textproduct: NWS Wilmington

WHAT HAS CHANGED

Updated aviation discussion for the 12Z TAF issuance.

KEY MESSAGES

1) Isolated strong to severe thunderstorms possible near the coast today.

2) Near-normal temperatures expected through the next seven days with shower and storm chances increasing mid to late next week.

DISCUSSION

KEY MESSAGE 1...Isolated strong to severe thunderstorms possible near the coast today.

A cold front is expected to move through the area during the afternoon as a mid-upper shortwave rounds the base of a developing closed low centered over southern Ontario. This front appears to be favorably timed with the daytime heating cycle to support at least isolated to perhaps scattered showers and thunderstorms, especially as it interacts with the sea breeze this afternoon. Precipitable water values are coming down considerably from their 2+ inch values of the last few days into the 1.3-1.6" range, which is near to below- normal for this time of year, and this reduction in moisture is primarily found in the middle to upper troposphere. Thus, while low- level moisture is supportive of showers and storms by allowing for moderate to strong instability to develop, there is a significant amount of dry and subsiding air above 700mb which will undoubtedly cause many initial updrafts to struggle, with up to a few or several of the most robust updrafts overcoming the dry air. For those which can grow tall enough and sustain themselves, effective shear values of 25-30kts, DCAPE in the 1200-1400 J/kg range, and a well-mixed subcloud layer present a ripe environment for damaging wind gusts. However, the very dry air aloft will significantly limit the coverage of severe storms, thus resulting in a marginal risk (5% chance) for severe weather today.

Given the reduced precipitable water values, very heavy rain rates capable of flash flooding (e.g., 2-4"/hr) are not anticipated, with mainly 1-1.5"/hr rates at the highest supporting ponding of water in typical poor drainage and low-lying problem spots. Storm motions will be mainly east to east-northeast at 15-20 kts, except where strong downdrafts produce an eastward-moving outflow boundary which could carry a storm along faster.

KEY MESSAGE 2... Near-normal temperatures expected through the next seven days with shower and storm chances increasing mid to late week.

An upper air pattern featuring a strong upper-high anchored over the Southwest and mean troughing over the eastern US will prevail through the period. This pattern will bring a welcomed reprieve from the recent extreme heat, with temperatures returning more to seasonable levels along with and lower humidity. Noticeably drier air and lower PWATs, potentially falling to around the 10th percentile of climatology will advect into the area for Sunday and Monday. Despite a lingering weak boundary and weak disturbances aloft swinging through the area, the dry air should limit rain chances to widely scattered showers and storms at the most, focused mainly around the sea breeze on Sunday and Monday.

Moisture and instability will gradually return to more typical levels from Tuesday onward, yielding increased chances of scattered diurnal showers and storms through the remainder of the period. Storm coverage could increase to numerous or widespread at times between Thursday and Saturday as the next cold front approaches the area.

AVIATION /09Z SUNDAY THROUGH THURSDAY/

VFR for coastal terminals this morning with inland terminals slowly breaking out from fog/low stratus. Restrictions may last longest at KLBT where hi-res guidance has low stratus lingering through ~15Z. Have added TEMPOs for inland terminals clearing up through the morning. Timing for afternoon showers/storms at coastal terminals has shifted later slightly reflected in the PROB30, bringing restrictions if any cells move over terminals. Showers/storms may linger later overnight at coastal terminals as a frontal boundary stalls in the area. Inland BR will again be possible, though there's some added uncertainty due to the drier air behind the front.

Extended Forecast... Mainly VFR with early morning fog and low stratus possible each morning. Scattered showers and storms will present a threat for transient vis restrictions near the coast through Monday before chances increase for inland terminals from Tuesday onward.

MARINE

Tonight through Thursday...Marine conditions are expected to remain below Small Craft Advisory criteria through the period. Expect generally south to southwest winds at 5-15 kts to prevail through the period with seas between 1-3 ft in the 0-20nmi zones and 2-4 ft in the 20-60nmi zones.

The biggest marine impact will likely be from periods of scattered to numerous showers and thunderstorms through this week as afternoon and evening storms move over the waters and disturbances aloft help to encourage new storms over the very warm waters.

ILM WATCHES/WARNINGS/ADVISORIES

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