Monday, November 12, 2012

How Big Was the Lake Effect Event

I thought I'd spend a moment today to put the weekend storm into a climatological context, especially the lake-effect phase.  To do this, I'll be concentrating on data collected by the NRCS SNOTEL stations located at mid mountain at Snowbird.  Based on the climatology developed by Yeager et al. (2012, in press, but available here), this site receives more lake-effect precipitation than any other regularly reporting site in northern Utah (Note: Alta might receive more, but we lack the data to verify this, and there is a site in the northern Oquirrhs that is a very close second).  In addition, during the weekend storm, the Snowbird SNOTEL received more lake-effect precipitation than any other SNOTEL, although Parleys Summit was a close second. 

As can be seen in the meteogram below, there were two major phases of precipitation during the storm.  The first was during the cold frontal passage on Friday.  The second was during the lake-effect period, which began Friday night.  The times are in UTC.  Subtract 7 for local (MST) time.  I have drawn a hard boundary between the frontal and lake-effect periods, but in reality the transition was not necessarily abrupt.  Nevertheless, we'll go with 0700 UTC 10 Nov as the time of the onset of lake-effect (it was a bit earlier to the north).  

SNOTEL stations aren't perfect.  The measurement tends to fluctuate due to gauge contraction and expansion from daytime heating and nighttime cooling, and snow occasionally builds on the gauge walls and falls in.  The green line above shows the accumulated precipitation by hour and you can see some of these effects in the trace.  Note the decrease after a peak at the end of the lake-effect period, as well as a rapid increase when a huge one hour accumulation of 0.6 inches of snow water equivalent that may have been produced by a clump of snow falling from the sidewall or rim of the gauge to the bottom where it could be measured.  We will use a 2 inch increase from 4.6 to 6.6 inches of SWE for the total precipitation produced during the lake-effect portion of the storm.  

Converted to metric, that is a total lake-effect SWE of 51 mm.  During the 1998–2009 period examined by Yeager et al. (2012), there was only one period that generated more lake-effect precipitation.  That period was the 2nd lake-effect period of the the Thanksgiving 2001 Hundred Inch Storm and it is by far the largest lake-effect period of the past 15 years.  Note how the scale in the graph below jumps from 40 to 80 mm so we can fit it in.  

SWE produced during lake-effect periods from 1998–2009.
Source: Yeager et al. (2012)
Although this weekends storm wasn't the biggest lake-effect event, it was clearly #2, at least at Snowbird.  It might be the biggest at other sites, such as Parleys Summit, but I don't have that data at my fingertips.  

The bottom line: Consider yourself blessed.  

No comments:

Post a Comment