We live in a world of imaginary lines in the sand.
When it comes to national rainfall patterns the biggest line in the sand — or in this case, sky — is the hundredth meridian.
That line jumps out clearly on the “Year in Rain – 2008” map shown below.
It runs through the Dakotas, Nebraska, Kansas, Oklahoma and Texas;
Meteorologically it corresponds to the Gulf of Mexico’s westernmost influence of moist air.
East of that line is the rainfall abundant east, with an annual average of 30 or more inches – with upwards of 50 inches falling in Florida and topping 60 along the Louisiana Gulf Coast. (This year the Ozarks in Arkansas tipped the charts with more.)
In practice, what we see today is “river water following the dams,” or rather, stacking up behind them.
Probably the most famous of the giant reservoirs out west is Lake Mead.
The Colorado River delivers around 9 million acre feet to the reservoir each year, courtesy of snow melt from the Rocky Mountains.
The west is also home to the wettest part of the nation: the Pacific Northwest,
Despite it soggy reputation, Seattle lies in the eastward rain shadow of those giants. It has ubiquitous cloud cover – registering 200 cloudy days per year, but the city averages a pedestrian 40 inches of rain per year.
Compare that to south Florida’s only 100 cloudy day count, but beefy 55 inches of rain per year.
And keep in mind:
In summer, a good portion of its 100 cloudy days are probably sunny for their first half – through the morning – before the afternoon showers arrive.
And in winter, south Florida’s weather pattern is dominated by a Mediterranean monotony of one blue sky day after the other.
It’s a swamp land of bountiful annual rains, as shown below.
That can be seen in the map below, which shows rainfall throughout the southeast since the start of the North American “water year” in October.
The new calendar year rings in the middle half of the dry season,
Or phrased differently, now the fire season is upon us.