Remembrance Day forecast and beyond...

After a fairly pleasant and benign Sunday, Monday will follow suit with even more improvement with more sunny breaks and warmer temperatures.

The rest of what remains of a warm front will dissipate and move north, so can't rule out a risk of some light drizzle early this evening with the passage of the front.  

A ridge is building offshore and is expected to move east over land for our Remembrance Day, so you will remain dry during the outdoor ceremonies tomorrow.

This is a huge improvement to last year's November 11th, which saw rain and temperatures less than 5°C. 

Maximum temperatures forecasted by the Canadian high resolution model for tomorrow afternoon (2pm):  

Monday Temps.png

I think this model might be a bit too ambitious but inland sections might be pleasantly surprised to see temperatures rise into the low teens, definitely a few degrees above normal.

Now late Monday night models have come up with a consensus that a cold front will sweep through the area with rain. Rainfall won't be monumental (~10-20mm), but unfortunately the snow-level will rise above most mountain ski resorts (2000 m+) with 850 hpa temperatures climbing above freezing, but look for a quick rebound to lower freezing levels after the front passes.  

Several disturbances and upper level troughs will follow the cold front, and Tuesday and Wednesday will have a risk of scattered showers.

NOW. The good stuff (i.e very speculative).  

The past couple of days, models have been waffling and entertaining the idea of a NW flow and eventually bringing in a much cooler air mass from the Arctic.

IF this to occur and uncertainty still remains high (as the event is 7 days out), several models have come into a bit of a consensus that I think it's a least worth mentioning at this point.

Below, is a few deterministic models (GEM, ECMWF, GFS), which all hint at cooler air infiltrating BC by next weekend...

Next Sunday, cool air possible.png

Even better, a relatively new forecasting technique (ensemble forecasting) is used to determine uncertainty of longer term weather predictions.

Ensemble forecasting runs a forecast model through many different runs all with slightly tweaked initial states and conditions to see if these minor changes produce vastly different long term solutions. After changing these initial conditions or altering the forecast model itself a consensus forms (or lack thereof in this case).

ENS GFS Vancouver 18 Zulu.gif

This particular ensemble series shows high confidence in the temperature forecast in the short term, but by this weekend all bets are off.

Seriously, never gamble on weather. You'll lose.

By now I'm sure you've mentioned the s-word inside your head... Didn't you?

Snow?

Snow is difficult to forecast even within 48 hours for the Lower Mainland; consequently, many fringe snow events can easily turn to rain with a little bit more warm air advection than forecasted. A past blog post discusses the difficulties in a bit more detail.

But you want a percentage don't you?  

Fine, but you won't like it snow fans.

Since the ensemble models are so uncertain right now and not really in agreement with regards to the strength of the cooler air mass it doesn't give much guidance for this upcoming weekend.

Probability graph using the NCEP Global Ensemble model

Probability graph using the NCEP Global Ensemble model

The graph above is for Vancouver International Airport, describing the probability that snowfall will occur at any given time during the forecast period.

Conditions for snowfall include

  1. Highest temperature is less than 2°C 
  2. Precipitation is greater than 2mm/day
  3. 850 mb temperature is less than 0°C  

This is very simplistic and I assure you for a snowfall for Vancouver, it's much more complicated than the simple set of conditions above.  

Nevertheless, the program above used a 21 member GFS ensemble dataset to come up with at maximum 10% chance of snowfall (using the mentioned conditions) for Vancouver during the forecast period.

I'll keep an eye on these probabilities the next few days and see how much they fluctuate, but there's simply too much uncertainty in the models to even anticipate such an event.  

#50shadesofVan

 ------------------------------------------------------------- 

Did you Know? 

A hole punch cloud was spotted over Minneapolis/St. Paul today!  

The rare type of cloud mesmerized social media. Take a look.

Photo posted by meteorologist Jerrid Sebestsa (@jerridsebesta)

Photo posted by meteorologist Jerrid Sebestsa (@jerridsebesta)

What causes such an interesting, and seemingly out of place cloud?  

The current hypothesis is that it's man-made.

The cause can be attributed to a ascending or descending airplane that passes through a layer of cloud, causing a hole punch and disrupting the cloud layer itself.  

And here are even more pictures and information on hole punch clouds.