textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Updated for 12Z Aviation Discussion.

KEY MESSAGES

1. Frost will be possible across much of the northwest Piedmont of NC, and parts of the northern foothills and northern part of the Charlotte metro area tonight. A Frost Advisory may be needed. Protection of sensitive vegetation will be required in some locations. 2. Fire weather remains a concern through the rest of the week as a dry air mass takes up residence across the region. Outdoor burning will become dangerous this afternoon due to low relative humidity values, gusty winds, and dry fuels. A Red Flag Fire Alert remains in effect for all of South Carolina. A Fire Danger Statement was issued for northeast GA from Noon to 8 PM today.

DISCUSSION

Key message 1: Frost will be possible across much of the northwest Piedmont of NC, and parts of the northern foothills and northern part of the Charlotte metro area tonight. A Frost Advisory may be needed. Protection of sensitive vegetation will be required in some locations.

A transient parent sfc high moving across NY/New England today and tonight will keep a cool and dry air mass across the region, in a configuration that basically looks like a dry wedge. In the wake of another reinforcing cold front that passes early today, temps will stay relatively cool, about five to ten degrees below normal for highs this afternoon and lows tonight. Across the I-40 corridor east of the mtns, lows are expected to drop into the middle 30s with dewpoints in the upper 20s to lower 30s. Winds will be light enough such that widespread frost is indicated across the northwest Piedmont zones and Cabarrus County. Frost will be more patchy over the northern foothills, but the more populated areas might have the greatest risk. Lingering uncertainty about the low temperature and dewpoint forecast prevents us from issuing a Frost Advisory at this time, but an Advisory should be anticipated in these areas. The urban heat island around Charlotte will probably keep frost more patchy across most of the metro area. The mountains could also have some patchy frost, particularly in the upper part of the French Broad River Valley. The rest of the region should be too warm even with lows more than five under normal.

The air mass continues to modify Thursday and Thursday night even as the parent high moves off the New England Coast but continues to ridge back. Some of the guidance breaks off a chunk of the sfc high over the srn Appalachians by early Friday morning, so radiational cooling conditions will be ideal. Patchy frost can be expected once again, but confidence is lower across the region because the low temps might not be low enough.

Key message 2: Fire weather remains a concern through the rest of the week as a dry air mass takes up residence across the region. Outdoor burning will become dangerous this afternoon due to low relative humidity values, gusty winds, and dry fuels. A Red Flag Fire Alert remains in effect for all of South Carolina. A Fire Danger Statement was issued for northeast GA from Noon to 8 PM today.

The surface high building in from the north will also be quite dry despite the cooler temperatures today, resulting in RH values into the 25-30 percent range for much of the area. After the reinforcing cold front moves through early today, wind will be gusty in the 20-25 mph range from the north through the rest of the morning and into the afternoon, which will also increase fire danger. Though the RH will be borderline across northeast GA and might not meet the four hour at 25 percent and below criteria, the fuel moisture should drop down below 10 pct and occasional wind gusts should reach 25 mph. The NWS office in Peachtree City issued one for all of north GA so we will comply with our northeast GA zones. The SC Forestry Commission has issued a Red Flag Fire Alert valid at 6 AM Wednesday until further notice. Winds will not be as gusty through most of the rest of the period with low RH being the main threat.

Return flow will finally start to bring in some increasing dewpts and higher min RH values early next week. Highs steadily warm back into the 80s by the weekend continuing into next week.

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/

At KCLT and elsewhere: A light easterly flow at low levels has forced the development of scattered low clouds up against/near the Blue Ridge Escarpment at daybreak, which could form a temporary MVFR ceiling from KHKY to KGSP/KGMU thru mid-morning. The lowest cloud should either scatter out or lift to VFR by 14Z, by which time deeper mixing should bring occasional wind gusts from the N down to the sfc. VFR conditions will prevail at all terminals after that point. Satellite imagery shows patchy cirrus moving in from the west with some other high-based stratocu for the middle part of the day. The model guidance was not handling this particularly well. Expect that scattered clouds will be possible around the LCL thru the afternoon, in the 040 to 060 range, so that will be included in most TAFs. Other than that, a wind forecast. Behind a reinforcing cold front, wind becomes occasionally gusty from the N to NE outside the mtns from around daybreak to the early part of the afternoon at least, but gusts could linger until wind starts to decouple in the early evening closer to sunset. Wind will go light again tonight.

Outlook: VFR thru the late part of the week courtesy of high pressure. A developing easterly low level flow could eventually bring a return of low clouds over the weekend.

GSP WATCHES/WARNINGS/ADVISORIES

GA...INCREASED FIRE DANGER from noon EDT today through this evening for GAZ010-017-018-026-028-029. NC...None. SC...None.