Sunday, April 23, 2017

Oh no! More snow!

It will be back to winter like weather over southern Manitoba Monday as a storm system intensifies over the Dakotas and tracks into northern Minnesota by Monday night. A band of snow is expected to spread into the Winnipeg area by mid morning Monday, with snow intensifying through midday into the afternoon before tapering off Monday evening. Snowfall accumulations will be tricky as some of the snow will be melting on impact, and there will be milder air over southeast MB that will change snow to rain for awhile over parts of southeast MB. For Winnipeg, precipitation should remain as snow with a good 5-10 cm expected by late afternoon, and perhaps 10-13 cm by the time it ends Monday evening if we get under some heavier bands. The best bet for heaviest snow will be towards the Ontario border where 10-20 cm is possible Monday into Monday night.    

UPDATE:  (9:30 am Monday): Latest guidance and radar indicating Winnipeg will be on western edge of this system with bulk of snow mainly east and southeast of the city. Winnipeg will likely still see some wet snow by late morning into this afternoon, but amounts should be minimal with perhaps 2 cm or less on grassy surfaces. Roads will just be wet. Wet snow may even mix with rain here at times today as temperatures stay above freezing. Heavier snow will be confined just to the east and southeast of Winnipeg in places like Steinbach, Whiteshell and Falcon Lake where 5-15 cm of snow is possible through this evening.  

How unusual is heavy snow in late April? 

Although not common, snowstorms are certainly not unheard of in late April or even May in Winnipeg and the Red River valley. Consider these top 10 late season snowfalls (daily) that have occurred in Winnipeg after April 15th. As the table shows, heavy snowfalls have occurred in Winnipeg well into the 3rd week of May.

TOP 10 LARGEST DAILY SNOWFALLS AFTER APRIL 15  
              (WINNIPEG DATA 1872 - 2016)

1.  29.0 cm ............ May 11 2004
2.  21.1 cm ............ May 1 1967
3.  20.8 cm ............ Apr 27 1966
4.  20.3 cm ............ May 19 1931
5.  20.0 cm ............ May 9 2002
6.  17.3 cm ............ Apr 24 1937
7.  16.5 cm ............ Apr 25 1960
8.  15.2 cm ............ May 20 1882
9.  14.0 cm ............ Apr 19 1996
10. 13.0 cm ........... May 5 1938

In 1958, a full fledged blizzard hit Winnipeg on April 28th with 5-10 cm of snow blown by 80-100 km/h winds along with frigid temperatures of -10 to -13C.

Monday, April 10, 2017

Dry April weather continues.. next significant rain threat Friday.

It's been a dry spring so far in southern MB, welcome news for residents in the Red River valley who were looking at potentially major flooding this spring. There has been no measurable precipitation so far in April in Winnipeg and much of the RRV, and this week is also looking dry, until Friday. (There is a slight chance of some light showers Tuesday night, but amounts will not be significant). The next threat of any appreciable rain over the Red River valley will be Friday as a storm system tracks through the Interlake bringing a band of rain across southern MB. Early indications are for rainfall amounts of 5-15 mm with this system, but it's still several days away and there's still a lot of model spread on overall precip amounts. Colder weather will follow in the wake of this system for Easter weekend, with even a chance of snowflurries for Easter Sunday. Long range guidance is indicating the potential for another precipitation bearing system over southern MB for the April 17-19th time period.

Friday, March 31, 2017

March goes out like a lamb in southern MB.. Winnipeg records 7th least snowy March on record

March 2017 will go down in the record books as the 7th least snowy March in Winnipeg in 145 years of records. Only 2.4 cm of snow fell during the month, compared to the "average" of 16.5 cm that usually falls in March. That comes as a relief to residents of the Red River valley after heavy snowfall in December increased fears that a potentially major flood situation would arise in the Red River valley come the spring melt.  A wet fall, soggy soil conditions and a heavy snowpack were leading to an elevated flood risk throughout the valley, contingent on late winter and spring precipitation.

Top 10 least snowy Marches
in Winnipeg
Thankfully, precipitation has been mainly light over the past few weeks in the Red River valley, and a major winter storm that clobbered much of western Manitoba earlier in the month largely spared the valley. Overall, the month of March finished with 14 mm of total precip at YWG airport (17 mm of rain at my site + 2.4 cm of snow) Normal March precipitation is around 24 mm (composed of about 10 mm of rain and 17 cm of snow)  so March precipitation was below normal. Snowfall in February was near normal with only 12.2 cm for the month. In fact, in the 11 weeks since Jan 10th, only 22 cm of snow has fallen in Winnipeg compared to 90 cm in the 6 weeks between Dec 1st and Jan 10th. That has led to a significantly reduced snowpack in the valley, which has gradually disappeared over the past 2-3 weeks.  The reduced snowpack and gradual thaw were ideal conditions to ease the Red River flood threat this spring although mild weather over the past few days has led to some local flooding due to ice jams. The Red River is expected to crest in the Emerson area sometime next week as a "moderate" flood which will gradually progress north over the following days. More major flooding is expected over western MB in the Souris and Assiniboine watersheds where they have had more snow.  

What about April?

So with only 2 cm of snow in March, does this mean winter is over? Well, for the most part.. yes. Now that snowcover has disappeared, it will be easier for the ground to warm up since snowcover acts to reflect heat. But that doesn't mean we won't see any more cold weather or snow. A look at past Aprils in Winnipeg shows that since 1872, only 8 Aprils have not seen ANY snow during the month (not even a trace). 95% of Aprils have seen at least a trace of snow, and more than half (56%) have seen at least 5 cm of snow. So although snow is currently not in the forecast, it would be highly unusual to go the entire month of April without seeing at least some snowflakes at some point. Hopefully, April 2017 is one of those months with little or no snow. 

Chart showing odds of snow in Winnipeg during April 

April snowfall stats for Winnipeg:

- Normal April snowfall: 10 cm (but highly variable year to year) 
- Normal days in April with measureable snow (>= 0.2 cm): 3
- Odds of at least 1 day in April with a snowfall >= 2 cm: 67% (2 out of 3 years)
- Odds of at least 1 day in April with a snowfall >= 5 cm: 41% (2 out of 5 years)
Odds of at least 1 day in April with a snowfall >= 10 cm: 17% (once every 6 years)
- Snowiest April on record: April 1997, 48.6 cm (year of the big flood)     
- least snow in April:  0.0 cm (8 years;  last occurrence was April 1998)

Graph of April snowfall in Winnipeg shows how variable it is year to year.
Snowy Aprils are just as likely as snowfree ones in any given year
(graph from @jjcwpg) 

Historic winter storm slams Manitoba March 6-10th .. Winnipeg and RRV escape worst of storm

The strongest winter storm in at least 20 years slammed Manitoba during the week of March 6th to March 10th, bringing widespread snow, high winds, and blizzard conditions to much of the province. The storm system, which originated in the western US on Sunday March 5th, crossed into North Dakota on the 6th and then tracked north across the Red River valley, with the center of the low tracking right over Winnipeg Monday evening March 6th with a deep central pressure of 978.7 mb, just 0.1 mb off the lowest pressure ever recorded in the city in the month of March. The storm then continued to intensify and track north, moving over Lake Winnipeg and then into northwest Ontario, where it would deepen to an incredible 964 mb near Big Trout Lake by Tuesday afternoon March 7th. Such a low pressure is rare for this part of the world, and is associated with only the most intense storms. And what an intense storm this was!

The massive storm brought prolonged blizzard conditions to western Manitoba March 6-7th, with powerful northwest winds gusting up to 90 km/h at times producing extensive whiteout conditions with severe blowing and drifting snow. Brandon recorded 31 straight hours of blizzard conditions beginning Monday evening before tapering off around midnight Tuesday night.  Officially, Brandon Airport reported 41 cm of snow during the 2 day blizzard, but accurate measurements were difficult due to the severe blowing and drifting  snow. The prolonged high winds led to massive drifting across Westman, with reports of 12-15 foot drifts south of Brandon that buried vehicles and structures.

The severe winter storm of March 6-7th left massive drifts across
western MB. This scene is from Crystal City area near the US border.
As the vicious storm headed north towards Hudson Bay Tuesday, it set its sights on northern Manitoba and pummelled the north with one of the worst winter storms on record there.  Churchill was particularly hard hit being exposed to 3 days of severe blizzard conditions from March 8th to 10th.. including zero visibility for 2 full days. The town was stranded for 2-3 weeks due to blocked rail lines that could not get supplies to the town. Some 40-70 cm of snow was reported in the north including 67 cm in Lynn Lake and around 60 cm in Thompson.        

Friday, March 03, 2017

Milder weekend ahead.. winter storm system looms for Monday

After a cold start to March, things will be turning milder this weekend as a southerly flow flushes out the Arctic airmass currently over the eastern Prairies. In Winnipeg, temperatures are expected to climb to the freezing mark on Saturday and +2C on Sunday. Note however that Saturday will see gusty south winds gusting 60-70 km/h, so that high of 0C will feel a lot colder. Sunday looks a lot more pleasant with lighter winds and temperatures above freezing.

12Z NAM model valid Monday afternoon shows
rain over SE MB and snow west
Attention then turns to a potential winter storm system that will be impacting southern Manitoba Monday into Tuesday. At this time, models are indicating the development of a storm system over the western United States Sunday that will track across the Dakotas Monday and intensify as it moves into NW Ontario by Monday night. This system will likely start off with some rain or freezing rain over the RRV and SE Manitoba with snow over western MB and he Interlake regions. As the storm pushes towards the Ontario border later Monday, strong northwest winds on the backside of the system will draw in colder air and spread snow and blowing snow across the remainder of southern Manitoba Monday afternoon into Monday night. Travel conditions could become hazardous across southern MB through the day Monday into Monday night, especially with falling temperatures and increasing winds that will freeze up any standing water from leftover rain or melted snow.

12Z GDPS model valid Monday evening shows
intensifying storm over Lake of the Woods 
There's still a lot of uncertainty on the track of this system and the timing when precipitation will change over to snow which will impact overall snow totals.  A track across southeast MB would push the heaviest snow over western Manitoba through the Interlake regions (possibly 15-25 cm) with lesser amounts (5-10 cm) over the RRV and SE MB.  A track through Lake of the Woods or east would bring heavier snow over the southern Interlake and RRV. We'll continue to monitor trends over the next few days to get a better idea of how this storm will track, and what impacts it will have for southern MB. In the meantime, be prepared for a potential return of wintery conditions Monday into Tuesday. Stay tuned..