Fourteen years ago today was a sizzler across the U.P., at least for early May. It hit 88 degrees at the National Weather Service (NWS) near Negaunee. Temperatures soared into the 80s the next two days, too. In Ironwood, a record high of 86 was achieved on the same day, while Iron Mountain hit 88 and 89 degrees on the 6th. The early season heat wave was fueled by a big upper-level low-pressure trough that developed over the western portion of the continent (Image 1). A surface low formed in response to the trough over the Northern Plains. The southerly flow ahead of the system pumped the heat into Upper Michigan. The six-day stretch from May 3-8 was 20.2 degrees above the long-term average at the NWS.
The early summer pattern broke down and more typical May weather was experienced the rest of the month. Still, May 2000 ended with a mean temperature 3.7 degrees above normal.
Through the first four days of the month, May 2014 is running 6.8 degrees below average. We still expect a turn-around to warmer and wetter the next few days. A big upper-level trough will form to our west, but not as far west as in 2000 (Image 2). Eventually low pressure will form on the east side of the trough over the Plains and head northeastward. It will drag a warm front northward toward the southern Great Lakes on Wednesday. That will be our first chance of getting some rain. However it appears, as is often the case in the early portion of the warm season, that the heaviest rains and warmest air will center to the south of us.