textproduct: Huntsville

KEY MESSAGES

Updated at 1048 AM CDT Fri Sep 4 2026

- A Heat Advisory remains in effect through 8 PM Saturday due to Major to Extreme HeatRisk, along with afternoon heat indices rising up to 105-109 degrees in portions of the forecast area.

- A few thunderstorms may occur this afternoon (north of the TN River), with a slight increase in coverage expected region-wide on Saturday afternoon/evening. Conditions will be favorable for locally damaging winds, frequent lightning and heavy rain.

NEAR TERM

(Rest of Today and Tonight) Issued at 251 PM CDT Fri Sep 4 2026

Forecast reasoning for the near term period has not changed significantly since the update earlier this morning, with a scattered coverage of showers and thunderstorms likely to continue (especially north of the TN River) through late this afternoon (before dissipating quickly between 23-0Z). However, for most of the forecast area (not impacted by either cooling rainfall, convective debris clouds or rain-cooled outflow air), dangerously hot/humid conditions will persist as current heat indices are in the 105-107F range in many locations. Mostly clear skies and dry conditions will exist overnight, and as temperatures gradually fall into the l-m 70s, development of patchy fog may occur in locations that experience wetting rainfall later today.

Previous Discussion: Over the course of the near term period, a mid-level high (initially centered across western NC) will weaken under the influence of a deepening northern stream trough digging southeastward across Ontario. However, heights will begin to rise across the central Plains, and a broad mid-level trough will continue to retrograde slowly westward across the central/western Gulf. At the surface, our forecast area will remain within a relaxed pressure gradient between a weakening high over the southern Appalachians and a subtle area of low pressure (related to the trough to our south) that will drift slowly northwestward over the north-central Gulf and adjacent portions of southern LA.

Although the greatest spatial concentration of showers and thunderstorms today in our general region should occur within a zone of enhanced low-level moisture advection to the east of the trough (across LA, southern portions of MS/AL/GA, and north FL) a diffuse streamline confluence axis across the TN Valley will likely initiate development of at least a few convective cells in our region (beginning in the 17-19Z timeframe). However, with this feature expected to lift slowly northward from an initial position along the AL-TN border, we will only include a low (10-20%) POP for locations north of the TN River. Regardless of storm coverage, steep low-level lapse rates, MLCAPE in the 2000-2500 J/kg range and favorable DCAPE values of 1200-1400 J/kg suggest that locally damaging wet downburst winds and frequent lightning may occur given PWAT values in the 1.7-1.9" range. For the vast majority of the region (that will not experience any convective impacts), it will be another hot/humid day featuring highs in the 95-100F range in the valley and 90-95F in elevated terrain. Even accounting for diurnal mixing lowering dewpoints into the u60s-l70s, HI will still reach 103-107F in outlying areas and 107-109F in urban locations, and a Heat Advisory remains in effect.

With no evidence of either a low or mid-level source of lift, we expect any afternoon convection that manages to develop in our region to quickly dissipate around or shortly before 0Z, with mostly clear skies and dry conditions anticipated this evening and overnight. Low temperatures will once again be in the l-m 70s, with brief development of patchy fog during the predawn hours in valleys and near large water sources.

SHORT TERM

(Saturday through Sunday night) Issued at 1048 AM CDT Fri Sep 4 2026

Latest global model consensus suggests that northerly flow aloft will become established across the TN Valley during the short term period, as our region will be situated between an amplifying ridge across the Great Plains and an amplifying trough that will shift slowly eastward into the western North Atlantic. With less negative influence from a weak mid-level subsidence inversion, the environment will become more favorable for the development of afternoon showers and thunderstorms region-wide tomorrow (but particularly in regions of favorable orographic ascent across northeast AL/southern Middle TN). Stronger convective updrafts will once again be able to take advantage of favorable thermodynamic profiles (similar to those from today) to yield a risk for locally damaging winds, frequent lightning and heavy rainfall.

Although the number of showers and thunderstorms during the early-mid afternoon hours will likely remain fairly low (warranting a continuation of the Heat Advisory through 8 PM), it appears as if coverage will increase from NE-to-SW during the late afternoon and evening hours as extensive convective outflow (originating from multiple small clusters of thunderstorms tracking southeastward from the Lower Great Lakes/OH Valley into the southern Mid-Atlantic states) begins to propagate southwestward into the TN Valley. Even with a nocturnally stabilizing boundary layer during the evening hours, conditions will remain favorable for gusty outflow winds, frequent lightning and locally heavy rainfall until storms dissipate around or shortly after Midnight.

In the wake of the outflow boundary, light NNE winds will begin to advect a drier airmass into the region, with no precipitation is expected for the remainder of the short term period. Dry advection is expected to continue on Sunday (when dewpoints may fall into the l-m 60s) and Sunday night, when dewpoints may fall into the u50s as a backdoor cold front (marking the leading edge of a Canadian airmass centered across southern Ontario/Quebec) arrives. At this point, we will not plan to extend the Heat Advisory, as apparent temperatures in this scenario would improve by the second half of the weekend.

LONG TERM

(Monday through Thursday) Issued at 931 PM CDT Thu Sep 3 2026

The upper level ridge is forecast to slight shift to the west the begin the week, allowing relatively (key word here) cooler temperatures to settle over the TN Valley. High temperatures will still be in the low 90s with overnight lows in the mid 60s to low 70s as Moderate (level 2 of 4) heat impacts continue through the week. As the ridge shifts back eastward, temperatures will gradually climb back into the mid 90s by the end of the week with diurnal heating contributing to low chances (20% or less) of thunderstorm development each day. One thing to watch will be where sfc high pressure sets up along the Appalachians and whether or not NE AL and southern middle TN experience CAD (cold used loosely). If this is the case, increased PoPs may be necessary as differential heating boundaries begin to set up along North Central AL. As far as heat headlines go, will likely not need anything past Sunday as heat indices drop to around 100 degrees.

AVIATION

(18Z TAFS) Issued at 1251 PM CDT Fri Sep 4 2026

Isolated showers and thunderstorms will continue to develop across the TN Valley this afternoon, with greatest coverage expected to occur along and north of a low-lvl convergence boundary situated near the AL-TN border. Although site-specific probabilities for impact remain too low to include convective impacts in the TAFs, near term amendments and AWWs may become necessary to address the risk for wind gusts in excess of 25 kts and CG lightning strikes. Present indications are that convection will dissipate around or shortly before 0Z, with only a few Ci and calm flow anticipated overnight. Normally, these conditions would support the development of BR/FG, but based on persistence, we will not mention vsby reductions attm. A scattered Cu field appears likely to develop once again by 16Z, with winds remaining lgt/vrbl thru the end of the period.

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.