Download North American Air Masses

North American Air Masses
1) Continental polar - form only in the N.H.; most developed in winter; develops in central &
northern Canada; & Arctic air (colder & drier) originates farther north; the areas covered
experience cold, stable air, clear skies, high pressure & anticyclonic flow (cw in N.H.).
S.H. lacks the necessary continental landmass
2) Maritime polar - normally originates as cold, dry cP air that has moved off land & stagnated
over the N. Pacific or N. Atlantic acquiring its mP characteristics only in the lower
portion of the air mass, thus the lower layers are cool, moist & relatively unstable while
aloft may be cold, dry & stable; Pacific mP brings widespread cloudiness & heavy
precipitation to the mountainous coastal regions but in the interior of the continent it has
moderate temperatures & clear skies; Atlantic mP air does not affect N. America because
the prevailing circulation is westerly
3) Maritime tropical - from the Atlantic/Caribbean/Gulf is warm, moist & unstable; influences
weather east of the Rockies & southern Canada; Pacific mT affects only the southwestern
U.S. & northwestern Mexico
4) Continental tropical - relatively unimportant in N. America because its source region is
not extensive
5) Equatorial - affects N. America only w.r.t. hurricanes