189
FXUS02 KWBC 301936
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
336 PM EDT MON SEP 30 2024
VALID 12Z THU OCT 03 2024 - 12Z MON OCT 07 2024
..OVERVIEW
THE MAJORITY OF GUIDANCE THROUGH THE NEW 12 UTC CYCLE STILL
SUGGESTS A MODERATELY PROGRESSIVE PATTERN FROM THE EASTERN PACIFIC
THROUGH THE NORTHERN LOWER 48 AND SOUTHERN CANADA, EVENTUALLY
TRANSITIONING TOWARD A LARGER SCALE WESTERN RIDGE/EASTERN TROUGH BY
NEXT MONDAY. FOR THE MOST PART, FRONTS PUSHED ALONG BY NORTHERN
TIER DYNAMICS SHOULD BRING ONLY SOME AREAS OF LIGHT RAIN AT TIMES.
MEANWHILE A PERSISTENT UPPER RIDGE OVER THE SOUTHWEST/FOUR CORNERS,
AT TIMES CONNECTING WITH RIDGING TO THE NORTH, WILL KEEP THE
SOUTHERN HALF OF THE WEST UNSEASONABLY WARM/HOT WITH SOME OF THE
HEAT REACHING THE PLAINS. MEANWHILE THE GUIDANCE SEEMS TO BE NO
CLOSER TO RESOLVING SIGNIFICANT DIFFERENCES WITHIN A GENERAL
EVOLUTION FAVORING LOW PRESSURE/HEAVY RAINFALL POTENTIAL OVER THE
GULF OF MEXICO AND POTENTIALLY EXTENDING INTO SOME AREAS ALONG THE
GULF COAST. THERE MAY BE MULTIPLE SURFACE FEATURES TO FOCUS
RAINFALL, INCLUDING ONE LIFTING FROM THE NORTHWESTERN CARIBBEAN
INTO THE GULF AND ANOTHER THAT MAY BE OVER THE WESTERN GULF.
..GUIDANCE/PREDICTABILITY ASSESSMENT
LATEST GUIDANCE STILL SHOWS THAT THE MOST SIGNIFICANT FORECAST
PROBLEM IN THE NORTHERN STREAM HAS BEEN THE EVOLUTION OF TROUGH
ENERGY REACHING THE NORTHEASTERN PACIFIC BY EARLY FRIDAY. OVER
RECENT DAYS THERE HAS BEEN A DECENT CLUSTER IN PRINCIPLE AMONG THE
DYNAMICAL ENSEMBLE MEANS, MORE THAN HALF OF THE MODELS, AND THE
MAJORITY OF MACHINE LEARNING (ML) MODELS PLUS ECMWF AIFS ENSEMBLE
MEAN, TOWARD INLAND PROGRESSION OF THE SHORTWAVE BY SATURDAY AND
THEN SOME TROUGH AMPLIFICATION INTO THE EAST BY EARLY NEXT WEEK AS
AN UPPER RIDGE BUILDS INTO WESTERN NORTH AMERICA. HOWEVER THE
ENSEMBLE SPAGHETTI PLOTS HAVE BEEN (AND STILL ARE) QUITE MESSY
AFTER FRIDAY, WHILE DIFFERENT MODELS ON DIFFERENT DAYS HAVE
DIFFERED FROM THIS MAJORITY CLUSTER. IN THE 00Z CYCLE, IT IS THE
GFS THAT STRAYS BY HOLDING THE PACIFIC SHORTWAVE BACK--WHICH SOME
EARLIER CMC/UKMET/ICON RUNS HAD DONE, BUT NOW THOSE LATTER MODELS
HAVE JOINED THE MORE CONSISTENT ECMWF CLUSTER. THE NEW 12Z GFS
HAS PARTIALLY TRENDED BACK TOWARD THIS MAJORITY.
THE FORECAST CONTINUES TO BE VERY UNCERTAIN OVER AND NEAR THE GULF
OF MEXICO. THERE HAVE BEEN SOME INDICATIONS THAT ONE FEATURE MAY
TRACK FROM THE NORTHWESTERN CARIBBEAN INTO THE CENTRAL/EASTERN GULF
AND POSSIBLY AFFECT FLORIDA. HOWEVER, LATEST GUIDANCE SEEMS TO HAVE
AT LEAST DELAYED APPROACH. THERE MAY BE A SEPARATE FEATURE OVER
THE WESTERN GULF, WHICH FROM COORDINATED CONTINUITY IS CURRENTLY
DEPICTED AS A TROUGH NEAR THE WESTERN GULF COAST. CONTINUE TO
MONITOR OUTLOOKS FROM THE NATIONAL HURRICANE CENTER FOR THE LATEST
INFORMATION ON FEATURES OF INTEREST.
..WEATHER/HAZARDS HIGHLIGHTS
IT GENERALLY REMAINS THE CASE THAT GUIDANCE DIFFERENCES OVER THE
GULF OF MEXICO AND GULF COAST REGION CONTINUE TO RESULT IN LOW
CONFIDENCE FOR RESOLVING WHERE HEAVY RAIN MAY AFFECT COASTAL AND/OR
INLAND AREAS DURING THE PERIOD. DURING THE THURSDAY-FRIDAY PERIOD
COVERED BY THE DAYS 4-5 EXCESSIVE RAINFALL OUTLOOKS, ML MODELS
SHOWED SOME SUPPORT FOR SOME RECENT GFS AND ECMWF RUNS WITH SOME
POTENTIAL FOCUS FROM SOUTHEASTERN LOUISIANA INTO THE WESTERN
FLORIDA PANHANDLE, WITH A LITTLE EASTWARD EXPANSION WITH TIME.
HOWEVER OTHER MODELS/ENSEMBLE PROBABILITIES ARE LESS ENTHUSIASTIC
OVER THIS REGION, WHILE ALSO SHOWING SOME ENHANCED RAINFALL
POTENTIAL ALONG PARTS OF THE TEXAS COAST. FLASH FLOOD GUIDANCE
VALUES ARE HIGH THROUGHOUT THE GULF COAST REGION, THOUGH FLORIDA
WOULD BE MORE SENSITIVE FROM RECENT WETNESS. CURRENTLY THE DAYS 4-5
EROS DO NOT DEPICT ANY RISK AREAS GIVEN THE WIDE DISPERSION OF
GUIDANCE, WHILE AWAITING A MORE COHERENT SIGNAL FOR RAINFALL FOCUS.
RECENT INDICATIONS HAVE BEEN FOR INCREASING RAINFALL TO REACH INTO
FLORIDA BY THE WEEKEND, THOUGH LATEST RUNS HINT AT SOME DELAY IN
THE MOISTURE'S ARRIVAL. IN ADDITION, THERE HAS BEEN SOMEWHAT OF A
MORE SUPPRESSED TREND FOR THE NORTHERN PERIPHERY OF RAIN THAT HAS
BEEN FORECAST TO EXTEND INTO THE SOUTHEAST.
ELSEWHERE, ANTICIPATE LIGHTER RAINFALL ALONG PORTIONS OF THE
FRONTS SUPPORTED BY NORTHERN STREAM DYNAMICS. ONE FRONT MAY PRODUCE
AREAS OF LIGHT RAIN OVER THE GREAT LAKES/NORTHEAST LATE THIS WEEK.
ANOTHER FRONT REACHING THE PACIFIC NORTHWEST AROUND FRIDAY MAY
PRODUCE SOME LIGHT RAIN, WITH TRENDS OVER THE PAST COUPLE DAYS
LEANING TOWARD LOWER AMOUNTS. RAINFALL MAY EXPAND ALONG THIS FRONT
WHEN IT REACHES INTO THE EAST BY NEXT SUNDAY/MONDAY.
LATEST GUIDANCE CONTINUES THE RECENT TREND TOWARD MORE PERSISTENT
UPPER RIDGING OVER THE WEST. AS A RESULT, THERE MAY BE DECENT
COVERAGE OF HIGHS 10-15F OR SO ABOVE AVERAGE EXTENDING ALL THE WAY
INTO EARLY NEXT WEEK WITH NUMEROUS DAILY RECORD HIGHS, ALBEIT
BECOMING A LITTLE MORE CONFINED TO THE DESERT SOUTHWEST TOWARD
MONDAY. THE HEAT WILL EXTEND INTO THE PLAINS AT TIMES, WITH
SATURDAY LIKELY TO FEATURE THE HIGHEST TEMPERATURES OVER THAT
REGION (PLUS 10-20F ANOMALIES), INCLUDING SOME DAILY RECORDS OVER
THE CENTRAL HIGH PLAINS. TEMPERATURES OVER THE EAST WILL VARY WITH
FRONTAL PROGRESSION, WITH HIGHS AVERAGING OUT CLOSE TO NORMAL AND
MORNING LOWS LEANING MORE ABOVE NORMAL.
RAUSCH/SCHICHTEL
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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