPER-TROUGHING SHIFTS SOUTHWARD AND THE UPPER-HIGH FLATTENS OUT.
HIGH TEMPERATURES WILL BE 5 TO 10 DEGREES ABOVE NORMAL WITH HIGH
HUMIDITY LEADING TO HEAT INDICES IN THE 110-115F RANGE IN SOME
AREAS, PARTICULARLY THE LOWER MISSISSIPPI RIVER VALLEY. RECORD
HIGH MAXIMUM AND ESPECIALLY MINIMUM TEMPERATURES ARE WIDELY
FORECAST IN THESE REGIONS. ADDITIONALLY, AFTER A BRIEF DROP IN
TEMPERATURES OVER THE DESERT SOUTHWEST, HIGHS WILL ONCE AGAIN WARM
INTO THE 110S. SOME ABOVE AVERAGE TEMPERATURES WILL ALSO SPREAD UP
THE WEST COAST FOLLOWING A BIT OF UPPER-RIDGE AMPLIFICATION, WITH
HIGHS IN THE CENTRAL CALIFORNIA VALLEYS CLIMBING INTO THE MID-100S
INTO THE WEEKEND AND EARLY NEXT WEEK. OTHERWISE, AN ORGANIZED
EASTERN CANADIAN SURFACE LOW AND TRAILING FRONT WILL BRING DRIER
AIR/MODERATED TEMPERATURES ACROSS PARTS OF THE CENTRAL TO EASTERN
U.S. THIS WEEKEND. EXPECT TEMPORARY MODERATE MOISTURE/RAINFALL
REBOUNDING EARLY NEXT WEEK WITH A NEXT MAIN LOW PRESSURE/FRONTAL
SYSTEM AND SECONDARY SURGES ACROSS THE CENTRAL TO EASTERN U.S.,
WITH SOME ADDITIONAL SHOWERS/STORMS TRAILING BACK TO THE ROCKIES.
KEBEDE/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:
- HEAVY RAIN ACROSS PORTIONS OF THE NORTHERN PLAINS, SAT, AUG 5.
- SEVERE WEATHER ACROSS PORTIONS OF THE CENTRAL PLAINS AND THE
MIDDLE MISSISSIPPI VALLEY, SAT, AUG 5.
- FLOODING POSSIBLE ACROSS PORTIONS OF THE MIDDLE MISSISSIPPI
VALLEY AND THE OHIO VALLEY.
- HAZARDOUS HEAT ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY,
THE SOUTHERN ROCKIES, CALIFORNIA, THE SOUTHEAST, THE SOUTHERN
PLAINS, AND THE SOUTHWEST, SAT-WED, AUG 5-AUG 9.
- HAZARDOUS HEAT ACROSS PORTIONS OF CALIFORNIA, SUN, AUG 6.
- HAZARDOUS HEAT ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY,
THE TENNESSEE VALLEY, THE MIDDLE MISSISSIPPI VALLEY, THE SOUTHERN
APPALACHIANS, THE SOUTHEAST, AND THE SOUTHERN PLAINS, SAT-SUN, AUG
5-AUG 6.
- HAZARDOUS HEAT ACROSS PORTIONS OF THE SOUTHEAST AND THE
MID-ATLANTIC, MON-TUE, AUG 7-AUG 8.
- HAZARDOUS HEAT ACROSS PORTIONS OF MAINLAND ALASKA, SAT-MON, AUG
5-AUG 7.
- HAZARDOUS HEAT ACROSS PORTIONS OF MAINLAND ALASKA, SUN, AUG 6.
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,
QUANTITATIVE PRECIPITATION FORECAST, 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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