A significant, and potentially historic October winter storm is set to impact parts of the northern Plains and southeast Prairies, as heavy wet snow and potential blizzard conditions could develop across the region on Friday and into Saturday as storm strength peaks during early occlusion.
Impacts
Given that the storm is expected to occur at the start of the Canadian Thanksgiving long weekend, impacts to travel will likely be significant. Highway travel could become difficult to impossible beginning early Friday and lasting into Saturday, and wind-driven snow leads to whiteout conditions across parts of southern Manitoba and North Dakota. All travel should be avoided during this time due to dangerous or impossible travel conditions and attendant risks of being stranded. Icing could also occur near the Red River Valley, resulting in slippery patches on roads there, prior to precipitation transitioning to snow.
Delays and possibly cancellations to flights are likely to occur at area airports. As well, heavy, wet snow could lead to tree damage, as many trees are still in foliage. This will also lead to a threat of power outages across the affected area.
Finally, a soggy Red River Basin from record-breaking fall precipitation will see potential flood conditions exacerbated owing to heavy precipitation totals. In fact, the Red River Floodway has already been opened for the first time ever in fall in Winnipeg - and while rivers aren't expected to crest their banks, high flows will continue to occur until they are projected to peak between October 17-20.
Meteorology
A truly classic Colorado Low, with textbook mid-latitude cyclone structure departs the Rockies and zips up the baroclinic zone across the northern Plains on Thursday and into NW Minnesota, when it begins to occlude on Friday. Well-developed airstreams will be observed as the cold conveyor belt wraps around the low, bringing heavy snow and possible blizzard conditions to its northwest, while the overrunning warm conveyor belt adds Gulf moisture to the system. Meanwhile, the dry conveyor belt descends as a dry slot and carves out the comma head of the system as it begins to occlude, and the surface low bottoms out sub 994mb per NAM guidance.
During early occlusion, very strong ascent occurs over southern Manitoba during the day on Friday, as DCVA, WAA, and ascent in the left exit region of a curved upper jet streak work in tandem. Embedded slantwise and upright convective elements will also occur on Friday, bringing locally very heavy precipitation rates and even a risk of TSRA/TSSN across the region around midday.
Thermodynamic profiles suggest that SLRs will generally be between 5:1 and 8:1 across southern Manitoba, and decreasing with eastward extent. However, as cold air wraps into the low post-occlusion, profiles should support higher SLRs with time later on Friday. DGZ depths will be unsubstantial. Meanwhile, low level stability profiles could permit some downward momentum transfer associated with a strong northerly low level jet stream on the order of 60-70 knots, which could yield wind gusts approaching 90-100km/h across south-central Manitoba on Friday, resulting in whiteout conditions as a potential blizzard develops causing extensive blowing and drifting snow - despite the snow being fairly wet. Moreover, expect to see enhanced snowfall totals along the elevated terrain features of the Manitoba Escarpment as a result of this storm.
The snow has already been occurring and will continue through Thursday along a deformation zone, where isolated bands could mean accumulations get a head start ahead of the main event on Friday and into Saturday. Winnipeg will continue to be the wildcard, as the rain/snow line sets up near or just east of the city. For what it's worth, SREF ensemble guidance as of Wednesday evening has been trending to cluster a greater number of members toward significant totals. Overall, downstream ridging will cause the system to stall somewhat - maximizing impacts for a longer period of time.
Impacts
Given that the storm is expected to occur at the start of the Canadian Thanksgiving long weekend, impacts to travel will likely be significant. Highway travel could become difficult to impossible beginning early Friday and lasting into Saturday, and wind-driven snow leads to whiteout conditions across parts of southern Manitoba and North Dakota. All travel should be avoided during this time due to dangerous or impossible travel conditions and attendant risks of being stranded. Icing could also occur near the Red River Valley, resulting in slippery patches on roads there, prior to precipitation transitioning to snow.
Delays and possibly cancellations to flights are likely to occur at area airports. As well, heavy, wet snow could lead to tree damage, as many trees are still in foliage. This will also lead to a threat of power outages across the affected area.
Finally, a soggy Red River Basin from record-breaking fall precipitation will see potential flood conditions exacerbated owing to heavy precipitation totals. In fact, the Red River Floodway has already been opened for the first time ever in fall in Winnipeg - and while rivers aren't expected to crest their banks, high flows will continue to occur until they are projected to peak between October 17-20.
Meteorology
A truly classic Colorado Low, with textbook mid-latitude cyclone structure departs the Rockies and zips up the baroclinic zone across the northern Plains on Thursday and into NW Minnesota, when it begins to occlude on Friday. Well-developed airstreams will be observed as the cold conveyor belt wraps around the low, bringing heavy snow and possible blizzard conditions to its northwest, while the overrunning warm conveyor belt adds Gulf moisture to the system. Meanwhile, the dry conveyor belt descends as a dry slot and carves out the comma head of the system as it begins to occlude, and the surface low bottoms out sub 994mb per NAM guidance.
During early occlusion, very strong ascent occurs over southern Manitoba during the day on Friday, as DCVA, WAA, and ascent in the left exit region of a curved upper jet streak work in tandem. Embedded slantwise and upright convective elements will also occur on Friday, bringing locally very heavy precipitation rates and even a risk of TSRA/TSSN across the region around midday.
Thermodynamic profiles suggest that SLRs will generally be between 5:1 and 8:1 across southern Manitoba, and decreasing with eastward extent. However, as cold air wraps into the low post-occlusion, profiles should support higher SLRs with time later on Friday. DGZ depths will be unsubstantial. Meanwhile, low level stability profiles could permit some downward momentum transfer associated with a strong northerly low level jet stream on the order of 60-70 knots, which could yield wind gusts approaching 90-100km/h across south-central Manitoba on Friday, resulting in whiteout conditions as a potential blizzard develops causing extensive blowing and drifting snow - despite the snow being fairly wet. Moreover, expect to see enhanced snowfall totals along the elevated terrain features of the Manitoba Escarpment as a result of this storm.
The snow has already been occurring and will continue through Thursday along a deformation zone, where isolated bands could mean accumulations get a head start ahead of the main event on Friday and into Saturday. Winnipeg will continue to be the wildcard, as the rain/snow line sets up near or just east of the city. For what it's worth, SREF ensemble guidance as of Wednesday evening has been trending to cluster a greater number of members toward significant totals. Overall, downstream ridging will cause the system to stall somewhat - maximizing impacts for a longer period of time.
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| EPS ensemble guidance suggests the heaviest totals will occur near the international border SW of Winnipeg. While it is displayed here as 10:1 (and not including the effects of melting and compaction), I would not rule out at least a foot of snow falling in the bullseye. |
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