Narrative Summary - December 1999

December 1999 was the 5th warmest December on record, averaging 37.7ºF, 6.3º above normal (31.4ºF).
The period from December 11 - 19 averaged 14.1º above normal. The warmest December occurred in 1957
and averaged 38.5ºF, while the coolest was 21.0ºF in 1985. The following daily temperature records were
established in December:

                          New          Old
Date   Category          Record       Record     Year
 12    High Maximum        57           57       1988 Tie
 15    High Minimum	   49           41       1956
 16    High Maximum        62           60       1997
 16    High Minimum        44           43       1973
 18    High Maximum        56           56       1956 Tie
 18    High Minimum        42           38       1994

Precipitation for December 1999 totaled 0.07 in., 7% of normal (1.03 in.) and was the driest December on
record. The previous driest December was 1976 with 0.11 in. The wettest December, in 1996, received 3.69
in. Snowfall for December 1999 totaled 0.6 in., compared to a normal of 5.7 in. The snowiest December
(1996) received 22.6 in., while December 1962 received only a trace. Snowfall for the 1999-2000 winter
season to date is 0.6 in., compared to a normal through December of 7.6 in.

The average wind speed for December 1999 was 7.5 miles per hour (mph), 1.6 mph above normal (5.9 mph).
The windiest December on record averaged 8.3 mph (1968), while the December with the lightest winds
(1985) averaged 3.3 mph. The peak gust for the month was 62 mph on December 18. The record wind gust
for December was 71 mph in 1955.

The atmospheric pressure on Christmas Day reached 30.91 inches of mercury, the highest pressure since
31.12 inches on January 1, 1979 (the highest on record).

The average temperature for calendar year (CY) 1999 was 54.4ºF, 1.1º above normal (53.3?F). The warmest
year (1998) averaged 56.4ºF, while the coolest (1985) averaged 49.6ºF. CY 1999 was the 4th driest on
record, receiving 3.75 in. of precipitation, 60% of normal (6.26 in.). The wettest year (1995) received 12.31
in., while the driest (1976) received 2.99 in. CY 1999 established a new record for least amount of snow
during a calendar year, receiving only 0.6 in.; the previous low was 0.9 in CY 1958. CY 1999 was also the
windiest year on record, averaging 8.8 mph (1.1 mph above normal). The previous windiest year was 1983
which averaged 8.4 mph. A comprehensive climatological summary for 1999 will be published later in the
spring.

The monthly climatological data summaries, as well as other information, are available
on the Internet. Address: http://etd.pnl.gov:2080/HMS/. Hanford Site personnel can
access the HMS Intranet site at: http://hms.rl.gov/

For additional information contact:
Ken Burk373-3215
Dana Hoitink372-6414

Note: The information in this summary pertains specifically to
the Hanford Meteorology Station (HMS), which is located
approximately 25 miles northwest of Richland, Washington. No
attempt should be made to infer meteorological conditions at other
locations from these data.