Orographic Precipitation Studies
of the
Cascade Mountains of Washington

Modeling Studies, 2010

October 5-26, 2003
Little cross-barrier temperature difference

All the precipitation in October occurred from the 5th through the 26th. For comparison purposes the mean surface temperatures and precipitation from the model were compared with monthly climatological values for 14 stations in the 2 km grid. Seven stations were on the west slope and seven stations on the east slope. The results are summarized in Table 6.

West Slope Stations:
    Snoqualmie Falls
    Cedar Lake
    Startup
    Darrington Ranger Station
    Concrete PPL Fish Station
    Newhalem
    Ross Dam

East Slope Stations:
    Wenatchee
    Leavenworth 3 S
    Plain
    Chelan - Lakeside
    Holden Village
    Stehekin 3 NW
    Winthrop

Table 6. Comparison of Model with Observations for 2 km grid.
Location    Mean Obs Temperature ° C Obs Precip. cm.    Mean Model Temperature ° C Model Precip. cm.    Model Temperature Error Model Precip. Error
West Slope    11.0 17.0    10.6 20.1    -0.4 +18%
East Slope    9.9 5.0    9.7 6.5    -0.2 +29%

At first glance the model seems to have done a pretty good job of estimating temperature and precipitation. The precipitation is overestimated on both sides of the mountains, but more so on the east slopes than on the west slopes. The fact that the model temperatures are so close to the observed temperatures is a little suprising when one considers that the elevation of the west slope station locations in the model grid are 350 m too high and 200 m too high for the east slope stations.

The video in Figure 25, shows the microphysical data fields for the three day period at the end of the simulation. In the video one can see a low-level cold air mass moving from the east creating a cloud band at the leading edge and pushing westward into the eastern valleys of the Cascades. This is followed by a snow band moving eastward across the mountains. This period will be used for a more in depth study of cold pool formation and its effect on precipitation.


Figure 25. MM5 Domain #2 (6 km grid) October 24-26, 2003. Cloud water is white, Rain water is blue, snow is yellow and graupel is green.

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