textproduct: Charleston

SYNOPSIS

An arctic cold front will sweep through today. Dry high pressure will then build overhead for much of the coming week.

NEAR TERM /THROUGH TONIGHT/

A strong cold front is quickly progressing through the forecast area this afternoon and as of 1 PM is located about halfway through the CWA, oriented from NE to SW. Behind the front gusty NW winds have developed, with gusts around 20 to 25 mph. A Lake Wind Advisory is in effect for Lake Moultrie beginning at 1 PM this afternoon and lasting into tomorrow morning. A dry forecast is in store through the remainder of the day, as any showers ahead of the front have dissipated offshore.

The main story through the remainder of this afternoon and into tonight will be the strong cold air advection (CAA) as strong high pressure quickly builds in behind the departing cold front. Most locations have likely reached their high temperatures for the day, with coastal locations seeing upper 60s to 70 in a few spots. These temperatures will quickly plummet as the CAA regime takes over, dropping into the 50s by later this afternoon and the 40s this evening.

The arctic high pressure will continue to build across the region tonight, setting up a bitterly cold overnight. Temperatures are forecast to drop into the low 20s across the region, which combined with the gusty winds, will yield wind chill values in the teens. A Cold Weather Advisory is in effect from 10 PM this evening into Monday morning. There is a low end chance (~20%) that some locations in the Charleston Tri-County area could see a brief moment or two of single digit wind chills in the early morning hours.

SHORT TERM /MONDAY THROUGH WEDNESDAY/

Overview: Bitter cold temperatures continue through Tuesday morning, then begin to moderate by mid week.

Monday: Deep, cold high pressure will be centered over the region. Even with full sun, highs not expected to make it much past 40, which are near record low max values for the date! Luckily, winds will be light as high pressure builds directly overhead, reducing any wind chill effects. The surface ridge axis remains directly overhead through Monday evening and overnight night, shifting a bit further east closer to daybreak. Given nearly ideal radiational cooling conditions and dew points in the lower teens to upper single digits, low temperatures into the teens away from the beaches, on the lower end of the guidance envelope, are reasonable. This would necessitate another Cold Weather Advisory for much of SE SC and SE GA inland of the Hwy 17 Corridor.

Tuesday and Wednesday: The surface ridge continues to move eastward into the Atlantic with zonal mid and upper level flow. This pattern is expected to allow a moderation in temperatures, reaching to near to slightly above normal by Wednesday. No precipitation is expected during this period.

LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/

The general zonal upper level pattern is shown by models to briefly be interrupted by a fast moving upper level trough axis and associated weak cold front Thursday. The most likely scenario with this front remains that frontolisis and waning moisture will lead to limited rainfall, with strong ensemble agreement that rainfall amounts will remain less than an inch across the area.

Friday through Sunday: the upper flow reverts back to generally zonal, with temperatures above normal, in the 60s to near 70. Models diverge again with the potential for another front and threat for precipitation to approach the area possibly by late in the period on Sunday. Confidence with whether or not this front will have any impact in our area is very low at this time.

AVIATION /18Z SUNDAY THROUGH FRIDAY/

VFR will dominate at KCHS/KJZI through the 18Z TAF period, with a brief period of MVFR cigs expected at KSAV through the first hour of the TAF period before going SKC. Thereafter, this afternoon will feature gusty winds, generally around 20-25 knots, as high pressure builds into the region behind a departing cold front. Gusty winds will continue into the overnight period, waning around daybreak.

Extended Aviation Outlook: VFR conditions prevail for KCHS, KJZI and KSAV through mid-week.

MARINE

A strong cold front will quickly push into the marine zones this afternoon, yielding a wind shift from the SW to the N/NW. As high pressure builds into the region behind the departing cold front winds are forecast to surge, with gusts reaching as high as 35 knots outside of the Charleston Harbor. A Gale Warning is now in effect for all offshore waters through Monday morning. The Charleston Harbor will see gusts around 25 knots and has a Small Craft Advisory in effect through Monday morning. It is worth noting that the 12Z HREF shows a 30-40% probability of the harbor seeing wind gusts greater than 30 knots. It is not out of the question that the Charleston Harbor may need to be upgraded to a Gale Warning at some point this afternoon/evening.

Monday through Thursday: Elevated seas at sunrise Monday morning will quickly subside through the day as high pressure passes overhead. Ridging at the surface will remain just east of the waters through at least Wednesday keeping benign marine conditions in place. A coastal trough may develop over the nearshore waters on Thursday as a cold front approaches from the west. Winds likely to increase from the south on Thursday, but still expected to remain below highlight levels.

CLIMATE

Record Low Temperatures:

December 15: KCHS: 15/1962 KCXM: 23/1943 KSAV: 19/1962

Record Low Maximum Temperatures:

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

CHS WATCHES/WARNINGS/ADVISORIES

GA...Cold Weather Advisory from 10 PM this evening to 10 AM EST Monday for GAZ087-088-099>101-114>119-137>141. SC...Cold Weather Advisory from 10 PM this evening to 10 AM EST Monday for SCZ040-042>045-047>052. Lake Wind Advisory until 4 AM EST Monday for SCZ045. MARINE...Small Craft Advisory until 9 AM EST Monday for AMZ330. Gale Warning until 7 AM EST Monday for AMZ350-352-354-374.