textproduct: Columbia

WHAT HAS CHANGED

Confidence continues to increase in hot, humid conditions with heat indices over 100F this week. Aviation discussion updated for 18z TAF issuance.

KEY MESSAGES

- 1. Generally dry weather and well above normal temperatures expected with heat index values over 100F becoming more likely this week.

- 2. Active weather and decreasing temperatures possible next weekend.

DISCUSSION

KEY MESSAGE 1. Generally dry weather and well above normal temperatures expected with heat index values over 100F becoming more likely this week.

A mid to upper level ridge is currently building over the eastern CONUS. Both deterministic and ensemble guidance continue to be in good agreement that this ridge slides over the eastern seaboard through mid to late week. The NAEFS ensemble indicates the 500 mb heights are forecast to be near the climatological max tomorrow into Wednesday before dropping slightly to end the week. With the ridge overhead, generally dry conditions are expected to persist through much of the work week. The bigger story is going to be the heat. Temperatures are forecast to gradually increase each day to the upper 90s for mid to late week. When factoring in humidity, heat index values are likely to exceed 100F, potentially as soon as tomorrow, in the afternoons for the remainder of the week. There is potential we approach Heat Advisory criteria late in the week, but that will largely be dependent on how well the atmosphere mixes out each day.

KEY MESSAGE 2. Active weather and decreasing temperatures possible next weekend.

Global ensembles are in good agreement that the ridge overhead late in the week retrogrades westward, allowing for a trough to slide down the eastern seaboard. As it does, chances for showers and storms are anticipated to increase at the end of the workweek into the weekend. Cooler afternoon highs are forecast for the end of the weekend as well.

AVIATION /18Z MONDAY THROUGH SATURDAY/

VFR conditions generally expected except possible early morning fog/stratus.

Upper ridging continues to strengthen aloft with easterly surface flow keeping low level moisture in place resulting in generally fair weather cumulus. Some isolated showers possible mainly favoring the eastern Midlands and CSRA but think coverage will be limited enough to not mention in forecast. Easterly winds around 5 to 7 knots should subside with sunset to light and variable or calm overnight.

Low level moisture trapped beneath the inversion and drier air aloft may again support fog/stratus formation, with fog more favored given clearing skies and light boundary layer winds. Guidance is suggesting OGB/AGS most favored for restrictions and have included prevailing MVFR vsbys starting 08z with tempo to lower restrictions 08z-12z time frame. Also included a tempo group for MVFR vsbys elsewhere although confidence is lower. Any restrictions should dissipate by 13z with light and variable winds eventually picking up an easterly direction around 5 knots or so with fair weather cumulus developing.

EXTENDED AVIATION OUTLOOK...Early morning restrictions still possible despite a drier outlook for the week.

CAE WATCHES/WARNINGS/ADVISORIES

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