Thursday, October 25, 2012

Morning Lake Effect

Lake-effect developed around 9 am this morning.

Playing a critical role in the initiation of the event is a convergence zone that separates strong westerly flow over the western Great Salt Lake from weak or easterly flow over Antelope Island and the northern Wasatch Front. This convergence zone shows up very well in the surface plot below and extends from just southwest of Promontory Point into the Salt Lake Valley.  

I'm still thinking the lake effect will weaken and become more widely scattered with time (see previous post), but if I'm wrong, I won't complain.


  1. That is very awesome to see the radar associated with the convergence in the surface wind field. Why is it that lake effect is more common at night and early morning? Is it because there is a larger delta T between the air near the surface and the lake because of radiational cooling of air over land before it flows over the lake?

  2. Is it my imagination, or does it look like the lake effect storms are triggered by the islands and promontory point?

    BTW - it was great fun to watch this throughout the day...

  3. I have often thought that Promontory Point (peninsula) helps to provide a focal point for low-level convergence, influencing the location of lake band development. It often looks as if the low-level wind field is distinctly different on the west vs east side of the peninsula. But I think that in the larger scheme of things, the contrast between the land surface and lake temperature (which peaks early in the morning) is the key factor as far as surface features are concerned. It seems like there are rarely any lake bands observed between about noon and 6 pm because of land surface heating.

  4. We have a paper we're about to submit on this soon. PPT does play a role in generating convergence over the upper half of the lake, but other factors are more dominant.

    The role of terrain-induced circulations on lake-effect will be the subject of a post once we're done with the paper. They are certainly important and likely contributed to yesterdays event.

  5. By the way, there was some heavy graupel and lightning in one of the convective showers yesterday morning (Oct 25) around 0730 local. This was before the main lake effect began, but I wonder if the lake played a role.