984
FXUS02 KWBC 091858
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
258 PM EDT WED OCT 9 2024
VALID 12Z SAT OCT 12 2024 - 12Z WED OCT 16 2024
..DESERT SOUTHWEST RECORD HEAT MODERATES/LINGERS INTO SATURDAY
..OVERVIEW
GUIDANCE CONTINUES TO SHOW DEVELOPMENT OF AN AMPLIFIED RIDGE-TROUGH
PATTERN OVER THE LOWER 48, DOWNSTREAM FROM A DEEP SYSTEM JUST
SOUTH OF ALASKA. A SHORTWAVE DIVING THROUGH THE NORTH-CENTRAL U.S.
THIS WEEKEND WILL BEGIN THE PROCESS OF AMPLIFYING EASTERN U.S.
TROUGHING AND SUPPORT A NORTHEAST SURFACE SYSTEM, WITH MULTIPLE
TRAILING IMPULSES HELPING TO REINFORCE THE TROUGH. MUCH BELOW
NORMAL TEMPERATURES AND FROST/FREEZE MAY BE A CONCERN OVER SOME
AREAS FROM THE PLAINS INTO THE EAST. THE FRONT LEADING THE COLDER
TREND SHOULD SUPPRESS THIS WEEKEND'S CENTRAL-SOUTHERN U.S. HEAT
THAT MAY CHALLENGE DAILY RECORDS AT SOME LOCATIONS. THE UPPER RIDGE
OVER THE ROCKIES WILL SUPPORT PERSISTENT WARMTH OVER THE INTERIOR
WEST AND ROCKIES, FOCUSING MORE OVER THE NORTHERN ROCKIES/HIGH
PLAINS TOWARD THE MIDDLE OF NEXT WEEK. EXPECT THE LEADING EDGE OF A
PACIFIC TROUGH TO PUSH A FRONT AND SOME ACCOMPANYING RAINFALL INTO
THE NORTHWEST BY NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
COMPARISONS OF LATEST DYNAMICAL AND MACHINE LEARNING (ML) GUIDANCE
SHOW GOOD AGREEMENT FOR THE LARGE SCALE PATTERN EVOLUTION OVERALL,
WITH THE MOST PROMINENT UNCERTAINTIES BEING THE SPECIFICS OF
SURFACE LOW DEVELOPMENT OVER THE NORTHEASTERN QUADRANT OF THE LOWER
48 AROUND SUNDAY-MONDAY AND HOW ENERGY EVOLVES WITHIN THE EASTERN
U.S. UPPER TROUGH BY NEXT TUESDAY-WEDNESDAY.
SOLUTIONS HAVE BEEN WAFFLING FOR PRECISE STRENGTH AND TRACK OF THE
SUNDAY-MONDAY SURFACE SYSTEM, WITH SENSITIVITY TO DETAILS ALOFT. AT
THE VERY LEAST, ML SOLUTIONS OFFER GOOD SUPPORT FOR MORE OF A
CLOSED UPPER LOW AND BETTER DEFINED SURFACE SYSTEM THAN WHAT
MULTIPLE CMC RUNS HAVE BEEN DEPICTING. GEFS/ECENS MEANS HAVE BEEN
TILTING TOWARD A MORE OCCLUDED SYSTEM REACHING NEW ENGLAND THAN
DEPICTED IN THE 00Z ECMWF OR PAST COUPLE UKMET RUNS, BUT THE ML
MODEL SPREAD INCLUDES THE RANGE OF DYNAMICAL MODEL DETAILS. THE
DYNAMICAL MODEL AVERAGE HAS WEAKENED THE SURFACE LOW SOMEWHAT
VERSUS THE PRIOR 12-HOURLY CYCLE, WITH THE AVERAGE OF ML MODELS
FAIRLY CLOSE TO THE DYNAMICAL GUIDANCE.
LATER IN THE PERIOD, MODEL/ENSEMBLE SPREAD DEVELOPS REGARDING
WHETHER AN UPPER LOW COULD FORM WITHIN THE EASTERN U.S. TROUGH. FOR
NOW SUCH AN UPPER LOW IS A MINORITY SOLUTION, SO THE DETERMINISTIC
PREFERENCE CONTINUES TO BE THE OPEN TROUGH PER A BLEND/ENSEMBLE
MEAN APPROACH. THERE WAS HARDLY ANY GUIDANCE SUPPORT FOR THE
MIDWEST UPPER LOW IN THE 00Z CMC, WHILE THE 12Z CMC HAS AT LEAST
TRENDED EASTWARD WITH IT TOWARD THE 00Z GFS (WHICH WAS STILL A BIT
ON THE WESTERN SIDE AMONG THE SUBSET OF GUIDANCE THAT HAD A CLOSED
LOW). ON THE OTHER HAND, THE NEW 12Z GFS BECOMES MORE PROGRESSIVE
WITH THE TROUGH VERSUS THE MAJORITY.
LATEST CONSENSUS HAS THE PACIFIC UPPER TROUGH AXIS REACHING JUST
OFFSHORE THE WEST COAST BY EARLY NEXT WEDNESDAY. ML MODELS SHOW
SIMILAR OR SLIGHTLY FASTER TIMING, BUT MULTI-DAY TRENDS HAVE BEEN A
LITTLE SLOWER--FAVORING THE DYNAMICAL GUIDANCE FOR THE TIME BEING.
GUIDANCE CONSIDERATIONS LED TO STARTING THE EARLY-MIDDLE PART OF
THE FORECAST WITH A BLEND OF THE 06Z GFS, 00Z AND 12Z/08 ECMWF, AND
A SMALL WEIGHT OF 00Z UKMET. THEN THE BLEND ADDED IN SOME OF THE
06Z GEFS/00Z ECENS MEANS BY NEXT TUESDAY-WEDNESDAY WITH THE
INCREASING DETAIL UNCERTAINTY.
..WEATHER/HAZARDS HIGHLIGHTS
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 INTO 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
AND LIGHT TO MODERATE RAINFALL INTO THE REGION BY THE START OF NEXT
WEEK. THE AMPLIFYING UPPER TROUGH AND ACCOMPANYING SURFACE SYSTEM
AFFECTING THE EAST LATE THIS WEEKEND INTO EARLY NEXT WEEK SHOULD
PRODUCE SOME AREAS OF LOCALLY ENHANCED RAINFALL ACROSS PARTS OF THE
GREAT LAKES/NORTHEAST. LITTLE IF ANY INSTABILITY AND FAIRLY MODEST
MOISTURE ANOMALIES EVEN ON THE HIGHER SIDE OF THE SPREAD SUGGEST
THAT SHORT-TERM RAIN RATES WILL LIKELY NOT BE HIGH ENOUGH TO POSE
A FLASH FLOOD THREAT. THEREFORE THE DAYS 4-5 EXCESSIVE RAINFALL
OUTLOOKS CONTINUE TO SHOW NO RISK AREAS.
AN UPPER RIDGE ALIGNED OVER/NEAR THE ROCKIES FOR MOST OF THE
PERIOD WILL MAINTAIN WELL ABOVE NORMAL TEMPERATURES OVER THE
SOUTHWEST/INTERIOR WEST INTO ROCKIES, AND EXTENDING INTO THE
NORTHERN HIGH PLAINS TOWARD MIDWEEK AS THE RIDGE SHIFTS EASTWARD A
LITTLE. THE CENTRAL/SOUTHERN PLAINS WILL ALSO HAVE A VERY WARM
START TO THE WEEKEND BEFORE NORTHERN STREAM TROUGHING AND A COLD
FRONT SUPPRESS ABOVE NORMAL READINGS TO THE SOUTH/SOUTHEAST.
GREATEST ANOMALIES OF PLUS 10-20F SHOULD BE OVER THE NORTHERN
ROCKIES MULTIPLE DAYS AND EVENTUALLY THE NORTHERN HIGH PLAINS, AS
WELL AS THE SOUTHERN PLAINS DURING THE WEEKEND. DAILY RECORDS WILL
BE POSSIBLE FROM THE SOUTHWEST THROUGH THE SOUTHERN PLAINS THIS
WEEKEND. MEANWHILE, THE EAST SHOULD SEE SOME NEAR TO SLIGHTLY ABOVE
NORMAL TEMPERATURES THIS WEEKEND FOLLOWED BY A COLDER TREND TOWARD
HIGHS 5-15F BELOW NORMAL NEXT MONDAY-WEDNESDAY UNDERNEATH
AMPLIFIED UPPER TROUGHING. MORNING LOWS NEXT WEEK MAY BE A TAD LESS
ANOMALOUS BUT STILL COLD ENOUGH TO RAISE SOME FROST/FREEZE
CONCERNS FROM THE NORTH-CENTRAL U.S. THROUGH THE MIDWEST/GREAT
LAKES AND NORTHEAST/APPALACHIANS.
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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