The Summer of 2004 was one of the coolest summers of record in North Dakota and also in much of the rest of the central portion of the United States. The National Climatic Data Center (NCDC) ranked the Summer of 2004 as the 5th coldest on record for North Dakota as a whole and the 3rd coldest of record in Minnesota. Below is the ranking per climatic zone for the lower 48 stats for the June through August 2004 time period.
Locally, the North Dakota Agricultural Weather Network (NDAWN) stations at the time, reported summer temperatures around 5 degrees below average that summer.
Often when the words summer and cool come in the same sentence you think rain, as the clouds associated with the rain, plus the wet soils would attribute to the overall cooling of the low level air temperature. Yet, the summer of 2004 was not a wet one, In fact, the NDAWN stations recorded on average only around 50% to 60% of average precipitation that summer.
The coolness that summer was associated with a very persistent northwest flow aloft over the north central part of the United States. Below is the 500 mb chart from August 20, 2004 as a representation of the flow that summer. Plus, August 20 was also the culmination of the cold that plagued the region for weeks on end that year. As the end of August was approaching, a strong 500 mb low moved south over Hudson Bay (Polar Vortex). This allowed a mid-level airflow from the Arctic Ocean to move into the northern plains. This also brought with it the coldest air of the summer.
Under that type of flow, you tend to have high pressure situated on the western edge of the 500 mb low. On the morning of August 20 an area of high pressure with an origination source in the arctic moved through the prairie provinces of Canada into North Dakota. Low temperatures under this area of clear sky and light wind were in the 30s that morning with some locations
recording low temperatures even in the upper 20s. This was an historic event to record temperatures near or below freezing so early in the season, even by our cold climate standards. Low temperatures that morning at the NDAWN stations are presented below.
The following morning of August 21, 2004 was not much warmer in the far eastern portion of North Dakota into western Minnesota with yet another morning with temperatures near the freezing point.
After two successive days near or below freezing, reports of crop damage was extensive, especially in the northern one-half of North Dakota and the northern one-fourth of Minnesota. The morning of August 20 was the colder of those two mornings with numerous records being broken for the date. Some of those are listed below.
LOCATION RECORD YEAR VALID DATES
That early season frost was the end of what was a terrible growing season for many, but those locations that did survive the frosty mornings of August 20 and 21, recorded much improved temperature conditions there after. The following several weeks were quite mild and September 2004 was one of the warmest Septembers of record. It was a month that did allow many of the surviving crops to reach maturity and also, after the next frost, which was in early October in much of the area, there was good drying weather to allow for a low moisture content crop to be harvested.