Puget Sound Convergence Zone Strikes Capitol Hill

The so called "Puget Sound Convergence Zone" (PSCZ) hit parts of the Seattle area yesterday evening leaving an icy mess for the commuters this morning. Especially hard hit areas were Capitol Hill, downtown, the U-district, and other parts of North Seattle.

The PSCZ occurs after a front passes, when air moving in from the west or northwest can not move over the Olympic Mountains but instead moves around them and converges on the eastern side. This convergence of the winds sometimes results in an often narrow band of precipitation, as apparent on radar last night (first image below). If you look at the weather station observations, south of the precip band winds are southerly and north of the band winds are northerly.

Precipitation was in the form of rain turning to a mix of rain/snow/sleet or completely changing over to snow in some areas. After it stopped, skies cleared and nighttime temperatures dropped to below freezing, allowing everything to freeze.

Photos below:
First: Radar and surface weather observations in Puget Sound Region Jan 14 7pm. The interstates are shown in red and Capitol Hill is marked as a reference.
Second: Harrison St looking west Jan 15 8:30am.
Third: Harrison St from Summit looking east toward Broadway. Despite the icy conditions, schools were not delayed and school buses were still running normally.
Fourth: Buses were rerouted along Broadway Avenue, and delays occurred. Bus stops were unusually crowded, such as the one at Broadway and E John.
Fifth: This was our first winter weather event without you Taco Bell, we'll miss you.

All pictures of Capitol Hill streets were taken at approximately 8:30am on Tuesday January 15, 2008.