After a night of barbeque and fireworks, some of us woke up to low temperatures we normally see in late September, causing us all to run to the closet and grab a jacket out of our Fall clothing bin.
It was a bit of a shock to the system. Saturday morning's low of 50 degrees at the TRI marks the thirteenth time that temperatures have dropped to or below the 50 mark in the month of July. That data comes over a 76 year span! Obviously, this is a rare occurrence, but the weather setup is oddly similar to a recent case. On July 2nd, 2008, we saw a low of 50 at the Tri Cities Regional Airport. Here was the setup we were dealing with:
High pressure was in control of our weather, feeding us with unseasonably cool air from the north, while a cold front with low pressure over New England had recently passed our viewing area. Now compare that with early Saturday morning's setup:
This looks nearly identical to the case six years ago. High pressure is bringing in cooler air from the north, while a cold front is off to the east, along with low pressure well off to the extreme northeastern US. Both the high and low were acting to bring in that cooler air, just like in our 2008 case. What is about high pressure that has made us so cool on both occasions? Get ready for more cool graphics!
High pressure means sinking air, which oftentimes leads to clear skies. On a day with clear skies, the surface receives more solar radiation as shown below:
So, where does this radiation go? It can't just stick around here, otherwise we'd be at a constant temperature and there would be no need for the meteorologist to tell you what it was going to be like today or tonight or tomorrow.
On a clear night/early morning, a lot of that radiation that came down to the surface is allowed to then escape back up into the atmosphere, like this:
When this happens and when winds are calm, temperatures plummet. That is exactly what happened on July 2nd, 2008 and July 5th, 2014. This goes to show how on some occasions, using past weather setups can really help us to forecast the extremes. And yes...50 in July in this area is considered an extreme, to me at least.
---Meteorologist Chris Michaels---
Facebook: Chris Michaels WCYB