"Nature Guide Journal"
7 February 2002
It seems the famous groundhog, Punxsutawney Phil, saw his shadow
Saturday.
Punxsutawney Phil is a marmot. More specifically, he's a member of Marmota
monax. And he is male, since female marmots tend to hibernate
longer. While there are a variety of gophers and ground squirrels in
western Oregon, the only marmot native to our state, the Yellow Bellied
Marmot (Marmota flaviventris), lives east of the Cascades.
In Coos County, all types of mammals saw our shadows this past
Saturday. What does that forecast for our weather?
The key to the prognostication is in the shadow, not the mammal. In
ancient Europe, a similar forecast was made on the actions of hedgehogs
and bears arising from hibernation. The point was that a clear Candlemas
Day—mid-point between Winter Solstice and Spring Equinox—meant more
cold, wintery weather ahead; a cloudy Candlemas Day meant a milder entry
into spring.
Certainly, one would expect such predictions to be right at least
some of the time by mere chance. But there may be another explanation
for this well-traveled folklore.
Though not entirely reliable, weather sometimes cycles in a two-week
pattern. Low-pressure systems generally bring precipitation and other
"bad" weather; high-pressure systems generally bring clear
skies and other "good" weather. In general, these pressure
systems alternate, normally moving—in the northern hemisphere—west
to east.
Putting all that together gives a plausible explanation to support
the myth of Groundhog Weather Forecasting. If the first week of February
is clear (high-pressure system dominating), the next low-pressure system
will likely hit in mid-February, when the timing makes a cold winter
storm probable.
If the first week of February is cloudy (low-pressure system
dominating), the next visiting weather system will be a high-pressure
one. A cloudy Groundhog Day would mean that it would likely be later in
the winter when the next low-pressure system came around. That two or
three weeks would likely make that low-pressure system more spring-like;
i.e., less snow and ice and more rain.
However, many factors can cause the "two-weeks" of the
cycle to be unreliable; such as, the relative size and the positions of
the high- and low-pressure systems and the speed they're traveling, as
well as various fronts and other interactions between the systems.
Based on the same principle of alternating pressure systems, is the
more reliable ditty: "Red sky at night, sailors delight; Red sky at
morning, sailors take warning."
High atmospheric pressure means the atmosphere is denser in that
region. More particles of air, and more particles of dust, increase the
refraction of the incoming sunlight. When the sun sets with a very red
sky, that's an indication of more dust (or pollution) or of a
high-pressure system to the west. The prevailing westerly winds would
drive a high-pressure system in the west our direction, bringing clear
weather.
"Red sky at morning" would mean a high-pressure system is
to the east at the rising sun. With the high-pressure system past, a
rain-bearing low-pressure system is probably bearing down on us from the
west: "sailors take warning."
"So, is the groundhog's forecast accurate?" Sometimes.
We'll know in May!
