Whenever you see the reference, the “Ring of Fire” pattern, this basically means the stagnant weather pattern is characterized by a large-scale heat dome-like cyclone that we’ve been dealing with for weeks now across the southern and southwestern regions. As this ridge cuts off from the atmospheric currents, the jet stream northwards as winds blow from west to east carrying gullies and turbulence downstream. The combination of shortwaves, humidity, vertical wind shear, and temperature advancement completes the ingredients needed for extreme weather, complex convection, storms and showers over a wide range. Meghan has wonderfully discussed the thermal impact this ridge will create on the eastern Rockies this week in her latest blog, but this also has two sides to it because of the positivity it causes.
Below, this shows 300mb (or 30,000 ft) representing our jet stream. We see massive clockwise circulation oscillating around the Southwest Desert. As the jet stream carries moisture and energy from the Pacific Ocean, it continues to travel through CONUS from NW to SE. Outlined in red is where we’ll have some of the key components that will support convection and thunderstorm systems downstream of the ridge that will impact areas from the Northern Plains to the Mid-Atlantic/Northeast.
Below, we see at 500mb, a number of short-wave oscillating continuous troughs delimited by cyclonic regions (yellow and orange). By now, we know that these trenches are our catalysts or “triggers” for precipitation and essentially convection.
What do we look for to forecast an area that will experience severe weather or any kind of active convection?
We can check (1.), and that is shown by using 500mb for the trough divergent areas that induce vertical motion and also let’s not forget that the jet trails at high elevation enhance the divergence on the surface.
We will certainly have a lot of uncertainty (2.). Our heat trough extends regionally to the southwest, and before it shifts east, you also have the Bermuda Mountains in the western Atlantic. With a clockwise flow, it transfers moisture and latent heat from the Atlantic and Gulf to the north.
So we have our moisture (3.), and not without it. Notice how well it fits nicely with the high values of CAPE? We have a large area of 60+F dew points from the Dakotas down to Texas and east. It is our instability due to the humidity provided by the advancement of humidity, combined of course with daytime heating.
Finally, don’t forget to cut the wind. With jet currents shifting heat and moisture towards the poles, this helps to provide wind shear as well as the predominant westerly/northwesterly wind at high altitudes, and helps to “carry” dry air overhead, which is also a major component of extreme weather as it aggravates the atmospheric environment. Note the narrow bands over 35-40 nautical miles from the Northern Plains to the Northeast, this is more than enough to help maintain countercurrents and ultimately determine the type of storm (i.e. super typhoon, cluster, etc.).
This type of model is also well known for long-lived derecho’s and MCSs, due to the fact that these convective complexes are able to maintain their average-scale periodicities due to all the factors discussed. As we put it together, keep an eye out for some MCS systems and daily thunderstorms from today through the weekend. Today across the Dakotas and into Nebraska, thunderstorms will develop this afternoon with possible hazards from (isolated) supercells and clusters causing gusty winds and large hail. Then tomorrow, our severe threat will shift to the Great Lakes region from Iowa to Ohio as MCS may be spreading into the area, continuing to be sustained due to favorable wind shear and current uncertainty. Heavy hail and severe gusts of wind are also likely to hit the complex and could continue into Thursday and we see this by looking at the ECMWF outputs. Then we see activity shift to the Northeast over the weekend and also the Mid-Atlantic, and into the Southeast.
This pattern mostly occurs every summer as we always see the subtropical ridge (Sonoran Ridge – its name derives from the Southwest desert) cut off from mean runoff and stalled across 48 lower regions sending around its northern periphery bringing in extreme weather and rainfall.
About the author
Hello! My name is Armando Salvadore and I am a Mississippi State graduate with a Bachelor of Professional Meteorology and an Activity Meteorologist working in the Private Sector. Stay tuned if you like technical, exotic, and general weather tweets! Also big on long-range forecasting as well! Twitter: @KaptMands