The drought that is currently affecting much of southern Quebec looks to be busted tonight and tomorrow as multicell clusters are expected to propagate to the northeast between midnight and 10 am from Cornwall to Montreal to Chibougamau, then between 4 am and 3 pm from the Eastern Townships to Saguenay, and then affecting New Brunswick in the late afternoon and evening hours on Tuesday.

Precipitable water values are expected to exceed 50 mm late tonight near Montreal and Sherbrooke, favouring significant water loading in updrafts and a high density of convection, which will result in storms being somewhat lower-topped (storms will not have the “breathing room” to take on CAPE and develop stronger updrafts with higher cloud tops), resulting in considerably more moisture content remaining below the freezing level of 4 km, further increasing rainfall efficiency and rates.

As observed farther south along the NY/PA border, multiple clusters have trained over the same area producing over 125 mm in some areas, according to NEXRAD estimates, and conditions will become more conducive than those downstream as the night wears on.

This rainfall amount forecast from the 00Z 3K NAM through 2 pm Wednesday shows the potential for rainfall amounts in excess of 75 mm locally across southern Quebec:NAMNSTNE_prec_precacc_042.png