Sugar Mountain

Forecast Discussion

Summary

SYNOPSIS

... Ridge of high pressure will allow for hot and humid conditions to persist through the weekend, with a cold front bringing relief from the heat early next week. Showers and thunderstorms will be possible each day.

NEAR TERM /THROUGH TONIGHT/... As of 329 AM Saturday...the late night convection has taken a weakening trend over the last hour...at long last...as the remaining instability has just about been used up. We will have a few large patches of light rain over the Upstate and upper French Broad Valley through the wee hours of the morning, but it looks like the threat for significant weather has finally diminished. So, for the remainder of the pre-dawn hours, we will look for patches of dense fog to develop where it rained. Temps will run about five degrees above normal.

An upper anticyclone and sfc high over the Ohio Valley region will be the dominant factor across our region today and tonight. Mid and upper forcing should be scant, but low level moisture remains plentiful enough for the sfc-based instability to make up for the lack of forcing. The convection-allowing models once again develop only widely scattered storms, but we suspect it might be underdone as was the case the past few days. Precip prob climbs up into the chance range across the whole area, with some likely over the higher terrain, based on recent performance and the depiction on the synoptic scale guidance. In general, lapse rates remain relatively poor, so severe storms will be isolated. The main story for today will be the heat, with temps climbing into the middle 90s over the Upstate and wrn Piedmont of NC, and dewpts remaining in the lower 70s. The result is a heat index up around 105 mainly in the nw Piedmont and Charlotte metro area in the mid/late afternoon, so the fcst continues to support the Heat Advisory issued yesterday. Actually, the 105 plus area has expanded westward a bit, so Lincoln and Catawba counties will be added as well. Expect a diurnal wane to the thunderstorm activity by late evening. Precip chances were retained along the TN border to guard against convection coming down from the NW in the pre-dawn hours on Sunday. Min temps will remain seasonally mild.

SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... As of 300 AM Sat: Not much remarkable change in the pattern from Saturday to Sunday. Strong, broad subtropical ridging will continue across the Southern states, with a weakness in the form of an inverted trough over the central Gulf region. This along with moist southerly flow in place to our west may allow some precip activity to continue and/or initiate around the start of the period Sunday morning. Otherwise the day looks fairly typical for the season, with 1500-2000 J/kg of SBCAPE developing by peak heating, very little shear, but strong theta-e lapses and DCAPE, so we may deal with a few severe pulse storms. Light southerly flow implies initiation along or north of the Escarpment and PoPs reflect that.

Sunday night a well defined upper trough will dig into the Mississippi Valley; with a weak axis of vorticity shown to approach the southern Appalachians overnight, can't rule out some nocturnal convection impinging on our area from the west. Heights fall gradually through Monday and into early Tuesday, but the arrival of the cold front no longer looks likely prior to 12z Tuesday. The falling heights suggest a bit better storm coverage on Monday, but the thermodynamic environment is more or less the same as Sunday, albeit with ever so slightly more shear. Pulse-mode convection should continue to dominate. Elevated PoPs are warranted thru Monday night as the front inches closer.

Thickness trends are virtually flat over the weekend, though Sunday's max temp guidance is not as hot as that for Saturday; given that and dewpoints expected to mix out into the upper 60s in many locations, heat indices currently look to remain below 105 and out of Heat Advisory territory. This trend continues into Monday.

LONG TERM /TUESDAY THROUGH FRIDAY/... As of 330 AM Sat: No major shake-up in the medium range fcst. Cold front will enter the area in earnest on Tuesday, which will bring us our best widespread precip chance of the period, gradually working its way southeast of the region through midweek. An amplified upper pattern will develop for the second half of the week, with a deep blocking anticyclone centered over the southern Rockies, and a couple of troughs swinging thru the East. Some PoPs will continue to be warranted mainly over the southern CWFA invof the stalling front, but fcst chances are slightly lower this cycle, with the front being shown more progressive. We will experience below- normal max temps thru Thursday, rising back to about normal on Friday.