textproduct: Charleston

WHAT HAS CHANGED

Ended the Winter Weather Advisory at 4 PM. Temperatures have trended cooler during the early week.

KEY MESSAGES

- 1) Wet and chilly conditions tonight.

- 2) Arctic air will yield very cold temperatures Monday night into next weekend, with Cold Weather Advisories possible.

DISCUSSION

KEY MESSAGE 1: Wet and chilly conditions tonight.

As of late this afternoon, temperatures have warmed above freezing, ending the threat for winter precip. By late this afternoon, temperatures are forecast to range from the 30s across northern Berkeley County to the low 60s along the Altamaha River.

Guidance continues to indicate a solid convective band will approach the CWA from the west later today, timed to reach the inland counties during the early evening and the coast before midnight. High resolution guidance shows a solid band of showers with embedded thunderstorms remain along and ahead of the cold front. Temperatures and dewpoints may continue to warm into this evening. However, forecast soundings indicate that temperatures in the 50s to low 60s should yield little to no instability under a significant temperature inversion. The environment will feature strong deep shear, which should aid in keeping the convective line organized. Line segments of strong storms may reach interior GA, possibly highlighted with Special Weather Statements for strong gusty winds. Overall, the convective line should trend weaker as it approaches the coast. Ragged showers may continue to develop ahead of the cold front into the late night hours. By the pre-dawn hours, conditions should become dry with gusty west winds.

KEY MESSAGE 2: Arctic air will yield very cold temperatures Monday night into next weekend, with Cold Weather Advisories possible.

Not too much has changed regarding the upcoming temperatures this week. As strong arctic high pressure (~1040 mb) ushers cold, dry air into the region post-FROPA conditions, temps. are forecast to be well below normal. The ESAT NAEFS standardized anomalies highlights this well with values ranging from -2 to -4 for minimum temperatures up through the weekend. Also, the ECMWF MSLP anomalies showcase values from +2 to +5 across the Southeast through the majority of the week. It's also fairly high model confidence as IQR shows a 1 to 2 degree spread for minimum temperature values Tues. and Wed. morning. Let's talk about the upcoming week.

Mon. night/Tues. morning: Minimum temperatures forecast to drop into the mid-teens and low 20s west of I-95 (including the Francis Marion Forest) with temps. a tad warmer near the coastline. Mixed the NBM/NBM10 into the overnight temperatures as the NBM appeared to be struggling to realize the strength of the arctic air funneling into the region. If you take a look at the 850 temps. aloft, they even dip below 0C overnight into the morning. These conditions combined with light west-northwesterly winds could result in widespread wind chill values in the low to mid teens from interior counties all the way down to the coastline. Some guidance has been indicating that minimum wind chill values could drop range around 10 degrees for counties like Bulloch, Evans, Tattnall, and Candler. A Cold Weather Advisory will likely be needed for the entire forecast region.

Tues. night/Wed. morning: Forecast remains a bit warmer as temperatures range in the low to mid 20s across the interior counties with upper 20s along the coastline. Highest chance for temperatures below 20 degrees seems to be across inland southeast Georgia. Thus, it seems more likely we would need a Cold Weather Advisory across those portions of the forecast region.

This cold airmass will likely stick around through late this week as a reinforcing cold front moves through on Wednesday night and pushes another shot of cold air into the region from the northwest. It's reasonable to say that we could have a few hours of wind chill values below 20 degrees every morning into the weekend and additional Cold Weather Advisories might be needed.

AVIATION /20Z SUNDAY THROUGH FRIDAY/

Prior to the 18Z TAFs, observations across the terminals indicated LIFR ceilings with at least IFR visibility in fog. In addition, model soundings and VWP from adjacent radars indicate strong winds aloft, resulting in LLWS of at least 35 kts at 2 kft. The fog should gradually improve to VFR by 21z, however, IFR ceilings will remain through late tonight. A band of moderate showers with some embedded thunderstorms is timed to push across the terminals this evening, mainly between 0-3Z. This convective band will be highlighted with TEMPOs. Following the cold front, winds will shift from the WNW with gusts developing into the low 20s kts by 10Z.

Extended Aviation Forecast: VFR.

MARINE

Through tonight: A fairly slow warm-up in temperatures this morning as the cold-air damming (CAD) holding firm across the region. Taking a look at the 15Z surface analysis indicates a nearly stationary warm front located across the local marines zones, yielding southeasterly winds at 10 to 15 kt. A bit of tough forecast this evening as it largely depends on how much of the CAD breaks down and if this warm front eventually lifts across the region. As a strong cold front extending across the Deep South approaches the region, this aforementioned dense fog should clear out. As this front marches towards the coastline, southeasterly winds will rapidly pick up this evening with speeds ranging from 15 to 20 with gusts up to 30 kt. This front should also haul a band of showers and thunderstorms along with it through the overnight into the early morning hours on Monday. It's important to note that a couple of these thunderstorms could be severe esp. as it passes over the Atlantic waters. Seas will range from 6 to 8 ft as the east-southeasterly swell continues to build into the local waters. As marine conditions remain quite hazardous, Small Craft Advisories have been issued for ALL marine zones (except for the Charleston Harbor).

Monday through Thursday: After the front passes through the marine zones, expect west-northwesterly winds to remain elevated at 15 to 20 kt with gusts up to 30 kt. Expect the swell to taper back with seas ranging from 4 to 7 ft through Tuesday. Therefore, Small Craft Advisories will be ongoing through Tuesday morning with the continuation of hazardous marine conditions. As for the remainder of the period , marine conditions become less chaotic with winds remaining under advisory criteria and seas backing down to 2 to 4 ft.

EQUIPMENT

The KCLX radar will remain out of service. Critical parts are on order and should arrive on Monday. Users should use adjacent WSR-88D sites, including KCAE, KLTX, KJAX, KVAX and KJGX.

CHS WATCHES/WARNINGS/ADVISORIES

GA...None. SC...None. MARINE...Small Craft Advisory until 6 AM EST Tuesday for AMZ350-352-354. Small Craft Advisory until 10 AM EST Tuesday for AMZ374.