MCS/ DERECHO THREAT FOR Monday — Monday night into Tuesday AM… WIS- southern MI -ne OH- western PA -MD- DEL -DCA/ BAL -northern VA

The past couple of days the various weather models have been indicating the potential for powerful significant severe thunderstorm event that is going to develop Monday afternoon in southern Minnesota and Wisconsin. This cluster of thunderstorms will move in a SE direction quite rapidly as it races across southern Michigan, northeast Ohio, western Pennsylvania, into Maryland/ Delaware and Northern Virginia by Tuesday morning.

This system has the potential to significantly impact the following areas
central Wisconsin (perhaps Green Bay and Madison)
In Michigan — Grand Rapids Michigan Lansing Battle Creek Kalamazoo and Detroit.

In Ohio –Toledo Cleveland Akron and Youngstown.
In Pennsylvania the entire of Pittsburgh metro area as ell as Johnstown Bedford Altoona Harrisburg Gettysburg.
In Maryland almost the entire State including western Maryland…. All of Delaware DC Baltimore and Northern Virginia.

The intense cluster thunderstorms may also reach into southern New Jersey and Central Virginia after 8 a. on Tuesday and could impact Charlottesville Fredericksburg and Richmond during the day on Tuesday

There are several reasons why this thunderstorm cluster — which in the weather business is known as the MCS — — going to be potentially extreme for SOME.

This system COULD become a Derecho.

Of course, that term is a loaded term because many of you remember the DERECHO in late June of 2012 during the incredibly hot and dry summer.

But let’s start from the beginning.

For those of you who are not particularly weather savvy/ Knowledgeable, this link will present a simple basic easy to understand information about the various types of thunderstorm clusters that are common across the United States and Canada. There is some really great information here and it’s easy to understand but we are concerned about are the type of thunderstorms which become clusters of storms that seem to operate in some sort of organized manner. So, when you look at this page please scroll down to the lower portion of the page.

https://www.nssl.noaa.gov/education/svrwx101/thunderstorms/types/

There are two terms here that I want you to focus on. The first one is the type of thunderstorm known as the BOW ECHO. This term refers a radar signature of a squall line that “bows out” as winds fall behind the line and circulations develop on either end. A strongly bowed echo may indicate high winds in the middle of the line, where the storms are moving forward most quickly. Brief tornadoes may occur on the leading edge of a bow echo. Often the north side of a bow echo becomes dominant over time, gradually evolving into a comma-shaped storm complex.

The second type of importance system that we are going to be talking about is known as the MCS — mesoscale convective system. This is when the thunderstorms in a particular cluster seem to act as a unified system. This image shows what a typical MCS system looks like on the satellite picture. An MCS can move slowly or can move quite rapidly and there are several different types of MCS categories.

MESOSCALE CONVECTIVE COMPLEX (MCC) — this is a special type of MCS that most often develops in the evening and lasts all night until dawn. They often drop huge amounts of rain and can be very important for the Plains and Midwest green areas with respect to rainfall. The MCS usually does not produce tornadoes or large hail and they are often fairly slow moving.

MESOSCALE CONVECTIVE VORTEX (MCV) — in this special type of MCS low pressure will develop within the thunderstorm cluster so it shows a clear cyclonic or curved signature to the thunderstorm clusters. In the classic MCV, the radar signature will often look like a inland hurricane or tropical storm. Interestingly there have been several cases over the decades where an MCV has moved out into tropical waters, such as the Gulf of Mexico, and transform into a tropical depression tropical storm even a hurricane.

DERECHO — A special and rare type of MCC. Many of you in the Middle Atlantic region and the Ohio Valley remember the historic DERECHO of 30 JUNE 2012. Many may also remember that that was an extremely hot and dry summer with extreme heat before the DERECHO hit and extreme heat afterwards (that was made worse by the lack of air conditioning because of the loss of power). And that brings up several important points about a DERECHO.

> The DERECHO type of MCC event ONLY occurs in a specific type of large-scale synoptic weather pattern.

>They don’t occur because of a passage of a cold front or warm front.

> They have very fast forward speed which is why the winds in a DERECHO can reach / 100 mph for a few hours.

>DERECHO almost always occur on the boundary between extreme warm and cool temperatures to the north. The DERECHO will track right along that boundary between the intense temperature contrast being carried along by the jet stream and a strong piece of energy in the mid levels of the atmosphere.

> DERECHO events almost never produced tornadoes. In all my years of research and understanding of the DERECHO, I personally have never heard of a tornado developing a DERECHO event.

> The winds associated with DERECHOs are not constant and may vary considerably along the derecho path, sometimes being below severe limits (57 mph or less), and sometimes being very strong (from 75 mph to greater than 100 mph). This is because the swaths of stronger winds within the general path of a derecho are produced by what are called downbursts, and these downbursts occur in irregularly-arranged clusters, along with embedded microbursts and burst swaths. Derechos might be said to be made up of families of downburst clusters that extend, by definition, continuously or nearly continuously for at least 250 miles (about 400 km).

This image is from the Saturday afternoon European model. It shows 500 mb pattern and the strong and bedded vorticity Maxima (think pieces of energy) that the 500mb pattern. I have highlighted the piece of energy in Minnesota and Wisconsin which is going to cause this intense MCC to develop and race in a SE direction across southern Minnesota, northeast Ohio, western and south-central Pennsylvania, Maryland, Delaware and possibly into West Virginia and Virginia from Monday night into Tuesday morning.

It is important to notice the RIDGE which I have highlighted that is centered across the Deep South. It is this Ridge which is going to bring temperatures into the mid-90s across much of the Ohio Valley, the southeastern states, and the Mississippi Valley during the next few days. Also, it is important to notice the large UPPER LOW in the jet stream in southeast Canada. This feature is bringing down much below normal temperature is in two New England and the northern Great Lakes.

So what happens is this piece of energy or Vortex Max in the jet stream in Minnesota on Monday afternoon will drop SE because of the overall pattern. The energy contrast between the extreme warm to the SOUTH of the thunderstorm clusters and the below normal temperatures to the NORTH side of the thunderstorm Cluster will feed energy into the system as it races SE at about 60 to 70 MPH Monday night into Tuesday morning.

Here is the Sunday afternoon GFS model and it shows the same kind of thing. There a very strong piece of energy or Vortex Max Monday morning in eastern and southern Minnesota. The system races ESE into southern Michigan by Monday evening, reaching DC Baltimore / northern Virginia and perhaps Philly by Tuesday morning. Now the surface maps from these two models do not look particularly impressive. But that’s because MCC systems are very small scale systems and are not handled well by the large-scale global models such as the GFS …the European …the Canadian… or the British model.

Fortunately, the high-resolution short-range models which are now being used by meteorologists and forecasters over the past 10 years are much better at detecting things like MCC and DERECHO events. And this case we will use the 12z Sunday HRRR which usually handles things like MCC/ MCS/ MCV and DERECHOS rather well.

As you can see the12z Sunday HRRR model does show a MCC moving out of Minnesota and racing across Southern Michigan into Northeast Ohio Monday night.

This system is really moving fast and as it drives to the southeast it appears to be expanding in size and intensity. This is the classic signature of a DERECHO. By early Monday morning the system is moving through southwestern Pennsylvania then into Maryland DC Baltimore the Eastern panhandle of West Virginia and Northern Virginia.

What is also significant s that the high-resolution short-range models Winfield’s depicting this possible MCC / DERECHO event for Monday night and Tuesday show the classic type of Winfield that you get from DERECHO events.

All that being said let’s keep a couple things in mind here.

Just because the 30 June 2012 DERECHO event was extreme and widespread and had wings over 100mph doesn’t mean that what is going to happen to some areas Monday night into Tuesday morning will also feature winds gusting over 100mph. The winds could be a lot less with this system Monday night into Tuesday morning.

Keep in mind that these things are extremely tricky to forecast and all of the short-range models could be total crap and nothing bad happening at all. It’s only in the last 5 to 10 years that we java even had the ability to forecast things like MCC and DERECHO with any great skill. But I think the threat is real. And it should not and cannot be ignored.

I hope to God I am completely wrong about all of this because nobody needs additional disruption in their lives at this point