October sunshine are not usually two words typed together around Seattle, but this year, it's becoming a theme. Tuesday marked a week since it last rained around here, and long range forecasts suggest it'll be another week until chances of rain return to the forecast.
We're not close to the record dry October stretch of 23 days set in 1986, but a fortnight of sunshine is still pretty impressive.
To get this much sunshine, we're pulling off a rare feat of sticking two, stable sunny patterns back-to-back.
The current sunshine is due to what's called an "omega block" -- named for the shape the jet stream makes on the upper level wind chart. It occurs when you have a high in the middle flanked by low pressure centers to its southwest and south east. If you were to draw the jet stream around this pattern, it makes sort of an upside-U like the Greek letter Omega.
Here is a current upper level wind chart -- see if you can spot the omega. I highlighted it a bit in yellow on the second image:
Here is another visualization, courtesy Earth.Nullschool.Net. (Click the link below to watch it animate). Note the lack of flow over Washington!
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Those two lows act a bit like weighted anchors on the high and keep things stable, and since the Northwest is stuck under the high, it's sunny -- with bonus warmth due to some east winds as well.
The southwest low, eventually fizzles out in the middle of the week, allowing the high to deflate a little bit. Still enough "air left in the balloon" to keep the sun around and the rain away, but it will allow the air mass to cool a bit and we'll come down off these 70 degree days closer to the low 60s, and also reintroduce the morning fog as we lose the drier east winds.
But the rain is far away because we go from Greek to Latin and start our second stable weather journey pattern: A "Rex" Block. Rex is Latin for "king" but it's not named that due to its weather fit for royalty or lording over land near and far, nor does it have anything to do with Sen. Orin Hatch's purported ancestry; it's named after the person who discovered it in the 1950s - Daniel Rex.
A Rex Block is when you have a low pressure center sitting below a high pressure center -- in this case it's the southeast low from our Omega block drifting west to settle under the high. When you have these two stacked on top of each other, the flow tends to drift north to south and not much west-to-east so it can stick around a while. And once again, the Northwest is still stuck under the High, which means more sunshine and dry weather!
Again, here is another visualization, courtesy Earth.Nullschool.Net. Click the link below to watch it animate (you can make out the U.S. borders there in white for reference.)
MORE | Full Animation Link
Looks like these blocks will finally break down by the middle of next week and it won't be Greek or Latin weather patterns that garner the attention but decidedly northwestern American pattern of gray with occasional showers.