916
FXUS02 KWBC 050637
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
237 AM 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 SOUTHERN TEXAS BY EARLY NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODELS SHOW BETTER CONSISTENCY WITH THE UPPER LOW OVER THE
NORTHEAST AS IT LIFTS NORTHWARD WITH TIME, AND A GENERAL MODEL
BLEND SEEMED TO SUFFICE FOR THIS FEATURE. THE GREATEST AREA OF
UNCERTAINTY DURING THE PERIOD IS OUT WEST AS THE NEXT AMPLIFIED
TROUGH (AND POSSIBLE CUT OFF LOW) SHIFTS EAST ACROSS THE EASTERN
PACIFIC TOWARDS THE WEST COAST. THERE ARE SOME NOTABLE TIMING
DIFFERENCES WITH THIS AND PLENTY OF RUN TO RUN VARIANCE. THROUGH
THE 12/18Z RUNS FROM YESTERDAY, THE GFS WAS BY FAR THE QUICKEST TO
BRING THIS SYSTEM INLAND, WITH THE ECMWF THE SLOWEST (WHICH HAD
SUPPORT FROM THE AI MODELS). HOWEVER, MOST OF THE NEW 00Z RUNS
TRENDED FASTER, INCLUDING THE ECMWF. FOR THE LATER PERIODS, THE WPC
FORECAST BLEND INCORPORATED INCREASING AMOUNTS OF THE ENSEMBLE
MEANS LATE PERIOD. DID LEAN MORE TOWARDS THE SLOWER SOLUTIONS WITH
THE WESTERN TROUGH, GIVEN SUPPORT FROM THE 12Z AI MODELS, BUT BASED
ON THE NEW 00Z MODEL TRENDS (WHICH WERE AVAILABLE AFTER FORECAST
GENERATION TIME), THE WPC FORECAST MAY WELL BE TOO SLOW NOW.
..WEATHER/HAZARDS HIGHLIGHTS
A LINGERING FRONT ACROSS NORTHERN FLORIDA AND ALONG THE GULF COAST
WILL CONTINUE TO FOCUS SHOWERS AND STORMS, LOCALLY HEAVY, INTO
NEXT WEEK. AT THIS TIME, NO EXCESSIVE RAINFALL RISK AREAS ARE
DEPICTED ON EITHER THE DAY 4/SUNDAY OR DAY 5/MONDAY GRAPHICS, BUT
DEPENDING ON WHAT FALLS WHERE DURING THE SHORT RANGE PERIOD, A
MARGINAL RISK MAY EVENTUALLY BE NEEDED ACROSS NORTHERN FLORIDA.
TROPICAL MOISTURE MOVING INTO THE SOUTHWESTERN GULF MAY BRING AN
INCREASING THREAT FOR HEAVY RAINS BACK INTO SOUTHERN TEXAS, WHICH
IS COVERED BY A MARGINAL RISK ON THE DAY 5 ERO. SOME GUIDANCE SHOWS
POTENTIAL OF LOCALLY SIGNIFICANT AMOUNTS TO MONITOR. OTHERWISE
MUCH OF THE COUNTRY SHOULD BE QUIET AND DRY, THOUGH SHORTWAVE
ENERGY WITHIN AND AROUND 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 AROUND NEXT TUESDAY.
ABOVE NORMAL TEMPERATURES ACROSS THE NORTHWEST ON SUNDAY SHOULD
SHIFT INTO THE NORTHERN PLAINS WITH TIME. DAYTIME HIGHS LOOK TO BE
10-15 DEGREES ABOVE NORMAL, BUT THIS MAY ONLY EQUATE TO A MODERATE
HEATRISK THREAT. ABOVE NORMAL TEMPERATURES MAY REACH INTO THE
MIDWEST/UPPER GREAT LAKES AS WELL LATE PERIOD. IN CONTRAST, A MUCH
COOLER AIRMASS WILL BE IN PLACE ACROSS THE EAST THIS WEEKEND, BUT
MAY TREND BACK TOWARDS NORMAL NEXT WEEK. AN ARRIVING UPPER TROUGH
SHOULD SIGNAL BELOW NORMAL TEMPERATURES BACK INTO THE WEST COAST
STATES MID NEXT WEEK.
SANTORELLI
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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