Potential MCS, 2 of them apparently. The first is now forming in MN, the second is progged to form in the AM and pass through mid-morning. Buf AFD explains it quite well:
There will potentially be two MCS (or remnants of) which will impact
the region tonight through Wednesday morning. Convective waves are
always challenging to forecast, with forecast confidence increasing
once the convection starts to develop. This is happening with the
first wave this afternoon, with this wave forecast to move across
Western NY tonight between 9 p.m. and 2 a.m.
SPC highlights a slight risk of severe weather with this wave, with
strong to damaging winds the primary threat and large hail a
possibility. Wind shear is forecast to increase, enhanced by winds
generated from the MCS which is forecast to develop. Timing is a bit
late for severe weather, but Western NY should be in the warm sector
by then with SB CAPE increasing to 500 - 1000 J/Kg this evening.
Some storms may produce locally heavy rains, but our region will be
on the southern flank of the circulation with cellular storms
expected to develop rather than a large area of rain.
After this moves through there will be a break in the action late
tonight, with only scattered showers. However, there is good
agreement among mesoscale guidance that a second MCS will move across
far Western NY around daybreak Wednesday. Unlike the first wave, our
region will be in the northern sector of this wave, which will limit
the severe weather potential but increase the risk for heavy rain.
Precipitable water values will increase to around 1.75 inches, which
supports the risk for heavy rain. If this complex materializes,
rainfall amounts of 1-2 inches are likely. One factor which will
help mitigate flood risk is that the system will move through
quickly, but depending on the extent of the system it could pose a
small risk for flooding. Most likely timing is between 7 a.m. and 11
a.m.