RC banging out a killer AFD on this one.
This then turns us to the main period of interest. Meteorologically,
the key piece of the puzzle will be a vigorous mid-level wave
closed at 500 mb as it moves onto the Pacific northwest shore
Saturday evening. This wave will dive into the desert Southwest by
Monday evening and from there eject northeastward toward the
western Ohio Valley by Wednesday morning. It now appears that this
primary "southern stream" wave will remain separate from
noteworthy northern stream influence, as recent guidance has
slowed an incoming short-wave trough diving southward from central
Canada later in the week. That said, an intensifying upper jet
streak wrapping around the base of our wave of interest may help
intensify the burgeoning mid latitude cyclone Tuesday into early
Wednesday.
Will spare much more in depth complex meteorological analysis at
this still several days out time range in which good overall
guidance agreement (and a bit of a northward tick in the ensemble
means) in the big picture still entrails meaningfully large spread
that will determine our bottom line precip/snow and impacts wise.
Most importantly, a fairly classic southern Plains, lower MS
Valley low pressure should take shape, with the question being
exact track and strength from there toward the eastern Great Lakes.
Barring major changes in the evolution, this pattern supports
injection of plenty of Gulf moisture (well above normal PWATs to
tap into) for higher snow rates and several inches of snow where
strongest banding sets up.
Ultimately, the primary southern stream wave is now expected to
be the main player and the strength of the wave (tied to it
becoming negatively tilted or staying more positively tilted for
longer) will determine the all important surface low track. A
track farther north of the OH River of 1000 mb or less surface low
would bring the higher accumulation risk farther north and west,
while a weaker and farther south track would result in a sharp
cut-off northwest and higher accums southeast. Conceptually
speaking as well, fairly sharp cut-offs on the northwest side of
the precip shield are common in these synoptic set-ups even with
stronger surface lows.
While there is a scenario in which a much stronger system could
bring in enough warm air aloft for p-type concerns if not rain
into portions of the area, for now have broad brushed snow chances
in the forecast, with likely PoPs in our southeast half/near and
southeast of I-55 Wednesday reasonable at this juncture. The not
very cold antecedent air mass suggests climo to slightly below
normal snow ratios, so still not looking like a fluffy snow. Gusty
northerly winds would nonetheless serve to knock down visibility
further. Plenty of time to iron out all these details and
certainly a much weaker system with little/no impacts in much of
the area remains on the table (with a lower % but not insignificant
number of ensemble members showing this).
Beyond the possible snow storm, the earlier mentioned northern
stream trough will bring the coldest air mass of this exceptionally
mild January into the region. At the least, expect flurries in
this setup and the lake effect machine to get going, with
potential for light snow accums to be addressed later. The pattern
does look quite active current day 7 (Friday) and beyond, with
cold enough air for additional winter weather threats into early
February. Needless to say, stay tuned for forecast updates on the
mid week storm system as we start to hone in on the details.