First thunderstorm

9:38 Watch expired - storms are off to the east of the city.

9am: A severe thunderstorm watch as been posted for Montreal until 10:30am. More thunderstorms are developing in the moist unstable air mass and producing very heavy rain, lightning and small hail. One passing over the West Island at this hour is dumping torrential rain with low visibility and very dark skies. These showers will move across the island over the next hour.

The first thunderstorm of this young 2010 season rattled across Ile Perrot and the western tip of Montreal island at around 3am this morning. Thunderstorms developed along a warm front that is stuck here in the St. Lawrence Valley. It will slowly begin to sag back south again into upstate New York leaving us on the cool and unstable side of it. A northeast breeze will hold temperatures around 12C today in Montreal while they will reach 20C in Toronto and Burlington and 30C in New York City. Low clouds and fog along with drizzle will also occur here in Montreal. In the last hour more thunderstorms have fired up in the Ottawa Valley and are rapidly moving east so we may have another rumble or two of thunder. The storm overnight dropped about 15mm of rain into my gauge at home.

Moving forward we can expect low pressure from the Midwest to move into our region Thursday with another 10-20mm of rain followed by much cooler weather and the risk of a flurrie or two Friday and early Saturday. Skies will then clear out for a sunny and seasonable weekend.

This morning temperatures are already approaching the mid 70's (22 to 24C) across the Ohio Valley and mid Atlantic, while in Denver and across Colorado, Wyoming and the Dakotas, light snow is falling with temperatures below freezing.