Monday, October 21, 2013

Is the ridge going away yet?

The ridge that won't go away

The last blog entry discussed the strong upper level ridge over the West Coast and how long it would stick around and this post will continue on that note. Since last week, there has been little change in the strength of the ridge although it shifted a little farther east, as seen on the satellite image below (green lines= 500 mb heights superimposed on the infrared satellite.  

So how will this pattern change through the week? The answer is not much. The model solutions are in strong agreement that the ridge will persist at least through Friday. Below is the 500 mb map with moisture (green infers a moist atmosphere with high level clouds). Looks somewhat similar to the image above, doesn't it. 
500 mb height pattern for 5pm 10/28
This pattern will continue to bring generally clear skies to the region with areas of fog reappearing over parts of northeast Washington and the northern Idaho Panhandle. Similar to what's seen in the visible satellite picture below (notice the fog extending from Spokane north and east to Sandpoint, Bonners Ferry, and Colville). The fog has been shallow enough over our area that its burned off over most if not all locations around noon or sooner. That's not the case west of the Cascades, where the fog has persisted through most of the day.

Visible Satellite 1200pm 10/21

So is there is there any sign that this stagnant pattern will ease or breakdown? Actually there are changes in the future, its just a question of to what extent will the changes occur. On the 500 mb height chart below, note the ridge axis retrogrades off the coast (moves west) and the flow over our area turns north-northwest and allows a disturbance to track south through southern Saskatchewan. This is likely too far east to deliver much in the way of precipitation (except for some light precipitation over the Idaho Panhandle) , but it would likely bring cooler air down the Purcell Trench, from Bonners Ferry to Coeur d'Alene, which should lessen the chances for fog. 

Taking a look at the same ensemble plots as the last blog entry it supports this change...with decent model agreement (note the line clustering and trough signature just to our east).

Spaghetti Charts of 500 mbs 10/27

Here's a look at what sort of temperatures we can expect with the transition to northerly flow. Notice we go from well above average temperatures in Spokane (the red land blue lines are forecast and the dotted lines are the averages) for most of the week to below normal temps by early next week. 
7-day temperature outlook for Spokane 10/22-10/28

This cooler weather will could persist into early next week, but look what the GFS is forecasting to appear by the middle of next week. The return of the ridge. There is some model disagreement with this notion, but its possible much of the region will remain dry through the end of the month. If no more rain falls in Spokane through the end of the month it will be the 4th driest October on record. 

500 mb height pattern for Wednesday 10/30

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