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Mesoscale Discussion 9 |
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Mesoscale Discussion 0009
NWS Storm Prediction Center Norman OK
1252 AM CST Fri Jan 05 2018
Areas affected...Portions of the eastern slopes of the Cascades and
Columbia Basin
Concerning...Freezing rain
Valid 050652Z - 051245Z
SUMMARY...Multiple waves of light to occasionally moderate freezing
rain will likely impact points east of the Cascade crest through the
overnight hours. Freezing rain rates of a few hundredths of an inch
per hour will be possible.
DISCUSSION...Ahead of a shortwave trough over the eastern Pacific,
southwesterly mid-level flow is transporting increased moisture
across the Pacific Northwest late this evening. Within this moist
conveyor, weak warm advection and related isentropic ascent will
yield two or more rounds of precipitation overnight, with one
currently advancing northward across western Washington. While most
of the heavier precipitation will likely fall west of the Cascades,
occasional light to moderate precipitation will likely occur across
eastern Cascade slopes and into the Columbia Basin. Antecedent high
pressure over the interior is maintaining a shallow layer of
near-surface temperatures in the upper 20s/lower 30s across this
region, and forecast soundings indicate a sufficiently deep warm
nose aloft for complete melting of most hydrometeors. In turn,
occasional freezing rain (characterized by rates of a few hundredths
per hour) will remain possible into the morning hours.
..Picca.. 01/05/2018
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...OTX...PDT...SEW...PQR...
LAT...LON 45682042 45692132 45742157 45852168 47172143 47652113
48952057 49011930 49011912 48781892 48171856 47641843
46391904 45682042
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