June 2015 – Weather Station Highlights – Gaithersburg 2WNW Maryland by Kevin Shaw, Observer and NJWO contributing member

June 2015 was wetter and warmer than normal. It was much more extreme
on the precipitation side. Three daily precipitation records were set,
highlighted by the 3.10″ on the 27th which was the third wettest June
day ever. Coincidentally it remained mostly in the 60s all day, topping out
at 69.6° which rounds to 70°, but still set a daily record low max
temperature record for that date. The lawns and gardens in the community
are now quite green after a drier than normal spring. Other daily
precipitation records were set on the 20th (1.52″ – remnants of Tropical
Storm Bill) and 23rd (1.43″ – mostly from a very intense thunderstorm
with a 26.18”/hr max rain rate at 1809 EDT) which also coincidentally
was the day of the highest temperature for the month (93°) that tied
(with 2010) the daily record high temperature for the date. The minimum
temperature of 72° on the 14th also set a daily high min temperature
record. This reading occurred during our mid-month hot spell, when we
hit 90° a few times, and recorded several 70+ minimum temperatures,
tying record high minimum temperature records on three dates (12, 15, 21).
Both the beginning (especially) and end of the month were generally

cooler than normal. During the month 17 days of measurable rain were
recorded, well above normal. The 9.68″ monthly precipitation total is
now the 3rd largest ever for June.

The average maximum temperature for the month was 81.6° (-1.3°), the
average minimum temperature was 65.0°(+3.9°), the second highest
average minimum in my 37 year POR (period of record), only topped
by the 66.7° recorded in 2010. The resultant mean average temperature
for the month was 73.3° (+1.3°). Both the average max and average mean
temp values were in the middle of the “POR pack” as to the wormest/
coolest ever. The highest temperature recorded during the month was
the record-tying 93° on the 23rd. We had a modest 4 days with max
temperatures at or above 90° (normal is about 5.4), and an above normal
amount of minimum temperatures at or above 70° (10).

The month’s total precipitation amount of 9.68″ was 5.28″ above the
normal June amount of 4.40″. The 17 days of measurable precipitation
during the month was well above the long term average of 11.4 days. This

June ties 2006 for second place all-time in my POR, 1998 had 20 days
of measurable precipitation for the top spot in that category. The year
to date (YTD) precipitation total of 25.10″ now puts us 2.56″ above the

normal YTD average amount for this time of year of 22.54″.

The monthly barometric pressure extremes were a very modest 30.21″
on the 3rd and 4th in the middle of our coolest spell of the month and
a 29.66″ recorded in the early morning hours of the 28th when our
biggest rainstorm of the month was just exiting our area. Average
barometric pressure for the month was 29.96″, not the same value
you would get if you averaged the two extreme values (29.94″)
I had for the month but pretty darn close. So far with four months
study under my belt, this relationship has shown up as the same in
March, 0.06″ difference in April, and 0.02″ in May and June.
It looks promising for developing some sort of relationship there.
Further study needed at least through the rest of the year.

The distribution of 8 sunny, 13 partly cloudy and 9 cloudy days did
not align particularly well with the much above normal precipitation
pattern, nor the number of days with measurable precipitation, but
the great amount of warm, humid days during the middle of the month
did align somewhat.

There was 16 heating degree days and 266 cooling degree days.
There were 6 days with fog (close to long-term averages) and 8
days with thunder (a bit above the long-term average of 6).
The peak wind gust during June was a modest 20 MPH (WSW)
during a strong thunderstorm on the 23rd. I observed the storm
and I believe winds were actually gusting in much more exposed
locations to an estimated 35-40 MPH. The current anemometer
siting is about 23 feet off the ground in the back of the house,
and surrounded by trees and in the middle of our townhouse
cluster so the readings are significantly muted at times.

My maximum temperature frequencies included 4 days at or
above 90°, 16 days at or above 80°, 7 days between 70°and 79°,
and 3 days between 60° and 69°, On the minimum temperature
frequency side of things, there were 5 days between 50°-59°,
15 days between 60°-69°, and 10 days with mins of 70° or

The diurnal range average was a bit below normal (16.6° vs
the normal 21.8°). The max daily range of 25.5° occurred on
the 11th as we headed into our mid-month heat wave. The lowest
daily temperature range of 4.2° occurred on the 3rd during our
coolest day of the month with lots of clouds and a bit of light
rain. We had a total of 3 days during the month with a diurnal
range lower than 10° while there were only 7 days with ranges
of 20° or more.

The month of June had a nice cool beginning and ending to the
month, with a warm to hot middle. As has been the case the
past few years, the warm nights persisted and were the reason
for the above normal temperatures. Precipitation was fairly
evenly dispersed during the month, with significantly more the
last half (7.26″) than the first half (2.42″) though the
number of measurable precipitation days was about even
(8 first half, 9 second half). So far in July it appears that
this relatively cool and wet pattern will be carrying over,
at least through the first part of the month. The details for July
will be coming next, in a few short weeks. Have a great summer!
I am hoping for a cool, active summer. Let’s see what happens!

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