textproduct: Charleston

WHAT HAS CHANGED

Aviation section updated for 12z TAFs.

KEY MESSAGES

- 1) Freezing fog could produce a few slick spots this morning across the South Carolina Lowcountry and Southeast Georgia.

- 2) Hazardous conditions are expected on Lake Moultrie tonight through Saturday morning.

- 3) Cold temperatures with low wind chills across coastal South Carolina Sunday morning.

DISCUSSION

KEY MESSAGE 1: Areas of freezing fog could produce a few slick spots this morning across parts of the South Carolina Lowcountry and Southeast Georgia.

The combination of light winds and low dewpoint depressions has led to the formation of fog this morning across inland areas. The lowest 1000 hPa condensation pressure deficits are progged to impact parts of the Charleston Tri-County into Colleton County through daybreak which could support some localized dense fog. Webcams along parts of I-95 and I-26 from Walterboro up to the I-95/I-26 interchange and down to just north of Summerville already confirm visibilities are slowly lowering with vsbys 1-3 miles at times. Temperatures were already near or just below freezing at 06/07z and will continue to cool, so the transition to freezing fog is likely already underway. Even some degree of freezing fog could impact parts of the Charleston Metro Area, including a few the elevated bridges along I-526. Freezing fog can lead to the development of slick spots on area roadways (especially bridges and overpasses) along with some very light icing on some colder, elevated surfaces such as tree branches, cars and fences. Based on the above trends, a Freezing Fog Advisory has been issued for the Charleston Tri-County west to Colleton, Hampton and Allendale Counties through 8 AM.

Farther south across the remainder of the Lowcountry and Southeast Georgia, the fog will be a bit more shallow in nature given the high condensation pressure deficits and the risk for any icing will be much more highly localized. A Special Weather Statement has been issued to address the situation.

Motorists are urged to remain alert for possible slick spots this morning.

KEY MESSAGE 2: Hazardous conditions are expected on Lake Moultrie tonight through Saturday morning.

Winds on Lake Moultrie are expected to increase overnight due to a combination of cold air advection strengthening behind a southward moving cold front and a tightening pressure gradient between developing low pressure well offshore of Cape Hatteras and 1034 hPa high pressure building south across the mid-upper Mississippi Valley. Winds should reach as high as 15-20 kt with gusts 25-30 kt along with waves of 1-2 ft, highest over the central/eastern portions of the lake. A Lake Wind Advisory is in effect from sunset through early Saturday afternoon. Boaters on Lake Moultrie should use extra caution since strong winds and rough waves can overturn small craft.

KEY MESSAGE 3: Cold temperatures with low wind chills across coastal South Carolina Sunday morning.

Unseasonably cold temperatures, around 10-15 degrees below early February normals, are expected this weekend as chilly high pressure builds into the region. The time period of greatest concern is Saturday night into Sunday morning when low temperatures are forecast to fall well into the 20s. There looks to be enough gradient wind present to bring a concern for wind chills dropping to the upper teens to around 20, especially across the Charleston Tri- county where LREF continues to highlight a 60-80% chance for seeing apparent T < 21 F. Probabilities are lower further south, but the potential is still there. A Cold Weather Advisory could be needed for portions of the area.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

06/12z TAF Discussion: KCHS/KJZI/KSAV: MVFR fog should lift shortly after daybreak at KCHS and KJZI. VFR will prevail through 07/12z.

Extended Aviation Outlook: There are no concerns.

MARINE

Conditions will deteriorate across the waters tonight as the pressure gradient tightens between low pressure developing well offshore of Cape Hatters and high pressure building south out of the Mid- Upper Mississippi Valley. In addition, cold air advection will intensify as a cold front drops through the waters. Winds should reach 20 kt with gusts to 30 kt nearshore waters where Small Craft Advisories are in effect, including Charleston Harbor. The risk for gales has increased across mainly the central/eastern portions of the Georgia offshore waters tonight where Version 5 NBM probs for gusts >34 kt are running 50-80%. The HREF is even higher with 80-100% probabilities. Per coordination with WFO Jacksonville and the Ocean Prediction Center, a Gale Watch has been issued from this evening into Saturday morning. The watch will either be upgraded to a Gale Warning or a high-end Small Craft Advisory later today.

CHS WATCHES/WARNINGS/ADVISORIES

GA...None. SC...Freezing Fog Advisory until 8 AM EST this morning for SCZ040- 042>045-050-052. Lake Wind Advisory from 7 PM this evening to 1 PM EST Saturday for SCZ045. MARINE...Small Craft Advisory from 7 PM this evening to 1 PM EST Saturday for AMZ330. Small Craft Advisory from 3 PM this afternoon to 6 AM EST Sunday for AMZ350. Small Craft Advisory from 3 PM this afternoon to 7 AM EST Saturday for AMZ352-354. Small Craft Advisory until 7 PM EST this evening for AMZ374. Gale Watch from this evening through Saturday morning for AMZ374.