So, here’s what your app might show: 34. Rain. And indeed, as you start out, your car’s thermometer reads 34 and it’s raining. But here’s what your app won’t show: that the road surface is colder than your thermometer reads. This is not at all uncommon when rain arrives following a cold spell.
I bring this up because, tragically, there were a number of fatalities in Maine on the 13th, and they were all caused by icy roads. The accounts generally said the “motorists were caught by surprise.” In my forecasts, I emphasized the fact that we were coming out of some very cold weather, and I specifically said, “don’t trust your car’s thermometer” to be your guide when the rain begins, due to deeply chilled road surfaces. Here’s the thing, apps can’t think for us.
So the next time we are coming out of a deep freeze, with rain in the forecast, please remember that the road surfaces may still be cold enough for any rain to initially form an icy glaze, even if the air temperature is in the mid-30s, according to your car’s thermometer.
Let’s switch gears and talk about some recent notable weather. The County saw two straight “thaw-storms,” the first on the 9th and 10th, and the second on the 14th and 15th. Together, they delivered 1.65 inches of rain, as measured at the National Weather Service in Caribou. During the first storm, the temperature reached a date-record high of 49 degrees in the early afternoon of the 10th. A second date-record high was set on the 15th, in the second storm. Caribou saw a high of 48, which was reached at 3 o’clock in the morning. (Highs and lows for a day are based on a “climate day,” which is midnight to midnight.)
Incidentally, the storm of Dec. 14-15 was, in the “hype parlance” of today, a bomb cyclone (it intensified at the rate that meets that definition, which is a pressure fall of at least 24 millibars in 24 hours (0.71″ in 24 hours). “Bomb cyclone” comes from the term “bombing out,” which is sometimes used by meteorologists. “Cyclone,” in this usage, is another word for low pressure system. You didn’t hear much about this “bomb cyclone” because it did not move through the big population centers of the East.
A rapid fall in pressure is tied to heavy precipitation rates and sometimes, lightning and thunder, while it is snowing. Be aware of the possibility of lightning when snowfall rates become very heavy. In terms of winter precipitation type, for your location to receive heavy snow, with little to no mixing, the Low has to be to your east. The air circulates in a counterclockwise fashion around a low pressure center. If the center of the Low is east of you, the mild air being drawn up from the south is also east of you. You will be on the cold side of the storm, with your airflow being from the northeast or north.
In the second “thaw-storm,” temperatures near 50 degrees in those pre-dawn hours of Dec. 15 prompted a number of people to comment that we were having “weird weather,” implying that something was out of whack with our weather.
However, the process that propelled the temperature all the way up to 48 degrees before sunrise was nothing new at all, and there certainly was nothing weird about it. It was simply a very strong low-pressure system that tracked up to our west, putting Maine on the warm side of the circulation.
The two consecutive rain/thaw events took a heavy toll on the snowpack, though at this writing, seasonal snow totals remain above normal. To show you that west-tracking lows are not uncommon, last December we had the “solstice soaker” (a great name coined for that particular storm by NWS Caribou). That storm, which dropped an inch and a half of rain, came with 50-degree temps, and took Caribou’s snowpack all the way down from 17 inches to 6 inches. Once again, west-tracking lows are neither uncommon nor weird.
In a given winter, the staying power of snow, week over week, is directly tied to not having major low-pressure systems track to the west of Maine. We had a very nice December (if you like snow) back in 2016, with deep December powder, top to bottom, and of course we had the “December to Remember” back in 2007 — four and a half feet for the month, in what would end up as Caribou’s snowiest winter on record.
Finally, at last check, there were still four free-of-charge slots for my weather course at UMPI. It starts Jan. 22, and meets on Mondays and Wednesdays from 12:30 to 1:45 p.m. Call Pam Easler at 768-9450 if you are interested. There is no charge for tuition, but the free slots also do not earn you college credit. However, if you just have an interest in learning how to read the sky, then this opportunity is for you.
If you have questions for me, send me an email to tshapiro@wagmtv.com. Please put “Weather Class” in the subject line.
Ted Shapiro holds the Broadcast Seal of Approval from both the American Meteorological Society and the National Weather Association. An Alexandria, Va. native, he has been chief meteorologist at WAGM-TV since 2006. Email him at tshapiro@wagmtv.com.
