Wasatch Weather Weenies

I'm pretty blown away (pun intended) by the model forecasts for tonight and tomorrow (Sunday) morning. The 0600 UTC NAM is generating strong easterly flow across the northern Wasatch Front with 700-mb (near crest-level) winds reaching 50 knots in places.  There is also a strong pressure gradient from Evanston to Ogden.  Coming overnight and in the early morning, these are ingredients for a strong downslope wind event. The National Weather Service has issued a high-wind watch for the Cache Valley and northern Wasatch Front for sustained winds between 30 and 40 mph with gusts in excess of 60 and localized gusts in excess of 75 mph in some areas, especially Davis and Weber Counties. Take the time today to secure loose outdoor items if you are in areas affected by these downslope winds and monitor forecasts at  http://www.wrh.noaa.gov/slc/ .

Here's one for you.  When did we have the biggest storm cycle of the ski season?  December?  January? February? Nope. The answer is right now, and it isn't even close.  The chart below shows the running 5-day accumulation of water equivalent at the Snowbird SNOTEL station since October.  In terms of water equivalent, the 5-day accumulated total through today is 4.3 inches.  The next highest is December 25th with 2.8 inches. All I can say is what an event, especially Tuesday and Tuesday night when we picked up 16 inches and about 2.25 inches of water at Alta-Collins.  Although snow was in the forecast, that was impressive. And we got a bit more last night and will get a bit more today.  Note the inexact terms "a bit more."  I'm feeling beaten and battered by these closed lows and their whimsical precipitation patterns.

Source: Rankin-Bass Just when you thought winter was over, it rises from the dead. A whopping 16 inches at Alta-Collins in the last 24 hours has pushed the total snow depth up to 115 inches, the deepest since late March.   That 16 inches contained 2.27 inches of water.  That's a water content of 14%.  Thick and creamy, but I bet anyone out this morning won't be complaining. The pattern remains showery and unpredictable for the next few days, but don't wait.  The best time to get good turns this late in the spring is when it is snowing.  

Although April 1st is commonly used as a key date for Utah snowpack, in the upper elevation north facing terrain in the Wasatch Range, the peak snowpack water equivalent isn't usually reached until late April. It's late April now and the results are clear. It really wasn't a very good snow year. Oh, you probably had some good skiing.  There were a few good stretches and 2015/16 was certainly better than 2014/15, but if we're interested in snowpack at the end of the snow accumulation season, this year fell well short of par. Let's take a look at the Snowbird SNOTEL.  Median (magenta line) and average (blue line) snowpack water equivalent both peak in late April at about 44 inches. In contrast, this year (green line) we peaked around April Fools Day at about 34 inches and subsequently lost several inches of water equivalent due to an early ripening and melting of the snowpack.  April is the new May, at least this year. What's that you say?  It snowe...

As far as closing days at Alta go, today was Cascadian, and there's nothing wrong with a baker's dozen (13 inches) of creamy crud in late April. I haven't skied at the resorts much this year, so we tried to make up for it by skiing the crud hard in the morning and enjoying the scenery, including this beautiful pileus cloud. My son Erik made his college decision yesterday.  He was accepted to a number of great schools, but will be attending the U and skiing the Greatest Snow on Earth next year.   Today confirmed it was the right choice (as will the reasonable tuition bill and high quality eduction he'll get the next few years).  No, he's not majoring in meteorology! He really made my day when he woke up and asked me if I wanted to ski with him today.  Such days are priceless. It was very apparent today that the student has become the teacher.  The kid can really outcharge me now.  Old age hasn't helped, but really, he's just better than m...

Dust is now obscuring South Oquirrhs #utwx pic.twitter.com/BNh9VMzyhM — Jim Steenburgh (@ProfessorPowder) April 22, 2016

The sun has risen on a day that I awake feeling strangely conflicted by an emotional mix of Earth Day cynicism, meteorological optimism, and scientific excitement.  A few reasons why in rapid-fire mode: Earth Day: So What?   Sorry to be a cynic, but I don't think Earth Day has accomplished much.  It should be retired.  I'm not against what it stands for in any way, shape, or form, but we spend too much time discussing simple things that we can do to reduce our carbon footprint.  Youngsters out there – you can think much bigger and do what my generation couldn't. Passing of Prince Although I never was a big fan, I came of age when Prince truly was a mega star and we tip the hat to him today for Purple Rain.  It's always great to see hydrometeors referenced in album and movie titles.   Wind and Dust? We should see some south winds today and possibly some blowing dust around the state.  The frontal timing isn't quite right for a rea...

As far as dust storms go, this past cool season has been pretty quiet.  We've had a few minor events, but nothing significant, and the Wasatch snow cover remains fairly white and relatively snirt free (snirt = part snow part dirt, the dirt meaning dust). The lack of dust so late into the spring is fairly unusual.  Estimates of total dust flux at the Salt Lake City international airport show a pronounced peak in April. Source: Steenburgh et al. (2012) What's been missing this year are strong south wind events that can tap into dust emission sources in southwest Utah.  We simply haven't had them, but that's about to change. With the approach of an upper-level trough, we will see the development of south winds tomorrow.  The 1200 UTC NAM forecast valid at 0000 UTC 23 April (6 PM MDT Friday Afternoon) shows the upper-level trough over northern California with 30–40 knot SSW 700 mb (10,000 ft) winds and 15–25 knot SSW surface winds over western Utah. The sit...

Data released yesterday by the National Centers for Environmental Information shows that 2016 got off to a sizzling start, with global temperature anomalies for January through March blowing away anything previously seen in the instrumented record. In terms of raw numbers January through March of 2016 was 2.1ºF warmer than the 20th century average and a whopping 0.5ºF warmer than the same period in 2015. With El Nino weakening and the and an increasing chance of La Nina developing later this calendar year, I have been wondering if 2016 would be warmer than 2015, but the numbers for January through March are so far off the scale that it's looking likely 2016 will set another new record. We've climbed another step on the global warming staircase.

A remarkable global snow climatology has recently been developed by scientists from the Space Science and Engineering Center (SSEC) at the University of Wisconsin–Madison (see Kulie et al. 2016 ; access to full article may be paywalled unless you or your institution are subscribers to the American Meteorological Society Journals).   Producing such a climatology is a major challenge.  Reliable snow observations are fairly limited over land, especially in the high latitudes, and nearly non existent over the oceans.  Thus, Kulie et al. (2016) take advantage of the cloud profiling radar on NASA's CloudSat satellite to develop their climatology.  The CloudSat profiling radar has a wavelength of only 3.2 mm, much smaller than the 3 to 10 cm wavelength commonly used for traditional weather radars.  This makes the radar more sensitive to smaller cloud droplets and ice crystals.   The Kulie et al. climatology incorporates CloudSat observations from June ...

The atmosphere is well into outlier mode over North America at present, contributing to high-impact weather over portions of the United States. The situation over the past couple of days is highlighted below.  A slow moving closed-low over the U.S. southwest is sandwiched between ridges along the west coast and over the eastern U.S. High-impact weather associated with this pattern includes a major snowstorm along Colorado's Front Range on April 16 and 17.   Snowfall totals reached over 4 feet in the foothills west of Denver. Source: NWS Denver/Boulder The big winner in preliminary reports appears to be Pinecliffe in the foothills southeast of Boulder where a trained spotter reports 51.3 inches with a water content of 3.55 inches. This morning, flooding is affecting the Greater Houston Area where as of this morning as much as 15 inches of rain has fallen in the past 24 hours. Source: Harris County Flood Warning System As of 5:20 AM, the Houston ...

It's mid April, winter is over, and of course Colorado's Front Range is getting pounded with snow. The 24-hour snow totals ending this morning show a swath of 30+ inches in the foothills west of Denver.  Add another 10 inches or so to that for the 2-day storm totals in that area. In the mountains, Loveland Pass is reporting a 48 hour snow total of 32 inches, Winter Park 24 inches, and Arapahoe Basin 25 inches (the latter is a 3-day total, but probably most fell in the last 48). This late-season snowfall is not unusual for the Front Range.  For sites near and east of the Continental Divide, March and April are the snowiest months climatologically.  For example, at Nederland west of Boulder (period of record 1970-1988), the monthly mean snowfall in March and April is 23.9 and 24.3 inches, respectively, compared with 13.3 and 13.1 in January and February.  At Berthoud Pass (period of record 1950–1985, the monthly mean snowfall in March and April is 57.9 and 54....

I had a Maalox moment around noon yesterday having issued a fairly confident forecast for 2-5" of upper-elevation snow only to see things explode in the southwesterly flow and produce some remarkable precipitation rates in upper Little Cottonwood (see prior post Big Water Amounts ). The Alta-Collins precipitation trace below tells the story.  For the 1-hour periods ending at 11 AM and 12 PM MST, water equivalents were 0.36 and 0.39 inches, respectively.  The 0.75 inches of water equivalent in that period was over half of the 1.4" that fell yesterday. I don't have a careful analysis to back this up, but during the cool season (Oct-Mar), I water equivalent precipitation rates of 0.3" per hour are about as high as they get at Alta.  I usually associate such precipitation rates with warm atmospheric-river events.  To get two hours > 0.3"/hr is quite impressive, although there is greater potential for larger water equivalent rates in the warmer storms of Ap...

For the last 2-3 hours, precipitation rates in Little Cottonwood Canyon have been exceptionally high.  During the cool season, it is quite unusual for snow water equivalents to exceed 0.3" an hour, but Alta-Collins reported 0.36" for the hour ending at 11 AM MDT and 0.39" for the hour ending at 12 PM MDT (ignore the 34" snow interval ob which is bad). These numbers are consistent with those measured at the Snowbird SNOTEL station, so water equivalent rates of .3" or more per hour seem likely. Radar imagery over and upstream of Little Cottonwood showed frequent initiation of radar echoes in central and Utah County extending downtream over the Wasatch Range.  These echoes have gotten more cellular and intense in the last few frames. At low elevation, all of this wonderful water has gone to waste.  The UDOT camera at the White Pine Parking lot (~7500 ft) shows just a hint of snow sticking here and there.  Nearly all rain here so far. At high eleva...

It's not quite the equivalent of Groundhog Day The Movie this morning, but it's close. As was the case yesterday, a frontal boundary and precipitation band are flirting with northern Utah.  The main difference is that they are a bit further north this morning than yesterday. The large-scale analysis from 1400 UTC shows a pronounced 850 mb (~1500 m/5000 ft) wind shift extending across central Nevada and northern Utah, including the Great Salt Lake, with a band of precipitation just to the north. MesoWest surface observations similarly show the wind shift extending through Dugway Proving Ground, across the Great Salt Lake, to north Ogden. Although we are south of the front this morning, temperatures are pretty similar to yesterday morning and in the mid 50s.  If you are outside and not paying attention to which way the wind is blowing, you will hardly notice a difference. The 1200 UTC initialize HRRR model  calls for the front and precipitation to push into ...

In Monday's post, I mentioned that on or about Tax Day we often get some interesting weather in northern Utah.  Well, change is here.  It's not too exciting by spring standards, but it is something to talk about.   This morning a surface cold front pushed through the Salt Lake Valley bringing a few showers.  As I write this, at about 11:45 AM MDT, the front sits right at Point of the Mountain.  North winds with temperatures in the 50s predominate the Salt Lake Valley, whereas in the Utah Valley, one finds south winds and temperatures in the 60s.  Perhaps the weather down there is nice, but BYU still sucks. The frontal precipitation band is just to our north, resulting in more frequent shower activity along the northern Wasatch Front, with the Salt Lake Valley getting the occasional brush by shower.   For today, I'd expect some frontal "wobbling" and more precipitation to the north, but still a chance of showers and thunderstorms for t...

Two quick tidbits today as we wait for some meteorological action on Thursday. New Book University of Utah Emeritus Professor of Geology and Geophysics Bill Parry has a new book out entitled Geology of Utah's Mountains, Peaks, and Plateaus . Although I haven't read it yet, I've skimmed it and it looks like a good one for Wasatch Weather Weenies readers.  You can pick up electronic, paperback, or hard cover versions here . Seminar Stanford Associate Professor of Earth System Science Noah Diffenbaugh will be giving the Global Change and Sustainability Center seminar next Tuesday, April 19, in 210 ASB on the University of Utah campus.  The seminar seeks to better understand how global warming affects extreme climate events.

If you are a meteorologist in Utah, there are few days on the calendar as fun as tax day. It seems like something exciting happens every year on or about April 15, and there are good reasons for it.  April 15 lies at the beginning of the Intermountain cyclone season, which spans from April to early June and frequently features the development of strong troughs or low pressure systems over the Great Basin downstream of the Sierra Nevada.  Such systems frequently bring strong winds and blowing dust.  April 15 also lies in the heart of the wettest month climatologically in Salt Lake, with April averaging a whopping 2.10 inches of precipitation, good for big storms.  Finally, April 15 is in the middle of the transition from winter to summer and we can get some extremely large temperature swings in April and everything from deluges to dumps.  If you don't like the weather in April, wait 5 minutes. Perhaps the biggest and baddest example of extreme weather on Apri...

Strong easterly winds (photo taking looking north) this morning in the Avenues foothills Easterly downslopes winds are creating blustery conditions along the east bench and on the University of Utah campus this morning.  Observations at about 8 AM showed strong esterly flow from Parley's canyon north with gusts to 31 in the Avenues, 35 on campus, and 39 at the mouth of Parleys (annotated numbers below are current wind gusts in mph).  Winds are stronger along the east bench than in the canyons and most upper-elevation bench locations.  There is also clear evidence of a rotor near the Salt Lake City International Airport.  Note how the easterlies extend to downtown, but the flow at the airport is westerly, as depicted below. Source: Whiteman (2000) Rotors sometimes feature sub-rotors (smaller-scale circulation centers embedded in the larger-scale rotor), strong wind shear, and turbulence.  I've often wondered if the airport is just far enough west t...

Thermally driven flows are produced by spatial variations in heating and cooling associated with topographic and land-surface contrasts.  Examples include sea and land breezes, up- and down-valley flows, and up- and down-slope flows. During the day, one typically expects up valley and up slope flows in areas of complex terrain, whereas at night and in the morning, one expects down valley and down slope flows. Schematics of thermally driven flows from Whiteman (2000) Within narrow valleys, the up- and down-valley flows usually dominate the slope flows once the former are fully developed, such as is found in the late afternoon or early morning. However, those generalizations apply to situations where the local forcings dominate and the larger-scale flows have little influence.  One can find many examples where the flows in canyons and along slopes deviate from what one would expect from local forcings.  One such example is lower City Creek Canyon. If you fr...

Although the wintertime PM2.5 period is now past us, a number of you have asked how much the air quality varies with elevation in the Salt Lake Valley.  I'll answer this question like a scientist.   It depends . First, let me note that the best situation for knowing the air quality before you recreate or go outside is to have high-quality real-time monitoring at many locations across the Salt Lake Valley.  The Division of Air Quality does not provide this.  We get data in real time (usually an hourly average with a bit of a delay) from Hawthorne Elementary and that is it.  The air quality can, of course, be considerably different in other areas of the valley. The University of Utah has recently installed sensors at a few locations as well as on TRAX trains, which helped during this past winter.  There is also the grassroots purpleair.org network.  Overall, these sensors helped last winter, but the coverage remains incomplete and we still still nee...