Wasatch Weather Weenies

If you love the central Wasatch Mountains, you might want to start following or get involved with the Mountain Accord, an initiative that is currently underway to develop a vision for an area spanning from the Wasatch Front to the Wasatch Back.  For more details see mountainaccord.com  or their Get Involved page . Knowledge of current climate and projections for the future are an important part of the Mountain Accord process. Court Strong (University of Utah), Tim Bardsley (Western Water Assessment), and I have been providing guidance and analyses to the Mountain Accord team to assist them in this effort, and I thought I would share some of the key graphs and figures below, as I thought they would be of interest to many readers.   One key point with regards to climate model projections for the Central Wasatch Range.  It's difficult to imagine a situation in which our climate does not warm, barring some dramatic change in volcanic activity, decrease in the outpu...

The atmosphere is transitioning into outlier mode this week with the development of a remarkably high amplitude wave pattern at upper levels.  The impacts of this anomalous pattern are already being felt in the western United States. The loop below shows the development of the high amplitude pattern over the past couple of days.  Note the amplifying upper-level ridge along the US West coast (black 500-mb height contours) and the strong high pressure system forming at the surface and eventually centered near the ID–MT boarder (color sea level pressure contours). This pattern is already having a major impact on southern California with the resulting pressure gradient driving strong Santa Anna winds. The strongest winds I've been able to find thus far are at Sill Hill at 3556 ft east of San Diego with a peak gust of just over 80 mph. Given the drought conditions present over California, let's hope that they escape this event without any fires. The ridge is expe...

I love it when a band comes together.   Lake-band panorama taken looking south (left) to northwest (right).  Click to enlarge. The view from space, showing the narrow, isolated nature of the band Source: College of DuPage The loop below shows the development.  Note in particular the surge of northerly or northeasterly flow along the northern Wasatch Front and into the North Salt Lake City/Bountiful Area as the band forms.  What is chicken and what is egg is unclear, but we have seen similar surges in other events, but don't understand their cause or their role in lake-effect events.  Click to enlarge

I wrote the previous post Korn Killer yesterday afternoon thinking it would be a good segue into a week in which we would see gradually rising temperatures and the eventual emergence of dust on the snowpack.  That's going to happen eventually, but it's going to take a bit longer thanks to last night's storm. Let me start this post by saying this morning could provide some of the best powder turns of the year.  Whether you are at Snowbird or in the backcountry, the snow this morning will probably be sublime at upper elevations and you probably have the whole mountain (or mountain range) to yourself.  All I can say is curses to you and the skins you climbed in on.  Yeah, I'm jealous.  Powder is fun, but late season powder is such a treat. Here's what's going on.  Alta-Collins got 11 inches of snow overnight.  Then, a lake band exploded shortly after 8 am this morning.  Check out the evolution in the radar loop below. The transition from a ...

Last week we experienced a couple of dust events that are going to have a significant impact on the melt of our snowpack this spring.   The first occurred late Tuesday when strong south winds produced a plume that extended from the Sevier Lake Bed to the Salt Lake Valley.  Satellite image source: College of DuPage Dust in the eastern Salt Lake Valley and Wasatch Mountains was thickest just ahead of, during, and immediately following the cold frontal passage.  The post frontal dust may have originated to the west.  In any event, the visibility at the Salt Lake airport dropped to 1/4 mile and PM2.5 concentrations reached 149 ug/m3, higher than achieved during wintertime inversions the past two years.  Nasty stuff.  The dust was followed by a relatively small storm on Tuesday night, but with a bit of wind to blow the snow around, plenty of dust-covered chocolate snow remained unburied at Alta on Wednesday. Photo courtesy Will Farr Then we had ...

Source: Alta.com It's looking Cascadian in the upper elevations of the Wasatch today.  Through 9 am, Alta-Collins has a storm total of 7 inches with 0.98 inches of water. Yeah, that's 14%, but it is fresh and it is late April.   With a trough passage this afternoon shifting winds to northwesterly and bringing in cooler weather, one might find some decent turns tomorrow morning.  Get up early and get high (I'm referring to altitude—this is Utah, not Colorado).

Following up on this morning's post , I thought I'd show that the HRRR is doing quite well for this event.  Below is the "analysis" for 2035 UTC (0235 PM MDT).  I've added a blue line showing a somewhat convoluted leading edge to the southerlies (note that I've ignored mountaintop obs for this analysis).  The southerlies have entered the southern portion of the Dugway Proving Grounds, have met the Great Salt Lake Breeze in the northern Tooele Valley, and have penetrated into the western Salt Lake Valley.  Note that the flow in the eastern Valley is either light southerly, easterly, or northwesterly. The HRRR image I have from this morning's forecast is technically for 2130 UTC (55 min later), but still is a remarkably good forecast, especially with regards to the strong southerlies pushing northward into the Tooele Valley and western Salt Lake Valley. The one quibble one might mike is that the surge of southerlies might have been a bit slow compa...

Yesterday's post discussed some of the uncertainty in the forecast for today (Friday) and Saturday.  At issue for today was the position of the trough that was expected to develop over the Great Basin and extend downstream from the Sierra Nevada into northwest Utah. Currently, that trough is located to the south of the Salt Lake Valley with northerly flow evident across much of northern Utah.  It is difficult to nail down the precise position during the early morning hours when shallow cold pools and drainage flows in the valley obscure the large-scale wind direction, but if I had to give my best guess I would probably put it somewhere in Utah county. That's a bit south of where the models had it yesterday, but as I said, this was an event where one needed to recognize there was uncertainty in the forecast trough position. Now I want to share with you some amazing images from a new forecast model called the High Resolution Rapid Refresh, known as the HRRR (pronounced...

Another spring storm will impact the Salt Lake Valley on Friday and Saturday, but unlike the one we "enjoyed" on Tuesday and Tuesday night, I'm less certain how this one will play out. The Tuesday/Tuesday night storm featured an upper-level trough preceded by flow from the south-southwest to southwest (lower left panel below).  The interaction of that flow with the high Sierra results in a trough that extends from the Sierra to northeast Nevada, well to the west of Salt Lake City and environs (lower right). As a result, we could be confident that we would be in the strong southerly flow ahead of the storm on Tuesday and that there would be a good chance that we'd see blowing dust, as noted prior to the event on Monday .  In addition, the upper-level trough was moving quickly to the east, so that precipitation would wind down fairly quickly after the cooler air moved into northern Utah. In contrast, the storm for for Friday and Saturday features a broader uppe...

Yesterday's Intermountain cold front delivered in spades. Wind Lower-elevation wind gusts of 78 mph in Eureka, 74 in Sherwood Hills, 74 at Diddle Knoll, 73 at Fish Springs, 73 in Lehi, 72 in Tremonton, 72 in Draper, 72 in Wendover (I-80 Milepost 1), and 71 near Magna.  The 72 in Tremonton toppled a couple of semis and occurred just ahead of the cold front. Source: MesoWest The 74 at Diddle Knoll in the West Desert occurred just after frontal passage, although this site had gusts to 70+ both ahead of and following frontal passage. Source: MesoWest.  Note data outage overnight.  I haven't heard of any reports of semis blown over on I-80.  This event, however, never reached the magnitude of the 25 March 2006 event that featured post frontal wind gusts of just over 80 mph.   Dust The previous post illustrates the plume that extended from the Sevier Dry Lake Bed over the Salt Lake Valley.  Online data from the Utah Division of Air Quality ...

Great view of the dust plume that is impacting the Salt Lake Valley ibelow.  The source is the Sevier Dry Lake Bed.  The plume has migrated eastward across the Salt Lake Valley in the past hour as the flow has veered just a bit from S to SSWerly. Satellite image source: College of DuPage Expect to see a spike in PM2.5 concentrations once the plume is over the DAQ sensor at Hawthorne Elementary. At 4:45 PM, the front is over the Great Salt Lake and will be reaching the Salt Lake Valley in the near future.

A remarkably strong Intermountain cold front developed rapidly over Nevada today.  Check out in the loop below how the lines of constant temperature (called isotherms by meteorologists) at 850 mb (about 1500 m in elevation - near valley level) become highly concentrated over eastern Nevada. If zoom in and add surface observations, we can see a temperature drop from 79ºF just west of the Great Salt Lake to 39ºF in Elko.  Unbelievable given that there was very little temperature contrast upstream over western Nevada and northern California. This is a classic example of what I call Intermountain frontogenesis.  Frontogenesis means the birth or intensification of a front.  These fronts tend to develop or intensify over western Nevada as that where confluence between southwesterly flow that wraps round the southern "high Sierra" meets westerly flow that moves across the lower northern Sierra and southern Cascades.  The boundary between these airstreams tend...

Last night was remarkably warm with a minimum temperature of 63ºF at the Salt Lake Airport occurring at about 11 PM.  That's the average high for today. Given that we will be cooler than that this evening, it won't stand as the official minimum for the calendar day.   This morning's sounding shows a surface temperature of 68ºF and about the weakest nocturnal stable layer possible.  Conditions above that stable layer are what meteorologists call "well mixed" to about 500 mb.  As soon as we mix out that shallow stable layer, we're going to see wind gusts picking up in strength.   Source: NWS/Storm Prediction Center Expect a warm, windy day today in advance of an Intermountain cold front that will be intensifying as it approaches northern Utah.  The NAM forecast below shows the front moving into northwest Utah at 3 PM, near ideal timing for maximum frontal intensity.   Winds both ahead of and immediately behind the front should be quit...

I've been waiting all spring for a nasty Intermountain cold frontal passage and it looks like we will get one tomorrow. The GFS shows a whopper of a front moving across Nevada at 1800 UTC (noon) tomorrow.  The Salt Lake Valley is in the strong southerly flow ahead of the front. This looks like a good setup for the usual pre-frontal spring mayhem, including gusty south winds and blowing dust.  The NWS has already issued a high wind watch for the Salt Lake Valley and most of western Utah. The front is expected to sweep across Utah late in the day tomorrow.  The GFS has it just on our door step at 6 PM.  That usually ensures a very healthy drop in temperature. The front will bring rain in it's immediate wake - possibly with some thunder.  Temperatures behind the front drop enough that we could see some bench snow overnight. The GFS is warm enough we'd probably see mostly rain before things let up, whereas the NAM is quite a bit colder.  We'l...