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The Manitoba Co-operator | June 14, 2012
WEATHER VANE
Weather now for next week.
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A W IND FROM THE SOUTH H AS R A IN IN ITS MOUTH.
An active weather pattern continues Issued: Monday, June 11, 2012 · Covering: June 13 – June 20, 2012 Daniel Bezte Co-operator contributor
D
e p e n d i n g o n w h e re you are in the province, last week’s forecast was either right on the money or off by a little bit. We saw the heat until Thursday as predicted, but over the weekend some regions saw nothing but rain and thunderstorms, while other regions saw only a little bit of rain and plenty of partly cloudy skies. By the start of the week the forecasted call for a cool, blustery day panned out, just a day earlier than expected. For this forecast period it looks like the unsettled weather will continue. After the cool, wet start to the week, temperatures should warm back into the low 20s for highs by Wednesday, and these mild temperatures should last right through this forecast period. Low pressure will slowly build to our west during the week and this low will help pull up the mild air, but along with the warmer air will come increasing moisture and the chances for showers and thundershowers almost
every day. By the weekend part of this western low looks like it begins to push east, bringing a bit more cloud along with more chances for showers or thunderstorms. Next week looks like it will start off with an upper trough of low pressure sitting just to our west. This will keep temperatures fairly mild as we see a continued southerly flow along with a mix of sun and clouds. This western upper trough of low pressure looks like it will stay in place for much of next week, kicking out pieces of energy every couple of days. This will result in temperatures remaining in the low 20s for highs, with overnight lows in the low to mid-teens. It also means we’ll see partly cloudy skies on most days and will likely see the chance for the odd shower or thunderstorm just about every day. Usual temperature range for this period: Highs, 19 to 29 C; lows, 7 to 16 C. Daniel Bezte is a teacher by profession with a BA (Hon.) in geography, specializing in climatology, from the U of W. He operates a computerized weather station near Birds Hill Park. Contact him with your questions and comments at daniel@bezte.ca.
WEATHER MAP - WESTERN CANADA
Precipitation Compared to Historical Distribution (Prairie Region) April 1, 2012 to June 7, 2012
Record Dry Extremely Low (0-10) Very Low (10-20) Low (20-40) Mid-Range (40-60) High (60-80) Very High (80-90) Extremely High (90-100) Record Wet Extent of Agricultural Land Lakes and Rivers
Produced using near real-time data that has undergone initial quality control. The map may not be accurate for all regions due to data availability and data errors. Copyright © 2012 Agriculture & Agri-Food Canada Prepared by Agriculture and Agri-Food Canada’s National Agroclimate Information Service (NAIS). Data provided through partnership with Environment Canada, Natural Resources Canada, and many Provincial agencies.
Created: 06/08/12 www.agr.gc.ca/drought
This issue’s map shows the total amount of precipitation that has fallen across the Prairies so far this spring compared to historical averages. After a prolonged period of dry weather it appears our wet spring weather has once again returned. A good portion of Alberta, nearly all of Saskatchewan, and western parts of Manitoba have seen very to extremely wet conditions with a few locations reporting record-wet conditions.
Severe summer weather: Wind
Straight-line winds, which form out of a thunderstorm’s downdraft can cause significant damage By Daniel Bezte CO-OPERATOR CONTRIBUTOR
W
ith the return of summer-like heat last week we also saw the return of severe summer weather. Plenty of thunderstorms rumbled across the Prairies, bringing examples of all of the different types of severe weather we can expect to see. There was plenty of lightning, hail, some really strong winds, heavy rains and, last but not least, a few possible tornadoes! So far this year we’ve discussed lightning and hail, which means we only have three severe weather phenomena left: heavy rain, strong winds and tornadoes. Probably the most life-threatening form of severe summer weather is strong winds. Most people associate strong thunderstorm winds with tornadoes. In reality, tornadoes only account for a very small percentage of wind damage caused by thunderstorms, but when tornadoes do occur, the damage is usually truly incredible! Before we start to discuss thunderstorm winds, I have a little bit of an issue I need to get off my back. I decided to take an
extra-long weekend and head out camping for a few days. Knowing I would be “off the grid” and not able to check out radar images and other near-real-time weather information, I checked the weather in detail before I left, then relied on good old radiobased weather forecasts. Well, I’m not sure who I should be more upset with: Environment Canada coming up with radi-
After thinking about it over the past couple of days I’ve become more and more upset with the quality of the weather forecasts put out by radio stations. Now I know I should have had a weather radio with me, but I didn’t, and to tell the truth, I’m not sure if I would have been close enough to the nearest station to pick up anything. What has got me
Falling rain pushes and pulls the air along with it, and when it hits the ground it has to spread out.
cally different forecasts every six hours, the poor weather information given out by radio stations, or myself for not being able to read the weather better. Needless to say, when it was supposed to be sunny or partly cloudy it was raining with thunderstorms, and when it was supposed to be raining with thunderstorms it was sunny to partly cloudy. All in all, it was a tough camping trip weather-wise.
upset about the radio weather reports is the fact that most radio personalities have no idea about the weather and if they simply read Environment Canada’s forecast, that would be OK (they’re not the best as it is, but I won’t go there), but instead they tend to “clip” the forecast and make it shorter, leaving out what they don’t think is important information in order to keep it short and
concise but often missing key pieces of information. OK, I feel a little better now, back to the topic of thunderstorms and wind.
Push and pull
To start our discussion about wind and thunderstorms we need to realize there are two types of destructive winds: straight-line winds and tornadoes. We will discuss tornadoes in the next issue. So let’s take a look at what causes straight-line winds and in which part of the thunderstorm we tend to find them. To understand where these straight-line winds come from you first have to remember how a thunderstorm forms. A storm forms when warm air rises, lifting tonnes of moisture into the air; this moisture then condenses and forms raindrops that eventually fall back to the ground. Now, if you have ever been near a hose spraying water, you know the spray of water pushes the air around it along with it, and the same thing happens within the thunderstorm. The falling rain pushes and pulls the air along with it, and when it hits the ground it has to spread
out. The spreading out of these downdrafts of air in a storm can create some very strong winds, especially when different downdrafts collide and merge together. Winds from these downdrafts can be as strong as 90 kilometres per hour, but are typically in the 50- to 70-km/h range. We often see this type of straight-line wind out in front of a thunderstorm and it can often be seen by the accompanying cloud wedge or roll cloud produced by these strong winds. These downdrafts can also tap into very strong winds high up in thunderstorms. Large, strong thunderstorms often have jet streaks associated with them. These are similar to jet streams in that they are rivers of fast-moving air and these jet streaks are often helping to fuel the storms. Within the thunderstorm, when a strong downdraft occurs, it can hit this jet streak and basically force it to the ground. This very fast-moving air then fans out along the ground just like a regular downdraft, only in this case, producing winds in excess of 100 km/h. It’s these straightline winds that tend to produce the most damage. Next issue: Tornadoes!