textproduct: NWS Wilmington

SYNOPSIS

Increasingly milder conditions finally return today and Saturday. An arctic cold front will move through on Sunday, bringing the coldest temperatures we've seen since last winter. Temperatures will gradually warm up next week as the center of high pressure moves overhead.

NEAR TERM /THROUGH TONIGHT/

The longwave upper trof continues to dominate the area, however it does temporarily de-amplifies this period. Mid- level s/w trof, ie. clipper type system, to track from the Midwest to off the Mid-Atlantic Coast, from early this morning thru late this aftn. Will observe SCT/BKN clouds from early this morning thru midday, improving there- after. Generally looking at mid and upper level clouds, ie. altocu and cirrus/cirrus stratus...generally AOA 10k feet. Conditions not conducive for any low level cloud development eventhough a weak sfc warm front will be in the neighborhood. Temps this period will see a slow moderation back to near normal or in the vicinity.

SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/

Quiet and mild Saturday, with mostly zonal flow aloft. High temperatures actually get a chance to reach a degree or two above normal for mid-December, which is the first time we've been able to say that all month so far.

Upper low in the Great Lakes tightens up as it pushes towards New England Saturday night, significantly pinching the associated trough. Southwesterly flow increases Saturday night, which helps push a weak warm front northward, moving from the coast to inland. This increases shallow moisture, creating more cloud cover overnight. Mild lows only dip down into the low-to-mid 40s inland, upper 40s at the coast. Then we transition the other way quite quickly and violently...

All eyes on a significant Arctic front that will race from the northwest to southeast Sunday. Moisture continues to increase ahead of this front, but it still remains rather shallow, most of it being locked to 850 mb and below. This creates only modest rain chances Sunday morning and midday. High temperature forecast still remains tricky here, depending on the timing of the front. Still expecting a gradient across the area, with some areas in the Pee Dee region struggling to hit 50, while other parts in the southern Grand Strand region might see 60. The current spread in the forecast guidance still shows a 6-10 degree swing in these highs, so the uncertainty continues. Now that we're entering the timeliness within the HREF, hoping to see this uncertainty decrease within the next forecast cycle.

Front moves through sometime Sunday afternoon, bringing a very sharp change in temperatures and dewpoints. Freezing temperatures already start settling in by around 7 PM EST that evening. Boundary layer winds still look breezy throughout Sunday night, creating a true advective freeze, nothing something we see much of around here. Low temperatures won't have any trouble at all dipping down into the mid- to-upper teens, while dewpoints crater towards the skin-cracking single digits. Winds may gust up to 20-25 mph, particularly earlier in the night. This combination of cold temperatures and breezy winds mean that wind chills very easily dive into the teens by bedtime, and then the single digits overnight. A Cold Weather Advisory looks all but guaranteed, where the apparent temperatures (wind chills) will hit 15F or lower.

For context, we issue Extreme Cold Warnings when apparent temperatures hit 5F or lower. Doesn't look like we'll get there, but it's very close (we could bottom out near 7F).

LONG TERM /MONDAY THROUGH THURSDAY/

Arctic high pressure settles in, and bone-chilling highs on Monday may not reach 40 degrees for most. The breeze gradually subsides throughout the day, calming by sunset. The air mass starts bouncing back just a tad by Monday night, with lows dipping down into the lower 20s. This resembles much of a radiational freeze, as opposed to an advective freeze. This is more of the status quo for the coastal Carolinas in winter. No Cold Weather Advisory here.

What goes down, must come back up, and that's the tone through the rest of the extended forecast. The Arctic high gradually settles into the Southeast and undergoes more air mass modification, looking more like the mild warmth that we're used to (it might even learn how to say "y'all"). Highs Tuesday creep into the upper 40s to near 50 under plenty of sunshine. Lows Tuesday night look to remain above freezing at the coast, dipping down a few ticks below freezing inland.

By Wednesday, the high pressure starts to make its way towards the Atlantic, setting up more onshore flow. Moisture and clouds rebound, and temperatures make a resounding comeback. Highs in the upper 50s to near 60 Wednesday become the mid-to-upper 60s by Thursday.

If you compare Sunday night's low temperatures to Thursday's high temperatures, that accounts for roughly a 50-degree swing in about 84 hours or so.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

VFR to dominate the next 24 hr 12Z Taf Issuance Period with the exception of the ILM terminal which may observe MVFR fog during the 06Z-12Z Sat period. Mid to upper level clouds to dominate thru 17Z, then just become thin/opaque cirrus there-after. Calm winds giving way to variable 4 kt or less...in lieu of going variable will identify a best direction. With a weak warm front poised to drape across portions of the Carolinas this aftn thru tonight and a weak sfc pg, will continue to identify a best wind direction at 4 to 6 kt speeds in lieu of going variable.

Extended Outlook...Predominantly VFR through the extended period except Sun morning where showers ahead of a cold front could potentially produce brief MVFR conditions at any 1 of the 5 terminals.

MARINE

Through Tonight...Light W to NW 10 kt or less winds early this morning will become SW to W 10 knots this afternoon thru tonight as a warm front lifts north across the area before stalling. Sfc pg to remain relaxed as evidenced by the progged wind speeds. Seas generally at 2 ft or less and comprised mainly by short period wind driven waves, with no measurable long period ground swell expected this period although a small SE swell tries to become more prevalent.

Saturday through Tuesday...Saturday, southwesterly winds linger near 10 kts and quiet seas hum near 1-2 ft. Overnight Saturday night, southwesterly winds increase to near 15 kts (gusts up to 20 kts) and seas increase to 2-4 ft ahead of an Arctic front that pushes through Sunday. Front moves through midday or early afternoon Sunday, and winds veer to the NNW, increasing significantly. At the very least, Small Craft Advisory conditions are a guarantee Sunday night into Monday morning, but with each forecast update, there is increasing confidence in gale force gusts. May need to consider a Gale Watch within the next 1-2 forecast cycles. Seas escalate to 3-4 ft at the coast, up to 6-7 ft 20 nm offshore. Gradient loosens throughout the day Monday, and winds around 10 kts gradually start to back towards the west Monday night through Tuesday, with seas slowly falling back down to 1-2 ft.

ILM WATCHES/WARNINGS/ADVISORIES

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