May 7th: Summer-like warmth & humidity on the way

While many gardeners and farmers use April 15th as the average last freeze/frost for southern Illinois, May 7th, 1944 marks the latest freeze on record. On a year like 2018, where the cold seemed it would never go away through the month of April, the pattern has flipped and as we expected, those large troughs pulling cold air out of Canada are becoming a thing of the past. For those that have been clamoring for warmer weather, it's about to go from Spring to feeling a bit like Summer in a matter of days. For those hoping for dry weather, well, the next two weeks are going to be tough.

NEXT TWO WEEKS

Figure 1: Zonal flow (fast moving west to east jetstream pattern)

The jetstream will flatten more than it has in quite some time for the second week of May. (See: Figure 1) Meteorologists call this "zonal flow" and it's characterized by a fast moving, west to east flow pattern. With the lack of north or south push, it usually results in cold fronts trying to move south, stalling in the Mid-Mississippi/Lower Ohio Valley and then retreating northward. Of course, where the two airmasses clash results in showers and storms this time of year. That'll be the case towards the middle of the week with a cold front moving in from the north, sitting near the region before lifting back north.

May 14-18th jetstream. Large ridge on the East Coast deflecting storm systems north

A pattern shift is expected towards the later part of the weekend (May 12-13th) that will put a big ridge of high pressure over the eastern seaboard. The position of the ridge will determine the amount of wet weather for southern Illinois. Typically, when I see this pattern, it screams hot, humid, and nearly daily chances for storms. Beyond May 20th, there are some signs the ridge along the East Coast will strengthen and shift westward a bit, which would lend a hand in prolonged dry weather the last third of May.