JULY 2013 MONTHLY SUMMARY – GAITHERSBURG 2 WNW MARYLAND

JULY 2013 MONTHLY SUMMARY – GAITHERSBURG 2 WNW MARYLAND
by Kevin Shaw, observer in charge

July 2013 was warm and wet. Not as hot as the past few years, but we still had
a respectable mid-month hot spell when most of my nine max 90 or greater days
were recorded. There were 20 days with mins of 70 or greater. July 2013 marked
the third July in a row with an average min temperature of 69.8, my highest ever
in 35 years of records. The 20 days with mins of 70 or greater ties 2010 for the
most ever. In July 2011 and July 2012, I had 17 days with mins of 70 or greater.
There was a modest 9 days with maxtemps of 90 or greater, actually below the
long-term norm of about 11. Most of these 9 days occurred in the mid-month heat
wave that started on July 14th and ended on July 21st. No record daily high or
low temp records were set, Five days set daily record high min records, two
additional days tied previous year(s) high min records. My warmest min temp of
this month of 77 failed to eclipse the record 79 for the date set back on 7/19/2010.
There was one tied-record low max temp on July 12 (73 – with 1999), our coolest
day of the month, in an all-day cloudy, rainy day. It was the 7th wettest July of all
time (5.07″), with a tied record amount (with 2000) of 17 days with .01″ or greater
daily amounts. The 1.58″ of rain that fell on July 22 did set a daily record. There
was a normal amount of thunderstorm days (6). Dew point temperatures mostly
stayed above 70 all month.

July 2013 fit in with the patterns of most months the past few years, mean and low
average temps above normal, max average temps above normal but not enough
to offset the warm average min temps.

Actual statistics for July 2013 shows an average maximum temperature of 85.4° (- 1.4°)
with the average minimum temperature of 69.8° (+ 4.1°) resulting in a mean monthly
temperature average of 77.6° (+0.8°). After the previously mentioned hot spell between
July 14-21, we finished out the month on a cooler than average note, with no further 90
max temps and in fact a few sub-80 max days and a sub-60 min day that mitigated the
averages a bit towards more normal levels.

There were no real wet spells – the 17 measurable days with precipitation were spread out
nicely throughout the month with no more than a modest 5 day streak with no measurable
rain that coincided with our hot spell previously mentioned. The monthly precipitation total
of 5.07″ was 1.33″ above the normal amount of 3.74″. I am now running 4.63″ above the
normal precipitation amount for the year through July 31 (30.91″ vs. 26.28″).

The modest high barometric pressure reading for the month of 30.34″ on the 14th occurred
at the beginning of the month’s hottest and driest period. The 29.65″ lowest pressure value
of the month occurred on the 23rd, on the day after our largest rainstorm of the month.
The 23 MPH PWG (peak wind gust) for the month from the north occurred on the 7th, during
a frontal thunderstorm early that evening. The distribution of 11 clear/sunny, 12 partly cloudy
and 8 cloudy days fit in fairly well with the balanced wet to dry conditions during the month.

There were only 2 days with fog. There were 390 cooling degree days and no heating degree
days in July. My maximum temperature frequencies included 9 days of 90 or above, 18 days
from 80-89, and 4 days from 70-79. On the minimum temperature frequency side of things,
there was 1 day below 60, 10 days between 60-69 and 20 days of 70 or greater.

The diurnal range average was quite a bit below normal (15.5° vs a normal of 21.1°) with a max
daily range of only 21.4° on the 30th on the day of our lowest temperature of the month (58.7).
The 7.6° lowest monthly range on the 12th occurred on the general cloudy, rainy day discussed
previously. There were only 2 days total with diurnal ranges less than 10°. Conversely there
were only 4 days with diurnal ranges of over 20° Generally cloudy, damp, high dew point
conditions helped to contribute to these less than spectacular diurnal range temperature data.

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