Monday, October 1, 2018

September in the Rain and Wet 2018 So Far: KDCA, KBWI, KIAD, & KDMH Summary Precip Statistics Year-to-Date Through 9/30/2018

**Entry updated 10:59 p.m. 10/2/2018: See below.**

Bright, warm, early autumn day, 12th and U Street NW, Washington, D.C., 12:37 p.m. Oct 2, 2018

I had gone to the Pivot place on U Street (only accessible, though, off 12th Street, I discovered) for a physical therapy session for my left shoulder, and was heading to the Metro to go to work.

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An elephant ear plant (or whatever it's really called) on a rainy evening, 25th St NW, Georgetown, Washington D.C., 6:24 p.m. Sept 23, 2018

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I had intended to post entry yesterday (Oct. 1st), and I even cheated on the calendar date by momentarily posting a shell of an entry just before midnight last night. You'll note the lead picture was taken after the entry's time stamp. That's because I actually posted the entry mid-afternoon on Oct. 2nd.

This entry is an overview of the regional rainfall and temperature stats through the end of September. That is, it ends on Sept 30th with no October numbers.

Note 1: Except for KDMH (the Maryland Science Center), the normal base period is 1981 - 2010. For KDMH, it is a partial base period beginning May 1, 1998 following the ASOS station commissioning.

Note 2: The term "seasonal" refers to climatological fall, which began Sept 1, as opposed to astronomical (seasonal) fall. For that reason, during September, monthly and seasonal are identical.

KDCA
Month-to-date: 9.73" +6.01" (normal 3.72")
Season-to-date: 9.73" +6.01" (normal 3.72")
Year-to-date: 49.83" +19.71" (normal 30.12")

How frickin' annoying is this -- but so characteristic of KDCA: Missing the 50-inch mark by 0.17" despite the fact it rained so much up until the 29th and missing the 10-inch mark for the month. In any event, this September ends up the 5th wettest September on record.


Top 10 rainiest Septembers in Washington, D.C., 1871 - 2018

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Of note, September 1945 was both the wettest September and wettest month ever in the historical period for D.C. back to Jan 1871 to include the pre-National Airport period. Also, my (quick) review of the D.C. monthly precipitation totals back to Jan 1871 indicates that Sept 2018 ties with July 2018 -- when 9.73 inches was also fell KDCA -- for the 18th wettest month ever.

Both July and Sept 2018 also tie for the second closest precipitation totals to the 10-inch mark for any month without actually reaching or surpassing it.

That is, only one month -- 9.97 inches in July 2013 -- was closer to the 10-inch mark without at least reaching it. In all, there were 16 months that had totals of 10.00 inches or greater. What's more, 6 of occurred in 1900 or earlier and 9 occurred before 1945, the year the KDCA became the official observation post.

About that, I've never been sure of the precise day that KDCA replaced the weather observation post at 24th and M St NW to become the official spot. I think KDCA was up and running by mid-1941, but that doesn't mean it has become the "official" spot.


That could have been as a late as Aug 1945 (when World War II ended??), which would put the 11.06-inch total in July 1945 in the pre-airport record and increase the number of 10+ inch months to 10 in the pre-airport period.)


Precipitation information source here. (It was last updated in April 2018.) To be clear, I may have missed a month -- I was scanning at these numbers quickly.

"The swampiest" part in that entry refers to the fact that it was also quite warm -- tying Sept 2018 for the fifth warmest on record at 75.5F. Of the other top 10 warmest Septembers, everyone of them except 2010 was drier than normal (and in couple cases, very dry):

1881: 78.2F / 2.19"
1980: 77.1F / 1.90"
1930: 76.0F / 0.76"
2016: 76.0F / 2.50"
2018: 75.5F / 9.73"
2010: 75.5F / 6.02"
1998: 75.4F / 1.83"
1970: 75.0F / 1.57"
2005: 75.0F / 0.11"
2015: 74.9F / 2.15"

One last bit of commentary for KDCA's weather records because, well, why not??

As background, the all-time wettest year is 61.33 inches set in the pre-airport period of 1889 and the second wettest is 60.83 inches in 2003.

There isn't the SLIGHEST chance that KDCA will surpass either of these tallies. Instead, it will bump up against the 60.83 total -- and then suddenly it will get totally dry for the last two weeks of the year. If it remains wet, then expect to the "tipping bucket" rain gauge at the airport to mysteriously stop tipping or have some other malfunction. The only records KDCA is ever permitted to hit in the current time is overnight record warm minima.

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As for the other three main regional ASOS spots:

KBWI
Month-to-date: 9.19" +5.16" (normal 4.03")
Season-to-date: 9.19" +5.16" (normal 4.03")
Year-to-date: 54.45" +22.57" (normal 31.88")

Through Sept 30th, KBWI is already up to its 8th wettest full year ever. This includes the pre-airport period back to Jan 1871. The wettest ever is 62.66 inches in 2003. Source here.

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KIAD
Month-to-date: 7.36" +3.44" (normal 3.92")
Season-to-date: 7.36" +3.44" (normal 3.92")
Year-to-date: 50.62" +18.70" (normal 31.92")

KIAD is already as of today at its 6th wettest full year ever. Its full record period stretches intermittently to April 1960 with continuous records starting in Jan 1964.

The wettest year ever for KIAD is 65.69 inches in 2003. Also, 2003 is the only year that KIAD ever surpassed the 60-inch mark. Source here.

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KDMH
Month-to-date: 10.47" +6.38" (normal 4.09")
Season-to-date: 10.47" +6.38" (normal 4.09")
Year-to-date: 52.71" +21.25" (normal 31.46")

The KDMH station was commissioned on April 30, 1998 -- which means that official-record keeping began May 1, 1998.

The first 30-year base period for KDMH will be 2001 - 2030, which won't be issued until early-to-mid 2031. Also, because the NWS hasn't yet posted a monthly precipitation file for it, I don't have any sense of where this 10.47-inch figure ranks. It is a touch higher than the 10.20-inch total in July 2018.

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Updated 10:59 p.m. 10/2/2018

I'm updating this entry to include the following map with explanation …


The map directly above is from Iowa Environmental Mesonet and adapted by the CWG in this entry by Angela Fritz. It shows the Sept 2018 mean overnight low temperature rankings for various climate regions of the U.S. Lower 48 compared to all Septembers between 1893 and 2018. In this way, "1" indicates Sept 2018 was the warmest September for average overnight lows in the 126-year period.

One minor item: I'm unsure about the specifics of the climate regions since they don't match exactly those of the NWS.

End of Update.

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The Northumberland, 2000 block New Hampshire Ave NW, Washington, D.C., 1:30 p.m. Oct 1, 2018

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My plan is to go the gym again tonight and then try to post an entry once I'm home. I had intended to do that last night but ended up watching MeTV reruns and making dinner and then going to bed around 1 am.

--Regulus

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