... A cold front will bring showers on Thursday.
NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... No changes were needed for the even update as eroding high pressure wl maintain dry weather tonight although strengthening WSW flow aloft will increase high, and eventually mid level cloudiness. Low temperatures will be some 5 to 10 degrees above the calculated normals under the increasing cloud and warm advection regime.
SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY NIGHT/... The surface low will lift through Ontario and into Quebec by Thursday evening, with the surface front also getting a push from a shortwave trough that will reach Lake Erie by 00Z Friday. The boundary will cross during the afternoon and evening hours, with a band of low-topped showers and thunderstorms accompanying it.
SPC continues to outline much of the CWA in a marginal risk of severe weather Thursday afternoon and evening. Instability will be quite meager, with the HREF mean indicating MUCAPE on the order of only 300-500 J/kg. However, with strong synoptic support and 700 mb flow of about 50 knots, perhaps one or two showers or low-topped thunderstorms could produce strong to marginally severe wind gusts via momentum transport. The lack of instability should create a low ceiling on the overall severe threat.
Beyond Thursday evening, upper level low pressure will continue to meander near the southern tip of Hudson Bay. A weak secondary cold front may provide isolated showers late Thursday night/Friday morning. Meanwhile, the first departing shortwave will help to carve out a Great Lakes/NE CONUS troughing pattern that will linger into the weekend. A series of shortwaves rotating through the trough will contribute to low chances of showers through Friday night. Temperatures will drop back to more seasonable levels by Friday.
LONG TERM /SATURDAY THROUGH WEDNESDAY/... A relative lull in precipitation chances is possible later Saturday/Saturday night as the trough lifts out, leading to a brief period of zonal flow aloft along with weak surface ridging. Depending on the timing of clearing, there may even be enough of a window for at least patchy frost in some areas Sunday morning.
Rain chances start increasing again on Sunday as a warm front lifts into the Ohio Valley with deepening moisture. This front may initially have trouble lifting north into the upper Ohio Valley in the lingering zonal flow, and the models then disagree on how to handle a shortwave/potential closed low arriving from the upper Midwest early next week. Regardless, PoPs will be necessary for much of the period from Sunday through Wednesday. Temperatures will average out near to just above normal.