Elsewhere in Weather News: May 17th, 2014

Matthieu Leave a comment

Wildfires Torch California, Helped by Strong Winds and Drought

This past week several wildfires have been burning out of control in San Diego County, just north of San Diego. It is not known whether any of the fires were started intentionally or not, however, the weather has played a significant role in hampering firefighting efforts. As of Friday evening there were four wildfires burning in the county which were all over 1,000 acres in size, and only one of these four was above 25% contained. There are two main points to note of as to why weather has played such a significant role in fueling the fires.

A large pyrocumulus cloud could be seen on Wednesday from San Diego looking towards the Cocos San Marcos fire. (Source: Mashable/Kent Horner)
A large pyrocumulus cloud could be seen on Wednesday from San Diego looking towards the Cocos San Marcos fire. (Source: Mashable/Kent Horner)

The Santa Ana Winds are the first to have a big impact on wildfires currently burning out of control in Southern California. These winds occur when air blows towards the Pacific Ocean from the mountain ranges to the east. As the air descends the mountain sides it warms and its relative humidity decreases causing for hot and dry winds. This past week, relative humidity as low as 3% was observed by stations in southern California, coupled with winds of 50km/h, this produced prime wildfire conditions. The second reason as to why the wildfires have been difficult to contain is the current drought situation in the region. A large ridge of high pressure has been persistent over the west coast for most of this past winter and part of this spring, making precipitation difficult to come by. The drought index currently indicates that an extreme drought (second highest tier) is occurring in the region where the fires are burning. In turn, the wildfires have little trouble spreading to moisture-starved vegetation and dried out brush.

This weekend offers a mixed-bag to firefighters. Strong winds and scorching temperatures will persist during the day, but winds will now be out of the west causing for slightly moister air coming onshore from the Pacific. Regardless, the Storm Prediction Center maintains an “elevated” fire risk for this weekend.

Moderating Trend Gives Way to Rainy Holiday

Brad Leave a comment

Temperatures will moderate to seasonal values by the end of the weekend, but the Victoria Day holiday may end up being quite wet.

Relief is in store for Southern Manitobans weary of the prolonged cold weather as milder air is finally set to return to the region. The intense upper-level cold trough over Ontario that has been bringing a strong northerly flow and cool weather to the region will finally begin to collapse, allowing milder air to work its way eastwards again. Temperatures will remain fairly mild while the weather takes a turn for the worse on Victoria Day as a low pressure system brings the potential for substantial rains across much of Southern Manitoba.

Friday
14°C / 0°C
Mainly sunny.

Saturday
18°C / 6°C
A few clouds.

Sunday
18°C / 8°C
Mixed skies.

Today and tomorrow will see daytime highs climbing towards the high teens with minimal in the way of cloud cover. Both days will also see light winds thanks to a ridge of high pressure situated over the province. We’ll likely see temperatures dip to the freezing mark tonight[1], but milder air will be in place for Saturday night making the overnight low around 5°C warmer.

Sunday will be a more unsettled day. Most places in Southern Manitoba will see cloudy periods with a very marginal chance of a shower. Winds will shift out of the south to 20-30km/h as a warm front lifts northwards through the day. Temperatures should climb to around 18°C and the temperature will drop to around 8°C on Sunday night.

Potentially Stormy Victoria Day Holiday

Monday
15°C / 10°C
Mainly cloudy; rain likely.

A powerful low pressure complex will develop over Saskatchewan on Monday which will bring wet weather to Southern Manitoba as a conveyor belt of warm, moist air sets up all the way from the Gulf of Mexico. We won’t see that warm, humid air at the surface, but thanks to a strong southerly flow aloft, strong isentropic ascent over the warm front will produce a very saturated, potentially unstable atmosphere over Southern Manitoba.

Rainfall forecast (in inches) from NOAA's WPC for Sunday evening through Tuesday evening. The WPC is forecasting as much as 25-30mm of rainfall for Southern Manitoba.
Rainfall forecast (in inches) from NOAA’s WPC for Sunday evening through Tuesday evening. The WPC is forecasting as much as 25-30mm of rainfall for Southern Manitoba.

What does this mean? We could see fairly heavy rainfall on Monday. There is still enough time for things to change substantially between now and then, but amounts anywhere from 5-25mm seem quite possible. The rainfall does seem quite convectively driven, and with a moderately strong 850mb jet there’s always the possibility the rainfall becomes attached to the left-exit region and ends up remaining to our south/southeast. We’ll be tracking this system through the weekend and have updates below when things begin to take shape.

  1. Hopefully for the last time until the fall.  ↩

Mother Nature Mixes Up Months

Brad Leave a comment

Things will seem decidely early-April as extremely cool air settles in over the eastern Prairies bringing another stretch of days with temperatures some 10-15°C below normal. Seasonal weather doesn’t look to return until the end of the week when the cold air finally begins being shunted off to the east.

Wednesday
7°C / -4°C
Mainly cloudy. Clearing in the evening.

Thursday
10°C / -1°C
A few clouds.

Friday
12°C / 3°C
Mainly sunny. Cloudy periods overnight.

We’ll see a mainly cloudy sky today as we remain stuck under cloud wrapping around the backside of the low pressure system that impacted Winnipeg and the Red River Valley over the weekend and the first half of the week. Accompanying the cloud cover will be extremely cool temperatures for mid-May; the daytime high today will only reach 6 or 7°C, 10-15°C below the seasonal high of 19°C. The cloud cover looks to begin clearing out ovenright as we drop down to a low of -4°C, again nearly 10°C below our seasonal low temperature for this time of year. No precipitation is expected today or tonight.

Tomorrow will bring a few clouds as we sit on the fringe of the organized cloud pushing off to our east and then see some afternoon cumulus clouds develop. Temperatures will moderate a little to around 10°C, however that’s still nearly 10°C below normal for this time of year. We’ll drop to a low of around -1°C overnight under clear skies.

Friday will bring plenty of sunshine with just a few clouds through the afternoon hours. We’ll see a high temperature of around 12°C as milder air continues to slowly push eastwards. There will be a few cloudy periods overnight as a weak disturbance moves thorugh and we’ll see an overnight low near 3°C. Precipitation is unlikely with this disturbance.

Returning to Near-Normal on the Weekend

Things will get back into form by the end of the weekend as the cold trough finally collapses and pushes well off to the east, allowing milder air to spill across the Prairies. Saturday looks like it will have a high somewhere in the mid-teens followed by temperatures near 20°C on Sunday. The weekend looks to be a bit of a mixed bag with sunny skies and relatively light winds on Saturday, but more cloud and stronger winds developing on Sunday as a warm front pushes into the region ahead of a low approaching from Wyoming. Areas all across Southern Manitoba may end up wtih the threat of some showers or rain activity by Sunday aftenroon. We’ll have more details on this system in Friday’s blog post.

Nasty Week Ahead

Brad Leave a comment

After a nice weekend, we’re in for a nasty work-week. More rain and chilly temperatures are on the way.

Rain is expected in south-eastern Manitoba on Monday
Rain is expected in south-eastern Manitoba on Monday

Monday

Monday
9°C / 5°C
Rain

Today will see rainy weather return, or continue, in southern Manitoba, depending on where you live. Western sections of the province should remain mostly dry, but south-eastern sections will be getting wet, as another strong weather system moves up from the south. Rainfall accumulations of 10-20mm are expected in Winnipeg with 15-25mm in areas south-east of the city, including Steinbach. Locally higher amounts are possible in the south-east corner of Manitoba where heavier rain bands will likely develop. The rain will be accompanied by a strong northerly wind, just adding to the misery!

Tuesday

Tuesday
9°C / -1°C
Mix of Sun and Cloud. Chance of Showers.

There may be some lingering rain showers on Tuesday morning in south-eastern Manitoba, and some more pop-up showers in the afternoon, but generally speaking Tuesday will be a dry day. It will also be a fairly crummy day, with a cool airmass of Arctic origins surging southward into the province. High temperatures aren’t likely to crack the double digits in most areas.

Wednesday

Wednesday
8°C / -2°C
Mix of Sun and Cloud. Chance of Showers.

Wednesday will see a continuation of Tuesday’s nasty, cool conditions, with even colder Arctic air surging southward. Once again, temperatures are not expected to reach double-digits, except for maybe far western sections of southern Manitoba. Pop-up showers may develop in the afternoon, just to cap things off!

Long Range

We should see temperatures return to near normal values by the end of the week into the weekend, however no above-normal weather is in store for the foreseeable future.