1.  Will the airmass over northern Alabama/Southern Middle Tennessee recover ahead of the next round of convection
              enough for severe convection and be strong enough to overcome warm air aloft (weak cap)?

         2.  If it did, would we have a possibility of a strong tornado or two with the second round of activity due to enhanced
              low-level turning of winds left in the wake of the morning convection (assuming enough lows level
              instability (SBCAPE) develops)?
 
Although, this early morning convection did keep most of northern Alabama cloudy for several hours in the morning, water vapor imagery from our satellites did start to give us a clue that we might destabilize due to the thinning/breaking up of cloud cover. This feature seen on the imagery was quite a bit of dry air pushing into the convection from the southwest and can be seen in the image below.

However, the morning convection did keep instability very low through the mid-morning hours, so the airmass did have to recover significantly by later in the afternoon. The concern of just how much surface based instability would occur later that afternoon was based on not only insolation effects produced by decreasing cloud cover, but also how high the surface dewpoints could get. 

Early in the day, very moist air was seen southwest (upstream) of northern Alabama originating from a region over the Gulf of Mexico that had dewpoints in the lower to mid 70s. This can be seen in the image below. It was pooling in front of the dry-line, which at 8 AM was west of Mississippi and could provide the forcing needed to produce severe convection later that afternoon. This gave another clue that we could still destabilize later in the day. Between 10 am and noon most of the shower and thunderstorm activity and cloud cover moved east into Georgia, allowing temperatures to warm up.

This sunshine continued into the early afternoon hours (visible later at 207 PM). By then, temperatures had risen into the mid to upper 70s and dewpoints into the mid 60 due to the effects of sunshine and the advection of more moist air ahead of the dryline into northern Alabama (especially east of I-65). As a result instability increased to between 1000 J/KG and 2000 J/KG.  The images below show the progression these higher dewpoints into the area and increased instability.

Good shear was in place ahead of the dryline even in the early afternoon hours and this shear increased as the dryline moved east later in the afternoon. Area soundings provided by the VORTEX Southeast research group did show a cap in place in the late morning/early afternoon hours. This cap was evident further east as can be seen below on the left. Meanwhile, drier air was undercutting the dryline and cut off some of the instability immediately ahead of it as it moved into the northwestern Alabama (it was uncertain from the start of this event if the dryline would begin to develop convection that far west). This likely kept showers/storm activity very minimal to non-existent over the Huntsville Forecast Area, despite developing unstable conditions. 

However, strong shear and better instability combined with forcing ahead of the dryline near and east of I-65 to break the cap and initiate deep convection between 3 and 4 pm, as seen on the image on the right above. Isolated severe storms developed by 3 pm producing large hail and increased in coverage by 6 pm as it moved east. 

Earlier convection had modified low-level winds near the surface from the predominant synoptic wind flow pattern aloft ahead of the dryline. This can be seen in surface analysis shown above at 1 PM east of I-65. This increased low level directional shear in the atmosphere as dryline moved towards the I-65 corridor during the mid-afternoon hours. This continued into the late afternoon hours and increased low-level helicity values to between 300 m2/s2 and 400 m2/s2 east of I-65. Given instability in place, at 150 PM the National Weather Service in Huntsville issued Tornado Watch #127 for all of our northern Alabama and Southern Middle Tennessee counties, as can be seen above on the right. Although no tornadoes developed, storms did exhibit some rotation as they moved into northeastern Alabama.  Numerous reports of large hail from quarter to golfball size were confirmed near and east of I-65.

Why was the tornado/wind threat not realized and severe weather not more widespread on April 5th, 2017?

More stringent research will need to be done to find out. However, below are some possible factors that limited how
widespread the severe weather was on April 5th, 2017 and why no tornadoes occurred in the Huntsville
Forecast Area.

1. The dry slot - Area soundings showed mid to upper level drying in the atmosphere which likely
    inhibited storm growth in some areas. Instability ultimately did not increase enough to overcome
    this west of I-65.

2. A cap (warm temperatures aloft above 800 mb) was in place - This helped to inhibit storm initiation
    ahead of the dryline. It kept any storms from forming in northwestern Alabama.

3. The bulk shear was 70-80kts - This was possibly too much shear.

4. The warm sector and associated morning convection didn’t make it as far north as originally
    predicted in the early morning hours. (This mainly kept the initially morning round from becoming severe)

5. Directional shear was unidirectional even though the speed shear was substantial west of I-65. Further
    east, enough directional shear was present in the mid/late afternoon hours for tornadoes, but
    other factors kept the threat from materializing. 

Near and west of the dry-line, with a well mixed atmospheric profile, strong winds were able to be brought down to the surface outside of thunderstorms.  

A few different things were noted that could have contributed to the increased wind speed. 

1  - The pressure gradient was tightening quickly due to the strong surface high pressure departing to the west and the surface low was rapidly deepening over SE Missouri. This increased 700 mb winds from around 35 knots at 7 AM  to between 50 and 65 knots at 7 PM near and behind the dryline. This can be seen in top row of images below.

2  -  The heating produced by the dissipation of cloud cover helped to produce steep low level lapse rates, which allowed winds between 40 and 50 knots just above 850mb to be brought down to the surface in the form of gusty winds. This can be seen in the bottom row of images below.