textproduct: Charleston

WHAT HAS CHANGED

The aviation section has been updated for the 12z TAF issuance. Confidence remains low in regard to a wintry mix Sunday, whereas confidence continues to increase that cold morning lows will be possible Monday and Tuesday, especially across our interior counties.

KEY MESSAGES

- 1) Very cold temperatures will occur this morning, with lows in the upper teens to lower 20s away from the beaches.

- 2) Dry conditions and low relative humidity values are expected today.

- 3) Potential for a wintry mix Saturday night into Sunday as a coastal low develops over the Atlantic.

- 4) Cold temperatures in the low to mid 20s (upper 20s along the coast) possible Monday and Tuesday morning.

DISCUSSION

KEY MESSAGE 1: Very cold temperatures will occur this morning, with lows in the upper teens to lower 20s away from the beaches.

A Cold Weather Advisory remains in effect until 9 AM this morning. Recent satellite and sfc observations indicate that conditions will remain clear with little to no wind early this morning. Temperatures appear on track to range from the upper teens west of I-95. Along and east of I-95 to about US Highway 17, expect low temperatures in the lower to mid 20s. Along the beaches, expect low temperatures in the mid to upper 20s (including the Charleston Peninsula).

KEY MESSAGE 2: Dry conditions and low relative humidity values are expected today.

The center of the dry air mass will slide across SE GA and the SC Lowcountry today. Dewpoints could be as low as the single digits along and west of I-95, to the west, dewpoints between 10 to 15 degrees should be common. As temperatures warm to around 50 degrees this afternoon, RH values may range from the upper teens to around 20 percent west of I-95, to the mid to upper 20s to the east. Fortunately, the weak pressure gradient should only support winds around 10 mph. No Fire Danger Statement planned for today. However, low relative humidity was headlined in the Fire Weather Forecast.

KEY MESSAGE 3: Potential for a wintry mix Saturday night into Sunday as a coastal low develops over the Atlantic.

As noted in days past, expect an upper level trough over the central CONUS to deepen as it ejects eastward across the Tennessee River Valley. This system and its attendant sfc cold front will move in tandem toward the region while a coastal low simultaneously develops across the Atlantic, causing precipitation chances to return Saturday evening through Sunday.

With temperatures in the upper 50s to lower 60s expected at onset, should see rain remain the dominant p-type. Strong CAA then begins to infiltrate the region in the wake of the aforementioned cold front, with temperatures dropping into the mid to upper 30s across our interior GA counties near daybreak. Thus, may begin to see a rain- snow mix develop across these areas through mid-morning, with rain continuing elsewhere across the region. Regardless of p-type, folks should prepare for a pretty dreary Sunday, as highs struggle into the mid to upper 40s. Should then see precipitation gradually diminish through Sunday evening, though some timing variations still exist (GFS/CMC suggest dry conditions will return by 00Z Monday, whereas the ECMWF/NAM suggest precipitation may linger until 03-06Z Monday).

So, what has changed and what are the forecasted impacts? Latest guidance (both deterministic and ensemble) continue to trend slightly warmer - keeping confidence for a rain-snow mix relatively low. With highs in the 60s expected Saturday, will also have a fairly hard time getting any accumulations to stick given the warm ground temperatures in place. That being said, do want to emphasis that slick spots will still be possible regardless of what p-type occurs. Latest probabilistic Winter Storm Severity Index (WSSI-P) continues to advertise a 15-25% chance of minor impacts, so again, want to encourage folks to exercise caution if you must commute.

KEY MESSAGE 4: Cold temperatures in the low to mid 20s (upper 20s along the coast) possible Monday and Tuesday morning.

Influx of CAA persist across the region heading into the new week, resulting in morning lows in the low to mid 20s across much of our area Monday and Tuesday, with areas along the coast hovering near freezing. With clear skies and light winds in place, expect wind chill values to plummet into the upper teens to lower 20s, with the highs probabilities (40-50%) of this occurring across our interior counties. Thus, a Cold Weather Advisory may be needed in the coming days.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

VFR conditions will prevail at KCHS, KJZI, and KSAV through 12z Saturday.

Extended Aviation Outlook: VFR conditions will continue for KCHS, KJZI and KSAV through the majority of Saturday, before another system could result in a period of flight restrictions across the terminals between late Saturday night through the daylight hours Sunday.

MARINE

The center of surface high pressure will remain over the coastal waters today and tonight. Conditions today will feature winds around 10 kts and 1-2 ft wave heights.

On Saturday, return flow should develop ahead of a strong cold front approaching from the west. Wind speeds on Saturday should favor values between 10-15 kts with 2-3 ft seas. The cold front is timed to sweep across the GA and SC coastal waters late Saturday night. A coastal low may develop off the SC coast over the Gulf Stream Sunday morning, but should track quickly to the northeast. Small Craft Advisories might be needed across a portion of the waters on Sunday, primarily the outer GA waters for gusts around 25 kts. High pressure should begin to build across the marine zones Sunday night, with a ridge remaining over the waters through mid-week. This pattern should yield conditions less than Small Craft Advisory criteria.

CHS WATCHES/WARNINGS/ADVISORIES

GA...Cold Weather Advisory until 9 AM EST this morning for GAZ087- 088-099>101-114-115. SC...Cold Weather Advisory until 9 AM EST this morning for SCZ040- 042>045-047. MARINE...None.