Tuesday, August 9, 2016

August 9, 2016: Gusty east wind, much cooler around Lake Superior Wednesday. Potential for heavy rain and t-storms Wednesday into Thursday (Flooding possible in parts of the Northland)

/Issued 5:32 PM CDT, Tuesday, August 9, 2016/

Water vapor satellite image from 5:40 PM CDT, Tuesday, August 9, 2016.  Source, http://weather.cod.edu/satrad/

The system currently over the northwest U.S. will be one ingredient; Moisture coming in from the southwest, and also from the central Plains will be another ingredient; And finally a warm front which should setup south of the Northland for Wednesday and Thursday...All these things coming together could spell trouble in the form of heavy rainfall in portions of the Northland during the next few days.

Red=Moderate risk of rainfall exceeding flash flood guidance (10-15% chance)
Yellow=Slight risk of rainfall exceeding flash flood guidance (5-10% chance)
Green=Marginal risk of rainfall exceeding flash flood guidance (2-5% chance)

Source:  Weather Prediction Center

Note:  The slight risk for severe thunderstorms is generally west of a line from Hibbing to Holyoke to Webster.  Source, Storm Prediction Center.

Surface map forecasts for Wednesday.  Source, Weather Prediction Center.

-Periods of heavy rain are possible near and slightly north of that boundary which is forecast to be over southern or central portions of Minnesota on Wednesday.

Slight and marginal risks of rainfall exceeding flash flood guidance on Thursday, August 11 in all of northwest Wisconsin and in most of northeast and east central Minnesota.  Source, Weather Prediction Center.

Forecast for Duluth and Superior

Normal temperatures for Wednesday

High:  76
Low:   55

Sunrise Wednesday:  6:00 AM CDT
Sunset Wednesday:   8:26 PM CDT

Tonight's low temperature forecast.  Source, National Weather Service Duluth, Minnesota.

Wednesday's high temperature forecast.  Source, National Weather Service Duluth, Minnesota.

Weather Summary for NE Minnesota and NW Wisconsin
Date:  August 9, 2016

A warm and muggy day with high temperatures generally in the 80s with dew points ranging from the upper 60s to lower 70s in northeast Minnesota and northwest Wisconsin to the low 60s farther west from Brainerd and Aitkin north to Bigfork and International Falls.  Winds today were out of the west or south at 10 to 20 mph.

Surface map late this afternoon had a cold front over northeast and central Minnesota.  There were isolated showers and thunderstorms over portions of the area this morning with brief downpours and some lightning.  By this afternoon skies were generally partly cloudy to mostly sunny.

Forecast Discussion for NE Minnesota and NW Wisconsin

Tonight (August 9)

A cold front will drop south into the southern half of Minnesota with high pressure building into Ontario Province.  A few spotty showers and thunderstorms are possible this evening although that threat looks very low despite favorable parameters in place that would support strong to severe thunderstorms if a storm can develop.  Partly to mostly cloudy skies are expected tonight with lows in the 60s to around 70 degrees with 50s in far northern Minnesota.  Winds will be out of the southwest, north or east at 5 to 15 mph.

Wednesday and Thursday (August 10-11)

...Potential for periods of heavy rain and thunderstorms...

The setup will include a warm front which should be over southern or central Minnesota into central Wisconsin on Wednesday -- This boundary might move a little more to the north on Thursday but probably won't be able to lift very far to the north due to continued thunderstorm development along this front which may prevent it from moving much farther north than central Minnesota and central Wisconsin.  A widespread area of 65-70+ degree dew points with PWATS of 1.50"-2.00"+ will lift up and over that boundary resulting in a threat for very heavy rainfall at times.

Thunderstorms are also expected with CAPE possibly exceeding 1000 j/kg at times into Thursday...A lot of the instability especially around Lake Superior will be elevated as warm/unstable air moves over a cooler/more stable environment near the surface.

A few strong to severe thunderstorms are possible both Wednesday and Thursday although Thursday's risk is lower than Wednesday's as the location and timing of key frontal boundaries is uncertain, that plus how much clearing if any will occur during the day on Thursday which will play a role in whether or not will get any more strong or severe storms Thursday afternoon/evening.

High temperatures on Wednesday and Thursday are forecast to be in the 70s but 80s are possible if there is enough clearing both days.  It will be cooler around Lake Superior as a stronger lake wind kicks in for Wednesday, and possibly lingering into Thursday.

Note:  There is a pretty good chance that parts of the Northland could be in a Flash Flood Watch by early Wednesday morning.