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 2024-04-25.

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% 7% 3 5% 5% 3 5% 5% 5% 7% 38%	83135
	Night	17% 7% 3 5% 5% 3 4 4 5% 6% 40%	85970
Transparency	Day	45% 6% 11% 21% 15% 2	82840
	Night	44% 6% 11% 22% 14% 2	85799
Seeing	Day	25% 16% 30% 19% 8% 2	14192
	Night	23% 15% 31% 24% 7% 1	23268

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	13% 8% 3 6% 5% 3 5% 4 6% 6% 42%	2517
	11th to 20th	Day	16% 8% 3 7% 6% 3 4 5% 5% 6% 38%	2520
	21st to end	Day	18% 12% 4 7% 5% 3 4 4 5% 6% 33%	2772
February	1st to 10th	Day	17% 8% 2 6% 6% 4 6% 5% 6% 6% 34%	1726
	11th to 20th	Day	13% 7% 3 7% 5% 3 6% 5% 6% 8% 38%	1848
	21st to end	Day	16% 11% 4 7% 5% 3 4 5% 4 5% 37%	1570
March	1st to 10th	Day	22% 14% 4 6% 6% 3 4 4 4 5% 29%	3116
	11th to 20th	Day	13% 9% 3 5% 5% 4 5% 5% 6% 7% 39%	3306
	21st to end	Day	20% 9% 3 6% 6% 3 4 4 5% 7% 34%	4085
April	1st to 10th	Day	18% 9% 3 6% 5% 3 4 4 4 6% 37%	2280
	11th to 20th	Day	17% 6% 2 5% 6% 3 4 5% 6% 7% 39%	2259
	21st to end	Day	22% 7% 3 6% 6% 3 5% 5% 4 6% 34%	2395
May	1st to 10th	Day	23% 7% 3 6% 5% 4 4 4 4 5% 34%	2340
	11th to 20th	Day	18% 6% 3 5% 5% 3 5% 4 5% 6% 40%	2394
	21st to end	Day	15% 5% 2 5% 6% 3 5% 4 4 7% 42%	2725
June	1st to 10th	Day	19% 6% 3 6% 6% 4 5% 5% 7% 8% 33%	2520
	11th to 20th	Day	18% 5% 2 6% 5% 3 5% 5% 6% 9% 36%	2520
	21st to end	Day	19% 6% 3 6% 6% 3 5% 4 6% 8% 34%	2520
July	1st to 10th	Day	15% 6% 2 5% 5% 3 6% 5% 5% 8% 40%	2520
	11th to 20th	Day	12% 5% 3 6% 6% 4 5% 5% 7% 10% 37%	2520
	21st to end	Day	13% 5% 3 5% 6% 4 6% 6% 6% 8% 39%	2744
August	1st to 10th	Day	11% 5% 2 6% 5% 4 6% 6% 6% 8% 39%	2403
	11th to 20th	Day	13% 6% 2 5% 6% 3 6% 7% 7% 9% 37%	2267
	21st to end	Day	13% 4 2 4 5% 3 5% 5% 6% 8% 44%	2376
September	1st to 10th	Day	13% 5% 2 4 5% 3 5% 5% 5% 7% 45%	2160
	11th to 20th	Day	15% 5% 2 4 3 2 3 4 3 5% 53%	1997
	21st to end	Day	16% 5% 3 4 5% 2 4 5% 4 7% 47%	1980
October	1st to 10th	Day	24% 6% 3 5% 5% 3 4 3 5% 6% 37%	1980
	11th to 20th	Day	16% 6% 3 4 4 3 4 5% 4 8% 44%	1733
	21st to end	Day	23% 7% 2 5% 5% 3 5% 4 5% 5% 36%	1782
November	1st to 10th	Day	15% 7% 3 5% 4 3 3 4 3 5% 49%	1671
	11th to 20th	Day	18% 5% 2 4 4 3 4 4 5% 6% 45%	1710
	21st to end	Day	19% 7% 2 5% 4 3 4 5% 4 6% 41%	1681
December	1st to 10th	Day	18% 8% 3 4 6% 4 4 6% 5% 7% 35%	1520
	11th to 20th	Day	22% 6% 3 4 4 3 3 5% 4 5% 41%	1906
	21st to end	Day	22% 11% 3 6% 5% 3 4 4 5% 6% 31%	2772
January	1st to 10th	Night	17% 7% 2 4 4 3 4 4 4 6% 46%	4429
	11th to 20th	Night	14% 7% 3 7% 6% 3 5% 5% 5% 7% 37%	4440
	21st to end	Night	21% 13% 5% 7% 5% 3 4 4 4 4 31%	4884
February	1st to 10th	Night	15% 9% 3 5% 6% 3 4 4 5% 7% 38%	2449
	11th to 20th	Night	12% 8% 4 5% 5% 3 6% 5% 6% 7% 40%	2218
	21st to end	Night	15% 8% 3 6% 5% 2 4 5% 5% 7% 39%	1884
March	1st to 10th	Night	26% 10% 2 5% 4 3 4 4 4 6% 33%	3724
	11th to 20th	Night	12% 8% 3 6% 6% 3 5% 6% 6% 7% 37%	3653
	21st to end	Night	22% 8% 3 5% 4 2 3 5% 6% 6% 35%	3544
April	1st to 10th	Night	19% 8% 3 6% 5% 3 5% 5% 5% 6% 37%	1900
	11th to 20th	Night	19% 7% 3 4 4 2 5% 4 5% 6% 40%	1870
	21st to end	Night	21% 7% 3 6% 4 3 4 4 4 7% 39%	1665
May	1st to 10th	Night	21% 8% 3 6% 7% 3 5% 4 5% 6% 32%	1620
	11th to 20th	Night	18% 6% 2 6% 6% 3 6% 4 5% 6% 38%	1514
	21st to end	Night	16% 6% 3 6% 5% 3 5% 4 6% 7% 39%	1550
June	1st to 10th	Night	20% 8% 2 6% 5% 3 4 4 5% 7% 37%	1440
	11th to 20th	Night	20% 5% 3 4 4 3 5% 4 5% 7% 39%	1440
	21st to end	Night	18% 5% 2 5% 4 3 6% 4 6% 8% 40%	1440
July	1st to 10th	Night	15% 5% 3 4 4 3 5% 5% 5% 7% 43%	1440
	11th to 20th	Night	13% 4 2 5% 6% 2 5% 6% 6% 9% 42%	1440
	21st to end	Night	12% 5% 2 3 4 2 5% 5% 6% 9% 47%	1574
August	1st to 10th	Night	10% 6% 2 5% 5% 3 4 5% 6% 8% 46%	1517
	11th to 20th	Night	13% 6% 3 5% 6% 4 5% 5% 6% 9% 39%	1631
	21st to end	Night	15% 4 2 4 4 3 3 4 4 8% 49%	1980
September	1st to 10th	Night	13% 5% 2 4 4 2 3 3 5% 7% 51%	1800
	11th to 20th	Night	15% 4 2 4 3 2 3 3 5% 6% 53%	1962
	21st to end	Night	14% 4 2 4 4 3 4 4 5% 6% 50%	1980
October	1st to 10th	Night	22% 6% 3 5% 5% 2 4 4 4 5% 41%	1980
	11th to 20th	Night	16% 5% 2 4 5% 3 5% 5% 5% 7% 43%	2221
	21st to end	Night	23% 8% 2 5% 4 3 4 5% 4 6% 36%	2574
November	1st to 10th	Night	15% 6% 3 5% 4 3 4 4 4 5% 46%	2407
	11th to 20th	Night	17% 6% 3 4 4 3 4 4 5% 5% 45%	2470
	21st to end	Night	15% 7% 3 5% 4 3 3 4 6% 7% 43%	2498
December	1st to 10th	Night	18% 9% 3 6% 5% 3 5% 5% 4 6% 36%	2660
	11th to 20th	Night	19% 7% 3 4 4 2 4 5% 5% 6% 40%	3288
	21st to end	Night	21% 10% 4 6% 5% 3 4 4 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% 16% 4	2395
May	1st to 10th	Day	53% 4 7% 20% 13% 2	2340
	11th to 20th	Day	44% 6% 8% 20% 18% 3	2398
	21st to end	Day	42% 7% 13% 22% 13% 3	2725
June	1st to 10th	Day	48% 8% 11% 21% 11% 1	2520
	11th to 20th	Day	44% 7% 11% 19% 16% 3	2520
	21st to end	Day	47% 8% 12% 21% 12% 1	2520
July	1st to 10th	Day	41% 8% 11% 22% 17% 2	2450
	11th to 20th	Day	41% 8% 13% 24% 12% 1	2445
	21st to end	Day	39% 8% 13% 23% 14% 2	2591
August	1st to 10th	Day	40% 9% 14% 23% 13% 1	2389
	11th to 20th	Day	42% 8% 12% 24% 12% 2	2267
	21st to end	Day	36% 8% 12% 25% 17% 3	2376
September	1st to 10th	Day	37% 7% 12% 24% 18% 2	2160
	11th to 20th	Day	35% 5% 8% 25% 24% 2	1997
	21st to end	Day	38% 5% 9% 23% 21% 3	1980
October	1st to 10th	Day	48% 5% 9% 21% 13% 3	1980
	11th to 20th	Day	38% 6% 12% 30% 12% 2	1733
	21st to end	Day	50% 5% 9% 20% 13% 3	1782
November	1st to 10th	Day	39% 4 13% 25% 17% 2	1671
	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% 16% 4	1665
May	1st to 10th	Night	52% 5% 8% 19% 13% 3	1620
	11th to 20th	Night	46% 7% 11% 17% 17% 3	1515
	21st to end	Night	43% 8% 13% 22% 12% 1	1551
June	1st to 10th	Night	47% 6% 11% 23% 12% 1	1440
	11th to 20th	Night	45% 8% 12% 19% 13% 2	1440
	21st to end	Night	41% 9% 14% 21% 14% 1	1440
July	1st to 10th	Night	40% 8% 14% 24% 14% 2	1400
	11th to 20th	Night	38% 9% 14% 26% 13%	1392
	21st to end	Night	32% 8% 15% 29% 13% 2	1486
August	1st to 10th	Night	34% 8% 14% 25% 16% 1	1507
	11th to 20th	Night	41% 9% 13% 23% 13% 1	1631
	21st to end	Night	35% 6% 11% 28% 19% 1	1980
September	1st to 10th	Night	34% 6% 13% 27% 19% 1	1800
	11th to 20th	Night	33% 5% 10% 27% 24% 2	1962
	21st to end	Night	36% 6% 10% 28% 18% 2	1980
October	1st to 10th	Night	46% 6% 11% 22% 13% 3	1980
	11th to 20th	Night	39% 7% 12% 28% 14% 1	2221
	21st to end	Night	49% 6% 11% 21% 12% 2	2574
November	1st to 10th	Night	40% 5% 10% 23% 19% 3	2407
	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	32% 19% 28% 14% 6% 2	437
May	1st to 10th	Day	35% 18% 26% 14% 5% 2	423
	11th to 20th	Day	23% 17% 37% 16% 5% 2	447
	21st to end	Day	19% 16% 34% 22% 8% 2	485
June	1st to 10th	Day	20% 15% 37% 15% 10% 2	450
	11th to 20th	Day	18% 15% 36% 21% 8% 2	450
	21st to end	Day	19% 14% 34% 21% 8% 3	450
July	1st to 10th	Day	20% 9% 27% 29% 11% 4	445
	11th to 20th	Day	16% 7% 31% 30% 13% 3	444
	21st to end	Day	13% 9% 33% 32% 10% 2	488
August	1st to 10th	Day	13% 9% 29% 30% 15% 3	446
	11th to 20th	Day	16% 9% 30% 25% 15% 4	439
	21st to end	Day	16% 11% 31% 24% 14% 5%	495
September	1st to 10th	Day	19% 11% 25% 22% 17% 6%	450
	11th to 20th	Day	21% 13% 26% 18% 13% 9%	450
	21st to end	Day	19% 12% 32% 20% 12% 5%	450
October	1st to 10th	Day	31% 12% 23% 20% 11% 4	450
	11th to 20th	Day	22% 15% 30% 21% 10% 2	405
	21st to end	Day	33% 13% 28% 19% 6% 1	396
November	1st to 10th	Day	22% 18% 25% 23% 10% 1	365
	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	27% 19% 30% 21% 4	555
May	1st to 10th	Night	27% 14% 34% 21% 5%	540
	11th to 20th	Night	21% 15% 33% 26% 4	453
	21st to end	Night	20% 9% 33% 30% 8%	389
June	1st to 10th	Night	19% 12% 31% 28% 9% 1	360
	11th to 20th	Night	21% 9% 30% 32% 8% 1	360
	21st to end	Night	18% 5% 32% 36% 8%	360
July	1st to 10th	Night	17% 7% 29% 37% 9% 1	350
	11th to 20th	Night	14% 4 26% 40% 15% 2	348
	21st to end	Night	13% 5% 29% 41% 12%	394
August	1st to 10th	Night	14% 4 26% 41% 15%	443
	11th to 20th	Night	14% 8% 27% 35% 14% 2	567
	21st to end	Night	16% 6% 23% 36% 17% 2	792
September	1st to 10th	Night	15% 7% 32% 29% 16% 1	720
	11th to 20th	Night	18% 8% 28% 27% 18% 2	720
	21st to end	Night	17% 9% 30% 28% 13% 2	720
October	1st to 10th	Night	27% 11% 23% 27% 11% 1	720
	11th to 20th	Night	21% 11% 32% 25% 11% 1	720
	21st to end	Night	29% 15% 28% 22% 6%	792
November	1st to 10th	Night	21% 14% 30% 27% 8% 1	740
	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 2024-04-22 09:25:43. Version ac07

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