Some Simple, Seasonal Weather

After a hectic few days across Southern Manitoba, Winnipeg is in for a few relatively calm, seasonal days before the next system moves into the region this weekend.

We’ll see the clouds breaking up this morning with a temperature that makes it up to around 19°C by this afternoon. We’ll see a slight chance of showers this afternoon, however they shouldn’t amount to very much and will quickly move out this evening. Tonight’s low will be around 10°C here in Winnipeg. Thursday and Friday will bring us a mix of sun and clouds with chances of afternoon showers across most of the Red River Valley as the upper low from yesterday’s system slowly tracks out of the Province. The daytime highs over the next couple days should be near 19°C.

A more significant system is forecast to move into our region this weekend, bringing what currently looks like a pretty rainy day to this year’s Teddy Bears Picnic.

Stormy Weather To Return to Southern Manitoba

After a cool night, temperatures will rebound nicely today before more unsettled weather pushes into the province tonight and lingers through mid-week.

850mb temperatures valid Tuesday Evening

850*mb* temperatures valid 00Z Wed May 23 (Tuesday Evening). Warm and cold front are represented by red and blue lines, respectively. Orange arrows represent warm air lifting northwards over the warm front.

Temperatures today will work their way to 20°C today with increasing cloud. The first of several impulses forecast to track across Southern Manitoba will push a warm front across the Red River Valley late this afternoon, bringing with it a good chance of showers
through regions along the Trans-Canada highway and northwards into the Interlake. Regions in the southern half of the Red River Valley will see just a chance of showers through the afternoon and evening today.

Tomorrow, a low pressure system will push into North Dakota, strengthening a warm front draped across the region. Southern Manitoba will stay north of the warm front, keeping daytime highs in the 20-23°C range. Strong capping will restrict surface-based thunderstorms to Central/Southern North Dakota where a cold front advancing across the Plains will help trigger storms later in the day. For us, however, we’ll be in great placement for the development of nocturnal convection. A strong 30-40kt low-level jet overriding the warm front will pump fairly moist air northwards; dewpoints at 850mb over Southern Manitoba are expected to rise to the mid-teens. Combined with negative lifted indicies, CAPE values are expected to climb to nearly 1500J/kg.

This will likely result in the development of showers and thunderstorms on Tuesday evening, developing somewhere over Southern Manitoba and pushing northeastwards through the night. Nocturnal convection is always a very tricky thing to forecast, so we’ll definitely keep a close eye on things and provide updates in the comments as we get closer.

The upper low associated with this system will push across the Prairies through the week, bringing a mix of sun and clouds and some unsettled weather and more chances of showers.

Elsewhere in Weather News: May 19th, 2012

Strong Winds, Wildfires Rage On

South-eastern Manitoba has seen its fair share of fires burning this spring but it wasn’t comparable to the conditions experienced this past week in Arizona and Colorado where wildfires are burning out of control across the states. Fanned by very strong southwesterly winds associated with a ridge of high pressure that is strengthening over the west coast, the fires quickly grew out of control in Arizona. Wind gusts of 80km/h were recorded in the area which easily spread the flames and expanded the fire by blowing embers, making it nearly impossible for firefighters to contain the blazes. In addition to the strong winds, both states have been impacted by severe droughts this month; especially Arizona where soil moisture content is bone dry.

Fire map

Map showing in red where the largest fires are. (Map provided by Google Maps.)

As of Friday morning, one dangerous fire was burning in north-eastern Colorado; a couple in the Tonto National Forest just north-east of Phoenix, Arizona; and other smaller fires had flared up in New Mexico and Utah.

As for the Colorado fire, conditions will improve slightly as thundershowers are in the forecast and will bring rain however cloud-to-ground lightning from the storm could potentially spark more fires. The Colorado fire was 11% contained as of Friday afternoon; it consumed more than seven thousand acres and has forced a couple dozen people out of their homes.

Colorado wildfire

Image of the large Colorado fire burning just west of Fort Collins. (Source: Denver Post)

For the Arizona fire it’s a different story though – as a big ridge builds over the region, relative humidity will continue to drop dramatically, reaching values in the low teens to single digits. This, combined with extremely hot temperatures of around 40°C, will surely cause hardship and less than ideal conditions for firefighters as they work feverishly to battle the flames. The Arizona fire was 5% contained and 80 homeowners were on alert to get ready to leave on Friday afternoon. With the tinder-dry conditions persisting in the area for the next couple of days, residents must pay attention to every slight fire danger they may pose during everyday activities –whether it’s having a barbeque or using their ATV in the wilderness.

Arizona wildfire

Cloud of smoke coming from the couple wildfires in Arizona’s Tonto National Forest. (Source: MSNBC)

Showers and Thunderstorms on Tap for Southern Mantioba

While temperatures will soar to the 30°C mark today, much of the Red River Valley should be prepared for showers and thunderstorms to develop by mid-to-late afternoon as a low pressure system moves into the area and taps the available heat and moisture.

850mb Theta-E Values

850mb Theta-E values at 00Z May 19th (this evening) from the NAM. A sharp warm front is evident jsut north of the US border in Southern Manitoba.

With a strong capping inversion in place over the Red River Valley today, heat and moisture being pumped northwards will be trapped at the surface, allowing our temperature to soar to the 30°C mark and pooling moisture that will push our dewpoints up to around 15°C. Much of the day will be a beautiful day, especially given that it’s only May 18th. Conditions will deteriorate somewhat by late afternoon, though, as a surface low lifts northwards into Southern Manitoba.

The surface low will travel along a pre-existing surface trough and be supported by a shortwave ejecting northeastwards from the main upper trough, still anchored through Montana and Wyoming. With the heat trapped near the surface, the Lifted Index is expected to drop to the -2 to -8 values, with the lowest values running along a line from Gretna, MB to Bisset, MB and increasing to the southeast of that line. The heat combined with ample moisture is also expected to produce high CAPE values generally from 2000 to 3000J/kg. Increasing mid-level lapse rates with the approach of the shortwave will provide enough destabilization to erode the capping inversion through the afternoon and allow showers and thunderstorms to develop along and ahead of the warm front, initially concentrated near the triple point of the system. The showers and thunderstorms will expand in coverage as the evening progresses and the low-level jet intensifies.

Severe Weather Threat

Today marks one of the first severe weather threats of the season. Things look promising, and have even caught the attention of some seasoned storm chasers from the United States:

On paper, things look fairly good that there’s a risk for severe weather. EHI values rise to between 1.5-2.0 by late afternoon, which when combined with the presence of 30-35kt of bulk shear certainly presents the chance for supercell storms to develop. A few things hamper my excitement, though:

  • Bulk shear isn’t really all that impressive; the really good shear moves through Western Manitoba through the day today, lifting northwards into the Interlake. The shear diminishes to the SE and isn’t particularly strong where the greatest CAPE is. When it comes down to it, it’s likely that we’ll end up with marginally strong shear on top of marginally high CAPE this afternoon, with the most favorable conditions missing each other.
  • CAPE values may be too high. The NAM & GFS have been forecasting dewpoints slightly higher than have materialized. The amount of energy for storms to work with is going to be heavily dependant on the dewpoints that develop this afternoon, and if they don’t make it as high as forecast then we’ll be seeing weaker storms.
  • Too many storms. With so many marginally severe features, we may see quite a few showers and thunderstorms develop this afternoon as the cap erodes. If too many fire off, then it will be difficult for any one storm to oragnize itself into anything that poses a severe weather threat.

All that being said, a potential for severe weather does exist today across south-central and southeast Manitoba. The main threats should severe weather develop will be hail and/or the possibility of a tornado.

Thunderstorm Outlook for May 18th

Thunderstorm Outlook for May 18th to May 19th. Please note: Analysis has only been done for Manitoba. Storms may develop elsewhere in the Canadian Prairies.

Residents in Southern Manitoba should stay up-to-date on the weather today to ensure that if severe storms do develop, the appropriate precautions can be taken.