How Long Will Major Heat Stay? Weather Models Disagree

While expectations of major heat across the center of the country continue to generate headlines, an aspect of the story may be missing: exactly when that heat is expected to abate. That is due to relatively widespread uncertainty with regards to the exact timing and movement of any ridging across the center of the country. Models agree through Day 9 that strong ridging remains across the center of the country is strong. The ECMWF ensembles for late Saturday July 23rd can be seen below with a strong "heat dome" over the center of the country (image courtesy of Tropical Tidbits). 

(Click on image to enlarge)

Below we show the Canadian GEPS ensembles for the same time. 

(Click on image to enlarge)

And below are the American GFS ensembles for the same time. 

(Click on image to enlarge)

The agreement is relatively strong in this timeframe, and thus confidence is high in widespread warmth focused in the center of the country. There are minor differences over exactly wear the strongest ridging and where this "dome" of heat will set up, but broadly the center of the country is targeted. Taking a look at the surface, on the GFS ensembles, we see almost all of the country is expected to have temperatures above average with the heat strongest over Nebraska/Iowa and the surrounding Plains Day 9. 

(Click on image to enlarge)

The question then becomes: when does this heat break down? That is where the model agreement begins to ease. The American GFS ensembles show ridging begin moving slightly off to the west by early on July 28th, allowing slightly more cool weather to move down into the East Coast but keeping much of the center of the country hot. 

(Click on image to enlarge)

The GEPS Canadian ensembles, meanwhile, do not have remaining ridging nearly as strong, and show more of a trough across the East that would keep temperatures even more seasonable, as seen below. 

(Click on image to enlarge)

Below we compare the 2-meter temperature anomalies side-by-side between the GEFS (left) and GEPS (right). 

(Click on image to enlarge)

The European ECMWF ensembles would seem to side more with the GFS ensembles currently, decreasing confidence in the cooler GEPS Canadian ensemble guidance. However, over the past few weeks we have noticed less of a warm bias in the Canadian ensembles than the American ensembles, so its solution cannot be entirely discarded. Instead, we will have to look towards other longer-term atmospheric indicators to show when this heat may break down such as the Southern Oscillation Index (SOI, which saw a sudden drop today. This indicates yet another roadblock in the way of the forming La Nina, and could re-introduce western ridging or eastern trough action in the long-range forecast. Over the coming days, it should become more clear on models and other indicators whether this SOI drop was mostly noise or more indicative of a late July/early August pattern shift. 

Timing the breakdown of this very hot pattern is so crucial due to how these heat expectations are propping up energy prices, as we explained yesterday. Another week of hot weather could continue to support energy prices through July and potentially into August, while indications of the heat breaking down sooner than currently expected could send fuel prices, especially natural gas, plummeting. It remains too early to know exactly when this hot pattern will break down, but when it does we should see national energy demand fall off accordingly. Until then, though, we could in some places be seeing record power burns, something that will certainly keep a bid under energy spot prices.