Tranquil Weather to Continue

Saturday, August 6, 2011
12:52 A.M. (up late)

When storms come our way, I usually look at multiple weather models, because they all show different outcomes from the same set of present conditions. Sometimes these different outcomes are pretty similar, and other times, they are completely out of sync. When there is an especially tricky situation for the models to handle (such as a moderately-sized windstorm or a lowland snow event), events can change drastically from each iteration of the same model. This is especially common as forecast time increases, as the models become much less accurate due to the magnification of the approximations made after the input data goes in (I will talk about this some other time/search the blog for a post on it... I may have done it before).

However, when there are calm times like these, I use one model over all of the others because it is easy and it usually works. This is the "Extended WRF-GFS Model" from the UW, which can be found here: http://www.atmos.washington.edu/mm5rt/extendedgfsinit.html.

I've looked over this model for several days, and it has been pretty consistent in continuing the trend of cloudy mornings and bright afternoons. Some mornings are more cloudy than others; today only got to 66 degrees in downtown Seattle as the morning clouds proved too thick to burn off, but other mornings in the future may have little or no clouds at all. Regardless, I predict that over the next two weeks, we will see average temperatures with slightly below-normal precipitation. We've got that big blocking high over the Pacific that will shield us from any storms coming from our west.

 

00z Extended WRF-GFS 36km - 300mb isotachs - 2 A.M. August 6, 2011

Above is a shot of the current winds at the 300mb level of the atmosphere. As you can see, we are stuck in the doldrums between the northern and southern branches of the summer jet stream.

00z Extended WRF-GFS 36km - 3-hour precipitation - 2 A.M. August 6, 2011

The above model shows the predicted precipitation over the previous three hours. There are a few showers to our north, but these will not affect us and are weak anyway. This map confirms that there is a large ridge of high pressure  blocking any systems that come into our area. However, you can see that the center of the ridge is way out at sea (40N, 150W), so it doesn't totally block clouds and precipitation. I still don't expect us to get much rain over the next two weeks though.

00z Extended WRF-GFS 36km - 300mb isotachs - 5 A.M. August 13, 2011

This shows the 300mb winds approximately a week from now. The ridge has broken down some, and the flow is more zonal. However, if you look at the 3-hour precipitation chart from the same time, you will find that no organized systems are anywhere near the Pacific Northwest. The jet stream is still too disorganized to allow any storms to hit the Pacific Northwest. To top it off, the flow still splits around Washington and Oregon, although it is not as clear-cut in this chart as the one before.

00z Extended WRF-GFS 36km - 3-hour precipitation - 5 A.M. August 13, 2011

Even though the details change, the general idea is that Washington will be stranded between two weak jet stream branches and will see typical summer weather. We will have varying levels of cloudiness in the morning, with corresponding burn-off times in the afternoon. No heat waves, no ice ages, and no real precipitation to speak of. Just cloudy mornings, sunny afternoons, and that great natural air conditioning at night.

Thanks for reading,

Charlie