Bill and Ted’s Most Excellent Forecast

Thursday, December 8, 2016 at 7:41 am

Update:

Some changes in the models today.  Generally, the wave for tonight into Friday is a bit weaker and favoring areas north of SLC.  Would not be surprised if totals tomorrow weren’t overly impressive.  Models now bring the heaviest precipitation in on Saturday into Saturday night.  This is reflected well in the 18z NAM:

So good news for the weekend warriors, as long as the wind doesn’t get too bad…

WSF

Previous:

 

Summary:

A very moist system will begin to impact the area today with periods of mountain snowfall lasting through Saturday, perhaps into Sunday morning.  Heavy accumulations are likely for all mountains of Northern Utah.  Additional waves are possible for early next week, with a potential stronger system for late next week.

Details:

Warm advection precipitation is going to fill in today across the region.  There is plenty of cold air left from our frigid early week airmass, so that means that snow levels will be fairly low later today into tonight before rising overnight off the valley floors and up into the 6-7k feet range for Friday, maybe even higher.  I would expect a period of snowfall for tonight into tomorrow.  Anywhere from 5-15″ is likely in the mountains between now and tomorrow afternoon.

We should see a relative lull in precipitation Friday night, although showers will still be likely.  Then, a second push of precipitation for Saturday into Saturday night with an additional 5-15″ likely by Sunday morning.   Total accumulations by early Sunday should be 10-30″.  Higher amounts will be in the highest elevations and west-facing slopes of Northern Utah.  Lower amounts for the lower elevations of the Wasatch Back, such as the lower elevations of PCMR.

12km NAM shows the following for the Upper Cottonwoods:

1208_nam

Univ of Utah

Showing just over 20″ thru late Saturday.  I think it might not be picking up some of the orographics and totals could be a bit higher than indicated by this model.

While the totals might seems less than our big storm last week, don’t be fooled.  This is much denser snow so we’ll actually have a higher SWE than any previous storm.  This type of snow won’t compact as much and will better adhere to uncovered surfaces.  It’s the perfect base-building snow to “fill in the cracks”.

Here you can see the forecast from the Canadian and GFS ensembles for the next 7 days:

1208_gfs_plumes

Notice the Canadian (light green) are pulling the mean up.  I trust the GFS far more, so I think the mean is overdone.  Still, QPF by midday Sunday (red line), should be 2-3″ of liquid for the Cottonwoods.  Which, at 10:1 ratios, means 20-30″.  So I think my forecast is in good order still.

The other thing to notice is that the second AR event for early next week is all but dead.  RIP AR#2…  you died long before you even had a chance to bring us snow.  Life of a storm is so fleeting…

1208_dust

So the potentially historic back-to-back AR events is unlikely to happen.  Before you despair, we should still have a chance for occasional snow early next week as there will still be a lot of unorganized moisture pushing into the Great Basin.  Then, models are starting to zero in on the potential for a significant storm system for late next week.  This one could have more cold air to work with… 10-day snowfall totals still look mighty fine to me….

1208_gfs

Most excellent!

Long range:

GFS wants to keep the storm train going right up until Christmas.  The Euro tries to give us a bit of a break with some ridging.  Too much going on in the short term that I honestly can’t give much thought to the long-range at this time.

WSF

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