The recent rain / cold weather has attributed to some abrupt statistical differences in the past couple of weeks. For example, on May 8, Jamestown (State Hospital) was reporting the 12th driest year for that date.
Just ten days later, on May 18, the Jamestown State Hospital was reporting the 3rd wettest year to date. Records at that location go back to 1893.
The rapid change from dry to wet was associated with two rain systems during the period from May 9 through May 18. Although the graphic below has a total during that time period of 4.60 inches at the NDAWN (North Dakota Agricultural Weather Station) 10 miles west of Jamestown, in the city of Jamestown, much more rain was recorded. The climate site at the State Hospital in Jamestown recorded nearly 8 inches of rain during this period. Through the first 18 days of May 2015, that location has recorded 8.24 inches or rain. That makes this May the wettest on record at that site. That is nearly 1 inch greater than the previous record with nearly 2 weeks left in the month.
In the graphic above, Fargo was another site with a substantial rainfall during that 10 day period. On May 8, 2015 Fargo was recording the 17th driest year to that point,
on May 18, Fargo was recording the 15th wettest year on record.
Precipitation amounts from average for the month through May 18 are presented below. Although statistics for Jamestown and Fargo were used, there are other locations where similar results would occur. Plus, the map below also demonstrates that not every location in North Dakota recorded extremely wet conditions over the past two weeks as many locations in western North Dakota are either near or below average for May to this point in the month.
On May 18, 2015, Fargo (KFAR) recorded a high of 40°. That is 30° below the average of 70° for that date. Had the high been 39° instead, it would have been the 3rd latest 30s high on record, although that 40° record did set the record for the lowest maximum for that date with the previous record being 44°.
Even with such cold highs in Fargo and other locations in North Dakota and northwestern Minnesota yesterday, the warmth at the beginning of the month has made for negative temperature anomalies for the month through May 18 in the -2 to -5 degree range.
With such cold high temperatures yesterday, most of the NDAWN mesonet recorded minimums below freezing (32°) this morning. Although the freeze this morning would be considered near the average date for locations near the Canadian border, the southern one-half of North Dakota this freeze came approximately 10 days later than normal.