September Marks a Return to Seasonal Weather

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

Streamers This Morning; Seasonal Weekend

After lake-effect streamers diminish this morning, we’ll see mainly sunny skies for the rest of the weekend with daytime highs near or just above 20°C.

GFS 500mb Wind Speeds

500mb wind speeds from the GFS model valid mid-day today. Faster winds are shaded. This clearly depicts how Winnipeg is in between the cooler air of the upper low, situated over James Bay, and the warmer air of the upper ridge/high, situated over the Western Prairies.

We’ll see clouds this morning with some showers over the Northern Red River Valley. These showers will be lake-effect streamers, so they’ll impact fairly long, narrow areas downwind of the lakes; where exactly will see showers will be highly dependent on the exact wind direction, so checking out where they are using our RADAR Viewer is your most reliable way to see if you’ll be impacted by them. Winnipeg will likely escape mostly unscathed from the streamers this morning, although should the wind shift to be a little more northerly (more favourable) or westerly (less favourable) we certainly could see some precipitation.

A ridge will slowly start building eastwards across the Prairies today which will bring a more westerly component into our winds across the province this afternoon and help start clearing out the clouds. By mid-to-late afternoon we should see sunny skies with a high right around 20°C here in Winnipeg. Tonight we’ll see clear skies with an overnight low dipping down to about 10°C.

Saturday will bring sunny skies and a high near 21°C as the ridge continues to try and build eastwards. A weak disturbance sliding SE across Manitoba will, however, pull some cooler air southwards across the province which will cause us to have our coolest overnight lows in quite a while across the Red River Valley. Here in Winnipeg, it looks like the overnight low will dip to 6 or 7°C in outlying areas, with temperatures a couple degrees higher near the core of the city.

Warmer air finally is able to push in on Sunday, which will give us a high near 24°C under sunny skies.

The beginning of next week looks to be sunny with slightly above-normal daytime highs.

Seasonable Weather with A Chance of Showers

Feeling chilly after the weather we’ve had lately, more seasonable weather has returned to Southern Manitoba with a slight chance of showers tonight across most areas of the RRV.

The large captured upper low over Northern Manitoba

A GOES East multispectral satellite imagery from Tuesday evening showing the large captured low (denoted by the red L) anchored over Northern Manitoba.

A large upper trough is entrenched over Manitoba, bringing with it cooler air and clouds. Over the next several days, our temperatures will only climb to around the 20°C mark, right around the normal daytime high at this time of year of 21°C.

For today, temperatures will climb to about 23°C before the sky clouds over as a weak cold front passes and our winds increase out of the northwest to about 20km/h with gusts to 40km/h. Clouds will clear out in the evening and we’ll drop to a chilly low of 8°C.

Skies will cloud up again on Thursday as we struggle to hit 20°C. Well have a slight chance of showers through Winnipeg and the Northern RRV through lunch and the early afternoon, however it won’t amount to much if it does materialize.

Temperatures will slowly climb at the end of the week into the weekend. Friday will see mainly sunny skies with a high of 21°C as we have one more day under the influence of the upper trough. As we move into the weekend, warm air pushes in once again, and we should see above-normal highs near 25°C under sunny skies.

Normal Weather Continues; 5th Hottest July in the Books

“Normal” weather will continue over the next few days as a ridge of high pressure builds into the Eastern Prairies, bringing us plenty of sun and daytime highs in the mid-to-upper 20’s. Before that, though, we’ll see a slight chance of showers this afternoon. A trough of low pressure is forecast to push into Manitoba on Saturday, bringing with it a chance of rain.

GEM-GLB Forecast of Prominent Ridge

GEM-GLB surface winds valid on Thursday morning. A very large ridge is the dominant feature over the Eastern Prairies.

There is a very slight chance of a shower or two over the Red River Valley this afternoon as a trough of cold air digs southwards as it heads east out of the province; the best chances should remain to our east, through the Whiteshell and Berens River regions, but it certainly can’t be ruled out for us. Accumulations will be minimal and the showers will dissipate fairly early in the evening.

A strong ridge will continue building in across the Northern/Eastern Prairies, forecast to strengthen to a 1028mb high by tomorrow morning, with the ridge axis extending from the Red River Valley NE into Hudson Bay/James Bay. This feature will ensure fairly sunny skies over the next couple days, limiting clouds to just some shallow fair-weather cumulus, as well as induce a broad southerly flow over Manitoba. This would normally result in hot temperatures and high humidity, but in this case, it’s actually going to result in…well, more of the same. The reason for this is significant: instead of being a high pressure system created by an upper ridge, this will be a high pressure system created by a cold trough of air descending from the Arctic. The southerly flow that will develop over the province, instead of being a flow of warm, moist air from the Gulf of Mexico, will be a return flow of air out of the high. So while we’ll have sunny skies, our temperatures will only creep up little by little, and our dewpoints will only climb into the low-to-mid teens.

It’s also worth noting that as crops mature, we’ll be significantly less likely to see days with very high dewpoints (20°C+) for two reasons:

  1. When plants mature, the evapotranspiration (ET) rate dramatically diminishes. Corn, for example, will ET up to 0.33“ per day at peak growth rate. That value then diminishes to 0.23” at maturity[1]. Mature trees may ET up to 50 gallons of water each day during the growing season. Again, this value diminishes in late-summer when all the growth has become mature. Most plants follow similar patterns.
  2. The crushing drought through the Central US will diminish pretty much any advection of moisture that may occur. There’s a long way between us and the Gulf of Mexico, and the normal ET contributions from plants through the Central Plains is missing this year.

One of the side effects to this is that our severe thunderstorm season will likely come to a fairly rapid halt over the coming weeks as good setups become moisture-starved.

Evapotranspiration is the process by which plants take up moisture from the soil and expel it as vapour into the atmosphere through the stomata on their leaves.

For Saturday, it currently looks like a trough of low pressure will work it’s way across the province, bringing with it a chance for showers. The track is highly dependent on the positioning of an upper low over the northwestern Prairies, so it’s a little early to say where exactly precipitation will fall. Either way, it doesn’t look to be very powerful, and any areas that see precipitation look to receive small amounts.

The next chance for rain looks to be not until the middle of next week.

July 2012 Closes Out as 5th Hottest

July 2012 closed out as an extremely warm month. The average temperature[2] for the month was 22.3°C, 2.7°C above the normal 19.6°C[3]. This places July 2012 in 5th place for all-time hottest July:

Warmest Julys on Record
Year Average
1 1936 24.2°C
2 1935 22.4°C
3 1916 22.4°C
4 1914 22.4°C
5 2012 22.3°C

The warmest day we had was July 11th, which reached 34.5°C. Our coolest day was July 15th, where the mercury topped out at only 19.4°C. Our warmest overnight low was 20.5°C on the night of July 10th/11th. Our coldest overnight low was 7.9°C on the night of July 26th/27th. In total, the Winnipeg Airport recorded 14 days with temperatures above 30°C in July. The hottest day in July on record is 42.2°C set in 1936. The coldest night on record in July is 1.1°C set in 1972.

The biggest story was, perhaps, the sheer lack of rainfall last month. The airport recorded 23.5mm of rain, which is the 11th driest July on record:

Driest Julys on Record
Year Amount
1 2006 10.5mm
2 1875 13.5mm
3 1925 15.5mm
4 1894 16.0mm
5 1886 17.0mm
6 1960 17.0mm
7 1920 19.3mm
8 1910 20.3mm
9 1964 22.4mm
10 1979 23.1mm
11 2012 23.5mm

July 2012 was the 7th driest July in the last 100 years. Fortunately, the drought wasn’t as hard hitting as areas further south, as Winnipeg had several months preceding July with above-normal precipitation.

As we covered on Monday, August looks to be off to a dry start with daytime highs sitting near-normal to just above normal[4].

  1.  ↩
  2. The average temperature is a mean of all the daytime highs and overnight lows. It is not an integrated parameter, so take that as you will.  ↩
  3. Normal average temperature calculated for the years 1981–2010.  ↩
  4. Normal daytime highs for the beginning of August in Winnipeg are generally around 27°C.  ↩