STORM TRACK: July 31, 1987 (Volume 10 Issue 5)
Don't laugh. The Great Plains do not have precedence over all the beauty and excitement of storm chasing. Equally as spectacular, if not more violent, are the flash floods, waterspouts, dust-storms, and hurricane force winds of Northern Utah. These can be very picturesque against the mountain scenery and wonderfully clear visibility of the Central Rockies.
In fact, it is the mountains along with other topography that "stays put", which help me to predict where and when convection will occur. The Great Salt Lake provides a permanent "cool island". These stationary parameters interact to form local "hot spots" where convection occurs in the same place, day after day. This is in contrast to what you have out on the Great Plains. Variable parameters such as the jets, moisture, and drylines contribute to produce optimum conditions in various areas throughout the center of the country. Chasers on the plains find themselves driving wildly for thousands of miles trying to reach the best place for severe weather. However, it is the fairly predictable and organized interaction of topographical features that help make storm chasing in Northern Utah a leisurely and frequently successful effort. Although severe storms in Northern Utah capable of whisking you off to the land of OZ are rare, the probability is high that you can drive within 30 miles of Salt Lake City to see 75 mph winds, 2 inch hail, and 3 inch rains in 20 minutes.
The Salt Lake Valley is a broad north-south oriented plain at around 4500 foot elevation. On each side of the valley are north- south mountain ranges which vary from 7500 to 11000 feet. Bordering on the north end is the Great Salt Lake. See Figure 1.
The typical chase day begins with high and middle clouds more abundant than usual and moving from the south at about 20 knots. Air at low levels is too dry to produce clouds. About 10 am, I leave home in downtown Salt Lake City to check the weather conditions at the National Weather Service. I look for the following conditions: 1) a potentially unstable air mass which will not give way to pesky intrusions of the Pacific High which ruins convection, 2) the strength of the southerly drainage wind in the valley is above average, 3) lower than average temperatures at 500 mb (-12C), and 4) a surface temperature forecast of 92 degrees.
At noon, I'd like to see the following conditions: 1) the Oquirrh Mountains, nearly devoid of vegetation with a dry desert south and west, produces the first large cumulus, 2) strong south winds still exist over the valley, 3) middle clouds are still present assuring moist air at that level to assist convection.
If all goes well, the first thunderstorms should develop over the mountains to the southwest about 2pm. Hopefully, they rain-out and produce a downdraft which is not too intense and spreads eastward slowly across the valley. Storm anvils should move north toward the Great Salt Lake leaving valley skies still clear for plenty of heating. Now a developing lake breeze from the Great Salt Lake reverses the surfaces winds and they start moving south. See Figure 2. The result is a classic intersection between a gust front and cold front about 15 minutes away from me.
At the intersection, a thunderstorm reaching 50,000 feet is not uncommon. Winds underneath the storm are calm with all the air flowing upward in spectacular turbulence with frightening circular motion at times. Beautiful colors of purple, black, green, and copper contrast starkly with the bright blues and whites of the mountains to the east. The downdraft begins with stinging dust at the surface and intense lightning. Then, zero visibility with rain, wind, and hail. At the storm center, 3 inches of rain can cause flash floods. Winds can push cars off the road, take roofs off buildings, and down trees. Temperatures can drop from 92 to 48 degrees. Dense fog forms over the one foot hail drifts. One fifth of the annual precipitation has fallen. There's a feeling of exhilaration seeing so much for so little expenditure of time, money, and distance.
