Warm Atmospheric River Event Possible Later This Week

Atmospheric rivers are narrow corridors of strong atmospheric moisture transport, often connected in some way to moisture exported into the midlatitudes from the tropics or the subtropics.  Although Utah sometimes sees the remnants of weakened atmospheric rivers, bonafide atmospheric river conditions in Utah happen only a few times each cool season.

However, we have a shot at one making it to the state Wednesday night and Thursday if model forecasts hold.  The average integrated water vapor transport in forecasts produced by the Global Ensemble Forecast System for 0600 UTC 22 March (0000 MDT Thursday) shows strong values extending from the Pacific Ocean northeastward into Utah.  Values exceeding 250 kg/m/s (outlined by red line) indicate atmospheric river conditions, and most of Utah is covered.

Source: NWS
Two ingredients favor atmospheric river penetration into Utah in these forecasts.  The first is that the atmospheric river is strong on the coast, with integrated water vapor transport values over 750 kg/m/s.  The second is that the flow moves up the lower Colorado River Basin, missing the southern Sierra Nevada and other high terrain features that typically generate precipitation and deplete the water vapor content of airmasses moving into the western interior.

It is still a bit early to discuss details of where, when, and how much precipitation will fall.  Not all atmospheric river events are big precipitation producers in Utah, but some are.  Much depends on the orientation of the atmospheric river, the orientation of the flow relative to major terrain features, and the efficiency of the precipitation processes embedded in the flow.  Also important is the duration of the event.  Right now, it looks like we'll see a warm, humid (by Utah standards) precipitation event developing first in southwest Utah late Wednesday and then in other parts of the state Wednesday night and Thursday.  Until then, enjoy the spring break and monitor forecasts.

A Good Spring Break to Be Nimble

I've been surveying the forecasts for spring break and it is looking like a week where you can do just about anything if you are adaptive and pay attention to forecasts.

I think everyone is well aware that the weekend is for skiing in the Wasatch where the snow continues to pile up.  Alta-Collins got 10 inches overnight and has another 4" through 2 PM.  Between the cloud cover and the low temperatures, the snow should be holding up well on higher elevation north aspects.  Over three inches of water has fallen in the last three days, making this one of the more productive storm cycles of the period.  My advice is that you ski until you drop through the weekend.

Monday is a tougher call and one that you will need to make for yourself.  Good skiing may persist, or you might opt to head south for adventures in southern Utah.  It will be a cool day, but sunny statewide.  Tuesday looks spectacular, with upper-level ridging over the state. 

Wednesday looks to be the warmest day of the week for most of the state, but there's a threat of rain spreading into southwest Utah in the latter part of the day.  It's a bit too early to call that, so if you head south, pay attention to forecasts.

Depending on how things play out, it might be wise to be back in Salt Lake for skiing Thursday when we may see a warm storm.  Altitude will be your friend, as it almost always is so late in the season. 

Bottom line: Ski today and tomorrow.  Monday go with your instincts.  Southern Utah Tuesday, then check the forecast and adjust accordingly. 

Being nimble should allow you to maximize your hedonistic pursuits.  I, on the other hand, will be banished to a conference room in Seattle for the week.  Fortunately, there will be real, craft beer on tap each evening to dull the pain.

California’s "March Miracle" is Not Over

Some call it the "March Miracle"--the large amounts of precipitation and snow that fallen over California the past month.  The Sierra Nevada got hit by 2-5 feet this week alone. And this is a miracle that is not over, with a strong atmospheric river poised to occur over the next week.

Here are snow water equivalent maps (amount of water in the snowpack) from the National Snow Analysis for February 17 and March 17.   A huge increase in both depth and coverage.

The origin of the wet bounty over California was a shift in the large scale atmospheric circulation, with high pressure moving further offshore and persistent troughing (low pressure) developing over the West Coast.   To illustrate, here is mean upper level (500 hPa, about 18,000 ft) heights for March 10-16th. The left shows the heights (analogous to pressure) and the right shows the deviation (or anomaly) from normal.  A trough (low heights) is found right off the West Coast...that is culprit.

Well, this pattern is not going away...and in fact, it will amplify in a few days and our friends in California need to get prepared.  A trough will form west of California with strong southwesterly flow on its south side, which will entrain large amounts of tropical moisture (see map for 11 PM Tuesday below)

As a result, a strong atmospheric river will develop, which will bring tropical moisture into central and southern California (see plot of total moisture in the vertical for 5 PM Tuesday)

How much precipitation will those folks in California enjoy?   Here is the forecast accumulated precipitation over California for the next 7 days from the European Center Model:  up to 6-8 inches in the Sierra Nevada and coastal mountains.

And plenty around southern CA, such as the mountains that surround LA.

 Snowfall?  Up to 3- 4 feet in the Sierra Nevada (see below)

With all the recent snow, the Sierra Nevada snowpack is about 60% of normal.  It will get much closer to normal after the next few weeks.  And the reservoirs, already around 100% of normal, will get topped off for the upcoming dry summer.

The only negative of all this precipitation is that it will encourage the growth of grasses, which can enhance the potential for fire danger next fall after it has dried out.  

Here in the Northwest, our situation will be far less exciting than for California, with much of the big action going south of us.  The 7-day totals show the heaviest precipitation over western Oregon but only light precipitation over the Puget Sound area and the San Juans.

The Truth About Powder Skiing

"The best deep-powder skiing is not found in the lightest snow but rather in snow with enough 'body' to provide good flotation for the running ski."
- Ed LaChapelle, 1962

You can have your bottomless blower pow.  You can rave about pit deep 4%.  You can have it all.  The truth is, those deep, dry days don't provide the best powder skiing.  Give me some Cascade concrete and and put some cold smoke on top of it.  

And that's what we found on sheltered upper-elevation north aspects today. 

What we didn't find were people. We pulled into the White Pine lot at 8:15 and found only two cars in the lot.  Two!  While gearing up, I kept waiting for the yellow lights to start blinking and then the sound of incoming shells as there's no way that there can only be two cars in the lot on a powder day.  

Yet the dream was true.  

Then the day dawned clear, with a postcard view down Little Cottonwood on the climb up.  

After passing a snowshoer near the boundary for the Lone Peak Wilderness, we found no tracks.  None.  Just a hint of a skin track from a couple of souls from yesterday buried under the cold smoke to lead the way.   For hours we broke trail and did laps in perfect powder, not seeing a soul until about 2 PM.  It was like being on a hut trip in interior BC.  Nobody around.  Surfy hero snow with just the right body.  Zipping through well spaced trees as if there was no tomorrow.  Ed LaChapelle skiing. 

I need to get out more during the week.  So few people, so much enjoyment.  Add hero snow and my favorite touring partner, and you have a perfect day.

Gravity waves near Guadalupe Island

GOES-16 Low-level (7.3 µm, left), Mid-level (6.9 µm, center) and Upper-level (6.2 µm, right) Water Vapor images [click to play animation]

GOES-16 Low-level (7.3 µm, left), Mid-level (6.9 µm, center) and Upper-level (6.2 µm, right) Water Vapor images [click to play animation]

GOES-16 (GOES-East) Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images (above) revealed an interesting packet of gravity waves in the vicinity of Guadalupe Island (west of Baja California) on 15 March 2018. The mechanism forcing these waves was not entirely clear, making it a suitable candidate for the “What the heck is this?” blog category.

A similar animation of GOES-16 “Red” Visible (0.64 µm), Mid-level Water Vapor (6.9 µm) and Upper-level Water Vapor (6.2 µm) images (below) did show some smaller-scale waves on Visible imagery within the marine boundary layer stratocumulus cloud field, but they did not appear to exhibit a direct correlation with the higher-altitude waves seen in the Water Vapor imagery. Surface winds were from the northwest at 10-15 knots, as a dissipating cold front was stalled over the region.


GOES-16 “Red” Visible (0.64 µm, left), Mid-level Water Vapor (6.9 µm, center) and Upper-level Water Vapor (6.2 µm, right) images [click to play animation]

A larger-scale view of Mid-level Water Vapor (6.9 µm) images (below) showed that these waves were located to the north of a jet streak axis — denoted by the sharp dry-to-moist gradient (yellow to blue enhancement) stretching from southwest to northeast as it moved over Baja California.

GOES-16 Mid-level (6.9 µm) Water Vapor images [click to play animation]

GOES-16 Mid-level (6.9 µm) Water Vapor images [click to play animation]

GOES-15 (GOES-West) Water Vapor (6.5 µm) images with overlays of upper-tropospheric atmospheric motion vectors and contours of upper-tropospheric divergence (below) indicated that Guadalupe Island was located within the “dry delta” signature often associated with a jet stream break — the inflection point between 2 strong jet streaks within a sharply-curved jet stream. Upper-tropospheric winds were from the west/northwest, with upper-tropospheric convergence seen over the region of the gravity waves.

GOES-15 Water Vapor (6.5 µm) images, with water vapor wind vectors [click to enlarge]

GOES-15 Water Vapor (6.5 µm) images, with atmospheric motion vectors [click to enlarge]

GOES-15 Water Vapor (6.5 µm) images, with contours of upper-tropospheric convergence [click to enlarge]

GOES-15 Water Vapor (6.5 µm) images, with contours of upper-tropospheric convergence [click to enlarge]

An early morning Aqua MODIS Water Vapor (6.7 µm) image with NAM80 contours of 250 hPa wind speed (below) showed the two 90-knot jet streaks on either side of the jet stream break — it could be that speed convergence due to rapidly decelerating air within the exit region of the western jet streak was a possible forcing mechanism of the gravity waves seen on the GOES-16 Water Vapor imagery.

Aqua MODIS Water Vapor (6.7 µm) image, with NAM80 contours of 250 hPa wind speed [click to enlarge]

Aqua MODIS Water Vapor (6.7 µm) image, with NAM80 contours of 250 hPa wind speed [click to enlarge]

Using GLM data to monitor convective development

GOES-16 Band 13 (10.3) “Clean Window” Infrared Imagery, 0815-1400 UTC, and GLM Group Density.

Strong convection developed on 15 March over the Pampas of Argentina and Uruguay, as shown above. Full Disk imagery is available only every 15 minutes, and considerable convective development is possible during the 15 minutes between scans. If a Mesoscale sector with 1-minute imagery is not over convection, Geostationary Lightning Mapper (GLM) data from GOES-16 can be used to monitor convection during the time interval between Full Disk Scans: GLM updates every minute. The 18-minute animation below (from Real Earth) includes 3 Full-Disk images and every-minute updates of GLM Group Density. Group Density between 0700-0715 shows no sign of diminishing.  It should not surprise that cloud-tops continue to expand and cool when the 0715 UTC ABI Imagery appears at the end of the loop.

Note:  When GOES-16 or GOES-17 (GOES-S achieved Geostationary Orbit on 12 March and became GOES-17) are operating under Mode 6 (vs. the present-day Mode 3), Full Disk imagery will be available every ten minutes vs. current fifteen minutes.

GOES-16 Band 13 (10.3) “Clean Window” Infrared Imagery, and GLM Group Density 0658-0717 UTC.

After the Deluge…

Storms have produced some impressive precipitation amounts (water equivalent) for March from yesterday afternoon through this morning.  Some totals through 7-8 AM or so this morning include .78" at the Salt Lake City Airport, just over an inch in Olympus Cove, 1.25" at Spruces, and 1.54" at Alta Collins.  

Sadly, much of that water fell as liquid in the lower to middle elevations.  For example, 0.68 of the 1.54" that fell at Alta Collins fell at temperatures at or above 32ºF.  During that period, snow levels were initially at almost 9000 feet and lowered to about 8000 feet.  They have since dropped to the valley floor and as of about 8 AM, it is snowing at the University of Utah.

At Alta Collins, the automated interval snow-depth sensor suggests about 10 inches of snowfall.  Initially, that snow was probably a mixture of graupel and white sludge, but densities dropped with snow levels overnight, so what is there should be right-side-up.   

Radar imagery shows that the precipitation feature currently producing snow on campus is swinging through and that we will probably see things letting up soon.  

Expect some snow and rain showers today, and maybe even some thunder.  Similarly, the mountains will see periods of snow and don't be surprised if you hear a clap of thunder there too.  It won't be as active as yesterday and thankfully it is much colder.  Hit and miss snow showers, including the band moving through presently, will produce perhaps another 3-5 inches at Alta-Collins through 5 PM.  

It will be interesting to hear how the snow holds up today now that we're into mid-March.  Sunbreaks are welcome in January, but can be caustic this time of year.  South aspects won't last long.  A real challenge for backcountry skiers as we head deeper into spring is that monsters continue to live in the basement on high-north aspects that preserve powder so well.  

Is the Western U.S. Snowpack Declining "Dramatically"?

Last week a paper (Mote et al., 2018)  was published in the journal Climate and Atmospheric Science claiming "dramatic" declines in western U.S snowpack (you can access it here).

The article had all kinds of scary details. The loss in water resources would be "comparable in volume to the West’s largest man-made reservoir, Lake Mead" and the losses would be so great that "new reservoirs cannot be built fast enough to offset the loss of snow storage."

The principal author's (Phil Mote) institution put out a press release that amplified the message, with the lead author noting that:

It is a bigger decline than we had expected,

The media headlined this "dramatic" loss of western snowpack, with hundreds of stories in major outlets around the world, allowing millions of people to learn about the bad news. Here are a few examples. I could show you a hundred more, but you get the point.

But fortunately, the "dramatic" headlines and all the hype are not correct.  

There has been no "dramatic" loss of western snowpack during the past century, but rather a relatively slow, steady decline.  And as I will demonstrate, the scary paper's own research supports a less apocalyptic interpretation.  As does other research in the peer-reviewed literature.

But let's get our terminology down straight.  What does dramatic mean?  Let's look at a typical definition (Oxford)

Since we are not talking about a thespian document, definition (2) is the one we want:  an event or circumstance that is sudden and striking.  Has the trend of snowpack over the western U.S. during the past decades been sudden and striking?

The answer to this question is really important.   Many politicians and activist organizations are claiming that we have experienced a rapid decline in western snowpack driven by global warming.  And an accurate knowledge of snowpack changes is clearly important for making decisions about water resources. And what about the future of western U.S. snowpack?

The Mote et al. paper uses two approaches to evaluate past snowpack changes over the western U.S.  The first is to examine snowpack changes based on direct measurements.  The problem with that approach is that there are only a limited number of stations and the number and distribution of such stations have changed considerably over time.

The second makes use of a snow/hydrology simulation model called VIC (Variable Infiltration Capacity) model, developed by Professor Dennis Lettenmaier of UCLA (and formerly the UW).  This model uses precipitation and temperature inputs (there is a LOT more of these than snowpack measurements) to simulate the changing snowpack.

Below is a figure from the Mote et al paper showing the snowpack (actually the snow-water-equivalent or SWE) over the western U.S. on April 1 each year from 1915 to 2014 using the VIC model approach.  They also fitted a line to the variation over time.  You will note that there is huge amount of variability year to year, with an apparent slow decline in snowpack over the past century.    Specifically, they found a 21% decline over the past century or 2.1% decline per decade.   Hardly seems dramatic.  I should note that April 1 snowpack is a frequently used measure, since in the west snowpack generally peaks around then, and thus April 1 snowpack is a good measure of the water availability for the upcoming warm season.

Now imagine their line was not there.  In fact, you don't have to imagine, I have done it for you!  There doesn't seem to be any decline during the past few decades...if anything, the snowpack seems to be increasing.

In fact, here is the same figure, with only the last 40 years shown.  No decline, dramatic or otherwise is apparent.  Where did that headline come from?

Now a completely independent analysis of long-term snowpack trends over the Northwest U.S. is found in a peer-reviewed paper in the Journal of Climate (A New Look at Snowpack Trends in the Cascade Mountains by Stoelinga et al...found here).   They used a statistical approach to secure the snowpack from temperature, precipitation, and streamflow instead of the physical model (VIC) mentioned above.  But the same general idea.  Their results for 1930 to 2007 are quite similar to those found in the Mote et al (2018) paper, with a 23% decline for the entire period, and increasing snowpack since 1975.  I repeat, increasing.

Furthermore, they went one step further and tried to remove natural variability (like the Pacific Decadal Oscillation) and got the April 1 snowpack trend shown below. Plenty of variability and a very slow decline (16% over the period).  About a 2% decline per decade...similar to  the Mote et al. VIC results.

Nothing large, nothing sudden, nothing dramatic.  2% loss per decade.  No acceleration of snowpack loss.    And as I will explain late, this make perfect sense considering that the Pacific Ocean is just west of us.

But what about snowpack observations over the West?

As noted by Mote et al., there is a major problem using such observations:  the number of measurement sites is small and their numbers and distributions have changes substantially over the past 50 years.  To illustrate, here is a figure from the supplementary material from the Mote et al paper, showing changes in the number of observations for various subregions.  Few observations before 1940 and a major increase in the 60s and 70s.  The numbers have been relatively stable since roughly 1975-1980.

With those issues noted, below is a plot from Mote et al of the observed April 1 snowpack for three western regions: the Cascades, the Rockies, and  California.  The circles are the average snowpack for each region (ignore the red xs and red line...that is for the VIC model which we already covered).  I removed a blue trend line from these figures--I want you to make your own appraisal of the trends.    Specifically, look at the period since 1980, when the observational network as relatively stable.   

It is clear that there is little April 1 snowpack trend in the observations for the last 35 years.  Yes, 2015 has a very poor snowpack...but that was an isolated outlier....for climate studies we must look at the trend...and there simply has not been much of trend.  Just a lot of variability.

As an independent check on the observed trend in April 1 snowpack, research meteorologist Mark Albright, past WA state climatologist, did his own analysis of the April 1 snowpack changes over Oregon, Washington, Idaho, and Montana using the USDA Snotel observing stations.  He considered the period 1984-2017, since the SNOTEL network expanded into the early 1980s.  A seen below, there is virtually no trend over that period (and I might note that 2018 looks like an above-normal year).
Now to beat a dead horse, here is one more observed record of mountain snowpack, one encompassing a very long period (1879-2017):  the snowpack at Donner Summit, high in the Sierra Nevada (this is from the Central Sierra Nevada site associated with the University of California, Berkeley).  The color bars are April 1 snowpack).   More snowpack in the late 1800s, but only a slightly downtrend during the past several decades.

Now you might ask, why has western snowpack been so stable if the earth is warming?  A very good question.

A major part of the answer is that the eastern Pacific has NOT warmed very much and our temperatures are substantially controlled by the eastern Pacific surface temperatures.  To illustrate the lack of warming, here are the surface air temperatures from the NASA/GISS website, showing the trends from 1977-2015.  The eastern Pacific actually cooled during that period.

This pattern is similar to that indicated in climate models driven by increasing CO2.  The Arctic warms up more than anywhere, land warms more quickly than oceans, and eastern oceans generally warm the slowest.

I know that some of you are unhappy with the above analysis, even though the evidence is pretty compelling that the snowpack has not been dramatically reduced the past few decades.  You have heard the constant drumbeat from the media, some activist groups, and a few scientists who should know better.

But before some start calling me names (e.g., climate contrarian or denier) or the Seattle Stranger does another hit piece, or someone complains to my Dean, let me explain that global warming will have major impacts on snowpack during future decades and especially after 2050.  Increasing CO2 will cause increasing warming during the upcoming century that will reduce snowpack substantially.   Some regional climate runs that my group and Professor Eric Salathe completed a few years ago, show major snowpack reductions (see graphic).

But the loss of snowpack during the snowpack has been modest and slow, and certainly not dramatic. And the fact that it has been going on for over a century suggests that part of it is probably natural and not driven by anthropogenically driven increases in greenhouse gases such as CO2.  The planet experienced a cool period (the Little Ice Age) from the 1600s to the late 1800s, that produced more snow over our region.  With the end of the cool period (probably due to natural causes), snowpack has slowly declined.

Scary headlines and claims of dramatic snowpack loss are counterproductive in many ways.   They are clearly not true and thus undermine the credibility of those claiming such losses (activist scientists, politicians, and advocacy organizations).   They can result in poor public policy and infrastructure planning.   They unnecessarily scare people and make them anxious, an increasing problem (two days ago the Seattle Times had a front page article about a UW Bothell class dealing with dealing with anxiety about climate change).

And then there is the moral/ethical dimension.  Scientists and the media must communicate our best understanding of the truth faithfully and not exaggerate/hype to get people to "do the right thing."   As I have learned personally, there is a real cost to telling "inconvenient truths", but society can only make wise decisions if it is provided with unvarnished information based on the best science, and including information about uncertainty.

Another issue regards the press releases of universities and other research institutions.  There is a tendency to go for dramatic headlines and hype to secure the "currency of the realm" for PR people--lots of clicks and attention.   But the contents of the research papers are often distorted in the process.  This was clearly an issue for the Oregon State University press release regarding the Mote et al paper, and it occurs all the time here at the University of Washington and at other instituions.

Finally, the spread of such hyped material says something about the current state of online and print media.  Apparently, few "reporters" bothered to read the paper they were headlining.  Few completed a reality check on the claims.   But they were attracted to the big "dramatic" headline and were happy put out the excessive claims as a way of getting attention and "clicks."  This is  more than an inconvenient truth, but is a challenge for our democracy, since a misinformed public will not make good decisions.

Moisture Changes as viewed in the Cirrus Channel

GOES-16 ABI Band 3 (0.86 µm) Reflectance, hourly from 1632-1932 UTC on 14 March 2018 (Click to enlarge)

Skies were clear over much of the southern Plains on 14 March 2018, as noted in the animation above that shows hourly GOES-16 ABI Channel 3 (0.86 µm) Imagery. Differences in absorption/reflectance between water and land yield excellent discrimination between lakes and land over Oklahoma and adjacent states.  GOES-16 ABI “Cirrus Channel” (Band 4, at 1.38 µm) shows little reflectance in the area over Oklahoma, except where cirrus clouds are present over western Oklahoma.  The rest of Oklahoma is dark because water vapor in the atmosphere is absorbing energy at 1.38 µm. An animation — also at hourly intervals — is shown below.  This uses the default enhancement in AWIPS, with reflectance values between 0 and 50 shown.

GOES-16 ABI Band 4 (1.37 µm) Reflectance, hourly from 1632-1932 UTC on 14 March 2018 with default AWIPS Enhancement (Click to enlarge)

If you alter the Band 4 enhancement to change the bounds from 0-50 (the default) to 0-2 (!), as was done in the animation below showing data every 5 minutes, a gradient in reflectance becomes apparent, and surface features — specifically lakes — over central Oklahoma that are initially present slowly become obscured as the gradient moves to the east. This gradient shows differences in moisture. The atmosphere that is moving into eastern Oklahoma from central Oklahoma is slightly more moist.  (Compare the morning sounding at Amarillo, for example, with a total precipitable water of 0.38″ to the morning sounding at Little Rock, with a total precipitable Water of 0.14″)

GOES-16 ABI Band 4 (1.37 µm) Reflectance, from 1632-1947 UTC on 14 March 2018 with default AWIPS Enhancement modified as described in text (Click to animate)

GOES-16 data includes channel differences and level 2 products that also confirm the slow increase in moisture. The Split Window Difference field, shown below with the default enhancement (Click here to see the same animation with the Grid MidRange Enhanced enhancement), and the Total Precipitable Water, at bottom, show a slow increase in moisture. These increases were above the surface: surface dewpoints in this region (source) were not increasing greatly.

Split Window Difference (10.3 µm – 12.3 µm) from 1632 – 1947 UTC on 14 March (Click to enlarge)

GOES-16 Total Precipitable Water Baseline Product, 1632-1947 UTC on 14 March 2018 (Click to enlarge)

Expect the Unexpected from This Spring Storm

It's worth a look at the combined cloud/radar and NAM cloud/precipitation forecast loop below to get an idea of the lack of organization of precipitation systems forecast to impact the weather of northern Utah over the next 2-3 days.  Note their banded or "blobular" structures.  Blobular is of course a highly scientific word (ha ha) used here to describe cellular features produced by a model that due to it's sparse grid spacing (12-km) is incapable of producing convective storms that look like those of the real world. 

The chaotic nature of those precipitation features means if you are looking for a precise forecast of when and how much it is going to rain or snow over the next couple of days, you've come to the wrong place. 

Let's start with perhaps the easy part: Today.  A combination of instability, strong flow, and vertical wind shear means we will see some showers and thunderstorms this afternoon.  The NAM forecast sounding for 2200 UTC (4 PM MDT) shows 320 Joules/kg of surface Convective Available Potential Energy (CAPE), a measure of how much energy a surface parcel of air would gain if it were lifted vertically through the atmosphere.  Locally, values may be higher.  Although such CAPE values are pretty pathetic for those looking for midwest-type severe storms, but are enough to make things interesting for Utahns.  Strong flow and vertical shear is also indicated in the wind profile. 
As such, the Storm Prediction Center has us in marginal risk of severe thunderstorms in the mid to late afternoon when "thunderstorms will offer the potential for damaging gusts and hail near severe limits." 

Source: NWS
Beyond showers and thunderstorms, expect some gusty south winds today, with the possibility of some blowing dust.  There is no longer snow cover over valleys and basins to our south and west, so dust emissions are possible if the land-surface conditions are favorable and flows are sufficiently strong.  Temperatures today will remain mild, although snow levels may drop locally during stronger showers and thunderstorms and may include large graupel or hail. 

After today, the pattern might best be described as unsettled, which is a nice way of saying there will be precipitation, but where, when, and how much is unclear.  Snow levels will fall overnight and probably be near bench level early tomorrow morning. 

The now somewhat old 0300 UTC initialized SHREF shows a mean of about 1 inch of water total at Alta-Collins by 0000 UTC (6 PM MDT) tomorrow afternoon, but the range is colossal, spanning from about 0.1 to 2 inches. 

Everything will depend on the position and intensity of precipitation features accompanying the system as it swings through. 

Stuff that falls today will likely be of the wet, high-density variety at high elevations, possibly including some big graupel or hail.  A garbage bag might be required at times, especially at mid and lower elevations, which will probably see rain that could turn temporarily frozen precipitation of a "variety of forms" during periods with higher precipitation rates.  Snow levels and densities will drop later tonight. 

A reasonable guess for Alta-Collins would be 7-14 inches from today through 6 PM tomorrow, with more possible if they are lucky enough to get a pounding from one or more of these precipitation features.  Note that I use the scientific term "guess."  Expect the snow to come in fits and starts at times. 

Welcome to spring!