Wasatch Weather Weenies

Monsoon thunderstorms developed over the Salt Lake Valley this afternoon and brought heavy rainfall to the northeast corner of the Salt Lake Valley, especially the University of Utah.  The event started with the development of a cell over or just downstream of the Salt Lake International Airport.  This one moved off over North Salt Lake.  Shortly therafter, two cells formed just to the south of the track of the first cell and pounded the Avenues and Avenues Foothills.   Then things got interesting as a cell exploded west of Murray and moved northeastward to the University of Utah.  This was the beginning of a series of training storms that pounded the area around the U before things settled down.  The full sequence is below.  I'm hoping the video will upload properly as I'm working with some limitations currently.   Storm total Radar precipitation estimates through 2200 UTC (1600 MDT), which does not quite capture the entire storm period...

Wow, what a forecast.  Buckle up as a lot is going to be happening through Sunday.  Things get exciting around here when the mid-latitude storm track phases with monsoon moisture and we will have both in spades this weekend.   I'll start with the GFS forecast valid 1200 UTC 11 October (0600 MDT Saturday).  A deep trough sits along the Pacific coast and monsoon moisture is streaming into the four corners area, producing the Predecessor Rain Event (PRE) discussed the the previous post in advance of the remnants of Hurricane Priscilla over northern Arizona, southeast Utah, and southwest Colorado.  In addition, a strong cold front sits over eastern Nevada. By 0000 UTC 12 October (1800 MDT Saturday) that strong cold front is over northern Utah and lighting up parts of northwest Utah.   I'm not sure how Saturday is going to play out in the Salt Lake Valley ahead of the front.  There will be southwest flow ahead of the front but it's hard to say if ...

A lot of exciting things can happen this time of year when the mid-latitude storm track interacts with monsoon moisture.  The latest model runs really get my attention in this regard as they are putting out a good deal of precipitation in the southwest US. The latest GFS shows the precipitation picking up in northern Arizona on Thursday.  By 1200 UTC 10 OCT (0600 MDT Friday), precipitation is organized in a band that runs from SW to NE from northern Arizona and to western Colorado.  This precipitation region is to the north and northeast of Hurricane Priscilla, which is forecast to be off the coast of Baja California at that time.  Such a precipitation feature is sometimes referred to as a Predecessor Rain Event, or PRE and occurs as enhanced vapor transport north of a hurricane experiences large-scale lift.  Forecast soundings from Flagstaff at that time are saturated with precipitable water values of 25.4 mm (exactly 1 inch if you prefer US units), which is qu...

It's just after noon on Saturday with a very eventful 60 hours or so on tap for SoCal, Nevada, and possibly portions of adjoining states due to one of the more significant tropical cyclone events in recent memory for the southwest US.   According to the latest (12 PM MDT Saturday August 19), Hurricane Hilary is currently a category 3 hurricane with 115 mph winds.  Satellite imagery showed the circulation center of Hilary just west of the southern tip of Baja California with high clouds extending northward across Baja, SoCal, Nevada, and even northern Utah.   Source: College of DuPage Beneath those high clouds is a predecessor monsoon surge that is working its way up the lower Colorado River Valley and environs.  Radar imagery at 1200 MDT (1800 UTC) Saturday showed showers and thunderstorms in southwest Arizona and southeast California. The heaviest were near and within an area with precipitable water values at or above 50 mm (2 inches).   Precipit...

Yesterday brought another day of heavy monsoon convection to northern Utah.  The National Weather Service 24-hour precipitation analysis for the period ending at 1200 UTC 4 August (6 AM MDT Friday) shows totals in northern Utah reaching over 5 inches in the area north of Brigham City.   An observing site near Honeyville near that maximum reported a 48-hour total of 5.83".  There is some concern about the veracity of that sensor, so this will need to be verified, but other stations in that area reported over three inches.   Meanwhile a bit further south, convection moved across the southern Salt Lake Valley and northern Utah County yesterday evening.  The storms produced a remarkable amount of lightning.   Well played Mother Nature. Well played. pic.twitter.com/vyogDD4U2j — Jim Steenburgh (@ProfessorPowder) August 4, 2023 The analysis above indicates maximum accumulations of between 1.5 and 2 inches, although there is one pixel that may be abo...

Chances are you've seen some of the footage of the remarkable flooding in the northeast the past couple of days.   We will focus here on the Adirondack Mountains of New York and the Green Mountains of Vermont.  The National Weather Service Burlington Forecast Office produced a map earlier today of the storm total precipitation for their forecast area, which extends across northern New York.  The event featured impressive enhancement over the Green Mountains and portions of the Adirondacks.  In the case of the Greens, a broad area of more than 5" fell including more than 9" in Plymouth just to the south of Killington along Route 100.  In the Adirondacks, more than 5" fell in Newcomb.   Flooding, mudslides, and washed out roads have occurred in many areas.  Below is drone footage from yesterday in Montpelier, which was posted by The Weather Channel. WATCH: Drone footage captures the extent of yesterday's significant flooding in Montpelier, Verm...

These are eventful times, and there is much to talk about today. First let's talk about the temperatures.  The monster swing over the past 10 days or so is well illustrated by the graphic below which is produced by the National Weather Service Forecast Office in Salt Lake City.  It shows the range of average temperatures (1991-2020) in green, record highs (top of red), and record lows (bottom of blues).  The range of observed temperatures each day are the dark blue bars.  On April 4th, the high temperature was only 33˚F.  By April 11th, it was 83˚F, a record high for the date.  Source: NWS Yesterday was a touch cooler, although we still hit 78˚F, marking three days in a row above 70˚F and five days in a row above 60˚F. As readers of this blog are well aware, this led to elevated avalanche hazard as we transitioned from dry to wet avalanches, a prolonged closure of Little Cottonwood Canyon, and regular afternoon closures of Big Cottonwood Canyon.  ...

I woke up this morning to the smell of rain, or what is known as petrichor.  The UK met office has a nice web page explaining the origins of the word and what causes the smell.  It says, " Raindrops landing on dusty or clay soils trap tiny air bubbles on the surface which then shoot upward — as in a glass of Champagne — and burst out of the drop throwing aerosols of scent into the air where they are then distributed by the wind ." Radar imagery at 1402 UTC (8:02 AM MDT) showed showers over portions of northern Utah, some likely heavy, especially in the West Desert.  I'm quite glad to see this as although we had an active monsoon for part of the summer, the last couple of weeks have been hot and bone dry.  On the other hand, there are concerns about flooding produced by heavier downpours.   The HRRR suggests that in the Salt Lake Valley we may see more isolated to scattered showers for a time today before things pick up again in the afternoon.  We'll s...

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...

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...

Thunderstorms with heavy rain, frequent lightning, and nearly continuous thunder move north-northwestward into the Salt Lake Valley from the Wasatch Mountains, resulting in a number of issues related to flash flooding. Portions of the northern Wasatch Front were also affected.   The system that affected the northeastern Salt Lake Valley, including Mill Creek, Sugarhouse, St. Mary's, the University of Utah, Downtown, and the Avenues began to develope over the Wasatch Mountains just before 0000 UTC (6 PM) yesterday evening.  At 2352 UTC (5:52 PM MDT), the first strong cell appeared over Big Cottonwood Canyon. This cell exploded in intensity and coverage over the next 20 minutes.  Anyone recreating in Big Cottonwood or Mill Creek Canyon would have been quickly overwhelmed by heavy rainfall, and possibly small hail.  A second cell began to develop at this time on the Alpine Ridge south of Little Cottonwood.  At this point, all hell began to break loose as more ...

Flash flooding in Little Wildhorse Canyon sadly took the lives of two young girls on Monday.  The situation was one that is common on the Colorado Plateau with precipitation from an afternoon thunderstorm funneled into a narrow slot canyon.  The tweet thread below from University of Utah graduate student Tom Gowan, who was in the area, describe the situation. I was up Little Wild Horse Canyon (where this occurred) with @tayloragowan and a friend during this freak incident. We knew the chance of heavy rain producing thunderstorms was low, but when we heard thunder, we turned around and got out of the slots. (thread) https://t.co/tkKjsHyhAv — Tom Gowan (@tommgowan) May 12, 2020 After we found a high, sheltered spot, all hell broke lose. Heavy rain turned into the heaviest nickel-sized hail I've ever seen. After several minutes, we noticed a debris flow coming down Bell's Canyon. Video (warning: language): pic.twitter.com/o4hH4DQnjQ — Tom Gowan (@tommgowan) May 12, 2...

Yesterday, hazardous convective storms affected locations in Utah, resulting in at least one fatality. Northern Utah In northern Utah, convective storms produced strong microburst winds in several areas, resulting in a few downed tree branches and a lot of blowing dust and pollen.  The tweet below includes a video showing dust and probably pollen kicked up by microburst winds moving through downtown Salt Lake City. Updated loop of afternoon microburst in Salt Lake City. Watch how dust/pollen/or whatever cloud moves through downtown. Initiated early in loop by virga near Oquirrh Mts. Possible reinforcement west of downtown. #utwx pic.twitter.com/d6GTQAJU7p — Jim Steenburgh (@ProfessorPowder) May 12, 2020 There were some downed tree branches reported near Liberty Park according to NWS reports. Microbursts are produced by strong downdrafts that fan out when they contact the ground, as depicted below. Source: Fujita (1981) Yesterday's was a traveling microburst simi...

Over the past couple of weeks, the combination of snowmelt and frequent rainfall, including recent thunderstorms, has transformed the Inn River from a beautiful river with a tint of green into a muddy torrent. The  photos below were taken from the Inn Bridge near old town a few months ago and today, illustrating how the Inn River is filled nearly to the top of its human-made banks. Photo: Andrea Steenburgh Photo: Andrea Steenburgh Another perspective is provided by the photo below, taken from my building at the University of Innsbruck and looking down on the University Bridge. This morning, I noticed workers installing a temporary fence along the base of the building, presumably for protection.  On that lowest level is a library.  Gulp! The hydrogram below covers the past few days and shows a rise of about 2 meters in th epast two days, putting it above a "one in 30 year level."  A better way to think about it is that the odds of such a river...