textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

A Freeze Watch has been issued for the North Carolina mountains for Saturday night into Sunday morning.

Temperatures have trended slightly cooler for Saturday night and Sunday morning, such that most of the NC mountains now have good odds of falling to freezing, or colder.

Rain chances continue to increase for both the NC mountains and parts of the Upstate and Piedmont for late tonight into early Saturday morning. Cloud cover associated with this activity has also increased.

KEY MESSAGES

1. A cold front crosses the area this evening and tonight, bringing breezy conditions and a chance for widely scattered rain. 2. A Freeze Watch has been issued for Saturday night and Sunday morning, with temperatures expected to fall to near or below freezing across the NC mountains. Frost potential may return Sunday night, but confidence is limited. 3. Quiet conditions persist most of next week.

DISCUSSION

Key message 1: A cold front crosses the area this evening and tonight, bringing breezy conditions and a chance for widely scattered rain.

It's mostly clear across the area this morning following a stint of isolated dense fog across the mountain valleys, foothills, and even a few spots in the Upstate. Widely scattered stratocumulus remain in place in a few spots across the NC mountains, but otherwise skies are clear and a beautiful day is once again in store. To our west, a strong cold front is easily-discernible in the theta-e and dewpoint fields extending across the central Tennessee Valley into eastern Kentucky...and this feature will drive the interesting weather over the next 24 to 36 hours.

Models are in good agreement that the surface front will gain momentum as its upper-level trough sharpens this afternoon, and the system will arrive in the NC mountains by late afternoon or early this evening. The result will be an uptick in winds as the front crosses the region through the overnight hours...pushing to our east by Saturday morning. Strong CAA is depicted on the back side of the front, such that lingering wind gusts of 15-20mph are likely across the mountains through most of the overnight. Winds should also be favorable oriented for a gap wind to develop in parts of the Upstate and Foothills overnight. Winds will begin tapering off through the day on Saturday, but will remain breezy most of the day, not really quieting down until Saturday night.

A secondary issue will be the potential for rainfall in and behind the frontal zone tonight. For several consecutive cycles, models have been trending toward an increasing amount of low-level moisture embedded within the postfrontal air mass, and although models have struggled with it for the last couple days, there's an increasingly convincing signal in the hi-res guidance for patchy drizzle to develop. The latest HREF and REFS ensembles feature mainly <0.1" for most of the area...with the exception of some west-facing slopes in the NC mountains, which could receive higher totals. Forecast profiles also suggest some potential for gravity wave development in the lee of the mountains, with favorable orientation of low-level wind vectors and a strong postfrontal inversion developing across the area in response to the front. As a result, CAMs have trended sharply toward more cloud cover overnight tonight, along with somewhat greater coverage of drizzle.

Key message 2: A Freeze Watch has been issued for Saturday night and Sunday morning, with temperatures expected to fall to near or below freezing across the NC mountains. Frost potential may return Sunday night, but confidence is limited.

In the wake of Friday night's cold front, a dramatically cooler cP air mass will settle into the area for the weekend, allowing temperatures to drop sharply on Saturday and Sunday. Forecast highs still only climb into the lo 60s for most of the area on Saturday and again on Sunday as lingering CAA continues to cool the area off.

It currently looks like the coldest night should be Saturday night, when much of the high terrain will see overnight lows drop into the lower 30s. Many locations across the mountains will see temperatures drop to freezing, and a Freeze Watch has been issued, valid from 1AM through 9AM Sunday. The low terrain will likely not see freezing temperatures, though most of the area will cool into the mid to upper 30s. Winds here should remain just elevated enough to preclude a widespread frost risk...though patchy frost in secluded locations seems reasonable.

By Sunday night, just enough air mass modification should have occurred that the majority of locations even in the mountains will remain just above freezing. However, more widespread frost looks possible than on Saturday night, as by this point the core of the surface high will be situated just to our west, and winds should be calmer than on Saturday night. No plans for any product just yet, but one may become necessary depending on how the forecast evolves. Confidence is limited by the growing number of ensemble solutions that depict a stacked low developing off the NC coast...which would reinvigorate low-level northerly flow, raising winds and reducing frost potential. Regardless, frost potential should diminish past Sunday night.

Key message 3: Quiet conditions persist most of next week.

Long-range ensembles are in decent agreement that most of next week will be defined by a stout blocking ridge that'll strengthen across the eastern half of the United States and remain in place through the end of the seven-day forecast. The ridge should keep things stable and unperturbed, so no active weather is expected. Temperatures will steadily climb through the middle of the week as the air mass only slow modifies, such that by mid-week most locations will see highs in the low- to mid-70s, and lows in the upper 40s or lower 50s...more or less around climo for this time of year.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

At KCLT and elsewhere: A cold front is expected to cross the area from this evening through Saturday morning, bringing gusty winds and a chance for some light rain overnight tonight. General thinking is that winds will stay mostly S/SW through this evening, with gusts up to 25kts, as the front approaches, then toggle around to the at all terminals overnight as the front crosses the area. Some widely scattered light showers may develop near and behind the front...with most hi-res guidance featuring -SHRA across the NC mountains and even parts of the Upstate and Piedmont. In association with this, banded stratocu - mostly low-end VFR - is likely to develop across the mountains, and guidance increasingly supports expansion of ceilings into the Upstate and Piedmont during the late evening and after midnight. Restrictions should mainly be confined to areas where rain is actively falling...though there's a low-end chance for some MVFR ceilings to develop around daybreak Saturday...mainly along I-77 and in the NC mountain valleys. Confidence was too low for an explicit mention in the TAFs...but should any restrictions develop, they'll lift quickly on Saturday morning, giving way to a breezy but VFR day!

Outlook: Winds die down by Saturday night, and VFR conditions prevail for most of next week. Mountain valley fog and low stratus will be possible each morning.

CLIMATE

RECORDS FOR 10-16

MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 87 1897 49 1954 63 1928 29 1939 KCLT 87 1925 58 1937 68 1947 35 1939 1925 KGSP 85 1935 53 1937 67 1925 32 1907 1911 1892

GSP WATCHES/WARNINGS/ADVISORIES

GA...None. NC...Freeze Watch from late Saturday night through Sunday morning for NCZ033-048>053-058-059-062-063. SC...None.