Wednesday, October 27, 2010

DLE strikes again

Great mid-lake band last night.  One of the best I have seen in several years.

It's interesting to compare the last two nights and their contrasting lake-effect modes and intensity.  I'll concentrate on 1200 UTC for brevity.

At 1200 UTC 26 Oct, there was a dominant wind-parallel band near Bountiful (a.k.a. the Bountiful Band). Temperatures were in the high 30s over much of the lowland regions, including the northern Wasatch Front from Bountiful to Ogden.  Promontory Point was 29F with a WNW wind at 20 knots.  Westerly flow was observed at HAT and at many of the locations near Ogden.

This morning, at 1200 UTC 27 Oct, there is a strong wind-parallel band near the major lake axis (a.k.a. the mid-lake band).  Temperatures in the Ogden area are in the low 30s.  Temperatures are also cooler over the Lakeside Mountains compared to the previous day.  Promontory Point is 26 F with a NW wind at 15 knots.  The flow pattern is remarkably similar to the previous day on the western side of the lake, but the flow in the Ogden area is primarily southerly.

Consistent with the changes evident in the MesoWest data, comparison of the 1200 UTC 26 and 27 Oct soundings from KSLC (purple traces for the former) show 2-3C cooler conditions today below about 600 mb, which follows the the weak trough passage we observed last evening.

Some food for thought about this period:
  • Is the convective mode of these two events really different?  Are these simply wind-parallel bands of differing position and intensity or is there something fundamentally different about the underlying processes?
  • Changes in position appear to be consistent with the large-scale flow differences, but how does colder environment, larger (inferred) lake-land temperature difference, and weaker flow/shear contribute to the more intense and organized band on the 27th? Are any of these more significant than the others, or do they all contribute?
  • Is there any skill predicting such differences with a cloud-permitting model so that we can better forecast lake-effect intensity and position?

Hopefully this post will prompt some lively discussion.

1 comment:

  1. There was some pretty good lightning last evening (Oct 26) on the west side of the valley during the trough passage, several very close CGs in my neighborhood (Taylorsville area) between about 1900 and 2030. So a fairly convective atmosphere was in place. Also, alignment with the orientation of the lake was almost perfect on the night of Oct 26-27.