12 July 2016
The long range model guidance has been giving strong hints that some real heat is on the way next week, and it will cover a large portion of the U.S. and extend into Canada as well. Long range forecasting is best done by looking at an average of several different models and several different model runs over a few days and there seems to be very good agreement that well above normal temps. are on the way.
Below is some of the long range guidance. What you are looking at here is the average of several different model runs. When I see this much agreement in a long range forecast, my confidence is pretty high that it will happen. These ensemble model runs tend to have better accuracy with where the hot high pressure ridges will be than where the cooler long wave troughs will be.
The 594 (Yellow lines on the ensembles) indicates that you need to go up to 5940 meters to reach a pressure of 500 millibars. The hotter the air, the more the troposphere expands, and this pushes up the level of the 500 millibar pressure surface, to a higher level. In other words, on a hotter day, you have to climb higher to reach the 500mb pressure surface. (Note I have simplified this a bit, the pressure itself below plays a role). That said, the 5940 line is a good forecaster baseline for forecasting high heat. Note how widespread it becomes in 10-12 days!
How hot might it get- this is the long range temp forecast for a week from Friday from the GFS model:
The official global temp. data for June will not be out for a few more days, but you can see (below) that July so far has been rather cool across much of the Northern U.S. and quite hot across the south. Globally it may be one of the hottest months ever. NASA will have the data for June out late this week.
Lastly, here is the NOAA 6-10 day temp. outlook. Summer heat is coming!