Some Thunderstorms This Week

Slow and subtle changes in the large-scale circulation will cause some changes in the weather of northern Utah early this week.  The situation at 1800 MDT yesterday (0000 UTC 20 July) showed some scattered convection across Arizona, Utah, and Nevada with relatively weak radar echoes.  Precipitation was limited and the main influence of the convection was to produce some gusty winds. 

One measure of the amount of water vapor in the atmosphere is precipitable water, which is the depth of water you would have if you condensed all of the water vapor out of the atmosphere.  Yesterday, values across much of Nevada and Utah were less than 15 mm and in some cases less than 10 mm (see color contours in image above).  For the Great Basin in July, this isn't much to play with unless you have a deep trough over the area, which we don't.

Over the next few days, however, precipitable water values will be slowly increasing as a weak trough (emphasis on weak) approaches from the west.  The NAM forecast for 1800 MDT Tuesday (0000 UTC 22 July) shows values across most of Nevada and Utah > 15 mm and in some areas > 20 mm. 

By 1800 MDT Wednesday (0000 UTC 23 July), values near 25 mm are moving through northern Utah, with drier air that has wrapped around the weak trough moving into central Nevada. 

That's enough to increase the thunderstorm threat, but this is not a strong monsoon surge. Thunderstorms in northern Utah will probably be isolated tomorrow and scattered Wednesday, but if you happen to be near one, there will be a threat of lightning, gusty winds, and precipitation.  It will be worth keeping an eye to the sky.  When thunder roars, head indoors.