SUBJECT: Rainy and cooler, but no records, depending on where you measure. August and Summer 2002 St. Cloud weather summary
FROM: Bob Weisman
Earth Sciences, St. Cloud State University
August’s weather in Saint Cloud was the same song, but in a different key. The rainfall at the Saint Cloud Regional Airport was 5.59 inches, more than 1.6 inches above normal. However, this rainfall did not approach record levels. There have been three other Augusts during the past 10 years with at least 5 inches of rain. In August 1997, 5.80 inches fell while, in August 1995, the Airport received 7.35 inches. That August of 1995 ranked as the fourth wettest August on record. The August record for Saint Cloud rainfall was set in August 1900 when 9.28 inches fell.
Nearly half the August 2002 rain occurred on August 3 when 2.74 inches was recorded. Yet, no daily records for rainfall were set. The record rainfall for August 3 is 4.57 inches, the second highest daily rainfall in Saint Cloud history. In addition, there have been two August days in the past 6 years with even more rain: August 21, 1999 (2.81 inches) and August 26, 1995 (2.70 inches).
The August rainfall brings the total 2002 summer rainfall (June 1 through August 31) to 15.63 inches, nearly 4 inches above normal. This makes the meteorological summer of 2002 the 13th rainiest summer on record and the rainiest since 1990. In 1990, 19.05 inches of rain fell, ranking as the fourth rainiest summer on record. The summer of 1990 included 10.52 inches in June 1990, the second rainiest month in the 110 years of Saint Cloud rainfall records. The rainiest summer in Saint Cloud history occurred in 1897 when 22.06 inches of rain fell, including 12.81 inches in June 1897, the rainiest month in Saint Cloud history. The heavy rainfall is in huge contrast to last summer, when only 6.81 inches fell, the 10th lowest total in Saint Cloud records.
So, why did the Twin Cities and other nearby communities experience record or near record rainfall while Saint Cloud did not? One reason is the local nature of thunderstorms and where they tend to stall. For example, Wednesday morning’s complex of thunderstorms produced over 6 inches of rain in Kimball, but about 1.1 inches in Saint Cloud. The repeat of this pattern can be seen in the August 26 weekly precipitation and departure map from the Minnesota State Climatologists’ Working Group Web Site (http://climate.umn.edu/doc/weekmap.asp). Extreme eastern Stearns County, Benton County, and northern Sherburne County defines one of the only areas within an 80 mile radius of the Twin Cities Metropolitan area that has picked up less than one and a half times the normal rainfall since April 1 and this does not include Wednesday’s rainfall.
The local difference from thunderstorms is a large factor in the huge difference in summer rainfall between Saint Cloud State University (7.18 inches of rain during August, 21.51 inches of rain during the summer season) and the airport. Note that two of the four heaviest rain events during the 12 years of SCSU rainfall records were recorded this summer. This partly accounts for a nearly 6 inch difference between SCSU and the airport. While some of this can be explained by the local variation in thunderstorms, these statistics do show that the Airport rainfall could be regarded as an underestimate of the rainfall in eastern and central Stearns County.
However, the second factor could be problems with the recording equipment at the Saint Cloud Airport during periods of heavy rain. During the July 10 heavy rainfall, 2.70 inches were recorded at a manual gauge at Saint Cloud State University in a two-hour period while the Saint Cloud Airport reported .32 inches of rain. Manual rain measurements did indicate that, while the heaviest rainfall did not reach areas south and east of the airport, it did hit the Airport area for a period of time. This difference accounts for nearly the entire difference between the Airport rainfall and the University rainfall during July. If another two inches of rain were added to the Airport rainfall total, this summer would rank as the 6th rainiest in Saint Cloud records.
While the humidity continued to be often uncomfortable, Saint Cloud temperatures cooled substantially in August. The average temperature of 66.9 degrees was slightly below normal and it took a warming trend in the past week to get it that high. At mid-month, the average temperature was running more than 2.5 degrees below normal and it was nearly 1.5 degrees below normal through August 23. August included the coolest high since June 4 (67 on Aug. 18) and the coolest low since June 5 (43 on Aug. 18 and 3 days with lows in the 40’s).
Why was it cooler in August but still rainy? The persistent front that has separated cooler Canadian air from the heat and humidity, which has affected the central Plains and the southern Rockies nearly all summer, pushed a bit further to the south during August. Because of the position switch, we did not have any days with the extreme heat, only getting above 85 degrees one day during August. However, when the front moved closer to Minnesota, it was close enough to pump the humid air over the cooler ground air, producing more slow-moving, heavy rain-producing thunderstorms.
The cooler August offset some of the early heat, producing a summer average temperature of 69.4 degrees. This was two degrees above normal, but only ranks as the 36th warmest summer out of the 122 summers in Saint Cloud records. Saint Cloud had warmer summers last year (69.6 degrees, ranked 31st), in 1995 (69.7 degrees, ranked 30th), and in 1988, the hottest summer of recent memory (72.0 degrees, tied for 4th).
The above average temperatures during both August 2002 and the overall summer statistics were produced more by the warm average low temperatures than the average high temperatures. August’s average low temperature was above normal while the average high was below normal. In the summer statistics, the average low temperature was more than 4.5 degrees above normal while the average high was near normal. Consistent with these statistics, there were only 8 90-degree highs this warm season so far, 10 less days than last year and more than 2 days below normal. On the other hand, there were 8 days with a low temperature of at least 70 degrees, tied for 6th for the most 70-degree lows on record. This was the most days with a 70-degree low since 1955. The abnormally warm lows are consistent with the overall humidity of this summer.
What does this say about future weather? Why are you asking when we can’t even pin down where tonight’s thunderstorms will be?! If you must ask, the general pattern of being within a few hundred miles of that pesky front will continue this upcoming week, so there will be little change in the general August weather pattern. Beyond that, there had been signs that an El Nino event, the warming of ocean waters in the Tropical South Pacific, would develop. This warming has a fairly strong correlation with mild winters in the Northern Plains. As of early August, an El Nino event appears to be under way, but the degree of ocean warming is weaker than in recent years. This does NOT mean that it can’t get stronger (or dissipate for that matter). However, we appear to be headed for a weak El Nino winter, which makes the chance of a mild winter more uncertain.
AUGUST STATISTICS AUG 2002 NORMAL TEMPERATURE (oF) Average high temp 77.2 78.9 Average low temp 56.6 55.5 Average temp 66.9 67.2 Hottest high temp for the month 86 on the 11th Coolest high temp for the month 67 on the 17th Warmest low temp for the month 64 on the 9th, 31st Coolest low temp for the month 43 on the 18th DAILY RECORD TEMPS none AUGUST 2002 NORMAL Days with a high of 90 degrees or higher 0 4.7 Days with a low of 70 degrees or higher 0 1.8 WARM SEASON TOTALS 2002 NORMAL YEAR Days with a high of 90 degrees or higher 8 10.7 Days with a low of 70 degrees or higher 6 3.8 PRECIPITATION (IN) AUGUST 2002 NORMAL Total for month 5.59 3.93 Maximum daily amount 2.74 on the 3rd DAILY RECORD RAINFALL none SUMMER STATISTICS (Jul 1 - Aug 31) 2002 NORMAL TEMPERATURE (oF) Average high temp 79.8 79.3 Average low temp 59.0 55.4 Average temp 69.4 67.4 TOTAL RAINFALL (inches) 15.63 11.78 Saint Cloud State Total Rainfall (inches) 21.51 TOTAL GROWING SEASON RAINFALL (IN) TOTAL NORMAL Saint Cloud Airport April 1 - August 31, 2001 17.68 17.11 Saint Cloud Airport April 1 - August 31, 2002 21.03 17.11 Saint Cloud State University April 1 - August 31, 2002 27.66 HEAVIEST DAILY RAINFALL TOTALS IN SAINT CLOUD HISTORY (AIRPORT) AMOUNT (in) DATE 4.80 2 July 1903 4.57 3 August 1956 4.50 6 July 1897 4.12 19 August 1935 3.90 24 August 1895 3.62 8 September 1985 3.59 27 August 1960 3.52 22 April 2001 2.74 3 August 2002 1.96 10 July 2002 HEAVIEST DAILY RAINFALL TOTALS IN SCSU HISTORY (1991-2002) AMOUNT (in) DATE 4.40 25-26 August 1995 4.29 10 July 2002 3.83 23 April 2001 3.63 3-4 August 2002 2.57 2 August 1997 2.37 7 September 1991 2.35 19 August 1997 2.25 25 July 1997 2.16 16 June 1994 2.07 26 August 1993 ANNUAL HIGHS OF >= 90 DEGREES SAINT CLOUD: 1896-2002 (Average per year: 10.7) Year Days 1936 36 1900 34 1988 33 1931 31 1910 29 1933 28 1934 28 1937 26 1901 25 1930 25 2001 18 2002 8 ANNUAL LOWS OF >= 70 DEGREES ANNUAL LOWS OF >= 75 DEGREES SAINT CLOUD: 1896-2002(Avg: 3.1 days) SAINT CLOUD: 1896-2002 (Avg: 0.5 days) Year Days Year Days 1931 16 1931 7 1900 11 1901 4 1936 11 1936 3 1937 10 1898 2 1941 9 1905 2 1897 8 1916 2 1901 8 1964 2 1930 8 2001 2 1935 8 1947 8 2002 1 1955 8 50 days on record 2002 8 1932 7 1933 7 2001 7 LAST SAINT CLOUD HIGH OF 100 OR HIGHER: July 3, 1990 (101 degrees) LAST SAINT CLOUD AUGUST HIGH OF 100+: August 16, 1950 (only 7 August 100+ highs on record)
Last modified: September 3, 2002