677
FXUS02 KWBC 030700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 AM EDT MON JUL 03 2023
VALID 12Z THU JUL 06 2023 - 12Z MON JUL 10 2023
...MAJOR SOUTHERN TIER HEAT WAVE TO EASE THIS WEEK, BUT MAY START
TO REBUILD OVER THE SOUTHERN HIGH PLAINS AND VICINITY DURING THE
WEEKEND...
..OVERVIEW
THE MOST STABLE UPPER FEATURES DURING THE PERIOD WILL BE A
SOUTHERN ROCKIES/HIGH PLAINS RIDGE (POSSIBLY STRENGTHENING SOME BY
SUNDAY OR MONDAY) AND A CENTRAL CANADA MEAN TROUGH THAT WILL
EXTEND INTO AT LEAST NORTHERN PARTS OF THE LOWER 48. SHORTWAVE
ENERGY ON THE LEADING SIDE OF THE TROUGH WILL HELP TO PUSH A COLD
FRONT AND ITS ASSOCIATED SHOWERS/THUNDERSTORMS FROM THE GREAT
LAKES THROUGH SOUTHERN PLAINS EASTWARD TO THE EAST COAST.
UPSTREAM SHORTWAVES EMBEDDED WITHIN PROGRESSIVE FLOW BETWEEN THE
UPPER RIDGE AND TROUGH WILL LIKELY INTERACT WITH THE WESTERN END
OF THE FRONT (INITIALLY STALLED AND THEN RETURNING AS A WARM
FRONT) TO PRODUCE MULTIPLE CENTRAL U.S. CONVECTIVE SYSTEMS WHOSE
FOCUS SHOULD SHIFT GRADUALLY EASTWARD WITH TIME. LATEST GUIDANCE
IS SUGGESTING THAT ANOTHER FRONT MAY DROP INTO THE CENTRAL U.S.
DURING THE WEEKEND AND EARLY NEXT WEEK WITH SUPPORT FROM SOME
COMBINATION OF ENERGY EJECTING FROM THE WEST AND/OR AMPLIFICATION
OF THE CANADIAN/NORTHERN TIER U.S. UPPER TROUGH. MEANWHILE EXPECT
A WEAK TROUGH WITH ONE OR MORE EMBEDDED UPPER LOWS TO EVOLVE ALONG
THE WEST COAST FROM LATE THIS WEEK INTO THE WEEKEND, WITH SOME
QUESTION AS TO ITS PERSISTENCE OR RELOADING BY THE START OF NEXT
WEEK.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE LATEST GUIDANCE CONTINUES TO SHOW REASONABLE AGREEMENT FOR THE
MAIN THEMES OF THE LARGE SCALE PATTERN, BUT RECENT RUNS SINCE
12Z/02 ARE SHOWING MORE SPREAD FOR IMPORTANT DETAILS WITHIN THE
MEAN FLOW BY THE LATTER HALF OF THE PERIOD. THE LARGEST SCALE
ISSUES ARISE WITHIN THE CENTRAL CANADA INTO NORTHERN U.S. MEAN
TROUGH FROM THE WEEKEND INTO EARLY NEXT WEEK. THE 12Z ECMWF
AMPLIFIES DIGGING ENERGY MORE THAN OTHER MODELS (THOUGH STAYING
WITHIN THE FULL ENSEMBLE SPREAD BY A SMALL MARGIN), LEADING TO AN
UPPER MIDWEST/WESTERN GREAT LAKES UPPER LOW BY NEXT MONDAY.
LATEST GFS RUNS ARE NOT AS AMPLIFIED OVER THE LOWER 48 BUT BRING A
DEEP UPPER LOW FARTHER SOUTH OVER CANADA THAN OTHER GUIDANCE THAT
CLUSTERS OVER OR JUST NORTH OF NORTHERN HUDSON BAY (WHERE THE 12Z
ECMWF ALSO HAS A SEPARATE UPPER LOW). CMC RUNS THUS FAR HAVE BEEN
WEAKER WITH THIS TROUGH. CURRENT PREFERENCE TILTS SOMEWHAT MORE
IN THE DIRECTION OF THE ENSEMBLE MEANS THAT SHOW SOME TROUGH
AMPLIFICATION BY NEXT MONDAY BUT IN A MORE MEASURED FASHION THAN
THE GFS/ECMWF. THE DEVELOPING UPPER TROUGH ALONG THE WEST COAST
SHOWS FAIRLY GOOD CLUSTERING INTO SATURDAY ASIDE FROM TYPICAL
EMBEDDED DETAILS THAT HAVE LOWER PREDICTABILITY. THEN IT BECOMES
AMBIGUOUS WHETHER THE EMBEDDED UPPER LOW EJECTS WHILE UPSTREAM
ENERGY FILTERS INTO THE OVERALL TROUGH (WHICH SEEMS TO BE THE
MAJORITY SCENARIO AT THE MOMENT) OR SOME OTHER SCENARIO OCCURS,
SUCH AS LONGER PERSISTENCE OF THE MAIN UPPER LOW/COMBINATION WITH
THE UPSTREAM ENERGY. OVER THE EAST, PREDICTABILITY IS FAIRLY GOOD
TO START WITH AS A PRIMARY UPPER MIDWEST/GREAT LAKES SHORTWAVE
PUSHES ALONG A LEADING COLD FRONT. HOWEVER IT STEADILY DECREASES
AS DETAILS DIVERGE FOR THIS LEADING ENERGY AND WEAK UPSTREAM
SHORTWAVES REACH THE EAST WITHIN ZONAL TO SLIGHTLY CYCLONIC FLOW.
THERE HAS BEEN SOME CONTINUITY IN THE GENERAL IDEA OF SURFACE
WAVINESS ALONG/OFFSHORE THE MID-ATLANTIC COAST, BUT SPREAD AND
VARIABILITY FOR SPECIFICS. THIS IS TO BE EXPECTED GIVEN TYPICAL
SENSITIVITY OF WEAK SURFACE FEATURES TO SHORTWAVE DETAILS ALOFT.
BASED ON THE ARRAY OF LATEST GUIDANCE, THE UPDATED FORECAST
STARTED WITH A COMPOSITE OF 12Z/18Z OPERATIONAL MODELS FOR ABOUT
THE FIRST HALF OF THE FORECAST AND THEN STEADILY INCREASED 18Z
GEFS/12Z ECMWF MEAN INPUT SO THAT THE MEANS HAD A TOTAL OF 60
PERCENT WEIGHT BY DAY 7 MONDAY. THIS HELPED TO TEMPER THE VARIOUS
LESS CONFIDENT ASPECTS OF THE OPERATIONAL MODELS LATE IN THE
PERIOD.
..WEATHER/HAZARDS HIGHLIGHTS
THE WAVY COLD FRONT PROGRESSING EASTWARD FROM THE GREAT LAKES
THROUGH SOUTHERN PLAINS THURSDAY ONWARD WILL LIKELY PRODUCE
MULTIPLE EPISODES OF SHOWERS AND THUNDERSTORMS, WITH SOME LOCALLY
HEAVY. THE DAYS 4-5 EXCESSIVE RAINFALL OUTLOOKS COVERING THE
THURSDAY THROUGH FRIDAY NIGHT TIME FRAME DEPICT A BROAD MARGINAL
RISK AREA WITH THIS ACTIVITY, FROM THE OHIO VALLEY SOUTH-SOUTHWEST
TO THE GULF COAST (DAY 4) AND FROM THE NORTHEAST INTO THE
SOUTHEAST (DAY 5). THERE IS STILL NOT SUFFICIENT AGREEMENT FOR
LOCATION AND INTENSITY OF RAINFALL TO MERIT ANY EMBEDDED SLIGHT
RISK AREAS AT THIS TIME, BUT SHORTER-TERM GUIDANCE MAY EVENTUALLY
RESOLVE BETTER DEFINED AREAS OF FOCUS. DAY 4 CONTINUES TO DEPICT
A MARGINAL RISK AREA OVER PARTS OF THE CAROLINAS/EASTERN GEORGIA
WITH LINGERING MOISTURE AND INSTABILITY ALONG/SOUTH OF A STALLED
FRONT. MEANWHILE THE COMBINATION OF A STALLED HIGH
PLAINS/SOUTHERN PLAINS FRONT EVENTUALLY RETURNING AS A WARM FRONT
ALONG WITH PROGRESSIVE WEAK SHORTWAVES ALOFT WILL FAVOR A
MULTI-DAY PATTERN OF CENTRAL U.S. CONVECTIVE SYSTEMS WHOSE FOCUS
SHOULD DRIFT EASTWARD WITH TIME. THE DAY 4 OUTLOOK COVERING
THURSDAY-THURSDAY NIGHT PLANS TO INTRODUCE A SLIGHT RISK AREA
CENTERED OVER/NEAR THE WESTERN TWO-THIRDS OF KANSAS, REFLECTING
THE BEST OVERLAP OF GUIDANCE SIGNALS. THE DAY 5 OUTLOOK WILL
DEPICT A BROAD MARGINAL RISK AREA AS THERE IS A REASONABLE SIGNAL
FOR MORE LOCALLY HEAVY CONVECTION BUT POOR AGREEMENT FOR LOCATION.
IT APPEARS LIKELY THAT EVENTUAL GUIDANCE CLUSTERING WOULD SUPPORT
ONE OR MORE EMBEDDED SLIGHT RISK AREAS AT SOME POINT. BEYOND
FRIDAY NIGHT, THIS CENTRAL U.S. CONVECTION SHOULD CONTINUE THROUGH
THE EAST-CENTRAL PLAINS AND INTO THE MISSISSIPPI VALLEY WHILE
ANOTHER FRONT APPROACHING FROM THE NORTH/WEST MAY ALSO PRODUCE
SOME SHOWERS/THUNDERSTORMS. AREAS ALONG THE EAST COAST SHOULD
ALSO CONTINUE TO SEE EPISODES OF SHOWERS/STORMS AT LEAST INTO THE
WEEKEND.
THE HIGHEST HEAT INDEX VALUES ACROSS THE SOUTHERN TIER DURING THE
PERIOD SHOULD BE FOCUSED OVER SOUTHERN/EASTERN TEXAS WITH MAXIMUM
DAILY VALUES LIKELY REACHING 110F OR HIGHER, WITH SLIGHTLY LESS
EXTREME VALUES EXTENDING OVER OTHER PARTS OF TEXAS INTO THE
CENTRAL GULF COAST REGION. THE FAR SOUTHEAST/FLORIDA MAY SEE SOME
HEAT INDEX VALUES REACH AS HIGH AS 105-110F OR SO. MEANWHILE THE
UPPER RIDGE OVER THE SOUTHERN ROCKIES/HIGH PLAINS WILL KEEP THAT
REGION HOT THROUGH THE PERIOD, WITH SOME EXPANSION OF HIGHS 5-15F
ABOVE NORMAL BY SATURDAY-MONDAY AS THE UPPER RIDGE STRENGTHENS A
BIT. PACIFIC NORTHWEST HIGHS OF 10-15F ABOVE NORMAL ON THURSDAY
WILL LIKELY MODERATE THEREAFTER AS THE UPPER TROUGH DEVELOPS NEAR
THE COAST. MULTIPLE DAYS OF UPSLOPE FLOW OVER THE
NORTHERN-CENTRAL HIGH PLAINS SHOULD SUPPORT BELOW NORMAL HIGH
TEMPERATURES, WITH COOLEST READINGS UP TO 10-15F BELOW NORMAL ON
THURSDAY. THE NORTHEAST WILL SEE VERY WARM TO HOT TEMPERATURES OF
5-15F ABOVE NORMAL LATE THIS WEEK, ERODING FROM THE WEST AS THE
COLD FRONT APPROACHES. MUCH OF THE EASTERN U.S. SHOULD SEE NEAR
TO SLIGHTLY BELOW NORMAL TEMPERATURES AFTER FRONTAL PASSAGE.
RAUSCH
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, 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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