textproduct: NWS Wilmington

WHAT HAS CHANGED

A combination of slightly warmer temperatures tonight and no wind has resulted in apparent temperatures above Cold Weather Advisory thresholds.

KEY MESSAGES

- 1) Temperatures well below normal will result in periods of dangerously low wind chill temperatures below 16 degrees for the next week.

- 2) Developing low pressure off the Southeast coast this weekend could bring winter weather and hazardous travel conditions to the area.

DISCUSSION

KEY MESSAGE 1...Temperatures well below normal will result in periods of dangerously low wind chill temperatures below 16 degrees for the next week.

A series of arctic air masses moving over the Southeast the next week will keep temperatures 10-20 degrees below normal. A Cold Weather Advisory may be needed for a portion of the area Thu night and is likely for inland areas Fri night. Extreme Cold Warnings may be needed this weekend and potentially for the start of next week.

KEY MESSAGE 2:...Developing low pressure off the Southeast coast this weekend could bring winter weather and hazardous travel conditions to the area.

Confidence in the presence of a system off the Southeast coast this weekend continues to increase, but the finer details remain in question. Very cold air will be in place, with temperatures 10-20 degrees below normal. A southern stream shortwave helps develop a surface low along the Gulf coast late this week, which then moves across northern Florida before heading northeast off the coast. Meanwhile a 5h trough dropping south from the Great Lakes will interact with the offshore low. The timing of the interaction and the location of these 2 features at that time will determine if the local area gets precipitation (mainly in the form of snow given thermal profiles) and how much falls. There are several key differences in the way the 5h trough is being handled by the guidance. It's speed, tilt, strength will all be factors in determining where the snow falls and where the accumulation gradients set up.

This is likely to be a system where snow totals could range several inches across county. So needless to say, confidence with respect to the finer points of the forecast remains quite low given the event is still several days out. Do have high confidence in snow vs sleet/freezing rain, where precipitation falls, and do have high confidence in the presence of the surface and 5h lows. This will allow for rapid strengthening of the low offshore, with the general consensus suggesting this will happen north of the area. Dry air wrapping around the 5h low is another source of forecast uncertainty. If the dry slot is stronger and faster than the guidance is depicting, total QPF could end up lower. Considering all the sources of uncertainty and looking at the ensemble data and the probabilistic data sets of the NBM can make a few educated guesses. Best chance for any snow would be Sat into Sat night. Likely total QPF is on the order of 0.20"-0.40", however if everything lines up perfect QPF could be 2 or 3 times higher. Still a lot of details to be sorted out the next few days. No plans for watches tonight, but if trends continue would not be shocked to see them issued tomorrow.

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/

High confidence in VFR thruout the 24 hr TAF Issuance Period. Only clouds to contend with will be thin/opaque cirrus at 20k-30k ft thru this afternoon. Brief NW to N winds surge around 10 kt thru midday. Winds back to the W-SW this afternoon and drop to aob 5 kt this evening. Followed once again by another mini surge, NW-N 5-9 kt during the pre-dawn Thu hrs.

Extended Forecast... VFR to dominate through Friday. Increasing confidence for flight restrictions this weekend as a potentially strong winter storm affects the Carolinas.

MARINE

Through Tonight... Re-enforcing cold surge to affect the area waters this morning, instigated by a CFP during the pre-dawn hrs, followed by a brief CAA surge accompanied by a semi- tightened sfc pg thru midday. The NNW-N wind surge will diminish-some this afternoon thru tonight, to a SW-WSW direction as the sfc relaxes and the CAA turns neutral. Seas generally 2 to 4 ft and primarily associated with short period locally produced wind waves. An underlying small Easterly swell around 10 seconds will remain present and accounted for.

Thursday through Sunday... Northerly flow will be the theme into next week. Weakening northwest surge Thu morning with winds then veering to northeast Thu night into Fri. Low pressure developing off the coast moves northeast, rapidly strengthening at some point (likely once its north of the waters) with northerly winds increasing to at least gale force and possibly hitting storm force. Conditions Fri night will rapidly deteriorate, expect a weekend of headlines. Initially seas are limited to 2-3 ft by the offshore component, but as winds veer to northeast Fri into Sat seas will build. Strongest winds will be offshore/northwest later Sat and Sun, but even with the offshore component the strength of the winds builds seas to 6ft or higher with potential for double digit seas Sun. Although a weak easterly swell will be present, the wind wave, from the south Thu into Fri and then Northeast by the weekend, will be the dominant wave.

ILM WATCHES/WARNINGS/ADVISORIES

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