textproduct: Columbia

WHAT HAS CHANGED

Heat products may be needed over the weekend. Chances of convection increase early next week with increasing chances of severe weather. Aviation discussion updated for the 18z TAFs.

KEY MESSAGES

- 1. Above normal temperatures continue, peaking during the Independence Day weekend. - 2. Increasing chances of showers and thunderstorms late weekend into next week.

DISCUSSION

Key Message 1: Above normal temperatures continue, peaking during the Independence Day weekend.

Strong upper ridge affecting much of the eastern US will continue to be the dominant feature into the holiday weekend. The anomalously strong ridging will combine with highly anomalous 850mb temperatures (above the 90th percentile) at or above 20C to provide hot conditions across the forecast area. Ensemble guidance suggests lowering atmospheric moisture tomorrow with PWATs falling to around 1.5 inches around 50th percentile. Forecast soundings indicate deep mixing tapping into the drier air aloft which should mix out dewpoints into the 60s resulting in heat indices below advisory criteria, although they are expected to continue to be at or above 100 degrees. PWATs are forecast to lower even more on Friday to around 30th percentile but the upper ridge axis will be building into the Carolinas and Mid-Atlantic and temperatures are expected to be a bit warmer, yielding heat indices in the 100-105 range. Continued high temperatures in the upper 90s to around 100 degrees over the weekend may lead to heat related products for the holiday weekend as humidity increases again with increasingly southerly low level flow.

Key Message 2: Increasing chances of showers and thunderstorms late weekend into next week.

Ensembles continue to indicate the strong upper ridge impacting the eastern states will begin to weaken and break down Sunday into next week as ridging builds over the intermountain west and Plains states. This will allow for some weak height falls and shortwave energy to move into the region. Atmospheric moisture will be much higher with PWATs back up around 2 inches supporting stronger instability and better chances for convection. Some of the ML severe guidance is suggesting increased potential for severe storms early next week.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

VFR conditions expected through the TAF period.

Winds this afternoon remain light and variable at times, but will favor a E component at 5-7 kts. Thin cirrus continue to stream overhead with some fair weather cumulus decreasing tonight. Toward daybreak, some typical morning MIFG may develop around AGS/OGB, though confidence remains low at this time. Dry and hot weather continues Thursday with light winds generally out of the E/SE at 5-7 kts. A few VFR cumulus may develop by midday and into the afternoon.

EXTENDED AVIATION OUTLOOK...Convection unlikely for the remainder of the week as ridging builds overhead. Brief early morning restrictions possible. Rain chances and possible restrictions start to increase Saturday and especially Sunday.

CAE WATCHES/WARNINGS/ADVISORIES

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