textproduct: Charleston

SYNOPSIS

High pressure will prevail through Saturday, then an arctic cold front will sweep through late Sunday. Dry high pressure will then rebuild into the region.

NEAR TERM /UNTIL 6 AM FRIDAY MORNING/

Surface high pressure moving into the region is keeping our area very dry, while also causing winds to ease. Winds should remain very light near the coast and probably go calm inland. The combination of the mostly clear skies, calm winds, and dry conditions will lead to plenty of radiational cooling tonight. Based on temperature trends and new model data, we ticked low temperatures down a bit, especially further inland. Lows are forecasted to fall below freezing away from the coastal corridor, with a few of the typical cold spots dipping into the mid to upper 20s. Along the coast, mid to upper 30s will be common.

SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/

Friday and Saturday: Zonal flow across the Southeast U.S. will become increasing more cyclonic through the weekend as a powerful upper trough digs across the eastern CONUS on Sunday. The trough will help drive a bitterly cold airmass south into the United States with the arctic cold front progged to pass through the area during the day Sunday. Friday and Saturday look quiet as high pressure over the Southeast gradually shifts offshore into the Atlantic. Temperatures look to be fairly seasonable with highs peaking into the lower-mid 60s Friday and the mid-upper 60s Saturday. Lows Saturday morning will fall into the upper 30s well inland to the lower 50s at the beaches.

Sunday: Sunday will usher in a quick and dramatic change as an arctic cold front shifts offshore and bitterly cold weather settles into the Lowcountry and Southeast Georgia for Sunday night. There are some slight timing differences noted with FROPA Sunday, but the front should be well offshore and the south by the evening hours. A ribbon of PWATS >1" is forecast to align with the front. While there is no meaningful forcing noted aloft, there may be be enough forcing with the front itself to support a few showers. A handful of the GFS and ECMWF ensemble members, along with their AI counterparts, do show some measurable QPF Sunday afternoon and its great to see the 11/13z NBM follow a similar trend. Chance pops for showers have been introduced as a result. Highs will be closely tied to FROPA timing and it is possible that temperatures may fall during the afternoon hours. For now, highs look to peak in the upper 50s to lower 60s before FROPA, but some changes may be needed once confidence in FROPA timing increases.

LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/

Sunday Night and Monday: A brief, but intense outbreak of bitterly cold air will impact the region Sunday night into Monday as a modified arctic airmass passes through. This has the potential to the be the coldest airmass of the season, even colder than the one that brought a widespread freeze and cold wind chills the region back in November. Lows Sunday night could drop into the upper teens to mid 20s inland to upper 20s at the beaches. Lingering north winds of 5-15 mph aided by some persistent cold air advection and a fairly tight pressure gradient will likely push wind chill values into the upper single digits above zero to upper teens range early Sunday morning, which is well into the Cold Weather Advisory criteria and dipping into Extreme Cold Warning criteria. Confidence in reaching Cold Weather Advisory criteria is HIGH (LREF probabilities: 75-100%, highest inland) with lower confidence in reaching Extreme Cold Warning criteria (LREF probabilities 15-25% inland; 0-10% coast). Highs Monday will only peak into the upper 30s-mid 40s with wind chills in the mid-upper 30s. Lows Monday night will drop into the upper teens to lower 20s inland to the mid 30s at the beaches. Depending on the position of the surface high, there is a chance some degree of wind could persist into early Tuesday. Again, wind chills could approach Cold Weather Advisory criteria in spots, but confidence in reaching these levels is only in the moderate range this far out.

Tuesday through Thursday: Temperature will quickly moderate through the remainder of the extended period as high pressure shifts offshore and a warmer southerly flow develops across the Southeast States. Levels could actually reach above normal levels by Wednesday and Thursday. Some low-end rain chances may return Wednesday night into Thursday, especially at the coast, if a weak coastal trough develops offshore and impulses of vorticity aloft eject across the region ahead of an upper low that is forecast to dig across the Southern Plains.

Lake Winds: Winds are expected to surge on Lake Moultrie Sunday night into Monday as cold high pressure builds into the region. Strong cold air advection coupled with increasingly favorable mixing profiles should support winds surging above 20 kt with gusts near 30. A Lake Wind Advisory will likely be needed.

AVIATION /00Z FRIDAY THROUGH TUESDAY/

18Z TAFs: VFR.

Extended Aviation Outlook: Gusty winds possible Sunday afternoon into Monday morning.

MARINE

Tonight: Expect northwest winds mostly in the 10-15 knot range this evening. Overnight, wind speeds will remain similar while wind direction becomes more westerly. Seas will be mostly 2-3 feet overnight.

Thursday through Monday: The main concern for the period centers on the increasing risk for elevated winds Sunday night into Monday behind an arctic cold front. There is a moderate risk for gales with LREF probabilities for reaching Gale Warning criteria, at least in frequent gusts, increasing to 40-70% across the nearshore waters and as high as 85% over the Georgia offshore waters Sunday night. At the very least, Small Craft Advisories will be needed for all zones, but Gale Watches/Warnings may also be needed as the event draws closer. Seas could build as high as 4-7 ft nearshore waters and 7-9 ft over the Georgia offshore waters.

CLIMATE

Record Low Maximum Temperatures:

December 15: KCHS: 39/1943 KCXM: 38/1904

Record Low Temperatures:

December 15: KCXM: 23/1943

CHS WATCHES/WARNINGS/ADVISORIES

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