<blockquote>
<p>Note: These inputs are of a meteorologist who has quite actively tracked severe
weather around the US for a couple
decades... but also hadn't spent as much time in or attention on the west and northwest of the country.  So there could could theoretically be some degree of unintended bias.  I've tried to use objective data where possible, but it's something to keep in mind, regardless.</p>
</blockquote>
<p><strong>In terms of &quot;<em>a lot</em>&quot;, at least for tornadoes/hail, I'd suggest that nowhere west of the Rockies sees <em>a lot</em> truly:</strong></p>
<p><a href="https://i.sstatic.net/icihBm.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/icihBm.png" alt="tornado tracks" /></a>
<a href="https://i.sstatic.net/kB1nym.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/kB1nym.png" alt="hail" /></a>
<sub><sup>Tornadoes [left], hail [right]... source: <a href="http://www.spc.noaa.gov/gis/svrgis/" rel="nofollow noreferrer">Storm Prediction Center SVRGIS page</a></sup></sub></p>
<p>I'd offer the idea that there of perhaps two notable reasons for that:</p>
<ol>
<li>The <strong>lack of consistent and widespread surface wind fields favorable to tornadoes</strong>... due to a combination of the lack of the big <a href="http://glossary.ametsoc.org/wiki/Lee_cyclogenesis" rel="nofollow noreferrer">lee cyclogenesis</a> seen east of the Rockies, along with the complex topography.</li>
<li>The <strong>rarity of regular low-level moisture</strong> significant enough to allow for low <a href="https://www.youtube.com/watch?v=MbbjVUxtsDE" rel="nofollow noreferrer">LCLs</a>.  The higher the storm base is above the ground, the less likely a tornado<br />
[<a href="http://www.spc.noaa.gov/publications/edwards/part2.htm" rel="nofollow noreferrer">in figure 6 of Edwards and Thompson 2000, all the red boxes showing tornadoes are on the left side, which are lower LCLs</a>]</li>
</ol>
<p>The lack of rich low-level moisture is due in large part to the lack of accessibility from warmer moisture sources, particularly the Gulf of Mexico; the Rockies provide a barrier to much of the moisture reaching further west.</p>
<p>As you note, parts of Wyoming and Montana do see supercells and tornadoes a bit more often... but on a <a href="http://en-us.topographic-map.com/places/United-States-2241/" rel="nofollow noreferrer">good topographic map</a>, fair parts of those states are east of the <a href="https://en.wikipedia.org/wiki/Continental_Divide_of_the_Americas" rel="nofollow noreferrer">Continental Divide</a>, and so still on an &quot;<a href="http://www.theweatherprediction.com/habyhints/112/" rel="nofollow noreferrer">upsloping</a>&quot; area and thereby not blocked by sinking regions which prevent full moisture progress.  They're still less-tornado prone due to elevation and increased distance from moisture, but it does happen.</p>
<p>The desert southwest also does manage to get <a href="https://en.wikipedia.org/wiki/North_American_Monsoon" rel="nofollow noreferrer">monsoon moisture sneaking around the terrain further south</a>... but <strong>further north that monsoon moisture sees additional blocking by the more elevated terrain across Nevada and Utah</strong>.  (And in the southwest, a different key ingredient in tornadic supercell development is typically missing in the summer monsoon: <a href="https://en.wikipedia.org/wiki/North_American_Monsoon" rel="nofollow noreferrer">upper-air winds sufficient for supercell development</a>)</p>
<p>The Pacific Coast does see a few occasional tornadoes.  But from what I've seen, they typically form from smaller storms with much less classical and intense mesocyclones.  As you mention, they're a bit more in line with cold-core setups, which usually produce weaker short-lived tornadoes than classic supercells of the Plains and on east.  If you plug in the events you speak of into <a href="http://www.spc.noaa.gov/exper/archive/events/" rel="nofollow noreferrer">SPCs Severe Weather Events archive</a>, [pick the date, then click Obs and Mesoanalysis on the left, then use the dropdowns to find various parameters]
you can see that CAPE was typically very meager (well short of 1000 J/kg) and the storm structure quite weak in reflectivity in comparison to a classic supercell, more indicative of such cold-core setups.</p>
<p>Capping inversions may be helpful to &quot;keep the lid on the pot&quot; if you have strong CAPE (and therefore quality moisture) and intense updrafts to erode the cap during the day.  But as it is, <strong>there isn't enough moisture typically for the cap to be a positive factor</strong>.</p>
<p>Quite a bit of the area you mentioned, such as Spokane, makes up one of the <a href="https://en.wikipedia.org/wiki/United_States_rainfall_climatology#/media/File:Average_precipitation_in_the_lower_48_states_of_the_USA.png" rel="nofollow noreferrer">more arid regions of the country</a>.  Further removed from the rain shadow of the Cascades, the Idaho Panhandle does get more precipitation, but it's mostly in <a href="https://www.bestplaces.net/climate/city/idaho/lewiston" rel="nofollow noreferrer">cooler months</a> that lack the deep convective development needed for supercells, probably because of the <a href="https://climate.ncsu.edu/edu/HighLow" rel="nofollow noreferrer">proximity of the Pacific high</a> in summer months.  Further east in E ID/W MT, particularly in the Flathead Valley, there are <a href="https://www.e-education.psu.edu/meteo3/sites/www.e-education.psu.edu.meteo3/files/images/lesson8/tstrm_climo.jpg" rel="nofollow noreferrer">occasional summer thunderstorms</a>... but the storms may well be higher based due to the limited low-level moisture, and so have low potential of tornadic development.  For more on the climate complexities at play in the Idaho vicinity, <a href="https://wrcc.dri.edu/narratives/IDAHO.htm" rel="nofollow noreferrer">check out this article</a> from the Western Regional Climate Center.</p>
<p>In the end, the area you ask about is one of the weakest regions for supercell development in the entire United States.  The entire quarter of the country west of the Rockies isn't much better.  <a href="https://mesonet.agron.iastate.edu/plotting/auto/?q=92" rel="nofollow noreferrer">This page</a> from Iowa State University will create an image showing the number of days since each pocket of the country (sorted by National Weather Service forecast office areas) last saw a tornado warning.  It shows that the Idaho Panhandle hasn't seen a tornado warning in over 10 years:</p>
<p><a href="https://i.sstatic.net/cQ3a6.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/cQ3a6.png" alt="enter image description here" /></a></p>
<p>More than anywhere but northern California.</p>
<p>And another ISU <a href="https://mesonet.agron.iastate.edu/plotting/auto/?_wait=no&amp;q=90&amp;t=cwa&amp;v=yearavg&amp;ilabel=yes&amp;geo=polygon&amp;drawc=yes&amp;year=1989&amp;year2=2019&amp;sdate=1989%2F01%2F01%200000&amp;edate=2019%2F12%2F31%202359&amp;station=OTX&amp;state=IA&amp;phenomena=SV&amp;significance=W&amp;cmap=jet&amp;interval=1&amp;dpi=100&amp;_fmt=png" rel="nofollow noreferrer">page</a> allows it to be shown that:
<a href="https://i.sstatic.net/vlpdn.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/vlpdn.png" alt="enter image description here" /></a></p>
<p>... Most spots in northern Idaho only see about one severe thunderstorm warning per year on average (versus <a href="https://i.sstatic.net/X8L0n.png" rel="nofollow noreferrer">10-20 per year over Oklahoma</a>).</p>
<p><strong>So the danger of severe convective weather is remarkably low in that region of the country overall.</strong></p>

CC BY-SA 4.0
2018-06-01T01:39:43.960Z
Of course they do occasionally happen (especially in SE Idaho).  Go figure, [this](https://i.sstatic.net/a6z1P.png) was today [hopefully the imgur will stay alive long despite not adding to body]
JeopardyTempest
CC BY-SA 4.0
2018-05-30T10:22:31.357Z
2020-10-08T09:54:26.987Z
2020-10-08T09:54:26.987Z
JeopardyTempest
<p>Every storm season, supercells erupt in Montana and Wyoming. Wayward cold-core setups can trigger supercells or even long-tracked strong tornadoes in the Columbia/Willamette Valley and the rest of SW WA. Examples abound: 4/5/1972, 6/29/1989, 2/8/1993, 1/10/2008, 6/4/2009, <a href="http://www.spc.noaa.gov/products/watch/2014/ww0459.html" rel="nofollow noreferrer">8/12/2014</a>, <a href="http://komonews.com/weather/scotts-weather-blog/what-is-a-wet-microburst-the-cause-of-the-stormy-mayhem-in-thurston-county" rel="nofollow noreferrer">5/4/2017</a>, the list goes on, and on, and on.</p>

<p>However, I'm asking about severe weather in the region directly wedged in between the two aforementioned regions; all of WA east of the Cascades (East Slopes, Yakima Valley, Palouse, etc. This includes the southern Okanagan and the Kootenays in B.C.), and northern Idaho. Spokane/Coeur d'Alene, Pullman/Moscow, Lewiston, Wenatchee, Kelowna, Penticton, etc. Maybe even down to Boise.</p>

<p>Is this an area that can have favorable conditions for rotating supercell storms (the kinds that can spawn significant tornadoes or drop monster hail), like in neighboring Montana, Wyoming, or the Deschutes Basin in central Oregon? </p>

<p>Such a region is on the leeside of the Cascades (which means capping inversions), and right in the firing line of monsoonal plumes from the Four Corners states, so to me it seems logical that (at least on paper) the northern reaches of the Inland Northwest can support supercellular development.</p>

<p>Addendum: I was asked to source my "Deschutes gets monster hail and significant tornadoes" statement. For hail: if you look at the <a href="http://www.spc.noaa.gov/climo/reports/170504_rpts.html" rel="nofollow noreferrer">SPC storm reports for May 4, 2017</a>, you'll see that 1.75-2" hail was recorded in Bend, as well as the towns of Sisters OR and Madras OR, around 10:30-11:00 p.m. PDT (0530-0600Z) on the 4th. For the Pacific Northwest excluding Idaho, I'd say those are some pretty darned big hailstones, and qualify as "monster hail" in a relative sense. Supercelluar thunderstorms are also not unheard of in this area, like the <a href="https://www.weather.gov/media/wrh/online_publications/TAs/ta9601.pdf" rel="nofollow noreferrer">July 9, 1995 supercell in Redmond OR.</a> As for tornadoes, I was wrong. I checked the Tornado History Project map, and it looks like most tornadoes to hit the Beaver State are west of the Oregon Cascades.</p>

CC BY-SA 4.0
2018-05-30T05:58:13.740Z
Anecdotally, the Columbia Basin doesn't have much summertime thunderstorm activity. They are mostly restricted to mid to late spring. I would think that the dry rain-shadow conditions prevent the formation of severe storms. IIRC, heating in eastern Oregon and Washington drives adiabatic winds in the Columbia River Gorge that are loved by windsurfers, but aren't associated with thunderstorm development.
haresfur
CC BY-SA 4.0
2018-05-30T06:17:42.573Z
Please cite your source(s) for "supercells", "significant tornados" and "monster hail" in tbe Deschutes Basin.
Stu Smith
CC BY-SA 4.0
2018-05-31T09:06:55.167Z
I found sources for the hail and supercells, and added them to the post. I was mistaken about significant tornadoes. I just look at the Tornado History Project map and it looks like most tornadoes in Oregon, and most significant ones, are west of the Cascades.
spillthrill
CC BY-SA 4.0
2020-10-08T09:15:02.587Z
Moisture is probably the prime limiting factor. On https://prism.oregonstate.edu/normals/ you can plot mean dewpoint... [even in the heart of summer](https://i.sstatic.net/sTvoZ.png) the PacNW just doesn't get near Tds of the Plains\East in spring {at fairly low elevations, a reasonable rough low bound for severe wx might be 60F or even really 65F; higher elevation in ECascadia may allow it to be slightly lower, but [SPC's sounding climatology](https://www.spc.noaa.gov/exper/soundingclimo) shows how rare decent CAPE is}]. The monsoonal plume isn't really enough for the Pac NW... or the SW.
JeopardyTempest
CC BY-SA 4.0
2020-10-08T09:20:05.990Z
To further investigate the different in moisture levels, perhaps play around with [ISU's ADP](https://mesonet.agron.iastate.edu/plotting/auto/?_wait=no&q=60&network=ID_ASOS&zstation=LWS&var=dwpf&threshold=60&direction=above&cmap=jet&dpi=100&_fmt=png).  Compare how incredibly [rare 60F is in Lewiston](https://i.sstatic.net/Ip8pj.png) vs how common (particularly in afternoon's peak heating) [65F is in Oklahoma City](https://i.sstatic.net/5OE3I.png) or other cities. It certainly isn't the only factor (having ample moisture in July in OK doesn't mean tornadoes), but it is a base requisite.
JeopardyTempest
CC BY-SA 4.0
2020-10-08T09:24:52.103Z
Funny enough, in the two years since I wrote my original answer, life has changed a lot, and I ended up spending quite a bit of time in and around the Columbia Basin\Cascades\much of Cascadia... great area.  Ironically even happened to come into town the day there was a [tornado in the Portland metro](https://www.oregonlive.com/weather/2020/06/funnel-cloud-spotted-over-damascus-saturday-evening-video.html)!!!
JeopardyTempest
<meteorology><severe-weather>
Does the Columbia Basin, North Cascades and Idaho Panhandle/Clearwater get a lot of violent, rotating supercellular thunderstorms?
spillthrill
# Does the Columbia Basin, North Cascades and Idaho Panhandle/Clearwater get a lot of violent, rotating supercellular thunderstorms?

(Asked by: username_0 on 2018-05-30)

Every storm season, supercells erupt in Montana and Wyoming. Wayward cold-core setups can trigger supercells or even long-tracked strong tornadoes in the Columbia/Willamette Valley and the rest of SW WA. Examples abound: 4/5/1972, 6/29/1989, 2/8/1993, 1/10/2008, 6/4/2009, [8/12/2014](http://www.spc.noaa.gov/products/watch/2014/ww0459.html), [5/4/2017](http://komonews.com/weather/scotts-weather-blog/what-is-a-wet-microburst-the-cause-of-the-stormy-mayhem-in-thurston-county), the list goes on, and on, and on.

However, I'm asking about severe weather in the region directly wedged in between the two aforementioned regions; all of WA east of the Cascades (East Slopes, Yakima Valley, Palouse, etc. This includes the southern Okanagan and the Kootenays in B.C.), and northern Idaho. Spokane/Coeur d'Alene, Pullman/Moscow, Lewiston, Wenatchee, Kelowna, Penticton, etc. Maybe even down to Boise.

Is this an area that can have favorable conditions for rotating supercell storms (the kinds that can spawn significant tornadoes or drop monster hail), like in neighboring Montana, Wyoming, or the Deschutes Basin in central Oregon?

Such a region is on the leeside of the Cascades (which means capping inversions), and right in the firing line of monsoonal plumes from the Four Corners states, so to me it seems logical that (at least on paper) the northern reaches of the Inland Northwest can support supercellular development.

Addendum: I was asked to source my "Deschutes gets monster hail and significant tornadoes" statement. For hail: if you look at the [SPC storm reports for May 4, 2017](http://www.spc.noaa.gov/climo/reports/170504_rpts.html), you'll see that 1.75-2" hail was recorded in Bend, as well as the towns of Sisters OR and Madras OR, around 10:30-11:00 p.m. PDT (0530-0600Z) on the 4th. For the Pacific Northwest excluding Idaho, I'd say those are some pretty darned big hailstones, and qualify as "monster hail" in a relative sense. Supercelluar thunderstorms are also not unheard of in this area, like the [July 9, 1995 supercell in Redmond OR.](https://www.weather.gov/media/wrh/online_publications/TAs/ta9601.pdf) As for tornadoes, I was wrong. I checked the Tornado History Project map, and it looks like most tornadoes to hit the Beaver State are west of the Oregon Cascades.

**Tags:** meteorology, severe-weather

> **Comments:**
> **username_1**: Anecdotally, the Columbia Basin doesn't have much summertime thunderstorm activity. They are mostly restricted to mid to late spring. I would think that the dry rain-shadow conditions prevent the formation of severe storms. IIRC, heating in eastern Oregon and Washington drives adiabatic winds in the Columbia River Gorge that are loved by windsurfers, but aren't associated with thunderstorm development.  
> **username_2**: Please cite your source(s) for "supercells", "significant tornados" and "monster hail" in tbe Deschutes Basin.  
> **username_0**: I found sources for the hail and supercells, and added them to the post. I was mistaken about significant tornadoes. I just look at the Tornado History Project map and it looks like most tornadoes in Oregon, and most significant ones, are west of the Cascades.  
> **username_3**: Moisture is probably the prime limiting factor. On https://prism.oregonstate.edu/normals/ you can plot mean dewpoint... [even in the heart of summer](https://i.sstatic.net/sTvoZ.png) the PacNW just doesn't get near Tds of the Plains\East in spring {at fairly low elevations, a reasonable rough low bound for severe wx might be 60F or even really 65F; higher elevation in ECascadia may allow it to be slightly lower, but [SPC's sounding climatology](https://www.spc.noaa.gov/exper/soundingclimo) shows how rare decent CAPE is}]. The monsoonal plume isn't really enough for the Pac NW... or the SW.  
> **username_3**: To further investigate the different in moisture levels, perhaps play around with [ISU's ADP](https://mesonet.agron.iastate.edu/plotting/auto/?_wait=no&q=60&network=ID_ASOS&zstation=LWS&var=dwpf&threshold=60&direction=above&cmap=jet&dpi=100&_fmt=png).  Compare how incredibly [rare 60F is in Lewiston](https://i.sstatic.net/Ip8pj.png) vs how common (particularly in afternoon's peak heating) [65F is in Oklahoma City](https://i.sstatic.net/5OE3I.png) or other cities. It certainly isn't the only factor (having ample moisture in July in OK doesn't mean tornadoes), but it is a base requisite.  
> **username_3**: Funny enough, in the two years since I wrote my original answer, life has changed a lot, and I ended up spending quite a bit of time in and around the Columbia Basin\Cascades\much of Cascadia... great area.  Ironically even happened to come into town the day there was a [tornado in the Portland metro](https://www.oregonlive.com/weather/2020/06/funnel-cloud-spotted-over-damascus-saturday-evening-video.html)!!!  

---

## 1 answers

### Answer by username_3 on 2018-05-30. Score: 4 | Accepted answer

> Note: These inputs are of a meteorologist who has quite actively tracked severe
> weather around the US for a couple
> decades... but also hadn't spent as much time in or attention on the west and northwest of the country. So there could could theoretically be some degree of unintended bias. I've tried to use objective data where possible, but it's something to keep in mind, regardless.

**In terms of "*a lot*", at least for tornadoes/hail, I'd suggest that nowhere west of the Rockies sees *a lot* truly:**

[![tornado tracks](https://i.sstatic.net/icihBm.png)](https://i.sstatic.net/icihBm.png)
[![hail](https://i.sstatic.net/kB1nym.png)](https://i.sstatic.net/kB1nym.png)
Tornadoes [left], hail [right]... source: [Storm Prediction Center SVRGIS page](http://www.spc.noaa.gov/gis/svrgis/)

I'd offer the idea that there of perhaps two notable reasons for that:

1. The **lack of consistent and widespread surface wind fields favorable to tornadoes**... due to a combination of the lack of the big [lee cyclogenesis](http://glossary.ametsoc.org/wiki/Lee_cyclogenesis) seen east of the Rockies, along with the complex topography.
2. The **rarity of regular low-level moisture** significant enough to allow for low [LCLs](https://www.youtube.com/watch?v=MbbjVUxtsDE). The higher the storm base is above the ground, the less likely a tornado  
   [[in figure 6 of Edwards and Thompson 2000, all the red boxes showing tornadoes are on the left side, which are lower LCLs](http://www.spc.noaa.gov/publications/edwards/part2.htm)]

The lack of rich low-level moisture is due in large part to the lack of accessibility from warmer moisture sources, particularly the Gulf of Mexico; the Rockies provide a barrier to much of the moisture reaching further west.

As you note, parts of Wyoming and Montana do see supercells and tornadoes a bit more often... but on a [good topographic map](http://en-us.topographic-map.com/places/United-States-2241/), fair parts of those states are east of the [Continental Divide](https://en.wikipedia.org/wiki/Continental_Divide_of_the_Americas), and so still on an "[upsloping](http://www.theweatherprediction.com/habyhints/112/)" area and thereby not blocked by sinking regions which prevent full moisture progress. They're still less-tornado prone due to elevation and increased distance from moisture, but it does happen.

The desert southwest also does manage to get [monsoon moisture sneaking around the terrain further south](https://en.wikipedia.org/wiki/North_American_Monsoon)... but **further north that monsoon moisture sees additional blocking by the more elevated terrain across Nevada and Utah**. (And in the southwest, a different key ingredient in tornadic supercell development is typically missing in the summer monsoon: [upper-air winds sufficient for supercell development](https://en.wikipedia.org/wiki/North_American_Monsoon))

The Pacific Coast does see a few occasional tornadoes. But from what I've seen, they typically form from smaller storms with much less classical and intense mesocyclones. As you mention, they're a bit more in line with cold-core setups, which usually produce weaker short-lived tornadoes than classic supercells of the Plains and on east. If you plug in the events you speak of into [SPCs Severe Weather Events archive](http://www.spc.noaa.gov/exper/archive/events/), [pick the date, then click Obs and Mesoanalysis on the left, then use the dropdowns to find various parameters]
you can see that CAPE was typically very meager (well short of 1000 J/kg) and the storm structure quite weak in reflectivity in comparison to a classic supercell, more indicative of such cold-core setups.

Capping inversions may be helpful to "keep the lid on the pot" if you have strong CAPE (and therefore quality moisture) and intense updrafts to erode the cap during the day. But as it is, **there isn't enough moisture typically for the cap to be a positive factor**.

Quite a bit of the area you mentioned, such as Spokane, makes up one of the [more arid regions of the country](https://en.wikipedia.org/wiki/United_States_rainfall_climatology#/media/File:Average_precipitation_in_the_lower_48_states_of_the_USA.png). Further removed from the rain shadow of the Cascades, the Idaho Panhandle does get more precipitation, but it's mostly in [cooler months](https://www.bestplaces.net/climate/city/idaho/lewiston) that lack the deep convective development needed for supercells, probably because of the [proximity of the Pacific high](https://climate.ncsu.edu/edu/HighLow) in summer months. Further east in E ID/W MT, particularly in the Flathead Valley, there are [occasional summer thunderstorms](https://www.e-education.psu.edu/meteo3/sites/www.e-education.psu.edu.meteo3/files/images/lesson8/tstrm_climo.jpg)... but the storms may well be higher based due to the limited low-level moisture, and so have low potential of tornadic development. For more on the climate complexities at play in the Idaho vicinity, [check out this article](https://wrcc.dri.edu/narratives/IDAHO.htm) from the Western Regional Climate Center.

In the end, the area you ask about is one of the weakest regions for supercell development in the entire United States. The entire quarter of the country west of the Rockies isn't much better. [This page](https://mesonet.agron.iastate.edu/plotting/auto/?q=92) from Iowa State University will create an image showing the number of days since each pocket of the country (sorted by National Weather Service forecast office areas) last saw a tornado warning. It shows that the Idaho Panhandle hasn't seen a tornado warning in over 10 years:

[![enter image description here](https://i.sstatic.net/cQ3a6.png)](https://i.sstatic.net/cQ3a6.png)

More than anywhere but northern California.

And another ISU [page](https://mesonet.agron.iastate.edu/plotting/auto/?_wait=no&q=90&t=cwa&v=yearavg&ilabel=yes&geo=polygon&drawc=yes&year=1989&year2=2019&sdate=1989%2F01%2F01%200000&edate=2019%2F12%2F31%202359&station=OTX&state=IA&phenomena=SV&significance=W&cmap=jet&interval=1&dpi=100&_fmt=png) allows it to be shown that:
[![enter image description here](https://i.sstatic.net/vlpdn.png)](https://i.sstatic.net/vlpdn.png)

... Most spots in northern Idaho only see about one severe thunderstorm warning per year on average (versus [10-20 per year over Oklahoma](https://i.sstatic.net/X8L0n.png)).

**So the danger of severe convective weather is remarkably low in that region of the country overall.**

> **Comments:**
> **username_3**: Of course they do occasionally happen (especially in SE Idaho).  Go figure, [this](https://i.sstatic.net/a6z1P.png) was today [hopefully the imgur will stay alive long despite not adding to body]  

---

