May 30th: Alberto exits, but heat dominates long range

May 2018 Temperature Discussion

May 2018 will likely go down as the warmest May on record for the Continental U.S. and possibly the warmest for southern Illinois. Through May 28th, the Continental U.S. was running 4.09º warmer than normal, which is really a crazy number in terms of averages. It absolutely blows previous records away (of course, there's still three days to add to the month).

2018 May Temperature Anomaly through May 28th

Since 1981, May 2012 is the only year comparable with a temperature anomaly of +2.88º in the Continental U.S.

2012 May Temperature Anomaly

May 2018 Rainfall Discussion

Tropical systems are always a wildcard in the Summer and can sometime tilt the scales to offset drier years. As Alberto moves out, I have a feeling folks in the drier areas of southern Illinois are a little disappointed in the rain they received. A pattern more common in mid to late Summer has dominated the middle of the country through the month of May which has led to big rainfall discrepancies across southern Illinois. Spotty pop-up storms have been the main rain makers in what is historically the second wettest month of the year. Areas that have been hits with the storms are doing quite well with rain, while others are starting to hurt a bit.

Last 60 Days of Rainfall Through May 28th

Rainfall through 8:30AM May 30th from Alberto

LONG RANGE OUTLOOK

With the exit of Alberto, a fast moving "zonal flow" will set up over central U.S. around a large dome of high pressure camped over South Texas and northern Mexico. The northern edge of this dome is going to be active with fast moving storm systems likely resulting in a lot of chances for storms. The concern lies with signs the big ridge in South Texas building into the middle part of the country toward the second and third weeks of June. The key will be how far east the ridge stretches, but this could solidify the heat turning up and the rain turning off. Two potential examples are listed below:

Option 1: Ridge centered over the Central U.S. would spell extreme heat along with potential dry

Option 2: Ridge shifts westward spilling some heat east, but also keeping pattern ripe for storms

This pattern is definitely something that requires some monitoring. Hot and dry was our forecast heading into Summer 2018. Spots that have missed a lot of scattered storms last few weeks could see some serious trouble come late June into July IF that ridge takes hold.