Massacre Rim
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Massacre Rim clear sky chart from 2005-11-06 to 2025-04-26.

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	3 6% 3 6% 4 4 4 3 5% 7% 54%	117557
	Night	3 8% 3 7% 4 4 4 3 5% 7% 51%	119858
Transparency	Day	29% 5% 8% 19% 22% 16%	117298
	Night	32% 6% 10% 19% 21% 13%	119706
Seeing	Day	7% 9% 22% 30% 23% 9%	15332
	Night	7% 7% 20% 38% 24% 5%	24714

By Month

Percentage Cloud Cover SW (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	4 12% 8% 13% 7% 6% 7% 5% 6% 8% 26%	3639
	11th to 20th	Day	3 8% 5% 11% 5% 5% 5% 5% 7% 8% 38%	3640
	21st to end	Day	3 12% 4 9% 5% 5% 4 3 5% 7% 43%	4326
February	1st to 10th	Day	4 8% 3 10% 5% 4 5% 5% 8% 10% 38%	1800
	11th to 20th	Day	2 8% 4 10% 6% 6% 6% 5% 7% 8% 38%	1905
	21st to end	Day	2 9% 3 7% 4 5% 6% 7% 8% 9% 39%	1650
March	1st to 10th	Day	4 14% 6% 12% 5% 5% 4 4 6% 7% 32%	4518
	11th to 20th	Day	2 6% 3 7% 5% 5% 5% 4 6% 7% 50%	4855
	21st to end	Day	2 10% 4 10% 5% 5% 5% 5% 7% 10% 37%	5876
April	1st to 10th	Day	4 10% 5% 8% 6% 5% 6% 4 6% 8% 39%	2400
	11th to 20th	Day	5% 8% 3 7% 4 4 4 4 6% 8% 47%	2369
	21st to end	Day	4 9% 2 6% 4 4 4 4 6% 9% 47%	2356
May	1st to 10th	Day	4 8% 3 5% 3 3 3 3 5% 8% 56%	4185
	11th to 20th	Day	4 4 1 4 3 2 3 2 3 5% 69%	4377
	21st to end	Day	4 5% 2 5% 4 4 4 3 5% 7% 56%	4813
June	1st to 10th	Day	5% 5% 2 6% 5% 4 4 5% 6% 8% 50%	2660
	11th to 20th	Day	4 4 1 4 3 3 3 3 5% 6% 64%	2660
	21st to end	Day	3 2 1 2 3 2 3 2 3 5% 73%	2660
July	1st to 10th	Day	1 1 1 2 1 2 1 3 3 84%	4420
	11th to 20th	Day	2 2 1 3 2 2 3 2 4 5% 74%	4420
	21st to end	Day	2 2 1 3 3 3 3 3 4 5% 71%	4790
August	1st to 10th	Day	3 2 1 4 3 3 3 3 5% 7% 66%	4202
	11th to 20th	Day	1 2 2 2 2 3 2 3 4 79%	3762
	21st to end	Day	2 2 1 2 2 2 2 1 3 3 80%	4180
September	1st to 10th	Day	2 1 1 3 2 2 2 2 4 4 77%	2280
	11th to 20th	Day	4 3 1 4 3 3 3 3 4 5% 65%	2242
	21st to end	Day	4 4 1 3 2 2 3 2 4 4 70%	2090
October	1st to 10th	Day	4 3 1 4 2 3 3 2 4 5% 69%	3225
	11th to 20th	Day	6% 5% 2 4 3 3 3 3 4 6% 61%	3161
	21st to end	Day	4 4 3 7% 4 5% 4 4 7% 8% 50%	3241
November	1st to 10th	Day	7% 9% 3 8% 4 3 4 4 6% 7% 44%	1764
	11th to 20th	Day	6% 9% 3 7% 6% 5% 5% 5% 8% 9% 37%	1800
	21st to end	Day	4 9% 3 7% 5% 4 6% 5% 7% 7% 44%	1639
December	1st to 10th	Day	3 7% 3 7% 5% 4 5% 5% 5% 9% 49%	2620
	11th to 20th	Day	5% 14% 4 10% 6% 6% 7% 6% 7% 10% 24%	3028
	21st to end	Day	7% 12% 5% 10% 6% 6% 6% 5% 7% 10% 26%	4004
January	1st to 10th	Night	4 12% 5% 12% 6% 6% 6% 5% 8% 8% 27%	6306
	11th to 20th	Night	3 11% 4 10% 4 4 5% 4 5% 7% 42%	6320
	21st to end	Night	4 11% 4 9% 5% 5% 4 3 4 6% 45%	6630
February	1st to 10th	Night	4 9% 3 8% 5% 5% 6% 4 6% 8% 42%	2600
	11th to 20th	Night	2 8% 4 10% 7% 5% 5% 4 6% 9% 40%	2382
	21st to end	Night	3 9% 3 8% 6% 6% 6% 4 7% 9% 39%	1980
March	1st to 10th	Night	3 15% 6% 11% 5% 4 4 3 6% 7% 38%	5376
	11th to 20th	Night	2 8% 4 9% 6% 5% 4 4 5% 7% 46%	5142
	21st to end	Night	3 12% 4 9% 6% 6% 6% 5% 7% 9% 34%	5098
April	1st to 10th	Night	5% 7% 3 7% 6% 5% 5% 5% 7% 9% 41%	2000
	11th to 20th	Night	4 8% 3 6% 5% 4 4 3 5% 7% 51%	1979
	21st to end	Night	4 7% 3 6% 4 4 4 2 5% 7% 54%	1940
May	1st to 10th	Night	4 6% 4 5% 3 3 3 3 5% 7% 57%	2778
	11th to 20th	Night	4 3 1 3 3 3 3 3 4 5% 69%	2516
	21st to end	Night	4 4 2 5% 4 4 4 3 5% 7% 59%	2762
June	1st to 10th	Night	5% 6% 2 5% 4 3 4 5% 5% 8% 53%	1520
	11th to 20th	Night	4 5% 2 4 2 2 3 2 5% 6% 66%	1520
	21st to end	Night	3 3 1 3 2 2 2 3 4 5% 71%	1520
July	1st to 10th	Night	1 1 2 2 1 2 2 3 4 84%	2540
	11th to 20th	Night	3 2 1 3 2 2 3 2 3 4 75%	2540
	21st to end	Night	1 2 1 3 2 3 3 2 4 5% 74%	2761
August	1st to 10th	Night	3 3 1 4 3 3 3 2 4 7% 66%	2717
	11th to 20th	Night	2 2 1 2 2 2 2 2 3 3 80%	3087
	21st to end	Night	2 3 1 2 2 2 2 2 2 4 79%	3498
September	1st to 10th	Night	2 2 1 3 2 2 2 2 2 4 78%	1900
	11th to 20th	Night	4 4 1 3 2 2 2 3 4 5% 69%	1938
	21st to end	Night	3 3 1 3 2 2 2 2 4 6% 72%	2090
October	1st to 10th	Night	2 3 1 3 3 3 3 2 3 3 74%	3738
	11th to 20th	Night	2 4 1 4 3 2 3 2 4 5% 68%	3777
	21st to end	Night	3 5% 2 6% 4 4 4 5% 6% 7% 53%	4321
November	1st to 10th	Night	6% 7% 3 7% 5% 4 4 4 6% 8% 45%	2535
	11th to 20th	Night	5% 8% 3 6% 6% 6% 6% 4 7% 9% 40%	2600
	21st to end	Night	4 9% 3 7% 4 4 5% 3 6% 8% 45%	2759
December	1st to 10th	Night	4 5% 2 6% 4 4 4 3 5% 8% 55%	4560
	11th to 20th	Night	5% 13% 5% 11% 6% 6% 6% 6% 8% 10% 24%	5176
	21st to end	Night	5% 11% 4 12% 7% 6% 7% 5% 7% 9% 28%	6952

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	53% 10% 10% 16% 11% 1	3639
	11th to 20th	Day	42% 7% 8% 19% 18% 5%	3640
	21st to end	Day	41% 6% 7% 13% 21% 12%	4326
February	1st to 10th	Day	38% 8% 14% 23% 13% 5%	1800
	11th to 20th	Day	39% 8% 15% 20% 14% 4	1915
	21st to end	Day	36% 10% 15% 22% 12% 5%	1650
March	1st to 10th	Day	47% 8% 7% 16% 17% 4	4518
	11th to 20th	Day	30% 7% 11% 28% 23% 1	4855
	21st to end	Day	39% 11% 15% 22% 10% 2	5876
April	1st to 10th	Day	41% 8% 15% 22% 12% 2	2400
	11th to 20th	Day	34% 7% 11% 26% 20% 3	2372
	21st to end	Day	32% 7% 14% 27% 18% 2	2356
May	1st to 10th	Day	27% 6% 9% 33% 22% 3	4185
	11th to 20th	Day	20% 4 6% 20% 45% 5%	4380
	21st to end	Day	27% 6% 10% 34% 21% 2	4814
June	1st to 10th	Day	31% 7% 12% 26% 21% 3	2660
	11th to 20th	Day	21% 4 8% 24% 31% 12%	2660
	21st to end	Day	15% 2 5% 18% 36% 24%	2660
July	1st to 10th	Day	8% 1 2 7% 16% 65%	4351
	11th to 20th	Day	15% 1 3 7% 18% 55%	4345
	21st to end	Day	16% 2 3 8% 28% 42%	4639
August	1st to 10th	Day	19% 2 3 8% 22% 46%	4186
	11th to 20th	Day	12% 2 2 9% 34% 41%	3798
	21st to end	Day	12% 1 2 14% 38% 33%	4179
September	1st to 10th	Day	12% 2 3 11% 30% 41%	2280
	11th to 20th	Day	20% 4 6% 18% 27% 24%	2242
	21st to end	Day	18% 3 6% 21% 31% 21%	2090
October	1st to 10th	Day	19% 2 5% 15% 31% 29%	3225
	11th to 20th	Day	25% 2 6% 24% 32% 10%	3161
	21st to end	Day	28% 5% 11% 26% 22% 8%	3241
November	1st to 10th	Day	38% 6% 12% 18% 21% 6%	1764
	11th to 20th	Day	41% 7% 12% 22% 15% 3	1800
	21st to end	Day	37% 6% 13% 19% 20% 6%	1639
December	1st to 10th	Day	32% 4 9% 16% 29% 8%	2620
	11th to 20th	Day	51% 8% 13% 16% 10% 1	3028
	21st to end	Day	50% 9% 13% 19% 9%	4004
January	1st to 10th	Night	50% 10% 12% 19% 9% 1	6306
	11th to 20th	Night	42% 5% 9% 18% 18% 8%	6320
	21st to end	Night	41% 5% 8% 13% 24% 10%	6630
February	1st to 10th	Night	37% 7% 14% 21% 17% 3	2600
	11th to 20th	Night	39% 8% 13% 21% 15% 5%	2383
	21st to end	Night	38% 9% 14% 21% 13% 5%	1980
March	1st to 10th	Night	45% 6% 9% 17% 18% 5%	5376
	11th to 20th	Night	35% 5% 13% 27% 19% 1	5142
	21st to end	Night	41% 10% 17% 23% 9% 1	5098
April	1st to 10th	Night	35% 10% 15% 23% 13% 3	2000
	11th to 20th	Night	31% 8% 15% 24% 17% 4	1979
	21st to end	Night	29% 7% 16% 29% 16% 2	1940
May	1st to 10th	Night	25% 8% 9% 30% 22% 5%	2778
	11th to 20th	Night	18% 4 7% 23% 39% 9%	2516
	21st to end	Night	24% 6% 12% 35% 21% 2	2762
June	1st to 10th	Night	28% 7% 13% 30% 19% 2	1520
	11th to 20th	Night	20% 4 8% 26% 33% 9%	1520
	21st to end	Night	16% 3 5% 19% 35% 22%	1520
July	1st to 10th	Night	8% 2 3 8% 18% 62%	2500
	11th to 20th	Night	15% 1 3 7% 18% 55%	2492
	21st to end	Night	12% 2 4 7% 32% 42%	2674
August	1st to 10th	Night	19% 2 4 10% 21% 44%	2709
	11th to 20th	Night	11% 2 3 9% 39% 36%	3117
	21st to end	Night	12% 1 3 18% 35% 31%	3498
September	1st to 10th	Night	12% 3 3 11% 28% 43%	1900
	11th to 20th	Night	18% 3 5% 18% 31% 25%	1938
	21st to end	Night	15% 3 4 23% 31% 23%	2090
October	1st to 10th	Night	17% 2 5% 14% 34% 28%	3738
	11th to 20th	Night	19% 4 7% 28% 34% 9%	3777
	21st to end	Night	27% 4 10% 25% 25% 8%	4321
November	1st to 10th	Night	36% 7% 12% 20% 19% 6%	2535
	11th to 20th	Night	38% 7% 14% 20% 18% 3	2600
	21st to end	Night	36% 5% 14% 18% 20% 7%	2759
December	1st to 10th	Night	28% 5% 9% 18% 29% 12%	4560
	11th to 20th	Night	51% 8% 11% 16% 12% 2	5176
	21st to end	Night	48% 10% 14% 15% 12% 1	6952

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	16% 16% 20% 29% 16% 4	200
	11th to 20th	Day	7% 14% 19% 29% 23% 9%	200
	21st to end	Day	7% 8% 22% 31% 24% 8%	360
February	1st to 10th	Day	7% 14% 23% 30% 21% 6%	400
	11th to 20th	Day	8% 17% 23% 31% 19% 2	472
	21st to end	Day	6% 14% 24% 32% 20% 4	414
March	1st to 10th	Day	9% 10% 33% 29% 16% 3	500
	11th to 20th	Day	8% 12% 24% 29% 20% 7%	500
	21st to end	Day	8% 15% 25% 30% 17% 5%	550
April	1st to 10th	Day	7% 11% 24% 34% 20% 4	500
	11th to 20th	Day	9% 11% 24% 29% 20% 8%	492
	21st to end	Day	7% 9% 21% 30% 25% 9%	481
May	1st to 10th	Day	5% 9% 21% 32% 23% 10%	463
	11th to 20th	Day	12% 7% 21% 28% 19% 13%	488
	21st to end	Day	10% 7% 16% 24% 24% 19%	529
June	1st to 10th	Day	5% 9% 22% 23% 27% 14%	490
	11th to 20th	Day	7% 12% 29% 26% 19% 7%	490
	21st to end	Day	4 7% 20% 31% 26% 13%	490
July	1st to 10th	Day	3 3 20% 34% 29% 11%	486
	11th to 20th	Day	2 3 18% 37% 29% 11%	484
	21st to end	Day	4 2 17% 35% 29% 14%	531
August	1st to 10th	Day	4 3 18% 33% 28% 14%	487
	11th to 20th	Day	4 5% 19% 29% 27% 16%	477
	21st to end	Day	2 5% 20% 32% 27% 13%	539
September	1st to 10th	Day	3 3 19% 29% 31% 15%	490
	11th to 20th	Day	7% 8% 21% 28% 25% 12%	490
	21st to end	Day	5% 6% 25% 30% 27% 8%	490
October	1st to 10th	Day	7% 10% 24% 24% 23% 11%	490
	11th to 20th	Day	10% 12% 17% 28% 26% 8%	490
	21st to end	Day	7% 14% 27% 27% 19% 7%	420
November	1st to 10th	Day	10% 13% 23% 26% 21% 7%	300
	11th to 20th	Day	8% 13% 26% 28% 21% 4	300
	21st to end	Day	8% 15% 18% 32% 21% 7%	219
December	1st to 10th	Day	12% 11% 19% 23% 22% 15%	200
	11th to 20th	Day	10% 8% 30% 27% 19% 7%	200
	21st to end	Day	10% 16% 21% 29% 20% 5%	220
January	1st to 10th	Night	11% 8% 26% 33% 18% 5%	800
	11th to 20th	Night	8% 10% 22% 33% 22% 5%	800
	21st to end	Night	9% 7% 20% 34% 24% 6%	880
February	1st to 10th	Night	8% 10% 24% 36% 21% 2	800
	11th to 20th	Night	6% 11% 22% 40% 18% 3	784
	21st to end	Night	6% 9% 24% 40% 20% 2	660
March	1st to 10th	Night	10% 11% 26% 35% 16% 4	800
	11th to 20th	Night	8% 9% 23% 31% 25% 4	800
	21st to end	Night	9% 12% 25% 35% 17% 3	880
April	1st to 10th	Night	8% 7% 25% 38% 20% 2	800
	11th to 20th	Night	8% 10% 23% 33% 22% 5%	791
	21st to end	Night	7% 7% 19% 39% 24% 4	768
May	1st to 10th	Night	7% 7% 28% 35% 20% 4	527
	11th to 20th	Night	9% 5% 20% 32% 27% 8%	374
	21st to end	Night	8% 5% 18% 34% 29% 5%	411
June	1st to 10th	Night	5% 5% 19% 40% 28% 3	380
	11th to 20th	Night	5% 5% 24% 43% 21% 2	380
	21st to end	Night	4 2 16% 51% 26% 2	380
July	1st to 10th	Night	2 1 14% 54% 28% 2	370
	11th to 20th	Night	3 1 14% 56% 25% 1	368
	21st to end	Night	2 10% 50% 35% 2	416
August	1st to 10th	Night	3 1 11% 48% 34% 3	488
	11th to 20th	Night	3 2 11% 45% 34% 4	725
	21st to end	Night	2 1 11% 47% 35% 4	836
September	1st to 10th	Night	3 1 12% 41% 37% 6%	760
	11th to 20th	Night	5% 3 13% 34% 34% 11%	760
	21st to end	Night	5% 4 15% 35% 30% 12%	760
October	1st to 10th	Night	6% 4 17% 37% 29% 8%	760
	11th to 20th	Night	5% 8% 15% 37% 28% 8%	760
	21st to end	Night	6% 8% 17% 38% 23% 8%	836
November	1st to 10th	Night	9% 7% 20% 37% 21% 6%	780
	11th to 20th	Night	9% 8% 26% 33% 21% 3	800
	21st to end	Night	9% 8% 23% 34% 23% 5%	800
December	1st to 10th	Night	9% 10% 20% 37% 20% 5%	800
	11th to 20th	Night	12% 11% 21% 34% 20% 3	800
	21st to end	Night	12% 12% 29% 32% 13% 2	880

Page generated at 2025-04-23 06:25:01. Version ac07

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