textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Precip chances east of the mountains Saturday morning are slightly higher. Low temperatures Saturday night were nudged downward over the mountains, making it more likely that some mountain locations will see a freeze.

KEY MESSAGES

1. One more day of near record high temperatures today, then a strong cold front will cross the region tonight with gusty winds, especially at the higher elevations. Wind gusts are not expected to be high enough to warrant an advisory. 2. The strong cold front will also bring the coolest air of the season this weekend. Temperatures will likely drop low enough Saturday night for widespread frost and areas of freezing temperatures across the mountains. Frost will be possible again Sunday night.

DISCUSSION

Key message 1: One more day of near record high temperatures today, then a strong cold front will cross the region tonight with gusty winds, especially at the higher elevations. Wind gusts are not expected to be high enough to warrant an advisory.

A vigorous mid/upper trof is expected to dig down across the Midwest today with a strong cold front approaching from the west through the morning hours, while high pressure moves away to the east. The front is expected to reach the mtns in the early afternoon and get hung up. Warm advection ahead of the front will offset any increase in cloudiness to allow temps to warm up close to records once again this afternoon east of the mountains. Late in the day and into the evening, the front should get driven east across the forecast area, then temps will start dropping steadily and the wind will pick up from the NW. An advective freeze is unlikely Saturday morning because temps start out too warm and the cold air is too far to the west, but the highest peaks could make it down below 35F. The trend in the NBM has been to creep downward with wind gust potential, and this run does more of the same. Thus, the likelihood of reaching Advisory-level wind gusts anywhere but the peaks and ridges above 6k feet is very low. A Wind Advisory is not anticipated, though winds will be occasionally gusty through the morning hours on Saturday.

A more interesting trend in the guidance concerns the precip probs. We still expect the best chances near the TN border where W-NW upslope flow will support precip generation. However, models show the main vort max tracking farther south such that mid-level forcing looks more and more impressive as the upper trof axis crosses the region Saturday morning. Moisture remains limited, but the forcing looks strong enough to act upon whatever moisture is available to generate some light precip east of the mtns well behind the front, mainly across the foothills and western Piedmont. The air will be cold enough aloft that afew snowflakes are possible at the highest elevations of the Smokies and Mt Mitchell, but no accumulation is expected. Precip chances should end as the short wave moves east in the afternoon.

Key message 2: The strong cold front will also bring the coolest air of the season this weekend. Temperatures will likely drop low enough Saturday night for widespread frost and areas of freezing temperatures across the mountains. Frost will be possible again Sunday night.

The cold advection behind the cold front on Saturday looks impressive. The models continue to show temperatures on Saturday that will be ten degrees below normal and roughly 20 to 25 degrees cooler than what we have today. Although the new guidance keeps the center of the high quite a bit farther north than previous runs, which is to say the high center no longer looks like it will settle over our region on Sunday morning, the trend in the model blend is colder. In spite of radiational cooling not looking quite as favorable, the low temp forecast has dropped further, to the point where the northern four mountain counties are likely to have low temps at or below freezing. If this trend continues, a Freeze Watch might be issued by the day shift. Farther south, elevations above 3500 feet in the Smokies and Balsam Mountains also have a good chance of seeing 32F. Meanwhile, winds will be light, and temps get cold enough for frost in the big valleys. It would not be a surprise to see frost in places across the NC foothills and NW Piedmont. We often underestimate the frost potential with the first cold air mass in the autumn, so some downward drift is anticipated. The air mass modifies a bit by Sunday night, but not enough to alleviate the frost potential early Monday morning in the same locations.

The rest of the forecast looks relatively quiet as a blocking pattern develops early next week and we would be the NW/N flow between the trof off the East Coast and the high amplitude upper ridge over the MS River basin. Temps would climb back to normal for Tuesday onward with little to no chance for rain through the end of the period.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

At KCLT and elsewhere: More widespread radiation fog has formed than expected, with LIFR (and even VLIFR conditions possible at the TAF sites right around 12z TAF issuance. The exception is KCLT, which looks to be the furthest away from the fog. The fog should burn off by around 14z at the TAF sites, but could linger an hour or two longer in some of the mtn valleys. VFR condition should prevail for the rest of the day. Winds will gradually increase out of the SW and become gusty by early aftn. Expect frequent gusts in the 18-22 kt range. A cold front will cross the area this evening, shifting winds to NW and likely remain gusty. A band of low-VFR clouds will spill over the mountains, and may produce a few showers around KCLT late tonight/early Saturday morning. Showers along the TN border may struggle to reach KAVL, but low-VFR or MVFR cigs may form late this evening there.

Outlook: Gusty north winds expected on Saturday before gradually diminishing over the mtns Saturday night. Low-end gusts will likely linger thru at least Sunday east of the mtns. Some showers may spread east of the mtns early Saturday morning, but confidence remains low on whether any of these showers would directly impact any TAF sites. Drier conditions return Saturday afternoon and linger thru the middle of next week.

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...None. SC...None.