Category Archives: Snow

Mini Snow Eater Conditions

It's not quite like an east-coast snow-eater event when temperature are near 50, fog, and rain, but for Utah, this is as close as it gets.

Current (7-8 AM) temperatures in the central Wasatch are 37 at Spruces, 39 at the base of Park City, 38 at the base of Alta, and 33 at Alta-Collins, and 31 at Germania Pass.  That puts the freezing level at about 10,000 feet. 

In addition, dense, mid-level overcast is draped over the mountains, with some west snow at upper elevations, rain at mid elevations, and the transition zone in between.  The Alta webcam below summarizes the dreary conditions quite well. 


For the most part, snow on north facing aspects will survive just fine this time of year under clear, dry conditions, even when temperatures are above 32ºF.  Without direct sunlight, you simply don't have enough energy to melt snow.

However, if you can add humidity and cloud cover to the mix, things change.  You lose the cooling effect of snow sublimation and gain the energy input of infrared radiation from the clouds. 

The eastern U.S. gets these conditions in spades at times, with fog and rain doing it's number on snow frequently during the cool season. 

We don't really get such a snow-eating extreme in Utah.  Today is about as close as it gets.  Above 9000 feet, everything will be fine.  Below 8000 feet, we're going to see snow losses.  In between there may be a net loss, but it probably not a huge one. 

Fall continues it's grip on the Wasatch, with no desire to let go and let winter take control....

Three Thoughts on This Sunday

1. Yes Virginia, there is skiing

I debated for a while whether or not to ski this weekend.  I'm not a fan of low snowpack, bony conditions and often stick to skiing the main run along Alta's Collins lift under such conditions.  With Alta closed to uphill, we opted to take a couple of laps at Brighton in the Great Western area since rumors were that they were asking tourers to avoid other parts of the mountain.  I pulled out my oldest sticks for the day, a pair of Karhu Jak BCs that are probably 10-12 years old.


However, I was pleasantly surprised to survive both runs without harming a single rock.  I was also glad to rediscover that the Jak BC really was a great ski, even if you didn't see them much in Utah. 

We stuck to grassy runs that were heavily traveled.  The touring and skimo crowd cut up the area pretty good. 


Some sections of untracked could be found in some areas and we went home satisfied, without injury, which is the main goal of any first day.  

2. The snowpack isn't really all that meager

It's worth remembering that it is only November 19.  Thanksgiving is pretty early this year.  Our snowpack seems pretty meager, but really it isn't.  The Snowbird SNOTEL is measuring 3.1 inches of snow water equivalent (SWE).  Median is 4.1 inches.  An inch of water equivalent is basically one modest storm.  So, we're one storm below median.  Yes, it hurts to look at the snowpack in the Tetons and Sawtooths (or should I say Sawteeth?), but we're not really doing all that bad.........yet.

3. The next week may suck

The model forecasts for Thanksgiving week don't look so great for Wasatch skiers.  The NAM forecast for 5 PM MST tomorrow (monday) shows a classic "dirty ridge" scenario with moisture spilling over a low-amplitude ridge and into Utah.  700-mb temperatures are a balmy 0ºC.  This is a recipe for riming and perhaps some wet, rimed snow at times in the mountains.  It probably won't add up to much for the snowpack and we'll probably see a net loss at elevations below 7000 feet (not that there's much there currently).


Eventually, a high amplitude ridge builds over for Thanksgiving Day.  Beautiful weather across Utah for driving over the river and through the woods to grandmother's house.  Good valley mountain biking.  Good canyoneering. 


However, 700-mb temperatures are a whopping +6ºC, which would be a record for the last week of November (although we have observed 700-mb temperatures of +8ºC in mid December).   Brighton was making snow today where they could, with the low-angle sun and dry conditions allowing for it in shady spots.  The resorts will probably need to continue to selectively pick spots and times over the next few days for making snow.  

Core Dump on Our Pending Storm

The Doppler on Wheels (DOW) has been in town now for two weeks, and we've yet to have a significant storm during that period.  At Alta, the best we've done is 4 inches on November 4th, which isn't much of a storm.  We've kept ourselves busy with various educational and outreach activities, but are in desperate need of a storm.

Fortunately, it looks like Mother Nature will give us something tomorrow afternoon through Friday.  It's been an interesting storm to follow in the forecast models for a number of reasons.

1. It's taking forever to get here.

The GFS forecast initialized at 0000 UTC 12 November (5 PM MST Saturday) showed the upper-level trough making landfall onto the Pacific Northwest coast at 1800 UTC 16 November (11 AM MST Thursday), with precipitation across the Wasatch Mountains, Uintas, and even western Colorado.  Under this scenario, we'd want to be out storm chasing early tomorrow (Thursday).


During the past three days, however, the GFS has really slowed the progression of the trough.  The forecast from 0000 UTC 15 November (5 PM MST Tuesday) has the trough much farther west and well off the coast at 1800 UTC 16 November (11 AM MST Thursday).  Precipitation is just sneaking into the northern Wasatch and Bear River Range area, and there's no precipitation over Colorado.  Instead, we'll be able to sleep in tomorrow!


2. The Sierra Nevada really take a bite out of storms

Through flow blocking and water vapor depletion in mountain-induced rain and snowfall, the Sierra Nevada have a dramatic impact for the worse on moisture transport into the Great Basin.  This can be seen in the GFS forecast pannels immediately above.  Note in particular the how the column-integrated relative humidity in the lower left panel decreases abruptly across the southern "High" Sierra, with moisture only able to sneak in across the lower northern Sierra north of Lake Tahoe.  This effect is also apparent in theNAM forecast for the same time and, in this case, it is a contributor to the delay of precipitation spreading into northern Utah.  Without the High Sierra, moisture would penetrate more easily into the Great Basin and the Wasatch would light up even earlier.  Pity.


The time-height section from the NAM shows a classic "cloud-storm" environment tomorrow over the Salt Lake Valley.  Cloud storm is a phrase we jokingly call events with high clouds and virga, but little precipitation reaching the valley floor.  There's copious moisture at mid levels, but dry environment down low.  Deep moisture doesn't penetrate into the Salt Lake Valley until Friday night.  More evidence of further delays in the storm really getting going over the Salt Lake Valley.


Add all this up — the delay in the arrival of the trough, the drying influence of the High Sierra, and the dry low levels over northern Utah — and you have a recipe for restless natives anxious for the arrival of a storm that has been promised for Thursday.

3. Many storm chasing options

We of course have a mobile radar, so we can put it wherever we want and don't have to necessarily wait in the Salt Lake Valley for weather.  That being said, it takes time to move the DOW around and configure a reasonable scanning strategy to do real science.   We have a number of possible targets through Friday afternoon, including the spillover of precipitation across the northern Wasatch Mountains and into the Ogden Valley, multi-ridge interactions between the Stansbury and Oquirrh Mountains or Oquirrh and Wasatch Mountains, a cold frontal passage presently forecast for Friday morning, and post-frontal convection in northwesterly flow in the wake of the cold front.  It's going to be a busy time!  We'll have an interesting planning session this afternoon and then will need to keep a close eye on things in the field to maximize our opportunities.

4. Mountain snow possibilities

The situation this week has been pretty grim for skiers.  Not only has it been dry, but it has also been warm.  I don't follow the snowmaking activities at the resorts, but I suspect they were limited at best.  That situation will continue today and even tomorrow looks to be pretty warm.  In addition, the early phases of the storm when it does arrive look quite warm.  For example, the NAM forecast for 1200 UTC (5 AM MST) Friday morning has 700-mb temperatures of around -2ºC.  That equates to a snow level around 7000 feet or so.


Thus, while the upper elevations of Snowbasin are likely to get a pasting, the base may see rain for at least a portion of the storm.  PCMR may also see rain at the base during the early stages.

However, the snow level will be lowering during the period, especially on Friday.  Friday has some potential to be productive in the Cottonwoods due to cold, unstable, northwesterly flow.  Overall, the NAM-12km is generating about an inch of water and 9 inches of snow at Alta Collins through late Friday.  The numbers, however, vary widely across models and ensemble members.  At this point, I'd lean toward 6-12 inches at upper elevations in Little Cottonwood, with the potential for more if the post-frontal environment is highly productive.  Water totals in the northern Wasatch should be higher.

Snowmakers had better be ready to release the torrents Friday, Friday night, and Saturday morning.  After that, ridging returns and more marginal snowmaking conditions return for a couple of days.

Addendum at 10:15 AM 15 November

The SREF plume diagram below was unavailable when I wrote this post, but I've added it here and it shows remarkable spread for the event at Alta Collins.  Talk about forecaster heartburn!  Hope for the high members to verify.


Überströmungs Cyclogenesis!

A classic example of Alpine lee cyclogenesis of the "Überströmungs-type" is bringing heavy snowfall to portions of the Alps and southern Europe.

Alpine lee cyclogenesis is the birth of a cyclone in the lee (downstream side) of the Alps.  Überströmungs-type Alpine lee cyclones form in northwesterly large-scale flow as cold air is blocked and flows cyclonically to the west of the Alps, while the upper-level trough continues to move downstream, inciting cyclone development in the western Mediterranean region.  Terrain impacts are especially pronounced in cyclones that form in this fashion.

The satellite and sea level pressure loop below shows the situation from 1200 UTC 11 November through 1200 UTC 13 November.  The system begins as a surface trough that plunges southeastward across the British Isles, France, and Germany.  The cold air plunges southward through the low elevation region between the Alps and Pyrenees (note faint rope cloud in the loop), and strong cyclogenesis occurs over northern Italy.


@severe-weather.EU is the feed to monitor this morning as they are tweeting out some wonderful images from across the region.  Here are a few.

 Enjoy the look at the fresh snow.  Let's hope we can join the party later this week.

Curb Your Enthusiasm

We've reached the time of year where every wiggle in the jet stream becomes enticing. 

Call it what you want.  The November doldrums.  Purgatory.  There's not enough snow to ski in the central Wasatch and we need more.

I'm already getting inquiries about the storm later this coming work work week.  My advice?  Curb your enthusiasm.

That advice is not because I think the storm will be a bust, but because we are still a few days out and the ensembles are showing a wide range of possible outcomes, from relatively light accumulations to up to 14 inches at Alta-Collins.  Typically, ensembles are underdispersive, meaning that range probably underestimates the full range of possible outcomes.  In other words, we don't really know much yet except that a trough will be coming through and we'll probably see some snow. 

What I do know is that today will be a lovely mid November Sunday.  Enjoy it. 

November Doldrums

One of the great things about the central Wasatch is that they get snow from a great variety of patterns.  Unfortunately, the pattern we'll be in for the next week (and maybe longer) isn't one of them. 

For the next week, the northwest US will be active, but we're just to the south of the strong flow and moisture for much of the period.  Thus, we may get some brush by clouds and snow showers, but that's about it. The GFS forecast below shows the action in the northwest, but not a hint of precipitation over all but the far north of Utah. 


Is there hope in the ensembles?  Not really.  Most members generate an inch or less of snow for Alta-Collins.  A few go for more than that.  If a trough zipping through the jet can strengthen some, maybe that wetter member can verify, but I'm not optimistic. 

The November doldrums are here.  A good period perhaps to go to southern Utah for late fall adventuring, or the Tetons, where the snowpack looks pretty good for November.  Twelve inches of snowpack water equivalent at the Grand Targhee SNOTEL is more than double the median for this time of year. 

No Skiing This Weekend

Between now and late Monday, we are in this sort of bits and pieces pattern, one in which there is strong southwesterly to westerly flow at crest level, but the main moisture plume is to our north.  The Tetons are in the cross hairs and we're on the fringe. 

As a result, we will see some periods of snow and snow showers at upper elevations through Monday afternoon.  These snow and snow showers will add up some, with the average water equivalent produced at Alta-Collins by our downscaled SREF product reaching just over 1.5 inches by Monday afternoon (07/00Z). 

Most members are between about 0.5 and 2.0 inches of water, which would probably be anywhere from 5 to 20 inches of snow at these temperatures.  There's an outside chance that we'd do better if the orographics kick in or the plume drifts a bit further south than currently predicted, but my view is that there won't be any skiing this weekend. 

It's worth taking a look at the broader regional picture.  Note in particular that the highest water equivalents forecast by our downscaled SREF product through Friday afternoon are found in the mountains of eastern Idaho and western Montana, including the Tetons and Wind Rivers. 

The plume diagram for Rendezvous Bowl at Jackson Hole Mountain Resort is tightly clustered, with a range of accumulations of about 1.5 to 3 inches from midnight last night through the forecast period.  Much of this precipitation falls by late tomorrow afternoon.   
A break is likely after Monday.  There are hints of the potential for more action later next week, but it's too far out to waste energy on at this time. 

Typhoon Lan Has It In for Utah Skiers

Typhoon Lan has been rampaging in the western Pacific, reaching a maximum intensity of category 4 on the Saffir-Simpson scale.  It made landfall early Monday morning (local time) in Japan, southwest of Tokyo.  Some spectacular photos of LAN were taken from the International Space Station.

Although half a world away, Lan will have some dramatic influences on the upper-level flow and unfortunately has it in for Utah skiers.

The image below shows the situation at 1200 UTC 21 October (0600 MDT Saturday) when LAN was still south of Japan.  Sea level pressure contours are colored (cooler colors indicate lower pressure) and 500 mb (upper-level) height contours black.  At this time, the upper-level flow over the mid-latitude north Pacific was primarily zonal, meaning from west to east, with a broad trough over the high-latitude North Pacific and Bering Sea. 


Lan struck its first blow for Utah skiers as it moved northward and across Japan.  During this period, the northward transport of tropical warmth and moisture, combined with condensational warming near and ahead of the system, built a ridge over the western pacific and perturbed the midlatitude flow, which quickly broke down across the entire Pacific basin.  At 0000 UTC 23 October (1800 MDT Sunday), a broad ridge was amplifying upstream of Utah, deflecting Pacific moisture to our north with just a few high clouds spilling across our area. 


Blow two comes as Lan undergoes extratropical transition and explosively develops as a midlaitude cyclone off the Kamchatka Peninsula.  This encourages further amplification of the large scale flow, which by 0600 UTC 24 October (0000 MDT Tuesday) features a high-amplitude trough along the entire US west coast. 


Thus, the beautiful fall weather we will experience in Utah this week comes from Russia with love.  Beware in California, however, as Diablo and Santa Ana winds are possible.

But, Lan isn't finished yet.  Although she weakens weakens, she continues to drift eastward across the Aleutians where the southward flow ahead of her can link up with that associated with a closed low further south and north of Hawaii. 


This ultimately leads to a new tap of tropical warmth and moisture that connects well into the tropics and reinforces the west coast ridge. 


Here's the whole thing in motion.


So, what does this all mean?  Well, it means we won't be seeing any significant snow around here through the end of October.  It means the start of ski season is officially on hold until November.  And it means you should get that bike tune up you've been putting off because you will be spinning instead of skinning. 

Is this unusual?  Nope.  Disruptions of the midlatitude flow by tropical cyclones are common in the fall. 

Lessons from Orographic "Cumulus Patheticus"

After yesterday's dustpocalypse, the weather this morning seems relatively benign, but there's always something to be learned. 

Overnight and early this morning, orographically (i.e., mountain) forced cumulus clouds developed over the Wasatch Range. 



The unofficial name for such shallow cumulus clouds is "cumulus patheticus" as they are pretty wimpy compared to their cumulonimbus (towering clouds associated with rain and thunderstorms) brethren. 

Officially, they are stratocumulus clouds.  In this instance, lifting by the mountains appears to have been essential for their formation.  The GOES 16 satellite image for 1512 UTC (0912 MDT) showed the clouds were confined primarily to very near and downstream of the Wasatch Range, with lee waves generating wave-like clouds further downstream. 


This morning's satellite imagery shows that the clouds were confined to a layer between about 750 mb (about 8000 feet) and 550 mb (about 16,000 feet).  A pronounced stable layer with a base at 550 mb (16,000 feet) prevented penetration to greater heights. 

Source: SPC
The cumulus patheticus did produce some small snow pellets in the Avenues overnight.  I suspect there were a few snow showers in the central Wasatch as well.  

Shallow cumulus clouds like these can produce prolific mountain snowfalls under the right circumstances.  This morning, we appeared to be moisture limited given the large difference between the temperature and the dewpoint at low levels.  This, combined with the stable layer aloft, limited cloud depth and updraft strength.  More moisture at low levels would have likely enabled deeper clouds, stronger updrafts, and more rapid growth of ice crystals.   

Under such a scenario, snowfall rates of two ore three inches an hour are possible if the cloud exists at temperatures favoring the growth of dendrites, those wonderful 6-armed snowflakes that we all love.  


Orographic clouds do not necessarily need to be deep to be prolific snowfall producers, but they do need the right ingredients. 

Think of this the next time you're skiing, it's snowing hard, and yet you can make out the sun when you look up.  

Another Waste of a Trough

Ordinarily, a satellite image like this mornings (below) would get me excited.  There's a cold front over the Pacific Northwest, a deep upper-level trough over the eastern Pacific, and plenty of convection over the eastern Pacific, indicative of cold air. 


Unfortunately, the system has three things going against it.  One is it's moving into the ridge that is parked over the North American interior.  Two is that it's a fast moving system.  And third, there isn't much of a snowpack currently in the Wasatch, so a refresher doesn't do us much good. 

The loop below from the GFS summarizes the first two issues quite well.  Note the weakening of the trough as it moves into the western US and the associated precipitation falls apart and moves quickly across northern Utah. 


Our downscaled SREF forecasts for Alta show most members generating under 0.3" of water tomorrow (Friday) and tomorrow night.  0.7" is the upper end.  Most of this precipitation will fall as snow above 8000 feet, but that's still only an inch or two for about half the SREF members, with perhaps up to 6 or 7 inches for the wettest.  I suspect the wet members bring the trough in a little stronger and a bit further south. 

So, this will be another waste of a trough for the Wasatch, not providing enough for turns. 

If you need to feed the habit with a tour, the Grand Targhee SNOTEL appears to have the highest snowpack water equivalent of any SNOTEL site in the contiguous US with 5.4".  The base of the resort looks thin, but the summit web cam looks inviting.  They also look to do much better than us out of this storm.