textproduct: Charleston

WHAT HAS CHANGED

The aviation section was updated for the 00Z TAF issuance. Updated key message 2 to reflect recent trends for tonight.

KEY MESSAGES

- 1) Confidence is increasing in an accumulating snowfall event across a portion of SC Lowcountry and SE GA Saturday morning through Saturday night.

- 2) Unseasonably cold weather will continue to occur into next week, coldest Saturday night into Sunday.

DISCUSSION

KEY MESSAGE 1: Confidence is increasing in an accumulating snowfall event across a portion of SC Lowcountry and SE GA Saturday morning through Saturday night.

Guidance indicates that a strong H5 low will cut-off early Saturday over the Mid-West, swinging over the Southeast U.S. Saturday night. At the sfc, low pressure should develop off the Southeast coast early Saturday, deepening off the Carolina coast on Saturday, then tracking NE Saturday night. As the sfc low strengthens, a deformation zone should develop across the forecast area Saturday. The peak period of forcing should occur with the approach and passage of the deep H5 closed low Saturday night. Forecast soundings indicate that conditions across the CWA will start dry Saturday morning, resulting in very little QPF. However, moisture should increase through the day into Saturday night, enough to generate 0.01-0.05" per 6hrs. Forecast soundings indicate that measurable precipitation may begin as a mix of rain and snow over the interior counties Saturday morning, then snow Saturday afternoon. Snow should remain until the passage of the H5 low Sunday morning. Given the cold temperatures, the snow ratio could approach 20 to 1 Saturday night, which is quite high for our region, resulting in period of "dry" snowfall. This quality of snow may make reaching warning criteria snowfall, 2 inches, possible over inland Berkeley and Dorchester Counties. Advisory level snow, 1 to 2 inches, is possible across the Charleston Tri-County Area and inland SC and GA counties.

KEY MESSAGE 2: Unseasonably cold weather will continue to occur into next week, coldest Saturday night into Sunday.

Temperatures will remain on the cooler side of normal behind a weak surface cold front that pushed through earlier today. Tonight will see overnight lows in the mid to upper 20s for inland areas, and up into the lower to mid 30s along the coast. With weak winds in place, not expecting Cold Weather Advisory criteria to be met tonight.

Surface high pressure system dives down ahead of the next trough, continuing our cooler conditions on Thursday. Highs again are only expected to reach up into the mid 40s to mid 50s, with lows into Friday morning in the mid/upper 20s for inland areas and mid/upper 30s for those along the coast.

As a warm front lifts northwards across the area ahead of a developing coastal low on Friday, near-normal temperatures will briefly return to the area with highs in the upper 50s to lower 60s. On the backside of the surface low, much cooler temperatures are brought into the region, with highs on Saturday only expected to reach into the upper 30s for far inland areas and up towards the mid 40s along the coast. Models are in good agreement that very cold overnight temperatures are brought down into Sunday, ranging from the 0 to 1st percentile of climatological 850mb temperatures, resulting in overnight lows in the mid teens for inland areas and up towards the lower 20s for those along the coast. Unfortunately this is also when the surface pressure gradient will be highest, both from the surface low pressure and mid-level low/trough moving through, resulting in a period of breezy winds. Winds will be breezy out of the north-northwest starting Saturday gusting into the mid to upper 20s, possibly into the lower 30s for those along the coast, remaining breezy into Sunday morning.

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.

Probabilities for wind chills below 20 degrees F are at 100%, becoming a bit less certain for wind chills at or below 10 degrees in the 55 to 85% range. A Cold Weather Advisories and/or an Extreme Cold Warning will likely be needed for the area. The cold temperatures linger into next week, as a surface high pressure meanders around the region.

AVIATION /00Z THURSDAY THROUGH MONDAY/

VFR conditions will prevail at CHS/JZI/SAV through 00Z Friday.

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

Confidence is increasing in a significant coastal storm this weekend with the potential for gale force gusts over most of the marine area. Winds will increase as the Nor'easter passes off the NC coast late Saturday, with 34 kt gusts expanding across the coastal zones by Saturday evening. The CHS Harbor may remain just below gale criteria. Gale gusts may decrease during the daylight hours on Sunday. Wave heights are forecast to peak late Saturday night into Sunday morning between 4 to 8 ft across the nearshore waters to 8 to 13 ft across the outer GA waters.

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. The currently anticipated return to service is Thursday January 29th. Users should use adjacent WSR-88D sites, including KCAE, KLTX, KJAX, KVAX and KJGX.

CHS WATCHES/WARNINGS/ADVISORIES

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