Showers Today to Give Way to a Beautiful Week

Brad Leave a comment

A well-developed upper low will blanket the Winnipeg & the Red River Valley with showers today as it slides southwards into the Northern Plains. Its exit will leave room for an upper ridge to build in from the Pacific Coast, flooding the southern Prairies with some beautiful warm and sunny days.

GEMREG 24hr. QPF valid Tuesday morning

24 hour accumulated rainfall from the GEMREG model valid for Tuesday morning.

Winnipeg will see showers off and on today with a cool daytime high of around 13°C. Winds will be in the 20-30km/h range, starting out of the SW and switching to the NW this afternoon. Conditions will be similar through much of the Red River Valley, with temperatures generally between 12-15°C and similar winds. Showers will clear from north to south overnight, with only a slight chance of some lingering showers or drizzle through the Morder/Winkler, Altona & Gretna areas first thing tomorrow morning. In total, most areas in the Red River Valley, including Winnipeg, will see 4-8mm of rain by the time the showers clear out.

We’ll see sunny skies tomorrow through the entire Red River Valley, with highs from 12-15°C again and northerly winds from 20-30km/h. For the rest of the week, we’ll see a big warm up as mild Pacific air pushes into our area. Currently, it looks like Wednesday will have high temperatures near 20°C and Thursday will push even higher towards the mid-20’s. Things will cool off for the end of the week as a cold front pushes through and brings with it showers and a slight chance of thunderstorms across the Red River Valley.

Elsewhere in Weather News: May 5th, 2012

Matthieu Leave a comment

Editor’s Note: We’ve decided to move our weekly Elsewhere in Weather News from Monday’s post to it’s own post on Saturday mornings! We hope this will encourage a little more discussion in the comments about other significant weather and we feel that Matt has been doing a great job; since this “little segment” has become an interesting part of what A Weather Moment is, it’s only right to acknowledge Matt’s efforts and give him his own space! So without further ado, here is this week’s Elsewhere in Weather News, now on Saturdays!

Storms Run Rampant Across the United States

The SPC has had their hands full with severe thunderstorms across the Upper Mississippi Valley and most of the Midwest as the 2012 storm season gets into high gear as we enter the month of May. The strong storms have caused many power outages to several states, including Iowa and Minnesota. In addition to the dangerous gusts brought by these storms, tornadoes were spotted in Iowa on Thursday and in southern Minnesota on Friday. No injuries or deaths were reported.

Across most of the Midwest yesterday, storms ranging between strong to severe rolled through the area resulting in 163 large hail reports and significant flooding in some places. The line of storms crossed Lake Huron into Southern Ontario and dumped a quick 76mm of rain on Orangeville, Ontario –where the average rainfall is usually 75mm for the month of May. This deluge resulted in flash flooding which caused over $1,000,000 in damages to businesses and properties while forcing over a dozen people to be evacuated from their houses.

Storms near Orangeville

Infrared satellite picture taken at 6:45pm showing numerous storms around the time Orangeville got hit by the storm that caused the flash flooding. The colder the cloud top, the stronger the storm. (Source: Environment Canada)

On Friday afternoon an interesting sight could be seen associated with a thunderstorm rolling across Orange City, Iowa: a haboob, also known as a dust storm, was spotted crossing the city limits as the thunderstorm arrived. The haboob is created when a downdraft of a thunderstorm is strong enough to pick up dust and sand ahead of the approaching storm. As the dust gets picked up, a haboob forms and a wall of dust can be seen reaching as high as a couple kilometers into the sky. When the thunderstorm weakens and there are no more downdrafts, the haboob will either just settle or will become a “mud storm” if there is still rain falling that will combine with the dust particles.

Haboob in Orange City

Picture of the haboob entering Orange City (Source: Reed Timmer/TVN)

The best storm dynamics will stay in the High Plains for the beginning of the weekend, slowly shifting south and east as the weekend rolls along.

Cloudy With A Chance of Showers

Brad Leave a comment

A series of weak disturbances will bring more cloudy days for Winnipeg with a chance of showers across the entire Red River Valley overnight and through the weekend.

Total QPF for Friday Night

GEM-Global 12hr. QPF valid 00Z May 5 to 12Z May 5 (Friday night). Notice the relatively small amounts over Manitoba compared to the 2”+ rainfall accumulations near the North Dakota/South Dakota border.

A shortwave tracking northeastwards is pushing into Southern Saskatchewan this morning, supporting a band of rain in the associated trough over SW Manitoba. As this system pushes northeast, the upper-level support will weaken and the band of rain will begin to diminish and become more “shower-y”. As the weak upper trough passes through the Red River Valley overnight, an area of nocturnal convection will develop in southern North Dakota, centered around some slightly enhanced lift from a weak low pressure system.. Models want to initiate a band of showers all the way along the upper trough that will be positioned between the ND low and the SK shortwave; however, any showers that want to try and develop may have to contend against subsidence north of the nocturnal convection in ND. Should this happen, either the SK shortwave would need to track further south than currently forecast to provide enough lift to offset the increased subsidence from the storms or the storms would need to fire further south so that more instability remains over the RRV. Otherwise, we’ll likely see little to no precipitation in the Red River Valley tonight. Were I to produce a standard EC forecast, I’d say that the north half of the RRV has a 40% chance of showers tonight and the southern half of the RRV has a 60% chance of showers.

Another system is forecast to track through on Saturday night into Sunday, bringing with it another chance of showers for Southern Manitoba. Once again it’s a binary system: the band of precipitation will be supported by two shortwaves, one in Canada and one in the US. As the system moves into the Red River Valley, the northern shortwave pulls northwards and the southern shortwave slides SE a bit, resulting in a good chance that the main band of rain will split apart and miss much of the RRV with the northern half pulling into the Interlake and the southern half sliding into North Dakota.

Again, with these convective systems, forecasting is a challenge. Over the next few days, expect more cloud than sun, daytime highs between 10 and 15°C, and a chance of showers tonight, Saturday night and Sunday. We’ll be providing updated forecasts when possible in the comments below, so be sure to check them over the next couple days.

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.