362
FXUS02 KWBC 050700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 AM EDT SAT AUG 05 2023
VALID 12Z TUE AUG 08 2023 - 12Z SAT AUG 12 2023
..HEAT WAVE TO PERSIST OVER THE SOUTH INTO THE SOUTHWEST
...EXCESSIVE RAIN/FLASH FLOOD THREAT FOR THE EASTERN GREAT LAKES
INTO THE NORTHEAST NEXT TUESDAY...
..OVERVIEW
A STRONG UPPER RIDGE SHOULD PERSIST OVER THE U.S.-MEXICO BORDER,
PERHAPS WEAKENING SLIGHTLY AROUND MIDWEEK AND THEN REBUILDING BY
FRIDAY-SATURDAY. THIS RIDGE WILL MAINTAIN A SOUTHERN TIER HEAT
WAVE WITH DAILY RECORD HIGH TEMPERATURES POSSIBLE MOST DAYS NEXT
WEEK FROM THE WESTERN GULF COAST REGION THROUGH THE SOUTHERN
ROCKIES. GUIDANCE STILL SHOWS WEAKENING OF AN UPPER RIDGE THAT
INITIALLY BRIDGES ACROSS THE FLORIDA PENINSULA THROUGH TUESDAY OR
SO, TO THE SOUTH OF AN EASTERN NORTH AMERICA TROUGH WHOSE EMBEDDED
SHORTWAVES (FROM PACIFIC THROUGH NORTHERN TIER U.S. FLOW ALONG
WITH SOME POTENTIAL INFLUENCE FROM SOUTHERN CANADA) SHOULD SUPPORT
AT LEAST A COUPLE FRONTAL SYSTEMS THAT MAY FOCUS AREAS OF LOCALLY
HEAVY RAINFALL OVER PORTIONS OF THE CENTRAL/EASTERN U.S. FARTHER
WEST, A NORTHEASTERN PACIFIC UPPER TROUGH AND WEAKENING FRONTAL
SYSTEM COULD BRING SOME RAINFALL TO THE PACIFIC NORTHWEST AROUND
THE MIDDLE OF NEXT WEEK. AN UPPER LOW/TROUGH EXPECTED TO DEVELOP
NEAR THE CALIFORNIA COAST BY FRIDAY-SATURDAY MAY INCLUDE SOME
ENERGY ALOFT INITIALLY ASSOCIATED WITH AN EAST PACIFIC TROPICAL
SYSTEM FORECAST TO DEVELOP SOON, BUT WITH FAIRLY MODEST EFFECTS ON
SENSIBLE WEATHER.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
LATEST GUIDANCE CONTINUES THE THEME OF REASONABLE AGREEMENT FOR
THE OVERALL MEAN PATTERN BUT VERY LOW PREDICTABILITY FOR EMBEDDED
DETAILS DUE TO THEIR RELATIVELY SMALL SCALE AND IN SOME CASES
DEPENDENCE ON CONVECTIVE SPECIFICS. RESOLVING THE GREAT LAKES
INTO NEW ENGLAND SYSTEM TUESDAY-WEDNESDAY IS MERELY ONE EXAMPLE OF
THIS TYPE OF PATTERN'S SENSITIVITY. 24-36 HOURS AGO THERE WAS A
FIRM MAJORITY SUGGESTING THAT THE PRIMARY SURFACE LOW WOULD TRACK
NORTH-NORTHEAST INTO CANADA WITH THE TRAILING FRONT, POSSIBLY WITH
A TRIPLE POINT WAVE, CROSSING THE NORTHEAST IN FAIRLY PROGRESSIVE
FASHION. HOWEVER THE 12Z GUIDANCE WITH CONTINUATION OF NEW 00Z
RUNS SO FAR SHOW THE MAIN LOW TRACKING FROM THE GREAT LAKES
THROUGH OR NEAR NEW ENGLAND SOMEWHAT MORE SLOWLY, DUE TO SOMEWHAT
LESS INTERACTION OF SOUTHERN CANADA ENERGY WITH THE NORTHERN TIER
U.S. SHORTWAVE. 18Z/00Z GFS RUNS FROM YESTERDAY WERE THE FIRST TO
OFFER THIS IDEA. BEHIND THIS SYSTEM, ADDITIONAL COMPLEXITIES
AWAIT AS A SOUTHERN CANADA UPPER LOW AND SHORTWAVE ENERGY EMERGING
FROM THE NORTHERN ROCKIES SHOULD SUPPORT A POTENTIALLY WAVY
NORTHERN TIER INTO MIDWEST/GREAT LAKES FRONT (EVENTUALLY REACHING
THE EAST COAST). MOST GUIDANCE HAS BEEN DEPICTING THIS SYSTEM FOR
THE PAST DAY OR SO BUT SPECIFICS WILL LIKELY TAKE A WHILE TO GET
RESOLVED. MORE SHORTWAVE ENERGY TRACKING INTO NORTH AMERICA FROM
THE PACIFIC SHOULD PRODUCE YET ANOTHER WAVE/FRONTAL SYSTEM BUT
12Z/18Z GUIDANCE STRAYED OUT OF PHASE. THE AVERAGE OF
MODELS/MEANS TILTS SLIGHTLY TOWARD A WAVE/FRONT REACHING THE UPPER
MIDWEST/GREAT LAKES BY DAY 7 SATURDAY VERSUS THE HIGH PRESSURE
FORECAST BY THE 12Z/18Z GFS. THE NEW 00Z GFS HAS ADJUSTED MUCH
CLOSER TO THE 12Z ECMWF/ECENS/CMC SCENARIO. SHORTWAVE DETAILS ARE
ALSO QUITE UNCERTAIN FOR THE UPPER TROUGH/LOW FORECAST TO EVOLVE
NEAR CALIFORNIA. THERE IS GENERAL AGREEMENT THAT THIS FEATURE
SHOULD INCORPORATE UPPER LEVEL ENERGY ASSOCIATED WITH A
SOON-TO-DEVELOP EAST PACIFIC TROPICAL SYSTEM BUT THERE IS A LOT OF
SPREAD FOR TIMING ITS ARRIVAL. NOTE THAT THIS UPPER ENERGY WILL
BECOME DETACHED FROM THE SURFACE CIRCULATION THAT SHOULD WEAKEN
FARTHER TO THE SOUTH.
A BLEND OF 12Z/18Z OPERATIONAL MODELS REFLECTED THE CONSENSUS
SHIFT FOR THE NORTHEAST SYSTEM AND THE BEST INTERMEDIATE SCENARIO
FOR OTHER FEATURES EARLY IN THE PERIOD. THE INCREASING DETAIL
SPREAD LATER IN THE FORECAST FAVORED A STEADY INCREASE OF 18Z GEFS
AND 12Z ECENS/CMCENS INPUT, REACHING 60 PERCENT TOTAL WEIGHT BY
DAY 7 SATURDAY.
..WEATHER/HAZARDS HIGHLIGHTS
THE RATHER VIGOROUS SYSTEM FORECAST TO TRACK FROM THE EASTERN
GREAT LAKES THROUGH OR NEAR NEW ENGLAND DURING TUESDAY-WEDNESDAY
WILL SPREAD POTENTIALLY STRONG THUNDERSTORMS/HEAVY RAINFALL ACROSS
PORTIONS OF THE NORTHEAST. THE DAY 4 EXCESSIVE RAINFALL OUTLOOK
FOR TUESDAY-TUESDAY NIGHT HAS INTRODUCED A SLIGHT RISK AREA FROM
UPSTATE NEW YORK EASTWARD/NORTHEASTWARD, WITH THE RECENT SHIFT IN
GUIDANCE FOR THE SYSTEM'S STRUCTURE AND SLOWER TIMING LEADING TO
SOMEWHAT HIGHER RAINFALL POTENTIAL OVER THE REGION. SOME AREAS
WILL BE SENSITIVE GIVEN RECENT SIGNIFICANT RAINFALL. AS FOR OTHER
DAY 4 AREAS, PARTS OF THE LOWER MISSISSIPPI VALLEY AND SOUTHEAST
REMAIN IN A MARGINAL RISK WITH THE NORTHEAST SYSTEM'S TRAILING
FRONT SETTLING OVER THE REGION WHILE THE COMBINATION OF A COUPLE
FRONTS MAY PRODUCE LOCALLY HEAVY RAINFALL WITHIN A MARGINAL RISK
AREA OVER THE NORTH-CENTRAL PLAINS. DURING THE DAY 5 OUTLOOK
PERIOD OF WEDNESDAY-WEDNESDAY NIGHT, EXPECT A FAIRLY BROAD AREA OF
LOCALLY HEAVY RAINFALL POTENTIAL DUE TO A NORTHERN TIER FRONT
PROGRESSING SOUTHEASTWARD INTO THE MIDWEST AND PERSISTENCE OF THE
FRONT OVER THE SOUTH. WITH GUIDANCE THUS FAR NOT CLUSTERING WELL
ENOUGH TO RESOLVE ANY MEANINGFUL SLIGHT RISK AREAS, PLAN TO DEPICT
A MARGINAL RISK FROM THE MIDWEST/MISSISSIPPI VALLEY INTO THE
SOUTHEAST AND WAIT FOR IMPROVED CLARITY/FOCUS FOR ONE OR MORE
EMBEDDED SLIGHT RISK AREAS IN FUTURE RUNS. PARTS OF THE NORTHERN
PLAINS MAY BE WORTH MONITORING GIVEN A WAVY FRONT OVER THE AREA
AND A DIFFUSE SIGNAL FOR ENHANCED RAINFALL, BUT THERE IS NOT YET
ENOUGH CONSENSUS FOR A RISK AREA AT THIS TIME.
CONTINUED PROGRESSION OF THE MIDWEST FRONT SHOULD BRING SHOWERS
AND THUNDERSTORMS INTO THE EAST BY LATER IN THE WEEK, WITH SOME
HEAVY ACTIVITY STILL POSSIBLE THROUGH THURSDAY AND MAYBE BECOMING
SOMEWHAT LESS ORGANIZED BY FRIDAY-SATURDAY. CONFIDENCE IS LOWER
FOR ANOTHER POSSIBLE SYSTEM/FRONT THAT COULD PRODUCE SOME
SHOWERS/STORMS OVER PARTS OF THE PLAINS/MIDWEST TOWARD
FRIDAY-SATURDAY. MEANWHILE THE PACIFIC NORTHWEST SHOULD SEE SOME
RAINFALL TUESDAY-WEDNESDAY AS A WEAKENING FRONT APPROACHES.
AMOUNTS SHOULD BE LIGHT TO MODERATE IN ABSOLUTE TERMS, BUT STILL
SOMEWHAT UNUSUAL FOR EARLY AUGUST. CONVECTION OVER THE FOUR
CORNERS STATES/SOUTHWEST SHOULD BE LIGHTER AND MORE SCATTERED THAN
AVERAGE GIVEN BELOW-CLIMATOLOGY PRECIPITABLE WATER VALUES THROUGH
MIDWEEK OR SO. ACTIVITY MAY INCREASE SLIGHTLY TOWARD
FRIDAY-SATURDAY AS MOISTURE GRADUALLY INCREASES TOWARD MORE NORMAL
LEVELS.
THE ONGOING HEAT WAVE OVER THE SOUTHERN TIER SHOULD CONTINUE
THROUGH NEXT WEEK, WITH GREATEST EMPHASIS OVER THE SOUTHERN HIGH
PLAINS WHERE HIGHS COULD REACH 10-15F ABOVE NORMAL. TEMPERATURES
MAY REACH OR EXCEED DAILY RECORD HIGHS MOST DAYS NEXT WEEK FROM
THE WESTERN GULF COAST INTO THE SOUTHERN ROCKIES. THE DESERT
SOUTHWEST SHOULD BE QUITE HOT AS WELL WITH HIGHS REACHING AROUND
110F, BUT MAY STAY A BIT SHORT OF RECORD HIGHS. THE FLORIDA
PENINSULA COULD ALSO SEE A FEW RECORD HIGHS. RECORD WARM LOWS
WILL BE POSSIBLE ACROSS A BROADER PORTION OF THE SOUTHERN TIER.
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 COOLEST TEMPERATURES VERSUS NORMAL WILL BE OVER
THE NORTHERN ROCKIES/HIGH PLAINS NEXT TUESDAY-WEDNESDAY WITH SOME
HIGHS UP TO 10-15F OR SO BELOW AVERAGE. TEMPERATURES SHOULD TREND
CLOSER TO NORMAL THEREAFTER, WHILE OTHER LOCATIONS ACROSS THE
NORTHERN HALF OF THE PLAINS/MISSISSIPPI VALLEY MAY SEE ONE OR MORE
DAYS WITH HIGHS MODESTLY BELOW NORMAL. THE UPPER TROUGH/LOW
DEVELOPING NEAR CALIFORNIA SHOULD KEEP HIGHS OVER MOST OF THE
STATE NEAR OR SLIGHTLY BELOW NORMAL.
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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