Fall Storm Set to Slam Manitoba With Rain, Snow, and Strong Winds

A potent fall storm brewing in Alberta will race eastwards across the Prairies today, strengthening substantially as it does. It will move through Southern Manitoba tonight and tomorrow, bringing rain, snow, and strong winds to the region. As it passes, it will also mark a substantial shift in the large-scale weather pattern that will bring much cooler temperatures to Winnipeg over the next week.

Today will be Winnipeg’s warmest day for the foreseeable future as seasonably mild air moves into the region ahead of the incoming low pressure system from Alberta. Temperatures will climb to around the 9°C mark with light northerly winds this morning switching out of the south for the afternoon. Skies will start off partly cloudy to mixed, but more and more cloud will move through the day, making for mainly cloudy conditions this afternoon.

The winds will strengthen in the evening to around 30 km/h as the low approaches, keeping temperatures mild at around 8 or 9°C well into the night. As the centre of the low moves through shortly after midnight, rain will begin spreading into the Red River Valley. Winds will back to the north shortly after midnight and intensify, reaching 40 gusting to 60 km/h by Thursday morning. At this point, we expect precipitation to remain as rain overnight with temperatures dropping to a low near +3°C; between 5 to 15 mm of rain is likely to fall overnight throughout the Red River Valley, with lower amounts near the U.S. increasing northwards towards Winnipeg and the southern Interlake.

NAM Forecast Precipitation Type and Intensity valid 09Z Thursday October 26, 2017
The forecast rain/snow line at 4 AM Thursday morning will cut through the Parkland and into the Interlake

For those further west in the southwest corner of the province or in the Manitoba Parkland, rain will change to snow overnight with lower amounts of 2 to 5 mm of rain and a dusting of snow in the southwest and higher amounts of 5 to 10 mm of rain and 2 to 4 cm of snow. The exception to the snowfall amounts will the along the Riding mountains and western escarpment, where strong northerly winds will enhance snowfall amounts. Localized accumulations of 10 to 20 cm will be possible in these regions.

NAM Forecast Precipitation Type and Intensity valid 15Z Thursday October 26, 2017
The rain is forecast to completely change over to snow in the Red River Valley by 10AM

Rain will transition to snow – potentially fairly heavy at times – early on Thursday morning in Winnipeg and spread southeastwards quickly through the remainder of the morning. Temperatures will drop to around 0 to +1°C through the morning as the northerly winds further intensify to 50 gusting to 70 km/h with the chance for gusts as high as 80 to 85 km/h. The strong winds will combine with the heavier bands of falling snow to produce poor visibilities in blowing snow. Additionally, road conditions will likely deteriorate through the day, although will be very sensitive to temperature.1 By the end of the day, Winnipeg will likely see around 3-6 cm of accumulated snow, however it may end up a little more, or a little less, depending on how much manages to melt.

NAMNEST Forecast 10m Wind Speed valid 18Z Thursday October 26, 2017
Widespread strong winds will be in place across southern Manitoba and the Dakotas

The strong winds will begin to diminish late in the afternoon, and then gradually taper off to around 20 km/h by Friday morning. The snow will ease to a few flurries in the afternoon and taper off by evening. Temperatures will dip to a low near -4°C.

So in summary, for Winnipeg, winds will intensify tonight to 40 gusting 60 km/h as rain moves into the region. Winnipeg can expect anywhere from 5-15 mm of rain tonight, but will switch over to snow early Thursday morning as winds increase further to 50 gusting 70 km/h. The gusty winds will persist through much of Thursday with moderate snow through the morning tapering off to flurries in the afternoon. Snowfall accumulations will be very sensitive to temperature, but it looks like the most likely outcome will be between 3-6 cm of snow, but should more intense bands develop over the city, up to 10 cm could pile up.

Friday will be comparatively pleasant, but cool. Winds will continue to taper off with partly cloudy skies and temperatures climbing to a high near +3°C. The clouds will clear out for Friday night as temperatures drop to a low in the -6 to -8°C range.

Long Range Outlook

The weekend looks like a bit of a mixed bag. Saturday will be cool but pleasant with a high near 5°C, light winds and fairly sunny skies. Things change on Sunday, though, as another low pressure system pushes into the province, bringing more cloud and the chance for more rain or snow.

Winnipeg’s seasonal daytime high is currently 7°C while the seasonal overnight low is -3°C.

  1. If temperatures remain closer to +1°C, roads will likely remain in relatively good shape until the freeze occurs on Thursday night, but if it dips closer to the freezing mark, area highways may become a bit slick through the afternoon.
GFS Forecast Precipitation Type/Rate valid 06Z Thursday October 26, 2017

Mild Fall Temperatures On The Way Out

The first half of the week will bring seasonal conditions Winnipeg, but the writing is on the wall: a big pattern shift will usher in significantly cooler conditions for the second half of the week and into the next.

The cooler weather begins to arrive today in Winnipeg, drawn southwards across the province behind a low pressure system that passed through overnight. A few remaining showers and cloud will clear out this morning, leaving Winnipeg with mixed skies for the afternoon. Winds will be fairly breezy out of the northwest as a ridge of high pressure builds into the province; light morning winds will build to 40 gusting 60 km/h for the afternoon. Temperatures today will barely budge from this morning, remaining steady near 6 or 7°C through the day. Expect partly cloudy skies overnight with winds diminishing to around 20-30 km/h and a low dipping down to the freezing mark.

Tuesday will be a pleasant and crisp fall day with plenty of sunshine and a high near 9°C in Winnipeg. Winds will be much calmer out with a morning breeze out of the northwest at around 20 km/h diminishing to light midday. Some cloud will spread into Winnipeg later in the afternoon, announcing the approach of the low that will usher in a dramatic change in the general weather pattern.1 Temperatures will drop to a low near 4°C overnight as northwesterly winds move back in and usher cooler air into the region once again.

RDPS 2m Temperature Forecast valid 00Z Wednesday October 25, 2017
A low pressure system moving across northern Manitoba will draw warm air eastwards into the southern half of the province for Wednesday.

Wednesday will be the last day of mild conditions before things take a dive on Thursday. Temperatures will climb to a high near 10°C as skies become cloudy for the afternoon. Northwesterly winds around 15-25 km/h in the morning will taper off to light for the afternoon. As the low pressure system begins pushing into Manitoba in the late afternoon, the chance for showers will increase as an area of rain slumps southeastwards from central Saskatchewan. Temperatures will dip to a low near 2-3°C early Thursday morning as rain moves in overnight.

Long Range Outlook

Thursday looks rather unpleasant with rain likely changing over to snow in the morning as significantly colder air floods southwards behind a strong low moving across southern Manitoba. Temperatures will reach a high in the low single digits with a brisk northerly wind – likely reaching 40-50 km/h – as the snow tapers off in the afternoon.

GFS 850mb Temperature Forecast valid 00Z Thursday October 26 to 00Z Friday October 27, 2017
This animation of 850mb temperatures – approximately 1.5km above the ground – very clearly depicts the colder air moving into the region through the day

The remainder of the week looks quite cool with highs in the low single digits and overnight lows dipping below the freezing mark each night well into next week. The one saving grace will be the cloud cover, ranging from mixed skies to overcast, that will help moderate the temperatures from getting too cold.

This pattern of cooler conditions will continue through much of next week as a persistent west-coast ridge, eastern Canada trough pattern sustains a generally northwesterly flow over the eastern Prairies.

Winnipeg’s seasonal daytime high is currently 7°C while the seasonal overnight low is -3°C.

  1. Some cloud will likely be around in the Red River Valley through much of the day as it comes off of Lake Manitoba and Winnipeg in the northwest wind. Whether Winnipeg sees any of it will depend on the exact wind direction, but it will likely remain outside the city.

Potential Record-Breaking Warmth Friday Leads Into A Seasonably Mild Weekend

Temperatures will soar into the low 20’s today and challenge a long-standing daily record high . Temperatures will then cool for the weekend as a low pressure system tracks through the region, but will still remain seasonably mild with daytime highs in the mid-teens.

Today will be a gorgeous day with temperatures soaring towards record values as very mild air – shown well by 850 mb temperature anomalies of 15 to 20°C above seasonal – moves into southern Manitoba. This mild air is being drawn northwards by a broad area of low pressure strengthening over Alberta. In addition to the warmth, strong southerly winds will develop across the Red River Valley today, reaching a peak near 40 gusting to 60 km/h through the afternoon.

850mb temperatures are forecast to be over 15°C above normal over southern Manitoba.

The southerly winds and mild temperatures aloft will result in daytime highs climbing into the low 20’s today; in Winnipeg, the high should reach 23°C, or perhaps a tad warmer, challenging the current record daily high of 23.9°C set in 1958. Clouds will build into the region through the day, going from sunny skies this morning to mixed skies this afternoon. Tonight should bring variable cloudiness and a low near 15°C. While the overnight low will likely remain higher than the record warmest daily minimum temperature of 12.2°C set in 1953, Winnipeg won’t break a record due to this morning’s chillier low near 7°C.

Winnipeg will see more cloud on Saturday with mixed skies in the morning giving way to mainly cloudy conditions in the afternoon as a low pressure system moves through. Temperatures will be cooler than Friday, but still much warmer than seasonal as highs climb to around 18 or 19°C. Southerly winds of 20 to 30 km/h wills shift to the west-southwest behind a cold front pushing through in the morning. There will be a chance of showers along the cold front as well as a bit later in the afternoon, but at this point it looks like the odds are relatively low. Winds will persist at 20 to 30 km/h overnight as temperatures dip to a low near 6°C.

Several American models show the potential for a few isolated showers on Saturday across southern Manitoba.

Sunday will bring some sunshine back to Winnipeg with any remaining cloud from Saturday’s system clearing out in the morning. Temperatures remain warmer than seasonal with highs near 15 or 16°C as winds shift back to the south ahead of yet another low pressure system zipping across the southern Prairies. Cloud will begin to build back in through the afternoon with a slight chance of showers returning Sunday evening into the night. Lows will dip down to around 7°C.

Long Range

Next week will kick off with a return to seasonal temperatures with northwesterly winds predominant through the Monday and Tuesday. The remainder of the week looks like a bit of a temperature rollercoaster with unsettled conditions, however details remain fuzzy at this point. That said, it looks like much of the week will bring variable cloudiness and a few chances for rain (or snow!) as the storm track slumps southwards.

Winnipeg’s seasonal daytime high is currently 9°C while the seasonal overnight low is -2°C.

Forecast Update for Friday Night and Saturday

The disturbance that we wrote about in our forecast that went live early this morning is throwing a wrench into things as it has progressed eastwards much faster than models had anticipated, already spreading across southwestern Manitoba into the Red River Valley. This will dramatically change the forecast for Saturday morning and afternoon.

As of writing, the system is producing a line of precipitation extending from the Manitoba/Saskatchewan/North Dakota border east-northeast along a line that runs just through Boissevain and Deloraine into the Red River Valley. Much of the precipitation from this line is currently falling as rain, however snow is likely mixing in on the northern edge of the band, where temperatures have dropped towards the freezing mark.

HRRR Forecast Accumulated Precipitation valid 17Z Saturday October 14, 2017
The forecast total precipitation amounts from 9PM October 13 to 12PM October 14 reveal the narrow band that the rain/snow is expected to fall along.

Precipitation will push east-northeast throughout the night, however where it is expected to be heavy enough to accumulate in any meaningful way will lie along a very narrow band roughly located where the heaviest of the precipitation is as of this writing.

Much of this will likely remain as rain; there’s a fair amount of warm air aloft and temperatures are being maintained around 2-4°C underneath the precipitation. As mentioned before, some snow will likely mix through as it progresses eastwards, but no significant accumulations are expected.

Over the heaviest band in the southwest corner of the province, it will likely be a decent soaking, however, with 10-20 mm of rain possible.

Shift Southwards Spares Southwestern Manitoba From Snow

With the shift southwards, the southwest corner of the province will be spared from the 5 to 10 cm we suggested was possible in our earlier forecast. The closer proximity to the border has the precipitation falling in warmer conditions, causing that snow to fall as rain instead.

Winnipeg On The Edge

The forecast for Winnipeg continues to be difficult, with the city likely resting right on the northern edge of the precipitation. It seems most likely that the city will see some rain or snow beginning around 2 to 4AM and tapering off by 7 to 8AM. No significant accumulations are expected.

Still A Chance for Afternoon Showers

This disturbance won’t be completely gone for Saturday afternoon, with a chance for showers re-developing over the Red River Valley mid- to late-morning and persisting until mid-afternoon. Temperatures will be warm enough that snow won’t be a concern, but 2-4 mm of rain will be possible under the “heaviest” band of showers. The chance for rain should remain south of Winnipeg.

Slightly Warmer Highs Expected

With the shift in timing for this system, daytime highs will be slightly higher than we forecast earlier. With the higher intensity precipitation finished by mid-morning, highs will be able to climb a bit warmer into the 6 to 8°C range instead of near 5°C like we advertised before.

The faster and more southerly arrival of this system means that the daytime hours on Saturday will see less precipitation than expected and allow daytime highs to climb a bit warmer. The heaviest amounts will fall along a narrow band in the southwest corner of the province with 10 to 20 mm possible through the and Saturday morning. The precipitation is largely falling as rain instead of snow, thanks to the slightly warmer temperatures aloft due to the shift southwards of this disturbance’s track.

Hopefully this covers what to expect; sometimes these systems progress a bit unexpectedly and all model guidance just…fails. This is one of those cases. We think the newer runs of rapid-update models are getting a good handle on it, though, so hopefully this forecast is able to hold up a bit better than the last one.