265
FXUS02 KWBC 291843
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
243 PM EDT SAT JUL 29 2023
VALID 12Z TUE AUG 01 2023 - 12Z SAT AUG 05 2023
...HOT TEMPERATURES AND HIGH HEAT INDICES ARE LIKELY ACROSS THE
SOUTH-CENTRAL PLAINS AND MISSISSIPPI VALLEY INTO THE SOUTHEAST
NEXT WEEK...
...HEAVY RAIN/FLASH FLOOD THREAT POSSIBLE MID NEXT WEEK ACROSS
PARTS OF THE NORTH-CENTRAL ROCKIES...
..OVERVIEW
THE UPPER HIGH THAT HAS BEEN ANCHORING OVER THE
SOUTHWEST/SOUTH-CENTRAL U.S. FOR WEEKS NOW IS FINALLY FORECAST TO
DRIFT EASTWARD NEXT WEEK, FINALLY BRINGING TEMPERATURES IN THE
DESERT SOUTHWEST CLOSER TO NORMAL (THOUGH STILL HOT). RIDGING
STRETCHING NORTH FROM THE UPPER HIGH WILL ALSO PROMOTE ABOVE
NORMAL TEMPERATURES ACROSS THE CENTRAL PLAINS TO MID-MISSISSIPPI
VALLEY WITH THE SOUTHEAST ALSO LIKELY TO WARM ABOVE NORMAL, WITH
HIGH HEAT INDICES. A "RING OF FIRE" TYPE OF PATTERN IS LIKELY IN
THE PRECIPITATION FORECAST, AS MONSOONAL MOISTURE LEADS TO
DIURNALLY DRIVEN CONVECTION IN THE FOUR CORNERS STATES AND
VICINITY, SHORTWAVES PUSH THROUGH NORTHWEST FLOW AND SPARK STRONG
TO SEVERE THUNDERSTORMS IN THE NORTH-CENTRAL U.S., AND A
WELL-DEFINED COLD FRONT PRESSING UNUSUALLY FAR SOUTH INTO THE
MID-SECTION OF THE COUNTRY WITH A RISK OF HEAVY RAINFALL OVER THE
NORTHERN ROCKIES TO THE CENTRAL HIGH PLAINS MIDWEEK, AND PERHAPS
ACROSS THE NORTHEAST LATE NEXT WEEK.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE LATEST GUIDANCE CONTINUES TO HAVE A GOOD HANDLE ON THE OVERALL
PATTERN WHICH FEATURES VARIOUS SYSTEMS/SHORTWAVES ROUNDING THE TOP
OF THE STUBBORN SOUTHERN U.S. RIDGE. SOME TIMING/DETAILS
DIFFERENCES REMAIN, MOST NOTABLY WITH THE SHORTWAVE INTO THE UPPER
GREAT LAKES LATER NEXT WEEK. THE 00Z ECMWF WAS THE SLOWEST OF THE
GUIDANCE WITH THIS AND THE ASSOCIATED COLD FRONT THROUGH THE
MIDWEST, BUT THE NEW 12Z RUN (AVAILABLE AFTER FORECAST GENERATION
TIME) DID COME IN FASTER. SOME DIFFERENCES WITH AN UPPER LOW
MEANDERING OFF THE NORTHWEST COAST BY LATE WEEK/NEXT WEEKEND IN
THE 00Z CMC SO IT WAS DROPPED OFF FROM THE BLEND AFTER DAY 5. THE
WPC MEDIUM RANGE PRODUCT SUITE WAS PRIMARILY DERIVED FROM A
COMPOSITE BLEND OF THE DETERMINISTIC MODELS DAYS 3 AND 4, WITH
MORE EMPHASIS TOWARDS THE ECMWF AND GFS (WITH ENSEMBLE MEANS)
LATER IN THE PERIOD, ALONG WITH THE GENERALLY COMPATIBLE 13 UTC
NATIONAL BLEND OF MODELS. THIS MAINTAINS EXCELLENT CONSISTENCY
WITH THE PREVIOUS WPC FORECAST AS WELL.
..WEATHER/HAZARDS HIGHLIGHTS
A LEAD COLD FRONT SHOULD PUSH UNSEASONABLY FAR SOUTH TO OFFER A
MORE DEFINED THAN NORMAL SUMMERTIME CONVECTIVE FOCUS OVER THE
SOUTHEAST. A MARGINAL RISK HAS BEEN MAINTAINED IN THE UPDATED DAY
4/5 EROS FOR PORTIONS OF GEORGIA AND FLORIDA, WITH EXTENSION INTO
COASTAL SOUTH CAROLINA, AS THERE COULD BE HIGH RAIN RATES POSSIBLY
CAUSING EXCESSIVE RAINFALL GIVEN STALLING MOISTURE
POOLING/INSTABILITY FOCUS AND UPPER SUPPORT. THE COMBINATION OF AN
ADDITIONAL FRONTAL PASSAGE AS WELL AS THE LINGERING/WAVY SOUTHERN
FRONT IS THEN LIKELY TO FAVOR PERIODIC ACTIVITY THROUGH MID-LATER
NEXT WEEK.
MEANWHILE, THE NORTH-CENTRAL U.S. CAN ALSO EXPECT SCATTERED STORMS
AS SHORTWAVES TRACK THROUGH THE REGION. A HEAVY RAIN/FLASH
FLOODING THREAT WILL LIKELY BE TIED TO THE POTENTIAL FOR ORGANIZED
CONVECTIVE SYSTEMS IN THE NORTHWESTERLY FLOW. DAY TO DAY POSITIONS
OF HEAVY RAIN AND MCSS ARE UNCERTAIN AT THIS POINT, BUT THE
PATTERN IS THERE. MARGINAL RISKS HAVE BEEN INCLUDED ON BOTH DAYS 4
AND 5 TO COVER THIS POTENTIAL, WITH EVENTUAL MORE CONCENTRATED
SLIGHT RISK AREAS POSSIBLE. THE FOUR CORNERS STATES AND INTO
WYOMING ARE LIKELY TO SEE DIURNALLY DRIVEN CONVECTION EACH DAY AS
MONSOONAL MOISTURE COMES IN. AS THE UPPER HIGH SHIFTS EASTWARD
WITH TIME, THIS MAY INCREASE MOIST SOUTHERLY FLOW AND ALLOW FOR
ADDITIONAL SHORTWAVE ENERGY TO WORK INTO THE REGION. THERE WAS
ENOUGH SUPPORT IN THE QPF, MOISTURE, AND INSTABILITY FIELDS TO
INCLUDE A SLIGHT RISK ON DAY 5/WEDNESDAY ACROSS PORTIONS OF
CENTRAL WYOMING AND NORTH-CENTRAL COLORADO WHERE FLASH FLOOD
GUIDANCE VALUES ARE LOWER.
AROUND THE MIDDLE TO LATTER PART OF NEXT WEEK, AN ORGANIZED LOW
PRESSURE SYSTEM WILL TRACK EASTWARD ACROSS CANADA WITH A COLD
FRONT TRAILING BACK INTO THE CENTRAL PLAINS. SUSPECT AN AREA OF
RAINFALL WITH POSSIBLY LOCALLY HEAVY RAIN MAY FOCUS FROM
NORTH-CENTRAL ROCKIES TO THE CENTRAL HIGH PLAINS WHERE THE
MONSOONAL MOISTURE APPEARS TO INTERACT WITH THE TRAILING FRONT AND
WITH ANOTHER FRONTAL WAVE OVER THE CENTRAL PLAINS. THERE WAS
ENOUGH SUPPORT IN THE QPF, MOISTURE, AND INSTABILITY FIELDS FOR
THE ADDITION OF A SLIGHT RISK AREA ON THE DAY 5/WEDNESDAY ERO
ACROSS CENTRAL WYOMING INTO NORTH-CENTRAL COLORADO CONSISTENT WITH
LOWER FLASH FLOOD GUIDANCE VALUES. LATER ON, LEAD FLOW SHOULD ALSO
FUEL AN EXPANDING AREA OF PRECIPITATION FROM THE OHIO VALLEY
THROUGH THE APPALACHIANS/MID-ATLANTIC AND THE SOGGY NORTHEAST.
THE HOT UPPER HIGH THAT HAS BEEN CENTERED OVER THE
SOUTHWEST/SOUTH-CENTRAL U.S. WILL RE-POSITION EASTWARD INTO
EARLY-MID NEXT WEEK, ALLOWING FOR HIGH TEMPERATURES IN THE DESERT
SOUTHWEST TO FINALLY EASE TO NEAR NORMAL. HIGHS SHOULD STILL BE
OVER 100F IN MANY AREAS BUT AT LEAST THERE SHOULD BE MINOR RELIEF
COMPARED TO THE PAST FEW WEEKS. TEMPERATURES BY BEGIN TO CREEP
BACK UP LATER NEXT WEEK INTO THE WEEKEND THOUGH AS THE RIDGE TRIES
TO EXPAND BACK WESTWARD. THE MOST PERSISTENT/GREATEST ANOMALIES
SHOULD MOVE FROM THE CENTRAL PLAINS TO THE MID-MISSISSIPPI VALLEY,
WHERE ABOVE NORMAL TEMPERATURES BY 5 TO 15 DEGREES ARE LIKELY AS
ACTUAL TEMPERATURES NEAR OR EXCEED 100F. THE SOUTHERN PLAINS TO
LOWER MISSISSIPPI VALLEY AND SOUTHEAST MAY SEE SLIGHTLY LOWER
ANOMALIES OF 5-10F ABOVE NORMAL, BUT THE HEAT COMBINED WITH HIGH
DEWPOINTS WILL LEAD TO 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. THERE
IS HOPE FOR SOME RELIEF TO SLOWLY WORK INTO THIS HEAT DOME FROM
THE NORTH THROUGH LATER NEXT WEEK WITH POSSIBLE COLD FRONTAL
APPROACH.
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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page