Sunday, June 18, 2017

June to end on a cool note..



Temperature outlooks from CPC show favour below normal temperatures
across the Prairies for the next 1-2 weeks at least 

After a nice warm first half of June, the weather pattern has shifted over the Prairies this past week, with the warmest air now suppressed south of the international border. The jet stream has shifted south allowing cooler air from the north to move across the Prairies. And it looks like this pattern will likely persist for the rest of the month into early July. Tomorrow and Tuesday should see a mix of sun and cloud with highs of 18-21C, then a system passing through southern MB will likely bring some showers and thunderstorms Wednesday with highs in the low 20s. Cooler temps will follow for the end of the week, with below normal temps in the teens and scattered showers likely next weekend.  A return to sustained heat in southern MB isn't expected before early July.

Monday, May 29, 2017

Warming trend this week.. dry weather expected into next week

It's been a cool and wet couple of days over southern  Manitoba, but things will be clearing up nicely this week as a stubborn area of low pressure over northern Ontario finally pushes east allowing high pressure to build in from the west. Cloudy skies Tuesday will give way to increasing sunshine by afternoon as the high pressure ridge moves in from Saskatchewan. This will lead to some glorious weather through mid week with plenty of sunshine and temperature in the mid 20s Wednesday and Thursday. The warmer weather will retreat a bit on Friday and Saturday with highs around 20C as we get easterly outflow winds from a cooler high pressure system moving across northern MB into NW Ontario. But things should warm up again by Sunday into next week as we get a return flow of warmer air back into southern MB.

As far as precipitation goes, it looks generally dry through the first week of June with long range guidance showing little in the way of major systems or convection over much of southern MB through the next 7-10 days. There is a risk of some showers and thunderstorms over SW MB Friday, but the risk appears restricted to SW MB into North Dakota. Things are actually getting a bit dry over southern MB, especially over far SW MB which has received only 10-20% of normal rainfall so far this month. Even the RRV has only seen about half the usual rainfall in May (normal May precip is about 55-60 mm) Farmers will be getting increasingly anxious if the dry weather continues for much longer as it will start to affect their newly planted crop.

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)