textproduct: Greenville-Spartanburg

SYNOPSIS

A strong cold front with give rise to shower chances late tonight into Monday and ushers in a very cold airmass by Tuesday. Near- normal temperatures return mid to late week. A low pressure system could bring precipitation to the area for the weekend.

NEAR TERM /THROUGH MONDAY/

As of 707 pm EST Sunday:

Key message 1: Cool, damp weather continues into the early morning hours due to lingering cold air damming.

The 925mb flow over the CAD wedge has indeed veered a bit early this evening, resulting in less drizzle and light rain in recent observations. Temperatures will remain nearly steady within the wedge. The CAD boundary is expected to retreat late tonight as winds amplify at 925-850mb ahead of approaching front. Overnight min temps within the wedge likely will be during the evening, with temperatures warming there (and in the Lakelands) by midnight or so. Cloud cover should be enough to hold temps fairly steady near the TN border until just before dawn. Retreat of wedge is likely to be associated with lowering cloud bases and some areas of dense fog, mainly in areas northwest of I-85 and east of the Escarpment. Could see Dense Fog Advisory issuance at some point tonight if it proves sufficiently widespread. At this point, the visibility observations have been too variable to entertain an Advisory, but we will continue to monitor.

Key message 2: Cold front arriving Monday morning will induce brisk wind gusts across the area and bring sharply colder temperatures for the mountains.

Surface low pressure centered over Chicagoland as of 21Z Sunday will nearly meet the definition of a "bomb cyclone" as it tracks toward southern Ontario and deepens rapidly through 12Z Monday. Strong cold front will be pulled across the lower-mid Mississippi Valley, on track to reach the TN/NC border by around 09Z. Temperatures should plummet there as the front passes, so min temps probably will be around the usual time. Guidance in pretty good agreement that a line of precip, and some embedded shallow convection, will accompany the front into our westernmost zones--but also in agreement that this activity will be too weak to survive past the Appalachians. Hence PoPs reach 60-90% in the Smokies in the predawn hours but chances are only 20-30% east of the mountains, after 12Z. Some reorganization of convective showers does look possible in the I-77 corridor later in the morning, though HREF 90th percentile CAPE is less than 100 J/kg and shallow in nature. Thus no thunder or severe threat is expected to result.

Higher elevations, mainly above 5000 ft, will experience strong winds/gusts approaching advisory criteria during the overnight hours, preceding the front. Following its passage, mixing will bring 35-50 mph gusts down to lower mountain elevations. Confidence was high enough to go with a Wind Advisory beginning 1 PM Monday in our mountain zones NE of the French Broad. In Avery County, higher average wind across the county and opportunity for even stronger winds on the ridgetops warranted High Wind Warning. Downslope winds east of the mountains should bring temperatures to the warm end of the envelope, into the lower 60s for most Piedmont locations. The mixing also will allow gusts of 25-35 mph and appreciable post- frontal drying. Minimum RH should be below 30% across much of the NC/SC Piedmont, and 25% in a few spots. Consideration was given to a Red Flag Warning for Mon afternoon, given the marginally supportive wind gusts and RH values. Most models depict temperatures peaking earlier than peak heating, which is reflected in the official forecast and keeps min RH from meeting the 25% criterion over a large enough area to justify RFW. Will be closely monitoring this trend thru tonight and if nothing else could issue an Increased Fire Danger Statement.

SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/

As of 1100 AM EST Sunday...

Key Message #1: Blustery and colder Monday night.

Deep mixing within strong CAA regime will give rise to the potential for damaging wind gusts acrs the NC high terrain by Monday night. With the possibility of 50 mph wind gusts acrs the northern Blue Ridge, at a minimum, a wind advisory will be needed. As this dramatically colder airmass filters into the region, Piedmont minimums early Tuesday morning will plummet into the 20s. Many locations in the NC mountains will experience wind chill values at or below zero with portions of the Northern NC mountains continuing to flirt with cold weather advisory criteria which is 5 below.

The pressure gradient will loosen throughout the day on Tuesday, but despite full sunshine, maximum temperatures will top out several deg F colder than climo within the cold and very dry airmass. Quiet and seasonably cool weather conditions are on tap to round out 2025 within the ongoing dry and deep WNW flow.

LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/

As of 1145 AM EST Sunday...

Key Message #1: Dry with milder temperatures Thursday and Friday.

Ongoing dry WNW flow aloft and weak sfc ridging will keep weather conditions quiet to start off the period with maximum temperatures creeping up to a few deg F above the New Years Day climo followed potentially by an increase in clouds on Friday downstream of possible southern stream system.

Key Message #2: A southern stream low pressure system could bring precipitation to the region on Saturday.

Timing of the passage of southern stream s/wv is generally consistent with earlier model runs, with the better chances for a period of rainfall (with perhaps token p-type issues somewhere along the northern periphery of the pcpn shieid) limited to Saturday. It certainly remains to be seen on just how far north the low will track but at this point, ensembles continue to paint a mid-chance pop for Saturday with drying on tap for Sunday.

AVIATION /00Z MONDAY THROUGH FRIDAY/

At KCLT and elsewhere: Still dealing with widespread LIFR to VLIFR flight conditions outside the NC mtns this evening, and it may very well stay that way until the frontal band of precip arrives around daybreak. The guidance leans toward that conclusion and the conditional climo has caught on as alternate/previous scenarios have been dropped from consideration. So, LIFR it is. Some brief improvement was shown at KCLT, but that might be some wishful thinking out on the edge of the lingering cold air damming wedge. Will include some VLIFR at most terminals at least temporarily. The guidance is in good agreement with the frontal timing, with winds improving from the SW in the pre-dawn hours. Precip not assured with the front, so only a PROB30 in some places for the shower activity. Expect a fairly quick improvement to MVFR then VFR after frontal passage, with wind shifting to WNW or NW. Frequent strong gusts can be expected through the afternoon at all terminals.

Outlook: Dry and VFR conditions linger through Friday. Winds remain strong and northwesterly at KAVL and across the mountains into Tuesday.

GSP WATCHES/WARNINGS/ADVISORIES

GA...None. NC...High Wind Warning from 1 PM Monday to 7 AM EST Tuesday for NCZ033. Wind Advisory from 1 PM Monday to 7 AM EST Tuesday for NCZ049- 050-501-503-505. SC...None.