Robert's Post...

>> Friday, March 26, 2010

Clouds should begin to depart by this afternoon and remain clear through the day Saturday. Though clear today, expect temperatures to drop as we go through the morning and afternoon. A high of around 61 today has already been met or will be met again late this morning. A stiff Northerly wind will direct cool air into the area with sustained winds of around 15 mph. Saturday should see highs close to 60 with increasing clouds as we move into the overnight. Our next system should bring rain late into the afternoon on Sunday. Forecasted soundings currently show enough surface based CAPE to allow for a few thunderstorms to fire along the boundary. Convection outlook from SPC shows no real confidence, so expect little or no severe criteria to be met Sunday evening.

This morning Matthew and I were discussing the lag temperatures of the seasons and I figured it would make a good blog post. Basically when I say lag I mean the difference in time from solar wattage received and the time that radiation affects local temperatures. With the current solar declination angle, we receive the same amount of watts per meter squared as we do on September 15. The radiation received on a given day based on the sun's angle at a given latitude is known as solar insolation. However, we know that September 15 is much warmer than today with average daily temperatures 20 degrees warmer. This is because of differing heat capacities of the soils, oceans, and air.

Oceans have the highest capacity and air has the least. So the ocean takes longer to heat up and stays warmer longer as well. These lags affect many things beside the gradual warming or cooling of seasons. The local sea breeze on the coast is based on the daily temperature changes of the land along- side the steady ocean temperatures. Thermal differences sets up gradients and creates a local circulation, switching directions from daytime into the overnight (i.e land breeze and sea breeze). Hurricane season is also affected. The peak of hurricane season is in mid September when ocean temps are the highest; yet air temperatures are the highest in late July.

Locally in NC we have varying soil types from rocky, clay, and sandy. In the Piedmont we actually have a trough that sets up quite frequently due to the quick transition from clay soil to sandy soils. In the Summer this actually helps increases thunderstorm potential along this boundaries when instability is high. The higher moisture in clay differs greatly from the sandy soils setting up this local gradient.

Robert Elvington


Jeremy 4:28 PM  

Very cool post. I've never thought about that or even heard of it. Thanks for posting something interesting. I've wondered before why hurricanes aren't more numerous in July and August when we are sweating buckets from just breathing outside in the sun. But what you wrote makes perfect sense. I've also heard before that if we did not have clay soil around here that we would not have as much snow as we do b/c this clay soil somehow gets in the atmosphere and that acts as nuclei for the snow to form on. Was someone just talking a bunch of junk or is that the truth?

Robert Elvington 5:08 PM  

I haven't heard much about clay being a main factor but yes cloud development depends greatly on nuclei. Cloud condensation nuclei are how all clouds are created whether it be dust, smoke, or other aeorsols. Outside of the mountains our main factor for snow is called Cold Air Daming (CAD). There are three differing types and each ones affects temperatures or moisture differently. I'll probably make CAD a blog post soon since it affects our whether year round and not just in winter.

Jeremy 2:37 PM  

Cool. Thanks Robert, looking forward to learning more about CAD.

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