A warm weekend is on tap as the west coast ridge of high pressure strengthens through Sunday. Mostly sunny skies and valley highs in the low 80s will continue until Monday when a few clouds will move into the region, and a slow cooling trend begins. Highs drop to the upper 70s Monday to the upper 60s by Friday with a slight chance of a few showers by then.
We’ve been talking about how putting a tarp or a blanket over your tomato plants could keep them from freezing. But here’s a question that a surprisingly large number of people get wrong: Let’s say you take a thermometer and wrap it in a heavy blanket, and put it in an unheated garage overnight right next to an identical thermometer outside of the blanket. How much higher will the thermometer inside the blanket read in the morning than the one on the outside? Any guesses?
Alright… here’s the answer: Not any higher at all. A blanket will not warm up a thermometer unless you heat up the blanket beforehand, and then only for a short period of time. So why do we feel warmer if we get under a down comforter?
A blanket is an insulator. It is designed to prevent heat transfer from you to the outside world. We are endothermic (heat generating) creatures, and if we can keep the energy we create from being lost to the air around us, the temperature inside the blanket will rise. But if you wrap an inanimate object (like a thermometer) that doesn’t generate any heat in an insulator, unless it’s a perfect insulator (and there’s no such thing), eventually the inside of the blanket will reach the temperature of the outside of the blanket.
Of course it works the other way around as well. In extreme heat conditions (Death Valley in July), a heavy coat can keep you cooler than if you were naked.
And you’ll avoid some very unpleasant sunburn
A Word of Weather 
Good Morning Mike,
I have to disagree with your answer to your blanket question. This is a classic Thermodynamics Boundary problem with two boundaries in a non-equilibrium system.
Without getting into complex variable analysis or the second law of thermodynamics, let’s just walk it through given your example.
Unless your night is long enough for every thing to reach equilibrium or your boundaries, the blanket and garage walls, have no value, the insulated thermometer will always read higher then the other one. Here’s the reasoning.
1. During darkness, the ambient outside temperature continues to drop.
2. The temperature inside the garage will also drop but at a slower rate than the outside air due to the insulating property of the garage walls. My unheated garage never reaches equilibrium with the outside air. The temperature continues to drop until after sunrise.
3. For all practical purposes, the uninsulated thermometer will reflect the falling temperature of the air inside the garage.
3. The insulated thermometer will also register a drop but at a much slower rate than the uninsulated one due to the insulating properties of the blanket.
4. Unless the temperature in the garage is rebounding in the morning, the two thermometers will always read differently.
In real simple terms, the unisulated thermometer is chasing the outside temperature while the insulated thermometer is always chasing the uninsulated thermometer.
As mentioned above, the key here is that the entire system never reaches equilibrium and the heavy blanket has some insulating (boundary) value.
Have a Great Day,
Jim North
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