Early Winter Wallop

Parts of southern Manitoba will be white like this soon

     Just under a week after we experienced near 30°C weather, winter is expected to make an incredibly-early return to southern Manitoba and northwestern Ontario Thursday into Friday. An intense low-pressure system is currently forming south of the border in South Dakota and will move into northwestern Ontario tomorrow. A tight pressure gradient with this system will pull in very cold air from the north into the system, allowing for heavy precipitation amounts, both in the form of rain and snow.

     For tonight, most of the precipitation will remain in the form of rain for southern Manitoba, especially the further north and closer to the lakes you are. The heaviest amounts are expected to be south and east of Winnipeg with up to 30 mm of rain possible. Further west and north, rainfall will be lighter and not-so widespread. However, areas downwind of the lakes will get some enhanced precipitation, giving some higher amounts in those areas. Winnipeg is expected to get some lake-effect showers tonight as north/northeast winds blow off Lake Winnipeg.

     Tomorrow is uncertain still at this point, but tomorrow is also when things get very intriguing. Heavy precipitation is expected to move in again from the south and wrap around in southeastern Manitoba into Thursday night and to start Friday. Much of this is expected to be in the form of snow with upwards of 30 cm possible to the east of Winnipeg, especially in the Sprague area. In Winnipeg, at the moment it is expected that we will be on the western fringe of this band of snow, therefore we are expecting to receive lighter amounts. However, lake-enhanced precipitation may be an issue. Elevation-enhanced precip will also be possible along the Manitoba escarpment.

     However, uncertainty is strong at this point as some models (NAM/GFS) are still bringing over 20 cm for the city, while GEM is only giving about 5 cm. Keep up to date on this situation on Rob's Blog as I wont have much time to update over the next couple days.

Snow Potential - [Not Kidding!]

     It is beginning to look like our warm weather may end more viciously than anticipated a few days ago. A low is expected to form over the US rockies over the next 24 hours and move east/northeastwards. The question right now is just how far north and west this system will move, to determine how Manitoba will be impacted.

     The problem is that this system will bring in very cold air from the north, meaning that a lot of the precipitation to the northwest of the system's centre will likely be in the form of snowfall. And this snowfall is expected to be heavy, and significant accumulations are not out of the question. In addition, winds gusting over 50 km/h are likely, which would give serious travel problems. Due to many differences among the models, there is not much more I can say until later tomorrow. I can warn you however that you may need your shovels in the next 3 days... or maybe not! It will depend highly on the track of the system. Will keep a close eye!

September 2012 Continues a 15 Month Trend

September quick stats - click to enlarge

Drought-like conditions dominated

     September continued a trend 15 months in the making. The month averaged warmer and drier than normal. Drought-like conditions plagued not only us here, but also most of western Canada throughout the month. Here in Winnipeg, only 4.0 mm of rain fell, just 8% of normal putting September 2012 as the second driest on record. It was the 4th consecutive drier than normal month. It also makes it the 37th driest month in history. That may not seem like something of interest at first, until you consider that there are 1678 months of precipitation data.

Top 5 driest Septembers:
1.    1.3 mm    1948
2.    4.0 mm    2012
3.    6.1 mm    1938
4.    8.6 mm    1897
5.    9.9 mm    1976

     Another interesting note about September was the large diurnal temperature variations. While daily highs averaged 1.9°C above normal, daily lows averaged 1.3°C below normal and tied for 21st coldest. The average difference between day and night was 15.8 degrees when normally it is just 12.6 degrees.

     As a result, both record highs and record lows were seen. The month started hot with highs in the mid to high twenties, but then things began to change mid month. The growing season officially ended September 14, a week earlier than normal. But then even colder weather dominated the third week with several days of below zero overnight lows. Snow even fell in parts of northwestern Ontario. The morning of the 23rd was enough to be considered ''frigid'' to many as temperatures dipped well below the freezing mark. Winnipeg dipped to -7.1°C, making it the 5th coldest September night on record. It was also the coldest September night in 47 years. The coldest spot in the area was Dugald at -9°C.

     In total, 7 days had lows below zero during the month, tying for 3rd most on record for the month. The following is a diagram demonstrating the frequency of below zero nights in September since 1872, showing that the amount of below zero nights this September was in fact unusual:

      Only a week later, record daytime highs became the headline. Temperatures approached 30°C on the 29th and reached the low to mid twenties on the 28th and 30th. The hot and sunny weekend coinceded nicely with the peak of the colour change of the leaves, pehaps making it one of the nicest Fall weekends in a while.