Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC
Issued by NWS Raleigh/Durham, NC
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932 FXUS62 KRAH 251835 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 235 PM EDT Wed Sep 25 2024 .SYNOPSIS... Mid-level disturbances, in moist, southwesterly flow aloft, will interact with a stalled surface front that will weaken over the Carolinas and VA through mid-week. Tropical Cyclone Helene is forecast to make landfall in the Florida Big Bend late Thursday, then move quickly north, while weakening, through the southern Appalachians and OH Valley Friday and Friday night. && .NEAR TERM /TODAY AND TONIGHT/... As of 1120 AM Wednesday... Just minor forecast changes this morning. With the late-night / early-morning showers and storms having now pushed well to our north, the daybreak stratus is now evolving into streams of agitated cu as heating has pushed our SBCAPE to 1500-2500 J/kg thus far. With a SSE low level flow and 30-40 kt of effective bulk shear, development of isolated to scattered showers and storms is still expected. But the presence of some fairly deep dry air noted on WV imagery over all but our far NW will limit convective coverage, and will maintain lower chance pops, restricting higher pops to the Triad region and points NW. Temps are on pace to reach forecast highs in the low-mid 80s, so minimal changes there. -GIH Earlier discussion from 335 AM: Tropical Cyclone Helene is forecast to intensify as a hurricane as it begins to move north-northeastward across the eastern Gulf of Mexico. Deep southerly flow between a mid/upper-level low that will eventually cut-off over the lower MS and an upper level anticyclone over the western Atlantic will direct the deep fetch of tropical moisture north and set up a predecessor heavy rainfall event(PRE) over the spine of the Appalachians this evening and tonight. Across central NC, we`ll see a brief reprieve from the anomalous moisture, as drier air off the SE coast spreads west into the area. The ongoing area of heavy showers and storms over the northern Piedmont and northern coastal plain counties will lift north into VA through daybreak as the weak sfc boundary lifts north and drier spreads from the SE, ending the flooding rain threat. After a late morning/mid day lull in precip/rain, isolated to scattered weak convection will develop during the afternoon, with the best coverage expected across the western Piedmont. While scattered rain showers could linger across the far western zones overnight, the remainder of the forecast area should stay mostly dry. We`ll still have widespread cloudiness, with morning stratus lifting throughout the day. Slightly warmer with highs ranging from near 80 north t o mid 80s south. Lows 65-70. && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... As of 235 PM Wednesday... On Thursday morning, Hurricane Helene should be intensifying over the Gulf of Mexico as it moves north, likely to make landfall along the Florida Gulf Coast Thursday evening. Scattered showers and isolated thunderstorms will continue Thursday morning along the leftover boundary from today, slowly expanding to the east Thursday afternoon. Have maintained likely pops across western counties Thursday afternoon. As Helene weakens to a tropical storm by the time it reaches northern Georgia Friday morning, rainfall will expand farther across the forecast area Thursday night, with the greatest coverage and intensity of rainfall likely to occur Thursday night and Friday morning. 12Z models indicate that rain could come to an end a little quicker than previously forecast as the dry slot moves in from the south - likely pops will continue north of US-64 Friday afternoon, but pops should become more scattered across the south in the afternoon, and all locations should be dry by late Friday night. While there is still spread as to the exact time of Helene once it makes landfall, the overall trend across central North Carolina has been a reduction in rainfall totals. A general one to two inches of rainfall is expected, with greater amounts to the west. The maximum wind gusts remain generally unchanged, ranging from 20-25 mph across the east to 30-35 mph in the west. There have been some locations that have received as much as five inches of rain in the last three days. Considering how wet the ground is in some locations, despite wind gusts that are expected to remain below tropical storm status, there is the potential for many more trees to come down than would be expected for the given wind speeds. The preceding rainfall will also increase the risk for flash flooding and river flooding, although there is not enough confidence in higher rainfall rates to issue a flood watch. There will also be a risk for tornadoes on Friday with ample moisture and instability for thunderstorms. This threat will be evaluated more closely tonight and Thursday once additional high-resolution model guidance is available. High temperatures will range from the mid 70s in the northwest to the mid 80s in the southeast. Low temperatures will range from the upper 60s to the mid 70s Thursday night, then be in the mid to upper 60s Friday night as clouds clear out Friday night. && .LONG TERM /SATURDAY THROUGH TUESDAY/... As of 320 AM Wednesday... After a brief mostly dry period from Friday night into Saturday, tropical moisture associated with Helene`s remnants to our west will spread back into the area. There is a large amount of spread in ensemble guidance on where the low tracks. But regardless of the exact track, isolated to scattered showers and storms will again be possible on Sunday and especially early next week (maximized each afternoon and evening), when the latest deterministic guidance moves the system back east through the Mid-Atlantic as it opens up into a trough. The warmest day will be Saturday with mostly sunny skies, as forecast highs are in the lower-to-mid-80s. Highs then cool back to below normal by early next week as clouds and precipitation increase, but lows stay above normal (generally 60s). && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/... As of 225 PM Wednesday... Aviation conditions will be mostly favorable through this evening, but lowering cigs and increasing rain chances, esp W, will bring potential adverse conditions tonight. Pockets of MVFR cigs persist, but overall, conditions have improved to VFR over much of the area. Scattered showers are moving into southern sections currently, likely to affect FAY with brief MVFR conditions prior to 20z, and additional isolated to scattered showers and a few storms are possible through this afternoon, with low predictability at any given TAF site, although chances are best at INT/GSO/RDU. After 03z, low cigs are expected to form, dropping to IFR/LIFR at INT/GSO/RDU and MVFR at RWI/FAY, lasting through daybreak. A few showers are likely at INT/GSO late tonight and through Thu morning, but elsewhere, the best rain chances will hold off until after 16 Thu. Surface winds will be under 12 kts, lightest between sunset and sunrise, generally from the ESE or SE. Looking beyond 18z Thu, what is now Hurricane Helene is expected to make landfall in the central FL panhandle early Thu evening, then track N and NNE through GA and into eastern and central TN Thu night through early Fri afternoon. Moist flow ahead of and east of Helene will bring predominantly adverse aviation conditions to much of central NC Thu afternoon through early Fri morning, with periodic rain bands bringing occasionally sub-VFR conditions in moderate to heavy rain with isolated storms, along with frequent gusts over 20 kt. Low level wind shear may occur esp at FAY/INT/GSO early Fri morning, but confidence is low. Conditions will improve to VFR from S to N Fri, lasting through Sat. A chance of showers/storms will return esp to the NW Sun into Mon. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS/CBL NEAR TERM...Hartfield/CBL SHORT TERM...Green LONG TERM...Danco AVIATION...Hartfield