Chase Logs 2007
The First Test: Thunderstorm Reflections
July 3, 2007
12:30pm-5:00pm
Anoka and Ramsey Counties, MN
Despite a slight severe weather risk for this afternoon across central Minnesota, today's storms fell short of everyone's expectations. This storm complex, spurred by a weak cold front pushing east and south across the Midwest, developed in central South Dakota in the overnight hours. The northern cell in this multi-cell line attained severe status around the noon hour over Stearns County. This pulse cell weakened within twenty minutes of becoming severe, only to be replaced by another small cell 20 miles to its southwest. This second cell gradually grew in coverage area as it moved southeast, reaching its peak intensity over Wright County shortly after 1:00pm, where several chasers witnessed some small, brief funnels. I was, once again, stuck at work watching the storm on my WeatherScope weather data plotting program. The cell pushed progressively eastward, merging with the weaker northern cell and forming a squall line as it prepared to enter Anoka County.As the system entered Anoka County, I saw on radar what I thought to be a bow echo stretching the width of the county. I watched and waited, but no severe thunderstorm warning was issued for Anoka County and no storm reports of wind damage appeared on the MPX website. False alarm. In the meantime I was busy trying out several "new" software programs I had found on the web, such as WeatherScope and IDV. Actually I had used these programs many times before, but not for real-time storm tracking. Below are some screen shots of the radar data I used. The first three composite radar images from WeatherScope show the storm system as it developed from Stearns to Anoka County. Each of the images contain wind and hail data, depicted by various shaded circles (hail) and shear arrows (wind). On the second image from the left the arrows rotate in a circle over NW Wright County, highlighting an area of possible rotation and where spotters may have seen the weak funnel. The final WeatherScope image shows the possible bow echo moving over western Anoka County. The lone IDV image on the right is from the same radar scan as the third WeatherScope image, but I took a cross-sectional cut of the storm at radar elevations ranging from 0.5 to 12.5 degrees.
The cell continued rolling down Interstate 94, and arrived in Arden Hills at 2:00pm, accompanied by gusty winds, brief heavy rain, and occasional lightning. It even sported a small patch of whale's mouth on the back side of its raged gust front. Within 20 minutes the storm had cleared the area, although the 70 degree dewpoint had not fallen. The backside of the retreating, but now strengthening, system featured quite a few lightning bolts and was tinted with a faint green tint, a sign that hail might be falling. This squall line re-attained severe status in Washington County just to my east and continued its torrent well into western Wisconsin. It dissipated as the night fell across central Wisconsin. The photos below are from my work in Arden Hills, taken as the core of the cell tracked just to my north. The last two photos highlight the green-colored underside of the departing storm.
Despite not having straight-line winds at my house, the storm still managed to do a substantial amount of damage. Tree branches, some almost 8 feet long, littered the block along with hundreds of smaller twigs and leaves. I spent a good hour cleaning up the mess in the yard. But the really spectacular numbers came from my brand new Davis weather station, which had hardly spent a week on the roof. This was its first ever storm. The highest sustained wind speed it recorded was 38mph out of the southwest. Since I live in a wooded area, the actual wind speed was likely higher. The rain gauge measured a total of 0.62 inches of rainfall that fell at a rate of 6.06 in/hr!! While this number seems very high, the force of the water coming off the roof and down the gutters on my house was enough to blow off one of the downspouts. The water gouged a hole in the dirt underneath it and CARRIED the downspout 20 feet to the southwest (if the wind had blown it around it would have gone in the opposite direction). Photos of the severed downspout, flower damage, and tree damage are below. . .
That capped a day of firsts. The first time I had tracked a storm live with special radar software, the first ever storm I have recorded with a weather station (the old station didn't save weather data), and the first storm endured by the new station. Hopefully there are many more to come!! Happy Fourth of July!!
