Local Variation in Winter Morning Air Temperature
AUSTIN W. HOGAN AND MICHAEL G. FERRICK
PART I: A RIVER SURFACE REFERENCE
complexity and scale of the subzero frequency
INTRODUCTION
isopleths are comparable to those of cold day iso-
Many problems in engineering, hydrology, and
therms of the island of Hokkaido, given by
operational meteorology are further complicated
Nakamura and Magono (1982). The variation in
by local variation in winter surface air tempera-
frequency of subzero occurrences in the vicinity
ture. There are additional problems in preparing
of Stillwater Reservoir, New York (designated by
dispersion estimates over snow-covered terrain,
the plotted 45), is well known in that area, accord-
ing to L. Lansing.† The complexity and number of
which are related to the alteration of vertical tem-
isopleths in Figure 1 are probably diminished by
perature structure that accompanies these surface
the sparsity of reporting stations. This may in-
temperature variations. Locally severe ice dam-
duce unexpected problems if an activity depen-
age may occur when subfreezing air remains in
dent on operational, engineering, or air pollution
valleys as warm advection produces rain above.
meteorology is undertaken in this area.
Lakes and waterways may suffer early freezeup
The area in Figure 1 bounded by 4245N,
in the windless conditions that characterize strong
7080W, probably experiences a similar quasi-
local inversions. More complex problems arise
uniform distribution of tropospheric air masses
when estimates of frost depth, extreme tempera-
tures, or the frequency of strong local inversions
over a 30-year period. An inspection of the sta-
are required at a proposed operational site when
tion tabulation of NOAA (1982) is sufficient to
conclude that simple elevation difference cannot
only data from dissimilar reporting stations are
account for these great differences in subzero
available.
(<17.8C) temperature frequency. A comparison
An example of the magnitude of winter tem-
perature variation in the 42N to 45N latitude
of 0700 (1200 UTC ) winter temperatures observed
segment of the eastern United States and adjacent
at Mt. Washington, New Hampshire,** at eleva-
Canada is shown in Figure 1. This figure illus-
tion 1,920 m to those observed in the Connecticut
trates the mean annual number of subzero days,
River Valley at Z elevation 230 m, less than 60 km
having temperatures less than 17.8C (0F), from
distant is shown in Figure 2. The locations of Mt.
NOAA (1982) Climatography no. 20, The Climate
Washington and Z are noted on Figure 1. The
of Cities, for the period 19511980. The Canadian
lower elevation temperature is less than the po-
data was calculated from cooperator station
tential temperature and often absolutely lesser
than the mountain station. This systematic differ-
records for the same period by Dr. David Phillips.*
ence can be partially accounted for by the
Note the complexity of the frequency isopleths in
decoupling of the surface layer (Miller 1956a, b)
northern New York, Vermont, and New Hamp-
from the troposphere by one or more inversions
shire in Figure 1. The frequency of subzero
(17.8C) temperature occurrences varies by fac-
tors of two over distances of less than 30 km. The
† Personal communication, L. Lansing, Cooperative Observer,
National Weather Service, Boonville, New York, ca. 1970.
* Personal communication, Dr. David Phillips, Atmospheric
** Personal communication, K. Rancourt, Mount Washington
Environment Service (AES), Environment Canada, 1993.
Observatory, 199192.
Previous Page
