The “Queen’s English” Version of Ensemble Forecasting

Meteorologists utilize Ensemble forecast models in order to gain insights into how likely it is that a future weather event may occur (think of them as showing probability of an event). I’m sure everyone is familiar with the “cone of uncertainty” for Hurricane tracks and how wide they become the further out in time you go.  Ensemble forecast models can be used to determine whether there is a great deal of uncertainty in a modeled outcome in the future.

Someone commented that my last post was difficult to understand and requested that I use the “the Queen’s English” so that everyone wouldn’t be left in the dark.  The calculus that goes into forecast modeling is quite difficult to comprehend and highly dependent upon the accuracy of current conditions.

I found a video titled “What is Ensemble Forecasting” that does a great job of explaining the purpose behind ensemble modeling.  If you’re interested in watching this video please click here (it is in English too!).

Now with regards to next weekend…. The latest Ensemble Forecast Models are all over the place (meaning they lack consistency in exact storm track and speed) of a system that could potentially impact our area (or leave us high and dry).

The next set of images show the latest European Forecast Ensemble Models (there are 50 maps showing potential snow accumulation outcomes over the next 10 days):

Map 1 through 25

Notes on image below (in the Queen’s English):

ECMWF (European Centre for Medium-Range Weather Forecasts) EPS (Ensemble Prediction System) Total Snowfall (in inches) between 12Z31DEC2016 (12 Zulu time; to learn how to convert your local time to Zulu, click here) and 00Z09JAN2017.


  • Notice that some of the frames above show no snow on the ground (see the color scale on the right hand side of the image showing “inches of snowfall”) and others show nearly a foot.

Map 25 through 50:


  • Again, notice how some of the individual ensembles have snow on the ground and others do not.
  • The bottom right hand corner of each individual map contains an “e” and a number, so for example, the top left image is ensemble number 27 and the bottom right image is ensemble 51.

Ensemble models also show varying storm tracks or positions on the map

Well using “the Queen’s English”, the image below is showing the European Ensemble Model that was initialized today at 12Z (or 7AM Washington D.C. time).  The following images (all 50) are showing various surface pressure conditions (think of high and low pressure) at 7AM on Saturday January 7th, 2017.

  • Notice some of the ensemble images show a low pressure system(s) south, north, east and west of D.C. while others show high pressure controlling the D.C. Area at this ‘modeled time in the future’ of January 7th, 2017 at 7AM.
  • Again we are seeing a major lack of consistency in modeled outcomes at 7AM January 7th, 2017.



The Global Ensemble Forecast System (GEFS), an American built model:”

Using the “Queen’s English” (to describe the notations in the image below):

  • the first image labeled “eC” is the latest control model.
  • the following 20 images are showing 20 varying outcomes derived from tweaking initial conditions ever so slightly (watch YouTube video for details on this)
  • the last image labeled “eM” is the “Mean” or if you took ensemble 1 through 20 and blended or averaged them out.


  • Bottom Line Up Front (BLUF):  Again we have varying outcomes of no snow (e2, e3) to a dusting (e4, e9, e11, e15, e16, e17, e19) to a foot of snow (e20) or several inches (choose your ensemble from the image above).

Queen Elizabeth wishes everyone a Safe and Happy New Year! 





2 thoughts on “The “Queen’s English” Version of Ensemble Forecasting

  1. Tim, your post along with a Capitals win and watching the ball drop on Abc have all made my new year’s eve on point. Like the english consensus!

  2. I believe the closest thing you have to a consensus is a clipper event with a dusting to couple of inches. But that is just a guess this far out.

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