Category: Forecasts

A Rainy Weekend; Sunny Next Week?

Brad Leave a comment

Photo from Mike O’Flaherty to CJOB

Winnipeggers were woken by a severe thunderstorm on Friday morning around 5:40AM.  The storm ripped through Winnipeg leaving torrential rains in it’s wake.  Rob wrote an excellent summary of some of the damages that occurred in Winnipeg, including flooded underpasses, power outages, and explosive manhole covers.

Later that day, convection fired up through the RRV and brought another round of heavy rain.  Winnipeg had only heavy rainshowers that caused some localized flooding.  There was another tornado report out of Steinbach, however.  Looking through the damages, I’m highly doubtful that it’s a tornado.  While they’ve had more than their fair share of strong wind events this year, it’s a little ironic that we get more false tornado reports out of one of the only storm-ready communities than a lot of other places it seems.

Now moving on to this weekend’s weather for Winnipeg.

A large upper low positioned north of Winnipeg is bringing huge amounts of rain to the province.  A heavy rain warning exists for Grand Rapids right now, with Environment Canada expecting between 50-75mm of rain.  Through today, rain will wrap around the upper low and spread into the northern RRV by early afternoon.  The models are vary slightly in the exact positioning, but by this evening, areas in the RRV north of Morris can expect rain.  The upper low sinks to the SE overnight, drawing the wrap-around precipitation further south, and most communities within the RRV should expect a fairly rainy Sunday with unseasonably cool temperatures with daytime highs only in the mid-teens.

After this system clears out on Sunday night, the northern half of the RRV will see somewhere from 10-20mm of rain, while the southern half will see more along the lines of 5-10mm, perhaps as high as 15mm.  Following this system should be a relatively unremarkable week.  Cooler temperatures will be the name of the game, with daytime highs around 20 degrees.  The current forecast is for sunshine, however don’t expect completely clear skies as while we may be in a cooler airmass, we still have a strong August sun, which will likely produce lovely cumulus-filled afternoon skies.

One last thing to watch out for in the deceptive Environment Canada “a sunny week!” forecast is the fact that Winnipeg will be under a northwest flow for the duration of the week.  The weather has a sneaky habit of throwing little shortwaves down in a northwest flow that the model doesn’t pick up very well, and should any of these happen (as is even being hinted at for Monday evening), we could easily see another batch of showers and/or thunderstorms.

So instead of thinking this coming week will be a beautiful sunny week, wear thicker shirts, bring a jacket, and don’t be surprised if it ends up more unsettled than the forecasts are hinting at right now.

Slight Chance of Thunderstorms Tonight, Then Cooler

Brad Leave a comment

So, once again, the possibility of severe thunderstorms exists through the RRV this afternoon and into the overnight period; but how likely are they?

The various models are hinting at it:

The Canadian GEM-REG Model Output

The US GFS Model Output

The US NAM Model Output

Both the GEM-REG and GFS are showing convection over the RRV tonight, however the NAM keeps the convection almost exclusively in the states.

For us, I would lean towards a few showers tonight with maybe a thunderstorm, however I won’t completely rule out the current forecast of showers & thunderstorms.  The models have traditionally pushed the 850mb jet too far N pretty much every day, so colour me suspicious of real convection moving into the RRV (remember Tuesday night?).

The most likely scenario will be convection developing near the triple point of the low & fronts in ND this afternoon, then moving NE and just clipping SE MB.  If, however, the warm front manages to push into extreme southern Manitoba, there could be a higher likelihood of thunderstorms tonight.  Some convection may initiate in or just to the west of Winnipeg by late afternoon due to daytime heating that could become severe, however that would most likely die off as the sun goes down.

All in all, for Winnipeg, I’d say there was a 60% chance of showers or thunderstorms early this evening, and a 40% chance of thunderstorms overnight.  Ultimately, we won’t know what it will look like until things start happening in 4 or 5 hours from now.

After today, a cold front sweeps through Southern Manitoba on Friday and will bring us into a cooler regime with dewpoints in the high single digits to low double digits, and daytime highs in the low twenties.  In my opinion, a refreshing change from the sticky conditions we’ve had the past few days.

Severe Thunderstorms Tonight

Brad Leave a comment

Environment Canada has issued a severe thunderstorm watch for most of southern Manitoba for this evening. A few thoughts on the coming hours…

For Southwestern MB:

The main threat for severe storms should end this evening. High temperatures and dewpoints combined with daytime heating have contributed to a favourable environment for severe thunderstorms. These ones should primarily be driven by the sun, so once the sun starts going down, so too should the intensity of the storms.

For the Red River Valley:

The main threat for severe storms will continue through the evening as an 850mb jet pushes up out of North Dakota into the RRV. The main threat with these storms will primarily be rain. The storms are developing on the nose of the 850mb jet, just downwind of an area of moisture convergence, so as the evening continues, the storms will have more and more moisture to work with. This, combined with the fact that storms will most likely be training (multiple storms moving in rapid succession over the same area), will result in some areas in the RRV getting large quantities of rain. My initial estimate would be that some areas will receive total amounts of 70-90mm locally, however it could potentially be higher than that. Most areas will probably receive on average 15-25mm of rain.

Other threats from these storms will primarily exist during the evening hours when they still could be surface based. If any storms can develop by themselves this evening, there’s a slight chance they could become supercells given the SSE flow through much of the RRV. If that is able to happen, then there would be a chance of large hail (my estimates would be quarter to loonie sized) and strong winds (90+ km/h). Give the backed surface flow, there would also be a very slight chance of a supercell becoming tornadic, but the overall setup doesn’t look to favourable for that; you never know what storms will do when working with 3000+ joules of CAPE, though.

This MCS will stick around for a good portion of the night, resulting in a widespread wet and noisy evening for many residents in Southern Manitoba.

Extreme Heat in Store for Monday; Will be Short-lived

Brad Leave a comment

Monday will bring Winnipeg fully into the tropical airmass that has been building to our south for the past several days.  As the upper ridge over the central United States continues to push north, Winnipeg and the rest of the RRV will want to break out the air conditioners.

A building upper ridge will continue to push north out of the United States into Southern Manitoba overnight and tomorrow.  After a very slight chance of rain or a thunderstorm in the morning, the temperature will soar into the low 30’s through much of Southern MB.  Dewpoints close to the SK border will be low enough to not warrant too much of an issue, but as you move east towards the RRV, positively tropical dewpoints of 22C to 25C will persist resulting in Humidex values reaching into the low 40’s.

Fortunately, unlike as was forecast in the long range models last week, there is a fairly consistent agreement that the hot weather will not last.  A large MCS is forecast to develop on Tuesday night in northeastern Montana, which will likely head west of Winnipeg, however for most of the day we will be clouded over with debris cloud from the system and have a chance of showers or thunderstorm.  Tuesday will still be muggy, however, with dewpoints still in the low 20’s.  With all the cloud, though, the temperature will only climb into the mid 20’s instead of the low 30’s.

After that a powerful impulse is forecast to sweep across the northern Prairies on Wed/Thur/Fri, which will bring Winnipeg into a drier air mass next week.