/Issued 12:54 PM CDT, Sunday, June 21, 2015/
…Scattered strong to severe thunderstorms are possible in parts of Northeast Minnesota and Northwest Wisconsin on Monday… The best chance for severe weather looks to be in Southern portions of Northwest Wisconsin.
Looking at the early afternoon water vapor satellite image from today, June 21, 2015 we see a rather potent system over the Northwest U.S. Several areas of low pressure (Red L’s on the map) were over the Central Rockies with an upper trough with 500mb 12-hour height falls of 30-60 meters across the Northwest U.S. Of greater concern are the two areas of strong winds aloft. The first of 80-100 knots over Southern Alberta and Saskatchewan, the other covering Southeast Oregon. This entire system will move quite rapidly toward the east through Monday. Source, college of dupage website.
Upper level wind forecast for Monday afternoon per 12z NAM from Sunday morning. Often times the best chance for thunderstorms and severe weather is found on the nose of the strongest winds in the upper levels of the atmosphere. In this case will be dealing with two speed maxes with one to the northeast, the other coming in from the west/southwest. The red circled area on the map is where I think the greatest chance for severe weather would be for Monday Afternoon based on this model. Source, college of dupage website
Now lets see what the mesoscale models are showing for late tonight and Monday. Using the 12z 4km NAM from Sunday morning…Here we go: Source, OWxData.com
1 AM Tonight: One or more mesoscale convective systems (MCS) are forecast to develop over the Northern Plains…Once they form the movement should be toward the east or southeast, similar to what happened late Friday night/early Saturday morning.
7 AM Monday: Clusters of showers and thunderstorms should be ongoing Monday morning but this model tends to split the Central portion of Minnesota with one cluster up north, the other one down south. I think if there is any severe weather Monday morning it would likely be in Southern Minnesota and Northern Iowa where the best instability will reside. Storms here in the Northland could be on the strong side but I just don’t think will have sufficient instability for severe weather Monday morning.
1 PM Monday: Jumping ahead to early-mid afternoon Monday we see the main complex of rain/thunderstorms lifting into Ontario (See image below)
Now what happens Monday afternoon is unclear as a lot of it depends on how fast the surface low, warm front, and cold front move through Northeast Minnesota and Northwest Wisconsin. Its entirely possible that the system will be east and southeast of our local area already by mid afternoon Monday, if that’s the case then the chances for afternoon storm redevelopment would lower considerably.
2nd: Will the instability lift far enough north/northeast into our area Monday Afternoon? How much clearing will occur prior to Monday Afternoon? Will need some clearing to take place for temperatures to warm and to get the low level moisture to increase and of course the higher amounts of instability needed for storm development, and oh yeah the frontal boundaries will have to be over the Northland Monday Afternoon in order for storms to develop as we need some sort of lifting mechanism…Again as I mentioned above the surface low, warm front, and cold front could already be off to our south and east by Monday afternoon.
The 12z 4km NAM has enough clearing/warming taking place with sufficient instability overhead to allow for the redevelopment of scattered thunderstorms Monday afternoon. Again other models disagree and keep storm redevelopment much farther to the southeast on Monday.
4 PM Monday: Eastern and Northeast Minnesota and far Northwest Wisconsin should be rain-free while scattered possibly severe thunderstorms continue over Southern/Eastern portions of Northwest Wisconsin.
There’s no doubt will have enough wind shear in place for severe weather as the 0-6 KM bulk shear and effective bulk shear ranges from 40-60 knots per 09z SREF model. Winds will also change direction with height with westerly winds aloft and more of a southerly wind near the surface. Low level jet is forecast to be in the 30-50 knot range on Monday. Winds in the mid levels 60-80 knots. Upper level winds approaching 100 knots! All of these parameters are favorable for severe thunderstorms with damaging winds, large hail, and a few tornadoes.
In closing I think the chances that everything comes together for severe weather is quite low in Northeast and Eastern Minnesota on Monday, but can’t rule out an isolated strong or severe thunderstorm. Severe thunderstorm risk increases the farther south and southeast you get in Wisconsin.
The final map I’ll show is the 09z SREF calibrated severe thunderstorm probability forecast on Monday. Highest values cover far Southeast Minnesota, Southern Wisconsin, and parts of Eastern Iowa.
Tim
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