Unusual weather pattern: North Shore warmth

gmcam.jpg

Web cam from Grand Marais today shows a warm scene on the North Shore.

Welcome to the Scandinavian Riviera.

It’s not often Minnesota’s North Shore is the warmest spot in the state. Today it’s the place to be for summer temperatures.

An unusual weather pattern is causing temperatures along the North Shore this afternoon to be the warmest in Minnesota. As of 3pm Silver Bay is 82 degrees. Down by The Bay at Grand Marais, it’s a toasty 83 degrees. That’s pretty nice stuff for cities that are usually cloaked in forecast terms like “cooler by the lake.”

Often in July we’d expect to see the warmest temps in the usual places like Wheaton in western Minnesota. It’s 75 in Wheaton today. It’s only 73 in Ortonville and Madison in western Minnesota.

So what’s going on here?

There are two main weather factors at play today that are causing warmer readings along the North Shore.

First, the air mass over Minnesota is seasonably cool for mid-July. Average temperatures for this week are in the mid-80s in southern Minnesota. The current air mass features below average temperatures and is keeping readings on the cool side.

Secondly, there is a downslope wind on the North Shore. Winds today along the Shore are blowing from the northwest. Northwest winds cause air to rush down the hill toward Lake Superior. The elevation difference in places like Grand Marais is about 1,000 feet between the hilltop (1657 feet asl) and the surface of Lake Superior (610 feet asl).

As the air flows down the hill, it warms at the dry adiabatic lapse rate of about 5.5 degrees per 1,000 feet. Atmospheric lapse rates can vary, and today it is a full 10 degrees warmer at the Bay at Grand Marais than at Cook County Airport on top of the hill. The “urban” environment in Grand Marais may also be adding a couple of degrees today.

Today is an unusually enjoyable summer day along the North Shore. It’s also on of those rare days we get to say, “warmer by the lake.”

PH

Update 5:20pm:

What downslope giveth, the lake breeze taketh away. Winds turned off the lake in Grand Marais between 4 and 5pm. The temperature at The Bay at Grand Marais observing station dropped 24 degrees from 81 degrees to 57 degrees in under an hour. What’s that old saying… if you don’t like the weather just wait 15 minutes?

PH

  • http://www.thereandbackbooks.com Andrew Slade

    There are about six days a year when Duluth is the warm spot in Minnesota, about three every summer with these adiabitic winds, and about three every winter when a 30-below cold air mass covers the state and Lake Superior keeps us relatively warm…just 15 below or so.

    Unfortunately, those same westerly winds blow all the warm water out to sea, so swimming on the Park Point beach gets really challenging.