Severe risk tomorrow; Dakota Co. updates siren policy

March goes out like the relatively mild and dry lamb it was most of the month. April arrives with a warm and thundery rumble.

No foolin'.

Today goes down as one of the finest days of this early spring. Early morning fog burns off in the east metro, and sunshine boosts temperatures toward the 60 degree mark in the metro and southern Minnesota, with 50s up north.

Temperatures peak tomorrow afternoon in the 70s as Minnesota rides the northern edge of an unseasonably warm air mass. Summer-like 80s ride as far north as Des Moines, Iowa, Tuesday afternoon.

The reason for the abrupt warming trend? A stiff southerly breeze ahead of the next low pressure wave.

The system triggers a growing zone of showers and thunderstorms as it passes overhead Wednesday. It's the perfect setup: Strong sunshine warms the air, as a cold front cuts into the warmer, unstable air from the west.

The result? A rapidly blooming line of towering cumulus clouds, blossoming into scattered thunderstorms Wednesday afternoon.

A few of the storms have the potential to become severe. High winds (more than 58 miles per hour) and large hail (1 inch or more in diameter) are the primary severe threats Wednesday afternoon and evening.

Dakota County updates siren policy

Most communities around Minnesota sound outdoor warning sirens for tornadoes and very severe thunderstorms packing 70-plus mph winds. For years, Dakota County has been the most notable exception, sounding sirens for every severe thunderstorm warning. The result?

Dakota County blew the warning sirens 96 times over the past five years. That's about 19 times per year on average.

This year Dakota County has revised the siren policy and will blow the sirens for tornado warnings and when winds of 70 mph or greater are observed or expected. Here are some details from Dakota County.

New outdoor warning siren policy for Dakota County

In the past, outdoor warning sirens were activated during tornado warnings and severe thunderstorm warnings, which means that the winds have reached a sustained speed of 58 mph or greater. From 2010-2014, this resulted in 96 instances where sirens were activated.

The new policy continues to activate the outdoor warning sirens during tornado warnings, but increases the sustained wind speed needed to prompt sounding the sirens during a severe thunderstorm warning.

Instead of 58 mph, sirens will sound when wind speed is expected to meet or exceed 70 mph. If this policy was used over the last five years, the use of sirens would have been reduced by 75 percent.

The updated policy is a very positive change, in my opinion, as it is much more consistent with other metro counties. It should also reduce over-warning, and signify to residents of Dakota County that when the sirens do blow, damaging weather is likely occurring or imminent.

The Joplin effect: How we react to severe weather warnings

The Dakota County changes may also help avoid what I call the Joplin effect. A NWS study following the devastating EF5 Joplin, Mo., tornado in 2011 found that residents felt "over-warned" and that some did not take action when they heard sirens because they felt the sirens often sounded without consequence.

“The tornado that struck Joplin offers important lessons about disaster preparedness,” said National Weather Service Director, Jack Hayes, Ph.D. “Tragically, despite advance tornado outlooks, watches and warnings, 159 people died and more than 1,000 were injured. At NOAA we will do all we can – working with our partners throughout the weather enterprise and emergency management – to reduce the impact of similar disasters.”

Within days of the tragedy, Hayes sent an assessment team to Joplin to examine warning and forecast services provided to the community, warning communications, community preparedness and the public’s response to tornado warnings.

The team determined that a number of factors contributed to the high death toll. Through interviews with more than 100 Joplin residents, the team found that societal response to warnings is highly complex and involves a number of factors, such as risk perception, overall credibility of warnings and warning communications.

Keep in mind, sirens are an outdoor warning system. When severe weather is a threat, you should maintain a high level of situational awareness as storms develop and approach.

Have multiple safety nets in place -- NOAA weather radio, radio and TV broadcasts, weather apps, whatever it takes to stay ahead of potentially damaging storms. Take action before you hear sirens; they may be a last line of defense, or they may not sound at all if power is cut.

Minnesotans are pretty weather savvy, but this time of year it's a good reminder to all of us to brush up on our severe weather action plans.

Cooler late week

Cooler breezes kick in behind the storms and cold front by Thursday. The (welcome) next rain system arrives next Monday.

Keep an eye on the sky tomorrow!