textproduct: Charleston

WHAT HAS CHANGED

Key Message 1 and the Aviation section were updated.

KEY MESSAGES

- 1) Frost/freeze conditions tonight through Sunday night.

DISCUSSION

KEY MESSAGE 1: Frost/freeze conditions tonight through Sunday night.

The boundary layer is quickly decoupling this evening with calm to light/variable winds already being reported at a number of locations. Clear skies and calm/light winds will persist for much of the night, helping to maximize radiational cooling. The leading edge of a band of thicker cirrus will approach from the southwest Sunday morning, but most of this will not move into the area until after daybreak having little/no impact on overnight lows. 14/23z temperatures were already running a few degree cooler than expected and given how temperatures transpired this morning, a slight lowering of lows for Sunday morning was needed in places, especially in the coastal corridor.

The updated forecast expanded the freezing line east and south a bit which necessitated an upgrade of the Frost Advisory to a Freeze Warning for parts of Long, Inland Liberty and Inland Bryan Counties. Most of the RAWS sites in the open areas of Fort Stewart dropped to 33-34 this morning, so reaching freezing looks quite plausible in these same areas for Sunday morning. The Frost Advisory was also expanded into Coastal Jasper County given the slightly colder temperatures and greater risk for frost there. Freezing temperatures may briefly reach into the far northern portions of Tidal Berkeley County and possibly the far interior areas of upper Charleston County just before daybreak, but the impacted area look too small to justify an upgrade to a Freeze Warning at this time.

If widespread freezing temperatures occur tonight into Sunday morning, then this will end the local growing season and Frost/Freeze products will not be issued for Sunday night into Monday morning. However, if only some areas observe freezing temperatures, then the growing season continues and we will likely need Frost/Freeze products on Sunday night into Monday morning. Regardless of the outcome, overnight temperatures will be below normal for this time of year.

AVIATION /00Z SUNDAY THROUGH THURSDAY/

15/00z TAFs: KCHS/KJZI/KSAV: VFR through 16/00z.

Extended Aviation Outlook: There are no concerns.

MARINE

High pressure centered over the mid to upper Mississippi Valley tonight will gradually move eastward, becoming located over the Mid- Atlantic states by the middle of next week. A light to fresh breeze along with low seas should prevail through Monday. As the high gets closer to our region late Monday, the surface pressure gradient will become elevated, leading to increasing winds and building seas. Gusts to >=25 kts and seas >=6 ft (Small Craft Advisory) will develop across the GA waters Monday night, then spread into the SC waters on Tuesday. If this forecast holds, Small Craft Advisories may be needed for most of the marine zones by the middle of next week.

CHS WATCHES/WARNINGS/ADVISORIES

GA...Freeze Warning from 1 AM to 9 AM EST Sunday for GAZ087-088- 099>101-114-115-137-216-238. Frost Advisory from 1 AM to 9 AM EST Sunday for GAZ218-240. SC...Freeze Warning from 1 AM to 9 AM EST Sunday for SCZ040-042>045- 147. Frost Advisory from 1 AM to 9 AM EST Sunday for SCZ148>152. MARINE...None.