textproduct: Columbia

WHAT HAS CHANGED

New AFD format is in effect.

KEY MESSAGES

1) Near-below average temperatures through mid-week before a dry front moves through.

2) Dry, gusty winds expected Thursday with an enhanced fire danger risk.

3) Very cold temps, close to cold weather advisory criteria, Friday morning.

DISCUSSION

Key Message 1: Near-below average temperatures through mid- week before a mostly dry front moves through.

Broad troughing across the eastern US with weak north- northeasterly cold advection will keep at or below average temperatures through mid-week. Temps begin to bounce back above average on Wednesday ahead our next, mostly dry, front. Moisture convergence ahead of this front on Wednesday will be weak, with less than 25% chance for some showers in the pre- frontal trough, or when the 500mb trough axis pivots through. Given the extreme lapse rates under the trough axis and frontogenetic forcing, a few graupel-snow showers are possible overnight Wednesday into early Thursday but impacts would be null.

Key Message 2: Dry, gusty winds expected Thursday with an enhanced fire danger risk.

Following the mostly dry cold front late Wednesday, strong gusty winds are expected throughout Thursday within the post-frontal cold advection regime. Gusts between 30-35 mph are expected from the northwest throughout the morning and afternoon Thursday, coinciding with falling relative humidities in the afternoon. So a period of enhanced fire danger looks likely during this period given the already dry fuels, and wind-RH combination; Red Flag conditions are possible on Thursday as a result.

Key Message 3: Very cold temps, close to cold weather advisory criteria, Friday morning.

Behind the front Thursday, high pressure will steadily build into the region and bring the coldest airmass of the year so far. Overnight temps Thursday into Friday, thanks to a combination of cold advection and radiational cooling, will drop down into the low 20's in most spots; NBM interquartile range is roughly from 16-22 degrees across the Midlands. Winds will also remain slightly elevated as the surface high remains west, lingering a notable pressure gradient. So wind chills will likely fall into the upper 10's in many spots, close to Cold Weather Advisory criteria.

AVIATION /18Z MONDAY THROUGH SATURDAY/

High confidence in VFR conditions into Tuesday.

Cold and dry high pressure centered off to our west will continue to push eastward and into the forecast area through the taf period. Due to how dry the airmass is, vfr conditions are expected to prevail at all taf sites. Only clouds may be a few cirrus streaks moving across the region through the period. Even so, can not completely rule out patchy, shallow steam fog development along the warmer rivers late tonight, which could show up at ags/ogb. Winds will be northeasterly through this afternoon, around 5 knots before weakening late this afternoon towards sunset. Strong low-level inversion will set up after sunset, with ideal radiational cooling bringing calm winds to all taf locations overnight. Light and variable winds expected through the day again on Tuesday.

EXTENDED AVIATION OUTLOOK...A mid-week system moving through could bring brief restrictions although confidence is low due to limited moisture. Strong gusty winds expected on Thursday.

CAE WATCHES/WARNINGS/ADVISORIES

SC...None. GA...None.