145
FXUS02 KWBC 121848
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
248 PM 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 FEATURE AN UPPER
LEVEL TROUGH AMPLIFYING ACROSS THE WEST COAST, WITH ANOTHER WAVE
ACTING TO REINFORCE AND MAINTAIN TROUGHING ACROSS THE WEST INTO
NEXT WEEK. THIS COMBINED WITH A COLD FRONT WILL RESULT IN MORE
WIDESPREAD SHOWERS, MOUNTAIN SNOW, 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).
THIS FEATURE MAY LINGER FOR A FEW DAYS, WHICH WOULD LIMIT THE
EASTWARD PROGRESSION OF THE LARGE SCALE TROUGH OUT WEST.
..GUIDANCE/PREDICTABILITY ASSESSMENT
LATEST MODELS GUIDANCE CONTINUES TO SHOW GOOD OVERALL SYNOPTIC
SCALE AGREEMENT ON THE PATTERN DESCRIBED ABOVE, BUT DOES OFFER
PLENTY OF UNCERTAINTY IN THE DETAILS. THE REMNANT LOW FROM FRANCINE
SHOULD NOT BE MUCH MORE THAN A SURFACE TROUGH OR WEAK REFLECTION
BY SUNDAY, BUT THERE IS A LOT OF UNCERTAINTY REGARDING HOW THIS
LINGERING ENERGY MAY INTERACT WITH ADDITIONAL ENERGY OFF THE
SOUTHEAST COAST. THE GFS IS THE STRONGEST IN SUGGESTING POSSIBLE
TROPICAL OR SUB-TROPICAL DEVELOPMENT OF THIS SYSTEM NEAR THE
SOUTHEAST COAST, BUT THE REMAINDER OF THE GUIDANCE IS MUCH WEAKER
WITH THE SYSTEM. OUT WEST, THE INITIAL LOW SUNDAY-MONDAY HAS GOOD
AGREEMENT AS IT LIFTS THROUGH THE GREAT BASIN AND NORTHERN HIGH
PLAINS. SOME TIMING UNCERTAINTIES ARISE AS THE NEXT LOW ARRIVES BY
MID NEXT WEEK.
THE WPC FORECAST TODAY USED A BLEND OF THE LATEST DETERMINISTIC
GUIDANCE THROUGH DAY 5 AMID GOOD MODEL AGREEMENT. FOR 6 AND 7,
INCORPORATED 40 PERCENT OF THE ENSEMBLE MEANS WITH THE GFS AND
ECMWF TO ACCOUNT FOR GREATER DETAIL AND TIMING DIFFERENCES.
OVERALL, THIS MAINTAINED GOOD AGREEMENT WITH THE PREVIOUS WPC
FORECAST AS WELL.
..WEATHER/HAZARDS HIGHLIGHTS
THE REMNANT LOW FROM FRANCINE SHOULD BE NEARLY DISSIPATED BY
SUNDAY, THOUGH 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 MAY MOVE FARTHER INLAND ON DAY 5/MONDAY ACROSS NORTH
CAROLINA. THEREFORE, A MARGINAL RISK AREA IS PLANNED FOR BOTH DAYS
FOR PORTIONS OF THIS REGION. RAINFALL AMOUNTS AND LOCATION IS
HIGHLY UNCERTAIN GIVEN DIFFERENCES IN HOW THE MODELS HANDLE THIS
FEATURE OFF THE SOUTHEAST COAST. RAINFALL CHANCES COULD CONTINUE
INTO NEXT WEEK WITH THIS INTO PARTS OF THE MID-ATLANTIC.
SHOWERS AND THUNDERSTORMS ARE LIKELY SUNDAY FOR PARTS OF THE
SOUTHWEST WITH A INCREASED MOISTURE CONNECTION AHEAD OF TROPICAL
DEPRESSION NINE-E LIFTING NORTH OVER THE SOUTHERN BAJA PENINSULA.
MARGINAL RISK ERO AREAS ARE IN PLACE 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. FROST MAY BE
A CONCERN FOR SOME ACROSS THE NORTHERN-CENTRAL GREAT BASIN.
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.
SANTORELLI/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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page