Great Izzi writeup (excerpts)
Textbook La Nina pattern in place across the country and likely
to continue through the long term period with a powerhouse jet
stream, progged at times to exceed 200kt at 250 mb, separating
record breaking cold over the Pacific Northwest and southwestern
Canada from record heat over the southeastern U.S. Over the past
week or so long and then medium range models have been advertising
a gradual southward shift of the jet stream and storm track,
placing our area under the gun for more active, and potentially
wintry weather, during the long term period.
The timing differences among the various models have shrunk
considerably with precip expected to move into southern CWA
shortly after 12z Tuesday and then spread quickly north, likely
reaching the IL/WI border by around 18z. Unfortunately there
remain meaningful differences in thermal profiles Tuesday, with
the GEM and NAM both on the warm end of the spectrum and the ECMWF
on the cold end with the GFS sandwiched between. In the GEM/NAM
scenario, a brief period of wintry mix would quickly change to all
rain with little or no accumulation. The ECMWF holds onto a
deeper cold air mass longer and allows for a period of
accumulating snow Tuesday roughly north of I-80 with the most
significant accums north of I-90. Conceptually, a
weakening/filling surface low would be less effective in
dislodging low level cold air, which would lend a bit of credence
to the EMCWF solution suggesting a quick couple inches of snow
will accumulate, mainly northwest of I-90 Tuesday.
The hyper active, La Nina fueled Pacific jet is progged by medium
range guidance, which is in remarkably good agreement at this
distance, to develop a classic Panhandle to lower Great Lakes
strong storm late Friday into Saturday. If this system
materializes as advertised, it would have the potential to produce
a significant winter storm with heavy snow and strong winds
Friday night into Saturday somewhere in the Midwest. Our area is
certainly in the "cone of uncertainty" with this system and it
will bear close watching over coming days. It`s worth noting
that at this time range it isn`t the slightest bit uncommon for
there to be dramatic changes in model guidance in both the track
and strength of a potential storm systems, so it is way too early
to place any stock in any particular model`s current forecast
track or intensity, let alone their snowfall output. The primary
message this distance is: stay tuned, it could get messy next
weekend somewhere in the region.