Flash Floods In Early April

[qedcook]

With the forecast looking gloomy for this weekend, I'm wondering. I've heard that flash floods don't happen this early in the year. True? What do you think?

[tcott]

Flash floods can happen any time we get a good storm, it doesn't matter what time of year it is.

[Byron]

I've been backpacking on the Colorado Plateau for more than 25 years. I've seen some BIG floods, but very rarely in April. I wouldn't go into a slot canyon with little or no escape when it looks like it's going to rain. It's a judgement call though when you get there and it's just a light drizzle. Better safe than sorry considering the consequence is rubber bones...

[restrac2000]

Some of the biggest ones I have seen have been in the winter. Salt River basin jumped 60k overnight one winter. GC tribe flashed wicked on our January float. I was in the boat waiting for the decent team for the Pyscho Damage incident (early April) when it flashed majorly.

It definitely happens.

Phillip

[Scott P]

Flash floods have happened in every month, but statistically, in SE Utah April and June are the least likely months to flash flood.

[maarten.1975]

Flash floods have happened in every month, but statistically, in SE Utah April and June are the least likely months to flash flood.

Hmm, what happened to May, being in the middle of April and June?
I'll be there in May, don't tell me chances are much higher then in either April or June...
I think I wouldn't understand...

[qedcook]

So why does the national weather service stop issuing flash flood warnings and ratings during winter?

[tcott]

So why does the national weather service stop issuing flash flood warnings and ratings during winter?

Snow doesn't make very good flash floods.

[Iceaxe]

So why does the national weather service stop issuing flash flood warnings and ratings during winter?

I have no clue why the national weather service stops issuing flash flood warnings... but flash floods happen in winter.

I once saw the Paria develop a massive ice dam just below where Buckskin enters. The dam eventually burst when it rained hard upstream. The bursting dam released a major flash flood.

I have also seen a couple flash floods caused by warm rain on top of snow. There was a pretty big one that wiped out a couple homes in Utah County a few years back.

[restrac2000]

I am sure the National Weather Service would offer the services if they happened enough, they just have to allocate their resources where they are most needed or probable to be used. Just look at the PNW, there flood season is fall through spring.

Rain on snow events provide some of the biggest floods in river basins.

Phillip

[Byron]

Crystal Rapids in the Grand Canyon were made in December of 1969. If I remember correct it was something like three inches of rain in a matter of minutes on the rim. It's a great backpack trip, Tiyo point to Shiva Saddle down to Dragon Creek to Crystal to the river. It's a George Steck trip. You can see the flood damage, at least 25 feet high, reamed out.
By the way, today here in Denver we had thunder, lightning and street flooding. I can't remember the last time it occurred this early. Usually, these things don't fire up until the middle of May, at least.

[Scott P]

If I remember correct it was something like three inches of rain in a matter
of minutes on the rim.

Actually it was 14 inches of rain (estimated). And it fell on several feet of snow. Same storm hit SW Utah and southern Nevada as well. The North Fork Virgin River peaked at 9150 CFS and is still the record. The Littlefield gauge on the Virgin peaked at 35,200 CFS, also still the record. In the Grand Canyon, Crystal Creek that you mentioned peaked at an estimated 40,000 CFS. It was the biggest flood in at least 1000 years because it took out the indian ruins.

So why does the national weather service stop issuing flash flood warnings and
ratings during winter?

I don't know, but I do know that most winter flash floods (as mentioned the biggest ones are usually a result of rain falling on snow) usually only happen in certain areas (such as Zion National Park or Kanab Creek). In winter, usually it's only in canyons that come from the mountains rather than in the majority of slot canyons out there in the desert.

[trackrunner]

So why does the national weather service stop issuing flash flood warnings and ratings during winter?

I think you mean why does the NWS not forecast flash flood potential. Specifically the SLC office of NWS does not maintain the canyon country flash flood potential (advisory) page in winter months.

NWS does issue watches & warnings alerts in the winter months. I seem to recall flash flood watches, then flash flood warnings, & then flood warnings in the Zion & SW Utah areas during the recent winter floods of Dec 2010 & Jan 05.

A flash flood watch means a flash flood could occur. A flash flood warning means a flash flood is occurring or will occur.

Why does the NWS not maintain the flash flood potential page in the winter months? Probably because the chance & frequency is less likely & the demand for the forecast is low; similar to why avalanche forecast stop in April when avalanche (like wet & glide) can occur in May & June.

FYI the hydrologist forecaster & probably the person who issues the warnings & watches in SLC office of NWS is a member of bogley, Brian the NOAA guy. He could provide more accurate reason, definitions, & what goes into forecasting these alerts.

[restrac2000]

Sure you aren't talking about Bill Nye the Science Guy?

[qedcook]

So, are all winter flash floods due to snow? Because there is no snow near the roost right now.

[Scott P]

So, are all winter flash floods due to snow?

No, just the historically biggest ones.

Because there is no snow near the roost right now.

I wouldn't worry so much about flash floods there this weekend, but would worry instead about wet dangerous rock. Many (perhaps most?) of the exits in the Roost can be quite dangerous when wet and when it is raining. Wet sandstone is also weaker and more crumbly when wet.

[trackrunner]

Sure you aren't talking about Bill Nye the Science Guy?

He calls himself that
http://www.bogley.com/forum/member.p...-brian_noaaguy

analysis from him on a canyoneering flash flood accident with 2 fatalities can be found in this thread.
http://www.bogley.com/forum/showthre...060#post337060

and proof that watches & warning issued in the winter, this watch released from Brian in January.
http://www.bogley.com/forum/showthre...916#post391916

[jman]

I wouldn't worry so much about flash floods there this weekend, but would worry instead about wet dangerous rock.

You sure? The current weather status says that the central and southern mountains of Utah will receive 12-24" of snow (winter advisory for those mountains as well), and those regions will receive inches of rain everywhere else.

(Hmmm, hopefully that means Zero G will be refilled for my trip in two weeks!)

[ratagonia]

You sure? The current weather status says that the central and southern mountains of Utah will receive 12-24" of snow (winter advisory for those mountains as well), and those regions will receive inches of rain everywhere else.

(Hmmm, hopefully that means Zero G will be refilled for my trip in two weeks!)

Well, I would say it will be unpleasant down there, and some of the canyons will flow. Plenty of canyons I would not want to be in, in these circumstances.

But I would not call these flash flood conditions. Not every flood is a flash flood. Not every unpleasant, dangerous, wet, snowy, flooded condition in a canyon fits in the category "flash flood".

Tom

[jman]

Well, I would say it will be unpleasant down there, and some of the canyons will flow. Plenty of canyons I would not want to be in, in these circumstances.

But I would not call these flash flood conditions. Not every flood is a flash flood. Not every unpleasant, dangerous, wet, snowy, flooded condition in a canyon fits in the category "flash flood".

Tom

That's a good clarification point.