978
FXUS02 KWBC 160659
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 AM EDT SUN JUN 16 2024
VALID 12Z WED JUN 19 2024 - 12Z SUN JUN 23 2024
..RECORD-BREAKING HEAT FROM THE MIDWEST TO THE EAST COAST
...HEAVY RAINFALL THREAT ALONG THE WESTERN GULF COAST AND PARTS OF
THE NORTHERN TIER INTO CENTRAL PLAINS...
..OVERVIEW
LATEST MODELS/ENSEMBLES SHOW A STRONG UPPER RIDGE ALONG THE EAST
COAST ACHIEVING ITS GREATEST STRENGTH AND NORTHWARD POSITION AROUND
WEDNESDAY. FROM LATER IN THE WEEK THROUGH THE WEEKEND EXPECT THIS
RIDGE TO DRIFT SOUTHWARD, ELONGATE WESTWARD, AND WEAKEN A LITTLE--
ULTIMATELY LEAVING A BROAD AXIS OF RIDGING ACROSS THE SOUTHERN TIER
BY NEXT SUNDAY. THIS RIDGE WILL SUPPORT A BROAD AREA OF HOT AND
DRY WEATHER DURING THIS UPCOMING WEEK, WITH THE GREATEST ANOMALIES
AND POTENTIAL FOR DAILY (AND POSSIBLY MONTHLY) RECORDS EXTENDING
FROM THE OHIO VALLEY/LOWER GREAT LAKES INTO THE NORTHERN MID-
ATLANTIC AND NORTHEAST. BETWEEN THIS RIDGE AND MEAN TROUGHING ALONG
OR JUST INLAND FROM THE WEST COAST, THE AREA FROM THE NORTHERN
HALF OF THE PLAINS INTO UPPER MIDWEST MAY SEE MULTIPLE EPISODES OF
HEAVY RAINFALL FROM A COMBINATION OF A PERSISTENT WAVY MEAN FRONT,
ANOMALOUS MOISTURE, AND UPPER LEVEL IMPULSES. THIS ACTIVITY SHOULD
ALSO EXTEND INTO THE NORTHEAST LATE WEEK INTO THE WEEKEND. TO THE
SOUTH OF THE UPPER RIDGE, UPPER LEVEL ENERGY AND ABUNDANT DEEP
MOISTURE NORTH OF AN AREA OF LOW PRESSURE (SEE NHC FOR UPDATES)
WILL BRING THE POTENTIAL FOR A PERIOD OF HEAVY RAIN ALONG AND NEAR
THE WESTERN GULF COAST.
..GUIDANCE/PREDICTABILITY ASSESSMENT
REGARDING THE EASTERN UPPER RIDGE, THERE ARE STILL NOTABLE
DIFFERENCES THAT DEVELOP AMONG THE DYNAMICAL GUIDANCE AND ECMWF-
INITIALIZED MACHINE LEARNING (ML) MODELS. IN THE 12Z/18Z GUIDANCE
CYCLE, THE UKMET WAS BY FAR THE MOST EAGER TO SHIFT THE UPPER
RIDGE INTO THE WESTERN ATLANTIC SO THAT SOLUTION WAS NOT
INCORPORATED INTO THE FORECAST. BY MID-LATE PERIOD THE DYNAMICAL
AND ML SOLUTIONS STILL CONFLICT, AS THE DYNAMICAL MODELS AND TO
SOME DEGREE THE MEANS SHOW THE BEST DEFINED UPPER HIGH CENTER
EVENTUALLY BECOMING CENTERED OVER THE FAR SOUTHEAST U.S. OR EVEN
WESTERN ATLANTIC WHILE THE MLS WANT TO KEEP THE HIGH CENTER FARTHER
INLAND (SOMEWHERE BETWEEN THE SOUTHERN PLAINS AND NORTH OF THE
GULF COAST). THE MLS ALSO HAVE BEEN FAVORING GREATER SOUTHWARD
EXTENT OF THE UPPER RIDGE, REDUCING THE POTENTIAL INFLUENCE OF
EASTERLY WAVES/MOISTURE ALONG AND NEAR THE GULF COAST REGION.
DYNAMICAL AND ML GUIDANCE GENERALLY AGREES IN PRINCIPLE THAT ENERGY
WITHIN THE LINGERING WEST COAST TROUGH SHOULD EJECT AFTER EARLY
FRIDAY AS A NORTHEAST PACIFIC SYSTEM APPROACHES, WITH THE LEADING
FRONTAL SYSTEM REACHING INLAND BY SUNDAY. THE MOST COMMON IDEA IS
FOR A SHORTWAVE TROUGH TO REACH THE UPPER MIDWEST AND VICINITY BY
NEXT SUNDAY WITH AN ASSOCIATED NORTHERN TIER SURFACE WAVE. THE NEW
00Z GFS LOOKS A LITTLE FAST WITH THE SYSTEM COMING INTO WESTERN
NORTH AMERICA ON SUNDAY.
12Z/18Z GUIDANCE COMPARISONS LED TO A STARTING POINT CONSISTING OF
THE 18Z GFS AND 12Z ECMWF/CMC EARLY IN THE PERIOD AND THEN
GRADUALLY INCREASING ENSEMBLE WEIGHT (18Z GEFS AND 12Z
ECENS/CMCENS) THAT REACHES 60 PERCENT TOTAL BY NEXT SUNDAY WITH THE
REMAINDER CONSISTING OF THE 18Z GFS/12Z ECMWF.
..WEATHER/HAZARDS HIGHLIGHTS
DURING THE DAYS 4-5 EXCESSIVE RAINFALL OUTLOOK PERIOD COVERING
WEDNESDAY THROUGH THURSDAY NIGHT, LATEST GUIDANCE CONTINUES TO SHOW
AN AREA OF DEEP TROPICAL MOISTURE AND SOME DEGREE OF UPPER LEVEL
ENERGY SHIFTING WESTWARD ACROSS THE WESTERN GULF OF MEXICO INTO THE
SOUTHERN HIGH PLAINS. OPERATIONAL GFS/ECMWF RUNS SHOW PRECIPITABLE
WATER ANOMALIES POSSIBLY REACHING PLUS 4 STANDARD DEVIATIONS OR
GREATER. HOWEVER DYNAMICAL GUIDANCE AND ML SOLUTIONS STILL SHOW
IMPORTANT DIFFERENCES FOR MAGNITUDE/PLACEMENT OF HEAVIEST RAINFALL.
DURING DAY 4 THE MLS SUPPORT THE GENERAL THEME OF THE
GFS/GEFS/CMC/ICON WHICH BRING HEAVY RAINFALL FARTHER NORTH OVER THE
EASTERN HALF OF TEXAS THAN THE ECMWF/UKMET, WITH MODEST EXPANSION
OF THE EXISTING SLIGHT RISK AREA TO GIVE SOME ACCOUNT FOR THE
FORMER CLUSTER. NOTE THAT THE SOUTHERN PART OF THE TEXAS COAST HAS
DRIER ANTECEDENT CONDITIONS BUT RAIN RATES MAY STILL BE HIGH ENOUGH
TO CAUSE SOME RUNOFF ISSUES. AS THE MOISTURE/UPPER ENERGY CONTINUE
WESTWARD, THE NEW DAY 5 ERO PROPOSES A SLIGHT RISK AREA OVER PARTS
OF SOUTHWESTERN TEXAS ALONG/NORTH OF THE RIO GRANDE RIVER. THERE IS
STILL CONSIDERABLE UNCERTAINTY OVER RAINFALL SPECIFICS IN THIS TIME
FRAME.
ELSEWHERE DURING THE DAYS 4-5 ERO TIME FRAME, A PERSISTENT WAVY
FRONTAL BOUNDARY INTERACTING WITH ANOMALOUS MOISTURE AND SHORTWAVE
IMPULSES EJECTING FROM THE WEST COAST MEAN TROUGH WILL MAINTAIN A
THREAT FOR EPISODES OF HEAVY CONVECTION FROM PARTS OF THE
NORTHERN/CENTRAL PLAINS INTO UPPER MIDWEST. THUS FAR THE GUIDANCE
SIGNAL IS DIFFUSE ENOUGH (WITH SOMEWHAT LOWER AMOUNTS/MORE SCATTER
THAN IN THE SHORTER TERM) FOR THIS ACTIVITY TO MAINTAIN ONLY A
MARGINAL RISK EACH DAY. POTENTIAL REMAINS FOR AN UPGRADE IN RISK
AREA CLOSER TO THE EVENT. FINALLY, THERE IS A MARGINAL RISK AREA
ALONG AND INLAND FROM THE GEORGIA/NORTHERN FLORIDA COAST IN
ASSOCIATION WITH POSSIBLE ARRIVAL OF A WEAK WAVE/ENHANCED MOISTURE.
CONFIDENCE IS IN THE LOWER HALF OF THE SPECTRUM THOUGH.
GRADUAL FLATTENING OF THE UPPER PATTERN BY LATE WEEK INTO THE
WEEKEND, WITH A PERSISTENT WAVY FRONT NEAR THE SOUTHERN PERIPHERY
OF THE WESTERLIES, WILL SUPPORT CONTINUED NORTHERN PLAINS/UPPER
MIDWEST CONVECTION AND A GREATER EASTWARD EXTENT INTO THE GREAT
LAKES/NORTHEAST. CONFIDENCE IN SPECIFICS IS LOWER DUE TO THE LOW
PREDICTABILITY OF IMPORTANT SHORTWAVE DETAILS. SOME OF THE MOISTURE
REACHING THE SOUTHERN HIGH PLAINS BY THURSDAY COULD ULTIMATELY
FACTOR INTO DIURNAL CONVECTION OVER THE ROCKIES THEREAFTER WHILE
MOISTURE EMBEDDED WITHIN EASTERLY FLOW MAY ENHANCED RAINFALL AT
TIMES NEAR THE GULF COAST INTO THE WEEKEND. A WELL-DEFINED FRONTAL
SYSTEM COULD BRING A LITTLE SCATTERED LIGHT RAIN TO THE PACIFIC
NORTHWEST BY NEXT WEEKEND.
THE STRONG UPPER RIDGE BUILDING OVER THE EAST NEXT WEEK WILL TEND
TO PRODUCE THE GREATEST TEMPERATURE ANOMALIES FROM THE MIDWEST AND
OHIO VALLEY/LOWER GREAT LAKES INTO THE NORTHERN MID-ATLANTIC AND
NORTHEAST, WITH MULTIPLE DAYS OF READINGS 10-20F ABOVE NORMAL. THIS
WOULD TRANSLATE TO HIGHS WELL INTO THE 90S, ALONG WITH LOWS IN THE
UPPER 60S TO UPPER 70S PROVIDING LITTLE OVERNIGHT HEAT RELIEF.
DAILY RECORDS WILL BE POSSIBLE WITHIN THE ABOVE AREAS, WITH SOME
ISOLATED MONTHLY RECORDS POSSIBLE AS WELL. WITH SOME TYPICAL DETAIL
DIFFERENCES, THE AXIS OF GREATEST TEMPERATURE ANOMALIES IN THE
CURRENT FORECAST SHOWS SOME SIMILARITY TO THE 1994 HEAT WAVE THAT
WAS OBSERVED AROUND THE SAME TIME IN JUNE. SOME FLATTENING OF THE
NORTHERN PART OF THE RIDGE BY THE END OF THE WEEK MAY MAKE THE HEAT
A LITTLE LESS EXTREME OVER NEW ENGLAND, WHILE THE CENTRAL PLAINS
MAY TREND A LITTLE HOTTER (BUT WITH SINGLE-DIGIT POSITIVE
ANOMALIES). PARTS OF THE MID-ATLANTIC COULD ALSO TREND A LITTLE
HOTTER LATE WEEK INTO THE WEEKEND WITH A TRANSITION TO MORE
WESTERLY FLOW. IN CONTRAST TO THE EASTERN HEAT, SEPARATE AREAS OF
CLOUDS/RAINFALL OVER THE PLAINS WILL SUPPORT HIGHS 5-15F BELOW
NORMAL ON WEDNESDAY AND CONTINUING OVER THE SOUTHERN HIGH PLAINS
AND VICINITY THROUGH LATE WEEK. RISING HEIGHTS ALOFT OVER THE WEST
WILL SUPPORT A WARMER TREND, WITH INCREASING COVERAGE OF HIGHS
10-15F ABOVE NORMAL FRIDAY-SUNDAY.
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 (QPF), EXCESSIVE RAINFALL
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:
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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