FROM: Bob Weisman

Earth Sciences, St. Cloud State University

Common perception is that July 2002 was extremely hot, humid, and rainy. As was the case last month, the statistics from the Saint Cloud Airport do not bear that out. The July average temperature was 72.8 degrees, three degrees above normal. However, that only ties for the 32nd warmest July out of 122 years of Saint Cloud temperature records. It was the warmest July since 1988 (10th warmest all time), but that July was nearly two degrees warmer than July 2002. This mainly reflects that recent Julys have been relative cool. Only three of the past 13 Julys have had an average temperature more than a degree above normal. There were 5 days with a high of at least 90 degrees, which was nearly the normal amount. In comparison, July 2001 had 8 90-degree highs.

The low temperatures were more abnormal than the high temperatures. The average low temperatures were more than 4 degrees above normal, a sign of the high humidity during the month. There were 4 days with a low of at least 70 degrees, the highest July total since 1975. However, there have been 9 Julys with more July 70-degree days (the record is 10 days in 1936). Saint Cloud has now recorded 6 days with a low of at least 70 degrees, nearly double the normal amount and the most since 1964. The record for 70-degree lows in a year is 16, set in 1931.

Rainy conditions were demonstrated by the July 2002 Saint Cloud Airport statistics. More than 5 inches of rain was recorded this past month, about one and three-quarter inches above normal. That ranks as the 16th highest July rainfall since 1893. The prime contributor to this July’s total was the 1.96 inches during the calendar day of July 10, the day with the widespread flooding in Saint Cloud, Sauk Rapids, and Foley as well as much of central Minnesota. However, more rain fell in July 1997 (6.89 inches), July 1990 (5.15 inches), and July 1986 (7.53 inches).

Also, it must be pointed out that the Saint Cloud Airport July rainfall total is likely an underestimate of rainfall during the past month. One factor was the intense morning rainfall event on the morning of July 10. In the two-hour period between 7 and 9 AM, rainfall at Saint Cloud State University was 2.70 inches while the Saint Cloud Airport total was .32 inch. This period of heavy rain only grazed areas to the south of I-94 like Kimball and missed areas to the south and east of the airport. However, for the city of Saint Cloud, almost all of Benton County and other areas, the total event produced 4.0-4.5 inches of rain with 2+ inches of rain in a brief morning period. The Saint Cloud State University total for the month of July was 8.04 inches, more than 2.9 inches higher than the Airport total. Most of the month’s difference is accounted for by the morning of July 10, with rainfall gauge error strongly suspected at the Airport.

Also, it must be pointed out that the Saint Cloud Airport July rainfall total is likely an underestimate of rainfall during the past month. One factor was the intense morning rainfall event on the morning of July 10. In the two-hour period between 7 and 9 AM, rainfall at Saint Cloud State University was 2.70 inches while the Saint Cloud Airport total was .32 inch. This period of heavy rain only grazed areas to the south of I-94 like Kimball and missed areas to the south and east of the airport. However, for the city of Saint Cloud, almost all of Benton County and other areas, the total event produced 4.0-4.5 inches of rain with 2+ inches of rain in a brief morning period. The Saint Cloud State University total for the month of July was 8.04 inches, more than 2.9 inches higher than the Airport total. Most of the month’s difference is accounted for by the morning of July 10, with rainfall gauge error strongly suspected at the Airport.

In addition, the wide variation of thunderstorm-produced rainfall was a factor. The greatest example of this occurred on the evening of July 24. A slow-moving line of thunderstorms set up between Sauk Center and Monticello. Both the airport (.36 inch) and SCSU (.47 inch) missed this line of storms, but a cooperative report from 1 mile south of Saint Augusta showed 3.50 inches of rainfall.

The net effect of this heavy rain is that most of central Minnesota has received between 1 1/2 times and double the normal amount of rainfall since April 1. The latest weekly report from the Minnesota State Climatology Office (http://climate.umn.edu/doc/weekmap.asp) from Monday shows that the current growing season in all of the area, except parts of Benton and Sherburne Counties, ranks in the wettest 1-5% of years on record.

Why the humidity and the rain? Minnesota has spent most of the past 6 weeks just on the cool side of the front marking the boundary between the intense heat in the Rockies, Far West, and Southern Plains, and cooler Canadian air. This is a prime pattern for producing slow-moving large complexes of thunderstorms that develop both overnight and during the afternoon. There have been relatively few tornadoes this year, but several cases of heavy rainfall, damage from straight-line winds, and hail damage. After a break from this pattern the next couple of days, it looks like the humid and wet summer of 2002 will resume by the weekend.

JULY STATISTICS                                JULY 2002              NORMAL
TEMPERATURE (oF)
Average high temp                              83.4                    81.6
Average low temp                               62.3                    57.9
Average temp                                   72.8                    69.8
Hottest high temp for the month                95 on the 6th
Coolest high temp for the month                70 on the 10th
Warmest low temp for the month                 73 on the 1st 
Coolest low temp for the month                 50 on the 23th

DAILY RECORD TEMPS                            none

                                               JULY 2002              NORMAL
Days with a high at or above 90 degrees        5                      4.7
Days with a low at or above 70 degrees         4                      1.8

WARM SEASON TOTALS                             2002                   NORMAL
Days with a high at or above 90 degrees        8                      10.7
Days with a low at or above 70 degrees         6                       3.8

PRECIPITATION (IN)                             JULY 2002              NORMAL
Total for month                                5.12                   3.34
Maximum daily amount                           1.96 on the 10th (broke record; see below)

DAILY RECORD RAINFALL                          1.96 in on the 10th (old record: 1.76 inch in 1933)


TOTAL GROWING SEASON RAINFALL (IN)
                                                      TOTAL             NORMAL
Saint Cloud Airport April 1 - July 31, 2001           17.68             13.18
Saint Cloud Airport April 1 - July 31, 2002           15.44             13.18
Saint Cloud State University April 1 - July 31, 2002  20.48                    

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