975
FXUS02 KWBC 230657
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
257 AM EDT FRI AUG 23 2024
VALID 12Z MON AUG 26 2024 - 12Z FRI AUG 30 2024
..OVERVIEW
GUIDANCE SHOWS STRONG PLAINS/MISSISSIPPI VALLEY/SOUTHEAST UPPER
RIDGING AS OF EARLY MONDAY WEAKENING SOMEWHAT AS IT BECOMES
CONFINED MORE OVER THE SOUTHEAST AFTER MIDWEEK. GUIDANCE AGREES
THAT AN INITIAL NEW ENGLAND UPPER LOW/TROUGH WILL DEPART, BUT
GUIDANCE DIFFERS FOR IMPORTANT DETAILS OF OTHER NORTHERN STREAM
FEATURES, NAMELY SHORTWAVE ENERGY EJECTING FROM THE NORTHERN
ROCKIES/HIGH PLAINS AND A VIGOROUS TROUGH MOVING INTO THE NORTHWEST
U.S. AND WESTERN CANADA BY TUESDAY-WEDNESDAY AND CONTINUING ONWARD
THEREAFTER. THE NORTHEAST UPPER LOW AND NORTHERN STREAM SYSTEMS TO
THE WEST WILL PRODUCE AREAS OF RAINFALL WHILE DIURNAL CONVECTION
SHOULD CONTINUE OVER THE SOUTHERN ROCKIES AND ALONG THE GULF COAST.
THE UPPER RIDGE WILL FOCUS ABOVE NORMAL TEMPERATURES OVER THE EAST-
CENTRAL U.S. INTO SOUTHEAST, WHILE THE COMBINATION OF SYSTEMS
FARTHER WEST WILL GENERALLY PROMOTE BELOW NORMAL HIGHS FROM PARTS
OF THE INTERIOR WEST INTO THE NORTHERN HIGH PLAINS.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE PRIMARY FORECAST ISSUES INVOLVE THE INITIAL ENERGY EJECTING
FROM THE NORTHERN ROCKIES/HIGH PLAINS AND THE ULTIMATE EVOLUTION OF
UPSTREAM WESTERN NORTH AMERICA TROUGH ENERGY AFTER MIDWEEK. IN BOTH
CASES, THE MAJORITY OF OTHER DYNAMICAL GUIDANCE AS WELL AS A FAIR
CLUSTER OF MACHINE LEARNING MODELS SUGGEST THAT LATEST GFS RUNS
OFFER LOWER PROBABILITY SOLUTIONS FOR THESE FEATURES.
REGARDING THE LEADING SHORTWAVE, THE OVERWHELMING MAJORITY OF
GUIDANCE SHOWS A GREATER SPLIT OF ENERGY VERSUS THE GFS AS OF EARLY
MONDAY, LEADING TO A SLOWER PROGRESSION OF THE NORTHERN
ROCKIES/PLAINS SHORTWAVE. BEYOND THAT POINT MOST GUIDANCE DIVERGES
FOR HOW THIS ENERGY WILL EVOLVE AS IT POSSIBLY TRACKS ACROSS
SOUTHEASTERN CANADA AND NEARBY PARTS OF THE GREAT LAKES/NORTHEAST,
SO CONFIDENCE IS MINIMAL IN ANY SPECIFIC SOLUTION THERE.
SOLUTIONS ARE FAIRLY SIMILAR FOR THE INCOMING PACIFIC TROUGH INTO
WEDNESDAY. HOWEVER BY THE LATTER HALF OF THE WEEK, LATEST GFS RUNS
HAVE BEEN LIFTING THE CORE OF THE TROUGH WELL NORTH OF OTHER
GUIDANCE WHILE SOMETIMES LEAVING WEAK ENERGY BEHIND OVER THE
ROCKIES AND OVERALL YIELDING LESS TROUGHING THAN CONSENSUS OVER THE
NORTHERN TIER STATES--WITH A CORRESPONDING INFLUENCE ON SURFACE
DETAILS. GEFS MEAN RUNS ARE ALSO SOMEWHAT NORTH OF THE NON-GFS
MODELS FOR THE CANADA UPPER LOW BUT AT LEAST BETTER RESEMBLE THE
MAJORITY FOR THE NORTHERN U.S. TROUGH.
GUIDANCE COMPARISONS LED TO UPDATING THE FORECAST WITH AN
OPERATIONAL MODEL COMPOSITE EARLY WITH MODEST INCLUSION OF THE 12Z
ECENS/CMCENS MEANS LATER IN THE PERIOD, ALL DAYS WITH SOMEWHAT
LOWER THAN USUAL GFS WEIGHT DUE TO LOWER CONFIDENCE IN ITS NORTHERN
STREAM FEATURES.
..WEATHER/HAZARDS HIGHLIGHTS
UPPER RIDGE EVOLUTION WILL LEAD TO THE EAST-CENTRAL U.S. SEEING THE
MOST ANOMALOUS HEAT EARLY IN THE WEEK, FOLLOWED BY GRADUAL
SUPPRESSION INTO THE SOUTH/SOUTHEAST. SOME AREAS MAY SEE ONE OR
MORE DAYS WITH HIGHS UP TO 10-15 ABOVE NORMAL (AND A FEW DAILY
RECORDS) MONDAY THROUGH WEDNESDAY OR THURSDAY, WITH ANOMALIES
TENDING TO BE IN THE PLUS 5-10F RANGE BY FRIDAY. EXPERIMENTAL
HEATRISK SHOWS A FAIRLY BROAD AREA OF MODERATE TO MAJOR LEVEL
IMPACTS WITH EVEN SOME VERY ISOLATED POCKETS OF EXTREME SHOWING UP
BY MIDWEEK. IN CONTRAST, THE COMBINATION OF FEATURES OVER THE WEST
WILL YIELD BELOW NORMAL HIGHS FROM PARTS OF THE INTERIOR WEST INTO
NORTHERN HIGH PLAINS, WITH BEST POTENTIAL FOR LOCALLY MINUS 10-15F
ANOMALIES ON MONDAY AND WEDNESDAY-THURSDAY.
LEADING SHORTWAVE ENERGY AND ONE OR MORE WAVY SURFACE FRONTS MAY
PRODUCE RAINFALL OF VARYING INTENSITY OVER THE NORTHERN PLAINS AND
VICINITY EARLY IN THE WEEK. THUS FAR THE COMBINED CLUSTERING FOR
LOCATION AND MAGNITUDE ARE NOT SUFFICIENT TO MERIT A RISK AREA IN
THE DAYS 4-5 EXCESSIVE RAINFALL OUTLOOK, BUT THIS REGION IS WORTH
MONITORING IN CASE FUTURE TRENDS GRAVITATE TOWARD THE HEAVIER SIDE
OF THE BROAD GUIDANCE SPREAD. FARTHER SOUTH, BOTH MONDAY AND
TUESDAY EROS HAVE INTRODUCED A MARGINAL RISK AREA OVER PORTIONS OF
THE SOUTHERN ROCKIES GIVEN ADEQUATE MOISTURE/INSTABILITY, GFS/ECMWF
QPF SIGNALS, AND LIKELY EXISTENCE OF SHORTWAVE IMPULSES ALOFT.
THE NEXT SYSTEM PUSHING IN FROM THE PACIFIC SHOULD NOT PRODUCE MUCH
RAINFALL AS IT REACHES THE NORTHWEST EARLY IN THE WEEK, BUT WILL
LIKELY GENERATE MORE WIDESPREAD RAINFALL OVER PARTS OF THE
PLAINS/MIDWEST AFTER MIDWEEK. ELSEWHERE, THE NORTHEAST UPPER LOW
SHOULD PRODUCE SOME DIURNALLY FAVORED RAINFALL EARLY IN THE WEEK
WHILE SOME EPISODES OF SHOWERS/THUNDERSTORMS WILL BE POSSIBLE NEAR
THE GULF COAST. SOME DIURNAL CONVECTION MAY PERSIST OVER THE
SOUTHERN ROCKIES/ARIZONA BEYOND MIDWEEK.
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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