Elsewhere in Weather News: May 3rd, 2014

Matthieu Leave a comment

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.

Cool, Unsettled Start to the Weekend

Brad Leave a comment

Cool, showery weather will round out another week of below-normal temperatures in the Red River Valley. Unfortunately, we won’t see any significant warming through the next few days, keeping our daytime highs 3-6°C below seasonal1.

The RDPS shows convectively driven rainfall this evening through much of Southern Mantioba.
The RDPS shows convectively driven rainfall this evening through much of Southern Mantioba.

The weather over the next several days will be dominated by a series of disturbances sliding southeastwards across the province ahead of an incoming cold low aloft. The upper-level flow will keep us locked in cooler air until early next week – at the least – until any sort of significant shift in the overall weather pattern may begin to allow more seasonal warmth to begin working it’s way towards the province.

Friday

Friday
12°C / 2°C
Early morning showers ending then a slight chance of showers through the day. More showers in the evening.

We’ll see a few lingering showers from the overnight period this morning as a low pressure system exits the Red River Valley into Minnesota. The organized preciptiation should taper off fairly early this morning, leaving us with some mixed skies and temperatures on their way to a high of around 11°C.

A weak trough line will extend along a NW/SE line through the Red River Valley, and it’s possible that we may see a few disorganized showers through the day as a result of the daytime heating. If anything develops, it will likely be short-lived and relatively unremarkable thanks to fairly limited low-level instability.

Another low pressure system will slide along the trough line into the Red River Valley this evening, bringing with it another batch of showers. The instability associated with this second low looks rather decent, and if it arrives early in the evening while we’re still near our daytime high, the showers that develop – in particular further to the southwest near the Turtle Mountains and eastwards towards the Pembina Valley – could intensify enough to become a few thunderstorms. There’s no real risk of severe weather, but at this point I think that any sign of summer, even a thundershower or thunderstorm, would be a welcome sight to most people.

The Weekend

Saturday
8°C / -1°C
A few early morning showers, then mainly sunny.

Sunday
10°C / 0°C
Mainly sunny.

Saturday will start out similar to Friday morning, plus or minus a couple hours, as a few showers right underneath the upper-level disturbance associated with Friday night’s low pressure system exit out of the Red River Valley. We’re in for the coolest day of the weekend with a high of only around 8°C as a northerly flow continues to push unseasonal Arctic air southwards over the region. There will be some afternoon cloud that pops up and it should stay at that; the overall level of instability will be quite a bit less than Friday. Saturday night will be another late-season sub-zero night with temperatures dropping to -1 or -2°C through the Red River Valley under clear skies.

Sunday will feature light winds and mainly sunny skies with temperatures climbing to around 11°C. Some cloud cover looks to push in through the evening hours and we’ll see an overnight low near 0°C.

Next Week

The start of next week looks cool with mixed skies for much of the first half of the week. Early indications are that a series of low pressure systems tracking through the Northern Plains will bring showers to Southern Saskatchewan and perhaps southwestern Manitoba, however a blocking ridge will shunt precipitation southwards into the States, leaving us with cool, dry weather and variable cloud. The NAEFS2 continues to predict below-normal temperatures in the 8-14 day range.

  1. Seasonal daytime highs over the next few days sit around 16-17°C. ↩
  2. North American Ensemble Forecast System ↩

Cool Spring Drags On

Brad Leave a comment
The NAFES continues to forecast below-normal temperatures.
The NAFES continues to forecast below-normal temperatures.

Those looking for warmer, summer-like weather are going to have to look elsewhere as the unsettled, below-normal temperatures we’ve become so familliar are set to continue through the next week or two.

Wendesday
10°C / 1°C
Mixed skies with a chance of showers.

Thursday
10°C / 0°C
Mainly sunny.

Friday
10°C / 0°C
Increasing cloud; chance of showers.

We’ll see mixed skies today as cloud cover pushes westwards from Northern Ontario as the Colorado Low that’s been the genesis for the massive tornado outbreak in the Deep South over the past few days. Closer to home the weather won’t be dangerous in the least; we’ll see just a slight chance of some shower activity pushing into the Red River Valley from the east. We’ll see a high near 9 or 10°C with winds out of the north at 30 gusting 50km/h. Things will clear out tonight as we drop to around 0°C.

Thursday will be quite similar to Tuesday: mainly sunny, a high near 10°C and a bit of a wind out of the east. Otherwise quite unremarkable. We’ll drop to near 0°C on Thursday night.

Friday will bring the next batch of slightly unsettled weather as a disturbance slumps southeastwards out of the Northern Prairies. Our temperature will once again climb to around 10°C, but we’ll see more cloud than sun and what, at this point, looks to be a decent chance of some more shower activity. Expect a low near – surprise! – 0°C once again.

Cool Weekend

Things become sunnier for the weekend, but temperatures don’t look to improve for the weekend. Any potentially lingering shower activity will move off on Saturday morning, leaving us with some sunshine and a high near 9°C. Sunday will be mainly sunny with a high near 10 or 11°C.

The below-normal temperatures[1] will continue through the next week. Another chance for rainfall looks to move into the region early next week as a low pressure system works it’s way thorugh the Northern Plains of the United States.

  1. Normal daytime highs for this time of year are around 16°C.  ↩

A Glancing Blow

Brad Leave a comment

A Colorado low responsible for a tragic severe weather outbreak yesterday across the the Southern United States, and Arkansas in particular, has spread rain northwards into Southern Manitoba this morning. A decent soaking is in store today and then see a cooler, unsettled week ahead as the Colorado Low persists through much of central North America.

Monday
8°C / 0°C
Periods of rain ending by the evening. 10-15mm. Breezy.

Tuesday
10°C / 0°C
A few clouds.

Wednesday
7°C / 0°C
Showers likely.

Late last week it looked as if we were set to get as much as 25-30mm in a widespread swath through much of Southern Manitoba, however we pointed out the complexities of the setup and how minor changes in the positioning of features could cause big changes in how much precipitation is produced.

It turns out the models did fairly well with the overall picture. Thanks to a little more tilt to the upper trough and the upper low being captured a little sooner than originally forecast, the system as a whole won’t push as far northwards as it looked last week and as a result we’ll see a little less rain than it looked like then.

We’re still in for a decent soaking today, though. Periods of rain will persist through the late afternoon or early evening, and in general much of Southern Manitoba will see 10-20mm of rain. Areas further north, towards the Interlake and much of Parkland Manitoba will see in the 5-10mm range, but it does appear that, for the most part, anywhere along and south of the Trans-Canada corridor in SW Manitoba and the Red River Valley will see between 10 and 20mm with the higher amounts closer to the U.S. border. The temperature will sit around 8°C today with breezy winds out of the east at 30km/h with gusts to around 50km/h.

Total rainfall expected today across Southern Mantioba.
Total rainfall expected today across Southern Mantioba.

Near the border there’s a slight chance of accumulations creeping up towards 25mm (1”) or so, but that will depend on fairly heavy rain and some lingering rainfall a bit longer than it seems like it’s likely too. The rain will taper off by this evening and we’ll see gradual clearing through the evening. The temperature will drop to around 0°C.

Another Short-Lived Break

Tuesday looks to be a cool but pleasant day with a high temperature of around 10°C and mostly sunny skies. Temperatures will drop to around 0°C once again on Tuesday night with increasing cloudiness.

Wednesday brings back the showery weather as another shot of rainfall pushes into Southern Manitoba from east to west on the back-side of the Colorado Low. Accumulations don’t look significant at this point, perhaps 3-5mm on the high end, but it does seem like it will be a cool, dreary day with a high of only around 7°C. The showers should taper off by the evening as we drop to the freezing mark yet again, this time under cloudy skies.

Where’s Summer?

Unfortunately, not here. Below-normal temperatures are once again forecast for the 7-14 day outlook, meaning we’ll likely see high temperatures only in the high single digits or low teens for the next week or two.

But it’s gotta warm up eventually, right? Right? Here’s hoping for a big turnaround in May.