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Mesoscale Discussion 65
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   Mesoscale Discussion 0065
   NWS Storm Prediction Center Norman OK
   0542 PM CST Tue Jan 17 2017

   Areas affected...Portions of northwest Oregon and southwest

   Concerning...Freezing rain 

   Valid 172342Z - 180545Z

   SUMMARY...Moderate to locally heavy freezing rain rates are possible
   into the evening from the central/northern Willamette Valley through
   the Columbia River Gorge into adjacent parts of the Cascades.

   DISCUSSION...At 2330Z, the leading edge of a substantial
   precipitation shield is moving into western Oregon and Washington. A
   continuous feed of moisture ahead of an upper trough off of the
   Pacific Northwest coast will maintain moderate to locally heavy
   precipitation rates through tonight. Meanwhile, drainage of cold air
   from the east through the Columbia Gorge is maintaining subfreezing
   temperatures from the southern WA Cascades westward to the
   central/northern Willamette Valley. The KPDX ASOS site has reported
   0.20 inches of ice accretion over the last two hours, with nearby
   sites reporting at least 0.05 inch-per-hour rates. Rates of
   0.05-0.10 inches per hour will spread eastward with time this
   evening, leading to significant ice accumulations. 

   Some erosion of the shallow subfreezing layer is possible this
   evening across the western portion of the MCD area, including the
   Portland metro area. However, with a relatively strong pressure
   gradient being maintained and very cold temperatures across portions
   of eastern Washington and northeast Oregon, temperatures will be
   very slow to rise as strong easterly flow through the Gorge

   ..Dean.. 01/17/2017


   LAT...LON   45712314 46002288 46082264 45852229 45862196 46132127
               46282094 46302061 45692049 45492062 45452123 45522152
               45522176 45512199 45452221 45392240 45302269 45172311
               45422320 45712314 

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