The Big Warm-Up Begins; Moist, Gulf Air Mass Incoming

Today marks the beginning of skyrocketing temperatures over Southern Manitoba. Although daytime highs will be cooler again today, plenty of warming will be going on just off the surface, bringing us substantially warmer overnight lows and temperatures soaring into the upper twenties and low thirties by the end of the week.

Thursday Temperatures

Surface temperatures from the GEMREG model valid 00Z Friday (Early evening Thursday).

Winds will pick up out of the southeast today as we move onto the backside of the surface ridge that moved over our region behind the cold front that brought damaging winds to Southern Manitoba on Monday evening. This marks the beginning of a large-scale shift in the upper atmosphere that will rapidly push heat and moisture from the Gulf of Mexico northwards. Temperatures will only climb to around 20°C today, but our overnight low will show evidence of all the warm air moving in aloft by dropping down to only around 13°C, about 10°C warmer than our overnight low last night.

The heat and moisture will begin to build in on Thursday as the warm front lifts north of Winnipeg; our daytime high will push towards the upper twenties and settle around 28°C. This will feel quite different than our 29°C Monday afternoon because of one particular feature: moisture. While dewpoints will stay low today, they’ll begin to increase overnight and through the day on tomorrow, climbing into the low teens by Thursday evening. The heat and moisture will continue to build in for Friday, with daytime highs climbing to near 30°C with dewpoints climbing further into the mid-to-high teens. This will make things on Friday feel positively tropical, with Humidex values in the mid 30’s.

No precipitation is expected today or tomrrow, but as the heat and moisture build in, there’s certainly a chance of showers or thundershowers on Friday and Saturday. The chance for precipitation is elevated for Saturday as there will be additional lift and triggers present in the RRV as a low pressure system pushes through and drags a cold front across S. Manitoba. More on that later in the week.

Get out there and enjoy the summer-like weather! Friday and Saturday will see more cloud, but the higher dewpoints will help keep it feeling nice and warm out.

Warm, Dry Weather To Continue; Fire Risk To Remain High

Warm weather will continue over Southern Manitoba this week which, while great news for those of us who enjoy summer-like weather in May, will continue to sustain dangerous fire risk conditions. This news is not welcome to firefighters who are already battling two substantial fires: a 1,300 hectare fire southeast of Steinbach and a 200 hectare fire near Piney, MB.

Bush fire burning near Whitemouth Lake

Wildfire burning near Whitemouth Lake. This is one of two large fires crews are battling to contain in southeast Manitoba. Photo credit: Anonomous CJOB Listener

Hot, dry weather is expcted to continue today as Southern Manitoba continues to be flooded with a mild, Pacific flow. We’ll see a daytime high today of 28°C with winds once again out of the west/southwest at 30-40km/h with gusts up to about 50km/h. Dewpoints will remain in the low single digits, which will continue to challenge crews as they try to contain the wildfires.

A cold front will sweep through this evening, however one would be challenged to notice. Winds will shift to the north, but we’ll see overnight lows similar to before as the temperature dips to only 8°C tonight. Very little cloud is expected with this moisture-starved cold front over the Red River Valley, let alone any chance of precipitation. There is a slight chance of a shower or thundershower over the Whiteshell, however if they occur they will be short-lived and produce little rainfall accumulation. It looks like the best chance for any showers is on the Ontario side of the border.

If you enjoy sunshine, the rest of the week will be right up your alley. Temperatures will hover in the low 20’s for Tues/Wed. before a warm front pushes over S. MB and pushes temperatures up into the mid-to-high 20’s for Thursday and Friday. It looks like there may be a chance of showers or thunderstorms as the warm front pushes in on Thursday, however it currently looks like the best support will remain in North Dakota, leaving us with some clouds, but no precipitation. The biggest change with Thursday’s system will be the switch from a Pacific flow to a Gulf flow, which in addition to warm temperatures will also bring moister air to the area, which should lessen the fire risk somewhat.

Pacific Flows vs. Gulf Flows

These two flows are large-scale weather patterns that dictate where the air is coming from and, especially here in Southern Manitoba, are two of the main large-scale flows we deal with in the summer months. Those two words carry with them significant information about the weather and one can make a quick assesment of what sort of weather to expect if you have a basic understanding of the differences.

Pacific Flow Diagram

Diagram of a Pacific flow. Image is from the GEMGLB model, valid this morning.

First, the Pacific Flow. This is what Southern Manitoba is under right now. This flow occurs when there’s a large blocking high over the western United States. Moist Pacific Ocean air flows NE up and over the high and associated ridge into the NW United States and British Columbia (represented by the green arrows in the diagram above). Once it reaches the mainland, it begins to rise up and over the mountains. As the air rises, it cools and water is forced out of it, falling as rain or snow on the upwind side of the mountains (represented by the shaded green area above). Once it reaches the other side of the mountains, the air descends downwards, warming as it goes. What’s left on the leeward side of the mountains is air that’s warmer than it was when it started it’s trek over the rocks, but substantially drier. This air then spreads eastwards over the Prairies (represented by the brown arrows above), bringing pleasantly warm weather, but very dry and often windy conditions as well, usually with dewpoints in the single digits.

Gulf Flow Diagram

Diagram of a Gulf flow. Image is from the GFS model, valid Thursday evening.

A Gulf Flow also brings very warm conditions to Southern Manitoba as well, however it does so not through trickery of thermodynamics, but rather through brute force. This flow develops when a longwave trough is present over the west coast of the United States (as opposed to a ridge). The flow in the lower atmosphere organizes itself to flow from south to north in response, and heat and moisture from the Gulf of Mexico begins its trek up through the Plains of the United States. The longer this flow can stay in place, the further north the heat and moisture can travel; Southern Manitoba usually ends up under the influence of this air mass at least a couple times each summer. What characterizes this air mass? Hot weather, usually in the upper twenties, though often in the low-to-mid 30’s, and high dewpoints, often at least 18°C, but commonly in the 20-24°C range.

Under the influence of a stifling gulf flow, Carman, MB set the record for the highest Humidex value (a ‘feels-like’ for heat) ever recorded in Canada in 2007. On July 25, 2007, the temperature climbed to 34°C with an unbelievable dewpoint of 30°C, which produced a Humidex value of 53, beating out the old record of 52.1 set in Windsor, ON in 1953.

It’s always a good idea to keep an eye on the forecasts when under the influence of gulf flows; given the transport of so much heat and moisture, it is under the influence of these flows that we often see the risk for powerful thunderstorms.

Dewpoint vs. Relative Humidity?

You may notice that we often refer to the dewpoint on our blog, and not to the more commonly used term, Relative Humidity (RH). What’s the difference? There are several:

  • The dewpoint is an absolute measurement. Relative humidity is, obviously, relative.
  • The dewpoint is reported in °C, and is a measurement of how much water is contained in the air. Relative humidity is reported in % and is a measurement of how much of the water-bearing capacity of the air is being used. As air becomes warmer, it can hold more water.
  • The easiest way to understand the dewpoint is simple: how cold would something have to be so that when you put it out in the open air, it would “sweat”.
  • When dewpoints are low, the air has little moisture in it, and when they are high, it has more water in it. People often notice the moisture in the air once dewpoints reach around 12-13°C. Once they exceed 16-18°C, many people would actively notice that it was humid, and once the dewpoint exceeds 20°C, many begin to find it uncomfortably humid.
  • Conversely, one cannot make any absolute claim with a relative humidity measurement alone, nor does the RH actually let you know if it’s humid or not. A RH reading of 100% only means that the air is holding as much water as it can. There are two major problems with this. The first is that the RH changes through the day, even if the amount of water in the air (the dewpoint), does not. If the day starts off at 8°C with a dewpoint of 8°C, the RH is 100%. If the dewpoint stays at 8°C but it warms up to 21°C, the RH drops to 43%, despite the fact that there’s no more or less moisture in the air. The RH would then climb back towards 100% in the evening as the air cools. The second problem is that a RH of 100% can be extremely deceptive. If the temperature is 30°C and the RH is 100%, one could barely spend any time outside it would be so unbearably humid. Fortunately, this situation is extremely rare. If the temperature is -25°C and the RH is 100%…well it’s certainly not humid out. In fact, RH values are often quite high in winter since as the air cools, it can hold less water, so it uses more of it’s water-carrying capacity with smaller amounts of water.

All that to say that RH is a pretty messy, inconsistent measurement that when presented by itself doesn’t actually tell you much about anything. Dewpoint, on the other hand, is a consistent measurement that quantifies how much water is actually in the air and can tell you something about the weather when presented by itself. And that’s why we prefer to use dewpoint here on AWM.

Summer Returns to Southern Manitoba…For a Short While

Beautiful weather is on tap for Southern Manitoba with plenty of sunshine the next couple days and positively summer-like temperatures. Things will return back to normal on Friday, after a cold front sweeps across the province on Thursday night.

500mb Winds/Height for Wednesday Evening

500mb Winds & Heights from the GEMGLB, valid for 00Z Thursday 10 May. The upper ridge has been highlighted over Manitoba.

A deep southerly flow has moved into Southern Manitoba underneath an upper ridge sliding east over the Prairies, pushing warmth from the Central Plains of the United States into our area. Temperatures will climb to around 20°C today with winds increasing to 20-30km/h out of the south by the afternoon. Temperatures will only drop to around 10-12°C tonight as the southerly winds keep our temperatures up in this warmer air mass.

Tomorrow the real heat moves in, and we’ll see temperatures soar in the Red River Valley, with daytime highs between 24 – 27°C. We’ll see a bit more cloud, though, and dewpoints in the low teens will make it feel closer to 30°C.

Day 2 Thunderstorm Outlook valid 21Z May 10 to 12Z May 11

Day 2 thunderstorm outlook, valid from 21Z May 10 (Thursday afternoon) to 12Z May 11 (Friday morning). No severe thunderstorms are expected.

By tomorrow evening, a cold front sweeping across the province will move into the Red River Valley. With the extra moisture in the air from the higher dewpoints, CAPE values will be enhanced slightly, and we’ll be looking at 500-750J/kg of CAPE as the front pushes into the RRV. A band of showers and thunderstorms will fire along the cold front on Thursday afternoon over SW Manitoba and continue eastwards through the evening, crossing the RRV through the evening and pushing through the Whiteshell overnight.

Seasonal conditions are expected to return for Friday into the weekend.

Winnipeg Bakes Under Hottest Day In 16 Years; Summer Far from Over

It's a scorcher out there
Winnipeg baking underneath it’s hottest day in 16 years

An extremely warm air mass, combined with brisk westerly winds, brought record heat to much of southern Manitoba. Winnipeg officially reached 37.0C today, breaking the old record of 36.7C set in 1952 and marking the warmest day the city has seen since June 17, 1995 when the mercury soared to 37.8C.

The warm weather spread into Southern Manitoba ahead of a cold front sweeping cooler air into the province by Tuesday evening. A westerly, downslope flow coupled with extremely warm air at 850 mb pushed the mercury to record-breaking levels in many areas across Southern and Central Manitoba, including:

Location New Record Old Record
(Old Year)
Records Started
Winnipeg 37.2° 36.7° (1952) 1873
Fisher Branch 34.2° 31.0° (1990) 1977
Gretna 36.5° 31.1° (1965) 1955
Island Lake 29.1° 27.8° (1976) 1971
Melita 33.3° 32.2° (1997) 1993
Pinawa 35.4° 31.1° (1969) 1964

One thing that was very interesting, though, was that the International Airport in Winnipeg was actually one of the cold spots in the city. Various personal weather stations reported even higher temperatures:

Location Today’s High
Birds Hill Park 38.0°
Charleswood 38.0°
East St. Paul 37.0°
Island Lakes 36.9°
St. Vital 38.8°
Whyte Ridge 37.7°

Fortunately, a cold front passing through this evening will usher in cooler weather and stronger winds. An intensifying surface pressure gradient on the back-side of the cold front will bring strong winds into Winnipeg tomorrow with sustained winds expected to reach 50km/h with the potential for gusts as high as 80km/h. Temperatures will be about 13-15 degrees cooler than today, with highs of 23-25° expected for much of Southern Manitoba.

GEMGLB Temperature for Thursday Afternoon
12Z Aug 23 GEM-GLB Temperature valid 00Z Fri Aug 26

However, after just one cooler day, warmer weather is expected to return to Southern Manitoba. By Thursday afternoon, temperatures should push back up towards the 30° mark with a southerly flow that redevelops through the day. Late Thursday evening a cold front will pass across the RRV, bringing us back into daytime highs of 22-25° for the weekend. Currently, no precipitation is expected with this front, but I’ll keep an eye on it through the week.