Tag: Showers

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. ↩

A Mixed Bag in Store

Brad Leave a comment

Sunny skies will give way to clouds and a few scattered showers by midday today, but the threat will be short-lived as we move into a more stable, settled pattern for a brief reprieve from the wild weather of late. The calm weather won’t last too long, though, as more showers look to push into southern Manitoba on Friday.

Wednesday

24°C / 8°C
Becoming a mix of sun & cloud with a chance of midday showers.
Thursday

24°C / 12°C
Sunny
Friday

18°C / 12°C
Showers likely.

Today & Tomorrow

NAM Sounding for CYWG valid 18Z Wed May 15, 2013

Sounding for Winnipeg from the NAM valid at 18Z today.

We’ll see a sunny start to the day today, but as we warm up some convection will begin to bubble up by late morning. Widespread showers are not expected; while some marginal instability will be realized, moisture will be a limiting factor and increasingly so through the day. A few scattered showers will likely develop along a trough line extending from Swan River southeastwards through Lake Manitoba and the Red River Valley midday and then die out in the early afternoon as any remaining available moisture mixes out. We’ll climb to a high of 24°C and drop down to around 8°C overnight under clear skies.

Thursday will be a beautiful day as we sit under the influence of a weak ridge. We’ll climb to a high around 24°C again with an overnight low of only around 12°C with increasing cloudiness overnight ahead of the next weather system.

Friday

The main weather story on Friday will be an area of rain or showers that moves into Southern Manitoba ahead of a shortwave pushing through Saskatchewan. An area of showers with possible embedded thunderstorms will develop through western North Dakota and spread northwards on Thursday night into SE Saskatchewan and western Manitoba along a 850mb low-level jet (LLJ). The LLJ looks to maintain it’s strength or even strengthen through the day on Friday, which should make it able to maintain the area of precipitation as it spreads eastwards.

At this point, it looks like showers will push into SW Manitoba overnight on Thursday night and spread into the Red River Valley on Friday morning. The showers should push out of the Red River Valley by mid-afternoon after producing, in general, around 5–10mm of precipitation. We’ll be left with a chance for some lingering showers in the afternoon/evening.

The Long Weekend

Continuing in a long and storied history of May long weekends in Winnipeg, the weather does not look very good for this coming weekend. As the showers push through on Friday, it looks like a potent weather system will be busily organizing itself and preparing to deluge Southern Manitoba.

850mb theta-e values showing a southerly conveyor belt of gulf moisture setting up for the weekend.

A massive upper trough is forecast to move onshore from the Pacific Ocean this weekend, setting up a deep southerly flow that will transport large amounts of Gulf moisture northwards through the Great Plains into the Southern Prairies. A series of shortwaves is forecast to produce multiple shots of moderate rain and/or nocturnal convection. It’s still too early to get into specifics, but at this point it’s looking like it will rain over a majority of Southern Manitoba on Saturday, Sunday and Monday.

Different models currently have vastly different solutions: the GDPS[1] is forecasting absolutely unbelievable storm total precipitation amounts of anywhere from 5–10“ to upwards of 30”. This is impossible but does emphasize both the strength of the system and the amount of convection the GDPS is seeing. The NAEFS[2] is producing around 1–2“ of rain for most of Southern Manitoba. The GFS[3] is producing 2–3” of rainfall, but focused more over SE Manitoba with amounts diminishing westwards through the Red River Valley.

All in all it looks to be quite a rainy weekend. There are still plenty of details to be determined and we’ll take a much closer look at it for Friday’s post. We’ll leave a comment or two below with any interesting developments before then.

  1. Global Deterministic Prediction System (Canadian Long-Term)  ↩
  2. North American Ensemble Forecast System  ↩
  3. Global Forecast System (U.S. Long-Term)  ↩

Cold Snap This Weekend

Brad Leave a comment

Arctic air will continue to slump southwards behind yet another cold front moves through the Red River Valley today. We’ll see temperatures well below normal this weekend, but things should begin to rapidly warm up for the start of next week.

Friday

13°C / -1°C
Mix of sun and cloud. Chance of showers midday.
Saturday

7°C / -3°C
Cool and mainly sunny.
Sunday

12°C / 5°C
Sunny

We’ll see the busiest weather day today as a low pressure system and associated cold front sweeps through the Red River Valley, ushering in cooler Arctic air with breezy northerly winds.

12hr. QPF valid Friday evening.

Total precipitation through the day today.

An area of rain will push through the Interlake with this system while further south, just a few scattered showers will survive along the cold front as it passes through the Red River Valley. Here in Winnipeg, there’s a slight chance we’ll see a shower, but the better chance is further south and east of us, where a little additional daytime heating may help some showers develop with the frontal passage. Areas in the western half of the Red River Valley will likely see little or no rainfall today.

Winds will remain breezy through the day, with southerly winds of around 20km/h shifting to north-westerly behind the cold front and picking up to about 30km/h with gusts close to 50km/h. These north-westerly winds will usher in another shot of Arctic air giving the Red River Valley (hopefully just) one last cold snap through the weekend. Temperatures will climb to around 13°C before the cold front limits our warming and drop just below freezing tonight as winds diminish.

Saturday will bring very cool weather as Arctic air continues to infiltrate southwards. We’ll see a high of only around 7°C under mainly sunny skies and northwesterly winds of 20–30km/h, some 10+°C below normal. Temperatures will drop below zero on Saturday night as well, probably close to –3 or –4°C.

Sunday will see the warm air beginning to build back in, but we’ll only get to around 12°C under sunny skies. Overnight lows should be close to 10°C warmer than Saturday night, though, which will be welcome.

Into Next Week

Looking into next week, it seems like we’ll return to seasonal to above seasonal temperatures. The NAEFS correctly forecasted our cool down and seems to be indicating we’ll be trending upwards over the next 8–14 days. At this point it looks like we’ll return to the low-to-mid 20’s on Monday with potentially warmer weather on Tuesday.

It’s also looking like Tuesday night may bring Southern Manitoba’s first risk for nocturnal thunderstorms of the year. It’s still fairly early, but models are indicating that a low pressure system tracking through the region may develop & sustain an MCS on Tuesday night. We’ll definitely keep an eye on that system! Enjoy the sunshine this weekend and try not to forget that summer looks to arrive (for a more prolonged period, this time) next week!

Arctic Assault on Winnipeg

Brad Leave a comment

While we had a glimpse of how absolutely wonderful it will be for summer to be here over the past few days as temperatures shot up into the mid-20’s, the spring-that-never-ends is making an ugly return as multiple shots of Arctic air invade the Southern Prairies.

Arctic air invading the Southern Prairies

Cold Arctic air blasting south over the Prairies. Image from the NAM valid at lunchtime today.

Temperatures through the remainder of the week are going to go from below-normal to more-below-normal as the above pictured cold front continues to slump southwards. The cooler weather was ushered in overnight as the cold front passed through Winnipeg bringing strong, gusty northerly winds. Temperatures today will only climb to around 13°C with strong northerly winds gusting as high as 60km/h. Temperatures will dip down close to the freezing mark under clear skies tonight with widespread low temperatures of around 2°C.

Wednesday

13°C / 2°C
Clearing & windy from the north.
Thursday

15°C / 5°C
Mainly sunny.
Friday

12°C / 0°C
Cloudy with chance of late-morning showers. Clearing in the afternoon.

The rest of the week won’t fare much better. Temperatures will try to climb a little closer to normal tomorrow with highs reaching around 15°C. The low tomorrow night will be a little milder at around 5°C as some warmer air is pushed over the province ahead of an intense low pressure system working it’s way out of Alberta through Saskatchewan.

Friday will be fairly cloudy as yet another cold front sweeps through the Red River Valley. There may be a few showers along the cold front as it pushes through in the late morning and early afternoon, but only a couple mm of rain would be likely to fall, if any. Northerly winds in behind the cold front will clear the skies but limit our high as colder air is ushered in yet again. Overnight lows will drop close to 0°C on Friday night under clear skies.

Long-Term

A cold weekend is ahead of us as we move even deeper into the Arctic air mass. Saturday will be the coldest day with daytime highs only in the mid-to-high single digits with another night with temperatures at or just below 0°C. Conditions will improve on Sunday as the coldest air moves off to our east and the daytime high rebounds into the mid-teens.

At this point, it’s looking like we’ll be in for a huge turnaround early next week. Very warm air is expected to flood across the Prairies as an upper ridge begins building in. At this point it looks like we will start off next week with daytime highs rocketing back up into the mid-20’s. At this point it looks like 24 or 25°C is entirely possible with a slight chance we’ll see temperatures climb into the upper 20’s. The large-scale pattern shift looks like we’ll be moving into a more stable warm pattern, so just make it through the next 5 days and we’ll be enjoying summer!