textproduct: NWS Wilmington

WHAT HAS CHANGED

Coastal temperatures have been increased by a couple of degrees today, and increased for all areas Monday ahead of the front. Rain chances have decreased today due to dry air aloft.

Updated 12Z aviation discussion.

KEY MESSAGES

1) A stray storm is possible along the seabreeze this afternoon.

2) Good chances of showers and thunderstorms will accompany a cold frontal passage on Monday.

3) The next cold front expected to reach the area early Thursday could bring another round of showers.

DISCUSSION

KEY MESSAGE 1...A stray storm is possible along the seabreeze this afternoon.

A conditionally unstable environment could be in place this afternoon near the coast. Soundings are showing DCAPE >700 with decent instability that could support isolated convection along the seabreeze. The issue is the dry air in the mid levels and the uncertainty in the dryness of the low levels. Even guidance with storms along the coast show ample drying aloft that could mix out any stronger storms that try to develop. The threat for isolated strong winds is low at this time.

KEY MESSAGE 2: Good chances of showers and thunderstorms will accompany a cold frontal passage on Monday.

Models haven't changed appreciably with the timing of the arrival of Monday's cold front, still anticipated to enter southeastern North Carolina during the early afternoon hours. The new 00z GFS and most of the 00z CAMs show little if any convective activity during the morning hours Monday. Temperatures rising into the 80s should support uncapped surface CAPE of 1000 J/kg (GFS) to nearly 2000 J/kg (NAM) which when coupled with low level convergence along the front should support the development of showers and thunderstorms.

Model mid level winds have nudged up versus what we were seeing yesterday and it now appears 0-6 km bulk shear could reach 40 knots Monday. This implies multicells and perhaps even supercells may become the preferred storm type if sufficient instability is present. Damaging wind gusts and hail could develop in the strongest storms. CAMs suggest storm coverage will be best in the Cape Fear area during the late afternoon, with a minimum in coverage in the Bennettsville-Lumberton area given the earlier arrival of the front there.

As the surface front shifts south and offshore Monday night, warm and humid west-southwesterly winds aloft (above the frontal surface) will continue up until the 500 mb shortwave moves offshore late Monday night. This may keep rain and some elevated convection firing through much of the night. Storm total rainfall forecasts have been trimmed back slightly from yesterday but 0.75 and 1.00 inches still appears possible near the coast with lesser totals up to one-third of an inch along and west of I-95.

KEY MESSAGE 3: The next cold front expected to reach the area early Thursday could bring another round of showers.

A rather strong shortwave moving across the Great Lakes should push a cold front into the Carolinas early Thursday morning. Mid level west to northwest mid level winds will have no connection to Gulf or Atlantic moisture, so a forecast of 30-40 percent coverage of showers Wednesday night into Thursday morning seems reasonable, driven more by dynamics than by deep moisture or instability.

AVIATION /12Z SUNDAY THROUGH THURSDAY/

Some MVFR VSBYs from ground fog are around but not impacting terminals so have went with no fog to start out the TAF period. Into the day we'll have VFR stratocu in the afternoon and a seabreeze bringing winds from SW to more S at ~10 kts. Winds will decrease after sunset. Fog may be possible past 06Z with highest confidence at KLBT at this time.

Extended Forecast...MVFR/IFR likely Monday into Tuesday. VFR returns Tuesday. Potential for restrictions increases later Wednesday through Thursday.

MARINE

Through Tonight...SW winds will become more S with the afternoon seabreeze, gusts around 15 kts. Seas will be around 2 feet.

Monday through Thursday...Light south to southwest winds are expected Monday up until a cold front arrives during the afternoon hours. Showers and embedded thunderstorms may become rather widespread late in the afternoon and through the overnight period as this front slides offshore and moisture continues to overrun it. By Tuesday morning the back edge of the rain should be moving out across the offshore waters with nearshore conditions drying. However stiff northeasterly winds increasing to 20-25 knots mean we'll likely see Small Craft Advisory thresholds breached Monday night through Tuesday in a combination of winds and 6 foot seas.

Winds should gradually diminish Tuesday night into Wednesday as a narrow ridge of high pressure reaches the coast. Winds should quickly veer southerly, then southwesterly Wednesday night in advance of the next cold front which should sweep offshore before daybreak Thursday. At this time models paint only light northerly post-frontal winds Thursday.

ILM WATCHES/WARNINGS/ADVISORIES

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