081
FXUS02 KWBC 120653
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
253 AM EDT THU SEP 12 2024
VALID 12Z SUN SEP 15 2024 - 12Z THU SEP 19 2024
..GENERAL OVERVIEW
THE BEGINNING OF THE FORECAST PERIOD SUNDAY WILL BE FEATURED WITH
AN UPPER LEVEL TROUGH AMPLIFYING ACROSS THE WEST COAST, AND THEN
THE TROUGH SHOULD ENCOMPASS MOST OF THE INTERIOR WEST BY TUESDAY.
THIS COMBINED WITH A COLD FRONT WILL RESULT IN MORE WIDESPREAD
SHOWERS AND COOLER TEMPERATURES. ACROSS THE EASTERN U.S., A REX
BLOCK TYPE PATTERN IS LIKELY FOR SUNDAY INTO EARLY NEXT WEEK WITH
AN UPPER HIGH SITUATED OVER THE NORTHEAST U.S., AND A WEAK UPPER
LOW OVER THE CAROLINAS (PARTIALLY FROM THE REMNANTS OF FRANCINE AND
ANOTHER DISTURBANCE OVER THE ATLANTIC), AND THIS COULD HAVE SOME
STAYING POWER FOR SEVERAL DAYS. THIS WILL TEND TO LIMIT THE
EASTWARD PROGRESSION OF THE LARGE SCALE TROUGH OUT WEST.
..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 MODEL GUIDANCE
AND THE MACHINE LEARNING GUIDANCE HAS CONSOLIDATED WITH THE
ARRIVAL OF THE NEXT TROUGH ACROSS THE WEST COAST. THE LATEST GFS
HAS SLOWED COMPARED TO EARLIER RUNS AND BETTER MATCHES THE CMC AND
ECMWF MODELS. BY MIDWEEK, THE CMC IS STRONGER WITH A REINFORCING
TROUGH ACROSS THE PACIFIC NORTHWEST AND BEGINS TO STRAY MORE FROM
THE MODEL CONSENSUS.
FOR THE WPC FORECAST, A BLEND OF THE DETERMINISTIC GUIDANCE WAS
USED THROUGH EARLY TUESDAY AS A STARTING POINT IN THE FORECAST
PROCESS. ENSEMBLE MEANS WERE ADDED GRADUALLY TO MAKE UP ABOUT 40%
OF THE BLEND BY MIDWEEK, WHICH HELPED TO SMOOTH OUT INCREASING
MESOSCALE DIFFERENCES. OVERALL, GOOD CONTINUITY WAS MAINTAINED
WITH THE PREVIOUS WPC FORECAST.
..WEATHER/HAZARDS HIGHLIGHTS
THE REMNANT LOW FROM FRANCINE SHOULD BE NEARLY DISSIPATED BY
SUNDAY AND EVOLVE INTO A SURFACE TROUGH, WITH SOME LINGERING RAIN
ACROSS PORTIONS OF THE TENNESSEE RIVER VALLEY AND INTO THE SOUTHERN
OHIO VALLEY. SINCE THE GROUND ACROSS CENTRAL TENNESSEE AND NORTHERN
ALABAMA WILL BE QUITE SATURATED BY THIS TIME, A DAY 4 MARGINAL RISK
IS STILL PLANNED FOR SUNDAY ACROSS THIS REGION. FARTHER TO THE EAST
ACROSS THE COASTAL CAROLINAS, A DEVELOPING WAVE OF LOW PRESSURE
ALONG AN OLD STATIONARY FRONT WILL LIKELY RESULT IN A PLUME OF
ENHANCED MOISTURE AND ONSHORE FLOW WITH THE POTENTIAL FOR 1 TO 3
INCHES OF RAINFALL, AND THIS MOVES FARTHER INLAND ON DAY 5/MONDAY
ACROSS NORTH CAROLINA. THEREFORE, A MARGINAL RISK AREA IS PLANNED
FOR BOTH DAYS FOR PORTIONS OF THIS REGION.
SHOWERS AND THUNDERSTORMS ARE LIKELY SUNDAY 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 PORTIONS OF ARIZONA AND INTO WESTERN NEW MEXICO ON
SUNDAY, AND EXTENDING FARTHER NORTH INTO SOUTHERN UTAH AND
SOUTHWEST COLORADO ON MONDAY. 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. SOME SNOW IS LIKELY FOR THE HIGHEST MOUNTAIN RIDGES
OF THE NORTHERN ROCKIES AS SNOW LEVELS DROP.
ANOTHER COOL-DOWN IS EXPECTED 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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