Now that the much-awaited winter storm is unfolding across the region I thought I’d share a time lapse of today’s snow accumulation ending with a sudden changeover to sleet in Cary, NC (central Wake county). The attached animated GIF contains 17 frames at 15-minute intervals between 12:15 pm and 4:15 pm EST (1715-2115Z) today (February 12, 2014). Snowfall rates were around 1″/hr for roughly 4 hours. The last 2 frames of the time lapse show a dramatic improvement in background visibility, an indication of the quick changeover to sleet that occurred between 3:45 pm and 4:15 pm EST (2045-2115Z). You can also see my (relatively futile) attempts at shoveling the driveway.
I’ve also attached an animated GIF of KRAX 0.5 degree REF/CC from 3:45 to 4:15 pm EST (2045-2115Z). My precise location is marked by the ‘red dot’ at the center of the range rings in central Wake county. You can clearly see the SN/PL transition occurring along a SW-NE line of reduced correlation coefficient values across Chatham/Lee/Wake/Franklin/Nash counties. In this case, reduced CC values can be used as a reasonable proxy with regard to identifying the leading edge of the warm nose (~2+ C) advancing northwest across the Highway 1 corridor.
***Below Update at 4:00 pm (2100Z) February 13, 2014***
I’ve posted a more complete time lapse that captures virtually the entire event in central NC, from 1715Z on February 12 through 2045Z February 13. The time lapse shows:
1) the initial round of heavy snow between 1715-2045Z (Feb 12)
2) the transition to sleet between 2045-2115Z (Feb 12)
3) the gradual transition from sleet to freezing rain between 0000-0300Z (Feb 13)
4) the accumulation of ice as noted by the increasing ‘sag’ of trees between 0300-1000Z
5) the melting of ice (as indicated by ‘rebounding trees’) associated with strengthening
insolation and above freezing temperatures after ~1600Z
6) further melting and a transition from rain to snow after 1900Z in
association with the deformation band
WFO Raleigh, NC