104
FXUS02 KWBC 020700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 AM 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
THE WPC MEDIUM RANGE PRODUCT SUITE WAS MAINLY DERIVED FROM A BLEND
OF BEST CLUSTERED GUIDANCE FROM THE 18 UTC GFS AND ESPECIALLY THE
BEST PATTERN MATCHING 12 UTC ECMWF/ECMWF ENSEMBLE MEAN ALONG WITH
THE 01 UTC NATIONAL BLEND OF MODELS THROUGH THIS FORECAST PERIOD.
PREFER TO LEAN INCREASINGLY ON THE ECMWF ENSEMBLE MEAN OVER TIME,
CONSISTENT WITH FORECAST SPREAD GROWTH. THE LATEST 00 UTC
UKMET/CANADIAN HAVE AGAIN TRENDED A TAD MORE IN LINE WITH THIS
BLEND COMPARED TO THEIR PRIOR RUNS. LOCAL CONVECTIVE FOCUS RUN TO
RUN CONTINUITY HAS BEEN LESS THAN STELLAR DESPITE A REASONABLY
ESTABLISHED MID-LARGER SCALE SUMMERTIME PATTERN, BUT MORE
ORGANIZED THREAT AREAS HAVE TENDED TO SHOW SIGNALS IN GUIDANCE
WELL INTO MEDIUM RANGE TIME SCALES. WPC PRODUCT CONTINUITY IS
DECENTLY MAINTAINED.
..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 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.
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, 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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