A more important question than "when" to switch to synthetic, is "why" to switch to synthetic.
You're newly registered here; have you lurked for long? You will find many opinions differing on the usefulness of synthetic fluids in "moderate" applications. I'll present mine.
I am not a fan of using "synthetic" for the sake of the name of the fluid. Synthetic fluids are awesome, but they do have limitations, if you can accept a broad definition of what is "better" or "best".
Synthetic fluids do protect your engine at extreme temperatures, but they really, truly have to be "extreme". Your location in WV probably does not call for such capabilities. Synthetics also have an advantage of providing longer drain intervals. This is a distinct advantage over "dino" fluids. You can often get 2x or more distance out of a synthetic fluid, as compared to a conventional oil.
However, if you are not able (or willing) to extend your drain intervals, then synthetics make little sense in many applications. People often want to do the "best" for their vehicle, but some amount of common sense has to presented. If a synthetic fluid costs 2x as much money, do you get 2x the value out of the fluid? Do you get 2x the "advantage" with the synthetic? In your area, there is no need for synthetics temperature wise. So if you can't significantly extend your drain interval, then there is not much logic in spending the extra money for the priviledge of using a "better" fluid.
Check out the UOA section forums. Try to find (roughly) comparable examples of dino and synthetic fluids in similar applications. Synthetics run for the same moderate exposure (say 5k miles for an OCI) surely don't show 2x or 3x the wear metal reduction, overall.
Where's the sense in paying 2x or 3x the money for a quart of oil if you're still going to change it out at 3k, 5k, 6k miles? Today's conventional oils have some great capabilities. Most of the major brands can easily do 5k mile OCIs. You can really get your money's worth, and still protect your brand new vehicle very well, by choosing a quality conventional fluid.
The same concept can be said for filtration. 5k mile OCIs don't call for "super premium" filtration. All the major brands offer good quality filtration for moderate exposure. Many people (including myself) steer away from the orange can (Fram) due to constrution issues; but to be fair, the fear of failure is likely greater than the actual incidence of failure. Still, for such a low investment, there are better constructed filters available from other sources. Premium Plus, Wix, Napa, Motorcraft, etc, all offer good filters for moderate investments for 5k mile OCIs; many can go even further.
If you wanted to pair up synthetic fluids with a Pure One, a Mobil 1, (or other top-end filter) to greatly extend your OCI, then that plan would make sense. But many people simply cannot resist the "call of the wrench", and end up changing out premium products long before their time is due. If you negate the advantage of longer drain intervals, then there is little rationale to running a synthetic fluid with a high end filter.
Many people would also argue that they want the "best" for their vehicle, regardless of cost. OK, as long as you can acknowledge the inherent waste in that scenario, then fine. But another thing to consider is just how long will you own this vehicle? It is HIGHLY likely you'll either sell, trade, or crash the vehicle long before it would be worn out. Today's vehicles are so well made that even "normal" maintenance can make them go 200+K miles, and often more. Seriously, are you going to own it long enough to make that "best at all costs" approach worthwhile? Be honest with yourself; it likely won't happen. If anything, your use of synthetics is helping the 2nd or 3rd owner down the road; not you. And if you trade the vehicle in, precious few dealers could not give a rat's *** if you used synthetic this and super-filter that. They will base your trade value on mileage and appearance. It will either be a newer trade-in, and the use of synthetics will have no obvious advantage, or it will be very old, and the mileage/appearance will overwhelm any perceived internal engine cleanliness or "smooth running" comments you might make.
It really comes down to the issue of "wants" and "needs". If you want to run synthetic fluids, then do it by all means. But your vehicle does not "need" it for safe, proper, long-lived operation. Synthetic fluids are great, when "used as directed". They offer greater drain intervals, thereby making this a fiscal choice.
So, will this be a logical or emotional choice for you? It's OK to be emotional because after all, a new vehicle is a joy to own; just recognize and admit it, if so. Too many people on this site try to convince others that synthetics are the salvation to an otherwise condemned lubricant world; nothing could be further from the truth. Proper maintenance methodology preserves the life of equipment, not wonder-fluids.