Chris's Corner - December 2018 Thread

The second system still appears more interesting, but there
remains a lot of uncertainty as deterministic model guidance and
their ensembles show a high degree of spread. While guidance
continues to show a surface low moving to the south of the region,
the complex interaction (or lack thereof) between a northern
stream shortwave trough and another one crossing the south-central
Plains is of critical importance. Latest 1200 UTC GFS/CMC show at
least a partially phased system, which would have the potential
to tap into enough cold air to produce accumulating wet snowfall
within the deformation zone. The ECMWF model meanwhile keeps the
northern stream shortwave trough separate, which results in a
warmer solution at low-levels and just light rainfall across
southeastern parts of the forecast area. While there is still
plenty of time to see how this unfolds, accumulating snowfall
anywhere in the CWA seems quite low as a fairly specific sequence
of events would need to occur. First, the two aforementioned
shortwaves would need to at least partially phase so that the low-
level air would be cold enough for wet snow instead of a cold
rain. A partial or fully phased system would also allow for more
dynamic cooling of the boundary layer as the low-level cyclone
would have the potential to rapidly deepen. Second, the phasing of
the northern and southern stream shortwave troughs would need to
happen at precisely the right longitude. Too far west and any
chance of accumulating snowfall would be across western Missouri
or eastern Kansas. Too far east and much of the CWA would get
little to no precipitation at all. Main message for this storm at
this point in time is that a period of light rain is likely across
parts of the area Thursday night into Friday with a rain/wet snow
mix on the northwestern side of the stratiform precipitation
shield.