799
FXUS02 KWBC 110655
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
255 AM EDT WED SEP 11 2024
VALID 12Z SAT SEP 14 2024 - 12Z WED SEP 18 2024
..GENERAL OVERVIEW
THE REMNANT LOW ASSOCIATED WITH WHAT IS NOW HURRICANE FRANCINE WILL
CONTINUE TO DISSIPATE ACROSS THE OHIO VALLEY OVER THE WEEKEND.
MEANWHILE, A CLOSED UPPER HIGH IS EXPECTED TO RESIDE OVER THE GREAT
LAKES AND INTO THE NORTHEAST WITH ABOVE AVERAGE TEMPERATURES GOING
INTO EARLY NEXT WEEK. ACROSS THE WESTERN U.S., ANOTHER TROUGH
BUILDS IN NEAR THE WEST COAST AFTER THE FIRST ONE LIFTS OUT ACROSS
THE NORTHERN PLAINS LATE THIS WEEK, WITH MORE OF AN AMPLIFIED UPPER
LEVEL PATTERN EVOLVING. THERE MAY BE A COASTAL LOW THAT TRIES TO
DEVELOP NEAR THE COASTAL CAROLINAS BY MID-WEEK AS THE FRONTAL
BOUNDARY OVER THE WESTERN ATLANTIC TRIES TO LIFT BACK NORTH.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE 00Z MODEL GUIDANCE SUITE FEATURES GOOD OVERALL SYNOPTIC SCALE
AGREEMENT ACROSS THE NATION FOR THE UPCOMING WEEKEND. THE REMNANT
LOW FROM FRANCINE CONTINUES TO WEAKEN FURTHER AND BECOME JUST A
SURFACE TROUGH OR WEAK REFLECTION BASED ON THE GUIDANCE BY SUNDAY.
LOOKING AHEAD TO THE FIRST HALF OF NEXT WEEK, THE PAST FEW RUNS OF
THE GFS REMAIN QUICKER WITH THE ARRIVAL OF THE NEXT TROUGH ACROSS
THE WEST COAST. THE RECENT MACHINE LEARNING GUIDANCE SUGGESTS THE
TIMING OF THE TROUGH AND CLOSED LOW WOULD BE SLOWER, MORE IN LINE
WITH THE ECMWF/CMC SOLUTIONS.
FOR THE WPC FORECAST, A BLEND OF THE DETERMINISTIC GUIDANCE WAS
USED THROUGH THE WEEKEND AS A STARTING POINT IN THE FORECAST
PROCESS. ENSEMBLE MEANS WERE ADDED GRADUALLY TO MAKE UP ABOUT 40%
OF THE BLEND BY WEDNESDAY, WHICH HELPED TO SMOOTH OUT INCREASING
MESOSCALE DIFFERENCES. THE ECMWF WAS WEIGHTED MORE THAN THE GFS
LATE IN THE PERIOD GIVEN BETTER CONSISTENCY WITH THE ENSEMBLE MEANS
AND ML GUIDANCE. OVERALL, GOOD CONTINUITY WAS MAINTAINED WITH THE
PREVIOUS WPC FORECAST.
..WEATHER/HAZARDS HIGHLIGHTS
THE REMNANT LOW FROM FRANCINE SHOULD BE NEARLY DISSIPATED BY
SATURDAY AND EVOLVE INTO A SURFACE TROUGH, AND THE MAJORITY OF THE
REMAINING RAINFALL SHOULD BE LOCATED TO THE EAST AND SOUTHEAST OF
THE LOW. THERE WILL LIKELY BE A REMAINING INFLOW BAND ACROSS
CENTRAL TENNESSEE AND EXTENDING INTO NORTHERN ALABAMA, WHERE LOCALLY
HIGHER HIGHER RAINFALL TOTALS COULD BE OBSERVED. ORTHOGONAL LOW
LEVEL FLOW ACROSS THE SOUTHERN APPALACHIANS COULD ALSO RESULT IN
SOME HIGHER RAINFALL TOTALS HERE AS WELL, AND BOTH OF THESE REGIONS
ARE ENCOMPASSED IN A BROAD MARGINAL RISK AREA FOR DAY 4/SATURDAY.
SHOWERS AND THUNDERSTORMS ARE LIKELY THIS WEEKEND FOR PARTS OF THE
SOUTHWEST WITH A INCREASED MOISTURE CONNECTION AHEAD OF A POSSIBLE
TROPICAL DISTURBANCE LIFTING NORTH OVER THE SOUTHERN BAJA
PENINSULA. TO ACCOUNT FOR THIS POSSIBILITY, MARGINAL RISK AREAS ARE
PLANNED FOR SOUTHERN PORTIONS OF ARIZONA ON SATURDAY, AND
EXTENDING FARTHER NORTH INTO ARIZONA AND WESTERN NEW MEXICO ON
SUNDAY. ELSEWHERE ACROSS THE WEST, INCREASING SHOWERS AND STORMS
ARE LIKELY BY EARLY NEXT WEEK AS THE SECOND TROUGH BUILDS IN ACROSS
THE WEST COAST AND THEN THE INTERMOUNTAIN WEST, AND SCATTERED
SHOWERS/STORMS ALSO FOR THE SOUTHERN PLAINS AS TROPICAL MOISTURE
GETS WRAPPED IN AHEAD OF THE WESTERN TROUGH.
TEMPERATURES SHOULD MODERATE SOME ACROSS THE NORTHWESTERN U.S. BY
THE WEEKEND AS THE FIRST TROUGH LIFTS OUT, WITH HIGHS RETURNING TO
NEAR SEASONAL AVERAGES. ANOTHER COOL-DOWN APPEARS LIKELY GOING INTO
EARLY NEXT WEEK FOR THE WEST COAST WITH READINGS 10 TO PERHAPS 20
DEGREES BELOW NORMAL FOR PORTIONS OF THE INTERIOR WEST COAST STATES
BY TUESDAY. MEANWHILE, WARM CONDITIONS ARE FORECAST TO CONTINUE
FROM THE CENTRAL/NORTHERN PLAINS TO THE GREAT LAKES AND PARTS OF
THE NORTHEAST WHERE UPPER LEVEL RIDGING WILL TEND TO GOVERN THE
OVERALL WEATHER PATTERN.
HAMRICK
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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