Cold front Friday to usher in cooler airmass for first weekend of fall..

Things have cooled off over southern Manitoba this week as a northwest flow of cool air persists over the eastern Prairies. And things will get even cooler Friday into Saturday as a cold front pushes in from the north, ushering in the coolest airmass of the season so far, just in time for the first day of fall Saturday. The cold front is expected to push through Winnipeg from the north around midday Friday, accompanied by a few showers. Behind the front, northerly winds will increase gusting to 60 km/h, ushering in cooler air from the north with temperatures dropping into the single digits. In addition, the cool air over the 15C lake waters will generate bands of lake effect showers off Lake Winnipeg, and Lake Manitoba. Below normal temperatures are expected into the weekend before a gradual warming trend next week.    

Dry spell continues.. only 2 mm of rain in Winnipeg since mid August

Rainfall over past 30 days across Prairies.
Note large area with little or no rain
from southern AB to southern MB

It's been an exceptionally dry 4 weeks over the Red River valley with very little in the way of storms systems affecting southern Manitoba, or much of the southern Prairies for that matter (see top image left). In Winnipeg, only 2 mm of rain has fallen since August 15th, with only 4 days of minimal precipitation in that time. (NOTE: Winnipeg airport has recorded some false precipitation readings since August 15th, resulting in slightly higher amounts than actually have fallen) 

Rainfall in Winnipeg over past 30 days.
Moisture deficits are running over
50 mm now.

Normally we should see about 52 mm of rainfall in September, but we're far from that pace, and the prospects for significant rain in the next week or so are not promising. A system dropping from the Interlake may give us some rain overnight Tuesday into Wednesday morning, but at this point, amounts only look to be in the 2-5 mm range for Winnipeg, far from enough to ease soil moisture concerns. Other than that, things look persistently dry through the next week or so. Soil moisture levels are getting very low across the RRV, after a dry summer that saw only about half the normal rainfall.  This will become more of a concern for farmers if adequate moisture is not received by winter freeze up.   

2012 growing season ends with frost over much of southern MB..

7 am temperatures - southern MB
Sept 14 2012

Temperatures dropped below freezing across much of southern Manitoba early this morning, including at the Winnipeg airport with a low of -1.0C.  This marks the end of the official growing season for 2012 (as measured at YWG airport), which lasted 106 days since the last spring frost on May 30th (low of -0.1C). This is actually a bit shorter than normal for Winnipeg's average growing season, which generally runs 121 days between the average last spring frost of May 23nd and the first fall frost of  Sept 22nd.   However, this year's growing season length is a bit misleading. There were only 2 days of light frost in May, with low of -0.7C on the 16th and -0.1C on the 30th. The last hard freeze (temperature below -2C) was back on April 26th with a low of -7.0C.  Using this date gives a growing season length of 140 days, which is more representative of the ideal conditions experienced this year. Farmers were able to get in a crop much earlier than usual thanks to a record warm March, with warm conditions persisting through the summer along with adequate rainfall. The result was a record crop for many across southern Manitoba this year.  

And although frost was fairly widespread over the RRV this morning, downtown Winnipeg escaped frost with a low of only +5.0C at the Forks. Downtown Winnipeg has a much longer growing season than the airport, due to the urban heat island effect that keeps night time temperatures warmer than areas near and outside the perimeter. The average first fall frost downtown is Oct 5th, while the last spring frost is May 4th giving an average growing season of 159 days downtown, or 38 days longer than the airport (121 days). For most areas of the city, the length of the growing season lies somewhere between downtown and airport values. At my site in Charleswood, a low of +0.1C was recorded with some light frost.

Warmer weather for end of week before cooldown Sunday into next week

After some windy and seasonably cool weather, temperatures will be on the upswing again for Friday and Saturday over southern Manitoba as southerly winds spread warmer air back into the area.  Temperatures in the teens Thursday will warm into the mid 20s Friday and upper 20s Saturday as brisk southerly winds develop.  That however will be the last of warm weather for awhile as a cold front pushes through on Sunday, bringing significantly cooler air into southern MB for Sunday through much of next week.  High temperatures next week will only be in the low to mid teens, along with a possibility of some morning frost depending on cloud cover and wind conditions.

Some scattered showers may accompany the cooler weather next week as well, but overall there doesn't appear to be much in the way of significant rainfall over the next week or so.  Things are becoming quite dry over southern MB with only 2 mm of rain in Winnipeg over the past 4 weeks, following a much drier than normal summer, the 10th driest on record in Winnipeg.  

Blustery Saturday to give way to pleasant Sunday

It was a blustery start to the weekend over the Red River valley with strong northerly winds gusting over 70 km/h at times along with mainly cloudy skies and temperatures in the upper teens (a peak gust of 80 km/h recorded at the Brady landfill weather station)  The winds were associated with a strong push of cool air from northern Manitoba flooding southward. Winds will be diminishing this evening becoming light overnight along with clearing skies that will allow temperatures to drop into the single digits over much of southern MB, including Winnipeg where a low of +4C is forecast.  After a chilly start, Sunday will be a much more pleasant day with bright sunny skies, lighter winds and afternoon temperatures rebounding into the low 20s.  Conditions will be even warmer Monday as gusty south winds to 50 km/h push in a warm airmass with temperatures rising into the upper 20s along with sunny skies.