581
FXUS02 KWBC 071857
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
257 PM EDT MON OCT 7 2024
VALID 12Z THU OCT 10 2024 - 12Z MON OCT 14 2024
..HURRICANE MILTON SHOULD CLEAR FLORIDA BY THURSDAY
..OVERVIEW
BY THE START OF THE PERIOD ON THURSDAY, HURRICANE MILTON SHOULD BE
BEGINNING ITS EXTRATROPICAL TRANSITION AND EXITING THE FLORIDA
PENINSULA. MUCH OF THE HEAVY RAINFALL SHOULD BE OFFSHORE BUT SOME
LINGERING BACKSIDE SHOWERS ARE STILL POSSIBLE ACROSS EASTERN PARTS
OF FLORIDA. ELSEWHERE, AN INITIAL NORTHEAST/MID-ATLANTIC UPPER
TROUGH WILL LIFT OUT WHILE A CENTRAL U.S. RIDGE WILL CONTINUE TO
BRING MUCH ABOVE NORMAL TEMPERATURES BUT WITH PACIFIC ENERGY
DAMPENING THE NORTHERN PERIPHERY ON THE WAY TO CROSSING THE
NORTHEAST BY THE WEEKEND. EXPECT A STRONG LOW SETTLING INTO THE
GULF OF ALASKA TO SUPPORT AN AMPLIFYING RIDGE-TROUGH PATTERN TO THE
EAST BY NEXT SUNDAY-MONDAY, WITH DEVELOPING LOW PRESSURE POSSIBLY
GENERATING SOME AREAS OF RAINFALL OVER THE GREAT LAKES/NORTHEAST. A
COMPACT UPPER LOW/TROUGH MAY BRING SOME RAIN TO THE CENTRAL WEST
COAST AROUND FRIDAY-SATURDAY. HEIGHT FALLS AND MOISTURE AHEAD OF
THE GULF OF ALASKA SYSTEM MAY BEGIN TO PUSH INTO THE PACIFIC
NORTHWEST BY EARLY NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE UPDATED FORECAST STARTED WITH A 06Z GFS/00Z ECMWF BLEND FOR THE
EARLY TO MIDDLE PART OF THE PERIOD, FOLLOWED BY A TRANSITION TO
30-40 PERCENT TOTAL ENSEMBLE MEANS (06Z GEFS/00Z ECENS). THIS
SOLUTION YIELDED THE CLOSEST STARTING POINT POSSIBLE FOR THE
OFFICIAL NATIONAL HURRICANE CENTER TRACK OF MILTON AND BEST
REFLECTED THE RELATIVE MAJORITY OF GUIDANCE FOR OTHER SIGNIFICANT
FEATURES, WHILE ACCOUNTING FOR TYPICALLY INCREASING DETAIL
UNCERTAINTY LATER IN THE PERIOD.
MODEL GUIDANCE STILL SHOWS MEANINGFUL SPREAD FOR THE TRACK/TIMING
OF MILTON, THOUGH NEW 12Z RUNS ARE HELPING TO NARROW THE SPREAD
ESPECIALLY FOR TIMING. THE CMC/CMCENS HAD BEEN A SLOW EXTREME
RELATIVE TO OTHER DYNAMICAL AND MACHINE LEARNING (ML) GUIDANCE BUT
THE 12Z RUN HAS TRENDED CLOSER (BUT NOT YET TO) THE
MAJORITY/AVERAGE. MEANWHILE, THE FAST UKMET HAS SLOWED DOWN IN THE
12Z RUN (WITH THE ECMWF SLOWING DOWN SOME AS WELL).
AFTER THE DEPARTURE OF THE INITIAL NORTHEAST UPPER TROUGH, THE
PROGRESSIVE SOUTHERN CANADA/NORTHERN U.S. SHORTWAVE REACHING
SOUTHEASTERN CANADA AND NEW ENGLAND BY AROUND SATURDAY DISPLAYS
FAIRLY GOOD CLUSTERING OVERALL. RECENT UKMET RUNS HAVE BEEN ON THE
FAST SIDE THOUGH, WITH ML RUNS IN SUPPORT OF THE SLOWER MAJORITY.
THEN AS LARGER SCALE UPPER TROUGHING AMPLIFIES INTO THE EASTERN
HALF OF THE COUNTRY BY SUNDAY-MONDAY, THERE IS GOOD AGREEMENT IN
PRINCIPLE BUT WITH TYPICAL DETAIL DIFFERENCES WHICH REFLECT AT THE
SURFACE WITH GREATER SPREAD FROM THE MIDWEST/GREAT LAKES THROUGH
THE NORTHEAST. BY NEXT MONDAY THE ML GUIDANCE SHOWS SURFACE LOW
PRESSURE SOMEWHERE BETWEEN THE EASTERN GREAT LAKES AND SOUTHEASTERN
CANADA/NEW ENGLAND, MORE IN THE REALM OF RECENT GEFS/ECENS AND GFS
RUNS, WITH THE 12Z/06 ECMWF CLOSER TO THIS IDEA VERSUS THE FARTHER
SOUTH 00Z ECMWF OR EAST 12Z/07 ECMWF. THUS THE LATE PART OF THE
FORECAST BLEND SPLIT ECMWF INPUT BETWEEN THE 00Z ECMWF AND 12Z/06
ECMWF.
NEAR THE WEST COAST, THE 00Z UKMET/CMC STRAYED FASTER THAN OTHER
GUIDANCE WITH THE COMPACT UPPER TROUGH/LOW ARRIVING AROUND LATE
WEEK OR WEEKEND. ML MODELS RANGED BETWEEN THE ECMWF/GFS CLUSTER AND
INTERMEDIATE TIMING, AT LEAST FAVORING A SLOWER SOLUTION THAN THE
UKMET/CMC. THE 12Z UKMET HAS TRENDED BACK TO THE SLOWER CLUSTER AND
THE NEW CMC IS SLOWER BUT STILL RUNNING AHEAD OF OTHER SOLUTIONS.
ML MODELS VARY REGARDING HOW MUCH SHORTWAVE ENERGY COULD REACH THE
NORTHWEST BY NEXT MONDAY, RANGING BETWEEN THE DYNAMICAL
MODEL/ENSEMBLE CONSENSUS OF FAIRLY MODEST HEIGHT FALLS AT THAT TIME
VERSUS SOMEWHAT MORE ENERGY ARRIVING.
..WEATHER/HAZARDS HIGHLIGHTS
CONTINUE TO MONITOR NATIONAL HURRICANE CENTER ADVISORIES FOR THE
LATEST INFORMATION ON HURRICANE MILTON. CURRENT FORECASTS INDICATE
THE SYSTEM SHOULD BE TRACKING EASTWARD NEAR THE EAST COAST OF
FLORIDA AS OF EARLY THURSDAY. THE MAJORITY OF THE ASSOCIATED HEAVY
RAINFALL SHOULD BE IN PROCESS OF MOVING OFFSHORE BUT THERE IS STILL
SOME POTENTIAL FOR LINGERING HEAVY RAINFALL TO BE IMPACTING
NORTHEAST PARTS OF FLORIDA AND POSSIBLY AS FAR NORTH AS THE GEORGIA
COAST INTO THURSDAY SO A MARGINAL RISK PERSISTS FOR THAT REGION ON
THE DAY 4 EXCESSIVE RAINFALL OUTLOOK.
OTHERWISE, A LARGE PART OF THE LOWER 48 WILL SEE FAIRLY DRY WEATHER
FOR A MAJORITY OF THE PERIOD. A COMPACT EASTERN PACIFIC UPPER
TROUGH/LOW MAY BRING A BRIEF PERIOD OF MOSTLY LIGHT RAINFALL TO THE
CENTRAL WEST COAST AROUND FRIDAY-SATURDAY, WITH A LITTLE LIGHT
PRECIPITATION POSSIBLY REACHING FARTHER EASTWARD INTO THE WEST
THEREAFTER. THEN A FRONT APPROACHING THE PACIFIC NORTHWEST MAY
BRING SOME MOISTURE INTO THE REGION BY THE START OF NEXT WEEK. THE
AMPLIFYING UPPER TROUGH AND ACCOMPANYING SURFACE EVOLUTION SHOULD
BRING SOME AREAS OF RAINFALL TO PARTS OF THE GREAT LAKES/NORTHEAST
BY LATE WEEKEND INTO THE EARLY PART OF NEXT WORK WEEK, THOUGH WITH
FAIRLY LOW CONFIDENCE IN SPECIFICS AT THIS TIME.
A WESTERN-CENTRAL U.S. UPPER RIDGE WILL CONTINUE TO PROMOTE AN
EXTENDED PERIOD OF WELL ABOVE NORMAL TEMPERATURES WITH HIGHEST
ANOMALIES LIKELY FOR THE NORTHERN PLAINS ON THURSDAY, AND SOME
LOCATIONS SHOULD REACH 20-30F ABOVE NORMAL AS HIGHS IN THE 80S MAY
EXTEND TO THE CANADIAN BORDER. NORTHERN STREAM TROUGHING AND A COLD
FRONT COULD PUSH THE GREATEST WARM ANOMALIES SOUTHEAST INTO THE
CENTRAL PLAINS AND MID/UPPER MISSISSIPPI VALLEY FRIDAY-SATURDAY.
MEANWHILE HEIGHT FALLS SLOWLY PUSHING IN OVER THE WEST COAST WILL
SUPPORT A TREND TOWARD NEAR NORMAL TEMPERATURES BY WEDNESDAY OR
THURSDAY. HOWEVER, TEMPERATURES AROUND 10 DEGREES ABOVE NORMAL IN
THE SOUTHWEST COULD SET ADDITIONAL DAILY RECORDS THOUGH THE
TEMPERATURES HAVE MODERATED COMPARED TO RECENT DAYS AND THE SHORT
RANGE. THE NORTHERN ROCKIES/HIGH PLAINS MAY SEE TEMPERATURES REACH
UP TO 10-20F ABOVE NORMAL BY SUNDAY-MONDAY. MEANWHILE, COOLER THAN
AVERAGE TEMPERATURES ARE FORECAST ACROSS MOST OF THE EAST LATE THIS
WEEK AS UPPER TROUGHING SETS UP NEAR THE EAST COAST, WITH SOME
POTENTIAL FROST/FREEZE CONCERNS ACROSS PORTIONS OF THE APPALACHIANS
AND INTERIOR NORTHEAST EARLY THURSDAY. EXPECT TEMPERATURES TO
MODERATE NEXT WEEKEND AS THE UPPER LOW SCOOTS OUT OF THE REGION,
BUT COOL AGAIN EARLY NEXT WEEK UNDERNEATH ANOTHER TROUGH.
RAUSCH/SANTORELLI
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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