textproduct: Charleston

WHAT HAS CHANGED

The Aviation Section has been updated for the 12Z TAF issuance.

KEY MESSAGES

- 1) Warm and breezy today ahead of an afternoon/early evening cold front.

- 2) Frost/freeze conditions are possible Friday night through Sunday night.

DISCUSSION

KEY MESSAGE 1: Warm and breezy today ahead of an afternoon/early evening cold front.

Today: Breezy west-southwesterly winds will develop across the region well ahead of a cold front advancing across the Appalachian Mountains early morning, then reaching the local area mid-late afternoon. Gusts up to 25-30 mph will be common late morning and afternoon while sfc temps warm into the mid-upper 70s one last day this week. Guidance continues to support a dry forecast with soundings indicating minimal low-mid lvl moisture within a westerly flow off the sfc prior to and during fropa. Although modest mixing out of sfc dewpts is possible early afternoon, RH levels should only dip into the mid-upper 30s inland while breezy winds occur, thus limiting a fire danger risk locally.

Tonight: Strong cold air advection occurs in wake of the front overnight with a west-northwest flow bringing noticeably cooler air across the local area. This could maintain gusty west-northwest winds across much of the area into early-mid evening hours, but a notable decrease in low-lvl wind fields is expected through the night post fropa. Overnight lows should generally range in the mid 40s inland to low-mid 50s at the beaches.

Lake Wind: Breezy west-southwesterly winds developing across the area late morning and persisting through afternoon hours could approach 25 kt prior to and shortly after cold fropa today. Low-lvl wind fields trend weaker by sunset, which should support winds remaining just below Lake Wind Advisory criteria despite favorable low-lvl mixing in wake of the cold front. Conditions will continued to be monitored for a possible Lake Wind Advisory issuance for Lake Moultrie today.

KEY MESSAGE 2: Frost/freeze conditions are possible Friday night through Sunday night.

The first potential frost of the season will arrive on Friday night/Saturday morning as a cold air funnels into the region in the wake of the cold front. Expect low temperatures to drop into the mid 30s across portions of the interior southeast South Carolina and southeast Georgia. This combined with light winds could yield the formation of patchy frost. However, the greatest chance for frost will be on Saturday night/Sunday morning with areas west of I-95 in southeast Georgia and along/west of I-95 in the Lowcountry with lows in the low to mid 30s and light winds. Another chance of frost is possible on Sunday night/Monday morning as lows persist in the mid 30s across the interior counties again.

Nov 12 01z NBM 10km neighborhood probabilities for emergency management warming shelter planning:

Friday Night/Saturday Morning: Inland Areas Coastal Corridor Temps 35 degrees or colder: 30-60% <5% Temps 32 degrees or colder: 5% <5% Temps 30 degrees or colder: <5% <5%

Saturday Night/Sunday Morning: Inland Areas Coastal Corridor Temps 35 degrees or colder: 70-90% 10-30% Temps 32 degrees or colder: 30-60% <5% Temps 30 degrees or colder: 10-30% <5%

Sunday Night/Monday Morning: Inland Areas Coastal Corridor Temps 35 degrees or colder: 40-70% 10-30% Temps 32 degrees or colder: 10-30% <5% Temps 30 degrees or colder: 10-20% <5%

Frost Advisories, Freeze Watches and Freeze Warnings may eventually be needed, especially for areas roughly inland of US-17 in the Lowcountry and I-95 in Southeast Georgia.

Detailed information on first freeze dates for the area can be found online at: https://www.weather.gov/media/chs/climate/AverageFirstLastFreezeDates.pdf

AVIATION /12Z THURSDAY THROUGH MONDAY/

Gusty west-southwest winds (around 25 kt) are expected to develop late morning and persist through late afternoon hours today at CHS/JZI/SAV terminals, then trend weaker while becoming west- northwest through evening hours. Otherwise, VFR conditions are expected at all terminals through 12Z Friday.

Extended Aviation Outlook: After a cold front passes through on Thursday evening, west-northwesterly winds will remain elevated through Saturday morning with gusts up to 20 kts possible. Otherwise, VFR conditions will prevail.

MARINE

Today through Tonight: West-southeast winds will steadily increase across local waters this morning and afternoon as the pressure gradient tightens ahead of a cold front approaching the coast late afternoon into early evening hours. A Small Craft Advisory has already started across offshore Georgia waters and will begin by mid- late morning across nearshore SC/GA waters. Gusts upwards to 25-30 kt are possible prior to and following fropa late day and overnight, but a notable decrease in low-lvl wind fields should support improving conditions by daybreak Friday despite a favorable low-lvl mixing setup. Seas should build up to 4-6 ft, largest across offshore Georgia waters. On another note, there is also a risk for wind gusts to approach 20-25 kt across the Charleston Harbor prior to and immediately following cold fropa this afternoon. Conditions will need to be monitored for a possible Small Craft Advisory issuance today.

Friday through Monday: A brief period of weakening winds is expected across local waters Friday, with conditions below Small Craft Advisory levels. However, a secondary episode of cold air advection and tightening pressure gradient could be sufficient for Small Craft Advisory level conditions to return Friday night across offshore Georgia waters. High pressure will then build into the region through the weekend into early next week with wind/sea conditions remaining below Small Craft Advisory level thresholds through daylight hours Monday.

CHS WATCHES/WARNINGS/ADVISORIES

GA...None. SC...None. MARINE...Small Craft Advisory from 10 AM this morning to 4 AM EST Friday for AMZ360-362-364. Small Craft Advisory until 10 AM EST Friday for AMZ384.