Looking for a Dry Day

We're getting November-like weather during this last week of September.  Decidedly unusual.  Autumn has definitely had an early start this year.  And if you're like me, you probably still have outdoor work you want to get done before it gets cold and wet.  So are there any dry days in the near future?  Actually, yes there are.  As we said in the previous blog, after a stormy week this week, the pattern should change to drier and warmer next week.  But things may be changing a bit in the forecast.

For today, we have our wet Wednesday system that we were talking about.  The radar right now looks pretty wet this morning.  This will be followed by afternoon showers.

Here's the weather pattern causing all of this wet weather.  A deep area of cold low pressure over the Pacific NW.

Thursday will see mostly afternoon convective showers.  The morning should be dry, but with a low damp overcast cloud deck.

Friday is a little more iffy.  Another Pacific system dives into the Northwest, but this one will mainly go south of our area.  Still we could get some afternoon rain showers depending on how far south the system goes, but there's a good chance it could be a dry day.

The weekend look dry and much warmer as the cold weather sinks to our south and high pressure pushes in from the west.  Sunday will be back in the mid to upper 60s with sunshine.

Then the question becomes: how long will this last?  Initially it was looking like the high pressure would dominate next week.  But in the above weather map you can see another low in the northern Gulf of Alaska near Anchorage.  The computers now think this wave will knock down the high pressure and move into our area.  But there's a lot of disagreement on how significant this will be.

First, here's the "average" forecast for the end of next week. This sort of weather pattern would bring us more wind than rain, as the cold low pressure is moving by to our north.  

But notice I said that this is the "average".  There are 100 computer forecasts that predict out this far.  Averaging them all together is one way to predict the weather.  But a smarter way is to look for patterns of agreement in the 100 forecasts.  We call these clusters.  

Below is a figure showing 4 clusters along with the average of all 100 forecasts (bottom center).  Each of the clusters is labeled with how many forecasts are in that group. You can see that Cluster 1 (upper left) and Cluster 3 (upper right) have rather ominous cold low pressure over all of the Northwest.  61% of the models are going with this forecast.  Meanwhile, Cluster 2 (top center) has a much drier and warmer forecast for us, while Cluster 4 (lower left) is impressively warm.  These dry and warm forecasts only make up 39% of the models, so they are in the minority.

Based on the way this autumn has been going, I would favor the colder/wetter solutions for the end of next week.  This means that the dry weather should start this Saturday and last at least through Monday, probably into the middle of next week.  Those clear skies will mean chilly nights, so frost is definitely a possibility this weekend.  But then look for wetter weather to return for the latter half of next week.  Not a certainty though.

Here's a nice precipitation probability graph for the next 10 days at Deer Park.  Oh, if you look closely at the end of next week (right side of the graph), you see a blue line in addition to the green line.  Yes, that means a probability of snow.  Now don't get too excited about that yet.  It's a long way off, with lots of uncertainty.  And for early-season snow things have to come together just right.  At this point it's just something to keep our eye on.  If it happens, it will likely be what we refer to as "white rain", which is wet snow that doesn't accumulate, or melts quickly, and really has no impact.