textproduct: Columbia

WHAT HAS CHANGED

An wide spectrum of freezing rain impacts are expected across the area, from north to south as guidance trends continue. Winter Storm Watches have extended across areas north of I-20.

KEY MESSAGES

- 1) The chance for an impactful winter storm continues, focusing north of I-20 late Saturday into Sunday.

- 2) Ahead of this system, temps steadily moderate through the end of the week with some rain chances on Thursday night into Friday.

DISCUSSION

KEY MESSAGE 1: The chance for an impactful winter storm continues, focusing north of I-20 late Saturday into Sunday.

Overview: The threat for an impactful ice event north of I-20 continues, as guidance has trended more north and warmer with this system. While confidence remains that areas along and south of I-20 will see some freezing rain, the chances for a significant ice storm have decreased. However, a reminder that only a few hundredths of an inch of freezing rain can cause notable travel impacts.

Potential Impacts: A spectrum of impacts are expected across the forecast area with a steep gradient in freezing rain amounts likely. The potential remains across the northern Midlands and Pee Dee for an impactful ice storm from this system despite the trends in guidance. Primarily late Saturday and into Sunday, notable impacts remain possible in these locations, with potential for over 0.25" of freezing rain causing very difficult travel, power outages and downed trees. Confidence has decreased in this potential just along and south of the I-20 corridor, but at least some freezing rain does still appear likely leading to some travel concerns; again, only a few hundredths of an inch of freezing rain can quickly cause driving and travel impacts.

Trends and Forecast Challenges: The warm, northerly trend in guidance that the ECE started to capture 36 hours ago appears very legitimate, as guidance universally has trended persistently and significantly warmer and northward in temps and qpf totals; additional recon data in the 00z data increases confidence that this trend has staying power. This trend is driven by the more aggressive phasing of the southern stream ejecting trough and the northern stream diving shortwave, which then dramatically amplifies the pattern downstream and greatly increases flow below 500mb. This increased flow allows for a truly remarkable WAA setup, extending well into the Mid-Atlantic late Saturday and into Sunday; typically guidance under-does WAA leading up to an event, so this is another factor favoring the legitimacy of this trend. Strong CAD will still develop initially late Saturday as this WAA drives substantial moisture advection north, with a period of freezing rain expected across much of our area but with a range of impact potential; its important to note that even the warmest guidance has this period of freezing rain and this CAD will be impressive, at least initially. So even if some northerly trend continues, areas north of I-20 are still expected to see impactful freezing rain. Areas along and south of I-20 are where questions arise and the potential for a significant ice event has decreased, but at least some icing is still probable for much of the Midlands. By later in the day Sunday, the warm trend really comes to fruition with the 60-70 knot 850mb jet eroding the CAD and driving a very strong warm front northward, likely into the southern extent of our area. Questions remain in how much the CAD dome erodes, especially along and north of I-20, and whether or not those areas get above freezing. A tremendous temp gradient Sunday is consistent in all guidance now, with even some CAPE developing south of the warm front but the northern Midlands still around freezing.

Summary: Areas north of I-20 should remain prepared for an impactful winter storm, with freezing rain likely late Saturday and into Sunday. A period of freezing rain, with impacts to travel, remains likely south of I-20 but confidence is decreasing in the potential for a significant ice storm in those locations.

KEY MESSAGE 2: Temps steadily moderate through the end of the week with some rain chances on Thursday night into Friday.

High pressure moves off the Atlantic coast through the end of the week as upper level flow becomes more southwesterly. This is expected to allow temperatures to warm through the end of the week. Some shortwave energy ahead of the main weekend system is forecast to move over the area, bringing chances for some rain showers Thursday night into Friday. Any precipitation that does fall during this timeframe very likely will fall as rain as temps are forecast to be way too warm to be frozen.

AVIATION /06Z THURSDAY THROUGH MONDAY/

VFR conditions expected through the TAF period.

Moisture will be increasing through the period, but fog concerns are not expected this morning despite light and variable to calm winds. Mainly high and mid level clouds will be present most of the period, with lower CIGS around 5kft MSL developing this evening and tonight. As such, VFR conditions should persist this TAF period. SFC winds increase this morning out of the west to northwest at around 5 to 7 kts. A northerly direction becomes more dominant late this evening, but speeds should by then drop back below 5 kts.

EXTENDED AVIATION OUTLOOK...The next storm system will likely bring restrictions as early as Friday, but especially Saturday and Sunday.

CAE WATCHES/WARNINGS/ADVISORIES

SC...Winter Storm Watch from Saturday morning through Monday afternoon for SCZ016-018-020>022-029-115-116. GA...Winter Storm Watch from Saturday morning through Monday afternoon for GAZ040.