Posted: 3:52 pm Thursday, June 28th, 2018
By Kirk Mellish
It’s not just a great Johnny Cash song.
One of the classic weather patterns known in synoptic meteorology in the summertime is known as the “ring of fire” and Northwest Flow Aloft.
It can impact just about any part of the country and usually moves around from the South to the North as we move from Spring to late Summer as the jet stream migrates toward Canada, but it sometimes dips back south or oozes West and East from time to time.
It’s called the ring of fire because the worst storms occur along the outer ring of a big hot air mass of high pressure surface and aloft. No two are every exactly alike.
If you’re right under the center of the high pressure (sometimes an Omega Block pattern) then you are just very hot and precipitation free.
But along the edges of the jet stream pattern is where upper level disturbances (vorticity) or short-wave low pressure areas and cold pools of air move along providing a favored area for periodic rain and sometimes tornadoes, derecho storms or mesoscale convective complexes:
Timing when those disturbances will form or move into or out of a given region is very difficult and constantly changes.
Visualize you are looking at a creek or stream from the bank or down from a bridge. I am sure you’ve noticed little swirls within the flowing water that show up then disappear while others pop up and so on and so forth at random, and they move along within the water flow.
That’s what happens in the JET STREAM FLOW.
That flow can come from the Southwest, Northwest, Northeast or some slight variation.
We don’t get the storm part of the “Ring of Fire” pattern in these parts very often because we are usually under more of the core of the high not near it’s edges, which is why we have the hot summers we do.
However, several times already this spring and summer we have been on the edges of it with either a SW, NE, or NW flow and this has been a big factor in the above-normal rain and storm odds we’ve had the past couple months. Most recently four days in a row!
First the center of the high was off the Coast near Bermuda, giving us a SW flow. At other times the center of the high was well to our North giving us an Easterly flow. More recently the center of the high has been to our West giving us a NW Flow Aloft.
Embedded within that flow are the little swirls of energy and lift (like in the water of the creek example) that randomly come along and create extra storminess. The past few days the ring has included a Northwest flow into Georgia. See maps of Thursday morning and afternoon June 28th:
Dashed lines in chart above are the swirls. On this SPC chart pink X marks maximum vorticity in the 500mb jet stream flow. They produce thunderstorm clusters:
The swirls of vorticity produce the upward vertical velocities to lift up the air as it converges and rises:
Note this allows storms to form even-though we are far from the nearest surface front which was well to our North:
The air mass was very moist (high dew points/precipitable water) south of the front, the CAPE values in red (convective available potential energy in Joules/kg) are very high (1000-4500) indicating plenty of potential instability in the atmosphere (buoyancy), the blue shades show rain-cooled stable air setting up a NW to SE mini-cold front temperature gradient:
The charts above are between 8am and 9pm. The models are usually pretty good at detecting the swirls of energy, at least the larger ones, but small ones that pop up suddenly can often be missed. The models also struggle with getting the TIMING RIGHT of when such disturbances in the flow will arrive.
Thousand mile journeys are not unusual for these upper level disturbances and the thunderstorm clusters (MCC/MCS) they form:
We forecasters stole, I mean borrowed, the “Ring of Fire” terminology from volcanologists/seismologists who gave that name to the hot zones of the earth where volcanoes and earth quakes are most common, the “high” pressure center would be in the quiet middle just as in weather:
3-day Thunderstorm Outlook from Thursday from SPC shows the ring:
HERE is an example from minnesottaforecaster.com from 2009 when the high was over the Southeast U.S. keeping us hot and dry while the active storm ring was up in the Midwest and Great Lakes and Northeast:
So if you want a dry heat wave that is what you’re rooting for to develop.
As of now if the models are right there is no sign of that happening for more than a day or two at a time, then it eases off, then comes back etc. As a result places like Minneapolis, Milwaukee, Chicago and West of Boston will have more 90s than Atlanta.
We stay ‘somewhat’ hot and usually more humid than normal, but the location of the center of the high varies and is never right on top of us the next few weeks according to model guidance.
This allows the ripples or swirls in the stream to come along, or other forms of “weakness/low pressure” to form on the underbelly of the high pressure ridge aloft. (sometimes resulting in some type of tropical development in the gulf or off the SE coast):
10-day above and below normal rainfall areas show the pattern well:
As a side note, I did my Senior Thesis at university on developing a severe weather forecasting checklist flow-chart for the Midwest which included NW flow regime patterns of the Ring of Fire, I was fascinated with them as a kid.
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