Dry lightning becomes a concern as monsoonal moisture spreads north

As wildfires have been raging in the West over the past few weeks, there will be the threat for more new fires in the coming days.

Thunderstorms with dry lightning will be the main concern early in the week as monsoonal moisture spreads farther to the north and west.

We've already seen this at times of the past week, with Los Angeles picking up measurable rain on Tuesday. That is a rare feat this time of year, as Downtown Los Angeles only averages 0.01 of an inch of rain for the month of July.

There were a few more showers and thunderstorms roaming across Southern California again early Sunday morning.

We will see more thunderstorms farther north Sunday and Monday as a surge of moisture gets pulled up through California and Nevada.

The precipitable water shows this surge well, which will likely be enough to trigger some spotty showers and thunderstorms, especially across some of the higher terrain. Even some of the lower spots will see one too.

While rain can certainly be a help during this dry time of year, many times situations like this pose more harm than good. There can be little to no rain with some of these storms, allowing lightning strikes to start fires easily.

Dry lightning started fires last year in August, and some of those fires ended up burning hundreds of thousands of acres.

Why does this happen? We can look at a forecast sounding in Reno, Nevada, on Monday to get an idea.

Soundings like this allow us to get a visual look at the atmosphere. In this case, take a look at how close the blue and red lines are.

The blue line indicates dew points, the red line shows the temperature as you go up through the atmosphere. When the lines are close, the air is closer to saturation.

Notice how there is a decent amount of moisture in the mid-levels, but how much drier the air is near the surface.

As a result, while there can be enough moisture to aid in thunderstorm development, the rain falling from the clouds may mostly evaporate before reaching the ground.

When the rain doesn't reach the ground and lightning is striking already dry brush, numerous fires can be started.

In addition to the current concerns, both the GFS and the Euro are showing the potential for another surge of moisture up through California early next week.

The European is even more aggressive with the moisture.

We'll keep a close eye on that as we head through the next several days.

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