YOU CAN'T WIN FOR LOSING...
Sometimes to get a quick overview of where temperature trends are leaning, I pop up a meteogram of the latest EURO or GFS. It's a down and dirty way of seeing the future without doing the analysis. More often than not you get a solid idea of the short term but the further out you go, (as most of you know) the less accurate the skill scores.
When I see strong similarities in the EURO and GFS, that leads me to have good confidence that model initialization was similar and the chances of forecasts verifying are higher. Here's what I came up with when I brought up the 18z model runs in Cedar Rapids,
The next 10 days (July 1st to the 10th) the average high is 89.4. The hottest day is July 9th at 96 degrees. The trend was for well above normal temperatures, even hot conditions the the final 4 days of the period.
It was much kinder and gentler. It does not have a single day in the 90s during the same period July 1-10th. The hottest day is only 89 and the average high over the 10 day stretch is 84.8.
Well, that tells me that we have a systemic problem of some sort and my confidence in the heat wave the EURO is showing is limited. Clouds, precipitation, dew points, surface soil moisture, upper level wind flow, are all just a few factors that could cause the cooler trends on the GFS.
To assist me in solving this dilemma, I went to a teleconnection that has helped in the past. My friend, the Madden Julien Oscillation (MJO). As you can see in the side by side comparison both the GFS and EURO are headed into phase 2 for the next 14 days. See the progression of the dotted green lines
During the month of July, phase 2 is not a warm phase and certainly not one you would look at to establish a heat wave.
Phase 1 and 5 are your best bets for significant Midwest heat in July. So, the MJO phase 2 is a strike against the 90s shown on the EURO.
Another factor that can strongly inhibit heat is soil moisture. When the ground is wet temperatures are cooler through the process of evaporative cooling. It's also more humid. As you can see, NOAA'S soil moisture model CAS shows soil moisture anomalies well above normal in eastern Iowa and northern Illinois as of June 29th. This is due to significant rains since the beginning of June.
This factors heavily in the models forecast of July temperatures which are cooler than normal.
My gut feeling is that the GFS may be a bit too low on temperatures but the EURO is likely far to warm. I base this on the MJO phase and the wet soils that exist in much of my area. I think the ground water evaporation will lead to higher dew points which limits heat. I also think we are now going into the time of year where crops are mature enough to emit moisture through evapotranspiration. That further raises dew points. In the end, we may average cooler like the GFS suggests. However, we will pay for it with high humidity that will get us heat index values of 90-100 several days. So, you can't win for losing in that deal.
I would also argue that we'll add to moisture levels with at least normal rainfall over the next 10 days. That also increases cloud cover which lowers temperatures due to decreased solar insulation.
Whatever, happens you can see that I look at a lot of variables when I put together a temperature outlook. I think we are going into a warm muggy pattern typical of July starting the holiday weekend but probably not the extreme sizzler that the EURO indicates. Time will tell. Roll weather...TS