396
FXUS02 KWBC 041839
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
239 PM EDT WED SEP 4 2024
VALID 12Z SAT SEP 07 2024 - 12Z WED SEP 11 2024
...HEAVY RAINFALL THREATS TO IMPACT NORTHERN FLORIDA AND THE
NORTHEAST ON SATURDAY...
..OVERVIEW
AN AMPLIFIED UPPER-LEVEL PATTERN WILL BE IN PLACE BY THE WEEKEND
WITH AN UPPER RIDGE OVER THE WEST THAT SLUGGISHLY SHIFTS EAST WITH
TIME, AND AS A MEAN UPPER LOW SLOWLY WORKS THROUGH THE NORTHEAST.
THIS WILL SUPPORT A LINGERING PERIOD OF ENHANCED RAINFALL OVER
PORTIONS OF NEW ENGLAND THIS WEEKEND, WITH A FALL-LIKE DRY AND
COOL AIR MASS FILTERING IN BEHIND IT ACROSS MUCH OF THE EASTERN
HALF OF THE COUNTRY. A LINGERING AND WAVY FRONT WILL KEEP RAIN
CHANCES ACROSS THE GULF COAST TO FLORIDA, WITH THE BEST CHANCE FOR
HEAVY RAIN ON SATURDAY ACROSS NORTHERN FLORIDA. TROPICAL MOISTURE
MOVING INTO THE SOUTHWESTERN GULF COULD BRING HEAVY RAIN INTO
SOUTHERN TEXAS BY EARLY NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
ONE MAIN AREAS OF SYSTEM UNCERTAINTY DURING THE PERIOD CONTINUES
TO SURROUND THE DEEP UPPER LOW/TROUGH AS IT SHIFTS OUT OF THE GREAT
LAKES/NORTHEAST. THERE ARE ALSO TIMING INCONSISTENCIES WITH THE
NEXT AMPLIFIED TROUGH IN THE EASTERN PACIFIC NEXT WEEK, WHICH
GUIDANCE SHOWS POTENTIAL FOR A CUTOFF LOW OFF THE WEST COAST WITH A
POSSIBLE SLOW SHIFT OF THE LARGER SCALE TROUGH TO/INTO THE WEST.
A COMPOSITE BLEND OF MODEL AND ENSEMBLE GUIDANCE OFFERED A
SEEMINGLY REASONABLE FORECAST BASIS. HOWEVER, GIVEN AMPLIFIED FLOW
TENDS TO LINGER ON THE SLOWER SIDE OF THE FULL ENVELOPE OF
GUIDANCE, OPTED TO APPLY SLIGHTLY GREATER WEIGHTING TO THOSE
COMPONENTS. THIS STAYS IN LINE WITH THE NATIONAL BLEND OF MODELS.
..WEATHER/HAZARDS HIGHLIGHTS
ONE HEAVY RAINFALL FOCUS DURING THE PERIOD WILL BE ACROSS THE
NORTHEAST ON SATURDAY AS THE UPPER LOW/ASSOCIATED TROUGH PIVOTS
THROUGH THE NORTHEAST, AIDED BY WRAP BACK MOISTURE FROM A SURFACE
LOW ALONG THE COAST. THE WPC DAY 4 EXCESSIVE RAINFALL OUTLOOK
SHOWS A MARGINAL RISK. FARTHER SOUTH, A LINGERING FRONT ACROSS
NORTHERN FLORIDA AND ALONG THE GULF COAST WILL CONTINUE TO FOCUS
SHOWERS AND STORMS, LOCALLY HEAVY, THROUGH AT LEAST THE WEEKEND.
THE BETTER CHANCE FOR HEAVIER QPF IS ON SATURDAY, AS COVERED BY A
WPC MARGINAL RISK ON THE DAY 4 ERO. DEPENDING ON WHAT FALLS WHERE
DURING THE SHORT RANGE PERIOD, A MARGINAL RISK MAY EVENTUALLY BE
NEEDED ON THE DAY 5/SUNDAY ERO AS WELL, BUT THE QPF SIGNAL STILL
DOES NOT SHOW SUFFICIENT FOCUS. FROM SUNDAY INTO EARLY NEXT WEEK,
MUCH OF THE COUNTRY SHOULD DRY OUT, THOUGH SHORTWAVE ENERGY WITHIN
AND AROUND WESTERN U.S. UPPER RIDGING MAY PRODUCE ISOLATED TO
SCATTERED RAINFALL WITH MOSTLY LIGHT AMOUNTS. MEANWHILE, TROPICAL
MOISTURE MOVING INTO THE SOUTHWESTERN GULF MAY BRING AN INCREASING
THREAT OF HEAVY RAIN INTO SOUTHERN TEXAS BY EARLY NEXT WEEK. SOME
GUIDANCE SHOW POTENTIAL OF LOCALLY SIGNIFICANT AMOUNTS TO MONITOR.
HAZARDOUS HEAT ACROSS THE SOUTHWEST AND INTO CALIFORNIA DURING THE
SHORT RANGE PERIOD SHOULD BE WANING BY THIS WEEKEND AS THE UPPER
RIDGE BEGINS TO SHIFT OUT OF THE WEST. ABOVE NORMAL TEMPERATURES
WILL ALSO SLIDE EAST WITH TIME FROM THE WEST INTO THE CENTRAL U.S.,
HOWEVER IT DOES NOT LOOK TO BE PARTICULARLY HAZARDOUS AT THIS
TIME. IN CONTRAST, A MUCH COOLER AIRMASS WILL FILTER EASTWARD FROM
THE NORTHERN PLAINS AND GREAT LAKES INTO THE EAST THIS WEEKEND AND
EARLY NEXT WEEK, WITH DAYTIME HIGHS 10-20 DEGREES BELOW NORMAL.
SANTORELLI/SCHICHTEL
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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