textproduct: Morristown

KEY MESSAGES

Updated at 740 AM EDT Thu Aug 20 2026

- Widespread fog less likely this morning, but isolated patchy fog possible for some.

- Decaying bow echo may bring some gusty winds across the northern plateau later this morning.

- Another round of showers/storms becoming more likely for this afternoon and evening. Main threats: damaging winds and small hail.

- Mostly dry conditions with near normal temperatures through the weekend and early next week

DISCUSSION

Issued at 247 AM EDT Thu Aug 20 2026

Mid/high clouds currently streaming across the area, with more to come through the night. This will likely deter fog for most areas. Though isolated instances of patchy fog are certainly possible, especially near local waterways.

A cluster of storms is currently developing back across southern MO and is forecast to become more organized as they track across KY/TN through the night. Model consensus shows this line of storms weakening as they moves into the northern Plateau later this morning. However, this line of storms may still produce some gusty winds across the central/northern Plateau as they arrive. The most likely arrival time will be around 7 to 8 AM EDT. SPC has expanded the marginal risk eastward and included our northern Plateau counties to account for this activity. Thereafter, showers and perhaps a few remaining storms will make their way across the rest of the area through the late morning hours. Areas along and north of I-40 will have the best chances to see precip with this decaying line. Areas south of 40 may stay completely dry.

Then all eyes turn toward the afternoon/evening hours. Biggest change from previous forecast is that the 00Z NAM doesn't show the mid-level stable layer at 21Z that was previously shown. This means better chances for convective initiation. This is supported by the recent runs of the HRRR and RRFS as they show initiation as well, though timing varies. It seems like the earliest initiation would be around 18 to 21Z and the latest around 23 to 00Z. The environment will be favorable for a few strong to severe storms as MLCAPE values will be around 2000 J/kg and 0-6km shear at around 20 to 30kts. The main threats will be damaging straight line winds, and perhaps a microburst, along with small hail. Shear in the lowest levels do not look conducive for tornadic development with values less than 10kts. Also, LCL heights will be quite high this afteroon around 1500 meters, due to deep mixing, which can be seen in the "Inverted V Sounding Profiles".

The latest SPC Outlook for Day 1 (today) compared to when it was Day 2, pulls the marginal risk a bit more north covering more of the northern plateau, valley, and southwest VA.

Shower and storm chances continue Thursday night into Friday morning. Coverage and intensity is low confidence during this time. Additional showers and storms are expected on Friday afternoon, due to the frontal boundary still in the vicinity. A few strong to severe storms are once again possible, though lower chances compared to this afternoon/evening.

Dry conditions are expected on Saturday and Sunday due to building surface high pressure and the midlevel influx of drier air from the north. Next week, there are signs of another northwest flow pattern remaining across the area into next week. While NBM POPs are low, we will have to keep an eye out for any upstream impulses that may affect our area next week. Temperatures should be near normal throughout this time frame.

AVIATION

(12Z TAFS) Issued at 740 AM EDT Thu Aug 20 2026

Showers and a few storms moving into the central valley may impact TYS this morning. Showers possibly move into TRI next. There's great uncertainty as to how later on could be impacted by the activity this morning. It hasn't dissipated like models had shown. Left the later in the TAF period PROB30s except TRI, where it looks like they pose the least chance of precipitation tonight. MVFR CIG forecast there overnight tonight.

PRELIMINARY POINT TEMPS/POPS

Chattanooga Airport, TN 96 73 93 70 / 30 50 30 10 Knoxville McGhee Tyson Airport, TN 92 71 89 69 / 30 50 40 10 Oak Ridge, TN 90 70 89 67 / 30 50 30 0 Tri Cities Airport, TN 87 67 84 65 / 30 60 60 30

MRX WATCHES/WARNINGS/ADVISORIES

NC...NONE. TN...NONE. VA...NONE.