Scattered showers and thundershowers today.. a respite Sunday then more rain Monday into Tuesday..

Scattered showers and thundershowers are expected to develop today across southern Manitoba as an unstable airmass settles over the area. Partly sunny skies this morning will give way to convective cloud development as temperatures climb into the mid teens by the noon hour, setting the stage for scattered showers and thundershowers this afternoon. Any thundershowers will be fairly weak due to a lack of strong dynamics today, however small hail and brief downpours are possible. Conditions are even favourable for some cold core funnel clouds to develop today (with or without a thundershower) however these will be isolated and should not have enough energy to reach the ground. Things will dissipate this evening as we lose daytime heating, leading to drier weather Sunday with no precipitation expected.. welcome news for the large outdoor events planned tomorrow (including U2 concert and Teddy Bear picnic)

The dry weather will be short lived however as a stronger storm system develops over the Northern high plains and into southern Manitoba by Monday. This will bring a more general rainfall across southern MB Monday into Tuesday, with 10-20 mm possible for Winnipeg and the RRV, and heavier amounts for 20-40 mm likely across southwest MB into the interlake areas. This, in combination with gusty north winds will bring additional high water and flooding concerns to the Lake Manitoba area, and will be yet another setback for area farmers who desperately need a prolonged stretch of dry and warm weather to accelerate seeding operations. Long range guidance is hinting at warmer weather moving in by the end of next week, that hopefully signals the start of a trend to more summerlike weather finally moving into southern MB.

Joplin.. a terrible reminder of what a violent tornado can do in an urban center..

The Joplin tornado disaster should serve as a wake-up call for us in the Prairies as to what an F4 or F5 tornado is capable of doing when it moves into a populated area. By strong tornado standards, the Joplin tornado was relatively short lived.. lasting only about 20 minutes with a track length of about 20 km (often, violent tornadoes can track 100 km or more and last 1 or 2 hours or more). But much of those 20 km were right over a densely populated and commercialized area of a moderately sized city, leading to the deadliest single tornado event in the US in over 60 years. Even with today's technology and advanced warnings, these violent tornadoes are not survivable unless you're in a reinforced shelter, or underground. Although rare, F4 or F5 tornadoes can and do occur in the Prairies. We're fortunate that we have a lot of open space that's sparsely populated.. but it only takes one violent tornado hitting a populated area to do what we saw in Joplin. F4 tornadoes have occurred in Regina and Edmonton, and an F5 tornado struck just west of Winnipeg in Elie in 2007. The odds are remote, but they're not zero. It can happen here..

Wet weather moving in over holiday weekend..

Beautiful summer like weather will continue through Friday in southern MB with sunshine and temperatures in the mid 20s. Unfortunately, it doesn't look like the nice weather will hold through the upcoming May 24 holidays as an area of low pressure over the southwest US tracks into the Dakotas and across southern MB over the weekend. This system will spread an area of showers and isolated thunderstorms into southern MB on Saturday which will continue Saturday night into Sunday. Rainfall amounts from this system will depend on how much convection fires up Saturday but preliminary guidance indicates 15 to 25 mm of rain is possible over portions of southern MB and North Dakota over the weekend. Rain from this system will move out Sunday night with drier but cooler weather for holiday Monday.

Great stretch of weather this week..

It looks like Mother Nature is making amends this week after delivering a prolonged stretch of cloudy, cool and damp weather last week. A large area of high pressure over southern MB has brought a gloriously sunny weekend to the province with temperatures ranging from 19C in the south to 25C in the north. This area of high pressure will move slowly eastward over the next few days maintaining sunny skies and temperatures in the low 20s over southern MB. The good news is that high pressure in the upper atmosphere over Manitoba will block weather systems from affecting southern MB through the entire week maintaining dry and warm weather through Friday.. welcome news for the ongoing flood-fighting efforts. There are indications that the weather will turn more unsettled over the May 24 holiday weekend with some shower activity moving in .. especially for the latter half.. but this is still a ways ahead to be more specific. Until then.. get out and enjoy the much overdue stretch of sunny warm weather!

Cool and unsettled rest of week.. turning sunnier and warmer over weekend into next week..

Cool and cloudy weather will dominate southern MB through Friday as a stubborn area of low pressure over NW Ontario circulates clouds and northwest winds over southern MB. As a result, temperatures will be some 10 degrees below normal for this time of year, which are now approaching 20C for daytime highs. Little additional precipitation is expected through Friday, although there may be some light showers or drizzle from time to time, with even a stray snowflurry possible Friday morning. The good news is that models are indicating a significant clearing tend for the weekend into next week, with temperatures warming to near or even above normal values next week. That will translate to temperatures in the 20s over southern MB along with more prolonged sunshine that we've been seeing of late, and gusty south winds at times, some welcome news that will help start drying out the excessively moist soil conditions over southern MB. We need it..

Unsettled weather moving in Sunday night.. showers and thunderstorms with locally heavy rain possible

Today's scattered shower and thunderstorm activity over the Red River valley was a prelude to what looks to be an active period of weather coming up over southern Manitoba. A strong storm system is forecast to move into South Dakota late Sunday which will draw up a moist and unstable airmass northward. Shower and scattered thunderstorm activity is expected to develop over North Dakota and move into southern MB by late Sunday into Sunday night. Some of the rain could be heavy at times with amounts of 15-25 mm possible over portions of southern MB by Monday morning, including parts of the Red River valley. This system will be slow moving and will continue to generate showers and scattered thunderstorms over the northern plains and southern MB Tuesday into Wednesday. Of concern will be rainfall over this period, as river levels remain high across southern MB. Since much of this rainfall will be convective in nature, it will be difficult to pinpoint which areas will receive the heaviest rain and how much at this point.. but stay tuned as this situation develops.

EC predicting a hot dry summer.. or are they?

Environment Canada's preliminary 3 month summer outlook was issued May 1st, garnering some enthusiastic media headlines across the country about how EC was proclaiming a hot dry summer across the country. Stock up on the sunscreen and invest in that inground pool! This summer will be a scorcher according to the headlines. Unfortunately, this was more media hype than reality when taking a closer look at what EC's summer outlooks were really showing..

The image to the left is the outlook map that caused all the excitement. It shows most of Canada glowing red.. like some great fireball had landed on the country and oozed red hot lava all over the country. Only the coasts would be spared from this glowing fireball of a summer, and an inexplicable patch of coolness over southern Hudson Bay. Well, if the map is mostly red, it must mean a hot summer, right? Well, not really.

Let's take a look at the more revealing probabilistic forecasts from the very same model output.

This chart breaks down the odds of a warmer than normal, near normal, and cooler than normal summer for country, in increments of 10% probabilities. It is a far more revealing product than the grossly simplified image above and tells us a lot more information. For example, this map shows that the far north has the greatest chance of seeing an above normal summer, while it's not as likely over the south. It also shows a greater chance of a "near normal" summer over Eastern Canada, and cooler than normal over the West coast. Everywhere else, it's a tossup. This is a very different interpretation from the original map which showed virtually all of Canada above normal. This more detailed chart is known as the probabilistic forecast, and is a far more valid product than the oversimplified and misleading deterministic product that is so misinterpreted by the media and public. Simply put, the deterministic map is a poor reflection of the probabilistic output from the climate models, and should not be taken at face value without consulting the probabilistic forecast for additional interpretation.

What about precipitation? Again, here's the simplified deterministic map given to the media..

Blue areas denote drier than normal, and red denotes wetter than normal (shouldn't the colour scheme be the other way around when talking about precipitation?) Note that the Prairies and NW Ontario are shown as wetter than normal, while the West Coast and the Arctic are drier than normal, as well as parts of Ontario. The probabilistic precipitation forecast is much more informative (as well as having a more logical colour scheme) showing near normal pcpn over much of the country, drier than normal over the Arctic, and wetter than normal over BC and Alberta. Again, a vastly different story than what the oversimplified deterministic forecast here shows. It should be noted however, that summer precipitation forecasts have little or no skill, (less than 35% accuracy as national average) which means they're pretty much useless over much of the country.

Put it all together, and the forecasts are actually pointing to near normal temperatures and precipitation for much of the Prairies.. hardly the hot dry summer being advertised.

So how are these long range seasonal forecasts produced? Seasonal 3 month outlooks are produced by the Canadian Meteorological Center's supercomputer in Montreal by running an ensemble of 4 global climate models initialized by weather patterns over the last 10 days of the month. The models run simulated weather patterns for the next 90-120 days, and an average temperature map for the country over that time period is produced. This temperature map is compared to "normal" temperatures for the country for that 3 month period, and the outlook map shows areas of warmer than normal , colder than normal or near normal temperatures according to the model ensemble. This outlook is totally model driven with no human intervention or augmentation whatsoever. Since it initializes with the last 10 days of weather patterns, long range outlooks are heavily weighted towards climate anomalies over the past couple of weeks. It does not take into account expected changes in ENSO patterns or other major climatic influences and as a result, the seasonal outlooks predictive skill is very low.

In contrast, seasonal outlooks from NOAA's Climate Prediction Center (CPC) incorporate expertise and input from human forecasters who have experience in long range climate patterns. As a result, CPC seasonal forecasts tend to be more realistic and more accurate. Even here though, predictive skill with seasonal outlooks is limited, with the best skill noted during major climate episodes like El Nino or La Nina. For what its worth, CPC is predicting a cooler and wetter summer over the Prairies this year (see image above), at least through June, with a trend towards warmer and drier conditions towards the latter half of summer.

So, still think we're going to have a hot dry summer?

Satellite image shows aftermath of weekend storm

The satellite image to the left from this morning shows the aftermath of this weekend's powerful winter storm that moved across southern Manitoba. The white areas reveal snow on the ground over much of southern Manitoba and southeast Saskatchewan. Heaviest snowfalls from this storm were observed over eastern SK into west central Manitoba where amounts of 30 to 50 cm were reported Saturday April 30th - Sunday May 1st, along with large drifts caused by 80-100 km/h wind gusts. (Darker forested areas of Riding, Duck and Turtle Mountains are clearly evident)

Note the secondary axis of heavier snow to the south of Lake Winnipeg that brought a swath of 5-10 cm of snow from northeast of Winnipeg down to the US border near Emerson during Sunday May 1st. Note also how this snow band reveals the extent of the Red River flooding to the south of Morris into northern ND, which shows up as a narrow band of dark patches amongst the snow covered terrain.

Sunny skies and temperatures warming up to 10 degrees today will melt most of the snow today, although snowfall in heaviest hit areas will take another day or two to disappear. Watch satellite loops to see how quickly the snow melts today..