After enjoying a couple days of above-normal temperatures, a powerful low pressure system backing into Hudson Bay will drive a cold front southwards across Southern Manitoba today, bringing with it cooler weather.
850mb GEM-Reg Temperature Analysis valid 15Z this morning.
The cold front will sweep through Southern Manitoba late this morning, with winds picking up from the north and increasing to 30-40km/h. Scattered showers will develop along the front as it pushes through the interlake, so most regions in the Red River Valley have a chance of seeing some rain later this morning. It won’t last long, though, and cooler air will stream in on the backside limiting our daytime high in Winnipeg to around 11°C. Skies will clear quickly tonight as an Arctic ridge builds in and helps our overnight low drop to -4°C.
The aforementioned low backing into Hudson Bay will become captured today and will block the eastwards advancement of the Arctic ridge which means, unfortunately, that we’ll be under the influence of the ridge and its outflow for the next few days. Thursday will see sunny skies with a daytime high of only around 9°C, and Friday will be much of the same with a high just a couple degrees warmer. By Saturday it looks like the ridge will start to move off and although the day will still be cool, a southerly flow will begin to bring warmer weather back to our region.
Cooler weather has settled over Southern Manitoba and while it won’t stay below normal for long, we won’t really be hitting above normal temperatures any time soon, either. The week ahead looks like a middle-of-the-road week with some sun, some cloud, an a chance for some showers.
850mb Analysis of the θe field from the NAM, valid at 00Z Tuesday Evening
Today will bring clear skies to Winnipeg with diminishing winds. Our expected daytime high of 2°C will be a whopping 9°C below our normal daytime high of 11°C for this time of year. Tonight we’ll drop down to a chilly -7°C under clear skies.
Tomorrow will start off sunny and then cloud over in the afternoon as a low pressure system moves across Southern Manitoba. The main shortwave will track through the interlake, bringing in slightly warmer temperatures aloft across Southern Manitoba. The main surface low, however, will track just south of our border, keeping the warmer near-normal, temperatures to our south. Given that Southern Manitoba will have the southern low skirting just south of the International Border and be under the influence of large-scale ascent associated with the shortwave tracking further north, it looks quite likely that an area of showers will blossom as the system moves into Manitoba, and that regions along or just north of the Trans-Canada highway southwards to the U.S. Border will see showers on tomorrow afternoon. As ususal, the exact track will be key, however it’s fairly likely that most communities in the Red River Valley will see some showers tomorrow.
Shortwave vs. Surface Low? A shortwave is the term applied to a troughing disturbance in the upper atmosphere that travels along with the main flow aloft. A surface low is a low pressure system present in the lowest levels of the atmosphere. Each shortwave will often have a surface low pressure system associated with it and the two work in tandem to link the upper and lower atmospheres together. They are not co-located, however, and when compared on a map, can be hundreds of kilometers away from each other.
Things will clear out quickly tomorrow evening and then the rest of the week looks fairly benign, with daytime highs around 7°C and overnight lows around -5°C. Temperatures may jump back to normal on Friday with the approach a more significant low pressure system, but models disagree on it’s exact placement and some keep us on the cooler side of thigns; we’ll have more on that later in the week.
8-14 Day Temperature Anomoly Outlook from the NAEFS model from 12Z April 15, 2012.
Temperatures across the Eastern Prairies have been slightly below normal lately due to a persistant upper low anchored near Southampton Island in Hudson Bay. This low has maintained a trough and NW flow aloft over the Eastern Prairies and has been responsible for helping shunt systems further south and keeping us cooler. This large-scale pattern is expected to hold for the next 6-9 days, however signs are pointing to a breakdown of the low and a significant upper ridge to build across the Prairies in the Day 9-12 range. Ensemble models seem to agree with this idea, and as shown above, the NAEFS currently has fairly high confidence for a return to above-normal temperatures next week.
Elsewhere In Weather News
Tornado Alley Hit by Major Outbreak
The major tornado outbreak that occurred in the US Plains on Saturday, April 14th 2012 will be remembered for many years to come. Every single ingredient for long-tracked, damaging tornadoes was present. The storms developed due to a low pressure system centered over the Nebraska/Kansas border which drew in moist air from the gulf and into the Plains –- this spawned extremely strong supercells along its dryline as it slowly moved eastwards.
In anticipating major storms, the SPC had given plenty of warning to the affected areas, issuing a high risk in the 2-day outlook which is a very rare occurrence that has only happened once before. The high risk for tornadoes meant that within a 40km radius there was a 45% chance of an EF-2 to EF-5 tornado in parts of Nebraska and Kansas.
Probabalistic Tornado Graphic issued by the Storm Prediction Center on Saturday, April 14th.
Supercells had already exploded in the morning in the state of Kansas but did not produce any tornadoes until about 11:30am when a tornado had been spotted just north-east of North Platte, KS. From then on, tornado sightings were reported every 15 minutes until nightfall as just about every supercell from Nebraska to Oklahoma had a good chance of producing a tornado. Also to be kept in mind is that these supercells produce huge hail, reaching softball size (11.4cm in diameter), and cause significant damage to just about everything as they fall.
Violent tornado near Cherokee, OK
In all, around 100 tornadoes were sighted and luckily, many of them kept populated areas out of harm’s way as they missed villages and major cities. Unfortunately, there was one major city that had not been spared. The city of Woodward, OK (town of 12,000) was directly hit by a tornado, with a preliminary rating of EF-3. Five deaths and 29 injuries occurred in this city as the sirens did not go off, due to the tornado having cut their power. What aided the probability of injury and loss of life was also that the tornado had hit just after midnight, when most residents were asleep and it is extremely difficult to spot a tornado.
Some of the strongest tornadoes produced on Saturday – preliminary ratings:
EF-4 that just missed Salina, KS.
EF-3 that struck south-east Wichita, KS.
EF-3 that killed 5 in Woodward, OK.
EF-2 that damaged more than 75% of Creston, IA (town of 250).
Here are a couple of the many breath-taking photos/videos captured yesterday by storm chasers and those affected:
EF-4 tornado that just missed Salina, KS.
A large tree limb punched through the car’s side, product of the Wichita tornado. (Source: Cory Mottice)
Home moved off its foundation and destroyed in Wichita, KS.
Very powerful tornado north of Soloman, KS. (Source: AP)
Unfortunately the severe weather threat didn’t end there. More tornadoes were reported in the Upper Mississippi Valley on Sunday associated with the same system. As the system will race east on Monday, tornado probabilities are greatly reduced across the eastern half of the country however, severe thunderstorms are certainly not out of the question as cold air clashes with the warm air situated ahead of the system.
Southern Manitoba will see a much more pleasant second half to the work week as an Arctic high pressure system exits the region and allows warmer air to return to the region. Temperatures will moderate and rise to above normal by Friday before a complex weather setup brings showers this weekend.
Southern Manitoba has seen the coldest weather we’ve seen in quite a while. Sunday’s maximum temperature of -0.7°C was the coldest day we’ve had since the mercury topped out at -3.9°C on March 9th. The high pressure system responsible for the cooler temperatures brought a record daily overnight low temperature to Wynyard, SK on Monday morning where the temperature bottomed out at -18.0°C which beat out the old record of -15.6°C set in 1940 (records for Wynyard, SK began in 1940).
700mb temperatures valid 00Z Wednesday Evening
With the main ridge axis through the Red River Valley, winds will begin to pick up out of the SE today as warmer air pushes in aloft. This, combined with plenty of sunshine, should allow our temperatures to rebound nicely to around 7°C this afternoon. Warm air will continue to push into our region in advance of an upper low trundling into the northwestern United States and push our daytime high up into the mid-teens for Thursday.
The weather will take a turn on Friday as showers develop overnight Thursday and push into Southern Manitoba Friday morning. Currently it looks like we’ll see just some light showers; remants of nocturnal convection from North Dakota moving along with an area of lift associated with a dying surface low. What actually happens will depend significantly on how the rain develops in North Dakota, so we’ll be sure to keep an eye on that. For now, enjoy the next couple days! Just don’t forget a jacket out there for this morning, it’s chilly!
Southern Manitoba will continue to see unsettled weather through the weekend with system after system tracking through our region. Despite this, temperatures will remain above normal, contiuning this month’s summer-like trend.
We’ll start off with clear skies this morning with patchy fog through the Red River Valley which will burn off by mid-to-late morning as that late-March sun gets to work. We’ll see our temperature get up to 12 or 13°C before skies cloud over mid-to-late afternoon. Most areas in the Red River Valley, including Winnipeg, will then have a chance of seeing some showers as a weak warm front pushes eastwards through the area.
GEM-REG Accumulated Precipitation for Friday night.
Overnight, much of the Red River Valley has a decent chance to see rain as the mid-levels destabilize with an injection of cold air at 700mb associated with a shortwave tracking through Central Manitoba. Positioning of the shortwave will be crucial to where the precipitation falls, but current indications are that an area of rain will blossom overnight near Brandon and travel east, with lighter showers south of the Trans-Canada Highway and 4-8mm of rain along and north of the TCH.
That rain will clear out by midday Saturday, and the Red River Valley will be left with just a few clouds and beautiful temperatures around 15°C.
24-Hour Precipitation Accumulation from Monday evening to Tuesday Evening
It was not mean to last, however, as yet another low begins it’s trek into the Prairies. Winnipeg will get to 11 or 12°C before more clouds push in by mid-afternoon. Light rain will push into the Red River Valley overnight Sunday and then intensify Monday morning, dropping another 5-10mm of rain before it pulls out on Monday evening.
All of these systems are sensitive to exact tracks of subtle features, so we’ll be sure to provide updates in the comments as the weekend progresses. In short, for much of the Red River Valley, the next few days will be unsettled with pleasant temperatures in the low-to-mid teens when the sun manages to poke out and showers/rain every 24-36 hours.
