705
FXUS02 KWBC 251859
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 PM EDT WED SEP 25 2024
VALID 12Z SAT SEP 28 2024 - 12Z WED OCT 02 2024
..PATTERN OVERVIEW AND GUIDANCE/PREDICTABILITY ASSESSMENT
MODELS AND ENSEMBLES HAVE COME INTO BETTER OVERALL AGREEMENT FOR THE
WEEKEND INTO EARLY NEXT WEEK. THIS GENERALLY INCLUDES THE LATEST
GUIDANCE FROM THE 12Z CYCLE. A BLOCKY SPLIT FLOW PATTERN DEVELOPS
ACROSS MUCH OF THE COUNTRY AS HIGHLIGHTED ALOFT BY A WARMING
ROCKIES/SOUTHWEST RIDGE AND A LOW/TROUGH LIFTING OVER THE CANADIAN
MARITIMES, AND A CUTOFF LOW OVER THE MID-SOUTH. POST TROPICAL
CYCLONE HELENE WILL WEAKEN INTO THE WEEKEND OVER THE MID-SOUTH
ENTRAINED INTO THE CUTOFF LOW, BUT REMAINS A SLOW TRANSLATION
RAINFALL/RUNOFF THREAT THERE AND WITH TRAILING MOISTURE INTO THE
SOUTH-CENTRAL APPALACHIANS. MEANWHILE, FORECAST SPREAD INCREASES
OVER TIME WITH MORE PROGRESSIVE AND ENERGETIC FLOW FROM THE
NORTHEAST PACIFIC THROUGH THE NORTHWEST AND DOWNSTREAM. GUIDANCE
VARIES WITH THE EXTENT OF POTENTIAL SOUTHEASTWARD DIGGING OF UPPER
TROUGH ENERGY,
OVERALL, A GENERAL DETERMINISTIC MODEL BLEND, ALONG WITH THE
NATIONAL BLEND OF MODELS, SEEMS TO OFFER A GOOD COMPROMISE
FORECAST THROUGH MONDAY, ALBEIT WILL SMOOTHED DETAIL THROUGH
MEDIUM RANGE TIME SCALES. MORE OF THE ENSEMBLE MEANS WERE INCLUDED
GOING INTO TUESDAY/WEDNESDAY.
..WEATHER/HAZARDS HIGHLIGHTS
MOISTURE FROM WHAT WILL BE THE REMNANTS OF HELENE, IN COMBINATION
WITH A LINGERING UPPER LOW OVER THE OHIO VALLEY, WILL RESULT IN
CONTINUED SHOWERS AND SOME THUNDERSTORMS FROM KENTUCKY/TENNESSEE
EASTWARD TO THE MID-ATLANTIC REGION ON SATURDAY, ALBEIT MUCH
LIGHTER IN INTENSITY COMPARED TO THE DELUGE OF RAINFALL EXPECTED
PRIOR TO THIS. AFTER EVALUATION OF THE 12Z MODEL GUIDANCE SUITE,
THE MARGINAL RISK AREA FOR DAY 4/SATURDAY IS NOW DISPLACED SOME TO
THE EAST COMPARED TO THE INITIAL OVERNIGHT ISSUANCE, GIVEN A FASTER
TREND TO EJECT THE UPPER LOW FROM THE OHIO VALLEY. THIS ALSO HOLDS
TRUE GOING INTO DAY 5/SUNDAY, WITH THE MARGINAL RISK MAINLY
CONFINED TO THE CENTRAL/SOUTHERN APPALACHIANS WHERE UPSLOPE FLOW
MAY LEAD TO SCATTERED INSTANCES OF HEAVIER RAINFALL. EVEN THOUGH
THE EXPECTED RAINFALL DURING THIS PERIOD SHOULD NOT BE ALL THAT
HEAVY, THE EXTREMELY SATURATED SOILS WILL BE AN AGGRAVATING FACTOR
IN TERMS OF THE FLOODING POTENTIAL. THE MARGINAL RISK AREA THAT WAS
OVER FLORIDA ON DAY 4 HAS BEEN DROPPED WITH LESS OF AN EXCESSIVE
RAINFALL SIGNAL IN THE MODEL QPF.
TEMPERATURES ARE EXPECTED TO REMAIN WARM ACROSS MUCH OF THE WESTERN
U.S. AND INTO THE NORTH-CENTRAL U.S. FOR THE UPCOMING WEEKEND, WITH
HIGHS RUNNING UP TO 15-25 DEGREES ABOVE AVERAGE FOR PORTIONS OF THE
DAKOTAS AND INTO EASTERN WYOMING. EXCESSIVE HEAT WILL ONCE AGAIN
MAKE WEATHER HEADLINES FOR THE LOWER ELEVATIONS OF THE DESERT
SOUTHWEST WITH HIGHS APPROACHING 110 DEGREES FOR THE NORMALLY
HOTTER LOCATIONS OF SOUTHEAST CALIFORNIA AND SOUTHERN ARIZONA. MOST
OF THE EASTERN U.S. SHOULD BE NEAR AVERAGE FOR HIGHS, AND ABOVE
AVERAGE FOR OVERNIGHT LOWS OWING TO GREATER CLOUD COVER AND HUMIDITY
LEVELS.
HAMRICK/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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