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Mesoscale Discussion 1964
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   MESOSCALE DISCUSSION 1964
   NWS STORM PREDICTION CENTER NORMAN OK
   0604 PM CST THU DEC 04 2014

   AREAS AFFECTED...PORTIONS OF FAR NRN ORE AND SRN/CNTRL WA

   CONCERNING...FREEZING RAIN 

   VALID 050004Z - 050600Z

   SUMMARY...FREEZING RAIN WILL CONTINUE TO SPREAD ACROSS PORTIONS OF
   THE AREA INTO THE OVERNIGHT HOURS...WITH SOME AREAS EXPERIENCING ICE
   ACCRETION RATES OVER 0.05 INCHES PER 3 HOURS.

   DISCUSSION...WATER VAPOR SATELLITE IMAGERY AROUND 23Z INDICATED A
   WEAK SHORTWAVE TROUGH ALONG AN AXIS FROM WRN WA TO N-CNTRL ORE. AS
   THIS TROUGH CONTINUES TO TRANSIT NE...BROAD ADIABATIC ASCENT IN
   CONJUNCTION WITH WEAK HEIGHT FALLS WILL CONTINUE TO PROMOTE AREAS OF
   PRECIPITATION ACROSS THE REGION. SFC OBSERVATIONS INDICATE
   SUB-FREEZING TEMPERATURES EXIST ALONG THE UPPER HOOD RIVER
   VALLEY...EXTENDING N INTO WA IN SHELTERED VALLEYS TO THE E OF THE
   CASCADE RANGE. WITH DENSE COLD AIR UNLIKELY TO BE SCOURED FROM THESE
   LOCATIONS QUICKLY...MODEL GUIDANCE INDICATES THAT MANY OF THEM WILL
   CONTINUE TO SEE SUB-FREEZING TEMPERATURES THROUGH MUCH OF THE NIGHT.
   AS SUCH...THE CONTINUATION / NWD EXPANSION OF THE PRECIP SHIELD WILL
   RESULT IN ICE ACCRETION RATES UPWARDS OF 0.05 INCHES PER 3
   HOURS...WITH LOCALIZED HIGHER RATES LIKELY. 

   OF NOTE...DUAL-POLARIZATION DATA /E.G. REDUCED CORRELATION
   COEFFICIENT AND INCREASED DIFFERENTIAL REFLECTIVITY/ INDICATE THE
   HIGHER REFLECTIVITY VALUES OVER SKAMANIA COUNTY ARE A RESULT OF
   MELTING SNOW/BRIGHT BANDING. NONETHELESS...BASED UPON RECENT SFC
   OBS...PRECIP RATES WILL LIKELY BE OF HIGH ENOUGH INTENSITY TO RESULT
   IN SUBSTANTIAL ICE ACCRETION.

   ..PICCA/THOMPSON.. 12/05/2014


   ATTN...WFO...OTX...PDT...SEW...PQR...

   LAT...LON   45502165 45642215 46252220 47832105 47892016 47692022
               45832121 45562139 45502165 

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Page last modified: December 05, 2014
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