29. Hopefully I'll cover everything I want to in chronological order: Arthur, May Precip Summary, cool start to June.
The first tropical system of the 2008 Atlantic Hurricane Season (Jun 1 - Nov 30) formed as a former Pacific tropical circulation crossed Central America and reformed in the Atlantic Basin on May 31st.
This image (to the right) is from the evening of May 31st, from the NHC, which shows the color-enhanced IR satellite over the Gulf of Mexico and the Caribbean Sea.
I've drawn an arrow pointing to the center of Tropical Storm Arthur. On May 29th a tropical system formed in the Pacific Ocean near the Panama/Nicaragua border and moved north as Tropical Storm Alma. As Alma died over land & mountains, the system came back to life as Arthur when it entered the Atlantic basin.
Arthur has brought the first deaths from the 2008 Atlantic Hurricane Season... 4 people in Belize. In fact, Belize was hit especially hard by massive flooding. A write-up of this storm with details & pictures from Belize can be found on Dr. Jeff Masters' blog on Wunderground.com. And finally, the track of the system with more information from Wunderground can be found here.
May's Precipitation Wrap-up.
It looks like a long list of rain, right? Despite the length of the list, a majority of the precipitation that fell in May was light. Two hundredths, three hundredths, four hundredths... it's rain that produced numbers, but didn't soak in and stick around. I recorded 2.84" of liquid for the month, which is 87% of average (3.28"). If it wasn't for a huge amount of rain and snowflakes on May 3rd, it would have been a dry month. January through May usually sees about 7.73" of liquid, and by May 31st I've measured 10.22", so we're a bit above average 132%). This extra moisture, mainly from a wet April, has kept the ground moist and rivers full. However, we'll need to continue to receive healthy rainfall to keep from falling into the same drought we've experienced during the last two years.
Unfortunately, the weather pattern of the last half of May was keeping the thunderstorms and rain south of northern Wisconsin, and this looks to continue at least through June 7th.
A cold front passed through on June 1st, bringing a cool pattern.
This radar image (to the right), from the radar site in Duluth, shows the line of showers at 18:09 as they moved east through the area. This line of rain preceded a cold front which brought a air mass change.
0.02" of rain was in my rain gauge the next morning, and I heard no thunder from this line, I suspect it was weaker than it looked on radar.
From the weather stations' point of view.
I took a screenshot from my personal weather station (to the left), which clearly shows the abrupt change of airmass on Sunday evening. I measured a high temperature of 80.1 on Sunday afternoon before the cold front moved through. The barometer was falling and winds were gusting above 10 mph from the NW.
Temperature suddenly fell, barometer suddenly began rising, and the winds quickly peaked at 22 mph. The dewpoint matched the temperature as several hundredths of rain fell. The next day the winds switched to the NE and has remained there until today.
Incidentally, the 80 degrees on Sunday was the highest temperature of the year so far. The last time I measured 80 degrees was on October 7th, 2007, 7 months and 25 days previous.
Cool and dry air in place.
The change in airmass brought Canadian high pressure to the region, which across northern Wisconsin means northeasterly winds, clouds, and cool temperatures.
A sharp boundary has been in place since Sunday, keeping the rain to the south with clear and cold conditions north. Clear and cool enough to warrant Frost Advisories last night across far northeastern Minnesota. Two locations reported 33 degrees: Embarrass and 3E of Orr.
May's Precipitation Wrap-up. 
A cold front passed through on June 1st, bringing a cool pattern.
From the weather stations' point of view.
Cool and dry air in place.