Tuesday, February 7, 2017

The Big Bad Wolf Is Coming to Town

Much to talk about this morning.  Let's first talk about what has been going on overnight at a few locations.

At Powder Mountain, they are up to about 1.7 inches of water in the past 24 hours and about 1.4 inches since 5 PM yesterday.

Source: MesoWest
The resort took the unusual and proactive step of closing for the day today, announcing it yesterday.  I say kudos to them.  We are currently in a "lull" with regards to wind (lull being relative), but all evidence, as discussed below, suggests that we are in for a hell of a mountain blow this afternoon and evening.

In the northern Wasatch, the precip gauge at Ben Lomond Peak hasn't been sending us any data in a few hours, but the snowpack water equivalent is up 1.8 inches in the past 24 hours and 1.6 inches since 5 PM yesterday. At Snowbasin, totals are a bit lower, with just over 1.2 inches in the past 24 and about 1.05 since 5 PM yesterday.

Source: MesoWest
Temperatures at the base of Snowbasin (~6500 ft) are currently sitting at 32ºF and at least for now, all of that water is falling in the form of snow down to that level.

Alta-Collins has comparatively been skunked, as is sometimes the case with flow from the WSW.   They'v had about 0.38 inches of water in the past 24 hours and about 0.29" since 5PM yesterday.  

Source: MesoWest
Go further south to areas favored in WSW flow and you can find some bigger numbers.  For example,  the UDOT sensor on Bunnels Ridge has had about 1.6 inches in the past 24 hours and about 1.4 inches since 5 PM yesterday.

Source: MesoWest
Snow will continue this morning throughout the region, and temperatures will be on the increase, with snow levels probably reaching 7000-8000 feet this afternoon.  Precipitation this afternoon might become more convective, with a potential for a thunderstorm or two.  However, the big story is going to be the wind, so we will focus on that.

Currently, we are in a relative "lull" for the wind.  At Ogden Peak (above Snowbasin) and Mt. Baldy (above Alta), peak gusts occurred around 2000 MST (8 PM) last night.  At present, winds at the former are gusting to about 50 mph and at the latter about 40 mph.  NOTE: These sites are above the ski resorts and not necessarily representative of the wind speeds at the resorts.

Source: MesoWest 
Source: MesoWest
What will be happening today, however, is that the remnants of a decaying low pressure system will be passing just to our north.  Watch in the loop below how the low center at the beginning of the loop (0900 UTC/0200 MST this morning) decays, but rolls through southern Idaho, resulting in an intensification of the pressure gradient over northern Utah this afternoon before it moves downstream and the pressure gradient slackens.

Now, let's take a look at the 700-mb (10,000 ft) winds forecast for by the high-resolution HRRR.  Contours begin at 50 knots and continue every 10 knots above that level.  Note how the patch of strong winds moves with the decaying low center across northern Nevada and Utah during the period of the loop, which runs from 1200 UTC/5 AM MST to 0200 UTC/7 PM MST.

Further, these 700-mb winds are quite strong compared to climatology.  I don't have graphics available for comparing the HRRR to climatology, but thanks to the National Weather Service, we can compare the 700-mb wind speed forecast from the NAEFS to climatology ad we find that along the Utah-Idaho border, were looking at forecast wind speeds that are outside the climatology and an area across much of northern Utah where the return interval is once every 5 to 10 years.

Source: NWS
How strong the winds blow on the ridges and more generally in the mountains this afternoon will depend ultimately on local effects, but all indicators point toward a strong wind event.  I would not be surprised to see tree damage in some areas.  I'm working today, but this forecast is concerning enough that I would probably skip ski touring altogether this afternoon.  The Big Bad Wolf is coming to town.  

1 comment:

  1. In Eden as of 14:00 MT 2/7/17 we are at 1.9 inches rain in last 36 hours.