140
FXUS02 KWBC 051853
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
253 PM EDT THU SEP 5 2024
VALID 12Z SUN SEP 08 2024 - 12Z THU SEP 12 2024
..OVERVIEW
AN AMPLIFIED UPPER-LEVEL PATTERN WILL BE IN PLACE THIS WEEKEND
WITH AN UPPER RIDGE OVER THE WEST THAT SHIFTS EAST WITH TIME, AS A
MEAN UPPER LOW/TROUGH SLOWLY WORKS THROUGH THE NORTHEAST. THIS WILL
USHER IN A FALL-LIKE DRY AND COOL AIR MASS ACROSS MUCH OF THE
EASTERN HALF OF THE COUNTRY. ELSEWHERE, A LINGERING AND WAVY FRONT
WILL KEEP RAIN CHANCES ACROSS THE GULF COAST TO FLORIDA, WHILE
TROPICAL MOISTURE MOVING INTO THE SOUTHWESTERN GULF COULD BRING
HEAVY RAIN INTO SOUTH TEXAS BY EARLY NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODELS HAVE BEEN VERY CONSISTENT WITH THE UPPER LEVEL PATTERN IN
THE EASTERN AND SOUTHERN U.S., BUT THEY HAVE BEEN STRUGGLING WITH
AN AMPLIFIED TROUGH THAT'S FORECAST TO MOVE INTO THE WEST DURING
THE SECOND HALF OF THE PERIOD. THE 00Z ECMWF SEEMS TO DEVIATE THE
MOST FROM THE CONSENSUS AND YESTERDAY'S ECMWF RUNS, IT SPLITS THE
TROUGH ENERGY, RESULTING IN A MUCH WEAKER WAVE IN THE WEST
COMPARED TO OTHER GUIDANCE LIKE THE GFS AND CMC. TODAY'S 12Z ECMWF
RUN WAS NOT AVAILABLE AT THE TIME THE FORECAST WAS MADE, BUT IT
HAS FALLEN BACK INTO LINE WITH THE CONSENSUS, HAVING A STRONGER
TROUGH MOVE INTO THE WEST MID/LATE NEXT WEEK.
FOR THE WPC AFTERNOON FORECAST, A BLEND OF THE DETERMINISTIC
GFS/CMC/UKMET/ECMWF WAS USED FOR THE FIRST HALF OF THE PERIOD,
OPTING TO USE YESTERDAY'S 12Z ECMWF RUN INSTEAD OF THE 00Z RUN.
ENSEMBLE MEANS WERE ADDED GRADUALLY TO MAKE UP TO 50% OF THE BLEND
FOR THE SECOND HALF OF THE PERIOD, WHICH HELPED TO SMOOTH OUT
DIFFERENCES IN THE WEST BY DAYS 6 AND 7.
..WEATHER/HAZARDS HIGHLIGHTS
A LINGERING FRONT ACROSS NORTH FLORIDA AND ALONG THE GULF COAST
WILL CONTINUE TO FOCUS SHOWERS AND STORMS, LOCALLY HEAVY, INTO NEXT
WEEK. HEAVY RAIN THAT IS FORECAST ACROSS NORTH FLORIDA AND
SOUTHERN GEORGIA IN THE SHORT TERM PERIOD WILL LIKELY SATURATE
SOILS AND COULD MAKE THIS REGION MORE PRONE TO FLOODING WITH ANY
LOCALLY HEAVY RAIN THAT MAY FALL ON DAYS 4 AND 5 (SUNDAY AND
MONDAY). A MARGINAL RISK AREA WILL LIKELY BE INTRODUCED IN THE DAY
4/SUNDAY ERO, AND AN ADDITIONAL MARGINAL RISK MAY EVENTUALLY BE
NEEDED ON DAY 5/MONDAY.
TROPICAL MOISTURE MOVING INTO THE SOUTHWESTERN GULF MAY BRING AN
INCREASING THREAT FOR HEAVY RAIN TO SOUTH TEXAS, WHICH IS COVERED
BY A MARGINAL RISK ON THE DAY 5/MONDAY ERO. SOME GUIDANCE SHOWS
POTENTIAL FOR LOCALLY SIGNIFICANT AMOUNTS THAT WILL NEED TO BE
MONITORED. OTHERWISE, MUCH OF THE COUNTRY SHOULD BE QUIET AND DRY,
ALTHOUGH SHORTWAVE ENERGY WITHIN AND AROUND THE WESTERN U.S. UPPER
RIDGING MAY PRODUCE ISOLATED TO SCATTERED RAINFALL WITH MOSTLY
LIGHT AMOUNTS. RAINFALL AHEAD OF THE NEXT WESTERN U.S. TROUGH
SHOULD BEGIN TO MOVE INTO THE REGION LATE TUESDAY.
ABOVE NORMAL TEMPERATURES ACROSS THE NORTHWEST ON SUNDAY WILL
SHIFT INTO THE NORTHERN PLAINS EARLY NEXT WEEK AND INTO THE
MIDWEST BY MID-NEXT WEEK. DAYTIME HIGHS ARE FORECAST TO BE 10-20
DEGREES ABOVE NORMAL, BUT THIS MAY ONLY EQUATE TO A MODERATE
HEATRISK THREAT. IN CONTRAST, A MUCH COOLER AIRMASS WILL BE IN
PLACE ACROSS THE EAST THIS WEEKEND, BUT MAY TREND BACK TOWARDS
NORMAL NEXT WEEK. BELOW NORMAL TEMPERATURES SHOULD ALSO DEVELOP
ALONG THE WEST COAST MID-NEXT WEEK AS AN UPPER TROUGH MOVES
ONSHORE.
SANTORELLI/DOLAN
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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