textproduct: Columbia

WHAT HAS CHANGED

Aviation updated for 12z TAF.

KEY MESSAGES

- 1. Isolated convection possible today with hot/humid temperatures and heat indices near 105F.

- 2. Increased chances of rain and severe weather over the weekend with highest chances Sunday into Monday.

DISCUSSION

Key Message 1: Isolated convection possible today with hot/humid temperatures and heat indices near 105F.

Another hot/humid day is in store today as upper ridging remains in place. 850mb temperatures currently near 20C are expected to rise a bit further toward 22C and strong heating is expected to bring temperatures into the mid to upper 90s. Deeper mixing is expected today, but despite this, surface dewpoints in the mid 70s may only mix out toward the lower 70s with 925mb dewpoints progged to be near 69-72F. This should bring heat indices above 100F by the late morning, with heat indices peaking around 105F during the afternoon. A couple locations briefly reaching 108F cannot be ruled out, but confidence in widespread 108F heat indices is low, thus a Heat Advisory was not issued with this forecast package. The other potential fly in the ointment is convection during the afternoon. The mean HREF solution and HRRR keep coverage rather isolated and mainly confined toward the sea breeze later in the afternoon, but with convective temperatures between 94-96F, I would not be surprised if coverage ends up being a bit more scattered, and gets going a bit earlier than modeled. If this scenario pans out, afternoon highs may end up a bit cooler than forecast, but either way, hot/humid conditions should be expected today.

Widespread severe weather is not expected with today's activity as greater moisture and kinematics is expected to move in this weekend. With that said, strong heating and dewpoints in the 70s should yield MUCAPE values between 2500-3000 J/kg. Deeper mixing should also yield DCAPE values near 1000 J/kg with TEI values between 24-27. If a strong updraft can establish its self in this weakly sheared environment, an isolated stronger storm with the risk of gusty downburst winds.

Key Message 2: Increased chances of rain and severe weather over the weekend with highest chances Sunday into Monday.

There has not been a significant shift in the outlook heading into this weekend and early next week. Subtle mid level height falls are progged to occur Saturday as a deepening trough moves into the Great Lakes. Strengthening moisture advection is also expected as a developing weak tropical disturbance in the northeastern Gulf brings PWAT's above 2". This should yield relatively weak, but sufficient forcing for scattered convection during the afternoon/evening Saturday. Overall, a fairly typical strong to marginally severe pulse environment is expected to develop as MUCAPE values in the 00z HREF remain near 2500 J/kg, but even deeper mixing may yield DCAPE values near 1200 J/kg. Isolated microbursts and the associated damaging wind risk would be the main concern. With fairly weak kinematics still in place, mean storm motions are expected to be near 10kts, bringing a locally heavy rainfall risk as well.

Greater height falls are shown in ensemble guidance Sunday and Monday as the upper trough deepens a bit. At this point, PWAT's are expected to rise up near 2.10-2.20" with the weak low level circulation in the northeastern Gulf becoming a bit more collected. There should also be enhanced surface troughing over the region, yielding solid moisture convergence. Cloud layer shear around 30-35 kts is expected on Sunday, possibly bringing better storm organization during the afternoon/evening as LREF probabilities for SBCAPE over 2000 J/kg are near 50%. This could yield a greater Severe risk (mainly in form of damaging winds) with the area remaining in SPC's Slight Risk (level 2 out of 5). AI/ML guidance hint a couple strong to marginally severe storms could be possible again on Monday as the weak tropical disturbance slowly drifts northeastward, but there is still generous uncertainty in the evolution of this disturbance. Heavy rainfall could also accompany this activity each day with the deep moisture in place and fairly long/skinny CAPE profiles.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

Scattered afternoon storms may lead to brief restrictions but otherwise VFR.

VFR conditions in place at all terminals with light and variable winds. Winds generally expected to remain light, out of the south around 5 knots. Scattered thunderstorms expected to develop this afternoon into evening with greater coverage than yesterday. Probability remains around 30 percent of storms impacting the terminals so have included prob30 mention from 19-00z.

EXTENDED AVIATION OUTLOOK...Potential for restrictions from showers and thunderstorms continue this weekend into early next week.

CAE WATCHES/WARNINGS/ADVISORIES

SC...Air Quality Alert from 10 AM this morning to 8 PM EDT this evening for SCZ115-116. GA...None.