Weeks Bay Watershed Project Management Plan - Mobile Bay ...

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In 1991, the WBNERR Advisory Committee proposed the designation of
Weeks Bay as an “Outstanding National Resource Water” (ONRW). The
ONRW status provides for special protection of waters for which ordinary
use classifications and water quality criteria do not suffice. ONRW
regulations limit the type and number of potential polluting discharges into
Weeks Bay. After a period of public comment and agency review, the EPA
conferred ONRW status in August 1992.
C. CLIMATE (Paraphrased from Schroeder 1996)
The Weeks Bay Watershed lies in the humid subtropical climate region
(Trewartha and Horn 1980), a climate that dominates the Gulf Coast States
and Florida peninsula. Summers are characteristically warm while winters are
relatively mild with occasional cold waves. In the contiguous United States,
this region is second only to the Pacific Northwest in total annual rainfall
(Baldwin 1973), receiving precipitation from a combination of winter storms,
thunderstorms and tropical systems.
Summer Climate
High barometric pressure over the Atlantic Ocean is a dominant factor in the
summer weather pattern. This semi-permanent weather system, called the
subtropical anticyclone, provides a persistent southerly flow of humid air
from the Gulf of Mexico. This air is normally unstable and thus, is easily
lifted and condensed through convective heating or sea breeze convergences.
As a result, thunderstorms are frequent and account for the major portion of
summer rainfall. The frequency of thunderstorms over coastal Alabama is
surpassed in the United States only by the Florida peninsula.
The influx of moisture from the Gulf of Mexico, in combination with
numerous thunderstorms, produces a small diurnal temperature range during
the summer. Average maximum air temperatures during the summer months
vary from the upper 20ºC (80ºF) to the low 30ºC (90ºF) range in the vicinity
of the Weeks Bay Watershed. Although temperatures may rise rapidly during
the morning hours, the high frequency of thunderstorms usually limits the
daily temperature peak at around 32 to 33ºC (90 to 92ºF) (Williams 1973).
Because of the high absolute humidity during this period, temperatures of
38ºC (100ºF) or higher are occasionally observed in the Bay area.
Winter Climate
During the winter months, the Atlantic subtropical anticyclone retreats
southward allowing the polar front to make numerous incursions into the
Gulf States region from September to May. The arrival of polar air is
frequently marked by heavy rain and a strong wind shift from southerly to
northwesterly. When extremely low temperatures occur for at least two
successive nights, freezing of the Bay may take place near shore.
Winter Storms
Weeks Bay Watershed Management Plan