Strong to severe thunderstorms are possible across much of the Northland tonight, with an Enhanced Risk (3) for severe thunderstorms covering portions of northeast and east-central Minnesota and much of northwest Wisconsin (area in orange on map) while a Slight Risk (2) for severe thunderstorms covers areas farther north and south of the enhanced risk area (yellow area on map) The lowest threat for severe weather tonight is along the Borderland, or around the International Falls area (green area on map)
Note: The last time parts of the Northland were in an Enhanced risk for severe weather was back on August 14, 2020. 2020 saw a total of 5 enhanced risk days in the Northland, but so far in 2021 only 1 enhanced risk day, that being today, July 26.
Primary severe weather threats tonight include
-Large hail of quarter size to baseball size (1.00″ to 2.75″ diameter)
-Damaging Wind Gusts of 60 to 70 mph
Stay Weather Aware tonight!
Some portions of the Northland will likely be under a severe thunderstorm watch tonight, and severe thunderstorm warnings are also likely in some parts of the area tonight.
Low level moisture is still pretty low in the Northland as of mid-afternoon, with dew points generally in the mid 50s to low 60s, but we should see those values climb a bit this evening, with dew points possibly inching toward the 63-66 degree range across southern portions of the Northland.
Low level jet (850mb winds) is on the weak side this afternoon, but the low level jet is forecast to crank up a bit tonight, reaching speeds of ~20 to 35 knots, this combined with even stronger winds in the mid/upper levels of the atmosphere will create a decent amount of speed shear, while we also have directional wind shear as SW winds at 850mb turn NW at 500mb — These ingredients will lead to the potential for some rotating/supercell thunderstorms tonight, and an increased risk for large damaging hail and or damaging winds (white outlined area on map) Note: Very steep mid level lapse rates of 7.0-8.0 c/km will also be over the Northland tonight which will also increase the risk for large hail, especially if storms remain scattered and not form into a line.
With the warm air already in place, and a continued warm/moist advection pattern, we’re seeing some high values of CAPE (instability) this afternoon, so we have the fuel in the atmosphere, but we still need a trigger, some sort of front or disturbance to help develop some storms, and that source of lift is in the form of a warm frontal boundary which stretched from northwest to east-central Minnesota to north-central Wisconsin this afternoon.
Here is the approximate location of the aforementioned warm front this afternoon. Will see this warm front turn into a stationary front this evening, before sagging south as a cold front later tonight. Scattered storms should develop near/slightly north/south of this boundary tonight.
Timing for when we could see some showers and thunderstorms and possible severe weather in the Northland is from ~6 PM to 3 AM tonight, but locally in Duluth and Superior our chances look to hold off until after 8-9 PM this evening.
Note: There is a chance that some parts of the Northland could be hit by more than one round of storms tonight, that chance is greatest from east-central Minnesota into northwest Wisconsin.
Here are two computer model radar simulation forecasts ending at 7 AM Tuesday.
18z NAM 3km model
18z HRRR model