DECEMBER 2017 MONTHLY SUMMARY ROCKVILLE 2.8 WNW MARYLAND
                         by Kevin Shaw, Observer in Charge

December wrapped up the 2017 year with slightly below temperatures and significantly drier than normal precipitation according to the official regional DC area NWS report PRESTO. Temperatures were seasonable to seasonably mild till Christmas after which we had a cold wave that extended through the first week of 2018. Temperatures remained below freezing all day from December 27 through January 7. The last day of the year featured our coldest day of 2017 on both maximums and minimum values of 20 and 13. Ice formed on local rivers and ponds, and meager snowfalls remained on the ground for several days. The first measurable snowfall of the season (3.1″) fell on the 9th. Just before we headed into the deep freeze right after Christmas, we had our meager wettest day of the month (0.36″) on the 23rd, when we also had our warmest day of the month (62°). The highest barometric pressure reading of the month (30.71″), and actually the highest since early March, occurred on the 28th
along with our second coldest day of the month. The lowest barometric pressure reading of the month (29.53″) occurred on the 12th and 14th, a few days after our only significant snowfall of the month. Only 6 days had measurable precipitation was below the normal amount of about 10. There were also 4 additional days when trace daily amounts occurred. The month was pretty cloudy despite the meager precipitation, with only 4 clear days logged along with 13 partly cloudy and 14 cloudy days. It was a slightly different ending to the generally warm year of
2017, totally attributable to the month’s end cold wave when daily average temperatures averaged over 10° below normal. Low precipitation fit the mold for most months of 2017.

There were 564 heating degree days (HDD) and 0 cooling degree days (CDD) during the month. There was only 1 day of fog with no other weather types logged.

My maximum temperature frequencies included 1 day between 60° and 69°, 10 days between 50° and 59°, 7 days between 40° and 49°, 9 days between 30° and 39° and 4 days between 20° and 29°. On the minimum temperature frequency side of things, there was 4 days between 10° and 19°, 11 days between 20° and 29°, 13 days between 30° and 39° and 3 days between 40° and 49°. The coldest daily max temp was 20° on the 31st and warmest daily min temp was 45° on the 5th.

The diurnal range daily monthly average was 13°. Our greatest daily range of temperature was 23.3°, formed from a high of 45° and low of 22° on a partly sunny day on the 12th. There were only 4 days total with daily ranges at or above 20°.while our lowest range of temperature was 4.8° on a cloudy day on the 8th, formed from a high temperature of 39° and a low temperature of 34°. There were a total of 7 days with diurnal temperature ranges less than 10.0°, an increase of 5 over last month. Most of the days occurred during the cold wave at the end of the month.

With yet another month to study the instrument changes made in mid-August, data appears to be stable and an overall data quality improvement success. I am still constantly checking on my data quality frequently along with some of my Maryland weather cohorts. I got to fully utilize my recently installed snowboards after the snow on the 9th. I now only have the outer cylinder in place on my cocorahs gauge to minimize freezing of some of the parts of the gauge, and to better catch snow for water equivalent purposes. I swap out gauges when frozen precipitation occurs to allow for casual, comfortable melting inside my apartment. Unfortunately the newly established “snow stake” has not really been utilized with the lack of significant snowfalls so far since installation (which was after
the 9th). I did get a nice pair of binoculars recently to better read the snow stake from my balcony. Interestingly enough one of the two flagpoles in the immediate vicinity fell twice within the past month, apparently due to high winds. At least the snow stake remained fully upright! Anyway, I will still go out to the snowboard as long as it is safe to take measurements. Please ask me any questions you want at any time about my station setup and/or my data through any means available to you.

DECEMBER 2017 – ROCKVILLE 2.8 WNW MARYLAND – SUMMARY STATISTICS

Average high temperature 42.7°
Average low temperature   29.7°
Mean temperature             36.2°

Precipitation                           0.84″
Greatest daily amount (date)  0.36″ (23)
Snow                                       3.8″
Greatest daily amount (date)  3.1” (9)
Final 2017 precipitation total 38.60″

High temperature for the month (date) 62° (23)
Low temperature for the month (date)   13° (31)

Highest barometric pressure (date)  30.71” (28)
Lowest barometric pressure (date)   29.69” (12)

Peak wind gust (date/direction): N/A

Heating degree days for the month: 893
Cooling degree days for the month:    0

Greatest diurnal range (date):           23.3° (12)
Least diurnal range (date)                   4.8° (8)

Number of days:

Fog                        1
Thunder                0
Cloudy                  14
Partly Cloudy        13
Sunny/Clear          4
Max temp => 70°   0
Min temp =< 32°   17
Max temp =< 32°   6

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