Thread by @NWSVegas

Let's talk Monsoon!! 🤓⛈️

Been hearing weather people talking about rain/storm chances and the prospect of monsoon 2020 to make an appearance next week? Follow along with this thread and we will break down why that's the case... 👀

First, let's look at our #GOESW satellite...

Ok...ok...it's a little hard to pick out things that zoomed out. Let's zoom into the Southwest US and add some other features. 🛰️ 👀

Nevada is pretty quiet, but Arizona and New Mexico look pretty stormy. What about that big blob of storms in Mexico? These are key! Here's why...

Let's refresh on what the monsoon is and what you need to have a good set up...

The "monsoon" is not a storm, a series of storms, or even moisture in the air. It's a shift in the winds aloft that *enables* moisture to filter in to the arid desert climates of the southwest.

Typically, the flow from the Pacific can be dry, but even when it's moist, the Sierra Nevada block the majority of it to the west. The flow shifts in the summer and high pressure builds over the southwest. If over the 4 corners, that's the best for moisture here in Vegas.

And let's recap what you need to create thunderstorms in general....

1. Moisture ✅
2. Buoyancy (desert summer heating) ✅
3. Lift ❓

So the monsoon enables the moisture and we already have the heat, so add some focused lift and now we're talking. 👍

So remember this satellite loop from today? Storms in Mexico like this means we got the moisture tap down there but it looks like it ends in Central Arizona. Why? 🤔

Let's answer that by looking at the atmosphere a different way. This is water vapor in the upper atmosphere. Red/orange is drier, white/blue is moisture. Looks like plenty for most of the western US right? But wait...

Let's look lower in the atmosphere...a lot more red! Except for Arizona/New Mexico and north. We may have elevated moisture, but not enough in the low levels. So at best we get elevated and isolated storms and well east of Vegas. So is this going to change? 🤔

Possibly! This is the forecast "Precipitable Water". Think of it as an indicator of total water vapor in the vertical atmosphere. Doesn't mean low or high in the atmosphere, but throughout all of it. See the darker greens creeping north by Thu/Fri? 👀

So why are you hearing us say "possible" and not sounding the alarm? See how that moisture ends right at around Vegas? What if that shifts? It can and will. That's why this job is so tough...clarity comes as we get closer to the event. We're still 6+ days out.

So are rain/storms in the forecast for late next week for Vegas?? 👀

No not yet. Best moisture still looks east of Vegas, but it won't be far east. Here's our forecast for Kingman, AZ, a little over 100 miles to the southeast.

So it's Friday night, we're talking about weather about a week from now. What should you do? Number 1 thing is to stay weather aware. Keep checking the latest at weather.gov/vegas! We got some videos on monsoon education, the latest forecast, and much more.

Also, don't forget we are always updating here on Facebook and Twitter at @NWSVegas! We're here 24/7 keeping an eye on the skies for you. Need proof? We caught #NEOWISE in our sky the last few nights... ☄️

Have a good weekend everyone! 🤓⛈️🛰️