It Snowed in Boise in May! Here's Why

Simple and cozy spring outfit idea with cotton sweater, demi-boot jeans, and white sneakers | Cotton Cashmere Cat Hair

You may remember that in Monday’s blog post, I wrote that it was snowing as I was writing. And boy did it snow: some places in town ended up with 3-6 inches by the time it was done, and the foothills got even more (up to a foot!). Higher up, Bogus Basin ended up with just over a foot and half of snow! On May 9th. As much as the moisture is helpful (and I’m happy it’s not yet 100 degrees out), the snowfall devastated countless trees and other foliage; the extra weight from the wet snow on the leaves and branches resulted in downed branches and split trunks all over the north and east ends of town where the snow amounts were highest.

While snow in Boise in May is not impossible, it’s certainly unlikely. Getting measurable snow in Boise in May is even more unlikely: it’s happened fewer than 10 times since the National Weather Service (NWS) started official record keeping in the late 1800s. The airport is where the official records are taken, and it received half an inch of snow during the storm on Monday. It’s unfortunate that there’s no way to fully capture the effects of each storm, especially one like this; if the worst of the storm hits one part of town and not the NWS gauge, it’s like it barely or never happened. Anyway, let’s chat about what exactly led to the May snowstorm in Boise!

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Why It Snowed in Boise, Idaho In May

The past few weeks, in typical spring fashion, we have seen a really active weather pattern in Idaho in general. We’ve seen rain with the occasional thunderstorm one day followed by sun the next, and then the rain again the day after that. It’s fun! There’s a little something for everyone. 😉 We had an incredible thunderstorm two evenings before it snowed; I savor all the storms we can get since they don’t happen here that often.

You may be wondering why exactly Boise got snow in May, with some parts of town getting a significant amount. The answer lies in the upper levels of the atmosphere: There was an extremely cold upper level low pressure system centered over eastern Oregon overnight Sunday, May 8th into Monday the 9th. In fact, the NWS Boise SOO (Science Operations Officer) tweeted that the lowest 500 mb height ever recorded in the month of May in Boise was observed during the Monday morning sounding (that’s the balloon launch most NWS sites do twice a day to examine what’s happening vertically in the atmosphere).

500 mb GFS geopotential height at 6Z on May 9, 2022. Note cold airmass over Pacific Northwest. Image courtesy Tropical Tidbits.
2 meter GFS temperature anomaly at 18Z on May 9, 2022. Note unseasonably cold airmass over the western US. Image courtesy Tropical Tidbits.
Radar image of May 9, 2022 snow storm over Boise, Idaho with low pressure circulation marked. Image courtesy NWS Boise.

What does this mean? It means the airmass was unseasonably cold—cold enough to produce snow showers and accumulating snow down to the valley floor (the figure above illustrates how cold it was—as cold as the polar latitudes!). Boise ended up under a vorticity max in the area of the occluded front of the surface low pressure system that allowed the air to circle counterclockwise around the system, forcing the air to upslope over north and east Boise, the foothills (that are oriented northwest-southeast), and nearby mountains (including Bogus Basin). The cold air aided in the lift and upsloping that resulted in heavy snowfall, and since the storm was so localized (small!), the models had a difficult time resolving what would exactly happen.

Weather is cool, huh?! 🤩 I was in shock watching the snow fall. Korri went out and shook it out of our trees so it wouldn’t break them. I was thinking the snow wouldn’t be there when I woke up, but it was! I didn’t mind so much because it didn’t stick to the roads—that’s the worst part of snow during real winter and why I really don’t like it. As long as I get to stay inside, I’m good, haha.

As for my outfit? The cooler weather was the perfect excuse to pull out a cozy combo—a cotton sweater and my newest pair of Cali demi-boot jeans from Madewell—possibly for the last time this season! As much as I’m looking forward to warmer weather, I know that it’s better to have cooler weather now and to push the heat (and fire season) back for as long as possible.

OUTFIT DETAILS

Everlane sweater / old; similar by BP or Quince
Madewell jeans / exact (also available from Zappos and Nordstrom)
Earth sneakers c/o / old; similar by Reebok or New Balance (last seen here)
Madewell hat / old; similar from Amazon
ABLE earrings / exact or similar from Wolf & Badger
Le Specs sunglasses / exact via Revolve, Shopbop, or Nordstrom
Dior Lip Glow in rosewood / exact

outfits, IdahoKimi, Cotton Cashmere Cat Hairspring, Boise, weatherComment