textproduct: Charleston

WHAT HAS CHANGED

The Aviation section was updated for the 06z TAFs. Key message 1 was added to address the cold front moving through the area today. Key message 2 discusses a potential system moving through late this weekend.

KEY MESSAGES

- 1) A cold front will pass through southeast South Carolina and southeast Georgia from the north today bringing showers and breezy conditions to the area.

- 2) A more impactful system arrives late this weekend, resulting in additional chances for precipitation and perhaps a few thunderstorms.

DISCUSSION

KEY MESSAGE 1: A cold front will pass through southeast South Carolina and southeast Georgia from the north today bringing showers and breezy conditions to the area.

Aloft, a dampening shortwave will pass through the Southeast through the evening within a broader zonal flow regime. At the surface, a cold front will approach from the north this morning and entering the northern edge of the forecast area late this afternoon. The front will make steady southward progress through the evening and should clear the area by the early morning hours on Thursday. We will see radar reflectivity start to fill in from the west in the pre-dawn hours and this very light shower activity will spread across the region through the morning. Model soundings show a notable amount of mid and low- level dry air that will take some time to moisten and erode away. So through the morning, very light rain will fall with many places not measuring and those that do will be limited to a hundredth or two. The main time period of more significant shower activity is expected to come in the late afternoon and into the evening immediately along the actual cold front. Hi-res model is in good agreement showing a somewhat robust line of showers developing and dropping through. There is even some support for an embedded thunderstorm or two, with both the HREF and NBM carrying high chances (60+%) of CAPE values getting into the 200-400 J/kg range. This period of convection along the front will be the potential for short-lived periods of higher rainfall rates. Rainfall amounts should mostly be in the 0.10-0.20" range, but it isn't out of the question for there to be a stripe or two where amounts are more into the 0.25-0.50" range. Hardly a drought busting rainfall, but every little bit helps.

Ahead of the approaching front, a tightening pressure gradient will yield elevated west-southwest flow across the forecast area. With temperatures warming into the low to mid 70s for most of the area, mixing heights will rise into the 3-3.5 kft range allowing for breezy conditions. Frequent gusts into the 20-25 mph range can be expected, and some isolated stronger gusts possible with the line of showers in the late afternoon and evening hours.

KEY MESSAGE 2: A more impactful system arrives late this weekend, resulting in additional chances for precipitation and perhaps a few thunderstorms.

Attention turns to a more substantial rainfall event this weekend, as models show a pronounced upper level trough near the Four Corners region deepening as it advances eastward toward the southeast CONUS. Overall PoPs haven't deviated too much since the last issuance, with perhaps a slightly slower onset, now slated for Saturday evening. That being said, still expect the better chances (70-90%) to arrive Sunday afternoon as the region become warm-sectored ahead of an advancing cold front. Nonetheless, model consistency concerning the overall track of this system still remains fairly poor, making it difficult to put too much confidence behind any one solution just yet. In fact, the most recent run of the GFS now splits the precipitation shield, resulting in a largely dry forecast for our area. While this is just one solution, it showcases that we are far from narrowing down the exact details just yet. In terms of rainfall totals, latest ensembles continue to support a 70-80% chance for QPF amounts > 0.5" and 50-70% for QPF amounts > 1.0". Lastly, with a bit of instability in place, can't rule out seeing a few thunderstorms, which may result in localized pockets of higher accumulations. So, will continue to monitor trends in the coming days.

AVIATION /06Z WEDNESDAY THROUGH SUNDAY/

The 06z TAF period begins with VFR conditions at KCHS, KJZI, and KSAV. Weak and light showers are expected to spread across the region after daybreak, though little to no measurable rainfall is expected through the morning. Instead, the best chance of rain and perhaps even brief MVFR conditions will come late in the afternoon and into the early evening, roughly from 22z through 02z. This band of showers will accompany the leading edge of a cold front and could bring short-lived MVFR ceilings and some moderate rainfall. Given that this is still near the end of the TAF period we will not include a TEMPO group with the 06z TAFs. Westerly winds will be elevated today, with gusts increasing into the 20-25 knot range staring by late morning or midday and continuing through the afternoon. The front, and any shower activity with it, will pass to the south and winds will turn northwesterly by around 02z.

Extended Aviation Outlook: Flight restrictions are possible this weekend as a system tracks across the region.

MARINE

Through tonight: Ahead of a cold front approaching from the north, elevated west-southwest flow will continue across the local waters. This will support a solid 15-20 knots of flow for most of the waters. The shelf waters across the nearshore marine areas are quite cool, meaning that mixing profiles will be quite limited. However, out near the 20 nm line in the Charleston County waters and the 40- 60 nm area of the outer GA waters, frequent gusts to 25 knots are expected and a Small Craft Advisory is in effect. The other zone that will have to be considered is Charleston Harbor where winds will be close to advisory criteria. The front will pass through this evening and winds will turn northwest and then northerly. Speeds will drop off initially but then surge back closer to 15-20 knots by sunrise Thursday.

Thursday Onward: Breezy northeasterly winds continue to diminish Thursday, allowing tranquil conditions to prevail across the waters through Saturday. Attention then turns to a pronounced system late this weekend, which will result in the breezy S/SE winds Sunday ahead of an advancing cold front. Winds looks to remain breezy through Monday as direction shifts more W/NW in the wake of FROPA. Seas during this time could also approach 6-8 ft. Thus, SCAs may be needed in the coming days.

CHS WATCHES/WARNINGS/ADVISORIES

GA...None. SC...None. MARINE...Small Craft Advisory until 4 PM EST this afternoon for AMZ350- 374.