I thought I'd discuss our upcoming weathermaker a little differently. Don't be scared off by the image to the left - it describes the complexity of the situation excellently.That image is called a Skew-T diagram (since the temperature lines are skewed to the right). We're basically taking a vertical look through the atmosphere at 7 p.m. Thursday using our friendly GFS weather model. I've highlighted a few important features.
First, the red line is the temperature, and the green line is the dew point. The two lines are right next to each other, which means a good chunk of the atmosphere is saturated at the time we're looking at. So, the precipitation won't be evaporating as it falls - it'll be making it to the ground without a problem. The blue line is the freezing line. If the temperature goes to the right of it, then it's above freezing at that point... to the left, below freezing. Now that we've got those introductory bits out of the way, let's explore the numbered parts.
#1: In the lower-levels, a wind out of the northeast is occurring. This will be pulling in air from the northeast, where there will still be some snowcover (it takes a while to melt a foot of snow, as we all know) as well as the cool waters of Lake Michigan.
#2: The temperature at the surface is barely above freezing. If we can stay above that critical temperature, we won't have to deal with ice. However, any change in the surface temperature will have a significant impact on the forecast... especially if it drops only one or two degrees. If we get below freezing at the surface but keep a warm layer aloft (which I'll discuss next), then we'll be facing a more icy situation.
#3: A nose of warm air aloft will try to work its way in here. That would cause precipitation to be in a liquid state, then freeze as it descends. So snow wouldn't be a big issue - it'd become more of a sleet/ice scenario at that timeframe.
This is just a snapshot that one model is showing. The GFS has performed fairly well this winter, so we're not straying too far from what it's been showing. Through the day Thursday, we're still expecting to be very close to that oh-so-important rain/snow/mix area. As explained above, the precipitation type hinges on what our temperatures are doing at the surface and aloft. I really am not exaggerating when I say that a one-degree change will affect what we see falling to the ground and if it sticks.
Let's hope that things become more clear in the next 24 hours!
9 comments:
Justin, I just wanted to let you know that I love these little mini-meteorology lessons! They're my favorite kind of blog posts.
Eric wanted to scold me for showing that diagram, too. ;)
Tell Eric it's great! It is very interesting to see how such small changes can affect the type of precipitation, and to see how changes in one level of the atmosphere may be different from changes in another level --so many variables to work with. The graph did a great job of illustrating that. A picture is worth a thousand words :-)
Don't want to come between you's guys at the 13 Weather Center ... you all do a great job.
Also (slightly unrelated, but not totally) today I took the afternoon off from w*rk to attend one of the NWS storm spotter presentations put on in my state by the Milwaukee office of NWS.
Okay, I knew I was in trouble when Rusty Kapala looked at me and said, "Don't I know you from somewhere?"
"Oh, I come to these every year," I mumbled.
But then I was talking to the guy who had put together a great on-line advanced storm spotter class (I was going to give the URL here but can't find it at the moment), y'know, just "talking shop" about a common interest ... and a meteorologist from Emergency Management came bouncing over to say, "Gee, you know, you should take a couple of meteorology classes!"
I knew then I couldn't hide it any more. I think I was "outed" as a confirmed geek.
Anyway, that was fun. Driving home I had the windows down on the Jeep, was just enjoying the heck out of the first Spring-like day ... turned on my computer to find that the WI counties to your north (including mine) are under a Winter Storm Watch. Talk about bursting the bubble.
Excuse me while I go take my dogs out for a nice hike before it starts snowing again (grr)...
Justin: How much did you pay these people? ;) -ERIC haha Good stuff!
Well at least you have for my Birthday on Wednesday it's going to be nice, I won't even remember Thursday I will be sleeping it off!
Its gonna be snowing in June.
Its happened before...
How about Snowing in July? Look at nice firework! Oh wait minute that's snowflake!
I might be wrong, but I believe it does snow in July .... at the top of large storm clouds.
When you have a thunderstorm with cloud tops at, say 40,000 feet, when it starts precipitating out of the top of that cloud, well, I think its too cold up there for anything but snow to form ... but the snowflake would change to a raindrop as it hits the warmer layers of air closer to the ground.
Uh, maybe the professional meteorologists can correct my fractured fantasies about precip if this is way off base....
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