textproduct: Charleston

WHAT HAS CHANGED

A Tornado Watch is now in effect for Tattnall, Long, and McIntosh Counties in GA. Key Message 1 and 2 have been swapped to highlight the severe potential this afternoon across the region, mainly south of I-16 in SE GA. The Aviation section has been updated to reflect the 18Z TAF issuance. Added a Climate Section to highlight the possibility of breaking the precipitation records at KCHS/KSAV today.

KEY MESSAGES

- 1) A squall line of strong to severe thunderstorms is expected to impact portions of southeast Georgia, the South Carolina Lowcountry, and the adjacent Atlantic waters this afternoon and evening.

- 2) A storm system will move across the region today into tonight bringing widespread rain.

DISCUSSION

KEY MESSAGE 1: A squall line of strong to severe thunderstorms is expected to impact portions of southeast Georgia, the South Carolina Lowcountry, and the adjacent Atlantic waters this afternoon and evening.

A cold front associated with a low pressure system is approaching the forecast area today, progged to reach the region tonight. Ahead of the approaching cold front is a line of showers and thunderstorms capable of producing severe weather. A reanalyzed 12Z KCHS RAOB sounding with the forecast high temperature confirms previous thinking that the severe risk this far north is low, with only 170 J/kg of CAPE shown. However, forecast soundings further south, especially across southeast Georgia are expected to see 300- 400 J/kg of MU CAPE. The main threat this afternoon will be damaging wind gusts, with 200-300 J/kg of DCAPE expected across southeast Georgia. However, given impressive 0-1 km SRH values around 200 m2/s2 there is also a low end tornado threat as well. An increase in low level moisture is evident across the region given the southerly flow and dew points rising into the upper 50s to low 60s. Hi-res guidance, namely the RRFS and the HRRR, have remained consistent in the timing of the line of showers and thunderstorms, pushing into the far interior GA counties around 3 PM and reaching coastal zones around 5 or 6 PM. A Tornado Watch is now in effect for Tattnall, Long, and McIntosh Counties in GA through 8 PM.

KEY MESSAGE 2: A storm system will move across the region today into tonight bringing widespread rain.

An impressive shortwave is clearly visible on mid- level water vapor satellite imagery, slowly progressing eastward across the deep south. This feature is forecast to continue its trek towards the southeastern coast through the remainder of today and into tonight. The 12Z KCHS RAOB sounding showed a PWAT value of 0.95", with hi-res model soundings indicating that by this afternoon PWATs at KCHS will reach 1.4 inches. Guidance remains consistent in the rainfall totals, with amounts between 0.5-1" expected across the region. These values could exceed the record precipitation at both KCHS and KSAV, see the Climate section for more details.

AVIATION /18Z SUNDAY THROUGH FRIDAY/

Flight restrictions will impact KCHS/KJZI/KSAV this afternoon as a line of showers and thunderstorms pushes through the region. Cigs are expected to bounce between MVFR/VFR at KCHS over the next few hours ahead of the approaching line of showers and storms. The general timing of the showers and storms is between 21 and 01 Z at KCHS/KJZI and slightly earlier, 20 and 24Z at KSAV. Reduced vsbys, low cigs, rain, and lightning are all possible with the line of showers/tstorms. After the showers/tstorms clear the region lower cigs are expected to develop, likely dropping into the IFR category or even LIFR. These cigs will linger into daybreak Monday before lifting and developing into an MVFR cig through the remainder of the 18Z TAF period.

Extended Aviation Outlook: Flight restrictions could linger into Monday afternoon before becoming SKC Monday night.

MARINE

Gusty southerly winds expected through this evening ahead of a strong cold front. Seas will also steadily build through early this evening, with some 6 footers reaching the outer periphery of the 0-20 nm waters for a few hours. Small Craft Advisories in effect for all waters.

Winds will quickly shift to the WNW after midnight behind the cold front. Wind speeds should drop off for a few hours, then start gusting again Monday morning. The Small Craft Advisory continues through much of the day Monday for the SC nearshore and GA offshore waters due to frequent 25 kt wind gusts.

High pressure will build over the area Monday night through Friday, with conditions below advisory thresholds.

Sea fog could be a concern mid to late week as southerly flow brings increasing temperatures and dewpoints.

CLIMATE

Record Precipitation:

February 15: KCHS: 0.87/1952 KSAV: 0.91/1894

CHS WATCHES/WARNINGS/ADVISORIES

GA...None. SC...None. MARINE...Small Craft Advisory until 7 PM EST this evening for AMZ330. Small Craft Advisory until 5 PM EST Monday for AMZ350-374. Small Craft Advisory until 1 PM EST Monday for AMZ352. Small Craft Advisory until 9 PM EST this evening for AMZ354.