textproduct: Charleston

WHAT HAS CHANGED

The aviation section was updated for the 12Z TAF issuance.

KEY MESSAGES

- 1) Confidence continues to increase in an accumulating snowfall event across a portion of the SC Lowcountry and SE Georgia Saturday morning through Saturday night.

- 2) Unseasonably cold weather will continue through early next week with the coldest conditions expected Saturday night.

DISCUSSION

KEY MESSAGE 1: Confidence continues to increase in an accumulating snowfall event across a portion of the SC Lowcountry and SE Georgia Saturday morning through Saturday night.

A sharp trough is forecast to dig southward out of the Great Lakes on Friday, dropping into the southeastern states Saturday. Simultaneously a surface low is forecast to develop off the southeastern coast before trekking to the northeast. Precipitation along the backside of the low is forecast to impact the region Saturday into early Sunday morning. Forecast soundings indicate dry conditions will dominate prior to daybreak Saturday and into the first few hours of Saturday morning. Conditions will then saturate as precipitation moves into the region. Unique to the SC Lowcountry and SE Georgia is the fact that this event will be rain/snow, with no meaningful probabilities of freezing rain/sleet. Forecast soundings show that the entire column of air will be below freezing, leading to an all snow forecast once surface temperatures drop below freezing. Given the very cold temperatures, the snow ratio could approach 20 to 1, also unique for the area. This snow ratio is quite high and would result in a "dry" snowfall. Given these details, Winter Storm Warning criteria (2 inches) is possible across northern and inland areas of the SC Lowcountry, with Winter Weather Advisory criteria (1-2 inches) possible across the rest of the region, except for counties south of I-16 in Georgia.

KEY MESSAGE 2: Unseasonably cold weather will continue through early next week with the coldest conditions expected Saturday night.

A reinforcing Arctic high will slide into the region Friday night and then persist through Monday before shifting off the Southeast coast. Cold advection during the day Saturday will prevent high temps from climbing out of the mid 30s over inland SC/GA. Closer to the coast where there will be fewer hours of cold advection, highs should reach the low to mid 40s.

Saturday evening, temperatures will rapidly plummet, with most areas in the 20s by 9pm. Overnight lows in the mid to upper teens and 10-15 mph winds will produce wind chills in the single digits for most of the night. We will likely need an Extreme Cold Warning for the entire area Saturday night into Sunday morning.

Sunday night lows will be in the upper teens, but wind speeds will be notably weaker, so wind chills will mainly be 10-15 degrees. A Cold Weather Advisory is likely for Sunday night.

Lake Moultrie winds: Winds out of the northwest sustained in the 20 to 25 knot range with gusts of 25 to 30 knots may require a Lake Wind Advisory Saturday night into Sunday morning.

AVIATION /12Z THURSDAY THROUGH MONDAY/

VFR conditions will prevail at CHS/JZI/SAV through the 12Z TAF period.

Extended Aviation Outlook: Predominantly VFR through the extended period, with increasing potential for impacts Saturday associated with developing low pressure offshore of the Southeastern coast.

MARINE

A potent surface low will develop off the SC coast on Saturday, then shift northeast on Sunday. A period of Gale force winds is expected during this period in all zones except Charleston Harbor where solid Small Craft Advisory conditions are anticipated. It's a bit too early to issue a Gale Watch, but there is high confidence that we'll eventually need one.

CLIMATE

Record Low Temperatures:

January 31: KCHS: 15/1966 KCXM: 19/1966 KSAV: 16/1966

February 1: KCHS: 21/1977 KCXM: 23/1900 KSAV: 23/1977

February 2: KCHS: 19/1980 KCXM: 17/1917 KSAV: 18/1917

Record Low Maximum Temperatures:

January 31: KCHS: 36/1948 KCXM: 34/1936 KSAV: 37/1909

February 1: KCHS: 38/1980 KCXM: 36/1900 KSAV: 38/1900

February 2: KCHS: 38/1980 KCXM: 38/1898 KSAV: 38/1951

Record Snowfall:

January 31: KCHS: 0.6/1977 KSAV: 1.3/1977

February 1: KCHS: no record established KSAV: no record established

EQUIPMENT

The KCLX radar remains out of service. More parts are on order. We hope to have the radar restored by Saturday. Users should use adjacent WSR-88D sites, including KCAE, KLTX, KJAX, KVAX and KJGX.

CHS WATCHES/WARNINGS/ADVISORIES

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