Tag: Thunderstorms

Uneven Start and a Clean Finish to the Weekend

Brad Leave a comment

Unsettled weather will mark the start of the last weekend of July, but conditions will improve for a rather pleasant end and persist into a fairly dry and seasonal start to next week.

Friday: Thunderstorms Possible

Friday
25°C / 15°C
Chance of showers or thunderstorms

Today is off to a cloudy start with a few showers likely through the Red River Valley[1] as the remnants of the overnight activity push off to our east. Skies will remain mostly cloudy until the cold front that brought copious amounts of severe weather to Saskatchewan yesterday pushes through the Red River Valley early this afternoon.

As that cold front moves eastwards, it’s likely that more thunderstorms will fire up along it. Dewpoints in the upper teens will combine with daytime highs in the mid–20’s to produce MUCAPE values as high as 2000J/kg ahead of the front. Shear will be marginal with only around 25–30kt of surface-to–500mb bulk shear and the vertical wind profile isn’t particularly favourable for severe weather. The cold front will be enough of a trigger, although it will be weaker than yesterday and not offer nearly as much forcing as it did then.

As a result, thunderstorms will likely fire up somewhere in the central or eastern Red River Valley and push into the Whiteshell and far SE Manitoba this afternoon. At this point it doesn’t look like there will be an organized severe weather threat, but we’ll be taking a look a little later this morning to assess whether or not the severe threat needs upgrading.

The HRRR forecast shows a line of showers and thunderstorms pushing eastwards along the cold front this morning.
The HRRR forecast shows a line of showers and thunderstorms pushing eastwards along the cold front this morning.

Other than the storms, the day will be pleasant. Before the cold front passes the Red River Valley will be under a relatively light southerly or southeasterly wind. It will be fairly humid and temperatures in the low 20’s until the passage of the front, after which westerly winds at 30–40km/h bring in much drier air. The afternoon sunshine should help our daytime high climb to around 25°C.

Temperatures will drop to around 14°C under clear skies and light winds tonight.

Showery Saturday

Saturday
24°C / 13°C
Mainly cloudy with widespread showers

Tomorrow will be the least pleasant day of the next few. A strong upper-level low will slide across Southern Manitoba through the day, producing widespread showers underneath it. There may be a few isolated thunderstorms, but for the most part most areas in Southern Manitoba will be seeing a fairly wet day. Winds will generally be 20–30km/h through much of the day, shifting from southwesterly or westerly to northerly through the day and overnight.

Skies will begin to clear overnight as the temperature drops to around 13°C.

Sunny Sunday

Sunday
24°C / 13°C
Mainly sunny

Sunday will likely start off with some low cloud trapped in the boundary layer making for mixed to mostly cloudy skies. As the temperature rises through the morning, the clouds will gradually break up leading to a mainly sunny afternoon with some scattered clouds. Highs will be around the 24–25°C mark and temperatures will drop to around 13°C once again on Sunday night.

This pleasant weather will continue through the first half of next week. Another strong ridge is forecast to build into BC/Alberta, which will keep temperatures seasonal[2] and the weather dry.

  1. Full discretion: I’m writing this on Thursday evening, and still unsure on how much of Thursday night’s convective activity will survive to the Red River Valley.  ↩
  2. Seasonal highs in Winnipeg right now are around 26°C. Seasonal lows are around 13°C.  ↩

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).  ↩

Turning Up The Heat

Brad Leave a comment

A long-deserved taste of summer is in store for Southern Mantioba as the temperature rises with little chance of precipitation until the end of the week.

An upper-level ridge of high pressure building into the region will tap some of the record-breaking heat over British Columbia and slowly spread it eastwards over the Prairies. While we won’t see temperatures nearly has hot as the 40°C+ they’ve seen in B.C., temperatures will push towards the 30°C mark by week’s end. While some scattered thunderstorm activity is possible Thursday night, in general it looks like it will be quite dry in many places over the next couple days. With all the heat, it does look like a more organized thunderstorm threat is set to re-develop on Friday in the Red River Valley.

Wednesday
26°C / 15°C
Mainly sunny

Thursday
29°C / 17°C
Mainly sunny

Friday
30°C / 16°C
Chance of showers or thunderstorms.

Today will be a beautiful summer day with a seasonal high of 26°C and relatively light winds out of the south at 15-25km/h. Tonight will be mainly clear with light winds and a temperature dropping to around 15°C.

Thursday will see the heat really begin to show up with temperatures climbing into the upper 20’s to just over the 30°C mark across much of Southern Manitoba. Winds will be out of the south or southwest at 20-30km/h. By evening, a weak cold front will move in from the northwest and will likely spark of some scattered thunderstorm activity over Western Manitoba that may slowly spread SE into the Red River Valley overnight. At this point, it doesn’t appear that there will be a significant threat of severe thunderstorms with Thursday’s activity.

Thunderstorm Threat Returns Friday

Friday will start off with a slight chance of showers or thundershowers if Thursday night’s convection manages to make it this far east, but then see temperatures once again approach 30°C with winds building out of the south to around 30km/h. The cold front that moved in Thursday will lift back northwards ahead of another approaching low pressure system and the associated incoming upper-level trough will likely generate thunderstorm activity through the Red River Valley on Friday afternoon into the evening.

GFS-forecasted upper-level winds (500mb) for Friday evening.
GFS-forecasted upper-level winds (500mb) for Friday evening.

With in excess of 1500J/kg of CAPE, 30-40kt of bulk shear, fair surface moisture and the strong dynamical forcing of the upper-level trough coupled with enhanced lift in the right entrance region of the jet, it looks like there will probably be a slight risk for severe thunderstorms. At this point, the main threats look to be wind and hail, although if things continue to trend in a similar direction, the Red River Valley could see one of it’s first organized tornado threats of the year. We’ll be keeping a keen eye on things and have updates later in the week.

Cooling Trend Brings More Unsettled Weather

Brad Leave a comment

The system that brought severe thunderstorms to the Interlake and southwestern Manitoba will bring a huge shift in the weather pattern over the next couple days as it moves over Hudson Bay and stalls, setting up an extremely abnormal pattern for July that will see cool Arctic air spilling southwards unhindered. In the process another cold front will slump through Southern Manitoba bringing another day of unsettled weather on Saturday.

Friday
25°C / 15°C
Becoming mainly sunny.

Saturday
26°C / 11°C
Showers or thunderstorms likely.

Sunday
19°C / 9°C
Mainly cloudy.

Today will be a fairly nice day all things considered. Winds will be out of the west to northwest at 20-30km/h as temperatures climb into the mid-20’s. No precipitation is expected today. Temperatures will remain somewhat mild tonight, dropping only into the mid-teens.

The RDPS, among other models, is forecasting widespread shower activity in Southern Manitoba on Saturday.
The RDPS, among other models, is forecasting widespread shower activity in Southern Manitoba on Saturday.

Saturday will bring another bout of unsettled weather as a cold front slumps southward through the Interlake into the Red River Valley. Instability will build throughout the morning with showers and thunderstorms developing along the cold front by midday through the Interlake. The activity will slump southwards through the day, with showers and thunderstorms likely through the Red River Valley, particularly the northern & eastern halves.

Saturday is also the Morden triathlon. Conditions will be fairly pleasant, with temperatures around 15°C in early in the morning warming to around 24°C by lunch time. Winds will start the morning out of the southwest at around 15km/h and increase to 30km/h or so by midday. There will be a very slight chance of a shower beginning late in the morning and through the early afternoon, although precipitation is most likely to hold off until the cold front passes through the region late in the afternoon.

Sunday will mark our first day in a very unseasonably cold air mass. Most of Southern Manitoba will see a northwesterly wind at 30-40km/h. The high will only be around 19°C – some 7 or 8°C below normal. There will be a chance of showers on Sunday night while temperatures dip below the 10°C mark.

How Long Will The Cold Last?

The CPC is forecasting a 100% chance of below-normal temperatures for the Eastern US in the 6-10 day range.
The CPC is forecasting a 100% chance of below-normal temperatures for the Eastern US in the 6-10 day range.

There’s no question the incoming cold air is hugely abnormal for this time of year: 1000-500mb thicknesses[1] are expected to fall below 546dm through Northwestern Ontario into MN/WI/MI. These values are more appropriate for late in the fall than in the middle of July. Depending on exactly how deep this cold trough becomes, record low thicknesses for July may be set in those regions.

Here in Manitoba, we’ll avoid the core of the coldest air, but we’ll still be well below normal. Fortunately this setup doesn’t appear to want to remain locked in for very long. The cold trough is expected to push off to the east fairly quickly with warm air pushing back into the province by mid-week.

As the warm air pushes in, it actually looks like we may finally move into a warm and dry summer-like pattern. All long-range weather models are showing a nice dry spell developing from mid-week into next, with temperatures gradually warming up towards the 30°C by the end of the week!

  1. The 1000-500mb thickness is literally the distance between those two levels in the atmosphere. The colder the column of air is, the lower the thickness while the warmer the column is, the higher the thickness is.  ↩