Below Normal Temperatures Continue over the Region - July 2009

TEMPERATURES THIS SUMMER REMAIN WELL BELOW NORMAL OVER MUCH OF THE NORTHERN PLAINS...INCLUDING PORTIONS OF SOUTH DAKOTA AND WEST-CENTRAL MINNESOTA. THIS IS NOT A NEW TREND...AS TEMPERATURES HAVE GENERALLY BEEN BELOW NORMAL SINCE THE WINTER OF 2007-2008 (SEE TABLE 1 BELOW). RECALL THAT LAST SUMMER PIERRE FAILED TO REACH 100F FOR ONLY THE SECOND TIME SINCE 1933.

A QUICK LOOK AT THE TEMPERATURE NUMBERS THIS YEAR INDICATE THAT THE NUMBER OF CALENDAR DAYS WHEN THE HIGH TEMPERATURES HAVE EXCEEDED 90F, 95F OR 100F AT PIERRE, ABERDEEN, AND WATERTOWN ARE WELL BELOW CLIMATOLOGICAL AVERAGES (SEE LISTINGS BELOW) AND VERY MUCH MIMIC THE TRENDS FROM THE SUMMER OF 2008.

THE CAUSE OF SIGNIFICANT TEMPERATURE DEPARTURES CAN RANGE FROM CHANGES IN THE GLOBAL SCALE CIRCULATION (I.E. EL NINO/LA NINA) TO MORE LOCAL EFFECTS (I.E. DISTRIBUTION OF RAINFALL). IT IS OFTEN DIFFICULT TO PIN DOWN ONE UNDERLYING REASON FOR SIGNIFICANT TEMPERATURE DEPARTUES...AS THERE IS OFTEN A MULTIPLICITY OF CAUSES. TWO POTENTIAL FACTORS ARE LISTED BELOW:

1. ABOVE NORMAL PRECIPITATION FELL OVER MUCH OF THE REGION THIS PAST WINTER. AS SUCH -- SOIL MOISTURE LEVELS THIS SPRING WERE ABOVE NORMAL RESULTING IN AN ENERGY BUDGET WHERE MORE SOLAR RADIATION IS USED FOR EVAPORATION RATHER THAN PURE SENSIBLE HEATING.

2. THE UPPER AIR PATTERN HAS CONSISTENTLY FEATURED AT RIDGE OF HIGH PRESSURE OVER THE WESTERN US WITH A STRONG TROUGH OF LOW PRESSURE IN THE EAST. THIS HAS LED TO A PREDOMINANTLY NORTHWEST FLOW PATTERN OVER THE DAKOTA'S WHICH IS CONDUCIVE FOR ADVECTING COOL AIR SOUTHWARD FROM CANADA.

LISTED BELOW IS A SUMMARY OF SEVERAL INTERESTING HEAT RELATED FACTS FOR ABERDEEN...PIERRE...AND WATERTOWN.

TABLE 1: TEMPERATURE DEPARTURES SINCE NOVEMBER 2007:

Month/Year	Aberdeen	Watertown	Pierre
NOV 07	+1.8	+3.2	+2.2
DEC 07	-4.6	-2.6	-0.4
JAN 08	-3.8	-1.0	+0.5
FEB 08	-6.6	-4.6	-3.6
MAR 08	-2.2	-2.2	-0.7
APR 08	-3.5	-3.5	-2.8
MAY 08	-3.5	-3.1	-5.0
JUN 08	-2.7	-2.3	-4.3
JUL 08	-0.6	+0.2	-2.6
AUG 08	-0.5	+1.2	-0.3
SEP 08	-0.1	+1.4	-1.4
OCT 08	-0.8	+0.2	-1.7
NOV 08	+2.6	+2.4	+1.5
DEC08	-7.4	-5.9	-6.8
JAN09	-4.8	-3.7	+0.7
FEB09	-3.4	-1.6	+0.1
MAR09	-3.3	-1.4	-3.3
APR09	-2.6	-1.3	-2.8
MAY09	-1.8	-0.3	-2.1
JUN09	-3.6	-2.4	-3.5
JUL09 (so far)	-3.7	-4.2	-4.3

ABERDEEN (1893-2008) - AVG NUMBER OF DAYS IS BASED ON 30 YEAR NORMALS (1971-2000)

AVG NUMBER OF DAYS WITH TEMPERATURES AT OR ABOVE 100F: 2.3
2009….0

2008....0

2007....1
2006.....5
2005.....0
2004.....0

AVG NUMBER OF DAYS WITH TEMPERATURES AT OR ABOVE 95F: 7.7
2009…..1

2008.....0
2007.....4
2006....10
2005.....3
2004.....0

AVG NUMBER OF DAYS WITH TEMPERATURES AT OR ABOVE 90F: 20.5

2009…..5

2008.....10
2007.....13
2006.....17
2005.....14
2004.....2

RECORD HOTTEST TEMPERATURE:                            115 F (7/9/1936, 7/6/1936)
YEAR WITH THE MOST 100F TEMPERATURES:           1936 - 35 DAYS
YEAR WITH THE MOST 95F TEMPERATURES:             1936 - 44 DAYS
YEAR WITH THE MOST 90F TEMPERATURES:             1936 - 69 DAYS
EARLIEST 90F TEMPERATURE:                                    4/4/1921
LATEST 90F TEMPERATURE:                                       10/16/1991
EARLIEST 100F TEMPERATURE:                                  5/1/1959
LATEST 100F TEMPERATURE:                                      9/22/1936

PIERRE (1933-2008) - AVG NUMBER OF DAYS IS BASED ON 30 YEAR NORMALS (1971-2000)

AVG NUMBER OF DAYS WITH TEMPERATURES AT OR ABOVE 100F: 8.8
2009…...0

2008......0
2007.....10
2006.....14
2005.....14
2004.....4

AVG NUMBER OF DAYS WITH TEMPERATURES AT OR ABOVE 95F: 21.6
2009…..3

2008.....5
2007.....20
2006.....37
2005.....32
2004.....16

AVG NUMBER OF DAYS WITH TEMPERATURES AT OR ABOVE 90F: 42.7
2009…..9

2008.....19
2007.....44
2006.....60
2005.....53
2004.....32

RECORD HOTTEST TEMPERATURE:                            117 F (7/15/2006)
YEAR WITH THE MOST 100F TEMPERATURES:            1936 - 41 DAYS
YEAR WITH THE MOST 95F TEMPERATURES:              1936 - 58 DAYS
YEAR WITH THE MOST 90F TEMPERATURES:              1936 - 79 DAYS
EARLIEST 90F TEMPERATURE:                                    4/9/1976
LATEST 90F TEMPERATURE:                                       10/29/1933
EARLIEST 100F TEMPERATURE:                                  5/8/1934
LATEST 100F TEMPERATURE:                                      9/26/1974

WATERTOWN (1893-2008) - AVG NUMBER OF DAYS IS BASED ON 30 YEAR NORMALS (1971-2000)

AVG NUMBER OF DAYS WITH TEMPERATURES AT OR ABOVE 100F: 0.8

2009….0

2008.....0
2007.....1
2006.....4
2005.....0
2004.....0

AVG NUMBER OF DAYS WITH TEMPERATURES AT OR ABOVE 95F: 4.9
2009…..0

2008.....0
2007.....3
2006.....7
2005.....4
2004.....0

AVG NUMBER OF DAYS WITH TEMPERATURES AT OR ABOVE 90F: 14.9
2009…..2

2008.....4
2007.....13
2006.....17
2005.....14
2004.....2

RECORD HOTTEST TEMPERATURE:                            110 F (7/20/1934)
YEAR WITH THE MOST 100F TEMPERATURES:            1933 - 17 DAYS
YEAR WITH THE MOST 95F TEMPERATURES:              1936, 1933 - 34 DAYS
YEAR WITH THE MOST 90F TEMPERATURES:              1933 - 53 DAYS
EARLIEST 90F TEMPERATURE:                                    4/2/1910
LATEST 90F TEMPERATURE:                                       10/5/1963
EARLIEST 100F TEMPERATURE:                                  5/28/1934
LATEST 100F TEMPERATURE:                                      9/10/1931

Mike Fowle - Science and Operations Officer