Winter in the United States is an interesting topic. In the South, winter lasts for maybe a month, and then it’s gone; however, in the Northwest, Midwest, and Northeast, that is a completely different story. Most people associate winter beginning in November and ending around mid-April. Now depending upon how the trough and ridge are set up for the season will depend on how long winter lasts.
Before going further, troughs and ridges are a part of the jet stream over North America. When there is a valley in the flow, that is a trough. Troughs are normally associated with a low-pressure while ridges (the hills in the wave) are associated with high-pressure. During the summer, the jet stream becomes zonal over the mid-latitudes and during the fall and into the spring, the jet stream develops wave-like patterns. With that being said, typically by May the flow becomes zonal as spring is coming to an end. This is why snow is unlikely past this point because there aren’t any troughs to bring that arctic air further south to cause air masses to clash which inevitably leads to snowstorm development. So, while it isn’t necessarily common, it isn’t a rarity to have a few outlier snowfalls that can continue into May for some.
When delving deeper into this topic, the question came to mind, “How late in the year has there been a recorded snowfall?” After spending some time on researching this, there was an article about many people reporting snowfall on July 4 in 2008, but the article was vague if it occurred or not. Thankfully, XMACIS (NCDC) is a very useful tool when trying to find out any kind of climatological data. From what was found, there was evidence that there was 16” of snowfall recorded at a COOP station in Pelican Rapids, MN on this day.
It still sounded very odd to not have come across actual news reports of this day, as this would be quite a headliner to receive 16” of snow in early July in the United States, even if it is bordering Canada. When checking out previous surface maps from this day from the National Weather Service Archives and SPC Outlooks, there was nothing to back this statement up.
Looking at the event, the low-pressure system/cold front was too far south to have an impact in Minnesota this day. Going back a few days to when the cold front was passing through the area, on July 2, the surface maps still failed to support that the air mass behind the cold front was cold enough to cause wintry precipitation on this day (let alone on Independence Day). The images above support this thesis by showing temperatures throughout the country, including behind the front.
Minimum temperatures on July 2nd, 2008 prove to be entirely too warm to support snowfall in the coming days. The average maximum temperature was in the 80s, while the minimum temperature was in the 60s, and behind the front was 50s. Even if there was a significant polar vortex moving through that area on the 4th, the soil/ground temperatures would be entirely too high to support any accumulation.
Unfortunately, it appears that the rumor of Minnesota receiving 16” of snowfall on July 4 has been squashed. The latest recorded snowfall event was May 2, 2013 where the northern parts of the state received between 1-2”. Although, that doesn’t rule out that this could happen within the next few years as the troughs over the last couple winters have been pushing further south than normal.
To learn more about other interesting tropical cyclone topics and events from around the world, click www.globalweatherclimatecenter.com/weather-history-topics.
©2019 Weather Forecaster Ashley Lennard