textproduct: Huntsville

KEY MESSAGES

Updated at 1101 PM CDT Sun Sep 20 2026

- The coverage of showers and thunderstorms will remain fairly high from this evening through Tuesday. Conditions will be favorable for strong-severe thunderstorms, particularly Monday afternoon/evening and again on Tuesday afternoon. Locally damaging downburst winds, frequent lightning and heavy rainfall will be the main storm impacts.

- Hot temperatures will continue into Tuesday, with highs in the 90s accompanied by heat indices between 98-104F.

- A slightly cooler and drier airmass will begin to arrive on Wednesday. Highs will fall back into the lower-mid 80s from Thursday-Sunday, with lows in the mid-upper 50s this weekend.

NEAR TERM

(This evening through Monday) Issued at 1101 PM CDT Sun Sep 20 2026

In the mid/upper-levels, our forecast area will remain beneath a ridge (extending from the Lower Rio Grande Valley northeastward into eastern parts of the TN Valley) overnight. However, the ridge will continue to weaken as a southern stream shortwave trough advances eastward from the southern Plains into the Lower MS Valley. At the surface, a relaxed pressure gradient will exist between a lingering ridge axis extending southwestward into the central Gulf Coast and a weakening area of low pressure drifting eastward across the Ozarks. Outflow boundary collisions and light/veering flow in the low-levels (in advance of the approaching shortwave) have likely helped to sustain isolated thunderstorms across the TN Valley this evening. Although remnant convection over northeastern AL continues to spread southward, additional showers and thunderstorms may develop later this evening (and persist into the early morning hours on Monday) in the vicinity of another subtle confluence axis in the western portion of the CWFA. Even with weakening low-level lapse rates, sufficient elevated CAPE will exist within the moist airmass (featuring PWAT values of 1.7-1.9") overnight to support a risk for strong wind gusts (up to 40-45 MPH) and frequent lightning with the most intense cells. Otherwise, it will be another partly cloudy, warm and muggy night, with lows ranging from the u60s/E to m70s/W.

Latest model guidance suggests that the previously mentioned mid- level shortwave trough will gradually decay as it translates slowly eastward tomorrow, but should contribute to a minor increase in WSW flow aloft to 10-20 knots. As this occurs, the weakening surface low will gradually open into a trough as it drifts eastward over western TN. Forecast soundings suggest that convective temperatures will be breached in the 17-19Z timeframe as temperatures ascend into the l-m 90s and this should allow thunderstorms to initially develop in zones of orographic lift before additional convective development rapidly occurs in the vicinity of preexisting mesoscale boundaries (as well as in the vicinity of the surface trough to our northwest). Aside from a more pronounced westerly steering flow, little to no change is anticipated in the general kinematic or thermodynamic environment tomorrow. Thus, we expect MLCAPE in the 2000-2500 J/kg range (coupled with rich moisture and steep low-level lapse rates) to support a continued risk for locally damaging downbursts, frequent lightning and heavy rainfall.

SHORT TERM

(Monday night through Wednesday night) Issued at 1101 PM CDT Sun Sep 20 2026

Over the course of the extended period, a weakening mid/upper- level cyclone will shift slowly east-southeastward from the northern Plains into the central Appalachians (to the south of a blocking 500-mb ridge across Ontario). Although WSW flow aloft of 10-20 knots will persist Monday night, this pattern evolution will force winds aloft to veer to WNW and gradually strengthen beginning on Tuesday, with NNW flow aloft of 30-40 knots predicted to be established by the end of the period. In the low-levels, a surface trough is expected to lie from northern MS into WV at the beginning of the period, and this feature (along with multiple mesoscale boundary collisions) will likely help to sustain a fairly widespread coverage of showers and thunderstorms region- wide Monday evening, with redevelopment of thunderstorms on Tuesday expected to be focused to the east of the trough axis. Due to little change in the favorable thermodynamic environment, the risk for locally damaging wind gusts will persist Monday evening and Tuesday (with a slightly greater potential for storm organization into multicell clusters on Tuesday due to the increase in flow aloft).

During the period from Tuesday night-Wednesday night, there are indications that the surface trough will begin to shift slowly eastward across the region. However, the speed at which this occurs is uncertain, as its eastward motion will likely be retarded by a strengthening surface anticyclone across southern Quebec and related cold air damming to the east of the central/southern Appalachians. The most likely scenario at this point is for the trough axis to drift very slowly eastward, ushering a slightly cooler/drier airmass (featuring dewpoints in the u50s-m60s) into the northwest portion of the CWFA, while a moist airmass (featuring dewpoints in the u60s-l70s) remains in place across the southeast. Although a few showers will be possible to the east of the trough axis (particularly during the day Wednesday), strengthening NNW flow aloft will usher a drier mid/upper-level airmass into the region, and conditions will become less favorable for thunderstorms. After initially dropping back into the u80s-l90s on Tuesday, highs on Wednesday should merely reach the m-u 80s. Overnight lows will fall into the l-m 60s by Thursday morning.

LONG TERM

(Thursday through Sunday) Issued at 1101 PM CDT Sun Sep 20 2026

Global models suggest that a weak mid/upper-level low (initially across the central Appalachians) will phase with a smaller disturbance to its east later this week to form a deep low that will sit off the northern Mid-Atlantic Coast this weekend. This will ensure a continuation of dry NNW flow aloft across the TN Valley for much of the period, before this regime weakens Saturday and Sunday. With indications that low-level confluence across will progressively diminish on Thursday/Friday, the risk for showers in the east will continue to fall as light N-NE flow advects a drier airmass into the region from a high across southeastern Canada. Highs will be in the l-m 80s, with overnight lows dropping into the m-u 50s this weekend (when dewpoints could drop into the 40s).

AVIATION

(06Z TAFS) Issued at 1249 AM CDT Mon Sep 21 2026

There have been no significant changes to previous aviation forecast reasoning, as outflow boundary collisions and weak forcing for ascent ahead of an approaching shortwave trough will continue to sustain isolated-widely scattered SHRA/TSRA through the early morning hours. However, at this point, impacts appear most likely to occur at MSL, where a 1-hr TEMPO group has been included for the beginning of the TAF period. Otherwise, we expect VFR conditions to persist (featuring few-sct Ac and bkn Ci, with a lgt SSE wind). A greater coverage of thunderstorms is still anticipated later this aftn/evening, and PROB30 groups have been introduced btwn 18-22Z and 22-4Z to account for this. However, aside from convective impacts, VFR conditions will exist with a lgt SSW wind.

HUN WATCHES/WARNINGS/ADVISORIES

AL...None. TN...None.