Flash Flood Watch For the Western Mountains Today

The National Weather Service
Building a Weather-Ready Nation

Summary | Forecast | Monitoring & Reporting | Safety

An abnormally moist atmosphere will combine with day time heating and very slow moving thunderstorms to produce showers and thunderstorms along and west of the divide. Most of this activity will be focused in the mountains as they provide a more significant source of lift, with more focus shifting to the north in the evening, including Yellowstone National Park. Once the storms do form, their movement will be very slow.

This combination of factors raises the flash flood and mudslide risk for those in the mountains and near the 2012 burn scar areas in addition to the usual flash flood prone areas. 

NOW is the time to figure out if you are in danger if the right storm hits one of these burn scars - Why are they so dangerous? Because it only takes less than one half inch of rain in less than an hour to cause flash flooding and debris flows in burn scars! The Waldo Canyon burn scar near Colorado Springs has already produced a flash flood and debris flow twice so far this season.

Thunderstorms will form across the western mountains today as an upper level disturbance rotates around a high centered east of the Cowboy State. Storm motion will be slow and they will be moving in an abnormal direction: roughly from south to north. This direction also runs parallel to most of the mountain ranges, which will encourage storms to form and move repeatedly over the same location. Also, we have an abnormally moist atmosphere, both at the surface and aloft. This moisture provides fuel for the thunderstorms that will work with the instability from the approaching wave and from the normal surface heating that goes on every afternoon.

If you are camping in the mountains today or spending some time in Yellowstone National Park, please move away from nearby streams or dry washes as they could flood today and tonight, especially since an approaching wave will provide support for more of mother nature's fireworks well into the night (attention photographers!). Also, if you live near a burn scar please familiarize yourself with your level of risk. If one of these storms happens to form or move over one of these burn scars today, then flash flooding and debris flows are likely.

 July 16 PWAT - Click to enlarge  SREF Accumulated Precip - Click to enlarge
Click Loop To Enlarge

The above loop shows the preciptable water available for "rain-making" today and tonight. The loop shows gradual moistening of the atmosphere across the west through the afternoon hours, peaking early this evening at over an inch, which is quite high for this area.

Click Loop To Enlarge

The above loop shows the accumulated precipitation from this morning, ending at 5am Wednesday.

As the loop shows, the storms really increase begin adding up the rainfall after 21Z (or 3PM local) with heavier rain lasting into the evening, with the focus shifting north into Yellowstone toward sunset.

 Storm Prediction Center Thunderstorm Forecast - Click to enlarge  Thunderstorm Threats - Click to enlarge
Click Image To Enlarge

This image shows where the Storm Prediciton Center has highlighted areas that could see a thunderstorm today.

In summary, there is a high likelihood of thunderstorms today and tonight, with the highest impact storms expected to remain across the west. The main concerns with these storms will be flash flooding, damaging hail, and frequent lightning.

If you are one of the many visitors or residents enjoying the outdoors today, please keep an eye on the weather, do not camp near creeks, streams, or dry washes, and remember - if thunder roars, go indoors!

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