textproduct: NWS Birmingham

KEY MESSAGES

Issued at 613 AM CDT THU AUG 20 2026

- Heat: Major HeatRisk is expected to persist through the end of the workweek, with heat indices are forecast between 103 to 108 degrees. A Heat Advisory is in effect for portions of central Alabama through Thursday and may be needed for Friday.

- Thunderstorms: Isolated to scattered afternoon to evening thunderstorms will remain in the forecast through Saturday. Rain chances will increase this weekend.

- Severe: Isolated severe thunderstorms are possible this afternoon and early evening with damaging wind the main threat.

DISCUSSION

(Thursday through next Wednesday) Issued at 1157 PM CDT WED AUG 19 2026

A low pressure over the Great Lakes shifts northeast, dragging a cold front southward through the TN Valley and into northern Alabama by the afternoon. Enough instability will support scattered showers and thunderstorms late afternoon through at least Midnight, tapering off overnight. While thermodynamic parameters remain similar, greater boundary convergence should result in higher convective coverage. High CAPE, dry mid-level air, and fairly high DCAPE suggest damaging downbursts remain the primary threat with collapsing storms. The Heat Advisory continues through 9 PM and will likely need to be extended again through Friday as high moisture and lows in the 70s provide little relief.

By Friday, an amplifying trough east of the MS River will shift local flow to the northwest and eventually west. The aforementioned boundary will continue its southward push, focusing diurnal convection generally between the I-20 and I- 85 corridors. A continued risk for downburst winds exists given the persistent airmass. Temperatures may trend a few degrees lower, but high humidity will maintain heat indices in the triple digits.

Model uncertainty persists regarding the southern progress of the boundary on Saturday. While some guidance suggests widespread convection, recent runs favor the trough axis moving through with prevailing northwest flow. A weak mid-level jet could increase surface winds across the north, with gusts of 20-25 mph possible. Rain chances remain in the forecast pending better model consistency. Northwest flow and modest cold air advection will drop temperatures for the weekend; heat indices should finally fall below 105 degrees, though they will remain in the 100- 104 range.

Brief high pressure gives way to another developing low moving across the Tennessee Valley region toward the end of the period, bringing an increase in rain chances. Timing differences regarding the trough exit and low progression remain; will adjust the forecast as trends emerge.

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AVIATION

(12Z TAFS) Issued at 613 AM CDT THU AUG 20 2026

VFR conditions will prevail across much of the area through midday, followed by cumulus development becoming widespread with chances for showers and thunderstorms high enough to include PROB30 at all sites from the mid afternoon into the evening hours. Some outflow boundaries from overnight activity to our north has moved south into northern Alabama early this morning and is triggering some showers and storms across the far northern portions of the state. While low probability, a few showers or storms may develop earlier than forecast, but potential for this outcome is too low to mention at any terminal at this time.

Note: AMD NOT SKED for AUO due to a weather observation outage.

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FIRE WEATHER

MinRH values will generally range between 35 and 45% the next few days, before slowly climbing into the weekend ahead of increasing rain chances. Winds will remain light the next few days, before increasing into the weekend as well. Fire weather concerns are currently low, but they will start to increase by Monday no meaningful rainfall occurs with this weekend's system.

PRELIMINARY POINT TEMPS/POPS

Gadsden 98 72 94 70 / 30 50 30 10 Anniston 96 72 92 70 / 30 50 50 20 Birmingham 97 73 92 71 / 30 50 40 10 Tuscaloosa 100 74 96 72 / 30 40 30 10 Calera 96 73 93 71 / 30 50 50 20 Auburn 94 74 91 73 / 20 40 60 30 Montgomery 98 74 96 73 / 30 40 60 30 Troy 97 72 94 71 / 30 40 70 30

BMX WATCHES/WARNINGS/ADVISORIES

Heat Advisory until 9 PM CDT this evening for the following counties: Autauga-Barbour-Bibb-Bullock-Chilton-Coosa-Dallas- Elmore-Fayette-Greene-Hale-Jefferson-Lamar-Lowndes-Macon-Marengo- Marion-Montgomery-Perry-Pickens-Pike-Shelby-Sumter-Tuscaloosa- Walker.