textproduct: Huntsville

KEY MESSAGES

Updated at 1007 AM CDT Fri Sep 18 2026

- A Heat Advisory is in effect through 8 PM Saturday across all of southern middle Tennessee and northern Alabama.

- NWS Heat Risk highlights Moderate (Level 2/4) to Major (Level 3/4) heat impacts through the weekend across the Tennessee Valley. Localized Extreme (Level 4/4) impacts may occur in urbanized areas.

- A Marginal Risk (Level 1 of 5) for strong to severe thunderstorms exists Saturday afternoon and evening for gusty to damaging downburst winds.

NEAR TERM

(Tonight) Issued at 242 PM CDT Fri Sep 18 2026

No major changes were made to the forecast outside of expanding PoPs to 20% through NE AL and southern middle TN into the evening hours. Ongoing showers are capable of a low-medium chance of lightning and a very low chance of gusty winds up to 40-50 mph.

Previous Discussion: A stout ridge, 594 dam at 500 mb, will remain the dominant feature across our area through the near term. This will keep most of the CWA hot and dry today.

With high temperatures expected to be in the mid to upper 90s and NWS HeatRisk in the Moderate to Major (level 2-3 of 4) category, A Heat Advisory will remain in place area wide. With vertical mixing expected to keep dew points in upper 60s to lower 70s, maximum heat index values are expected to be around 100 to near 105 degrees.

With the core of the ridge shifted a bit west today, thinking we may see a bit more in the way of afternoon convection compared to previous days. Current expectations are for mainly low (15-20%) chances primarily across our higher terrain in the east. Storms that do form will move from NE to SW and could produce wind gusts in the 40-50 mph range given DCAPE values over 1000 J/kg and inverted V soundings. It may sound like a broken record at this point, however be heat smart: slow down, cool down, stay hydrated and NEVER leave people or pets in vehicles. Tonight, temperatures slightly cool into the low to mid 70s.

SHORT TERM

(Saturday through Sunday night) Issued at 1007 AM CDT Fri Sep 18 2026

Conditions will remain hot through the weekend as the TN Valley sits under strong upper ridging and while an upper low begins to retrograde over the eastern Gulf. This will provide additional support for diurnal showers and thunderstorms on Saturday, and model soundings show a good amount of mixing/dry air in the low levels Saturday afternoon. DCAPE values in excess of 1100 J/kg will support the threat for microbursts as highlighted by a Marginal Risk (level 1 of 5) by the SPC. Afternoon highs near 100 degrees will create a dual threat for those with outdoor plans, and the Heat Advisory will remain in effect through 8 PM tomorrow. While the synoptic pattern stays largely unchanged on Sunday, slightly lower atmospheric moisture will keep PoPs on the low side (<30%) and confined east of I-65. Highs on Sunday will once again approach 100 degrees with heat indices reaching 105F in some urban locations. Please protect yourself and others from the dangerous heat this weekend and remain weather aware if spending time outdoors!

LONG TERM

(Monday through Thursday) Issued at 930 PM CDT Thu Sep 17 2026

Extended range model solutions suggest that a 500-mb ridge will remain positioned across the forecast area on Monday. However, as we progress through the rest of the period, it is becoming increasingly likely the the southern edge of the mid-latitude westerlies will develop southward into our region, with indications of a flat subtropical ridge lying across the northern Gulf and development of an upper low (from phasing of 2-3 distinct northern stream shortwaves) over the Great Lakes. In the low-levels, a weak area of low pressure is predicted to migrate from the Mid-South into the TN Valley on Monday, before degenerating into a frontal wave as it lifts northeastward into the Upper OH Valley Monday night. Although the trailing cold front will make only gradual southeastward progression into the Ozarks and OH Valley by early Tuesday morning, mesoscale boundaries originating from extensive convection to our northwest should contribute to a higher coverage of thunderstorms across our CWFA Monday afternoon and evening. As surface pressures begin to rise within a high migrating eastward across southern Ontario/Quebec (and renewed cyclogenesis takes place over the eastern Great Lakes), the cold front will advance further southeastward on Tuesday, resulting in another episode of convection during the afternoon/evening hours. Sufficient CAPE will exist to support a risk for strong-locally severe thunderstorms both periods, especially given an increase in mid-level flow to 15-25 knots. As the cold front shifts further southeastward through the region Wednesday, light-moderate northerly flow will begin to advect a slightly cooler/drier airmass into the region, with highs on Wednesday and Thursday dropping back into the 85-90F range and lows falling into the l-m 60s.

AVIATION

(00Z TAFS) Issued at 728 PM CDT Fri Sep 18 2026

VFR conditions are expected to exist at the terminals overnight, featuring a few high-based Cu (beneath higher-lvl convective debris clouds) and calm winds. Although there is still a low chance that outflow (from clusters of TSRA currently across eastern TN and western parts of NC/SC) may initiate renewed development of a few thunderstorms in our region later this evening, this would likely be confined to the S/E of the HSV terminal. Otherwise, sufficiently clear skies and calm winds may support development of patchy BR/FG in a few locations btwn 10-13Z. Diurnal Cu will develop once again by 16Z, with weakening influence from an upper-lvl ridge perhaps resulting in a slightly greater coverage of terrain/outflow-induced convection during the mid/late aftn hours (compared to today). Thus, a PROB30 group has been included at both terminals from 20-24Z to indicate the most likely timeframe for impacts from TSRA (including potential issuance of AWWs for lightning and strong wind gusts).

HUN WATCHES/WARNINGS/ADVISORIES

AL...Heat Advisory until 8 PM CDT Saturday for ALZ001>010-016.

TN...Heat Advisory until 8 PM CDT Saturday for TNZ076-096-097.