Low oil light comes on after starting, then when car is warmed up light will turn off, temp. here in KY. has been 30 degrees.

20w-50 grade oil will not hurt the engine provided that it is not used in very low ambient temp areas (15 degrees to - degrees)
In these cases I would opt for a low viscosity oil like 10w-30 or at the lowest 15w-30
talk with a service centre dealer for recommended oil for cold /freezing condition

usually means your low on oil you should have that look at.

cold weather kills batteries this time of year...heres why..most batteries are a chemical factory..the acid and water separate as the battery discharges..also the chemical process is lessened when the air temps go below freezing by around 50% or more depending on the age of the battery..in extreme cold areas, external heat sources are required to keep engines warm enough to run..in alaska for example,the batteries are taken out entirely and put inside to keep warm..sometimes a fire pit is used to warm the engine from below (red hot coals no flame)..also in very cold weather, the engine oil will get very thick..in some cases the oil will actually glue the engine semi solid..locking it up..if its a cheaper oil that whathappens..I like 20 miles north of st louis in illinois and when it gets below 30 degrees outside i place a under cabinet 350 watt heater(used for keeping food warm to serve) upside down under my engine overnite..this keeps the block warm and the oil thinned out..and works very well for me..my car will start whe no one elses will in my neighborhood..hope tyhis helps you..

The thing to do is to remove the oil pressure sender and put a mechanical oil pressure gauge onto the fitting. Start the car (if it will start) and watch the mechanical gauge. If there is no oil pressure or very low oil pressure (less than 5 psi minimum), immediately stop the engine. Engine damage is sure to result with oil pressure that low. The cause of the low pressure will have to be diagnosed and corrected before running the engine again. Causes of low pressure could be worn engine bearings or a worn out oil pump. There could also be a restriction in the oil system such as a clogged filter or clogged oil pump pick up screen in the oil pan. The oil itself, if it is dirty and full of moisture will become like mayonnaise in the bottom of the pan at such cold temperatures and the oil pump will not be able to pick it up.

I know this won't be easy to do in -20 degree weather. But your car should be towed home or to a shop and not run again until this oil pressure check can be done. I'm hoping damage has not already occurred.

Have a block heater installation the day light things warm up at night it gets really dry cold that's when the block heater keeps the engine warm enough to start.

You probably need to change the oil and/or use a thinner viscocity oil for the cold.

What weight of oil are you using?
In cold temps it must be 5-20 or 5-30. Some newer oils are actually 0-20
Do not use thicker oils. They will not circulate in cold temps. And the oil pump will cavitatate. Meaning no oil circulation.
This is serious. An engine will last only 5-8 seconds with out oil pressure. 6-8 seconds not minutes. Engines must use much thinner oil in cold temperatures. Merely adding a quart of thinner oil to a crankcase of thicker oil... will ... not... help
If you can't change it yourself. Wait... wait... yes you can.... you can do this.

Check oil sending unit, i would use 10x 30 synthetic, walmart brand.

MOST COMMON ISSUE WITH THE OIL LIGHT IS THE ENGINE OIL PRESSURE SENDING UNIT, REPLACE IT, ALSO 3/4 SCALE TEMP IS NORMAL, THAT IS WHEN THE COOLING FAN KICKS ON, ABOUT 230 DEGREE'S F.