textproduct: Charleston

WHAT HAS CHANGED

Key messages have been updated for isolated severe weather risk Thursday and unsettled weather pattern this weekend.

KEY MESSAGES

- 1) Showers and thunderstorms expected Thursday with isolated severe weather possible.

- 2) Unsettled weather conditions this weekend with a stalled front nearby.

DISCUSSION

KEY MESSAGE 1: Showers and thunderstorms expected Thursday with isolated severe weather possible.

High pressure extending across the western Atlantic will favor a south/southwest flow across the Southeast United States well in advance of cold front approaching the region, driven by a longwave trough advancing across the Great Lakes region toward the Mid- Atlantic/Northeast Coast. Latest guidance continues to support Deep moisture (PWATs ~2.0 inches and sfc dewpts in lower 70s) arriving across the region well in advance of the approaching cold front, setting the stage for increasing chances of showers/thunderstorms as the local area remains warm-sectored for much of the day. The main issue continues to revolve around limited instability during timing of enhanced deep-layer shear and forcing associated with low-lvl jetting while a strong h25 jet core passing inland and north of the region. Latest guidance suggests increasing levels of isentropic lift supportive of nearly widespread cloud cover locally and pre- frontal convection within the warm-sector ongoing upstream and/or developing across the far interior during morning hours, which would limit instability across parts the Southeast South Carolina and Southeast Georgia to some degree prior to typical peak heating hours Thursday afternoon. However, some guidance does indicate an axis of modest instability (SBCAPE ~1500 J/kg) developing across Southeast Georgia into coastal parts of southern Southeast South Carolina, where a few breaks in cloud cover and/or warm air advection allow for sfc temps to reach the mid-upper 80s during afternoon hours. Sfc temps are likely to become warmest near the I-95 corridor in Southeast Georgia, possibly reaching the lower 90s before the onset on shower and thunderstorm activity.

The combination of deep moisture (PWATs 2.0 inches/sfc dewpts lower 70s) and 0-6 km Bulk Shear between 50-60 kt supports a severe weather threat locally on Thursday, dependent on sfc heating/instability realized Thursday afternoon and the timing of cold fropa, which should occur starting around Thursday evening. Mostly unidirectional wind profiles indicated by soundings and h85-h5 crossover winds along with low-lvl lapse rates around 7 C/km support primarily a strong/damaging wind concern for a few thunderstorms that become strong/severe within clusters and/or small linear segments. However, there is an non-zero risk for a tornado across Southeast Georgia should ample instability develop ahead of an afternoon sea breeze promoting a near sfc backing wind component. The bulk of thunderstorm activity should remain sub-severe, but capable of producing brief heavy downpours within a deep moisture environment, especially if the progression of the arriving cold front slows. The Storm Prediction Center continues to place a Marginal Risk (1/5) for severe weather across the entire area Thursday.

KEY MESSAGE 2: Unsettled weather conditions this weekend with a stalled front nearby.

Forecast confidence is quite low post cold fropa this weekend. Latest trends suggest some drying across northern areas on Friday, while precip activity holds across southern areas into Saturday as h5 vort energy ripples across a stalling front that attempts to lift back north across northern Florida/southern Georgia and into the local area. The position of the front will be key in regards to shower/thunderstorm activity each day during the weekend, and could potentially set up an unsettled precip pattern until another front arrives from the west early next week. Severe weather risk remains low this weekend, but gusty winds and brief heavy downpours are possible with shower/thunderstorm activity through the weekend.

AVIATION /08Z WEDNESDAY THROUGH SUNDAY/

VFR conditions will prevail at CHS/JZI/SAV terminals through 06Z Thursday. However, gusty south/southeast winds up to 20-25 kt are anticipated at all terminals this afternoon, and slightly breezy winds could continue at the terminals in the 00Z-06Z Thursday as well.

Extended Aviation Outlook: Flight restrictions from showers and thunderstorms are likely Thursday morning into Friday as a cold front moves through the region. Additional flight restrictions are possible late weekend into early next week with shower/thunderstorm developing ahead of and/or occurring with another front approaching the region early next week.

MARINE

Southerly flow will strengthen tonight as a cold front approaches. We're still showing a few short periods of 25 kt wind gusts later tonight and then Thursday afternoon, but it seems too marginal to pull the trigger on Small Craft Advisories just yet.

CHS WATCHES/WARNINGS/ADVISORIES

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