962
FXUS02 KWBC 100658
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
258 AM EDT TUE SEP 10 2024
VALID 12Z FRI SEP 13 2024 - 12Z TUE SEP 17 2024
..GENERAL OVERVIEW
THE MAIN THING THAT WILL MAKE WEATHER HEADLINES FOR THE END OF
THIS WEEK WILL BE THE EVENTUAL REMNANTS OF FRANCINE PROGRESSING
INLAND ACROSS THE TENNESSEE AND OHIO RIVER VALLEYS. THE RESULT
WILL BE MODERATE TO HEAVY RAINFALL THAT COULD PRODUCE SOME
INSTANCES OF FLOODING. ELSEWHERE, A TROUGH EXITING THE NORTHERN
ROCKIES FRIDAY WILL LIKELY BE REPLACED BY ANOTHER LARGE SCALE
TROUGH ACROSS THE WEST COAST BY MONDAY, BRINGING ANOTHER ROUND OF
COOLER WEATHER AND INCREASED RAINFALL CHANCES. MEANWHILE, A
GENERAL UPPER LEVEL RIDGE TO THE NORTH OF THE REMNANT LOW FROM
FRANCINE WILL BE IN PLACE FROM THE MIDWEST/NORTHERN PLAINS TO THE
GREAT LAKES, KEEPING SUMMER-LIKE TEMPERATURES IN PLACE.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE 00Z MODEL GUIDANCE SUITE FEATURES GOOD OVERALL SYNOPTIC SCALE
AGREEMENT ACROSS THE NATION ON FRIDAY AND CONTINUING INTO THE
WEEKEND. FOR THE REMNANT TROPICAL LOW MOVING INLAND ACROSS THE
OHIO VALLEY, THE 00Z IS SLIGHTLY FASTER THAN THE ECMWF/GFS
SOLUTIONS AND ALSO AHEAD OF THE NHC TRACK FORECAST. THE LOW
CONTINUES TO WEAKER FURTHER AND BECOME JUST A SURFACE TROUGH BASED
ON THE GUIDANCE BY SUNDAY. LOOKING AHEAD TO MONDAY, THE GFS IS
QUICKER WITH THE ARRIVAL OF THE NEXT TROUGH ACROSS THE WEST COAST,
AND IS A FEW HUNDRED MILES TO THE EAST OF THE CMC/ECMWF SOLUTIONS
BY TUESDAY. THERE IS GROWING MODEL SPREAD WITH TIMING OF NORTHERN
STREAM SHORTWAVES ACROSS CANADA, BUT THESE SHOULD NOT BE ALL THAT
IMPACTFUL FOR THE WEATHER FORECAST ACROSS THE U.S.
FOR THE WPC OVERNIGHT FORECAST, A BLEND OF THE DETERMINISTIC
GUIDANCE WAS USED AS A BASELINE ON FRIDAY, AND THEN TAPERED DOWN
THE CMC AND UKMET AND PLACED MORE WEIGHTING TO THE GFS/ECMWF FOR
THE WEEKEND. ENSEMBLE MEANS WERE ADDED GRADUALLY TO MAKE UP ABOUT
40-50% OF THE BLEND BY EARLY NEXT WEEK, WHICH HELPED TO SMOOTH OUT
INCREASING MESOSCALE DIFFERENCES.
..WEATHER/HAZARDS HIGHLIGHTS
THE CENTER OF STEADILY WEAKENING T.D. FRANCINE SHOULD BE REACHING
THE WESTERN OHIO VALLEY BY FRIDAY NIGHT, AND THE MAJORITY OF THE
RAINFALL SHOULD BE LOCATED TO THE EAST AND SOUTHEAST OF THE LOW
PRESSURE CENTER. THERE WILL LIKELY BE A REMAINING INFLOW BAND
ACROSS CENTRAL TENNESSEE AND EXTENDING INTO KENTUCKY, WHERE 1-2
INCHES OF RAIN CAN BE EXPECTED WITH LOCALLY HIGHER AMOUNTS.
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/FRIDAY. NOT MUCH IN THE OVERALL ATMOSPHERIC SET-UP CHANGES
FOR DAY 5/SATURDAY, EXCEPT FOR A SLIGHTLY WEAKER SIGNAL IN THE
MODEL GUIDANCE AND FURTHER WEAKENING OF THE REMNANT LOW. HOWEVER,
THE MARGINAL RISK IS STILL PLANNED FOR MANY OF THOSE SAME AREAS IN
DAY 4 GIVEN THE GROUNDS WILL LIKELY BE MORE SATURATED.
ELSEWHERE ACROSS THE COUNTRY IN TERMS OF RAINFALL, SHOWERS SHOULD
BE DECREASING IN COVERAGE ACROSS MONTANA AND THE NORTHERN HIGH
PLAINS AS THE FIRST WESTERN U.S. TROUGH LIFTS OUT OF THE REGION IN
TIME FOR THE WEEKEND. SHOWERS AND SOME THUNDERSTORMS ARE LIKELY TO
MAKE A RETURN GOING INTO EARLY NEXT WEEK FROM ARIZONA TO THE
PACIFIC NORTHWEST AS THE SECOND TROUGH BUILDS IN ACROSS THE WEST
COAST AND THEN THE INTERMOUNTAIN WEST, AND SCATTERED SHOWERS/STORMS
ALSO FOR THE SOUTHERN PLAINS.
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 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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