Thursday will mark the third consecutive day of cooler than normal high temperatures in the Twin Cities. Normally that wouldn’t be remarkable and it’s worth noting the ‘coolest’ of these days was still only a whopping 6 degrees below the normal high of 83. This year however? It’s a pretty big feat. The last time we had more than just a day or two of below normal high temperatures was mid May nearly seven weeks ago.
In fact, above normal high temperatures have outnumbered below normal ones by a ratio of nearly 4:1 since May 1 when things flipped from the March and April pattern.
We’ve also had some more frequent rainfalls in the last couple of weeks. It’s not nearly enough rain but the fact there have been more chances at rain recently is encouraging. Note the long gap below from about mid May through June 24 of almost no measurable rainfall at MSP!
Are all these things a sign of a shift away from a consistently hot and dry pattern? My hunch would say probably not.
I think the best case scenario is that July and August will be ‘less bad’ than May and June, i.e. we’ll still be warmer than normal and drier than normal but by lower margins than May and June. This would also be in keeping with the trends of the last few years which have all been eerily alike.
If we look at normalized temperature anomalies, i.e. how far above or below normal were temperatures compared to the normal range (standard deviation) for each month, we can see the big spike in June temperatures then a leveling out for July and August the last few years:
Note these are temperature anomalies, this isn’t showing a ‘cool down’ in July but rather less of a difference from the normal temperatures than June. If we look at the actual average temperatures for each month April through September we see what’s happening:
This is in line with the bigger trends overall I’ve talked about a lot: summer is starting earlier and ending later. Notably, June, July, and August are very close to the same average temperature whereas historically June should be the coolest summer month and July the hottest with August in between. June (and September) however are our fastest warming months in the warm season. This is entirely what we’d expect with climate change. The warm season getting longer and the cold season is getting shorter.
How about precipitation? Again we can use the example of the last few years, which normally is too small of a sample size to decipher trends, but as I’ve said the last few years have all been eerily alike: hot, dry mid May through June, followed by less hot (but still above average) July and Augusts with less dry (but still below normal overall) July and Augusts followed by dry Autumns.
Sure enough, June is the worst of the drought after a wet spring, followed by less dry but still dry conditions in July and almost a temporary recovery or at least ‘normal’ August. It then gets dry again in September.
So how about the forecast models? They appear to show something similar. All of the models agree on a drier than normal July, but maybe by less of a margin as June. This would mean drought continues to expand however because below normal rain and above normal temps in July mean things continue to dry out rapidly.
On the temperature front, the more reliable models (European and Canadian) continue the warmer than normal temperature trend for July but again, at less of a degree than June.
You’ll note the CFS and GEFS models forecast cooler than normal conditions. I’ve talked about before that these models are basically garbage. They forecasted cool May and June conditions also.
The encouraging thing, is that if we looked at the models a week ago, they were forecasting hotter conditions for July and have backed off that a bit. These are the same models a week ago:
I think all of this points to the same conclusion: July (and August) will continue to be above normal but less so than May and June. They’ll also continue to be dry, but less so than May and June.
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