I'll use an analogy. Let's say somebody tells me that they like the tie I'm wearing. Hey, that's great, right? But what if I then have 20 people tell me they don't like the tie? I'm much more likely to pay attention to the collective opinion of 20 people rather than a solitary opinion. Such is the case with our computer weather forecast models.
We have some individual models that we look at for guidance when putting together a forecast. There are also models that put together a bunch of variations of those individual models. They're called ensembles. The GFS model was suggesting a nice, generally dry Friday and Saturday, but the ensembles were suggesting those days would be cool with occasional showers. We decided to stick with what the ensembles were saying, since it was a bunch of models saying it was going to be cool, compared to one saying it was going to be warm.
Hopefully I haven't totally lost you yet! It can be difficult to explain. Hopefully an image will help. To the left is a graphic showing where at least 0.1" of rain is expected between 7pm Sunday and 7pm Monday. This graphic is typically called a spaghetti plot for pretty obvious reasons. There are 40 thin lines contouring the area that each model thinks will have 0.1"+ of rain. The thick red and thick blue lines are the ensembles - averaging what each individual model is saying. The thick black line is the plain ol' GFS. You can see how they differ for a time period just a little over a day away!Hopefully that made some sense. With some quiet weather this weekend, I thought I'd give you some insight on why we've switched gears a bit. As always, if you'd like to pick our brains some more, just leave a comment.
Tomorrow I'll blog about Project TWISTEX and post some cool storm pictures.
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