Wet start to the holiday weekend.. showers and thunderstorms developing today with locally heavy rain possible

A pair of low pressure systems, one over southwest MB this morning and another in the Dakotas, will slowly push eastward today, triggering showers and a few thunderstorms this afternoon into this evening over southern MB.  Depending on how much sunshine we get today, some of these thunderstorms may be strong to possibly severe, with large hail and heavy rain possible.  This system will slowly push into NW Ontario overnight into Saturday, with cooler and showery weather over southern Manitoba behind the system. In all, about 15-25 mm of rain is possible today into Saturday over southern MB including Winnipeg and the RRV, with locally heavier amounts of 25-50 mm possible with stronger or more persistent thunderstorms. Sunnier and warmer weather is expected for the latter half of the holiday weekend.

RAINFALL SUMMARY - Rainfall amounts Aug 3-4, 2012
 

Location            amount

Gimli               42.3 mm
Fisher Branch       37.2 mm
Steinbach           35.5 mm
Birtle              32.9 mm
Swan valley         32.8 mm
Portage la Prairie  32.0 mm
Starbuck            30.6 mm
Brandon             30.2 mm

Winnipeg locations

East st. Paul       50.0 mm
St. Vital           46.0 mm
The forks           35.4 mm
Whyte ridge         32.8 mm
Charleswood         30.5 mm
Airport             26.5 mm

Another 30c day to cap off warm July... More thunderstorms possible this evening

The hot July of 2012 will end with another round of hot and potentially stormy weather, as daytime highs rise into the low 30s once again this afternoon. This will mark the 14th day this month with highs of 30c or more at Winnipeg airport, the most since July 2006 which had 16 days. (record is 17 days of 30c or more in July 1936). July will end up with a monthly average just over 22c, over 2.5C above the normal July mean of 19.5C, and our 13th consecutive month that has averaged above normal. Today's hot weather will also lead to the potential for another round of strong thunderstorms later today into this evening as a disturbance tracks across southern Manitoba. The greatest threat will be over southwest MB late today with storms possibly spreading into the Red River valley this evening.

UPDATE: July 2012 ended with a monthly mean of 22.3C at YWG airport, 5th warmest July on record in Winnipeg since records began in 1872.  It was the city's hottest July since 1936, our hottest July on record at 24.2C.  It was also only 0.1C from being Winnipeg's second hottest July on record.

Top 5 warmest Julys in Winnipeg (since 1872) 

1. 1936 .... 24.2C 
2. 1935 .... 22.4C 
    1916 .... 22.4C  
    1914 .... 22.4C  
5. 2012 .... 22.3C 

July 2012 was also the hottest month on record in the contiguous United States, beating the former record holder of July 1936.

Summer pattern continues..

Temperature graph for Winnipeg
over the past 12 months showing
persistent warmth since last summer.
The past 12 months have been the
warmest 12 month period in
Winnipeg history.

The warm and generally dry weather pattern of the past month continues this week, with temperatures in the upper 20s under mostly fair conditions.  Thunderstorm potential will be limited this week, with a slight chance of storms overnight into Sunday morning over the RRV, and a better chance later in the week in the Wednesday-Thursday time frame.  Precipitation this July has varied greatly across the Red River valley with some localities receiving fairly generous rainfall amounts of 30-50 mm or more this month, while other places have been quite dry, including much of Winnipeg (only 15 mm so far this month at YWG airport)  Conditions have been drier south of the border with drought conditions starting to spread northward across much of North Dakota and Minnesota from the central plains.  Temperatures in Winnipeg so far this month are averaging some 2-3C above normal for July, with a mean temperature so far this month of 22.2C (normal = 19.5C) This is on pace for a top 10 ten warmest July based on current trends, and would also be a staggering 13th consecutive month with monthly temperatures that have averaged above normal in Winnipeg. The 12 month period of July 2011-June 2012 is the warmest 12 month period on record in Winnipeg at 5.9C, beating the previous warmest 12 month period of Dec 1877-Nov 1878 (5.6C)  Weather records in the city began 140 years ago in 1872.

UPDATE:  With an average of +6.0C, Aug 2011 - Jul 2012 is now the warmest 12 month period on record in Winnipeg. That 's almost 3.5C above the normal annual average of +2.6C.  This has also been the warmest 12 month period across most of the United States.

A comfortable start to the week before heat builds again by mid to late week..

A storm system which brought significant rain across southern Manitoba Sunday will be tracking eastward today leaving mainly cloudy skies in its wake. Temperatures will be slightly below normal with highs in the low 20s, a refreshing break for the heat of the past few weeks. Skies are expected to clear for Tuesday with seasonable temperatures around 26C, before the heat and humidity return Wednesday into the weekend with temperatures climbing over the 30C mark once again. Generally dry weather is expected through the end of the week, although scattered thunderstorms will be possible at times with the building heat and humidity.

Locally heavy thunderstorms today.. staying hot and muggy into the weekend..

Locally heavy thunderstorms have developed over southern Manitoba this morning as a weak disturbance tracks through North Dakota. Any thunderstorms today will have the potential to produce very heavy rain due to elevated humidity levels and slow storm motion. The scattered nature of these storms will mean some localities will see heavy rain, while others will see little. As an example, Oak Bluff recorded up to 30 mm of rain in this morning's thunderstorm activity, while just down the road in Charleswood, there was barely a drop!  This thunderstorm activity will likely persist through the morning over the Red River valley, with additional storms possible this afternoon into this evening, again with locally heavy rain, as well as the potential for hail and strong winds.  A return to sunnier and hot weather is expected Friday into the weekend before another chance of thunderstorms early next week.