textproduct: Columbia

WHAT HAS CHANGED

Aviation discussion updated for 12Z TAFs.

KEY MESSAGES

- 1. Scattered storms expected this afternoon with widespread showers and storms Sunday and Monday associated with a front.

- 2. Hot, humid, and breezy conditions continue with cooler conditions associated with the front late weekend into next week.

DISCUSSION

Key Message 1: Scattered storms expected this afternoon with widespread showers and storms Sunday and Monday associated with a front.

Scattered storms are expected once again this afternoon with coverage similar to Friday. Flow aloft is expected to become more zonal in response to a stronger shortwave translating around a larger scale trough. Weaker shortwaves are forecast to move over the area today, sparking the thunderstorm activity. In addition, PWATs are expected to increase with the SPC 00z HREF mean still showing values greater than 2 inches over most of the forecast area. Environment may be slightly weaker to support severe storms based on HiRes forecast soundings with weaker cloud layer shear and not quite as unstable an environment but we remain in a marginal risk for today with the potential for a few storms to produce strong to marginally severe wind gusts.

As a front approaches the area Sunday into Monday. Blended guidance supports widespread showers and storms near the front each day, favoring the afternoons where moderate instability will likely develop. While widespread severe weather is not anticipated, especially Monday where instability may struggle to develop, a few storms could approach severe limits. Storms will likely have efficient rain rates as evidenced by the latest forecast sounding. Although storm motion is expected to be fast enough to prevent major flooding concerns, it will be worth monitoring for the potential of training as the flow looks to be generally parallel to the front. Ensemble means then favor drier air pushing into the area by the middle of next week.

Key Message 2: Hot, humid, and breezy conditions continue with cooler conditions associated with the front late weekend into next week.

Hot, humid, and breezy conditions continue with today being the warmest of the next several days. The increased convective coverage this afternoon may limit the extent of our high temperature and heat index values, but expect triple digit heat indices for today with highs in the mid to upper 90s and dew points remaining in the 70s. Blended guidance IQR continues to favor lower temperatures associated with the approaching front and widespread clouds and convection each day. Given the recent hot weather, the NBM takes that into account and will likely have a warm bias. So, I would not be surprised if we end up toward the cooler end of the IQR early in the week ahead. This air mass is expected be very humid; however, with blended dew points continuing in the low to mid 70s.

AVIATION /12Z SATURDAY THROUGH WEDNESDAY/

VFR conditions will generally prevail through the forecast period, however afternoon/evening convection could result in temporary flight restrictions.

Winds will increase from the west by mid-morning, gusting upwards of around 20kt at times through the afternoon. Conditions will be typical for mid-summer, with an extensive cumulus field developing by afternoon along with scattered convection. Have included a PROB30 group at all terminals from 19-24Z to account for the thunderstorm potential and accompanying flight restrictions and gusty winds.

EXTENDED AVIATION OUTLOOK...Increasing chances for afternoon storms Sunday and into early next week.

CAE WATCHES/WARNINGS/ADVISORIES

SC...None. GA...None.