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 2026-08-30.

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% 2 6% 4 4 4 3 5% 7% 56%	152861
	Night	3 7% 3 7% 4 4 4 3 5% 7% 53%	146709
Transparency	Day	27% 5% 8% 18% 24% 18%	147751
	Night	30% 5% 9% 19% 22% 14%	142809
Seeing	Day	7% 9% 22% 29% 23% 10%	17122
	Night	7% 7% 20% 38% 24% 4	26291

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 13% 7% 12% 6% 5% 6% 5% 7% 8% 27%	4722
	11th to 20th	Day	2 6% 4 8% 4 4 4 4 6% 8% 49%	4740
	21st to end	Day	2 9% 3 8% 5% 6% 5% 4 6% 8% 42%	5603
February	1st to 10th	Day	3 8% 3 10% 5% 4 5% 5% 8% 9% 39%	1890
	11th to 20th	Day	2 8% 4 10% 6% 6% 6% 5% 7% 8% 38%	2003
	21st to end	Day	2 9% 3 7% 4 5% 7% 7% 8% 9% 38%	1730
March	1st to 10th	Day	4 14% 6% 11% 5% 5% 4 4 6% 8% 33%	4618
	11th to 20th	Day	2 6% 3 7% 5% 5% 5% 4 6% 7% 50%	4961
	21st to end	Day	2 10% 4 10% 5% 5% 5% 5% 7% 10% 37%	6006
April	1st to 10th	Day	4 10% 4 8% 6% 5% 5% 4 6% 8% 39%	2520
	11th to 20th	Day	5% 8% 3 8% 4 4 4 4 6% 8% 47%	2489
	21st to end	Day	4 9% 2 6% 4 4 4 4 6% 9% 47%	2536
May	1st to 10th	Day	3 6% 3 5% 3 2 3 2 4 7% 61%	7752
	11th to 20th	Day	3 5% 2 4 3 3 3 3 4 6% 65%	8160
	21st to end	Day	4 4 2 4 3 4 3 3 5% 7% 60%	8992
June	1st to 10th	Day	5% 5% 2 6% 5% 4 4 4 5% 8% 52%	2940
	11th to 20th	Day	4 4 1 4 3 3 3 3 5% 6% 65%	2940
	21st to end	Day	3 2 1 2 3 2 3 3 4 5% 73%	2940
July	1st to 10th	Day	1 1 2 2 2 3 2 4 4 79%	8219
	11th to 20th	Day	4 4 2 4 2 2 3 2 4 4 69%	8220
	21st to end	Day	3 3 1 4 4 4 4 3 4 5% 65%	8922
August	1st to 10th	Day	2 2 1 3 2 3 3 3 4 6% 70%	6072
	11th to 20th	Day	1 1 2 2 2 3 2 4 4 80%	5536
	21st to end	Day	4 3 1 3 2 2 3 2 3 5% 72%	6093
September	1st to 10th	Day	2 1 1 3 2 2 2 2 4 5% 75%	2400
	11th to 20th	Day	4 3 1 4 3 3 3 3 4 5% 64%	2360
	21st to end	Day	4 4 2 3 2 2 3 2 4 5% 70%	2200
October	1st to 10th	Day	4 4 1 4 2 3 3 2 4 5% 69%	3327
	11th to 20th	Day	6% 5% 2 4 3 3 3 3 4 6% 61%	3261
	21st to end	Day	4 4 3 7% 5% 5% 5% 4 7% 8% 49%	3344
November	1st to 10th	Day	7% 9% 3 8% 4 3 4 4 6% 7% 45%	1854
	11th to 20th	Day	6% 9% 3 7% 6% 5% 5% 5% 8% 9% 37%	1890
	21st to end	Day	4 9% 3 7% 4 4 6% 5% 7% 7% 44%	1721
December	1st to 10th	Day	3 7% 2 7% 5% 4 4 5% 6% 9% 49%	2700
	11th to 20th	Day	5% 14% 4 10% 6% 6% 7% 6% 7% 10% 25%	3108
	21st to end	Day	7% 12% 5% 10% 6% 6% 6% 5% 7% 10% 26%	4092
January	1st to 10th	Night	4 14% 5% 12% 6% 6% 6% 5% 7% 7% 28%	8172
	11th to 20th	Night	2 9% 3 8% 3 3 4 4 4 6% 53%	8220
	21st to end	Night	3 10% 4 9% 6% 6% 5% 4 5% 7% 42%	8585
February	1st to 10th	Night	4 9% 3 8% 5% 5% 6% 4 6% 8% 42%	2730
	11th to 20th	Night	2 9% 4 10% 7% 5% 5% 4 6% 9% 39%	2504
	21st to end	Night	3 8% 3 8% 5% 5% 6% 5% 8% 9% 38%	2076
March	1st to 10th	Night	3 15% 6% 11% 5% 4 4 4 6% 7% 38%	5496
	11th to 20th	Night	2 8% 4 9% 6% 5% 4 4 5% 7% 47%	5256
	21st to end	Night	2 11% 4 9% 6% 6% 6% 5% 7% 10% 35%	5210
April	1st to 10th	Night	5% 7% 3 7% 6% 5% 5% 5% 7% 9% 41%	2100
	11th to 20th	Night	4 8% 3 6% 5% 4 5% 3 5% 7% 51%	2079
	21st to end	Night	4 7% 3 7% 4 4 4 3 5% 7% 53%	2084
May	1st to 10th	Night	5% 6% 3 4 2 3 3 3 5% 6% 61%	5185
	11th to 20th	Night	3 6% 2 4 3 3 3 3 4 5% 63%	4700
	21st to end	Night	4 4 1 4 3 3 3 3 5% 7% 65%	5181
June	1st to 10th	Night	4 6% 2 5% 4 3 4 4 5% 8% 55%	1680
	11th to 20th	Night	4 4 1 3 2 2 3 2 5% 6% 66%	1680
	21st to end	Night	3 3 1 3 2 3 2 3 4 5% 71%	1680
July	1st to 10th	Night	1 1 1 2 2 2 2 2 3 4 79%	4740
	11th to 20th	Night	4 3 1 4 2 2 3 2 3 4 72%	4740
	21st to end	Night	2 2 1 4 3 3 4 3 5% 6% 67%	5153
August	1st to 10th	Night	2 2 1 3 3 3 3 2 4 8% 69%	3936
	11th to 20th	Night	2 1 2 1 2 2 2 3 3 82%	4551
	21st to end	Night	3 4 1 4 2 3 3 3 3 5% 69%	5105
September	1st to 10th	Night	2 2 1 3 2 2 2 2 3 4 76%	2000
	11th to 20th	Night	3 5% 1 3 2 2 2 3 4 5% 69%	2040
	21st to end	Night	3 3 1 3 2 2 2 2 4 6% 72%	2200
October	1st to 10th	Night	2 3 1 3 3 3 3 2 3 3 74%	3856
	11th to 20th	Night	2 4 1 4 3 2 4 2 4 5% 67%	3897
	21st to end	Night	3 5% 2 6% 4 4 4 4 6% 7% 54%	4459
November	1st to 10th	Night	6% 7% 3 7% 5% 4 5% 4 6% 8% 45%	2665
	11th to 20th	Night	5% 8% 2 6% 6% 6% 6% 4 7% 9% 39%	2730
	21st to end	Night	4 9% 3 7% 4 4 5% 3 6% 8% 46%	2897
December	1st to 10th	Night	4 5% 2 6% 4 4 4 3 5% 8% 55%	4700
	11th to 20th	Night	5% 13% 5% 11% 6% 6% 6% 6% 8% 10% 25%	5316
	21st to end	Night	5% 11% 4 12% 7% 6% 6% 5% 7% 9% 28%	7106

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	51% 9% 11% 19% 9%	4723
	11th to 20th	Day	33% 5% 7% 15% 20% 20%	4740
	21st to end	Day	38% 5% 9% 14% 20% 13%	5603
February	1st to 10th	Day	37% 8% 13% 24% 14% 4	1890
	11th to 20th	Day	40% 8% 15% 19% 14% 4	2013
	21st to end	Day	37% 9% 15% 22% 12% 5%	1730
March	1st to 10th	Day	47% 8% 8% 17% 17% 4	4618
	11th to 20th	Day	30% 7% 11% 28% 23% 2	4961
	21st to end	Day	39% 11% 15% 23% 11% 2	6006
April	1st to 10th	Day	41% 8% 15% 21% 13% 2	2520
	11th to 20th	Day	34% 7% 11% 25% 20% 3	2492
	21st to end	Day	32% 7% 14% 27% 18% 2	2536
May	1st to 10th	Day	23% 4 6% 26% 37% 3	7752
	11th to 20th	Day	21% 3 7% 21% 40% 8%	8163
	21st to end	Day	23% 4 8% 29% 32% 4	8994
June	1st to 10th	Day	29% 6% 11% 25% 24% 4	2940
	11th to 20th	Day	20% 4 8% 23% 31% 14%	2940
	21st to end	Day	15% 2 5% 18% 35% 24%	2940
July	1st to 10th	Day	10% 1 3 8% 23% 55%	8151
	11th to 20th	Day	20% 1 3 7% 17% 53%	8145
	21st to end	Day	21% 3 4 12% 21% 40%	8723
August	1st to 10th	Day	18% 2 3 9% 22% 46%	4454
	11th to 20th	Day	12% 2 3 9% 35% 40%	4040
	21st to end	Day	13% 1 2 14% 37% 32%	4420
September	1st to 10th	Day	13% 2 4 12% 31% 39%	2400
	11th to 20th	Day	21% 4 6% 18% 27% 24%	2360
	21st to end	Day	18% 3 6% 21% 31% 22%	2200
October	1st to 10th	Day	19% 2 5% 15% 31% 28%	3327
	11th to 20th	Day	24% 2 6% 25% 32% 10%	3261
	21st to end	Day	28% 5% 11% 27% 21% 7%	3344
November	1st to 10th	Day	37% 6% 12% 20% 20% 5%	1854
	11th to 20th	Day	41% 7% 12% 23% 14% 3	1890
	21st to end	Day	36% 6% 13% 21% 20% 6%	1721
December	1st to 10th	Day	32% 4 10% 17% 29% 8%	2700
	11th to 20th	Day	51% 8% 13% 16% 10% 2	3108
	21st to end	Day	49% 9% 13% 19% 9%	4092
January	1st to 10th	Night	50% 9% 13% 20% 7% 1	8172
	11th to 20th	Night	33% 4 7% 15% 21% 21%	8220
	21st to end	Night	41% 4 9% 13% 21% 12%	8585
February	1st to 10th	Night	37% 7% 14% 21% 19% 3	2730
	11th to 20th	Night	40% 7% 13% 20% 15% 5%	2505
	21st to end	Night	38% 9% 15% 21% 12% 5%	2076
March	1st to 10th	Night	45% 6% 9% 17% 18% 5%	5496
	11th to 20th	Night	35% 5% 13% 27% 19% 1	5256
	21st to end	Night	40% 10% 17% 23% 9% 1	5210
April	1st to 10th	Night	35% 10% 15% 23% 14% 3	2100
	11th to 20th	Night	32% 8% 14% 24% 17% 4	2079
	21st to end	Night	30% 7% 15% 29% 16% 2	2084
May	1st to 10th	Night	24% 5% 6% 24% 34% 7%	5183
	11th to 20th	Night	23% 4 6% 23% 38% 5%	4700
	21st to end	Night	19% 4 9% 32% 34% 1	5182
June	1st to 10th	Night	27% 6% 12% 29% 23% 3	1680
	11th to 20th	Night	19% 4 8% 25% 33% 12%	1680
	21st to end	Night	16% 3 5% 20% 34% 21%	1680
July	1st to 10th	Night	10% 1 3 10% 25% 51%	4700
	11th to 20th	Night	18% 1 3 6% 21% 51%	4692
	21st to end	Night	17% 3 5% 15% 20% 39%	5040
August	1st to 10th	Night	18% 2 4 11% 21% 44%	2881
	11th to 20th	Night	11% 2 3 10% 39% 36%	3314
	21st to end	Night	13% 2 3 18% 34% 30%	3698
September	1st to 10th	Night	14% 3 4 12% 28% 41%	2000
	11th to 20th	Night	18% 3 5% 18% 31% 25%	2040
	21st to end	Night	15% 3 4 23% 31% 24%	2200
October	1st to 10th	Night	17% 2 5% 15% 34% 27%	3856
	11th to 20th	Night	19% 4 7% 28% 34% 9%	3897
	21st to end	Night	27% 4 10% 25% 26% 8%	4459
November	1st to 10th	Night	35% 7% 12% 21% 18% 6%	2665
	11th to 20th	Night	38% 8% 14% 20% 18% 3	2730
	21st to end	Night	35% 4 14% 20% 20% 7%	2897
December	1st to 10th	Night	28% 5% 10% 18% 28% 11%	4700
	11th to 20th	Night	50% 8% 11% 16% 12% 2	5316
	21st to end	Night	48% 10% 14% 16% 12% 1	7106

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% 17% 20% 28% 15% 4	220
	11th to 20th	Day	6% 13% 17% 27% 27% 10%	220
	21st to end	Day	7% 7% 23% 31% 24% 8%	389
February	1st to 10th	Day	7% 14% 23% 30% 21% 6%	430
	11th to 20th	Day	8% 17% 23% 31% 18% 2	510
	21st to end	Day	6% 14% 27% 31% 18% 4	446
March	1st to 10th	Day	9% 11% 32% 29% 15% 3	540
	11th to 20th	Day	9% 12% 24% 29% 20% 6%	540
	21st to end	Day	8% 15% 26% 29% 17% 5%	594
April	1st to 10th	Day	7% 11% 23% 33% 20% 6%	540
	11th to 20th	Day	8% 11% 25% 29% 20% 7%	532
	21st to end	Day	7% 9% 22% 31% 24% 8%	540
May	1st to 10th	Day	5% 9% 22% 31% 23% 10%	543
	11th to 20th	Day	12% 9% 22% 27% 18% 11%	568
	21st to end	Day	9% 7% 17% 23% 24% 18%	617
June	1st to 10th	Day	4 9% 22% 24% 26% 14%	570
	11th to 20th	Day	6% 11% 28% 26% 21% 8%	570
	21st to end	Day	4 7% 20% 29% 26% 15%	570
July	1st to 10th	Day	3 3 21% 34% 28% 12%	566
	11th to 20th	Day	3 3 19% 36% 28% 11%	564
	21st to end	Day	3 2 17% 34% 29% 15%	619
August	1st to 10th	Day	3 3 18% 31% 29% 16%	567
	11th to 20th	Day	4 4 19% 29% 28% 16%	557
	21st to end	Day	3 5% 20% 31% 26% 14%	620
September	1st to 10th	Day	3 3 19% 28% 31% 15%	530
	11th to 20th	Day	6% 8% 20% 28% 25% 13%	530
	21st to end	Day	5% 6% 24% 29% 28% 9%	530
October	1st to 10th	Day	8% 10% 24% 24% 23% 11%	530
	11th to 20th	Day	10% 12% 18% 28% 25% 7%	530
	21st to end	Day	7% 13% 25% 28% 20% 7%	457
November	1st to 10th	Day	11% 12% 23% 26% 21% 7%	330
	11th to 20th	Day	10% 13% 25% 28% 21% 4	330
	21st to end	Day	7% 13% 21% 31% 21% 7%	241
December	1st to 10th	Day	10% 11% 20% 23% 21% 14%	220
	11th to 20th	Day	11% 8% 29% 26% 18% 8%	220
	21st to end	Day	10% 17% 21% 28% 19% 4	242
January	1st to 10th	Night	11% 9% 26% 32% 18% 5%	840
	11th to 20th	Night	8% 10% 21% 33% 23% 5%	840
	21st to end	Night	9% 6% 20% 35% 23% 6%	924
February	1st to 10th	Night	7% 9% 23% 38% 20% 2	840
	11th to 20th	Night	6% 11% 22% 40% 18% 3	824
	21st to end	Night	6% 9% 25% 39% 20% 2	692
March	1st to 10th	Night	9% 10% 27% 35% 15% 4	840
	11th to 20th	Night	8% 9% 24% 32% 24% 3	840
	21st to end	Night	8% 12% 26% 35% 16% 3	924
April	1st to 10th	Night	7% 7% 24% 38% 21% 2	840
	11th to 20th	Night	7% 10% 23% 34% 21% 5%	831
	21st to end	Night	7% 7% 20% 39% 23% 4	824
May	1st to 10th	Night	7% 7% 27% 35% 20% 3	583
	11th to 20th	Night	9% 6% 21% 33% 25% 7%	414
	21st to end	Night	8% 5% 18% 36% 29% 5%	455
June	1st to 10th	Night	5% 5% 19% 42% 27% 3	420
	11th to 20th	Night	5% 5% 23% 45% 20% 2	420
	21st to end	Night	5% 2 16% 50% 25% 2	420
July	1st to 10th	Night	1 1 14% 54% 28% 2	410
	11th to 20th	Night	3 1 14% 59% 23% 1	408
	21st to end	Night	2 11% 53% 32% 2	460
August	1st to 10th	Night	2 1 11% 48% 36% 3	540
	11th to 20th	Night	3 2 11% 46% 33% 4	802
	21st to end	Night	3 1 12% 46% 35% 3	916
September	1st to 10th	Night	3 2 12% 42% 37% 6%	800
	11th to 20th	Night	5% 3 13% 35% 35% 11%	800
	21st to end	Night	5% 4 15% 35% 30% 12%	800
October	1st to 10th	Night	6% 4 17% 37% 28% 7%	800
	11th to 20th	Night	5% 8% 16% 37% 28% 7%	800
	21st to end	Night	6% 8% 17% 37% 24% 8%	880
November	1st to 10th	Night	9% 7% 20% 37% 21% 6%	820
	11th to 20th	Night	10% 8% 26% 34% 20% 3	840
	21st to end	Night	8% 7% 23% 34% 23% 5%	840
December	1st to 10th	Night	9% 10% 19% 38% 20% 5%	840
	11th to 20th	Night	12% 11% 20% 34% 20% 4	840
	21st to end	Night	13% 12% 29% 32% 13% 2	924

Page generated at 2026-08-27 01:07:09. Version ac07

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