Heat Dome Sets Up Over Desert Southwest: Many Predict Record Breaking Heat, but is it True?

The National Weather Service seems to be over predicting the extreme heat in the Desert Southwest this weekend. They predict record breaking temperatures, but we are not so sure.

Extreme heat
Whichever forecast you look at, one thing is the same. There will be extreme heat in the Desert Southwest this weekend

The National Weather Service has issued excessive heat warnings across the Desert Southwest. They site a heat dome to be the culprit of these warnings. Many forecasting entities are predicting “record highs” this weekend, however we do not see this as the case.

What is a heat dome?

Heat domes in the US typically form in the west. The warm Pacific waters form a barrier on the west to the hot air moving off the coast. This combines with high pressure system remaining stationary over an area for a prolonged period.

High pressure areas cause fair weather and a lack of clouds allowing temperatures to continually rise. The hot air then rises further enforcing the rotation aloft trapping the air. This usually occurs when the jet stream travels north allowing the high pressure to dominate.

Will we really see record temperatures?

Many other sites including the National Weather Service predict temperatures to reach above 129°F Sunday in Death Valley, California. The record for this city is 134°F set in 1913.

Temperatures in Southwest
Temperatures will be hot, however, they will not be above 130°F as others are expecting.

The heat will be oppressive, however likely not as high as they are saying. We looked at the European (ECMWF) models predict a high of only 118°F Sunday in Death Valley. This is a discrepancy of 11°F.

Why are they different?

The National Weather Service relies on the GFS and NAM models to do their numerical forecasting. These models are better at predicting severe weather. This is useful in the US due to the amount of severe weather events that occur.

The ECMWF preforms better at a smaller resolution and therefore better at forecasting more local phenomena than the GFS. The GFS likely over predicts the high temperature due to the detailed nature of heat domes movement. Our models show the heat to be more widespread in the area not just concentrated a small area of the Southwest therefore showing a higher temperature.

ECMWF output
Here you can see the predicted flow aloft and how it is not anything unlike what we have seen before.

When comparing the models side to side, the GFS shows slightly higher geopotential height at 300hPa. This is indicative that the GFS would see the heat dome being more severe and therefore having higher temperatures.

The GFS also shows a slightly more meridional ridge and trough also showing a higher influence of the heat dome.

Overall, the GFS which the National Weather Service uses misses the small details that prove that record breaking temperatures is an overstatement. We predict there will be incredible heat in Death Valley, but nothing close to breaking the record set in 1913.