Elsewhere in Weather News: May 5th, 2012

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

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

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

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