Pattern change signals return of summer warmth to southern MB

After 4 weeks of below normal temperatures, a major shift in the upper atmospheric weather pattern will finally signal a return to more typical summerlike weather over southern MB.  The weather pattern over the past month has been dominated by a persistent upper trough over Hudson Bay into the Great Lakes that has resulted in  a prolonged period of below normal temperatures over the eastern prairies into Ontario. Including today (August 14th), Winnipeg will have gone 27 consecutive days below normal, at a time when the hottest weather of the season often occurs. During this stretch, Winnipeg has hit the 25C mark only twice, with a maximum of only 25.2C.  The normal high during this period is 26C.

The below normal streak however will be coming to end starting tomorrow. The persistent upper trough over central Canada will finally be shifting east and replaced by an upper ridge over the Prairies, allowing warmer air from western Canada to finally spread eastward. High temperatures in southern MB will climb from the mid 20s today to the 30C mark by Friday, with 30c+ weather expected over the weekend into next week. Things may start getting a little more unsettled as well Sunday into Monday as a weak impulse passes though southern MB, tapping warm and more humid air and triggering scattered thunderstorms. Above normal temperatures however are expected to persist much of next week, great news for those who weren't quite ready to say goodbye to the summer of 2013 just yet.      

Below normal pattern continues this week.. moderating trend expected over weekend into next week

500 mb pattern for Wednesday Aug 7
Note deep Hudson Bay vortex over
northern Manitoba 

Those waiting for summer heat to return to southern Manitoba will be disappointed this week as another surge of cooler than normal temperatures spreads across the eastern Prairies. A deep Hudson Bay vortex (image left) will drift across northern MB into NW Ontario, bringing a surge of cool air over Manitoba for the next few days. Temperatures will struggle in the mid to upper teens over Winnipeg and the Red River valley, some 5-10C below normal for early August.

Temperature graph for
Winnipeg past 30 days  

This will continue a trend of cooler than normal weather that began around July 19th over southern MB. Since then, Winnipeg has gone 19 consecutive days below normal as of today (August 6th) with temperatures more reminiscent of late August or September than mid summer.  The upper vortex is forecast to slowly drift east into Ontario over the weekend, with a gradual moderating trend expected over southern Manitoba into next week.

      

Cool week ahead..

It won't be very summerlike this week as a large-scale upper trough sets up over Ontario bringing a northwest flow of generally below normal temperatures over southern MB for the upcoming week.  High temperatures this week will generally be running in the low 20s, some 3-5C below the average high of 26C for this time of year, making it feel more like mid to late August. For today, brisk northwest winds and generally cloudy skies will keep temperatures only near 20C before skies clear tonight allowing temperatures to dip into the single digits overnight. Tuesday looks more pleasant with sunshine and lighter winds, and afternoon highs near 24C.  Another disturbance tracking through southern MB threatens more showers and possible thunderstorms for Wednesday into Wednesday night, followed by a reinforcing shot of cooler air for Thursday.  Highs pressure building into southern MB is expected to bring sunshine and pleasant conditions for the weekend with temperatures around the 22-24C mark. Long range guidance is hinting at a return to more summer like weather next week.

Showers and thundertorm possible overnight into Thursday.. cooler weather for weekend

A wave of low pressure moving along a frontal system just south of the US border will bring an increasing threat of showers and thunderstorms to southern MB overnight into Thursday morning. Locally heavy downpours are possible with this activity, with rainfall amounts of 15-25 mm possible in some areas.  As this precipitation moves out by midday, a trailing cold front will bring the threat of more thunderstorms Thursday afternoon into Thursday evening, especially across southwestern MB. This cold front will mark the leading edge of cooler air that will flood into southern MB Friday into Saturday.  Daytime highs Saturday will only be around 20C, with overnight lows likely dipping into the single digits by Sunday morning. Warmer weather is expected to return early next week with highs back in the upper 20s.  

Showers and thunderstorms likely Monday night into Tuesday.. then turning warmer and drier for end of week..

After a stormy end to June with bouts of heavy rainfall, Winnipeg has yet to see any precipitation in July as a drier and warmer weather pattern evolves. Strong thunderstorm activity last evening over western MB pushed into the RRV overnight, but only managed to produce a few raindrops in the city as the storms weekened or split. The next threat of significant rainfall for the city will be Monday night into Tuesday as a storm system from Montana tracks into North Dakota. This system will likely spread an area of showers and thunderstorms along the US border which will push into southern MB Monday night into Tuesday. Some of the rain will be heavy with these thunderstorms with rainfall amounts of 25-50 mm possible in some areas, along with the potential for hail and frequent lightning. Things should clear out Tuesday evening with a return to drier and warmer weather for the latter part of the week.