The SPC has issued a Marginal to Slight Risk for severe storms tomorrow; Wednesday, June 8th.

Storms are expected to develop relatively early according to the latest short-range model trends. Generally, around 10 AM across parts of the plateau and south of I-40. Strong deep layer flow will spread across the area with a mid-level shortwave trough approaching; which coincided with the daytime heating and overall supportive environment and could lead to several strong storms with some of those becoming severe later in the day. The NAM and HRRR show development kicking off around 10 AM near Knoxville/Plateau with an environment already charged to 1,000+ J/Kg of CAPE and LCLs of 120-140. A weak CAP does look to be in place, which could hinder the development; by keeping them as showers.

Looking later in the day, by 2 PM, models show cells exploding across the area with CAPE values over 3,000 J/Kg and no CAP in place. LCLs will be in the 500-600 range with decent shearing winds aloft, which could make some of these storms produce large hail and gusty winds for a long track before falling apart.

The atmosphere will not be supportive for tornado development – though an isolated supercell is possible, which could rotate as it moves through.

All in all, the threat of large hail and damaging winds definitely exists Wednesday as ingredients will be nearly perfect – mainly west of I-75 and south of I-40.

The SPC has issued a Marginal (1/5) risk for severe weather Tuesday. A supportive environment will move into place around 12-1 PM with CAPE values in the 1,500-3,000 J/kg range by 2 PM. Shear will be supportive enough according to the latest models – greatly around 3-4 PM with the side of supportive updrafts for large hail (1″+). Temperatures aloft along with the storm development will be supportive for significant lightning with isolated cells and damaging winds (40-60 MPH). The only issue will be the CAP, will it erode before the convection. Overall the storms will remain isolated but if you have outdoor plans, make sure you have a plan B.

All of the area remains under a Marginal (1/5) risk for stronger storms later on Thursday with the possibility of damaging winds.

Short-range forecast models seem to be in decent agreement, showing convection taking place around noon Thursday across portions of ETN, taking tracks east towards the TN/NC border where more isolated convection can take place. Somewhat moderate CAPE values will be in place for much of the noon/evening hours, coming in at 1,000-2,000 J/Kg across much of the area by 3 PM. Though that is supportive, shear aloft will not be “hugely” supportive of the organized development of these cells that fire. It looks like the greatest severe chances will be along the boundary later in the evening by 6-9 PM.

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While we take pride in our forecast, GWX should never replace the official forecast from the NWS and/or official meteorologists that have the diploma to say their meteorologist.

The latest 0z model runs suggest the greatest (low but non-zero) tornado threat is now across the plateau with mostly strong to severe storms elsewhere. The trouble is really coming in with the fact that morning rain possibly won’t clear fast enough for the development of storms. In that case, this will be a mostly sub-severe event. Strong gusty winds are still possible however with or without support due to the jetstream set up across the area. This now looks like a mostly rain event for NETN/SWVA. CAPE should remain generally around 700-1,300 J/kg area-wide.

Overall the risk is low-med. It really all depends on the morning convection. This is a hard forecast.

Two rounds of storms could affect our area Thursday afternoon, then again Thursday night.

Round 1: Cells should develop in our lower ETN counties (similar to May 6th) and travel east by 12-2 PM, developing a possible broken cell line as they move towards SWVA and upper ETN. CAPE values of 1,500-2,000+ look possible by 1 PM according to the latest short-term models. LCLs are not impressive coming in at 400-500 across the area. Shearing winds with height do appear to support an isolated tornado threat, mainly in Eastern TN, and SWVA. Forecast Updraft Helicity of ~80 does support the idea of isolated tornados across all of our ETN counties. While we mentioned tornadoes multiple times, the threat is still *somewhat* low, though the exact risk is unknown at this time.

The IF Factor: Can we get enough breaks in the clouds to develop stronger storms? That’s questionable.

Round 2: Modules agree on a broken cell line coming together towards Middle TN later in the evening, pushing east, bringing a threat for isolated damaging winds generally west of I-75 as they should weaken as they move east across the area. A CAP will be developing around 5-9 PM which will help calm these storms. Storms from earlier in the day will take most of the energy for this line, bringing CAPE down to 200-500 J/Kg.

Another update is planned for 10 PM today, though a special update may be needed.

The SPC has upgraded most of the area to a Slight (2/5) Risk for severe weather tomorrow, including large hail, damaging winds, and an isolated tornado possible.

Starting off tomorrow, we will see shower development (or leftovers) move in from Kentucky, but we will be pretty capped at that time with slight instability, so it should remain just rain. Later on in the day by 1 PM, the short-range models suggest that we gain a CAPE of 2,500-3,000 J/Kg with an updraft potential of 70-80 m2. Area soundings from the HRRR show slightly shearing winds aloft which brings a very low (but non-zero) chance of an isolated tornado; seemingly targeted generally north-west of I-81. LCLs will be in the 1,300-1,500 range supporting decent lapse rates for development.

Moving on towards later in the evening, models suggest we lose some of the CAPE but remain strong across the area; sitting in the 2,500-3,000 J/kg range. We do gain a very weak CAP but shouldn’t really help much in regards to cell growth. LCLs rise along with shearing winds aloft.

By late evening into night, we become strongly capped along East TN and SouthWest VA which should slow active cell development.

We do (as always) have an IF factor: Will the clouds and rain from morning storms move out fast enough in NETN and SWVA? I think the answer to that is yes.

Overall, our hail risk seems to be the worst factor along with damaging winds and isolated tornado potential.

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