SIOUX FALLS AREA
CLIMATIC SUMMARY
1999

By Richard Ryrholm
Climatic Focal Point
National Weather Service, Sioux Falls

 

...1999 CONTINUED THE TREND OF MILD WINTERS AND DRY LATE SUMMERS...

The total precipitation at Sioux Falls airport in 1999 was 21.91 inches which was 1.95 inches below normal. It seemed that Sioux Falls was heading for a wet year when in late July the significant precipitation events shut off and it was extremely dry for the rest of the year. The average temperature for 1999 was 47.5 degrees...exactly the same as in 1998...and 2.0 degrees above the yearly normal.

1999 started with a cold snowstorm on January 1st to 2nd with a total snowfall of 6.6 inches. 20 to 40 mph northerly winds caused blowing and drifting snow and dangerous wind chills in the area. Partly due to the fresh snow cover...the lowest temperature of the year of 21 below zero occurred 2 days later on January 4th. January 1999 was by far the most winter-like month since the notorious 1996/97 winter...but only averaged near normal for the month of January.

However February returned to unseasonably mild weather for winter averaging 10.2 degrees above normal and ranking as the 8th warmest February since records began at Sioux Falls in 1893. This was partly because of the lack of snow cover for much of the month...at least until the next decent snowfall of 5.9 inches on February 22nd.

The biggest snow event of 1999 was on March 8th when 2 separate periods of heavy snowfall produced a total of 9.3 inches and many area schools closed. The strongest wind of the year at Sioux Falls airport was 55 mph from the northwest on March 17th.

Spring was rather wet as there was 4.32 inches precipitation in April and 6.20 inches in May...the wettest month in 1999. The heaviest rain event at the airport for the year was 1.89 inches on May 20th. However the heaviest rain event in the city was in the early morning of July 19th when over 2.5 inches rain fell in a short time on the east side of Sioux Falls. The most severe thunderstorm in the Sioux Falls area in 1999 was on June 7th around 550 pm when high winds blew down a concrete wall of a store under construction...and there was tree damage and hail up to golf ball size in the area.

July was also the last month that Sioux Falls was above normal in precipitation with 4.81 inches for the month. August 1999 was the 10th driest August on record with only 0.80 inch recorded. The warmest temperature of 1999 was 95 degrees on both July 29th and August 27th. On July 29th the heat index rose to 111 degrees with a sultry dew point of 80 degrees...making it the most uncomfortably hot and humid day since august 1995.

The September to November period was the 3rd driest autumn on record...

Totaling only 1.26 inches compared to a normal of 5.89 inches for the period. About the only precipitation event worth mentioning in this period was the unusually early snowfall of 2.7 inches on October 1st when the leaves were still green on the trees. Only 0.05 inch precipitation was recorded in November 1999 and it was the warmest November on record...averaging 9.1 degrees above normal. The record high of 81 degrees on November 8th was the first temperature of 80 degrees or more ever recorded in November. Because of the unusually dry and warm weather...numerous grass and vegetation fires occurred in the area and the air was often smoky and dusty.

December 1999 generally continued the mild dry weather pattern... averaging 6.8 degrees above normal for the month. It was still a white Christmas...at least on Christmas Eve to the morning... before it all melted off in the afternoon. Record highs were again recorded near the end of the month...with 49 degrees on the 28th and a balmy 56 degrees on December 29th.

THE FOLLOWING TABLES GIVE A MONTH BY MONTH BREAKDOWN OF WEATHER IN 1999 AT THE SIOUX FALLS AIRPORT...

TEMPERATURES

AVERAGE             DEPARTURE  EXTREMES    MONTHLY
MONTH MAX MIN MONTHLY FROM NORM HIGH LOW RECORDS

JANUARY 23.1 4.9 14.0 PLUS 0.2 41 21B
FEBRUARY 38.7 21.0 29.9 PLUS 10.2 57 7 8TH WARMEST
MARCH 45.2 22.3 33.8 PLUS 1.3 73 5
APRIL 56.2 35.2 45.7 MINUS 1.2 72 21
MAY 69.2 47.8 58.5 PLUS 0.1 83 34
JUNE 76.6 57.2 66.9 MINUS 1.4 90 42
JULY 85.7 64.4 75.1 PLUS 0.8 95 50
AUGUST 82.3 58.8 70.6 MINUS 0.8 95 47
SEPTEMBER 73.1 46.3 59.7 MINUS 1.2 89 29
OCTOBER 63.0 34.0 48.5 MINUS 0.1 81 19
NOVEMBER 56.7 27.4 42.1 PLUS 9.1 81 17 1ST WARMEST
DECEMBER 37.5 12.7 25.1 PLUS 6.8 56 12B

1999 58.9 36.0 47.5 PLUS 2.0 95 21B

NORMAL YEAR 56.8 34.2 45.5

PRECIPITATION (INCHES) AND WINDS

DEPARTURE              DEPARTURE    MAX WIND GUSTS
MONTH FROM NORM SNOWFALL FROM NORM DIRECTION/MPH/DATE

JANUARY .35 MINUS .16 9.9 PLUS 3.2 NW 48 ON 17TH
FEBRUARY .28 MINUS .36 7.9 PLUS 0.2 NW 48 ON 11TH
MARCH 1.15 MINUS .49 11.2 PLUS 3.2 NW 55 ON 17TH
APRIL 4.32 PLUS 1.80 2.4 PLUS 0.2 NE 51 ON 8TH
MAY 6.20 PLUS 3.17 0 NW 44 ON 7TH
JUNE 2.57 MINUS .83 0 NW 49 ON 7TH
JULY 4.81 PLUS 2.13 0 N 44 ON 19TH
AUGUST .80 MINUS 2.05 0 S 40 ON 15TH
SEPTEMBER .84 MINUS 2.18 0 NW 40 ON 26TH
OCTOBER .37 MINUS 1.41 2.7 PLUS 2.1 N 38 ON 15TH
NOVEMBER .05 MINUS 1.04 T MINUS 5.1 N 48 ON 1ST
DECEMBER .17 MINUS .53 3.2 MINUS 4.6 NW 38 ON 19TH
ALSO N 38 ON 27TH

1999 21.91 MINUS 1.95 37.3 MINUS 0.8 NW 55 MAR 17TH

RICHARD S. RYRHOLM/ CLIMATIC FOCAL POINT

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