textproduct: Charleston

WHAT HAS CHANGED

Key Message 1 was updated. Aviation section was updated for the 00z TAFs.

KEY MESSAGES

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

- 2) Notable temperature swings through Wednesday.

- 3) Warm temperatures and chances of rain for late next week into the weekend.

DISCUSSION

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

GOES-E night time fog imagery, VIIRS imagery and coastal webcams show an extensive area of sea fog just offshore the Georgia and southern South Carolina coast and beginning to move inland. High clouds are obscuring the fog off the Colleton and Charleston County coasts, but webcams just before sunset suggested conditions have improved there, at least temporarily. The latest H3R captures trends and expands the sea fog across much of the coastal corridor over the next few hours before more radiation fog develops inland. Given current satellite and short term models trends, a Dense Fog Advisory has been issued for all the Georgia coastal counties including Beaufort and parts of Jasper Counties through 9 AM Monday. The advisory may very well need to be expanded later to include additional areas.

KEY MESSAGE 2: Notable temperature swings through Wednesday.

High resolution guidance indicates that a backdoor cold front will push south over the SC Lowcountry late tonight, reaching SE GA during the pre-dawn hours Monday. The rest of Monday will feature high pressure ridging SW along the east facing slopes of the Appalachians. As a result, conditions across the forecast area should remain at least mostly cloudy with steady northeast winds between 10 to 15 mph. Using a blend of the cooler MOS members, high temperatures are forecast to range from 60 to 65 across the SC Lowcountry and 65 to 72 across SE GA. Low temperatures Monday night should favor values around 50 degrees. On Tuesday, the wedge of high pressure will linger across the region, but will weaken. Light NE winds and thinning cloud cover should allow temperatures to peak in the low to mid 70s. An inverted coast trough should advance west across the forecast area Tuesday night, breaking down the sfc ridge. As a result, winds should shift from the ESE on Wednesday and temperatures are forecast to warm in the upper 70s to around 80 degrees.

KEY MESSAGE 3: Warm temperatures and chances of rain for late next week into the weekend.

Deep layered high pressure centered offshore will extend across southeast South Carolina and southeast Georgia late week into the weekend. This pattern will favor unseasonably warm temperatures. There continues to be a small spread in max temperature guidance, giving high confidence to temperatures in the upper 70s to low/mid 80s away from the locally cooler coastline. These values are around 10 degrees above early March normals. Lows will similarly lean on the mild side, ranging in the upper 50s to around 60.

Deeper moisture will also return with ensemble means indicating PWats reaching 1.1-1.2" which is around the 85th percentile of climo. Forcing for ascent is lacking but given the moisture and some weak instability, isolated to scattered showers will be possible especially in the afternoon and evenings. Thunder potential looks pretty limited, but a few rumbles cannot be ruled out. Flooding risk is minimal as probability for >0.25" of rainfall in any 24 hour period through Saturday is generally no higher than 20% per NBM.

AVIATION /00Z MONDAY THROUGH FRIDAY/

02/00z TAF Discussion: KCHS/KJZI/KSAV: Low confidence for the next 12 hours. Conditions look favorable for a combination of sea fog and radiation fog to impact all terminals overnight, but the confidence in fog timing, intensity and duration low. Guidance is split on the fog potential with some data supporting sea fog moving into KCHS and KJZI later this evening and persisting through until a frontal passage around 10z while at KSAV, radiation fog is more of a threat. Opted for a middle of the road approaching for now, showing LIFR cigs/vsbys readying KJZI shortly after 00z and KCHS by 07z. For KSAV, LIFR conditions were limited to a TEMPO group from 09-12z with prevailing IFR conditions 08-15z. After 15z, frontal passage should scour things out there. Low cigs may linger at KCHS and KJZI for much of the day Monday before possibly scouring out late. VFR may return to KSAV by mid/late morning.

Extended Aviation Outlook: Restrictive ceilings possible Tuesday night into Wednesday morning.

MARINE

The Marine Dense Fog Advisory has been extended until 9 AM Monday for all nearshore legs and Charleston Harbor.

High resolution guidance indicates that a backdoor cold front will push south over the SC Lowcountry late tonight, reaching SE GA during the pre-dawn hours Monday. The rest of Monday will feature high pressure ridging SW along the east facing slopes of the Appalachians. As a result, conditions across the marine zones should remain at least mostly cloudy with gusty northeast winds. Small Craft Advisories have been issued for all Atlantic waters, outside the CHS Harbor to highlight gusts around 25 kts and seas up to 6 ft. Wind speeds will begin to weaken late Monday night, though seas will be slower to subside. Small Craft Advisories will expire for the nearshore waters within 20 nm Monday night, and then the GA waters beyond 20 nm on Wednesday due to lingering seas.

Thursday through Friday: Southeast to south flow will persist late week into the weekend 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.

CHS WATCHES/WARNINGS/ADVISORIES

GA...Dense Fog Advisory until 9 AM EST Monday for GAZ116>119- 138>141. SC...Dense Fog Advisory until 9 AM EST Monday for SCZ048-051. MARINE...Dense Fog Advisory until 9 AM EST Monday for AMZ330-350-352- 354. Small Craft Advisory from 5 AM Monday to 7 AM EST Tuesday for AMZ350. Small Craft Advisory from 5 AM Monday to 1 AM EST Tuesday for AMZ352. Small Craft Advisory from 10 AM to 7 PM EST Monday for AMZ354. Small Craft Advisory from 10 AM Monday to 4 PM EST Wednesday for AMZ374.