textproduct: NWS Wilmington

WHAT HAS CHANGED

Isolated thunderstorms developing this afternoon and this evening may become strong or severe. The Storm Prediction Center has expanded the existing Marginal Risk (Level 1 of 5) to cover much of our forecast area.

KEY MESSAGES

1) An isolated strong or severe thunderstorm is possible this afternoon and this evening.

2) Unseasonably warm conditions are expected through mid week; near-record overnight lows expected.

DISCUSSION

KEY MESSAGE 1... An isolated strong or severe thunderstorm is possible this afternoon and this evening.

KEY MESSAGE 1 DESCRIPTION... A weakening cold front will move into central NC this afternoon before stalling and dissipating overnight. Showers and storms are expected to develop ahead of the boundary during the late afternoon and early evening. HREF favors development of showers and storms near the I-95 corridor and westward into central NC/SC. As these storms progress eastward, instability over eastern NC/SC should extend their lifetime into the early evening. Destabilization during the afternoon will produce MLCAPE in excess of 500 J/kg, up to around 1,000 J/kg. This instability will be coupled with rather weak shear of around 30 knots. This instability/shear profile is rather balanced for a early spring environment and should favor a few well-structured storms. Despite the favorable thermodynamic and kinematic profiles, dry air below 500 mb should limit coverage to isolated or widely scattered.

While winds below 500 mb do not exceed 40 knots throughout the day, dry air in the mid levels and at the surface could enhance any downdrafts that develop. This is highlighted by DCAPE exceeding 750 J/kg in an environment with a similar CAPE value. These downdrafts will have the capability to overperform, especially with a westerly storm motion of around 35 knots. Some hail will be possible, but updrafts will likely be too weak to support a widespread threat of large hail; the strongest storm may produce a report of quarter-sized hail.

The best chance for severe weather remains along and west of I-95 and north of a line from Florence, SC to Southport, NC. Immediate coastal areas will be shielded by the afternoon sea breeze. As showers and storms move eastward, the surface layer may decouple in the far eastern portions of our CWA which would mute an already low-end damaging wind gust threat.

KEY MESSAGE 2... Unseasonably warm conditions are expected through mid week; near-record overnight lows expected.

KEY MESSAGE 2 DESCRIPTION... SWly flow will advect warm air across the forecast area today, with highs in the lower 80s across inland areas. Typically we would expect highs in the mid/upper 60s for early March. Above normal temperatures will persist through the first half of the week, with the warmest readings expected to occur during Wednesday ahead of the next cold front. Highs Wednesday could reach the mid 80s. Meanwhile, along the immediate coastal areas the cool SSTs across the adjacent shelf waters (50s to around 60) will keep temperatures much cooler. A cold front passing through Thursday will help bring temperatures back closer to normal, with cooler air on tap Thursday night, Friday, and Friday night.

AVIATION /06Z SUNDAY THROUGH THURSDAY/

Increased boundary layer winds tonight should favor stratus over fog through early or mid morning. This should inspire some uniformity in restrictions across the area that we haven't seen in previous nights. Grand Strand terminals are the exception due to nearshore sea fog. VFR is expected for all terminals by mid or late morning. A deeper boundary layer in SW flow should promote a few gusts to around 20 knots this afternoon.

The main forecast challenge within this period is timing the potential for afternoon showers and storms. HREF guidance suggests the late afternoon arrival of a weak cold front should bring isolated thunderstorms to the region. Storms will be progressing west to east during the late afternoon and early evening with the highest chance of impacts over our inland terminals. The sea breeze and decoupling of boundary layer winds should keep impacts low for ILM and the Grand Strand.

Light winds tonight and no change in surface dew points may lead to additional restrictions late tonight into Monday morning. Confidence is low due to cirrus and lingering showers along the dissipating boundary.

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

Through Tonight... Southerly winds increase today ahead of weak and dissipating cold front. Sustained winds around 15 knots are expected with gusts between 20-25 knots. Seas elevate to 3-4 feet for the afternoon. Showers and thunderstorms developing onshore will push into the nearshore waters this evening. While these storms will be isolated in coverage, some lightning, strong wind gusts, and small hail are possible. Any sea fog that remains the afternoon should struggle to maintain its uniformity with the increasing surface winds this afternoon. However, as lighter winds return tonight, sea fog may begin to develop again.

Monday through Thursday... Light/variable winds Monday morning with a front stalling in the area will become light SWly during the day and Monday night as a weak inland trough develops. Relatively benign maritime conditions are expected Tuesday as well, the SWly pressure gradient will tighten, especially during late Wednesday into Thursday as the next cold front moves across the area. Small Craft conditions are possible during this time, including after the front moves away and the flow becomes offshore. The flow will quickly veer to NEly direction Thursday night as surface high pressure builds across the Carolinas. Seas will be highest Wednesday-Thursday, then slowly improve late in the forecast period. Otherwise, showers may linger Monday with the stalled/dissipating front, then showers and thunderstorms may become more widespread late Wednesday, but more-so Thursday with the cold front passage.

ILM WATCHES/WARNINGS/ADVISORIES

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