I own a 2019 Plug in touring clarity bought in 11/2019. Over the past 4 months there has been a steady increase in EV C harge from 44 mi to now 63 mi. I have two charger cords, one is the original 120 v and an aftermarket 120/240 v cord with adapter cords for 4 plug styes but have only fast charged once. Any other similar experiences and what is the technical explanation? Car running on EV almost exclusively without issues.
First to cover a basic in case it isn't clear, the displayed EV range is just an estimate based on recent driving. It doesn't always match actual EV range. In other words let's say after fully charging it says you have 50 miles of EV range. You then set the trip odometer to 0 and then start driving, odds are that you will not go exactly 50 miles before the EV range reaches 0 and the gas engine comes on. Might be more, might be less. That's normal as again it is just an estimate, or better stated it's just a prediction, which is no more accurate then predicting how far you will go on a full tank of gas because it depends on driving conditions of the specific trip. With experience you will find how much the estimated EV range differs from actual EV range.
Having said all of that, tracking actual EV range is sort of a pain so that's why most of us just pay attention to the estimated EV range since it's conveniently displayed right there on the dash, and at least it gives you and idea of up or down trends, like the one that you observed over the past four months.
EV range is at its worst in cold weather, for a number of reasons. First of all even gasoline cars get worse mpg during winter, but it's not enough to be that noticeable, and anyway most people don't pay that much attention to how many miles their car will go on a full tank of gas unless making a cross-country trip or something. Whereas with an EV (and even a PHEV) we tend to become pretty much transfixed by what our estimated EV range is each time we "fill up".
EV (and PHEV) have additional reasons why the range is lower during winter, one is that batteries inherently have less power when it is colder. Just like you might have experienced when using electronic devices outdoors in the cold. Or like when trying to start a gasoline car during cold winter weather and the 12V battery is cold. So with an EV or PHEV you get less miles per charge when the battery is cold, even though you are essentially putting in the same amount of electricity into the battery.
But the biggest issue during winter, as mentioned by N21HV is the electric heater, it really burns up EV range. Many EV's have a heat pump which generates heat more efficiently. Clarity uses a resistive heater which is less efficient, but is less complex than a heat pump take up less space. And unlike an EV a PHEV has plenty of "free" heat available when the gas engine is running. So for longer trips where you will be running the gas engine a lot it won't matter that much because even when the engine switches off there is some residual engine heat available. But if you do mostly EV driving during the winter, then you will probably be running the resistive heater most of the time and burning up EV range.
As the weather warms up, EV range for most people goes up pretty dramatically, as you have experienced. During summer as you crank the AC the range will go down somewhat, but not that much because modern AC is pretty efficient.
So enjoy the extra range, and then don't become too anxious when the range starts going down again next winter.