By the title, one might ask what in the world...there are 3? Sort of; astronomical, meteorological, and solar. I'm sure others can think of many other types of winters (Jonathan, nuclear, frosty...) but I will stick with these 3 for today. And I'd like to very much focus on the "solar" winter but will address the other two. The reason I'm doing this today is since the date is December 1, we are commencing on "meteorological" winter which corresponds to the coldest 3 months of the year when divided into quarters. Most people are familiar with the "astronomical" winter which begins this year on December 21 at 5:02 am EST. Let's start with the last...
The diagram above indicates the sun-earth relationship on or about December 21 most years (exact time and date above for 2020). At that specific point in time, the sun will stop (solstice) moving south from our northern hemisphere perspective and begin its 6 month journey moving north until the next "sun-stop" or solstice which is the 1st day of astronomical summer. On the December solstice, our noon sun angle is at its lowest (~26.5° altitude above the southern horizon) and our daylight is the shortest. The coldest days are seldom the shortest days in December since our planet is water laden and with water's ability to hold onto its heat much longer than the dry land, there is a good 3 week lag time for the coldest weather to occur in the NH. Hence the saying, "as the days lengthen, winter's chill strengthens"! With all of this said, astronomical winter 2020 will begin December 21 and end officially at 5:37 am March 20 when the sun's 90° vertical angle strikes the earth's equator still moving north until its next solstice. As a side note...for those of you not fond of winter, it is shorter than summer since the earth is moving faster in its orbit during our NH winter months as we are nearer the sun and therefore have a greater orbital speed than 6 months later in July! But all of that is slowly changing as well...just like everything does...including earth's climate! Isn't that kinda cool?
As for meteorological winter, today (Dec 1) is day 1 of 90 days of meteorological winter; the 3 coldest months climatologically of the year. Here in Pennsyltucky as my one friend affectionately refers to our stomping grounds, that marks cloudier, damper, cooler/colder, rainier, snowier, sloppier and darker weather conditions than the other 9 months. Here in the northern fringes of the sub-tropics, we often experience relatively milder winters than the folks living just 100-200 miles north of here. Due to our proximity to the ocean, our winter precip events are often a slop fest as the warmth of the unfrozen ocean often wins out over the polar and arctic air masses trying to move south and east off of the interior of the continent of North America. KMDT averages just around 30" of snow annually...but as you are quite aware, one good nor'easter is capable of delivering the majority of that total in one fell swoop! Below is a graphic of our average annual snow totals for PA. The lee of the Lakes and the Laurel Highlands certainly have enhanced snows as you can see...just like today!
Solar winter? It's linked to SAD (seasonal affective disorder). Today marks our earliest sunset at 4:41 pm EST. However, our sunrise continues get later until 7:30 am at the end of December. Yet, the absolute shortest day is Dec 21 where we will experience 09h 18m 03s of daylight. And if we have clouds, those days near the solstice are quite dark...even in the middle of the day! With the increasingly lower sun angle in November, days do tend to be dark but not like the 2-3 weeks either side of the solstice. Currently we are losing about 1 minute per day, but that rate slows as we approach the solstice. Again, the rate of change is rather confusing due to the curved surface of the earth, the tilt of the earth, and the elliptically shaped orbit of the earth. For those of you so inclined, The Equation of Time will better describe the whys of this occurrence. With that said, today is only ~12 minutes longer than the shortest day and our noon sun angle is only 1.5° higher...so we are certainly in the middle of "solar winter". Suffice to say, December is a month where the decorative lights can certainly shine brightly...even in the middle of many of the days! The graphic below shows the rise-noon-set time and position of the sun for here in Harrisburg this upcoming winter solstice...
Welcome to winter! Take your pick. On the "bright" side, we've completed one month of solar winter...but...we haven't even begun astronomical winter; kinda funny. I've been told my song sometimes works and sometimes not? I don't know what's going on! Darn Russians...ha! If this works, enjoy it, I know I did. And thanks for reading...
AA: 3 types of winter; Astronomical which is from the winter solstice until the vernal equinox which most people acknowledge as the official winter season. Meteorological winter which tends to be the 3 coldest months of Dec, Jan, and Feb. And then there's solar winter when the daylight is least and the sun's angle is lowest. That runs from Nov-Jan. Enjoy the winter memories with the youngins!
