textproduct: Columbia

WHAT HAS CHANGED

Minimal change to heat headlines today. A bit more convective coverage possible Sunday. Aviation discussion updated for 06z TAF issuance.

KEY MESSAGES

- 1. Heat Index values between 105-110 are expected this afternoon, elevating the risk of heat related illnesses.

- 2. Strong to severe storms possible late this afternoon into the evening.

- 3. Another round of strong to severe storms possible Sunday.

DISCUSSION

KEY MESSAGE 1. Heat Index values between 105-110 are expected this afternoon, elevating the risk of heat related illnesses.

The center of the ridge has already shifted west of the area and will continue to do so as the trough currently over the Northeast continues to dig in. Despite this, weak downsloping flow should aid in bringing afternoon high temperatures back into the upper 90s, with a few spots possibly nearing 100F. While the daily records at CAE/AGS are not currently expected to be broken (101F at CAE and 102F at AGS), temperatures could fall within a degree or two. A front will continue to work toward the area from the north, with afternoon dewpoints likely remaining in the upper 60s to mid 70s in some spots ahead of it. This is expected to yield one of the hotter days this summer with widespread heat indices likely falling between 105-110F. The uptick in outdoor activities today will bring much a much higher risk for heat related illnesses, so proactive measures to stay hydrated and remain cool should be taken. A Heat Advisory will be in effect starting at 11am, continuing until 8pm for the whole CWA.

The 00z suite of guidance continues to indicate the front and shortwave will slowly near this evening with the best chances of convection still expected during the late afternoon into the evening. Cannot rule out a few spotty showers or storms earlier, but confidence in this is low.

KEY MESSAGE 2. Strong to severe storms possible late this afternoon into the evening.

A shortwave is currently seen in mesoanalysis toward southern Lake Michigan with the surface front stretching from southern WI toward OH and southern PA. These features are sparking convection currently seen over southern MI, which are expected to persist in some degree through the morning, moving toward the south. Not all CAM guidance has initialized this activity well, but the 00z HRRR and mean HREF solution did capture this. There is slight disagreement how collected this convection will become as it approaches the western Appalachians later this morning, but with a strongly unstable environment developing across the region by the early afternoon, would expected it to continue southward, with new convection possibly sparking as the front and shortwave move in. Overall, this outlook keeps the forecast on track where the bulk of convection is expected mainly after 21z as better forcing and the aforementioned batch of storms attempts to push into the FA. This environment would be conducive for damaging winds and possible some sub-severe hail as large CAPE profiles (MLCAPE near 2500 J/kg) are seen with DCAPE values near or over 1000 J/kg. Features to keep an eye on this morning though are a few gravity waves are currently pushing through SE NC from earlier convection. Depending where these move in and any low level outflow resides, an area for convection to focus could develop later in the day. Cannot rule out a few storms earlier in the afternoon, possibly from the outflow/gravity waves mentioned above, but overall confidence in early timing is low. The CWA remains outlined in a Slight Risk (level 2 out of 5) for severe weather east of the I-26 corridor.

KEY MESSAGE 3. Another round of strong to severe storms possible Sunday.

The front is expected to slowly sag through the FA Sunday, where by mid day, it could still be bisecting the CWA. With seasonable moisture likely remaining in place and some more shortwave energy moving into the region, scattered to numerous storms will be possible, especially along and south of where the front ends up. Forecasting soundings support a precip-loaded downburst threat with MLCAPE near 2500 J/kg again with DCAPE values between 1000-1300 J/kg, and TEI values between 28-32. Lingering cloud cover could put a damper on this environment, but if clearing is seen the potential for more strong to severe storms will be possible again with much of the FA in another Slight Risk for severe weather.

AVIATION /12Z SATURDAY THROUGH WEDNESDAY/

Morning stratus favoring the the CSRA and eastern Midlands then VFR expected with possible convection late afternoon into tonight.

Little change in the air mass although the upper ridge will be retrograding today allowing for some possible convection late in the day to move into the Midlands. Satellite imagery already showing stratus expanding northeastward across the CSRA into the Midlands. Prevailing IFR/LIFR cigs at AGS/OGB with tempo to lower restrictions but IFR cigs possible all terminals so included some tempo groups for the other terminals. Conditions should improve by 14-15z. Winds generally light and variable through mid morning then picking up to around 5 to 6 knots from a southwesterly direction. Late afternoon scattered convection expected to move south into the area this evening ahead of a sinking frontal boundary.

EXTENDED AVIATION OUTLOOK...Chances for restrictions and thunderstorms continue Sunday. Diurnal storm chances continue early next week.

CAE WATCHES/WARNINGS/ADVISORIES

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