336
FXUS02 KWBC 020700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 AM EDT SUN JUL 02 2023
VALID 12Z WED JUL 05 2023 - 12Z SUN JUL 09 2023
...MAJOR SOUTHERN TIER HEAT WAVE TO EASE THIS WEEK, BUT MAY START
TO REBUILD OVER THE SOUTHERN HIGH PLAINS AND VICINITY NEXT
WEEKEND...
..OVERVIEW
NOT A LOT HAS CHANGED OVER THE PAST DAY REGARDING THE FORECAST
PATTERN EVOLUTION FROM MIDWEEK THROUGH NEXT WEEKEND. A WEAK
SHORTWAVE WILL DEPART FROM THE NORTHEAST ON WEDNESDAY AND TAKE ITS
ASSOCIATED FRONTAL SYSTEM WITH IT, ASIDE FROM THE TRAILING PART OF
THE FRONT THAT WILL LINGER OVER THE SOUTHERN MID-ATLANTIC.
FARTHER WEST AN UPPER TROUGH EXTENDING FROM CANADA INTO THE
NORTHERN PLAINS AS OF WEDNESDAY WILL PROGRESS EASTWARD WITH TIME,
PUSHING A CENTRAL U.S. FRONT TOWARD THE EAST COAST AND SOUTHERN
STATES. PROGRESSION OF THIS FRONT WILL PRODUCE A BROAD AREA OF
SHOWERS/THUNDERSTORMS OVER THE CENTRAL-EASTERN STATES OVER THE
COURSE OF THE PERIOD. IN ADDITION, PERSISTENCE OF THE WESTERN
PART OF THE FRONT OVER THE PLAINS AND ITS EVENTUAL RETURN
NORTHEAST AS A WARM FRONT MAY HELP TO GENERATE MORE LOCALLY HEAVY
CONVECTION OVER THE CENTRAL PLAINS LATE THIS WEEK INTO THE
WEEKEND. MEANWHILE CONSENSUS MAINTAINS THE IDEA OF A WEST COAST
UPPER TROUGH (WITH POSSIBLE EMBEDDED LOW) SETTLING OVER THE WEST
COAST FROM THURSDAY ONWARD IN RESPONSE TO AN EASTERN PACIFIC
RIDGE. AN UPPER HIGH OVER THE SOUTHERN ROCKIES/HIGH PLAINS
THROUGH THE PERIOD COULD BEGIN TO STRENGTHEN SLIGHTLY NEXT
WEEKEND, WITH A SOMEWHAT BETTER DEFINED INTERIOR WEST/ROCKIES
RIDGE EXTENDING TO THE NORTH-NORTHWEST LATE WEEK INTO THE WEEKEND
AS THE WEST COAST TROUGH BECOMES ESTABLISHED.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
ONCE AGAIN AN OPERATIONAL MODEL COMPOSITE EARLY IN THE PERIOD
FOLLOWED BY SOME INCLUSION OF LATEST ENSEMBLE MEANS (18Z GEFS/12Z
ECENS IN THE CASE OF THIS UPDATE) WITH THE MODELS BY THE LATTER
HALF OF THE FORECAST REFLECTED THE AGREEABLE THEMES OF THE
FORECAST AND YIELDED ONLY MINOR ADJUSTMENTS FROM CONTINUITY. ONE
EMBEDDED DETAIL UNCERTAINTY TO MONITOR IS WITH NORTHERN TIER
SHORTWAVE ENERGY THAT MAY SUPPORT AN UPPER MIDWEST/UPPER GREAT
LAKES FRONTAL WAVE AROUND WEDNESDAY. ECMWF RUNS HAVE BEEN ON THE
STRONGER/WESTWARD SIDE FOR MULTIPLE RUNS (WITH CORRESPONDING
HEAVIER/WESTWARD QPF) WHILE THE CMC IS ON THE WEAK SIDE. THE NEW
00Z GFS HAS TRENDED SOMEWHAT STRONGER THAN EARLIER RUNS BUT THE
NEW ECMWF HAS TRENDED WEAKER, FAVORING AN INTERMEDIATE SOLUTION.
GOING FARTHER OUT IN TIME, THE BLEND/MEAN APPROACH HELPS TO SMOOTH
OUT THE LOW-PREDICTABILITY SHORTWAVE DIFFERENCES THAT AFFECT
TIMING OF THE FRONT AS IT HEADS INTO THE EASTERN/SOUTHERN U.S.
NOTE THAT THE 00Z UKMET SEEMS TO STRAY TO THE FAST SIDE FOR WEAK
SHORTWAVE ENERGY THAT OTHER GUIDANCE SHOWS OVER THE SOUTHEAST BY
FRIDAY. THERE ARE STILL LOW-CONFIDENCE DETAIL UNCERTAINTIES
WITHIN THE UPPER TROUGH DEVELOPING NEAR THE WEST COAST BUT AT
LEAST THE LATEST GFS RUNS ARE GENERALLY CLOSER TO THE MODEL/MEAN
CONSENSUS IN PRINCIPLE THAN THEY WERE 24 HOURS OR SO AGO. THERE
ARE ALSO MEANINGFUL DIFFERENCES FOR SHORTWAVE ENERGY ROTATING
AROUND THE LARGER SCALE CANADIAN/NORTHERN TIER U.S. UPPER TROUGH
BY NEXT WEEKEND, LOWERING CONFIDENCE IN SPECIFICS OF A FRONT THAT
COULD EVENTUALLY REACH SOUTH OF THE CANADIAN BORDER.
..WEATHER/HAZARDS HIGHLIGHTS
THE WAVY COLD FRONT PROGRESSING FROM THE UPPER MIDWEST/CENTRAL
PLAINS INTO THE EASTERN/SOUTHERN U.S. WILL LIKELY PRODUCE MULTIPLE
EPISODES OF SHOWERS AND THUNDERSTORMS, WITH SOME LOCALLY HEAVY.
THE DAYS 4-5 EXCESSIVE RAINFALL OUTLOOKS COVERING THE WEDNESDAY
THROUGH THURSDAY NIGHT TIME FRAME WILL DEPICT A BROAD MARGINAL
RISK AREA FROM THE WESTERN GREAT LAKES THROUGH THE MID/UPPER
MISSISSIPPI VALLEY AND CENTRAL/SOUTH-CENTRAL PLAINS (DAY 4) AND
OHIO VALLEY SOUTH-SOUTHWEST TO THE GULF COAST (DAY 5). AT THIS
TIME GUIDANCE SIGNALS ARE NOT YET COHERENT ENOUGH FOR ANY SLIGHT
RISK AREAS BUT ONE OR MORE COULD EVENTUALLY ARISE IF SHORT RANGE
MODELS BEGIN TO CLUSTER BETTER. FRONTAL WAVE SPECIFICS WILL PLAY
A ROLE IN HOW MUCH RAIN FALLS OVER THE UPPER MIDWEST AND VICINITY
AROUND MIDWEEK. BY THURSDAY-THURSDAY NIGHT, GUIDANCE IS SIGNALING
POTENTIAL FOR LOCALLY HEAVY CONVECTION TO DEVELOP OVER THE CENTRAL
PLAINS AS THE TRAILING PART OF THE FRONT STALLS TO THE SOUTH AND
WEST OF THE REGION. THE DAY 5 OUTLOOK WILL REFLECT A MARGINAL
RISK FOR NOW, WITH A SLIGHT RISK POSSIBLE IN THE FUTURE IF
GUIDANCE BEGINS TO CONVERGE FOR THE AXIS OF HEAVIEST RAINFALL.
MEANWHILE THE DAYS 4-5 OUTLOOKS INTRODUCE A MARGINAL RISK AREA
MAINLY OVER THE CAROLINAS, WHERE ESPECIALLY ON DAY 4 LATEST
SOLUTIONS SHOW A DECENT COMBINATION OF INSTABILITY, ANOMALOUS
MOISTURE, AND CORRESPONDING LOCALLY HEAVY QPF, ALONG AND AHEAD OF
A STALLING SURFACE FRONT. THE FRONT MAY WEAKEN SOME BY DAY 5 BUT
THE MOISTURE AND INSTABILITY SHOULD PERSIST. BEYOND THURSDAY
NIGHT, EXPECT LOCALLY HEAVY RAINFALL TO CONTINUE EASTWARD
TOWARD/THROUGH THE EAST COAST INTO THE WEEKEND WHILE THE CENTRAL
PLAINS SHOULD SEE ADDITIONAL CONVECTIVE SYSTEMS WITH LOCALLY HEAVY
RAINFALL.
EXCESSIVE HEAT ACROSS THE SOUTHERN TIER SHOULD BECOME LESS
WIDESPREAD FOR A TIME THIS WEEK AS UPPER RIDGING RETURNS CLOSER TO
CLIMATOLOGICAL STRENGTH AND LATITUDE. THE BEST POTENTIAL FOR
MAXIMUM HEAT INDEX VALUES TO REACH 105-110F OR SO MID-LATE WEEK
SHOULD BE MORE CONFINED TO THE FAR SOUTHEAST/FLORIDA AND CENTRAL
GULF COAST THROUGH SOUTHERN TEXAS. HOWEVER UPPER RIDGING OVER THE
SOUTHERN ROCKIES/HIGH PLAINS MAY BEGIN TO STRENGTHEN NEXT WEEKEND
AND THAT WOULD LEAD TO TEMPERATURES GRADUALLY RISING AGAIN OVER
AND NEAR THE SOUTHERN PLAINS. OVER THE WEST, THE GREATEST
ANOMALIES WILL BE OVER THE PACIFIC NORTHWEST WITH HIGHS UP TO
15-20F ABOVE NORMAL INTO MIDWEEK (WITH SOME DAILY RECORD HIGHS
POSSIBLE) FOLLOWED BY GRADUAL MODERATION AS UPPER TROUGHING SETS
UP ALONG THE WEST COAST. MEANWHILE, TO THE NORTH OF THE PLAINS
COLD FRONT EXPECT UNSEASONABLY COOL HIGHS OF 10-20F BELOW NORMAL
OVER THE NORTHERN-CENTRAL HIGH PLAINS ESPECIALLY ON WEDNESDAY,
WITH GRADUAL MODERATION LEADING TO SINGLE-DIGIT NEGATIVE ANOMALIES
BY THE WEEKEND. THE LEADING WARM SECTOR WILL BRING ABOVE NORMAL
TEMPERATURES FROM THE MIDWEST INTO NORTHEAST MID-LATE WEEK,
FOLLOWED BY NEAR OR SLIGHTLY BELOW NORMAL READINGS 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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