Elsewhere in Weather News: May 25th, 2013

Powerful Tornado Devastates Moore, Oklahoma

As you may have heard through media reports these past few days, Oklahoma was subject to severe tornadic weather this week which resulted in catastrophic and tragic consequences for many. Supercells posed a threat to residents as they dropped a number of large tornadoes – including a historical tornado that struck Moore on Monday, May 20th. A longwave trough (same as talked about in last week’s EIWN) was in place on the west coast as were other factors that made the conditions ripe for strong, long tracked tornadoes.

Moore tornado

Supercell with hook echo and large debris ball (just west of Moore), May 20th, 2013. (Source: UCSB)

Moore, with a population of over 50,000, is located in the heart of Tornado Alley and has been struck directly by tornadoes 3 times in the past 15 years. The fact that they are situated where moist air comes in from the Gulf of Mexico and where a source of dry air from the south-west US not too far away, causes many dryline setups in mid-late spring – ideal conditions for triggering storms.

On May 20th, storm cells fired up early in the afternoon and quickly became supercellular and well organized with rotation. As the supercell approached the Moore area, a hook echo formed and not long after, a debris ball could be seen on radar just before it was passed over Moore – it was obvious that Moore was in dire trouble and a tornado had touched down. Thankfully, the National Weather Service in Norman provided generous lead time of 16 minutes before the tornado entered Moore, certainly saving many lives.

Moore damage

Aerial view of the damage in Moore. (Source: AOL)

Tragically however, even though advance warnings were given, 24 people perished that day. In some areas it was not possible to take refuge in interior rooms; EF-5 winds easily ripped apart any building in the tornado’s path. Damages are estimated to be in the billions of dollars with an estimated 1,300 homes destroyed and countless number of vehicles wrecked.

Incredible video of a close up view of the 2013 Moore tornado, not to be tried at home – very dangerous! (Source: Jeffery Lechus/Youtube)

It appears the storm track will remain active with troughing across the western part of the continent and intermittent shortwaves rounding down the ridge across Southern US. Severe weather looks likely in the High Plains region of the US (Nebraska, Kansas) in the coming week – not out of the ordinary for these locations at this time of the year.

Elsewhere in Weather News: May 18th, 2013

Severe Weather Event South of the Border: Possible AWM Chase Sat/Sun

Trough

Negatively-tilted trough on Saturday late afternoon. (NAM) (Map source: Twisterdata)

The same system that will cause Southern Manitoba to have a rainy May long weekend is expected to produce a string of severe weather days across the Central US, starting today, continuing through at least Tuesday. A negatively-tilted longwave trough approaching from the west will help to provide the necessary wind shear, lift, and instability for severe storms to develop. A broad surface low with an extending cold front from Central South Dakota through Nebraska will be in place with a warm front slicing through north-east South Dakota. Another, stronger, low pressure center will be in place in Kansas with an extending dryline all the way down to Texas. These features will offer enough lift for severe storms on Saturday. This, combined with other severe weather ingredients such as a stiff low level jet (LLJ), high amounts of instability, deep low level moisture and low cloud bases is ideal for severe weather and tornadoes. The Storm Prediction Center has issued a Moderate Risk for Nebraska and Kansas with a Slight Risk extending up to North Dakota for their 2 Day Outlook as of Friday night.

Surface Analysis

Surface analysis of the Plains. (Map source: Twisterdata)

As of Friday evening these ingredients appeared to be maximized in the vicinity of north-western Kansas near the Nebraska border. Storms will not be confined to this area though, as strong to severe storms will still be possible into South Dakota and down into Oklahoma, but whether they will be tornadic or not is still to be seen.

The ingredients that will be in place tomorrow in South Dakota:

  • Instability: about 2000J/Kg of MLCAPE (mixed layer)
  • Surface dewpoint: 18°C
  • Shear: 40 knots (0-6km shear)
  • LLJ: 20 knots
  • Lifting condensation levels (cloud bases): around 750m

With the LLJ being only 20 knots, an AWM Chase is still up in the air. If models tend towards a stronger LLJ, the chase will likely be on with a target somewhere in Central South Dakota.

Sunday also offers a significant severe weather threat as the trough continues its trek towards the east. Severe weather risk would extend into Southern Minnesota all the way down to Oklahoma. There is still some uncertainty about Sunday but it does look like another significant severe weather outbreak day for the Plains and Upper Mississippi Valley. Stay tuned in the comments section as the event approaches, updates will be posted.

AWM Chase is On!

Two of the AWM team members will be out chasing this setup along with a student from the University of Manitoba. You can keep up with their chase right here:

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Elsewhere in Weather News: May 11th, 2013

Cyclone Duo in Indian Ocean

Two separate cyclones formed in the Indian Ocean this week and will continue to intensify and organize over the weekend. A low shear environment combined with warm sea surface temperatures of around 30°C, were key factors in the formation of these two cyclones.
The first cyclone, located south of the equator, is named Jamala. This cyclone is headed west and is only expected to intensify to a category one hurricane for a short amount of time before weakening to a tropical storm again. Despite reaching category one and heading west towards land, Jamala is not expected to affect Madagascar or any parts of eastern Africa as models show it weakening to almost nothing before reaching the coast.

The second cyclone, cyclone 01B located north of the equator, is more of a concern to Bangladesh and surrounding countries. This cyclone has the potential to cause substantial damage to Bangladesh as land is prone to flooding there. Storm surge will likely be an issue, depending on the strength of the hurricane when it makes landfall. As of Friday evening, 01B had estimated maximum surface winds near the 95km/h mark but was expected to increase in strength as it moved north, towards Bangladesh. Landfall is still a ways away, but its stronger outer bands are expected to arrive near the Myanmar and Bangladesh shores early Tuesday.

Cyclone 01B

Enhanced infrared image of tropical cyclone 01B Friday night. (Source: CIMSS/NHC)

The Indian Ocean cyclone season is most active from the beginning of spring to early winter but it is possible to have cyclones form throughout the year.

Elsewhere in Weather News: May 4th, 2013

Let it Snow!

Record-setting snowstorms were the topic of conversation in parts of the US this week.

Snowfall reports

Snowfall map until Thursday morning. (Source: NOAA)

Springtime weather was delayed once again as a significant trough moved across Central US dragging down unseasonably cold arctic air with it. Friday morning, temperatures at 850mb reached below freezing all the way down to Mexico; and snow fell from Northern Ontario all the way down to northern parts of Arkansas and Oklahoma! Many snowfall records were shattered, some of the most significant being:

  • Britt, Iowa – Achieved a snow depth of 28cm, beating the old record of 25cm (in 1947).
  • Chippewa-Falls/Eau Claire, Wisconsin – Recorded a snowfall of 22cm shattering the old record of 5cm (in 1946).
  • Extreme north-west Wisconsin – Recorded a snowfall of 46cm.

The trough will not make it to the East Coast as the main jet stream is retreating north and a cutoff low will form in southern US. This cutoff low is expected to slowly drift across the region feeding into tropical moisture while dropping significant rainfall over parts of the south-east and east-central US. Accumulations of over 80mm are expected, increasing concerns that flash floods might be a problem over the weekend.

In other news, a category one cyclone formed off the north-eastern coast of Australia, however it had minimal impacts on land as it fizzled out and only brought lowland flooding and erosion to coastal areas.

Italy also saw an active week with a large tornado reported in it’s northern region. An approaching shortwave combined with significant instability and sufficient shear on Friday was the cause for severe storms in the area.

Short video of the Italian tornado as seen from the nearby city of Castelfranco Emilia. (Source: R. Melotti)