Category: Elsewhere in Weather News

Elsewhere in Weather News: May 10th, 2014

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Flooding Rains in New Orleans

A weak disturbance tracking across the southern Gulf States was the cause for some flash flooding in New Orleans last night. Precipitable water (PWAT) values exceeding 50mm were present in the area, meaning a very moist atmosphere was in place. Heavy rain fell in the wake of a squall line of storms Friday afternoon into early Saturday morning, causing significant flash flooding in New Orleans. Radar indicated that as much as 125mm fell across the New Orleans and reporting stations in the surrounding area showed widespread 80-100mm readings.

Storm totals according to radar (as of 1am today). Green boxes are flash flood warnings. (Source: GRLevel3)
Storm totals according to radar (as of 1am today). Green boxes are flash flood warnings. (Source: GRLevel3)

Flash flood warnings had also been issued by the National Weather Service for most of southeastern Louisiana, including New Orleans. In addition, several water rescues had to be executed in New Orleans due to cars being submerged up to their roof in water. This event comes just over a week after severe flooding affected the Florida Panhandle and dumped over 500mm over some areas.

Severe Weather Expected in the Plains

This weekend looks take an active turn weather-wise across much of the Central and Southern Plains of the United States. A strong low-level jet will aid in transporting significant moisture from the Gulf of Mexico northward ahead of the approaching system. CAPE values are expected to reach very unstable values, especially on Sunday across Tornado Alley; with limited capping (warm air aloft) storms are likely to become severe quickly and tornadoes are possible. Updates on this event will be available in the comments section as the event unfolds!

Following this event, a lull in the storm season is expected across the region for about a week before a return flow sets up and more Gulf moisture is able to start making its way poleward.

Elsewhere in Weather News: May 3rd, 2014

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Severe Weather, including Tornadoes Rip through United States

It’s been a rough week in the south-central United States for tornadoes. Monday and Tuesday warranted two consecutive high risk outlooks by the SPC for central Arkansas and Mississippi/Alabama, respectively. The system did continue on further to the Carolinas, but conditions weren’t as ripe for tornadoes. As of Friday evening, NWS had confirmed 67 tornadoes from the outbreak and from these, 11 were of EF-3 strength or higher.

Sunday was predicted to be a big day tornado-wise across Arkansas but cloudy conditions in the morning prevented much daytime heating from occurring. A mesoscale convective system (MCS) had also passed through the region the night prior which could have further disturbed the environment. With that said, the environment did manage to sustain a violent supercell in central Arkansas on Sunday which spawned the EF-4 Mayflower/Vilonia tornado. The tornado was on the ground for a length of 66.5km, at its peak produced winds of 300km/h and had a width of 1.2km. Unfortunately 15 people perished from this tornado.

Velocity data of the Mayflower/Vilonia supercell before it hit Mayflower on Sunday. Notice the intense couplet (red and blues are close), a sign of strong rotation. (Source: Radarscope)
Velocity data of the Mayflower/Vilonia supercell before it hit Mayflower on Sunday. Notice the intense couplet (red and blues are close), a sign of strong rotation. (Source: Radarscope)

Monday was a threatening day with numerous supercells lined up from southern Tennessee all the way down to southern Mississippi, all a posing threat to drop a tornado because of the volatile environment. The Louisville, MS tornado was one of the most significant one spawned on this day, with an EF-4 rating. It tore through the town killing 9 people and injuring several more. The tornado was on the ground for about an hour, traveling 57km. Another town that took a direct hit on that day was Tupelo, MS. The tornado, which had an EF-3 rating, passed through the northern part of the city taking the life of one person.

Supercells across the US South on Monday, notice the overshooting tops associated with the powerful updrafts. (Source: NOAA)
Supercells across the US South on Monday, notice the overshooting tops associated with the powerful updrafts. (Source: NOAA)

Tornadoes were not the only thing that this system produced on Tuesday night as the MCS stalled out over the Pensacola area of Florida producing flash flood conditions across the region. Interstates were underwater, roads got washed out and parking lots full of cars could be seen underwater. Record-breaking amounts were recorded from this event (provided by Jeff Masters blog):

  • 144mm of rain in one hour
  • 520mm of rain for the event

This weekend the pattern is much calmer across the Southern US and Plains as the atmosphere recharges for the next trough coming ashore next week.

Elsewhere in Weather News: April 26th, 2014

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Tornadoes Tear through North Carolina

It was an active day severe weather-wise for parts of East Coast yesterday, where tornadoes, large hail and strong winds were all experienced. These severe storms were triggered by a shortwave racing across the mid-section of the US and approaching the East Coast. Moisture was plentiful streaming up from the tropics which promoted low cloud bases and sufficient amounts of Convective Available Potential Energy (CAPE). In addition to this, wind shear was significant enough to support supercells as well as an approaching cold front from the west acting as a trigger mechanism. Considering all of these, conditions were primed for supercells in North Carolina and Virginia.

Trucked flipped in Chicod, NC. (Source: WITN)
Trucked flipped in Chicod, NC. (Source: WITN)

Supercells quickly formed Friday afternoon across eastern parts of North Carolina and Virginia as the atmosphere destabilized. Elizabeth City appeared to be the hardest hit, likely by straight line winds and not a tornado. As of Friday evening, several injuries were reported because of the strong winds downing trees and power lines in the city. According to the SPC there were 10 different tornado reports which appeared to account for three different tornadoes. Fortunately, no injuries or deaths were reported to be associated with any of the tornadoes.

This event comes at the same time a significant negatively-tilted trough arrives ashore on the west coast. The trough is expected to bring severe weather from the US plains this weekend, to the East coast for the beginning of next week. Sunday through Tuesday look to be the most dangerous days where numerous tornadoes could touch down across Dixie Alley and the Midwest. As of Friday evening, the SPC had already issued a Moderate Risk, mentioning strong tornadoes in their discussion and suggesting a high risk (highest tier) upgrade could be in order in future updates.

With only 89 tornadoes reported in the US as of April 13th, that number could easily double within the next few days.

Elsewhere in Weather News: April 19th, 2014

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Extratropical Storm Ita Brings Soaking Rains to New Zealand

The same cyclone as discussed in last week’s Elsewhere in Weather News article has continued its trek southeast and has brought torrential rains as well as strong winds to New Zealand. After making landfall on Australia’s northeast coast, Ita curved back out to sea while transitioning to an extratropical storm. Extratropical storms are characterized by well-defined frontal features as well as cold core as opposed to cyclones which are tropical in nature and have warm cores.

Surface map analysis on Friday evening (local time) of extratropical cyclone Ita just offshore of New Zealand. (Source: Met Service NZ)
Surface map analysis on Friday evening (local time) of extratropical cyclone Ita just offshore of New Zealand. (Source: Met Service NZ)

The remnants of Ita brought torrential rains and fairly strong winds to New Zealand’s islands. These adverse conditions knocked out power to around 22,000 people in addition to washing away roads, wreaking havoc on Easter weekend travelers. Some water rescues also had to be executed due to people being trapped in their cars. It appears as though a general 100mm fell across the northern part of the island. Locally higher amounts (200mm+) were possible as upslope winds contributed to higher amounts where higher topography was present. The highest wind gusts also affected the northern and western side of the country, where winds coming straight off the ocean produced gusts as high as 115km/h in Westport.

Thankfully the extratropical cyclone is expected to exit the region and continue its track south, bringing more pleasant conditions to New Zealand for Sunday and Easter Monday. Another significant cyclone is churning this weekend, but thankfully in the open waters of the Indian Ocean. Although it is expected to reach category one, it will remain over open waters and is not expected to make landfall.