Can you tell me why I would be concerned by these temperature meteograms for Cedar Rapids in the coming 10 days?



Hopefully you've figured out the problem which is tied to a huge temperature differential next week. On the 9th for example the EURO has a high of 89 while the GFS has 65. The 9th is no better with the EURO at 83 and the GFS 59. Both are discrepancies of 24 degrees. Even more dramatic is the low September 9th when the EURO rocks a 70 and the GFS has a meager 38. That's a 32 degree difference. What in the wide world of sports is going on!!!

For the last week there had been very good consistency between the two models that a dramatic cool down was in order for all of the central Midwest, very much like what the GFS is still advertising. However, over the past 24 hours the EURO has reverted to a dramatically different solution regarding its handling of energy that drops into the northern Rockies Monday. Here's the side by side comparison.

Even to the untrained eye there is a stark difference. The GFS maintains a phased jet with a strong connection between the polar and sub-tropical branches. That brings cold air into the Midwest. On the other hand, the new solution presented by the EURO depicts a split flow, meaning the polar branch with its cold air remains largely in Canada. The energy in the pattern instead of being directly over Iowa is back in Nevada. Instead of it being cold and unsettled like the GFS depicts, the EURO is warm and dry. We see this issue come up a lot in the winter when phasing (or lack of it) makes the difference between a big snowstorm or an Arctic blast.

Aside from the extremes in temperature, one is a wetter solution and the other is not. Here's the storm the GFS outcome spins up.

The EURO on the other hand is bright, shiny, and dry. A completely different outcome.

So what do you do as a forecaster? Well, I have no choice but to hedge my bet. I have looked at the MJO for help and its not clear cut showing a transition from phase 3 to 4 about the time the discrepancies begin.

A phase 4 analog shows the greatest temperature departures over the west which is more in line with what the EURO is showing. I do like the EURO for picking up trends and since the MJO often leads the way, perhaps the model is on to something. If the GFS ends up being right that would be a big victory for it.

One thing is for sure, one of these solutions is going to be wrong. That said, whatever model comes out on top, it will lead to differences in temperatures next week that could be as great as 25 to 30 degrees. We shall see in the coming days which model blinks first.

Meantime, Thursday should be a fine day. Sunny skies, a good breeze and highs in the upper 70s. That's a combination that's tough to beat. Roll weather...TS

Before I sign off, here's a little tid-bit. Here in Portland, Maine, we just set the record for the warmest summer on record. The average temperature of 70.5 degrees beat out 2018 when the previous record of 68.9 degrees was set. Always nice to be a part of something historic, bragging rights for Terry!

© 2020 Terry Swails