Tuesday, December 6, 2016

Snow Prospects in the Short, Medium, and Extended Forecast

Plenty to discuss today as there's all sorts of action in the short-, medium-, and extended-range forecast periods.


When it comes to snow, sometimes the most difficult forecasts are for light accumulations.  

The 1300 UTC initialized HRRR simulated reflectivity forecast below shows the challenges for today.  A relatively weak weather system over Oregon and Idaho is forecast to strengthen some as it moves into the Wasatch Front later today.  

For Salt Lake City, most ensemble members produce less than 0.1" of water equivalent through 0200 UTC (7 PM MST), although there are a couple that to for around 0.15".  
NCAR Ensemble forecast for the Salt Lake City International Airport

Thus, this could be everything from a few snow showers to an inch or two of snow.  On a meteorological scale of 0 to 10, that's about a 1, but it's coming in around rush hour.  If precipitation is light and intermittent, it probably won't be a big deal, but a brief burst of heavier precipitation, while a lower probability possibility, could cause some snafus.  Best to keep an eye on this as the day evolves.

A couple of members go for some significant snow overnight due to lake effect.  As usual, that's a tough forecast, so consider yourself fortunate if you get some.  

Best guess is perhaps 2-4" of cold smoke in the Cottonwoods later this afternoon and tonight.  Emphasis on guess as the models have been erratic and the lake is always a dicey proposition.  These amounts are a little lower than one might infer from the NCAR ensemble or overnight NCEP model runs (not shown), but reflect the fact that the system seems pretty weak right now.  Thus, hope we do better.  

Medium Range

We've already discussed the big cool down for tomorrow (Wednesday) and how it will be short lived.  The models bring in a pretty juicy pattern beginning late Thursday through Saturday night.  The NAEFS plume for Alta shows the weak system passing through later today (~0000 UTC 7 December), a break for tomorrow and early Thursday, and then the action picking up.  By 1200 UTC 11 December (5 am MST Sunday), our downscaled accumulation estimates fringe from about in inch of water equivalent to just over 4 inches of water equivalent.  You can further excite yourself by looking at the snowfall plume.  

NAEFS forecast for Alta
   Personally, I think it's too early to be talking about accumulations, but the pattern does suggest we will be adding to our base at upper elevations.  There will, however, be some yo-yoing of the snow levels, which could reach or even exceed 7000 feet Friday night.  

Extended Range

Most ensemble members suggest an active, stormy pattern through next week.  The Utah Avalanche Center and snow-safety teams at the resorts and along the highways will have their work cut out for him if the advertised pattern verifies.  I've already said more than I should as I put little faith in 5-10 day forecasts, but lets keep our fingers crossed. 

Monday, December 5, 2016

Dramatic Swings in Weather This Week

If the computer models hold, we are in for quite a roller coaster this week as far as weather is concerned, especially in the mountains.

First, we have two troughs moving through the area, one that went through last night, the other scheduled for tomorrow (Tuesday).  Temperatures will really bottom out in the wake of the 2nd trough and by Wednesday we are looking at 700-mb (10,000 ft) temperatures near -18ºC over the Wasatch Front.  That means temperatures below zero fahrenheit above 10,000 ft.

GFS 700-mb temperature forecast valid 1800 UTC (11 AM Wednesday MST) 7 December
If you look at the forecast above, however, you will also see that it is quite warm over the north Pacific off the coast of California, where 700-mb temperatures are above 0ºC.

If we look at the precipitable water forecast for that time, we also see a tongue of vapor-rich air just upstream of the California coast.  

GFS precipitable water forecast valid 1800 UTC (11 AM Wednesday MST) 7 December
That airmass pushes inland very rapidly, and by 0000 UTC (5 PM Thursday MST) we've rebounded to -5ºC.

GFS 700-mb temperature forecast valid 0000 UTC (5 PM Thursday MST) 9 December
So, our flirtation with brutally cold air should be brief and it appears we'll be in for milder weather later in the week through the weekend.

How much moisture will get into northern Utah will depend, however, on the inland track of the atmospheric river and the impacts of the Sierra Nevada.  A direct track across the southern high Sierra is usually bad for moisture transport into the Intermountain West due to the blocking of low-level moisture and the loss of water vapor on the western (windward) side of the range.  As is often the case, and suggested in the precipitable water and precipitation forecast for Thursday afternoon (below), there is a major decrease in precipitable water across the Sierra due to these effects.

GFS precipitable water forecast valid 0000 UTC (5 PM Thursday MST) 9 December
The NAEFS plume diagram for Alta is, however, fairly optimistic for some base-building water-laden storms late Thursday through the weekend.

That would be good news for the upper elevations of the Wasatch, but let's take a closer look in a couple of days as this is still too far out for me to get excited about details.

Sunday, December 4, 2016

Damn Cold by Wednesday

Although some snow is on tap for tonight and tomorrow, the big story this week is going to be the cold.

The coldest air of the season is scheduled to push into Utah mid week and by 1800 UTC (11 AM MST) Wednesday, we are looking at 700-mb temperatures near -18C at 700 mb (10000 ft).

That means ridge-top temperatures below zero fahrenheit.

Get the rum and hot chocolate ready!

Friday, December 2, 2016

Shameless, Self-Serving, Christmas Gift Recommendation

Like this blog?  Be sure to pick up my book Secrets of the Greatest Snow on Earth.

It's an ideal Christmas gift for lovers of Utah snow and skiing, or even skiers in other regions (yes, I cover that).  Available online from Amazon and Barnes and Noble, and local booksellers Weller Book Works, Kings English, and Dolly's Bookstore (call ahead for availability).

Thursday, December 1, 2016

Record Warmth for the First 11 Months of 2016

Following up on the previous post, we did set a record for the warmest November on record in Salt Lake City.  We are also in record territory for the first 11 months of the year (January – November), as illustrated below. 

Source: NOAA Regional Climate Centers

Wednesday, November 30, 2016

This Will Be the Hottest Fall on Record

Given the fact that we are experiencing our coldest temperatures since February, much of the Salt Lake Valley is snow covered, and we have a 40" base in upper Little Cottonwood Canyon, it may be hard to believe this is going to be the hottest fall on record, but it is going to be the hottest fall on record. 

With one day left to go into the record books (today), the average temperature for this fall at the Salt Lake City International Airport sits at 57.7ºF, 0.7ºF warmer than 2015.  

Source: NOAA Regional Climate Centers
Although we are going to lose a little ground today, my hazy, jet-lagged, early morning math suggests we will come out ahead of 2015 when today is in the books.  Regardless, both years add to our string of five consecutive years with exceptionally warm falls.  How much the recent fall warmth is due to long-term global warming or climate variability is an interesting question.  Thanks to global warming, the dice are loaded for above average temperatures, but my view is that the last few years the large-scale flow has also been favorable for us to have warmer falls.