textproduct: Charleston

WHAT HAS CHANGED

All Key Messages and sections were updated.

KEY MESSAGES

- 1) Areas of fog, locally dense, are possible across the South Carolina Lowcountry and Southeast Georgia this morning.

- 2) Rain chances likely to increase late in the week, though no hazardous weather is anticipated at this time.

DISCUSSION

KEY MESSAGE 1: Areas of fog, locally dense, are possible across the South Carolina Lowcountry and Southeast Georgia this morning.

Low-level moisture appears to be a tad deeper compared to the past few mornings with higher 1000 hPa condensation pressure deficits noted. The risk for shallow fog will increase over the next few hours as the boundary layer decouples and radiational cooling maximizes. With slightly favorable fog parameters in place, shallow fog layers could thicken a bit more than what has been experienced over the past few mornings resulting in a bit more in the way of meaningful fog and lower visibilities. The fog that does form could be locally dense at times with visibilities dropping to 1/4 NM or less at times, especially near bodies of water and other low-lying areas such as marshes, swamps and large ditches. The area from Reidsville to Townsend north to Hampton, Beaufort and Walterboro, including parts of the Savannah Metro Area, looks to be the corridor of most concern for more meaningful fog development through daybreak. The need for a Special Weather Statement or even a Dense Fog Advisory will be reassessed as the early morning progresses.

KEY MESSAGE 2: Rain chances likely to increase late in the week, though no hazardous weather is anticipated at this time.

The area will remain along the western flanks of Atlantic high pressure centered well offshore. Early morning water vapor imagery shows a well defined Tropical Upper Tropospheric Trough (TUTT) low positioned near 29N/75W at 20/06z. Broad subsidence aloft along the western flanks of the TUTT will continue to reside over the area through tonight with subtropical ridging progged to hold aloft across much of the Southeast States. The TUTT is forecast to slowly weaken and remain well offshore as the it propagates west/northwest along the backside of the Subtropical Anticyclone meandering near Bermuda. The net result will be a continuation of warm, rain-free conditions with some high clouds spreading in at times.

Low-level thicknesses are progged to max out about 10-30 meters higher than Tuesday as subsidence aloft builds. Highs are poised to warm into the lower-mid 90s inland with upper 70s/near 80 at the beaches. Temperatures across the coastal counties will remain what somewhat tempered as another robust, pure sea breeze circulation propagates steadily inland through the afternoon. Similar to the past few nights, it will take until the early morning hours Thursday before the boundary fully decouples and influences from the afternoon sea breeze wane. Lows will range from the mid 60s inland to the lower 70s at the beaches. Low- level moisture profiles and 1000 hPa condensation pressure deficits do not look as favorable for fog development compared to this morning, but some shallow ground fog appears likely, especially away from the immediate coast.

Upper level ridging lingers across the southeastern CONUS Thursday, as a sfc cold front stalls out along the Tennessee River Valley. As such, should see largely dry conditions prevail across our area, with highs forecast to rise into the lower 90s under mostly sunny skies.

Will see the aforementioned cold front sag southward over the Carolinas by Friday, causing the upper level ridge to shift over the Atlantic. While the exact position of the front and how far south it progresses will be the key factor in determining rainfall coverage and amounts, current trends continue to favor a strong Atlantic ridge. This would keep the front displaced just to our west and north, and thus limit our chances for seeing meaningful rainfall. Ensemble guidance continues to follow this trend as well, with probabilities for seeing rainfall greater than an inch through Saturday remaining less than 25%. So, while trends currently favor a drier, less impactful event, still encourage folks to monitor the latest forecast as subtle shifts in track may still occur. Otherwise, expect the severe potential with any shower/storm to remain low, given the lack of forcing and moisture in place.

AVIATION /06Z WEDNESDAY THROUGH SUNDAY/

20/06z TAF Discussion: KCHS/JZI: The risk for fog will increase through daybreak. It is not exactly clear how significant any fog will become with the better fog parameters forecast to remain west and southwest of both terminals; however, guidance is trending lower with vsbys and the 06z TAFs will reflect this trend. Prevailing vsbys were limited to low-end MVFR at both terminals with TEMPO groups dropping right to alternate minimums at KCHS and just below alternate minimums at KJZI. The fog will likely remain somewhat shallow so cig establishment is not expected. The fog will quickly mix out after daybreak with conditions quickly returning to VFR by 13z. VFR will then prevail for the remainder of the 06z TAF period.

KSAV: The risk for fog will increase through daybreak. The terminal looks to be positioned the area of most favorable fog parameters, but it remains unclear how low vsbys will go given low-level moisture still remains fairly shallow. Expect MVFR vsbys by 09z with prevailing conditions dropping to alternate minimums by 10z. Opted for a TEMPO group for 1/2SM BR BKN003 with the anticipation of some pockets of dense fog occurring. The fog will quickly mix out after daybreak with conditions quickly returning to VFR by 13z. VFR will then prevail for the remainder of the 06z TAF period.

Extended Aviation Outlook: There are no high confidence concerns.

MARINE

Through Tonight: Quiet conditions will persist with the region positioned along the western flanks of Atlantic high pressure centered well offshore. East/southeast winds will prevail with speeds less than 15 kt, although some local enhancement along the land/sea interface and Charleston Harbor will likely occur with the sea breeze. Seas will average 2-4 ft.

Thursday through Sunday: No marine concerns are expected. High pressure to the east will drive onshore east-southeasterly flow each day, with wind speeds mostly topping out in the 10-15 knot range. Each afternoon and evening there could be some local enhancement along the land/sea interface with the diurnal sea breeze. Seas will average 2-4 feet through the period.

Rip Currents: A lingering 9 sec, 2-3 ft swell will keep a moderate rip current risk in place for all beaches through this evening.

CHS WATCHES/WARNINGS/ADVISORIES

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