Tuesday, May 2, 2017

Springtime in Washington, D.C., Disunited States of Trump 2017: The Record Heat and Humidity of April Recapped; Outook for a May Cool Snap

Fair weather cumulus humilis clouds (or maybe just cumulus fractus?) clouds in a clean, clear blue sky as seen in the 2100 block of 13th Street NW, Washington, D.C., 12:17PM May 2, 2017.

I was walking to the U Street/Cardozo Metro to head to work -- but I detoured over to W and 14th to go to the Bank Ho America ATM.

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This is the entry that I started last night but could not finish given the very late (or rather, very early) hour. However, I've adjusted it markedly, and it focuses just on the weather -- and does not have any of the Sunday picture I intend to post.

Pretty yellow flowers and a birdbath, 1433 W Street NW, Washington, D.C., 12:11PM May 2, 2017.

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So after another spell of inappropriately out-of-season hot and humid weather -- which pushed the April temperature departures to record warmest (see discussion below) -- a cold front blew through last night, and while that has ushered in noticeably drier (if not yet all-that-much cooler air), it did so in the usual way in which all the frickin' dynamics instantly sheared away from the Baltimore / Washington region-- and we were left with a few rain showers that dropped, like, one-quadrillionth of an inch of rain.

OK, the actual numbers for May 1st were:

KDCA: Trace (screw you)

KBWI: 0.01"

KIAD: 0.24"

KDMH: 0.00"

This is the same weather system that brought days and days of torrential rains and tornadic storms to the mid-Mississippi River valley and a late season blizzard to western Kansas.

No, I didn't want floods or tornadoes, but I also can't stand the fact that we get no "weather" here except endless record warmth. Rather, that the Trump-worshipping Red State flyover country is always battered by monstrous weather while the mid-Atlantic gets zilch -- other than record heat -- is just annoying.

The top 10 1-day average temperatures for the month of April for Washington, D.C., as found by taking the mean of the daily high and daily low. The 80.5F on April 29th, 2017 as measured at KDCA -- based on a daily high of 91F and morning low of 70F -- tied for the highest ever recorded for April in Washington, D.C., in the climate record period back to 1872.

The two previous occurrences -- April 20, 1941 and April 19, 1896 -- are from the pre-National Airport record when readings were kept in the District proper at 24th and M Street NW.

Of note, the 91F was a daily record high and the 70F was not just a daily record high minimum (high low), but the warmest low ever in the month of April -- something that is more typically seen in August.

And just FYI, the April all-time record high of 95F set on four previous occasions was not breached.)

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April temperature anomalies (in degrees Fahrenheit [⁰F]) for the Lower 48 CONUS in a map created by CommodityWx.com. (CWG blogger Matt Rogers heads CommodityWx.com.)

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So for April at KDCA, the average temp was 63.8⁰F or +7.0⁰F above the 30-year normal of 56.8⁰F -- which makes this the warmest April on record. The CWG had this entry about it: Washington posts warmest April on record, and 2017 is off to warmest start.

The warm weather records for Washington, D.C., continue their relentless march ...

Washington, D.C., warm weather records for the period 2010 - 2017 (through April 29th).

This is happening in many places around the world, most notably the sub-Arctic and middle latitudes. Indeed, Greenland is still melting like crazy and the Arctic is losing its summertime ice cap. These changes are why we keep getting more "transient" episodes in which the wintertime polar vortex is displaced from its polar source region.

Melting Greenland ...

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This follows, of course, the warmest February on record herein D.C. -- and a March that managed to be both simultaneously a bit above normal (+0.4⁰F at 47.2⁰F) and yet cooler in absolute terms than February (+8.7⁰F at 47.7⁰F).

Given the big cool down forecasted for the next week to ten days, maybe May will manage the same feat.

The 0Z May 2, 2017 ECMWF ("European") model showing the 5-day mean 850-hPa (850-mb) temperature anomaly (in degrees Celsius [⁰C]) for the period 0Z May 7th through 0Z May 12th, 2017 over a portion of North America (as prettied up by WeatherBell.com).

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Looking ahead, there is now talk about much cooler weather and a rainy spell later this week into the weekend, but I'm going to call Trumpelstiltskin fake news / bullshit on the wet part. (I'm happy to be wrong here.)

Yesterday's Global Ensemble Forecast System (GEFS) ensemble model run for 2-meter high and low temperature (converted into degrees Fahrenheit [⁰F]) at KDCA for the period May 1 - 16, 2017.

I can say that the KDCA actual high of 84⁰F on May 1st and 80⁰F today (May 2nd) surpassed the GEFS by 4⁰F and 5⁰F, respectively. Let me put on my surprised face.

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The significantly cooler-than-normal weather is anticipated as a result of a high-latitude blocking pattern sets up over Greenland -- the sort of pattern that would be ideal for a cold, snowy pattern in mid-winter (not May).

Animated loop of the daily 500-hPa (500-mb) geopotential height anomalies* for the period May 5 - 11, 2017 over a portion of North America (as prettied up by WeatherBell.com).

*To be clear, I think this is the 500-mb geopotential height anomalies -- the CWG entry from which I took this animated image (see bottom of this post) wasn't clear on that. Also, this "bowling ball" 500-mb low is not the polar vortex itself -- it's really too late in the season for that, anyway.

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In addition to the record warmth of April here in D.C., it also featured some of the most humid conditions for any April on record. As explained in this CWG entry:

"With an air temperature of 90 and dew point of 70 degrees at 3 p.m. Saturday, the heat index -- how hot it feels factoring in humidity -- surged to 96 degrees. On Sunday morning, the dew point, which is a measure of humidity, reached 72 degrees. This tied the highest dew point observed in April, dating to 1936:

List of the highest dew points (in degrees Fahrenheit [⁰F]) in Washington, D.C., since 1936 -- and as recorded at Reagan Washington National Airport (KDCA) since August 1945. This list does not include the 72⁰F reached April 30, 2017 -- a reading that ties the highest-ever April KDCA dew point set on April 19, 2002.

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The steamy weekend weather placed an exclamation mark on what was Washington's warmest April in recorded history."

Color-coded plot of 500-mb geopotential heights over the North Atlantic and Greenland for May 9, 2017 in a recent run of the operational GFS, as prettied up by WeatherBell.com.

This shows a highly negative North Atlantic Oscillation (NAO).

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The CWG entry on the upcoming cool spell is available here: Big chill to invade eastern U.S. this weekend, and it may get stuck.


OK, that's all for now. Tonight is a non-gym night, and while I'll stop to get some dinner and a drink, I intend to be home watching my usual trio of old sitcoms. I'm unsure if I'll be able to post a new entry tonight or tomorrow night.

--Regulus

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