Warming Up, Just to Get Knocked Back Down

Brad Leave a comment

Temperatures will rebound early this week, but a big weather-maker may interrupt that warm-up by midweek.

Warmer air will move into Southern Manitoba on Monday, but it will be windy.

Monday

Monday

Sunny
21°C / 9°C

Today will be bright and sunny with temperatures improving over Sunday’s cool values. Highs will be in the low twenties over Southern Manitoba, which is quite a recovery from this morning’s lows, which were around freezing. The only downside to today’s weather will be a stiff southerly wind that will be 30 to 40km/h gusting to 50 to 60km/h by late afternoon.

Tuesday

Tuesday

Mainly Sunny
27°C / 13°C

Tuesday will be one of the warmest, if not the warmest, days this week with high temperatures in the mid to upper twenties. The humidity may even increase a bit by late in the day over some portions of Southern Manitoba. It certainly won’t be an oppressive mid-summer type of humidity, but may be noticeable nonetheless. Tuesday will be slightly less windy compared to Monday, but the wind will still be fairly strong and from the south.

Wednesday

Wednesday

Mix of Sun and Cloud. Rain late. Risk of a thunderstorm.
25°C / 17°C

What has been a fairly boring weather pattern so far this September may begin to take an interesting turn on Wednesday. A strong low pressure system is forecast to develop in the lee of the Rockies on Tuesday and move eastward into North Dakota by Wednesday. This system will prompt seasonably high moisture values to stream northward into the Dakotas and Southern Manitoba. This moisture will help to destabilize the atmosphere over a large part of the North-Central US, perhaps extending up into Southern Manitoba. This system will also pump warm air up into the region, with models currently suggesting temperatures will once again reach the mid to upper twenties in Southern Manitoba on Wednesday.

As this strong low pressure system interacts with that unstable environment, numerous thunderstorms may develop on Wednesday through Wednesday night. These storms may affect parts of Southern Manitoba at some point on Wednesday or early Thursday. Given the nature of this system it looks like the main severe threat will be heavy rain. However, it is too early to rule out the possibility of other forms of severe weather. We’ll have more updates on this system as the week progresses.

Long Range

The long range forecast will largely be determined by what happens with Wednesday’s system. At this point it appears likely that we’ll receive rain from this system, but the timing of that rain is too early to predict. Unfortunately, once this system moves out of our area it will deliver a parting shot of cold air, which will probably set up a chilly weekend. Again, how cold it will get is still not certain, but getting above seasonal values next weekend may be a struggle.

Elsewhere in Weather News: September 14th, 2013

Matthieu Leave a comment

Historical Flooding in Colorado

This past week Colorado has been absolutely swamped thanks to moisture streaming up from the Gulf of Mexico, riding up the Rocky Mountains (upslope flow) and then falling as rain. High pressure sliding down from the north in the US Plains as well as an upper-level low to the west drew in the moist air from the southeast. Generally, 850mb dewpoints could be found in the 15°C range and PWAT values around 40mm in Eastern Colorado. Plentiful moisture was in place – a recipe for heavy rains that had the possibility to fall for a long period of time. This became the case for Wednesday evening through Friday morning for Boulder, Colorado and surrounding communities.

850mb moisture transport

Radar with overlay of the 850 moisture transport, notice the vectors all pointing towards the Rockies. Taken Friday 3am. (Source: SPC Mesoanalysis image archive)

As best described by NWS Boulder, flooding of “biblical” proportions took place is continues as of Friday night. Small creeks easily turned into raging rivers that inundated whole towns and mudslides blocked highways, took out buildings. The death toll is already at four but concerns of more as 172 people are still missing and some communities are literally cut off, with no roads leading in or out of town. Interstate 25 had been closed due to water running over it as well as numerous other highways that had simply been washed away.

The average rainfall per year for Boulder, CO is around 525mm, this means that in a few days Boulder got over half its annual rainfall at 310mm. This easily beats out the old record for rainfall in September (243mm), and average of 43mm (this month; 721% above average September rainfall). Interestingly enough, the area which received all this rainfall was under a moderate to extreme drought as per the Drought Index.

Rainfall estimates

Estimated rainfall from KFTG as of Friday 3am. Notice the dark purples/white; areas above 200mm estimates. Map storm total accumulation. (Source: GRLevel3)

It appears as though Boulder might get a break from the rain today as the upper-level low weakens and moves further east though there is still a slight chance for pop-up (non-severe) storms. Tomorrow will likely bring with it more rain for the region, unfortunately.

Warm Weather Gives Way to Cool Weekend

Brad Leave a comment

Well above-seasonal temperatures will wash over Southern Manitoba today as a powerful low pressure system in the Arctic drags a swath of very warm air eastwards across the Prairies. It won’t be meant to last, though, as a strong ridge of high pressure builds in behind a cold front that pushes through on Saturday, bringing cool Arctic air with it for the weekend.

Friday

25°C / 15°C
Mainly sunny.
Saturday

22°C / 4°C
Cloudy with a good chance of showers or thundershowers, then clearing through the afternoon.
Sunday

19°C / 6°C
Mainly sunny and cool.

We’ll see a breezy wind out of the southwest today as temperatures climb into the mid–20’s thanks to a warm front that pushed through overnight. We might see a little bit of cloud, but for the most part skies should be mainly sunny. Still in the warm sector of this system, we’ll only drop to the mid-teens tonight with some increasing cloudiness towards Saturday morning as the cold front approaches.

Saturday morning will bring a fairly decent chance for some scattered shower activity as the cold front pushes into the Red River Valley from the north. There may be a few thundershowers as well but no significant or widespread thunderstorm activity is expected. Gusty northerly winds will move in behind the cold front – which should be through much of the Red River Valley by midday – with clouds scattering out to a mix or partly cloudy skies. The temperature should be able to climb a degree or two above the 20°C mark, however cold air advection will limit our high very close to that mark.

Skies will clear overnight as we drop down to a very chilly 4°C or so. Areas outside the city of Winnipeg may even see temperatures dip a little cooler than that. We may end up seeing the first frost of the year in some places on Saturday night but I don’t expect a widespread frost to occur.

Sunday will be a sunny but very cool day as the ridge of high pressure dominates the weather pattern over Southern Manitoba. We’ll see temperatures climb to only around 17 or 18°C by late afternoon but at least the winds should be relatively light, picking up out of the south later in the day to only around 15–20km/h. We’ll see an overnight low of around 7°C on Sunday night with clear skies.

Pleasant Second Half of the Week

Brad Leave a comment

After some unsettled weather the past couple days, we’ll be seeing pleasant, slightly warmer-than-normal days through the second half of the week as a ridge of high pressure builds into the Prairies.

Wednesday

22°C / 8°C
A few clouds and breezy. Slight chance of isolated late-day showers.
Thursday

21°C / 7°C
Mainly sunny.
Friday

24°C / 12°C
Mainly sunny.

We’ll see a few clouds today with a breezy northerly wind as cooler air moves in behind yesterday’s cold front. We may see some isolated showers late in the day thanks to weak convergence along the western shores of Lake Winnipeg, however they would certainly not be widespread and they would have very limited duration. We’ll see a high of around 22°C tomorrow and we’ll drop down to a chilly 8°C overnight under clear skies.

Thursday will be the coolest day of the week with temperatures topping out only around 21°C and an overnight low dropping down to around 7°C. It may actually end up being one or two degrees colder than that at night depending exactly where the main axis of the surface ridge lines up, but suffice to say it will be quite cool on Thursday night. Winds will be light through the day and we’ll see mainly sunny skies and a clear night.

Outgoing Longwave Flux for 00Z Saturday Sept. 14, 2013 -- approximates cloud cover -- showing a potent low pressure system pushing through the Kivalliq region of Nunavut.

Outgoing Longwave Flux for 00Z Saturday Sept. 14, 2013 – approximates cloud cover – showing a potent low pressure system pushing through the Kivalliq region of Nunavut.

Friday looks to be a fairly nice day as an incredibly potent low pressure system moving through the Kivalliq region of Nunavut into Hudson Bay draws warm air from the Alberta Foothills eastwards across the Prairies. At this point it looks like Winnipeg will get into that warm air and see a high temperature around 25°C, although if the warmth ends up occluding slightly faster, the mid–20’s may be confined to Montana and North Dakota while we remain in the low 20’s. We’ll see a few clouds through the day, but for the most part it should be quite nice with winds out of the south or southwest at around 20km/h. Friday night will cool off to the low teens under clear skies.

A Look Ahead to the Weekend

The weekend looks pretty great at this point. A large ridge of high pressure will move in behind the powerful Arctic low bringing sunny skies, light winds and highs in the low 20’s. Saturday & Sunday nights will be quite chilly, though, with temperatures dipping down into the 4–5°C range, and perhaps even cooler outside the City of Winnipeg. We may end up seeing our first significant risk of frost this weekend depending on exactly how strong that ridge of high pressure ends up being.