textproduct: Charleston

WHAT HAS CHANGED

Current observations show that there is no longer dense sea fog along the Charleston County coastline and therefore the Marine Dense Fog Advisory for the Charleston Harbor and the Charleston County nearshore waters has been canceled.

KEY MESSAGES

- 1) Sea fog will expand across the nearshore waters and coastal counties early this morning.

- 2) A Cold Air Damming regime will set up over the SC Lowcountry and Southeastern GA today, leading to a low confidence high temperature forecast today.

- 3) Unseasonably warm temperatures are expected this week with increasing rain chances late week into the weekend.

DISCUSSION

KEY MESSAGE 1: Sea fog will expand across the nearshore waters and coastal counties early this morning.

Sea fog remains across the nearshore GA coastal waters early this morning, however high clouds are obscuring it on GOES satellite imagery. Guidance continues to trend towards the sea fog expanding inland along the coastal counties of SE GA early this morning, where a Dense Fog Advisory remains in effect through 9 AM. A dry cold front is forecast to push across the region this morning, with guidance trending towards a later FROPA. This would aid in fog development across the region early this morning as the moist airmass and calm winds dominate. High clouds present over a good portion of the forecast area remain a fly in the ointment and the progression of fog development across the region remains a very low confidence forecast.

KEY MESSAGE 2: A Cold Air Damming regime will set up over the SC Lowcountry and Southeastern GA today, leading to a low confidence high temperature forecast today.

This morning a dry cold front is forecast to push through the region. Behind the cold front high pressure will build into the region from the northeast. The high pressure will be centered over the Mid- Atlantic, building into the southeastern states along the eastern side of the Appalachian Mountains. Guidance tends to not handle CAD events well, typically eroding the wedge too early. High temperatures today are a blend of the NBM and the NAM. While the temperature forecast today remains a low confidence forecast, there will likely be a tight gradient of temperatures across the region. Areas in the northeastern portion of the forecast area (Berkeley Co and northern Charleston Co) could struggle to reach 60, while along the Altamaha River in GA temperatures could reach into the mid 70s.

KEY MESSAGE 3: Unseasonably warm temperatures are expected this week with increasing rain chances late week into the weekend.

On Tuesday, the wedge of high pressure/CAD setup will gradually erode and shift offshore as a 586 dm ridge builds over the Florida Peninsula. This will establish a deep-layered high pressure pattern centered offshore around midweek, persisting through the weekend. The pattern will promote a drastic warming trend and unseasonably warm conditions. Despite a small spread in maximum temperature guidance, confidence remains high that, aside from Tuesday, highs each day will reach the upper 70s to lower and middle 80s away from the cooler coastline, around 10 degrees above early March normals. Overnight lows will also trend milder, gradually rising into the upper 50s to lower 60s. There is potential for overnight temperatures to approach within a couple of degrees of record high minimum values this weekend. See the Climate section below.

Additionally, moisture will increase late week as ensemble guidance indicates precipitable water values rising to around 1.1 to 1.2 inches, near the 85th percentile for early March. While large scale forcing appears weak, the presence of deeper moisture and modest instability should support isolated to scattered showers from late week into the weekend, primarily during the afternoon and evening hours. Thunder chances remain low, though an isolated storm cannot be ruled out. Flooding risk appears minimal at this time, with probabilities of more than a quarter inch of rainfall in any 24-hour period through Saturday night generally at or below 20% per NBM.

AVIATION /09Z MONDAY THROUGH FRIDAY/

A tricky forecast for the 06Z TAFs at KCHS/KJZI/KSAV. Conditions remain favorable for a combination of sea fog and radiation fog to impact all terminals this morning, but confidence remains low in regards to timing, intensity, and duration. Guidance continues to be split on impacts from fog across the terminals. Opted to include restrictive cigs and vsbys within a TEMPO group initially at the terminals. Additional amendments will almost certainly be required as observations help paint a better picture of the fog development this morning. The threat of fog will likely end around 15Z, with restrictive cigs lingering over KCHS/KJZI into the afternoon. KSAV should see VFR return mid morning. Another round of low cigs/vsbys is possible tonight into Tuesday morning at all terminals.

Extended Aviation Outlook: Restrictive ceilings are possible overnight into the early morning hours each night through late week due to low stratus/fog.

MARINE

A Marine Dense Fog Advisory remains in effect for the Georgia nearshore waters and the southern SC nearshore waters through 9 AM. Current observations show the bulk of the fog is off the GA coast, however high clouds are obscuring satellite imagery of the rest of the coastline. Conditions will remain favorable for sea fog through the morning. A backdoor cold front is progged to push through the region mid-morning and should end the threat for sea fog as winds out of the NE increase as high pressure builds in behind the backdoor front. Small Craft Advisories are in effect for all waters outside of the Charleston Harbor for wind gusts of 25 knots.

Surface flow will shift out of the east by midweek then out of the southeast by late week on the backside of high pressure, with speeds and seas staying well below Small Craft Advisory levels. We will need to monitor the potential for sea fog given the warm, moist air that is expected to move over the cooler shelf waters.

CLIMATE

Record High Minimum Temperatures:

March 7: KCHS: 63/1992

March 8: KCHS: 63/2022 KSAV: 65/1880

CHS WATCHES/WARNINGS/ADVISORIES

GA...Dense Fog Advisory until 9 AM EST this morning for GAZ116>119- 138>141. SC...Dense Fog Advisory until 9 AM EST this morning for SCZ048-051. MARINE...Small Craft Advisory until 7 AM EST Tuesday for AMZ350. Dense Fog Advisory until 9 AM EST this morning for AMZ352-354. Small Craft Advisory until 1 AM EST Tuesday for AMZ352. Small Craft Advisory from 10 AM this morning to 7 PM EST this evening for AMZ354. Small Craft Advisory from 10 AM this morning to 7 AM EST Tuesday for AMZ374.