Tag: dry

September Marks a Return to Seasonal Weather

Brad Leave a comment

September closed out with a few beautiful days, bringing a month that had a bit of a cool start back to seasonal conditions. As for whether Winnipeg continued it’s 14-month above normal streak, that depends on which average you use. If you’re partial to the 1971-2000 means, then yes, we’ve extended the streak to 15 months. If you use the 1981-2010 means (which are the ones we use here at AWM), then unfortunately, our streak has come to an end.

September 2012 Summary

2012 Departure from Normal Temperature, with Year-to-Date mean

2012 departure from normal (or monthly anomaly of) temperature. The year-to-date mean is also plotted.

September 2012 closed out with an average temperature of 12.6°C, 0.28°C below the the 1981-2010 normal of 12.9°C. At -0.28°C below normal, the month of September ended Winnipeg’s above-normal streak at 14 consecutive months1. The warmest day in September 2012 came near the end of the month on the 29th when the mercury climbed to 29.6°C, a mere 0.4°C off the record for that day of 30°C set in 1905. No new daily high record temperatures were set this September. The coldest night was the night of September 22/23 when the mercury dropped to -7.1°C. This broke the previous record low for that night of -6.1°C set in 1879 and was 1.2°C off the record coldest night in September of -8.3°C, set on September 29, 1899. In total, just the one record low temperature was set this September.

2012 Departure from Normal Precipitation, with Year-to-Date total

2012 departure from normal (or monthly anomaly of) precipitation. The year-to-date total is also plotted.

September continued the significant precipitation deficit when compared to the normal. Usually we see about 48mm2 in September, but this year we saw a mere 4mm of precipitation. Receiving less than 10% of our normal rainfall for the month continues the precipitation deficit to 4 consecutive months in Winnipeg.

In other miscellaneous September statistics:

  • We finished the month with 0 days above 30°C, but 7 days at or above 25°C.
  • September 2012 did not break the top 50 warmest Septembers on record.
  • Despite our practically non-existent precipitation for the month, we still nearly quadrupled the record driest September of 1948, where only 1.3mm fell.
  • Our 4mm precipitation total for the month was only 2.5% of the precipitation that fell in the record wettest September of 1872, when 156.2mm fell.

2012 So Far

Year-to-Date Temperature Anomalies for Winnipeg, MB

Year-to-date temperature anomaly, by month, for 2012 (red) compared to the other 139 years on record for Winnipeg, MB, with the five warmest years (orange) and five coldest years (blue) noted.

As mentioned before, September’s deviation of -0.28°C from normal has brought an end to the above-normal conditions of 2012. Until September, every single month this year had been above-normal. Looking again at our Winnipeg temperature anomaly climatology, we can see that despite our slightly below-normal September average, we’ve managed to still remain the most above normal (by a hair) that we’ve ever been. Things still look to be on track for us to end up in the top 5 warmest years ever and we’ll keep updating each month to see where we end up.

Rest of 2012

As mentioned last month, sea ice in the Arctic is at a record low, which while it hasn’t prevented us from getting the odd cold outbreak, still looks to have the potential to reduce the strength/onset of the Hudson Bay arctic vortex that sets up and maintains a cool, northwest flow over the Eastern Prairies. While a month ago it also looked like El Niño was going to help us possibly see a warmer-than normal winter, over the past couple weeks the El Niño signal in the Eastern Pacific has significantly weakened. This means that any large-scale hints towards what sort of winter we’ll see are becoming rather muddled and no strong signal currently exists.

  1. Based on 1981-2010 normals. Winnipeg sits at 15 months above normal if using the 1971-2000 normals. ↩
  2. The normal precipitation for September is 47.6mm. ↩

August Continues Winnipeg’s Heat Streak

Brad Leave a comment

August closed out with another 30°C+ day, rounding out what ended up being another above-seasonal month, continuing Winnipeg’s above normal temperature streak to 14 consecutive months.

August 2012 Summary

2012 Departure from Normal Temperature, with Year-to-Date mean

2012 departure from normal (or monthly anomaly of) temperature. The year-to-date mean is also plotted.

August 2012 closed out with an average temperature of 19.2°C, 0.51°C above the normal of 18.7°C. At +0.51°C above normal, the month of August ended as the closest-to-normal month so far this year; the next closest was May which ended at 0.8°C above normal. The warmest day in August 2012 occurred on August 29th, where the mercury soared to 35.4°C, just shy of that day’s record of 36.1°C set in 1972. No new daily record high temperatures were set this August. The coldest night this August was on the night of August 18/19th where the temperature dipped all the way down to a chilly 4.5°C. This was well above August’s record low temperature of –1.1°C set in 1888. New new daily record low temperatures were set this August.

2012 Departure from Normal Precipitation, with Year-to-Date total

2012 departure from normal (or monthly anomaly of) precipitation. The year-to-date total is also plotted.

August ended with a significant deficit of precipitation compared to normal. Usually we see close to 80mm[1] of precipitation, however this month we saw just 44mm. This continues the Winnipeg’s precipitation deficit to 3 consecutive months.

In other miscellaneous August statistics:

  • We finished the month with 6 days at or above 30°C.
  • August 2012 ended up as only the 45th warmest August on record.
  • The greatest precipitation event this august was 23mm on August 4.
  • This month’s precipitation accumulation of 44mm pales in comparison to the record wettest August that occurred in 1985, where Winnipeg received a whopping 218mm of rain.
  • We quadrupled the record driest August’s (1915) total precipitation amount of 10mm.

2012 So Far

As mentioned before, August’s deviation from normal temperature of 0.51°C has continued the above normal trend for 2012. Every single month this year has been above normal temperature-wise and August marks the 14th consecutive month of such weather.

September 1st marks the start of meteorological fall, so we can take a quick look at Summer[2] 2012. Temperature-wise, we ended up as the 14th warmest summer, although it was an extremely close race…

Top 15 Warmest Summers on Record
Year Average Summer
Temperature
1 1988 21.0°C
2 1983 20.6°C
3 1961 20.4°C
4 1955 20.2°C
5/6 1930 20.1°C
5/6 1963 20.1°C
7/8 1933 19.9°C
7/8 1995 19.9°C
9 1991 19.87°C
10/11/12 1919 19.83°C
10/11/12 1921 19.83°C
10/11/12 2006 19.83°C
13 1936 19.767°C
14 2012 19.761°C
15 1932 19.7°C

If you round to tenths, then there is a 5-way tie for 10th place, however looking closer, we can see the finer details and sort things out.

Year-to-Date Temperature Anomalies for Winnipeg, MB

Year-to-date temperature anomaly, by month, for 2012 (red) compared to the other 139 years on record for Winnipeg, MB, with the five warmest years (orange) and five coldest years (blue) noted.

Looking again at our Winnipeg temperature anomaly climatology, we’ve added in August of this year, and we can now see that we are the most above normal that we’ve ever been. While we were chasing 1987 last month, with August’s +0.51°C temperature anomaly we’re now 0.25°C above 1987’s August YTD anomaly. At this point, it’s pretty much guaranteed that 2012 will end upon the top 5 hottest years on record, it’s just a matter of where exactly we end up.

June, July and August all had below-normal amounts of precipitation which has left us with a 118mm deficit for the summer months. Typical summer rainfall is 247.5mm, which puts this summer at only 52% the normal amount of precipitation. This is a troubling trend; 2011 placed as the 5th driest summer on record, and 2012 managed to sneak into the top 10:

Top 10 Driest Summers on Record
Year Summer Rainfall
1 1929 76.7mm
2 1886 77.2mm
3 1961 91.0mm
4 2006 91.5mm
5 2011 93.0mm
5 1889 96.0mm
7 1894 97.1mm
8 1915 114.8mm
9 1936 121.4mm
10 2012 129.5mm

Due to our wet spring, however, we’re “only” 67mm below our normal precipitation amounts on the year so far.

The Rest of 2012

While seasonal forecast have very little skill, there are a few things that can give us an idea of how the rest of the year is going to shape up. With Arctic sea ice at a record low, it will take longer than normal to establish a pool of cold Arctic air. In particular, the delayed onset of ice over Hudson Bay can inhibit the development of a true Arctic vortex over the area. This feature sets up a strong NW flow over the NWT and eastern Prairies and is often responsible for the advection of Arctic air southwards into the Prairies and Northern Plains. The inhibition or absence of this feature means that, while cold outbreaks can never be ruled out, it’ll be much more difficult for the cold air to actually stick around.

Another feature to keep an eye on is El Niño, the feature responsible for bringing warmer waters to the eastern equatorial Pacific. When El Niño is weak, it’s effects can be limited to areas further west in the Prairies[3], however in moderate-to-strong El Niño events, Southern Manitoba will often see warmer-than-normal winters. In weak-to-moderate events, precipitation can be increased over the region as the storm track cuts through the area, but in stronger events, the storm track is often to our north and Winnipeg enjoys relatively warm, dry winters in a bit of a no-man’s-land in the middle of a strong split upper flow.

That being said, it’s quite likely that the onset of winter will be delayed due to the delay in development of a pool of cold Arctic air, and it’s all but guaranteed that 2012 will go down as one of Winnipeg’s warmest years on record.

  1. August’s 1981–2010 normal precipitation amount is 79.4mm.  ↩
  2. Meteorological summer runs through June, July and August.  ↩
  3. British Columbia and Alberta, mainly. Saskatchewan marginally.  ↩

Warm, Dry Weather To Continue; Fire Risk To Remain High

Brad Leave a comment

Warm weather will continue over Southern Manitoba this week which, while great news for those of us who enjoy summer-like weather in May, will continue to sustain dangerous fire risk conditions. This news is not welcome to firefighters who are already battling two substantial fires: a 1,300 hectare fire southeast of Steinbach and a 200 hectare fire near Piney, MB.

Bush fire burning near Whitemouth Lake

Wildfire burning near Whitemouth Lake. This is one of two large fires crews are battling to contain in southeast Manitoba. Photo credit: Anonomous CJOB Listener

Hot, dry weather is expcted to continue today as Southern Manitoba continues to be flooded with a mild, Pacific flow. We’ll see a daytime high today of 28°C with winds once again out of the west/southwest at 30-40km/h with gusts up to about 50km/h. Dewpoints will remain in the low single digits, which will continue to challenge crews as they try to contain the wildfires.

A cold front will sweep through this evening, however one would be challenged to notice. Winds will shift to the north, but we’ll see overnight lows similar to before as the temperature dips to only 8°C tonight. Very little cloud is expected with this moisture-starved cold front over the Red River Valley, let alone any chance of precipitation. There is a slight chance of a shower or thundershower over the Whiteshell, however if they occur they will be short-lived and produce little rainfall accumulation. It looks like the best chance for any showers is on the Ontario side of the border.

If you enjoy sunshine, the rest of the week will be right up your alley. Temperatures will hover in the low 20’s for Tues/Wed. before a warm front pushes over S. MB and pushes temperatures up into the mid-to-high 20’s for Thursday and Friday. It looks like there may be a chance of showers or thunderstorms as the warm front pushes in on Thursday, however it currently looks like the best support will remain in North Dakota, leaving us with some clouds, but no precipitation. The biggest change with Thursday’s system will be the switch from a Pacific flow to a Gulf flow, which in addition to warm temperatures will also bring moister air to the area, which should lessen the fire risk somewhat.

Pacific Flows vs. Gulf Flows

These two flows are large-scale weather patterns that dictate where the air is coming from and, especially here in Southern Manitoba, are two of the main large-scale flows we deal with in the summer months. Those two words carry with them significant information about the weather and one can make a quick assesment of what sort of weather to expect if you have a basic understanding of the differences.

Pacific Flow Diagram

Diagram of a Pacific flow. Image is from the GEMGLB model, valid this morning.

First, the Pacific Flow. This is what Southern Manitoba is under right now. This flow occurs when there’s a large blocking high over the western United States. Moist Pacific Ocean air flows NE up and over the high and associated ridge into the NW United States and British Columbia (represented by the green arrows in the diagram above). Once it reaches the mainland, it begins to rise up and over the mountains. As the air rises, it cools and water is forced out of it, falling as rain or snow on the upwind side of the mountains (represented by the shaded green area above). Once it reaches the other side of the mountains, the air descends downwards, warming as it goes. What’s left on the leeward side of the mountains is air that’s warmer than it was when it started it’s trek over the rocks, but substantially drier. This air then spreads eastwards over the Prairies (represented by the brown arrows above), bringing pleasantly warm weather, but very dry and often windy conditions as well, usually with dewpoints in the single digits.

Gulf Flow Diagram

Diagram of a Gulf flow. Image is from the GFS model, valid Thursday evening.

A Gulf Flow also brings very warm conditions to Southern Manitoba as well, however it does so not through trickery of thermodynamics, but rather through brute force. This flow develops when a longwave trough is present over the west coast of the United States (as opposed to a ridge). The flow in the lower atmosphere organizes itself to flow from south to north in response, and heat and moisture from the Gulf of Mexico begins its trek up through the Plains of the United States. The longer this flow can stay in place, the further north the heat and moisture can travel; Southern Manitoba usually ends up under the influence of this air mass at least a couple times each summer. What characterizes this air mass? Hot weather, usually in the upper twenties, though often in the low-to-mid 30’s, and high dewpoints, often at least 18°C, but commonly in the 20-24°C range.

Under the influence of a stifling gulf flow, Carman, MB set the record for the highest Humidex value (a ‘feels-like’ for heat) ever recorded in Canada in 2007. On July 25, 2007, the temperature climbed to 34°C with an unbelievable dewpoint of 30°C, which produced a Humidex value of 53, beating out the old record of 52.1 set in Windsor, ON in 1953.

It’s always a good idea to keep an eye on the forecasts when under the influence of gulf flows; given the transport of so much heat and moisture, it is under the influence of these flows that we often see the risk for powerful thunderstorms.

Dewpoint vs. Relative Humidity?

You may notice that we often refer to the dewpoint on our blog, and not to the more commonly used term, Relative Humidity (RH). What’s the difference? There are several:

  • The dewpoint is an absolute measurement. Relative humidity is, obviously, relative.
  • The dewpoint is reported in °C, and is a measurement of how much water is contained in the air. Relative humidity is reported in % and is a measurement of how much of the water-bearing capacity of the air is being used. As air becomes warmer, it can hold more water.
  • The easiest way to understand the dewpoint is simple: how cold would something have to be so that when you put it out in the open air, it would “sweat”.
  • When dewpoints are low, the air has little moisture in it, and when they are high, it has more water in it. People often notice the moisture in the air once dewpoints reach around 12-13°C. Once they exceed 16-18°C, many people would actively notice that it was humid, and once the dewpoint exceeds 20°C, many begin to find it uncomfortably humid.
  • Conversely, one cannot make any absolute claim with a relative humidity measurement alone, nor does the RH actually let you know if it’s humid or not. A RH reading of 100% only means that the air is holding as much water as it can. There are two major problems with this. The first is that the RH changes through the day, even if the amount of water in the air (the dewpoint), does not. If the day starts off at 8°C with a dewpoint of 8°C, the RH is 100%. If the dewpoint stays at 8°C but it warms up to 21°C, the RH drops to 43%, despite the fact that there’s no more or less moisture in the air. The RH would then climb back towards 100% in the evening as the air cools. The second problem is that a RH of 100% can be extremely deceptive. If the temperature is 30°C and the RH is 100%, one could barely spend any time outside it would be so unbearably humid. Fortunately, this situation is extremely rare. If the temperature is -25°C and the RH is 100%…well it’s certainly not humid out. In fact, RH values are often quite high in winter since as the air cools, it can hold less water, so it uses more of it’s water-carrying capacity with smaller amounts of water.

All that to say that RH is a pretty messy, inconsistent measurement that when presented by itself doesn’t actually tell you much about anything. Dewpoint, on the other hand, is a consistent measurement that quantifies how much water is actually in the air and can tell you something about the weather when presented by itself. And that’s why we prefer to use dewpoint here on AWM.

Dry Streak Finally Over

Brad Leave a comment

In a new post over at Rob’s Blog, Rob describes exactly how dry it has been this summer in Winnipeg. I recommend you head over and read it, but the highlights are:

  • This summer the CYWG airport site recorded 93.0mm of rain from June to August.
    • This value is over 140mm below average
  • This year was the driest summer since 2006, when only 91.5mm of rain was recorded.
  • Southwest Manitoba and the Southern RRV experienced near-normal amounts of rain while the Northern RRV and Eastern MB experienced the dry conditions this summer.
  • This summer was the 5th driest summer on record.

Be sure to head over to Rob’s Blog to see the whole post and some more details on this summer compared to climatology. All in all, if you enjoy the sun, this summer in Winnipeg has been the summer for you!

The hot and dry weather came to an abrupt end early Thursday morning when Winnipeg received ~20mm of rain as a large complex of thunderstorms rolled through Southern Manitoba, giving large amounts of rain and winds as high as 110km/h over portions of extreme Southern MB. After a day of sun with much cooler temperatures, Winnipeg is set to likely receive another round of showers tonight. Read on to find out what’s in store!

18:15Z Water Vapor Image
Water Vapor (7µm) Image of Canada from 2:15PM CDT. L – Low; Blue Line – Cold Front; Red Line – Warm Front; Green Arrows – Expected Track of Low

A moderately strong upper low is tracking southeastwards across the Prairies today and will slump to the International Border near Melita by late this evening and then slide east along the border, crossing over the RRV overnight. A frontal wave associated with this system will mirror its parent’s motion and slide along the same track ahead of the system, arriving at the western edge of the RRV by early-to-mid evening.

6 Hour QPF from GEM-REG 12Z Model Run valid at 06Z 03 Sept. 2011
6 Hour QPF from GEM-REG 12Z Model Run valid at 06Z 03 Sept. 2011 (1AM CDT)

Showers and isolated thunderstorms will develop along the warm front early this evening, pushing into the RRV around midnight. The rain will push across the RRV and through Winnipeg overnight. Most of the RRV will see only 2-4mm of rain, and there is no risk of severe thunderstorms. Perhaps a bigger story with this system is rainfall totals in areas north of the the low track.

24 Hour QPF from GEM-REG 12Z Model Run valid at 12Z 03 Sept. 2011
24 Hour Total QPF from GEM-REG 12Z Model Run valid at 12Z 03 Sept. 2011

The above picture shows the total amount of rain that is expected to fall from Friday 7 A.M. CDT to Saturday 7 A.M. CDT. Over 40mm of rain are expected to fall across portions of Eastern Saskatchewan, across the Parkland areas of Manitoba including Dapuhin and Minneodsa, through the Interlake and into Northwestern Ontario.

For Saturday, Winnipeg and the rest of the RRV will see the chance of showers as the cold front pushes through in the morning. By early afternoon things will begin to stabilize with the passage of the front, and most of the RRV will see winds of 30-40km/h behind the cold front with gusts up to 60km/h.


Chart of 500mb Heights and Temperatures valid for the evening of Wed. Sept. 7

Things look calm in the long-term, as after this system the upper ridge begins to redevelop aloft. It will continue to intensify through the next week, bringing sunny skies and the return of warmer weather. We should see relatively light winds most of next week with daytime highs in the mid-20’s. Summer isn’t over yet!