Good Saturday to you one and all...
This morning is going to be one of the colder times we've been seeing lately, but if you hit the snooze button a few times and head out later in the morning you'll notice we'll be rapidly moving to pleasant skies. The reason for this is a phenomenon called 'radiational cooling'. To explain this concept, anything that has a temperature above "absolute zero" radiates heat energy outward. If you've ever packed 15 people into an elevator and then got stuck for a few hours, you'll agree that this includes people too :-) When it comes to the Earth, a "radiative equilibrium" is always trying to be reached. In this image (from NASA), all the incoming radiation is balanced by the outgoing radiation. Now, the picture in real life is easily more complicated than this, but this will suffice for now. The point here is, when the Sun is shining on part of the Earth, that part of the Earth is not going to be radiating enough heat energy back to space to balance out what's coming in from the Sun-- not at first anyway. What will happen is that part of the Earth's surface will warm up, causing more radiative heat energy to go out from the Earth's surface. In the end the increasing temperature of the Earth's surface is a direct response to the net increase of incoming radiation. At night, the process is reversed. There is drastically less incoming radiation, so anything the Earth radiates outward is not met in balance. As the surface radiates heat energy outward, the surface itself cools (because not enough is coming in to balance it). Eventually, a low temperature is reached, at another equilibrium of sorts. The best nights for radiational cooling are the crisp, clear nights of low humidity, low winds, and great looking stars. Exactly like right now (and this coming night).
For meteorologists, a good rule of thumb on one of these great radiational cooling nights is to keep an eye on the "Dew Point" Temperature. The Dew Point is the temperature at which water would become saturated in the air (any further cooling would cause fog to form as the water has to condense out of the air because it just can't hang around in there as vapor any more; there just isn't the same capacity at a cooler temperature compared to a warmer temperature). I'll be making some maps of this when I get back in to work, but for now, I'll use these from another source:
These are the Dew Points as of 6 PM on Friday Evening. If this night lives up to it's billing as a good "radiational cooling" night, we should see plenty of morning temperatures in the low 20s (and even an upper teen or two in the hollows). We can track that in the tracking tools below. Once the Sun is up, all those temperatures will warm quickly (perhaps as much as 10 degrees in an hour).
Keeping an eye on our next rain-maker, it still looks like it's going to be all the way until Monday before rain comes back to the area:
|GFS - 8am MON||CMC - 2pm MON||NAM - 2pm MON|
The GFS is a little out ahead of the others, but they're all presenting more or less the same sort of weather when they get here.
The mid-range picture for weather in our area going through the next two weeks appears to be one of above-normal temperatures (big surprise, right?). One model that attempts to describe the weather out to that middle range, the DGEX, is currently showing a persistent weather pattern of high pressure mulling around the southeastern United States:
This means more for the mid-west and plains states than it does for us, but this pattern is known for above-normal temperatures across a wide swath of the east/central US, with the greatest impacts in the central plains. There the clash of air masses appears to be a common-place event, which means severe weather tracking may be in order for folks just west of the Mississippi River.
Here is a map of the current expected temperature anomaly (departure from average) for the week ahead:
The folks that are going to experience the warmest weather (compared to normal) are those in the northern plains, where temperatures could get 15-20 degrees above normal. However, this sort of experience is ironically 'normal' for them, because that area is prone to wild temperature extremes. For example, the state with the largest difference in state record high temperature (117 F) and low temperature (-70 F) is Montana. Not coincidently, Montana is home to the greatest 12-hour temperature change (84-degrees!) South Dakota is in the mix there too, with a 47-degree temperature drop in just 15-minutes at Rapid City back on January 10, 1911.
Okay, that's enough for now ;-) Here are some tools with which to keep an eye on things locally:
|Temperatures||HD Doppler Radar||Estimated Rainfall||Active Warnings|
|Click For Larger||Click For Interactive Radar||Click For Larger||Click For Larger|