COME AND GO HEAT...
Our latest batch of hot steamy weather has come and is already on the go. While here it made an impact, especially Tuesday when heat index values of 105 were common thanks to highs in the mid 90s and dew points in the low 70s. Steve Gottschalk in Lowden, Iowa texted me to report a heat index of 109.
That resulted in plenty of surface based CAPE and towards evening a broken line of storms fired along a late day cold front. Deep layer shear was minimal and the updrafts struggled at times to maintain intensity. Thus, severe weather was not much of a problem with only a few locations coming close to reaching warning criteria. Some spots did manage some brief downpours but others missed out altogether. We've seen that act before.
Interestingly enough, yesterday dawned as the first time since April 25th that no place in the contiguous United States was not under at least a slight risk of severe thunderstorms from the Storm Prediction Center. That lasted until the mid-day update when SPC made an upgrade to "slight" that included much of my area,
Additionally, after a fast start to the severe weather season in March and early April in central Iowa, thunderstorm and tornado warnings in my area (eastern Iowa and western Illinois) have been limited, meaning this is again turning into another sub-par year for severe weather...actually a good thing. As you can see in the graphic below, we are less than half the average number of tornado and thunderstorm warnings we would typically see at this point in the year. The data goes back to 1986.
Nationally, after ranking near the all-time high going into April, the tornado season has ground to a halt and now ranks near the 50th percentile. That's quite surprising considering this was a La Nina year which typically supports above normal tornado activity.
Even though we are nearing July, severe weather can still be a major factor in mid to late summer. Tornadoes are usually not the issue but MCS events and derechos now become a seasonal issue. Those can be big wind producers as we know from 2020's August 10th derecho. As shown in the graphic below, tornado events peak in late May and early June and steadily decline after that. Limited cold air and shear are the primary reasons.
Thunderstorms are still a big factor, they just tend to be wind producers instead of tornado makers. Notice that wind events are still near their seasonal peak in late June and July.
With Tuesday nights cold front through the region, temperatures and humidity will be far less of a factor the remainder of the week. Both should be down about 10 degrees Wednesday and Thursday. That leaves us with highs in the low to mid 80s in most areas with dew points upper 50s to low 60s. Far more manageable.
If the EURO is correct, Friday may not get out of the 70s as it generates a thunderstorm complex (potential MCS) Thursday night over western Iowa that carries into my area Friday. Clouds and potential rain would greatly limit highs. The GFS shows a scaled back version and thus is not as cool with highs generally in the low 80s. Here's what the rain cooled EURO shows for highs Friday.
What this signals is a 36 hour period Friday through Saturday where the region is in what looks to be a favorable position for showers and thunderstorms. Friday night looks promising with MCS potential and Saturday afternoon or evening could be fruitful too with storm development on a strong cold front. Mesoscale details will be critical to how this plays out and at this point it's still too early to determine intensity or placement of storms or rain totals. In fact, recent data has come in faster with Saturday's front which would push the storm threat further east. These are all issues simmering on the back burner later this week. For now, here's what models are indicating for rain totals Friday through Saturday.
One thing I feel confident about is that after Saturday, we won't have to deal with any major heat for some time. The GFS shows 7 day temperature departures well below normal during the period June 26th through July 3rd. That translates to highs in the 70s and low 80s. Good stuff!
That's the long and short of it for now. Make it a rock solid day and of course, roll weather...TS