/Issued 5:31 PM CDT, Tuesday, September 19, 2017/
20z HRRR model run
A risk for a few severe thunderstorms continues from late this evening through the overnight hours across most of northeast Minnesota and northwest Wisconsin with a greater risk for severe thunderstorms covering west central Minnesota and the eastern Dakotas.
18z NAM Nest model – Updraft Helicity Forecast for tonight. Note: The brighter colors on the map indicate higher potential for rotating thunderstorms tonight.
More active weather is possible beginning Thursday night and lasting into the weekend.
Haven’t seen this type of weather pattern very often the last few months — Trough out west, ridge to the east…Typically this leads to periods of wet/stormy weather for us in Minnesota and Wisconsin, and that’s what’s in the forecast later this week into early next week especially for Minnesota.
Low clouds, areas of fog and drizzle earlier in the day gave way to a mix of sun and clouds across the area by this afternoon with high temperatures ranging from the low to mid 60s near Lake Superior to the upper 60s and low 70s elsewhere.
-The main focus for tonight is on the strong low pressure system which will affect the Northland — Low pressure of 994mb was over southeast Saskatchewan Province at 4 PM today with another surface low of 996mb over central South Dakota. There was a cold front over the central Dakotas while a warm front was over the eastern Dakotas toward far southern Minnesota. 60-80 knot mid level jet was over the central Rockies this afternoon along with 100-130 knot upper level winds so this system has lots of upper level support.
-Ahead of this storm was a southerly low level jet at around 40 knots late this afternoon — This low level jet is forecast to increase to 50-65 knots tonight which will lead to a rapid return of humid air across the Northland. Note: 4 PM PWATS were generally in the 0.90-1.00″ range in northeast Minnesota and northwest Wisconsin, these values will climb to between 1.40-1.80″ after midnight. The low level jet will also advect higher elevated instability levels into our area tonight with CAPE ranging from 500-1500 j/kg.
-Showers and thunderstorms are forecast to develop by mid or late evening across western portions of the area. Those storms would be associated with the warm frontal boundary as well as with the low level jet (Warm/Moist advection pattern) Another line of showers and thunderstorms associated with the cold front and main upper level system is then forecast to move through the Northland early Wednesday morning. As I mentioned above this storm has a lot of upper level energy with strong forcing, so as that moves closer to the Northland later tonight we should see rather widespread coverage of showers and thunderstorms.
-Locally heavy rain is likely in any thunderstorm tonight, but the rapid movement of these storms should keep the potential for flooding fairly low, but still could be some ponding of water in some areas. Lightning will also occur with these storms later tonight.
-The threat for strong to severe thunderstorms continues as well but the one negative for severe weather is the timing on which these storms will affect the Northland, however, there should be enough elevated instability in place to produce a few strong or severe thunderstorms in parts of the area later tonight with the main threats from large hail and or damaging wind gusts. Note: A greater threat for severe weather including a risk for a few tornadoes exists until around Midnight in eastern North Dakota, eastern South Dakota into west central/southwest Minnesota where 1km shear of 30-35 knots was in place along with Effective Storm Relative Helicity values of 300 m2/s2 to 400 m2/s2 (Both of those parameters are very favorable for tornadic development if storms develop this evening)
With gusty southerly winds tonight, lows won’t fall very much with readings generally in the mid 50s to mid 60s.
Wednesday: Strong low pressure will be centered well to the northwest while a cold front makes steady eastward progress, exiting the Northland by the afternoon hours. Scattered showers and isolated thunderstorms tomorrow morning into early afternoon followed by clearing skies from west to east during the afternoon. Highs in the mid 60s to low 70s.
Forecast for Duluth and Superior
.Tonight… Breezy. Mostly cloudy. Showers and thunderstorms developing after midnight. Low 56 to 61. Wind east to southeast at 15 to 25 mph.
.Wednesday… Scattered showers mainly during the morning under mostly cloudy skies. Clearing skies later in the afternoon. High 66 to 71. Wind south to southeast at 5 to 15 mph becoming west at 10 to 20 mph during the afternoon.
.Thursday… Partly to mostly sunny. High around 70. Wind east to southeast at 10 to 15 mph.
Normal temperatures for Wednesday
Sunrise Wednesday: 6:53 AM CDT
Sunset Wednesday: 7:10 PM CDT