textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

A Fire Danger Statement was issued for Upstate South Carolina and northeast Georgia for Tuesday afternoon.

Confidence increasing for dry forecast Wednesday and Thursday.

KEY MESSAGES

1. Very dry conditions develop on Tuesday, with widespread critical relative humidity in the afternoon. A Fire Danger Statement is in effect for Upstate South Carolina and northeast Georgia. 2. Most likely, no precipitation Wednesday through Thursday night under weak high pressure. Temperatures moderate back above normal by Thursday. 3. Near-record high temperatures Friday ahead of another cold front. The front brings a chance of showers, and below-normal temperatures for much of the area next weekend.

DISCUSSION

Key message 1: Very dry conditions develop on Tuesday, with widespread critical relative humidity in the afternoon. A Fire Danger Statement is in effect for Upstate South Carolina and northeast Georgia.

Quiet conditions tonight. A 1031mb surface high currently centered over southern Michigan is driving NE winds across most of the western Carolinas, beneath flat, WNW flow aloft. Some upstream moisture is driving a band of high-level clouds which on satellite imagery appear to be anchored to the Appalachian ridge...possibly within a vertically-propagating gravity wave originating in a subsidence inversion depicted on KAVL sounding data at around 850mb. Other locations remain clear.

Today will be markedly cooler than the last few days. With a cold front now well to our south and cooler air spilling into the region from the north, high temperatures should only climb into the upper 50s to low 60s across the low terrain...a solid 1-2 categories below normal...beforaga tonight should drop into the 40s or even upper 30s along the I-40 corridor.

Fire danger will again be an issue today, though not to the extent it was on Monday. Sporadic gusts of 10-15kts are still being reported at some sites across the area, and this will continue through mid-morning, before gusts die down and a steady ENE wind prevails the remainder of the day. The potential for dewpoint mixing is also more limited today, with the drier air aloft trapped within a deep subsidence inversion (the same one responsible for ongoing orographic cirrus!). Even without much deep mixing, however, incipient air is quite dry, with RH in the 20-25% range...and any mixing will just push things further into critical RH territory. Therefore, a Fire Danger Statement has been issued for Upstate South Carolina and Northeast Georgia from noon until 8 PM Tuesday, in coordination with neighboring offices and local land managers.

Key message 2: Most likely, no precipitation Wednesday through Thursday night under weak high pressure. Temperatures moderate back above normal by Thursday.

High pressure will be centered off the Mid-Atlantic coast Wednesday. Somewhat ill-defined 850mb ridge will extend over the Southeast CONUS and weak S to SW flow will occur over the high. This regime is close to, but not quite cold-air damming. However, if the S or SW flow bears enough moisture to maintain low cloud cover--and especially if light precip were to result--diabatic effects could lead to a chilly day. The NAM is pretty much alone among our models in depicting this type of event; other models don't saturate the low levels and are dry and sunnier, which makes more sense from the pattern as a whole. We will keep PoPs less than 10%. There is a signal for increasing high altitude cloud cover during the day, but model consensus suggests that will have minimal impact on temps. Accordingly we will advertise temps rising a few degrees warmer than Tuesday, back to around normal.

Late Wednesday, on multiple models a very weak shortwave is shown to originate in the mid-MS Valley, possibly resulting from convection; this feature tracks southeast toward our CWA early Thursday, with some model QPF response developing near the Ohio River which reaches the Appalachians. However, they vary widely in the location/extent of the depicted precip, and moisture/thermal profiles are not very impressive near the TN/NC border. No mention appears warranted in the forecast. Upper flow effectively becomes quasi-zonal Thursday as the Atlantic trough drifts east and the Southwest anticyclone flattens with next shortwave moving into the northern Plains. Heights and thicknesses rise, with mostly sunny skies and breezy SW winds. Max temps rise into the mid-upper 70s, 10-15 above normal, excepting the high elevations.

Key message 3: Near-record high temperatures Friday ahead of another cold front. The front brings a chance of showers, and below-normal temperatures for much of the area next weekend.

Trough surrounding polar vortex will dig across the Great Lakes early Friday, with strong Canadian high pressure expanding into the upper Mississippi Valley. A cold front will push south and east as a result, now timed to reach our part of the Appalachians late Friday afternoon. Dynamic lift looks to remain across the Midwest and Northeast; moisture return ahead of the front looks to be limited by low-level flow having a strong westerly component on the periphery of the flat ridge. Profiles become sufficiently saturated to maintain modest 30-50% PoPs for the mountains and NC Piedmont Friday afternoon and evening, with chances peaking Friday night in the GA/SC zones. Low surface relative humidity will limit our ability to destabilize, but lapse rates are fairly poor anyway owing to the deep warm advection prior to the front. Global ensembles suggest very little chance of seeing even 500 J/kg Fri afternoon. QPF looks unlikely to be enough either to make a dent in the drought conditions, or for a wetting rain to mitigate dry fuel moisture and provide fire weather relief.

The late arrival of the front into the CWA Friday should allow for another day of airmass modification, plus some degree of downslope wind and compressional warming. Max temps in the Piedmont are now progged to be in the upper 80s, with lower 80s for the mountain valleys, a bit warmer than previous forecasts. The current NBM max for Friday would break the record at CLT and GSP. Gusty northerly winds look to bring temps back to around normal, or slightly above, by Saturday morning. Under the influence of the Canadian airmass, temps remain below normal Saturday through Sunday, with low minimum RH below 30% likely both afternoons. A freeze appears possible for most of the mountains Saturday night, though it probably will be too dry for frost in the non-mountain areas where temps reach the mid 30s. This said, the first group of zones in the spring frost-freeze program (GA/SC zones outside the mountains and southern tier of NC Piedmont zones) do not activate until April 1.

AVIATION /06Z TUESDAY THROUGH SATURDAY/

At KCLT and elsewhere: Largely a wind forecast for the 06z TAF cycle. Currently seeing increasingly sporadic gusts of 10-15kts at terminals across the western Carolinas, and should see these gusts steadily become less frequent through mid morning Tuesday, before they disappear entirely in favor of a steady 5-9kt ENE wind. Could have some intermittent crosswinds at KCLT, but should favor the N for most of the day. An upper shortwave will cross the region from the northwest today with little fanfare...resulting in a period of BKN cloud cover from late morning through mid-afternoon...returning to FEW/SKC by evening. VFR cloud cover will begin to increase again Tuesday night, and winds will toggle to the SE.

Outlook: VFR conditions continue through most of the week. Rainfall and associated restrictions may return by Friday as a cold front crosses the area, but confidence is limited.

CLIMATE

RECORDS FOR 03-27

MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 85 2020 32 1955 60 1921 11 1955 1894 KCLT 85 1950 40 1894 62 1949 19 1955 1944 KGSP 86 2020 45 2011 60 1921 15 1894 1947

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...INCREASED FIRE DANGER from noon EDT today through this evening for SCZ008>014-019-101>109.