textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Increased Fire Danger Statement issued for Northeast Georgia today.

Updated details on precipitation event Saturday night through Sunday night.

KEY MESSAGES

1. Increased Fire Danger across northeast Georgia this afternoon and early evening. Dry conditions persist through Saturday allowing low relative humidity to develop each afternoon, mainly east of the mountains. 2. Widespread rain is expected over the weekend, with precipitation most likely early Sunday morning through Sunday evening. This generally should be beneficial rain for most of the area. Localized heavier rainfall is possible, which could lead to nuisance flooding of poorly drained areas, and/or isolated bankfull conditions on area streams.

DISCUSSION

Key message 1: Increased Fire Danger across northeast Georgia this afternoon and early evening. Dry conditions persist through Saturday allowing low relative humidity to develop each afternoon, mainly east of the mountains.

High pressure builds into the Carolinas from the northwest through Friday and lingers over the area Saturday keeping dry conditions and above normal temperatures around. Lighter winds return for most locations today into Saturday, although gusty winds will linger across portions of the North Carolina mountains today before diminishing tonight. Gusts will remain below advisory criteria, ranging from 20 to 30 mph. However, some locations across the higher elevations will see gusts up to 35 mph. Low relative humidity develops mainly east of the mountains each afternoon through Saturday allowing low-end fire weather concerns to return each day.

Today and tomorrow appear to be the driest days with minimum relative humidity falling near or below 25% for locations mainly east of the mountains. However, light winds will limit fire weather concerns across the western Carolinas. The exception will be northeast Georgia where low relative humidity of 25% or less for 4 hours as well as fuel moisture less than or equal to 8% qualifies for an SPS for Increased Fire Danger. We meet this criteria today so an SPS for Increased Fire Danger was issued for northeast Georgia and is in effect from noon to 6 PM this evening. Please refer to your local burn permitting authorities on whether you can burn today. If you do burn, use extreme caution since fires can quickly get out of hand under these conditions.

Relative humidity recovers slightly on Saturday with dewpoints steadily increasing as low-level flow turning southwest ahead of an approaching low pressure system. This should allow minimum relative humidity to remain above 25% Saturday afternoon leading to lower fire weather concerns compared to this afternoon and Friday afternoon.

Key message 2: Widespread rain is expected over the weekend, with precipitation most likely early Sunday morning through Sunday evening. This generally should be beneficial rain for most of the area. Localized heavier rainfall is possible, which could lead to nuisance flooding of poorly drained areas, and/or isolated bankfull conditions on area streams.

Still expecting a mature low pressure system, driven by strong shortwave with embedded closed low, to cross the southern Plains Saturday and lower MS Valley early Sunday, and for that system to induce warm upglide atop a dry area of high pressure centered off the South Atlantic coast, leading precip chances to ramp up Saturday night. Precip chances develop along the warm front of that system, though NBM has trended a little later with arrival of slight-chance PoPs in our far west, becoming likely from west to east after midnight Sunday morning. There continue to be some timing differences as precip shield crosses the CWA, which has led to a slower decline in PoPs Sunday night and Monday morning. The peak of the event, precip-wise, still is expected Sunday.

As the consensus continues to be for the sfc high to be centered basically ESE of the CWA, in-situ cold-air damming still looks to be the most likely flavor of CAD, and relatively weak at that. Blended in raw model guidance Sat night and Sunday to slightly warm mins and cool maxes. LREF ensemble probs of precip occurring at wet-bulbs at or below 32F remain no better than about 15% even on the GEPS, which over several runs had the most members showing stronger CAD and colder sfc temps in the northern mountains and below the east-facing Blue Ridge Escarpment. Those chances are lower than on earlier LREF cycles, which lends more confidence to an all-rain event. That said, moistening will occur from the top down at the onset of the event, with profiles below freezing except in the surface layer. Thus some light snow/sleet can't be ruled out in high elevations at onset late Saturday night, though rain does look more likely. Any snow/sleet accumulation that did occur would be minimal and soon overwhelmed/melted by liquid rain.

There still are some differences in the placement and magnitude of QPF among the models and ensemble means which limits confidence on rainfall totals. This previously appeared mostly due to differences in the strength of CAD, and in the orientation of 925-850mb flow on the warm side of the system, affecting to some degree the amount of upslope forcing which occurs. Those still are factors, but there is now more support among models for a secondary low to form along the CAD wedge boundary south or east of the area. Such development could enhance low-level convergence and increase rates on a small scale away from the Blue Ridge, but also disrupt or shorten the duration of upglide over the wedge as our area looks more likely to be on the back side of that low. Mean PWATs from the ensembles have actually remained similar or trended slightly higher over the CWA so the availability of moisture would not seem to be the issue. NBM mean/percentiles have trended lower. The axis of heaviest QPF has jumped north and south over several forecast cycles from run to run and model to model, and accordingly we think there is still time for guidance to trend back up. It still seems reasonable to expect storm totals mostly in the 1-2" range with potential for localized totals of 2.5" to 3" near the south-facing Escarpment near the southwest border of NC. MMEFS and HEFS probabilities of reaching action (bankfull) stage remain less than 10% at sites in the French Broad or Saluda river basins, but a few tributaries still could reach bankfull. As of Wednesday, we received reports that soils are still frozen in some areas of the northern mountains, and though QPF is likely to be lower there than in the aforementioned areas, frozen soil is much more impervious to rain and thus runoff and flood impacts would occur with less rainfall than usual. Otherwise the dry antecedent conditions will be a mitigating factor for runoff.

Precip most likely will end prior to daybreak Monday and temps remain above normal to the end of the period. Next chance for precip would be with a weak cold front and trough late Wed or early next Thu, but confidence is low.

AVIATION /06Z THURSDAY THROUGH MONDAY/

At KCLT and elsewhere: Dry and VFR through the 06Z TAF period. Wind direction at KAVL will remain NW through the TAF period with gusts of 18-20 kts lingering through at least daybreak. However, gusts may persist through this afternoon but confidence is low. Intermittent gap wind gusts will linger at KGSP through the next few hours. Winds east of the mountains will be mainly N/NW through the TAF period with speeds ranging from 4-6 kts. Lighter winds speeds return late this evening into tonight across the terminals. VFR cirrus will gradually increase in coverage later this morning into this afternoon, becoming SCT to BKN (perhaps even OVC), before decreasing in coverage this evening.

Outlook: Dry and VFR through Saturday before precipitation chances and associated restrictions return Saturday night into Sunday ahead of a low pressure system. Drier conditions and VFR return behind the system on throughout Monday.

GSP WATCHES/WARNINGS/ADVISORIES

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