TWISTER NUMBERS WAY UP...
This past weekend was a brutal one for tornadoes, especially from SW Iowa into Oklahoma. Preliminary numbers from the Storm Prediction Center indicate 170 tornado reports since last Thursday. 2/3rds of those occurred on Friday with SPC indicating 112, many of those in SW Iowa.
A number of the tornadoes were strong, long tracked storms that were particularly violent, not something you regularly see in Iowa. One of the storms that hit Minden, Iowa was a high end EF3 tornado with winds of 160. The storm was on the ground for 41 miles and at one time reached a width of 1 mile! A Doppler radar on wheels known as DOW-(funded by a National Science Foundation project, measured 224 mph winds with the mesocyclone near Harlan, northeast of Minden.
224 mph winds would easily make the tornado an EF5, the strongest possible. However, my guess is that the storm was over open fields when the measurement occurred and there was no visible damage to support 224 mph surface winds. Storm ratings require hard structural damage evidence from survey teams, which apparently was no more than 160 mph. (It takes winds of 166 to reach an EF4 rating). Looking at some of the videos showing multiple vortices and intense vorticity, I thought the Minden to Harlan storm would reach EF4 status. Not quite. In these images though, one can clearly see suction vortices rotating within the funnel. Perhaps as many as 6, which takes some serious helicity, a known feature of the strongest twisters. I also saw images with satellite tornadoes, smaller tornadoes rotating around the parent circulation.
Here are a couple chilling images of the storm, which is exhibiting the classic structure of a violent and deadly tornado. One man was killed in Minden. Fortunately, the beast remained in the open country most of its life, limiting damage, injuries, and loss of life. Warnings from the NWS were also accurate and timely, providing ample time for preparation and shelter.
The volume of storms this weekend dramatically increased this year's tornado count. According to SPC, the preliminary count nationally has reached 486.
Below you can see the April count, indicating many of the storms in the central US have occurred this month.
Before the weekend outbreak, SPC was showing the 2024 inflation adjusted tornado percentile close to normal at 50 percent. (The inflation adjusted count is the number of tornadoes multiplied by .85 to remove overcount). Following the weekend, it shot up to 75 percent, with the count measured at 411. All of a sudden, we are having a very active (above normal) year, with the heart of the season still ahead us. Where do we go from here?
Below, you can see all the preliminary reports since January 1st for tornadoes, severe wind, and severe hail. The combined total is 4,247.
By the way, these are all the tornado tracks since 1950. As you can see, the central Midwest is well represented. It's interesting to note at the lower right, that of 67,558 tornadoes, only 59 have gained EF5 status, a percentage rate of .0008. EF0 and EF1 storms, the weakest, comprise the greatest majority of tornadoes, with 81 percent of the total. The EF3 tornadoes in Iowa Friday make up only 3 percent of all tornadoes since 1950.
There is a chance of more severe weather around the central U.S. this week, I'll have more on that part of the weather story below.
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TRAINS ON A TRACK...
In the next few days, regular weather systems will be crossing the central Midwest like trains on a track. Before the next one arrives, Tuesday promises to be a fine day to mow the yard (mine appears to be growing on steroids)! Mostly sunny skies, a light breeze, and springlike temperatures in the mid to upper 70s will make for a delightful day, except for the fact I'll be mowing the yard. So it goes...
Tuesday night, a shower or storm may reach the area with disturbance number one. However, any storms will be waning as moisture is meager, timing of forcing is poor, and the energy wants to split north and south. I'm not looking for much out of this event locally. Further west in central Iowa, some far stronger storms are anticipated, and SPC has a moderate risk outlook in place.
Wednesday dawns dry, but already another system is coming together over the Plains. My area looks to stay dry during the day, but we may have to fight some passing high and mid-clouds with warm advection underway by afternoon. Wednesday night, over-running ahead of a warm front, should crank up scattered showers and thunderstorms. These look elevated and with instability limited, the primary concern would be with heavier rain in some of the stronger cells. The GFS indicates MCS development in the NW half of my area. There is low confidence on potential. That will be determined by the position of the front and intensification of the low level jet, still to be determined. The severe weather risk remains well to the SW during the day.
Temperatures Wednesday will be seasonal, in the upper 60s to low 70s in most locations. Winds will pick from the SE at 10-20 mph.
Thursday could start with showers and storms, then a break before new development ahead of a cold front late in the day or early evening. Moisture will be plentiful, but the strength of any storms will be highly tied to heating. While some CAPE is available, most models keep it marginal. That means most of the storms would be more of the garden variety, with some scattered downpours possible. If we get a little more sunshine, things might get a little more interesting in terms of storm intensity. Highs of 70-75 seem like a good bet north to south. SPC currently has only a marginal risk of strong storms.
Friday, the above disturbance slips east and weak high pressure rules the day. Under partly sunny skies, a dry day is anticipated, with highs clustered around 70.
Saturday, another wave of energy may kick up a shower or storm, but forcing is rather broad and amounts should be light. I would look for quite a few dry hours, certainly no wash-out. However, with plenty of clouds and some pockets of rain cooled air, highs look restricted to the upper 60s to near 70.
Sunday is a rain free day with sunshine back in the picture along with seasonal conditions. Highs will likely hold in the range of 69 north to 74 south.
HOW MUCH IN THE RAIN BUCKET?
This past weekend, rain varied considerably from north to south, with some areas seeing as little as 1/4 inch while others knocked off 3–4 inches. Unfortunately, most of the heavier amounts managed to miss the parts of eastern Iowa where severe to extreme drought continues to be found.
All we can do for the dry spots is try, try, again. With additional rain chances, here's what models are suggesting for total rainfall through Sunday morning. Another 1–2 inches is certainly on the table.
The EURO
The GFS
The National Blend of Models.
For what it's worth, the Weather Prediction Center has my area in a slight risk hazard outlook for heavy rain May 2-6th. Locally, the emphasis would most likely be May 1st and 2nd in my opinion.
Well, that's the long and short of it for now. Until next time, enjoy the lovely day and roll weather...TS
