Tuesday, November 5, 2013

Widespread DLE

Last nights storm brought a serving of cold smoke for just about everyone along the east bench from Sandy to Ogden.  Yup, widespread DLE (Dreaded Lake Effect-The "technical" term used by forecasters).

A wintery scene in the Avenues this morning
When people think of lake-effect events, they usually recall banded "firehose" events that are quite narrow and generate heavy precipitation (see right hand image below).  The reality is that lake-effect events are banded only about 20% of the time.  Non-banded events comprise the majority (55%) of all events and typically result in modest accumulations over a broader area.  About 25% exhibit mixed characteristics.  

Frequency of lake-effect events by storm type.  Based on Alcott et al. (2013)
Last night's event was of the non-banded variety.  It never developed a banded-like structure.  As a result, modest accumulations were observed over a fairly broad region.

It's tough to tell from the available observations how much lake effect fell in the mountains.  Alta-Collins has a 5 inch storm total since yesterday, but only about two inches fell during the main lake-effect period.  The Parleys Summit SNOTEL did a bit better, with perhaps a 7 inch storm total and anywhere from 3–5 inches during the lake-effect period (the observations are automated and thus it is difficult to precisely determine accumulations).

Some lake-effect events feature dramatic enhancement of precipitation in the mountains, but the data available suggests the enhancement in this event was modest.  Perhaps limiting mountain enhancement was the shallow nature of the storm.  The sounding below was taken from the Salt Lake City airport around 5 am (the photo is from ~9:15 am and they are roughly overlaid to illustrate storm depth).  The dramatic divergence of the temperature (red line) and dewpoint (green line) profiles at ~600 mb very clearly indicates cloud top at an altitude of about 4000 m (~13,000 feet), which is fairly shallow, although the storm may have been deeper at times.  

Sounding source: NCAR/RAL
With snow on the ground on campus, U students are now fully infected with powder fever.  

1 comment:

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