Please help Im totally lost on this question....Suppose we have a parcel starting out at 1000mb with a temp?

Question

of 35 degrees celsius and a dew point of 20 degrees celcius. If this parcel was to be forced up a 4km mountain, could this mountain be responsible for triggering a thunderstorm? If so, why? (Think stability)

Answer 1

Initally, your parcel of air would cool following the dry adiabatic lapse rate.  This lapse rate is 1 deg C per 100 meters of ascent.

This parcel will continue to cool, until the humidity reaches 100 percent.

When 1pp percent humidity is attained, the parcel continues to cool following the moist adiabatic lapse rate of .55deg C per 100 meters of ascent.

As the parcel rises, making the humidity incease, it is HIGHLY possible that this effect can initiate the development of thunderstorms.

The reason...warm air begins to ascend the mountain.  It cools, as it rises.  It will continue to rise until it becomes more dense than the surrounding parcels of air.  Warm air is less dense and will weigh less than the cooler air already at the altitude the rising parcel has entered.  This is clearly an  unstable condition.

Hope this bit of info helps.

Answer 2

Yes, and this happens a lot along the Rocky Mountains in the Spring and Summer.  What happens is the air is forced upward along the mountain, and if the temperature profile of the atmosphere is right, that air will reach a level in which it becomes warmer than the surrounding air (becomes unstable) and continues to rise into the atmosphere, producing a thunderstorm.

Answer 3

Because (I'll assume) your question is a hypothectical one and because your asking "Could" then Yes its possible.

The Mountain(s) of course plays a role but then, so does the front if its a high or low pressure system.  I (in my opinion) would not use the dew point as my indicator to trigger a thunder storm if the mountain rose 4km but rather, a Barometer. Under the conditions outlined, my dew point could be way up (or down) but I think barometric pressure would give your scenario a plasuable "yes"