Broch nam Broc Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Broch nam Broc Observatory clear sky chart from 2005-11-06 to 2024-11-28.

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	22% 9% 3 7% 4 4 4 3 5% 6% 35%	105679
	Night	26% 9% 3 7% 4 4 4 3 4 5% 31%	102465
Transparency	Day	50% 9% 15% 17% 8% 1	105430
	Night	55% 8% 13% 15% 7% 1	102360
Seeing	Day	26% 9% 20% 25% 16% 5%	15340
	Night	33% 7% 14% 24% 19% 3	23595

By Month

Percentage Cloud Cover NW (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	41% 12% 4 9% 4 4 4 3 3 4 10%	2219
	11th to 20th	Day	28% 13% 4 7% 5% 4 3 3 3 6% 25%	2259
	21st to end	Day	51% 13% 3 7% 4 2 2 2 3 3 10%	2807
February	1st to 10th	Day	33% 12% 4 8% 5% 5% 4 3 4 5% 17%	1710
	11th to 20th	Day	29% 12% 4 8% 4 4 4 3 4 5% 22%	1665
	21st to end	Day	27% 16% 4 7% 5% 3 4 3 6% 5% 20%	1447
March	1st to 10th	Day	23% 16% 4 8% 6% 5% 4 3 5% 6% 19%	3219
	11th to 20th	Day	20% 9% 3 7% 5% 4 5% 3 5% 6% 33%	3490
	21st to end	Day	25% 13% 4 9% 5% 5% 5% 4 5% 5% 21%	3943
April	1st to 10th	Day	26% 13% 3 8% 5% 5% 4 4 6% 6% 19%	2280
	11th to 20th	Day	22% 10% 3 8% 7% 5% 5% 4 6% 6% 26%	2319
	21st to end	Day	24% 9% 4 9% 5% 4 4 4 5% 6% 26%	2536
May	1st to 10th	Day	16% 8% 3 6% 4 4 4 3 5% 6% 42%	4420
	11th to 20th	Day	13% 7% 2 6% 4 4 4 4 6% 9% 40%	4377
	21st to end	Day	26% 10% 4 7% 4 4 4 4 5% 6% 25%	4831
June	1st to 10th	Day	22% 7% 3 7% 5% 5% 4 4 6% 7% 30%	2850
	11th to 20th	Day	21% 9% 3 8% 6% 4 5% 4 5% 7% 29%	2850
	21st to end	Day	13% 8% 3 7% 5% 6% 5% 4 5% 7% 39%	2850
July	1st to 10th	Day	8% 4 1 4 3 2 3 2 4 5% 65%	4740
	11th to 20th	Day	5% 2 1 2 2 2 2 2 4 5% 70%	4740
	21st to end	Day	13% 4 1 4 2 3 3 3 4 6% 58%	4800
August	1st to 10th	Day	5% 3 1 4 2 2 2 2 4 6% 68%	4381
	11th to 20th	Day	12% 5% 2 6% 4 4 4 3 6% 7% 48%	4026
	21st to end	Day	17% 7% 3 6% 4 4 4 3 5% 8% 41%	4380
September	1st to 10th	Day	12% 7% 2 7% 4 4 4 3 4 6% 49%	2280
	11th to 20th	Day	16% 8% 3 8% 5% 4 4 3 5% 6% 39%	2280
	21st to end	Day	24% 7% 3 6% 4 3 3 3 6% 6% 35%	2005
October	1st to 10th	Day	21% 6% 2 7% 5% 5% 5% 4 6% 7% 32%	3180
	11th to 20th	Day	35% 8% 2 6% 3 3 3 4 5% 6% 24%	3161
	21st to end	Day	31% 12% 3 8% 4 5% 4 4 6% 6% 16%	3207
November	1st to 10th	Day	39% 10% 3 6% 5% 4 4 3 4 6% 17%	1568
	11th to 20th	Day	36% 12% 2 6% 5% 4 3 2 4 4 22%	1600
	21st to end	Day	35% 13% 4 8% 5% 4 3 3 5% 4 17%	1576
December	1st to 10th	Day	33% 13% 3 7% 4 4 3 3 3 4 25%	1520
	11th to 20th	Day	35% 14% 3 9% 4 3 3 4 4 5% 15%	1721
	21st to end	Day	34% 15% 5% 10% 5% 5% 3 3 3 5% 12%	2442
January	1st to 10th	Night	38% 14% 4 9% 5% 4 4 2 3 3 13%	4726
	11th to 20th	Night	32% 8% 2 5% 3 4 4 3 5% 7% 26%	4636
	21st to end	Night	48% 13% 3 7% 4 3 2 2 2 4 12%	4848
February	1st to 10th	Night	35% 12% 3 7% 5% 3 3 3 3 4 20%	2470
	11th to 20th	Night	29% 14% 3 7% 5% 4 3 3 3 4 24%	2402
	21st to end	Night	29% 12% 4 6% 4 4 3 3 4 4 25%	2006
March	1st to 10th	Night	24% 16% 4 7% 4 5% 5% 3 5% 6% 21%	3653
	11th to 20th	Night	23% 8% 2 6% 4 4 4 3 5% 7% 35%	3489
	21st to end	Night	31% 14% 4 9% 5% 4 3 3 3 4 20%	3709
April	1st to 10th	Night	28% 11% 3 7% 6% 5% 4 3 6% 6% 21%	1900
	11th to 20th	Night	22% 11% 2 8% 5% 6% 5% 3 5% 5% 28%	1809
	21st to end	Night	26% 11% 3 8% 5% 4 4 4 5% 5% 24%	1644
May	1st to 10th	Night	15% 10% 3 7% 4 3 3 3 3 5% 45%	2540
	11th to 20th	Night	10% 7% 2 6% 4 4 4 4 5% 7% 46%	2516
	21st to end	Night	19% 11% 4 10% 5% 5% 5% 4 5% 5% 27%	2742
June	1st to 10th	Night	20% 7% 3 9% 5% 5% 4 4 5% 7% 31%	1330
	11th to 20th	Night	19% 10% 3 8% 5% 4 5% 4 6% 7% 27%	1330
	21st to end	Night	13% 6% 2 6% 4 6% 4 3 5% 8% 42%	1330
July	1st to 10th	Night	6% 3 1 4 4 2 3 2 3 5% 66%	2220
	11th to 20th	Night	5% 3 1 3 2 2 2 2 3 3 76%	2220
	21st to end	Night	11% 3 1 4 3 3 3 3 3 5% 60%	2750
August	1st to 10th	Night	5% 2 1 3 2 2 2 3 5% 6% 70%	2547
	11th to 20th	Night	11% 4 2 5% 3 3 3 3 5% 8% 51%	2812
	21st to end	Night	14% 5% 2 6% 5% 3 4 4 6% 8% 41%	3291
September	1st to 10th	Night	9% 3 1 5% 4 3 4 3 5% 6% 56%	1900
	11th to 20th	Night	19% 6% 2 6% 3 4 3 3 5% 6% 43%	1900
	21st to end	Night	20% 6% 3 7% 4 4 4 3 4 6% 40%	2171
October	1st to 10th	Night	20% 7% 3 7% 5% 5% 5% 4 5% 6% 33%	3800
	11th to 20th	Night	32% 6% 2 5% 4 4 4 3 5% 6% 29%	3777
	21st to end	Night	33% 9% 2 7% 5% 3 3 3 4 5% 25%	4353
November	1st to 10th	Night	38% 9% 3 7% 5% 4 4 3 4 4 18%	2730
	11th to 20th	Night	37% 10% 2 7% 5% 4 3 3 3 4 22%	2800
	21st to end	Night	36% 12% 3 8% 4 4 4 3 3 4 19%	2758
December	1st to 10th	Night	31% 10% 3 6% 4 4 4 3 5% 6% 24%	2660
	11th to 20th	Night	40% 14% 4 9% 4 3 4 3 3 4 14%	3482
	21st to end	Night	37% 14% 4 9% 5% 3 4 2 3 3 16%	5214

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% 8% 7% 5% 2	2219
	11th to 20th	Day	61% 8% 10% 12% 6% 3	2280
	21st to end	Day	81% 6% 6% 6% 2	2807
February	1st to 10th	Day	71% 7% 9% 6% 5% 2	1710
	11th to 20th	Day	65% 9% 9% 9% 7% 1	1674
	21st to end	Day	66% 9% 9% 10% 5% 1	1447
March	1st to 10th	Day	61% 10% 14% 11% 4	3219
	11th to 20th	Day	52% 8% 14% 23% 2 1	3490
	21st to end	Day	62% 11% 13% 10% 3	3943
April	1st to 10th	Day	65% 11% 14% 9% 1	2280
	11th to 20th	Day	58% 9% 12% 11% 7% 2	2319
	21st to end	Day	59% 10% 13% 11% 6% 1	2536
May	1st to 10th	Day	44% 10% 15% 21% 10%	4420
	11th to 20th	Day	39% 13% 25% 18% 5%	4380
	21st to end	Day	58% 12% 17% 11% 2	4832
June	1st to 10th	Day	54% 10% 16% 14% 6% 1	2850
	11th to 20th	Day	55% 12% 16% 12% 4	2850
	21st to end	Day	44% 11% 17% 19% 8% 1	2850
July	1st to 10th	Day	22% 7% 12% 25% 23% 11%	4666
	11th to 20th	Day	18% 5% 12% 38% 24% 3	4659
	21st to end	Day	27% 8% 23% 28% 12% 2	4648
August	1st to 10th	Day	19% 7% 16% 40% 17% 1	4364
	11th to 20th	Day	34% 11% 25% 20% 7% 2	4065
	21st to end	Day	42% 8% 18% 22% 9% 1	4379
September	1st to 10th	Day	37% 9% 16% 22% 13% 4	2280
	11th to 20th	Day	45% 10% 12% 17% 14% 2	2280
	21st to end	Day	48% 9% 16% 16% 9% 2	2005
October	1st to 10th	Day	48% 9% 18% 19% 6%	3180
	11th to 20th	Day	60% 7% 14% 12% 7% 1	3161
	21st to end	Day	64% 11% 11% 10% 5%	3207
November	1st to 10th	Day	70% 7% 10% 9% 3 1	1568
	11th to 20th	Day	68% 7% 8% 10% 5% 2	1600
	21st to end	Day	69% 6% 9% 9% 6% 1	1576
December	1st to 10th	Day	65% 9% 6% 11% 9% 1	1520
	11th to 20th	Day	69% 9% 9% 8% 3 1	1724
	21st to end	Day	74% 10% 9% 5% 2 1	2442
January	1st to 10th	Night	76% 8% 6% 7% 2 1	4726
	11th to 20th	Night	56% 7% 12% 14% 8% 2	4677
	21st to end	Night	78% 5% 6% 8% 2 1	4848
February	1st to 10th	Night	68% 7% 9% 9% 4 3	2470
	11th to 20th	Night	65% 8% 9% 10% 6% 2	2404
	21st to end	Night	63% 7% 11% 13% 6% 1	2006
March	1st to 10th	Night	60% 9% 13% 11% 6%	3653
	11th to 20th	Night	48% 9% 15% 24% 3	3490
	21st to end	Night	67% 10% 12% 10% 1	3709
April	1st to 10th	Night	62% 11% 12% 13% 2	1900
	11th to 20th	Night	57% 9% 11% 14% 6% 3	1809
	21st to end	Night	61% 9% 12% 11% 7% 1	1644
May	1st to 10th	Night	43% 8% 13% 26% 10% 1	2540
	11th to 20th	Night	35% 12% 27% 20% 6%	2516
	21st to end	Night	57% 12% 17% 11% 3	2742
June	1st to 10th	Night	52% 9% 16% 15% 6% 2	1330
	11th to 20th	Night	53% 12% 18% 14% 3	1330
	21st to end	Night	40% 9% 21% 20% 7% 3	1330
July	1st to 10th	Night	22% 5% 11% 27% 22% 12%	2185
	11th to 20th	Night	16% 4 11% 36% 29% 3	2178
	21st to end	Night	26% 6% 14% 29% 22% 3	2663
August	1st to 10th	Night	15% 5% 16% 38% 25% 2	2539
	11th to 20th	Night	30% 8% 28% 22% 8% 3	2839
	21st to end	Night	39% 9% 21% 21% 10%	3291
September	1st to 10th	Night	29% 9% 18% 25% 15% 4	1900
	11th to 20th	Night	42% 9% 13% 17% 15% 3	1900
	21st to end	Night	45% 9% 15% 19% 10% 2	2171
October	1st to 10th	Night	49% 10% 19% 16% 6%	3800
	11th to 20th	Night	56% 6% 14% 17% 7%	3777
	21st to end	Night	60% 10% 13% 12% 5%	4353
November	1st to 10th	Night	70% 7% 10% 9% 4 1	2730
	11th to 20th	Night	68% 7% 9% 8% 5% 2	2800
	21st to end	Night	69% 7% 9% 8% 6% 1	2758
December	1st to 10th	Night	61% 9% 10% 12% 7% 1	2660
	11th to 20th	Night	74% 8% 8% 5% 4 1	3478
	21st to end	Night	73% 8% 8% 8% 2 1	5214

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	41% 13% 21% 11% 8% 6%	180
	11th to 20th	Day	45% 13% 17% 12% 9% 3	180
	21st to end	Day	46% 13% 14% 13% 13% 1	211
February	1st to 10th	Day	44% 11% 19% 17% 7% 3	370
	11th to 20th	Day	37% 11% 21% 19% 10% 2	365
	21st to end	Day	35% 14% 25% 15% 9% 2	324
March	1st to 10th	Day	35% 12% 22% 20% 10% 2	460
	11th to 20th	Day	34% 10% 18% 21% 14% 3	460
	21st to end	Day	38% 12% 18% 21% 9% 2	506
April	1st to 10th	Day	33% 12% 23% 19% 12% 2	460
	11th to 20th	Day	26% 11% 27% 22% 11% 3	452
	21st to end	Day	27% 11% 25% 22% 12% 3	460
May	1st to 10th	Day	18% 9% 25% 31% 15% 3	463
	11th to 20th	Day	23% 7% 18% 30% 18% 5%	488
	21st to end	Day	21% 12% 24% 23% 15% 5%	534
June	1st to 10th	Day	23% 8% 25% 29% 13% 3	680
	11th to 20th	Day	22% 10% 24% 30% 11% 3	680
	21st to end	Day	16% 9% 21% 31% 19% 3	680
July	1st to 10th	Day	15% 5% 21% 35% 20% 4	671
	11th to 20th	Day	9% 6% 20% 40% 20% 6%	668
	21st to end	Day	9% 4 16% 38% 24% 9%	541
August	1st to 10th	Day	11% 4 16% 30% 26% 12%	487
	11th to 20th	Day	10% 2 14% 36% 29% 10%	477
	21st to end	Day	14% 8% 20% 28% 22% 7%	539
September	1st to 10th	Day	18% 6% 18% 32% 19% 8%	490
	11th to 20th	Day	21% 8% 17% 28% 21% 5%	490
	21st to end	Day	25% 7% 21% 23% 19% 5%	490
October	1st to 10th	Day	30% 5% 19% 22% 19% 5%	490
	11th to 20th	Day	36% 6% 16% 20% 17% 5%	490
	21st to end	Day	39% 11% 17% 17% 11% 4	402
November	1st to 10th	Day	40% 16% 16% 17% 11% 2	200
	11th to 20th	Day	42% 10% 17% 13% 13% 7%	200
	21st to end	Day	45% 6% 21% 11% 11% 7%	194
December	1st to 10th	Day	46% 11% 15% 11% 10% 8%	180
	11th to 20th	Day	49% 11% 15% 16% 9% 1	180
	21st to end	Day	47% 10% 19% 17% 7% 1	198
January	1st to 10th	Night	49% 12% 15% 14% 9% 1	850
	11th to 20th	Night	44% 9% 13% 20% 13% 1	832
	21st to end	Night	44% 9% 14% 21% 12% 1	836
February	1st to 10th	Night	43% 12% 18% 19% 7% 1	760
	11th to 20th	Night	38% 10% 17% 25% 9% 1	744
	21st to end	Night	37% 10% 21% 21% 10% 1	628
March	1st to 10th	Night	34% 9% 19% 22% 15% 2	760
	11th to 20th	Night	39% 7% 18% 21% 13% 1	760
	21st to end	Night	39% 8% 17% 22% 11% 2	836
April	1st to 10th	Night	34% 8% 16% 26% 14% 2	760
	11th to 20th	Night	27% 7% 21% 27% 15% 3	681
	21st to end	Night	33% 6% 16% 28% 15% 2	504
May	1st to 10th	Night	22% 6% 13% 31% 27% 3	380
	11th to 20th	Night	19% 4 9% 28% 36% 5%	374
	21st to end	Night	21% 4 11% 32% 27% 5%	411
June	1st to 10th	Night	24% 6% 13% 28% 25% 4	380
	11th to 20th	Night	21% 8% 14% 31% 21% 4	380
	21st to end	Night	15% 4 10% 31% 34% 5%	380
July	1st to 10th	Night	11% 3 8% 31% 42% 4	370
	11th to 20th	Night	11% 3 8% 30% 39% 8%	368
	21st to end	Night	6% 2 7% 27% 50% 8%	416
August	1st to 10th	Night	11% 1 6% 21% 46% 15%	383
	11th to 20th	Night	9% 2 3 25% 47% 13%	564
	21st to end	Night	12% 5% 9% 26% 39% 8%	707
September	1st to 10th	Night	13% 2 9% 36% 33% 8%	760
	11th to 20th	Night	21% 4 11% 22% 32% 9%	760
	21st to end	Night	26% 5% 13% 27% 26% 4	760
October	1st to 10th	Night	25% 5% 12% 28% 25% 5%	760
	11th to 20th	Night	36% 5% 13% 24% 18% 4	760
	21st to end	Night	38% 7% 17% 24% 11% 2	836
November	1st to 10th	Night	45% 7% 18% 23% 7% 1	780
	11th to 20th	Night	47% 8% 18% 16% 9% 2	800
	21st to end	Night	44% 10% 14% 17% 12% 2	788
December	1st to 10th	Night	38% 7% 18% 23% 14% 1	760
	11th to 20th	Night	50% 9% 18% 17% 4 1	832
	21st to end	Night	49% 11% 19% 17% 4	935

Page generated at 2024-11-24 21:22:21. Version ac07

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