Turtle Rock Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Turtle Rock Observatory clear sky chart from 2005-11-06 to 2024-03-06.

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	15% 9% 4 7% 6% 3 5% 5% 6% 7% 34%	78910
	Night	15% 9% 4 6% 5% 3 5% 4 5% 7% 37%	80618
Transparency	Day	49% 5% 10% 20% 14% 2	78633
	Night	48% 4 10% 20% 15% 2	80414
Seeing	Day	21% 12% 21% 22% 16% 7%	14106
	Night	19% 10% 19% 31% 18% 2	24294

By Month

Percentage Cloud Cover SE (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	17% 14% 7% 10% 6% 2 3 3 4 6% 28%	2836
	11th to 20th	Day	16% 17% 9% 11% 8% 2 4 4 3 3 23%	2840
	21st to end	Day	16% 17% 6% 8% 6% 3 4 4 3 4 29%	3124
February	1st to 10th	Day	18% 12% 4 8% 5% 3 4 5% 5% 5% 31%	1715
	11th to 20th	Day	21% 11% 5% 9% 4 4 4 3 4 4 31%	1848
	21st to end	Day	22% 11% 4 8% 5% 2 3 3 4 5% 33%	1570
March	1st to 10th	Day	14% 10% 4 5% 5% 3 4 4 4 7% 40%	2006
	11th to 20th	Day	19% 9% 4 8% 5% 3 5% 4 5% 6% 31%	1980
	21st to end	Day	19% 11% 3 6% 5% 2 5% 4 5% 6% 33%	2178
April	1st to 10th	Day	14% 7% 3 5% 5% 3 6% 5% 5% 8% 39%	1980
	11th to 20th	Day	15% 8% 2 6% 5% 3 4 5% 5% 6% 41%	2173
	21st to end	Day	17% 7% 3 5% 7% 4 5% 5% 4 6% 37%	2340
May	1st to 10th	Day	16% 6% 3 6% 7% 4 5% 6% 6% 8% 33%	2340
	11th to 20th	Day	19% 7% 3 7% 6% 4 6% 6% 5% 7% 31%	2301
	21st to end	Day	12% 6% 3 6% 7% 4 6% 6% 8% 9% 33%	2531
June	1st to 10th	Day	11% 6% 3 6% 6% 4 5% 6% 7% 10% 36%	2340
	11th to 20th	Day	9% 5% 2 8% 7% 4 7% 7% 7% 9% 34%	2340
	21st to end	Day	10% 5% 3 8% 6% 4 6% 6% 8% 9% 35%	2340
July	1st to 10th	Day	11% 7% 4 6% 6% 4 7% 7% 9% 9% 31%	2340
	11th to 20th	Day	13% 6% 4 6% 5% 3 7% 7% 9% 10% 30%	2340
	21st to end	Day	14% 6% 3 7% 7% 4 8% 6% 7% 10% 28%	2547
August	1st to 10th	Day	10% 6% 3 8% 8% 5% 6% 6% 8% 11% 30%	2327
	11th to 20th	Day	13% 7% 3 7% 8% 5% 7% 6% 7% 9% 29%	2303
	21st to end	Day	9% 6% 2 6% 6% 4 5% 7% 7% 9% 38%	2458
September	1st to 10th	Day	11% 5% 2 5% 6% 4 4 6% 7% 9% 40%	1980
	11th to 20th	Day	13% 6% 2 6% 5% 3 5% 6% 6% 7% 39%	1980
	21st to end	Day	15% 6% 3 5% 6% 4 5% 4 5% 8% 39%	1980
October	1st to 10th	Day	15% 5% 2 4 4 3 4 4 5% 7% 47%	1909
	11th to 20th	Day	16% 6% 2 4 4 3 4 4 5% 5% 47%	1800
	21st to end	Day	17% 8% 3 4 5% 3 3 3 4 7% 43%	1980
November	1st to 10th	Day	12% 7% 2 5% 4 2 3 4 4 7% 51%	1777
	11th to 20th	Day	11% 10% 2 5% 5% 3 5% 4 5% 7% 43%	1710
	21st to end	Day	15% 9% 4 6% 4 3 4 3 5% 6% 42%	1710
December	1st to 10th	Day	20% 14% 4 8% 5% 3 3 4 4 6% 30%	1710
	11th to 20th	Day	17% 14% 3 7% 4 2 3 5% 6% 8% 32%	2153
	21st to end	Day	16% 15% 7% 8% 6% 3 5% 6% 6% 5% 24%	3124
January	1st to 10th	Night	18% 17% 7% 9% 6% 3 4 3 4 4 25%	4109
	11th to 20th	Night	20% 12% 4 8% 6% 3 4 3 4 4 32%	4120
	21st to end	Night	20% 11% 5% 7% 6% 3 5% 4 4 5% 29%	4532
February	1st to 10th	Night	16% 10% 4 8% 5% 2 4 4 5% 7% 34%	2461
	11th to 20th	Night	21% 11% 5% 7% 6% 3 5% 4 4 5% 30%	2218
	21st to end	Night	21% 12% 3 8% 5% 3 3 4 4 6% 30%	1884
March	1st to 10th	Night	16% 13% 4 6% 4 2 3 4 4 5% 39%	2070
	11th to 20th	Night	18% 9% 4 6% 6% 3 4 4 5% 7% 32%	1980
	21st to end	Night	14% 9% 3 7% 6% 3 5% 5% 5% 6% 36%	2178
April	1st to 10th	Night	14% 7% 3 7% 4 3 5% 5% 5% 7% 40%	1980
	11th to 20th	Night	14% 8% 2 5% 4 3 5% 5% 6% 7% 42%	1747
	21st to end	Night	14% 8% 3 5% 5% 4 5% 5% 4 6% 41%	1620
May	1st to 10th	Night	16% 6% 4 6% 5% 4 5% 5% 5% 8% 36%	1620
	11th to 20th	Night	14% 8% 3 6% 6% 3 6% 5% 6% 10% 32%	1592
	21st to end	Night	10% 6% 2 6% 6% 4 6% 5% 7% 11% 37%	1744
June	1st to 10th	Night	10% 4 3 6% 5% 3 6% 6% 7% 11% 40%	1620
	11th to 20th	Night	6% 4 3 5% 6% 5% 5% 7% 7% 10% 42%	1620
	21st to end	Night	9% 6% 3 6% 6% 4 5% 5% 7% 11% 39%	1620
July	1st to 10th	Night	12% 6% 3 6% 6% 3 5% 6% 7% 9% 38%	1620
	11th to 20th	Night	10% 5% 2 5% 5% 4 6% 5% 8% 13% 37%	1620
	21st to end	Night	10% 5% 3 6% 7% 4 6% 7% 7% 11% 35%	1771
August	1st to 10th	Night	11% 6% 3 6% 7% 3 6% 5% 7% 12% 36%	1611
	11th to 20th	Night	11% 7% 4 6% 7% 4 6% 6% 7% 8% 35%	1598
	21st to end	Night	9% 6% 3 5% 5% 3 5% 6% 7% 10% 41%	1876
September	1st to 10th	Night	12% 6% 3 6% 5% 4 5% 4 4 7% 44%	1980
	11th to 20th	Night	13% 7% 3 6% 5% 3 4 4 5% 7% 44%	1980
	21st to end	Night	13% 6% 2 5% 4 3 4 4 5% 7% 46%	1980
October	1st to 10th	Night	15% 5% 2 5% 4 2 4 4 4 6% 49%	2049
	11th to 20th	Night	16% 6% 2 4 4 2 3 4 5% 5% 48%	2160
	21st to end	Night	16% 7% 2 5% 4 2 3 4 5% 6% 45%	2376
November	1st to 10th	Night	13% 7% 3 4 3 2 3 3 4 5% 51%	2298
	11th to 20th	Night	14% 9% 3 5% 4 2 4 4 4 7% 44%	2470
	21st to end	Night	13% 9% 3 5% 4 3 4 4 5% 5% 45%	2470
December	1st to 10th	Night	20% 12% 5% 8% 5% 3 4 4 4 6% 29%	2470
	11th to 20th	Night	17% 12% 5% 9% 5% 3 4 4 4 5% 33%	3042
	21st to end	Night	16% 15% 7% 8% 6% 3 5% 4 5% 8% 23%	4532

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	60% 3 5% 16% 13% 3	2837
	11th to 20th	Day	68% 3 4 14% 10% 1	2840
	21st to end	Day	62% 2 5% 15% 15% 1	3124
February	1st to 10th	Day	56% 3 7% 18% 14% 1	1715
	11th to 20th	Day	59% 3 6% 17% 14% 2	1858
	21st to end	Day	55% 2 8% 15% 16% 4	1570
March	1st to 10th	Day	46% 2 7% 24% 18% 3	2006
	11th to 20th	Day	55% 4 9% 18% 11% 3	1980
	21st to end	Day	52% 4 9% 24% 8% 2	2178
April	1st to 10th	Day	45% 3 10% 24% 15% 3	1980
	11th to 20th	Day	44% 3 8% 21% 19% 4	2173
	21st to end	Day	49% 3 11% 23% 11% 2	2340
May	1st to 10th	Day	49% 5% 12% 22% 11% 1	2340
	11th to 20th	Day	52% 6% 14% 20% 6% 2	2305
	21st to end	Day	45% 7% 14% 25% 8% 1	2531
June	1st to 10th	Day	42% 8% 16% 21% 13% 1	2340
	11th to 20th	Day	44% 9% 14% 18% 13% 2	2340
	21st to end	Day	44% 7% 14% 20% 15% 1	2340
July	1st to 10th	Day	47% 7% 16% 16% 12% 2	2275
	11th to 20th	Day	45% 8% 16% 17% 12% 2	2271
	21st to end	Day	49% 7% 15% 19% 9% 1	2405
August	1st to 10th	Day	46% 9% 17% 21% 8%	2314
	11th to 20th	Day	50% 8% 13% 18% 10% 1	2303
	21st to end	Day	41% 7% 16% 20% 14% 2	2458
September	1st to 10th	Day	38% 8% 14% 22% 13% 5%	1980
	11th to 20th	Day	42% 7% 9% 23% 17% 2	1980
	21st to end	Day	44% 4 10% 22% 17% 3	1980
October	1st to 10th	Day	39% 3 8% 25% 20% 5%	1909
	11th to 20th	Day	40% 3 8% 26% 19% 4	1800
	21st to end	Day	43% 3 6% 26% 17% 5%	1980
November	1st to 10th	Day	36% 3 7% 21% 28% 5%	1777
	11th to 20th	Day	41% 3 7% 22% 21% 6%	1710
	21st to end	Day	45% 3 7% 21% 19% 4	1710
December	1st to 10th	Day	58% 3 8% 18% 11% 2	1710
	11th to 20th	Day	51% 3 8% 16% 18% 3	2150
	21st to end	Day	62% 2 6% 21% 8% 1	3124
January	1st to 10th	Night	65% 2 5% 14% 12% 2	4109
	11th to 20th	Night	58% 3 5% 15% 17% 2	4120
	21st to end	Night	59% 3 7% 17% 14% 1	4532
February	1st to 10th	Night	51% 3 10% 20% 14% 2	2461
	11th to 20th	Night	58% 3 6% 18% 11% 4	2219
	21st to end	Night	57% 3 7% 18% 11% 4	1884
March	1st to 10th	Night	49% 3 7% 19% 19% 3	2070
	11th to 20th	Night	52% 4 10% 22% 11% 1	1980
	21st to end	Night	48% 6% 11% 21% 12% 2	2178
April	1st to 10th	Night	43% 5% 10% 23% 16% 3	1980
	11th to 20th	Night	41% 5% 10% 21% 18% 5%	1747
	21st to end	Night	45% 4 11% 25% 12% 1	1620
May	1st to 10th	Night	48% 5% 14% 22% 10% 1	1620
	11th to 20th	Night	48% 8% 15% 22% 7% 1	1593
	21st to end	Night	41% 8% 18% 23% 9% 1	1745
June	1st to 10th	Night	38% 8% 19% 20% 15% 1	1620
	11th to 20th	Night	36% 7% 21% 21% 12% 2	1620
	21st to end	Night	39% 10% 15% 22% 12% 3	1620
July	1st to 10th	Night	42% 6% 17% 19% 14% 2	1575
	11th to 20th	Night	37% 8% 20% 20% 11% 4	1566
	21st to end	Night	40% 8% 18% 24% 9%	1672
August	1st to 10th	Night	40% 8% 19% 23% 10% 1	1600
	11th to 20th	Night	45% 8% 17% 18% 12% 1	1598
	21st to end	Night	36% 7% 17% 26% 12% 1	1876
September	1st to 10th	Night	41% 6% 14% 21% 15% 4	1980
	11th to 20th	Night	39% 6% 11% 23% 20% 1	1980
	21st to end	Night	39% 5% 10% 26% 18% 2	1980
October	1st to 10th	Night	37% 4 9% 24% 21% 4	2049
	11th to 20th	Night	40% 3 8% 27% 19% 4	2160
	21st to end	Night	41% 2 5% 24% 21% 6%	2376
November	1st to 10th	Night	37% 3 8% 21% 24% 6%	2298
	11th to 20th	Night	42% 3 7% 19% 23% 6%	2470
	21st to end	Night	42% 3 7% 25% 19% 3	2470
December	1st to 10th	Night	58% 3 8% 18% 11% 2	2470
	11th to 20th	Night	55% 3 7% 17% 15% 3	3044
	21st to end	Night	62% 3 8% 15% 11% 1	4532

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	30% 30% 26% 11% 3 1	270
	11th to 20th	Day	38% 24% 27% 10% 1	270
	21st to end	Day	34% 26% 26% 12% 3	297
February	1st to 10th	Day	31% 19% 33% 11% 5%	270
	11th to 20th	Day	43% 26% 23% 8% 1	270
	21st to end	Day	41% 23% 26% 8% 1	225
March	1st to 10th	Day	22% 21% 27% 22% 7% 1	411
	11th to 20th	Day	27% 23% 26% 19% 4 1	420
	21st to end	Day	32% 17% 23% 20% 7% 1	462
April	1st to 10th	Day	27% 16% 24% 20% 10% 2	420
	11th to 20th	Day	21% 18% 26% 20% 12% 3	412
	21st to end	Day	26% 15% 23% 22% 10% 4	420
May	1st to 10th	Day	24% 17% 27% 18% 9% 5%	423
	11th to 20th	Day	20% 9% 23% 25% 15% 8%	447
	21st to end	Day	16% 7% 19% 22% 21% 15%	485
June	1st to 10th	Day	14% 5% 20% 30% 22% 10%	450
	11th to 20th	Day	11% 6% 20% 26% 25% 11%	450
	21st to end	Day	13% 8% 24% 24% 22% 8%	450
July	1st to 10th	Day	16% 5% 12% 24% 25% 17%	445
	11th to 20th	Day	13% 4 13% 31% 26% 14%	444
	21st to end	Day	14% 5% 13% 31% 26% 11%	488
August	1st to 10th	Day	13% 6% 16% 25% 24% 16%	446
	11th to 20th	Day	15% 4 12% 28% 24% 16%	439
	21st to end	Day	13% 2 11% 28% 27% 19%	495
September	1st to 10th	Day	13% 4 13% 26% 30% 14%	450
	11th to 20th	Day	15% 6% 10% 24% 31% 15%	450
	21st to end	Day	18% 8% 18% 28% 21% 7%	450
October	1st to 10th	Day	19% 5% 18% 28% 23% 7%	450
	11th to 20th	Day	17% 15% 20% 26% 18% 4	450
	21st to end	Day	22% 12% 23% 25% 13% 4	495
November	1st to 10th	Day	18% 13% 24% 28% 14% 4	375
	11th to 20th	Day	20% 21% 28% 21% 8% 1	270
	21st to end	Day	18% 20% 36% 19% 6% 1	270
December	1st to 10th	Day	31% 18% 31% 16% 3	270
	11th to 20th	Day	27% 20% 27% 18% 8%	270
	21st to end	Day	31% 18% 29% 15% 6% 1	297
January	1st to 10th	Night	26% 19% 27% 25% 4	760
	11th to 20th	Night	29% 16% 27% 24% 4	760
	21st to end	Night	22% 19% 32% 24% 2	836
February	1st to 10th	Night	23% 16% 29% 30% 3	760
	11th to 20th	Night	30% 21% 28% 20% 1	743
	21st to end	Night	30% 18% 28% 22% 1	628
March	1st to 10th	Night	22% 14% 30% 27% 5%	743
	11th to 20th	Night	25% 15% 26% 26% 7%	720
	21st to end	Night	19% 14% 29% 29% 8%	792
April	1st to 10th	Night	20% 15% 25% 31% 9%	720
	11th to 20th	Night	18% 13% 24% 31% 12% 1	644
	21st to end	Night	17% 8% 24% 38% 11% 2	540
May	1st to 10th	Night	17% 10% 22% 34% 14% 2	540
	11th to 20th	Night	16% 7% 17% 35% 22% 2	531
	21st to end	Night	10% 4 12% 33% 35% 6%	584
June	1st to 10th	Night	10% 4 10% 41% 31% 5%	540
	11th to 20th	Night	8% 2 13% 34% 36% 6%	540
	21st to end	Night	12% 2 10% 38% 35% 3	540
July	1st to 10th	Night	15% 3 6% 34% 37% 4	525
	11th to 20th	Night	14% 1 3 32% 42% 7%	522
	21st to end	Night	10% 3 7% 35% 36% 10%	591
August	1st to 10th	Night	12% 2 6% 32% 43% 5%	537
	11th to 20th	Night	14% 2 6% 32% 39% 6%	534
	21st to end	Night	12% 3 4 31% 41% 8%	656
September	1st to 10th	Night	13% 3 8% 32% 38% 5%	720
	11th to 20th	Night	15% 4 9% 29% 37% 5%	720
	21st to end	Night	14% 5% 15% 34% 30% 2	720
October	1st to 10th	Night	19% 4 15% 29% 28% 5%	720
	11th to 20th	Night	20% 8% 20% 33% 18% 1	720
	21st to end	Night	21% 11% 18% 35% 14% 2	792
November	1st to 10th	Night	18% 9% 16% 39% 16% 2	740
	11th to 20th	Night	19% 12% 22% 36% 10% 1	760
	21st to end	Night	19% 11% 26% 33% 10% 1	760
December	1st to 10th	Night	28% 13% 26% 27% 6%	760
	11th to 20th	Night	24% 14% 25% 31% 5% 1	760
	21st to end	Night	27% 13% 24% 31% 5%	836

Page generated at 2024-03-03 06:28:59. Version ac07

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