Elsewhere in Weather News: July 7th, 2012

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?

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.

One Last Shot at Some Rain

Another frontal system tracking across Southern Manitoba today will bring one last shot at precipitation before the sub-tropical high begins to edge northwards and push us back into a hot, dry pattern.

15Z GEM-REG Analysis

Analysis of the GEM-REG model for this morning. The red and blue lines represent warm and cold fronts, respectively.

A cold front that brough severe thunderstorms and numerous tornadoes to Saskatchewan yesterday will push across the Red River Valley late this morning into the early afternoon. What sort of weather we’ll see from this depends highly on how much sunshine we’re able to see beforehand.

A rather large MCS will slowly decay as it moves through SW Manitoba this morning on approach to the Red River Valley. Some uncertainty exists as to what this system will do, however, and the result is dramtically different outcomes.

The NAM wants to keep this system quite progressive and push it eastwards fairly consistently. Under this solution, we’ll see a cloudy morning with some showers and thundershowers pushing through late morning/early afternoon. There’s a chance that rain could be fairly heavy under some of the thundershowers. Westerly winds would build in this afternoon flushing out the moisture in the Red River Valley and returning us to much more comfortable dewpoints in the low teens.

The growing trend in allh the other models, though, is for this system to stall out for a while over SW MB / extreme western RRV. If this is indeed what happens, things could be a little more interesting. Should the sun be able to poke through even a bit, that heating combined with the high surface dewpoints (should be in the 20-23°C range tomorrow morning) would build our CAPE values into the 2000 – 3000 J/kg range. That, combined with good deep shear and a SE wind at the surface veering to SW aloft, could provide an environment favorable for strong storms. The main threats would be heavy rainfall due to the slow-moving nature of the system (this threat would be centralized over the Western Red River Valley), strong winds and large hail. Stronger winds pushing in on the backside could favor the development of a squall-line type feature, but if they’re late to the party, a few isolated supercells certainly aren’t out of the question.

My take on all this? I think we’ll see some middle-ground solution play out. I think we’ll have a chance at seeing a bit of sun this morning, and by late morning some showers and thunderstorms will start pushing through the RRV. One can’t ignore the potential that exists for strong convection, and in that regard I would agree with the SPC’s “See Text” analysis for ND into Southern MB. The potential is there, but I wouldn’t say it’s likely. I hope that many places across the RRV see some rain as this front comes through, because it may be our last chance for a while…

8-14 Day Temperature Anomoly Outlook

NAEFS 8-14 Day Temperature Anomoly Outlook. The large area of red over the Canadian Prairies indicates a high probability of warmer than seasonal temperatures through the 8-14 day time period.

After this system, the sub-tropical high will begin to build northwards again, pushing plenty of heat into Southern Manitoba. Daytime highs will remain in the high 20’s to low 30’s through much of the next 7-10 days, with nary a drop of rain in sight for the Red River Valley. After many places have gone two weeks without any measureable precipitation, perhaps not the best of news.

We’ll keep a close eye on the storms this morning and post updates in the comments as the system develops!

Staying Hot, Storms Possible

This week will start out right where last week left off – hot!

Monday's temperatures at 1pm

Temperatures at 1pm on Monday. The dark green colour represents temperatures between 30 and 35C.

Today will be another hot and humid day in Southern Manitoba. High temperatures are expected to be in the upper twenties, or possibly thirty degrees, with thunderstorms possible both in the morning and later in the day. There will some cloud and possible rain or thunderstorms during the morning from a decaying thunderstorm complex. The speed at which this complex clears the region will determine how hot it will get. The progress of this complex will also determine if there is a second round of storms on Monday afternoon and evening. If it stays cloudy all day with temperatures remaining low then it is unlikely that there will be a second round of storms later in the day. Based on current model guidance it does appear that the clouds will clear out in the afternoon, but there remains some uncertainty with this.

Tuesday will be hot once again, but somewhat less humid than Monday. Temperatures will be up near 30C, but thunderstorms are not expected.

Wednesday will be yet another tricky forecast. A cold front is expected to swing through Manitoba at some point on Wednesday, but it is not entirely clear when that will happen. If the cold front goes through in the morning the day will be warm, but not humid, with highs in the mid to upper twenties. However, if the front only goes through in the evening it will be hot and humid with the risk of severe thunderstorms. The details of Wednesday should become more clear over the next day or two.

You’ll probably be surprised to hear that more hot weather is expected to start July (hint, I hope you’re NOT surprised). Models point to continued hot weather for at least the next 7-10 days as we roll smoothly in the heart of summer.

A quick note…Myself and Matt will be chasing south of the border today! You can keep tabs on our progress using the twitter feed by clicking through below.

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