Crystal Creek Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Crystal Creek Observatory clear sky chart from 2005-11-06 to 2024-01-16.

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	13% 6% 3 5% 5% 3 5% 5% 6% 7% 43%	74815
	Night	12% 6% 2 5% 4 3 4 4 5% 7% 47%	75000
Transparency	Day	39% 6% 11% 22% 18% 4	74533
	Night	36% 6% 10% 22% 20% 5%	74803
Seeing	Day	17% 10% 23% 25% 18% 7%	14119
	Night	17% 10% 24% 28% 18% 3	24000

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	18% 9% 3 5% 4 3 4 4 3 5% 43%	1517
	11th to 20th	Day	19% 9% 3 6% 6% 2 5% 4 4 5% 37%	1657
	21st to end	Day	15% 7% 3 5% 3 3 3 3 5% 5% 48%	1833
February	1st to 10th	Day	20% 9% 4 6% 4 3 3 3 4 5% 40%	1800
	11th to 20th	Day	21% 10% 3 5% 4 3 4 3 4 5% 38%	1748
	21st to end	Day	22% 9% 3 6% 5% 2 3 4 4 7% 36%	1480
March	1st to 10th	Day	17% 7% 3 6% 5% 3 4 4 4 5% 42%	1800
	11th to 20th	Day	17% 8% 4 7% 7% 3 5% 4 4 6% 35%	1905
	21st to end	Day	16% 7% 4 6% 6% 3 5% 4 5% 7% 37%	2359
April	1st to 10th	Day	13% 6% 3 5% 4 4 4 4 5% 6% 46%	2160
	11th to 20th	Day	18% 6% 2 5% 4 2 3 3 4 7% 45%	2134
	21st to end	Day	13% 6% 2 6% 5% 3 5% 4 6% 8% 43%	2160
May	1st to 10th	Day	15% 5% 2 5% 6% 3 5% 4 5% 7% 43%	2191
	11th to 20th	Day	12% 6% 2 7% 6% 3 5% 5% 6% 9% 41%	2301
	21st to end	Day	9% 5% 3 7% 7% 4 6% 7% 7% 10% 38%	2538
June	1st to 10th	Day	10% 5% 2 6% 6% 4 6% 5% 7% 9% 40%	2520
	11th to 20th	Day	4 3 2 4 5% 4 6% 7% 7% 11% 48%	2520
	21st to end	Day	5% 3 3 5% 6% 4 6% 6% 7% 9% 45%	2520
July	1st to 10th	Day	8% 5% 3 6% 8% 4 8% 8% 8% 11% 33%	2520
	11th to 20th	Day	8% 4 2 5% 6% 4 6% 6% 7% 12% 38%	2520
	21st to end	Day	6% 4 2 5% 7% 4 7% 6% 9% 11% 39%	2476
August	1st to 10th	Day	6% 4 2 6% 7% 4 6% 7% 9% 11% 38%	2148
	11th to 20th	Day	9% 5% 2 6% 5% 5% 6% 7% 7% 9% 39%	2125
	21st to end	Day	10% 5% 2 5% 7% 4 5% 5% 6% 10% 40%	2376
September	1st to 10th	Day	9% 5% 2 5% 6% 3 5% 5% 7% 8% 45%	2160
	11th to 20th	Day	12% 5% 3 4 5% 3 4 5% 6% 8% 45%	2053
	21st to end	Day	11% 4 2 4 4 2 4 4 5% 7% 53%	1980
October	1st to 10th	Day	9% 5% 2 3 5% 3 4 4 4 5% 56%	1962
	11th to 20th	Day	10% 4 2 5% 4 2 3 4 4 5% 56%	1800
	21st to end	Day	18% 5% 2 4 4 2 3 4 4 3 51%	1954
November	1st to 10th	Day	11% 4 2 4 3 2 3 3 4 6% 58%	1672
	11th to 20th	Day	13% 5% 3 5% 3 2 3 3 4 7% 52%	1710
	21st to end	Day	18% 7% 3 4 3 3 3 5% 5% 6% 43%	1710
December	1st to 10th	Day	20% 8% 3 7% 6% 3 3 4 4 5% 38%	1710
	11th to 20th	Day	16% 8% 3 5% 5% 3 3 4 4 5% 43%	2013
	21st to end	Day	13% 11% 4 7% 6% 4 4 4 6% 6% 35%	2783
January	1st to 10th	Night	18% 7% 3 6% 5% 2 3 3 3 5% 44%	2648
	11th to 20th	Night	18% 10% 4 8% 5% 3 4 4 4 4 37%	2428
	21st to end	Night	18% 7% 3 4 5% 2 3 3 3 6% 46%	2520
February	1st to 10th	Night	19% 10% 3 6% 5% 3 4 3 3 6% 38%	2160
	11th to 20th	Night	19% 8% 3 6% 5% 3 4 3 4 4 42%	2098
	21st to end	Night	21% 7% 3 5% 5% 2 4 4 4 5% 38%	1776
March	1st to 10th	Night	16% 6% 2 5% 4 3 5% 4 4 5% 47%	2160
	11th to 20th	Night	19% 8% 2 5% 5% 3 4 4 5% 7% 39%	2070
	21st to end	Night	14% 7% 3 5% 5% 3 5% 5% 5% 6% 41%	1995
April	1st to 10th	Night	12% 6% 2 5% 4 3 4 4 5% 8% 47%	1800
	11th to 20th	Night	14% 5% 2 5% 4 2 4 4 4 7% 49%	1775
	21st to end	Night	11% 6% 2 5% 5% 3 4 5% 6% 7% 47%	1800
May	1st to 10th	Night	12% 6% 2 5% 4 2 3 4 4 8% 50%	1768
	11th to 20th	Night	9% 5% 3 6% 5% 3 5% 4 6% 8% 45%	1592
	21st to end	Night	6% 4 2 5% 6% 3 5% 6% 8% 11% 44%	1732
June	1st to 10th	Night	8% 5% 3 5% 4 3 6% 5% 7% 11% 43%	1440
	11th to 20th	Night	2 3 1 3 3 3 4 6% 7% 10% 58%	1440
	21st to end	Night	3 3 2 3 4 2 4 6% 6% 11% 56%	1440
July	1st to 10th	Night	4 4 2 6% 5% 4 6% 6% 7% 12% 45%	1440
	11th to 20th	Night	5% 4 3 4 4 2 4 5% 7% 14% 48%	1440
	21st to end	Night	4 3 2 4 4 3 5% 5% 7% 11% 52%	1836
August	1st to 10th	Night	3 3 1 3 5% 3 5% 6% 8% 10% 52%	1790
	11th to 20th	Night	6% 3 2 4 5% 4 4 6% 8% 12% 46%	1776
	21st to end	Night	7% 5% 2 5% 4 3 5% 5% 7% 11% 47%	1980
September	1st to 10th	Night	7% 5% 3 5% 5% 3 5% 4 6% 7% 52%	1800
	11th to 20th	Night	9% 5% 2 4 5% 3 4 6% 5% 7% 51%	1887
	21st to end	Night	9% 4 2 4 3 2 3 3 5% 7% 58%	1980
October	1st to 10th	Night	9% 3 1 3 4 2 3 3 4 7% 61%	1993
	11th to 20th	Night	11% 6% 2 4 3 3 3 3 4 6% 55%	2160
	21st to end	Night	17% 6% 2 4 4 2 3 3 3 5% 52%	2400
November	1st to 10th	Night	10% 4 2 4 5% 2 3 3 4 5% 57%	2406
	11th to 20th	Night	11% 4 2 4 3 2 4 4 5% 7% 52%	2470
	21st to end	Night	16% 6% 2 3 4 3 4 4 4 5% 49%	2470
December	1st to 10th	Night	20% 8% 2 5% 4 2 3 4 4 6% 41%	2470
	11th to 20th	Night	16% 7% 3 5% 4 2 3 3 4 5% 48%	3176
	21st to end	Night	15% 9% 3 7% 6% 4 5% 6% 6% 7% 34%	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	45% 3 8% 20% 19% 4	1518
	11th to 20th	Day	50% 4 8% 19% 16% 2	1657
	21st to end	Day	39% 3 9% 24% 23% 2	1833
February	1st to 10th	Day	49% 3 6% 21% 18% 3	1800
	11th to 20th	Day	50% 4 5% 20% 17% 4	1758
	21st to end	Day	50% 3 8% 14% 16% 7%	1480
March	1st to 10th	Day	45% 4 8% 16% 18% 8%	1800
	11th to 20th	Day	51% 4 10% 15% 17% 3	1905
	21st to end	Day	47% 5% 9% 23% 16%	2359
April	1st to 10th	Day	38% 6% 8% 24% 20% 4	2160
	11th to 20th	Day	41% 4 9% 20% 22% 6%	2134
	21st to end	Day	39% 5% 10% 24% 20% 1	2160
May	1st to 10th	Day	40% 7% 11% 22% 18% 2	2191
	11th to 20th	Day	39% 8% 15% 21% 15% 2	2305
	21st to end	Day	40% 9% 15% 24% 11% 2	2538
June	1st to 10th	Day	37% 8% 13% 22% 18% 2	2520
	11th to 20th	Day	28% 8% 16% 28% 17% 3	2520
	21st to end	Day	31% 9% 15% 23% 19% 4	2520
July	1st to 10th	Day	39% 10% 18% 19% 12% 3	2451
	11th to 20th	Day	36% 10% 20% 20% 10% 3	2445
	21st to end	Day	35% 11% 15% 28% 11% 1	2338
August	1st to 10th	Day	34% 11% 20% 23% 10% 1	2136
	11th to 20th	Day	38% 10% 13% 21% 16% 2	2125
	21st to end	Day	38% 6% 14% 25% 14% 4	2376
September	1st to 10th	Day	35% 8% 12% 25% 16% 4	2160
	11th to 20th	Day	37% 7% 11% 19% 22% 5%	2053
	21st to end	Day	31% 5% 10% 25% 23% 7%	1980
October	1st to 10th	Day	29% 4 10% 24% 25% 7%	1962
	11th to 20th	Day	30% 4 8% 21% 29% 8%	1800
	21st to end	Day	37% 5% 5% 21% 26% 7%	1954
November	1st to 10th	Day	30% 4 7% 23% 29% 8%	1672
	11th to 20th	Day	34% 3 9% 19% 26% 9%	1710
	21st to end	Day	42% 3 8% 19% 24% 4	1710
December	1st to 10th	Day	50% 4 5% 20% 16% 4	1710
	11th to 20th	Day	45% 4 6% 21% 21% 3	2010
	21st to end	Day	47% 6% 11% 21% 14% 2	2783
January	1st to 10th	Night	44% 3 8% 20% 20% 4	2648
	11th to 20th	Night	51% 4 6% 19% 15% 4	2428
	21st to end	Night	41% 3 8% 23% 22% 3	2520
February	1st to 10th	Night	50% 4 8% 17% 18% 3	2160
	11th to 20th	Night	47% 4 7% 19% 18% 5%	2099
	21st to end	Night	48% 4 8% 16% 17% 6%	1776
March	1st to 10th	Night	40% 4 9% 16% 21% 10%	2160
	11th to 20th	Night	45% 7% 9% 19% 17% 4	2070
	21st to end	Night	43% 5% 10% 21% 18% 3	1995
April	1st to 10th	Night	37% 5% 11% 24% 20% 5%	1800
	11th to 20th	Night	35% 4 8% 21% 24% 8%	1775
	21st to end	Night	35% 6% 10% 26% 20% 3	1800
May	1st to 10th	Night	34% 7% 10% 23% 22% 4	1768
	11th to 20th	Night	36% 8% 16% 22% 17% 2	1593
	21st to end	Night	31% 10% 14% 28% 15% 2	1733
June	1st to 10th	Night	33% 9% 13% 23% 21% 2	1440
	11th to 20th	Night	19% 8% 15% 31% 22% 4	1440
	21st to end	Night	23% 7% 16% 29% 20% 5%	1440
July	1st to 10th	Night	29% 13% 19% 24% 12% 3	1400
	11th to 20th	Night	26% 9% 22% 25% 13% 5%	1392
	21st to end	Night	24% 10% 20% 30% 14% 1	1734
August	1st to 10th	Night	24% 10% 19% 32% 15% 1	1778
	11th to 20th	Night	28% 10% 19% 23% 17% 3	1776
	21st to end	Night	30% 8% 17% 25% 15% 6%	1980
September	1st to 10th	Night	30% 7% 10% 25% 21% 6%	1800
	11th to 20th	Night	31% 7% 12% 18% 27% 4	1887
	21st to end	Night	27% 5% 8% 28% 24% 8%	1980
October	1st to 10th	Night	24% 4 10% 25% 26% 11%	1993
	11th to 20th	Night	32% 4 7% 18% 29% 10%	2160
	21st to end	Night	37% 3 6% 21% 26% 8%	2400
November	1st to 10th	Night	30% 4 5% 24% 28% 9%	2406
	11th to 20th	Night	31% 5% 7% 21% 26% 10%	2470
	21st to end	Night	38% 5% 7% 20% 25% 6%	2470
December	1st to 10th	Night	45% 4 8% 21% 18% 4	2470
	11th to 20th	Night	39% 3 7% 22% 24% 4	3178
	21st to end	Night	45% 7% 11% 20% 13% 4	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	26% 24% 35% 11% 3	270
	11th to 20th	Day	32% 19% 35% 9% 4 1	257
	21st to end	Day	23% 28% 33% 12% 3	264
February	1st to 10th	Day	29% 23% 33% 11% 3	240
	11th to 20th	Day	41% 23% 28% 6% 2	240
	21st to end	Day	36% 25% 30% 7% 2	198
March	1st to 10th	Day	30% 20% 35% 11% 4	240
	11th to 20th	Day	32% 21% 34% 12% 1	240
	21st to end	Day	29% 18% 33% 13% 7%	445
April	1st to 10th	Day	24% 15% 31% 23% 7%	420
	11th to 20th	Day	24% 14% 32% 20% 8% 2	412
	21st to end	Day	22% 15% 28% 22% 10% 2	420
May	1st to 10th	Day	20% 16% 31% 22% 10% 3	423
	11th to 20th	Day	16% 7% 29% 27% 16% 6%	447
	21st to end	Day	10% 5% 25% 30% 19% 10%	492
June	1st to 10th	Day	11% 5% 19% 30% 24% 11%	630
	11th to 20th	Day	5% 3 18% 35% 28% 11%	630
	21st to end	Day	6% 4 21% 36% 23% 10%	630
July	1st to 10th	Day	9% 3 13% 30% 32% 14%	621
	11th to 20th	Day	8% 2 12% 27% 34% 17%	618
	21st to end	Day	5% 2 12% 32% 32% 17%	606
August	1st to 10th	Day	7% 2 13% 28% 37% 14%	446
	11th to 20th	Day	12% 3 11% 32% 32% 10%	439
	21st to end	Day	12% 2 9% 26% 34% 16%	495
September	1st to 10th	Day	9% 2 13% 33% 33% 10%	450
	11th to 20th	Day	10% 2 14% 28% 30% 15%	450
	21st to end	Day	15% 4 14% 32% 24% 11%	450
October	1st to 10th	Day	9% 6% 22% 31% 26% 6%	432
	11th to 20th	Day	10% 14% 40% 27% 7% 1	270
	21st to end	Day	27% 12% 31% 21% 7% 2	297
November	1st to 10th	Day	18% 11% 29% 29% 11% 2	270
	11th to 20th	Day	12% 19% 38% 26% 4 1	270
	21st to end	Day	26% 14% 27% 18% 13% 2	270
December	1st to 10th	Day	32% 17% 29% 17% 4 1	270
	11th to 20th	Day	27% 20% 27% 19% 6% 1	270
	21st to end	Day	29% 17% 37% 14% 2	297
January	1st to 10th	Night	25% 19% 31% 21% 4	950
	11th to 20th	Night	26% 20% 29% 19% 5%	930
	21st to end	Night	24% 16% 36% 23% 2	936
February	1st to 10th	Night	28% 15% 33% 21% 4	720
	11th to 20th	Night	27% 18% 32% 21% 2	703
	21st to end	Night	28% 19% 33% 19% 2	592
March	1st to 10th	Night	21% 16% 30% 28% 4	720
	11th to 20th	Night	24% 14% 34% 23% 4 1	630
	21st to end	Night	21% 15% 29% 26% 10%	594
April	1st to 10th	Night	16% 13% 36% 26% 9%	540
	11th to 20th	Night	19% 9% 34% 27% 10% 1	533
	21st to end	Night	15% 10% 35% 28% 11% 1	540
May	1st to 10th	Night	14% 9% 28% 33% 14% 2	540
	11th to 20th	Night	12% 6% 28% 32% 17% 4	531
	21st to end	Night	7% 3 20% 37% 26% 6%	584
June	1st to 10th	Night	11% 2 14% 35% 31% 6%	540
	11th to 20th	Night	3 2 17% 35% 38% 5%	540
	21st to end	Night	4 1 14% 38% 34% 8%	540
July	1st to 10th	Night	4 2 10% 29% 42% 12%	525
	11th to 20th	Night	7% 2 11% 25% 42% 14%	522
	21st to end	Night	4 1 9% 28% 45% 13%	591
August	1st to 10th	Night	5% 1 6% 28% 49% 11%	537
	11th to 20th	Night	6% 2 8% 38% 39% 7%	534
	21st to end	Night	8% 2 9% 29% 42% 10%	594
September	1st to 10th	Night	9% 2 10% 34% 41% 5%	540
	11th to 20th	Night	10% 3 14% 31% 35% 8%	627
	21st to end	Night	12% 4 15% 33% 32% 4	720
October	1st to 10th	Night	10% 4 19% 32% 32% 4	720
	11th to 20th	Night	14% 8% 25% 33% 17% 2	720
	21st to end	Night	21% 9% 24% 29% 15% 1	792
November	1st to 10th	Night	13% 8% 26% 34% 18% 2	740
	11th to 20th	Night	16% 10% 33% 31% 10% 1	760
	21st to end	Night	23% 10% 28% 27% 11% 1	760
December	1st to 10th	Night	25% 13% 29% 27% 6%	760
	11th to 20th	Night	22% 16% 27% 29% 7%	850
	21st to end	Night	27% 15% 30% 24% 4	1045

Page generated at 2024-01-13 18:28:32. Version ac07

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