textproduct: Charleston

WHAT HAS CHANGED

The aviation discussion was updated for the 18z TAFs. A key message was also added for low wind chills Sunday morning.

KEY MESSAGES

- 1) A risk for isolated drizzle will linger today with cloudy skies keeping temperatures well below normal for early February.

- 2) Cold temperatures with low wind chills across coastal South Carolina Sunday morning.

DISCUSSION

KEY MESSAGE 1: Surface low pressure is well offshore this afternoon with a weak CAD front starting to undergo frontolysis near the South Carolina/ Georgia border. KCLX was changed to long pulse/ VCP 31 and the decaying CAD was analyzed just near Interstate 16.

Behind the CAD, temperatures have slowly fallen with drizzle mostly coming to an end, but overcast skies remain. Hourly temperatures continue to slowly fall through the day, with Moncks Corner already at 34 degrees. Mid 30s are being reported down to Colleton County.

There is still a low-end chance that a period of sub-freezing temperatures could work south into northern portions of Berkeley County later this afternoon into early evening. NBM probabilities for freezing drizzle are around 10 - 20% in the Saint Stephen to Jamestown corridor. If precipitation were to occur, it would be freezing drizzle given the dry air in the mid-levels and lack of sufficient ice nucleation in the cloud. This scenario is still considered an outlier solution, but trends are being monitored.

Later tonight, temperatures will fall below freezing across the entire area (except at the beaches), but drier air will filter into the region with precipitation chances near zero.

KEY MESSAGE 2: Arctic high pressure will settle across the Virgina/ North Carolina border Sunday morning. The pressure gradient does appear tight enough for at least some wind, and with temperatures in the lower to mid 20s, wind chills in the teens are possible. The latest run of the LREF shows probabilities in the 50% to 75% range across the TriCounty with percentages in the 25% to 50% range for coastal Georgia. A Cold Weather Advisory might be required for portions of the area.

AVIATION /18Z THURSDAY THROUGH TUESDAY/

05/18z TAF Discussion: KCHS/KJZI/KSAV: The surface cold front has cleared KCHS and KJZI and is currently just north of KSAV. Widespread IFR and even LIFR remains across all of the TAF sites with a persistence of IFR into the evening. By late this evening/ early tonight, cigs will start to go BKN and then SCT with a recovery to VFR expected. It should be noted that some of the guidance has a recovery to VFR occurring only for IFR to then return. This is possible given that a partial decoupling of the boundary layer is expected. This could also be manifested as fog, especially across the TriCounty ahead of the incoming drier air.

Extended Aviation Outlook: VFR Friday through Tuesday.

MARINE

A cold front will continue to move offshore this afternoon with winds backing from the northwest. A Small Craft Advisory remains in effect for the offshore Georgia Waters for this afternoon, but now has been extended to 7 PM Saturday. This is due to another cold front pushing across the waters early Saturday morning. The pressure gradient looks tight enough that a Small Craft Advisory has been issued for all zones Friday night into Saturday. For waters beyond 20 nm, isolated Gale gusts are possible, but probabilities of reaching gale gusts only peak at 15% to 30%. Given that, have opted for Small Craft Advisories instead. Future forecast packages will continue to monitor and refine.

EQUIPMENT

KCLX is now back in service with calibration being completed.

CHS WATCHES/WARNINGS/ADVISORIES

GA...None. SC...None. MARINE...Small Craft Advisory from 6 PM Friday to 6 AM EST Sunday for AMZ350. Small Craft Advisory from 6 PM Friday to 6 AM EST Saturday for AMZ352-354. Small Craft Advisory until 7 PM EST Saturday for AMZ374.