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.

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.

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.

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.