10 am – HATCHED AREA! These are the severe weather outlook probabilities from the Storm Prediction Center for this Monday PM. These are the forecast maps from the 8 am update…so…they will not update automatically when the outlook may be updated later this morning …however you can click on these images to enlarge or on the link here to make sure you have the latest outlook maps: The General Outlook has an Enhanced Area that covers much of Wisconsin, Lower Michigan, far SE Minnesota, E. Iowa, N. Illinois, far northern Indiana and a small part of NW Ohio. Surrounding the Enhanced Outlook is a large Slight Risk Area that covers everyone from Rochester NY to Kansas City to Duluth to S. Ste. Marie, including N. Lower Michigan and the U.P. Surrounding the Slight Risk is a Marginal Risk. The most favorable time for severe storms in West Michigan is late afternoon/evening, roughly 2 pm to 1 am, though I can’t rule out something earlier or later. Two threads down is radar and lots of links. A line of strong to severe storms has been pushing from MN and maybe N Iowa into Wisconsin and far NW Illinois…that line has produced 70 mph winds. The first question is how long that t-storm complex can maintain itself as it chugs thru Wisconsin toward/over Lake Michigan. Then we have to worry about storms that develop this afternoon along an approaching cold front in WI/IL and push east. Look at the storms headed our way! Damage in S. MN. “The Hammer” is coming! Side note: Looks like a relatively cool first half of July.
We now have hatched areas! The 2nd map is the probability of a tornado. The hatched area is a 10% chance of an EF2 to EF5 tornado within 25 miles of a given point. So the odds of a tornado according to SPC are twice as high in WI and far N. Illinois than in Michigan (5% – with no hatch). The third map is the important one. It now has a hatched are from far N. Indiana (along I-80) up to roughly Whitehall to Saginaw. In this area, they have a +30% chance of a gust to 75+ mph within 25 miles of a given point (more on that here). The last map is for hail…with a hatched area over S. Wisconsin and far N. Illinois. The hatched area is a +10% chance of a report of 2″ diameter or greater hail within 25 miles of a given point.
The second map is the probability of a tornado occurring within 25 miles of a specific point. The 10% chance is over S. Wisconsin and far N. Illinois. We have a lesser, but still noteworthy 5% chance in Lower Michigan. The third map from the left is the probability of a severe wind report within 25 miles of a specific point. This is a hefty 30% over the Enhanced Area, including much of Wisconsin and Lower Michigan. Finally, the fourth map is the probability of severe hail (1″ in diameter or greater), which is highest in Wisconsin, N. Illnois and E. Iowa. This is typical, with the initial supercell storms more likely to produce hail or a tornado…then the storms gel into a bowing line and the most common and widespread threat is damaging winds. Note that the probably of a severe wind gust report within 25 miles of a specific point is 30%, while the probably of a tornado is 5%. So the probability of wind damage is 6 times greater than a tornado. Also, keep in mind that a tornado might affect a relatively small area compared to a widespread wind event like a derecho (and I’m not implying that we’ll get a derecho here). In a situation like this, if a tree gets blown down in your front yard…it’s probably more than 100 times more likely to be blown down by severe t-storm wind than by a tornado. While it’s very important to have a safety plan for tornadoes and to take any tornado warning seriously…it’s also important to get in a safe place when there is a threat of severe winds.
Here’s the full SPC Severe Weather Discussion. They say in part: “…STORM REDEVELOPMENT /SCATTERED COVERAGE/ WILL OCCUR LATER IN THE AFTERNOON NEAR THE RESIDUAL BOUNDARY OVER THE WRN GREAT LAKES OR ALONG THE FRONT LOCATED OVER CNTRL WI SW INTO ERN IA. THE STRENGTH OF THE DEEP LAYER SHEAR VECTOR /50-70 KT/ AND ITS ORIENTATION TO THE BOUNDARY COUPLED WITH A VERY STRONG TO EXTREMELY BUOYANT /3000-4500 J PER KG MLCAPE/ BOUNDARY LAYER WOULD PROMOTE EXPLOSIVE UPDRAFT DEVELOPMENT AND A SUPERCELLULAR MODE EARLY IN THE STORM LIFECYCLE. ALL SEVERE HAZARDS WOULD BE POSSIBLE WITH THIS ACTIVITY…INCLUDING SIGNIFICANT HAIL/WIND/TORNADO. FURTHER STORM DEVELOPMENT ALONG THE FRONT WILL FAVOR A TRANSITION TO A MIXED MODE AND PROBABLY YIELD A WIND/HAIL THREAT BECOMING PREDOMINATE WITH TIME. STORMS SHOULD MOVE DOWNSTREAM AND INTO THE SRN AND LOWER GREAT LAKES STATES OVERNIGHT WITH THE PRIMARY RISK BEING ISOLD LARGE HAIL/WIND.” Here’s current SPC severe weather watches, meso-discussions and storm reports.
Detroit NWS 2:35 am discussion at this link says this in part: “A LEGITIMATE TORNADIC THREAT WOULD ALSO EXIST DURING THE SUPERCELL PHASE AS LCLS LOWER WITH THE HELP OF ADVECTION OF RICH LOW-LEVEL MOISTURE AND DECREASED MIXING DURING THE NOCTURNAL PERIOD. INCREDIBLY HIGH VGP AROUND 1 IS A TESTAMENT TO THE MAGNITUDE OF SHEAR AVAILABLE FOR TILTING WHILE SUFFICIENT CAPE IN THE LOWEST LEVELS LOOKS TO BE AVAILABLE TO ENHANCE STRETCHING PROCESSES. A FEW TORNADOS CANNOT BE RULED OUT MAINLY NORTH OF M59. MAGNITUDE OF ENVIRONMENTAL WIND FIELD ALONE WILL ALSO SUPPORT STRAIGHT LINE WIND GUST POTENTIAL TO 70 MPH.” Here’s the forecast discussion for N Indiana and the Michigan Counties that border Indiana and the latest NWS forecast discussion for SW Michigan, N. Lower Michigan, NE Illinois and S. Wisconsin.
What can you do now? Run errands in the AM if you can so you can minimize driving when storms arrive later in the day. Check your yard…take down hanging baskets, pick up toys, make sure the garbage bin won’t take off down the street. You might turn your trampoline upside down…it’ll be less apt to fly into the neighbor’s yard. Don’t park your car under trees if possible. Keep the garage door closed, especially if it faces west. After the storm stay away from any downed power lines and perhaps check on your neighbors. Storm Team 8 will be tracking the storms on the air and online. Extra staff has been called in and we have specific assignments in a situation like this. TV comes first, so I may not be updating the blog all the time, but there are some very smart people who will keep the blog fresh with their comments. Stay safe and thanks for checking my blog.