SPC MD 72

MD 0072 CONCERNING HEAVY SNOW FOR PORTIONS OF THE SIERRA NEVADA IN CENTRAL/NORTHERN CALIFORNIA

Mesoscale Discussion 0072
NWS Storm Prediction Center Norman OK
0616 PM CST Wed Jan 18 2017

Areas affected...Portions of the Sierra Nevada in central/northern
California

Concerning...Heavy snow 

Valid 190016Z - 190515Z

SUMMARY...Heavy snowfall (generally above 3500-4500 ft) will
continue and develop southward across the northern/central Sierra
Nevada this evening into tonight. Snowfall rates upwards of 2+
inches per hour will be possible across higher elevations.

DISCUSSION...An expansive area of precipitation exists across much
of central/northern California late this afternoon, in response to a
mid-level jet streak progressing southeast along the CA coast and a
related plume of enhanced tropospheric moisture (e.g., PW values
near 1 inch). Near-term guidance and regional radar data depict
increasing southwesterly 700-mb flow approaching portions of the
western Sierra slopes, which will enhance upslope flow and
precipitation rates. Heavier rates will expand down the Sierra range
as this stronger flow evolves southward this evening into the
overnight. Moreover, KBBX velocity data illustrate strong veering
with height, indicating ample warm-air advection which is also
contributing to higher rates. Recent KDAX data show pockets of
higher specific differential phase (KDP) around 15000 ft, likely
suggesting efficient crystal growth supporting higher snowfall rates
(upwards of 1-2+ inches per hour) at higher elevations. Strong wind
gusts will also combine with this snowfall to occasionally restrict
visibility across higher passes.

KBBX correlation coefficient (CC) data indicate snow levels
currently around 3500-4000 ft across parts of the northern Sierra
range, while KDAX CC data indicate these levels rising to around
5000-6000 ft farther south. These levels will fluctuate slightly
through the evening (with diabatic effects in heavier bands
periodically lowering levels) before they more consistently descend
overnight with the arrival of mid-level cooling.

..Picca.. 01/19/2017

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...REV...HNX...STO...

LAT...LON   36511883 38502036 38782043 39422090 39942150 40322170
            40552136 40442101 39932036 37881917 36731841 36391840
            36211858 36511883 

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