Summer Weather Turns Unsettled at Weeks End

Brad Leave a comment

Southern Manitoba is in the middle of one of the most pleasant stretches of summer weather so far this year; humidity is relatively low with plenty of sun and daytime highs sitting in the mid-to-upper 20’s. This beautiful weather will continue for another couple days before an upper-level low pressure system begins impacting our region on Friday, bringing unsettled weather back to the region.

Wednesday
26°C / 13°C
Mainly sunny

Thursday
26°C / 18°C
Mixed skies with a chance of showers in the evening

Friday
26°C / 15°C
Chance of [thunder]showers

Today and tomorrow will both be beautiful days with highs around 26°C and light winds as a ridge of high pressure moving through the province quashes any unwelcome weather. Both days will also feature ample sunshine and fairly light winds, although around the end of tomorrow winds will likely begin to pick up out of the southeast to around 20–30km/h. Tonight’s overnight low will hover around 13°C.

Thursday evening will mark the arrival of the leading edge of a major low pressure system developing over the western Prairies. A leading disturbance will swing into Southern Manitoba through the night, bringing a good chance of shower activity to most places[1] with around 5mm of rain expected in most places that see the showers. It may end up being more hit and miss and we’ll be able to refine the forecast as we get closer to the event.

A moderate risk of severe thunderstorms this afternoon will translate into a slight risk over SW Manitoba this evening.
A moderate risk of severe thunderstorms this afternoon will translate into a slight risk over SW Manitoba this evening. See our discussion below.

Perhaps of heightened concern for Thursday evening is the potential for severe thunderstorms over extreme Southwestern Manitoba. It’s worth being aware of the potential at the moment, however there are a lot of potentially complicating factors that will become clear tomorrow as to whether or not that threat will be able to be realized or not. We’ll update in the comments below with more details early in the day on Thursday.

Friday will bring unsettled weather. While morning showers will be possible, the weather will transition into a mix of sun and cloud fairly early before the threat for showers or thunderstorms redevelops in the afternoon. The redevelopment will not affect all of Southern Manitoba; it will mainly be of concern for the Red River Valley/Interlake and areas eastwards. Despite the unsettled weather, temperatures will be warm with highs sitting near 26°C. The humidity will be a little more noticeable, but nowhere near the humid days we’ve had so far this year.

Mixed Weekend

Looking ahead to the weekend, Saturday looks like showers will push through the region through the day underneath the upper-level low as it pushes through. Highs on Saturday will once again be in the mid–20’s. Sunday will be a return to pleasant weather as a ridge of high pressure begins building back into the area. Highs will likely be, you guessed it, in the mid–20’s!

  1. Including the Parkland region, southwest Manitoba, the Red River Valley, southeastern Manitoba and the Interlake.  ↩

Seasonal Weather Ahead

Brad Leave a comment

This week will feature near normal conditions as we cool down a bit from a sultry Sunday.

The weather will be mostly calm in southern Manitoba on Monday, but dangerous storms will be possible south of the border
The weather will be mostly calm in southern Manitoba on Monday, but dangerous storms will be possible south of the border

Monday

Monday
26°C / 16°C
Mix of sun and cloud with a chance of showers

Today will feature near normal weather in southern Manitoba as temperatures climb into the mid twenties. There will be a chance of showers through the day as an upper-level impulse rolls through, but little in the way of accumulation is expected. Despite the calm weather in Manitoba, conditions just south of the border look to be quite different.

A very hot and extremely humid air mass are located over the eastern Dakotas and Minnesota today. This air mass will become extremely unstable by late afternoon, characterized by MLCAPE values of 4000-5000 J/kg (CAPE is a measure the potential energy/fuel for a thunderstorm), or perhaps even higher in localized pockets. Favourable wind profiles will allow for supercell thunderstorms and tornadoes early in this thunderstorm event, but cells will likely transition into a powerful convective system by mid to late evening. Given the potency of the thunderstorm environment tomorrow, all modes of severe weather will be possible, including very large hail and destructive winds. If your travels take you into this region today, you’ll want to pay close attention to the latest weather watches and warnings in the area.

Tuesday

Tuesday
26°C / 14°C
Mix of sun and cloud

Tuesday will be a relatively benign day. Temperatures will once again be in the mid twenties. Precipitation is unlikely as a surface high pressure system builds into Manitoba. Winds will be relatively light and from the north.

Wednesday

Wednesday
27°C / 15°C
Mainly sunny

The surface high from Tuesday looks to stick around for Wednesday, bringing continued pleasant weather to southern Manitoba. Temperatures look to be in the mid to upper twenties with light winds. Some precipitation may edge into western Manitoba late in the day as thunderstorms are potentially triggered to our west in Saskatchewan.

Long Range

The long range forecast looks to have ups and downs. Models strongly suggest that a low pressure system will move into Manitoba late this week, potentially bringing us some rain and generally unsettled conditions. Once that system exits the region we’ll likely return to more summer-like weather next week.

Elsewhere in Weather News: July 19th, 2014

Matthieu Leave a comment

Another Super Typhoon Spins Up in the Western Pacific

The Western Pacific Ocean has been very active in the past few weeks, churning up numerous typhoons including its most recent – super typhoon Rammasun. Rammasun made landfall at least twice; once in the Philippines and China, respectively, during its trek across the Western Pacific.

The first landfall occurred southeast of Manila, Philippines, where it brought with it winds of 185km/h. Many precautions were taken ahead of this storm in the Philippines as it was the first typhoon to hit the country since super typhoon Haiyan. Over 500,000 people decided to ride out the storm in evacuation centres and plenty of warning (3 days) was given to residents before the typhoon made landfall. Despite the warnings, many homes could not be saved – as many as 7,000 as reported by authorities. Unfortunately 38 people died due to the typhoon in the Philippines.

After making landfall in the Philippines, Rammasun quickly strengthened with help from the very warm sea surface temperatures (SSTs) that approached 30°C in the South China Sea. With these warm SSTs conditions were primed for the storm to reorganize. Rammasun quickly developed a well-defined eye and became a super typhoon (category 4) as it approached China for a second landfall. The typhoon made landfall on Friday morning with sustained winds of 250km/h gusting to 280km/h on one of China’s southern provinces; Hainan. All modes of damage were possible with a storm of this intensity; including flooding rains, landslides and severe storm surge. It is still unclear how the region is doing in the aftermath of the storm as of Friday night. A report of 178mm of rain in the coastal city of Haikou (pop. 900,000) in 6 hours on Friday combined with expected storm surges of 20 feet in the general area made for big flooding/landslide concerns. Rammasun is expected make a turn for China’s mainland and die off this weekend, but not before bringing widespread torrential rains to the region.

IR image of Rammasun just before it made its second landfall. (Source: NASA/NOAA)
IR image of Rammasun just before it made its second landfall. (Source: NASA/NOAA)

More tropical storms are expected to spin up this week with possibilities in both the Atlantic and Western Pacific as depicted by some models. The strength or paths of these are uncertain.

Severe Thunderstorm Threat Returns

Brad Leave a comment

A threat of severe thunderstorms returns to Winnipeg and the Red River Valley today as a cold front advances eastwards into a hot, increasingly humid air mass that has been building into the region over the past few days.

Friday
29°C / 16°C
Afternoon/evening thunderstorms. Slight risk of severe thunderstorms.

Saturday
28°C / 18°C
Mainly sunny

Sunday
29°C / 17°C
Mixed skies; chance of showers or thunderstorms

Before thunderstorms develop this afternoon, we’ll see another hot summer day. We’ll see temperatures climb towards the 30°C mark with a fairly breezy wind out of the south at 40-50km/h. A fair amount of smoke will still be lingering aloft, so temperatures may struggle getting those final couple degrees towards the 30 mark.

Thunderstorms will develop this afternoon along the cold front through the western Red River Valley and Interlake and push eastwards. We’ve assessed a slight risk for severe storms from the MIST assessment:

  1. Moisture: Surface dewpoints will climb into the high teens today and although they are forecast to drop off somewhat through the boundary layer, there should be ample moisture in place for storm development.
  2. Instability: A capping inversion will keep things fairly quiet through much of the day today. Moderate mid-level lapse rates will develop through the day (possibly enhanced by the EML[1] from Saskatchewan’s overnight convection). Low-level instability will be somewhat limited today by diminished heating due to cloud cover and smoke aloft, however temperatures in the upper 20’s will come very close to breaking the cap.
  3. Shear: Looks very good. Around 30kt of surface to 6km bulk shear will be in place which will support organization of thunderstorms. 0-2km shear values of around 20-25kt reflect the moderate veering of the winds that will exist through the lower levels of the atmosphere and will support the development of supercell thunderstorms early in the event. As the storms mature, shear becomes more linear and will help support the development of a squall line.
  4. Trigger: Check! A strong cold front with good convergence will either erode the cap to initiate thunderstorms or provide enough forcing to overcome the cap.

Once thunderstorms develop this afternoon, they will likely quickly organize into discrete supercells capable of all modes of severe weather[2]. More unidirectional shear above 850mb will marginalize the tornado threat as more energy will have to be expended to develop the mesocyclone through the vertical, but with potentially as much as 2500-2700J/kg of MLCAPE, tornado(es) cannot be ruled out given the wind profile.

A slight risk of severe thunderstorms is possible over south-central and south-eastern Manitoba this afternoon into the evening.
A slight risk of severe thunderstorms is possible over south-central and south-eastern Manitoba this afternoon into the evening.

Storms will then increase in coverage and develop into a line along the cold front. Severe weather will still be possible, although the primary threats will shift to damaging winds and large hail. With strong unidirectional shear profiles through the Interlake, the development of bowing segments giving damaging winds is possible through that region.

The thunderstorms will push off into southeastern Manitoba this evening with a continued severe weather threat before tapering off in northwestern Ontario overnight. Winnipeg will see clear skies and a low around 16°C.

Mixed Weekend

Saturday will be a fairly pleasant day with weak ridging producing mainly sunny skies with light southerly winds and a high near 28°C.

Clouds will push in on Saturday night as we drop to a low around 17 or 18°C. There is a very slight chance of a shower or thundershower in the overnight period.

Sunday will be another warm day with a high close to 30°C under mixed skies. The afternoon will bring another chance for showers or thunderstorms as a trough line works into the province.

  1. Eleveated Mixed Layer  ↩
  2. Torrential rain causing localized flash flooding, large hail in excess of 20mm, damaging wind gusts in excess of 90km/h, and/or tornado(es).  ↩