I am looking at www.uavforecast for my location in Maryland, USA

It's showing only four GPS satellites visible at 9 AM EDT July 4th with a zero percent elevation mask.  This means, if you are flying above the trees at my location, the most GPS satellites you will get is four.  Which means you will be in ATTI.  If you are flying below the trees, you will likely have less than four satellites.  Perhaps as few as two.  This is the lowest I've ever seen.  

Obviously this only directly affects the P3S, P3 4K, and lower generation Phantoms.  

Good luck

www.uavforecast.com



Edit next morning, 7:40 am EDT:

Now for 9 AM, , which is in an hour and 20 minutes, the same site is saying five satellites with 0% elevation mask, up one from last night's forecast.  And it's saying one (1) satellite with 20% elevation mask, down one from last night's forecast.  Strange.  

LMAO.  What a load of crap!  

Just a couple minutes past 9 AM, I placed the P2V+ on the ground at the back of my property and fired it up - with NO intention to fly.  I am surrounded by tall 100' trees all around me so that the sky is blocked at 45 degrees all around me, so I didn't expect a GPS connection.  After a minute or two, it found its sixth satellite and marked the home point.  I checked the app and the homepoint was marked very accurately.  

Since there was virtually no wind, I launched.  I went up about 50 feet and it found its 7th satellite.  Then I went to 150 feet and it found its 9th satellite!  What?????  Then I climbed all the way up to 400' and it found its 11th satellite!!!  HAHAHAHAHAHAHAHAHAH

Conclusion:  If you're worried about visible satellites, DON'T WASTE YOUR TIME CHECKING UAVFORECAST DOT COM.  

Edit after overlaying data:

Mark The Droner Posted at 7-4 05:21
LMAO.  What a load of crap!  

Just a couple minutes past 9 AM, I placed the P2V+ on the ground at the back of my property and fired it up - with NO intention to fly.  I am surrounded by tall 100' trees all around me so that the sky is blocked at 45 degrees all around me, so I didn't expect a GPS connection.  After a minute or two, it found its sixth satellite and marked the home point.  I checked the app and the homepoint was marked very accurately.  

There are always going to be plenty of satellites anywhere you go.
The idea that you need to check for sats might have worked back in the early days of the GPS satellite deployment but it not needed any more.

This subject still pops up occasionally.  Absolutely no need for worry.

Labroides Posted at 7-4 13:32
There are always going to be plenty of satellites anywhere you go.
The idea that you need to check for sats might have worked back in the early days of the GPS satellite deployment but it not needed any more.

I once had a loss of GPS at 400' during an RTH because of inadequate satellites in the sky.  Fortunately it only happened once - still it makes me wary.  

Thanks for the warning