textproduct: Columbia

WHAT HAS CHANGED

A Frost Advisory is now in effect for the whole CWA Saturday morning. Aviation Discussion updated for 18z TAF issuance.

KEY MESSAGES

- 1. Frost Advisory now in effect tonight and a Freeze Watch is remains in effect late Saturday night into Sunday morning. - 2. Below normal temperatures to persist through early next week, moderating by mid next week.

DISCUSSION

Key Message 1: Frost Advisory now in effect tonight and a Freeze Watch is remains in effect late Saturday night into Sunday morning. Below normal temperatures to persist early next week. Cooler and drier air continues to filter in the area this afternoon with downslope northwesterly flow off the Southern Appalachians and a closed 500mb low centered over southern Ontario. In fact, 500mb heights across the Carolinas today into tonight will fall into the 1 to 2 percentile of climo per the LREF. Highs will top out in the upper 50s to low 60s this afternoon, with dew points mixing out into the low to mid 30s. CAA will bring the first night of a string of cold overnight lows in the 30s tonight through early next week. Although winds will not die down entirely due to the relatively tight pressure gradient and troughing aloft, winds should fall enough (3-5 kts) to allow some patchy to scattered frost formation tonight as temps fall into the mid to upper 30s. This would be most favored in sheltered locations where winds may fall calm for a hour or two around sunrise (which was noted this morning at LKR. This would be most favored across northern and western counties in the forecast area, and least favored in the Columbia and Augusta Metros and along area lakes where low temperatures will be warmer. With coordination with surrounding offices, have elected to issue a Frost Advisory for a few hours Saturday morning for the whole CWA. The coldest conditions will be Saturday night into Sunday morning as the pressure gradient relaxes, winds remain light, and skies remain largely clear. While the NBM has trended a tick warmer in the past couple of runs, there remains a 40 to 90% chance of lows falling to or below freezing Sunday morning, which the greatest chances for the northern Midlands. Have kept with the Freeze Watch for the whole CWA for now but will reevaluate with this evening's forecast package for an upgrade to a Freeze Warning.

Key Message 2: Below normal temperatures to persist through early next week, moderating by mid next week.

With the surface high in place to our northwest and trough aloft, temperatures will remain 5 to 10 degrees below normal through Tuesday, with highs remaining in the upper 50s to mid 60s and lows in the 30s. Temperatures will begin to moderate toward normal as a mid-level ridge builds the eastern CONUS mid to late next week. A shortwave trough will deamplify as it translates east across the Southern US early to mid week, keeping any precip chances displaced to our south across the Gulf Coast into Florida.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

VFR conditions expected through the period.

NW flow through the period will drive cool, dry air into the forecast area. Westerly winds between 5 and 10 knots are still expected through much of the afternoon hours, but wind gusts should be somewhat limited. Still, can not rule out a few up to 15 knots through sunset though. With afternoon heating and mixing, there has been the development of a broken cu field across much for the forecast area, but cloud bases remaining vfr between 5-6 kft. Should see these clouds become more scattered this evening once the sun goes down. Fog not expected with a dry air mass over the region, and with some low-level mixing still possible overnight.

EXTENDED AVIATION OUTLOOK...Dry air will likely prevent widespread restrictions through the extended.

CAE WATCHES/WARNINGS/ADVISORIES

SC...Frost Advisory from 3 AM to 8 AM EST Saturday for SCZ016-018- 020>022-025>031-035-037-038-041-115-116-135>137. Freeze Watch from late Saturday night through Sunday morning for SCZ016-018-020>022-025>031-035-037-038-041-115-116- 135>137. GA...Frost Advisory from 3 AM to 8 AM EST Saturday for GAZ040- 063>065-077. Freeze Watch from late Saturday night through Sunday morning for GAZ040-063>065-077.