ZCZC SPCSWOMCD ALL ACUS11 KWNS 100215 SPC MCD 100215 CAZ000-100615- Mesoscale Discussion 0092 NWS Storm Prediction Center Norman OK 0815 PM CST Sat Feb 09 2019 Areas affected...Northern Sierra Nevada Concerning...Heavy snow Valid 100215Z - 100615Z SUMMARY...Heavy snow rates of 2-3+ inches per hour will continue to develop across the northern Sierra Nevada (into elevations as low as 2000-2500 feet) through 7-10 PM PST, before gradually shifting southward into the southern Sierra Nevada overnight. Gusty winds will create considerable blowing and drifting, and sharply reduced visibilities. DISCUSSION...An initially deep lower/mid tropospheric cyclone is forecast to begin migrating or redeveloping inland of the Oregon coast, and east of the southern Cascades this evening into the overnight hours. It may weaken as it does, but guidance indicates that a significant short wave impulse will pivot around its southwestern periphery into/through much of northern California between now and 06-09Z. Ahead of the associated cold front, flow is already strengthening out of the southwest, from mid to lower levels (including 40+ kt to around 850 mb), across the northern California coastal ranges and Sacramento Valley into the northern Sierra Nevada. In the presence of a cold (and cooling) environment (including freezing levels falling to 2000-2500 feet), strengthening orographically forced ascent is contributing to intensifying snow rates across the northern Sierra Nevada. This is occurring within a pre-frontal plume of modest moisture (including precipitable water up to around .5 inches) advecting off the mid-latitude Pacific. Latest Rapid Refresh forecast output suggests that snow rates may increase up to 2-3+ inches per hour along the Sierra Nevada, west through southwest of Tahoe Valley, between now and 03-06Z, before the heaviest snow slowly begins to shift to the southwest of Tahoe Valley and into the southern Sierra Nevada between 06-09Z. ..Kerr.. 02/10/2019 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...REV...STO... LAT...LON 40082141 39392034 38711990 38301960 37932007 38152048 38782083 39702168 40082141 NNNN