Today’s extensive cloud cover kept temperatures in the 50s for the most part. It may sound elementary that clouds prevented us from warming up. And if you’ve watched 13 News for a while, you’ve heard me talk about the clouds at night acting like a blanket, trapping the warmth under the blanket for the night.
Over the next few weeks an months, the timing of the cloud cover will be the biggest challenge for us putting together your accurate forecast. Let’s look at a few case studies on what will give us the warmest and coolest days this fall.
Our first example shows the scenario for a bright, warm autumn day. If there is extensive cloudiness during the night, the heat is trapped within the lower atmosphere. However, even high clouds can prevent the heat from escaping. If the clouds scour out during the morning hours, there’s a warmer start-up temperature, thus the sun doesn’t have to work hard to warm us up. In addition, cloudy skies prevent frost from forming.
Again, this may seem elementary, but the exact opposite brings about the coldest fall days. Clear skies at night allow all of the built-up heat from the previous day to be radiated into space. Couple that with calm wind and we can mighty chilly in October and November! These clear skies often allow the temperature to fall so quick, the temperature nears the dewpoint (or frost-point), causing frost to form within a few hours of sunset! If an incoming system brings clouds to the area during the morning hours, there’s no way to really get the thermometer to move much.
But these two examples don’t make up a steadfast rule! There’s one thing I didn’t mention: WIND. A southerly or northerly component to the wind direction can produce much different results. Consider this, we have a clear night with chilly temperatures, but the clouds stream in ahead of a storm system which bring us clouds AND a southerly wind. That wind, advecting warmer air from lower latitudes, can be enough to get those temperatures warmer with the absence of sunshine.
So, over the next few weeks we will be working harder on the timing of the clouds. In fact, this weekend has some high “bust potential.” We will be quite dry at the low levels of the atmosphere with clear skies at night. But instability clouds will halt any growth in temperature as the days wear on. If we can hold onto a few more sunny hours, our temperatures could be boosted by as much as 4-8 degrees!
Fun times are ahead! -Eric
Posted under weather geek