Why does "Lake Shadowing" Peak in July?

[Frank Kienast]

I was reading the NWS forecast discussion for Buffalo this morning, and it mentioned that chances of thunderstorms would be left out of the forecast for the immediate Buffalo area due to shadowing effects from Lake Erie.

I understand the principle of lake shadowing, but I do have a question as to why it appears to peak in July. I would expect the lake shadow effect to be at its peak in the spring, since at that time of year the difference between water temperature and land temperature is greatest. Although the lake does decrease the intensity of thunderstorms in the spring months in Buffalo, generally some storms still occur. By August, the lake has warmed enough that some of the inhibiting effect is lost, and a few thunderstorms occur. In July though, many years no thunderstorms occur in the immediate Buffalo area.

Rainfall averages seem to confirm this.
April 3.0
May 3.1
June 3.1
July 2.9
Aug 3.9

So why does the inhibiting effect peak in July instead of earlier?

Thanks,
Frank Kienast

 

[Amanda Farnham]

I noticed this two days ago when a large field of rain crossed Michigan into the WNY area. It totally disintegrated on the lower end, so that we didn't even get rain here in Chautauqua Co. I would think that as warm as we have been this year, the lake would have lost it's inhibiting effect earlier this year as well.

 

[John Vandehei]

It might be because both the ground and the water are still warming up in spring. By summer, the ground surface has likely reached its maximum average daily temperature, while the water in the Great Lakes continue to warm up until sometime in early September.

 

[Justin Turcotte]

It might be because both the ground and the water are still warming up in spring. By summer, the ground surface has likely reached its maximum average daily temperature, while the water in the Great Lakes continue to warm up until sometime in early September.

This would make sense. I'm guessing general maximum instability is around this time of year yet there is still a substantial lake/land delta T during peak heating. Come August and September this delta T is is a smaller absolute value.

 

[Frank Kienast]

One other thing I have thought of is dynamics. In earlier months (April - June), maybe dynamics are strong enough to override the inhibiting effects of the lake shadow, but in July the dynamics are so weak that lake influences almost totally override them? A ways away from the lakes (say 50-100 miles), it seems (based on radar observations) that the outflow boundary may actually be enhancing thunderstorm activity over that experienced in other areas that have no lake influence at all (particularly in July). This effect seems absent earlier in the season.