textproduct: Columbia

WHAT HAS CHANGED

Winter Weather Advisory remains for Burke, Columbia, Lincoln, McDuffie, and Richmond Counties from 4 AM to 3 PM EST today.

KEY MESSAGES

- 1) Mix of rain and snow may cause travel impacts, primarily in the CSRA today.

- 2) An arctic air mass arrives tonight and into early next week.

DISCUSSION

Key Message 1: Mix of rain and snow may cause travel impacts, primarily in the CSRA today.

Winter Weather Advisory remains in effect for eastern GA.

The forecast overall remains on track for the expected mix of snow and rain today, with some accumulation possible. Overnight observations and updated model guidance continues to paint a similar picture with how this system will progress throughout Sunday.

As the forcing shortwave aloft begins to tilt slightly negative and isentropic lift strengthens, widespread light rain overnight and into the early morning will steadily drop temps down into the 40's region-wide. Low level dry air trailing the area of overrunning precip will then undercut the precip shield as we move into the morning, which will then wet bulb temps down into the 30's across the western flank of the precip. This should allow for period of snow (or at least a rain-snow mix) to develop across central GA and into the CSRA by ~9am. As seen in the HREF soundings and frontal cross sections, there will be band of enhanced frontogenesis and modest DGZ omega within this precip shield, but not necessarily aligned the coldest wet bulb temps; overall, temps are extremely marginal (at best) with this event and greatly limits accumulation potential. If we apply the typical behavior and biases of the HREF with respect to frontogenesis, WAA, and low level dry air, I expect to see a band of fairly strong precip during the 12-16z window thanks to the enhanced WAA-frontogenesis, pulling to the northwest of HREF guidance, and slightly drier low levels. The NAMs remain outliers but do handle the frontogenesis and WAA in what I believe to be a somewhat more realistic manner; however, surface temps are extremely borderline even in the most aggressive guidance. So this forecast thinking blends that in to some extent.

So for impacts in GA and western SC first: a mix of rain-snow looks likely across eastern GA and into extreme western SC starting after ~8am and lasting into the early afternoon. A period of snow only also is likely during that same window, but accumulation will quite difficult given the surface temps. A brief heavier period of snow is possible during this window as well and this would be the only way to see any sort of impactful accumulation, but still only 1.0" is the upper end for this event. Moving up I-20 into the Midlands, a mix of rain- snow is likely in the late morning and early afternoon with a period of all snow possible in that window. Accumulation looks rather unlikely as the precip rates will struggle to adequately wet bulb this area during the early morning. Further east towards I-95, mostly rain is expected with a period of rain- snow in the late morning- afternoon but no accumulation is expected.

Key Message 2: An arctic air mass arrives tonight and into early next week.

Following this system from Sunday, very cold air will fill in throughout the first half of the week. Both high and low temps will run ~10-15 degrees below average through Wednesday. Low temps overnight Sunday, Monday, and Tuesday will down into at least the low 20's with excellent agreement across the ensembles. Tuesday morning looks the coldest, with some low temps into the teens likely and therefore the best chance of a cold weather advisory as high pressure settles directly overhead.

AVIATION /06Z SUNDAY THROUGH THURSDAY/

Rain moving in with conditions beginning to deteriorate through sunrise.

Regional radars showing swath of rainfall beginning to push into the CSRA, with some light sprinkles/rain across the central Midlands. This area of rainfall will continue to become more widespread through sunrise. As the rain gets heavier, ceilings and visibilities will begin to drop down to mvfr briefly, then into ifr between 09-10z. In the CSRA at ags/dnl, there is some probability of seeing some snow mixed in with the rain through the daytime hours on Sunday, with some light accumulation possible at both sites. In addition, a mixture may be seen at the Midlands sites of cae/cub through the daytime, but do not expect to see any accumulations at those locations. This area of precip is forecast then to begin pushing off to the east of the area towards 22z, with skies then clearing out and vfr conditions returning to the area.

EXTENDED AVIATION OUTLOOK...VFR expected beginning this evening and lasting through at least mid week as cold, dry high pressure moves into the region.

CAE WATCHES/WARNINGS/ADVISORIES

SC...None. GA...Winter Weather Advisory from 4 AM early this morning to 3 PM EST this afternoon for GAZ040-063>065-077.