W. Armitage Memorial Dark Sky Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the W. Armitage Memorial Dark Sky Site clear sky chart from 2005-11-06 to 2024-11-05.

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	18% 12% 4 10% 5% 5% 4 4 5% 6% 27%	101836
	Night	17% 14% 5% 10% 6% 5% 4 3 5% 5% 26%	97172
Transparency	Day	59% 3 10% 19% 9% 1	105319
	Night	61% 3 10% 17% 8% 1	101778
Seeing	Day	27% 13% 31% 19% 7% 2	14532
	Night	27% 11% 28% 24% 9% 1	23347

By Month

Percentage Cloud Cover NE (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	15% 19% 8% 17% 9% 4 5% 3 3 5% 12%	2517
	11th to 20th	Day	13% 15% 6% 20% 9% 6% 3 3 4 4 16%	2520
	21st to end	Day	12% 20% 10% 15% 5% 5% 5% 3 5% 4 15%	2815
February	1st to 10th	Day	9% 19% 7% 14% 9% 7% 4 4 4 6% 17%	1710
	11th to 20th	Day	12% 18% 6% 15% 8% 5% 4 3 4 5% 20%	1663
	21st to end	Day	16% 20% 6% 10% 5% 5% 5% 3 5% 4 21%	1522
March	1st to 10th	Day	19% 18% 4 9% 5% 4 4 3 3 5% 26%	3138
	11th to 20th	Day	12% 17% 7% 15% 6% 5% 3 3 3 4 25%	3480
	21st to end	Day	12% 10% 4 9% 6% 6% 5% 4 5% 5% 33%	4002
April	1st to 10th	Day	22% 17% 3 8% 4 3 3 3 3 5% 28%	2280
	11th to 20th	Day	23% 12% 4 8% 4 4 3 3 4 6% 30%	2254
	21st to end	Day	21% 11% 4 9% 5% 4 4 3 4 4 32%	2517
May	1st to 10th	Day	22% 12% 3 7% 5% 4 5% 4 5% 5% 28%	4426
	11th to 20th	Day	20% 8% 3 7% 4 5% 5% 4 5% 7% 32%	4398
	21st to end	Day	18% 8% 3 7% 5% 5% 5% 4 6% 7% 33%	4837
June	1st to 10th	Day	22% 9% 3 9% 5% 5% 5% 4 6% 7% 25%	2660
	11th to 20th	Day	15% 8% 3 7% 5% 5% 5% 5% 7% 7% 33%	2660
	21st to end	Day	20% 8% 3 9% 6% 5% 5% 5% 6% 7% 27%	2843
July	1st to 10th	Day	16% 8% 3 7% 5% 6% 5% 5% 7% 9% 28%	4486
	11th to 20th	Day	16% 8% 3 7% 5% 6% 5% 5% 6% 8% 32%	4440
	21st to end	Day	14% 8% 3 6% 4 4 5% 4 6% 7% 38%	4814
August	1st to 10th	Day	15% 8% 3 9% 6% 7% 6% 4 6% 7% 29%	4423
	11th to 20th	Day	17% 8% 3 7% 5% 5% 6% 4 7% 7% 31%	4046
	21st to end	Day	14% 7% 3 8% 4 5% 5% 4 6% 8% 35%	4222
September	1st to 10th	Day	18% 8% 3 8% 4 4 3 3 5% 7% 37%	2280
	11th to 20th	Day	17% 8% 3 6% 4 4 4 4 4 6% 38%	2280
	21st to end	Day	22% 10% 3 7% 3 4 3 3 5% 7% 33%	2014
October	1st to 10th	Day	21% 13% 4 8% 4 4 3 4 4 6% 30%	1900
	11th to 20th	Day	28% 17% 5% 8% 5% 4 3 2 4 5% 19%	1900
	21st to end	Day	29% 16% 4 9% 5% 4 3 3 4 5% 18%	1923
November	1st to 10th	Day	18% 20% 6% 9% 5% 3 3 2 4 5% 26%	1628
	11th to 20th	Day	19% 18% 9% 13% 7% 4 4 2 4 4 16%	1520
	21st to end	Day	23% 22% 8% 14% 6% 5% 3 3 3 3 10%	1520
December	1st to 10th	Day	22% 21% 7% 12% 7% 5% 4 2 4 5% 11%	1520
	11th to 20th	Day	20% 17% 6% 15% 9% 5% 4 5% 4 3 14%	1906
	21st to end	Day	21% 21% 8% 14% 6% 3 3 2 4 4 14%	2772
January	1st to 10th	Night	15% 19% 7% 16% 8% 5% 4 3 3 4 14%	4429
	11th to 20th	Night	13% 16% 6% 15% 10% 6% 5% 4 6% 5% 15%	4440
	21st to end	Night	9% 18% 10% 16% 7% 8% 6% 3 5% 5% 13%	4838
February	1st to 10th	Night	10% 16% 5% 11% 11% 8% 5% 4 5% 5% 20%	2470
	11th to 20th	Night	12% 17% 6% 12% 7% 6% 5% 4 5% 6% 20%	2403
	21st to end	Night	12% 17% 6% 11% 7% 5% 6% 4 5% 6% 22%	1931
March	1st to 10th	Night	17% 18% 4 7% 5% 4 5% 3 4 5% 26%	3697
	11th to 20th	Night	16% 19% 5% 13% 4 4 4 3 4 5% 22%	3479
	21st to end	Night	13% 10% 4 11% 6% 6% 5% 4 6% 5% 30%	3629
April	1st to 10th	Night	20% 13% 5% 10% 6% 4 3 2 4 4 29%	1900
	11th to 20th	Night	17% 11% 3 7% 5% 4 4 3 5% 5% 35%	1875
	21st to end	Night	22% 10% 4 8% 4 3 4 3 4 6% 32%	1678
May	1st to 10th	Night	22% 10% 4 8% 5% 4 4 3 5% 5% 30%	2514
	11th to 20th	Night	18% 10% 3 9% 5% 4 4 3 5% 6% 34%	2495
	21st to end	Night	17% 9% 3 8% 5% 4 5% 3 5% 8% 34%	2738
June	1st to 10th	Night	18% 9% 3 8% 5% 4 5% 5% 7% 7% 29%	1520
	11th to 20th	Night	17% 8% 3 7% 4 4 4 5% 5% 6% 38%	1514
	21st to end	Night	20% 8% 2 5% 4 5% 5% 4 5% 8% 35%	1330
July	1st to 10th	Night	16% 9% 4 8% 6% 6% 5% 4 6% 6% 30%	2451
	11th to 20th	Night	17% 7% 3 7% 4 4 6% 4 7% 7% 34%	2520
	21st to end	Night	12% 6% 2 6% 5% 4 5% 3 5% 8% 43%	2739
August	1st to 10th	Night	13% 6% 2 7% 4 5% 5% 4 7% 8% 38%	2506
	11th to 20th	Night	19% 8% 3 7% 4 4 4 4 5% 6% 37%	2780
	21st to end	Night	16% 7% 3 8% 5% 5% 5% 4 6% 8% 34%	3401
September	1st to 10th	Night	17% 8% 2 6% 3 3 3 3 5% 8% 42%	1900
	11th to 20th	Night	18% 6% 2 5% 4 4 4 3 5% 6% 41%	1900
	21st to end	Night	22% 8% 3 6% 4 3 3 3 4 6% 38%	2162
October	1st to 10th	Night	22% 10% 3 7% 4 4 4 3 5% 5% 32%	2280
	11th to 20th	Night	25% 17% 4 7% 4 3 4 3 4 5% 24%	2280
	21st to end	Night	26% 17% 4 9% 4 4 4 3 4 5% 20%	2674
November	1st to 10th	Night	19% 17% 5% 9% 6% 4 3 3 4 5% 25%	2547
	11th to 20th	Night	19% 18% 6% 11% 8% 5% 4 2 4 5% 17%	2660
	21st to end	Night	24% 20% 6% 13% 7% 4 4 2 3 3 13%	2660
December	1st to 10th	Night	19% 22% 7% 14% 7% 4 4 3 3 4 13%	2660
	11th to 20th	Night	21% 20% 5% 11% 6% 5% 5% 3 4 5% 15%	3288
	21st to end	Night	20% 21% 7% 16% 7% 4 3 2 3 4 14%	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	78% 2 8% 8% 4	2518
	11th to 20th	Day	72% 3 5% 15% 6%	2520
	21st to end	Day	72% 2 7% 12% 7%	2815
February	1st to 10th	Day	69% 2 6% 14% 8% 1	1710
	11th to 20th	Day	68% 2 8% 12% 10% 1	1672
	21st to end	Day	67% 2 6% 15% 9% 1	1522
March	1st to 10th	Day	64% 2 6% 15% 12% 1	3141
	11th to 20th	Day	65% 3 7% 13% 10% 2	3480
	21st to end	Day	52% 4 7% 19% 16% 3	4002
April	1st to 10th	Day	60% 2 8% 15% 12% 2	2280
	11th to 20th	Day	57% 3 6% 22% 11% 2	2254
	21st to end	Day	57% 2 7% 17% 14% 2	2517
May	1st to 10th	Day	57% 4 8% 20% 9% 2	4440
	11th to 20th	Day	51% 3 11% 25% 9% 1	4402
	21st to end	Day	51% 4 10% 18% 16% 1	4837
June	1st to 10th	Day	57% 4 9% 19% 10% 1	2660
	11th to 20th	Day	48% 5% 12% 22% 12% 1	2660
	21st to end	Day	55% 4 11% 20% 9%	2843
July	1st to 10th	Day	52% 3 14% 25% 5%	4416
	11th to 20th	Day	50% 3 15% 26% 7%	4365
	21st to end	Day	46% 3 16% 27% 8%	4661
August	1st to 10th	Day	54% 3 13% 25% 5%	4409
	11th to 20th	Day	52% 2 15% 23% 7%	4085
	21st to end	Day	48% 2 10% 28% 11% 1	4222
September	1st to 10th	Day	47% 3 12% 24% 13% 1	2280
	11th to 20th	Day	47% 4 16% 24% 9% 1	2280
	21st to end	Day	52% 3 14% 23% 7%	2014
October	1st to 10th	Day	61% 2 8% 24% 5%	3160
	11th to 20th	Day	62% 2 13% 18% 5%	3140
	21st to end	Day	69% 3 13% 11% 4	3148
November	1st to 10th	Day	63% 2 11% 17% 7%	1628
	11th to 20th	Day	73% 3 8% 10% 5%	1520
	21st to end	Day	81% 3 6% 6% 4	1520
December	1st to 10th	Day	79% 3 6% 10% 3	1520
	11th to 20th	Day	75% 4 4 12% 5% 1	1906
	21st to end	Day	75% 2 6% 13% 3	2772
January	1st to 10th	Night	76% 2 11% 9% 2	4429
	11th to 20th	Night	71% 3 8% 13% 4 1	4440
	21st to end	Night	74% 2 6% 9% 7%	4838
February	1st to 10th	Night	66% 3 6% 16% 8% 1	2470
	11th to 20th	Night	66% 3 7% 15% 7% 1	2405
	21st to end	Night	63% 2 8% 15% 10% 1	1931
March	1st to 10th	Night	62% 3 9% 12% 11% 2	3707
	11th to 20th	Night	66% 3 8% 15% 7% 1	3480
	21st to end	Night	52% 6% 7% 20% 12% 2	3629
April	1st to 10th	Night	60% 2 6% 16% 14% 2	1900
	11th to 20th	Night	50% 3 8% 23% 13% 2	1875
	21st to end	Night	54% 3 8% 19% 14% 2	1678
May	1st to 10th	Night	56% 4 12% 17% 10% 2	2520
	11th to 20th	Night	53% 3 12% 19% 12% 1	2496
	21st to end	Night	50% 4 11% 20% 13% 2	2739
June	1st to 10th	Night	51% 5% 10% 22% 11% 1	1520
	11th to 20th	Night	47% 3 12% 22% 14% 2	1514
	21st to end	Night	49% 3 12% 25% 10% 1	1330
July	1st to 10th	Night	55% 3 13% 21% 8% 1	2411
	11th to 20th	Night	49% 3 20% 21% 6%	2472
	21st to end	Night	41% 3 15% 28% 12%	2651
August	1st to 10th	Night	44% 3 20% 26% 7%	2496
	11th to 20th	Night	49% 3 15% 25% 7%	2807
	21st to end	Night	49% 3 13% 25% 9% 1	3401
September	1st to 10th	Night	42% 3 18% 26% 11%	1900
	11th to 20th	Night	45% 3 17% 26% 9%	1900
	21st to end	Night	49% 4 13% 27% 7%	2162
October	1st to 10th	Night	54% 2 11% 21% 12%	3800
	11th to 20th	Night	61% 2 10% 22% 5%	3779
	21st to end	Night	63% 2 15% 12% 8% 1	4399
November	1st to 10th	Night	64% 2 11% 16% 6%	2547
	11th to 20th	Night	71% 3 9% 12% 5% 1	2660
	21st to end	Night	78% 3 7% 9% 3	2660
December	1st to 10th	Night	78% 3 7% 9% 4	2660
	11th to 20th	Night	72% 3 5% 13% 6%	3288
	21st to end	Night	77% 2 4 12% 5%	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	26% 19% 39% 13% 2 1	180
	11th to 20th	Day	24% 14% 38% 16% 7% 1	180
	21st to end	Day	25% 18% 33% 20% 4	213
February	1st to 10th	Day	26% 24% 39% 8% 3 1	270
	11th to 20th	Day	27% 26% 36% 11% 1	270
	21st to end	Day	33% 21% 33% 10% 2 1	334
March	1st to 10th	Day	26% 18% 33% 17% 5%	460
	11th to 20th	Day	28% 18% 33% 16% 5% 1	460
	21st to end	Day	29% 17% 33% 16% 4 1	506
April	1st to 10th	Day	35% 15% 26% 16% 7% 1	460
	11th to 20th	Day	34% 15% 26% 16% 7% 2	452
	21st to end	Day	28% 17% 33% 16% 4 1	460
May	1st to 10th	Day	33% 13% 31% 16% 5% 2	463
	11th to 20th	Day	28% 14% 29% 18% 10% 2	487
	21st to end	Day	26% 17% 30% 22% 5% 1	529
June	1st to 10th	Day	28% 10% 35% 22% 4 1	490
	11th to 20th	Day	22% 14% 34% 18% 10% 2	490
	21st to end	Day	24% 11% 31% 23% 10% 1	673
July	1st to 10th	Day	19% 8% 36% 28% 7% 2	518
	11th to 20th	Day	20% 8% 35% 26% 10% 2	484
	21st to end	Day	18% 8% 31% 28% 12% 2	532
August	1st to 10th	Day	19% 8% 34% 26% 11% 3	486
	11th to 20th	Day	21% 5% 28% 27% 13% 7%	479
	21st to end	Day	21% 9% 31% 21% 12% 6%	539
September	1st to 10th	Day	24% 8% 30% 23% 12% 3	490
	11th to 20th	Day	20% 9% 27% 23% 13% 7%	490
	21st to end	Day	26% 13% 24% 19% 16% 3	490
October	1st to 10th	Day	32% 12% 24% 21% 8% 3	490
	11th to 20th	Day	35% 14% 29% 15% 5% 2	490
	21st to end	Day	40% 13% 25% 18% 4	451
November	1st to 10th	Day	35% 15% 30% 16% 4 1	298
	11th to 20th	Day	30% 19% 33% 13% 4 1	180
	21st to end	Day	34% 22% 32% 8% 2 2	180
December	1st to 10th	Day	35% 14% 28% 19% 3 2	180
	11th to 20th	Day	31% 20% 33% 12% 3 1	180
	21st to end	Day	32% 13% 37% 13% 5% 1	198
January	1st to 10th	Night	31% 13% 33% 19% 4	760
	11th to 20th	Night	32% 11% 30% 20% 7%	760
	21st to end	Night	20% 9% 35% 26% 8% 1	836
February	1st to 10th	Night	19% 16% 35% 24% 6% 1	760
	11th to 20th	Night	24% 15% 34% 22% 4 1	743
	21st to end	Night	23% 18% 32% 22% 4	628
March	1st to 10th	Night	24% 16% 31% 23% 5% 1	760
	11th to 20th	Night	28% 15% 31% 20% 5% 1	760
	21st to end	Night	22% 15% 33% 24% 6%	836
April	1st to 10th	Night	30% 13% 27% 24% 6%	760
	11th to 20th	Night	26% 15% 28% 22% 9% 1	751
	21st to end	Night	28% 11% 29% 24% 7% 1	538
May	1st to 10th	Night	25% 7% 28% 31% 9%	380
	11th to 20th	Night	25% 8% 27% 27% 12% 1	374
	21st to end	Night	23% 8% 34% 28% 7%	411
June	1st to 10th	Night	24% 7% 31% 30% 8% 1	380
	11th to 20th	Night	21% 8% 27% 31% 13% 1	380
	21st to end	Night	24% 3 25% 33% 13% 1	380
July	1st to 10th	Night	16% 4 28% 41% 11%	370
	11th to 20th	Night	17% 4 24% 41% 13% 1	368
	21st to end	Night	16% 3 24% 40% 16% 1	416
August	1st to 10th	Night	18% 3 22% 34% 22% 1	378
	11th to 20th	Night	20% 3 17% 34% 23% 3	559
	21st to end	Night	20% 5% 25% 29% 19% 2	787
September	1st to 10th	Night	22% 5% 27% 32% 12% 2	760
	11th to 20th	Night	24% 5% 25% 26% 17% 3	760
	21st to end	Night	26% 7% 25% 27% 13% 2	760
October	1st to 10th	Night	28% 8% 28% 23% 13%	760
	11th to 20th	Night	36% 10% 25% 20% 8% 1	760
	21st to end	Night	37% 11% 27% 21% 4 1	836
November	1st to 10th	Night	31% 12% 30% 19% 7% 1	760
	11th to 20th	Night	31% 16% 29% 16% 7% 1	760
	21st to end	Night	38% 15% 22% 19% 5% 1	760
December	1st to 10th	Night	33% 13% 30% 18% 5% 1	760
	11th to 20th	Night	32% 15% 26% 21% 6% 1	760
	21st to end	Night	34% 14% 27% 19% 5% 1	836

Page generated at 2024-11-03 02:11:12. Version ac07

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