The result (in the NH) is there will tend to be northwesterly winds at the ground locations near where the axis of the trough is passing over (and so southwest of the surface low\northeast of the surface high). Such northwesterly winds will tend to bring cooler air and lower relative humidities in most places, but it just how cold or dry the air will be depends upon the source region of the airmass the northwest winds are blowing in (which itself relates in large part back to the strength and larger history of the trough itself).

Overall, fundamental cause of connections between motion\pressures at different atmospheric heights is the fact mass continuity must occur (if air rises, it must be replaced, and it must eventually sink somewhere else to maintain the weight-density to prevent continuing mass buildup/loss), and works out to clearer relationships such as thermal wind (the reality that different winds at different height levels is a direct consequence\identity of temperature advection in the layer between the levels) and the fact the two main terms that cause vertical motion in the quasigeostrophic approximation are differential vorticity advection with height (i.e. different spin changes at different levels causes vertical movement) and maxima of temperature advection below (plus two other terms on friction and external heat).

In a sense, the fact pressure at one elevation induces changes\motion in another elevation maybe shouldn't seem any less weird than the fact that a low-level low pressure system can affect the wind and weather hundreds of miles away from it horizontally. This isn't spooky action at a distance, this is a continuous fluid where changes to one part of it causes impacts on another part.