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:

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.

May 22, 2013 Comments

benign weather

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

Monday and Tuesday

Monday

Periods of Rain
11°C / 7°C

Tuesday

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

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.

May 20, 2013 Comments

rainlong weekendlow pressure

Severe Weather Event South of the Border: Possible AWM Chase Sat/Sun

The same system that will cause Southern Manitoba to have a rainy May long weekend is expected to produce a string of severe weather days across the Central US, starting today, continuing through at least Tuesday. A negatively-tilted longwave trough approaching from the west will help to provide the necessary wind shear, lift, and instability for severe storms to develop. A broad surface low with an extending cold front from Central South Dakota through Nebraska will be in place with a warm front slicing through north-east South Dakota. Another, stronger, low pressure center will be in place in Kansas with an extending dryline all the way down to Texas. These features will offer enough lift for severe storms on Saturday. This, combined with other severe weather ingredients such as a stiff low level jet (LLJ), high amounts of instability, deep low level moisture and low cloud bases is ideal for severe weather and tornadoes. The Storm Prediction Center has issued a Moderate Risk for Nebraska and Kansas with a Slight Risk extending up to North Dakota for their 2 Day Outlook as of Friday night.

As of Friday evening these ingredients appeared to be maximized in the vicinity of north-western Kansas near the Nebraska border. Storms will not be confined to this area though, as strong to severe storms will still be possible into South Dakota and down into Oklahoma, but whether they will be tornadic or not is still to be seen.

The ingredients that will be in place tomorrow in South Dakota:

• Instability: about 2000J/Kg of MLCAPE (mixed layer)
• Surface dewpoint: 18°C
• Shear: 40 knots (0-6km shear)
• LLJ: 20 knots
• Lifting condensation levels (cloud bases): around 750m

With the LLJ being only 20 knots, an AWM Chase is still up in the air. If models tend towards a stronger LLJ, the chase will likely be on with a target somewhere in Central South Dakota.

Sunday also offers a significant severe weather threat as the trough continues its trek towards the east. Severe weather risk would extend into Southern Minnesota all the way down to Oklahoma. There is still some uncertainty about Sunday but it does look like another significant severe weather outbreak day for the Plains and Upper Mississippi Valley. Stay tuned in the comments section as the event approaches, updates will be posted.

AWM Chase is On!

Two of the AWM team members will be out chasing this setup along with a student from the University of Manitoba. You can keep up with their chase right here:

May 18, 2013 Comments

EIWNOutbreakSevere WeatherTornadoesPlainsChase

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

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…

Read More

May 17, 2013 1 Comments

RainThunderstormsShowers

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

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.

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.

May 15, 2013 Comments

showers