Matthieu, Author at A Weather Moment • Page 6 of 39

Deluge of Rain Falls on Eastern Australia

April 25, 2015April 25, 2015 Matthieu 1 Comment

A persistent area of low pressure off the coast of Eastern Australia is to blame for extreme amounts of rainfall that fell during the mid-week.

[map autofit=”1″ disable_scrollwheel=”1″] [pin]Sydney[/pin] [pin tooltip=”Maitland”]Maitland, Australia[/pin] [pin tooltip=”Dungog”]Dungog, Australia[/pin] [/map]

An upper level low that was cut-off from the main jet stream to the south was the reason for the slow movement of the surface low. Sydney and surrounding regions were hardest hit from the storm where over 300mm fell in some areas in less than 24 hours. Dungog and Maitland, towns north of Sydney, received some of the highest amounts in the region; 312mm fell in Dungog in 24 hours and 301mm fell in Maitland in the same amount of time. Sydney received 225mm during a two-day span – relatively speaking, this is a significant rainfall for them. According to the Australian Bureau of Meteorology this was the most rain Sydney has received during two-day period in more than a decade. What made conditions even worse was that winds howled to 80km/h in Sydney and over 130km/h in three separate regions on the east coast of Australia. The high winds made for swells of over 6m out at sea.

The state of New South Wales is pictured with one-week rainfall totals. Bright pink shaded areas are areas that saw over 300mm of rain fall throughout the week.

Due to the high winds and flooding rains, power to 215,000 people was knocked out in the region. In addition to that, creeks quickly became dangerous, fast-flowing rivers in the Dungog region. Several houses in Dungog were washed away due to the floodwaters and unfortunately four people perished. There were also 150 water rescues that had to be executed. As of Friday morning where were still a few thousand people isolated by floodwaters that cut off main roads. In total, 12 communities were officially declared a natural disaster area by the government – insurance companies estimate the damage to be around 100 million dollars.

Since then the soggy weather has continued, off and on, throughout the end of the week. With another system and associated cold from arriving from the west today, the chance for rain continues – amounts will be nowhere near the ones that were observed this past week, however.

Elsewhere in Weather News: April 11th, 2015

April 11, 2015April 11, 2015 Matthieu Leave a comment

Severe Weather Outbreak Strikes Plains and Midwest

As April rolls around the severe weather season in the United States is on an uptick, and with that comes a higher threat for tornadoes. The latest severe weather outbreak occurred Wednesday and Thursday of this past week and hit hardest a few small communities of northern Illinois.

[map autofit=”1″ disable_scrollwheel=”1″] [pin]Medicine Lodge, Kansas[/pin] [pin]Fairdale, Illinois[/pin] [/map]

The setup on Wednesday was a fairly typical setup that you would see for a Southern Plains outbreak – surface low in central Kansas with sharp warm front extending eastwards and dryline extending southwards. This, combined with an upper-level trough moving in aloft, destabilized the environment sufficiently for supercells. Only a few tornadoes were observed on Wednesday, with most spotted just west of Wichita (including a large cone tornado near Medicine Lodge) and one unconfirmed in western Oklahoma. No damage was reported as tornadoes mainly touched down in open areas.

Picture of the Fairdale tornado near Ashton Ill. (Source: Tom Purdy)

Aerial picture of the tornado path and damage in Fairdale. (Source: @jessycamalina)

Ground scars from the EF-4 tornado near Fairdale, Ill. (Source: @jessycamalina)

Sounding from central Ill at 7pm (about the time of the tornado) shows a veering wind profile that’s nearly uncapped with sufficient CAPE for supercells.

Thursday was a different story however, as the system progressed eastwards. The main risk for the day zeroed in to an area near the triple point where both CAPE and shear values were high and surface winds were slightly more backed compared to further south along the cold front. Once again, supercells were triggered in the early evening hours – this time in northern Illinois. One supercell near the triple point stood out from the others however; there no other cells to its southeast to inhibit growth and it latched along the warm front. What came of this supercell was a long tracked tornado that was on the ground for an estimated 25-35km and measured just less than a kilometre in width. It tore through mostly rural area and outskirts of two other towns before striking the town of Fairdale, Ill, which sustained heavy damage from the twister. On Friday, National Weather Service teams were out to examine the damage and gave it a preliminary rating of EF-4 (winds of about 315km/h). Two people were killed and a dozen more injured by the tornado. Cleanup is currently underway in the town as calmer weather sets in for the weekend.

Note: there is some strong language near the end of the video clip

Elsewhere in Weather News: April 4th, 2015

April 4, 2015April 4, 2015 Matthieu Leave a comment

Rare Rainfall Event Strikes Chile

A rainfall event that occurred near the end of March in Northern Chile did some major damage to numerous towns in the region. The storm system that brought the rain was the product of an upper level low that remained nearly stationary for several days in the area. The rainfall amounts, which might seem insignificant to Manitobans, are significant for that area because the storm system brought rain to one of the few places on the planet that receives very little precipitation every year – the Atacama Desert.

[map autofit=”1″ disable_scrollwheel=”1″][pin]Santiago[/pin][pin]Antofagasta[/pin][/map]

The flooding and mud flow event affected about 30,000 Chileans and destroyed 5,900 houses. In the hardest hit regions only about 65mm of rain fell, but due to the extremely dry soil conditions in the region – which have trouble letting rainfall percolate through – flooding occurred. According to Wundergroud meteorologist Jeff Masters, Antofagasta recorded 24.4mm of rain in 24 hours while their average precipitation per year is 3.8mm. Santiago, Chile recorded 35.7mm of rain during the event, which is a significant amount in comparison to the 6mm total rainfall they typically receive during the entire month of March.

Aerial images of a flooded region in the Atacama just south of Antofagasta. (Source: Reuters)

The flooding rains triggered flash floods which swept away cars, houses and washed away one of Chile’s main highways in 3 places in the normally arid part of northern Chile. In total, 24 people have perished from this event and there are still over 50 that are missing where the mud flows occurred. Rescue efforts are still ongoing for people in remote locations and the cleanup in the towns has begun as 7,000 troops have been brought in.

In other news, the Philippines are expecting typhoon Maysak to make landfall this weekend. Maysak was once a super typhoon (category 5) but has since encountered cooler waters of the Western Pacific and has weakened to a category 1 typhoon as of Friday night. The main risk with this storm is the heavy rainfall that it will bring to the Northern Philippines.

Elsewhere in Weather News: March 28th, 2015

March 28, 2015April 3, 2015 Matthieu Leave a comment

First Significant Severe Weather Event of the Season Strikes Oklahoma

This past Wednesday severe storms erupted across much of Oklahoma bringing with them very large hail and even tornadoes. It was the biggest severe weather day this year in the states, up to now (but many more are to come). A surface low was located in central Oklahoma with dryline extending southward, cold front crashing south from the north side of the low, and a warm front extending northeastwards from the low. There were two main focus areas for the storms – along the dryline and near the triple point/along the warm front. A moderate risk was issued by the SPC and covered the areas of concern. The outlook also included a 5% tornado risk with 45% hatched hail probabilities. A moderate jet streak was in place with dewpoints in the high teens, which together provided sufficient shear and CAPE for supercells.

[map type=”terrain” autofit=”1″ disable_scrollwheel=”1″] [pin]Sand Springs[/pin] [pin]Moore[/pin] [/map]

As expected, several storms initiated on Wednesday afternoon and grew into supercells. Two supercells were of most concern before storms consolidated into squall lines: one near Tulsa and one near Oklahoma City. The storm that approached Tulsa showed strong rotation on radar early in its lifetime –a tornado warning was able to be issued well before it hit the city. By the time it reached a suburb of Tulsa, Sand Springs, a tornado touched down and tore through a trailer park. In addition to that, hail, the size of tennis balls, were reported in Tulsa’s metro region as the supercell’s hail core passed over the city. The tornado (preliminary rating of EF-2) injured over a dozen people and one person lost their life in the trailer park.

Aerial view of the damage to the trailer park in Sand Springs. (Source: Tulsa World)

The Oklahoma City storm fired off the dryline initially but then got undercut by the cold front – meaning it had little tornado potential. Interestingly enough, the supercell was able to catch up to the cold front and interact with it, enhancing the vorticity in the area – likely being a contributing factor to the formation of the tornado. With this mesoscale interaction playing a significant part in the cause of the tornado, not much lead time was provided to residents (it happened quickly). Unfortunately the twister (preliminary rating of EF-1) touched down in the city of Moore, OK which got hit by a devastating twister in 2013 and had seen two other strong tornadoes since 1999. No injuries were associated with this one, thankfully.

Compilation of radar images before/during/after the Moore tornado showing the storm's interaction with the cold front. (Image compilation by @VORTEXJeff / Twitter) — Compilation of radar images before/during/after the Moore tornado showing the storm’s interaction with the cold front. (Image compilation by @VORTEXJeff / Twitter)

The pattern could become active again by the middle of next week, but it is still too early to be certain. April to late May is typically the busiest time of the year for severe weather in the Southern US Plains, due to plentiful moisture before the jet stream shifts further north for the summer.

A Weather Moment

Author: Matthieu