textproduct: Charleston

WHAT HAS CHANGED

Key Messages have been adjusted to address latest severe weather potential and non-thunderstorm wind potential. Little change was made to Key Message 3 in regards to Frost/Freeze concerns. The Aviation Section has been updated for the 18Z TAF issuance. The Marine Section has been updated to reflect minor trend changes for marine hazards.

KEY MESSAGES

- 1) Isolated thunderstorms could briefly become strong through late afternoon.

- 2) A powerful cold front will sweep through southeast GA and southeast SC on Monday, bringing a heightened risk for severe thunderstorms, very gusty winds outside of storms, and brief bursts of moderate to heavy rainfall. An Enhanced Risk (3/5) of severe weather has been highlighted for the entire region.

- 3) Frost/freeze is possible Monday night and Tuesday night.

DISCUSSION

KEY MESSAGE 1: Isolated thunderstorms could briefly become strong through late afternoon.

A warm and moist southeast to south flow is expected to persist this afternoon, helping produce greater instability during peak diurnal heating hours. Latest mesoanalysis indicates an axis of SBCAPE approaching 2000-2500 J/kg along the I-95 corridor, which despite more substantial larger-scale forcing, should continue to support diurnally driven convection for at least another few hours. Given ample instability and 0-6km bulk shear between 25-30 kt, there remains a potential for a thunderstorm to become strong or even briefly severe. However, the bulk of thunderstorms should display brief downpours and gusty winds below severe weather thresholds through late afternoon.

KEY MESSAGE 2: A powerful cold front will sweep through southeast GA and southeast SC on Monday, bringing a heightened risk for severe thunderstorms, very gusty winds outside of storms, and brief bursts of moderate to heavy rainfall. An Enhanced Risk (3/5) of severe weather has been highlighted for the entire region.

A strong cold front will track through southeast Georgia and the Lowcountry mid to late Monday morning and shift off the coastline by the evening. This system will bring a multitude of hazards to the region.

Severe Thunderstorms: As a large deepening mid-lvl trough ejects out of the Ohio River Valley tomorrow morning, it'll slowly track eastward towards the Mid-Atlantic throughout the evening. Simultaneously, an associated strong cold front will also track into the region mid to late morning and offshore by the evening. Isolated convection will likely develop ahead of the front in the early morning tomorrow, followed by linear convection forced by the front in the afternoon. It's possible a couple of these isolated cells in the early morning could become severe fairly quickly as the near- storm environment appears favorable for supercell development. However, the primary concern remains to be in the afternoon as the front nears. The forecast area will be positioned within the warm sector ahead of the front with temps. warming into the mid to upper 70s and dewpoints rising into the upper 60s, yielding a high degree of destabilization within the atmosphere. This will support MLCAPE values ranging into the 1000-1500 J/kg coincident with a rather impressive wind field (0-6 shear ~50kt and 0-3km shear ~40kt). Mid- lvl lapse rates continue to be modest, however sufficient low-lvl moisture and strong forcing should compensate and allow for robust updraft development in the afternoon. 12Z HRRR forecast soundings show some indication of low-lvl backing (esp. in southeast South Carolina), but the majority display unidirectional flow despite the magnitude of shear. 12Z HREF indicates 0-3 SRH ranges from 200-300 m^2/s^2 with some isolated pockets of 350 m^2/s^2, suggesting the tornado threat still appears present in the afternoon. Recent model guidance displays a broken QLCS line with a favorable environment for embedded supercells as it passes in the afternoon (between 2- 6PM). With all this to consider, it appears damaging wind gusts are certainly the primary threat, followed by a an isolated tornado threat, and hail threat being a distant third. The SPC has highlighted the entire forecast area in an enhanced risk (level 3/5) for tomorrow.

Gusty Winds: As mentioned within the severe threat above, the wind field will be fairly impressive as it strengthens and expands across the region ahead of the front tomorrow morning. Strong momentum aloft should easily mix to the surface tomorrow morning, allowing for strong non-thunderstorm wind gusts from the early morning and through the afternoon. Some wind gusts could exceed 40 mph outside of any thunderstorms, with gusts of 30-35 mph being more common. Therefore, a Lake Wind Advisory has been issued for Lake Moultrie beginning at 4AM tomorrow through 2AM Tuesday. There is still the possibility of a Wind Advisory being needed for a portion, or the entire forecast area.

Rainfall: Forecast precipitable water values are expected to reach around 1.2-1.5 inches ahead of the front, which is well above climatological normals for mid-March. This is an indication that the atmosphere is capable of producing efficient rainfall rates within thunderstorms, however these heavier bursts will likely be short- lived given the expected forward speed of these storms. This will reduce the overall threat of excessive rainfall. Rainfall amounts range from 0.25-0.50 inches, with localized higher amounts possible within training thunderstorms. Thus, at this time, the risk for intense rainfall producing flooding appears rather low.

KEY MESSAGE 3: Frost/freeze is possible Monday night and Tuesday night.

Cold high pressure will build behind a cold front late Monday afternoon and night, setting the stage for an advection freeze across interior portions of southwest SC/GA late Monday night. Confidence remains higher for a Freeze Watch for Bulloch, Candler, Evans, Jenkins, Screven, Tattnall, Allendale and Hampton Counties. Elsewhere, low temps are expected to dip into the mid 30s, but frost formation doesn't seem likely due to persistent southerly winds through the night.

Tuesday night should be slightly cooler with winds decoupling early (going light/calm) under clear skies as the high settles over the area. Another Freeze Watch will likely be needed for most non- coastal zones, and a Frost Advisory is possible for the remainder of the area.

AVIATION /19Z SUNDAY THROUGH FRIDAY/

Brief MVFR conditions are possible at CHS/JZI/SAV terminals this afternoon as showers (and potentially a thunderstorm) track across the area. The risk for this is increasing at CHS/JZI terminals during in the 19-22Z timeframe. Otherwise, VFR conditions should prevail at all terminals through about 04Z Monday. MVFR cigs should then prevail at all terminals late tonight prior to more substantial shower and thunderstorm activity starting a few hours prior to daybreak. TEMPO groups of IFR or lower could eventually be needed for thunderstorm activity Monday morning into Monday afternoon. Additionally, gusty southerly winds are expected at all terminals outside thunderstorms, with speeds approaching the 25-30 kt range mid- late Monday morning and likely continuing through the afternoon.

Extended Aviation Outlook: Periods of flight restrictions are possible with showers and thunderstorms Monday afternoon as a strong cold front passes by. Very gusty winds are expected outside of any shower and thunderstorm activity at all terminals Monday.

MARINE

Gusty southerly winds will develop across local waters tonight well in advance of a cold front approaching from the west Monday. An abrupt wind shift will occur early Monday evening as fropa occurs. Solid Small Craft Advisory conditions are expected across all waters late tonight through Tuesday morning. Gale force wind gusts remain a concern across nearshore waters along the Charleston County Coast and in the Charleston Harbor immediately ahead of the front and perhaps shortly after the front when cold air advection is strong. However, confidence remains too low for a Gale Watch and could be mostly tied to shower and thunderstorm activity that shift offshore with the front during what would be the peak of the event.

EQUIPMENT

The KCLX radar is scheduled for radome panel replacement March 17-20, 2026. The radar will be down during this time. Users are encouraged to use data from the following nearby radar sites during the maintenance outage:

KCAE - Columbia, SC KLTX - Wilmington, NC KJAX - Jacksonville, FL KVAX - Moody AFB, GA KJGX - Robbins AFB, GA

CHS WATCHES/WARNINGS/ADVISORIES

GA...Freeze Watch from late Monday night through Tuesday morning for GAZ087-088-099-100-114-115. SC...Freeze Watch from late Monday night through Tuesday morning for SCZ040-042. Lake Wind Advisory from 4 AM Monday to 2 AM EDT Tuesday for SCZ045. MARINE...Small Craft Advisory from 8 AM Monday to midnight EDT Monday night for AMZ330. Small Craft Advisory from midnight tonight to noon EDT Tuesday for AMZ350-352-354-374.