textproduct: Columbia

WHAT HAS CHANGED

Aviation discussion updated for 12z TAFs.

KEY MESSAGES

- 1. Isolated diurnal storms possible each day this week. A strong storm cannot be ruled out.

- 2. Increasing heat and humidity is expected next week.

DISCUSSION

- 1. Isolated diurnal storms possible each day this week. A strong storm cannot be ruled out.

Southerly to southeasterly near surface flow is expected to continue today and into early next week, before becoming a bit more southwesterly to westerly late in the week. Overall, with the region remaining between the upper ridge over the western US and the strong area of high pressure off the East Coast, seasonable moisture should persist through the forecast period with surface dewpoints likely remaining in the low to mid 70s much of the forecast period (as well as PWAT's near to just below 2"). This moisture combined with strong heating should bring SBCAPE values greater than 2000 J/kg most days but with lacking upper kinematics, creating an environment conducive for spotty to isolated pulse convection each afternoon through the mid to late week, though the latest NBM has come in a bit drier. As is typical this time of the year, a strong storm or two cannot be ruled out with the risk of strong downburst winds, but widespread severe weather is unlikely. A bit more uncertainty in terms of precip chances enters late this week into the weekend. This is driven by greater spread amongst global deterministic and ensemble guidance with the strength of a shortwave moving out of the northern Great Lakes and thus it's ability to push a surface front near the region. A more amplified solution could bring increased rain chances/coverage, but details still need to be sorted out.

- 2. Increasing heat and humidity is expected next week.

As previously discussed, 500mb heights are expected to gradually rise through the week, peaking near the NAEFS 90th percentile by the late week. As this occurs, 850mb temperatures currently near 18C should rise to between 20-23C by the mid week. With these warming low level temperatures, rising mid level heights, and the expected spotty nature of afternoon convection, high temperatures are progged to peak in the mid to upper 90s Tuesday onward. Due to the uncertainty in potential troughing by this weekend discussed in Key Message #1, larger NBM IQR spreads exist, but near normal to just above normal temperatures still seem likely. Surface dewpoints remaining in the low to mid 70s through the period bring increased confidence in heat indices rising back above 100F with LREF probabilities reaching above 70% by Tuesday with probabilities for indices above 105F between 30-50% Thursday and Friday. Overall, confidence in reaching Heat Advisory criteria is low, but spots of 105-108F could be possible mainly between Wednesday and Friday so be prepared for returning hot/humid conditions this week.

AVIATION /12Z SUNDAY THROUGH THURSDAY/

Outside of some predawn fog/stratus restrictions this morning, the remainder of the TAF period should feature VFR conditions.

Little change in the environment overall with plenty of low level moisture in place. Overall south to southeasterly surface flow should persist through the period once again, though near calm winds are expected through the night and only about 5-8 kts during the day. Stratus has developed in the last couple of hours with CIGS generally around 400-700 ft MSL. This has limited VSBY reductions at those sites, but where stratus hasn't formed there are some VSBY reductions, especially near the northern Midlands. Have maintained the tempo groups for mainly CIG restrictions, though a few MVFR VSBYs can't be totally ruled out. Expect stratus to start to lift and scatter out between 13z and 15z, with VFR returning late morning. Isolated convection expected again this afternoon but confidence in coverage remains too limited for any mention in the TAFs at this time. Stratus and fog tonight are less likely as winds turn southwest and cut off the onshore flow that has reinforced the low level moisture over the last several days.

EXTENDED AVIATION OUTLOOK...A seasonal pattern of early morning restrictions and diurnal thunderstorms is likely through much of the extended.

CAE WATCHES/WARNINGS/ADVISORIES

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