Complex System

Posted Thursday, March 30th, 2017 by Tom Gowan

Showers have entered the region out ahead of our next storm system.  Expect southerly winds to increase as we head into the early evening.  Between 5 and 6 PM I expect a fairly strong cold front to push through the the Salt Lake Valley.  It’ll cross through the northern Wasatch an hour or two before then(3-4 PM) and the southern Wasatch an hour or two after then (7-8 PM).  The time height cross section from the NAM 12-km below highlights this frontal passage nicely:

NAM-12km time height cross section for SLC

I wouldn’t be surprised to hear a rumble or two of thunder as the front passes through.  Associated with the front will be a band of steady precipitation.  Models are forecasting this band of precip to stall somewhere in Utah as the low pressure system closes off in southern Utah.  Uncertainty remains as to where this will happen – hence why we aren’t confident in snowfall totals.

As we head into Friday winds will shift to easterly, which could lead to very strong winds in the valley.  Periods of precipitation will continue throughout the day tomorrow, but the easterly flow may limit accumulations at resorts on the west side of the Wasatch.  With so many small scale features at play combined with high uncertainty, the high resolution NCAR Ensemble appears to be a useful toll in forecasting snow amounts.  Here is its output for the Upper Cottonwoods:

NCAR Ensemble for Upper Cottonwoods
NCAR Ensemble for Upper Cottonwoods

Accounting for the low snow ratios and uncertainty in this system I am going with 6-12″+ for the Cottonwoods and Northern Wasatch.  This system will sit and spin in southern Utah, providing them with additional snowfall.  I expect totals in the southern Wasatch to range from 10 to 20 inches.

We clear out for this weekend, then another storm early next week.  An active spring pattern looks to continue for the foreseeable future.

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