textproduct: NWS Wilmington

WHAT HAS CHANGED

Updated 00Z discussion covering the 00Z TAF period. No significant changes to the rest of the forecast. Cold temperatures remain a concern tonight, expect lows in the low to mid 20s. A few of our cold spots could fall into the upper teens.

KEY MESSAGES

1) Very Cold Temperatures Tonight, But Remain Above Cold Weather Advisory Criteria.

2) Warming Trend Kicks Off Wednesday.

3) Significant impacts appear likely from a winter storm this weekend. Freezing rain and sleet appear to be the most probable precipitation types, however accumulating snow cannot completely be ruled out.

4) An extended period of much-below normal temperatures will follow the winter storm early next week.

DISCUSSION

KEY MESSAGE 1: Very Cold Temperatures Tonight, But Remain Above Cold Weather Advisory Criteria.

High pressure currently over parts of the Mid South and Deep South will gradually scoot eastward towards the Carolinas and Virginia late tonight. We currently have a stream of cirrus pouring in from the west, but skies will clear out as the high approaches, pushing that cirrus southward. Calm winds and cold air will create some ideal radiational cooling tonight. Temperatures won't have a problem diving into the lower 20s across much of the area, sans perhaps the upper 20s at the coast. The traditional cold spots in parts of Bladen and Pender Counties will likely dip into the teens, thanks to the peat soils in these regions.

The apparent temperatures (in this case, wind chills) will be diving towards similar readings, thanks to the calm wind. In a breezier regime, we would perhaps consider a Cold Weather Advisory for tonight, but alas, that will not be the case. Advisory criteria calls for apparent temperatures in the 6F to 15F range, and we just don't get there.

Even so, that's bitterly cold. Wear your layers and stay warm!

KEY MESSAGE 2: Warming Trend Kicks Off Wednesday.

It's ironic, given what's coming this weekend. But a warming trend is on the way in the near term forecast, starting Wednesday. High pressure will move offshore, creating some return flow and moderating temperatures. Highs Wednesday afternoon get into the low- to-mid 50s inland, mid-to-upper 50s at the coast. This is still a pretty mild day by mid-late January standards, as these temperatures hover near or just 2-3 degrees below normal.

KEY MESSAGE 3: Significant impacts appear likely from a winter storm this weekend. Freezing rain and sleet appear to be the most probable precipitation types, however accumulating snow cannot completely be ruled out.

Shallow cold air will build in behind an arctic cold front Friday night. The high pushing this arctic airmass in may have a surface pressure in excess of 1050 mb and will source dry air with dewpoints between 925-850 mb falling to near 0 F across the eastern Carolinas.

While the low levels become cold and dry, a strong shortwave digging southeastward across the Rockies will nudge a cutoff low in the Desert Southwest back into the main jet stream flow. Pacific subtropical jet moisture aloft, plus increasing mid level Gulf moisture, will advect across the across the Carolinas.

Precipitation generated through mid level isentropic lift (300K-310K theta surfaces or approximately 700-550 mb) falling into the cold and very dry air below the cloud base will fall as a mix of precipitation types on Saturday. Sleet may end up being the most predominant type given the large evaporational cooling potential between the cloud base and the ground. This initial wave of precipitation could be rather light, at least until mid to late afternoon.

As the low levels saturate Saturday night via continued precipitation, we anticipate a transition over to mainly freezing rain with some sleet continuing inland. The heaviest precipitation rates are expected Saturday night into Sunday, coinciding with a long period of subfreezing surface temperatures. Regardless of how much heat was stored in road surfaces from the relatively warm mid-week weather, widespread icing may develop on surface roads and elevated structures.

Obviously there remains a good deal of model spread with possible accumulations at this extended time frame. NBM ensemble mean freezing rain probabilities for the event are 90 percent for 0.01" ice thickness, 50-70 percent for 0.25", and 20-50 percent for 0.50". The highest probabilities for large ice accumulations will exist for locations 20 or more miles inland for the coast. In addition to travel issues, tree damage and power outages may occur in association with these larger ice accumulations. Additionally, the 00z and 06z ECMWF maintained a slightly colder thermal structure through the event compared to model ensemble means from the same time. This alternate solution would keep more sleet and even snow falling (as opposed to freezing rain) across portions of Bladen, Robeson, Dillon, and Marlboro counties, resulting in less ice but possibly several inches of snow and sleet in this region.

Mid level winds should gradually veer more westerly Sunday night into Monday, shunting the best moisture offshore. Forecast precipitation chances fall below 10 percent by Monday afternoon.

KEY MESSAGE 4: An extended period of much-below normal temperatures will follow the winter storm early next week.

Models are showing strong signals for at least several days of well- below normal temperatures following the winter storm this weekend. From a human impact perspective this is particularly worrisome given the potential for power outages and difficult travel conditions.

Some melting will occur Monday as highs are expected to reach the mid to upper 30s, however temperatures should plunge into the teens Monday night away from the immediate coast. These temperatures will refreeze water on road surfaces and will pose a concern for people in unheated homes without power. Similarly cold conditions appear likely Tuesday into Tuesday night with continuing impacts expected for those without warm shelter.

AVIATION /00Z WEDNESDAY THROUGH SUNDAY/

VFR through 00Z Thursday. Calm winds overnight will gradually veer on Thursday from easterly in the morning to southerly by the end of the period. At the coast, winds may approach 5-10 knots and vary with marine influences, predominately southeasterly.

Extended Forecast... Chance of flight restrictions Thursday. Greater confidence in restrictions Thursday night and Friday with the next frontal system. This will give way to a winter storm over the weekend. High confidence in prolonged restrictions this weekend due to a winter storm impacting the region. Restrictions will likely start Saturday afternoon and continue through at least Sunday night.

MARINE

Through Wednesday...NNW winds at 5-10 kts will gradually veer to the NNE late tonight, to the NE by around sunrise Wednesday morning, and then to the east by late Wednesday morning, Winds then decrease slightly in the afternoon and become more variable as surface high pressure nears the waters. Seas linger near 2-3 ft.

Wednesday Night through Sunday...Light and variable winds are expected Wednesday night as a weak coastal trough develops offshore. Winds should become more uniformly northwesterly on Thursday as the trough drifts away.

An arctic cold front should reach the coast Friday afternoon or Friday night. This boundary will move offshore and will be followed by increasing north to northeasterly winds and much colder air building across the area through the weekend. Arctic high pressure will move eastward across the Great Lakes and New England late this week. Small Craft Advisory conditions (25 kt winds and 6 ft seas) are likely to begin late Friday night and continue into early next week. There is even some potential for gusts to reach gale force Saturday afternoon and evening. Widespread very cold rain (with even some sleet and accumulating freezing rain) is expected at the beaches beginning Saturday afternoon and lasting through Sunday.

ILM WATCHES/WARNINGS/ADVISORIES

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