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Alastair Thompson @althecat
, 15 tweets, 8 min read Read on Twitter
An animation of the Heat Dome #HeatDome presently over the United States which is responsible for the heat wave. The dome appears to be pretty stationary and covering the entire U.S. land mass. /1
The animation shows a period from today till July 23 (a bit over a fortnight). And as you can see this Heat Dome is not forecast to depart. Below are images from the beginning and the end of the sequence. Today on the left, July 23 on the right. /2
The darkest red contour line shows the height of the atmosphere as 597 dm (decameters) or 59.7kms. The lighter dark red shows 59.4kms. The higher the atmosphere the higher the average air pressure on the ground. /3
Last July NOAA defined the term Heat Dome which appears to have only been used over the last decade "A heat dome occurs when high pressure in the upper atmosphere acts as a lid, preventing hot air from escaping." Source:… /4
The Heat Dome moves slowly. Its high mass (inertia from the weight of an additional 9kms of atmosphere) makes it a relatively stable persistent phenomena. Beneath it the normal cycle of weather continues, albeit all in a relatively high pressure state. /5
The only time the barometer dips below 1000hpa over the entire U.S. over the next 15 days is when the storm shown in green comes through on its way to Canada. The first image below shows the current high pressure system bringing NY its heat wave. /6
So that's the explanation. And here is the consequence. This gif shows 850mb (air temperatures at approximately 1500m) over the United States over a 10 day period through to the 17th. The temperatures at ground level are higher and follow. /7
Here, 10 days of maximum 2m temps (at 12h intervals) across the U.S.

Highs near 100 F (37 C) can be expected most days throughout.

Constant temperatures in that range are forecast for the South West, & a continuous heat wave up the Eastern Seaboard. /8
Here 7 days of maximum 2m temps (at 6h intervals) in the South West.

The South West has often born the brunt of U.S. heatwaves and this one is no exception. Only at night will temperatures fall briefly below 70 F and then only in the north. #HeatDome
Here 10 days of maximum 2m temps (at 12h intervals) for California and Nevada.

In this forecast you can see that the heat wave moves north and digs in. Extreme temps can be expected till 23rd July at a minimum, assuming the Heat Dome forecast is accurate. /10 #HeatDome
In the North East the forecasts are not as life threatening, but they only show 18 hours of relative respite before daily maximum temps in the 70s, 80s and 90s resume and continue for 10 days (getting hotter at the end). /11 #HeatDome2018
And finally 2m MINIMUM temperatures (12h intervals) for the entire U.S.for 10 days/ Except for mountains, around the great lakes & in the extreme NE and NW temperatures rarely fall below 70 F (21 C) anywhere - even in the middle of the night. /12
In these 2018 #HeatWave forecasts the end is not within the forecast range. On July 23 the #HeatDome looks almost identical to how it is now., and the temperature forecasts over the period suggest it will get gradually hotter for 15 days. /13
In 2006 there was a long deadly U.S. wide #HeatWave from Jul 15 to Aug 27. But its effects were not continuous everywhere like this one appears to be.…

The current heatwave began early July . The #HeatDome driving it appears to be stronger. /14
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