402
FXUS02 KWBC 070705
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
304 AM EDT MON AUG 07 2023
VALID 12Z THU AUG 10 2023 - 12Z MON AUG 14 2023
..HEAT WAVE TO PERSIST OVER THE SOUTH INTO THE SOUTHWEST
...EXCESSIVE RAIN/FLASH FLOOD THREAT OVER THE TENNESSEE
VALLEY/SOUTHERN APPALACHIANS THURSDAY...
..OVERVIEW
AS OF THURSDAY EXPECT AN ELONGATED UPPER RIDGE AXIS TO EXTEND FROM
THE RIO GRANDE VALLEY EASTWARD THROUGH THE FLORIDA PENINSULA. BY
THE WEEKEND AND EARLY NEXT WEEK THE WESTERN PART OF THIS RIDGE
SHOULD BECOME STRONGER/MORE DOMINANT AND BUILD FARTHER WESTWARD,
FOCUSING OVER TEXAS AND THE SOUTHERN ROCKIES. 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 LATE THIS
WEEK. FARTHER NORTH, LOW AMPLITUDE FLOW ALOFT WILL INITIALLY HINT
AT A MEAN TROUGH AXIS OVER THE EAST-CENTRAL U.S. THE MEAN TROUGH
SHOULD GAIN BETTER DEFINITION BY SUNDAY-MONDAY AS A BUILDING
NORTHEAST PACIFIC UPPER RIDGE MAY EXTEND ITS INFLUENCE INTO THE
PACIFIC NORTHWEST AND FAR SOUTHWESTERN CANADA. THE UPPER RIDGE
MAY START TO BRING VERY WARM TO HOT TEMPERATURES TO THE PACIFIC
NORTHWEST BY THE START OF NEXT WEEK. SHORTWAVES WITHIN THE
CYCLONIC DOWNSTREAM FLOW WILL PRODUCE A SERIES OF CENTRAL-EASTERN
U.S. WAVES/FRONTAL SYSTEMS THAT ARE LIKELY TO PRODUCE EPISODES OF
LOCALLY HEAVY RAINFALL, BUT WITH SOME UNCERTAIN SPECIFICS DUE TO
THE LOWER PREDICTABILITY OF IMPORTANT DETAILS. THE NATIONAL
HURRICANE CENTER IS ISSUING ADVISORIES FOR TROPICAL STORM EUGENE
IN THE PACIFIC, WITH DISSIPATION OF THE SURFACE REFLECTION
EXPECTED BEFORE EARLY THURSDAY. HOWEVER THE SYSTEM'S REMAINING
UPPER LEVEL ENERGY AND POSSIBLY SOME MOISTURE COULD GET
INCORPORATED INTO AN UPPER TROUGH/LOW FORECAST TO EVOLVE NEAR THE
CALIFORNIA COAST.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE LATEST MODELS AND ENSEMBLES MAINTAIN A LOT OF THE GENERAL
IDEAS SEEN OVER THE PAST COUPLE CYCLES BUT WITH CONTINUED DETAIL
SPREAD AND IN SOME CASES TRENDS. CONSENSUS STILL SHOWS A LEADING
SOUTHERN CANADA INTO GREAT LAKES/NEW ENGLAND UPPER TROUGH LATE
THIS WEEK HELPING TO PUSH A COLD FRONT INTO THOSE REGIONS WHILE A
SEPARATE SHORTWAVE TO THE SOUTH PROMOTES SOME DEGREE OF SURFACE
WAVINESS FROM THE OHIO VALLEY/MIDDLE MISSISSIPPI VALLEY TO THE
EAST COAST. THE SMALL SCALE NATURE OF THIS SHORTWAVE AND
DIFFERENCES IN STRENGTH/TIMING HAVE BEEN PRODUCING CONSIDERABLE
SPREAD FOR SPECIFICS OF THE SURFACE REFLECTION BY FRIDAY. THE NEW
00Z UKMET IS A NOTABLE STRONG EXTREME WITH ITS WAVE. BEHIND THESE
FEATURES, GUIDANCE IS GRADUALLY GETTING BETTER DEFINED WITH WHAT
MAY BE A FAIRLY VIGOROUS SYSTEM REACHING THE GREAT LAKES BY
SATURDAY. RECENT GFS RUNS HAVE STRAYED A BIT ON THE FASTER SIDE
OF THE SPREAD DUE TO A COMBINATION OF FASTER TIMING/MORE
SOUTHEASTWARD AMPLITUDE OF THE UPPER SHORTWAVE. THE NEW 00Z RUN
HAS COME BACK SOME FROM ITS 18Z RUN, NOW MATCHING THE GEFS MEAN.
AN INTERMEDIATE SOLUTION SEEMS REASONABLE GIVEN TYPICAL
PREDICTABILITY/ERROR RANGES A FEW DAYS OUT IN TIME. THE TRAILING
COLD FRONT SEEMS TO BE TRENDING SOMEWHAT FARTHER SOUTHWARD OVER
THE CENTRAL U.S., PERHAPS IN RESPONSE TO MODEL CONSENSUS BETTER
RESOLVING THE STRENGTH OF THE UPPER TROUGH. THIS SYSTEM SHOULD
CONTINUE INTO EASTERN CANADA AFTER SATURDAY. THE NEXT SYSTEM IN
THE SERIES MAY REACH THE NORTHERN TIER BY SUNDAY-MONDAY. AS WAS
THE CASE FOR THE PRECEDING SYSTEM 6-7 DAYS OUT, THE SIGNAL FOR
THIS LAST SYSTEM IS FAIRLY DIFFUSE IN THE MODELS/MEANS OVERALL BUT
WITH ENOUGH OVERLAP TO DEPICT A DEFINED, ALBEIT WEAK, SYSTEM. BY
NEXT MONDAY THE 00Z GFS/CMC DEVELOP ISSUES NOT SEEN IN THE 12Z-18Z
MODEL/MEAN CYCLE, WITH THE GFS BRINGING A FAIRLY STRONG SHORTWAVE
THROUGH THE NORTHEAST PACIFIC/WESTERN NORTH AMERICA MEAN RIDGE AND
THE CMC SHOWING MORE AMPLITUDE/SHARPNESS OF A NORTHERN PLAINS
SHORTWAVE. AN OPERATIONAL MODEL BLEND TRANSITIONING TOWARD A
MODEL/ENSEMBLE MEAN MIX REFLECTED CONTINUITY FOR THE LARGE SCALE
FORECAST WHILE INCORPORATING SOME TRENDS WHERE SUGGESTED BY THE
MAJORITY OF GUIDANCE.
..WEATHER/HAZARDS HIGHLIGHTS
THE POTENTIALLY HEAVY CONVECTIVE EVENT EXPECTED OVER PARTS OF THE
MISSISSIPPI/TENNESSEE VALLEY REGION ON WEDNESDAY (NOW IN THE SHORT
RANGE TIME FRAME) SHOULD EXTEND EASTWARD TOWARD THE SOUTHERN
APPALACHIANS AND VICINITY BY THURSDAY, FAVORING MAINTENANCE OF THE
SLIGHT RISK AREA DEPICTED IN THAT REGION FOR THE NEW DAY 4
EXCESSIVE RAINFALL OUTLOOK. SIMILAR TO YESTERDAY, GUIDANCE OFFERS
SOME CONFLICTING IDEAS FOR SURROUNDING DETAILS FROM THE
MISSISSIPPI AND OHIO RIVERS THROUGH THE MID-ATLANTIC WITHIN AN
OVERALL SIGNAL FOR SOME LOCALLY HEAVY RAINFALL. THIS RECOMMENDS
NO CHANGE TO THE MARGINAL RISK AREA. DURING DAYS 4-5
THURSDAY-FRIDAY, THE OUTLOOKS SHOW A MARGINAL RISK AREA FROM THE
NORTHERN PLAINS INTO THE CENTRAL GREAT LAKES WITH THE SYSTEM
APPROACHING/CROSSING THE REGION. SOME LOCALLY INTENSE RAINFALL
MAY OCCUR BUT ANTECEDENT GROUND CONDITIONS ARE ON THE DRIER SIDE
AND MODERATE PROGRESSION MAY TEMPER TOTALS SOMEWHAT OVERALL. FOR
DAY 5 FROM THE EAST-CENTRAL PLAINS INTO THE SOUTHEAST, THERE ARE
SOME DIFFUSE GUIDANCE SIGNALS FOR LOCALLY HEAVY RAINFALL WITHIN AN
ENVIRONMENT OF MODERATELY ABOVE NORMAL PRECIPITABLE WATER VALUES
AND DECENT INSTABILITY. IN ADDITION ONE OR MORE WAVES/FRONTS MAY
PROVIDE SOME SYNOPTIC FOCUS FOR CONVECTION. THIS SCENARIO APPEARS
TO SUPPORT A MARGINAL RISK AREA AT THIS TIME, WITH BETTER
DEFINITION PERHAPS ARISING IN A FEW RUNS.
FROM THE WEEKEND INTO EARLY NEXT WEEK, EXPECT SOME SHOWERS AND
THUNDERSTORMS TO CONTINUE INTO THE EAST WITH PROGRESSION OF THE
GREAT LAKES SYSTEM AND TRAILING FRONT, AND POSSIBLY OVER THE
NORTHERN TIER AGAIN WITH ANOTHER SYSTEM SUNDAY-MONDAY. EXPECT
FLORIDA TO SEE AN INCREASE OF RAINFALL THIS WEEKEND AS AN AREA OF
ENHANCED MOISTURE MOVES IN FROM THE EAST. THE FOUR
CORNERS/SOUTHEAST/CALIFORNIA SHOULD SEE DIURNALLY FAVORED EPISODES
OF CONVECTION, THOUGH MODEL/ENSEMBLE DIFFERENCES IN THE
DISTRIBUTION/MAGNITUDE OF MOISTURE ANOMALIES (INCLUDING WHAT MAY
HAPPEN WITH ANY UPPER LEVEL MOISTURE FROM EUGENE) KEEP CONFIDENCE
LOWER THAN DESIRED FOR SPECIFICS. ONE OR MORE FRONTS SETTLING
INTO THE CENTRAL/SOUTH-CENTRAL PLAINS MAY PROVIDE A FOCUS FOR
HEAVIER SHOWERS AND THUNDERSTORMS OVER THAT REGION, WITH SOME OF
THE MOISTURE OVER THE WEST POSSIBLY DRIFTING EAST TO CONTRIBUTE.
THE ONGOING HEAT WAVE OVER THE SOUTHERN TIER SHOULD CONTINUE
THROUGH THE WEEKEND AND EARLY NEXT WEEK, WITH GREATEST EMPHASIS
OVER THE SOUTHERN HIGH PLAINS WHERE HIGHS COULD REACH 10-15F ABOVE
NORMAL ESPECIALLY LATE THIS WEEK. TEMPERATURES MAY REACH OR
EXCEED DAILY RECORD HIGHS FROM THE CENTRAL/WESTERN GULF COAST INTO
THE SOUTHERN ROCKIES THURSDAY-FRIDAY, WITH THE COVERAGE OF
POSSIBLE RECORD HIGHS TENDING TO DECREASE GRADUALLY THEREAFTER.
THE DESERT SOUTHWEST SHOULD SEE A BRIEF LULL IN THE 110F+ HIGHS
THROUGH LATE WEEK BUT TEMPERATURES MAY REACH INTO THE LOWER HALF
OF THE 110S ONCE AGAIN BY SUNDAY-MONDAY AS THE UPPER RIDGE
STRENGTHENS OVER THE WEST. THE FLORIDA PENINSULA COULD ALSO SEE A
FEW RECORD HIGHS. RECORD WARM LOWS WILL BE POSSIBLE ACROSS A
BROAD PORTION OF THE SOUTHERN TIER EACH NIGHT. MEANWHILE
STRENGTHENING UPPER RIDGING SHOULD BRING HIGHER TEMPERATURES TO
THE PACIFIC NORTHWEST DURING THE WEEKEND AND EARLY NEXT WEEK, WITH
HIGHS REACHING 10F OR MORE ABOVE NORMAL OVER SOME LOCATIONS. VERY
WARM TO HOT TEMPERATURES MAY EXTEND BEYOND THE MEDIUM RANGE
FORECAST PERIOD. 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 MODERATELY BELOW NORMAL HIGH TEMPERATURES
FROM THE NORTHERN ROCKIES 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 AT LEAST THROUGH LATE
WEEK.
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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