A Strong storm is poised to make a big impact across all of Newfoundland on Wednesday. Rainfall amounts 50 to 80 mm are expected, with rainfall warnings currently in effect that were issued by Environment Canada yesterday. Wind warnings were also issued for tomorrow’s storm for St. John’s and the Avalon and Burin Peninsula, as winds are expected to guts to at least 100, perhaps 120 km/h over coastal locations.
Here’s the set up: An area of low pressure will rapidly strengthen northeast of Sable Island, and over the Grand Banks- just off the coast of St. John’s. The latest 12z weather models that came in this afternoon has the pressure down to 960 mb or briefly lower. The pressure of a system can be categorized as how powerful it is. The lower the pressure the stronger the storm will be. Some hurricanes have pressures of the same magnitude as this storm does! Most of the precipitation will fall as rain for central and eastern Newfoundland, however there will probably be some mixing, if not totally changing to snow over higher areas in the west. 5 to 10 cm of slushy snow is not out of the question. Due to the nature of the time of year ( transition from fall to winter), temperatures are still generally warm for rain, however – when precipitation falls in large quantities it can cool the atmosphere through a physical process called latent heating. You can read more about the process here: http://en.wikipedia.org/wiki/Latent_heat Basically if it rains a lot, it can cool the atmosphere enough so that it changes to snow. I expect this to happen in heavier rain bands in western and central Newfoundland with this system, so periods of snow are possible.
Outlook: Our next system on Saturday, as mentioned in yesterday’s article: http://knotmove.com/weather-in-montreal/series-of-fall-storms-expected-to-hit-newfoundland-this-weekis looking like more snow for the island. Right now the GFS, GEM global and NOGAPS model have an idea of where the low will be placed, but it is not exact. The GEM global and NOGAPS model gives more snow where GFS is warmer and more rainy for the east coast. They all agree on snow for western Newfoundland though, so readers in Corner Brook, St. Anthony, Port Aux Basque and the Gros Morne region should keep an eye on the system.
A bit of good news: The Halloween storm I mentioned in yesterdays article seems to have better consensus that it will move well off shore of the Grand Banks, not impacting much of St. John’s and the Avalon. The storm will still be monitored of course, as the track can change.