503
FXUS02 KWBC 030700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 AM EDT THU OCT 3 2024
VALID 12Z SUN OCT 06 2024 - 12Z THU OCT 10 2024
...ANOMALOUS HEAT WILL PERSIST ACROSS THE SOUTHWEST INTO EARLY NEXT
WEEK...
...CHANCES FOR HEAVY RAINFALL ACROSS THE FLORIDA PENINSULA WILL
INCREASE INTO NEXT WEEK...
..OVERVIEW
LATEST MODELS AND ENSEMBLES STILL SHOW THE UPPER PATTERN SETTLING
INTO A SLOWER-EVOLVING PATTERN DOMINATED BY LARGE SCALE FEATURES.
EXPECT AN UPPER RIDGE COVERING THE WESTERN-CENTRAL U.S. TO PRODUCE
A BROAD AREA OF MUCH ABOVE NORMAL TEMPERATURES OVER THAT PART OF
THE COUNTRY WHILE A TROUGH SETTLING OVER THE EAST (ANCHORED BY AN
UPPER LOW THAT MAY TRACK OVER OR NEAR NEW ENGLAND) WILL BRING A
COOLER TREND. THE LEADING EDGE OF A PACIFIC TROUGH WILL PRODUCE
GRADUAL HEIGHT FALLS OVER THE PACIFIC NORTHWEST AND BRING SOME
PRECIPITATION TO THE NORTHERN PARTS OF THE REGION. 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. FARTHER SOUTH, EXPECT THE HEAVIEST RAINFALL OVER
THE LOWER 48 TO BE OVER PARTS OF FLORIDA, DUE TO THE COMBINATION OF
ABUNDANT MOISTURE PLUS A COMBINATION OF ONE OR MORE GULF OF MEXICO
SURFACE FEATURES AND A FRONT DRAPED ACROSS THE PENINSULA.
..GUIDANCE/PREDICTABILITY ASSESSMENT
GUIDANCE CONTINUES TO SHOW TYPICAL DETAIL DIFFERENCES FOR THE
EVOLUTION OF THE UPPER TROUGH SETTLING OVER THE EAST AND THE
ANCHORING UPPER LOW. GENERAL TRENDS OF THE GFS/ECMWF AND THEIR
MEANS OVER THE PAST COUPLE DAYS HAVE BEEN A LITTLE SLOWER WITH THE
UPPER LOW, OFFERING SOME SUPPORT FOR IDEAS FROM RECENT CMC RUNS
THAT HAVE BEEN ON THE WESTERN SIDE OF THE SPREAD. HOWEVER BY THE
END OF THE PERIOD THE FULL ARRAY OF DYNAMICAL AND MACHINE LEARNING
(ML) GUIDANCE WOULD RECOMMEND A FARTHER EAST POSITION (OVER OR EAST
OF NORTHERN MAINE) VERSUS THE CMC. THE 12Z UKMET HELD THE CORE OF
THE UPPER TROUGH NORTHWEST OF CONSENSUS BY THE END OF ITS RUN BUT
THE 00Z VERSION COMPARES BETTER TO CONSENSUS. AN AVERAGE OF THE
GFS/ECMWF AND THEIR MEANS HAS GOOD SUPPORT FROM THE AVERAGE OF ML
MODELS BY LATE IN THE PERIOD.
SOME ASPECTS OF THE FORECAST OVER AND NEAR THE GULF OF MEXICO
STILL 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 MULTIPLE IMPULSES ALOFT. LATELY THERE HAS
BEEN SOME IMPROVEMENT IN THE SIGNAL FOR THESE FEATURES TO PHASE
EARLY NEXT WEEK AS THEY APPROACH AND INTERACT, WITH THIS
POTENTIALLY MESSY EVOLUTION INVOLVING FRONTS AND MOISTURE
GRADIENTS POSSIBLY YIELDING A MORE CONVENTIONAL WAVY FRONT THAT
SAGS JUST SOUTH OF THE FLORIDA PENINSULA BY THE END OF THE PERIOD.
CONTINUE TO MONITOR OUTLOOKS FROM THE NATIONAL HURRICANE CENTER FOR
THE LATEST INFORMATION ON FEATURES OF INTEREST OVER THE GULF.
A BLEND OF MOST GUIDANCE LOOKS GOOD FOR THE HEIGHT FALLS REACHING
THE PACIFIC NORTHWEST BY THE LATTER HALF OF THE PERIOD. THE ONE
EXCEPTION WAS THE 12Z CMC WHICH BROUGHT A STRONGER SHORTWAVE INTO
THE REGION. THE NEW 00Z CMC LOOKS BETTER IN THIS REGARD.
BASED ON 12Z/18Z GUIDANCE, THE EARLY PART OF THE FORECAST STARTED
WITH AN OPERATIONAL MODEL COMPOSITE. THE FORECAST PHASED OUT THE
LAST PART OF THE UKMET MID-PERIOD AND THEN THE 12Z CMC, WHILE
INCREASING 18Z GEFS/12Z ECENS WEIGHT. THIS YIELDED A HALF GFS/ECMWF
AND HALF GEFS/ECENS MIX BY THE END OF THE PERIOD NEXT THURSDAY.
..WEATHER/HAZARDS HIGHLIGHTS
THE MAJORITY OF THE LOWER 48 SHOULD SEE DRY WEATHER FOR MOST OR ALL
OF THE SUNDAY-THURSDAY PERIOD, WITH MOST PRECIPITATION FOCUS
AROUND THE CORNERS. BY FAR THE HEAVIEST RAINFALL POTENTIAL SHOULD
BE OVER THE FLORIDA PENINSULA, WITH SLOW-MOVING LOW PRESSURE OVER
THE GULF OF MEXICO ALONG WITH A WAVY FRONT DRAPED OVER THE STATE
AND A BROAD AREA OF ANOMALOUS MOISTURE EXTENDING OVER/EAST OF THE
GULF. THERE IS STILL A FAIR AMOUNT OF UNCERTAINTY FOR DETAILS
THOUGH. DURING DAY 4 SUNDAY, MOST DYNAMICAL MODELS/ENSEMBLE
PROBABILITIES KEEP THE HIGHEST RAIN RATES JUST OFFSHORE THE WESTERN
PENINSULA BUT MACHINE LEARNING MODELS SHOW FASTER PROGRESSION OF
GULF LOW PRESSURE AND LEADING ENHANCED RAINFALL. FOR NOW WILL
MAINTAIN NO RISK AREA IN THE DAY 4 EXCESSIVE RAINFALL OUTLOOK UNTIL
A DYNAMICAL MODEL TREND TOWARD THE ML MODELS BECOMES EVIDENT. ON
MONDAY THERE IS BETTER CONSENSUS THAT ENHANCED MOISTURE AND
POTENTIALLY HEAVY RAINFALL WILL EXTEND FARTHER EASTWARD ACROSS AT
LEAST THE SOUTHERN HALF OF FLORIDA, MERITING THE INTRODUCTION OF A
MARGINAL RISK AREA FOR THE DAY 5 ERO. SOUTHERN FLORIDA MAY CONTINUE
TO SEE PERIODS OF SIGNIFICANT RAINFALL FOR ANOTHER DAY OR SO, WITH
THE AXIS OF HIGHEST TOTALS SAGGING SOUTH WITH TIME ALONG WITH THE
FOCUSING WAVY FRONT.
ELSEWHERE, THE FRONTAL SYSTEM CROSSING THE EASTERN GREAT LAKES AND
NORTHEAST SUNDAY-MONDAY MAY GENERATE RAINFALL OF VARYING
INTENSITY. THIS REGION MAY THEN SEE SHOWERY CONDITIONS AT TIMES AS
SHORTWAVE IMPULSES FLOW AROUND AN UPPER LOW EXPECTED TO TRACK OVER
OR NEAR NORTHERN NEW ENGLAND AND THE CANADIAN MARITIMES. 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 LIGHT TO LOCALLY MODERATE RAIN AND NONZERO CHANCES OF
SNOW IN THE HIGHEST ELEVATIONS.
THE STRONG AND PERSISTENT WESTERN-CENTRAL U.S. UPPER RIDGE WILL
PROMOTE AN EXTENDED PERIOD OF WELL ABOVE NORMAL TEMPERATURES OVER
THAT PART OF THE COUNTRY. GRADUAL EASTWARD DRIFT OF THE RIDGE AXIS
WILL SHIFT THE HIGHEST ANOMALIES FROM THE WEST ON SUNDAY, WITH
SOME HIGHS AT LEAST 10-15F ABOVE NORMAL, MORE INTO THE PLAINS BY
TUESDAY-THURSDAY WHEN SOME NORTHERN LOCATIONS COULD REACH 20-25F
ABOVE NORMAL. EXPECT NUMEROUS DAILY RECORDS FOR WARM MINIMUM AND
MAXIMUM TEMPERATURES, ESPECIALLY OVER THE SOUTHWEST THROUGH
SUNDAY-MONDAY. HEIGHT FALLS SLOWLY PUSHING IN OVER THE WEST COAST
WILL SUPPORT A TREND TOWARD NEAR NORMAL TEMPERATURES THERE BY
WEDNESDAY OR THURSDAY. MODERATELY ABOVE NORMAL TEMPERATURES OVER
MOST OF THE EAST AS OF SUNDAY SHOULD THEN DECLINE TO NEAR OR
SOMEWHAT BELOW NORMAL AS UPPER TROUGHING SETS UP NEAR THE EAST
COAST. THIS MAY LEAD TO FROST/FREEZE CONCERNS ACROSS PORTIONS OF
THE UPPER GREAT LAKES REGION AND INTERIOR NORTHEAST, WITH THE
TIMING AROUND THE MEDIAN TO A BIT LATE FOR THE FIRST FROST/FREEZE
OF THE SEASON.
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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