DES MOINES — There’s the potential for precipitation in southeast Iowa tonight, but State Climatologist Justin Glisan says it’s likely this November will rank among the 20 driest Novembers on record.
“The first 20 days we were at 5% of normal, so a very dry first two-thirds of November,” Glisan says.
As of this morning, the statewide average for precipitation is just four-tenths of an inch. “That’s almost an inch and a half below average,” Glisan says.
This is the 178th week of moderate drought somewhere in Iowa — the longest drought in Iowa since the U.S. Drought Monitor was launched 23 years ago. “If you combine November with the other meteorological months of October and September, it looks like around the 36th driest fall on record,” Glisan says. “Interestingly enough, last fall was drier. It was the 22nd driest, so you can see that we’ve just really stacked up precipitation deficits through various seasons.”
Last spring was the 16th driest on record and this past summer was the 17th driest summer in the past 151 years.
“When you’re not getting the expected precipitation in spring and summer, which is the dominant season for rainfall that supplies soil moisture and stream flows, that’s where we’ve seen the drought just expand and intensify,” Glisan says.
The current drought is different from the droughts that struck Iowa in 2012 and 1988, according to Glisan. “This has definitely been longer, but it hasn’t been coupled with extremely warm temperatures for long periods of time,” Glisan says, “so we’ve kind of termed this drought a ‘cool drought’ in that, again, we haven’t seen those exceedingly warm tempatures that would really push drought conditions to lead to widespread crop failure and things of that nature.”
Glisan says there are some positives in preliminary forecasts for the middle of December. “There’s a very high probability of above average temperatures,” Glisan says, “and why that’s a good signal to see is perhaps we won’t see soils freeze as deep or as fast if we have warm temperatures through December.”
It means precipitation could be absorbed rather than run off frozen ground.”As you’ll remember from last year, in early December we had widespread rainfall before we froze up that really helped supply moisture for this growing season,” Glisan says. “Also, wetter soils don’t freeze as fast or as deep, so as we get into winter melt into early spring, there’s faster infilatration if we don’t have a deep frost level.”
Preliminary forecasts indicate there are slightly elevated signals for wetter conditions in December.