First Alert Weather In-Depth: Starry night can be a frosty night

This time of the year, Western New York can still can get some pretty cold weather, especially during the nighttime hours. That is exactly what happened early Monday morning with almost winter-like temperatures for several communities. The Rochester airport recorded a low temperature of 32 degrees, but some of the southern valleys got even colder.  The town of Rush recorded a low temperature of 27 degrees and along the Southern Tier the town of Olean got all the way down to 22 degrees. What’s going on?

We know during the daytime portion of the day we get incoming solar radiation, also known as short wave radiation. That is one of the ways warm temperatures will arrive in Rochester. However, when the sun sets and we lose that sunshine, the opposite is true.  Much of that heat begins to escape into the atmosphere. We call this long wave radiation. There are many ingredients that go into forecasting the temperature such as wind, precipitation and humidity, but a big deciding factor can be the amount of cloud cover. For example, if you have a lot of clouds at night the overcast skies will inhibit or block that outgoing radiation. This will reduce the loss of heat and slow the drop to the temperature.  Conversely,  if we have an morning like Monday and there are no clouds to blanket the sky,  then that heat will rapidly escape into the atmosphere. This is especially true in the southern valleys when the colder, more dense air drains into the deeper valleys. So how do you dress this time of the year?  In this particular scenario, you may need the winter coat for the early morning and then you will probably carry it home by the afternoon