North Spokane Snow Event on Tax Day Eve - April 14, 2009

Photo courtesy of Ray Kresik

On the morning of April 14th, 2009, a cluster of snow showers developed over the Spokane Valley and moved northwestward over the Five Mile Prairie, the Indian Trail Community, Whitworth College, and north Spokane. By late morning, the mesoscale cluster of snow showers had dissipated over Nine Mile Falls and the Spokane/Stevens County line, but not before producing some heavy snowfall.

Snowfall totals are below...

Below is a zoomed in sequence of radar images showing at least a portion of the event. The radar image below shows by 5am PST (1200 UTC) it was snowing heavily (dark green and yellow colors indicate 30-40dBz returns) over the North Spokane, Whitworth College, Five Mile Prairie and vicinity. These snow showers slowly shifted west-westnorthwestward between 5-7AM (1200-1400UTC). Also evident during this time is the lack of significant returns on the radar over downtown Spokane, the Spokane International airport and the NWS office (radar location) where little to no snow accumlation occurred. By 10am (1700 UTC), the cluster of snow showers had moved westward towards Long Lake and weakened considerably.

1200 UTC Radar Image...

1300 UTC Radar Image...

1400 UTC Radar Image...

1700 UTC Radar Image...

Below is a visible satellite image taken just after sunrise at 7:15AM (1415 UTC). Note, most of the clouds over eastern WA and northern ID look a rather uniform gray color. However we can see the clouds appear both lighter and darker than surrounding clouds between Spokane and Deer Park (another similar area existed southeast of Coulee City). The lighter shades were a result of the clouds extending higher into the atmosphere, and thus were receiving more morning sunshine (and appeared brighter) than surrounding clouds. Notice there is a subsequent darker area just to the west (left in the image) of these brighter clouds. This is a result of these higher (deeper) clouds casting a shadow on clouds just to their west. This illustrates the clouds causing the snow over this region extended much higher into the atmosphere than clouds across much of eastern WA and northern ID where flurries to no snow fell.

1415 UTC Visible Satellite Image...

Below is an image from 500 mb (~18,000 ft) showing the wind speed and wind direction among other variables at 11am (1800 UTC). Notice the winds are coming from the south over southeastern WA and far eastern WA and coming from nearly the opposite direction (north to northeast) just to the west over much of WA. The line separating these two wind patterns is something meteorologists call a deformation zone, which can act to produce vertical motion in the mid levels of the atmosphere. This in combination with the cold air aloft (-33C at 500mb) likely aided in the formation of the snow showers on April 14th, but admittedly does not explain the localized nature of the event.

Below are two more images from the event courtesy of Ray Kresik.