Saturday, March 18, 2017

Saturday Evening Post for March 18th, 2017: General Weather Update -OR- The Waters of This March and the Past 12 Months

**This entry was posted March 18th, 2017.**

**Updated 12:41AM 3/20/2017: See bottom of entry.**

Camelot River, Fiordland National Park, South Island, New Zealand; source image Duskybay blog.

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Saturday evening.

I intend to post a general update but I want to separate out this weather portion. I'm not feeling that well -- last night really sucked and I wasn't able to get out of the apartment today to go to the gym. I intend to go tomorrow, which is just as well since it's that's a nice way to end the weekend. More on this in the entry to follow.

View from my apartment overlooking 16th and U Streets and New Hampshire Ave NW, Washington, D.C., 7:30PM March 18, 2017.

Yes, it's a blurry image. My cellphone camera is cheap.

The bright, blurry object on the horizon are the LED flood lights on the enormous skyscraper under construction in Rosslyn -- located about 2-1/2 miles from where I live as the crow flies.

That building looks as if it is going to be higher than the 1812 N. Moore skyscraper, which is advertised as the tallest building in the "Greater D.C." area. (Remember, the D.C. building height restriction doesn't apply in Virginia.)

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So let's start with the weather ...

It's an overcast, now showery-rainy evening -- and that's a good thing because it has been so goddamn dry for months and the Baltimore / Washington area and larger Mid-Atlantic region remains locked in a drought with the immediate D.C. area in D2 / severe drought.

Drought monitor for Maryland, Virginia, the District of Columbia, and West Virginia, updated March 14, 2017.

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To be clear, it is mostly light rain associated with a weather system but there are embedded heavier showers. We'll take what we can get.

Recent radar images ...

Sterling (LWX) NWS radar in standard base mode reflectivity, looped between 6:18PM and 7:13PM EDT March 18, 2017.

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Sterling (LWX) NWS radar in standard composite mode, looped between 5:42PM and 7:01PM EDT March 18, 2017.

Those bits of orange and red are showing areas of small hail and/or sleet in the clouds -- not severe weather.

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Here is a portion of the Sterling (LWX) near-term area forecast discussion (AFD) from 2:46PM this afternoon.

.NEAR TERM /THROUGH SUNDAY/...
As expected, showers have developed to our west this afternoon in association with an approaching shortwave and cold front. There have even been a couple thunderstorms near the surface low center, which will move across our southern counties this afternoon. As a result, showers look pretty likely with a chance of thunderstorms. The storms may be vigorous enough to produce small hail, perhaps close to severe-sized hail if a storm gets particularly strong. The window of occurrence looks pretty short -- perhaps 3 to 7 pm, but the convection has had a history of small hail over West Virginia, and we are a little bit warmer / more unstable. Thunder potential should generally be south of the US 48/I-66/US 50 combined corridor.


The shortwave moves across the area, and as mentioned in the morning discussion, energy transfers to an offshore low, leaving an inverted trough behind, followed by the upper low itself. This combination will keep precipitation chances in the eastern half of the forecast area virtually all night. Forecast soundings show precipitation changing over to snow at the tail end of the precip (say after 08z tonight)...but temperatures are at or above freezing and today has been reasonably warm with a lot of sun.

Temperatures do get close to freezing in extreme northeast Maryland -- places like Frederick, Westminster, and northern Baltimore and Harford Counties. I`ve added some light accumulations to these areas (1/2 inch or less, generally), but there's some potential for around an inch of fresh snow there.

Further south in the cities, some flakes may fly late tonight or early Sunday, but it currently looks too warm to accumulate.

Precip quickly ends Sunday morning, even in the upslope region, leaving a partly to mostly cloudy day, and temperatures around 10 degrees cooler than today with a brisk north/northwest wind.

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Looking ahead, the forecast calls for brisk weather for the upcoming week with highs between 45F and 50F a few chances of light rain showers (Monday night, Tuesday night, and Friday).


Below are the latest precipitation numbers for the three main regional NWS climate stations through yesterday, March 17th, 2017. The baseline period is 1981 - 2010. I am omitting the fourth one -- KMDH (Maryland Science Center) -- since it does not yet have a full 30-year normal (average) data set. Keep in mind, as well, that for the D.C. area (as measured at both KDCA and KIAD), precipitation is off by 25 percent for the past 12 months.

KDCA

Precipitation:

Month-to-date: 1.44 inches
Normal: 1.77 inches
Departure: -0.33 inches

Year-to-date: 4.89 inches
Normal: 7.32 inches
Departure: -2.43 inches

Past 12 months (since March 17, 2016)
Observed: 29.60 inches
Departure: -10.20 inches


Normal: 39.80 inches corrected to 39.74 inches.

Note: The 30-year annual average for precipitation at KDCA is 39.74 inches. The total here is off by 0.06 inches but I'm not going to try to figure out why.

MODUS high-resolution image of NECONUS showing extensive snow cover after big nor'easter; March 16, 2017.

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Snow:
Month-do-date: 2.0 inches (+0.9 inches)
Season: 3.4 inches (-11.8 inches)
Season-to-date normal: 15.2 inches
Full seasonal normal: 15.2 inches
(In the average, no more measurable snow falls at KDCA for the remainder of the season.)

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KBWI

Precipitation:

Month-to-date: 1.64 inches
Normal: 2.04 inches
Departure: -0.40 inches

Year-to-date: 5.79 inches
Normal: 7.99 inches
Departure: -2.20 inches.

Past 12 months (since March 17, 2016)
Observed: 36.57 inches
Departure: -5.49 inches

Normal: 42.06 corrected to 41.88 inches

Note: The 30-year annual average for precipitation at KBWI is 41.88 inches. The total here is off by 0.18 inches but I'm not going to try to figure out why.

MODUS high-resolution image of NECONUS focused on the Mid-Atlantic region including the Baltimore / Washington area showing extensive snow cover after big nor'easter; March 16, 2017.

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Snow:
Month-do-date: 2.2 inches (+0.7 inches)
Season: 2.9 inches (-16.8 inches)
Season-to-date normal: 19.7 inches
Full seasonal normal: 20.1 inches
(In the average, another 0.4 inches of snow falls at KBWI for the remainder of the season.)

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KIAD

Precipitation:

Month-to-date: 1.42 inches
Normal: 1.70 inches
Departure: -0.28 inches

Year-to-date: 4.86 inches
Normal: 7.12 inches
Departure: -2.26 inches

Past 12 months (since March 17, 2016)
Observed: 31.18 inches
Departure: -10.38 inches

Normal: 41.56 inches corrected to 41.54 inches

Note: The 30-year annual average for precipitation at KIAD is 41.54 inches. The total here is off by 0.02 inches but I'm not going to try to figure out why.

MODUS high-resolution image of NECONUS focused on southern New England showing extensive snow cover after big nor'easter; March 16, 2017.

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Snow:
Month-do-date: 5.7 inches (+2.0 inches)
Season: 7.3 inches (-13.6 inches)
Season-to-date normal: 20.9 inches
Full seasonal normal: 22.0 inches.
(In the average, another 1.1 inches of snow falls at KIAD for the remainder of the season.)

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This concludes the weather update. I'm going to try to post another entry tonight, but it's already damn near quarter to ten and I'd like to get out of this apartment as soon as my laundry is done. I'm just going to Old Ebbitt -- my standby place.

As for the rainfall tonight so far, it has been distinctly underwhelming with just 0.03" at KDCA and trace at KBWI. KIAD picked up a bit more at 0.15".

UPDATED 12:41AM 3/20/2017

Sterling (LWX) NWS radar in standard base mode reflectivity, looped between 10:13PM and 11:20PM EDT March 18, 2017.

So we ended up getting some relatively decent rainfall on Saturday night into Sunday morning (esp. in the immediate D.C. area), and it ended as a period of mixed rain and snow (which I missed as I was asleep).

Total precipitation (rainfall) amounts were between 1/4" on the low end and almost 2/3" on the high end, so half inch median. In particular, for the event were as follows:

KDCA: 0.63 inches
KBWI: 0.41 inches
KIAD: 0.46 inches
KDMH: 0.23 inches

End of Update and of Entry.

--Regulus

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