Posted at 8:33 AM on June 11, 2009
by Paul Huttner
Sioux Falls NEXRAD clearly shows echoes from wind turbines along the Buffalo Ridge northeast of the radar site today. These echoes can be mistaken for showers or thunderstorms.
Wind farms in southern Minnesota and northern Iowa are clearly visible on both the Twin Cities and Sioux Falls doppler radars this morning. The radar echoes often mimic showers or even thunderstorms, and it takes a trained eye to differentiate between the two types of radar returns.
Usually the radar beam will shoot over the top of wind farms at distances from the radar site. But if conditions are right such as a when a temperature inversion is present, an atmospheric process called superrefraction bends the radar beam. The beam can follow the curvature of the earth for over a hunderd miles and bounce back off of the wind turbines.
Take a close look at the Twin Cities doppler image below. You can see the light green smudge of light rain showers north of Eau Claire and a little shower near Mankato. You can also see the bright yellow echoes throughout southern Minnesota and northern Iowa. Those are likely wind farms or some other man made tower. You can see how they could easily be mistaken for heavier showers or thunderstorms. Meterologists seek correlation from other data sources and ground truth to confirm the presence of rainfall.
You just never know what you're going to see on radar. Hiding among a few spotty showers today? Wind farms. Who knew?
Posted at 3:07 PM on June 11, 2009
by Paul Huttner
U.S. Drought Monitor released today shows Minnesota's drought virtually unchanged from last week.
It could have been worse.
If not for two shots of rain totaling over an inch in most locations, the drought would have deepened again this week in Minnesota. As it is, we're right where we were a week ago. An inch of rain sounds like a lot. But the powerful June sun and high evaporation rates this time of year can eat up an inch of soil moisture in about 3 to 4 days. The cool damp cloudy weather this week has helped to keep some of the precious moisture that fell in the topsoil.
The next 5 days look dry around much of Minnesota. There is a slight chance for a few showers late Friday, but I don't see any meaningful widespread one inch plus rains like we had last weekend. There is a chance for some increased thunderstorm activity toward the middle of next week.
Looking ahead, it still appears that 90 degree heat could build into the Midwest just after Father's Day. Drought conditions and effects could increase dramatically if we do not receive significant rainfall in the next 10 days.
Let's hope we can get some serious rain in here next week, mostly at night, so everybody is happy. Easier said than done!