textproduct: Charleston

WHAT HAS CHANGED

An Air Quality Key Message was introduced.

KEY MESSAGES

- 1) Poor air quality with smokey conditions to linger into Thursday, possibly longer.

- 2) Above normal temperatures with low afternoon humidity expected through Friday.

- 3) A cold front could provide some much needed rainfall across southeast Georgia and South Carolina this weekend.

DISCUSSION

KEY MESSAGE 1: Poor air quality with smokey conditions to linger into Thursday, possibly longer.

The South Carolina Department of Environmental Services (SCDES) has issued an Air Quality Alert for all of the Lowcountry through late Thursday evening.

A band of smoke generated by wildfires over southern Georgia continues to impact far inland portions of Southeast Georgia into the Lowcountry. Visibilities in this area of smoke were running about 3-5 miles at 22/22z, but could drop lower overnight as the nocturnal inversion sets up. It is unclear is the smoke will become dense enough for a Dense Smoke Advisory, but trends will be monitored. Some degree of smoke could linger across expand east back to the coast as the inversion deepens. Smoke with "areas of" and "patchy" qualifiers were introduced through tonight.

For Thursday, the latest vertically integrated smoke guidance expands smoke across all of the Lowcountry and Southeast Georgia as the wildfires to the south persist. It is unclear how much smoke will remain at the surface given the fairly high mixing heights expected, but at least some degree is likely to persist. Again, smoke with a "patchy" qualifier was introduced to trend. Smoke may linger into the weekend depending on how much rain falls and how the primary steering trajectories change with time.

KEY MESSAGE 2: Above normal temperatures with low afternoon humidity expected through Friday.

Quiet weather conditions will prevail across the region through late week while sfc high pressure remains centered across the western Atlantic under modest ridging building from the west- southwest aloft. High temps will peak above normal this afternoon, generally in the low-mid 80s away from the coast (warmest across inland Georgia). Afternoon temps will be a few degrees warmer for Thursday and Friday as subtle ridging persists aloft, with highs in the mid- upper 80s away from the coast where a sea breeze turns sfc flow onshore during peak heating. Dry conditions will prevail during this period and moisture return remains modest, suggesting RH values dropping into the low-mid 20s west of I-95 each afternoon as strong sfc heating promotes deep mixing into drier air. Although RH values are considered critical, sfc winds are only expected to gust up to around 15 mph, strongest in higher RH locations (near the coast) where a marine layer/influence occurs with an afternoon sea breeze each day. Given very dry fuels and low RH, fire danger will remain the primary concern each afternoon. In fact, recent/ongoing fires across southern Georgia could result in air quality issues across the local area during the next few days.

KEY MESSAGE 3: A cold front could provide some much needed rainfall across southeast Georgia and South Carolina this weekend.

Latest guidance continues to support H5 vort energy rippling across the Southeast United States on Saturday, helping force a sfc cold front across the region late day and overnight. Ahead of the front, weak instability and increasing moisture/convergence associated with a sea breeze could support few to scattered showers/thunderstorms Saturday afternoon. However, precip coverage is likely to increase Saturday evening with the passage of the cold front. The bulk of precip should occur with FROPA and although precip doesn't look particularly heavy, some locations could experience upwards to 0.25- 0.50 inches of rainfall accumulation. Some guidance continues to suggest that rainfall could linger into Sunday as weak low pressure attempts to develop along the front offshore.

AVIATION /21Z WEDNESDAY THROUGH MONDAY/

23/00Z TAF Discussion: KCHS/KJZI/KSAV: VFR through 24/00z for all terminals. Large wildfires burning over southern Georgia continue to produce smoke. Some of this may reach KSAV around break and could spread into KCHS just before the sea breeze pushes through Thursday afternoon. Vsbys were limited to 6SM in FU for now, but there is a chance lower vsbys could occur. Confidence in the smoke/vsby forecast is low.

Extended Aviation Outlook: VFR conditions will prevail through Friday with a sea breeze likely to occur during afternoon hours. Scattered showers and/or thunderstorms could impact the terminals late Saturday and Sunday.

MARINE

Conditions are expected to remain below Small Craft Advisory thresholds this week with high pressure remaining centered across the western Atlantic. The setup continues to favor a southerly flow across local waters into Saturday with wind speeds generally in the 10-15 kt range at times, although slight enhancement is likely along the land/sea interface where a daily seabreeze develops, then shifts inland. A cold front should then shift across the region this weekend, tightening the pressure gradient across local waters and favoring 15-20 kt winds on Saturday that turn more offshore with fropa Saturday night into Sunday. Seas should generally range between 2-3 ft through late week, then slightly build to 3-4 ft near fropa late weekend. However, both winds/seas are anticipated to remain below Small Craft Advisory levels this weekend into early next week.

CHS WATCHES/WARNINGS/ADVISORIES

GA...None. SC...Air Quality Alert until midnight EDT Thursday night for SCZ040- 042>045-147>152. MARINE...None.