textproduct: NWS Wilmington

WHAT HAS CHANGED

Confidence in a strong winter storm affecting the Southeast this weekend continues to increase.

KEY MESSAGES

1) An arctic front and a plume of Pacific moisture will come together this weekend creating a strong winter storm. Significant ice accumulations are possible, making travel dangerous while causing widespread power outages.

2) Temperatures well below normal expected early next week.

DISCUSSION

KEY MESSAGE 1: An arctic front and a plume of Pacific moisture will come together this weekend creating a strong winter storm. Significant ice accumulations are possible, making travel dangerous while causing widespread power outages.

Weak front moves into the area from the west on Fri, this front may be accompanied by some light showers, although the forcing is not very impressive. Flow aloft is progressive and while there will be a weak shortwave moving through the flat flow, its intensity in the guidance seems suspect so there could be a bit of feedback going on. Either way, not looking for much rain Fri. The shortwave exits late Fri into Fri night with post wave subsidence helping to end any lingering rain. The arctic front arrives Fri night into Sat with temperatures rapidly dropping and dewpoints crashing. Isentropic lift develops after midnight then gradually strengthens early Sat. The very dry low level air will help delay the onset of sleet or freezing rain, but only for so long. By midday most of the area could be seeing sleet and/or freezing rain. Interestingly some of the more reliable guidance has a drier Sat, possible indications the arctic air ends up being drier than expected? The front shifts offshore later Sat into Sat night and lingers into the start of next week. Precipitation continues through Sat night and Sun as a series of surface waves move along the front. These surface waves coupled with some slight warming in the low levels during the day could lead to frozen precipitation changing to liquid closer to the coast Sun. Hard to pick when and where several days out, but this will be something to watch. Event comes to an end as h5 shortwave dropping south across the Upper Midwest Sun night into Mon kicks the system east- northeast and shunts a large amount of dry air into over the region.

The cold air this weekend is very strong, but also very shallow with a prominent warm nose above it, even well inland. The depth of the cold air farther inland suggests sleet will be favored. There is likely to be a zone where the bulk of the event is freezing rain, but hard to pin down exactly where. Right now this appears to be east of I-95 and inland from the coastal counties. However, the location of the frontal zone offshore (and when it happens to waver closer to the coast or farther away) and timing of the waves will all play a role in determining precipitation type at any given time. Still a lot of details that need to come into focus before being able to say what impacts a specific area can expect. Does appear that at least a couple inches of sleet, with some snow mixed in, and significant ice accumulations (approaching or even exceeding 0.25")are possible. Worth noting those values are for areas that only see 1 type of precipitation during the event and not a mix of types. Although confidence in the storm occurring continues to increase ,confidence in the finer details remains much lower. For instance the 00Z CMC (and even the CMC Ensembles) backed off on the strength of the arctic air (especially along the coast), drastically reducing ice accumulations. Until these large swings in finer details are resolved it confidence in the what and when will remain low.

KEY MESSAGE 2: Temperatures well below normal expected early next week.

Temperatures well below normal this weekend will linger into the middle of next week, enhanced by left over ice and snow following the storm this weekend. Dangerously cold temperatures can be expected which will prolong travel issues and have significant impact on areas without power.

AVIATION /06Z WEDNESDAY THROUGH SUNDAY/

VFR. Winds ~5-7 kts after sunrise will come around from the NE to SE through the day. Increasing high clouds.

Extended Forecast...Restrictions may return as early as Thursday with an approaching front. A winter storm will impact the area this weekend with prolonged restrictions expected. VFR should return Monday.

MARINE

Through Tonight... Benign marine conditions. NE winds ~10 kts will become light and offshore tonight. Seas 2-4 ft.

Thursday through Sunday... Benign marine conditions Thu and Fri will start to deteriorate Fri night as an arctic front moves into the region. Gradient tightens early Sat with northeast flow increasing to 25-30 kt Sat. Strong northerly flow continues through the end of the weekend and headlines will be required into the start of next week. Depending on the strength of the surface high and any offshore waves of low pressure there is potential for winds exceeding gale force. Seas 2-3 ft through Fri start building Fri night as the winds ramp up. Potential for 10ft seas exists well away from shore over the weekend with a northeast wind wave becoming dominant.

ILM WATCHES/WARNINGS/ADVISORIES

NC...None. SC...None. MARINE...None.