895
FXUS02 KWBC 060706
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
305 AM EDT SUN AUG 06 2023
VALID 12Z WED AUG 09 2023 - 12Z SUN AUG 13 2023
..HEAT WAVE TO PERSIST OVER THE SOUTH INTO THE SOUTHWEST
...EXCESSIVE RAIN/FLASH FLOOD THREAT FOR PORTIONS OF THE MIDDLE
MISSISSIPPI AND TENNESSEE VALLEYS WEDNESDAY...
..OVERVIEW
AN ELONGATED UPPER RIDGE EXTENDING FROM NORTHERN MEXICO/SOUTHERN
TEXAS ACROSS THE GULF OF MEXICO AND FLORIDA PENINSULA AS OF
WEDNESDAY SHOULD WEAKEN A BIT INTO THURSDAY BUT THEN STRENGTHEN
ONCE AGAIN OVER THE SOUTHERN ROCKIES/PLAINS AND NORTHERN MEXICO
LATE WEEK THROUGH THE WEEKEND. THIS RIDGE WILL MAINTAIN THE
ONGOING SOUTHERN TIER HEAT WAVE WITH DAILY RECORD HIGH
TEMPERATURES POSSIBLE EVERY DAY OF THE FORECAST PERIOD, WITH THE
MOST ANOMALOUS TEMPERATURES LIKELY TO BE OVER TEXAS. TO THE
NORTH, EXPECT BROADLY CYCLONIC FLOW WITH THE AXIS OF A BROAD
TROUGH CENTERED OVER THE EASTERN HALF OF THE LOWER 48. EMBEDDED
SHORTWAVES PROGRESSING FROM THE PACIFIC INTO/THROUGH THE TROUGH
WILL PRODUCE A SERIES OF CENTRAL-EASTERN U.S. WAVES/FRONTAL
SYSTEMS THAT COULD PRODUCE EPISODES OF LOCALLY HEAVY RAINFALL.
THE SCALE OF THE SHORTWAVES IS SMALL ENOUGH TO YIELD LOWER
PREDICTABILITY FOR DAY-TO-DAY SPECIFICS VERSUS THE LARGER SCALE
PATTERN BY THE LATTER HALF OF THE PERIOD. IN THE WEST, UPPER
LEVEL TROUGHING AND A WEAKENING FRONTAL SYSTEM WILL BRING RAINFALL
TO THE PACIFIC NORTHWEST INTO WEDNESDAY FOLLOWED BY RISING UPPER
HEIGHTS DOWNSTREAM FROM AN UPPER LOW SETTLING OVER OR NEAR THE
ALEUTIANS. MEANWHILE THE NATIONAL HURRICANE CENTER IS ISSUING
ADVISORIES FOR TROPICAL STORM EUGENE IN THE PACIFIC. THE SURFACE
REFLECTION SHOULD DISSIPATE WELL OFFSHORE AFTER WEDNESDAY BUT THE
SYSTEM'S UPPER LEVEL ENERGY AND POSSIBLY SOME MOISTURE COULD GET
INCORPORATED INTO AN UPPER TROUGH/LOW FORECAST TO EVOLVE ALONG OR
A LITTLE OFFSHORE THE CALIFORNIA COAST.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE LATEST CYCLE OF MODEL/ENSEMBLE GUIDANCE OFFERS NOTHING NEW IN
TERMS OF THE RECENT THEME OF GOOD PATTERN AGREEMENT BUT LOW
CONFIDENCE IN VARIOUS SPECIFICS DUE TO THE LOW PREDICTABILITY OF
EMBEDDED SHORTWAVES. THEREFORE THE FORECAST APPROACH CONTINUES TO
FAVOR AN OPERATIONAL MODEL BLEND EARLY AND THEN A STEADY SHIFT
TOWARD MORE ENSEMBLE INPUT (12Z ECENS/CMCENS AND 18Z GEFS) TOWARD
THE END OF THE PERIOD NEXT WEEKEND.
AFTER THE UNSEASONABLY STRONG SYSTEM DEPARTS FROM NORTHERN NEW
ENGLAND ON WEDNESDAY, THERE ARE AT LEAST SOME COMMON IDEAS FOR THE
TRAILING WAVY SOUTHERN TIER FRONT WHOSE EASTERN END SHOULD LIFT
NORTHWARD AS ONE EMBEDDED WAVE REACHES INTO THE MID-ATLANTIC.
HOWEVER SHORTWAVE DIFFERENCES ALOFT LEAD TO A FAIR AMOUNT OF
SPREAD FOR SPECIFICS ALONG THE EAST COAST BY FRIDAY. MEANWHILE A
PACIFIC NORTHWEST/BRITISH COLUMBIA SHORTWAVE WILL LIKELY CONTINUE
EASTWARD AND BRING AN AREA OF LOW PRESSURE AND ASSOCIATED FRONTAL
SYSTEM INTO THE UPPER MIDWEST TOWARD THE END OF THE WEEK. FROM
THAT POINT ONWARD THERE IS NOTABLE TIMING SPREAD, WITH LATEST
GFS/CMC RUNS TENDING TO BE ON THE FAST SIDE AND RECENT
ECMWF/ECENS/CMCENS RUNS SLOWER. WITH MODEST CONFIDENCE THE BLEND
HAS MAINTAINED SOMEWHAT MORE ECMWF/ECENS/CMCENS WEIGHT LATER IN
THE PERIOD GIVEN THEIR RELATIVE MAJORITY STATUS WITH BETTER
CONTINUITY. SOME GEFS RUNS HAVE HAD DIFFICULTY DEPICTING THIS
SYSTEM. GFS/ECMWF RUNS AND TO SOME DEGREE ENSEMBLE MEANS ARE
SUGGESTING ANOTHER FRONT MAY REACH THE NORTHERN TIER BY NEXT
SUNDAY.
..WEATHER/HAZARDS HIGHLIGHTS
DURING THE WEDNESDAY-THURSDAY NIGHT PERIOD COVERED BY THE DAYS 4-5
EXCESSIVE RAINFALL OUTLOOKS, THE MOST PROMINENT AREA OF FOCUS FOR
HEAVY RAINFALL/FLASH FLOOD POTENTIAL WILL EXTEND FROM THE
EAST-CENTRAL PLAINS INTO THE APPALACHIANS AND MID-ATLANTIC. THE
DAY 4 ERO DEPICTS A SLIGHT RISK AREA EXTENDING FROM EASTERN KANSAS
INTO PARTS OF THE LOWER OHIO VALLEY AND TENNESSEE VALLEY AS A
SOUTHERN PLAINS WAVE SHOULD INCREASE THE FLOW OF MOISTURE
INTERACTING WITH A LEADING WARM FRONT WHILE A SEPARATE FRONT DROPS
FROM THE NORTHERN TIER INTO THE MIDWEST. GUIDANCE SIGNALS ARE
STEADILY IMPROVING WITH SHOWING THE POTENTIAL FOR HEAVY CONVECTION
OVER THIS GENERAL AREA, THOUGH WITH TYPICAL DETAIL SPREAD FOR THIS
FAR OUT IN TIME. AN EMBEDDED UPGRADE MAY BE POSSIBLE DEPENDING ON
HOW SHORTER-TERM GUIDANCE RESOLVES THIS CONVECTION AND POTENTIAL
OVERLAP WITH SENSITIVE AREAS DUE TO ANTECEDENT CONDITIONS. BY DAY
5, THE BEST MODEL/ENSEMBLE CLUSTERING BECOMES MORE CONFINED OVER
THE SOUTHERN APPALACHIANS WHERE THE OUTLOOK SHOWS A SLIGHT RISK
AREA. SIGNALS ARE MORE DIFFUSE WITHIN THE SURROUNDING MARGINAL
RISK AREA. MEANWHILE MOST GUIDANCE IS SHOWING AN AREA OF LOCALLY
HEAVY RAINFALL POTENTIAL OVER PARTS OF THE NORTHERN PLAINS/UPPER
MIDWEST IN THE DAY 5 PERIOD DUE TO THE APPROACHING NORTHERN TIER
SYSTEM. THE COMBINATION OF FORECAST RAINFALL TOTALS, MODERATE
PROGRESSION, AND DETAIL SPREAD MERIT A MARGINAL RISK AREA FOR THIS
ACTIVITY.
FROM FRIDAY ONWARD EXPECT ADDITIONAL AREAS OF RAIN AND
THUNDERSTORMS ACROSS THE EASTERN U.S. BUT WITH STEADILY DECREASING
CONFIDENCE FOR SPECIFICS DUE TO UNCERTAINTY WITH DETAILS/TIMING OF
INDIVIDUAL WAVES/FRONTAL SYSTEMS. ANOTHER AREA OF SHOWERS/STORMS
MAY DEVELOP OVER THE PLAINS DURING THE WEEKEND. THERE HAS BEEN
SOME CONTINUITY RECENTLY FOR A POTENTIAL INCREASE OF DEEP MOISTURE
TO REACH THE FLORIDA PENINSULA NEXT WEEKEND, WITH CORRESPONDING
HIGHER RAINFALL TOTALS. THE PACIFIC NORTHWEST SHOULD SEE SOME
RAINFALL CONTINUE INTO WEDNESDAY AS A WEAKENING FRONT REACHES THE
AREA. SCATTERED SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE OVER
THE FOUR CORNERS STATES AND THE SIERRA NEVADA. SOME UPPER LEVEL
MOISTURE FROM TROPICAL STORM EUGENE MAY ENTER THE WEST BUT AT THIS
TIME IT IS NOT CLEAR HOW MUCH THIS COULD AFFECT RAINFALL TOTALS.
THE ONGOING HEAT WAVE OVER THE SOUTHERN TIER SHOULD CONTINUE
THROUGH THE WEEK AND NEXT WEEKEND, WITH GREATEST EMPHASIS OVER THE
SOUTHERN HIGH PLAINS WHERE HIGHS COULD REACH 10-15F ABOVE NORMAL
ESPECIALLY MID-LATE WEEK. TEMPERATURES MAY REACH OR EXCEED DAILY
RECORD HIGHS MOST DAYS DURING THE PERIOD FROM THE CENTRAL/WESTERN
GULF COAST INTO THE SOUTHERN ROCKIES. THE DESERT SOUTHWEST SHOULD
SEE A BRIEF LULL IN THE 110F+ HIGHS MID-LATE WEEK BUT TEMPERATURES
MAY REACH INTO THE LOW 110S ONCE AGAIN BY NEXT SUNDAY AS THE UPPER
RIDGE STRENGTHENS. THE FLORIDA PENINSULA COULD ALSO SEE A FEW
RECORD HIGHS. RECORD WARM LOWS WILL BE POSSIBLE ACROSS A BROADER
PORTION OF THE SOUTHERN TIER EACH NIGHT. HIGH HUMIDITY SHOULD LEAD
TO MAXIMUM HEAT INDICES AT LEAST IN THE 110-115F RANGE ALONG AND
NEAR THE WESTERN HALF OF THE GULF COAST. IN CONTRAST, THE FORECAST
PATTERN WILL TEND TO FAVOR NEAR TO BELOW NORMAL HIGH TEMPERATURES
FROM THE NORTHWESTERN U.S. INTO THE MIDWEST/OHIO VALLEY. THE
UPPER TROUGH/LOW DEVELOPING NEAR CALIFORNIA SHOULD KEEP HIGHS OVER
MOST OF THE STATE NEAR OR SLIGHTLY BELOW NORMAL AS WELL. AREAS
NEAR THE PACIFIC NORTHWEST COAST MAY BE AN EXCEPTION WITH A
BUILDING UPPER RIDGE HELPING TO PUSH READINGS ABOVE NORMAL BY LATE
WEEK AND NEXT WEEKEND.
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 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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