[#severe climo thread] Is there something about late May? I totaled all severe reports for NY, NJ, PA, DE, MD and DC for the months of April to July (data source SPC, 1955-2018). For severe wind reports, they increase overall from April to July (but notice late May rise). (1/8) 
In terms of severe hail, notice the peak in reports happens in late May to early June with the 10-day average peak right around the infamous date of 5-31. (2/8)
Tornadoes overall gradually increase from the start to the end of the period. However, the notorious period of the end of the May into early June again sticks out with peak in daily counts and rolling averages. (3/8)
How many of the years produced an event on a given date? There are 64 years in the data set and below is the count plotted for each report type. As you move forward in the period, more years normally produce a severe report on any given day. Hail plateaus~ late June. (4/8)
I took a rolling 14-day average of the sum of all reports and divided it by 14 and then divided that by the number of years with an event on a given day. Here is what the chart looks like: (5/8)
Instead of a rolling average of 14 days, I grouped 2 week periods together and did the same division. Each report type sees a maximum in late May into early June. A large portion of the severe reports come in enough years in the dataset to make the time period significant. (6/8)
So while severe climo probabilities go up for the area as you continue into the summer, there is still something special about the end of May into early June. Below is a moving 2-week 700mb mean zonal wind climo for AMJ. Watch the max move north up the East Coast. (7/8)
The end of May into first half of June is a time when the 700mb jet is mostly continental; when max is over the northern Mid Atlantic; and it occurs when source EML region expands north into the Great Basin/Rockies. It's when flow has the most ease to eject EMLs into area. (8/8)
