The top map is the Canadian ensemble average, the maps below are the individual members that make up the average
Each member is like the parent, Canadian model operational model.......with a slight tweek/variation in parameters. Since we know the equations to represent the physics of the atmosphere in the models are not perfect, its useful to vary some of the equations that are uncertain(can make a difference) to see if it effects the outcome and how.
The average of all these variations(ensembles) often yields a better tool for forecasting. It's always more consistent. The individual operational model, like each individual ensemble member can vary greatly from run to run.........and represent an extreme end of the spectrum at times. The ensemble average of all the members, because it averages the extremes.............from opposite ends of the spectrum.........changes much less from run to run.
End of week 2....................0z ensembles from FRIDAY:
Analysis starting from a week ago, ending with today:
Last week+ of analysis, starting with the day farthest in the past:
Last Monday: Still wet as we go into mid April. Will the upper level ridge in the Southeast be strong enough to keep the flow from being progressive? Any amplification of the ridge or upper level lows/troughs in the southern stream will result in some excessive rains.
Tuesday: Very wet from the southern stream. Looking at the potential for excessive rain events in the S.Plains and points east/northeast again.....depending on how stout the ridge in the Southeast is.
Wednesday: Much drier for this ensemble model and run at the 2 week time frame. Also cooler in the Midwest/East. Will ridge West/trough East couplet in Canada to Upper Midwest take over and suppress the southern stream?
Thursday: Yesterday, the Canadian ensembles were the only model to look much drier. Today, they are much wetter and back to the old solution, so yesterday was a fluke. In fact, they and all the other models are the wettest yet for week 2 of any forecasts going back some time. Potent southern stream and cut off low potential with excessive rains from the S.Plains to point east/northeast. Still several members that like yesterdays colder and drier solution(especially Upper Midwest) with a stronger northern stream.
Friday: The mean looks more zonal today for both the southern and northern stream. This results in milder temperatures in the north and less precip most places, especially with the less amplified southern stream.
Saturday: Less zonal but the upper level low/trough from the southern stream on numerous solutions, backs up so far west that it results in a warmer and especially drier Midwest.
Sunday: Wide disparity on solutions, howeverer: 1. The mean is much more zonal and drier than the previous one and most of them last week! 2. Temperatures will be mild unless the northern stream amplifies and/or look like a minority of solutions show.
Monday: The mean/average is zonal but many solutions don't look like the average, they have an amplification of the pattern somewhere(possibly just transient). Majority are not nearly as wet as last week. No major cold intrusions.
Tuesday: The mean is zonal and mild but the flow could still be fairly active......just not featuring excessive rain events because of being progressive.
Wednesday: Very wide spread in solutions from very strong and wet southern stream dominant(a slight majority) to dry and chilly northern stream, new pattern. The Canadian ensembles is by far the wettest for late week 2 as the other models are much drier today.
Thursday: The mean looks fairly zonal again but the individual solutions which offset each other in the average have a wide spread. Still looking for a potential drier pattern but there are still some with enough southern stream to cause it to be wet............if those solutions are correct.
Friday: The mean and also individual solutions are looking zonal and drier..........this is the driest looking model for week 2.
360h GZ 500 forecast valid on Apr 27, 2019 00 UTC