Predictability of flash floods

[kaniukr]

[FONT=Calibri]I wondered if any

[Deathcricket]

maybe not the answer you want to hear, but I think most of us just wing it. We check the weather the night before and make a decision. If it looks sketchy we bail out and plan a safer canyon. Sometimes we decide to go and then the next morning as we are driving it looks like rain so we change the plans again. I think the main thing is just to have a backup plan(s) so if the weather looks bad you can do something else.
Kannarra creek is pretty safe IMO. In the absolute worst case scenario where you get caught in a flash flood, there are plenty of places to find high ground and really only a couple sections of 400 feet where you would be trapped. it's not like some canyons where it's a good 1/2 mile before a safe exit is available. Fat man's misery is a very dangerous one so I would stay very far away if it looks like rain, havent done bull valley gorge so not sure.

I also have a pretty cool flash flood from last year caught on film if you want to check it out. This was late in the afternoon after we did Behuinin one day.

[stefan]

awesome video, DC!

[kaniukr]

Scary video. Within 30 seconds of you starting filming it would certainly sweep a child away. It's probably only hip deep, but the flow soon gets fast.
How long before you started filming did you realise it was coming? As they say, no signs in the sky which looks blue and dry.

[Bluff-Canyoneer]

I will leave it to others with more experience in his intended routes to comment on the specific flash flood risks.

Here is a flash in North Wash I caught on video.

youtube.com/watch?v=87KYee4bjNs

[peakbaggers]

Kaniukr,
I certainly understand your dilema - investing the time & money to come here and trying to get in some real canyon adventure with minimal risk of failure due to weather. I am by no means the most experienced of canyoneers, but have climbed in Colorado for 35 years and am more than familiar with the overall weather patterns of the southwest in the summer.
Locally, some of us refer to July, August and the early half of September as "monsoon" season. This is when weather patterns combine to send in surges of moisture from the Gulf of Baja and Mexico into the desert southwest and into the Rocky Mountain region, hence, "flashflood" season. The so-called monsoonal rains tend to come in wave periods where for several days the chance of severe thunderstorms may increase dramatically and then subside for several days as a high pressure ridge may position itself to block that moisture flow out of Mexico. This moisture flow is easy to observe on water-vapor loops provided through various weather sources. As for the accuracy of weather forecasts, no one can accurately predict the exact time & location of a potential flash flood, but the National Weather Service and local weather sources do issue "Flash Flood" warnings for general geographic areas that are fairly specific. I would heed those warnings. In our weather forecasts here, the chance of rain is often presented as a percentage chance. In a discussion on this forum maybe a year ago, there seemd to be a fairly good consensus that if the percent chance goes over 30% for any particular day, you may want to change your plans. That would be erring on the safe side. Always do your own visual check before entering a canyon, but even that may not guarantee safety.
Kanarra Creek has limited, shorter sections of narrows as pointed out above and plenty of escape options. It is also basically a non-technical canyon. Fat Man's Misery does have a large catch-basin. The canyon tends to vary from narrow sections to wider open sections where escape would be easier, but the risk would be much higher than Kanarra. As for Bull Valley Gorge, again, basically a non-technical canyon and I have not been there in years, but I do remember a long stretch of narrows that could not be easily escaped and I think it has a fairly large catch basin. In general, the chance of rain is lower at lower elevations, however this doesn't guarantee safety, (see videos above) but if the higher elevation canyons are showing a higher percent chance of rain, you may want to alter plans and head for a lower elevation canyon that's farther away from mountainous terrain.
If you have not already accessed them, some of the local canyoneering sites should be of some help in assessing the risk. Shane's site, Climb-Utah, seems to make consistent reference to the catch-basin size of each canyon and potential flood risk and if you focus on the Zion area, Tom's Canyoneering site will provide helpful beta. Local, outdoor gear shops in the St. George/Zion/Springdale area also provide weather data.
Good luck on your venture. Hope the weather cooperates and you get to enjoy some of our scenic canyons, but have a backup plan.

[Brian in SLC]

I know that weeks ahead, and even probably just one week ahead, it’s impossible to predict what the weather might turn out to do on a certain day. But are weather forecasts accurate and reliable for predicting rainstorms the day before, or even perhaps 2 or 3 days before, so that I can enter a canyon reasonably sure it will be safe? In other words if I keep checking while I’m in Utah, are forecasters pretty accurate in their ability to say “there’s not going to be rain in the next couple of days.....or, there’s a risk of it.” Or can the weather change so unpredictably and suddenly that no-one knows what will happen later that day or the next day.

Secondly, “on average”, what percentage of days in August are usually too risky or safe? – obviously this will change every year, but are more than half the days safe.

I’ve been told most storms come in the afternoon – I realised there’s no guarantees, but is it the case that generally up to perhaps 3pm you’re probably safe?

I've seen microburst type t-shower activity in the mornings, some times its afternoon but I wouldn't rely on that.

I look at weather trends in a short span of time. When its hot and the monsoon is in season, its only a matter of time before you get flash flood type weather. It seems to kinda build. But, its hit or miss. I guess I'd try to study it, look for what trends to pay attention to, and, if the weather is either unusually dry, go for it, or, if unusually juicy, don't.

If the monsoon is in full effect, most of us just avoid being in a place at risk.

[Deathcricket]

Scary video. Within 30 seconds of you starting filming it would certainly sweep a child away. It's probably only hip deep, but the flow soon gets fast.
How long before you started filming did you realise it was coming? As they say, no signs in the sky which looks blue and dry.

In this case we knew it was coming hours ahead. If you notice the background people even drove out to see it coming (from town) and there is a cop right behind me who was driving ahead of it to make sure people were clear. It flashed in behuinin as we were leaving, had dinner, then this is a sheep's bridge road down in Virgin when it got there. The water turned from clear to very very muddy a good half hour before it reached this place. So while you don't get a huge warning, you do get "some" warning. And where it actually flashed the clouds were super nasty and pretty obvious. The problem is when it hits and you have no place to escape or high ground like a slot canyon. And to be fair when we left to start the canyon it was a clear sunny day. 8 hours later - Bam! And make no mistake child or adult in this would be dead no questions. The video doesn't really so it justice but those are huge logs in there and the grinding sound was hellacious it was like being near a herd of stampeding buffalo's.

[Iceaxe]

It would not bother me in the least to plan a trip for the UK to visit the Southwest in August. Flash floods are something that can be avoided with a little commonsense. The one thing you want to do is have some back up ideas if you have a thunderstorm or two.... a thunderstorm in the desert southwest is not exactly a bad thing, if fact it can be one of the most spectacular things you will ever witness... The pictures below were taken when a thunderstorm was predicted so plans were changed to hike Angel's Landing (which is always a reasonable backup when in Zion).... Heck, just riding the tour bus through Zion Canyon during a thunderstorm is a fun adventure.

[Slot Machine]

maybe not the answer you want to hear, but I think most of us just wing it. We check the weather the night before and make a decision.

Sometimes we watch the NOAA video feeds while driving to a canyon. You know what a cloud looks like. You can do the math when watching the video feed.

FWIW, by closely monitoring the NOAA video feed we were able to do Fat Man's Misery just hours after a major storm. That canyon is AWESOME after a storm fills it up!

[dlofting]

We come to Utah every year to canyoneer, usually in August. I generally plan to do a canyon every other day, so if one day looks bad from a flash flood perspective we can change our plans. If we can't canyoneer we hike instead....coming from the Pacific Northwest it doesn't bother us to get a bit wet as long as we're on a trail and not in a canyon.

[Deathcricket]

a thunderstorm in the desert southwest is not exactly a bad thing, if fact it can be one of the most spectacular things you will ever witness...

That's another really good point. The video doesn't do it justice, but being that close to such a force of nature was the highlight of my summer, better than any slot canyon I did. I know I sound like the "double rainbow OMG" guy but it was so impressive in a way that unless you are actually there before it to witness, you'll never understand. It makes so much noise grinding boulders and snapping trees, it has this "earthy smell" and you don't doubt for one second it could kill you. Kinda surreal.

[kaniukr]

Thanks everyone who has been kind enough to reply

[goindeep]

some great videos and pics. Those logs in the first video looked big, would not want to get caught in something like that. If you do get caught in a flash flood and swept away, what should you do?? try to stay afloat and grab on to something and climb out.... any tips? not that I ever want to get caught in one, but it would be good to have a strategy.

[ratagonia]

I wondered if any “regulars” at Utah canyoneering/hiking could help with a question about the flash flood risk. I live in the UK and I can only come to Utah in August because of my daughter’s school holiday dates, but I know it’s flash flood season and I want to go to slots like Kanarra Creek, Fat Man’s Misery, Bull Valley Gorge and probably do some driving on clay roads like Skutumpah which are impassable when wet.

I know that weeks ahead, and even probably just one week ahead, it’s impossible to predict what the weather might turn out to do on a certain day. But are weather forecasts accurate and reliable for predicting rainstorms the day before, or even perhaps 2 or 3 days before, so that I can enter a canyon reasonably sure it will be safe? In other words if I keep checking while I’m in Utah, are forecasters pretty accurate in their ability to say “there’s not going to be rain in the next couple of days.....or, there’s a risk of it.” Or can the weather change so unpredictably and suddenly that no-one knows what will happen later that day or the next day.

Secondly, “on average”, what percentage of days in August are usually too risky or safe? – obviously this will change every year, but are more than half the days safe.

I’ve been told most storms come in the afternoon – I realised there’s no guarantees, but is it the case that generally up to perhaps 3pm you’re probably safe?

(oh, and where does the rain catchment area for Kanarra start - how far away?)

Thanks in advance for any answers.

There have been some good answers... but here is mine, from 13 years of Southern Utah Canyoneering. Heck, I've only been caught in flash floods 5 times!

August is NOT Flash Flood season. August CAN BE Flash Flood season.

The weather condition that produces flash floods is called the Monsoon - a condition of very moist air blowing up from the Sea of Cortez. The Monsoon mostly hangs out in Arizona, and the question is, where is the upper edge of it? Sometimes the Monsoon reaches up into Utah, and sometimes it does not. Sometimes it does so for 3 weeks at a time, sometimes it shows up for a day or two, then subsides. The weather predictions are pretty good, and if taken conservatively, will keep you out of trouble. But it does get in the way of doing things, at least canyons. It is possible to carefully choose canyons and do some carefully, but generally it is better to hike (sometimes in the rain) when the Monsoon is in town.

Look at the map, and study the watersheds. Kanarra Creek, for instance, has a small watershed with a lot of vegetation in it, so is relatively unlikely to flash. Also, the canyon has only very short sections of narrows, and no technical sections (unless you count the ladder), so that is a relatively safe canyon to do on a threatening day.

Fat Man's Misery is a good canyon to do on a threatening day, as the narrows sections are short, and technical sections are discontinuous. I would not want to do it on a sunny day in August, but it would be good on an overcast or drizzly day. Even a little rain would not be a problem, though the watershed is not all that small, AND is mostly slickrock, so it would build a flash quickly, should a thunderstorm stall out in the headwater position.

Tom

[Deathcricket]

Bump!

Forgot about this video. this is same flash flood I caught but a couple miles further up but he is standing like 10 feet away from it instead of up on a cliff. Way better sound IMO.

[goindeep]

wow the amount of wood at the front of that flash flood was ridiculous! it was like a slow moving 3ft high wooden beast coming to get you.