Is a temperature fluctuation like this possible, or is the temp reader on my car malfunctioning?

The rain storm caused the coolant in the radiator to cool down more than you are used to. When the thermostat opened up, the cooler coolant made the temp gauge go down.
Your temp gauge reads between 81 and 92 degrees FAHRENHEIT? Are you sure it doesn’t read in centigrade/Celsius? If it was Fahrenheit it would read about 180 degrees.

I assume it was Fahrenheit, it had the same reading as a bank temp sign I noticed on the way in. That was after it went back up in the 90s range.

Yes it is very real !

Very freaking strange as well. Never noticed anything like that before. And my car temp reader is usually spot on.

@Nomore_lockout

Are you referring to a gauge that reads the temp outside your car?

Right. Outside temperature. Not engine temp. @Brian1946

The rain would evaporate very quickly, removing heat. Evaporation changes the temperature of metal very quickly. Yes, it would cause a rapid cool, but the moisture would then be gone, and cooling reverses just as quickly as it started.

@Patty_Melt well that’s as good an explanation as any. I thought maybe my outside temp thing was on the fritz and I was looking at a major repair. Short of tune ups and oil changes I always take my car to a shop to be worked on. I don’t mess with anything that probably has to do with the internal computer. Just never saw such a huge fluctuation in temps as that was. Down ten degrees and back up 12 or 13 degrees in less than thirty minutes. Crazy…

Give it a test. Have a hose ready, or head to a self serve car wash. During heat of the day, pull into shade, do a quick drenching. Don’t wait. Drive right away. The wind will make evaporation faster.
If you try a car wash, full service won’t leave it wet enough for a drive to make much difference.

I have seen extreme temperature changes in the course of one day. I think the worst was 75F in the morning and 32F in the evening. But I guess a good shower/thunderstorm could cool off the ambient temperature. It might also be that where your temperature sensor on your car is located might have played a role. If it suddenly got wet, it is possible for it to read lower. Once it dried off it could read normal again.

Outside temp is never accurate on those car gauges. The rain brought down the temp. If you want the real temperature use a weather app.

It could fluctuate that much in one direction, meaning temperatures can drop as a weather system comes through a geographical location, but to pop back up to the 90’s, I think it’s inaccurate.

I have an outside gauge on my house air conditioner and it is wildly inaccurate. If the sun is beating on it, way higher than the actual temperature.

@Nomore_lockout You never have to worry about a sensor being broken – unless the onboard diagnostics tells you it is broken. Every sensor on the car is continuously compared with other sensors and rationality checks are run dozens if not hundreds of times per second to verify the output signal is correct. If an error or degraded performance is suspected it will be flagged and the software will begin to use other sensors for input until it can verify the original sensor is working or not.
For example: Imagine a 3 dimension a map of engine RPM, throttle position, and manifold absolute pressure. That main map is called a speed – density map and is used for fuel control. Of course there are minor adjustments to it, oxygen sensor, adaptive memory etc but the basic idea is still speed density. Your car also has an air flow sensor that can be used for fuel control.
For a given engine rpm and throttle position you can always expect to see a certain manifold absolute pressure, MAP, within a certain range. If it is out of range, the other sensors are interrogated and their output is used to calculate expected MAP. The vehicle might check the MAP sensor for a few driving cycles to see if it has drifted and can be corrected or it might decide to ignore it. If it does ignore it a check engine code will be displayed.but you will still be able to drive normally.
The air temperature sensor has similar rationality checks. It uses the temperature of the car when it was shut off, the temperature at start up, time since start up, the coolant temperature corrected for the driving load since start up, air density calculation, and other temperature sensors located around the car. All systems have built in redundancy to keep you on the road and driving even if there is a failure. In fact some systems are double redundant to make sure nothing goes wrong.
The car’s electronic control unit does not look for one answer before making a correction.
It looks at many inputs from different sources and then acts.
That sounds a bit like asking a question on Fluther.