Sunday, June 21, 2015

Overview of Yesterday's June Monsoon Regional Rainfall Totals; Suddenly, Summer -OR- Vertical Sun Beams on the Tropic of Cancer

The Georgetown Branch (or "Future Capital Crescent") Trail, Silver Spring, Md., 3:56PM June 14, 2015.

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The first day of astronomical summer. The summer solstice. It arrived / occurred at 12:38PM EDT. More on that below.

NWS radar estimated precipitation for the extended Baltimore/Washington area of the mid-Atlantic region, 15Z June 20 - 15Z June 21, 2015.

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First, though, here is an overview of the official rainfall totals from last night's drenching, noisy thunderstorms. The totals are through midnight as taken from the Sterling LWX climate page. Looking at the hourly observations, it appears that another 0.03 to 0.09 inches fell at the four main climate stations (KDCA, KBWI, KIAD, and KDMH).

National Airport (KDCA) had the jackpot.

Here are the totals. Note the comparison to last year through June 20th:

KDCA

6/20: 2.33" (daily record) (old record: 1.35" - 1983)

Month-to-date: 7.79" +5.27" (2.52")

Year-to-date: 22.57" +4.09" (18.48")

Last year-to-date: 25.06"

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KBWI

6/20: 1.76" (record: 2.45" - 1962)

Month-to-date: 8.02" +5.65" (2.37")

Year-to-date: 25.22" +5.82" (19.40")

Last year-to-date: 26.78"

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KIAD
6/20: 1.11" (record: 1.20" - 1963)
Month-to-date: 4.44" +1.73" (2.71")
Year-to-date: 18.30" -1.23" (19.53")
Last year-to-date: 28.82"

KDMH
6/20: 1.09"
Month-to-date: 2.97" +0.74" (2.23")
Year-to-date: 19.31" +0.99" (18.32")
Last year-to-date: 29.30"

Note: KDMH (Maryland Science Center) does not yet have a full 30-year "normal" climate record. The averages and departures are based upon its existing record of approx. 25 years.

As for the storms, while there were power outages, esp. in the suburbs, and some localized flooding, it doesn't look like they caused any major damage. See this WaHoPo article.

Of note, other climate stations in the Sterling LWX county warning (forecast) area (CW(F)A) had a lot less.

Charlottesville (KCHO) had only 0.28" while Martinsburg (KMRB) had 0.74" and Hagerstown (KHGR() had 0.73". As for Hagerstown (as measured at the airport), only 13.22" of precip has fallen this year so far or -5.95" and nearly a foot less than KDCA.

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Suddenly, Summer ...

Today is the first day of astronomical summer. It was at 12:38PM EDT -- or 11:38AM EST (i.e., true "sun time" as opposed to the bullshit construct of daylight savings time) -- that the midpoint of the solar disk touched the Tropic of Cancer at 23.5N latitude.

Look at this this year, if I have figured it out correctly, it occurred in the Eastern Time Zone itself, 22 minutes before local noon on the 75W meridian (the theoretical middle meridian of this entire time zone -- i.e., the meridian at which "local noon" corresponds to noon for the entire time zone). The Sun transits 15 degrees of longitude per hour (the theoretical width of every time zone), so 22 minutes works out to be 5.5 degrees east of it at 69.5W longitude at 23.5N latitude.

CORRECTION / UPDATED:

In my initial version of this entry, I was thinking Tropic of Cancer (#correct) but then placed the Sun over the Equator (#wrong!). This paragraph is corrected.


This puts the actual solstice event in the far western portion of the Brazilian state of Amazonas near the Colombian border over the Atlantic Ocean just to the northeast of the Turks and Caicos Islands.

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It is "astronomical" summer because it is based on the position of the Sun in the sky and marks the arrival of the summer season -- i.e., that period when the Sun transits from the Tropic of Cancer to the Equator.

It should not be confused with "climatological" summer, which arrived at the more statistically convenient breakpoint of June 1st. (All "climatological" seasons start at these convenient break points -- i.e., June 1st (summer), Sept. 1st (fall/autumn), Dec. 1st (winter), and March 1st (spring).)

Schematic of the solstices and equinoxes showing the Earth and Sun and corrected for a mistake on the date of aphelion (it's around July 4th); the image sideways in order to post a larger version of it.

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There is a Capital Weather Gang entry (re)posted today discussing some interesting facts about the summer solstice (link embedded): First official day of summer: Questions and answers about the year's longest day.

Hours of daylight between sunrise and sunset on the summer solstice across the United States; image by Brian Brettschneider.

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Hours of daylight and twilight combined on the summer solstice across the United States; image by Brian Brettschneider.

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What's slightly annoying about this otherwise interesting entry is that it fails to mention that the latest sunsets and earliest sunrises are offset from the summer (and winter) solstice(s) (in reverse order). True, CWG has covered this topic before but that is immaterial to THIS entry and it should have at least had an explicit sentence on this topic with link.

This omission was mentioned in the comment section, but comment sections are to be avoided at all costs. (Actually, the CWG comment section is quite a friendly place and any less-than-totally-upbeat and happy ones are not appreciated. It's the Washington Weather Consensus, sort of an old-school Georgetown or McLean dinner party -- THUMBS UP! -- rather than a descent into a Yahoo News or rightwing alternate reality news / opinion site comment section Dante's Inferno.

Hours of daylight versus latitude versus ay of the year (non-leap years); image sideways for resolution purposes.

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North Cornerstone of the District of Columbia off East-West Hwy, Silver Spring, Md., 3:42PM June 14, 2015.

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As the briefest of updates ...

I went to dinner last night at Trio and then over to Larry's Lounge. It was the usual show there of all kinds of people. I have a complicated relationship with that place and do not go as often as I used to. Gunther put on the movie The Karate Kid (muted but with closed-caption) on one of the TVs.

Let me just say that I have avoided that movie for 30 years (since it first came out). I watched about half of it before getting distracted.

There is a lot more I could write but I really do want to take a bike ride today rather than frickin' blogging all day, so I am signing off now. I'm not sure where to go -- either the Maryland side and involving Bethesda and the Capital Crescent Trail or perhaps in Virginia.

Yours truly touching (again) the North Cornerstone of the District of Columbia off East-West Highway in Silver Spring, Md., 3:41PM June 14, 2015.

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My next planned update will be late Monday / early Tuesday.

--Regulus

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