Risk of Thunderstorms to Start the Week

Brad Leave a comment

One of our first risks for thunderstorms will come early this week.

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The green area outlines the risk of thunderstorms on Tuesday

Monday

Monday
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Mainly cloudy. Chance of showers.
21°C / 15°C

Today should be a generally dry day in Southern Manitoba with only a chance of showers. There is also a slight risk of a thunderstorm, but any storms that develop will be relatively weak. Temperatures will be in the upper teens or lower twenties in most areas under mainly cloudy skies. The wind will be from the south-east.

Our next reasonable chance for rain will likely come tonight night as a powerful impulse generates an area of rain. This rain is currently expected to be heaviest over Western Manitoba, but may affect the Red River Valley as well, albeit with lesser amounts. It is entirely possible that this rain could miss us completely, but it is too early to say exactly what will happen.

Tuesday

Tuesday
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Risk of a Thunderstorm
23°C / 10°C

Tuesday should feature our best chance of thunderstorms this week. A low pressure system and its associated cold front will pass through Southern Manitoba at some point during the day – likely through midday – and may trigger some storms. These storms are expected to be non-severe, but if there is a bit more instability than currently expected, there is a very slight chance that one of two may become marginally severe. The main risks with any storms that develop will be hail, perhaps up to nickel size, and gusty winds. The storms should be fairly fast moving so heavy rain is a lesser concern. Other than this chance of thunderstorms, there will also be a general chance of showers through the day. Temperatures will be in the low, or maybe mid twenties (depending on how the weather features setup), with a southerly flow switching to a westerly flow after the frontal passage.

Wednesday

Wednesday
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Mainly Sunny
23°C / 8°C

No significant precipitation is expected in Southern Manitoba on Wednesday, except again for the odd shower. Temperatures will be in the upper teens or lower twenties with mainly sunny skies.

Long Range

At this point the long range forecast is fairly ambiguous, as it often is at this time of year. In the nearer term, it appears we may experience another significant rainfall event later this week as a powerful low pressure system develops to our south. This system may trigger severe storms in the US Plains, while bringing us a bought of rainfall. In fact, this system is looking quite similar to the one that brought parts of Southern Manitoba 200mm of rain and triggered severe storms, including the Moore, OK tornado, in the US a week ago. There is still significant uncertainty in terms of how this next system will play out and at this time it isn’t expected to produce the massive rainfall amounts that the last one did. We’ll have more details on this system on Wednesday. What happens beyond the end of this week is too uncertain to discuss right now.

Elsewhere in Weather News: May 25th, 2013

Matthieu Leave a comment

Powerful Tornado Devastates Moore, Oklahoma

As you may have heard through media reports these past few days, Oklahoma was subject to severe tornadic weather this week which resulted in catastrophic and tragic consequences for many. Supercells posed a threat to residents as they dropped a number of large tornadoes – including a historical tornado that struck Moore on Monday, May 20th. A longwave trough (same as talked about in last week’s EIWN) was in place on the west coast as were other factors that made the conditions ripe for strong, long tracked tornadoes.

Moore tornado

Supercell with hook echo and large debris ball (just west of Moore), May 20th, 2013. (Source: UCSB)

Moore, with a population of over 50,000, is located in the heart of Tornado Alley and has been struck directly by tornadoes 3 times in the past 15 years. The fact that they are situated where moist air comes in from the Gulf of Mexico and where a source of dry air from the south-west US not too far away, causes many dryline setups in mid-late spring – ideal conditions for triggering storms.

On May 20th, storm cells fired up early in the afternoon and quickly became supercellular and well organized with rotation. As the supercell approached the Moore area, a hook echo formed and not long after, a debris ball could be seen on radar just before it was passed over Moore – it was obvious that Moore was in dire trouble and a tornado had touched down. Thankfully, the National Weather Service in Norman provided generous lead time of 16 minutes before the tornado entered Moore, certainly saving many lives.

Moore damage

Aerial view of the damage in Moore. (Source: AOL)

Tragically however, even though advance warnings were given, 24 people perished that day. In some areas it was not possible to take refuge in interior rooms; EF-5 winds easily ripped apart any building in the tornado’s path. Damages are estimated to be in the billions of dollars with an estimated 1,300 homes destroyed and countless number of vehicles wrecked.

Incredible video of a close up view of the 2013 Moore tornado, not to be tried at home – very dangerous! (Source: Jeffery Lechus/Youtube)

It appears the storm track will remain active with troughing across the western part of the continent and intermittent shortwaves rounding down the ridge across Southern US. Severe weather looks likely in the High Plains region of the US (Nebraska, Kansas) in the coming week – not out of the ordinary for these locations at this time of the year.

Increasingly Unsettled

Brad Leave a comment

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

Brad Leave a comment

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.