I posted this blurb on the WHDH Yahoo Group this moring. Thought you might
find it useful. Comments and critiques appreciated!
----------------------------
For this analysis of precipitation behavior so far in year 2004, I define
³wet day² as any day where I measured .01² or more precip. . Therefore, a
day with .01² rain gets as much credit as a day with 2². [I think this
concept takes the rough edges off what we consider a rainy day]

I once again invoke the useful concept of moving averages. In this case, I
look at successive 30 day moving averages of wetdays. Excel 2004 makes this
analysis a snap.

Results here in Ashland, MA:

(1) The 30 days ending March 4 had the lowest density of measurable precip
with only 13% or 4 days with measurable precip. (Happily for this rare
snow hater, this meant not lots of that 4 letter word!)

(2) Notably, just one month later; the 30 days ending April 5, featured the
highest density of precip; namely 64% or 19 out of 30 days with measurable
observed. Put another way, I was 5 times more likely to observe measurable
precip in the 30 days ending April 5 as I was in the 30 days ending just one
month earlier on March 4. This 30 day period is the highest so far this
year. We went from very dry to very wet very quiclky!

(3) Since that prolific 30 day late Winter/early Sprinig span, percentage
has declined somewhat erratically to where over the past month or so of 30
day periods, we are hovering around 30% or 9 days per 30 day span.

(4) It is difficult to locate official statistics regarding ³wet days². I
did find in Jack Williams ³The Weather Almanac 1995 Edition², some data
for Boston. According to this, we expect to observe measurable precip 35%
of days or about 10 days per 30 day span. Using this, the driest period (30
days ending March 4,) was 13/35 or about 40% or normal. In stark contrast,
the 30 days ending April 5 was 64/35 or about 180% or normal.

Jot - Ashland, MA


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