.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
...Winter storm watches issued for potentially significant lake
snows Wed night and Thu...
Deep upper low aloft gradually opens up as it lifts across southern
Quebec. At the sfc, 995mb sfc low over Upper Great Lakes slowly
weakens while reaching Ottawa Valley on Wednesday night before
exiting to the Canadian Maritimes on Thursday. Wednesday starts off
quiet but then primary cold front arrives mid to late aftn. Expect
swath of rain/snow quickly switching to snow as H85 temps drop off
to less than -8c by late aftn. Once the front goes by, much colder
air, down to -14c at H85 sweeps across Lake Erie and later in the
evening across Lake Ontario. Water temps on both lakes sitting
around 40F/4c so there will be more than ample over-water
instability for a lake response into Thu.
Even as main sfc low is well to the east by Thu, cold air pouring
across the wide open lakes leads to lake induced troughing
persisting through most of Thursday over the lower Great Lakes.
Result of the low then the lake induced trough is a persistent SW
240 flow Wed evening through most of Thu. Convergent and well-
aligned sw flow will support plumes of lake effect off both
Lake Erie and Lake Ontario. BUFKIT profiles continue to show
inversions 6- 8kft which is certainly not at the top end of
significant lake effect events, but majority of DGZ will be
within the lake convective layer so SLRs will be higher, likely
reaching toward 20:1. This combined with more reasonable and
superior performing Canadian model QPF results in several inches
of lake effect maximizing Wed night through Thu morning off
both Lake Erie (Metro Buffalo toward Southtowns) and Lake
Ontario (northern portion of Jefferson and Lewis counties).
During this time snowfall rates over an inch per hour are
likely.
One other thing to note, it still looks quite windy with gusts up to
40 mph, especially NE of the lakes through Wed night before
diminishing on Thu. Winds this strong will result in considerable
blowing and drifting snow. Though there are signals that beyond Wed
night, primary plume of snow off both lakes will waver slightly,
enough snow accumulation and impact from blowing snow to hoist
winter storm watches northeast of both lakes. Watches begin on Wed
evening (except midnight east of Lake Ontario) and go through early
Thu evening. This is for the core of where biggest impact will be.
Eventually more headlines (mainly advisories) will be needed on the
edge of where the watch headlines are at present.
Otherwise, Wed look for temps to peak in the upper 30s to low 40s
then rapidly fall off Wed evening. Temps will then be found in the
20s by sunrise Thursday and not change much at all through the day.
Later Thu into Thu night there are still differences on how far west
low pressure developing over the southeast CONUS will track. Though
the heaviest portion of that system likely stays toward Mid Atlantic
should be enough forcing/lift and moisture wrapping back into the
colder air to result in some light snow, with lake enhanced snow
possible east of the lakes. Increased pops to categorical for all
areas to cover it at this time.
.LONG TERM /FRIDAY THROUGH SUNDAY/...
Lake effect snow will likely continue east of the lakes Friday as
seasonably cold air continues to flow across the lower Great Lakes.
Additional accumulations will likely be tacked on during this time.
There is some uncertainty in how long the broad troughing lingers
over the Great Lakes, which will affect not only the persistence of
lake effect chances as we move into the weekend, but also how long
the cold air hangs out over the region, and how quickly ridging
returns to the area.
That's only through 7 pm too.
