274
FXUS02 KWBC 250728
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
328 AM EDT FRI AUG 25 2023
VALID 12Z MON AUG 28 2023 - 12Z FRI SEP 01 2023
...HOT AND HUMID CONDITIONS COULD PERSIST ACROSS THE GULF COAST
INTO MONDAY BEFORE SOME RELATIVE RELIEF WITH MODERATING
TEMPERATURES AS THE WEEK PROGRESSES...
...INCREASING CHANCES FOR A TROPICAL SYSTEM TO MOVE THROUGH THE
EASTERN GULF OF MEXICO AND AFFECT FLORIDA WITH AT LEAST HEAVY
RAINFALL...
..OVERVIEW
UPPER TROUGHING OVER THE EAST FOR THE FIRST HALF OF NEXT WEEK WILL
HELP DRIVE MULTIPLE FRONTAL SYSTEMS ACROSS THE REGION, PRODUCING A
HEAVY RAINFALL AND FLASH FLOODING THREAT LIKELY FOCUSED AROUND THE
CAROLINAS. THESE COLD FRONTS COULD EVENTUALLY PUSH THROUGH THE
GULF COAST STATES AND HELP TO LESSEN THE HEAT AND HUMIDITY THERE
AFTER MONDAY. MEANWHILE FARTHER SOUTH, THE NATIONAL HURRICANE
CENTER IS MONITORING A DISTURBANCE IN THE CARIBBEAN THAT SHOWS A
HIGH CHANCE OF TROPICAL DEVELOPMENT. THIS SYSTEM COULD MOVE
THROUGH THE EASTERN GULF OF MEXICO AND POSSIBLY TRACK INTO
FLORIDA, WITH HEAVY RAINFALL AND FLOODING LIKELY TO BE THREATS
THERE. RAIN WILL ALSO RETURN TO THE PACIFIC NORTHWEST MID-NEXT
WEEK AS AN UPPER LEVEL LOW MOVES ONSHORE, WHILE PERIODIC SURGES OF
MONSOONAL MOISTURE AFFECT THE FOUR CORNERS STATES WITH RAIN.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE IS GENERALLY IN GOOD AGREEMENT WITH THE
SYNOPTIC-SCALE FLOW, FEATURING AMPLIFYING TROUGHING ACROSS THE
EAST MONDAY-WEDNESDAY AND SHIFTING EASTWARD, WHILE AN UPPER LOW
OVER THE EASTERN PACIFIC ON MONDAY TRACKS EASTWARD INTO THE
NORTHWEST AND NORTH-CENTRAL U.S. THROUGH THE WEEK, WITH RIDGING IN
BETWEEN AND SOUTHWARD INTO THE SOUTHWESTERN U.S. (ALBEIT WEAKER
THAN MOST OF THE RIDGING THAT HAS OCCURRED THIS SUMMER). HOWEVER,
THERE ARE CERTAINLY SOME MODEL DIFFERENCES IN THE DETAILS--FOR
EXAMPLE, WITH FRONTAL POSITIONS IN THE NORTHEAST AROUND
TUESDAY-WEDNESDAY THAT PRODUCE LARGE DIFFERENCES IN THE ASSOCIATED
QPF. THE WESTERN UPPER LOW BEGINS THE MEDIUM RANGE PERIOD IN GOOD
AGREEMENT BUT SOME TIMING DIFFERENCES ARISE BY AROUND MIDWEEK--THE
12Z ECMWF TRACKS THE LOW SLIGHTLY MORE QUICKLY EAST THAN OTHER
GUIDANCE, AND THE ENSEMBLE MEANS WERE GENERALLY EVEN SLOWER THAN
THE REST OF THE DETERMINISTIC GUIDANCE. MODELS DIVERGE FURTHER
WITH THE FLOW UPSTREAM FROM THIS FEATURE IN THE PACIFIC BY THE
LATTER PART OF NEXT WEEK. THE 12Z CMC CLOSED OFF AN UPPER LOW MORE
QUICKLY THAN OTHER GUIDANCE, BUT MOST MODELS DO CLOSE IT OFF
EVENTUALLY NEAR THE PACIFIC NORTHWEST, WHILE THE 12Z ECMWF SEEMED
TO BE ON THE EASTERN SIDE OF THE GUIDANCE ENVELOPE. OVERALL
THOUGHT THE GFS HAD A GOOD SOLUTION HERE SO MAINTAINED SOME OF IT
THROUGH DAY 7. BUT MAINLY TRANSITIONED FROM A MULTI-MODEL
DETERMINISTIC BLEND EARLY IN THE MEDIUM RANGE PERIOD TO HALF BY
DAY 6 AND JUST OVER HALF DAY 7 CONSIDERING THE INCREASING MODEL
SPREAD.
MEANWHILE SOME OF THE MOST NOTABLE DIFFERENCES IN THE MODEL
GUIDANCE OCCUR WITH THE TROPICAL DISTURBANCE. THE NON-NCEP
GUIDANCE HAS ALL SHOWN A TROPICAL SYSTEM FOR SEVERAL RUNS IN A
ROW, WHILE GFS RUNS HAVE HAD A CONSIDERABLY WEAKER FEATURE IF ANY.
THIS IS INTRIGUING PARTICULARLY CONSIDERING GFS TENDENCIES TOWARD
HAVING TROPICAL SYSTEMS THAT OTHER MODELS DO NOT. BUT EVEN SETTING
THE GFS ASIDE, THERE HAVE BEEN SOME CONSIDERABLE VARIATIONS AMONG
AND BETWEEN MODEL RUNS WITH THE TRACK OF THE FEATURE AND EVEN MORE
SO ITS TIMING. CMC RUNS HAVE BEEN AMONG THE FASTEST TO TRACK THE
SYSTEM NORTHEAST. THE 12Z ECMWF AND UKMET WERE RATHER AGREEABLE IN
A SLOWER TIMING AND THE FORECAST FOR THE TRACK LEANED MORE TOWARD
THIS INSTEAD, ALONG WITH THE EC MEAN THAT WAS SLIGHTLY SLOWER. THE
FORECAST POINTS WERE COORDINATED WITH THE NATIONAL HURRICANE
CENTER AND WE AGREED ON A CLOSED LOW RATHER THAN A SPOT LOW, GIVEN
THE HIGH CHANCE FOR DEVELOPMENT INTO A TROPICAL CYCLONE. THE 00Z
GFS DOES FINALLY SHOW MORE SEMBLANCE OF A TROPICAL FEATURE IN THE
EASTERN GULF OF MEXICO FOR TUESDAY, THOUGH WEAKER AND TRACKING
FARTHER EAST. THE 00Z ECMWF SLOWED DOWN, AS DID THE 00Z CMC, SO
THE TIMING WILL CONTINUE TO BE REFINED IN FUTURE FORECASTS.
..WEATHER/HAZARDS HIGHLIGHTS
AS THE WORKWEEK BEGINS, A STALLING FRONT WITH MOISTURE POOLING
ALONG IT WILL LIKELY PRODUCE A HEAVY RAINFALL THREAT FROM THE
CENTRAL GULF COAST THROUGH THE SOUTHEAST AND INTO THE
MID-ATLANTIC, REMAINING INTO TUESDAY AND POTENTIALLY SPREADING
INTO THE NORTHEAST TUESDAY AS WELL DEPENDING ON FRONTAL POSITIONS.
A PRIMARY FOCUS IS LIKELY TO BE ACROSS THE CAROLINAS, AND PER
COORDINATION WITH THE LOCAL OFFICES A SLIGHT RISK HAS BEEN ADDED
TO MONDAY'S ERO. DESPITE DRY CONDITIONS OVERALL IN THE PAST FEW
WEEKS THERE, A WET DAY ON DAY 3/SUNDAY WILL LIKELY PRIME THE AREA
TO EXPERIENCE SOME FLASH FLOODING ISSUES. ALSO BY MONDAY AND
ESPECIALLY TUESDAY, THE POSSIBLE TROPICAL SYSTEM IN THE EASTERN
GULF COULD BEGIN BRINGING HEAVY TROPICAL RAINS TO PARTS OF
FLORIDA, FOR A MARGINAL RISK IN SOUTHERN FLORIDA ON MONDAY AND A
SLIGHT RISK FROM THE FLORIDA BIG BEND SOUTHWARD ALONG THE GULF
COAST AS THE FEATURE COULD BE APPROACHING. THE MODERATE SPEED OF
THE SYSTEM COULD LIMIT TOO MUCH FLASH FLOODING, BUT TROPICAL
DOWNPOURS WITH HIGH RAIN RATES SHOULD POSE SOME FLASH FLOODING
THREAT. THE SYSTEM COULD TRACK ACROSS NORTHERN FLORIDA OR SO INTO
THE WESTERN ATLANTIC, WHICH COULD SPREAD HEAVY RAINFALL TO THE
COASTAL CAROLINAS BY WEDNESDAY BUT WITH UNCERTAINTY WITH HOW MUCH
FALLS ONSHORE. STORMS COULD LINGER ACROSS FLORIDA INTO LATE WEEK
WITH A FRONTAL BOUNDARY IN A MOIST ENVIRONMENT.
ABOVE NORMAL MOISTURE IS IN PLACE ACROSS PORTIONS OF THE
CENTRAL/SOUTHERN ROCKIES TO THE FRONT RANGE ON MONDAY, AND
SCATTERED TO WIDESPREAD SHOWERS AND STORMS THAT MAY BE SLOW-MOVING
COULD LEAD TO LOCALIZED FLOODING. A MARGINAL RISK WAS MAINTAINED
IN THIS AREA FOR MONDAY. MUCH OF TEXAS COULD GET SOME WELCOME RAIN
AS WELL NEAR A FRONTAL SYSTEM. SOME CONVECTION MAY REMAIN INTO
TUESDAY WITH LESSER AMOUNTS OVERALL. BY WEDNESDAY MONSOONAL
CONVECTION COULD FOCUS FARTHER WEST LIKELY INTO THE MOGOLLON RIM,
WITH INCREASING COVERAGE ONCE AGAIN BY THURSDAY FOR THE FOUR
CORNERS STATES. IN THE NORTHWEST, THE STRONG UPPER LOW COMING
THROUGH FOR THE FIRST HALF OF THE WEEK WILL PROVIDE SUPPORT FOR
RAINFALL THERE. THERE DOES LOOK TO BE SOME INSTABILITY IN PLACE,
SO LOCALIZED RAIN AMOUNTS/RATES MAY BE HIGH ENOUGH TO CAUSE A FEW
INSTANCES OF FLASH FLOODING.
ANOTHER DAY OF HOT TEMPERATURES AND HIGH HUMIDITY IS POSSIBLE FOR
THE GULF COAST REGION ON MONDAY. ADDITIONAL HIGH MAXIMUM AND
MINIMUM TEMPERATURES ARE LIKELY TO BE SET WHILE HEAT INDICES RISE
WELL ABOVE 110F. FINALLY SOME RELIEF IS IN STORE BY TUESDAY AND
WEDNESDAY WITH NEAR TO JUST ABOVE NORMAL HIGHS EXPECTED, BUT
CONSIDERABLY LOWER HEAT INDICES AS A FRONT OR TWO COME THROUGH.
MEANWHILE HEAT IS FORECAST TO BUILD AGAIN ACROSS THE LOWER
ELEVATIONS OF THE DESERT SOUTHWEST WITH SOME 110S LIKELY ON MONDAY
AND TUESDAY, BUT THIS SHOULD ALSO ABATE SOME BY WEDNESDAY AND
BEYOND. MULTIPLE FRONTS CROSSING THE EAST WILL KEEP TEMPERATURES
SOMEWHAT COOLER THAN AVERAGE THERE FOR MUCH OF NEXT WEEK. THE
CENTRAL U.S. COULD START OFF SOMEWHAT COOLER THAN AVERAGE BUT WITH
A WARMING TREND THROUGH THE WEEK.
TATE
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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