textproduct: Huntsville

NEAR TERM

(Tonight) Issued at 252 PM CDT Tue Jul 15 2025

Despite a fairly buoyant airmass with MLCAPE values between 1500-2500 J/kg, showers and thunderstorms have struggled to maintain any intensity and have been short lived so far this afternoon. The main impact will continue to be the dangerous heat as afternoon heat indices currently range from the mid 90s to lower 100s. Will maintain very low chance PoPs between 10-20% through the afternoon with the low chance of a thunderstorm producing brief heavy rainfall and gusty winds. We will have to monitor for dense fog once again late tonight into tomorrow morning, but have no current plans to issue a dense fog advisory. Otherwise, the previous discussion remains on track.

Previous discussion: Although a few diurnally-initiated showers and thunderstorms will be possible (especially in the higher terrain of northeast AL/southern Middle TN), coverage of convective cells should be higher both to our northwest (from the Ozarks into the central OH Valley -- where the influence of the shortwave trough will be greatest) and to our east (from the central FL Panhandle north- northeastward into northern GA -- where a surface trough related to the easterly wave will exist). Regardless of storm coverage, the local thermodynamic environment will be characterized by MLCAPE in the 2000-3000 J/kg range, DCAPE of 750-1000 J/kg and PWAT in the 1.7-1.9" range. Thus, brief strong outflow wind gusts (up to 40-50 MPH), frequent lightning and heavy rainfall will be possible with stronger cells as they drift slowly east- southeastward.

This evening, the surface trough to our east is predicted to drift slowly west-northwestward and should reside across the eastern portion of the CWFA by early Wednesday morning. A few showers and thunderstorms will be possible throughout the night in the vicinity of the trough, but mostly clear skies and dry conditions are expected elsewhere. With calm winds and narrow dewpoint depressions, patchy fog will also be possible in a few locations around sunrise as temps fall into the l-m 70s.

SHORT TERM

(Wednesday through Thursday night) Issued at 1100 AM CDT Tue Jul 15 2025

During the period from Wednesday through Thursday night, the western portion of the southeastern CONUS 500-mb ridge (discussed above) will begin to weaken, with the configuration of the ridge taking on a more zonal orientation from the Arklatex into the southeastern Atlantic Coast (as it becomes conjoined with a stronger subtropical high retrograding across the southwestern North Atlantic). Although this suggests that there will be little (if any) change in the general synoptic environment across our forecast area through the duration of the short term period, the presence of the surface trough (discussed above) should focus an increase in the coverage of showers and thunderstorms across our region beginning late tomorrow morning. With forecast soundings indicating similar thermodynamic parameters in place tomorrow (compared to today), storm impacts will be similar. However, collapsing steering currents will result in even slower and more erratic cell motions, perhaps increasing the risk for heavy rainfall/minor flooding. In the event that early initiation of showers/storms (and convective debris clouds) are not very impactful, HI readings may reach 105-110F readings across the valley. For that reason, a Heat Advisory has been issued for 10 AM through 7 PM Wednesday.

The increasingly ill-defined surface trough is predicted to progress further northwestward and through the region on Wednesday night/early Thursday morning, as southerly flow strengthens in the low-levels between a Bermuda high building into the southeastern Atlantic Coast and a weak area of low pressure over the north-central Gulf, and this may support a continuation of scattered showers and thunderstorms for much of the night. The modest increase in southerly flow in the boundary layer will continue on Thursday/Thursday night, with precipitable water values expected to rise above 2" during this timeframe. Although this will support an increase in the coverage of afternoon thunderstorms across southern portions of the central Gulf Coast states, our main source of convective initiation may come late Thursday afternoon or Thursday evening as outflow spreads southeastward across western/Middle TN from frontal precipitation across the Mid-MS/Lower-OH Valleys. With highs once again predicted to reach the l-m 90s (and slightly higher dewpoints), a Heat Advisory may be warranted on Thursday as well.

LONG TERM

(Friday through Monday) Issued at 1017 PM CDT Mon Jul 14 2025

Our attention in the extended will focus on the progress of Invest 93L that will be moving westward over the northern Gulf during the middle of this week. Some guidance indicates this system may develop tropical characteristics before it veers into the LA/MS/AL coastline during a Thursday night to Friday timeframe. All this would mean for the Tennessee Valley will be the potential for a gradual increase in PoPs Friday and potentially into the upcoming weekend. How widespread this activity will be will depend on the eventual track of this system, but long range ensembles are honing on at least medium chances for showers and thunderstorms. This would especially be true if this feature begins to interact with a weak frontal boundary attempting to push southeast from the Ohio/Mid-Mississippi Valley. Given the deep tropical moisture that will be present across the Deep South, locally heavy rainfall and potentially flooding would be the primary concerns. Thus, the track of this system and how it evolves is something we'll need to watch in the coming days. Given the added cloud cover and potentially higher rain chances, heat impacts don't appear to be as high during this late week timeframe.

AVIATION

(18Z TAFS) Issued at 117 PM CDT Tue Jul 15 2025

VFR conditions will exist at the HSV/MSL terminals this forecast period, as diurnally-enhanced Cu will dissipate around 0Z before redeveloping by 16Z Wednesday. Although a few SHRA/TSRA may occur within the vicinity of each terminal this aftn (18-24Z), coverage in our region will be quite low (compared to points to our NW and E) and for this reason we will not mention TS in the TAFs at this point. Overnight, we will need to monitor the progression of a sfc trough (as it shifts west-northwestward into our region from GA) as this feature may initiate a few convective cells throughout the night. However, at this point, it appears as if the slow- moving boundary will remain to the S/E of HSV thru 12Z, but could potentially result in redevelopment of storms closer to the terminals prior to the end of the TAF period. Overnight, mostly clear skies and calm winds may support development of patchy BR/FG, but with precipitation coverage uncertain today we will not include vsby reductions in the forecast attm.

HUN WATCHES/WARNINGS/ADVISORIES

AL...Heat Advisory from 10 AM to 7 PM CDT Wednesday for ALZ001>007- 016.

TN...None.