textproduct: Charleston

WHAT HAS CHANGED

Key Message 1 was updated to reflect current cold weather trends. The Aviation Discussion was updated for the 06z TAFs.

KEY MESSAGES

- 1) Bitterly cold temperatures will persist this morning with cold weather lingering into tonight.

- 2) A cold front will bring rain showers to the South Carolina Lowcountry and Southeast Georgia late Tuesday night into Wednesday night.

DISCUSSION

KEY MESSAGE 1: Bitterly cold temperatures will persist this morning with cold weather lingering into tonight.

Today: The boundary layer is slowly decoupling across the area early this morning with temperatures at 02/05z already in the mid-upper 20s with wind chills upper teens/lower 20s. Temperature falls will remain somewhat steady over the next few hours then accelerate a bit with the approach of the diurnal minimum once a patch of thicker high clouds pushes offshore and skies clear. Lows from the mid-upper teens inland to the lower-mid 20s at the coast look on track. The combination of lingering light winds and low temperatures yield minimum Apparent Temperatures in the mid-upper teens, so the ongoing Cold Weather Advisory looks well placed.

Tonight: High pressure extending over the northern Gulf will meander east overnight and extend north through the Carolinas. This should allow the boundary layer to decouple quickly after sunset. The combination of calm winds, clear skies and a dry low-level airmass will support strong radiational cooling. The 02/01z NBM (version 4.3) is exhibiting its well documented warm bias in strong radiation regimes. Its Tuesday morning low temperature forecasts are outliers and well outside of the warmer side of the Interquartile Range (IQR) for all sites. The colder side of the guidance was favored with additional adjustments made to reflect better mesoscale influences (i.e. larger rivers and harbors, the Francis Marion National Forest and the Santee-Cooper lakes to name a few). Lows will range from the lower 20s inland to the mid-upper 30s at the beaches. Some areas across far northern Berkeley and Dorchester Counties away from the Santee-Cooper lakes could drop into the upper teens to around 20 just before daybreak. While this is right at Cold Weather Advisory criteria, the limited spatial and temporal extent of advisory conditions suggest conditions are too marginal for an advisory at this time. The need for an advisory will be reassessed later today.

KEY MESSAGE 2: A cold front will bring rain showers to the South Carolina Lowcountry and Southeast Georgia late Tuesday night into Wednesday night.

The mid-levels Tuesday night will consist of a positively tilted trough axis stretching from the Great Lakes region down into the Southern Plains. It'll gradually shift eastward, with its axis located from New England down into the Deep South by Wednesday night. This will cause WSW flow over us Tuesday night to shift more to the SW by Wednesday night. At the surface, High pressure off the Southeast U.S. Tuesday night will shift further offshore, while a cold front approaches from the west and northwest. There will be a decent plume of moisture ahead of the front, with PWATs peaking ~1.1" Wednesday afternoon. This remains close to the 90% mark for CHS, per SPC Sounding Climatology. Both deterministic and ensemble models are in fairly good agreement having rain showers overspreading our far inland areas late Tuesday night, then making it to the coast Wednesday morning. The highest POPs across our entire area are generally Wednesday afternoon. The cold front will quickly move through our area Wednesday night, with rain showers gradually ending from west to east. By daybreak Thursday, there could be a few isolated light rain showers near the beaches that will quickly move offshore. Storm total QPF should be in the 0.1- 0.3" range. Though, there are some models that have these values peaking ~0.5". Temperatures are expected to stay warm enough at the surface and higher up to only generate rain showers. Low temperatures Tuesday night will be in the upper 30s across the northern tip of Berkeley County, to the low to mid 40s everywhere else. Highs Wednesday will range from the low to mid 50s near the Santee River, to the low to mid 60s near the Altamaha River. Low temperatures Wednesday night will generally be in the mid to upper 30s, mainly reached towards daybreak Thursday.

AVIATION /06Z MONDAY THROUGH FRIDAY/

02/06z TAF Discussion: KCHS/KJZI/KSAV: VFR through 03/06z.

Extended Aviation Outlook: A cold front will bring flight restrictions Wednesday through Wednesday evening, mainly due to rain showers. VFR returns on Thursday.

MARINE

The Small Craft Advisory for the South Santee-Edisto Beach nearshore leg was extended through 4 AM to account for a few more hours of gusts 25 kt.

Today: Northwest winds will steadily diminish through the day as high pressure builds in from the west and southwest. Elevated seas above 6 ft will linger through sunset for the Georgia offshore waters where a Small Craft Advisory is in effect.

Tonight and Tuesday: Quiet conditions will linger into Tuesday as high pressure prevails. West winds tonight will back more southerly on Tuesday as the center of the high crosses the Florida peninsula. Speeds will average less than 15 kt and seas will be 4 ft or less, except 4-5 ft tonight over the Georgia offshore leg.

Tuesday Night through Friday: Surface High pressure will be over FL on Tuesday. It'll shift offshore Tuesday night into Wednesday. A cold front will approach from the west on Wednesday, quickly moving through the coastal waters and then offshore Wednesday night. High pressure builds in from the distant west on Thursday, followed by a dry cold front late Friday. Wind gusts may be high enough that we could need Small Craft Advisories for portions of our waters Wednesday night into Thursday. More Small Craft Advisories will be needed due to winds and seas on Friday.

CLIMATE

Record Low Temperatures:

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

February 3: KCHS: 21/1940

EQUIPMENT

The KCLX radar is operational, but could go down at any time. Additional repairs are needed.

CHS WATCHES/WARNINGS/ADVISORIES

GA...Cold Weather Advisory until 9 AM EST this morning for GAZ087- 088-099>101-114>119-137>141. SC...Cold Weather Advisory until 9 AM EST this morning for SCZ040- 042>045-047>052. MARINE...Small Craft Advisory until 4 AM EST early this morning for AMZ350. Small Craft Advisory until 7 PM EST this evening for AMZ374.