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| Intense July in Des Moines, IA |
After the fiery heat of summer delivered a severe drought, a storm of
change is on the horizon. Extreme heat and desert dryness to our west will collide
with the inevitable cold of winter descending from the north. In Iowa, we call this season of change Fall.
It’s home to some of the most dynamic swings we’ll see all year. In the last few weeks, we’ve already had a
preview of Autumn weather; but Fall 2012 will be unlike most years. So lets take a long shot and talk about the Fall forecast.
Long-range weather prediction is similar to taking that long
shot with your gun or bow. The further you are from your target the less likely
you are to hit exactly where you’re aiming. Climate prediction is incredibly complex. We need to
consider numerous factors such as; regional conditions, geography, seasonal rain/snow distribution,
vegetation response and especially ocean currents. Meteorologists place the
current conditions and the trends into historical perspective much the same as
you might set your rifle into your shoulder. We line up the parameters,
consider the stats, and fire off a prediction. Here we go!
One significant factor in cool season long range patterns is
the Arctic. This cold weather making machine throws down bone
chilling air like a snow blower. We have already seen signs of an active Arctic with some
cool surges in August, and if this trend continues, stronger westerly Jetstream
winds will keep large storm systems on the move sending powerful surges of cool followed by waves of warmth. For everyday folks it just
means the weather will rarely stay stagnant. Instead of being locked into hot
or cold for weeks on end, the pendulum will always be swinging. Yee Haw!
The majority of Iowa's weather comes from the west. As we look westward towards Alaska, it is likely that an
Aleutian Low Pressure in the Jetstream will become the storm-making factory
pushing out one or two systems each week. A ridge would build in the Rocky
Mountains (we’ve seen that), and the buckling Jetstream would form a trough
along the east coast. Under this scenario we’d see a
warm-up for several days and then see a quick hitting rain chance followed by
radically cooler weather.
Sometimes storm systems run into the one in front of them,
resulting in an atmospheric traffic jam of sorts. So lets look east to see if there are any traffic snarls to the east that would affect our storm systems. We think the Atlantic Ocean
will become a storm magnet on the eastern seaboard this Fall and winter. That means storms should cruise right on through Iowa. Once
they’re on the east coast storms should really develop as Canadian cool
interacts with the warm waters of the Gulf Stream current.
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| Sea Surface Temperature Departures from Average |
Another major climate player is the cool Pacific Ocean. This beast has the power and mass of the world’s largest
ocean behind it and it carries significant and lasting weather pattern effects.
The northern Pacific can stay in the same phase (warm or cool) for a decade or
more. Currently, the Pacific is in a cool phase as indicated by the horseshoe of cooler-than-normal
waters along the edge of the eastern Pacific stretching from the Aleutian
Islands of Alaska to the west coast of Mexico. Research suggests this massive
swath of cool ocean can offset El Nino and can magnify the effects of La Nina.
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El Nino and La Nina are the fighting features of El Nino SouthernOscillation or ENSO where waters of the equatorial eastern Pacific Ocean off
the coast of South America become abnormally warm or cool. The waters of the equatorial Pacific are warming and a weak
El Nino is expected to develop within the next few months. There is currently
an El Nino Watch in effect from the Climate Prediction Center. It seems far-fetched, but for Iowans but El
Nino can have significant effects during the cool season. La Nina in Iowa
historically gives us warm and dry winters. Last winter we were in a weak La
Nina and the warm/dry winter fits the mold quite nicely. El Nino typically gives Iowa a wetter
and cooler winter. It's important to understand, even in true El Nino or La Nina years, the
effects of The Ninos in Iowa is not always very pronounced. ENSO weather weenies
learn more here. I am expecting the
cool Pacific to dampen the effects of our weak El Nino. As much as I’d
like to see more rain/snow to help with the drought, I just don’t think it’s in
the cards.
Iowa’s Severe to
Extreme drought will be the biggest factor in the Fall weather
pattern. Intense summer heat wicked water out of the ground leaving Iowa’s
croplands parched and baked. If Iowa had a more pronounced rainy season it could outweigh our current
dryness. But we don't, so it will be tough to climb out of our rainfall deficit. Because of
this, the Midwest only has a 25%-30% chance of ending the drought in the next 6 months. More on Midwest drought here. After putting together all these pieces, here’s my long range Fall forecast.
A strong Arctic storm system has
been feeding off the intense heat all summer, and it’s growing larger. That
system will collide with a persistent drought likely to keep the inter-mountain
West and Plains states hot and dry. I expect temperatures in Iowa to be above normal
from September through November. But it wont be a stable pattern. Waves of western heat will be chased by the northern cold. We
could even see record highs followed by chilly or even freezing weather within
just a few days of each other. Once-a-week chances of rain should spice up the forecast most of the fall. I expect precipitation to be at or (more likely) below normal. This pattern will likely hold right on into November or even December, but it will eventually break down. Once it does we could be talking about an early start to the snowy season. I think we'll see at least one significant snow in November. So as you enter the Fall fishing and hunting arena, be prepared to have your gear and your patience tested by tumultuous weather. We'll likely face several wild and perhaps record-breaking swings in the weather patterns that will have sportsmen and the wildlife alike on their toes.
In my next blog I’ll talk about the prevailing winds for
October, November and December and then make a prediction on how our drought
and this fall will affect forage and deer patterns. These factors might make
you reconsider where to place that tree-stand!
Become a member of the outdoors blog and please leave me a
comment! I’ll leave you with some fun climate links:
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