Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 260155 AFDRAH AREA FORECAST DISCUSSION National Weather Service Raleigh NC 955 PM EDT Wed May 25 2022 .SYNOPSIS... High pressure will remain north of the area through Thursday, bringing continued cool weather to the region tonight. Low pressure will approach the region Thursday night into Friday, bringing the potential for showers and storms, along with locally heavy rainfall on Friday. Weak high pressure will follow the front into the weekend. && .NEAR TERM /THROUGH TONIGHT/...
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As of 955 PM Wednesday... Thick low clouds and patchy drizzle will be the story tonight, esp across northern & NE sections. The latest surface analysis shows low pressure just off the central Outer Banks along an inverted trough off the Southeast coast and connected to a CAD front stretching across S SC into N GA, while a narrow ridge of cool/stable high pressure noses in from the NE. The strong low level stability is evident on the 00z GSO sounding, with high RH through the surface to 850 mb depth across central NC and to the NE and E. The nearshore surface low will reinforce the diffluent NE flow into central NC, and this is topped by E and ESE flow around 930-900 mb, generating sufficient weak moist upglide for patchy drizzle esp across the NE sections. This should persist overnight as the low drifts WNW to the central and N coast of NC. The surface cool air advection is rather weak, and with the clouds inhibiting radiational cooling, current temps are already within a category or so of expected low over much of the area, except in the far S where clouds have been minimal thus far this evening but where stratus should eventually spread into by midnight or soon thereafter. Lows in the upper 50s to lower 60s. -GIH Earlier discussion from 215 PM: CAD regime remains in place across the area this afternoon but as expected, some of the cloud cover to the south has eroded considerably. This has yielded mostly sunny skies across the Sandhills along with an increase in temperatures into the mid 70s. Meanwhile to the north (generally along and north of US 64), skies remained overcast with temps still lingering in the low to mid 60s. For the rest of the afternoon, expect the clearing line to continue moving northward up to, and through, the Triangle and at least parts of the Triad, before returning southward again as stratus redevelops by mid evening into the overnight hours. Where clearing is realized, there could be a quick late-day jump in temperatures into the mid 70s but elsewhere (along the NC/VA border) expect temp to remain steady in the mid 60s. Tonight temperatures will be fairly uniform with upper 50s to lower 60s the most likely range for low temps.
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&& .SHORT TERM /THURSDAY AND THURSDAY NIGHT/... As of 215 PM Wednesday... Warm advection aloft will increase during the day tomorrow as a 590dm H5 ridge slides farther off the coast. A deepening upper low and associated upper divergence (presently over the southern Plains and Deep South) will migrate eastward throughout the day, beginning the process of eroding the wedge front and ushering in a return of warm temps and elevated dewpoints. As WAA strengthens throughout the day, a few showers should develop across the far western Piedmont and should eventually make a run at the Triad during the afternoon hours. Instability and shear aren`t terribly impressive tomorrow ahead of this approaching low, but 0-1km shear could be maximized in the vicinity of the rapidly retreating wedge front across the Triad late in the day. Will carry some likely PoPs in the west, tapering down to less than 10 percent from the Triangle eastward where the upper ridge will remain the dominant factor in tomorrow`s weather. Surface based instability wanes quickly with the loss of daytime heating Thursday night but with falling heights aloft and steepening mid level lapse rates, some degree of elevated instability is likely to persist through the overnight hours and I`ll maintain a mention of thunder throughout the night. Showers are likely to develop and re-develop at times Thursday night into Friday morning in the west and I will keep PoPs elevated west of the Triangle through 12Z Friday. Ridging to the east should keep conditions dry elsewhere. Temperatures will be noticeably warmer tomorrow with highs returning to the low/mid 80s. Lows on the mild side within the pre-frontal warm sector in the mid/upper 60s. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... As of 300 PM Wednesday... Friday and Friday night: A potent mid/upper low (around two standard deviations below normal) across the Ohio Valley Friday morning will lift northeast towards the Mid-Atlantic by Friday night and weaken through the period. The associated trough will swing across central NC Friday during the day, and exit east off the coast Friday evening. A surface low will follow a similar path to the mid/upper low, with the cold front lagging behind the trough and not pushing across our region until late Friday. Precipitable water values will increase to around 1.75" (around two standard deviations above normal) ahead of the trough as south to southwesterly flow at H500 increases to 50 kts. Heavy rainfall and training storms on already saturated soils will increase the risk of flash flooding across the region. WPC has increased the Excessive Rainfall Outlook to a Slight Risk of flash flooding throughout the period. MLCAPE of 2000-2500 J/kg, 0-6km shear of 40-50 kt, plentiful moisture and diurnal heating will all help develop organized strong to severe storms across the region as the main line of storms pushes east during the day. Damaging wind gusts and large hail are the main threats, however 0-1 km shear to 30 kt and 0-1 SRH of 200-300 m2/s2 will increase the chance of tornadoes, as well. Timing of the main line of convection still varies among model solutions, however general consensus has slowed down the line slightly, moving across the western half of the region by early afternoon and the eastern half of the region by late evening. SPC still has most of our area under a Slight Risk of severe thunderstorms through the period. Showers and thunderstorms should exit the region by late Friday night as conditions dry out behind the weak cold front. Highs will range from the mid 70s to mid 80s, with lows in the 60s. Saturday through Sunday: The mid/upper trough exits off the coast early Saturday, then heights slowly build through the weekend as an upper ridge builds north from the Deep South to the OH Valley. At the surface, high pressure will build across the Mid-Atlantic, and switch surface flow from westerly to northerly to easterly by the end of the weekend. Subsidence will help keep conditions dry for most of the holiday weekend, with highs slowly increasing to just above seasonal normals by Sunday. Lows will be near normal, ranging from the upper 50s to mid-60s. Memorial Day through Wednesday: The large ridge will remain to our north through the period, and slightly flatten over time. PWs will increase early to mid-next week, and increase chances of diurnal showers and thunderstorms through the period, with less confidence in storms Memorial Day compared to later in the period on Wednesday. Highs will slowly increase to the upper 80s and low 90s, with lows in the 60s. && .AVIATION /00Z THURSDAY THROUGH MONDAY/... As of 819 PM Wednesday... The CAD regime will remain firmly in place tonight over central NC with predominantly northeasterly flow at the surface. MVFR stratus this evening are expected to steadily lower tonight to IFR/LIFR area wide. A weak low pressure system just off the NC coast will retrograde inland tonight and bring the potential for LIFR fog to northeast NC. Confidence is medium-low on whether or not this fog will reach the RWI terminal or if just enough flow/moisture will lead to a light drizzle. As for the 00z TAF package, have opted for the fog scenario, but this may need to adjusted as the surface low creeps inland tonight. Conditions will slowly improve Thursday morning with VFR returning to all terminals expect for the Triad (GSO/INT) which will likely have some lingering MVFR ceilings through the remainder of the TAF period. Looking beyond 00z Friday, showers and storms currently over MS/AL border will slowly move northeast Thursday and begin encroaching on INT/GSO after 00z Friday, but recent guidance depicts the heaviest precipitation remaining west of the terminals until Friday morning. Sub-VFR conditions likely at times at all sites on Friday as a slow moving strong cold front moves through the area. Thunderstorms with gusty winds and locally heavy rain possible at all terminals. A gradual improvement in conditions is expected Saturday through Monday. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Leins NEAR TERM...Hartfield/Leins SHORT TERM...Leins LONG TERM...JJT AVIATION...Swiggett/Leins

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