Enviro-BC Weather Forecasting Services

Heavy rains coming to the coast!

rpigott — Fri, 25 Nov 2011 17:35:55 +0000

Beautiful day across much of the province today (Nov. 25, 2011) as a transient ridge of high pressure moves through. A major wind and rain storm is now developing off the coast and will bring heavy rain and strong winds to the BC Coast Saturday through Sunday morning. Rain amounts in excess of 100 millimetres are expected on the outer coast, especially along western slopes of Vancouver Island. The central coast will be hardest hit on Saturday spreading to the south coast Saturday night and early Sunday. Freezing levels will be coming way up as the system taps sub-tropical air from just north of Hawaii. This is setting up to be a pineapple express type of event that will likely cause flooding especially in areas where melting snows and high tides are added to the mix. Have a look at the 48 hour total precip map issued this morning (5 am Friday) - rain amounts will be quite a bit less over inland areas but still heavy at times. Winds will also be fairly strong but the main impacts from this storm will be the heavy rain and high freezing levels.

Upslope rain BC Peace

rpigott — Fri, 24 Jun 2011 18:58:11 +0000

A very moist easterly flow aloft north of an upper low centre moving through the Cariboo is giving heavy rain to the Dawson Creek and Chetwynd areas this morning (June 24, 2011). The rain will continue for the next 24 hours or so. Over 100 millimetres of rain is possible in the Rocky Mountain foothills before the rain tapers to scattered showers Saturday afternoon. This is a classic pattern to give heavy rainfalls as the low is moving very slowly giving a longer time for the rain to persist. Check the radar animation below to see the echoes indicating moderate to heavy rain headed from Alberta towards the southern Peace. Warmer and drier conditions will finally reach the area on Sunday as a ridge of high pressure builds from the west.

Peace upslope rain June 24, 2011

The satellite photo taken at 11 am this morning shows the thick cloud over the Peace stretching all the way to the Central BC coast. The purple lines show the flow around the low and coming from Alberta.

Strange weather pattern!

rpigott — Sat, 14 May 2011 22:19:54 +0000

There is huge contrast in the weather today. A southerly flow aloft (about the fifth day in row) is bringing extremely variable conditions this afternoon. At 3 pm today (May 14, 2011) it is currently 7 degrees and raining at Quesnel and 24 and sunny at Blue River! A disturbance embedded in the flow is responsible for the thicker cloud and rain. The clouds seem to be channelling up the Fraser. To the west over the Chilcotin, it is cloudy but dry with temps in the mid teens. The reason for the very warm conditions in Blue River is due to downslope winds coming from the east. Tomorrow it looks like a rapid rise in temperatures in the Cariboo northward through the Central Interior as a ridge of high pressure extending from Alberta builds westward. The warm weather shifts northward on Monday with more rain speading to southern and central BC as yet another disturbance moves up from the south!

La Nina still having an effect

rpigott — Fri, 29 Apr 2011 18:51:09 +0000

Although there have been signs that the cool unsettled Spring is at least temporarily changing to a warmer and drier pattern, the longer range doesn’t look too optimistic. The 8-14 day map this morning - http://www.cpc.ncep.noaa.gov/products/predictions/814day/814prcp.new.gif predicts below normal temps and above normal precip out to two weeks from now. So enjoy the sun while it lasts!

Weather forums and blogs

rpigott — Tue, 12 Apr 2011 18:12:47 +0000

There are several weather forums and blogs that I use to stay in touch with the current situation, forecast discussion and other weather related subjects. I enjoy reading people’s views on weather and sources of information that are available on the internet. Here are some of my favourite websites. Please pass on any sites that you like to use.

http://forums.weathercity.com/?id=114 Discussion mostly around the BC Lower Mainland but at times a bit farther afield.

https://www.facebook.com/TomSkilling Tom is one of the most respected weather broadcasters in the US. He operates out of Chicago but has a keen interest in major weather events throughout North America and the rest of the world.

http://www.accuweather.com/blogs/anderson/story/48300/snowfall-forecast-out-west.asp Brett Anderson is a forecast for Accuweather. He has a blog with a Canadian perspective. There are other blogs on Accuweather also worth checking.

Satellite photo interpretation

rpigott — Mon, 04 Apr 2011 01:06:18 +0000

On almost every weathercast on the nightly news, there is either a still satellite photo or more likely a satellite animation depicting cloud elements looking down from space. The two main types are Visual and Infrared. A visual image is taken by a standard camera and is basically what we would see if we were on a satellite looking down to earth. The infrared camera records images in a different light spectrum that relates to temperature. After some practice, interpretation of the images becomes easier to determine what kind of cloud you are looking at and what weather they will likely produce.

The images below were all taken at the same time – noon PST on April 3, 2011. The first photo is a visual shot, the next two are infrared using two different ways to show temperatures, one using grey scale and the other false colour. Look at the legend on the side of the image to determine the temperature. Normally the colder the cloud top temperature, the more intense the type of weather is being experienced under the cloud. However it is not quite so simple as this as sometimes the infrared image is showing cloud top temperatures of high cirrus type clouds when there is little if any cloud below it.

The visual shot below shows fairly milky looking cloud extending from the Pacific towards Vancouver Island. This is normally associated with cirrus type cloud. To the north there is what appears to be lower topped cloud over Haida Gwaii. Notice that this cloud has a banded appearance. Checking out the weather at the surface, Port Hardy is showing overcast skies but with no rain falling. Sandspit is reporting light showers. So the bands or lumpiness on the satellite photo is likely indicating convective buildups. The cloud over Port Hardy isn’t thick enough to produce any rain.

Notice way off to the east over southern Alberta. There is a lot of what appears to be cloud but Calgary is showing mostly sunny skies on the surface report. So what do you think the white area might be showing? If you were in Calgary yesterday you experienced a late season snowstorm. So what appears to be cloud is actually fresh snow. If you look at a satellite animation it is easier to understand as the snow area isn’t moving or changing shape.
(Click on the images to get a larger view).

The ‘grey scale’ image below doesn’t have as much detail on it as it is a lower resolution image than the visual picture – 4 km versus 1 km on the Vis. The bright white cloud shows up quite well over the Pacific indicating cold topped cloud. The snow over southern Alberta is still evident but it is much easier to see on the visual shot.

Finally on the ‘false colour’ image below, it is easy to see that the cloud tops west of Vancouver Island are quite cold. Using the legend on the bottom of the photo, the tops are in the range of minus 45 to minus 55.

Each photo is useful both for a diagnosis of the current weather situtation and as a forecast tool. It is always a good starting point to look at satellite images. ‘Ground proofing’ by checking current weather observations on the surface, analysing RADAR and computer prognosis charts are other tools in the forecast process.

Sunny day on the coast!

rpigott — Sat, 02 Apr 2011 22:50:13 +0000

A building ridge of high pressure has brought sunshine to the entire BC coast today(April 2, 2011)! As often happens with ridge development, gusty north to northwest winds were reported in many areas. Here is a satellite animation, courtesy of of the University of Washington Atmosperic Services, showing the mostly cloud free skies.

Notice that with heating during the day that isolated convective clouds have formed mostly along the spine of Vancouver Island and the Coast Mountains. (See the RADAR at 6 pm PDT showing cells over southern Vancouver Island). Some showers have developed with a thunderstorm giving a couple of lightning strikes on the Sunshine Coast. There was also local hail reported in Surrey – http://www.youtube.com/watch?v=5c24P9j8VpE

Looks like the dry conditions will unfortunately come to an end on Sunday. The cloud mass on the western edge of the animation will spread to the coast early in the day with a good chance of showers by afternoon. The Lower Mainland however will likely stay dry throughout the day. (Click on the animation to get a larger view).

Change in weather pattern

rpigott — Tue, 29 Mar 2011 23:29:54 +0000

For the past few weeks, there has been a persistent trough of low pressure over the Eastern Pacific with a light southerly flow over southern BC. Weak disturbances embedded in the upper flow have given occasional showers to lower elevations while the ski resorts have continued to add to their snowpacks. Their is a big change going on in the atmosphere at this time. The upper flow is evolving into a strong westerly or zonal flow aloft.

Rainfall amounts will be quite heavy over the next couple of days especially along windward slopes of Vancouver Island and the Coast Mountains. A heavy rainfall warning has been issued for the Fraser Valley where up to 85 millimetres of rain will likely fall by Thursday morning. The mountains will be even wetter where over 100 millimetres are anticipated. With rising freezing levels, only the higher elevations will have significant snowfalls.

In the map below, you can see where the heaviest amounts are expected. Notice the subsidence or rain shadow effect over the Gulf Islands. Gusty winds are also expected over the next couple of days but nothing severe is foreseen at this time. More rain is expected at least until Friday as the storm track continues to pass through southern BC.

Olympic rain shadow

rpigott — Fri, 18 Mar 2011 17:38:17 +0000

With a south to southwest flow aloft, there is a pronounced rain shadow effect over the south shore of Juan de Fuca strait (Port Angeles and Sequim) as well as southern Vancouver Island. Have a look at the video below that demonstrates the effect on the RADAR this morning. The flow is southerly bring moisture northward from an upper low centre off the BC Coast. Notice how the echoes disappear at the summit of the Olympics. This is the main reason that the area to the lee of the mountains gets considerably less rain than other coastal locations.

Olympic rain shadow

Long range outlook

rpigott — Wed, 16 Mar 2011 19:14:05 +0000

So with a weakening La Niña expected in the next couple of months, what kind of weather might we expect later in the Spring and into the Summer in BC? Brett Anderson discusses how this might play out for Canada. Check out his blog entry here.

There is a prediction of above normal temperatures and below normal rainfall in the BC Southern Interior suggesting the possibility of an enhanced wildfire season.

Environment Canada’s long range forecasts also show a similar trend in temperature. Notice the big difference between March to April compared to June to August. Too early to predict this with any confidence but something to think about.