Clearing Up the Fog

By Matt Makens Atmospheric Scientist

I want to begin by thanking those who found me during CattleCon and giving us a chance to meet; there were many great weather discussions during that week in New Orleans. Regardless of year or event, there is usually a “theme” to questions or comments discussed with folks.

This year there was a lot of curiosity around two things, fog and the duration of the snowpack on the Northern Plains. I thought I would discuss both as there is quite an interest in both.

First, let’s talk about how foggy it has been and whether or not rainfall indeed comes 90 days after the fog. Folks from Montana, the Dakotas, parts of Nebraska and Minnesota noted how foggy this winter has been; some say the foggiest they can remember. This comment is followed up by the question, “Is it true rain will fall 90 days after a fog?”

Before we get to the question, I decided to pick a central location and run some numbers on the fog. Aberdeen, South Dakota, has a lengthy period of record and is roughly central to all the folks who asked about this topic. The period of record starts in the 1890s, but it was the mid-1960s before fog records became reliable. For this particular station, the process of identifying a ‘fog day’ is not in the official records until the mid-1960s. This is not to say that fog was not observed previously, but from the tidiness of reporting, the mid-1960s to date are easiest to work with. And, what do I mean by ‘fog days?’ This is a day when fog was observed for at least one hour and created less than a quarter of a mile visibility — any fog that is not that dense will not be officially recorded as a fog day.

Since 1965, Aberdeen has averaged 19 days per year with fog, and the most was 44 days from 2019; 18 days is the tally this year through early February. This result didn’t quite “feel right” because it felt a lot gloomier than the official fog reports.

Depending on the exact location, yes, it is a record. There are places in Colorado, Wyoming, Montana and Nebraska where a bit of a warm-up in mid-January melted snowpack and ended the consecutive days. Still, a storm blew through the following day to start the tally again. At the end of the season, I’ll share with you where there were record days of snowpack this season. Right now, I’ll tally up the consecutive days with snowpack through Valentine’s Day. Sioux Falls tops the list (see above).

I found the consecutive days with snowpack, not the total number of days, but how many days in a row there has been snow on the ground. As of the deadline for this article, there were several spots at a record number or within a few days of a record. I created a map to show you the locations, which I’ll update and share again with you later — it will be a historic snowpack year for parts of the Northern Plains. Of these two topics — the fog and snowpack — the snowpack will have the most significant impact on the spring outlook. I’ll break that down now by region.

Northwest: The mountains will collect some additional snowfall before a rapid snowmelt, especially in the southern Cascades. For the most part, lower elevations will have equal chances of above and below average precipitation. Temperatures will be normal to warmer than average.

West: Drier than average precipitation returns, following that wet winter for many. Sierra Mountains snowpack will melt quickly, improving surface water conditions for much of California. Temperatures will be quite warm for the season.

So, I found some data that isn’t just of fog but of total overcast, and I found that most of the Dakotas, Nebraska, and parts of Colorado did have their first or second cloudiest January on record. So, if it has felt gloomy – it has been.

Now, onto the idea that rain will fall precisely 90 days after a fog event. That’s a common talking point in many regions. Scientifically, it is a myth because there will be rain anyway, and to say it comes exactly 90 days after the fog is just a coincidence — or is it?

So, again, I pulled down the data, and for Aberdeen, it did have precipitation 90 days following fog 27% of the time. So, one out of four times, that assertion was correct. But, technically, the two are not connected. There is accuracy to say that weather is cyclical, but using fog as a forecasting tool for precipitation will only randomly work 27% of the time in Aberdeen. It’s a myth — popular, but the two are not tied together.

Now, the second most asked question during convention was, “We’ve had snow on the ground for weeks; is it a record this year?”

Northern Rockies: Periods of snow/rain will continue. This is true of both the mountains and isolated areas on the Northern Plains. Snowpack will contribute to cooler than normal spring temperatures. This may lead to a slower start to planting/grazing. A near normal amount of snowpack will melt to contribute into the rivers, and eventually the Mississippi.

Southwest: Still under the influence of a drought-like pattern, expect drier than average conditions this spring along with warmer than normal temperatures. Mountain snowpack will melt quickly with a surplus to come into the Colorado River system from parts of the northern Rockies of this region. The Rio Grande and Arkansas Rivers will have below normal snowpack to contribute runoff into those systems.

South: Soil moisture for western areas will recover in isolated cases, but by-in-large soils will take time to recover and this will delay crop/pasture growth this spring for the west. However, a normal to wetter than normal pattern is favored for the eastern parts of this region. In total, temperatures will be warmer than average.

Upper Midwest: Due to the snowpack, temperatures will be cool for quite some time before thaw. In total, the season will be cooler than average, but this is particularly true for March and early April before thaw progresses northward. Any rapid spikes in temperatures may lead to flooding and ice damming, so a slower progression is preferred. Precipitation is neutral for the spring.

Ohio Valley: Moisture favors this region, especially eastern states, which may get too much at once in some instances. Soil moisture will be healthy and will also lead to runoff to support the Mississippi River. With neutral to warmer than normal temperatures, the start to growing season looks like a typical one.

Southeast: This is another region that will favor from precipitation, perhaps too much in instances. A flow of moisture will continue to move in from the Gulf at times, but we may see some drier areas over Florida versus their neighbors to the north and west. Temperatures will be warmer than average.

Northeast: There are neutral conditions headed here this spring. Temperatures will be near normal as will precipitation. The start to growing season will be on schedule.