textproduct: Columbia

WHAT HAS CHANGED

A Heat Advisory remains in effect through 8 pm this evening for Lancaster and Chesterfield Counties. A Heat Advisory has been issued for tomorrow for the entire area. Aviation discussion updated for 18z TAF issuance.

KEY MESSAGES

- 1. Heat Index values up to 110 Saturday elevating the risk of heat related illnesses.

- 2. Heat Advisory continues for Lancaster and Chesterfield Counties through 8 pm today.

- 3. Severe storms possible Saturday afternoon or evening.

DISCUSSION

KEY MESSAGE 1. Heat Index values up to 110 Saturday elevating the risk of heat related illnesses.

The center of the upper ridge shifts west on Saturday. Weak downslope winds and increasing moisture ahead of a cold front will push afternoon temperatures into the upper 90s to near 100 degrees and Heat Index values to near 110. There will also be a greater vulnerability to heat related illness due the uptick in outdoor activities this Saturday. A Heat Advisory has been issues for the entire forecast area.

There is some potential for thunderstorms, especially in the northern FA late Saturday afternoon and evening. But we believe that the later timing of the storms will still allow Heat Index values to exceed advisory thresholds through the bulk of the afternoon.

KEY MESSAGE 2. Heat Advisory continues for Lancaster and Chesterfield Counties through 8 pm today.

Temperatures will rise in the mid to upper 90s this afternoon. Dewpoints have mixed into the low 70s, but a few locations in the northern Midlands could tick up into the mid 70s. Overall, this should yield heat indices between 105-108. A few areas near Chesterfield and Lancaster Counties could briefly reach Heat Advisory criteria and due to this, a Heat Advisory will remain in effect until 8pm this evening for these counties.

KEY MESSAGE 3. Severe storms possible Saturday afternoon or evening.

As ridging shifts west, we will see shortwave energy dig into the Mid Atlantic States on Saturday afternoon and evening. A cold front well to our north will be the focus for convective initiation. As storms develop and move south and east during the day they will encounter very steep lapse rates which would support damaging winds in some of the stronger storms. The overall limiting factors for severe weather into SC will be the limited moisture available and the fact that the stronger dynamics should remain to our north. With PWAT values only 1.6 to 1.8 inches we may only see scattered thunderstorms that do not develop into an MCS. However, even if the stronger storms do remain to our north, an outflow boundary could still push into the northern FA in the evening. This could spark at least scattered convection through the evening and overnight as it progresses southward through the forecast area.

With a surface boundary over the region on Sunday we can expect at least a chance of showers and thunderstorms as an upper level shortwave crosses into the forecast area. With a deeper trough and higher atmospheric moisture we would expect scattered to numerous thunderstorms Sunday afternoon and evening. Cloud cover could ultimately hinder potential instability and lowers the threat of severe weather. That said a few storms may still become severe, especially if cloud cover starts breaking earlier than expected.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

Mainly VFR conditions through the TAF period, with some fog possible near daybreak.

A cumulus field is being noted across the forecast area this afternoon with bases around the 4k-5k ft range. Expect the cumulus field to continue through sundown. Southerly winds in the 5-10 kt range for the afternoon as well before becoming light and variable to calm overnight. There is potential for fog at the terminals around daybreak. As of now, the highest confidence for reduced vis is at AGS, so have included it in the TAF there. Leaving it out of the other terminals for the time being; however.

EXTENDED AVIATION OUTLOOK...Chances for restrictions and thunderstorms increase Saturday afternoon and Sunday as a cold front approaches.

CAE WATCHES/WARNINGS/ADVISORIES

SC...Heat Advisory from 11 AM to 8 PM EDT Saturday for SCZ016-018- 020>022-025>031-035-037-038-041-115-116-135>137. Heat Advisory until 8 PM EDT this evening for SCZ016-115-116. GA...Heat Advisory from 11 AM to 8 PM EDT Saturday for GAZ040- 063>065-077.