Active Weather Pattern, but Inactive Weather?

Brad Leave a comment

A couple of weather systems are in store for this week, but that doesn’t mean the forecast is wet for everyone.

A Cold Front Will be Positioned Through Manitoba on Monday

Monday

Monday

Mix of Sun and Cloud. Chance of Showers.
22°C / 8°C

Today will be a warm day by late September standards. High temperatures will be in the low twenties in the Red River Valley. A bit further east in south-eastern Manitoba some areas may approach the mid twenties. But a bit further west in western Manitoba, temperatures will struggle to reach the upper teens. The discrepancy in temperatures over Southern Manitoba today is resulting from a cold front located over western Manitoba. In the vicinity of this front there is extensive cloud cover and some rain activity. Further east, skies are clearer, allowing for the atmosphere to heat up a bit more. Some of the rain showers over western Manitoba may sneak into the Red River Valley later today (as cloudiness increases later today), but little in the way of accumulating rain is expected. Over western Manitoba the rain will probably amount to between 5 and 15mm in general.

Tuesday

Tuesday

Mainly Sunny
21°C / 7°C

Surprisingly, Tuesday will be quite a nice day despite the passage of a cold front on Monday night. High temperatures on Tuesday will be in the upper teens or lower twenties in Southern Manitoba, under sunny skies and light westerly winds.

Wednesday

Wednesday

Mainly Cloudy
22°C / 14°C

Wednesday will see cloudier conditions return ahead of a developing weather system. Temperatures on Wednesday are expected to max out in the low twenties in Southern Manitoba and the wind will be gusty and from the south-east. Some rain may occur over Western Manitoba on Wednesday, but it’s too early to speculate on the location or intensity of it.

Long Range

The long range outlook will be dominated initially be the weather system mentioned in Wednesday’s forecast. This low pressure system is currently expected to track through Manitoba, with its main impacts likely to be confined to the Western half of the province. However, it is possible that this system may change track, so it could potentially affect other parts of Manitoba as well – more details on that will be available in Wednesday’s post.

Once that weather system passes by, conditions should return to near seasonal values for the end of the week. Next weekend is looking fairly pleasant, with near to slightly above seasonably temperatures…but of course that could change before the weekend actually arrives!

Elsewhere in Weather News: September 21st, 2013

Matthieu Leave a comment

Super Typhoon Usagi Takes Aim at Hong Kong

The strongest typhoon of the year up to date has formed in the Pacific and is taking aim at Hong Kong. Super typhoon Usagi is currently located in the Luzon Strait between Taiwan and the Philippines and is moving in a west north-westerly fashion. Thursday and Friday morning, Usagi was packing sustained winds of around 260km/h – considered category five strength. It has since slightly weakened but is still a dangerous category four super typhoon as it eyes (no pun intended) Hong Kong and the southern coast of China.

Usagi

Awesome image of Usagi Thursday afternoon. (Source: Colorado State University/Capital Weather)

This super typhoon is not only a very powerful typhoon but also a very large one; its diameter reaching over 1,000km. A very distinct eye could be seen on satellite as well as more than one eyewall present; it is not as common for a tropical system to have more than one eyewall, though it does happen with storms of category three or higher.

Usagi is expected to make landfall sometime on Sunday along the south China shores. Its impacts remain to be seen though, with seas expected reaching 10 meters in the South China Sea all vessels will have to steer clear or dock. Another concern is the rainfall; already copious amounts of rain have fallen in Taiwan, especially on its east coast where about a meter of rain was not out of the question before the weekend’s end.

In addition to Usagi, a second typhoon is expected to form this weekend behind (to the east) of Usagi, it will be named Pabuk. Although still a ways out, Pabuk has a good chance at becoming a severe typhoon due to the warm sea surface temperatures and low shear in the area. Currently, the models show Pabuk reaching the eastern shores of Japan but then quickly curving back out to sea – this would suggest minimal impacts to Japan.

A Cool Weekend Ahead

Brad Leave a comment

A cooler weekend lies ahead for Southern Manitoba as cooler air pushes southwards through the Prairies behind a strengthening low pressure system in Northern Ontario. Some of our coolest temperatures of the fall lie ahead although it does seem like warmer air will begin to nudge back in by the end of the weekend.

Today

Friday

14°C / 2°C
Mainly cloudy. Lake-effect showers or drizzle has a chance of moving into Winnipeg.

Today will be the most “active” weather-wise thanks to a surge of cold air at 850mb that will be diving southwards through the day today. As this air pushes over the lakes it seems quite likely that lake-effect showers or drizzle will develop and push inland in the lee of the lakes. It’s very difficult to attribute a chance of precipitation to these features as they will almost certainly form, but they produce narrow ribbons (often ≤ 50km wide) that extend along great lengths.

What are the ingredients for Lake-Effect Precipitation?

There are a few ingredients that work together to produce lake-effect precipitation. The basic ingredients are:

  • At least a 13°C temperature difference between the water surface and 850mb
  • At least 100km of fetch (the wind must travel at least 100km over the water surface).
  • Less than 60° of directional shear between the surface and 700mb; less than 40kt of speed shear between the surface and 700mb.

Which areas see precipitation will be extremely sensitive to the wind direction. Here in Winnipeg it seems that the wind will be a little too northerly for the lake effect precipitation from Lake Manitoba to move into the city, but should the winds have a slightly more westerly component we may see some light shower or drizzle activity move in. That being said, some areas in the lee of Lake Manitoba and Lake Winnipeg will likely see some showers or drizzle today. The temperature will struggle to a mere 13 or 14°C and we’ll see temperatures dip to around 2°C tonight. While there should be widespread clearing, some stratus cloud may still be advecting off the lakes. Areas that remain in cloud through the night may end up a couple degrees warmer.

Frost will certainly be a possibility through the Red River Valley tonight as skies clear and winds let up.

Saturday & Sunday

Saturday

16°C / 5°C
Sunny.
Sunday

21°C / 13°C
Sunny. Windy out of the south.

We’ll see a pleasant but cool day on Saturday with mainly sunny skies, light winds and a high near 21°C. Saturday night will bring clear skies and a low of around 4–5°C. Sunday will also be a mainly sunny day although winds will begin to pick up out of the south through the day as a low pressure system pushes towards the province. With cool air in the valley and warmer air struggling to push eastwards, it could actually become quite breezy. At this point it looks like winds will be around 30km/h with gusts to around 50, but if the cold air is a little more stubborn it could end up windier than that and closer to 40–50km/h.

Next week looks to start off with a disturbance pushing through on Monday or Monday night bringing a chance of some rain to the Red River Valley, but at this point it’s far to early to make any real judgements on what it will do. The rest of the week looks fairly quiet with seasonal temperatures.

Severe Thunderstorms Possible in Late-Season Setup

Brad Leave a comment

Severe thunderstorms will be possible across much of Southern Manitoba today as a rare late-season setup develops through the day today.

Severe thunderstorm outlook for Wednesday afternoon through Wednesday night.

Severe thunderstorm outlook valid Wednesday afternoon through Wednesday night.

Today

Wednesday

26°C / 15°C
Mostly cloudy; thunderstorms likely late in the afternoon into the evening.

A low pressure system will be pushing it’s way out of North Dakota into SW Manitoba through the day today, bringing with it a push of warm air that will lift a warm front northwards into the extreme southern portions of the province by late this afternoon. Plenty of cloud will stream into the province ahead of this system which will result in us having a mostly cloudy day with our high temperature climbing somewhere near 25°C.

This system will develop a fairly potent severe weather setup, especially for this time of year. A deep layer of moisture will build over the Southern Manitoba through the day with dew points climbing to around 18°C and extending through the boundary layer. Steep mid-level lapse rates will develop with falling 500mb heights, contributing to a large amount of instability ready to be realized should an appropriate trigger develop. 500mb winds are forecast to increase to nearly 50kt by late afternoon which when coupled with a developing low-level jet, contributes to anywhere from 40–60kt of bulk shear in place tomorrow evening/night. There’s plenty of moisture, instability and shear.

So how about that trigger? Things will remain capped through most of the province through the day thanks in no small part to the cloud cover that will inhibit much of our potential heating. Thunderstorms will likely develop in SE Saskatchewan or SW Manitoba mid-to-late afternoon as the cold front associated with this system pushes eastwards and is strengthen by an incoming upper-level disturbance. Over the SW portion of the province, the storms will likely be surface-based which will be a very important distinction. With the strong shear profiles in place, surface-based storms in SW Manitoba will have the potential to become tornadic due to a relatively strong southeasterly inflow wind. Any residents of SW Manitoba should stay alert for watches and warnings that may be issued with this storm system.

The storms that develop along the cold front will likely quickly grow upscale and develop into a squall line pushing eastwards. As it moves towards the Red River Valley the storms will become elevated as surface temperatures cool and a very strong low-level jet develops. This jet will sustain these storms as they push eastwards over the rest of the province through the evening.

Elevated thunderstorms present very little tornado risk. Thunderstorms today will have the potential of producing heavy rain, very large hail and damaging winds, all afternoon and evening.

After the storms push through (and I won’t rule out that we’ll see the umpteenth split around Winnipeg this year), we’ll see clouds break up as we drop to around 15°C.

Thursday and Friday

Thursday

20°C / 9°C
Mix of sun and cloud; chance of scattered showers.

We’ll see things cloud back up early on Thursday as another cold front pushes through. There will be a chance of some scattered showers behind the cold front in some lingering instability as we climb to a high of around 20°C. Winds will be a little breezy out of the northwest to around 20–30km/h. Things will clear up for the most part on Thursday night, although there will likely be a narrow band of stratus cloud coming off of Lake Manitoba overnight. Where that cloud will end up depends entirely on the exact wind direction, but suffice to say it’ll likely end up somewhere in the Western Red River Valley.

Friday

17°C / 4°C
Mainly sunny.

Friday will be a cool and sunny day. Temperatures will only climb to around 16 or 17°C and colder Arctic air slumps southwards over the Prairies. We may see a few clouds in the afternoon, but not anything significant. Temperatures continue to cool aloft through the overnight period with 850mb temperatures dropping to nearly 2–3°C on Friday night. This should translate to an overnight low dipping into the low single digits, likely to around 3 or 4°C.

The weekend looks fairly quiet with sunny skies and temperatures rebounding back towards the mid–20’s by the start of next week.