Hottest Day of the Year to Give Way to Unsettled Weather

Brad Leave a comment

Winnipeg may see the warmest day of the year today as temperatures soar into the mid-30’s under the influence of an upper ridge and southwest wind. The upper ridge that has brought us our sunny weather will then be weakend by multiple upper disturbances tracking across the Prairies, bringing us a few days of more unsettled weather across Southern Manitoba.

850mb Temperatures for this afternoon.

850mb temperatures from the NAM for this afternoon.

A southwest wind, combined with significantly warmer temperatures under the upper ridge (around 22 or 23°C at 850mb) today will help Winnipeg’s temperature soar to a scorching 35°C if we can stick to sunny skies. Today will be the warmest day of the week, with temperatures returning to near 30°C for Thursday and Friday. Overnight lows will be mild with the temperature bottoming out at only around 19°C.

Several disturbances are set to track through the southern portion of the province beginning this afternoon/evening, which will bring us a risk of thunderstorms late this afternoon and this evening as well as tomorrow afternoon/evening. While some storm parameters will be significant given the heat, a distinct lack of wind shear will ensure that any storms that form will likely be relatively slow moving pulse-type storms. They may strengthen to severe levels, but they will likely be scattered and it will be quite hit and miss as to who sees them and who doesn’t. The main threat from the storms would be large hail and heavy rain. Strong winds area also a possibility. Extremely weak wind shear will likely preclude the development of tornadoes, but it’s important to remember that any thunderstorm has the potential to produce a tornado; some are just more likely than others.

Things clear up a bit for Friday (although a few hit and miss storms are possible through the Red River Valley) before another system pushes in for the weekend and we’ll see more significant chances for thunderstorms return.

Surprise! More Hot Weather

Brad Leave a comment

This week will be another hot one in Southern Manitoba and indeed all over Western Canada. The potential for thunderstorms during the week may temper the heat somewhat.

A large ridge of high pressure will reside over Western Canada this week

A large ridge of high pressure will reside over Western Canada this week

The weather forecast for this week will be rather tricky. What we do know for sure is that it will be hot all week, with high temperatures being near 30C every day. However, what is somewhat unclear is the risk of thunderstorms during the week. Let’s start with the easy part – the heat.

Temperatures will start out the week in the upper twenties or near thirty on Monday and Tuesday in Southern Manitoba. Humidity levels should remain low on these day making conditions hot, but not excessively so. By Wednesday high temperatures should be be in the low thirties with the humidity making it feel closer to 40. It currently appears that temperatures for late week will remain around the 30C mark, with humidity levels remaining elevated.

A shortwave will move toward the Eastern Prairies on Wednesday, potentially helping to trigger thunderstorms

A shortwave will move toward the Eastern Prairies on Wednesday, potentially helping to trigger thunderstorms

The presence of heat and humidity over the Prairies this week will cause the atmosphere to become unstable, creating the risk of thunderstorms on many days. Unfortunately, the thunderstorm forecast is not entirely certain. The issue is that a large region of high pressure, such as the one we’ll be under, does not typically promote widespread thunderstorm activity. In fact high pressure usually suppresses convective activity. It looks like this ridge will not be very good at suppressing thunderstorms, which complicates the forecast significantly.

At this point it looks most likely that Southern Manitoba will see thunderstorms mainly during the second half of this week, from Wednesday onward. During that time period the atmosphere will be most unstable and there will be some weather features moving through the region which may trigger storms. The jet stream has weakened significantly over the Prairies as of late, meaning that most storms will be non-severe in nature. Heavy rain will likely still be a concern though due to slow storm motion. Some severe storms will also be possible just simply due to the instability present in the atmosphere. Although stronger storms will certainly be less widespread than weaker ones. As the week progresses we’ll have to reassess the thunderstorm risk one day at a time.

While my forecast for this week might seem a bit equivocal, that will just be the nature of the weather in the short-term. Unfortunately thunderstorms are just simply unpredictable a frustrating but unavoidable aspect of mother nature.

Elsewhere in Weather News: July 7th, 2012

Matthieu Leave a comment

Devastating Derecho Races Across US States

An extremely powerful storm raced across part of the Midwest and Atlantic region the night of Friday, June 29th and into Saturday, shutting down power to millions of people. The type of storm, called derecho (pronounced day-RAY-cho) is a severe thunderstorm that produces severe wind gusts –downbursts that can produce a large swath of damage in a short amount of time. In addition to the wind threat normally associated with this type of storm, the intense lightning also poses a great danger to residents.

Time lapse video of the derecho trekking across the Midwest and Atlantic states. (Source: NOAA/NASA)

On this occasion, the derecho moved over 10 states and traveled for over 24 hours before reaching the Atlantic Ocean. Over three-and-a-half million people in the Midwest and Atlantic states were without power following the event. Boundless amounts of trees were uprooted, electrical poles taken down, and mobile homes that flipped, could be seen throughout the storm’s path. In all, 27 people lost their lives due to the storm. Hundreds of others were injured. In the storm’s aftermath, searing heat moved back into the region inciting more deaths as heat stroke became a major concern with no electricity to work with. As of Thursday night, July 5th, almost one week since the event passed through these states, there were still a quarter of a million people without power, mostly people north of Washington DC. Many cooling shelters had to be put in place across the area. Heat and humidity advisories were posted, urging residents to limit time spent outdoors to no more than a half-hour at a time. Some cities even cancelled July 4th celebrations due to power outages and excessive heat.

Wind damage

Just one of the many pictures taken of wind damage in the Washington, DC area, product of the derecho. (Source: Associated Press)

The tremendous heat and humidity is expected to stay in place throughout most of the eastern US where 3,000 temperature records were already broken this week, as of Thursday. There is a chance of relief from these extreme conditions next week, as a cold front is forecast to slice its way in a southerly motion through the Midwest and Atlantic states.

Heat warnings

Heat advisories in orange and excessive heat warnings in purple scattered across the Midwest and Atlantic states. On Friday the 6th of July, even a larger area was covered in warning and advisories. (Source: National Weather Service)

Powerful Storm Hits Bemidji

On Monday July 2nd, a few AWM team members headed down to Fargo to chase supercells. The targeted supercells quickly became a cluster of severe storms as they moved into Minnesota. Shortly afterwards, the cluster merged into a bow echo segment, which is very similar to a derecho but smaller in size. Locally, significant damage, similar to what was observed in the Midwest, was reported in Bemidji with the passing of this storm. One boater died as his vessel capsized due to the severe winds and torrential rains. Many trees over 100 years old and power lines snapped easily in the storm’s path, causing widespread power outages locally, in Central Minnesota. Because of all the damage and not much time to tend to downed power lines, the city issued a curfew to residents on Monday night from 11:00 pm to 6:00 am. The Storm Prediction Centre had warned of a bow echo in the days before the event, stressing the severe wind potential. Weather in Central Minnesota this weekend will be similar to Southern Manitoba’s, perhaps a little warmer.

Bemidji storm

Picture of the back side of the storm as it approaches Bemidji, taken north-east of Fargo in Minnesota. (Source: AWM chase team)

More Showers Than Thought?

Brad Leave a comment

A few systems are expected to bring chances for showers and thunderstorms to Southern Manitoba over the next few days as the upper ridge takes a few days longer to build in than previously thought.

30-Day Rolling % of Normal Precipitation for the Canadian Prairies

30-day % of normal precipitation for the Canadian Prairies. This map depicts the increasing drought conditions over much of the Red River Valley, with most areas only seeing only about 60% of the normal amount of precipitation over the last 30 days.

Offering a slight bit of relief to the dry conditions over the Red River Valley, an area of rain blossomed in North Dakota overnight and has pushed into Southern Manitoba this morning. Amounts are generally expected to be between 5-10mm along the International Border with amounts dropping off quickly to the north. This system will push into NW Ontario by late morning and skies will clear out behind it. Under sunshine our temperatures will soar to nearly 30°C in the afternoon.

The subtropical ridge that was previously progged to push into the Southern Prairies has instead decided to stay more or less where it was for a few extra days, which will leave us with a more zonal flow through this weekend. Fortunately, this means that we’ll have more chances for precipitation than previously thought.

The next chance for rain will come on Saturday afternoon/evening as a shortwave that will move across Saskatchewan today slumps southeastwards across the Interlake and Red River Valley. A couple showers and thunderstorms are likely to fire up underneath the shortwave as it crosses the RRV in the late afternoon. Currently all the convective parameters look to be fairly middling, so I don’t expect any severe weather to occur. Saturday will have a daytime high of 28°C before clouds move in in the afternoon. The low on Saturday night will be around 15°C.

Sunday should be a sunny day with a high near 28°C.

The next chance for rain will be Monday night as a shortwave slumps down the upper ridge that will build into the Western Prairies over the weekend. After that, it looks like the ridge will continue building into the Eastern Prairies, bringing us sweltering hot temperatures ove 30°C by the end of next week.