SEPTEMBER 2018 MONTHLY SUMMARY FOR ROCKVILLE 2.8 WNW MARYLAND
by Kevin Shaw, Observer in Charge
September 2018 kept up the patterns of the 2018 summer with warm and wet
conditions most of the month. No really big one-day rains this month, but there
were 5 days with over an inch of rainfall, and a total of 17 days of measurable
rain (which coincidentally was the same amount of cloudy days during the
month). There were two 7 day streaks of measurable rain during the month
(7-13 – 5.43” and 22-28 – 3.69”). Those 2 groups (about half the month)
constituted about 88% of the total monthly precipitation (10.34”). The rainiest
day of the month was on the 7th (1.58”) when a strong front came through
with a thunderstorm, cooling us off from our big early month heat spell.
This heat spell featured 4 straight days with max temps of 90° or more (the
only ones of the month, from the 3rd through the 6th), and also a string of
minimum temperatures of greater than 70° with similar high dew point
temperatures, mostly in the 70s. The nights were particularly oppressive,
especially when looking forward to more pleasant fall temperatures coming
in to the area. All the rain that fell thereafter the rest of the month helped cool
us off a bit, but we still had several humid days.
The highest temperature reached during the month was 90.5° on the 6th
while the lowest temperature in September was 55.5° on the 27th. The
highest dew point temperature reached during the month was 79° during
our early month heat spell on the 3rd while the lowest dew point temperature
value reached during September was 50° on the wet, cool, rainy 27th.
Barometric pressure differences during the month increased a bit over the
previous summer months, with the lowest values found on the 18th, when
29.78” was reached. During that time I was having weather station
connection problems, so several readings (but not the barometric
readings) had to be estimated from very nearby, trusted weather
observers. September’s pressure extremes included the extreme
highest pressure for the month (30.38”) on the last day of the month
while the extreme lowest (29.78”) was on the 18th. The low reading
matched the low reading in August, ironically. This rainy September
had 17 cloudy days, 9 partly cloudy days, and 4 clear/sunny days.
There were 17 heating degree days and 219 cooling degree days
during the month. There were 14 foggy days, 8 windy days and 5
days with thunder The windy day category is subjective with no
personal real data values to back it, just based on my
descriptive email daily weather posts that are posted on
weathertogether.net.
Daily max/min temperatures varied about the same as the previous
summer months. My maximum temperature frequencies included 4
days of 90° or greater, 9 days between 80° and 89°, 13 days between
70° and 79°, and 4 days between 60° and 69°. On the minimum
temperature frequency side of things, there were 6 days between 50°
and 59°, 13 days between 60° and 69°, and 11 days at or above 70°.
The coolest daily max temperature was 61.8° on the 23rd with the
warmest daily min temp 74.7° on the 4th.
The diurnal range daily monthly average was only 11.7°. Our greatest
daily range of temperature was 17.5° on the 5th, formed from a high of
90.3° and a steamy low of 73.1°. We had a total of 22 days with daily
ranges at or above 10°. Our lowest range of temperature was 3.2°
(71.3° – 68.1°) on the 11th which was one of our many wet days
during the month. There were 8 total days with diurnal temperature
ranges of less than 10.0°, mostly on cloudy, rainy days. The wet, cloudy
month really muted our diurnal ranges. Normally I get several days
with above a 20° range (at least) and sometimes days with 30° or greater.
I had power (battery) problems with my VP2 weather station several days
mid-month. Several readings (but not rain or pressure) had to be
estimated for about a week (roughly the 12th – 18th) as noted on my
spreadsheet comment entries. I am still constantly checking on my
data quality frequently, along with discussion and data comparison with
several of my Maryland weather cohorts and reliable online close by
observer data. I continue to occasionally (as time allows) submit GLOBE
Cloud observations, complete with submission of sky pictures at the time
of the observation, usually timed with the passage of satellites and/or
solar noon (about 70 minutes past actual EDT noon). Please ask me
any questions you want at any time about my station setup and/or my
data through any means available to you.
SEPTEMBER 2018 – ROCKVILLE 2.8 WNW MARYLAND – SUMMARY STATISTICS
Average high temperature 77.6°
Average low temperature 65.9°
Mean temperature 71.7°
Precipitation 10.34″
(+6.35” – long-term PRISM normals from CoCoRaHS)
Greatest daily amount (date) 1.58″ (7)
Greatest storm total (dates) 3.55” (7-9)
2018 year-to-date precipitation total 48.42″
High temperature for the month (date) 90.5° (6)
Low temperature for the month (date) 55.5° (27)
Highest barometric pressure (date) 30.38” (30)
Lowest barometric pressure (date) 29.78” (18)
Peak wind gust (date/direction): N/A
Heating degree days for the month: 17
Cooling degree days for the month: 219
Greatest diurnal range (date):17.2° (5)
Least diurnal range (date) 3.2° (11)
Number of days:
Fog 14
Windy 8
Thunder 5
Cloudy 17
Partly Cloudy 9
Sunny/Clear 4
Max temp ≥ 90° 4
Min temp < 60° 7
Precip ≥ 0.01” 17
