I had a conversation Tuesday, October 15, with South Dakota state climatologist Dennis Todey about the background and inside detail of the monstrous and devastating snowstorm that hit the Black Hills in western South Dakota October 4-5. Here is that conversation, with my questions summarized and Dennis Todey's replies near-verbatim.
BA-- Are there any comparisons between the Black HIlls blizzard and the heavy flooding rains near Estes Park, Colorado in September?
Dennis Todey-- No there are not. The Estes Park storm was monsoonal in its character. Rapid City had a very strong anomalous low pressure area for this time of fall. It brought up tons of moisture from the Gulf of Mexico. The low pressure center was strong enough to catch enough cold air to form the snow and for that to be heavy snow.
It's ironic considering that temperatures were well above average up until then. That was part of the problem. With the very warm temps so far--folks (ranchers) had not moved cattle--also, the cattle were not putting on their winter coats of hair yet. That made them very susceptible to what happened. And the storm began as rain, so the cattle got wet. Then came the very wet snow and winds of 40-50-60 mph.
BA--Where did that anomalous low come from?
Dennis Todey-- That's a good question, and one problem with the government being shut down is that there aren't that many folks around to do analysis. It must have come out of the southwest. And it was slow-moving enough that there was an open Gulf of Mexico for a long period of time. (Gulf moisture got drawn into the Black Hills area in tremendous amounts). Actually, the forecast model runs were pretty close to the actual moisture--but it was so great that it was hard to believe them. (One veteran meteorologist in the western U.S. referred to the moisture forecast by the weather models as being so heavy that "Some of the moisture this thing is putting out is just nuts." It looked overdone but the models were relatively close regarding precipitation and how much snow would occur.
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BA-- I was stunned to see the snowfall totals. How wet did that turn out to be?
Dennis Todey-- Totals of snow--there was widespread over 20 inch amounts. Mid-50 inches over the northern Black Hills.But this was not midwinter snow. It had high moisture content--much less than 10 to 1 snow to water content. 30 inches of snow--that's crazy. And then you put 50 mph winds behind that, and anything exposed will take a beating. High moisture. Much less than 10 to 1 snow to water content. 30" snow "is crazy". Then you put 50 mph winds behind that--anything exposed will take a beating.
BA-- Have you seen anything like this before??
Dennis Todey-- I have not seen anything this early in the season like it. There have been some other events historically but those would be midwinter or spring events. This early in the fall is historic. Rapid City set alltime October snowfall record in one event--23 inches. In the Black Hills you expect to see something like that but to have that heavy snow over multiple counties is impressive.
BA-- Is there any climate change effect in this storm??
Dennis Todey-- I don't know. It would take some more modeling to put a handle on that. Would climate change make an event like this more likely--I don't know. But--certainly it is an indication that there is something going on in regard to fall precipitation.
South Dakota twice in the last 4 years has had some flooding in the fall. We had flooding on the Big Sioux River in fall 2010 and now had flooding with this event. This turned into a "double dip" storm, with heavy snowfall followed by rain on top of that. And with the heavy fall precipitation, now we look to the spring, and the saturated soils in the fall mean we have very little soil moisture capacity to handle any heavy precip next spring.
There is something going on. Lemmon South Dakota (far northwest corner of the state) has 32.37 inches precip so far this year. The previous annual record was 25.57 inches. The record has been obliterated with 2 and a half months still to go in the year. And there's another station nearby that has also broken its annual record too--and a couple more that are within an inch of the record. An individual station in individual year--you're going to break records. But with the number of stations and number of records--and you obliterate a record--something's going on here. This is part of an increase in precipitation overall that is not new for the northern Plains and upper Midwest.
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