Cobblestone Creek Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cobblestone Creek Observatory clear sky chart from 2005-11-06 to 2024-07-03.

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	16% 11% 4 8% 5% 5% 5% 4 5% 7% 31%	90151
	Night	16% 11% 4 8% 5% 4 4 3 5% 6% 34%	88999
Transparency	Day	51% 6% 11% 19% 11% 1	89918
	Night	50% 6% 11% 20% 12% 2	88837
Seeing	Day	19% 10% 26% 23% 15% 7%	14844
	Night	19% 8% 27% 30% 14% 2	24412

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	20% 19% 7% 14% 5% 5% 4 3 4 4 14%	2836
	11th to 20th	Day	17% 21% 6% 12% 5% 6% 8% 3 3 5% 14%	2840
	21st to end	Day	28% 19% 10% 11% 6% 5% 3 2 3 3 10%	3124
February	1st to 10th	Day	18% 16% 6% 10% 7% 6% 4 2 5% 4 22%	1710
	11th to 20th	Day	15% 12% 7% 14% 7% 5% 4 3 4 6% 23%	1829
	21st to end	Day	18% 14% 4 10% 5% 5% 4 3 5% 6% 27%	1570
March	1st to 10th	Day	22% 15% 6% 10% 6% 4 4 3 4 5% 21%	3238
	11th to 20th	Day	13% 12% 4 8% 6% 4 4 3 5% 7% 35%	3480
	21st to end	Day	21% 11% 5% 9% 5% 4 4 3 5% 6% 28%	3815
April	1st to 10th	Day	15% 13% 3 8% 6% 5% 4 4 5% 7% 30%	2161
	11th to 20th	Day	18% 10% 2 7% 5% 4 4 4 6% 7% 35%	2392
	21st to end	Day	19% 9% 3 7% 5% 4 5% 3 5% 7% 33%	2470
May	1st to 10th	Day	20% 10% 3 7% 5% 5% 6% 4 5% 7% 29%	4082
	11th to 20th	Day	20% 8% 2 7% 5% 4 4 3 5% 7% 34%	4081
	21st to end	Day	11% 6% 2 7% 5% 5% 6% 5% 7% 9% 38%	4476
June	1st to 10th	Day	12% 6% 2 7% 6% 5% 5% 4 6% 9% 37%	2470
	11th to 20th	Day	11% 7% 3 6% 5% 5% 5% 5% 7% 9% 38%	2609
	21st to end	Day	11% 4 2 6% 4 5% 5% 6% 7% 11% 39%	2660
July	1st to 10th	Day	10% 6% 3 6% 5% 5% 5% 5% 7% 9% 39%	2549
	11th to 20th	Day	10% 5% 2 4 5% 4 5% 5% 7% 11% 44%	2381
	21st to end	Day	8% 4 2 6% 5% 5% 5% 5% 8% 11% 41%	2547
August	1st to 10th	Day	8% 5% 2 7% 5% 5% 4 5% 7% 9% 43%	2327
	11th to 20th	Day	10% 5% 2 7% 5% 5% 5% 4 8% 10% 38%	2303
	21st to end	Day	9% 6% 2 6% 5% 5% 5% 4 7% 11% 42%	2527
September	1st to 10th	Day	12% 6% 2 6% 4 4 5% 3 5% 7% 46%	2003
	11th to 20th	Day	10% 6% 2 6% 4 5% 5% 4 5% 9% 44%	1980
	21st to end	Day	16% 7% 2 5% 4 4 4 3 4 6% 44%	1980
October	1st to 10th	Day	15% 7% 2 7% 4 4 4 4 5% 7% 41%	1936
	11th to 20th	Day	16% 8% 2 7% 5% 4 4 4 5% 7% 39%	1800
	21st to end	Day	20% 10% 3 7% 5% 5% 4 4 5% 7% 29%	1896
November	1st to 10th	Day	11% 8% 3 6% 5% 3 4 3 4 7% 44%	1672
	11th to 20th	Day	17% 14% 4 6% 4 5% 4 3 4 7% 33%	1710
	21st to end	Day	18% 15% 6% 7% 5% 3 4 3 5% 6% 28%	1710
December	1st to 10th	Day	18% 19% 7% 11% 7% 4 3 3 4 5% 19%	1710
	11th to 20th	Day	16% 15% 7% 9% 6% 5% 5% 4 6% 6% 21%	2153
	21st to end	Day	25% 23% 7% 10% 6% 4 4 3 4 4 9%	3124
January	1st to 10th	Night	17% 19% 8% 14% 5% 5% 5% 3 4 4 17%	4109
	11th to 20th	Night	16% 20% 7% 15% 6% 5% 6% 4 4 4 14%	4120
	21st to end	Night	29% 20% 7% 10% 6% 3 3 3 3 4 13%	4532
February	1st to 10th	Night	21% 15% 4 9% 5% 5% 4 3 4 5% 25%	2470
	11th to 20th	Night	16% 13% 5% 9% 6% 5% 5% 4 5% 5% 27%	2234
	21st to end	Night	20% 15% 5% 10% 4 4 3 3 4 4 27%	1884
March	1st to 10th	Night	21% 14% 4 7% 4 3 4 3 4 5% 31%	3614
	11th to 20th	Night	13% 9% 2 6% 4 4 4 3 5% 7% 42%	3480
	21st to end	Night	19% 9% 3 7% 5% 4 3 3 4 5% 38%	3817
April	1st to 10th	Night	16% 10% 3 6% 5% 4 4 3 6% 7% 35%	2033
	11th to 20th	Night	17% 8% 3 6% 4 4 4 4 6% 7% 36%	1735
	21st to end	Night	16% 7% 2 8% 4 4 5% 3 6% 7% 36%	1710
May	1st to 10th	Night	22% 10% 3 8% 5% 5% 5% 4 5% 6% 28%	2813
	11th to 20th	Night	18% 8% 3 6% 3 3 4 3 6% 7% 39%	2812
	21st to end	Night	9% 5% 1 6% 4 4 5% 4 7% 10% 45%	3079
June	1st to 10th	Night	9% 7% 2 7% 4 4 4 4 6% 8% 44%	1710
	11th to 20th	Night	9% 5% 2 4 4 4 5% 4 8% 10% 45%	1564
	21st to end	Night	9% 4 2 5% 5% 4 5% 5% 7% 10% 45%	1520
July	1st to 10th	Night	10% 5% 2 5% 3 5% 5% 4 7% 8% 46%	1456
	11th to 20th	Night	6% 4 1 5% 5% 3 6% 6% 7% 9% 49%	1574
	21st to end	Night	7% 6% 2 6% 4 4 5% 4 6% 8% 47%	1771
August	1st to 10th	Night	6% 4 2 5% 5% 5% 6% 5% 9% 10% 43%	1611
	11th to 20th	Night	8% 6% 3 6% 4 5% 3 5% 6% 8% 46%	1598
	21st to end	Night	6% 4 2 5% 5% 4 4 4 7% 8% 51%	1826
September	1st to 10th	Night	12% 6% 2 5% 4 4 4 4 5% 7% 49%	1938
	11th to 20th	Night	10% 5% 2 4 3 3 3 3 5% 6% 55%	1980
	21st to end	Night	12% 6% 3 5% 4 4 4 3 5% 6% 47%	1980
October	1st to 10th	Night	10% 6% 2 7% 4 4 4 3 6% 7% 48%	2023
	11th to 20th	Night	18% 8% 3 6% 4 5% 3 3 5% 6% 40%	2160
	21st to end	Night	21% 9% 3 7% 4 4 4 3 5% 6% 35%	2456
November	1st to 10th	Night	14% 7% 3 6% 4 4 4 3 5% 6% 45%	2406
	11th to 20th	Night	16% 13% 3 7% 3 4 4 3 6% 6% 35%	2470
	21st to end	Night	19% 13% 4 7% 5% 4 4 3 6% 6% 28%	2470
December	1st to 10th	Night	20% 16% 5% 10% 5% 4 4 4 4 6% 23%	2470
	11th to 20th	Night	19% 15% 5% 11% 5% 4 3 4 5% 5% 24%	3042
	21st to end	Night	25% 21% 7% 10% 4 4 3 3 4 5% 14%	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	72% 5% 7% 11% 4	2837
	11th to 20th	Day	75% 4 9% 8% 4	2840
	21st to end	Day	82% 3 5% 7% 3	3124
February	1st to 10th	Day	66% 5% 9% 12% 7%	1710
	11th to 20th	Day	65% 4 7% 15% 8% 1	1839
	21st to end	Day	58% 5% 13% 15% 7% 2	1570
March	1st to 10th	Day	65% 6% 9% 16% 4	3238
	11th to 20th	Day	49% 5% 10% 26% 9% 1	3480
	21st to end	Day	57% 5% 12% 20% 6%	3815
April	1st to 10th	Day	52% 6% 12% 17% 11% 1	2161
	11th to 20th	Day	49% 6% 12% 19% 13% 2	2392
	21st to end	Day	50% 6% 10% 20% 11% 2	2470
May	1st to 10th	Day	53% 7% 12% 21% 6% 1	4120
	11th to 20th	Day	48% 7% 14% 23% 8% 1	4085
	21st to end	Day	38% 9% 14% 21% 14% 3	4489
June	1st to 10th	Day	42% 7% 10% 25% 14% 1	2470
	11th to 20th	Day	40% 8% 15% 22% 15% 1	2609
	21st to end	Day	37% 10% 14% 21% 15% 3	2660
July	1st to 10th	Day	40% 8% 12% 21% 17% 2	2480
	11th to 20th	Day	34% 8% 14% 26% 17% 1	2309
	21st to end	Day	34% 9% 16% 26% 13% 3	2405
August	1st to 10th	Day	35% 8% 15% 26% 15% 1	2314
	11th to 20th	Day	39% 8% 13% 27% 11% 1	2303
	21st to end	Day	35% 8% 14% 21% 17% 5%	2527
September	1st to 10th	Day	38% 6% 11% 23% 18% 4	2003
	11th to 20th	Day	37% 6% 11% 25% 18% 3	1980
	21st to end	Day	41% 5% 11% 22% 21% 1	1980
October	1st to 10th	Day	42% 6% 10% 23% 17% 1	1936
	11th to 20th	Day	44% 4 13% 22% 15% 2	1800
	21st to end	Day	55% 6% 11% 18% 9% 1	1896
November	1st to 10th	Day	40% 5% 11% 24% 17% 2	1672
	11th to 20th	Day	52% 4 11% 20% 11% 2	1710
	21st to end	Day	58% 4 10% 18% 9% 1	1710
December	1st to 10th	Day	68% 5% 10% 14% 4	1710
	11th to 20th	Day	61% 6% 11% 16% 6%	2150
	21st to end	Day	79% 4 8% 6% 3	3124
January	1st to 10th	Night	70% 5% 8% 12% 5%	4109
	11th to 20th	Night	75% 5% 8% 10% 2	4120
	21st to end	Night	76% 3 8% 9% 3 1	4532
February	1st to 10th	Night	62% 5% 11% 14% 7% 1	2470
	11th to 20th	Night	58% 5% 10% 16% 10% 1	2235
	21st to end	Night	62% 4 9% 14% 9% 2	1884
March	1st to 10th	Night	54% 6% 11% 19% 9% 1	3614
	11th to 20th	Night	40% 6% 13% 28% 12% 2	3480
	21st to end	Night	49% 5% 10% 26% 10% 1	3817
April	1st to 10th	Night	47% 5% 13% 19% 14% 2	2033
	11th to 20th	Night	46% 5% 12% 18% 17% 3	1735
	21st to end	Night	46% 6% 12% 19% 15% 2	1710
May	1st to 10th	Night	55% 7% 10% 18% 9% 1	2840
	11th to 20th	Night	42% 8% 12% 25% 12% 1	2813
	21st to end	Night	31% 9% 14% 27% 16% 2	3087
June	1st to 10th	Night	37% 7% 12% 22% 20% 2	1710
	11th to 20th	Night	32% 9% 13% 27% 16% 3	1564
	21st to end	Night	34% 8% 15% 24% 16% 4	1520
July	1st to 10th	Night	35% 7% 13% 21% 19% 6%	1416
	11th to 20th	Night	29% 8% 14% 29% 18% 2	1523
	21st to end	Night	32% 7% 15% 27% 15% 4	1672
August	1st to 10th	Night	31% 9% 16% 25% 17% 1	1600
	11th to 20th	Night	35% 7% 14% 26% 18% 1	1598
	21st to end	Night	29% 8% 15% 23% 21% 4	1826
September	1st to 10th	Night	35% 6% 12% 25% 17% 6%	1938
	11th to 20th	Night	29% 6% 10% 28% 25% 3	1980
	21st to end	Night	37% 7% 10% 21% 23% 2	1980
October	1st to 10th	Night	35% 6% 11% 26% 21% 1	2023
	11th to 20th	Night	46% 5% 8% 25% 15% 1	2160
	21st to end	Night	51% 4 9% 21% 12% 2	2456
November	1st to 10th	Night	40% 4 12% 22% 18% 3	2406
	11th to 20th	Night	50% 4 9% 22% 13% 2	2470
	21st to end	Night	57% 4 12% 19% 7% 1	2470
December	1st to 10th	Night	64% 5% 9% 16% 6%	2470
	11th to 20th	Night	60% 5% 12% 18% 5%	3044
	21st to end	Night	74% 5% 9% 9% 3	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% 13% 33% 16% 7% 1	270
	11th to 20th	Day	26% 18% 38% 14% 4	270
	21st to end	Day	31% 15% 31% 16% 6%	297
February	1st to 10th	Day	32% 16% 32% 17% 3 1	270
	11th to 20th	Day	26% 19% 33% 17% 5%	270
	21st to end	Day	25% 18% 41% 13% 2	225
March	1st to 10th	Day	25% 17% 34% 19% 6%	336
	11th to 20th	Day	25% 15% 33% 20% 5% 2	460
	21st to end	Day	30% 14% 28% 22% 5%	506
April	1st to 10th	Day	22% 14% 30% 22% 8% 2	460
	11th to 20th	Day	21% 16% 28% 20% 9% 6%	452
	21st to end	Day	24% 12% 31% 23% 8% 2	460
May	1st to 10th	Day	25% 10% 29% 24% 9% 3	463
	11th to 20th	Day	23% 7% 25% 23% 15% 7%	487
	21st to end	Day	12% 7% 24% 24% 22% 12%	529
June	1st to 10th	Day	12% 7% 22% 29% 23% 8%	490
	11th to 20th	Day	13% 7% 23% 28% 23% 7%	629
	21st to end	Day	13% 6% 28% 27% 19% 8%	680
July	1st to 10th	Day	13% 2 17% 26% 24% 19%	632
	11th to 20th	Day	12% 3 18% 25% 25% 17%	482
	21st to end	Day	10% 3 18% 22% 29% 17%	488
August	1st to 10th	Day	11% 3 12% 25% 31% 18%	446
	11th to 20th	Day	13% 1 18% 27% 26% 14%	439
	21st to end	Day	9% 5% 16% 24% 29% 18%	495
September	1st to 10th	Day	14% 2 17% 24% 28% 14%	450
	11th to 20th	Day	9% 4 15% 22% 30% 20%	450
	21st to end	Day	17% 8% 20% 25% 18% 11%	450
October	1st to 10th	Day	13% 6% 24% 28% 18% 12%	450
	11th to 20th	Day	16% 13% 35% 20% 13% 3	450
	21st to end	Day	26% 16% 33% 20% 6% 1	411
November	1st to 10th	Day	14% 13% 34% 25% 10% 4	270
	11th to 20th	Day	23% 17% 27% 20% 10% 2	270
	21st to end	Day	29% 12% 38% 19% 3	270
December	1st to 10th	Day	25% 17% 34% 16% 7% 1	270
	11th to 20th	Day	23% 15% 41% 18% 4	270
	21st to end	Day	34% 16% 27% 20% 3	297
January	1st to 10th	Night	24% 14% 35% 23% 4	760
	11th to 20th	Night	31% 13% 33% 18% 4 1	760
	21st to end	Night	25% 13% 34% 25% 3	836
February	1st to 10th	Night	27% 10% 34% 26% 3	760
	11th to 20th	Night	25% 11% 34% 26% 3	743
	21st to end	Night	28% 11% 38% 19% 3	628
March	1st to 10th	Night	24% 9% 33% 27% 7% 1	760
	11th to 20th	Night	21% 13% 34% 27% 6% 1	760
	21st to end	Night	24% 10% 31% 28% 6%	836
April	1st to 10th	Night	21% 11% 35% 28% 5% 1	703
	11th to 20th	Night	20% 9% 35% 25% 9% 1	563
	21st to end	Night	19% 9% 37% 26% 8% 1	570
May	1st to 10th	Night	22% 7% 28% 31% 11% 1	570
	11th to 20th	Night	23% 4 25% 33% 14% 1	561
	21st to end	Night	10% 4 22% 39% 23% 2	617
June	1st to 10th	Night	9% 4 23% 41% 20% 1	570
	11th to 20th	Night	11% 2 18% 45% 22% 1	570
	21st to end	Night	11% 2 20% 41% 23% 2	570
July	1st to 10th	Night	11% 1 16% 34% 34% 4	531
	11th to 20th	Night	6% 4 14% 41% 31% 5%	522
	21st to end	Night	8% 2 15% 38% 35% 2	591
August	1st to 10th	Night	8% 1 10% 45% 32% 4	537
	11th to 20th	Night	9% 2 11% 40% 33% 5%	534
	21st to end	Night	8% 2 13% 36% 37% 5%	594
September	1st to 10th	Night	13% 2 17% 33% 30% 6%	678
	11th to 20th	Night	12% 3 14% 33% 33% 6%	720
	21st to end	Night	15% 6% 19% 32% 25% 3	720
October	1st to 10th	Night	13% 5% 23% 33% 22% 4	720
	11th to 20th	Night	21% 9% 29% 29% 12% 1	720
	21st to end	Night	26% 10% 30% 25% 9% 1	792
November	1st to 10th	Night	18% 8% 29% 29% 14% 1	740
	11th to 20th	Night	22% 15% 28% 27% 8% 1	760
	21st to end	Night	26% 9% 30% 27% 7% 1	760
December	1st to 10th	Night	26% 12% 33% 24% 5%	760
	11th to 20th	Night	25% 10% 35% 25% 5%	760
	21st to end	Night	31% 12% 30% 23% 4	836

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