Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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543 FXUS62 KRAH 301627 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 1230 PM EDT Thu Mar 30 2017 .SYNOPSIS... Weak high pressure will extend into the area from the north today, then move offshore tonight. A storm system will approach from the west tonight, cross the area Friday, then move off the coast Friday night. High pressure will build in from the north over the weekend. Another storm system will affect the region Monday into Tuesday. && .NEAR TERM /THROUGH TODAY/... As of 1010 AM Thursday... Clouds are hanging tough over much of central NC this morning, not surprising given the deep (over 5k ft) low level moist layer noted on the 12z GSO sounding. High-res models show this thinning as the day progresses mainly along the edges (indirectly supported by fairly dry low levels seen on the experimental GOES-16 low level water vapor channel), although the moist isentropic upglide is expected to persist through the day over the NC Foothills and W Piedmont, so the broken to overcast skies should hold on over the NW and far W CWA today, with partial sunshine over the far E/SE Piedmont and Sandhills/Coastal Plain. Precip chances appear slim until evening at the earliest, given the lack of deep moisture and forcing for ascent until well after nightfall, so have trimmed back pops for today, leaving just isolated in the extreme W. In areas where the cooler/drier surface air building in from the NNE overlaps with the thickest cloud cover, temps will be coolest this afternoon, likely struggling to reach the 60 degree mark, while far southern and SE sections top out near 70. -GIH Earlier discussion from 425 AM: The southern edge of a surface high extending down into the area from the north is bringing easterly flow to the area but southeasterly flow along the Appalachians and as a result a growing area of MVFR stratus is starting to build in across the northwest Piedmont. This feature will be influential on today`s weather when it comes to sky cover, precipitation and ultimately temperatures. Later this morning drizzle or even light rain will be possible across the northwest Piedmont as more moisture flows into the area. Depending upon how thick the stratus becomes, and model soundings show a significant cloud deck about 8 kft thick, high temperatures under the stratus could be overdone. As a result have slashed temperatures across the north to below guidance with upper 50s in the Triad but a fairly tight gradient with lower 70s across the southern counties. The triangle will be a major gamble today with anything from lower to upper 60s possible. For now have chosen to go on the lower end but a safe bet will be the mid 60s.-RE && .SHORT TERM /THURSDAY NIGHT AND FRIDAY/... As of 420 AM Thursday... Attention will turn to the southwest on Thursday night as a warm front surges in and temperatures should actually begin to rise overnight at most locations. Good isentropic lift in the west will begin to encourage precipitation over the western portion of the CWA between 0-6Z Friday. Model forecast soundings are virtually saturated throughout the column with PW values near 1.3 inches. The low level jet structure is fairly unorganized early Friday morning and there are several small disturbances in the flow so expect several smaller waves of precipitation which could be scattered in nature at times. As the precipitation pushes eastward it could become a bit more organized into more multicellular or broken lines but shear will be decreasing at this time particularly in the lower levels as winds become southwesterly and more unidirectional with height. Instability will increase slightly with peak heating and a dynamic push from the left exit region of a 500 mb jet could cause a storm or two to become severe. SPC has the eastern half of the area in a marginal risk for severe wx with damaging winds the most likely threat. With decent moisture in this system expect rainfall totals anywhere from a half of an inch on the low end to about an inch on the high end. Temperatures will be tricky on Friday given the convection but with central NC in the warm sector for much of the day expect highs in the low to mid 70s in most locations. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... As of 405 AM Thursday... An energetic Pacific jet will send a series of significant shortwave perturbations into the west-central U.S., where the models indicate they will amplify toward the Four Corners/Srn Plains region and interact with an equally energetic southern stream. That interaction will ultimately shear the perturbations ENEwd into the Middle Atlantic states, with associated episodes of precipitation/convection, about every 72 hours in central NC. This a relatively persistent pattern from recent days, which included the round of convection from this past Mon night, and which will likely result in another one later tonight (highlighted in the short term discussion above). Fri night: The models are now in good agreement with the progression of the upper low initially over the Central Plains, to the nrn Middle Atlantic coast by late Fri night. An accompanying surface trough axis/secondary front will cross the ne Piedmont/nrn Coastal Plain with a lingering chance of showers and a storm or two Fri evening. Otherwise, clearing and cooling will occur, with lows in the lower to middle 50s. Sat-Sun: Beneath longwave ridging bulging Nwd from the Caribbean to central Canada, the weekend is expected to be dry, and mild, with a reinforcing dry frontal passage (the leading edge of a Pacific high) Sat night. Periods of stratocumulus may bubble beneath a strong, 5 k ft subsidence inversion, but not with enough coverage to significantly impact temperatures through the period. Highs in the upper 60s to 70s, warmest ahead of the reinforcing front on Sat. Lows, coolest Sun morning in the 40s, and about a category higher in return SEly flow and increasing deep moisture by Mon morning. The next couple of strong shortwave perturbations will follow on schedule and cross central NC late Mon-Mon night and again just beyond this forecast period (Thu). The result will be another likely probability of showers and storms late Mon-Mon night, preceded by possible weak in-situ CAD during the day Mon. It will otherwise be mild through the period, with temperatures mostly in the 70s and 50s for highs and lows, respectively. && .AVIATION /18Z Thursday through Tuesday/... As of 1230 PM Thursday... MVFR cigs over the far W (INT/GSO) will lift to VFR during the mid afternoon, while farther east at RDU/FAY/RWI, VFR cigs will hold for the rest of the daylight hours. Scattered showers will move into INT/GSO after 21z, however VFR vsbys and cigs should persist, with only brief MVFR conditions within short-lived heavier showers through this evening. Cigs are likely to drop back to MVFR then IFR around midnight (04z) at INT/GSO, after 2 am (06z) at RDU/FAY, and after 4 am (08z) at RWI, all as a storm system approaches from the W and SW tonight. Widespread MVFR to IFR vsbys within showers and thunderstorms are expected starting late tonight, tracking eastward through early Fri afternoon, ahead of an eastward moving cold front. The showers/storms and sub-VFR conditions are expected to push east of INT/GSO after 15z Fri, and RDU around 18z. Ahead of the front, through tonight, surface winds will be from the SSE, shifting to SW Fri morning, then to WSW with frontal passage at western sites late in the TAF valid period. Looking beyond 18z Fri: The trend from MVFR to VFR will progress eastward through RDU/RWI/FAY prior to 21z, as a cold front crosses the area. VFR conditions are expected to dominate through Sun as high pressure builds in from the north, although the moist low level flow from the NE may bring a short period of MVFR cigs mainly at RWI 03z-12z Sun (Sat night). Another storm system will bring a good chance of sub-VFR conditions and strong/shifting winds with height starting after 06z Mon (Sun night), dominating until Tue morning, when the system will move to our east with a trend back to VFR by Tue afternoon. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Hartfield NEAR TERM...Hartfield/Ellis SHORT TERM...Ellis LONG TERM...MWS AVIATION...Hartfield

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