Enviro-BC Weather Forecasting Services

The snow just keeps falling at Mount Washington. Another 95 centimetres (over 3 feet) has accumulated in the past 48 hours. There have been a series of weather systems in the past week or so, (I think the count is up to seven now) that have kept groomers and snow maintenance equipment very busy. Between disturbances the air mas has been fairly moist and unsettled so heavy flurries have added to the total. There was even some thunder flurries a few nights ago when a cloud band associated with very unstable air moved through.

Have a look at the forecast precipitation over the next 12 hours (up to 5 pm PDT March 15).

Notice the enhanced amounts on Vancouver Island and Coast Mountains. (Click on image to get a larger map) With freezing levels staying fairly low, around 800 to 1000 metres, even the lower elevations of Mount Washington  will continue to get lots of snow. It appears that La Niña is still having a large impact on the weather in BC. The outlook shows that La Niña is weakening but the effect will still produce colder and wetter conditions going into Spring. So even more snow is likely for the next few weeks!

Have you ever noticed when looking at satellite animations in BC that on certain days there is a rapid formation of what seems like significant cloud east of the Coast Mountains? The IR (Infrared) satellite images display it well with yellow to red colours indicating very cold cloud top temperatures. So what is going on here? Is there any cause for concern…is this a big storm brewing? Satellite photos are only one source of information.  Ground weather observations and webcams will indicate a lot of high cloudiness (if no low cloud is present). Meteorologists call this cloud formation ‘Lee Cirrus” You may have heard of wave cloud (altocumulus lenticularis) that is fairly common downwind of mountain ranges like the Coast and Rocky Mountains. This cloud is present at elevations around 2500 to 5000 metres. Lee Cirrus forms at a much higher level, near or above 6000 metres (20,000 feet). The airmass at this level is fairly stable with sufficient moisture to create cloud. Also the upper wind direction must be from the Southwest to West to create the wave effect. Have a look at the animation this morning (March 11, 2011) -



Notice how fast the cirrus cloud formed in just a few hours. Here are the weather observations from Kamloops for the same time period.

CYKA 111400Z 19003KT 40SM FEW100 SCT250 05/M05 A2995 RMK AC1CI1 SLP151
SKY25=
METAR CYKA 111500Z 07004KT 40SM FEW100 BKN250 03/M05 A2999 RMK AC1CI6 SLP169
53035 SKY89=
METAR CYKA 111600Z 06003KT 40SM FEW100 OVC220 04/M04 A3000 RMK AC1CI5 SLP172
SKY7X=
METAR CYKA 111700Z 00000KT 40SM FEW100 OVC230 05/M03 A3002 RMK AC1CI6 SLP178
SKY8X=
METAR CYKA 111800Z 00000KT 40SM FEW100 OVC200 06/M04 A3003 RMK AC1CI6 SLP180
52011 SKY9X=

At 1400z (6 am), there was only scattered cloud at 25,000 feet (SCT250). It was broken at 25,000 feet at 1500Z (7 am) then was overcast between 20,000 to 23,000 feet for the next three hours.

Not the most exciting weather phenomenon but an interesting one nonetheless!

The recent dry pattern has come to an end as a series a systems are once again moving through the province. The first disturbance is now bringing rain and gales to the inner BC coast. Storm force winds are being reported along the west coast of Vancouver Island and on Haida Gwaii. Here is the satellite image taken at 8 am this morning (March 9).  Notice that the back edge of the cloud indicating the surface position of the cold front passes through the southwest coast of Vancouver Island, extending northward along the central coast to near Sandspit.

Looking at the current weather reports at Sartine Island off the northern tip of Vancouver Island, you can see by the latest wind velocity i.e. 18033G42KT that the front has just gone by.  The first three numbers are wind direction – 180 means a direction from the south, and the 33 is the speed in knots with gusts (G) to 42 knots. Looking at the previous report at 1500Z (7 am PST) the wind was from 120 at 44 knots gusting to 62 knots. So the wind has shifted (veered from 120 deg., an ESE wind to 180 deg. a south wind. Also the wind speed has dropped which is normal after frontal passage. The strongest wind is usually right along the front and  then the wind drops dramatically behind it.

UNOFF WFG 091100Z AUTO 11038G44KT 03/01 RMK PK WND 1146 1048Z PRESFR ALTM MISG
      SLP011 56065=
UNOFF WFG 091200Z AUTO 10037G43KT 03/02 RMK PK WND 1145 1127Z PRESFR ALTM MISG
      SLP971 58081=
UNOFF WFG 091300Z AUTO 10036G42KT 04/03 RMK PK WND 1043 1248Z PRESFR ALTM MISG
      SLP949 58082=
UNOFF WFG 091400Z AUTO 13032G46KT 06/05 RMK PK WND 1356 1336Z ALTM MISG SLP930
      56080=
UNOFF WFG 091500Z AUTO 12044G62KT 06/05 RMK PK WND 1262 1455Z ALTM MISG SLP919
      56051=
UNOFF WFG 091600Z AUTO 18033G42KT 07/06 RMK PK WND 1557 1521Z ALTM MISG SLP924
      55024=

If you look at the satellite image off to the west, you can see the next disturbance developing over the Pacific. There is a break between systems but this next storm should hit the coast again tonight with more rain and strong winds expected.

Some significant winds have been reported this morning especially on the northwest coast of Vancouver Island. Solander Island auto station, had sustained winds of 130 km/h with gusts to 165 between 7 and 9 am. Gusts to near around 100 km/h have also be experienced at Comox, Abbotsford and other locations on the Island and Lower Mainland.

The low tracked a bit further west than predicted yesterday by the Canadian Regional GEM model as can be seen on the following charts. Notice that the path is close to 130 W which has kept it offshore. Thus winds haven’t been quite as strong as expected.

A major Pacific disturbance is now developing off the Oregon Coast and will bring rain and strong winds to the outer BC coast this evening. Check out the sattelite image  taken at 1 pm today (Tuesday, Mar. 1, 2011). Notice the low starting to form around 40 deg N and 135 deg W. with extensive cloud from the warm front extending northeastward from the low.

 The low will deepen and intensify as it moves toward western Vancouver Island. Here is the forecast position along with the frontal structure at 10 am Wednesday morning.

The southern track of the low is somewhat unusual for this time of year, looking more like a Fall pattern. As the disturbance approaches, very strong east to southeast winds will develop overnight in all coastal waters. Storm force winds are expected in many locations with even hurricane force likely off the northwest  coast of Vancouver Island. Coastal inlets, especially Howe Sound will see very strong outflow winds. Winds will switch to south to southwest on Wednesday as the low heads northward. Winds will still be quite strong during the day, finally abating towords evening.

Over land, winds will also be significant. There is a high wind warning out for most areas with gusts in excess of 120 km/h anticipated in exposed locations.

Rainfall amounts shouldn’t be excessive as the system is moving fairly fast. Freezing levels are now rising but will stay relatively low so snowfalls of 30 to possibly 50 centimetres are expected at elevations above around 700 metres.

There is a good chance of some downed trees and power outages beginning overnight and especially Wednesday morning as the most intense winds kick in. There could also be some ferry delays or possible cancellations.

Showery weather with much less wind on Thursday behind the storm.

Atmospheric river, Pineapple express, subtropical moisture feed - call it what you want, a very wet pattern is about to hit southern Vancouver Island, the BC Lower Mainland and especially northern Washington State later on Saturday through Sunday. Have a look at the current satellite photo (2:30 pm Friday Dec. 10, 2010).

Notice that the clouds stretch from just west of Vancouver Island all the way to the Hawaiian Islands. Honolulu has been experiencing fairly heavy rains and gusty winds the past day or so at the origin of the moisture plume. Now have a look at the projected 24 hour rainfall amounts ending at 5 am Sunday -

On the Olympic Mountain western slopes over 150 millimetres is forecast! (Click on photo for full size image and legend). Over 50 millimetres is likely in most areas over the 24 hour period, the exception being in the rain shadow to the lee of the mountains towards Port Angeles and Sequim on the south shore of the Strait of Juan de Fuca. And the rain isn’t going to taper off until Monday so rainfall amounts and river levels will continue to rise. A flood warning is out for many western Washington State rivers.

As this is sub-tropical air, temperatures are quite mild with freezing levels rising close to 2000 metres. The 850 mb chart (conditions at 1500 metres) for Sunday morning show temperatures in the 1 to 5 deg. C range. (Click on photo for full size image and legend).

Unfortunately Coastal ski hills will see heavy rains wash away a lot of the early season snow pack. However Interior Resorts will fair a lot better with temperatures continuing below freezing.

The longer range pattern shows a cooling trend next week with considerably less precipitation anticipated.

It was a spectacular day over all of Vancouver Island today with rather unusual weather for December 4th! An upper ridge of high pressure along with outflow winds from the BC Interior  combined to give sunny skies to all areas. And it wasn’t even that cold, something that often accompanies winter outflow winds. Most locations rose to a few degrees above the freezing mark. Ski conditions were excellent at Mount Washington after a recent 90 centimetre snowfall!

The MODIS high resolution satellite image below shows just how clear it was near noon today. Notice a couple of other cloud features on the photo – extensive low cloudiness in most Interior valleys and some lumpy looking cumulus and towering cumulus west of Haida Gwaii. Looks like this will be a one day wonder as cloud  and a threat of showers moves up from Washington State tomorrow. 

The computer models show a considerable  amount of rain and wind developing on Tuesday as you can see on this forecast map from Enviroment Canada. Up to 100 millimetres is possible at some of the upslope weather stations on the western slopes of the Island.

An unusual pattern for November brought a variety of extraordinary weather conditions to southwestern BC and Washington State on Monday (November 22, 2010). Heavy snowsqualls, strong outflow winds and even some thunderflurries made this a day to be remembered for a long time. Looking at the 500 mb mid atmosphere flow chart at 4 pm yesterday, a deep low lies over southern Vancouver Island. This low started as an innocuous upper trough over Central BC in the morning but quickly developed into a major vortex by afternoon as it headed southward.

The surface chart for the same time shows the low centre over the southwestern Washington coast. Notice the strong pressure gradient to the north of the low extending back into BC. 

The obvervations from 2300z to 0300z (3 pm to 7  pm) show the very strong winds that developed with gusts to 93 km/h at Abbotsford and 89 km/h at Bellingham. Numerous power outages were reported as a result of the winds.

Abbotsford:
Date/Time     Cloud/Weather          T(C)   W(kmh)    WindChill Factor RH
Nov 22 2300   Overcast                -5   NE63 G81    -10    27
Nov 23 0000   Overcast                -6   NE54 G70    -10    25
Nov 23 0100   Overcast                -6   NE61 G83    -11    24
Nov 23 0200   Overcast                -6   NE50 G93    -11    25
Nov 23 0300   Overcast                -6   NE63 G80    -11    26

Bellingham:
Date/Time     Cloud/Weather          T(C)   W(kmh)    WindChill Factor RH
Nov 22 2353   Overcast                -6    N50 G76    -10    35
Nov 23 0053   Overcast                -6    N57 G85    -11    35
Nov 23 0153   Overcast                -6    N54 G89    -11    35
Nov 23 0253   Overcast                -6    N48 G74    -11    35

The visible satellite photo at 2200z (2 pm) shows cloud over southern Vancouver Island and all of Washington State. Notice a small area of enhanced brighter white cloud near the back edge of the cloud over Vancouver Island near the town of Parksville. This is an indication of a convective cell that was responsible for a heavy snowsquall. I was driving through this area heading southbound around 10:30 am and then again around 3 pm on a return trip going northward. During this short interval of time, over 10 centimetres of snow had fallen from the cell and traffic was crawling along at 50 km/h when the normal speed limit is 110!  Also notice in the image the ‘streamers’ that begin off the west coast of the Island, head southward and then move eastward over northwestern Washington. Some very heavy snow squalls were reported on the northern slopes of the Olympics where the upslope effect produced over 30 centimetres at some locations! The convection extended eastward across Puget Sound and eventually all the way to Spokane.

The Great Lakes are famous for ‘lake effect’ snow storms. Typically a west to northwest flow aloft of unstable air picks up moisture as it crosses the lakes and deposits it on the other side in the form of heavy snow squalls. Heaviest amounts occur with at least a 13 degree difference between the lake temperature and the 850 mb temperature or around 1500 metres aloft. A ‘fetch’ meaning the distance crossed by the air of at least 100 km aids in the formation of the convection. The outflow winds crossing Georgia Strait met the criteria for temperature change i.e. plus 8 sea surface water temperature ( measured at Halibut Bank and Sentry Shoal buoys) and the upper air sounding at Port Hardy showed an 850 mb temperature of -16 making a 24 degree difference, much more than the 13 degrees needed for formation of cells. What was missing was the fetch to create bigger storms. Starting from Jervis Inlet to the Island is around 30 or so kms. The cells had the opportunity to grow much larger on their trip across the Pacific Ocean. Some of these cells produced thunderstorms with heavy snow associated!

With the weather forecasts all showing much colder temperatures in the coming week I thought I would show one of the techniques forecasters use to predict temperature. When I worked at the weather office in Kelowna one of our rules of thumb that worked pretty well was looking at the 1000-500 mb thickness to predict temperature change. Without going into a lot of explanation, thickness is an indicator of air mass temperature. The higher the thickness, the warmer the temperatures. The lower the thickness the colder it is.

For example, on the surface chart this morning (5 am Friday), there is a 522 decametre (5220 metre) thickness line running through the Lower Mainland. A quick way to locate the dashed thickness line, is to find the 540-534 shaded area on the chart. The 534 line is most often on the north side. Then count down 6 decametres for each line going northward. On the Canadian Gem Global prediction for 5 am Monday, the thickness drops to around 510 decametres. Notice that the lines on this chart are lined up west to east, showing the lower thickness and associated colder temperatures to the east.

We used half a degree Celsius for each decametre change so a drop of thickness from 522 to 510 decametres would mean a 6 degree drop. So if you used zero for this morning’s low at for instance Abbotsford  you would consider minus 6 as a forecast low on Monday.  However this assumes nothing is changing in the three days. Weather prediction is never simple! Other factors to consider are cloud coverage and wind speeds. With drier air streaming from the north, clearing skies are likely by Monday. This would lead to colder temperatures  with outgoing radiation. Less wind would also indicate colder. However looking at the pressure gradient (spacing of isobars, there should still be some wind. Okay so we start with minus 6, take off a few degrees  for clearing skies but wind should keep the temperature from dropping much more. So a forecast of minus 9 or 10 would seem reasonable. One thing that is likely though is Windchill readings, with the cold temperatures and associated wind, will likely be close to minus 20 on Monday!

Okay that’s quite a lot to take in. If you need any explanation, please don’t hesitate to contact me.

envirobc@telus.net

There has been a lot of talk this Fall about the developing La Niña   pattern. Apparently sales of winter tires, snow shovels, ski passes etc. across the province are way up this year with anticipation that this is going to be a snowy and cold winter. This effect that is related to colder than normal sea surface temperatures across the equatorial East Central Pacific Ocean is now starting to show itself.

The current weather situation and forecast for the next few days is typical of what happens in a La Niña winter. On the surface chart for 5 am this morning notice the low pressure centre south of Haida Gwai.

This is a common location for lows in the winter as they sweep in from the Pacific with an associated frontal system running ahead giving rain and fairly strong winds to the coast. A couple of other features to observe on the chart - the 1053 mb high centre in the Central Yukon and the pressure gradient (closely packed isobars) in the Central BC Interior. From this you would expect strong NEly winds to be drawn into the low offshore which the current weather observations bear out. Prince George has NNE winds of 35 km/h gusting to 50. Also visibility is limited in snow as a south to southwest flow of moist air aloft overrides the cold Arctic air flow at the surface.

Some other strong winds reported  -  Sandspit NE 85 gusting to 100km/h,  Terrace NE 30 G 50 km/h while the strongest winds enhanced by the funnelling effect down Portland Inlet is Green Island with NE winds of 100 gusting to 120 km/h!

The motion of the low centre is critical to the evolving weather pattern over the next few days. The most likely scenario and one that happens repeatedly in the Fall and Winter seasons is for the low to either move north or northeastward and gradually weaken in the next 12 to 24 hours.  A weak ridge of high pressure brings some clearing , then a day or so later if the storm track remains stationary, another low and frontal system will follow a similar path towards the coast bringing more rain and gales.

So lets look at the chart for Thursday  morning to see where the low is forecast to move -

Notice that the low has not moved northeastward but is edging southward. Also you can see the high pressure ridge is extending into northern BC from the Yukon and the pressure gradient is shifting southward into the Cariboo now. This suggests that the Arctic front is moving southward bring much colder air with it’s passage. So as often happens in a La Niña year, the flow of weather systems occasionally moves counter to the norm i.e. from north to south instead of west to east.

So lets jump ahead to Saturday morning. Now things are getting interesting. The low is now off the Washington coast. A 1045 high centre is over northern BC with the strongest pressure gradient in the southern half of the province. So by this time Arctic air will have completely covered the BC Interior and strong ’outflow’ winds are bringing the cold temperatures to the south coast through the coastal passes and inlets.

This is a typical snow pattern for the Lower Mainland and southern Vancouver Island as bands of moisture rotating around the low mix with the cold air streaming out from the Interior. Too soon to say how much snow but this pattern has been responsible for record breaking snowfalls in the past!