You may wonder, “How can it snow & drizzle at the same time?”
Short answer: when clouds aren’t cold enough to produce snow (exclusively or at all) drizzle can form.
Longer answer: If the air is sufficiently cold and wet, only snowfall is possible. But when precipitating cloud top temperatures are above -10° C (14° F) but still below freezing, the ice nucleation process requires help. Unstable, rising air can induce the formation of snowfall. Failing that, with only slightly below freezing temperatures, snow crystallization needs smoke, dust, pollution or any other tiny airborne surface upon which to bond. Otherwise precipitation can fall as drizzle/mist.
Why today? We’ve had a shallow layer of moist, sub-freezing air (< 5,000 ft) “capped” by warmer, drier air above since Sunday evening (1/26/20). Cloud tops have been just below -10° C. The moist air from sublimating snow/ice and weak low pressure has combined with onshore, upslope winds to induce some lift in the lower atmosphere. This, along with whatever particulates were aloft, produced snowfall. The remaining moisture has fallen as drizzle which froze upon contact depending on the surface composition. Most surfaces weren’t cold enough to allow much, if any, ice accumulation. A light glaze has been observed in places around our property — just enough to increase stopping distances on untreated pavement.
Normally this time of year clouds are much colder. But we have been running well above normal throughout the atmosphere recently. That’s why we’ve had several wet snow events in December & January.
During the 2:00 – 4:30 PM time frame on Tuesday afternoon (12/17/19), Marquette saw two distinct lines of heavy snowfall that spanned approximately 75-100 miles west to east on radar (~ 10 miles north to south). The first hit about 2:15 PM EST. A second line had formed 2 hours later. Both only lasted for about 15-30 minutes. In between were light to moderate lake-enhanced snow showers. During each burst of snowfall, visibility dropped well below a quarter mile and winds were gusting near or above 20 mph in town according to our instruments and the U.S. Coast Guard station. Continue reading “Were Those Snow Squalls?”
You may have seen the widely circulated story that the local National Weather Service office has measured over 200 inches of snow this season as of Monday morning, February 25th. Unfortunately, some articles have explicitly assigned the total to Marquette. Others have allowed readers to conclude that this is a representative total for the area. In fact, the NWS office is located well outside of the city limits in the highlands which receive substantially more snow.
A helpful rule of thumb is that for every 100 ft you gain in elevation, you can expect 10 additional inches of yearly snowfall.* Of course, there are other factors, such as differing lake exposure, that come into play in the wider area. For this comparison, however, elevation is the key difference. So, given that the NWS office is 800 ft higher than the lakeshore of Marquette, that represents approximately 80″ of additional snowfall per year. In fact, that’s very close to the 30 year normals. Marquette normally receives close to 120″, and Negaunee Township gets a little over 200″ per year.
So far this season (October 1 – February 25) in Marquette, the city’s official NOAA COOP weather station has recorded 96.3″. That’s less than HALF the amount the NWS office received. Just a mile away from the COOP station at our location, 3 blocks south of downtown, we recorded 108″ in that period. We are about 100 ft higher than the COOP station, which explains why we’ve had a bit more snow. To be more than fair, I would allow for an additional foot or so lost to high winds this winter at our station (which would give us about 120″).
So, in other words, both Marquette and Negaunee Twp have received something close to their normal seasonal totals thru the end of February. That would be the proper way to frame a story if, indeed, you were writing about Marquette.
Continue reading “200″ of snow in Marquette? Not even close.”
Long story short… freezing rain occurs when the atmosphere is warmer higher up than at ground level. It’s called an inversion. Usually it’s a shallow layer of warm air fairly close to the ground (below about 5000 ft) that precipitation falls through and melts. There is insufficient time for it to reform into snow before hitting the ground. Since the ground is frozen and the temperature is below 32 degrees, it will freeze.
We expect the lower atmosphere to continue cooling this afternoon so if any additional precip develops, it should fall as sleet or snow. Knock on wood.