358
FXUS02 KWBC 020658
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
258 AM EDT WED OCT 2 2024
VALID 12Z SAT OCT 05 2024 - 12Z WED OCT 09 2024
...ANOMALOUS HEAT WILL PERSIST ACROSS THE SOUTHWEST INTO THE
WEEKEND...
..OVERVIEW
GUIDANCE CONTINUES TO SHOW THE EXPECTED PATTERN TRANSITION FROM
PROGRESSIVE NORTHERN TIER FLOW EXTENDING INTO THE WEEKEND TOWARD
AN AMPLIFYING EASTERN U.S./ATLANTIC COAST TROUGH EARLY NEXT WEEK
(WITH POSSIBLE NEW ENGLAND OR VICINITY UPPER LOW) WHILE A MEAN
RIDGE COVERING MUCH OF THE WEST EXTENDS INTO THE PLAINS, PRODUCING
AN EXTENDED PERIOD OF UNSEASONABLY WARM TO HOT WEATHER. AHEAD OF
THE DYNAMICS THAT WILL ULTIMATELY ESTABLISH THE EASTERN UPPER
TROUGH, A FRONT CROSSING THE GREAT LAKES AND NORTHEAST SHOULD
PRODUCE SOME ORGANIZED RAIN AND POSSIBLE SURFACE LOW DEVELOPMENT
COULD ENHANCE AMOUNTS FOR PARTS OF NEW ENGLAND. MEANWHILE, DETAILS
REMAIN UNCERTAIN WITHIN THE GENERAL GULF OF MEXICO EVOLUTION
FAVORING LOW PRESSURE AND HEAVY RAINFALL POTENTIAL. MOST GUIDANCE
SUGGESTS HEAVIEST RAINFALL WILL INITIALLY STAY OVER THE GULF BUT
THEN EVENTUALLY SOME OF IT MAY SPREAD EASTWARD INTO FLORIDA. THERE
MAY BE MULTIPLE SURFACE FEATURES TO FOCUS RAINFALL, INCLUDING ONE
LIFTING FROM THE NORTHWESTERN CARIBBEAN INTO THE GULF AND ANOTHER
THAT MAY START OUT OVER THE WESTERN GULF, WITH SOME POTENTIAL FOR
THESE TO COMBINE BY THE FIRST HALF OF NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
ASIDE FROM TYPICAL SMALLER-SCALE DETAILS, THE PRIMARY QUESTION MARK
WITH THE NORTHERN STREAM FLOW IS HOW UPPER TROUGHING WILL EVOLVE
ONCE IT REACHES EASTERN NORTH AMERICA DURING THE EARLY TO MIDDLE
PART OF NEXT WEEK. ALTHOUGH NOT UNANIMOUS, THERE HAS BEEN A
MAJORITY CLUSTER SUGGESTING THAT AN UPPER LOW WILL CLOSE OFF
SOMEWHERE OVER EASTERN CANADA OR NEW ENGLAND. THIS IS CERTAINLY
PLAUSIBLE WITH THE OVERALL PATTERN LOOKING MORE BLOCKY AS AN UPPER
RIDGE STRENGTHENS OVER/NEAR GREENLAND. CMC RUNS HAVE BEEN LEANING
TO THE WESTERN SIDE OF THE SPREAD FOR THE OVERALL TROUGH/UPPER LOW,
WHILE OTHER MODEL RUNS HAVE BEEN VARYING FOR SHORTWAVE DETAILS THAT
DETERMINE THE TIMING AND PATH OF THE UPPER LOW. MACHINE LEARNING
(ML) MODELS LIKEWISE SHOW SUCH SPREAD AND WITH A TILT TOWARD A NEW
ENGLAND/CANADIAN MARITIMES UPPER LOW ON AVERAGE.
THE FORECAST OVER AND NEAR THE GULF OF MEXICO CONTINUES TO HAVE
LOW PREDICTABILITY DUE TO A COMBINATION OF SMALLER-SCALE FEATURES.
ONE WAVE MAY TRACK INTO THE CENTRAL/EAST-CENTRAL GULF FROM THE
NORTHWESTERN CARIBBEAN WHILE ANOTHER FEATURE MAY EVOLVE OVER THE
WESTERN GULF, WITH THE SURFACE/QPF DETAILS ALSO POTENTIALLY
AFFECTED BY ENERGY ALOFT NEAR THE WESTERN GULF COAST. PER
YESTERDAY'S COORDINATION WITH NHC, THESE FEATURES MAY PHASE AT
SOME POINT NEXT WEEK AS THEY APPROACH AND INTERACT. GUIDANCE SHOWS
THE SYSTEM(S) COULD LINGER AND MEANDER OVER THE GULF EVEN THROUGH
THE FIRST HALF OF NEXT WEEK, THOUGH PERHAPS BEGINNING TO DRIFT
EASTWARD WITH TIME AS GUIDANCE SHOWS SOME PROGRESSION OF A
POSITIVELY TILTED UPPER TROUGH. THIS APPEARS TO BE A MESSY
EVOLUTION AS FRONTS AND MOISTURE GRADIENTS ARE ALSO EVIDENT NEARBY.
CONTINUE TO MONITOR OUTLOOKS FROM THE NATIONAL HURRICANE CENTER
FOR THE LATEST INFORMATION ON FEATURES OF INTEREST.
THE UPDATED FORECAST STARTED WITH A 12Z/18Z OPERATIONAL MODEL
COMPOSITE EARLY IN THE PERIOD AND THEN TRANSITIONED TOWARD A BLEND
OF THE 18Z GFS/12Z ECMWF AND THEIR MEANS LATE, AS THE CMC
INCREASINGLY STRAYED FROM THE MAJORITY CLUSTER OVER THE EAST.
OPERATIONAL MODEL WEIGHT ALSO TILTED MORE TOWARD THE ECMWF BY THE
END OF THE FORECAST DUE TO THE LOW-CONFIDENCE EASTERN GULF
DEVELOPMENT TRACKING INTO FLORIDA IN THE 18Z GFS.
..WEATHER/HAZARDS HIGHLIGHTS
THE RAINFALL FORECAST FOR AREAS ALONG THE GULF COAST DURING THE
WEEKEND CONTINUES TO BE IN THE PROVERBIAL HOLDING PATTERN, WITH A
RELATIVE MAJORITY OF GUIDANCE KEEPING MOST OF THE SIGNIFICANT
TOTALS OVER THE GULF OF MEXICO, ESPECIALLY ON SATURDAY. THE
GUIDANCE MESSAGES BECOME MORE MIXED BY SUNDAY. IN VARYING WAYS, THE
GFS/UKMET/CMC AND MACHINE LEARNING GUIDANCE SHOW POTENTIAL FOR SOME
HEAVY RAINFALL TO REACH WESTERN FLORIDA BUT OTHER MODELS AND
ENSEMBLE PROBABILITIES SUGGEST THAT IT WILL TAKE ADDITIONAL TIME
FOR THIS ACTIVITY TO REACH FLORIDA. AT THE VERY LEAST, REASONABLE
CONSENSUS OF THE GFS/ECMWF AND THEIR MEANS WOULD HAVE MOISTURE
ANOMALIES INCREASING OVER THE STATE AS AN EAST-WEST FRONT BECOMES
ALIGNED ACROSS THE PENINSULA SO SOME INCREASE IN RAINFALL ON
SUNDAY RELATIVE TO SATURDAY SEEMS REASONABLE. THE QUESTION IS TO
WHAT DEGREE. THE DAYS 4-5 EXCESSIVE RAINFALL OUTLOOKS FOR SATURDAY-
SUNDAY MAINTAIN NO RISK AREAS FOR NOW, BUT WITH AN EYE TO PARTS OF
THE FLORIDA GULF COAST REGION FOR POSSIBLE INTRODUCTION OF AN AREA
ON DAY 5 IF THERE IS FURTHER CLUSTERING/CONTINUITY IN FUTURE
CYCLES. THE PATTERN CONTINUES TO LOOK FAVORABLE FOR ENHANCED
RAINFALL OVER FLORIDA DURING THE FIRST HALF OF NEXT WEEK WITH A
GENERAL AREA OF LOW PRESSURE EXPECTED TO DRIFT INTO THE EASTERN
GULF AND A POTENTIALLY WAVY FRONT STILL DRAPED ACROSS THE
PENINSULA.
ELSEWHERE, THE FRONTAL SYSTEM REACHING THE GREAT LAKES AND
NORTHEAST BY SUNDAY-MONDAY AND POSSIBLE LOW DEVELOPMENT NEAR NEW
ENGLAND AND THE CANADIAN MARITIMES THEREAFTER MAY GENERATE RAINFALL
OF VARYING INTENSITY. THERE IS STILL A FAIRLY WIDE RANGE OF
POSSIBLE QPF TOTALS FROM THE EASTERN GREAT LAKES INTO NEW ENGLAND
DEPENDING ON EXACTLY HOW THIS SYSTEM EVOLVES. A MEAN FRONTAL ZONE
WITH ONE OR MORE EMBEDDED WAVES SHOULD REACH NEAR THE NORTHERN
PACIFIC NORTHWEST BY EARLY-MID WEEK, PRODUCING SOME PERIODS OF
MOSTLY LIGHT RAIN.
THE STRONG AND PERSISTENT UPPER RIDGE COVERING THE WEST AND
EXTENDING INTO THE PLAINS WILL SUPPORT A LENGTHY PERIOD OF WELL
ABOVE NORMAL TEMPERATURES OVER MANY PARTS OF THE WESTERN/CENTRAL
U.S. HIGHS 10-20F OR SO ABOVE NORMAL WILL BE COMMON AND NUMEROUS
DAILY RECORDS APPEAR LIKELY FROM THE SOUTHERN HALF OF THE WEST INTO
PARTS OF THE HIGH PLAINS, ESPECIALLY DURING THE WEEKEND BUT ALSO
LINGERING INTO EARLY NEXT WEEK TO SOME EXTENT. BEST POTENTIAL FOR
SOME HIGHS 20-25F ABOVE NORMAL WILL BE OVER THE CENTRAL PLAINS AND
MIDWEST ON SATURDAY AND NORTHERN PLAINS BY MIDWEEK. ABOVE NORMAL
TEMPERATURES OVER MOST OF THE EAST DURING THE WEEKEND SHOULD
DECLINE TO NEAR OR SOMEWHAT BELOW NORMAL AS UPPER TROUGHING SETS UP
NEAR THE EAST COAST.
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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