textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

No major changes to forecast thinking over the next week.

KEY MESSAGES

1. Low-impact weather expected through late in the week, with a steady warming trend continuing through Thursday night. 2. Record high temperatures possible Friday ahead of another cold front. The front brings a chance of showers late Friday and Friday night. 3. Cool, dry high pressure builds in for the weekend with moderating temps early next week.

DISCUSSION

Key message 1: Low-impact weather expected through late in the week, with a steady warming trend continuing through Thursday night.

Not much to write home about for the next couple days. The synoptic pattern right now is dominated by deep subtropical ridging over the Desert Southwest and northern Mexico, which is essentially acting as a large-scale block, deflecting would-be Rossby waves to the north so that they only skirt our northern zones. One of these waves, a low-amplitude shortwave axis barely discernible on water vapor imagery, is responsible for ongoing cloud cover and should drift east of I-77 by mid-morning today, allowing cloud cover to briefly diminish. Another weak embedded shortwave will drift across the Mid- Atlantic this evening, prompting additional mid-and high-level clouds to develop Wednesday night. As the high drifts farther offshore during this time, whatever weak surface CAA is in place will cease...giving way to gradually-intensifying low-level WAA...and allowing a steady influx of low-level moisture. So, after several days of enhanced fire danger, the window for issues is likely over through at least Thursday...and increasingly moist conditions are expected each day.

Temperatures through the period reflect this setup. Today's highs should hover around normal in most locations, but by Thursday temps will creep 2-3 categories above normal...and low temperatures may flirt with records by Thursday night. By Friday morning, a cold front will ooze across the upper Ohio Valley...and winds will start to pick up...but the front should not make it to us before daybreak Friday.

Key message 2: Record high temperatures possible Friday ahead of another cold front. The front brings a chance of showers late Friday and Friday night.

As strong high pressure expands out of Canada and the northern Plains Friday, a zonally oriented cold front will push through the Southern states, from west Texas to the Tidewater region. Prior to the front our region will be under the very broad upper ridge centered over the Mexican Plateau, characterized by heights and temperatures at 850, 700, and 500mb being above the 95th percentile for late March; owing to the breadth of the ridge flow at those levels will be predominantly westerly. Lapse rates look to be poor in the low levels The front still looks to arrive late enough in the day Friday that skies will be mostly sunny, and the exceptionally warm airmass and possibly some downsloping lead to max temps which will threaten the daily records at CLT and GSP that day.

Moisture return will be limited owing to the westerly flow ahead of the front, but PWATs still are progged to become anomalously high. The front initially will have very little in the way of dynamic support, with the jet and primary trough axis being kept across the northern states by the ridge, but there will be respectable frontogenetic response owing to the strong thermal gradient across it. Profiles do appear likely to saturate along/west of the Appalachians, and low-level lift appears sufficient to warrant likely PoPs near the TN border Friday afternoon. Lapse rates will be weak and thunder chances are too small to mention in the forecast at that time/area. In the lee of the mountains, vertical profiles feature only marginally supportive lapse rates atop what looks to be a deeply mixed boundary layer late Fri afternoon and evening, though dynamic lift eventually should increase there as the trough amplifies slightly over the CWA once the front passes the mountains. Slight-chance to chance PoPs do result for the foothills areas; the best overall chance outside the mountains is in the I-77 corridor Friday evening ahead of the trough axis. Still not seeing enough viable instability to warrant a thunder mention. Owing to the weak forcing and instability, it continues to look like this front is unlikely to bring meaningful rainfall to the area, particularly east of the Appalachian spine; NBM probs of 0.25" 48-hr rainfall ending Saturday morning are no better than 20% in the NW NC Piedmont, and increasingly low as one heads south from there.

Key message 3: Cool, dry high pressure builds in for the weekend with moderating temps early next week.

The Canadian high will build into the area Saturday; winds look to remain breezy with some gusts possible during the morning, but those trend lower by afternoon. Temperatures should top out a few degrees below normal. Dewpoints look to fall into the teens or lower by afternoon, although mixing will be limited by strong subsidence aloft. RH is likely to drop below 20 percent over most of the Piedmont, with values less than 30 percent even in mountain valleys where low afternoon RH is less common. There could be a brief overlap of gusty winds with low RH such that Red Flag conditions are not out of the question. SPC Day 5 fire outlook issued Tue afternoon already highlights most of our area in a 40% contour for low RH and wind. As the high centers north of the area Saturday night, winds become very light and strong radiational cooling is expected, and a light freeze is expected in the mountains, NC foothills, and perhaps some spotty locations in the I-40 corridor. 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.

The sfc high remains transient as the upper pattern progresses; southerly sfc flow redevelops over the area Sunday afternoon, and temps rebound a few degrees east of the mountains. By early Monday, upper ridge axis extends from the Gulf to the northern Rockies, with a broad warm sector taking shape in the Mississippi Valley ahead of low pressure system passing south of Hudson Bay. Models/ensembles vary in their placement of the associated frontal zone, but some cloud cover and light precip are not out of the question near the TN border as the front nears the mountains Monday or Tuesday. As the ridge migrates eastward over that timeframe, thicknesses increase and temps trend well above normal again.

AVIATION /13Z WEDNESDAY THROUGH SUNDAY/

At KCLT and elsewhere: VFR continues for the 12z TAF cycle. Scattered to broken cirrus visible on satellite, along with a scattered mid-level altocu deck, mainly over the Upstate. As anticipated winds have begun to trend ESE, and should turn more decided SE in the next few hours. They'll turn S by afternoon, and eventually to SSW by evening.

Outlook: VFR continues through at least Thursday night. A cold front may bring rain and associated flight restrictions on Friday or Friday night.

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...None. NC...None. SC...None.