Sugar Mountain

Summary

SYNOPSIS

... High pressure will linger over the region leading to continued dry weather through tonight. Moisture will return from the west beginning early Friday, with off and on rain chances through the weekend as low pressure systems move across the Eastern states. Drier conditions will return early next week as high pressure builds into the region.

NEAR TERM /THROUGH TONIGHT/... As of 230 AM EST Thursday: The nighttime Microphysics satellite loops show high clouds streaming across the area from the west this morning. Cloud cover will gradually thicken through daybreak, becoming scattered to broken. This will act to limit radiational cooling somewhat. However, a cold start to the day is still expected with lows dipping into the 20s and lower 30s.

Sfc high pressure will be centered over the Carolinas through daybreak before the center gradually pushes offshore throughout the morning hours. The southwestern periphery of the sfc ridge will extend across the Southeast this afternoon into late tonight leading to continued dry weather. High clouds will briefly push out of the area later this morning, but will return this afternoon becoming few to scattered. Light and variable winds will develop around daybreak and will linger through the late morning hours. Winds will pick up out of the south by early this afternoon, with any low-end gusts confined to the higher elevations. Afternoon highs will be ~5-10 degrees warmer compared to yesterday thanks to rising heights aloft. Temps across the lower elevations will climb into the upper 50s and lower 60s. Cooler temps can be expected across the higher elevations, with highs only reaching into the 40s.

A low pressure system will lift northeast out of the Southern Plains and into the Lower Midwest this evening into tonight, allowing moisture to increase across the forecast area. This will lead to gradually increasing cloud cover from west to east tonight, with cloudy skies expected across the CWA by the end of period. Rain chances will also gradually increase after midnight across the western half of the forecast area. Capped PoPS to chance as CAMs are not in agreement regarding the coverage of PoPs towards the end of the near term. Cloud cover will limit radiational cooling overnight, leading to above freezing lows (or just above freezing lows) across the CWA. Thus, no p-type issues are anticipated at this time.

SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... As of 130 AM Thu: Plume of moist WAA will remain over the CWA much of Friday, within warm conveyor belt of mature cyclone moving thru the Midwest. Dynamic lift is somewhat lacking when moisture is deepest early to midday Friday. It is now more evident the dry slot of the low will shift east over the area over course of Friday, such that moisture becomes shallow and PoPs fall to only a chance for the NW part of the CWA Friday night. WAA won't come to an end, and a sharp inversion should be maintained aloft. Although lapse rates above the inversion aren't great, a few rumbles of thunder could occur in the southern CWA at times from Friday evening onward. Model QPF on the 00z cycle runs overall is pretty similar to runs from the previous cycle, although most models show less QPF Friday morning and in some cases, more QPF Friday evening before the dry slot advances.

Those runs with more evening QPF seemingly are responding to upper divergence ahead of amplifying jet near the Gulf Coast. This results from the longwave western CONUS trough swinging into the Plains, tightening the upper level gradient. The jet divergence develops over a stationary front in the lower Mississippi Valley and several models depict a frontal wave developing along it. This reinforces WAA over GA and the Carolinas. Model consensus has increased slightly further that this will occur, but more notably models are quicker to develop the low than before. This suggests any lull in precip will end earlier. Whereas Saturday morning had looked dry for a portion of the area, now precip likely will have returned in many areas by daybreak. The same models show precip tapering from the west Saturday night as frontal wave passes, flow begins to veer and moisture becomes shallow again. Isolated thunder will remain possible until that occurs.

Although model QPF is lesser for Friday, it still looks likely that in-situ CAD will develop, with erosion not likely to occur as long as some degree of upglide continues--so basically the entire short term period. Accordingly max temps Friday and Saturday were bumped toward the lower end of the guidance envelope.

LONG TERM /SUNDAY THROUGH WEDNESDAY/... As of 230 AM Thu: Precip chances in the medium range period will be due to a series of shortwaves rotating thru the longwave trough as it moves east out of the central CONUS.

The first shortwave should spawn another sfc low and carry it thru the Great Lakes or up the Ohio Valley Sunday into Monday. A stationary boundary will be present to our south following the departure of the Saturday frontal wave. It appears that boundary could be reactivated by the new system, and precip could develop again from the south Sunday. Even if that does not occur, the passing low should finally pull a cold front through the area late Sunday, eroding what's left of CAD. With the erosion and downsloping, Sunday is likely to be warmer than Saturday. Timing still varies from model to model, but generally allowed PoPs to diminish steadily from NW to SE Sunday. We had previously entertained the idea of a small high-shear low-CAPE severe weather threat on Sunday preceding this front. Shear parameters increase markedly due to the impressive mid to upper level flow, and a small amount of SBCAPE may develop ahead of the front. However, the dynamics won't be there given the track of the shortwave, and in particular the near-sfc flow likely will be veered, so the ingredients don't look likely to come together. Temps will trend down each day after Sunday as colder continental high pressure spreads in.

The next shortwave will dig thru the mid-Mississippi Valley Sunday night and rocket east to our area by Monday. It won't have a lot of moisture to work with, and we will already be in a westerly flow regime when it arrives. Profiles feature good lapse rates over a deep layer, and with winds backing to NW along the TN border, a few sprinkles or flurries could be seen dependent on the sfc wet-bulb temp at arrival, with slight-chance PoPs. There just doesn't look like enough moisture to be concerned about accumulation at this point. The final shortwave, a true Alberta Clipper behind which wholesale height rises look to occur, will arrive Tuesday night or early Wednesday, warranting another round of small PoPs near the TN border, and a slight chance of light snow accums.