Nice Today, Then Showers & Rain

Brad Leave a comment

Winnipeg and the Red River Valley will get a bit of a reprieve from the unsettled weather of late today with some sunshine and daytime highs in the mid-teens for Winnipeg and closer to 20°C for regions in the Southern Red River Valley. Conditions will deteriorate tonight, however, as Southern Manitoba deals with another low pressure system that will move through on Thursday.

12hr. QPF -- GEMREG

12 hour precipitation accumulation from the GEMREG model. Valid 12Z Thursday to 00Z Friday.

Clouds and showers will push into the Red River Valley tonight as a low pressure system makes it’s way through North Dakota. A very slight risk for a thundershower exists along the US border, however the odds aren’t very likely. For everyone else, just plain old rain will be pushing your way. Models disagree on how far northwards the precipitation will push: the American models keep the northern edge on a line that cuts from Morden to Bisset, south of Winnipeg, while the Canadian models push the precipitation as far north as Gimli. It seems fairly certain that the southern half of the Red River Valley will see showers tonight and Thursday; Winnipeg will likely see at least a few passing showers out of this next system, with a chance that we’ll see rain tonight through much of tomorrow.

12 Hour QPF -- NAM

12 hour precipitation accumulation from the NAM model. Valid 12Z Thursday to 00Z Friday. Notice how the NAM keeps the precipitation much further south; whereas the GEMREG has Winnipeg in the highest accumulations of the system, the NAM keeps us on the Northern fringe of the rain with very little accumulation.

For areas that do see steady rain, total accumulations should be in the 5-10mm range with localized areas that see some convective enhancement seeing as much as 15-20mm. My current feeling is that Winnipeg will see at least 5-10mm through Thursday evening.

Rainfall in systems like this is typically hard to predict because it is so dependent on the initiation of elevated convection at night; something that models do not have a great handle on and humans struggle with not because we don’t understand it, but because there’s simply so little data to work with. Small errors in the location or strength of initiation of the nocturnal convection can result in huge errors in the model for later times, which can cause the model to end up forecasting tons of rainfall for one location that ends up seeing nothing and completely missing other areas that might see plenty of rain. For this reason, working off of real data is often the best way to go; satellite & RADAR imagery can be a forecaster’s best friend in dealing with nocturnal convection. A drawback to this, though, is that you can’t make your forecast as early. As soon as things begin to take shape, a forecaster can act quickly and make a fairly accurate forecast for the next 12-24 hours. It’s crucial to make sure that the starting point is correct, though, which is why when dealing with convectively driven situations, it’s important to talk in terms of probabilities and likelihoods while still a ways away from the event actually happening.

A Warmer, But Stormier, Week Ahead

Brad Leave a comment

After a spell of cool, uneventful weather, things are set to become a little more interesting this week. We’ll see temperatures close to 20°C many days, but it won’t be all sunshine as we’ll have to contend with a more active storm track that will bring multiple storm systems through our region. How rainy will it be, and when can we expect thunderstorms? Read on to find out…

850mb Temperatures for Monday Night

850mb temperatures on Monday night, valid at 09Z May 1st, depicting the sharp warm front aloft present over Southern Manitoba.

We’ll see a beautiful day today with highs right around 20°C for the RRV and a fair amount of sunshine with some clouds developing in the afternoon due to some lingering instability from yesterday’s system. A low pressure system tracking it’s way into Saskatchewan through the day will be lifting warm air northwards over Southern Manitoba, and by evening, a fairly strong warm front will exist aloft, running W-E through Southern Manitoba, with a cold front draped southwards from SW Manitoba to Wyoming. A 30-40kt LLJ will help thunderstorms trigger near the triple point in North Dakota, where additional lift will aid the jet as it overrides the surface warm front.

The triple point is the location where the warm front and cold front of a system intersect, signalling the location of the surface low or the associated occlusion. Triple points are an important feature in forecasting thunderstorms as they often are areas with enhanced lift and wind shear.

The first storms will likely fire in North Dakota and begin to lift into Southern Manitoba travelling NE with the upper flow, with more developing as they do so. Once more mature, the storms will tap into the convergence present aloft in a trough extending eastwards from the low heading into Saskatchwan and continue their way across Southern Manitoba. By morning, a line of thunderstorms present over Southern Manitoba will merge into a line of rain and showers extending all the way from SE Saskatchewan all the way back to the Rocky Mountains.

Thunderstorm Outlook for Monday Night

Thunderstorm outlook for Monday night (April 30/May 1).

The storms are not expected to be severe, however any regions that may see multiple thunderstorms training over the area could see in excess of 20mm of rain and cool temperatures aloft raise the possiblity of marginally severe hail (which, in Canada, is about the size of a nickel). Current indications are that the greatest risk for hail would be over the south-central RRV and back into the western RRV, from the US Border to near Carmen. Other than that slight risk, no severe weather is expected from the night’s storms.

Things will continue to lift northwards on Tuesday, however we may see some afternoon showers through the RRV as a secondary system tracks through the Dakotas. Temperatures will be warm, though, with daytime highs once again near 20°C despite the cloudy skies.

Wednesday and Thursday look nice, with more sunshine and highs continuing near 20°C with overnight lows in the mid to high single digits. A powerful system is forecast to track into the region on Friday bringing with it showers and thunderstorms. It’s far to early to say with any certainty where it will end up, but we’ll keep a close eye on it through the week and provide updates.

Elsewhere in Weather News

Suspected Tornado in UK Causes Damage

Britain’s dreadful spring continues to be plagued by extreme weather as flooding, very high winds and even a suspected tornado hit the Rugby area on Wednesday, April 25. Investigations are still underway, however, most evidence does point to a tornado. A path of destruction about a mile long through the neighbourhood could be seen – sheds tossed, a roof blown off – evidence that this was a tornado and not straight-line winds. More damage was reported where telephone lines had been snapped or torn down and roof tiles scattered across yards and roads. No injuries or deaths were reported but residents were in shock as only 30 tornadoes are reported yearly across the UK.
A separate incident occurred in Essex County where severe damage was caused to a barn and house, killing the 20 chickens inside. The farmer, who was outside at the time, got picked up off the ground and threw by what he described as a tornado swirling around him. Thankfully, he survived the ordeal.

Large Tree Down

Large tree down in Rugby as a result of the suspected tornado. (Source: Diane Slater)

Roof blown off house

Roof blown off a house in Rugby by suspected tornado. (Source: Sky News)

Destroyed Barn

Barn completely destroyed in Essex. (Source: Huntley/HVC)

Soggy April in UK

Britain’s odd weather doesn’t end there however. This past month, Britain has experienced very wet conditions, a big contrast from the extremely dry conditions experienced the past two winters. As restrictions are in place for water use because of the drought, UK is experiencing one of its wettest Aprils officially recorded. The main reason that they are still experiencing drought as this very soggy month moves on are for a couple reasons:

  • Spring/summer rainfall doesn’t refill aquifers (underground reservoirs of water).
  • Vegetation soaks up a significant amount of the rain that falls.
  • Downpours don’t reach very deep underground due to the hard soil on the surface, causing water to have trouble penetrating the ground and even worse, creating lots of runoff that leads to flooding.
    As of April 25th, the southern half of UK has placed 9th in all-time rainfall for the month of April since records began in 1910. With this being only 40mm off the record, they have a shot surpassing the old record before the end of the month as a strong system came ashore Saturday and is forecast to persist until at least May 1st.

UK Sat Image

On Sunday a very large area of low pressure could be seen off UK’s coast, bringing soggy conditions to most of the region. On Monday the low is expected to move slightly west, bringing another round of rain to the UK, perhaps dumping enough rain to reach the wettest April ever recorded. (Source: SAT24)

Elsewhere in Weather News is provided by Matt

Summer-Like Weather Set to Return

Brad Leave a comment

After a few days with below-normal daytime highs, a southerly flow is setting up to return early-summer warmth to Southern Manitoba; however, an upper trough will bring wet conditions to portions of Southwest Manitoba

Accumulated Precipitation from Thursday Evening to Saturday Evening

Total precipitation from Thursday evening through Saturday evening. Notice the sharp drop-off in precipitation amounts near the Red River Valley.

Under the influence of a strong arctic surface ridge, temperatures in Winnipeg have been 4 to 5°C below normal the past fews days. Fortunately, the low pressure system in Hudson Bay that has been blocking the ridge from moving out of our area is beginning to move off as it becomes caught up in a powerful storm system forecast to bring upwards of 50mm to portions of the Maritimes, including New Brunswick and Newfoundland.

However, as the ridge moves off, a large upper trough will continue its trek into the Prairies, pushing into Saskatchewan over the next 36 hours. Multiple shortwaves are embedded in the trough, with two main ones to watch:

  • One shortwave is lifting northwards from British Columbia and will track eastwards near the 60th parallel.
  • A second shortwave will track along the base of the trough into Eastern Montana/Western North Dakota before becoming cut-off and stalling out.

For today, a large area of precipitation will link the two shortwaves, but weaken later in the day as they move further apart and the overall lift weakens a little bit. As the line of precipitation moves eastwards into Manitoba, it will also have to battle with the dry air flowing out from the high over the eastern portion of the province. This should keep most of the rain out of the Red River Valley, with only a slight chance of a passing sprinkle this afternoon and overnight right along the Western Escarpment.

We should see mostly sun today and tomorrow, with daytime highs near 12°C. Sunday will mark the beginning of the big warm up as the southern shortwave, after stalling out over Eastern Montana for a day or two, heads our way. We should see temperatures climb into the upper teens on Sunday with a mix of sun and clouds before the system moves in overnight.

For next week, Moday looks showery but then skies clear out and we’ll have beautiful weather for most of the week with highs near 20°C.

Cool Weather Returns

Brad Leave a comment

After enjoying a couple days of above-normal temperatures, a powerful low pressure system backing into Hudson Bay will drive a cold front southwards across Southern Manitoba today, bringing with it cooler weather.

850mb Temperature Analysis valid 15Z this morning

850mb GEM-Reg Temperature Analysis valid 15Z this morning.

The cold front will sweep through Southern Manitoba late this morning, with winds picking up from the north and increasing to 30-40km/h. Scattered showers will develop along the front as it pushes through the interlake, so most regions in the Red River Valley have a chance of seeing some rain later this morning. It won’t last long, though, and cooler air will stream in on the backside limiting our daytime high in Winnipeg to around 11°C. Skies will clear quickly tonight as an Arctic ridge builds in and helps our overnight low drop to -4°C.

The aforementioned low backing into Hudson Bay will become captured today and will block the eastwards advancement of the Arctic ridge which means, unfortunately, that we’ll be under the influence of the ridge and its outflow for the next few days. Thursday will see sunny skies with a daytime high of only around 9°C, and Friday will be much of the same with a high just a couple degrees warmer. By Saturday it looks like the ridge will start to move off and although the day will still be cool, a southerly flow will begin to bring warmer weather back to our region.