textproduct: NWS Wilmington

WHAT HAS CHANGED

Temperatures tonight and Tuesday night, although well below normal, are expected to remain above Cold Weather Advisory criteria of 15F. The chance for accumulating wintry precipitation has increased for Saturday into Sunday. While significant uncertainty remains with regard to precipitation type, there is better than a 50-50 chance we'll see impacts from ice or snow this coming weekend.

KEY MESSAGES

1) Unseasonably cold weather will be in place through Tuesday night.

2) The chance for accumulating wintry precipitation is increasing for Saturday into Sunday. While significant uncertainty remains with regard to specific P-type and timing, there is better than a 50-50 chance we'll see impacts from ice or snow this coming weekend.

3) Well-below normal temperatures are expected to persist behind the arctic cold front through at least early next week.

DISCUSSION

KEY MESSAGE 1...Unseasonably cold weather will be in place through Tuesday night.

A dry cold front will move across the area late this evening, with quickly dropping dewpoints and veering winds behind it. Low temperatures tonight will be in the low to mid 20s, with some lingering winds behind the front hindering true radiational cooling conditions. Reinforced cold air will keep high temps Tuesday roughly 10 degrees below normal in the mid to upper 40s under clear skies. Dewpoints could drop into the single digits inland Tuesday afternoon as dry air aloft is mixed down. High pressure overhead Tuesday night will allow for good radiational cooling, dropping temperatures down to around 20F. Lows in the teens will be likely in traditional cold spots, such as northern Pender and Bladen counties.

KEY MESSAGE 2...The chance for accumulating wintry precipitation is increasing for Saturday into Sunday. While significant uncertainty remains with regard to specific P-type and timing, there is better than a 50-50 chance we'll see impacts from ice or snow this coming weekend. Confidence is increasing that we will have a period of impactful wintry precipitation developing this weekend. While it's obviously too early for specifics given the inherent uncertainty in a 5- 6 day forecast, the potential for significant accumulations of freezing rain, sleet, or snow does exist across our portion of eastern North and South Carolina.

An arctic cold front should advance southward across our area Friday night or early Saturday. Shallow and very cold arctic air will build in behind the front. While the lowest 4000 feet of the atmosphere is cooling, a significant shortwave will move eastward across the Mid- Mississippi Valley and Mid Atlantic states Saturday into early Sunday, pulling Gulf and Atlantic moisture northward across the Carolinas.

Precipitation should begin as rain Friday Night, then gradually transitioning over to freezing rain or sleet Saturday and Saturday night as the cold air builds southward beneath the precipitation being generated aloft. The GFS has trended colder on its 12z run, limiting the strength and northward push of the mid level warm nose which would imply less freezing rain and more sleet/snow, however a large number of ensemble components within the NBM continue to indicate warm enough 850- 700 mb temps for freezing rain to be the primary P-type as the heart of the low level cold air builds in Saturday night into early Sunday. If you want to view a deterministic model that shows a strong warm nose, check the 00z Monday ECMWF which has 700 mb temps of +3C and 850 mb temps of +7C occurring with sub-freezing surface temps and precipitation Saturday night.

In terms of the probabilities of various precipitation types, we're up to about a 70 percent chance of at least 0.01" of freezing rain, and nearly 50 percent chance of 0.25" of freezing rain accumulating over a 48-hr period Saturday into Sunday night. Probabilities for snow are lower given the anticipated thermal structure aloft but still are as high as 40 percent in Wilmington and Florence for a measurable 0.1 inches of snow over the coming weekend.

Until a majority of models begin to look similar with temperatures aloft, we'll need to continue to indicate a broad range of possible precipitation types in our forecast.

KEY MESSAGE 3...Well-below normal temperatures are expected to persist behind the arctic cold front through at least early next week.

In addition to the threat posed by wintry precipitation, temperatures are expected to remain well below normal beginning Saturday and continuing through at least early next week.

Low temperatures will likely end up deep in the 20s Saturday night, followed by teens or lower 20s on Sunday night. The intensity of the cold may ultimately depend on how much snow vs. ice falls Saturday into Sunday since snow-covered ground on calm, clear nights can result in exceptionally cold temperatures.

00z ECMWF ensembles show below normal temperatures continuing through the end of January!

AVIATION /00Z TUESDAY THROUGH SATURDAY/

VFR conditions will prevail through TAF period.

Extended Outlook...VFR likely through Wednesday. Restrictions may return with another frontal passage Thursday and Friday.

MARINE

Through Tuesday...Westerly winds 10-15 kts through this evening will shift to northerly by Tuesday morning as a dry cold front moves offshore. Wind speeds will then weaken during the day Thursday with high pressure building in from the west. Seas 2-3 ft through Tuesday, combination of a 2 ft 9 sec SE swell and wind chop.

Tuesday Night through Saturday...Canadian high pressure will move off the Mid Atlantic coast Tuesday night. Northeast winds 10-15 kt should veer a little more easterly Wednesday, then should diminish Wednesday night as a weak coastal trough develops near the Carolina coastline. This could lead to a period of variable winds less than 10 knots and maybe even some patchy rain. The trough should push out to sea Thursday with light offshore winds anticipated.

Big changes will arrive Friday night or early Saturday as a strong arctic cold front moves through from the north. Wind speeds will increase behind this front to 25 knots, and perhaps even higher later in the weekend. There's also a growing potential for rain, sleet, or even snow over the coastal waters this coming weekend.

Seas should remain 3 feet or less through Friday, but should build substantially after the arctic front moves through Friday night or Saturday. Small Craft Advisory conditions appear likely on Saturday with gale force winds possible later in the weekend.

ILM WATCHES/WARNINGS/ADVISORIES

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