*Updated 10AM* Rainy Pattern Setting Up Through the Weekend

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Summary | Forecast | Safety

An upper level low slowly shifting northeastward will bring an unsettled pattern to the region for the next several days. An abnormally moist atmosphere will increase chances for heavy rain (see graph below) and some upper level dynamic support will increase the coverage of the rain and turn it into a more widespread event. Most of the heavy rain will be focused in the mountains as they provide a more significant source of lift, and in the foothills on the east and north side of mountain ranges like Lander, Jeffrey City, Casper, and Dubois.

Precipitable Water Normals and Extremes - Click to enlarge Precipitable Water Normals and Extremes - Click to enlarge
Click Image To Enlarge

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 value (dashed line), we can anticipate precipitation records at the surface to be threatened as well as some localized flooding.
Precipitable Water Normals and Extremes - Click to enlarge

This combination of factors raises the flash flood and mudslide risk for those in the mountains and near the recent burn scar areas in addition to the usual flash flood prone areas (small, steep, rocky basins and dry washes). 

Blacks Fork Hydrograph - Click to enlarge Green River Near La Barge - Click to enlarge
Click Image To Enlarge

The above graph shows the real time measurement of the Blacks Fork near Little America. Click here for more information on the location of this gauge, the impacts that occur when the river reaches action stage and the various flood stages.
Click Image To Enlarge

The above graph shows the real time measurement of the Green River near La Barge where flooding occurred nearby on Thursday night. Click here for more information on the location of this gauge, the impacts that occur when the river reaches action stage and the various flood stages.

 

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 Sheepherder Hill burn scar has already produced a damaging flash flood this year and it could easily do so again. If you are unsure whether or not you are at risk from one of these scars after checking out the website, please give us a call at 800-211-1448 and we will do our best to help answer your questions.

An upper level low in the Great Basin will work northeast and bring plenty of moisture with it. Much of the state is covered in fog this morning, once this clears, then thunderstorms are expected to form just about anywhere as the instability is evenly distributed across western and central Wyoming. Unfortunately, yesterday's rain has eroded away some of the buffer that we used to have in the very low river levels and storm motion is expected to be very slow - raising flooding concerns with the storms today.  Heavy rain brought flooding and mud slides to the La Barge area last night, and this area is at risk again today. Areas of northeastern Colorado have received over 12 inches of rain from this system with multiple Flash Flood Warnings, mudslides, road closures, and even loss of life.

 6 Hourly Precipitation Forecast - Click to enlarge  GFS Accumulated Precip - Click to enlarge
Click Loop To Enlarge

The above loop begins at 18Z Wednesday (Noon Wednesday) and ends at 18Z Monday, showing the amount of rain expected in 6-hourly time steps through the weekend.

*Note* This raw model data is being shown to give you an idea of the precipitation trends over the next few days - where and when the heavier rain is expected to fall. The actual rainfall amounts should be taken with a grain of salt.

Click Loop To Enlarge

The above loop shows the expected accumulated precipitation from noon Wednesday through noon on Monday.

As the loop shows, most of the rain will fall across the southwestern half of the state today and tonight ...spreading across the rest of the state by Friday and continuing through the weekend. The heaviest rain is expected across the Absarokas, Wind River Range, and Upper Wind River Basin near Dubois.

 Precipitable Water Forecast and 500MB Flow - Click to enlarge  
Click Loop To Enlarge

This image shows the amount of moisture available for rain (called Precipitable Water or PWAT) from noon Wednesday through Monday morning. The blue and green shades show where the most moisture is available. The 500MB pattern is represented by the white lines and the low level winds are represented by the orange arrows (the longer the tail, the stronger the winds). 

As the chart at the top of the page shows, "normal" precipitable water for this time of year should be less than one half of an inch (gray shades in this image) anything in the green and light blue shades is well above normal with the dark blue shades representing near record amounts of PWAT.



In summary, there is a good chance of measurable rain and even some localized flooding over the next several days with more steady rain expected through tonight, transitioning to a more showery regime for the weekend.

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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