Get it while you can

Man, what a weekend. Yesterday and today were probably the best snow conditions of the year, with storm totals finally tapering off over 2 feet for the upper Cottonwoods, cold dry powder, and a snowpack deep enough to cover most of the rocks.

Get it while you can though, cause a warming trend starts tomorrow (Tuesday) and there aren’t any more good storms lined up in the near future. You can see this below in the time-height diagram from today’s 12Z run of the GFS below:

Screen Shot 2018-03-05 at 7.09.58 PM
Time-height cross section from the GFS model

Highs today were in the upper teens/lower 20s in the mountains, but they will rise into the upper 20s on Tuesday, and the 30s on Wednesday and Thursday. There is a slight cool down and a weak storm forecasted for Thur night/Fri, but the Euro model disagrees with this, delaying any action until late weekend. You can see this in the precip plot below for SLC:

Screen Shot 2018-03-05 at 7.13.50 PM

 

Hopefully these model solutions trend a bit wetter, which is certainly possible that far out. Until then, enjoy the great snow!

 

 

A Deep Sunday (And Free Refills!)

A brief recap and thoughts for this evening – 

Late Saturday night the highly anticipated front finally moved through the Salt Lake Valley, and brought with it copious amounts of snow for all elevations. While all resorts in the central Wasatch faired well, Little Cottonwood canyon was the obvious winner with storm totals of 20”+ since yesterday afternoon.
Here are two of the highest reports I’ve seen:
Alta-Collins Snow Stake (via MesoWest): 21”
Snowbird: 22”
As expected, when powder days occur over the weekend, the traffic becomes a real problem, especially up Big and Little Cottonwood. This morning, if you waited for the canyons to open and sat in the long line of cars, it probably took you several hours to reach your destination. I think its safe to say it was worth the wait, though!

The upper-level low associated with this storm system will linger over the intermountain west through this evening. Some remnant vorticity coupled with strong upward motion should produce some additional snowfall in the higher elevations this evening and into the overnight hours. This vertical motion will result in some crest-level (and higher) instability, resulting in snow showers that could be convective in nature. Think isolated, heavy snow showers rather than a widespread frontal band like we saw last night. Its likely that the upper elevations of the central Wasatch could see an additional 3-5 inches through tomorrow morning, especially the areas favored in northwest flow.

NAM 12Z time-height cross-section via weather.utah.edu
NAM 12Z time-height cross-section via weather.utah.edu

After the departure of this trough, a ridge builds in, bringing sunshine and warming temperatures for your work week. A rather quiescent forecast after the exciting weekend we just had.

In the mean time, get out there and enjoy improved mountain conditions and pleasant bluebird days at your favorite resort!

Snow tonight…Finally!

This storm has been a major headache to forecast.  There has been considerable uncertainty over the last few days as to where the front would stall out.  Initially, it looked like it might stall over the Wasatch and produce huge snow totals.  Then Thursday night and Friday the model consensus began to indicate that the front would make it to the SLC and then retrograde back to northwest Utah.  As I type this, the front is still stalled out in northwest Utah.  This evening it will finally begin to progress to the east.  Around midnight it’ll reach the Wasatch, which is when snow will begin to fall in earnest (we have high confidence in this).

Snow will continue, heavy at times, through tomorrow night as shown by the HRRR:

hrrr_2018030322_ref_slc

By 9AM tomorrow, I’m expecting a general 8-16 inches across the Wasatch.  A moist, NW flow will continue throughout the day tomorrow.  Storm totals should range from 15-25 inches in the mountains, with up to 30 inches in the Cottonwoods.  Enjoy the storm!

In Like a Lion

TGIF! Winds are whipping across much of the state today ahead of a storm that could potentially be the largest snowmaker of the season so far. A cold front is strengthening across the Great Salt Lake as we speak, and will be entering the Salt Lake Valley this afternoon. As Marcel mentioned yesterday, this weekend will feature a one-two punch of snowfall, the first being this afternoon/evening, and the second starting midday Saturday. While I don’t think it will necessarily stop snowing in the mountains between the two major storm components, the second one is definitely stronger.

Current surface conditions show the southerly prefrontal winds over the Salt Lake Valley with a surface cold front over the lake which is headed in our direction. Here’s what it looks like on Mesowest. Note the wind shift around Antelope Island and colder temperatures to the northwest.

1:30 PM surface conditions from Mesowest
1:30 PM surface conditions from Mesowest

And here what the strengthening front looks like from above – note the clouds moving SE across the lake.

Past 12 frames of COD GOES-16 imagery  as of 1:30 PM (http://weather.cod.edu/satrad/exper/?parms=local-Salt_Lake-truecolor-48-0-100-1&checked=map)
Past 12 frames of COD GOES-16 imagery as of 1:30 PM (http://weather.cod.edu/satrad/exper/?parms=local-Salt_Lake-truecolor-48-0-100-1&checked=map)

This afternoon will be exciting in terms of the frontal passage and the start of snow for the weekend, but snowfall by Saturday morning will be small compared to what is to come Saturday evening and overnight into Sunday. I won’t be super detailed, but Saturday afternoon is when the main portion of the low pressure system moves across the area and really pumps up snowfall rates! Here’s what you can expect as you head to the mountains on Saturday morning as well as the projected snow amounts for the entire weekend. You might want to dig out your snorkel for the Cottonwoods on Sunday.

Forecast snow totals through Saturday morning:

  • Cottonwoods: 4-8″
  • Northern Wasatch Mtns: 6-12″
  • Park City Resorts: 3-6″

Forecast storm snow totals through Sunday evening:

  • Cottonwoods: 20-30″
  • Northern Wasatch Mtns: 18-24″
  • Park City Resorts: 10-20″

As always, locally higher amounts are possible. What a treat for our first weekend in March. So as the saying goes, March will be “in like a lion”,  but I’m hoping it isn’t “out like a lamb” and that we get some more great storms this month! Have a great weekend!

-Lucas

Storm to Dump Big Snow in the Wasatch this Weekend

TLDR: Big snow underway as we head into the weekend. It’s another two-punch system with a lot of uncertainty, beginning maybe sometime Friday afternoon, lasting into early Sunday. Most resorts could see a foot or more snowfall, with higher amounts favoring the cottonwoods.

It couldn’t be a better time to dream about the weekend—there’s a lot to unpack for the upcoming storm. So … I’m just going to jump right into it:

The Forecast


General Overview

We’ll see a complicated wave push through between Friday and Sunday this weekend. Complicated, but I think we can break it down to two-ish events. As timelines go…first, the full system pushes south along the Pacific coastline. As it deepens, a smaller wave breaks off, moves east and then northeast across northern UT. That’s Friday.

This is a shortwave
GFS 500 mbar relative vorticity, spanning 11AM MT Thursday to 11AM MT Saturday. This is a wide view of North America, including Alaska and the eastern Pacific. SLC is located below and left of the figure’s center point. Notice the large trough tracking south along the Pacific coast, its axis just passing into Oregon. There’s a small lobe on the system’s eastern side that tracks up through Idaho, Montana, and into SW Canada. That’s Part one. (courtesy tropicaltidbits.com)

Part two, the main trough, hits perhaps late Saturday night into Sunday.

Part Two
GFS 500 mbar relative vorticity, spanning 11AM MT Saturday to 11PM MT Sunday. See the first figure for further orientation. As the lobe associated with Part One moves off, the main trough begins to swing east into the Rockies, bringing us Part Two. (courtesy tropicaltidbits.com)

Breaking the system down into two distinct storms makes it easier to understand what is going on, but I don’t think we’ll be able to distinguish the two as it’s happening. It might easily seem like one big, long storm. Nevertheless, establishing the storm’s parts will clarify some of its finer details.


Details

Next, I’ll give you my thoughts on the timing for each storm, followed with their individual strength, ending with preliminary snow totals.

Timing

Kickoff: Most ensemble members have snowfall beginning Friday morning in the North Wasatch, afternoon further south. Valleys I think will see similar start times. Still, perhaps moderate uncertainty there—a sizeable amount of notoriously skeptical ensemble members doubt the first punch bringing much, until maybe late Friday night.

Shutdown: End times are even less certain: most ensemble members still predict a shutoff between Saturday morning and Sunday evening. Count on cutoff time changing a bit in the next day or so.

Strength

We have low confidence of the strength for each storm over northern UT, and thus a vague idea of overall snow timing. Again, it’s a complicated system.

That said, I’m inclined to trust a weaker first burst and a stronger second storm, and therefore later start times. The latest forecasts seem to trend toward this solution, and we only have about a day to go before the show begins. I think we’ll have a late afternoon Friday kickoff across most of the Wasatch (first north, then south), and a Sunday morning-early afternoon closing.

Amounts

Most models are cranking over an inch of liquid precip across the northern Wasatch, closer to 1.5” in the Cottonwoods. In terms of snowfall amounts, I’d say pretty good confidence of snow totals exceeding a foot at many resorts, with higher totals favoring the cottonwoods, and locally even higher amounts.

First call…maybe 18-24” snow in the cottonwoods, 12-18” in the north Wasatch, 8-12” in the east slopes. At this point, please be flexible with these amounts.


Whoo—that’s all I can think of. A foot, two feet…either way looks like we’re getting hit pretty nicely. I just want to end by suggesting you prepare to check online for avalanche hazards in case you plan to explore the backcountry. A big snow dump like this can make for issues with the snowpack stability.

But…enjoy, and happy skiing.

-marcel

Two More Days

In case you didn’t notice with all the excitement, it snowed last night. Parts of the Cottonwoods got an inch, and I woke up to a skiff on the east bench. It’s always nice to have freshly fallen snow on the ground, even if it’s just a trace.

After last night’s system passed, we had partly cloudy skies. Now that the next storm is approaching, they will start to cloud up. Multiband infrared satellite imagery shows a classic comma cloud draped across the far western United States with some high clouds preceding it near northern Nevada/southern Idaho. I could have used imagery from the old GOES-West satellite to get a better angle, but I’m so stoked for the GOES-S launch tomorrow that I’ll stick with GOES-16. Also the details in the loop are gorgeous. Notice all the small, low clouds over the ocean. This is indicative of how insanely cold this storm is.

Via NOAA
Via NOAA

Likely a surface cold front is underneath where the thickest clouds are in the loop–aka it just came ashore. Before a cold front makes it as far inland as Utah, we’ll have the typical pre-frontal weather that happens here. The wind will blow, and the dust will gather (unless it’s all weighed down by wet right now). This NAM forecast from weather.utah.edu for mountaintop winds shows rocking gusts from the south starting tomorrow afternoon and continuing into Friday. It won’t really be a good time to be on any exposed ridges. There will also be snow showers Thursday afternoon.

NAM12 00Z 2018-03-01 via weather.utah.edu
NAM12 00Z 2018-03-01 via weather.utah.edu

I still can’t get over that gif because it’s so stunning. Like wow. Anyways, the real fun starts Friday afternoon as a cold front finally reaches northern Utah. As per usual, it will come from the northwest and affect the northern Wasatch Front first before moving into Salt Lake and Utah Counties. The timing of the front is somewhat uncertain, but it’s looking more and more like late afternoon. From a meteorological perspective, late afternoon is the most exciting time to have a cold front because then the air mass ahead of the front can warm up during the day. This makes for a storm that packs a wallop, and it often makes for good photos. The timing could fall apart, or it could be cloudy here Friday during the day, so I’m not making any promises. But check the forecast Friday morning and maybe have a camera ready to point northwest.

With the front will come the snow. The way this storm is setting up, however, is that the precipitation band will stall out somewhere near northern Utah. Someone is going to have a good night. The problem is that there is still quite a bit of uncertainty as to who is going to have a bonanza and who is merely going to have a good storm. For example, the 00Z NAM 12 km tonight shows Salt Lake County and the Cottonwoods sitting under heavy precipitation for most of the night. Its forecast would bring a foot of snow to the valley and more to the mountains. However, that model’s 4 km child stalls out the snow band over Box Elder and Cache Counties. That would bring feet to the Wellsville and Bear River Mountains and maybe a foot and a half or so for the Cottonwoods. I’m bringing this up to illustrate the uncertainty that we’re still dealing with two days out.

Via weather.utah.edu
Via weather.utah.edu

Above is an ensemble plot of precipitation at Alta for the next few days. The first storm are the showers Thursday afternoon. Those will bring 3-6″ to the Cottonwoods. For the next part of the storm on Friday, the uncertainty increases. The orange lines and blue lines represent ensemble members that use two different “dynamical cores”, or the piece of the weather model that deals with moving air. What’s important is that the two cores will represent the front differently, and it shows in how the ensemble splits. The orange ARW lines show heavy precipitation in the Cottonwoods Friday evening. If you go to the website and click around you’ll see that the NMB members show a spike like that for sites in Weber County, indicating that it positions the frontal precipitation up there Friday night. Then Saturday during the day a precipitation band forms over the Cottonwoods in both models.

Looking across all the models, two different stories emerge. Story A is that a frontal band sets up across far northern Utah near Weber/Box Elder/Cache counties Friday night. Then the band reforms Saturday and pushes south across Salt Lake County and the Cottonwoods. Out of the 00Z models tonight, this story is supported by the European model, NAM 4km, and SREF NMB members. Story B is that a frontal band sets up across Salt Lake and Davis Counties Friday night. Then the band reforms Saturday and gives the Cottonwoods a second heap of snow. Out of the 00Z models tonight, this story is supported by the GFS, NAM 12km, and SREF ARW members. At this point there’s really no way to know what story is right. Hopefully tomorrow will bring some more clarity, and, either way, it’s going to be a good weekend.

Don’t Count your Chickens Before they Hatch

TLDR

Party cloudy skies with calm winds are expected Wednesday.  Southwesterly winds ramp up Thursday afternoon with snow showers beginning across mountain resorts.  Snow is likely Friday through the weekend with significant accumulations possible. 

Short Term Forecast

Skies will begin to clear out Wednesday afternoon with calm winds and mostly sunny skies expected.  Our next storm system is expected to arrive in Utah Thursday afternoon.  A deep closed low will dig off the coast of the Pacific Northwest Thursday evening into Friday morning.  Southwesterly winds will increase Thursday afternoon with a round of mountain snow showers expected.  Snow shower activity will continue through Friday morning before briefly tapering off ahead of the cold front Friday afternoon.

ecmwf-ens_z500a_namer_4
ECMWF 500 mb ensemble height anomaly for Friday morning. A deep closed low is located just off the coast of the Pacific Northwest. Courtesy of www.tropicaltidbits.com

The main story ahead of the cold front will be strong prefrontal winds on the order of 60-80 mph along ridge lines.  Dust is likely to be kicked up across the deserts in western Utah and will be brought into the Wasatch Front and mountain resorts in the Cottonwoods and surrounding areas.  Along the cold front, there will be the potential for very heavy snowfall as the front lifts an abnormally moist air mass.  The air mass along the frontal boundary is expected to have column integrated water vapor values in the 90-95th percentile for this time of year.  As the front moves into northern Utah, models are suggesting the boundary will stall, allowing for a period of prolonged heavy snowfall.  The main forecast challenge is determining the exact area the boundary will set up.

gfs_pwat_anom_west2_12
GFS total column integrated water vapor anomaly for Friday morning.

Currently, ensemble members are in surprisingly good agreement with the frontal boundary stalling out across northern Utah bringing a period of prolonged heavy snowfall to mountain resorts.  As you can see below, the ensemble members are fairly close to each other generating anywhere from 25″ to 45″ of snowfall.  However, there is still plenty of uncertainty with this system.  If the upper level low moves slightly further to the north or west, the boundary could set up to our west or north, leaving the Wasatch high and dry.

NAEFSPL_CLN2018022712F168
NAEFS ensemble precipitation and snowfall in the Upper Cottonwoods. Courtesy of weather.utah.edu

For now keep monitoring the latest forecasts as there is the potential for one of the biggest snow storms of the year Thursday through Sunday morning.

Long Term Forecast

High pressure will return to the area late Sunday into early next week with mostly sunny skies and warmer temperatures expected.

-Alex

Changes in the weather…

An important component of forecasting is keeping track of how the model forecasts evolve over time. These trends can be imperative to an accurate forecast, and can also help explain a bust. In the case of the significant mid-week storm we were expecting, models have backed off significantly. Largely, this is due to observed conditions not stacking up to modeled conditions, and the models use the observations to adjust and inform the next forecast.

We’re still likely to get some snow, but totals have been cut back quite a bit as the best dynamics are now much further north than the central Wasatch. If there was one figure to sum up my thinking right now, it’s the following:

ECMWF Salt Lake City QPF dProg/dt
ECMWF QPF dProg/dt for Salt Lake City

To explain what we’re looking at – from the top down, the forecast becomes more recent with the bottom row initialized this morning and the top row initialized 120 hours prior. From left to right is 30 hours ago (verification) to 240 hours into the future. The numbers are the precip totals up to that hour, with green < .5″ water, blues < 1″ water, and yellow/orange < 1.5″ water.

What’s important: the midweek storm has been trending drier, from once ~.5″ water to now < 0.1″. Keeping in mind this is a global model that often under-forecasts orographic precip, we are still expecting some snow up high tonight/tomorrow but 1-4″ seems about it.

Next, the weekend storm: what once looked to be a potent system producing over 1″ of water in the valley has weakened quite a bit in the forecasts, and we see this reflected in the QPF trends. There has been a steady decline over the recent ECMWF runs which seems to be leveling out around ~0.5″. This is still far out enough that we could see these numbers vary significantly in the next few runs, so not all hope is lost yet. For the sake of completeness, I’ll include the GFS forecast, which began much lower than the ECMWF and has been trending upward towards the ~0.6″ mark.

GFS QPF dProg/dt for Salt Lake City
GFS QPF dProg/dt for Salt Lake City

Either way, tomorrow will be snowy with a little fluff on top for a refresh, and I have high hopes for another stellar weekend of skiing. Either way, it seems appreciable snow totals are likely for the mountains by Sunday morning. We’ll keep you up to date as the models keep rolling in!

-Mike

The Hits Keep Coming

After all that beautiful low-density powder we had yesterday, the atmosphere gave us a quick break this morning. As I write this around 3pm though, the storm track is quickly reloading. Clouds are thickening up and snowflakes are starting to fall with our next system moving in. And it won’t be the only storm this week…there are at least 2 more lined up behind it! Here’s the breakdown:

Time-height digram from the 12Z GFS model for the upcoming week. The hits keep coming!

Storm # 1 (Sat pm-Sun am)

Snow showers will pick up overnight, with cold temperatures (single digits at the resorts) and more low-density blower powder. The models don’t show this system producing a ton of liquid (0.2-0.6″ of water), but snow-liquid ratios will be high (potentially 20:1) and there is a period of cold northwest flow that will benefit the Cottonwoods. The high-resolution models are also going for a period of lake-effect snow overnight tonight that may add a couple more inches for them as well. With that in mind, I’ll go with 6-12″ of snow for the Cottonwood resorts, with 4-8″ of snow elsewhere.

Screen Shot 2018-02-24 at 3.55.06 PM
Precip amounts from the 12Z run of the ECMWF model for Storm #1

Storm #2 (Mon am-Wed am) 

This systems looks a bit warmer than those we’ve had lately, but still with snow levels at or near the valley floors. It also looks to meander around us for 48 hours, which is good in that it increases the time for snowfall to stack up, but bad in that this increases the uncertainty we have in where and how much snow will fall. Hopefully Trey will have a first stab at snowfall totals for this one tomorrow.

Storm #3 (Thur-Sun)

The uncertainty in the details really increases looking this far out, but it looks pretty likely that we’ll have a storm in this period. It also looks like it could be a good one.

Another Good Storm

It has been quite a good storm today. The roads in the valleys (sans benches) have been clear for the most part, but the snow has been piling up in the mountains. Alta reported 8″ by 4 PM, and it’s still falling (as of 4). The sensor at Alta-Collins picked up 0.4″ of snow water equivalent, which would mean a healthy 20:1 snow ratio. Not quite white smoke, but definitely still good powder.

There are two storms on the immediate horizon. We get a break tonight and through most of the day tomorrow. It should get windier as the day goes on and the clouds will thicken before the next round of snow starts late in the day. There’s a chance for some pre-frontal snow, and the northern Wasatch have a somewhat higher chance of taking advantage of that.

Once the sun goes down snow will be widespread in the mountains, though there is a chance it will be showery in nature. The models have been predicting snowfall totals in the mountains similar to today’s storm, though the fact that it will be a night storm will make roads messier. I’m forecasting 3-5″ in most of the mountains and 5-8″ in the Cottonwoods.

The next storm will be Monday, and, as the image below shows, how it will behave is not yet determined. This ensemble of models shows how with today’s storm (on the far left) and Saturday’s storm all the lines are close together and there is not much known uncertainty. But for Monday’s storm there’s a wide range of known possibilities, and, of course, a large fraction of possible storm outcomes fall outside the ensemble range. This ensemble is predicting anywhere from 0″  to 25″ Sunday night through Monday with a mean of about 10″. I’m hoping it’s a good one to keep up this snowy pattern.

Via weather.utah.edu
Via weather.utah.edu