CHAPTER 3
Average Monthly
Precipitation and
Snow Depth
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T |
wo tables contained in this chapter display average monthly precipitation and snow depth. Information in these tables is self-explanatory and each table is formatted by city and state into twelve columns, January through December.
As with the tabulated information of the previous chapters, information in these tables represents the 50-year averages extracted from the ISMCS* 1996 database.
Information in these tables complements leisure thermal comfort values in previous chapters. For example Table 5-1, pages 59-67, of Chapter 5, displays PRECIP for comfort paradises.
Average Monthly Precipitation
The average monthly precipitation in Table 3-1,
pages 21-30, includes snow, hail, sleet and rain. As with other tables, entries
represent monthly averages of day-to-day observations.
Example: Table 3-1, page 28, shows that Astoria, OR has 1.1
inches of precipitation in July and 10.4 inches in November. Miami, Fl, page 23, has 2.0 inches of
precipitation in January and 8.5 inches in September.
High Precipitation
As Table 3-1 shows, Yakutat, Alaska and Hilo, Hawaii, have very high annual precipitation, about 146 and 130 inches, respectively.
Mt. Waialeale, Hawaii*,
(not listed in the table) is reportedly the wettest region in the world – with
a twenty-year average annual rainfall of about 460 inches.
Low Precipitation
Greenland Ranch, Death Valley†,
California (not listed in the table) is reportedly the driest region in the
U.S. with an average annual rainfall of less than 1.5 inches. Table 3-1 shows
that many locations within the United States have little or no rainfall during
the summer months.
Average Monthly Snow Depth
Table 3-2, pages 31-40, displays average monthly
snow depth at specified U.S. locations. “T” indicates trace amounts.
Example: As shown by Table 3-2, page 31 (first row), snow
depth in Adak, AK is 20 inches in January and zero inches in July and August.
Alaska: Abundant Snow in the Winter, But Generally
None in the Summer
Valdez, Alaska has
unusually high levels of snow as shown by Table 3-2. Snow is 67 inches deep in
January and 79 inches in December – less in the other months. As with most of
Alaska, snow depth and snowfall are generally zero during June, July and
August.
Because
snow depth depends on other factors like ambient temperature, pressure (as a
function of depth) and time, depth is not simply a sum of daily snowfalls. Snow
depth has been observed to decrease by 57% during a five-day period during
which time the temperature never exceeded 30ºF. The snow’s water content
remains the same, even though major changes occur in the snow particle structure.
Tables
3-1 and 3-2 can help the reader schedule activities according to expected
seasonal precipitation. ■