Well, here's something you don't see too often. The Storm Prediction Center has issued a slight risk for severe weather across parts of the desert southwest—including Las Vegas and surroundings—for the chance of tornadoes, 60+ MPH wind gusts, and hail larger than quarters.
Severe weather isn't all that uncommon in the southwestern United States, but this is unusual because it includes an unusually high risk for tornadoes.
Why is this happening?
Southerly winds are shoving a pocket of warm, moist air north from the Gulf of California into parts of the southwestern United States, giving the atmosphere enough moisture and instability necessary to support thunderstorm activity. The above map shows the predicted dew points from this morning's run of the NAM valid for this afternoon.
Remember that beautiful low pressure system that's brought parts of the West Coast some much-needed rain? That deep trough is also producing some pretty hefty wind shear that's approaching the southwest. Winds up in the jet stream (about 30k feet up) are greater than 70 MPH in some spots. Add in the fact that the winds are ever so slightly veering (twisting) with altitude, and it will allow the thunderstorms to strengthen and reach severe levels.
What are the risks?
According to the SPC, all modes of severe weather are possible today.
The above map shows the risk for tornadoes this afternoon. 5% warrants concern anywhere in the country, so it's worth paying close attention today for residents in and around Las Vegas. Clark County, Nevada has reported just one tornado in the past ten years, showing how rare they are in this region. Tornadoes need ample low-level moisture in order to develop, and that's one ingredient that's normally in short supply around these parts...except for today.
Here's the risk for damaging winds today, which are the most common type of severe weather in the southwest. The risk for large hail (quarter size or larger) is roughly the same.
What about tomorrow?
The threat for severe weather shifts east tomorrow, threatening Phoenix, Prescott, and Flagstaff with the same hazards as today—tornadoes, large hail, and damaging winds.
Tornado Safety Tips
Homes and buildings in these areas don't have basements, so the typical tornado safety tip of "get underground" does local residents no good. If your location goes under a tornado warning, you'll want to get to the lowest level of your house/building and find an interior room that puts as many walls between you and the outdoors as possible. Many homes have a closet or bathroom on the first floor in the middle of the house.
Even a weak tornado is dangerous—60 to 80 MPH winds don't sound too bad until it picks up debris and throws it at you at those speeds. If you're in a vehicle and a tornado warning is issued, try to get to a sturdy building nearby and ride it out inside. Tornadoes can pick up and toss cars with relative ease, so they're not safe places to ride a storm out.
The Storm Prediction Center issues severe thunderstorm and tornado watches, while local National Weather Service offices handle urgent warnings. Stay tuned to local weather sources today and tomorrow, and keep an eye on the radar.
[severe weather maps by the author, model image via WeatherBELL]