Mason Neck State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mason Neck State Park clear sky chart from 2005-11-06 to 2024-03-18.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	14% 5% 2 5% 5% 3 5% 5% 6% 8% 43%	78715
	Night	15% 6% 2 5% 5% 3 4 4 5% 7% 44%	81074
Transparency	Day	38% 6% 12% 23% 17% 3	78426
	Night	39% 6% 11% 23% 17% 4	80882
Seeing	Day	18% 10% 26% 25% 15% 6%	14109
	Night	18% 9% 29% 29% 13% 1	23791

By Month

Percentage Cloud Cover SE (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	17% 5% 2 4 3 2 3 4 5% 7% 49%	2619
	11th to 20th	Day	16% 9% 3 5% 5% 3 4 5% 4 6% 40%	2840
	21st to end	Day	18% 8% 3 5% 6% 3 4 5% 4 6% 38%	3124
February	1st to 10th	Day	15% 6% 3 5% 5% 3 6% 5% 4 7% 40%	1710
	11th to 20th	Day	19% 6% 2 4 4 2 3 4 5% 7% 43%	1723
	21st to end	Day	18% 8% 3 6% 5% 3 4 4 4 6% 39%	1570
March	1st to 10th	Day	14% 6% 2 4 4 3 5% 4 4 7% 49%	2057
	11th to 20th	Day	17% 6% 2 5% 5% 3 4 5% 5% 6% 43%	2058
	21st to end	Day	17% 8% 3 6% 6% 3 5% 4 4 6% 40%	2209
April	1st to 10th	Day	12% 6% 2 4 5% 4 4 4 5% 7% 46%	2160
	11th to 20th	Day	13% 5% 2 4 5% 2 5% 4 4 6% 49%	2134
	21st to end	Day	17% 5% 2 5% 5% 3 4 5% 5% 8% 42%	2160
May	1st to 10th	Day	14% 7% 3 4 4 3 5% 5% 6% 9% 40%	2286
	11th to 20th	Day	17% 6% 2 5% 5% 3 5% 6% 6% 8% 38%	2393
	21st to end	Day	14% 4 3 5% 5% 3 5% 5% 6% 8% 42%	2725
June	1st to 10th	Day	11% 4 2 5% 5% 3 5% 5% 6% 10% 45%	2520
	11th to 20th	Day	10% 5% 2 6% 5% 3 6% 5% 6% 10% 43%	2520
	21st to end	Day	9% 3 1 5% 5% 3 6% 6% 8% 10% 44%	2520
July	1st to 10th	Day	9% 5% 2 6% 5% 4 5% 6% 7% 10% 43%	2520
	11th to 20th	Day	5% 3 2 4 5% 3 7% 6% 8% 11% 46%	2423
	21st to end	Day	8% 4 3 5% 5% 4 7% 6% 9% 10% 38%	2547
August	1st to 10th	Day	8% 6% 2 5% 6% 4 7% 6% 8% 9% 38%	2327
	11th to 20th	Day	11% 3 2 5% 5% 4 6% 6% 7% 9% 40%	2201
	21st to end	Day	10% 4 3 4 5% 4 6% 6% 7% 9% 43%	2376
September	1st to 10th	Day	14% 4 3 4 5% 3 5% 5% 4 7% 46%	2160
	11th to 20th	Day	11% 5% 2 4 4 3 4 4 6% 8% 50%	2160
	21st to end	Day	18% 6% 3 5% 5% 2 5% 4 5% 7% 39%	1893
October	1st to 10th	Day	17% 4 2 4 4 2 4 4 5% 6% 48%	1800
	11th to 20th	Day	17% 4 2 4 3 2 4 3 5% 6% 50%	1800
	21st to end	Day	15% 5% 2 5% 4 3 3 4 5% 7% 48%	1980
November	1st to 10th	Day	12% 5% 1 3 3 3 4 3 5% 7% 53%	1772
	11th to 20th	Day	14% 5% 1 4 2 2 4 4 5% 6% 52%	1706
	21st to end	Day	16% 4 2 5% 3 3 3 5% 5% 5% 49%	1520
December	1st to 10th	Day	16% 5% 3 6% 4 3 5% 4 5% 7% 42%	1520
	11th to 20th	Day	16% 6% 2 4 4 2 4 4 4 6% 47%	1910
	21st to end	Day	17% 7% 3 5% 5% 3 5% 5% 6% 8% 37%	2772
January	1st to 10th	Night	15% 7% 2 5% 4 3 4 4 4 6% 47%	4324
	11th to 20th	Night	17% 7% 2 4 4 2 3 4 3 6% 46%	4120
	21st to end	Night	18% 9% 3 5% 5% 2 3 3 4 5% 42%	4532
February	1st to 10th	Night	15% 7% 2 4 5% 3 4 4 5% 7% 43%	2470
	11th to 20th	Night	20% 6% 2 5% 4 2 4 3 4 5% 44%	2342
	21st to end	Night	17% 8% 3 4 4 2 3 3 5% 6% 43%	1884
March	1st to 10th	Night	15% 5% 2 5% 5% 2 4 4 5% 5% 48%	2120
	11th to 20th	Night	18% 6% 2 4 4 2 4 4 5% 8% 43%	2068
	21st to end	Night	16% 6% 3 6% 5% 3 4 5% 5% 7% 42%	2146
April	1st to 10th	Night	15% 7% 2 6% 6% 2 5% 4 5% 7% 42%	1800
	11th to 20th	Night	13% 5% 2 5% 5% 2 5% 4 5% 7% 49%	1775
	21st to end	Night	18% 5% 2 3 4 3 4 6% 5% 7% 43%	1800
May	1st to 10th	Night	15% 7% 2 6% 5% 3 5% 5% 6% 8% 40%	1690
	11th to 20th	Night	15% 7% 3 5% 6% 3 4 4 6% 8% 39%	1497
	21st to end	Night	13% 5% 3 3 5% 4 5% 4 7% 10% 40%	1550
June	1st to 10th	Night	11% 5% 2 4 4 3 5% 5% 8% 10% 44%	1440
	11th to 20th	Night	12% 6% 3 5% 4 3 5% 5% 7% 9% 41%	1440
	21st to end	Night	10% 4 2 5% 5% 3 6% 6% 7% 9% 43%	1440
July	1st to 10th	Night	9% 5% 3 6% 5% 3 6% 6% 7% 9% 41%	1440
	11th to 20th	Night	6% 5% 2 5% 5% 3 5% 7% 7% 10% 46%	1533
	21st to end	Night	7% 4 2 5% 6% 4 6% 6% 8% 11% 40%	1771
August	1st to 10th	Night	9% 4 2 6% 6% 4 5% 6% 8% 11% 40%	1611
	11th to 20th	Night	11% 6% 3 6% 6% 4 5% 6% 6% 9% 37%	1680
	21st to end	Night	10% 6% 3 6% 5% 3 5% 6% 5% 10% 42%	1980
September	1st to 10th	Night	14% 6% 2 4 4 3 5% 4 6% 7% 44%	1800
	11th to 20th	Night	10% 5% 2 5% 4 3 4 4 6% 9% 49%	1800
	21st to end	Night	17% 7% 3 6% 5% 2 4 5% 5% 7% 39%	2061
October	1st to 10th	Night	18% 6% 2 4 4 3 3 4 4 7% 45%	2160
	11th to 20th	Night	17% 4 2 5% 3 3 3 3 4 5% 50%	2160
	21st to end	Night	15% 4 2 5% 4 2 4 4 5% 7% 48%	2376
November	1st to 10th	Night	13% 4 3 4 3 2 4 4 3 6% 53%	2304
	11th to 20th	Night	15% 5% 2 4 3 2 3 3 4 6% 50%	2471
	21st to end	Night	13% 4 2 4 4 3 4 5% 5% 7% 50%	2660
December	1st to 10th	Night	17% 7% 3 5% 5% 2 4 4 5% 6% 42%	2660
	11th to 20th	Night	18% 5% 2 4 5% 3 4 4 5% 7% 44%	3285
	21st to end	Night	17% 7% 2 6% 5% 4 5% 5% 6% 8% 36%	4884

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	36% 4 9% 32% 16% 4	2620
	11th to 20th	Day	46% 3 10% 20% 16% 6%	2840
	21st to end	Day	48% 5% 10% 22% 13% 3	3124
February	1st to 10th	Day	44% 5% 11% 25% 13% 2	1710
	11th to 20th	Day	42% 5% 8% 24% 18% 4	1732
	21st to end	Day	46% 6% 12% 16% 17% 4	1570
March	1st to 10th	Day	36% 5% 11% 24% 20% 3	2057
	11th to 20th	Day	42% 5% 9% 19% 18% 7%	2058
	21st to end	Day	45% 6% 10% 18% 17% 4	2209
April	1st to 10th	Day	37% 6% 11% 20% 20% 6%	2160
	11th to 20th	Day	36% 5% 10% 21% 21% 7%	2134
	21st to end	Day	41% 7% 10% 21% 16% 5%	2160
May	1st to 10th	Day	39% 8% 13% 20% 17% 2	2286
	11th to 20th	Day	42% 8% 13% 21% 14% 2	2397
	21st to end	Day	38% 9% 13% 26% 12% 2	2725
June	1st to 10th	Day	34% 7% 15% 26% 16% 1	2520
	11th to 20th	Day	36% 8% 13% 24% 16% 2	2520
	21st to end	Day	31% 10% 15% 25% 17% 2	2520
July	1st to 10th	Day	36% 9% 14% 22% 16% 4	2450
	11th to 20th	Day	30% 10% 16% 26% 16% 3	2349
	21st to end	Day	36% 10% 15% 20% 18% 1	2405
August	1st to 10th	Day	39% 9% 14% 25% 12% 1	2314
	11th to 20th	Day	38% 9% 14% 22% 14% 1	2201
	21st to end	Day	35% 8% 15% 24% 14% 4	2376
September	1st to 10th	Day	37% 6% 14% 19% 19% 4	2160
	11th to 20th	Day	32% 6% 10% 27% 21% 4	2160
	21st to end	Day	44% 5% 10% 20% 19% 2	1893
October	1st to 10th	Day	37% 6% 9% 26% 18% 3	1800
	11th to 20th	Day	36% 4 9% 26% 21% 3	1800
	21st to end	Day	36% 4 9% 25% 23% 4	1980
November	1st to 10th	Day	32% 5% 11% 27% 21% 5%	1772
	11th to 20th	Day	33% 5% 10% 24% 21% 6%	1706
	21st to end	Day	37% 4 11% 27% 19% 3	1520
December	1st to 10th	Day	42% 5% 12% 26% 13% 3	1520
	11th to 20th	Day	38% 5% 9% 31% 13% 4	1906
	21st to end	Day	44% 6% 13% 25% 12% 1	2772
January	1st to 10th	Night	39% 3 9% 25% 19% 4	4324
	11th to 20th	Night	40% 3 9% 23% 20% 4	4120
	21st to end	Night	45% 3 8% 26% 17% 2	4532
February	1st to 10th	Night	42% 5% 11% 25% 16% 2	2470
	11th to 20th	Night	44% 3 7% 22% 18% 6%	2344
	21st to end	Night	42% 4 11% 21% 16% 5%	1884
March	1st to 10th	Night	38% 4 9% 25% 20% 3	2120
	11th to 20th	Night	40% 6% 10% 21% 19% 4	2068
	21st to end	Night	42% 6% 9% 21% 16% 6%	2146
April	1st to 10th	Night	41% 5% 9% 18% 22% 4	1800
	11th to 20th	Night	36% 5% 11% 20% 21% 6%	1775
	21st to end	Night	40% 7% 10% 25% 14% 6%	1800
May	1st to 10th	Night	42% 7% 12% 20% 15% 4	1690
	11th to 20th	Night	43% 7% 12% 19% 16% 2	1498
	21st to end	Night	38% 9% 16% 23% 13% 1	1551
June	1st to 10th	Night	35% 9% 12% 27% 16% 2	1440
	11th to 20th	Night	38% 9% 15% 22% 14% 3	1440
	21st to end	Night	34% 9% 15% 20% 19% 3	1440
July	1st to 10th	Night	37% 10% 16% 19% 13% 4	1400
	11th to 20th	Night	31% 10% 17% 24% 17% 2	1484
	21st to end	Night	33% 9% 17% 26% 15% 1	1672
August	1st to 10th	Night	36% 11% 16% 22% 14% 1	1600
	11th to 20th	Night	41% 10% 14% 21% 13% 2	1680
	21st to end	Night	38% 8% 13% 24% 15% 3	1980
September	1st to 10th	Night	38% 7% 12% 20% 17% 6%	1800
	11th to 20th	Night	32% 7% 9% 26% 22% 4	1800
	21st to end	Night	43% 6% 11% 19% 17% 4	2061
October	1st to 10th	Night	40% 5% 9% 23% 19% 4	2160
	11th to 20th	Night	37% 5% 8% 25% 22% 4	2160
	21st to end	Night	36% 5% 9% 24% 22% 4	2376
November	1st to 10th	Night	34% 4 9% 26% 21% 7%	2304
	11th to 20th	Night	36% 4 8% 22% 23% 7%	2471
	21st to end	Night	34% 5% 10% 26% 21% 4	2660
December	1st to 10th	Night	43% 5% 10% 24% 15% 3	2660
	11th to 20th	Night	40% 4 10% 23% 18% 4	3288
	21st to end	Night	44% 7% 15% 21% 12% 1	4884

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	25% 19% 32% 18% 5%	211
	11th to 20th	Day	26% 26% 28% 17% 4	270
	21st to end	Day	21% 19% 36% 15% 8%	297
February	1st to 10th	Day	23% 19% 39% 15% 4 1	270
	11th to 20th	Day	30% 21% 35% 13% 1	330
	21st to end	Day	28% 19% 31% 20% 3	382
March	1st to 10th	Day	22% 20% 31% 21% 5%	460
	11th to 20th	Day	25% 18% 31% 18% 6% 1	449
	21st to end	Day	21% 18% 31% 23% 5% 2	462
April	1st to 10th	Day	21% 16% 31% 23% 7% 1	420
	11th to 20th	Day	16% 16% 29% 21% 13% 4	412
	21st to end	Day	24% 13% 30% 25% 7% 2	420
May	1st to 10th	Day	23% 13% 28% 19% 14% 3	423
	11th to 20th	Day	19% 10% 31% 24% 14% 3	447
	21st to end	Day	20% 4 22% 26% 21% 8%	485
June	1st to 10th	Day	13% 5% 27% 25% 23% 7%	450
	11th to 20th	Day	13% 7% 24% 30% 19% 8%	450
	21st to end	Day	10% 3 25% 35% 20% 7%	450
July	1st to 10th	Day	12% 3 15% 32% 26% 13%	445
	11th to 20th	Day	4 1 14% 36% 31% 14%	444
	21st to end	Day	10% 2 19% 33% 25% 11%	488
August	1st to 10th	Day	11% 4 14% 29% 31% 10%	446
	11th to 20th	Day	13% 3 16% 27% 29% 12%	439
	21st to end	Day	9% 2 19% 30% 25% 15%	495
September	1st to 10th	Day	15% 4 20% 23% 21% 17%	450
	11th to 20th	Day	12% 6% 16% 33% 22% 12%	450
	21st to end	Day	23% 9% 23% 27% 13% 4	450
October	1st to 10th	Day	21% 5% 21% 26% 19% 9%	450
	11th to 20th	Day	16% 11% 26% 29% 15% 3	450
	21st to end	Day	17% 11% 34% 26% 9% 3	495
November	1st to 10th	Day	17% 10% 28% 28% 14% 3	415
	11th to 20th	Day	18% 12% 34% 25% 10% 1	366
	21st to end	Day	21% 18% 29% 22% 10% 1	180
December	1st to 10th	Day	18% 12% 44% 18% 6% 2	180
	11th to 20th	Day	23% 15% 32% 22% 6% 1	180
	21st to end	Day	26% 12% 33% 22% 7% 1	198
January	1st to 10th	Night	21% 17% 39% 20% 3	760
	11th to 20th	Night	22% 13% 35% 25% 5%	760
	21st to end	Night	22% 14% 39% 23% 2	836
February	1st to 10th	Night	20% 13% 36% 27% 4	760
	11th to 20th	Night	25% 17% 40% 16% 2	743
	21st to end	Night	25% 16% 33% 22% 3	628
March	1st to 10th	Night	21% 13% 40% 24% 3	760
	11th to 20th	Night	22% 13% 38% 21% 6% 1	752
	21st to end	Night	18% 13% 38% 26% 4 1	792
April	1st to 10th	Night	18% 16% 38% 24% 4	720
	11th to 20th	Night	15% 12% 33% 31% 9%	711
	21st to end	Night	21% 7% 33% 31% 9%	720
May	1st to 10th	Night	18% 10% 31% 28% 12% 1	610
	11th to 20th	Night	18% 5% 28% 35% 13% 1	436
	21st to end	Night	16% 3 18% 40% 21% 1	389
June	1st to 10th	Night	10% 3 23% 41% 21% 3	360
	11th to 20th	Night	14% 4 20% 38% 23% 1	360
	21st to end	Night	10% 2 22% 46% 18% 2	360
July	1st to 10th	Night	9% 2 17% 39% 29% 3	350
	11th to 20th	Night	8% 2 11% 37% 38% 5%	440
	21st to end	Night	8% 2 16% 37% 33% 3	591
August	1st to 10th	Night	9% 1 13% 40% 32% 4	537
	11th to 20th	Night	13% 3 16% 38% 28% 3	616
	21st to end	Night	12% 2 14% 35% 30% 6%	792
September	1st to 10th	Night	16% 2 16% 32% 30% 4	720
	11th to 20th	Night	11% 3 15% 37% 30% 3	720
	21st to end	Night	21% 4 22% 32% 20% 1	720
October	1st to 10th	Night	21% 5% 21% 29% 21% 4	720
	11th to 20th	Night	17% 8% 27% 31% 17% 1	720
	21st to end	Night	18% 9% 31% 27% 14% 1	792
November	1st to 10th	Night	15% 8% 32% 30% 12% 2	740
	11th to 20th	Night	18% 12% 31% 29% 10%	760
	21st to end	Night	16% 14% 32% 28% 10% 1	760
December	1st to 10th	Night	21% 11% 34% 25% 8% 1	760
	11th to 20th	Night	18% 10% 41% 26% 5%	760
	21st to end	Night	20% 11% 33% 32% 4	836

Page generated at 2024-03-15 14:01:41. Version ac07

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