Area Forecast Discussion
Issued by NWS Wilmington, NC

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276 FXUS62 KILM 170520 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 1220 AM EST Wed Jan 17 2018 .SYNOPSIS... Weak high pressure will slip offshore tonight. A cold front will cross the coast late Wednesday, bringing a mix of rain and snow, with accumulations possible inland Wednesday and Wednesday evening. Cold and dry arctic air will build in late Wednesday and Thursday. Temperatures will warm into the weekend, as high pressure moves offshore. Another cold front will bring rain chances early next week. && .NEAR TERM /THROUGH WEDNESDAY/... As of 830 PM Tuesday...No changes to the Winter Wx Advisory for the 6 counties. Applied some modifications to hourly temps, dewpoints and winds mainly lowering all of these parameters this evening based on observed temps with fcsts running too mild. Thin cirrus overhead and winds decoupling after sunset aided by a sfc based inversion setting up, these rad cooling conditions aren`t the best but enough for temps to fall quicker than what was fcst from guidance. With opaque cirrus increasing late this evening along with mid-level clouds during the pre-dawn hrs, temps will likely bottom around midnight followed by either remaining steady or exhibit a slow rising trend toward daybreak Wed. Previous..................................................... As of 300 PM Tuesday...Main headline for the near term, `Winter Weather Advisory` posted for inland portions of the area, for the potential of around an inch of snow, possibly closer to 2 inches over northern Marlboro county. A rain/snow mix will be underway at daybreak west of I-95, spreading eastward, with the leading edge of stratiform precipitation reaching the coast midday to early in the afternoon. Areas outside of the advisory, may see snow as well, but less than 1 inch of accumulation expected. The rain and snow will be off the coast in the evening Wednesday. Adjustments to the Advisory may be made overnight with new data, and we cannot rule out completely, a `Winter Storm Warning` if 2 inches is expected within 12 hours for portions of the I-95 corridor. Evaporative cooling and cold air advection will keep maximum temperatures locked into the 30s inland, and 40s near the coast Wednesday. Snow may not change over to rain near coastal zones, or if so, not until evening, when temperatures finally become cold enough, chasing the moisture to sea. && .SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/... As of 300 PM Tuesday...A northwest flow aloft will prevail through the period as surface high pressure builds in from the west. Essentially a temperature forecast as any moisture will be well off to the northeast. Lows Thursday morning will be in the lower 20s with daytime highs in the lower to middle 40s. Some air mass modification will keep temperatures a little warmer Friday morning with mostly middle 20s. && .LONG TERM /FRIDAY THROUGH TUESDAY/... As of 300 PM Tuesday...Surface high centered over southern AL Fri morning will shift east for the weekend, moving offshore. Very dry air in place, precipitable water will be under a quarter inch Fri and Sat, ensure the region remains dry. Near climo temperatures Fri will start warming Sat as weak low level warm advection begins. The progressive mid-level pattern, responsible for the surface high`s rapid shift east, will become a little more amplified as a southern stream shortwave moves along the Gulf Coast this weekend. The wave weakens/opens up as it lifts into the southeast and it seems unlikely that it will be accompanied by any rainfall as it passes late Sat night and Sun. Weak 5h ridge starts to build over the western Atlantic early next week which, coupled with low level warm advection, leads to a warming trend Sun and Mon. Best precip chances during the period continue to be associated with cold front crossing the area late Mon or Mon night. Parent low remains displaced well north of the area, moving across the Great Lakes and southern Canada. Although there is a brief period of moisture return ahead of the front, moisture will be limited and current chc pop Mon and Mon night seems reasonable. Cold advection is limited behind the front as the 5h trough lifts northeast instead of moving overhead. Lack of cold advection combined with the return of the 5h ridge over the western Atlantic will keep temperatures near to slightly above climo in the post front environment. && .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/... As of 06Z...Thickening and lowering clouds are expected through 15-18Z across the area as an arctic cold front approaches from the west. Light precipitation occurring on and just behind the front will reach FLO and LBT around 17Z, probably beginning as just a cold rain. Cold air pouring in from the west should change this rain over to snow at FLO and LBT by 19-20Z with visibilities expected to fall to 1-3 miles and ceilings diving below 1000 feet at times. Models still have a good 3 hours difference between them as to the exact time of the changeover to snow making this the lowest confidence portion of the forecast. An inch or two could accumulate in the LBT area, with lesser amounts expected at FLO. For the coastal airports (ILM, MYR, CRE) rain won`t arrive until around 21Z, and the changeover to snow here may not occur until 01Z Thursday. Wilmington has a better potential than the Myrtle Beach airports to experience IFR conditions during the evening hours with any snow. Clearing should advance across the area from west to east late in the forecast period. Extended Outlook...VFR. && .MARINE... NEAR TERM /THROUGH WEDNESDAY/... As of 830 PM Tuesday...Raised a brief SCA for all waters from Wednesday Evening thru midday Thursday. Have staggered the beginning and ending of the SCA across the ILM SC and NC waters using a 3 hour window. Weak sfc bubble high across the area waters this evening and overnight resulting in a relaxed sfc pg that will produce a northerly wind at only 10 kt or less overnight. Significant seas will basically be a function of a rather decent 2.5 to 3.5 foot Easterly ground swell at 9 to 11 second periods. Not much input from locally produced wind waves. Previous......................................................... As of 300 PM Tuesday...A decent marine period, prior to worsening late on Wednesday, as a cold front spills colder air over the waters. N-NW winds and wind-chop, mainly light, will mix with E swell this period tonight and Wednesday, with significant wave heights of 4 feet or less. Late Wednesday, rain may begin to reduce visibilities. SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/... As of 300 PM Tuesday...Expect blustery winds behind a departing potent mid level system on the order of 20-25 knots from the northwest for a few hours. With the new airmass coming in from the west, cold air advection isn`t as strong as we have seen the past few events and winds diminish quickly Thursday to 10-15 knots from the west/northwest where they will remain for the most part through Friday morning. Significant seas will be 4-7 feet early on falling in concert with the winds to 2-4 feet by Friday morning. LONG TERM /FRIDAY THROUGH SUNDAY/... As of 300 PM Tuesday...Weak surface high southwest of the waters Fri morning will quickly shift east. Southwest flow on the low end of the 10 to 15 kt range Fri drops to around 10 kt by Sat morning. The center of the high expands over the western Atlantic with the surface pressure gradient becoming ill-defined. Winds will drop under 10 kt late Sat night and remain light and variable Sun with the surface ridge axis in the region. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...Winter Weather Advisory from 4 AM early this morning to 7 PM EST this evening for SCZ017-023-024. NC...Winter Weather Advisory from 4 AM early this morning to 7 PM EST this evening for NCZ087-096-105. MARINE...Small Craft Advisory from 7 PM this evening to 10 AM EST Thursday for AMZ254-256. Small Craft Advisory from 10 PM this evening to 1 PM EST Thursday for AMZ250-252. && $$ SYNOPSIS...SHK NEAR TERM...DCH/MJC SHORT TERM...SHK LONG TERM...III AVIATION...TRA

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