Issued at 3:27 PM CDT, Monday, July 26th, 2010
...Severe weather possible beginning late Tonight and continuing through Tuesday Evening...Damaging wind, large hail, heavy rainfall, dangerous lightning and isolated tornadoes are possible!
Weather History: On this date in 1991, a record low temperature of 40 degrees occurred at Duluth Minnesota.
Forecast Discussion for Northeast Minnesota and Northwest Wisconsin
Another warm day across our area with high temperatures mostly in the lower to middle 80s. Dewpoints have come up compared to 24 hours ago, but even muggier air will head into our area on Tuesday. Dewpoints This Afternoon were generally in the 60-64 degree range with upper 50s in the Arrowhead of Minnesota. 70+ degree dewpoints covered portions of Western Minnesota and the Dakotas and even as far north as Manitoba Province Canada Today! PWS This Afternoon ranged from 0.90"-1.30" across Northern Minnesota and Northwest Wisconsin with 850 mb td's of +8/+12 degrees C per SPC meso-analysis page. Partly to mostly sunny skies were found in our area Today with southerly breezes of 10-25 mph. Surface map as of 3 PM featured low pressure of 1006 mb centered over the Western North Dakota-Eastern Montana area. A warm front was situated over Northwestern Minnesota with a cold front extending from Southeast Manitoba Province Canada through Northwest North Dakota. Scattered showers and thunderstorms developed This Morning in a warm/moist advection pattern along the North Dakota/Minnesota border with a couple reports of large hail in that area. Those storms have lifted into Southern Ontario Province Canada This Afternoon where some additional severe weather has been occurring.
Today's Upper Level Analysis:
Westerly flow aloft was found over the Upper Midwest Today per water vapor satellite imagery. A potent 500 mb low was dropping southeast through Northeast Alberta/Western Saskatchewan Province Canada This Afternoon with a 70 knot upper level jet found on the south-southeast side of that upper level low Today per RUC model analysis.
Partly to mostly cloudy skies will cover our area Tonight with mild temperatures. Lows will be mainly in the 60s with southerly winds at 10-20 mph. Dewpoints should hold in the 60/65 degree range for most areas Tonight making it feel somewhat muggy. A warm front situated over Northwest Minnesota This Afternoon will head east-northeast during the night while a cold front remains centered to our west-northwest.
The atmosphere has become very unstable across Northern Minnesota and North Dakota This Afternoon with CAPES as high as 4000-6000 j/kg across North Dakota with values ranging from 1000-3000 j/kg in Northcentral Minnesota! Instability is expected to remain quite high through the night in Northern-Western parts of our area and this should allow for the development of scattered showers and thunderstorms Tonight along and west-northwest of a line from Brainerd to Grand Marais Minnesota.
The greatest potential for severe weather is expected to be over Koochiching, Itasca, Cass and Northern St. Louis Counties Tonight, including cities such as...International Falls MN, Bigfork MN, Cass Lake MN, Walker MN, Longville MN, Grand Rapids MN, Cook MN, Crane Lake MN and Ely MN.
Shear of 25-35 knots in combination with the amount of instability in place will support a severe threat once storms develop or move into those aforementioned areas Tonight...The main risks will be from damaging winds of 60 mph or greater along with large hail of 1.00" in diameter. There is also an isolated risk for a tornado mainly before Midnight across Koochiching and Northwestern Itasca Counties MN.
Locally heavy rainfall is also expected in any thunderstorm Tonight in Northern-Western areas due to the increasing amounts of low level moisture during the night.
Tuesday and Tuesday Night:
A very unstable and moist airmass will reside across our local area on Tuesday. CAPES from 2000-3500 j/kg and Lifted Index values of -3/-7 degrees C will be found in our area along with quite a bit of directional and speed shear. 0-6 KM and Effective Bulk Shear values of 30-40 knots are forecast in our area along with a change of wind direction with height as S winds near the surface veer more S-SW at 850 mb and westerly at 500 mb. A stregthening upper level jet >85 knots will be located to our northwest on Tuesday while 500 mb wind speeds increase to 40-50 knots throughout Northern Minnesota and Northwest Wisconsin. Dewpoints will easily climb into the 65-75 degree range on Tuesday with 850 mb td's of +12/+18 degrees C while PWS rise to between 1.30"-2.00"!
A cold front which was situated near the Manitoba Lakes region This Afternoon will settle southeast into this very unstable, warm and moist airmass on Tuesday and this should cause scattered to numerous showers and thunderstorms in Northern Minnesota and Northwest Wisconsin from Tuesday into Tuesday Evening.
The main threats from severe storms during this period will be from damaging winds and large hail, but there will be a risk for rotating supercells and possibly a few tornadoes between 2PM-6PM.
Some of the forecast models over the past 24 hours have been indicating that there could be a secondary warm front and possibly even a weak surface low that develops Tuesday Morning while moving through Central and Eastern Minnesota and Northwest Wisconsin Tuesday Afternoon. Should this occur, then we could see a somewhat higher chance for supercells including a risk for isolated tornadoes Tuesday Afternoon as surface winds back more toward the S-SE.
Another hazard Tuesday and Tuesday Evening will be from locally very heavy rainfall which may lead to some areas of flooding due to the abundant moisture that is expected to be in place.
The threat for showers and thunderstorms along with the risk for severe weather will end from northwest to southeast Tuesday Evening as the cold front exits to our east.
Partly-mostly cloudy skies will cover our area during this period with highs Tuesday in the 70s and 80s, but some 90s are possible mainly in Southern areas. Lows Tuesday Night will be in the 50s and 60s.
Winds will be out of the south or southwest on Tuesday at 10-25 mph with winds turning north or west Tuesday Night at 10-20 mph.
Note: Severe thunderstorm and or tornado watches/warnings will likely be issued at times for portions of our area beginning late Tonight and continuing through Tuesday Evening.
Quieter weather with less humid conditions will return to Northern Minnesota and Northwest Wisconsin for Wednesday and Thursday as high pressure builds into the Upper Midwest. High temperatures will be mainly in the 70s both days with lows in the 50s with some 40s possible in the typical cool spots, especially Wednesday Night.
5 Day Forecast for Duluth/Superior
.Tonight... Mild and a bit humid. Partly cloudy. Low 65 to 70. Wind south at 10 to 20 mph.
.Tuesday... Muggy and warm. Scattered showers and thunderstorms. A few storms could be severe. Locally heavy rain also possible. Variable cloudiness. High 82 to 87. Wind south at 10 to 20 mph. Chance of rain 60%.
.Tuesday Night... Scattered showers and thunderstorms possible before 8 PM. A few storms could be severe. Locally heavy rain also possible. Partly to mostly cloudy. Low 58 to 63. Wind becoming west at 10 to 20 mph. Chance of rain 50%.
.Wednesday... Less humid. Partly cloudy. High 75 to 80.
.Wednesday Night... Mostly clear. Low 53 to 58.
.Thursday... Partly cloudy. High 75 to 80.
.Thursday Night... Partly cloudy. Low 53 to 58.
.Friday... Partly sunny. High 75 to 80.
Normal High Temperature Today 77 degrees
Normal Low Temperature Today 56 degrees