910
FXUS02 KWBC 301849
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
248 PM EDT SUN JUL 30 2023
VALID 12Z WED AUG 02 2023 - 12Z SUN AUG 06 2023
...HOT TEMPERATURES AND HIGH HEAT INDICES FROM THE SOUTH-CENTRAL
PLAINS AND MISSISSIPPI VALLEY TO THE SOUTHEAST THIS WEEK...
...HEAVY RAIN/FLASH FLOOD THREAT TO FOCUS ACROSS THE NORTH-CENTRAL
ROCKIES STATES AND VICINITY MIDWEEK...
..OVERVIEW
AN AMPLIFIED AND SLOW MOVING UPPER RIDGE WILL SUPPORT ABOVE NORMAL
TEMPERATURES FROM THE SOUTH-CENTRAL PLAINS THROUGH THE
MID-MISSISSIPPI VALLEY TO THE SOUTHEAST FOR MUCH OF THIS WEEK
ALONG WITH HIGH HEAT INDICES. DEEPENED MONSOONAL MOISTURE LIFTING
ON THE WESTERN PERIPHERY OF THE RIDGE THIS PERIOD WILL FAVOR A
SLOW SHIFT OF A MAIN CONVECTIVE RAINFALL FOCUS FROM THE GREAT
BASIN TO THE NORTH-CENTRAL ROCKIES/HIGH PLAINS. MEANWHILE,
SHORTWAVES ROUNDING THE TOP OF THE RIDGE IN THE NORTHWEST FLOW
WILL SPARK STRONG TO SEVERE THUNDERSTORMS, AND LOCALLY HEAVY RAIN,
MIDWEEK ACROSS THE MIDWEST TO THE APPALACHIANS/MID-ATLANTIC AND UP
TO THE NORTHEAST LATE WEEK. THIS IS ALSO ALONG AND IN ADVANCE OF
AN ORGANIZED SURFACE LOW/FRONTAL SYSTEM THAT SHOULD MODERATE
TEMPERATURES IN THE WAKE OF ITS PASSAGE.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
MODELS AND ENSEMBLES STILL HAVE A GOOD HANDLE ON THE OVERALL
LARGE-SCALE PATTERN BUT PLENTY OF UNCERTAINTY IN THE DETAILS AND
TIMING OF SYSTEMS ROUNDING THE TOP SIDE OF THE UPPER RIDGE. 06Z
GFS WAS NOTABLY FASTER WITH AN INITIAL SHORTWAVE SKIRTING THE
UPPER GREAT LAKES MIDWEEK, ALSO FASTER WITH SURFACE COLD FRONT
PROGRESSION INTO THE EAST LATER IN THE WEEK TOO. MAJORITY OF THE
REST OF THE GUIDANCE SUGGESTS A LITTLE SLOWER PROGRESSION, WHICH
IS THE DIRECTION THE WPC FORECAST TRENDED AS WELL. THIS CONTINUES
TO OFFER PLENTY OF UNCERTAINTY IN THE RESULTING QPF FORECAST FROM
THE MIDWEST INTO THE EAST LATER THIS WEEK. OTHERWISE, GOOD
AGREEMENT ON THE GRADUAL EXPANSION OF THE UPPER RIDGE ACROSS THE
SOUTHERN U.S. AS WELL AS AN UPPER LOW MEANDERING OFF THE NORTHWEST
COAST.
THE WPC MEDIUM RANGE PRODUCT SUITE USED A GENERAL DETERMINISTIC
MODEL BLEND FOR THE FIRST HALF OF THE PERIOD, WHICH DOES HELP
MITIGATE THE TIMING DIFFERENCES WITH THE GREAT LAKES SHORTWAVE.
INCORPORATED MORE ENSEMBLE MEAN GUIDANCE LATE PERIOD TO TONE DOWN
SOME OF THE NOISE WITH ANY ONE INDIVIDUAL SOLUTION. THIS
MAINTAINED PRETTY GOOD CONSISTENCY WITH THE PREVIOUS WPC FORECAST,
THOUGH SOME ADJUSTMENTS (ESPECIALLY TO QPF) WERE NEEDED BASED ON
CURRENT GUIDANCE TRENDS.
..WEATHER/HAZARDS HIGHLIGHTS
THE GREATEST HEAT ANOMALIES SHOULD SETTLE THIS WEEK ACROSS THE
SOUTH-CENTRAL PLAINS TO THE LOWER MISSISSIPPI VALLEY, WHERE ABOVE
NORMAL TEMPERATURES BY 5 TO 10+ DEGREES ARE LIKELY AS ACTUAL
TEMPERATURES NEAR OR EXCEED 100F. THE SOUTHERN PLAINS TO LOWER
MISSISSIPPI VALLEY AND SOUTHEAST MAY EXPERIENCE HEAT INDICES
SOARING ABOVE 105F, EVEN ABOVE 110-115F IN SOME AREAS. RECORD HOT
HIGHS AND WARM MINIMUM TEMPERATURES ARE WIDELY POSSIBLE IN THESE
REGIONS NEXT WEEK. HEAT SHOULD SETTLE SOUTHWARD WITH TIME AS
HEIGHTS LOWER ACROSS THE CENTRAL U.S. AND INTO THE EAST.
AREAS FROM THE GREAT BASIN TO THE NORTH-CENTRAL ROCKIES/HIGH
PLAINS WILL SEE DIURNALLY AND TERRAIN DRIVEN CONVECTION AS FUELED
BY DEEP MONSOONAL MOISTURE AND EMBEDDED SHORTWAVE ENERGIES
ON/AROUND THE PERIPHERY OF THE MAIN UPPER RIDGE. QPF, MOISTURE,
AND INSTABILITY FIELDS SEEM TO SUPPORT SLIGHT RISKS OF EXCESSIVE
RAINFALL CONTINUING INTO WEDNESDAY AND THURSDAY ACROSS PORTIONS OF
IDAHO/UTAH/WYOMING AND COLORADO WHERE FLASH FLOOD GUIDANCE VALUES
ARE LOWER AND BURN SCARS. FOR DAY 5/THURSDAY, NEW GUIDANCE TRENDS
NECESSITATED A NORTHWARD SHIFT IN THE SLIGHT RISK TO ACROSS
NORTHERN WYOMING AND FAR SOUTHERN MONTANA. STILL A LOT OF
UNCERTAINTY IN THE DETAILS SO FURTHER REFINEMENT OF THESE RISK
AREAS IS LIKELY IN THE COMING DAYS.
MEANWHILE, THE NORTH-CENTRAL U.S. CAN ALSO EXPECT SCATTERED STORMS
AS SHORTWAVES/UPPER TROUGHING WORK INTO THE REGION. A HEAVY
RAIN/FLASH FLOODING THREAT WILL LIKELY BE TIED TO THE POTENTIAL
FOR ORGANIZED CONVECTIVE SYSTEMS IN THE NORTHWESTERLY FLOW.
MARGINAL RISKS HAVE BEEN INCLUDED ON BOTH DAYS 4 AND 5 TO COVER
THIS POTENTIAL FROM THE MIDWEST TO THE APPALACHIANS/MID-ATLANTIC,
WITH EVENTUAL MORE CONCENTRATED SLIGHT RISK AREAS POSSIBLE. THIS
ACTIVITY WILL LIKELY WORK ACROSS THE NORTHEAST LATER WEEK IN A
PATTERN TO MONITOR. ACTIVITY WILL ALSO BE AIDED AS AN ORGANIZED
LOW PRESSURE SYSTEM SUBSEQUENTLY TRACKS EASTWARD ACROSS CANADA,
AND A COLD FRONT TRAILS BACK ACROSS THE LOWER 48 AND STALLS BACK
INTO THE CENTRAL PLAINS.
THIS ALL OCCURS WELL TO THE NORTH OF A LEAD COLD FRONT PUSHED
UNSEASONABLY FAR SOUTH EARLY IN THE PERIOD TO OFFER A MORE DEFINED
THAN NORMAL SUMMERTIME CONVECTIVE FOCUS OVER FLORIDA. THERE COULD
BE SOME LINGERING LOCALIZED HIGH RAIN RATES GIVEN STALLING
MOISTURE POOLING/INSTABILITY FOCUS AS THE FRONT SLOWLY WEAKENS
OVER TIME.
SANTORELLI/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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