Thursday, October 3, 2019

Weather Overview: Disgusting All-Time Record October Heat -OR- Just Your Typical Globally Warmed, Screwed Up Fall Day in TrumpWorld -- Mixed with Komodo Dragon Pics ... Just Because


OK, let's talk heat, a topic and phenomenon I hate …

… as in, the record October heat set here in the "DMV" -- District (of Columbia), Maryland, and (Northern) Virginia -- and across much of the eastern United States yesterday, October 2nd, 2019 …

For starters, here were the day's record highs at the three main regional airport climate stations:

KDCA: 98F
KBWI: 98F
KIAD: 96F

All of these were October MONTHLY records and easily blew away the daily records (89F at each).

The KDCA and KBWI records surpassed the all-time October records of 96F and 97F, respectively, set on Oct 5, 1941 (both in the pre-airport periods).

The KIAD record surpassed the 94F set on Oct 9, 2007.

Below is a chart showing the nine hottest October days for Washington, D.C. (yes, that October 1941 heat wave was monstrous):


Note: My understanding is that the full D.C. record stretches back to Jan 1, 1871 (see this Sterling LWX webpage) but the CWG references 1872 as the start date.

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Just for book-keeping purposes, the Oct 2nd highs shattered the daily records at the three stations -- all of which happened to be 89F and set in 1986, except the KDCA high was also set in 1881 (pre-airport period).

For reference, the Oct 2nd average high for the 1981 - 2010 base period is 73F at both KDCA and KIAD and 72F at KBWI.

Also, KDMH reached 95F today but it does not yet have a full 30-year data set and the NWS doesn't have records for it.

However, I suspect it was the hottest Oct 2nd in its records stretching back to May 1, 1998.

The NWS Eastern Region office put out this infographic showing the vast number of daily and monthly record highs set across the United States under this hideous heat dome …

Click on image for a larger version.

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As today's CWG entry on the matter notes:

The abnormally hot weather follows what was the third hottest September on record, with 25 of 30 days in the 80s and 90s, and the seventh hottest summer on record (using the June through August definition).

The complete entry is here (with link embedded): Washington soars to 98 degrees, breaking all-time October heat mark.

For September 2019, KDCA's average monthly temperature was 76.5F or +5.5F, which is behind the 77.1F in 1980 and 78.2F in 1881. (The 1881 record seems suspect to me, but it is supported by the Baltimore 1881 records as well.) .

KBWI's average monthly temperature was 73.8F or +6.0F -- tying it with Sept 1900's 73.8F (from the pre-airport record) as the 5th warmest September on record. However, it is the warmest in the period of the (inherently cooler) airport records (i.e., since 1950).

KIAD's average monthly temperature was 72.5F or +4.5F -- and the third warmest behind 1998's 72.7F and 2016's 73.1F and just ahead of last year's 72.4F.

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On the rainfall side for September -- and as part of our sudden "flash drought" following 18 months of tremendous rainfall -- the (measly) 0.14 inches of rain that fell on Monday at KDCA upped its monthly total to 0.25 inches.

This made it the 2nd driest September on record (stretching back to 1871 to include the pre-airport period). Normal September precipitation (1981 - 2010 base period) is 3.72 inches.

KBWI had only "TRACE" on Monday, and its September monthly total was 0.16 inches. This is also the 2nd driest September on record (stretching back to 1871 to include the pre-airport period). Normal September precipitation is 4.03 inches.

KIAD received 0.07 inches on Monday, bringing its monthly total to 0.41 inches.

As with the other two airport stations, this too was the 2nd driest September on record (stretching back to 1960). Normal Sept precipitation is 3.92 inches.

Of note, the above-linked CWG entry had this wonderful tweet issued from the D.C. City Council's Twitter account (and, I'd be willing to bet cash money, by a gay guy on staff):


Yes, it says 61 days -- it should actually be 62 days. That'll just be our little secret.

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The good news is that this current heatwave has come to an end, although rainfall will still be difficult to come by for the time being. At present, a "backdoor cold front" is pushing in from the northeast -- and bringing with it a MUCH cooler maritime airmass.

The Sterling (LWX) area forecast discussion earlier tonight states:

The front will continue into the D.C. metropolitan area Thursday morning. Low clouds and a north-easterly flow will continue through the day Thursday. How far the front makes its way south and southwest will determine where the gradient of temperatures set up. We could see a temperature range from 60 to 90 from northeast to southwest across our CWA.

FYI: "CWA" = "county warning area" (i.e., Sterling's forecast area).

NWS high-resolution surface weather map for a portion of the eastern U.S. as of 0300UTC 03 Oct 2019

You can see the backdoor front on this analysis.

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Another front will cross the region late Thursday -- but, unfortunately, mostly dry. The weekend is forecasted to be sunny to partly cloudy and, believe it or not, below normal temperature-wise on Saturday with highs around 68F.

NCEP/WPC 7-day QPF for the Lower 48 U.S. and southern Canada, valid 0Z 03 Oct 2019 - 0Z 10 Oct 2019

If this verifies, we would get 1/4 to 1/2 inch of rainfall by next Thursday. Typically, it substantially overpredicts.

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Another frontal boundary is progged to approach the region on Monday but it is unclear how quickly it will progress or if there will be any substantial rainfall.

But the fucking 90F heat SHOULD be over for the season.


By the way, what is now post-Tropical Cyclone Lorenzo is racing toward "landfall" in the British Isles. The former hurricane -- which briefly achieved category 5 strength, making it the farthest east and northeast Atlantic basin tropical cyclone to do so -- underwent a recurvature over the middle tropical Atlantic Ocean and is now caught up in the westerlies even while transitioning to an extratropical cyclone. The system was tearing along at 43 mph as of the final NHC update.

Final NHC advisory track for Post-Tropical Cyclone Lorenzo, issued 11 a.m. AST Oct 2, 2019

You don't often see the NHC map showing what was a tropical cyclone making "landfall" on the British Isles -- and after having clipped the Azores.

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Suomi NPP composite image of Hurricane Lorenzo, Sept 30, 2019; Credit: Credit: NASA Worldview, Earth Observing System Data and Information System (EOSDIS)

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Top winds as of the last NHC advisory were at 80 mph -- but tropical storm-force winds extended over an unusually large area as were the large waves it was producing. As NHC advisory 35 issued 11pm AST Monday night stated:

It is also worth mentioning that there will be some enormous seas on the eastern side of Lorenzo. The hurricane will be accelerating to the northeast in the same general direction for a couple of days. Combined with the large size and intensity, this is a recipe for an amplified wave field on the eastern side due to a phenomenon called trapped-wave fetch.

This storm could cause problems in parts of the British Isles -- especially on the west coast of Ireland.

OK, I'm going to end this entry here rather than veering off into other topics including political ones.

Good night.

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--Regulus

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