textproduct: Charleston

SYNOPSIS

High pressure will prevail through this weekend. A cold front will move through the area early next week.

NEAR TERM /THROUGH TONIGHT/

Today: A weak cold front is currently stalled near the Berkeley/ Dorchester county line with a stratus deck expanding on the cool side of the boundary. The southern push of the cold front does look limited though as the mid-level wave that is responsible is rapidly pulling east of Nova Scotia. As such, the front will likely wash out relatively quickly this afternoon with the stratus deck slowly lifting through the afternoon. The main noticeable difference behind the front will be the high temperatures in the 60s (mainly due to the increased cloud cover), while temperatures across southern Georgia will approach 80 degrees. No precipitation is expected.

Tonight: A mid-level disturbance will cross the Mid-Atlantic states with winds turning from the southwest. Higher theta-e air will sweep northeast with dewpoint depressions nearing zero. Low temperatures are forecast to be in the mid to upper 50s, or right near the afternoon crossover temperature. However, winds will likely not go calm everywhere due to the slightly increased pressure gradient, as such, patchy fog is expected, with some areas of fog possible were the PBL completely decouples. Dry weather to persist.

SHORT TERM /SATURDAY THROUGH MONDAY/

Saturday: Patchy to areas of fog in the morning, will quickly dissipate as the mid-level disturbance from tonight exits the Mid- Atlantic. Behind this wave, low level winds will turn from the northwest or downslope flow. During this type of regime, high temperatures normally over perform. Even the GFS and ECMWF 850mb temperature fields advertise an expanding zone of 14 to 17C across eastern Georgia and southwest South Carolina. Forecast soundings are showing near dry adiabatic lapse rates, or a completely mixed PBL, up to around 900mb. High temperatures tomorrow are forecast to be near 80 degrees, or just shy, in multiple locations. One main limiting factor for high temperatures along the coast though will be an inland moving sea breeze. Water temperatures along the coast are in the mid to upper 50s, so as soon as the sea breeze moves through temperatures will drop. Given the persistent offshore flow, it does appear a delayed sea breeze, or warmer temperatures, is the way to go. This will put high temperature records in jeopardy at both KCHS and KSAV for Saturday. More details can be found in the climate section below. A weak backdoor cold front will then start to ooze southwest with winds turning from the northeast overnight. Expect low temperatures in the lower 50s (towards the TriCounty) and upper 50s across interior Georgia.

Sunday: Surface high pressure will be located across central North Carolina with easterly flow over South Carolina and Georgia. 850mb temperatures do relax to around 10 degrees C and with onshore flow (winds off of the cooler shelf waters), expect highs 5 to 10 degrees cooler Sunday compared to Saturday (or in the lower to mid 70s). No precipitation is forecast.

Monday: The forecast area will remain under llvl return flow as a cold front approaches from the west. West winds will increase during the afternoon to 15 to 20 mph with gusts around 25 mph. It is possible that a Lake Wind Advisory will be needed for late Monday. NAM12 indicates that 1000-850mb thicknesses may increase to 1377m by Monday afternoon. Using a blend of MOS, high temperatures are forecast to generally range in the mid 70s. Short term guidance indicates that a thinning band of showers along and ahead of the cold front. The forecast will indicate 20 to 30 PoPs for rain showers during the afternoon and evening.

LONG TERM /MONDAY NIGHT THROUGH FRIDAY/

Monday night, northwest winds will remain around 10 mph through the overnight hours. GFS indicates that H85 temperatures will cool from 11C along a line from KSAV to KCXM at 0Z to around 6C by 12Z. The ongoing CAA and clearing cloud cover should allow freezing to sub- freezing temperatures generally along and west of I-95 by daybreak Tuesday, mid 30s to the east.

Cold air advection will continue across the forecast area on Tuesday. The forecast will indicate very dry conditions, RH in the mid to upper 20s, and below normal temperatures. In fact, with mostly sunny conditions high temperatures may only reach the low 50s. The coldest conditions forecast for Tuesday night into Wednesday morning, with low temperatures in the upper 20s to low 30s. The cold temperatures combined with wind speeds around 5 mph may result in wind chill values in the low to mid 20s degrees across the inland counties. LREF probs of wind chill values less than 20F peaks across inland GA with values around 20 percent.

Wednesday through Thursday, the forecast area will remain between a sfc trough centered over the east facing slopes of the Appalachians and broad high pressure across FL. This pattern should support light west winds with mostly clear sky. Temperatures should slowly moderate, with temperatures returning to normal by Thursday.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

Today and Tonight: VFR conditions this afternoon as a surface cold front remains stalled just to the northwest of KCHS. Overnight, some patchy fog is possible at the terminals as moisture rich air surges northeast. Crossover temperatures will likely be reached at the terminals, but not exceeded by more than a degree. The other related inhibiting factor will be the persistent southwest wind. Some decoupling is likely at rural locations (such as KJZI), but not as likely at KCHS and KSAV. Some restrictions from fog are possible (especially at KJZI).

Saturday and Sunday: Some morning fog will quickly dissipate with all terminals going VFR. Northwest winds Saturday will turn from the east Saturday night and persist into Sunday.

Extended Aviation Outlook: VFR. Gusty winds are possible on Monday.

MARINE

Today and Tonight: A weak cold front has stalled across the nearshore South Carolina waters and will quickly dissipate this evening. Winds will turn from the southwest 10 to 15 kt. Expect seas 1 to 2 ft. No Small Craft Advisories are forecast.

Saturday and Sunday: Westerly winds on Saturday will start to back from the southeast as a sea breeze circulation initiates. Easterly flow will then persist Sunday as surface high pressure anchors across central North Carolina. Seas 2 to 4 ft. No marine headlines are expected at this time.

Monday through Wednesday: Winds will strengthen through Monday as a cold front approaches from the west. West winds across the Atlantic waters are forecast to increase to 15 to 20 kts with gusts around 25 kts. As a result, sea should build to 3 to 6 ft by Monday evening. Small Craft Advisories will likely be needed for all marine zones outside the CHS Harbor beginning on Monday.

The cold front is timed to push offshore Monday evening, resulting in winds to shift from the northwest. The pinched pressure gradient and CAA should allow gusts to increase to around 30 kts across the outer GA waters Monday night.

The arrival of high pressure will allow wind and sea conditions to gradually improve Tuesday through Wednesday. Winds are forecast to remain less than 15 kts with seas ranging to 1 to 3 ft by Wednesday.

CLIMATE

Record High Temperatures:

December 27: KCHS: 78/2021 KCXM: 76/2015 KSAV: 80/2015

CHS WATCHES/WARNINGS/ADVISORIES

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