textproduct: NWS Wilmington

WHAT HAS CHANGED

Forecast high temps have been nudged a bit higher Tuesday through Thursday. The anticipated timing of Thursday's cold front has shifted a little later in the day.

KEY MESSAGES

1) Early morning fog on land as well as periods of sea fog will continue to impact the area and coastal waters through Wednesday.

2) An extended period of warm temperatures will continue through the first half of Thursday.

3) A strong cold front arriving Thursday will bring thunderstorms, then a significant airmass change late Thursday into Friday.

DISCUSSION

KEY MESSAGE 1: Early morning fog as well as intermittent sea fog will continue to impact the area and coastal waters through Wednesday.

Continued advection of abnormally warm and moist air will maintain a risk for the development of sea fog over the waters, mainly during the overnight through midday period. Light winds over Monday night and Tuesday night will also bring a risk for fog, especially for areas closer to the coast. Fog over land and water may become dense at times, with visibilities reduced to one quarter mile or less during the early to mid-morning hours. An approaching cold front will bring an increase in winds on Wednesday which will continue through its passage on Thursday. These increased winds will significantly lower the risk for fog on land, although areas right along the coast may still see sea fog reduce visibilities until winds are high enough to mix out fog over the waters.

KEY MESSAGE 2: An extended period of warm temperatures will continue through the first half of Thursday.

A humid subtropical airmass brought northward by the flow around Bermuda High Pressure will continue for the next few days. Inland from any cooling seabreeze effects, high temperatures will continue to run in the 80s, perhaps even approaching 90 degrees across parts of the Pee Dee region on Wednesday. This is well-supported by forecast 850 mb temps in the +13 to +14C range, about 5-6C above normal and a full degree C above the climatological 90th percentile values for mid March.

Unseasonably high dewpoints and steady south to southwest winds Tuesday night and again Wednesday night should keep lows generally in the 60s, around 20 degrees F above normal for this time of year.

Assuming our forecast works out, we'll end up with six consecutive days of 80+ degree highs in Lumberton and seven in Florence, the first time this has happened since late September of last year. Historically March usually records three days in the 80s in Lumberton and five in Florence, so this month is already above normal for warm days with over half the month still to go.

KEY MESSAGE 3: A strong cold front arriving Thursday will bring thunderstorms, then a significant airmass change late Thursday into Friday.

Today's new suite of models have slowed the arrival of the strong cold front on Thursday down significantly. The 12z GFS and Canadian both show the front swinging across the eastern portions of North and South Carolina between 10am and 2 pm, with last night's 00z ECWMF even a couple hours behind that. This should allow enough time for temperatures to rise into the 70s before strong cold advection begins behind the front.

On Thursday there should be an expansive area of showers and embedded thunderstorms produced by the good low-level convergence along the front paired with ascent ahead of a well-positioned upper trough racing in from the west. Forecast wind profiles at this time range don't show significant helicity that would support a tornado threat, however CAPE in the 500 J/kg (GFS) to 1500 J/kg (NAM) range along with 0-6 km bulk shear approaching 50 knots could support organized multicells and bowing line segments with a potential for damaging wind gusts. This severe weather threat will at least partially depend on just how many hours of destabilizing sun can sneak in ahead of the front's arrival.

Behind the front, colder and much drier Canadian air will build across the Carolinas. Lows in the 30s and 40s are expected Thursday night and Friday night before rising back above normal again for the remainder of the weekend.

AVIATION /18Z MONDAY THROUGH FRIDAY/

Predominantly VFR is expected to continue into this evening with transient MVFR cigs possible for the next couple hours before the boundary layer deepens enough to keep daytime cumulus above 3kft. Otherwise, with light or calm winds expected again tonight, another round of mist/fog should develop. However, this is complicated by a deck of mid-upper clouds which is timed to pass overhead during the middle to latter portions of the night. As a result, confidence in the development of vis restrictions is limited for the inland terminals near I-95 and slightly higher for coastal terminals, where there is greater time to cool and develop mist. Thus, TEMPO groups have been added to the coastal terminals and focus on earlier in the night prior to the arrival of dense cloudiness. It is expected that the cloudiness will either stop or reverse any vis reductions that would be in place, but if the clouds are too thin, then vis reductions would continue. Sea fog may affect the Grand Strand terminals with LIFR vis as well, but this will also be modulated by the clouds. Any vis restrictions due to mist/fog should abate by 14Z- 15Z, if not sooner. In addition, some light showers may accompany this deck of clouds into the daylight hours, but any vis restrictions should be brief.

Extended Forecast...VFR conditions are expected for much of the extended period, but periods of fog could bring late night/early morning restrictions. Sea fog could advect into the Grand Strand terminals at times during this week.

MARINE

Tuesday night through Friday...Gradually increasing southwest winds are expected between high pressure centered east of Bermuda and an approaching cold front from the west. Winds near 10 knots Tuesday night should increase to 15 knots Wednesday afternoon, then to near 20 knots late Wednesday night into Thursday. Areas of sea fog may continue to develop as subtropical moisture brought northward from Florida is chilled to its dewpoint across our still-cold nearshore ocean where water temperatures are only in the lower to middle 50s.

Models over the past 24 hours have slowed the approach of the front down Thursday, implying it may not arrive at the Carolina coastline until afternoon. The front will be accompanied by a sudden shift to northwest and north winds and possibly a line of gusty showers and thunderstorms too. A transitory area of high pressure will build across North Carolina on Friday with much drier (good visibility) air, lighter winds speeds, and quickly veering easterly wind directions expected.

Through Tuesday... A surface high pressure ridge over the Atlantic will maintain generally south to southwest winds at 5-10 kts over the waters through the period with seas around 2-3 ft. Sea fog will remain a concern primarily during the overnight through morning timeframe with it becoming patchy during the late morning and afternoon. Seas will be primarily driven by a SE swell with a period of 9 sec. A lingering southerly wind wave of 1-2 ft with a period around 6 sec is expected to decay through tonight.

..................... Tue Mar 10 ... Wed Mar 11

Thu Mar 12 Wilmington NC......... 88 in 1974 ... 86 in 2016 ... 87 in 1990 Lumberton NC.......... 87 in 1974 ... 87 in 1925 ... 85 in 1925 N. Myrtle Beach SC.... 76 in 2017 ... 82 in 1997 ... 80 in 1943 Florence SC........... 92 in 1974 ... 86 in 2015 ... 88 in 1990

Lumberton and Florence are currently forecast to break record highs on Wednesday.

ILM WATCHES/WARNINGS/ADVISORIES

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