Through the day on Wednesday upper low that is currently bringing
the wintry weather to the intermountain west today slides east from
the central Plains to northern part of Mexico. As jet energy rounds
the base of this trough, increasing southerly flow off the Gulf of
Mexico and associated low-level convergence helps develop low-level
cyclogenesis lower Mississippi River valley. There are differences
in placement of actual sfc low on Wednesday evening (possibly due to
the convection that will be ongoing in that region), but there is
better agreement in the development of H85 low centered on Arkansas.
As the northern portion of the upper trough lifts across the middle
CONUS, H85 low and associated warm air advection along with some sfc
wave of low pressure will head toward western Ohio valley into the
lower Great Lakes on nose of 40 kt low-level jet. The warm air
advection along with height falls ahead of the upper trough and exit
region forcing from 160+ kt jet will aid in spreading a widespread
shield of precip over the lower Great Lakes that should last 3-6
hours with best chances late Wednesday night through mid morning on
Thursday. Ptype is the main question. It does look like precip
arrives before the stronger warm air advection does, so snow or
maybe sleet is looking more probable to start, but based on latest
suite of models and GEFS ensembles a trend to warmer temps aloft
eventually shows up around or after 12z on Thursday. Forecasted qpf
attm would support low-end advisory level snow/sleet amounts on
leading side, but if ptype is more fzra then the expected qpf would
certainly cause issues. Would see more qpf from this first wave of
precip if the stronger moisture advection of pwats over 1 inch was
aimed into our region instead of the Mid Atlantic as models and
ensembles are very locked onto right now. Timing of any wintry
precip would also heighten the impact as it would affect the
Thursday morning commute time. Likely we will need headlines for
this initial event late Wednesday night into Thursday.
Now, once the precip moves through on Thursday morning, there is
good agreement there will be some sort of break in steadier precip
rest of Thursday, though could see a wintry mix hanging on over
northern forecast area. Tough to time this break though, so the pops
will stay likely for most all day Thursday. At least based on the
pattern the break makes sense as we will be awaiting arrival of main
upper level trough and strong upper jet moving east from the
southern Plains. Then, unlike the late Wednesday Night into Thursday
time frame, there are large disagreements on extent of precip on
Thursday night and ptype is also in question. GFS and GEFS peg most
of the qpf over our far eastern forecast area, mainly in form of
snow, while the ECMWF and Canadian-NH have qpf over most of
forecast area, but are either warmer with rain (Canadian-NH) or
colder with snow (ECMWF). Models have been jumping around for this
time frame for a while now in terms of extent and thermally, so
best to stay tuned.
Finally, on into Friday, it will eventually become colder,
possibly enough for lake enhanced snow as main trough axis and
colder air aloft crosses the northeast CONUS whle main sfc low
heads toward Atlantic Canada. Not sure how quick the transition
occurs and extent of deeper moisture present, but could see the
need for headlines for the lake enhanced snow. This would
especially be the case into the typical higher terrain areas
downwind of the lakes favored by wnw-nw winds.