About half the wind gust - an extra 50 kts is an awful lot. For example, with wind blowing at 10 gusts to 50 that's only a 40 kt gust so add an extra 20 kts to Vr. It also helps that the airplane will fly well below any of the V speeds. Minimum unstick speed is part of the certification testing that all new plane designs go through - raise the nose to drag the tail on the runway (actually a wooden block attached to the tail) as soon as the elevator can exert enough force to do that, continue the acceleration and see at what speed the plane will lift off the runway. Something in the 80-100 kt range if pretty standard and that's at least 20 kts under Vr for a lightly loaded airplane.

A micro-burst is a very specific phenomenon and I've seen nothing to indicate that the factors that produce microbursts were present in PHL.

One thing I forgot to mention in the last post - gusts shouldn't cause the plane to be airborne early. With the leading edge flaps/slats extended the wing has a negative angle of attack and absolutely won't fly until a positive angle of attack is attained - it'll run off the end of the runway first no matter how much runway there is. Normal procedure is to apply a slight forward pressure on the controls (stick in the Airbus) for the purpose of ensuring that gusts won't cause the plane to get airborne early since the trim setting should be about right to start raising the nose about Vr.

Gusts do bring wing sweep into the picture since all transport airplanes are designed with some amount of wing sweep to decrease drag at higher mach numbers. With a quartering crosswind the upwind wing is closer to having a headwind than the downwind wing because of the sweep (in this case wind out of the NW while taking off to the west, the right wing is the upwind wing). That means that the right wing in this case would develop more lift when a positive angle of attack is reached and would tend to rise faster than the left. But again, this is as the plane is rotated to the initial climb attitude, not prior.

There is a phenomenon that can be present at airports along the downwind side of mountain ranges that is called a rotor wave and was initially blamed for a UA crash at Colorado Springs. As the wind flows over the mountain range, aerodynamics says that the wind will fill in the lower pressure area on the downwind side of the range, creating a rotor-like effect - the wind on the downwind side of the range rotates around a horizontal axis. The wave itself remains in place just on the downwind side of the range. In the case of the UA flight making an approach to the north, it was speculated that the left wing entered the downward portion of the rotor wave, causing a sudden roll to the left which in turn caused the nose to drop. The flight was close enough to the ground that there wasn't room to recover before impact.

This was several years before the US 737 crash at PIT, which was finally found to be a fault in the rudder actuator which caused the rudder to go to the mechanical stop (a rudder hardover) and consequently the plane rolled nearly inverted and the nose dropped to nearly straight down. Again, there wasn't sufficient altitude to recover and everyone on board perished. I don't know if the NTSB then reopened the UA crash or not. However, in somewhere like PHL there's nothing to cause a rotor wave strong enough to have much effect and at least the 737's had their rudder actuators fixed. It's never been reported as a problem on the Airbus.

Jim