Strong Thunderstorms Today and Tonight

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 across the state. 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. The storms will move along a bit quicker today, but storm movement will still be on the slow side. Also, there will be more upper level support today which may encourage the storms to become more organized and therefore, stronger.

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 produced a flash flood and debris flow on Monday from similar storms.

Forecast PWAT- Click to enlarge Friday Morning Dewpoint - Click to enlarge
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The above graph shows the Climatologically "normal" precipitable water values at Riverton (red line). It also shows the record high (light green) a low (black)  values recorded by the balloon launch at Riverton/Lander through the years. Once the expected value nears 2 standard deviations above the mean, represented by the dark green dashed line, then we can expect some storms to cause flooding. In these cases, if any storms do form and they happen to be moving slow enough or if several storms move across the same area, then flooding becomes much more likely.

The models are forecasting anywhere from 0.85in to 1.00in of precipitable water this afternoon and evening, if the highest and lowest values are thrown out, then we end up with a range of values that falls within the 90th-99th percentile, which is around or above 2 standard deviations above the mean value (around 0.58in this time of year).
Click Image To Enlarge

The above image shows the water vapor satellite this morning with the dew point values overlaid. Most of the observed dew points in the area are in the 50's, which is very moist for this area. Moisture is the "fuel" that thunderstorms need to get started and we will have plenty both at the surface and aloft.

A high pressure ridge to our southwest will continue to break down today, that event alone can trigger thunderstorms - especially over the higher terrain. Today, we have the added support of an approaching trough and associated jet streak that will encourage the atmosphere to destabilize further. Also, we have an abnormally moist atmosphere, both at the surface and aloft. Surface dew points are in the 60's at Powell and well into the 50's almost everywhere else, which is very, very high for this area; and the precipitable water values are over the 90th percentile, which is not seen too often. This moisture provides fuel for the thunderstorms that will work with the instability from the approaching trough and from the normal surface heating that goes on every afternoon. In addition, the storm motion will still be quite slow, but not as slow as yesterday; that does not mean that there is no chance for flash flooding today though, especially if storms happen to pass repeatedly over the same area or if they move over areas that received a lot of rain on Thursday.

If you are camping in the mountains today, please move away from nearby streams or dry washes as they could flood today and tonight, especially since an approaching upper level jet streak 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 5 Pattern - Click to enlarge  Afternoon Instability and Storm Motion - Click to enlarge
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The upper level pattern shows a large ridge continuing to dominate the four corners region. An approaching trough will provide broad instability while an upper level jet streak adds some reenforcement.


Shaded image = 700MB Temperature
White Contours = 500MB Height

Wind Barbs = 700MB Flow

Click Image To Enlarge

Instability will be present everywhere this afternoon (blue shades) with the greatest instability residing in the north (dark blue to red shades).

The blue arrows show the average storm motion over a given point this afternoon. The shorter the arrow, the slower the storms will move, and therefore the greater the flash flood threat with any given storm.
 Storm Prediction Center Hail Forecast - Click to enlarge
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This image shows where the Storm Prediciton Center has highlighted an increased threat for severe hail (the size of quarters or larger).

In summary, there is a high likelihood of thunderstorms today and tonight, with the best chance of a strong storm or two across the north. 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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