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      Source Regions

      The High Plains and Rockies from Montana to western Nebraska and New Mexico are in the grip of a serious drought.

      The source regionâ??the location from where our air mass originatesâ??is all-important in determining how warm, cold, wet or dry we will be here in Upper Michigan. Yesterday, a dry, hot blast of air moved in off the High Plains to our southwest. This is a source of extremely dry air where persistent, serious drought continues (Image 1 above). Temperatures in a narrow corridor from southwest Nebraska into extreme southern Minnesota reached 100 or above yesterday afternoon (Image 2). At Sioux City, Iowa reached 106 degrees, the hottest on record in May. The previous record of 105 occurred in late May 1934 during the withering Dust Bowl days. That month featured three consecutive days above 100 degrees. It got up to at least 100 in both Mankato and Albert Lea in far southern Minnesota.

      The air can heat up so much because itâ??s so dry in the High Plains of Nebraska, Kansas and Colorado all the way down to the Texas Panhandle. That source region must be kept in mind as we head into the summer season. If the conditions are right, some of that heat could make it up here. However, unlike last year it is quite wet to our south so any heat wave would likely be brief and transient.

      Up north, there is still a source, although diminishing, of cold. A visible satellite image from this morning still shows ice-covered lakes in central and northern Ontario (Image 3). It is this cold source that helped to keep winter entrenched here for so long this spring. It is now becoming less important, however, and I expect to see Lake Nipigon ice-free within a couple of days. The warm season is encroaching quickly now that the last major blast of cold air retreated from this weekend. The lakes in northern Minnesota opened up yesterday.

      So the bottom line is that summer is just around the corner. It is less than a month until the longest day of the year, the heat is building in the Plains and it will not be long before weâ??ll be flipping on the air conditioners.