The Oquirrhs Got the Snow

If you are looking for snow, perhaps you should look to the west to the Oquirrh Range instead to the Cottonwoods. The latest snow water equivalents from SNOTEL sites show the highest amounts at the three SNOTEl stations in the Oquirrhs.  These numbers do not include the lake-effect snow that fell out there last night and this morning.   

Source: NRCS

Shall we have a closer look?  The fattest snowpack is at Rocky Basin Settlement (8704 ft) where the snow water equivalent sits at 2.7". 

That's well above median for that site, although median so early in the season isn't a very robust statistic.  

For comparison, the Snowbird SNOTEL (9177 ft) is at only 1.2 inches.

Why are the Oquirrhs so blessed?  A big chunk of the snowpack at Rocky Basin Settlement fell on October 29.  They got some snow in the southwest flow like the Cottonwoods, but they did very well in the north-northwesterly flow following trough passage.  For example, the radar image below for 1821 UTC 29 October shows strong echoes just to the west of the Oquirrh crest.  These echoes persisted for a good chunk of the afternoon. 

It's hard to say exactly what the role of the lake was during that period, but the echoes are suggestive that both lake-effect and orographic (mountain lifting) processes contributed to snow enhancement over the Oquirrhs.

Then, in the evening, some lake-effect snow developed. 

For a while, as midnight approached, a very localized band developed.  

So, the Oquirrhs have done much better in the post-trough north-northwesterly flow than the Cottonwoods.  

Is this unusual?  It depends on what you use as a baseline.  It is unusual for the Oquirrhs to have more snow than the Cottonwoods.  At Rocky Basin Settlement, peak median snow water equivalent is 23.9 inches compared to 42.9 inches at the Snowbird Snotel. 

On the other hand, lake-effect periods produce about the same amount of snow in the Oquirrhs as in the Cottonwoods.  The figure below shows the water-equivalent produced by lake-effect periods during the 1998-2009 water years (adapted from Yeager et al. 2013).  During those water years, lake-effect periods produced an average of 2.12 and 2.37 inches of precipitation water equivalent at the Rocky Basin Settlement and Dry Fork SNOTEL stations in the Oquirrhs, respectively, compared to 2.06" and 2.38" at the Mill D North and Snowbird SNOTEL stations in the Wastach, respectively (see left figure below).  

However, since the Oquirrhs are otherwise drier, lake-effect periods constitute a greater fraction of the cool-season precipitation there (right figure above), including 6.3% and 8.4% of the cool-season precipitation at the Rocky Basin Settlement and Dry Fork Snotels.  For comparison, lake-effect periods produce 5.9% and 5.1% of the cool-season precipitation at Mill D North and Snowbird.  

So, such lake-effect snow is not unusual in the Oquirrhs.  They are currently ahead of the Cottonwoods because they were favored given the north-northwesterly flow in the wake of the trough on 29 November.  A similar situation occurred last night and this morning.  

As the saying goes, it's better to be lucky than good.