Elsewhere in Weather News: October 20th, 2012

Severe Weather Outbreak in Dixie Alley

This past Wednesday evening a severe weather outbreak comprised of severe winds and strong tornadoes occurred in the southern United States, causing damage to rural areas of Northern Mississippi. This was brought on by the same system we experienced over the past couple of days. The polar jet stream along with a strong low level jet overhead and plenty of moisture from the Gulf of Mexico combined to create conditions ripe for tornadoes in Dixie Alley.

Trough

500mb heights/temperatures with trough (arrow) and circled area where the tornado outbreak occurred. (Source: Twisterdata)

The strongest, a half-mile tornado, rated EF-3 by the National Weather Service, touched down near Jackson Mississippi and caused quite a bit of damage, tearing up large trees and wrecking mobile houses. As the tornado trekked for 26 kilometers, nine people taking cover inside mobile houses were injured but thankfully no fatalities occurred during this event. As the night wore on, more tornadoes touched down in Mississippi and Arkansas, doing damage to rural homes and cutting off power to residents.

Tornado damage

Tornado damage in Leake County, MS. (Source: WLBT)

A few colder days will follow the trough this weekend and a return flow will set up, bringing warm and humid weather back to the region. Weather models are showing another large trough will likely develop late next week, bringing the potential for more dynamic weather. Of course, it is not uncommon to have severe weather in the southern US during the spring and fall, when the polar jet is in the vicinity.

Elsewhere in the world the weather has remained relatively calm, except for this unusual tornado in France.

Video of the tornado in Marseille, France. (Taner Ozdil)

Tornadoes in France are not rare but are not a common sight in October.

Lingering Showers Give Way to Unsettled Weekend

A few lingering showers will persist through the Red River Valley this morning as the low pressure system that has been bringing us rain the last couple days slowly pushes eastwards. Conditions won’t improve too much, however, as we’ll be dealing with unsettled weather, albeit a little dryer, through the weekend.

Rainfall accumulations through the day today.

This 12 hour rainfall accumulation map shows the total rainfall that the RDPS model is forecasting for the daytime today.

Showers will slowly taper off through the Red River Valley today from west to east with only a further 2-4mm in rainfall accumulations. This system has brought hugely varying rainfall amounts across the RRV, with general amounts from 20-60mm across the Red River Valley. After spending several months in a row with below-normal precipitation, this system has pushed Winnipeg back to above-normal accumulations for October, which will begin to chip away at our deficit for the year. Winds will also taper off through the day today as we move to a high of only 7 or 8C.

Saturday will be a mainly cloudy day with a slight chance of showers and a high near 11C.

A frontal wave pushes across Southern Manitoba on Sunday, occluded from the parent low that will be captured over Northern Saskatchewan by an upper low in the area. Some uncertainty exists to the amount of precipitation associated with this wave as it moves through. Some models have next to no precipitation, while the GDPS is suggesting as much as 10-15mm of rain. My personal feeling is that we’ll likely see some rain push through with general amounts in the 4-8mm range across much of the RRV. We’ll keep an eye on this system and provide some updates through the weekend in the comments below. Sunday will likely be mostly cloudy again, with a high near 10C.

The biggest weather feature next week looks to be the potential for a significant low pressure system to push into North Dakota, bringing rain, snow, and potentially blizzard conditions to the Red River Valley for the second half of the week. That’s a long ways away, though, and a lot can change between now and then. We’ll be sure to follow this potential system closely through the week ahead.

Wet & Windy Weather On The Way

Yesterday’s beautiful mid-October weather will be replaced in a hurry today and tomorrow, as a intense 985mb low pressure system brings unsettled weather into the Red River Valley with strong winds moving across the area as the low pushes eastwards.

RDPS 3hr. QPF for this afternoon.

3-hour accumulated precipitation for mid-afternoon from the RDPS. Precipitation will be oriented in a band NW-SE ahead of the main surface trough.

Cloudy skies will be dominant over the Red River Valley over the next couple days. While temperatures are fairly mild this morning, and of note is how high our dewpoint has climbed, we won’t gain too much temperature-wise through the day today. Showers will push into portions of the Red River Vally & SE Manitoba this morning, however it’s likely that precipitation will be sporadic for any one location through the day today with fairly minimal accumulations. Conditions don’t look too favourable for drizzle today; you generally want saturated low-levels of the atmosphere with a sharp contrast into dry air immediately above the cloud deck for drizzle generation. Today, we’ll actually have dryer low-levels with a fairly moist atmosphere above, so it’s more likely that any light precipitation would be somewhat-evaporated rain, not drizzle. Temperatures will climb to 12 or 13°C today.

A band of steady rain will begin to push into the Red River Valley this evening as an area of strong frontogenesis1 on the northwest side of the 850mb low orients itself over the region. The band of rain looks to be fairly narrow, and positioning of it will be very sensitive to the positioning of the 850mb low. All areas in the Red River Valley will see some periods of rain tonight, however any locations that end up under this sharp band of rain will likely see 5-10mm of rain. Amounts remain low, despite the strong forcing, as this system, while energetic, is relatively low in moisture. Precipitable water values look to be only in the 20-25mm range, instead of the closer to 40-50mm range we look for for higher-accumulation rainfall events.

Winds will pick up overnight into Thursday as the Red River Valley moves into a strong pressure gradient on Thursday. Winds will climb to 40-50km/h with gusts up to 60km/h. Showers will be widespread through the Valley as general “wraparound” precipitation moves in on the backside of this system. Total amounts for tomorrow will generally be 4-8mm across the Red River Valley. The rain and wind will taper off tomorrow night as the system moves off towards the Great Lakes. Temperatures will drop down to 6 or 7°C.

Friday will be a slow recovery day, as the clouds will begin to break up a bit through the day. With skies remaining fairly cloudy with only a few breaks for sunshine, temperatures will end up fairly steady through the day; likely only around 8°C. Looking ahead to the weekend, it looks to be a fairly seasonal weekend with a mix of sun and clouds and highs near the seasonal 10°C.


  1. From the AMS Glossary: In general, an increase in the horizontal gradient of an airmass property, principally density, and the development of the accompanying features of the wind field that typify a front. 

Decent Start to the Week

The weather to start this week will be decent, with normal to above-normal temperatures expected. However, some change is in store closer to the middle of the week.

A strong low pressure system will move through Southern Manitoba this week

A strong low pressure system will move through Southern Manitoba this week, pulling down cooler air from the north

Monday will be a fairly good, albeit cloudy day. Temperatures will be in the low teens in the Red River Valley, with perhaps a couple of light showers in the afternoon. These showers are expected to develop ahead of a trough that will move through the Red River Valley during the day. Further west, in portions of south-western Manitoba, temperature should climb up around the 20C mark as sunnier conditions prevail. Tuesday looks to be the warmest day of the week, with highs close to 20C possible in the Red River Valley. Unfortunately that is where nice weather ends.

A powerful low pressure system will slide through Manitoba on Wednesday, bringing some rain and changing weather with it. Temperatures on Wednesday will remain near normal at around 10C with gusty west to north-westerly winds developing behind the low pressure system. On Thursday the system’s passage will be felt more noticeably as temperatures drop back down into the mid single digits and gusty north winds make for a chilly day.

There is some uncertainty in the forecast for late week into the weekend. Models currently suggest that another strong low pressure system may move through Manitoba, but the timing and strength of this system are not clear. This is what the end of the week will probably look like, but as we all know models like to change their solutions from time to time.