Good disco by LWX:
.SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/...
The coveted shortwave trough responsible for the rather dramatic
shifts in the forecast for the second half of the weekend moved
onshore of western North America overnight, and is expected to be
amplify over the Tennessee River Valley Saturday night. This will
result in cyclogenesis (development of low pressure) off the
southeast coast. It appears the northwestward trend in the track of
this low pressure closer to the coast is due at least in part to (1)
a slightly stronger ridge over the southwestern Atlantic Ocean
deflecting the low pressure closer to the coast, and (2) slightly
more separation and amplification between the incoming shortwave
trough, and low pressure associated with today`s cold front
departing over southeastern Canada; this results in a subtle
yet all-important opportunity for phasing between the northern
and southern branches of the jet stream.
What this means in terms of sensible weather locally is that the
chances for precipitation have increased markedly for Saturday night
into Sunday. The airmass will be marginally cold (see: high
temperatures near 50 the preceding day on Saturday), but should be
cold enough for the bulk of the precipitation to fall as snow
(though a start as light rain or a mix is possible). The late-
night timing of precipitation and dynamic cooling aloft from
lift between the phasing shortwave troughs on the northwest side
of the surface low should keep temperatures cold enough for
(wet) snow during the height of the event, and the dynamics may
result in a few bands of moderately heavy snow at times,
particularly SE of US-29.
The potential for a warning-level snowfall event (5"+ in 12
hours east of the Appalachian Mountains) seems modest despite
the dynamics given the marginal temperatures and the short
duration of the event. Still, any further shifts may result in
an uptick (or downtick) in forecasted snowfall amounts.