Posted at 2:34 PM on July 16, 2011
by Mark Seeley
Early morning hours of Saturday, July 16th brought very heavy rainfalls to parts of Minnesota, including the Twin Cities area. Between 4:00 am and 8:00 am waves of thunderstorms produced very intense rains. Between 5:00 and 6:00 am on the University of Minnesota St Paul Campus 1.77 inches of rainfall was recorded, with over three-quarters of an inch coming in just 15 minutes. The total rainfall between 4:00 and 7:00 am was 3.20 inches. Over a similar time span North St Paul reported 4.79 inches. As a result many roads and intersections were flooded for a time on Saturday morning
Over the 24-hour period from 8:00 am Friday (July 15) to 8:00 am Saturday (July 16) many Twin Cities area observers reported record or near-record amounts of rainfall, including:
4.04 inches at Lakeville
4.85 inches at Plymouth
5.26 inches in Roseville
4.65 inches at Lake Elmo
4.67 inches at Belle Plaine
5.93 inches at Fridley
5.44 inches at Little Canada
4.54 inches at Maplewood
Elsewhere around the state some remarkable amounts of rainfall occurred as well, including:
5.26 inches at Eyota
5.79 inches at Byron
4.54 inches near Rochester
4.13 inches at Mantorville
5.66 inches at Montgomery
Many other observers around the state reported 2 or more inches of rainfall over July 15-16 pushing monthly rainfall totals to very high levels. Some monthly totals for July through the 16th include:
Worthington 7.96 inches
Kimball 8.43 inches
Glenwood 7.48 inches
Since there are still two weeks left in the month it appears some Minnesota observers may exceed 10 inch rainfall totals for the month. We'll see what happens.
Help, please. I am trying to understand why, when it's 98F out there today, DP of 75 degrees, and the RH is only 47%. Does this mean that the air could get more saturated with moisture?? I would think the RH would be near 100% under the conditions like we're having today? Please explain.
The RH in the ratio of the amount of vapor in the air to the amount of vapor the air can hold. The dewpoint temperature is the temperature at which air with a given amount of water vapor is saturated i.e. 100% RH. The amount of water vapor that air can hold increases with increasing temperature. For example if you were to take a bag of today's air and dropped the temp to 75F you would be at 100% RH, if you dropped the temp further you would get condensation on the walls because the air is not able to hold as much vapor. If you were to heat the bag to 110F the RH would drop below the 47% you mention above. Hope this helps.
Yes, thanks. That does, except where does the 110F temp come in in your example? It wasn't that hot, i don't think...?