Wasatch Weather Weenies

I've ran out of fingers and toes to count, so thankfully the alta.com snow report states that the storm total as of 4 AM this morning reached 67".  I'm not sure when they started that tally, but suffice to say the past few days have been pretty huge.  A reminder though that this is not unprecedented.  During Thanksgiving weekend 2001, Alta got 100 inches in 100 hours. The end of this storm cycle is, however, nigh.  Currently we're still seeing snow showers in the northwesterly flow over the Oquirrhs, Salt Lake Valley, and central Wasatch. Source: NCAR/RAL Overnight, this led to about 9 inches of snow since 5 PM yesterday. Source: MesoWest It's low-density stuff and on the heavier snow that fell yesterday, should be right-side up and ski well. The models suggest that we will see a break after this morning.  The NAM time height for Salt Lake City shows significant drying out of the lower atmosphere after about 1800 UTC (1100 MST). Sunday should...

Skiers, snowboarders, and snow lovers have much to be thankful for this Thanksgiving.  Twenty-four hour snow totals reported by the ski resorts this Thanksgiving morning include 22" at Powder Mountain, 23" at Snowbasin, 19" at Brighton, 17" at Alta, 15" at Snowbird and Solitude, 7" at Deer Valley, and 4" at Park City.  I'm a little surprised the totals on the Wasatch Back aren't higher as the flow has been persistently southerly to southeasterly at upper levels and they did well earlier in the storm.  Perhaps the position of the precipitation band was a bit too far west.  The snow depth sensor at the Thaynes Canyon SNOTEL is indeed consistent with the totals reported by the resorts, showing an increase from Tuesday to about 21 inches this morning. Source: MesoWest As I type this, the Utah Avalanche Center has not yet updated their forecast for the Salt Lake Area Mountains, but they did issue a  backcountry avalanche warning this morning...

Storm 1 is in the bag.  Total snowfall at Alta-Collins was 9-11 inches depending on how you read the automated depth sensors.  The resort is reporting 11", which is consistent with measurements collected on the interval board, which reached 5" at 1700 MST, when the board was wiped, and then peaked again at 6" at 2200 MST.  Source: MesoWest Most of the snow that fell during the day yesterday was associated with the front.  From about 1700-2200 MST, post-frontal pixie dust fell with a water content of only 3.5%, adding up to 6" of snow with only .21" of water.  Good for chin ticklers and face shots, although our priority right now should be base.  During this period of bone-dry snow radar imagery showed the strongest echoes confined to over the central Wasatch west of the Wasatch crest.  Source: NCAR/RAL The overnight post-frontal period was largely quiet, although a little lake and possibly playa effect got going toward morning (more on this...

A few of the students here have commented on how "jumpy" the model forecasts have been for the post-frontal period later today, tonight, and tomorrow morning.  To illustrate this, the loop below shows a succession of downscaled NAM 6-hour snowfall forecasts for northern Utah beginning with the 84 hour forecast and ending with the 24 hour forecast, all valid at 1200 UTC 26 November (0500 MST Tuesday). You can see quite well that the location and intensity of the snowfall during the period is quite variable.  In the last three forecasts, there is a bit of "convergence" toward a solution that has a band of snowfall extending from southeast Wyoming across Salt Lake County.  However, the amount of snowfall varies from run to run, with some evidence of a drying trend.  All of this is evident of the chaotic nature of precipitation and snowfall in the post-frontal environment.  There is a lot of sensitivity to the initial conditions given the model....

OMG, my cup runneth over.  So much weather and so little time.  I know you are interested in mountain snow, but it is necessary this morning to look to the west at the forecast of a truly remarkable cyclogenesis event.  In some respects, this is the storm that "stirs the drink" for the weather that follows. The GFS forecast loop below shows the development of the cyclone off the Pacific Northwest coast.  It forms along the pre-existing warm front associated with a parent cyclone south of the Aleutian Islands as an upper-level trough (indicated by color fill) approaches from the west.   GFS forecast loop of sea level pressure (black contours), 925 mb temperature (red contours), and dynamic tropopause pressure (color fill) Deepening rates are quite remarkable and consistent with "bomb" cyclone classification (i.e., > 24 mb in 14 h or 18 mb in 12 h).  Central pressures fall 25 mb in 12 hours, 35 mb in 18 hours, and 40 mb in 24 hours for the p...

All is quiet on the western front this morning as Saturday dawns with clear skies.  It should be a nice weekend for whatever you have planned as Sunday also looks nice, although there could be high clouds in the afternoon. The coming holiday week looks wild as two complex systems affect the weather and are sure to keep meteorologists, skiers, and travelers on their toes. The first is a surface cold front that is expected to move across northern Utah Monday.  Snow levels will be dropping to the valley floor by Monday afternoon and there is a prolonged period of moist, unstable northwesterly flow in its wake with the potential for orographic (i.e., mountain induced) and lake-effect snow showers.  Through Tuesday morning, the 6Z NAM produced 0.29" of water and 7" of snow at Alta, whereas the GFS was quite excited with 0.81" of water and 17" of snow.  Such is the way it is in the "post-frontal" crap shoot given the fickle nature of orographic and...

The North American Ensemble Forecast System (NAEFS) includes forecasts from the Canadian Global Ensemble Forecast System (hereafter the "Canadian Ensemble") and the U.S. Global Ensemble Forecast System (hereafter the GEFS).  At weather.utah.edu, we take these low-resolution forecasts and downscale them based on climatological precipitation distributions to produce higher resolution forecast guidance for the western continental United States. Users of this forecast guidance and readers of this blog are likely aware that one or more members of the downscaled Canadian ensemble occasionally produce extreme and sometimes non-physical precipitation accumulations (water equivalent and snowfall).  One of the more extreme examples occurred last night when one of the downscaled Canadian ensemble forecasts generated 8 inches of water and nearly 140 inches of snow for Alta, including an unrealistically large 5 inches of water and 80 inches of snow in about 24 hours (Canadian ensemble m...

Precipitation analyses for the 30-day period ending yesterday at 1200 UTC (0500 MDT) show that northern Utah has clearly gotten the shaft.  Totals are highest across the far northwest, dropping down through Wyoming and Colorado.  To our south, this week's storm has even given them something.  Source: NWS Things may, however, be changing for Thanksgiving week as there is a shift in the large-scale pattern expected to begin later this weekend into early next week.  GEFS forecasts valid 0000 UTC 26 November (1700 MDT Monday) predominantly favor a trough  over the west.   As do most (but not all) forecasts valid 1200 UTC 27 November (0500 MDT Wednesday).  Source: Penn State E-Wall Thus, at a minimum, cooler, possibly much cooler temperatures are likely to prevail next week.  It is also likely that we will see some mountain and possibly some valley snow.  When one here's the phrase "pattern change" there is a tendency to get...

Tomorrow is a very difficult forecast day due to the fact that we have multiple systems potentially affecting the weather of northern Utah.  The NAM forecast valid 2100 UTC (2 PM MST) Tuesday shows a complex upper-level pattern with a 500-mb closed low over southern California with an inverted trough extending through Nevada and connecting with a trough in the westerlies over southern California (500-mb contours and wind barbs in black below).  A short-wave trough is moving through northern utah with southwesterly flow south of the Great Salt Lake and southerly flow over southern Idaho.  Meanwhile, at low levels, high pressure is pushing through Wyoming (sea level pressure color contours below).  Because of that high pressure,  low level winds forecast by the NAM over southwest Wyoming are easterly, and northeasterly, with flow splitting apparent where the cold air impinges on the Uinta Mountains.  The resulting easterly branch pushes across the Wasa...

We're now in mid November, so the time is ripe for taking a look at the snowpack across the western U.S. In terms of the percentage of median snow-water equivalent as of November 17, a pronounced dipole pattern exists across the western U.S. with most stations near or above median near and east of the Continental Divide and most stations further west below median.  The pattern is a strong one with many stations east of the divide well above median and many west of the divide well below median.  Source: NRCS Percent of median can be a somewhat misleading indicator of snowpack robustness since much depends on the station's snowpack climatology.  Many of the stations east of the Continental Divide are relatively dry, and thus 200% of median this time of year doesn't necessarily mean a lot of snow.  If we look at the actual snowpack water equivalent, there are no sites that have crested the coveted 10" mark.  The highest values I could find were in the Lewis ...