textproduct: Charleston

WHAT HAS CHANGED

The Aviation Section has been updated for the 18Z TAF issuance.

KEY MESSAGES

- 1) A cold front will bring an increased risk for showers and thunderstorms to the region Thursday into Saturday.

DISCUSSION

KEY MESSAGE 1: A cold front will bring an increased risk for showers and thunderstorms to the region Thursday into Saturday.

High pressure across the Atlantic will continue to yield light southerly winds across the Eastern Seaboard, while an upper-lvl trough scoots across the Great Lakes. Expect this trough move into the lower Mississippi Valley by Wednesday. Simultaneously, an associated cold front will march across the central Gulf States on Wednesday, and then into the Southeast on Thursday night. This will lead to scattered showers and thunderstorms as the front approaches on Thursday.

Ahead of the front, a seasonably moist airmass from the Gulf will advect into the region with PWATs ranging 1.8 to 2.0 inches. Along with this rich moisture, the kinematic environment remains favorable for strong to severe thunderstorms on Thursday. Moderate 0-3KM shear (250-300 m^2/s^2) coupled with strong deep-layer flow could aid to the severity of Thursday. The limiting environmental factor remains to be the cloud cover ahead of the front as this might temper destabilization, however if there are some breaks in cloud cover, pockets of stronger daytime heating could yield modest MLCAPE values. The Storm Prediction Center (SPC) has highlighted the entire region in a Marginal Risk (1/5) for severe thunderstorms on Thursday. The primary threat will be isolated damaging wind gusts within thunderstorms that evolve, with locally heavy pockets of rainfall possible given the anomalously moist environment.

However, substantial uncertainty remains in regards to the phasing of the upper-lvl trough and it's interaction with the upper-lvl closed low situated across Southern California. With the latest guidance, the front remains to be on the progressive side of the hi- res guidance as the 12Z HRRR indicates most of the shower and thunderstorm activity will transpire in the early morning hours on Thursday. This matches well with the 12Z GFS as it suggests a more progressive solution as well. As of right now, it seems like this will be the more likely solution, however model guidance remains still split with the 06Z ECMWF displaying a less progressive solution (w/ an afternoon arrival of convection). A more progressive solution would reduce the severe risk, while a slower solution coupled with good afternoon heating would support a higher risk. Thus, forecast confidence remains low as the severe threat is dependent on the frontal timing and the degree of destabilization that takes place ahead of the front. Regardless, the front should push offshore overnight on Thursday as drier, more stable air filters in behind it.

AVIATION /18Z TUESDAY THROUGH SUNDAY/

18Z TAFs: VFR conditions will prevail at CHS/JZI/SAV terminals through 18Z Wednesday. It's important to note that breezy south- southeasterly winds (near 20-22 kt) was maintained for all terminals this afternoon.

Extended Aviation Outlook: Flight restrictions from showers and thunderstorms are possible Thursday and Friday as a cold front passes through the region.

MARINE

Through tonight: As surface high pressure situates itself across the Atlantic, expect light south-southeasterly winds to prevail. Expect light north-northeasterly winds to become more southerly overnight. Otherwise, marine conditions should be quite tranquil with seas ranging from 2 to 3 ft.

Wednesday through Sunday: Ahead of an approaching cold front, the pressure gradient will become pinched on Wednesday, leading to marginally breezy south-southeasterly winds. Heading into Thursday (as the front inches closer), winds will become breezier with models supporting gusts up to 22-23 kts through Thursday evening across the most of the local waters. Simultaneously, seas should gradually build to 3-5 ft across the South Carolina waters and 3-4 ft across the Georgia waters. Small Craft Advisory conditions remain borderline across the nearshore Charleston waters on Thursday, and this will continue to be monitored. After the front pushes offshore, marine conditions should stabilize overnight on Thursday into the weekend.

CHS WATCHES/WARNINGS/ADVISORIES

GA...None. SC...None. MARINE...None.