This very unusual late summer and early fall continues in the Pacific Northwest with more October sunshine and little chance of rain in the forecast.

While we have seen light showers in spots over the past two months, August and September of this year are down as the driest stretch of those two months on record as measured at the official weather station at Sea-Tac Airport.   Only 0.03" fell during those months.

Wednesday, we pass another milestone of sorts: 75 days since the last truly "soaking" rain in Seattle.

On July 20, 0.60" of rain was measured at the airport.

Huge atmospheric "blocking" responsible for continued dry forecast

A meteorological phenomenon called a "Rex block" is responsible for our continuation of this dry forecast.

A Rex block consists of a high pressure cell north of a low pressure cell.  These features are disconnected, or "cut off" from the primary jet stream pattern.

This pattern is presently in place in the eastern Pacific.

The flow around these pressure systems creates a static force, almost like a force field, which deflects the jet stream flow well to the north.   

It most often takes a significant disruption to the upstream flow to break a strong blocking mechanism like a Rex block.  This can come in the form of tropical storms or typhoons in the western Pacific becoming entrained in the wind pattern of the atmosphere.  

Other times, slow movement of the low pressure system to the south can allow the block to fall apart.

In the long range forecast, the block looks to break down by this weekend into early next week as the low pressure part of the feature moves east.  Eventually, the upper-level winds will become more west-to-east, allowing storm systems to come a bit closer to the Northwest.

Just precisely when more typical October weather returns is unclear, though one long-range forecast model hints at a change around the middle of October.