Saturday, September 29, 2012

Stellar weekend to wrap up September..

It will be a beautiful weekend to wrap up September with mainly sunny skies and warm temperatures. Today will be a spectacular fall day with a southerly breeze and clear blue skies allowing temperatures to soar into the upper 20s this afternoon across the Red River valley, with highs of 27C expected in Winnipeg. A great day to enjoy the fall colours. Sunday will see a continuation of the warm weather, although it will be a few degrees cooler as a frontal trough crosses the Red River valley by midday, with some patchy clouds and winds shifting into the northwest. Still, temperatures in the low 20s are expected to close out the month. Enjoy the warm weather while it lasts however because this may be the last mid 20 temperatures we see this season. Significantly colder weather is expected by mid week with high temperatures only in the single digits expected by Wednesday or Thursday.

Monday, September 24, 2012

Dry finish to a dry month.. 2nd driest September on record possible

September 2012 will be ending on a sunny and dry note over the Red River valley and southern Manitoba.. a fitting end to what has been an exceptionally dry month. As of today, only 4 mm of rain has fallen at Winnipeg airport this month, with no precipitation forecast all this week through the end of the month.  If so, September will end up as the 2nd driest September on record in Winnipeg since records began 140 years ago in 1872. Only September 1948 will have been drier in the city at 1.3 mm for the month.

Top 5 driest Septembers on record (Winnipeg) - since 1872

1.  1948 ..... 1.3 mm
2.  2012 ..... 4.0 mm  (through the 24th)
3.  1938 ..... 6.1 mm
4.  1897 ..... 8.6 mm
5.  1976 ..... 9.9 mm

Rainfall past 30 days across Prairies.
Note large area with little
or no rain over the past month. 
Normal September rainfall is around 52 mm, so this month's rainfall has been less than 10% of normal. The last appreciable rainfall in Winnipeg was back on August 15th when 9 mm was recorded. Since then, only about 5 mm of rain has fallen in the past 6 weeks, coming off a dry summer that saw a little more than half our normal summer rainfall.  This is resulting in very low soil moisture levels, with cracking and shifting clay causing problems with city watermains and house foundations.  The dry soil conditions will also become an increasing concern for agriculture and forestry interests if adequate moisture is not received over the winter months.  Why has it been so dry?  Simply put, the jet stream has been steering storm systems away from the southern Prairies over the past month, with storms systems tracking mainly across northern regions. This has been mainly due to a persistent upper ridge over western Canada that has effectively blocked moisture laden systems off the Pacific from tracking across the southern Prairies (see image of rainfall over past 30 days across Prairies)  A pattern change will be needed in October to bring some precipitation bearing systems across southern Manitoba, but past history suggests that may not happen. Of the top 5 driest Septembers in Winnipeg, all but one were followed by much drier than normal Octobers.

Sunday, September 23, 2012

Record cold September morning across RRV and southern MB..

7 am temperatures across southern MB
Sept 23 2012
Clear skies, light winds and a cool airmass over southern Manitoba brought a widespread freeze over southern Manitoba this morning, with record low temperatures set at many locations. In Winnipeg, temperatures fell to a low of -7.1C at YWG airport, beating the previous record low for Sept 23rd of -6.1C set way back in 1879.  In fact, it was the coldest September temperature in Winnipeg in almost 50 years, since a -7.2C reading on Sept 26 1965 (we had a -7.0C reading on Sep 28 2002)  Even the normally balmier downtown core registered its first fall freeze with a low of 0.0C, about 2 weeks earlier than usual (normal first freeze date is Oct 5th downtown)   Even colder temperatures were registered elsewhere in southern Manitoba including a frigid -8.5C in Emerson and Fisher Branch, unusually cold for this time of year.  It's possible that the very dry soil conditions over the past month helped to accelerate heat loss from the ground, allowing for the very cold temperatures to develop.

Record lows across southern MB today.. 

Site .....................................  New record ....... Old record....  Year .... Records began

Brandon airport        -6.7     -6.7(tie) 1976    1890
Fisher Branch          -8.5     -5.5      2001    1977
Gretna                 -6.3     -2.8      1995    1955
Pilot Mound            -5.0     -5.2      1976    1938
Pinawa                 -4.3     -2.5      1989    1964
Sprague                -6.9     -6.0      1989    1915
Winnipeg               -7.1     -6.1      1879    1872

It will be a nice turnaround today though as sunny skies and light southwest winds send temperatures back into the mid teens this afternoon. Normal highs for this time of year are 16C, with normal lows of +4C.

Thursday, September 20, 2012

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.    

Monday, September 17, 2012

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.   

Friday, September 14, 2012

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.

Wednesday, September 12, 2012

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.  

Saturday, September 08, 2012

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.      

Monday, September 03, 2012

Cooling off this week as kids head back to school

The traditional last weekend of summer ended up on a sunny and warm note over Winnipeg with temperatures rising to 29C for Labour Day Monday .. some 8C above normal for early September. But the summerlike temperatures will be on their way out this week as a large storm system over the northern Prairies pushes cooler air towards southern Manitoba over the next few days. Tuesday will see a mix of sun and cloud with highs of 24C, about 5C cooler than today but still seasonably warm for early September. Tuesday night, a cold front will track across southern Manitoba bringing a chance of showers, along with a push of cooler air for Wednesday and the rest of the week. Temperatures will be noticeably cooler as the kids head back to school, with autumn like highs in the upper teens to near 20C through Friday. Sunny and warmer conditions are forecast for the upcoming weekend.      

Saturday, September 01, 2012

Showers/thunderstorms possible tonight.. clearing and warmer for remainder of holiday weekend. Cooler conditions for back to school..

A warm front along the international border will push northward across southern Manitoba tonight bringing a threat of showers and thunderstorms, mainly across the south this evening pushing into the Interlake areas overnight. This activity will move into northern Manitoba and northwest Ontario Sunday morning, with a clearing trend over southern Manitoba.  This will allow temperatures to rise to the 30C mark once again over the Red River valley with sunshine and a southwest breeze. Sunny and warm conditions are expected to continue into holiday Monday with temperatures again near the 30C mark. Cooler conditions are forecast for the remainder of the week as an upper trof pushes across the Prairies, with temperatures more typical for early September (highs near 21c) along with partly cloudy skies and a threat of showers by mid week.

Warm end to August continues above normal streak.. summer of 2012 ends up as 10th warmest/driest on record in Winnipeg

Daily temperature summary
for Winnipeg - August 2012
A warm end to August helped extend Winnipeg's streak of above normal monthly temperatures to an amazing 14 straight months.. the longest such period of warmth in the city since weather records began in 1872.  August finished with an average temperature of 19.3C at YWG airport, or 0.6C above the normal August mean of 18.7C (1981-2010 normal)  The month was actually cooler than normal through the 20th, but above normal temperatures over the last 10 days of the month, including 6 days of 30C or more (max of 35.4C on the 29th) helped to extend the above normal monthly temperature streak.

As a whole, the summer of 2012 finished with an average temperature of 19.8C for the 3 month period of June, July and August, about 1.5C above normal. This makes the summer of 2012 the 10th warmest on record in Winnipeg, tied with 4 other summers (1919, 1921, 1936 and 2006)  Records for Winnipeg started 140 years ago in 1872.

Top 10 warmest summers in Winnipeg (since 1872) 

 1.  1988 ....... 21.0C
 2.  1983 ....... 20.6C
 3.  1961 ....... 20.4C
 4.  1955 ....... 20.2C
 5.  1930 ....... 20.1C
 5.  1963 ....... 20.1C
 7.  1933 ....... 19.9C
 7.  1995 ....... 19.9C
 7.  1991 ....... 19.9C
10. 1919 ....... 19.8C
10. 1921 ....... 19.8C
10. 1936 ....... 19.8C
10. 2006 ....... 19.8C
10. 2012 ....... 19.8C

Normal summer average ... 18.4C  (1981-2010 average)

Summer rainfall in Winnipeg
June-August  2012. A wet start to the
summer turned dry by late June
August 2012 was also dry in Winnipeg with only 44 mm of rain for the month at YWG airport, about 30 mm below normal for the month (1981-2010 average of 79 mm)  This was the third straight month that was drier than normal, coming off a dry July (55 mm below average) and June (27 mm below average)  The total summer rainfall of 129.5 mm was over 100 mm below normal (248 mm based on 1981-2010 normals), and makes 2012 the 10th driest summer on record in Winnipeg. This comes on the heels of a very dry summer last year (93 mm) which ranked as the 5th driest summer of all time. To put this dryness into perspective, the total rainfall over the past two summers combined (222.5 mm) has been less than what we usually see in one typical summer (247.5 mm). Also interesting to note that three of Winnipeg's top 10 driest summers have occurred within the past 6 years. Could this be the start of a dry cycle in southern Manitoba after a prolonged wet cycle in the 1990s and early 2000s? Or is it just a couple of dry summers in nature's variable precipitation pattern?  Whatever the case, the summer rainfall pattern over the past decade in Winnipeg seems to be one that's either too wet or too dry..  

Top 10 driest summers in Winnipeg (since 1872)

 1.  1929 .........   76.7 mm
 2.  1886 .........   77.2 mm
 3.  1961 .........   91.0 mm
 4.  2006 .........   91.5 mm
 5.  2011 .........   93.0 mm
 6.  1889 .........   96.0 mm
 7.  1894 .........   97.1 mm
 8.  1915 ......... 114.8 mm
 9.  1936 ......... 121.4 mm
10. 2012 ......... 129.5 mm

Normal summer rainfall ....  247.5 mm (1981-2010 average)

For additional data and analysis of the warmth this year, consult "A Weather Moment" website.