What a Difference a Week Can Make

Brad Leave a comment

The difference between the weather experienced last week and that which is coming for early this week will be quite extraordinary. Temperatures on Monday look to be nearly 20 degrees cooler than values experienced last week.

850mb temperatures (about 5000ft above the ground) are forecast to sink to near or below zero degrees on Monday

850mb temperatures (about 5000ft above the ground) are forecast to sink to near or below zero degrees on Monday

High temperatures on Monday are not expected to stray far from the 10C mark in Southern Manitoba. Eastern most sections in the south may manage to hit the mid teens, but the rest of Southern Manitoba shouldn’t be much warmer than 10 degrees. This comes as quite a contrast to the 30 degree temperatures of last week. The above graphic shows the extent of the cold air, with freezing temperatures just 5000 or so feet above the ground. We will most likely see some shower activity develop across Southern Manitoba on Monday, but amounts should be relatively light in most areas. Thankfully Tuesday and Wednesday will be warmer, with highs moving sharply higher. Tuesday should be near or above twenty degrees (depending on which model you believe), while Wednesday is expected to be in the low to mid twenties. There may be some convective rain and/or thunderstorms on Wednesday as humidity levels increase ahead of an approaching low pressure system.

The Preliminary outlook for later this week is for more warm to hot weather. Highs back in the middle or upper twenties will be possible on Thursday and Friday according to the latest modelling. However, my confidence level in the late week forecast is lower than normal since there is some uncertainty as to how quickly a series of fronts will pass through the province late in the week. Given my lack of confidence in the Thursday-Friday forecast I won’t say much about the weekend. You can read more about longer range predictions in the next paragraph.

The long-range forecast calls for above-normal temperatures in Southern Manitoba for the second half of June

The long-range forecast calls for above-normal temperatures in Southern Manitoba for the second half of June

The NAEFS forecast seen above shows the long-range temperature forecast for the June 18-25 period. It appears that we will stick with above-normal weather for most of the second half of June. Also note that we are on the edge of the warmest air, meaning that approaching systems coming out of the colder air to our west (a trough) could potentially trigger strong thunderstorms as they interact with the warmer air to the east. This type of trough-meets-ridge pattern is to blame for the severe thunderstorms on Saturday night.

AWM Chases!

The A Weather Moment team took to the highways of Southern Manitoba on Saturday for our first chase of the year. Hot and humid surface weather combined with an approaching low pressure system and a strong jet stream aloft made conditions ripe for severe supercells thunderstorms which could potentially produce tornadoes.

A thunderstorm east of Altona on June 9, 2012

A thunderstorm east of Altona on June 9, 2012

The AWM team decided to drive toward Holland, MB to start the day. After arriving in Holland it was decided that Pilot Mound would be an appropriate new target given the new weather information available. Upon arriving in Pilot Mound and watching the latest weather conditions evolve we felt our location was ideal. At that point it was time to wait…and wait..and wait. After watching numerous towering cumulus clouds fail to breach the cap we decided to abandon Pilot Mound and follow some storms to our east which were approaching the Red River Valley. As we began to get a good visual of the storms around the Altona region it was clear that there was little chance of a tornado. Cloud bases were high and there were no significant lowerings to be found – the storms were elevated – not surface-based tornado producers. Nevertheless we stopped for awhile near Altona to take a closer look at the storms, a look which revealed nothing of significance. Having taken a few anvil and sunset photographs it was time to head back toward Winnipeg, just missing the infamous hailstorm (which put down tennis ball sized hail) that hit the city around sunset.

Overall it was a good chase. It was not a complete bust since there were storms, but it was definitely a bust in the fact that tornadoes were really nowhere to be found (I’ve kept the door open here for you to decide whether or not this is a tornado: http://tornadohunter.ca/tornado-hunter-blog/2012/6/10/the-longest-chase-day-ever-but-we-got-a-tornado.html). It is only early June and the severe weather season is just beginning, the next chase will be here before we know it.

The AWM team (Brad, Scott and Matt) would like to thank the 311 unique visitors who made 624 visits to this website yesterday, a new record number of visits for this website. Thank-you.

Elsewhere in Weather News: June 9th, 2012

Matthieu Leave a comment

Colorado and Wyoming Battered by Storm System

A low pressure system that has brought tornadoes, hail and large amounts of rain to the western half of the United States this week has caused significant damage in Colorado and Wyoming. The warm, moist, air rushing north from the Gulf of Mexico made for a volatile atmosphere Wednesday and Thursday afternoon as it clashed with the Rocky Mountain range.

Piles of hail

A woman walks where bulldozers piled up huge amounts of hail. This picture was even taken the morning following the storm! (Source: The Gazette)

On Wednesday, storms dumped huge amounts of rain and hail in many parts of Colorado and Wyoming, prompting the National Weather Service to issue flash flood warnings in areas where storm cells were nearly stationary. Colorado Springs had a very intense thunderstorm pass through it where over 20cm of hail fell in the area and snow plows had to be used to clear roads and parking lots. Fire and rescue were also kept busy, saving people from submerged cars that had water up to their roofs. On Thursday morning residents there were surprised to see what one man described as a “scene that you’d only see in the winter”. A little further north, on Wednesday, was where most of the tornadic action was happening. In total five tornadoes were sighted touching down in the northern tier of Colorado, however only minor damage occurred and thankfully no injuries were reported. One tornado, reported as a landspout, even scooted to the north of Denver’s international airport, causing a scare to many passengers, but no damage was done to aircraft.

Precipitation map - Colorado Springs

Map of the rain the fell (inches) in Colorado Springs, CO. (Source: CoCoRaHS)

The harsh weather didn’t end there however. On Thursday the 7th, another round struck the same area spawning more tornadoes, dropping huge hailstones and more significant rainfall. On Thursday the heaviest of the rain occurred in extreme northern Colorado and south-eastern Wyoming, where it was greatly appreciated to help combat a moderate drought and wildfires present in the region. In total, the SPC received another 10 tornado reports, some being more serious, ranging from roofs being blown off to windows being blown out. Only one non life-threatening injury was reported with that round of tornadoes thanks to the great work of the National Weather Service who provided early warning.

Wyoming tornado

A large funnel 100km north of Cheyenne, WY. (Source: Andrew Kniss)

As the trough spawning the severe weather shifts west, the region will experience cooler weather, thus, giving way to a stable atmosphere and calmer weather.

This system that that the western half of the United States experienced this week is expected to spawn severe thunderstorms in North Dakota and in southern Manitoba today.

Tornado Threat To Develop Over Southern Manitoba on Saturday

Brad Leave a comment

3km EHI Values

3km EHI Values. This measures the potential strength of a tornado should one develop. As can be seen, the GFS EHI values have gone off the chart over extreme SW Manitoba on Saturday afternoon.

A slow-moving low pressure system pushing into our region will set the stage this weekend for the potential of supercell thunderstorms capable of producing localized flooding, extremely large hail, damaging wind gusts and tornadoes. Read past the break to get all the details, our thoughts on the main threat areas, and to see updated information in the comments.

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An extremely slow-moving long-wave trough has been slowly pushing it’s way eastwards this week. While it’s been a good distance from us, we’ve been able to enjoy the benefits of such a setup: plenty of nice, warm weather with comfortable humidity. Our friends in the Western Prairies haven’t had it quite as nicely; multiple rounds of storms have pushed into Southern Alberta & Southwestern Saskatchewan over the past couple days, bringing multiple tornadoes to Southern AB and torrential rain that caused localized flooding after 2-3” fell in a short period of time. Large hail was also reported in many storms across the Western Prairies, as well as with some severe thunderstorms that developed over SE Saskatchewan on Wednesday evening.

Entrance of this system in our region has been marked by the thunderstorms and showers that developed overnight. We should see most of these clear from the Red River Valley this morning or by early afternoon if they’re really tenacious. We’ll see a relatively pleasant afternoon, with some lingering cloud and temperatures in the low-to-mid 20’s. The dewpoint will be quite high, making it feel a little sticky, though.

The main surface low begins to move into our area on Saturday, pushing a warm front up from North Dakota into extreme Southern Manitoba. Using the basic MIST principles of thunderstorm forecasting:

  • Moisture: Plentiful. Surface dewpoints will be sitting near 20°C across Southern Manitoba, with 850mb dewpoints pushing up towards 15-17°C. This deep layer of moisture will provide plenty of energy for storms to work with.
  • Instability: The major inhibition to storms will be a layer of warm air at 700mb. Temperatures will climb to 10-13°C at 700mb on Saturday morning, however cooler air will push in later in the afternoon, helping destabilize the mid-levels. LI values of -8 to -11, combined with CAPE values anywhere from 2500 J/kg to 5500 J/kg are evidence of an extremely unstable atmosphere.
  • Shear: With a decent upper-level jet pushing in through the day, most areas across southwest and south-central Manitoba will see bulk shear values increase to 30-40kt by evening.
  • Trigger: A warm front draped across Southern Manitoba will be strong enough to initiate convection in the mid-to-late afternoon as the cap begins to erode.

Prog Tephi for SW MB

Prognosis tephigram for Southwestern Manitoba on Saturday afternoon. Note the extremely favorable veering wind profile present.

Models strongly disagree about the speed of this system, but agree that it has a very strong potential to produce damaging supercell thunderstorms capable of producing tornadoes. The greatest uncertainty, then, is where exactly the storms may form. Unfortunately, as I write this it’s still too early to tell exactly where the greatest threat lies. The slowest solutions would place the main risk over extreme SE Saskatchewan across SW Manitoba, while the quicker solutions would place the risk over SW Manitoba into the Red River Valley. Personally, I feel that the slower solutions are probably a little more true to what’s going to happen. With that in mind, here’s my threat area for Saturday:

Day 2 Storm Outlook

Day 2 Thunderstorm Outlook, valid Saturday afternoon through Sunday morning. This is subject to refinement as this system develops and more certainty exists on it’s track and speed.

A large MCS will likely develop as the whole system lifts northwards overnight, which will continue to provide a severe weather threat in the form of strong winds and large hail. It will push through the RRV by Sunday morning. We may see the threat for another round of thunderstorms on Sunday afternoon, however they are not expected to be severe. Things will finally cool off on Monday as the main upper low moves through and draws in cooler, dryer air from the west.

We’ll be sure to refine the forecast in the comments below as the day approaches. In addition, it looks like the AWM crew will be out chasing, so we’ll be sure to have some live updates should everything work out. Stay sky aware out there this weekend!

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A Scorching Week to End With A Bang

Brad Leave a comment

Temperatures are set to soar for the remainder of this week as heat sourced from the Gulf of Mexico builds into Southern Manitoba. Residents across all of Southern Manitoba should begin to prepare for a potentially dangerous end-of-week though, as a powerful low pressure system will threaten the first significant severe weather outbreak of the season.

850mb Theta-E Chart for 06Z Thursday

850mb theta-e (a form of measuring temperature) chart valid for 06Z Thursday 07 May. The light-red arrows depict the advection of heat from the Gulf of Mexico through Southern Manitoba.

A southerly flow of air aloft, aided by a long-wave trough over the Rocky Mountains to our west and a blocking high to our east, will bring us our hottest days of the year through the rest of this week. Temperatures at 850mb are expected to rise to nearly 20°C today, which will result in daytime highs between 25-30°C through the second half of this week.

A weak low will move through Southern Manitoba on Thursaday night ahead of the main upper trough and while parameters don’t look too great for severe weather, a band of thunderstorms will likely develop in the late afternoon or early evening, intensify, and slowly move east-northeast. While tornadoes aren’t a likely threat with these storms on Thursday afternoon/night, CAPE values in the range of 1250-1750 J/kg combined with LIs near -5 and 20-30kt of bulk shear should provide enough for a threat of large hail. The slow-moving nature of the line of storms could potentially also produce a risk of locally heavy rainfall, with as much as 0.75-1.25” falling over a relatively short period of time. While showers will be commonplace over southwest Manitoba throughout the day on Thursday, the risk for showers does extend eastwards through the western and central Red River Valley in the afternoon. The bulk of precipitation will occur with the thunderstorms that develop in the evening, though.

This is still about 36 hours away, though, and things could change quite a bit between now and then. Models are having a hard time degrading the blocking pattern that’s in place right now, and some are much more progressive with features and some are much slower. If things end up more progressive than they look right now, there may be minimal storm threat for Thursday night.

Night 2 Thunderstorm Outlook

Thunderstorm Outlook for Night 2 (00Z to 18Z June 08).

Taking into account the various speeds, the current area that might see storms on Thursday afternoon/evening looks to be the area bounded from the US border north to Brandon, up towards Dauphin/Swan River, then eastwards across the Interlake and southwards down the eastern Red River Valley. Storms will exit through the Central/Northern Whiteshell. While the potential for heavy rainfall exists, I do not feel enough confidence in it to justify any slight risk categorization on the outlook. The storms will likely be marginally severe, though, so it’s important that they are not ignored with the prospect of even bigger storms on the weekend.

Friday looks to be another warm day; debris cloud left behind from Thursday night’s convection should clear bout by lunch time or early afternoon which will allow the sunshine to warm us up to the mid-to-high 20’s. Dewpoints will build through the afternoon pushing up to 18 or 19°C, making it feel quite humid. The main upper trough is set to move in on the weekend, though, and what a system it looks to be.

SPC Day 4-8 Outlook

SPC Day 4-8 Severe Thunderstorm Outlook

I’m not going to talk too much about Saturday’s setup yet, as it’s still a ways out and in this particular setup, the exact specifics are sure to change with every model run until it’s much closer. We’ll be under the influence of two strong shortwaves that will push copious amounts of instability over Southern Manitoba. CAPE values look to exceed 2500 J/kg and potentially be as high as 5000-5500 J/kg; this, combined with a weak cap north of the warm front and favorable shear profiles looks to point at a potent setup for severe thunderstorms with high probabilities of (extremely) large hail, strong winds, and elevated risks of tornadoes. The setup is similar to other tornado-producing setups of years past, including the Pipestone tornado of 2007.

We’ll have plenty of discussion about the upcoming storm threats in the comments, so be sure to check back often for the latest information about this weekend’s potentially dangerous storm outbreak.