Chance of Freezing Rain Over The Red River Valley

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A large upper trough swinging across the Prairies is supporting two low pressure systems, one in central Saskatchewan and one in the Northern Plains of the United States, that will move across Manitoba overnight and tomorrow morning, bringing with them snow and the risk of freezing rain.

Dec. 31 Prog

For southern Manitoba, the main concern will be the precipitation generated along the apex of the frontal wave as it occludes southeastwards from the northern low in Central Manitoba to Minnesota. The warm front will align somewhere near a line from Winnipeg to Sprague, and slowly shift south/southeast through the day. Areas near the International Border have the greatest risk of freezing rain, due to the higher intensity of the precipitation expected there. The risk diminishes as you head north towards Winnipeg. I agree with the latest Environment Canada forecast that calls for ice pellets in Winnipeg; the warmest air should stay south of the city and we will likely have enough cold air entrenched to freeze any rain that comes out of an above-freezing layer. I can’t exclude the chance of a brief period or two of freezing rain, especially late overnight and early tomorrow morning. As this system develops, snow will become the predominant weather type, and much of the RRV can expect between 2-4 cm of the white stuff, while a few localities may get up to a couple inches.

I think it’s likely areas south of Morris will see some duration of freezing rain before sitching over to snow. The good news is that this doesn’t have the makings for a large-scale freezing-rain event, so there shouldn’t be any concern of widespread highway closures. Given that some roads are already very slippery, however, drivers should take caution when travelling overnight or tomorrow as fresh snow may be hiding a layer of ice underneath. Always drive with care when freezing rain and snow occur.

This system should clear out tomorrow afternoon, bringing in strong northwesterly winds behind it gusting up to 70 km/h. Fortunately, the arctic cold front is well to our north, so while chilly, we likely won’t even seen our temperature drop to even -15 to -20°C for overnight lows before the next swell of warm air pushes across the Prairies, bringing us continued pleasant winter weather with daytime highs in the -5 to 0°C range! The strong winds will move in tomorrow evening and last through much of the day on Sunday before tapering off, bringing us wind chill values as low as -25 in Winnipeg.

So hang in there, a couple chilly days and we’ll be back to pleasant temperatures with a fresh coat of snow! Happy New Year!

What Happened to Our La Nina?

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What Happened to Our La Nina?

Earlier this year, the NWS issued their winter forecast that called for colder than normal temperatures and higher than normal precipitation. I expressed my doubts about the physical practicality of such a forecast.

Well, that forecast isn’t working out, and the NWS has issued quite a good little summary on what’s happening. It’s definitely more technical than a newspaper article, but it’s certainly not a research article or anything like that. If you’re interested in knowing why our winter has been how it is, this is a really good read!

I still stand by the original forecast not making much sense. As for the near-future, one of my best cold-weather predictors, Vladivostok, Russia, is still relatively warm (only -20°C), so a cold outbreak is probably a long ways off yet.

Handy forecasting trick: Most of the Prairie cold-outbreaks occur when a large ridge slides over the pole from Siberia and then down through Yukon (the Yukon? Any Yukon-ites able to enlighten me?) into the Prairies. When doing medium-term forecasts (8-15 days), I’ll often look at Vladivostok. If they’ve hit below -35°C, then within 6-12 days we’ll often get the cold weather here with daytime highs between -20°C and -25°C. If they get more towards -50°C, then within two weeks the Prairies will have widespread cold temperatures and extreme wind chills.

I still wonder why we bother with seasonal forecasts. Understanding how these oscillations all work is great, but our ability to accurately forecast them individually is often lacking, and we’re a long, long ways off from being able to resolve numerically how all these things interact together. If anything, this just shows how constant analysis and diagnosis of ongoing weather and climate patterns are the best method of forecasting.

Slight Chance of Showers Saturday Evening

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A system tracking across the Rockies into Alberta will slide quickly across the Prairies, brining increasing cloudiness to Winnipeg and the RRV Saturday afternoon with a slight chance of showers in the evening. For more info, read on!

GEM-REG 3HR. QPF
12Z 21 October GEM-REG 3 hour precipitation accumulation valid at 00Z Sunday (Saturday Evening)

Overnight a low pressure system will track across the Central Prairies towards Manitoba with a developing N-S trough intensifying as it moves eastwards. As it enters The Pas and Norway House areas on Saturday, Winnipeg and the RRV will see increasing clouds and a strengthening southerly wind to 30-40 km/h. As the trough swings through Winnipeg in the late afternoon and early evening, we’ll see a slight chance of a shower or two. The bulk of the precipitation should stay north of the city, closer to the low, where there is more significant lift. All models bring the edge of the rain close to Winnipeg, though, so it certainly isn’t out of the question for us to end up getting 2-4 mm out of an hour or two of rain. It seems most likely, though, that late afternoon and the evening will be overcast with a scattered shower or two.

After this system passes through, we’ll enter a stagnant pattern for a couple days with daytime highs just below 10°C and overnight lows slightly below 0°C.

Ensemble 500mb Theta-E
Ensemble Mean 500mb θe

The next chance for significant weather looks to be next Tuesday night / Wednesday morning as a rather sharp 500mb cold trough swings across the province. This will present us with a slight chance of flurries overnight, but shouldn’t amount to too much. More on that next week.

Have a great weekend and enjoy these crisp fall days!

Significant Rainfalls On The Way for Tuesday

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A low-pressure system approaching Manitoba will rapidly develop this evening as it enters the province, bringing one of the most substantial widespread rainfalls of the last several months. The largest amounts will lie along a narrow axis called the deformation zone which makes these events hard to predict: a slight change in the track of the low can cause shifts in the placement of the deformation zone. So where will Winnipeg lie? What can other areas of the Red River Valley expect? Click through to find out!

12hr. QPF GEM-REG
12hr. Rainfall from the GEM Regional Model, valid 00Z Wednesday Evening

This system is slowly built into Southern Alberta through the night last night, and is now beginning to quickly move eastwards across the Prairies. Currently, the system is fairly weak, giving only light showers to many areas across Southern SK/AB, however a shortwave ejecting onto the Prairies from the Canadian Rockies will slidealong the US/Canada border this evening and overnight and will be able to tap into warmer air aloft over the Eastern Prairies and a pool of extremely cool, Arctic air over the Northwestern Prairies.

The combination of a powerful shortwave with access to these two air masses will result in a rapidly deepening low pressure system. Currently, the low sits just east of Regina and has a central pressure of about 100.8kPa. By mid-morning Tuesday, the low will sit over the Southern Red River Valley with a central pressure of 99.5kPa, which is a significant drop in pressure over 12-18 hours.

Rain will push into SW Manitoba by this evening, with a few scattered showers across the Red River Valley before midnight. Rain will intensify and build across the RRV into SE Manitoba overnight as the system really starts tapping into some of the cooler air across the Northern Prairies. The deformation zone will become quite apparent by tomorrow morning, which will make the precipitation forecasts easier, but right now it’s looking like it will set up just over or the southeast of Winnipeg.

So! What does this all mean?

Rain will push into Winnipeg and areas south overnight and be quite intense at times. Widespread amounts through these areas will likely be 5-10mm overnight, with the chance of some higher amounts over the Western Escarpment. Tomorrow will be quite an active weather day, with continuous rain for much of the RRV and strong winds with gusts as high as 70-80km/h from the north. These strong winds will likely cause some localized erosion on the lee beaches of the lakes which are still dealing with high water levels.

Areas south of Winnipeg will see an additional 15-25mm of rain tomorrow with few areas getting as much as 30mm, as will the Whiteshell. Winnipeg itself, however, will be trickier. If the deformation zone sets up to the southeast of us, we’ll likely only get perhaps 5-10mm. If we end up under it, or it moves to our NW, we could see substantial amounts of rain. Right now, the likely scenario is 10-15mm, with the potential for amounts as high as 30mm.

The system will clear out by Wednesday and we’ll be left with daytime highs in the mid to high teens for Wed/Thursday as we sit in cooler air behind the cold front associated with the system. By the end of the week, another upper ridge begins to build into the Prairies which will push sunshine and warm temperatures back into Southern Manitoba. Currently, it looks like we’ll see highs in the mid-20’s by week’s end.

So enjoy that (most of) you’ll be at work tomorrow during our kind of miserable day, and we’ll all enjoy the sunshine and warm temperatures in another taste of summer this weekend!