What Preps are you doing this week? Part 13

[Frnc]

Just popped out and inside the car was somewhat oven like. I have a lifepo battery jump starter that i normally leave in the boot. If it's going to get as hot as predicted then decided to bring it inside, because inside a car just sitting on the drive,it's going to get stupid hot.

If Met says 35 at a weatherstation, in urban areas it can reach 38-40, in a car it could reach 70. Dashboard could reach 85.

Thermometer in a weather station is in a white box with louvre doors. Sunlight generates heat when it hits solid objects, not the air. Anything dark absorbs more sunlight, and then gets hot. It then radiates heat as infrared radiation (also there is conduction and convection).

[diamond lil]

A high of 20 here which suits me fine

[Frnc]

Quick reminder of Heat Index.

For 35°C with 65% relative humidity, the heat index (“feels like” temperature) is approximately:

49–52°C

There are slight variations to formula used, but this shows similar.

[Ahastyatom]

Don't understand the logic of these "heat alerts". Down here, Met Office are saying 30C for monday and tuesday, and we have an amber heat alert. But they are also predicting 34C for Thursday, but no alert.

You can understand why people take these alerts with a pinch of salt..

I did wonder the same thing early this morning. But then got a notification that the heat wave was being extended to Thursday, there is probably lots of paperwork in the background before they can officially issue an alert causing a bit of a lag.

Overall I think they are a good idea, traditionally we go a bit mad when the sun comes out so I think it's good to remind people to be responsible.

[GeraldTheBonzai]

I did wonder the same thing early this morning. But then got a notification that the heat wave was being extended to Thursday, there is probably lots of paperwork in the background before they can officially issue an alert causing a bit of a lag.

Overall I think they are a good idea, traditionally we go a bit mad when the sun comes out so I think it's good to remind people to be responsible.

What I find interesting is the variation of prediction. I get the weather on my iphone app, the bbc and the met office. They are all different, to a degree. This is obviously down to the different models that are used for the prediction. However, did read that the Met Office tends to lean towards an Impact bias, rather than a pure accuracy prediction. So if the highest probability is, for instance 34C, but there is a lesser probability it could be 36C, the Met will says is 36C.

[GeraldTheBonzai]

Thermometer in a weather station is in a white box with louvre doors. Sunlight generates heat when it hits solid objects, not the air. Anything dark absorbs more sunlight, and then gets hot. It then radiates heat as infrared radiation (also there is conduction and convection).

This is why I tend to smile when you see those cars with the big silver reflective shields across the dash / inside the front screen. Has no effect at all. (And neither do blinds on the inside of the window). Glass / windshields block long infrared but allow short infra red to pass. The short infrared is absorbed by the inside of the car. This is then retransmitted, but as both long and short infrared. The short infrared can pass back out but the long infrared is trapped in the room/car. Which then adds to the heating effect or as we commonly call it, a green house...

[Frnc]

Thermometer in a weather station is in a white box with louvre doors. Sunlight generates heat when it hits solid objects, not the air. Anything dark absorbs more sunlight, and then gets hot. It then radiates heat as infrared radiation (also there is conduction and convection).

This is why I tend to smile when you see those cars with the big silver reflective shields across the dash / inside the front screen. Has no effect at all. (And neither do blinds on the inside of the window). Glass / windshields block long infrared but allow short infra red to pass. The short infrared is absorbed by the inside of the car. This is then retransmitted, but as both long and short infrared. The short infrared can pass back out but the long infrared is trapped in the room/car. Which then adds to the heating effect or as we commonly call it, a green house...

I think I'd phase it like this

1. Sunlight passes through glass.
2. Interior surfaces absorb it and warm up.
3. Warm surfaces emit longwave infrared radiation.
4. Glass is less transparent to this infrared, so heat escapes slowly and the interior warms up.

[GeraldTheBonzai]

I think I'd phase it like this

1. Sunlight passes through glass.
2. Interior surfaces absorb it and warm up.
3. Warm surfaces emit longwave infrared radiation.
4. Glass is less transparent to this infrared, so heat escapes slowly and the interior warms up.

You can phrase it like that if you want. It would be wrong, but your call.

[Frnc]

I think I'd phase it like this

1. Sunlight passes through glass.
2. Interior surfaces absorb it and warm up.
3. Warm surfaces emit longwave infrared radiation.
4. Glass is less transparent to this infrared, so heat escapes slowly and the interior warms up.

You can phrase it like that if you want. It would be wrong, but your call.

Sunlight is mostly shortwave radiation, peaking around ~0.5 µm, with most of its energy in visible light and near-infrared (0.4–2.5 µm). Very little of the Sun’s output is in longwave infrared (>3 µm). Glass transmits visible and some near-IR well, which is why solar energy enters a car and heats interior surfaces. Those warmed objects then emit thermal radiation peaking around ~9–10 µm, and standard glass is largely opaque in that longwave infrared range, so most of that heat radiation does not escape efficiently.

[Frnc]

Ran the portable AC til 10.30 yesterday and left kit in window. Didn't even bother removing the dust sheets from the sides until I got up. Rebound was about 2.5 degrees. It took all night, like the first hot night in May. But 1.5 of that took only about 1.5 hours. Got the windows open now, but by 10 am it will be 23 outside, so they'll be closed for the day. On Thursday it'll be 23 by 7 am!

It's a shame the AC's too noisy to run at night, but even if I could sleep, it could bother the neighbours. They have a window open about 5 m away.

I expect the rebound to be a bit quicker tonight, and maybe a bit higher. Last time it was going to about 25.3 on 30 deg days. But I'm going to run it a degree colder.