textproduct: Charleston

SYNOPSIS

High pressure will prevail for the remainder of the week, followed by a cold front moving through the area this weekend.

NEAR TERM /THROUGH TONIGHT/

Through Daybreak: A considerably colder and drier airmass continues to filter into the region this morning. Temperatures are still expected to drop into the upper 20s well inland to the upper 30s at the beaches. Wind speeds will slowly come down, but enough wind will be present through daybreak to push wind chills into the mid-upper 20s with some spots across far interior Southeast Georgia possibly bottoming out in the 20-25 deg range. A few spots could see wind chills get as low as 20 degrees, which is right at Cold Weather Advisory criteria, but as noted for the past few forecast cycles, the situation looks too marginal and brief to support the issuance of an advisory. The issuance of a Special Weather Statement highlighting brief advisory conditions will be considered should wind chills approach 20 degrees. Winds on Lake Moultrie continue to subside and the Lake Wind Advisory has been cancelled.

Today: High pressure centered over the Southern Plains this morning will slowly build across the Deep South into the Southeast U.S. today. Temperatures aloft will be rather cold with the area remaining under the influence of a deep, long- wave trough across the eastern CONUS. Temperatures at 850 hPa are expected to bottom out in the -1 to +2C range this afternoon with the mean 925-700 hPa flow forecast to hold too much of a westerly component with the approach of yet another shortwave to become fully downslope dominated. A blend of the 30/01z NBM with output from full sun low-level thickness schemes supports highs in the upper 40s/lower 50s.

Tonight: It will be another cold night for the region, but there is uncertainty on how much boundary layer decoupling will occur and how it will impact overnight lows. There are signals that the boundary layer will decouple this evening as a nebulous pressure pattern develops over the Southeast U.S. downwind of the southern Appalachians. There are signals that the gradient may tighten up a bit after midnight in response to a shortwave crossing the central Appalachians and inducing a weak lee-side trough from the South Carolina Upstate into western Virginia. This could disrupt the radiative process.

30/00z guidance is mixed on how much recoupling will occur early Wednesday which is reflected in a wider than normal range of low temperature forecasts considering there will likely be some degree of a radiational component. A blend of the colder NAM/GFS/ECMWF statistical guidance packages with the warmer 30/01z NBM was used to construct overnight lows. This approach favors a bit more decoupling and a stronger radiational cooling regime, especially over southern South Carolina. It should be noted direct output both the RAP and H3R runs are about a full category warmer across the area and favor a bit more wind overnight. Adjustments to the low temperature forecast will most certainly be needed as trends become more apparent later today. Wind chills are forecast to be a degree or two colder than lows across southern South Carolina (mid-upper 20s) and about 3-4 degrees colder across Southeast Georgia (lower- mid 20s) where a bit more wind will linger through sunrise. Conditions are not expected to drop to Cold Weather Advisory thresholds.

SHORT TERM /WEDNESDAY THROUGH FRIDAY/

While not quite as cool, Wednesday will remain on the cooler side of normal as northwesterly flow persist. Ample sunshine should help make it feel a little warmer, with afternoon highs expected to be in the lower to mid 50s. Overnight, lows dip down into the mid 30s across inland areas while areas near the beaches are a bit warmer in the upper 30s to lower 40s. A weak front moves through on Thursday, bringing a resurgence of westerly winds across the area which become marginally gusty in the teens, along with high temperatures in the upper 50s to lower 60s. Overnight into Friday, radiational cooling brings overnight temperatures back into the mid 30s inland and up to the lower/mid 40s along the coast. Temperatures continue to moderate on Friday as a warm front lifts across the region, bringing afternoon temperatures in the lower to mid 60s.

LONG TERM /FRIDAY NIGHT THROUGH MONDAY/

Behind the warm front, overnight lows into the weekend will be much warmer in the mid 40s to lower 50s. A weak shortwave looks to move across the area on Saturday, accompanied by a surface low pressure system in some models. This will bring chances for light to moderate rain showers starting early Saturday morning and ending overnight into Sunday, along with temperatures in the lower to upper 60s. Ensemble clustering analysis shows that model agreement is fairly high, with the two dominant clusters showing 70-80% probabilities for a quarter inch of rain across across southeast South Carolina, and 50-70% probabilities across southeast Georgia. Probabilities for half an inch of rain are about 20-30% less across the board. Temperatures cool into the mid 50s to lower 60s on Sunday as a cold front moves through, warming up into the lower to mid 60s on Monday.

AVIATION /12Z TUESDAY THROUGH SATURDAY/

30/12z TAF Discussion: KCHS/KJZI/KSAV: VFR through 31/12z.

Extended Aviation Outlook: VFR conditions expected to prevail through the rest of the week. Chances for rain return on Saturday, along with possible flight category restrictions from both lowered cigs and vsbys.

MARINE

The Small Craft Advisory for the nearshore waters has been extended until 9 AM. Wind and wind gusts are still near advisory thresholds. The advisory continues for the Georgia offshore waters through 1 PM.

Through Tonight: Northwest winds 10-15 kt will persist across the waters through tonight with high pressure displaced well the west and southwest. Seas will subside 2-4 ft this afternoon and 1-3 ft tonight.

Wednesday through Saturday: Winds remain out of the northwest throughout most of Wednesday as surface high pressure builds across the southeast. Winds pickup overnight into Thursday as a front moves towards and then through the area, bringing the waters from Savannah to Altamaha Sound 20-60nm out to Small Craft Criteria, due to wind gusts near 25 knots for a few hours Thursday morning. Westerly winds remain gusty throughout the day, weakening overnight into Friday. Chances for rain return on Saturday as a cold front begins to move through, with gusty winds near Small Craft Criteria possible, especially in the outer Georgia waters Saturday morning/afternoon.

CHS WATCHES/WARNINGS/ADVISORIES

GA...None. SC...None. MARINE...Small Craft Advisory until 9 AM EST this morning for AMZ350- 352-354. Small Craft Advisory until 1 PM EST this afternoon for AMZ374.