Overheating (leaking?) 1999 ford taurus?

I just drove my '99 Taurus for about three hours. I topped off the coolant before I left and had no abnormal gauge reading along the way, but when I pulled into a parking lot and stopped the car, it leaked a huge puddle of what I can only assume is coolant/water and I could hear the whistling of air under pressure escaping. Do I have a blown head gasket? I feel like my temperature gauge is broken because it gave me no indication of high temperature on the drive. If there's something I can look for to indicate what went wrong that would be very helpful.

Look for wet spots, after the car cools down and the antifreeze cools, it will appear white on stuff under the hood. This could give you a good idea of where it is coming from, wherever there's more white, it is most likely coming from that area. I would say a headgasket is not likely the issue, however something simple like a leaking radiator, leaking hose, stuck thermostat. If you are careful, pop the hood while it is hot, careful not to scorch yourself from steam, and you can listen for the hissing, and possibly see bubbling of antifreeze from somewhere. Hope this helps

Were you running the AC? It is entirely possible that what you saw was condensate draining out (most probably right at the front of the passenger compartment, and the pressure equalizing in the AC system when the pump was not circulating refrigerant.

Head gaskets, they were recalled, usually leaks into the end cylinder for each bank like 1 and 6 I think.

If coolant leaks the indicator may not give a reading sometimes if enough is gone from the head, the sender is no longer immersed in the liquid, this means the sender won't have anything to sense.

The whistling has me perplexed, better check that cap with the tester they use specially for that.
The thermostat is going to have leaked its wax pellet, so replace that, but when you pull your spark plugs, try cranking it and looking for coolant spraying out during a system pressure test,
You can easy crack heads on these since the castings were updated in 96 I think.
The older casting # can be found at the u-pull-it yards for cheap.
Then use the update gasket set from Mc Cord thru Ford or equivalent.
They are a good place to get your testing, diag. And estimate because they had so many to do.
They can get it faster and charge less to get your business if they want to.
The procedure is outlined in the recall if you had them print a copy for you to better understand what's involved.
Of course the time expired long ago for factory paid help.