Elsewhere in Weather News: November 24th, 2012

Matthieu Leave a comment

Severe Flooding Strikes England

Intense flooding has hit parts of the UK these past couple of days and more is to come this weekend. A strong low pressure system approaching England from the south-west has brought with it plenty of moisture which has already flooded out 300 properties and caused one death.

Flooding

Roads flooded out quickly in South-West England as torrential rains fell this past week, more is to come. (Source: The Guardian)

South-West England is most at risk. Areas including Exeter and Bristol were included in the ‘amber risk’ (second highest level) which was issued by the Met Office as more localised flooding was likely to occur. By Saturday afternoon, it will not be uncommon to see rainfall reports exceeding 50mm in South-West England. This, coupled with ground already saturated to its maximum, will cause flash flood conditions where streams could easily overflow in a matter of hours. In total, 70 flood warnings and 150 flood alerts had already been put in place as of Friday. High winds add to the storm’s grave concern, as gusts of 90km/h are not out of the question for Saturday’s event.

Surface analysis

Surface analysis of the UK on Saturday at 7pm. (Source: Met Office)

Areas of South-West England typically see an average of 16 rainy days and 70mm of rainfall in November. Therefore it’s not unusual to see rain in that area during the month of November but the expected amount to be seen this weekend is on the high end of the spectrum. The highest 24-hour rainfall ever recorded in South-West England (Martinstown) was in 1955 where 279mm, over half of Winnipeg’s annual precipitation, fell!

A Mixed Bag

Brad Leave a comment

We’ll see some sun, some more snow, and temperatures all over the place as we see a wild weather pattern over the next few days.

12hr. QPF for Saturday

Precipitation accumulation for Saturday, showing some snow pushing through Southern Manitoba with greatest accumulations north and east of Winnipeg.

Sunshine will dominate today as a very strong Arctic high slumps through the Prairies. This high pressure system is a result of cold Arctic air pushing southwards behind a cold front that passed through yesterday. This will limit daytime highs today in the Red River Valley to only about -12°C. Temperatures will plummet towards -20°C tomorrow night as the ridge pushes through Southern Manitoba and breaks up remnant cloud left behind.

More cloud will begin pushing in late overnight into Saturday morning as another system tracks through the Northern Prairies. This system will warm things up a bit for us, bringing our daytime high on Saturday to a comparatively balmy temperature climbing just over -5°C. To go with those warmer temperatures will be some light snow with accumulations only around 2cm for much of the Red River Valley, including Winnipeg.

This system moves out on Saturday night, and we’ll move into a slightly more stable pattern. Sunday will likely be a mix of sun and cloud as we deal with a little bit of cloud left behind from Saturday’s system, with a high near -12°C again. As we head into next week, things look fairly steady with overnight lows near -15°C and daytime highs starting in the high minus teens and climbing into the low minus single digits.

A Return to Winter

Brad Leave a comment

Colder air is set to return by the end of the week as a low pressure system ushers in Arctic air as winds shift to the northwest behind it.

GFS Sounding for 06Z Thursday

A sounding for 06Z Thursday (midnight-ish tonight) from the GFS model depicting an above-freezing level.

Before the cold weather returns we’ll have one more pleasant day. Although skies will be cloudy today, we’ll see temperatures once again climbing above 0°C through the Red River Valley with a light southerly flow. Conditions will begin to degrade overnight as a low pressure system pushes into Southern Manitoba.

The first threat with this system will be the potential for freezing rain tonight. As the sounding1 above shows, an AFL (Above Freezing Level) with sub-zero surface temperatures will be in place through much of the overnight period before eroding early Thursday morning. The saving grace for the Red River Valley could be that most of the precipitation looks to push north of the valley through the Interlake. If, however, any precipitation manages to wander through the RRV overnight, then there’s certainly a decent chance it’ll fall as freezing rain. Cooler air begins pushing in at all levels early Thursday as we move to the back side of this system and winds switch to the northwest.

Winds will strengthen out of the northwest on Thursday to 40km/h with gusts towards 60km/h as a band of snow slumps southwards with the cold front. At this point, it looks like snow will push into the Red River Valley mid-morning and last until the early evening (6-8PM). Snowfall accumulations will likely be around 5cm. Temperatures will start near -5°C tomorrow morning and fall to -8 or -9°C by the evening. We’ll head to an overnight low of around -15°C tomorrow night.

Sunny skies should dominate Friday and Saturday with highs near -10°C. A weak disturbance looks to bring a chance of light snow to the Red River Valley again on Sunday.

  1. A “sounding” is a way of plotting how the temperature and dewpoint change with height. The sounding is for a single location and plots the temperature/dewpoint with height in pressure coordinates as the vertical axis. ↩

Mild Weather Continues

Brad Leave a comment

The warm weather from the weekend will continue into this week. High temperatures at or above zero will continue.

850mb temperatures will be around 8C in Southern Manitoba on Tuesday

850mb temperatures will be around 8C in Southern Manitoba on Tuesday

Temperatures will drop off slightly on Monday compared with Sunday as the wind switches to a more westerly direction. High temperatures will be held down a bit as cooler air moves in from the vast expanse of snow covered land to our west. Highs will generally be in the -4 to 0C range over Southern Manitoba, with more widespread above zero temperatures in south-eastern areas. On Tuesday most of Southern Manitoba should get above zero, with the exception of heavily snow covered areas which will hover close to the freezing mark. Warm air just above the surface (seen in the graphic above) will offer the potential for high single digit or even low double-digit temperatures in snow-free areas if it can stay sunny (mainly south-eastern Manitoba). Southern Manitoba should once again remain mainly above freezing on Wednesday as a light south-easterly flow allows warm conditions to continue.

Current forecasts show a low pressure system sliding through Manitoba on Thursday. This system will bring more snow to parts of Manitoba, though it is unclear at this point if Southern Manitoba will see any significant amount of the white stuff. What does appear likely at this point is that colder air will be pulled down as this system passes through. As a result colder conditions are expected on Friday and may last into the weekend. More details on the potential impact of this system will be available in Wednesday’s post.

Enjoy one of the last mild stretches before our real winter sets in!