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Wednesday, March 20, 2024

Season forecast update for 3/20, hail shields progress

By DAN ROBINSON

Editor/Photographer

Meteorological spring 2024 has started out active, with four convective severe storms outings and two big supercell/tornado setups already logged for the year. Now that the "official" (astronomical) spring date is here, what do the next couple of weeks look like? Well, unfortunately, not great for storm chasing in the Midwest and Plains.

Models do show a progression of multiple major upper troughs across the country, a scenario that normally would portend thunderstorm and severe weather chances. This weekend, a nice-looking trough with great shear profiles will be ejecting through the Plains, providing a supercell setup on Sunday:

GFS 500mb forecast for Sunday evening, March 24

The limiting factor for this event will be moisture, with a narrow ribbon of dewpoints only shown reaching into the 50s into Oklahoma. Some high-based supercell hailers look possible, but at this point, the lack of moisture and attendant low tornado risk is not enough for me to consider this for the first Plains chase of the year.

Also shown by models is significant cold air barely being held at bay just to our north, with multiple winter precipitation events indicated for the northern third of the US. The good moisture and instability for severe weather is shown mostly confined to the Gulf Coast region, with barely enough MUCAPE for lightning in the central Plains/Midwest over the next 10 days. Some model ensemble members indicate a possible system of note around April 1, but that's just too far in the future to look at in any more detail. Right now, I don't see a storm chasing opportunity being likely over the next 2 weeks.

The following table charts the probabilities for a Plains storm chase expedition taking place for the date ranges shown:

2024 Plains Chase Expeditions - Probabilities as of March 20

March 21-25

10%

March 26-April 1

10%

Hail Shields Update

I promised I'd do a blog update on the hail shield build once it was under way, and I finally have some progress to report. Since 2015, I'd been using a full-vehicle rig based on wire shelving panels. These were very effective and saved multiple windows over the years! However, they were heavy, noisy at highway speeds and severely impacted fuel economy when driving into a headwind (by as much as half).

When I started driving a Subaru Outback starting in 2019, the rear window guard of my setup had to be rebuilt from scratch. It needed to be cantilevered out from the roof rack using rubber casters in order to allow the rear liftgate to open. The shelving panels were just too heavy to have that single cantilever support on only one end, so I used the much lighter-weight galvanized hardware cloth (a type of wire fencing, not-coincidentally also called "hail cloth") for the rear guard section on that vehicle. That new material proved to be effective, saving the rear window from a softball-sized hailstone on May 29, 2022.

Rear window guard with softball-sized hail dent

Rear guard roller with the liftgate open

Since the hardware cloth proved itself in a real-world giant hail encounter, I decided to retire the shelving panels and rebuild the entire rig on my latest vehicle with hardware cloth. This new setup weighs less than a fifth of the old one, is much quieter and much easier to both mount and take down. The light weight allows for using primarily zip ties to secure the material instead of the 1/4" bolts needed for the shelving panels. The new rig uses the main rails from the old one, the only additional hardware required was the construction of an outer frame using 1/2" aluminum u-bars.

Side guards with u-bar frame

I had this installed for our two-day severe weather event on the 13th and 14th, and while I didn't encounter any big hail on those days, the new rig held up just fine under the normal road stresses of storm chasing.

Yet to be done is the second-stage fold-down guards for wind-blown hail. Those will operate like the old 2nd stage guards did, but I have plans for a mechanism that will allow them to be deployed from inside of the car. I'll include more details on that once that phase is completed.