/Issued 4:05 PM CDT, Wednesday, September 18, 2013/
*The 18z NAM shows a lot of clouds covering MN and WI on Thursday. Extensive cloud-cover would tend to limit the amount of heating and instability that is usually needed for severe thunderstorms. Note: White areas on this map represent where clouds will be Thursday PM.
*There remains a SLIGHT risk for severe thunderstorms on Thursday for Eastern Minnesota and much of Wisconsin (Yellow shaded area on the map) Green=Non-severe thunderstorms.
Source: NWS Storm Prediction Center; Weather Underground
*Here’s the SPC’s SREF model’s (15z run) take on the severe potential on Thursday. This is the calibrated severe t-storm probability forecast with the highest numbers lining up pretty much where they have the Slight risk for Tomorrow.
*Upper level winds are strong Tomorrow with a corridor of 80-110 knot winds centered over the Eastern Dakotas and Northwest Minnesota…Locations south/east of this wind max are typically in a favored area to see precipitation as lift is maximized out ahead of the strongest corridor of upper level winds. (Source, 18z NAM)
Today’s Weather Summary for Northeast Minnesota and Northwest Wisconsin
Low pressure averaging 1000mb covered Central South Dakota late This Afternoon with a warm front stretching from Eastern North Dakota to Southern Minnesota and a cold front over the Western Dakotas. The Northland was north of the warm front Today and this resulted in a day of east winds, low clouds, along with some fog and drizzle. High temperatures ranged from the upper 50s to lower 60s near Lake Superior with 60s and a few 70 degree readings elsewhere. It’s quite humid Today as well with dew points in the 55-65 degree range. Winds Today were from the east at 5 to 15 mph.
Forecast Discussion for Northeast Minnesota and Northwest Wisconsin
Short Term Forecast – Confidence: High.
Tonight (September 18)
Probably won’t have much clearing Tonight as a moist southerly flow continues out ahead of a storm system over the Northern Plains. Areas of fog and drizzle will be common Tonight, some of the fog could be dense with visibilities as low as 1/4 mile especially around Lake Superior. Elevated instability will continue to increase Tonight as a warm front lifts NNE into the Northland. Scattered showers and thunderstorms may begin to impact Western parts of the area Overnight. Low temperatures will be in the 50s and 60s with south or east winds at 5 to 15 mph.
Thursday and Thursday Night (September 19)
Low pressure will be affecting the Upper Midwest/Western Great Lakes and Central Canada this period. A warm front and cold front will be moving through the Northland on Thursday, this alone should be enough to generate some showers or thunderstorms from Thursday into Thursday Evening. The approach of an upper level trough could also aid in shower/storm development Tomorrow.
There remains a possibility for a few strong – severe thunderstorms on Thursday, primarily in Northwest Wisconsin and Eastern Minnesota, but if clouds and precipitation linger I don’t think there’ll be much of a severe risk in our area.
The computer models show just enough breaks developing in the cloud-cover to allow CAPE values to rise to 1000-2500 j/kg with Lifted Indices of -3 to -7C…If this happens then yes there would likely be an isolated severe thunderstorm threat. Note: Mid level winds look strongest west of our area with generally 25-30 knot H5 winds overspreading the Northland. Wind shear looks marginal too with 0-6 KM Bulk Shear and Effective Bulk Shear generally around 30 knots or less. I would like to see all 3 of those parameters a bit stronger for a more robust severe thunderstorm threat. Will just have to wait and see how things set up Tomorrow. Stay tuned!
High temperatures on Thursday will be in the 60s and 70s with lows Thursday Night in the 40s and 50s. Winds will shift from the south/east to the west at 10 to 20 mph. Note: Rain chances should decrease beyond Thursday Evening as this weather system exits to our north/east.
Extended Forecast – Confidence: High.
Friday through Sunday (September 20-22)
A cooler airmass will cover the Northland Friday and Saturday with 850mb temperatures dropping to around -2 to +4C. Can’t rule out a few showers on Friday but the majority of the area should be dry Friday through Sunday. High temperatures will be in the 50s and 60s through this period with lows Friday Night and Saturday Night in the 30s and 40s with a few 20s possible as well.
Long Range Forecast – Confidence: High.
Near normal temperatures are forecast through this period. Some rain/showers are possible as well. The 1st chance looks to be on Monday (23rd) The other – possibly greater chance comes during the 25th-28th time frame.
5 DAY FORECAST FOR DULUTH/SUPERIOR
.Tonight… Fog and drizzle. Low 55 to 60. Wind east at 10 to 20 mph.
.Thursday… Areas of fog and drizzle. Scattered showers. Isolated thunderstorms also possible. High 65 to 70. Wind south to southeast at 10 to 15 mph.
.Thursday Night… Scattered showers possible early, otherwise partly to mostly cloudy. Low 45 to 50. Wind becoming west to southwest at 10 to 20 mph.
.Friday… Cooler. Mostly cloudy. Afternoon showers possible. High 55 to 60.
.Friday Night… Partly to mostly cloudy. Low 37 to 42.
.Saturday… Partly sunny. High 55 to 60.
.Saturday Night… Mostly clear. Low 35 to 40.
.Sunday… Partly cloudy. High 60 to 65.
Normal temperatures for Today
Sunrise Thursday: 6:52 AM CDT
Sunset Thursday: 7:12 PM CDT