Thursday Evening's Balloon Launch Sets New Record

The balloon launched at 6 pm on January 10th, 2013 (midnight GMT January 11th) set a record for the most moisture ever recorded by a weather balloon in the month of January since balloons began to be released regularly twice a day at St. Cloud in 1948 (moved to Chanhassen in 1995).  The amount of moisture measured in the atmosphere is expressed in a term known as precipitable water (PWAT), which is a measure of how much water is in a column of air from the surface to the top of the troposphere (where weather occurs).  Basically, PWAT is an estimate for how much liquid one could expect if all of the water vapor in a column of air were to be rung out.  This parameter is often used by forecasters during the summer to help determine the potential for heavy rainfall and flash flooding, but can also be used as an estimate for the source region of the air.  In the summer, when tropical airmasses make it into the upper Mississippi River valley, PWATs often exceed 1.75 inches, while cold and dry arctic airmasses in the winter often bring PWAT values of less than 0.1 inches to the region.

The PWAT measured on the evening of January 10th was 0.97 inches, which beat the previous record for January of 0.92 inches from a balloon released on the evening of January 29th, 2001. In comparison, the average PWAT for January at MPX is just 0.25 inches, with the record low measured PWAT being 0.03 inches.  

Why was the PWAT so high?  The surface analysis that evening showed deep south and southeast flow across most of the United States east of the Rocky Mountains, with rich moisture getting pulled up into the United States from the Gulf of Mexico.  Beside Gulf moisture getting pulled north, unseasonably mild air was getting pulled north by these winds as well (see highs much of last week around 15 degrees above normal).  The sounding from that evening captured the depth of the warm air well, with the freezing level that night at an astounding (for the middle of January standards) 8569 ft. above ground level.  One of the characteristics of warmer air is that it holds more water (hence higher PWATs in the summer) and this warm air combined with moisture coming up from the Gulf conspired to give us the record PWATs. 

 

Surface analysis January 10th

Surface analysis at 6 pm on January 10th.

 

Sounding from 6pm January 10, 2013

Sounding from 6 pm January 10th, 2013.  The red line represents temperature, the dashed green line is the dewpoint, and the think blue line is the freezing line.  The highlighted number is the PWAT calculated from this sounding.

 

Average and record monthly PWAT values for MPX and STC.

Average and record monthly PWAT values for MPX and STC.



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