textproduct: Huntsville

KEY MESSAGES

Updated at 1135 AM CDT Tue Jun 30 2026

- An Extreme Heat Warning is in effect for all counties in northern AL and southern Middle TN through 7 PM Wednesday due to a combination of afternoon temperatures in the mid-upper 90s and heat index up to 112F. A Heat Advisory remains in effect from 7 PM Wednesday - 7 PM Thursday.

- There is a low (10-20%) chance for afternoon thunderstorms across northeast AL today, with chances increasing to 20-40% region-wide tomorrow and Thursday. Conditions will be favorable for locally damaging winds (55-65 MPH), excessive lightning and perhaps small hail with this activity.

NEAR TERM

(Rest of Today and Tonight) Issued at 204 PM CDT Tue Jun 30 2026

There have been no significant changes to near term forecast reasoning since the update earlier this morning, with current temperatures and dewpoints on track to reach Extreme Heat Warning criteria across portions of the forecast area. Latest CAMs also suggest that a few showers and thunderstorms (10-20% coverage) may occur in the higher terrain of northeast AL late this afternoon, with any sustained updrafts capable of producing strong downburst winds and frequent lightning. Any lingering storms should dissipate by 2Z (if not sooner), with a very warm night in store (featuring lows in the m-u 70s).

Previous Discussion: In the mid/upper-levels, the center of a strong anticyclone will shift slowly east-northeastward into eastern KY/TN over the course of the near term period, maintaining a light ESE flow of 10-20 knots across the local forecast area. At the surface, a narrow ridge of high pressure (initially positioned across the central Appalachians) will spread east-northeastward off the northern Mid- Atlantic coast as a weak area of low pressure (located well east of the southeastern Atlantic Coast) begins to drift westward.

Although (at least for today) there is no evidence of a mid-level wave translating around the southeastern periphery of the ridge that would enhance development of afternoon thunderstorms, a subtle low-level confluence axis (initiated by northeasterly flow across the Carolinas) will assist in convective development by early this afternoon from northwest GA southward into southeastern AL (with additional cells likely to develop in the higher terrain to our north/east). Storm coverage appears as if it will be highest across southern AL and adjacent portions of the FL Panhandle (where broad scale subsidence associated with the ridge aloft will be comparatively weaker). However, we will retain a low (10-20%) for our northeast AL zones. After thunderstorms mature, they will drift slowly west-northwestward with time, and will be occurring within a weakly sheared by highly favorable thermodynamic environment (featuring very steep lapse rates in the boundary layer, MLCAPE of 2500-3500 J/kg and DCAPE of 1000-1500 J/kg) to support a risk for locally damaging downburst winds up to 55-65 MPH, excessive CG lightning strikes and perhaps some small hail. Otherwise, temperatures appear on track to reach the m-u 90s for most of the forecast area (lower 90s atop the Cumberland Plateau), with afternoon HI in the 108-112F for a large portion of the region. Thus, we will be upgrading our Heat Advisory to an Extreme Heat Warning that will run through 7 PM Wednesday.

Any thunderstorms in the southeastern portion of the forecast area will begin to diminish in coverage/intensity quickly after sunset this evening, and should dissipate entirely by 2-4Z (if not sooner). After a period of mostly clear skies late this evening and early Wednesday morning, a layer of mid-level altocu will develop during the predawn hours, resulting in very warm overnight lows in the m-u 70s (and no relief from the heat). Patchy fog will be possible in agricultural areas and in locations that experience wetting rainfall around sunrise.

SHORT TERM

(Wednesday through Thursday night) Issued at 1135 AM CDT Tue Jun 30 2026

Latest model guidance suggests that the center of a strong mid- level high to our northeast will migrate eastward across the central/southern Appalachians and into VA/NC by the end of the period. Although this configuration will sustain ESE flow of only 10-20 knots aloft, a notable mid-level vorticity maxima is predicted to travel anticyclonically around the ridge and across the northern Gulf Coast states tomorrow, providing additional support for thunderstorms that should begin to develop by late morning in the vicinity of a lengthy outflow boundary extending from the Arklamiss vicinity into northern GA/southwestern NC. Although there is still some uncertainty regarding storm coverage and timing in our specific forecast area, we are becoming increasingly convinced that coverage will be fairly high (particularly from mid-late afternoon). With even less mixing of low-level moisture predicted to occur tomorrow, dewpoints in the mid 70s will support very high CAPE (3000-4000 J/kg), which coupled with steep low-level lapse rates and PWAT values around 2" will be extremely conducive for damaging downburst winds (up to 65 MPH), excessive lightning and small hail. Storms will again progress slowly west-northwestward (propelled by outflow), ending in the northwest between 0-2Z. Although timing and location of initial convective development casts a bit of uncertainty on the Extreme Heat Warning for tomorrow, we feel fairly confident that criteria (generated by temps in the m-u 90s and dewpoints in the mid 70s) will be achieved immediately prior to convective impacts, but should end by 7 PM as rain-cooled air begins to overspread the region.

A similar convective scenario (featuring identical thermodynamic profiles and an attendant risk for severe downburst winds) is likely to unfold on Thursday, as another subtle mid-level wave will track westward across the local area during the afternoon hours in the flow between the subtropical high to our northeast and a broad scale easterly wave translating across the FL Peninsula and into the eastern Gulf. Although there may eventually be a need to upgrade the Heat Advisory to an Excessive Heat Warning for this day as well, confidence is not sufficiently high at this point.

LONG TERM

(Friday through Monday) Issued at 1040 PM CDT Mon Jun 29 2026

The apex of the upper level ridge will shift over the eastern seaboard by Friday and also start to flatten as ripples of shortwaves progress over the Midwest, Great Lakes, and upper Ohio Valley regions. Some global guidance suggests that a few of these shortwaves will dig towards the Southeast late in the weekend and into early next week. Meanwhile, surface high pressure will persist over the Appalachians down through the ArkLaMiss region through Sunday; however, a cold front may approach the Tennessee Valley by early next week, pushing the high pressure to the southeast.

Overall, expect a diurnal pattern to set up by late week, with daily chances of showers and storms (generally 20-40%) in the afternoon and evening. With the continued warm and humid conditions, along with DCAPE values near or just over 1000 J/kg, we'll be keeping an eye on downburst potential during this time as well. By Sunday, and especially Monday, shower and storm chances then increase as the aforementioned cold front approaches the region. While there looks to be more than enough instability for storms, bulk shear values are fairly weak (10 knots or less). Therefore, severe weather is not anticipated Sunday or Monday at this time.

As for temperatures, Friday and Saturday will continue to be very warm with highs in the lower to upper 90s along with heat index values in the 98-106 degree range. NWS HeatRisk looks to mainly be in the Major category (Level 3 of 4) by late week, but WBGTs remain in the upper 80s to around 90. Therefore, heat products may need to be extended into the first part of the weekend to account for the lingering heat. Make sure to take precautions for the dangerous heat! Wear light-colored, loose-fitting clothing, stay hydrated, and take frequent breaks in the shade if you work outside or have outdoor activities! Look before you lock - never leave people or pets in vehicles! By Sunday and Monday, the increased precipitation chances will result in an ever so slight cooldown, with highs topping out in the lower to mid 90s on Sunday and in the upper 80s to lower 90s on Monday.

AVIATION

(18Z TAFS) Issued at 1259 PM CDT Tue Jun 30 2026

Conditions will remain VFR at the HSV/MSL terminals for the duration of the valid TAF period, with isolated thunderstorm activity across our region this afternoon confined to portions of northeast AL. As the diurnally-enhanced Cu field begins to dissipate shortly before 0Z, skies will become mostly clear for several hours this evening before a broken layer of Ac develops prior to sunrise. Although this should reduce concern for development of lgt BR/FG, minor vsby reductions may still briefly occur at both terminals btwn 9-12Z. Cu will redevelop by the end of the forecast period, with an increasing risk for TSRA beginning just beyond 18Z. Sfc winds will range from NW at 5 kts during the daylight hours to calm at night.

HUN WATCHES/WARNINGS/ADVISORIES

AL...Extreme Heat Warning until 7 PM CDT Wednesday for ALZ001>010-016.

Heat Advisory from 7 PM Wednesday to 7 PM CDT Thursday for ALZ001>010-016.

TN...Extreme Heat Warning until 7 PM CDT Wednesday for TNZ076-096-097.

Heat Advisory from 7 PM Wednesday to 7 PM CDT Thursday for TNZ076-096-097.