textproduct: Charleston

WHAT HAS CHANGED

The aviation section has been updated for the 06Z TAF issuance. Cold temperatures are likely this morning and Wednesday morning and remain in key message 1. The potential for a winter weather event remains addressed in key message 2.

KEY MESSAGES

- 1) Cold temperatures in the low to mid 20s (upper 20s to lower 30s along the coast) likely this morning and Wednesday morning. - 2) Widespread precipitation is expected to occur this weekend, bringing increasing potential for a winter weather event to impact the region.

DISCUSSION

KEY MESSAGE 1: Cold temperatures in the low to mid 20s (upper 20s to lower 30s along the coast) likely this morning and Wednesday morning.

Dry high pressure centered across the Central United States will continue to build/spread east into the region tonight, before passing to the north late Tuesday into Wednesday. The high will bring colder than normal temperatures to the local area as a light wind under clear skies favors strong radiational cooling. Latest guidance supports low temperatures in the low-mid 20s late tonight into daybreak and again early Wednesday, except near the coast where temps remain in the low-mid 30s. Additionally, overnight lows early Wednesday appear to be 1-2 degrees warmer than what is likely to occur prior to daybreak this morning. Given a light wind associated with high pressure, wind chill is likely to be limited each morning. Cold Weather Advisories are not expected for either morning at this time.

KEY MESSAGE 2: Widespread precipitation is expected to occur this weekend, bringing increasing potential for a winter weather event to impact the region.

Models continue to support potential for a winter weather event impacting at least portions of southeast South Carolina and southeast Georgia this weekend. The synoptic pattern will feature strong, cold high pressure wedging down the Eastern Seaboard through the weekend, with an area of low pressure favored to develop off the Southeast coast. Broad mid level troughing will largely be in place to start, with a stronger wave diving into the region later in the weekend. Further aloft, we can find an impressive upper level jet possibly on the order of 160+ knots. The conditions will certainly be in place to support precipitation spreading across the area, with increasing confidence of some overlap with colder temperatures.

Attention then turns to precipitation type as cold air settles into the region. While forecast details on timing, amounts, and p-types will continue to be refined in the coming days, a perusal of model soundings indicate a notable warm nose centered around 850 mb with surface temps dropping to near or below freezing Saturday night into Sunday morning. This would suggest freezing rain as a primary threat, which also jives with the latest NBM precip probabilities. The Probabilistic Winter Storm Severity Index (WSSI-P) shows chances of minor winter storm impacts across the entire area, with even a 20- 40% chance of moderate impacts especially north of I-16.

The column begins to dry out later Sunday into Monday, but if precipitation lingers, the threat for winter weather could continue into early Monday as ensemble guidance shows high likelihood for sub- freezing temperatures again Sunday night. We will also need to be on the lookout for temps/wind chills approaching Cold Weather Advisory criteria Sunday night and beyond.

AVIATION /06Z TUESDAY THROUGH SATURDAY/

VFR conditions will prevail at CHS/JZI/SAV terminals through 06Z Wednesday.

Extended Aviation Forecast: VFR through Friday. Periods of MVFR and/or IFR conditions possible with a rain and/or mix of frozen precip over the weekend.

MARINE

Today and Tonight: High pressure will spread across the Southeast, leading to a weaker pressure gradient across local waters. This will result in a west-northwest wind between 10-20 kt to slightly weaken and turn north late day and overnight. Seas will generally range between 2-3 ft nearshore and 3-4 ft across outer Georgia waters. Small Craft Advisories are not expected during this timeframe.

Wednesday through Friday: Quiet marine conditions prevail mid week while high pressure centered north of the region shifts across the western Atlantic. A cold front will approach the Southeast late week, likely shifting across the region Friday. Northeast winds will increase post fropa, generally to the 15-20 kt range while seas build up to 3-6 ft Friday night. It is possible a Small Craft Advisory could be needed across nearshore waters off the Charleston County Coast prior to daybreak Saturday.

Saturday and Sunday: This is the period of greatest concern in regards to deteriorating wind and sea conditions across local waters. Low pressure could develop along a cold front positioned offshore, favoring a strong pressure gradient across local waters while cold air advection promotes ample mixing into enhanced low-lvl wind fields. Conditions look to support Small Craft Advisory level conditions across a majority of local waters with even a low-end risk for gale force wind gusts across northern South Carolina nearshore waters during the peak of the event Saturday night. Northeast winds gusting up to 25-30 kt appear common across most waters while seas build upwards to 7-10 ft (largest away from the coast).

CHS WATCHES/WARNINGS/ADVISORIES

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