Showing posts with label Thunderstorms. Show all posts
Showing posts with label Thunderstorms. Show all posts

Thursday, July 30, 2026

Natural Air Conditioning

Residents of the northern Wasatch Front and northern Salt Lake Valley were treated to some natural air conditioning thanks to a complex of thunderstorms that moved across the area yesterday evening.  

Source: ral.ucar.edu

Some of the thunderstorms were severe and produced wind gusts of 60 mph in Sugarhouse, 64 mph in Tremonton, and 72 mph at the I215/I80 exchange.  

There was also beneficial rain and cooling. Temperatures at the Salt Lake City International Airport dropped to 67°F, the lowest temperature observed there since July 4, and I was able to get temperatures in my house below 70°F for the first time since we returned from Austria.  

We were also treated to a beautiful double rainbow as the storm moved off to the east.  


Unfortunately, as has been forecast for a few days, the heat is expected to return in spades by the weekend, with the National Weather Service issuing an Extreme Heat Watch for SaturdayAfternoon through Sunday Evening with temperatures up to 105°F and lows in the low to mid 70s for the Salt Lake Valley and other lowland areas of northern Utah.  

The cool was brief but fun while it lasted. 

Monday, July 20, 2026

Thunderstorm Safety

In the wake of recent tragedies, it's worth a bit of review of flood and lightning safety.  In the case of floods, here's some data from the National Weather Service and their partners:

  • More deaths occur due to flooding than any other thunderstorm hazard.
  • Over half of all flood-related drownings occur when a vehicle is driven into flood waters.
  • The next highest percentage of flood-related deaths is due to walking into or near flood waters.

Source: National Weather Service

A full run-down of National Weather Service flood products, including outlooks, watches, advisories, and warnings is available at https://www.weather.gov/safety/flood-products.  In Utah, the National Weather Service also provides flash flood potential ratings for southern Utah and covering 12 recreation areas at https://www.weather.gov/slc/flashflood.  

As evident in near the Cottonwood Fire and Beaver, fire scars can be especially problematic for flash flooding and debris flows.  

National Weather Service lightning safety tips and resources are available at https://www.weather.gov/safety/lightning.  Lightning kills about 20 people a year nationwide, most commonly in summer, but deaths have occurred in all seasons (and in fact lightning is a threat for skiers in Utah which has a relatively high rate of thundersnow).  If you can hear thunder and are outdoors, you should move indoors or into a hard-topped car if you can.  If you are car camping and are in a tent of soft-sided trailer, move into a vehicle.  If you are at an outdoor sporting event, move indoors or into your car.  

Source: https://www.weather.gov/media/owlie/backcountry_lightning.pdf

In the backcountry, more than 30 minutes from an enclosed modern building or vehicle, lightning safety is about minimizing risk.  The most important thing is to monitor forecasts and time your visit to high-risk areas such as mountain peaks, ridgelines, and open water areas accordingly.  Think of it as being the equivalent of selecting the proper terrain for a given avalanche hazard.  Next is to move to safer terrain, as quickly as safely possible, if you hear thunder or believe the thunderstorm hazard is increasing.  This will not eliminate risk, but strikes are more random in lower elevation areas.  Avoid high trees, open areas, and if you can find a dry, lower elevation area, move there.  Pick tent sites to minimize risk too, but be careful when looking at ravines and other gullies if there is a possibility of flash flood.  

Below is more detailed information from a brochure put together by the National Weather Service and NOLS.  Note that getting into the lightning position is a last resort.  If you can move to a safer location focus on that.  For example, if I was on a ridge, I would move down in elevation as fast as I safely could rather than stay there in the lightning position.  

Source: https://www.weather.gov/media/owlie/backcountry_lightning.pdf

Many of the "FACETS" heuristic traps in avalanche accidents also apply to lightning safety.  

F=Familiarity.  Something that feels familiar feels safer, but just because you've survived lightning storms at high elevations in the past doesn't mean you will today.  

A=Acceptance.  You want to fit in or impress your friends by climbing a line or bagging a peak, which might increase your tendency to push it as weather hazard increases.   

C=Commitment.  You don't want to turn around from the summit when you have invested time and effort and are more likely to to push it as weather hazard increases.

E=Expert Halo.  There's a tendency to defer decisionmaking to others with more experience.  Don't assume your friend with years of mountaineering experience is going to make the right weather-related decisions.

T=Tracks/Scarcity.  This one might be more seasonal, but since there is lightning risk in winter, don't ignore it because you want to get first tracks of the top of Mt. Superior. 

S=Social Facilitation.  This one is actually very valid to lightning safety.  It is much harder to move to a building or car, turn around from high elevations, or get off the lake when noone else is doing it.  However, just because nobody else is doing it doesn't mean you shouldn't be doing something to reduce risk.  

All of that said, I've been there.  In fact, the event that I often think of as pushing me into meteorology happened when I was a teenager backpacking with my Dad and we had to run very rapidly from and Adirondack peak to a lower-elevation pass as a thunderstorm moved in.  I've been pelted by hail and graupel during thunderstorms in the Uintas, keeping to the lowest terrain without flood potential possible.  And I've spent time in the lightning position on backpack trips.  On Saturday, we hiked in the morning because of the increasing thunderstorm hazard during the day, yet were just getting to our car when the thunder started at 11:30.  

Use the tips above to adventure at the safest times and to know what to do to minimize risk when you are caught out.  

Wednesday, August 13, 2025

Weak Monsoon Surge

You know you are desperate when you get excited about the shallow cumulus that are developing over the Salt Lake Valley today,  Below is a loop showing the development of these clouds looking south from the University of Utah through about 1450 MDT.  There's even some virga! 

Those clouds are developing ahead of a weak upper-level trough that is near the Pacific Coast and a weak surface boundary that is in advance of the upper-level trough near the boarder of Idaho and Nevada/Utah.  The 2119 UTC radar image shows that area is producing stronger cells than the "cumulus patheticus" that we've had over the Salt Lake Valley so far today.  

Source: NCAR/RAL

Moisture will, however, be on the increase through Friday.  This is not a major monsoon surge, but we will see the coverage of clouds and possibility of thunderstorms and precipitation increasing. 

Let's have a look at what the Rapid Refresh Forecast System (RRFS) ensemble does over the next few days.  I'll focus on 24-hour precipitation totals ending at 0600 UTC (0000 MDT), but note that most of this precipitation is produced during the afternoon and evening when convection is strongest.

For the period ending at 0600 UTC 14 August (0000 MDT Thursday), which covers today, the RRFS gives a nothing burger to the Salt Lake Valley and most of the west desert areas of Utah.  The action is in that area around the aforementioned boundary.  Mean forecast precipitation (upper right panel) is greatest right along the ID-UT border.  Maximum forecast precipitation (lower right) is over 0.5" in some areas.   


For tomorrow, that area near the UT-ID border generally remains active, but we see a bit more action in Tooele Valley, Salt Lake Valley, and environs.  Mimium precipitation (lower left) is still zero in many areas, but the mean of all ensemble members is > 0 across most of the Salt Lake Valley.   


I would not interpret that as meaning everyone in the Salt Lake Valley will get precipitation, especially since there are only six members in this ensemble, but I would expect that we will see deeper convection tomorrow and perhaps storms that can produce rain to the valley floor.  For Salt Lake City, the NWS is going with a 30% chance of showers and thunderstorms after noon tomorrow and a 40% tomorrow night before midnight.  There's a chance!

This weak monsoon surge will keep some shower and thunderstorm chances around until Saturday.  Will we get measurable rain at the airport?  Time will tell.