Category: Forecasts

Increasingly Unsettled

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A massive upper low currently bringing copious amounts of rain to Southern Alberta will bring increasingly unsettled weather to Southern Manitoba as it flattens the upper ridge over the Eastern Prairies allowing weaker disturbances to push further east.

Today and Tonight

Friday

19°C
Increasing cloudiness in the afternoon; becoming windy.
Friday Night

10°C
Showers beginning in the evening.

We’ll see a pleasant day today with sunny skies for most of the day and our temperature recovering fairly quickly from our chilly overnight temperatures. We’ll see a high of 19°C today with winds increasing out of the south through the day to 40km/h with gusts as high as 60–65km/h. Clouds will begin pushing into the region later in the afternoon ahead of this evening’s weather.

RDPS 12hr. QPF valid 12Z Saturday

Rainfall accumulations for Friday night from the RDPS.

This evening, a low-level jet will push into the Red River Valley which will initiate and sustain an area of scattered showers stretching from North Dakota north-northwestwards across Southern Manitoba and into Saskatchewan. These showers will slowly push eastwards through the Red River Valley overnight giving generally 2–4mm accumulations with the potential for 5–10mm of rain under any slightly heavier showers that may get going.

The Weekend

A few remnant showers will linger through Saturday morning before tapering off and leaving more cloud than sun through the Red River Valley in the afternoon as we climb to a high of 19°C. More cloud will push in overnight as we drop to around 9°C.

Saturday

19°C / 9°C
A few showers ending in the morning then a mix of sun and cloud.
Sunday

17°C / 10°C
Mainly cloudy. Chance of afternoon showers.

Sunday will be a cloudy day with a chance of afternoon showers as a weak disturbance skips along the international border. Areas close to the border will see a much greater chance than we will in Winnipeg but anywhere that sees showers will likely see fairly minimal amounts, only a mm or two. The clouds will keep the high a bit cooler than the previous couple days at only around 17°C. Sunday night will be mainly cloudy with the temperatures dropping to about 10°C.

A Chance to Dry Off

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We’ll see sunny skies through the rest of the week and a chance to dry off after as much as 100mm of rain fell over Southern Manitoba over the weekend. The heavy rain caused a few problems of the weekend, mainly constrained to rapidly rising streams and rivers (which rose as much as a meter) and significant overland flooding. Thornhill, MB was particularly hard hit with enhanced rainfall occurring from the upslope enhancement of the western Red River Valley escarpment under northeast winds. It has been reported that 200mm or greater fell in the region, but with such sharp contrast to how much fell in nearby Morden (89mm) and CoCoRaHS reports totalling 2–3” (~ 50–80mm), it has to be considered an extremely localized event. Nonetheless, areas very close to the western escarpment were hit very hard by this rainfall event.

All that to say it was a very wet weekend that was easily the biggest rainfall event of the year. Some notable rainfall totals:

City/Town Rainfall (mm)
Deerwood 101
Morden 89
Somerset 81
Winkler 77
Manitou 76
Sprague 73
Letellier 71
Killarney 69
Carman (Ag.) 68
Altona 67
Boissevain 62
Carman (EC) 58
Gretna 58
Deloraine 55
Emerson 55
Morris 54
St. Pierre 52
Kleefeld 46
Treherne 41
Pilot Mound 40
Winnipeg 18–24 (Official)
29–34 (Unofficial)
Portage la Prairie 18
Brandon 16

It’s easy to see that the heaviest rainfalls fell in the SW Red River Valley, with lesser amounts east of the Red River and rapidly diminishing amounts near the Trans-Canada Highway. Fortunately, no rainfall is in the forecast for this coming week, which should provide the opportunity for things to dry off and a chance to get out there and cut your grass which, if it’s anything like mine, decided to grow about 4” over the past few days.

Wednesday

20°C / 3°C
Mainly sunny & breezy.
Thursday

17°C / 4°C
Mainly Sunny
Friday

19°C / 9°C
Mainly Sunny

We’ll see mainly sunny skies the next few days as a large surface ridge pushes through the province. High temperatures will be restricted into the mid-to-upper teens as cooler air aloft dominates along with a northeasterly wind that will keep cooler, dryer air feeding into southern Manitoba. Winds will still be a factor today as they increase to around 30–40km/h once we warm up a little bit. Winds will be a lesser issue on Thursday as the surface ridge lies right on top of us and the light winds slowly shift to southeasterly as we enter the return flow on the back-side of the ridge. For Friday, winds will likely pick up late in the day or overnight as the surface pressure gradient tightens up over southern Manitoba again as a low pressure system pushes into eastern Montana/the western Dakotas. Before then, though, the winds will likely be quite calm. Our high on Friday will push back towards the 20°C mark, but likely stop just short of it.

The return flow also looks to be tapping into a bit of moisture in the Central Plains which will begin increasing our dew points heading into the weekend. For us, it will just mean the assurance that we’ll stay much warmer at night (closer to 10°C than 5°C), but for further west in Eastern Saskatchewan it looks like the moistening air may provide fuel for the first organized thunderstorm events of the year.

The Weekend

The weekend looks to be fairly benign at this point over Southern Manitoba. It looks like the atmosphere is setting up into a weak blocking pattern once again with a large upper low spinning over the B.C. Interior and Alberta with upper ridging over the Eastern Prairies. There may be a few shortwaves that ride up the ridge, but at this point it looks like if any shower activity were to push into Southern Manitoba, it would be constrained close to the Saskatchewan border. At this point, I’m comfortable saying that we’ll probably see a mix of sun and cloud with highs in the low 20’s here in the RRV this weekend, with more showery, stormier weather confined mainly to our neighbours in Saskatchewan.

Wet End to a Wet Long Weekend

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This long weekend will end on a rainy note – big surprise! Conditions should gradually improve as we move into the work week.

image

A significant weather system will spin just to our south for the next couple days

Monday and Tuesday

Monday
image
Periods of Rain
11°C / 7°C
Tuesday
image
Periods of Rain Ending
14°C / 5°C

A powerful weather system over the Dakotas/Minnesota region will continue to bring rain to Southern Manitoba on Monday. Weather models wrap a band of rain through much of Southern Manitoba through all of Monday and even into Tuesday. Models are struggling to resolve the intensity of this rain and therefore total accumulations are a major question mark. If this band does indeed stall through Southern Manitoba for the next day and a half as models indicate, then storm total accumulations could well be in the 50 to 100mm range that models are predicting. On the other hand if things pan out differently than the models predict, which looks probable, then we’re probably looking at more like 30 to 60mm on a widespread basis (these numbers include Sunday accumulations as well by the way). I believe there is a sufficient moisture feed for those high end amounts (close to 100mm) on a localized basis. However, the intensity of rain appears to be lower than model predictions, so I think in general storm totals will be closer to the 30-60mm range mentioned above. Either way a lot of rain will be had today and tomorrow, not the way most people had hoped to spend their Victoria Day.

Wednesday

Wednesday
image
Mainly Sunny.
20°C / 5°C

Conditions should improve for Wednesday as we experience a brisk north-easterly flow behind Monday’s system. Temperatures should be in the upper teens or lower twenties.

Long Range

The late week outlook looks fairly seasonal temperature wise, with little or no additional precipitation. Long range guidance doesn’t give a clear picture of how the rest of May will play out. It doesn’t appear that we’re headed for any kind of significant cool down, but a large warm up doesn’t look likely…hopefully the long range forecast will show more clarity later this week.

Unsettled Weekend Ahead

Brad Leave a comment

An unsettled weekend lies ahead of us as the atmosphere slowly organizes itself into a major low pressure system to start next week.

North America Satellite Image - Annotated

North America satellite image showing the intense long-wave trough developing over the Rocky Mountains and associated convection with shortwaves pushing northeastwards into the Plains/Prairies. Orange arrows depict the jet stream.

We’ll see several batches of showers/thundershowers over the next few days before a significant area of rain develops through the Dakotas may push into Southern Manitoba for the start of next week. How stormy is it going to get? Lets take a look…

Today & Tonight

Friday

20°C
A few morning showers then mainly cloudy with a chance of afternoon showers.

Today will bring mainly cloudy skies over most of Southern Manitoba ahead of a weak shortwaves ejecting northeastwards from Wyoming towards north-central North Dakota which will be coupled with a decent 500mb jet streak. There may be a few light showers over southwest Manitoba or the Red River Valley this morning as some scraps of overnight convection drift in from North Dakota, then the next slight chance of precipitation will come this afternoon.

Whether or not the afternoon convection materializes is very questionable; if it does, it would likely be driven by a phenomenon called jet coupling1 as the nose of a 70-80kt jet pushes into Southern Manitoba from Wyoming/North Dakota catches up to a weaker 40kt jet sliding across the Interlake. The most likely area for showers would be south of the lakes in the Red River Valley and west towards Brandon and the Pilot Mound area. If any showers form they’ll be relatively weak and short-lived as most convective parameters aren’t all that favourable. We’ll climb up to around 20°C today.

Friday Night

12°C
Cloudy. Showers or thunderstorms possible overnight.

Things will begin to get more organized tonight as the first impulse pushes into Southern Manitoba. An area of showers and thundershowers should develop early in the evening through Montana and North Dakota and advect east-northeastwards into Southern Manitoba. The bulk of the system looks to track along the international border but will extend northwards towards Portage la Prairie & Winnipeg.

There’s uncertainty to exactly how far north these storms will push; the Trans-Canada corridor (including Winnipeg) may miss out on all of the precipitation or may end up seeing the bulk of it if things set up even 50-100km further north. It’s a fairly sensitive situation that we’ll be monitoring and providing updates below if necessary.

The precipitable water values are expected to rise to around 25-30mm tonight, which means that while the storms are not expected to really even approach what would be considered a severe thunderstorm, they may have the potential to produce quite a bit of rain, perhaps locally as much as 1 to 1.5” (25-35mm), in short periods of time under any heavier showers that may develop.

Saturday

Saturday

18°C / 11°C
Cloudy. Showers likely.

On Saturday we’ll likely see leftover convection pushing into the Red River Valley maintained by a weak low pushing northeastwards out of North Dakota. Whether or not this happens will depend on the low being able to initiate and support convection on it’s northern/northwest quadrant overnight, so it’s by no means a sure bet. If it does develop that convection, we’ll likely see some showers/rain in the Red River Valley through the day. Any left over precipitation will pull out of the region by Saturday evening at the latest with up to 10-15mm of rain falling through the day through the RRV and the Whiteshell. Mostly cloudy skies will remain through Southern Manitoba on Saturday night with temperatures dropping to around 10 or 11°C.

Sunday

Saturday

18°C / 11°C
Cloudy. Chance of heavy rain or thunderstorms…or not.

Sunday is a massive wildcard. What up until now has looked like a slam-dunk significant rainfall event for Southern Manitoba has been thrown into question by the latest long-range model runs which have pulled all the precipitation further south into the United States. Interestingly enough, it’s for different reasons:

  1. The GDPS2 pulls the precipitation further south due to a rather bizarre closed high it develops at 500/250mb that interacts the the long-wave trough in really, really bizarre ways. I’ve never quite seen anything like what the GDPS is doing with the upper flow and would say that I would err on the side of the past 4-5 runs which have all, definitively, placed the precipitation further north into Southern Manitoba. Importantly, the position of the main upper low has not changed with the latest GDPS run; it’s actually moved it a little east and a little further north, emphasizing the impact of the closed high it’s developing.
  2. The GFS3 is also pulling the precipitation further south, not because of bizarre acts of physics in the upper-levels, but for a rather boring reason: it’s faster and more progressive with the system. Overall it is now producing a little less precipitation than before and shifting everything further east. Instead of the deformation zone (which marks the northern/western extent of the precipitation) laying west-east through the southern Interlake region, it has the deformation zone laying along a line from Bismark, ND through Sprague, MB.

If the models are right about the rain staying to our south, then I’ll definitely believe it’s for the GFS’ reasons before I give the GDPS honours for a correct forecast. If they’re wrong, though…

If the previous runs of the models turn out to be correct, then we’d see heavy rain or thunderstorms push up into the Red River Valley on Sunday afternoon, pushing as far north as the southern Interlake by evening. The precipitation would then stall out and slowly spread east and westwards across Southern Manitoba overnight. In this scenario, it would also be likely that there would be some embedded thunderstorms on Monday night.

The Start of Next Week

…will play out in one of two ways:

  1. We’ll see heavy rain through the first day or two of the week as multiple shots of precipitation wrap across Southern Manitoba.
  2. We’ll see mainly sunny skies as the deformation zone of this system sets up through North Dakota, locking the precipitation up to our south.

It’s simply too early to tell which will come true; again, we’ll update below when things become a little more clear.

  1. When looking at jets in the atmosphere, meteorologists will look towards the left side of the nose of the jet and the right side of the tail of the jet. These regions are areas of atmospheric lift which can be very vital in forecasting convection. Jet coupling occurs when two separate jets organize in such a way that the right side of the tail of one and the left side of the nose of the other cover the same area. When this occurs, the lift can be increased substantially. ↩
  2. GDPS stands for the Global Deterministic Prediction System; it’s Canada’s long-range forecast model. ↩
  3. The GFS is the Global Forecast System, the US’ long-range forecast model. ↩