A STORMY WEEKEND PATTERN...
Back on the 21st of May the state of Iowa had not reported a tornado. Less than a month later the number has risen to 33.
The majority of the storms occurred during a 10 day period late in May when warm, humid air was in place setting the table for thunderstorms and severe weather. As you can see many of the storms were concentrated over eastern Iowa. According to the NWS in the Quad Cities which warns much of that area, 104 warnings (both severe thunderstorm and tornado warnings) have been issued out of that office in 2019. Here's a count of warnings since 1986.
In comparison, the Marquette, Michigan NWS, which is heavily influenced by its northern latitude and the chilly waters of Lake Superior has not issued a single severe thunderstorm or tornado warning this year. That's the least ever in Marquette's history.
In contrast, the Norman, Oklahoma NWS office (Oklahoma City) has punched out 723 warnings, second only to 2008 when it put out 808.
The past 2 weeks have been relatively quiet for severe weather. You can see the black line depicting tornado reports (which was shooting straight up the end of May) has significantly leveled off since.
There should be an uptick in severe weather and heavy rain potential in coming days as a warm, humid, and highly unstable air mass returns to the Midwest. The Storm Prediction Center has these outlooks in effect through Friday. I expect them to be pushed into more of my area come Saturday and Sunday, perhaps even Monday.
The first really good chance of strong storms in my area comes Friday. The NWS in the Quad Cities put this out in their AFD Tuesday afternoon.
Friday...An ominous looking synoptic set-up indicated by several medium range models as the thermal ridge axis adjusts right up the mid to upper MS RVR Valley. Warmer and more humid conditions and increasing gulf moisture feed will look to set up a potential strong storm cluster or MCS track from the northern plains acrs to the GRT LKS. Building temps in the low to mid 80s, and possibly warmer in the south along with DPTs in the upper 60s to near 70, will make for a large MUCAPE gradient from north to south. Long range indications suggest very high CAPEs possible over 4000 J/KG over at least the south half of the CWA, along with good shear for a potentially explosive airmass. Some signs of a warm wedge aloft/cap to overcome, but the models still eventually either develop strong convection off tot he west over the MO RVR Valley Fri afternoon which then propagates east acrs the local area as a mature MCS Friday night. Or they develop storms overhead which could be supercellular in nature. Besides the severe weather threat, a PWAT feed of near 2 inches suggest a heavy rain threat and possible flash flooding in spots.
Saturday and Sunday...The stormy, more summer-like pattern/active ridge periphery unfortunately will look to linger for much of the weekend, before a trof looks to sweep acrs the upper midwest and flatten the flow into early next week. Thus chance for storms each day through Sunday night, with what happens the day and night before determining where or when the storm chances will build for the next day. Examples such as lingering cloud and precip debris, as well as outflow boundaries from the previous day/night and how long they linger into the next day for the next ridge-riding vort or MCV to act upon for renewed storms development. This depending on instability build and airmass reload. Rounds of heavy rain may produce more flash flooding, as well as renewed rises on area rivers.
Since we are still 60 hours away, the devil is in the details as to how this all plays out. Suffice it to say, much attention will be paid to developing trends with regards to the severe weather and heavy rain threat. More to come. Roll weather...TS
