Hidden Creek Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hidden Creek Observatory clear sky chart from 2005-11-06 to 2024-11-25.

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	14% 6% 2 6% 4 4 4 4 6% 8% 42%	101240
	Night	15% 6% 2 6% 4 4 4 3 5% 7% 43%	98196
Transparency	Day	38% 6% 12% 23% 17% 4	104886
	Night	38% 6% 11% 22% 18% 4	102689
Seeing	Day	18% 11% 28% 25% 14% 5%	15130
	Night	17% 10% 29% 30% 13% 1	24815

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% 6% 2 4 3 3 3 3 4 5% 50%	2802
	11th to 20th	Day	15% 9% 3 6% 4 4 4 4 5% 5% 42%	2840
	21st to end	Day	18% 9% 3 7% 4 3 4 4 4 6% 38%	3124
February	1st to 10th	Day	13% 7% 2 6% 6% 4 5% 4 6% 6% 40%	1710
	11th to 20th	Day	20% 7% 2 6% 3 3 3 3 4 6% 43%	1691
	21st to end	Day	18% 8% 3 7% 5% 4 5% 3 5% 7% 37%	1601
March	1st to 10th	Day	20% 8% 2 7% 4 4 4 3 4 6% 38%	3435
	11th to 20th	Day	10% 4 2 5% 4 3 4 3 6% 7% 52%	3480
	21st to end	Day	20% 6% 2 6% 5% 5% 4 3 5% 6% 38%	3815
April	1st to 10th	Day	11% 4 3 5% 4 4 4 4 6% 7% 49%	2272
	11th to 20th	Day	13% 6% 2 5% 4 4 3 3 5% 7% 49%	2254
	21st to end	Day	17% 6% 2 5% 4 5% 4 4 5% 6% 42%	2280
May	1st to 10th	Day	18% 8% 2 7% 5% 5% 5% 4 6% 8% 32%	4046
	11th to 20th	Day	21% 7% 2 6% 4 4 5% 4 6% 9% 32%	4081
	21st to end	Day	9% 5% 1 5% 4 4 5% 4 7% 11% 45%	4812
June	1st to 10th	Day	11% 5% 2 5% 4 4 5% 5% 7% 9% 43%	2660
	11th to 20th	Day	11% 4 1 5% 5% 5% 5% 4 7% 10% 41%	2660
	21st to end	Day	9% 3 1 5% 7% 4 5% 5% 7% 10% 43%	2660
July	1st to 10th	Day	6% 4 2 5% 4 5% 6% 5% 9% 11% 42%	4349
	11th to 20th	Day	10% 5% 2 6% 5% 4 5% 5% 8% 13% 36%	4120
	21st to end	Day	12% 6% 3 7% 6% 6% 5% 6% 7% 9% 33%	4466
August	1st to 10th	Day	16% 6% 3 7% 5% 5% 6% 5% 8% 10% 32%	4104
	11th to 20th	Day	9% 5% 2 7% 6% 5% 6% 5% 7% 9% 39%	3898
	21st to end	Day	9% 4 2 5% 3 4 4 3 6% 10% 49%	4180
September	1st to 10th	Day	13% 5% 2 6% 5% 4 4 5% 4 6% 46%	2280
	11th to 20th	Day	12% 6% 2 5% 4 4 4 4 6% 7% 45%	2252
	21st to end	Day	22% 7% 2 5% 5% 3 4 4 6% 6% 37%	1995
October	1st to 10th	Day	15% 6% 2 5% 4 4 3 3 4 6% 49%	1900
	11th to 20th	Day	16% 4 1 5% 4 4 4 3 4 4 52%	1900
	21st to end	Day	14% 5% 2 5% 3 3 3 3 3 6% 53%	2090
November	1st to 10th	Day	12% 4 1 4 4 4 4 2 4 5% 55%	1957
	11th to 20th	Day	14% 7% 2 3 3 3 3 3 5% 6% 50%	1772
	21st to end	Day	16% 5% 1 4 4 3 3 4 5% 5% 51%	1552
December	1st to 10th	Day	16% 7% 2 5% 4 4 4 4 5% 6% 41%	1520
	11th to 20th	Day	16% 6% 2 5% 3 3 3 3 3 6% 50%	1910
	21st to end	Day	18% 7% 2 7% 4 4 4 3 6% 7% 38%	2772
January	1st to 10th	Night	14% 8% 2 5% 4 3 3 2 5% 6% 48%	4140
	11th to 20th	Night	18% 7% 2 5% 3 3 4 2 4 5% 47%	4120
	21st to end	Night	20% 9% 3 6% 3 3 3 3 3 4 43%	4532
February	1st to 10th	Night	14% 7% 2 6% 4 4 4 4 6% 6% 43%	2470
	11th to 20th	Night	20% 8% 2 5% 3 4 3 3 3 5% 43%	2374
	21st to end	Night	16% 8% 2 6% 4 3 3 3 5% 5% 45%	1851
March	1st to 10th	Night	20% 7% 2 6% 4 3 4 3 5% 6% 39%	3418
	11th to 20th	Night	13% 4 2 4 3 3 3 3 5% 9% 50%	3480
	21st to end	Night	15% 7% 2 5% 3 3 3 3 4 6% 48%	3817
April	1st to 10th	Night	14% 7% 2 6% 4 4 3 3 5% 7% 47%	1907
	11th to 20th	Night	11% 6% 2 4 4 3 4 4 5% 8% 49%	1875
	21st to end	Night	15% 6% 1 5% 4 4 4 4 6% 8% 44%	1900
May	1st to 10th	Night	19% 8% 3 7% 4 4 4 4 5% 9% 33%	2876
	11th to 20th	Night	23% 7% 2 7% 3 4 4 4 6% 6% 32%	2812
	21st to end	Night	10% 5% 2 6% 4 4 4 5% 7% 11% 43%	2741
June	1st to 10th	Night	10% 5% 2 6% 5% 4 5% 3 7% 10% 43%	1520
	11th to 20th	Night	10% 5% 3 5% 5% 4 5% 4 8% 9% 41%	1520
	21st to end	Night	8% 6% 2 5% 5% 5% 6% 5% 7% 10% 43%	1520
July	1st to 10th	Night	6% 5% 2 7% 5% 5% 5% 5% 9% 10% 40%	2606
	11th to 20th	Night	9% 6% 3 7% 5% 6% 6% 5% 7% 12% 35%	2840
	21st to end	Night	10% 9% 4 7% 6% 7% 6% 5% 7% 8% 32%	3087
August	1st to 10th	Night	16% 5% 3 7% 5% 5% 6% 4 6% 9% 33%	2825
	11th to 20th	Night	10% 7% 3 9% 5% 4 5% 4 6% 9% 37%	2899
	21st to end	Night	10% 6% 2 6% 5% 5% 5% 4 5% 9% 43%	3476
September	1st to 10th	Night	14% 5% 2 6% 3 3 5% 4 6% 7% 44%	1900
	11th to 20th	Night	12% 6% 2 6% 3 3 4 4 4 8% 47%	1924
	21st to end	Night	22% 7% 3 6% 3 3 4 3 5% 5% 39%	2183
October	1st to 10th	Night	18% 6% 2 5% 4 3 3 3 4 6% 47%	2280
	11th to 20th	Night	16% 5% 2 5% 3 3 3 3 5% 6% 49%	2280
	21st to end	Night	14% 4 1 5% 3 3 4 3 5% 5% 53%	2508
November	1st to 10th	Night	12% 6% 2 5% 4 3 3 3 5% 5% 52%	2341
	11th to 20th	Night	14% 6% 2 5% 4 4 4 3 4 6% 49%	2622
	21st to end	Night	13% 4 1 5% 3 4 4 4 6% 6% 50%	2723
December	1st to 10th	Night	16% 7% 3 6% 4 3 4 3 5% 6% 42%	2660
	11th to 20th	Night	17% 7% 2 5% 4 3 3 3 5% 6% 46%	3285
	21st to end	Night	16% 7% 2 5% 4 4 4 4 6% 6% 40%	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	37% 3 7% 32% 17% 5%	2803
	11th to 20th	Day	42% 5% 8% 19% 20% 6%	2840
	21st to end	Day	46% 5% 9% 22% 15% 3	3124
February	1st to 10th	Day	43% 5% 10% 27% 13% 3	1710
	11th to 20th	Day	43% 4 6% 22% 20% 5%	1700
	21st to end	Day	47% 5% 10% 15% 18% 4	1601
March	1st to 10th	Day	47% 5% 9% 19% 14% 6%	3435
	11th to 20th	Day	30% 5% 8% 25% 24% 8%	3480
	21st to end	Day	47% 5% 10% 18% 16% 3	3815
April	1st to 10th	Day	34% 5% 11% 24% 18% 8%	2272
	11th to 20th	Day	36% 4 11% 20% 22% 6%	2254
	21st to end	Day	41% 6% 11% 23% 14% 5%	2280
May	1st to 10th	Day	48% 9% 12% 18% 11% 2	4083
	11th to 20th	Day	47% 9% 13% 21% 10% 1	4085
	21st to end	Day	31% 8% 17% 22% 20% 2	4826
June	1st to 10th	Day	34% 9% 16% 26% 14% 2	2660
	11th to 20th	Day	35% 9% 15% 23% 16% 2	2660
	21st to end	Day	33% 9% 16% 25% 16% 2	2660
July	1st to 10th	Day	33% 9% 23% 19% 11% 6%	4281
	11th to 20th	Day	37% 8% 19% 27% 8% 1	4051
	21st to end	Day	44% 8% 13% 20% 15% 1	4324
August	1st to 10th	Day	45% 7% 17% 23% 7% 1	4091
	11th to 20th	Day	37% 8% 16% 24% 14% 1	3937
	21st to end	Day	30% 6% 17% 28% 17% 2	4180
September	1st to 10th	Day	38% 6% 12% 18% 21% 4	2280
	11th to 20th	Day	37% 6% 8% 26% 19% 4	2252
	21st to end	Day	46% 6% 10% 19% 16% 4	1995
October	1st to 10th	Day	35% 4 7% 19% 30% 5%	3160
	11th to 20th	Day	26% 3 6% 22% 31% 12%	3140
	21st to end	Day	21% 3 10% 30% 24% 13%	3428
November	1st to 10th	Day	33% 4 8% 24% 26% 4	1957
	11th to 20th	Day	35% 3 11% 21% 22% 7%	1772
	21st to end	Day	34% 4 9% 25% 23% 5%	1552
December	1st to 10th	Day	42% 5% 11% 23% 14% 5%	1520
	11th to 20th	Day	37% 3 8% 30% 16% 6%	1906
	21st to end	Day	44% 6% 11% 25% 12% 1	2772
January	1st to 10th	Night	37% 5% 7% 25% 21% 5%	4140
	11th to 20th	Night	41% 4 7% 21% 23% 5%	4120
	21st to end	Night	45% 4 6% 23% 17% 4	4532
February	1st to 10th	Night	41% 5% 10% 25% 16% 3	2470
	11th to 20th	Night	44% 3 7% 20% 19% 7%	2376
	21st to end	Night	42% 3 9% 21% 17% 7%	1851
March	1st to 10th	Night	44% 5% 9% 23% 16% 3	3418
	11th to 20th	Night	31% 5% 8% 22% 27% 7%	3480
	21st to end	Night	38% 5% 9% 22% 22% 5%	3817
April	1st to 10th	Night	38% 6% 9% 18% 23% 7%	1907
	11th to 20th	Night	32% 6% 13% 21% 22% 6%	1875
	21st to end	Night	37% 6% 12% 24% 16% 6%	1900
May	1st to 10th	Night	48% 7% 14% 18% 11% 2	2904
	11th to 20th	Night	48% 10% 13% 19% 9% 2	2813
	21st to end	Night	33% 9% 17% 25% 14% 2	2748
June	1st to 10th	Night	35% 9% 13% 25% 16% 1	1520
	11th to 20th	Night	36% 9% 17% 22% 14% 1	1520
	21st to end	Night	33% 8% 15% 22% 18% 3	1520
July	1st to 10th	Night	36% 11% 22% 17% 12% 2	2564
	11th to 20th	Night	40% 9% 22% 22% 7% 1	2786
	21st to end	Night	47% 9% 14% 18% 11%	2988
August	1st to 10th	Night	48% 7% 16% 22% 6% 1	2814
	11th to 20th	Night	42% 7% 14% 24% 12%	2926
	21st to end	Night	37% 6% 12% 29% 15% 1	3476
September	1st to 10th	Night	38% 8% 13% 20% 15% 7%	1900
	11th to 20th	Night	35% 7% 10% 23% 21% 3	1924
	21st to end	Night	47% 5% 9% 19% 17% 3	2183
October	1st to 10th	Night	41% 4 9% 18% 22% 6%	3800
	11th to 20th	Night	25% 4 8% 22% 31% 11%	3779
	21st to end	Night	21% 3 6% 32% 26% 12%	4120
November	1st to 10th	Night	34% 5% 8% 23% 24% 6%	2341
	11th to 20th	Night	36% 5% 7% 20% 24% 8%	2622
	21st to end	Night	33% 4 10% 25% 22% 5%	2723
December	1st to 10th	Night	43% 6% 9% 23% 16% 4	2660
	11th to 20th	Night	39% 5% 9% 21% 20% 6%	3288
	21st to end	Night	41% 6% 11% 24% 16% 2	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	27% 22% 29% 19% 3	261
	11th to 20th	Day	27% 25% 33% 12% 3	270
	21st to end	Day	25% 21% 41% 10% 3	297
February	1st to 10th	Day	22% 24% 40% 10% 4 1	270
	11th to 20th	Day	38% 21% 31% 10% 1	298
	21st to end	Day	31% 17% 30% 19% 3	382
March	1st to 10th	Day	23% 18% 37% 18% 4	460
	11th to 20th	Day	22% 22% 34% 16% 5% 1	460
	21st to end	Day	25% 17% 34% 18% 4 1	506
April	1st to 10th	Day	23% 19% 32% 19% 5% 1	460
	11th to 20th	Day	19% 15% 30% 22% 10% 4	452
	21st to end	Day	23% 12% 36% 20% 7% 1	460
May	1st to 10th	Day	21% 16% 32% 20% 9% 3	463
	11th to 20th	Day	22% 9% 31% 23% 13% 2	487
	21st to end	Day	17% 5% 27% 28% 19% 4	529
June	1st to 10th	Day	12% 6% 27% 31% 20% 4	490
	11th to 20th	Day	12% 7% 24% 32% 18% 7%	490
	21st to end	Day	10% 6% 28% 32% 20% 5%	490
July	1st to 10th	Day	11% 3 18% 32% 26% 9%	485
	11th to 20th	Day	6% 2 16% 40% 26% 10%	484
	21st to end	Day	10% 4 22% 31% 22% 10%	532
August	1st to 10th	Day	12% 4 20% 30% 24% 10%	486
	11th to 20th	Day	11% 4 19% 31% 26% 10%	479
	21st to end	Day	10% 5% 17% 28% 25% 14%	539
September	1st to 10th	Day	14% 5% 18% 27% 21% 14%	490
	11th to 20th	Day	16% 3 20% 31% 21% 10%	490
	21st to end	Day	28% 9% 20% 28% 10% 5%	490
October	1st to 10th	Day	20% 7% 24% 25% 17% 7%	490
	11th to 20th	Day	16% 12% 23% 28% 18% 2	490
	21st to end	Day	15% 13% 32% 27% 10% 2	539
November	1st to 10th	Day	17% 10% 31% 28% 11% 4	495
	11th to 20th	Day	19% 12% 35% 23% 9% 2	370
	21st to end	Day	21% 15% 33% 21% 9% 1	188
December	1st to 10th	Day	21% 21% 36% 16% 7% 1	180
	11th to 20th	Day	22% 16% 34% 19% 8% 2	180
	21st to end	Day	26% 17% 31% 19% 7% 1	198
January	1st to 10th	Night	21% 16% 40% 20% 4	760
	11th to 20th	Night	22% 16% 34% 25% 4	760
	21st to end	Night	20% 15% 41% 22% 2	836
February	1st to 10th	Night	19% 14% 38% 26% 3	760
	11th to 20th	Night	25% 17% 38% 17% 1	743
	21st to end	Night	22% 18% 36% 21% 3	628
March	1st to 10th	Night	18% 17% 37% 25% 3	760
	11th to 20th	Night	23% 17% 35% 20% 6%	760
	21st to end	Night	18% 15% 38% 23% 5%	836
April	1st to 10th	Night	18% 17% 38% 22% 5%	760
	11th to 20th	Night	14% 14% 36% 28% 9%	751
	21st to end	Night	17% 10% 35% 31% 6%	760
May	1st to 10th	Night	19% 10% 32% 27% 12%	608
	11th to 20th	Night	19% 5% 28% 32% 15% 1	561
	21st to end	Night	13% 2 21% 39% 22% 2	421
June	1st to 10th	Night	9% 3 21% 42% 24% 1	380
	11th to 20th	Night	10% 3 18% 45% 22% 1	380
	21st to end	Night	8% 3 23% 45% 20% 1	380
July	1st to 10th	Night	11% 3 16% 39% 27% 4	415
	11th to 20th	Night	6% 3 11% 40% 33% 6%	552
	21st to end	Night	8% 2 19% 41% 28% 3	624
August	1st to 10th	Night	12% 2 11% 40% 31% 3	567
	11th to 20th	Night	14% 3 12% 41% 27% 2	626
	21st to end	Night	11% 2 14% 39% 28% 6%	836
September	1st to 10th	Night	16% 2 14% 35% 29% 5%	760
	11th to 20th	Night	14% 4 16% 37% 28% 3	760
	21st to end	Night	25% 5% 19% 31% 19% 1	760
October	1st to 10th	Night	21% 5% 20% 30% 20% 4	760
	11th to 20th	Night	18% 8% 26% 31% 15% 1	760
	21st to end	Night	16% 8% 31% 32% 13% 1	836
November	1st to 10th	Night	13% 8% 33% 31% 13% 2	780
	11th to 20th	Night	18% 12% 33% 29% 8%	800
	21st to end	Night	14% 12% 34% 30% 9% 1	779
December	1st to 10th	Night	22% 11% 35% 24% 8% 1	760
	11th to 20th	Night	19% 11% 36% 29% 5%	760
	21st to end	Night	20% 12% 30% 34% 4	836

Page generated at 2024-11-22 08:02:25. Version ac07

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