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Re: Mesozoic snow - refined
Let's review what I already said...
GCMs, continental interiors, freezing temperatures in winter, large seasonal
variation in temperatures, climate not equitable, ice rafted deposits through
much of Phanerozoic, small ice sheets favorable at high latitudes...
Granted, you'd have to take a few steps out side of the box in order to apply
what I said to the coastal regions of the interior seaway during the esrly late
Maastrichtian. All things considered, seasonality within the vicinity of the
seaway would have been minimal. But, given the probable extent of the seaway at
that time, and the location of the Hell Creek formation, the occurrence of snow
was most definitely a viable possibility.
It's a meteorological truth; Cold air always wins. During the winter, I should
like to think that up north would have radiated out enough to produce a dry
continental polar air mass that would have been cold enough to kick off
snowfall as it moved south and encountered that moist marine tropical air mass
from the south. The denser cold air stays at the surface and lifts the warm air
aloft. In other words, a cold front. The warm air adiabatically cools and the
moisture precips out directly into the cold air below. If the air is freezing,
you get snow. If the surface is freezing, you get accumulation. If it snows
long enough over that above freezing surface, evaporative cooling will
eventually drop the surface to freezing and accumulation will take place. Even
if you back off slightly when it comes to the dynamics by weakening atmospheric
temperature contrasts, you'd still get the type of scenario, though at a
reduced scale. With a continental polar air mass during the winter !
at was less potent than today's (the most-likely case), whenever a surge of
cold air advection took place, fronts and their precip would push south, though
they wouldn't have been as vigorous.
In any case, given the situation, such events normally wouldn't have lasted for
very long, with only a slight accumulation before the pattern shifted enough to
allow warm marine air to once again advect north and into the region.