Wasatch Weather Weenies

Apparently the phrase "dog days of summer" originates with the Greeks and Romans, who recognized that the hottest, most miserable part of the summer occurred in late July when the constellation Sirius rises along-side the sun in Late July.   However, the Greeks and Romans didn't live in Salt Lake City in the 21st century when the dog days just seem to go on and on.   Really, late July is climatologically the hottest part of the year here and that was the case this year.  The hottest days of the year, in terms of average temperature, were July 17 and July 22 (91.5 and 91.0˚F, respectively).  Given the long nights, we won't be touching that this week or weekend, but it's going to be hot.    Below is the GFS forecast valid 0000 UTC 2 September (6 PM MDT Thursday).  Monsoon moisture is confined mainly to southern Arizona and New Mexico and ridging predominates to our west.  700-mb temperatures at KSLC are around 16–17˚C.  The long-term ...

Brian Schott has an excellent article discussing the Moab flood and some of the problems with the use of phrases like "100 year event" that was published yesterday in the Salt Lake Tribune .  In it, Moab's city engineer, Chuck Williams, does a good job describing some of the concerns about that phrasing and also how prior rainfall set the stage for the event by saturating soils (where they exist in that red rock country).   I'll talk a little here about the precipitation piece of the puzzle.  Below is the  National Severe Storms Laboratory's Multi-Radar Multi-Sensor (MRMS) system 1-hour accumulated precipitation estimate for the period ending at 1:50 UTC 21 August, or 7:50 PM MDT 20 August.  Based on my visual inspection, this was the 1-hour period with the greatest coverage and intensity of precipitation in the Moab area.  Precipitation is heaviest along US-191 and in the Behind the Rocks area to the west, with pixel-level values maximizing at about 1...

As of August 23rd, there have been 25 days with a maximum temperature of 100˚F or higher at the Salt Lake City International Airport.  This is a new record for a calendar year, eclipsing the 21 days of 100˚F or higher observed in 1960, 1994, and 2021.   Over the years, I have had many people contact me concerning the veracity or representativeness of observations collected at the airport.  It is something that I have written about previously, including in 2013 (see What's Up @KSLC ).   The reality is non-climatic factors related to instrumentation changes and biases, observing techniques, land-surface change, urbanization, irrigation, and in some instances station moves affect trends and extremes at many observing sites.  Some of these are documented, some not. A good deal of processing is done to identify and adjust for these effects to identify climate trends, a process known as climate data homogenization .   Climate trends are typically d...

Convection associated with the North American Monsoon had a major impact on southern Utah (and even parts of northern Utah) over the past few days when several notable flash floods occurred.   One was in Moab where a state of emergency was declared after downtown and environs were flooded severely on Saturday night.   Video of Main Street in Moab turned into a river. A car in this video was pinned to the curb by the Main Street water current pic.twitter.com/I4bt3rAtvo — Swat Lake City (@Neildos) August 21, 2022 Radar imagery during the period showed a cluster of thunderstorms moving slowly eastward.  In the image below, an especially strong cell is due east of Moab (southeast of CNY, the 3-letter identifier for Canyonlands airport) over the headwaters of Mill Creek, which became a raging torrent.   Source: NCAR/RAL On the previous day, Friday, Aug 19, multiple hikers experienced a flash flood in the Virgin Narrows in Zion National Park, apparently nea...

Forecasting during the monsoon is often very challenging.  We talk a lot about monsoon surges, which sound quite dramatic, but sometimes the changes are more subtle.   Currently there is a weak upper-level trough off the coast of California that will serve as an important driver of convective storms as it moves across the western United States.   This afternoon the trough will be near the coast of California. It will help to coax monsoon moisture northward over the Sierra Nevada and western Nevada, with the HRRR producing clouds and showers (and presumably thunderstorms) that through that area and into Oregon.   By tomorrow afternoon, the trough is near the Oregon-Nevada-California triple point and shower and thunderstorm activity has shifted eastward into eastern Nevada and western Utah.   By Friday afternoon, the trough is moving into northern Utah and the GFS has moved the action into northern Utah (switching to GFS forecast below since th...

I hope you are enjoying the pleasantly moist and cool weather this Sunday.  We've had a pretty good run of monsoon moisture and thunderstorms in recent days and I think it is quite enjoyable. Weather observations over the past 14 days, roughly covering the first 2 weeks of August, show three major surges of monsoon moisture during which dewpoints (blue line) predominantly sat near or above 55˚F.  These are separated by a couple of monsoon breaks during which the dewpoint was generally below 55˚F.   Despite the hit-and-miss nature of monsoon showers and thunderstorms, most of northwest Utah has gotten a good deal of rain, with widespread areas over an inch and local accumulations of more than 3 inches in places over the past 14 days.   Source: https://water.weather.gov/precip/ For our part of the world, that represents more than 300% of average for the period, although there are a few spots that haven't done as well (note that there are a lot of artifac...

Upgrades to products on weather.utah.edu continue.  Today I added new hourly and total precipitation graphics for the GFS-13km dataset.   There are actually products available on weather.utah.edu from three GFS datasets.  Products under GFS-0.25deg are based on a GFS dataset with quarter degree by quarter degree latitude/longitude grid spacing.  Products under GFS-13km are based on a GFS dataset with 13-km grid spacing.  Finally, the GFS-Downscaled products are downscaled here at the U to 800-meter grid spacing from the quarter degree GFS dataset.   Confusing?  Try being me.   Most people don't bother with the 13-km dataset for a few reasons.  Perhaps the main one is that it doesn't include many atmospheric variables, limiting its use for forecasting.  I don't know why this is, but it mostly includes land-surface variables.  Even precipitation is not provided except as a mean precipitation rate, which to make things c...

It's been an awful year for glaciers and summer skiing in the European Alps.  In 1985 there were 32 operating glacier skiing resorts in the European Alps. Not all of these operated year round, but most provided skiing for part of the warm season.  Only a handful remain today.  Two, Hintertux in Austria and Zermatt in Switzerland, have historically operated 365 days a year on upper-elevation glaciers.  Glacier areas in Saas Fe (Switzerland) and Passo Stelvio (Italy) are open in the summer but closed for other parts of the year.  Other resorts that operate for parts of the summer include Kitzsteinhorn (Austria), Mölltal (Austria), Les 2 Alpes (France), Tignes (France), and Cervinia (Italy).  Racing camps are probably a big part of their business.   This year, however, Zermatt suspended operations on July 29.  As announced by Zermatt Bergbahnen, " The mild winter of 2021/2022, which saw little snowfall, leaving only a thin covering of snow in Ze...

I'm liking what I am seeing in the latest model runs, which advertise a major surge of monsoon moisture and precipitation into northern Utah for Friday combined with forcing from a weak surface boundary to force the action.  Storminess could persist in some areas into Saturday.   Below is the latest HRRR forecast of surface wind and 1-h accumulated precipitation valid 0000 UTC 6 August (6 PM MDT Friday).  Precipitation is mainly near or northwest of a surface boundary (shift in winds from southwesterly to the southeast to northerly or northwesterly near and behind) draped across central Nevada and northern Utah.   The flow aloft favors the transport of deep monsoon moisture to this region, resulting in widespread shower (and thunderstorm) activity developing on Friday near and northwest of this boundary.  Showers and thunderstorms may also occur to the south of the boundary, but will be more scattered.   Total accumulated precipitation throug...

We tied or broke virtually every temperature record related to "heat" that you can imagine during the month of July in Salt Lake City.  Buckle up.  Here we go.   The average temperature for the month was 87.3˚F, 1.6˚F higher than the previous record set just last year and 6.1˚F higher than the highest mean July temperature observed in the 20th century (81.2˚F in 1960).  This is also the hottest month ever in Salt Lake City.  There's never been anything hotter. http://xmacis.rcc-acis.org/ The average maximum temperature was 99.7˚F, which beats the prior record set last year by 1.3˚F.  If you want the psych point, you can round that up and say we had an average high temperature of 100˚F for the month.   http://xmacis.rcc-acis.org/ The average minimum temperature was an incredible 74.9˚F.  This is 1.8˚F higher than the prior record set just last year and obliterates everything from the 20th century.  The 20th century record was 68.5˚F ...