Broken Tooth Rock Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Broken Tooth Rock Observatory 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	17% 8% 2 6% 5% 4 5% 4 6% 7% 37%	101301
	Night	17% 8% 3 6% 4 4 4 3 5% 6% 39%	97745
Transparency	Day	45% 6% 11% 22% 15% 2	104839
	Night	43% 6% 11% 23% 15% 2	102296
Seeing	Day	25% 16% 30% 19% 8% 2	14948
	Night	23% 15% 31% 24% 7% 1	23847

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	12% 8% 2 6% 4 4 5% 3 6% 6% 42%	2517
	11th to 20th	Day	16% 8% 3 8% 5% 4 4 4 5% 6% 38%	2520
	21st to end	Day	18% 12% 4 7% 4 4 4 3 5% 5% 33%	2772
February	1st to 10th	Day	17% 9% 2 7% 5% 5% 5% 4 6% 6% 34%	1726
	11th to 20th	Day	12% 8% 3 8% 5% 4 5% 4 6% 8% 38%	1848
	21st to end	Day	16% 12% 3 8% 5% 4 3 4 5% 4 36%	1570
March	1st to 10th	Day	22% 15% 3 6% 5% 4 4 3 4 5% 29%	3116
	11th to 20th	Day	13% 9% 2 5% 4 5% 5% 4 6% 7% 39%	3306
	21st to end	Day	20% 9% 3 7% 5% 3 4 3 6% 7% 34%	4085
April	1st to 10th	Day	17% 10% 3 7% 5% 5% 4 3 4 6% 37%	2280
	11th to 20th	Day	17% 6% 2 6% 5% 5% 4 4 6% 7% 38%	2259
	21st to end	Day	21% 8% 2 7% 5% 4 4 4 4 6% 34%	2470
May	1st to 10th	Day	23% 10% 3 8% 5% 5% 4 3 5% 5% 28%	4106
	11th to 20th	Day	22% 7% 3 7% 5% 5% 4 3 5% 6% 32%	4258
	21st to end	Day	14% 5% 2 5% 4 4 5% 3 6% 9% 44%	4837
June	1st to 10th	Day	19% 7% 2 6% 5% 5% 4 4 7% 7% 33%	2660
	11th to 20th	Day	17% 5% 2 6% 5% 5% 5% 4 6% 9% 36%	2660
	21st to end	Day	19% 6% 2 7% 5% 5% 5% 3 6% 8% 33%	2660
July	1st to 10th	Day	13% 6% 2 6% 5% 5% 5% 5% 7% 10% 37%	4440
	11th to 20th	Day	11% 5% 2 6% 5% 5% 6% 5% 8% 11% 37%	4440
	21st to end	Day	16% 8% 3 6% 5% 5% 5% 4 6% 7% 36%	4814
August	1st to 10th	Day	15% 5% 3 8% 5% 5% 5% 5% 6% 8% 35%	4237
	11th to 20th	Day	14% 8% 2 7% 4 4 5% 5% 6% 7% 36%	3966
	21st to end	Day	8% 5% 2 5% 4 5% 6% 5% 8% 9% 42%	4180
September	1st to 10th	Day	12% 6% 1 5% 4 4 5% 4 5% 7% 47%	2280
	11th to 20th	Day	14% 6% 2 5% 3 3 2 3 4 5% 53%	2107
	21st to end	Day	16% 6% 2 5% 4 3 4 3 4 6% 45%	2090
October	1st to 10th	Day	23% 6% 2 6% 4 3 4 2 5% 6% 37%	2090
	11th to 20th	Day	16% 6% 2 4 3 3 4 4 4 8% 45%	1829
	21st to end	Day	22% 8% 2 6% 4 4 4 3 5% 5% 38%	1881
November	1st to 10th	Day	14% 7% 2 6% 4 4 3 3 4 5% 48%	1708
	11th to 20th	Day	18% 6% 2 5% 3 4 4 3 5% 6% 45%	1710
	21st to end	Day	19% 7% 2 5% 4 4 4 4 4 6% 41%	1681
December	1st to 10th	Day	18% 8% 3 5% 5% 5% 4 4 5% 7% 35%	1520
	11th to 20th	Day	22% 7% 2 5% 4 3 3 4 4 5% 41%	1906
	21st to end	Day	22% 11% 3 6% 5% 4 4 3 5% 6% 31%	2772
January	1st to 10th	Night	17% 7% 2 4 3 4 3 4 4 6% 46%	4429
	11th to 20th	Night	14% 8% 3 8% 5% 4 4 4 6% 7% 37%	4440
	21st to end	Night	21% 13% 5% 8% 4 4 3 3 4 4 31%	4884
February	1st to 10th	Night	15% 9% 3 6% 5% 4 4 4 6% 6% 38%	2449
	11th to 20th	Night	12% 9% 2 6% 5% 5% 5% 4 6% 7% 40%	2218
	21st to end	Night	15% 9% 3 6% 4 3 4 4 5% 7% 39%	1884
March	1st to 10th	Night	26% 10% 2 6% 4 4 3 3 4 6% 33%	3724
	11th to 20th	Night	12% 8% 3 8% 5% 4 5% 4 6% 7% 37%	3653
	21st to end	Night	22% 9% 3 6% 3 3 4 4 6% 6% 35%	3544
April	1st to 10th	Night	19% 8% 2 7% 4 4 4 4 5% 6% 37%	1900
	11th to 20th	Night	19% 8% 2 5% 4 4 4 3 5% 6% 40%	1870
	21st to end	Night	21% 7% 3 6% 3 4 3 3 5% 6% 39%	1710
May	1st to 10th	Night	25% 10% 3 7% 5% 4 4 3 5% 6% 26%	2834
	11th to 20th	Night	19% 7% 3 7% 6% 6% 6% 4 6% 6% 28%	2664
	21st to end	Night	16% 5% 2 6% 4 3 5% 3 6% 8% 42%	2738
June	1st to 10th	Night	19% 8% 2 7% 4 4 4 3 5% 6% 37%	1520
	11th to 20th	Night	20% 6% 3 4 4 5% 4 3 6% 7% 39%	1520
	21st to end	Night	18% 6% 2 5% 4 4 5% 3 6% 8% 39%	1520
July	1st to 10th	Night	11% 5% 3 6% 5% 5% 6% 4 6% 9% 40%	2520
	11th to 20th	Night	13% 5% 2 7% 4 4 5% 3 6% 8% 43%	2520
	21st to end	Night	16% 7% 3 5% 4 4 4 3 5% 7% 42%	2739
August	1st to 10th	Night	21% 7% 2 7% 5% 4 4 4 5% 6% 35%	2661
	11th to 20th	Night	12% 8% 3 7% 5% 5% 4 3 6% 8% 39%	2845
	21st to end	Night	9% 4 1 4 3 3 4 3 5% 8% 56%	3476
September	1st to 10th	Night	13% 5% 2 5% 4 3 3 3 5% 7% 51%	1900
	11th to 20th	Night	14% 5% 2 4 3 3 2 2 5% 6% 53%	2071
	21st to end	Night	15% 5% 2 5% 4 4 3 3 5% 6% 48%	2090
October	1st to 10th	Night	21% 6% 2 7% 4 3 4 3 4 6% 40%	2090
	11th to 20th	Night	16% 5% 2 4 4 4 5% 4 5% 7% 45%	2345
	21st to end	Night	22% 8% 2 5% 4 4 4 4 4 6% 37%	2717
November	1st to 10th	Night	15% 7% 3 5% 4 4 4 3 4 5% 46%	2470
	11th to 20th	Night	17% 7% 2 5% 4 3 4 3 5% 5% 45%	2470
	21st to end	Night	15% 8% 2 6% 4 4 3 3 6% 6% 43%	2498
December	1st to 10th	Night	18% 9% 3 6% 4 4 5% 4 5% 6% 36%	2660
	11th to 20th	Night	19% 8% 2 5% 4 4 4 4 5% 6% 40%	3288
	21st to end	Night	21% 11% 4 7% 4 4 4 3 5% 5% 33%	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	41% 6% 9% 32% 11% 1	2518
	11th to 20th	Day	47% 5% 12% 24% 10% 2	2520
	21st to end	Day	52% 5% 10% 22% 9% 2	2772
February	1st to 10th	Day	49% 5% 13% 20% 11% 2	1726
	11th to 20th	Day	43% 7% 11% 21% 16% 3	1857
	21st to end	Day	50% 4 10% 19% 14% 3	1570
March	1st to 10th	Day	59% 3 10% 14% 12% 3	3119
	11th to 20th	Day	40% 7% 14% 21% 16% 3	3306
	21st to end	Day	49% 4 6% 16% 18% 7%	4085
April	1st to 10th	Day	49% 5% 8% 19% 16% 4	2280
	11th to 20th	Day	44% 6% 11% 19% 17% 2	2259
	21st to end	Day	51% 5% 8% 16% 17% 3	2470
May	1st to 10th	Day	57% 7% 9% 16% 11% 1	4120
	11th to 20th	Day	51% 7% 14% 16% 10% 2	4262
	21st to end	Day	36% 8% 12% 24% 18% 2	4837
June	1st to 10th	Day	47% 8% 11% 22% 12% 1	2660
	11th to 20th	Day	43% 7% 11% 20% 16% 3	2660
	21st to end	Day	48% 8% 12% 20% 12% 1	2660
July	1st to 10th	Day	42% 6% 13% 20% 18% 1	4370
	11th to 20th	Day	40% 6% 16% 25% 12% 1	4365
	21st to end	Day	46% 5% 12% 20% 15% 1	4661
August	1st to 10th	Day	45% 6% 15% 22% 11% 1	4223
	11th to 20th	Day	45% 5% 14% 25% 9% 1	4005
	21st to end	Day	35% 6% 13% 29% 16% 2	4180
September	1st to 10th	Day	36% 7% 12% 25% 19% 2	2280
	11th to 20th	Day	35% 5% 8% 26% 24% 2	2107
	21st to end	Day	40% 5% 9% 23% 20% 3	2090
October	1st to 10th	Day	45% 5% 8% 23% 18% 2	3480
	11th to 20th	Day	34% 4 9% 29% 21% 4	3019
	21st to end	Day	36% 4 8% 31% 19% 4	3081
November	1st to 10th	Day	39% 4 13% 25% 17% 2	1708
	11th to 20th	Day	40% 5% 10% 22% 19% 3	1710
	21st to end	Day	44% 5% 16% 20% 13% 2	1681
December	1st to 10th	Day	48% 6% 14% 17% 14% 1	1520
	11th to 20th	Day	46% 5% 11% 19% 17% 3	1906
	21st to end	Day	54% 6% 11% 17% 10% 1	2772
January	1st to 10th	Night	39% 5% 13% 28% 11% 3	4429
	11th to 20th	Night	45% 7% 11% 23% 11% 3	4440
	21st to end	Night	57% 5% 9% 17% 11% 2	4884
February	1st to 10th	Night	46% 6% 12% 21% 13% 2	2449
	11th to 20th	Night	43% 6% 11% 21% 16% 3	2220
	21st to end	Night	43% 5% 10% 24% 13% 4	1884
March	1st to 10th	Night	54% 4 9% 19% 11% 3	3734
	11th to 20th	Night	44% 9% 10% 20% 15% 2	3654
	21st to end	Night	48% 4 7% 14% 20% 7%	3544
April	1st to 10th	Night	47% 5% 11% 18% 17% 3	1900
	11th to 20th	Night	45% 5% 9% 21% 19% 2	1870
	21st to end	Night	46% 5% 11% 18% 17% 4	1710
May	1st to 10th	Night	56% 7% 10% 17% 8% 2	2840
	11th to 20th	Night	52% 10% 13% 14% 9% 2	2665
	21st to end	Night	38% 10% 15% 21% 15% 2	2739
June	1st to 10th	Night	46% 7% 11% 23% 12% 1	1520
	11th to 20th	Night	44% 8% 13% 20% 13% 2	1520
	21st to end	Night	43% 9% 13% 21% 13% 1	1520
July	1st to 10th	Night	40% 7% 14% 24% 14% 1	2480
	11th to 20th	Night	39% 7% 13% 24% 16%	2472
	21st to end	Night	42% 5% 11% 25% 15% 1	2651
August	1st to 10th	Night	49% 6% 12% 20% 11% 1	2651
	11th to 20th	Night	44% 7% 15% 24% 10% 1	2872
	21st to end	Night	27% 5% 16% 32% 19% 1	3476
September	1st to 10th	Night	33% 6% 13% 27% 20% 1	1900
	11th to 20th	Night	33% 5% 10% 27% 23% 2	2071
	21st to end	Night	37% 5% 10% 28% 17% 2	2090
October	1st to 10th	Night	41% 5% 15% 23% 14% 2	3480
	11th to 20th	Night	30% 4 11% 27% 25% 4	3894
	21st to end	Night	37% 4 10% 33% 15% 2	4467
November	1st to 10th	Night	40% 5% 10% 23% 19% 3	2470
	11th to 20th	Night	42% 5% 9% 23% 19% 3	2470
	21st to end	Night	41% 5% 14% 26% 13% 1	2498
December	1st to 10th	Night	48% 6% 12% 22% 11% 1	2660
	11th to 20th	Night	44% 5% 14% 17% 18% 2	3288
	21st to end	Night	52% 6% 9% 24% 9% 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	34% 19% 29% 13% 5%	180
	11th to 20th	Day	30% 24% 33% 10% 1 2	180
	21st to end	Day	26% 21% 35% 13% 4 1	198
February	1st to 10th	Day	32% 25% 28% 12% 2	324
	11th to 20th	Day	32% 27% 27% 12% 1	456
	21st to end	Day	30% 23% 29% 15% 3	382
March	1st to 10th	Day	32% 20% 32% 13% 3	460
	11th to 20th	Day	33% 22% 29% 11% 3 1	460
	21st to end	Day	32% 20% 30% 12% 4 2	506
April	1st to 10th	Day	33% 20% 30% 10% 6% 2	460
	11th to 20th	Day	32% 22% 27% 13% 5% 2	452
	21st to end	Day	31% 18% 30% 14% 6% 2	460
May	1st to 10th	Day	34% 18% 27% 15% 5% 2	463
	11th to 20th	Day	23% 16% 37% 17% 6% 1	487
	21st to end	Day	18% 17% 34% 22% 7% 2	529
June	1st to 10th	Day	20% 15% 38% 15% 10% 2	490
	11th to 20th	Day	17% 15% 34% 22% 9% 2	490
	21st to end	Day	21% 15% 34% 20% 7% 3	490
July	1st to 10th	Day	19% 8% 30% 28% 11% 4	485
	11th to 20th	Day	15% 7% 33% 30% 12% 3	484
	21st to end	Day	15% 10% 33% 30% 10% 2	532
August	1st to 10th	Day	13% 9% 30% 30% 14% 3	486
	11th to 20th	Day	17% 9% 29% 25% 14% 5%	479
	21st to end	Day	15% 11% 31% 24% 15% 5%	539
September	1st to 10th	Day	19% 11% 26% 22% 16% 6%	490
	11th to 20th	Day	20% 12% 25% 18% 15% 10%	490
	21st to end	Day	19% 11% 32% 21% 13% 5%	490
October	1st to 10th	Day	30% 12% 23% 20% 11% 4	490
	11th to 20th	Day	23% 15% 28% 21% 10% 2	440
	21st to end	Day	31% 13% 29% 20% 6% 1	429
November	1st to 10th	Day	23% 18% 26% 22% 10% 1	378
	11th to 20th	Day	33% 17% 24% 20% 5% 1	370
	21st to end	Day	31% 19% 26% 16% 6% 1	341
December	1st to 10th	Day	26% 27% 31% 10% 6% 1	180
	11th to 20th	Day	36% 19% 32% 11% 2	180
	21st to end	Day	34% 19% 28% 15% 3 1	198
January	1st to 10th	Night	23% 22% 32% 19% 3	760
	11th to 20th	Night	28% 19% 31% 18% 3	760
	21st to end	Night	22% 20% 36% 19% 3	836
February	1st to 10th	Night	24% 19% 35% 19% 2	760
	11th to 20th	Night	23% 23% 35% 17% 2	743
	21st to end	Night	26% 21% 32% 18% 2	628
March	1st to 10th	Night	27% 19% 33% 18% 2	760
	11th to 20th	Night	26% 21% 29% 20% 4	760
	21st to end	Night	26% 19% 32% 19% 5%	836
April	1st to 10th	Night	27% 18% 32% 19% 4	760
	11th to 20th	Night	25% 19% 32% 19% 5%	746
	21st to end	Night	26% 19% 29% 21% 4	570
May	1st to 10th	Night	26% 14% 34% 21% 5%	570
	11th to 20th	Night	21% 14% 32% 28% 4	478
	21st to end	Night	19% 9% 34% 29% 8%	411
June	1st to 10th	Night	19% 12% 32% 28% 9% 1	380
	11th to 20th	Night	20% 9% 30% 32% 8% 1	380
	21st to end	Night	18% 6% 32% 35% 8%	380
July	1st to 10th	Night	16% 7% 29% 38% 8% 1	370
	11th to 20th	Night	14% 5% 26% 39% 15% 2	368
	21st to end	Night	13% 6% 29% 40% 12%	416
August	1st to 10th	Night	16% 4 25% 40% 15%	468
	11th to 20th	Night	14% 8% 28% 34% 14% 2	599
	21st to end	Night	15% 6% 24% 36% 17% 2	836
September	1st to 10th	Night	15% 7% 32% 29% 16% 1	760
	11th to 20th	Night	17% 8% 26% 28% 19% 2	760
	21st to end	Night	18% 9% 29% 29% 13% 2	760
October	1st to 10th	Night	26% 11% 23% 27% 12% 1	760
	11th to 20th	Night	21% 11% 32% 25% 11% 1	760
	21st to end	Night	28% 16% 27% 22% 6%	836
November	1st to 10th	Night	20% 14% 30% 27% 7% 1	760
	11th to 20th	Night	23% 18% 31% 19% 7% 1	760
	21st to end	Night	26% 17% 29% 22% 6% 1	760
December	1st to 10th	Night	25% 20% 33% 17% 4	760
	11th to 20th	Night	27% 19% 33% 17% 3	760
	21st to end	Night	27% 21% 30% 19% 3	836

Page generated at 2024-11-03 02:11:21. Version ac07

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