Ross Creek Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ross Creek Observatory clear sky chart from 2005-11-06 to 2024-11-30.

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	5% 4 2 4 3 3 3 3 5% 6% 61%	105209
	Night	6% 6% 2 5% 4 4 4 3 5% 7% 54%	103127
Transparency	Day	22% 5% 9% 19% 24% 20%	104967
	Night	26% 7% 12% 18% 21% 17%	102959
Seeing	Day	7% 11% 23% 31% 21% 7%	15524
	Night	8% 5% 15% 34% 31% 7%	24913

By Month

Percentage Cloud Cover SW (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	12% 9% 4 7% 5% 5% 5% 4 5% 7% 37%	2712
	11th to 20th	Day	11% 10% 4 11% 6% 5% 5% 4 6% 5% 33%	2860
	21st to end	Day	14% 11% 4 9% 5% 5% 5% 5% 5% 8% 29%	3146
February	1st to 10th	Day	11% 8% 3 6% 4 4 4 3 5% 6% 45%	1710
	11th to 20th	Day	11% 7% 2 6% 4 6% 4 3 6% 7% 44%	1772
	21st to end	Day	11% 9% 2 6% 5% 4 4 3 5% 6% 46%	1570
March	1st to 10th	Day	8% 10% 4 10% 8% 7% 7% 5% 7% 7% 27%	3371
	11th to 20th	Day	7% 5% 2 5% 4 5% 4 3 5% 8% 53%	3490
	21st to end	Day	10% 8% 3 9% 7% 6% 6% 4 7% 7% 32%	3902
April	1st to 10th	Day	10% 7% 2 6% 5% 4 4 4 5% 7% 46%	2280
	11th to 20th	Day	9% 6% 2 4 3 3 3 3 6% 7% 55%	2249
	21st to end	Day	5% 5% 2 4 3 4 3 3 5% 8% 59%	2280
May	1st to 10th	Day	5% 3 1 3 2 2 3 2 4 6% 70%	3858
	11th to 20th	Day	2 2 1 2 2 2 2 2 4 7% 75%	4156
	21st to end	Day	3 3 1 4 2 3 3 2 3 6% 69%	4813
June	1st to 10th	Day	4 4 1 4 3 2 3 3 5% 7% 64%	2660
	11th to 20th	Day	2 2 1 1 1 2 3 2 4 7% 77%	2660
	21st to end	Day	1 2 1 2 1 2 2 2 3 5% 80%	2660
July	1st to 10th	Day	1 1 1 1 2 1 3 4 87%	4420
	11th to 20th	Day	1 1 2 2 2 2 2 4 5% 79%	4117
	21st to end	Day	1 1 1 2 2 2 4 6% 81%	4455
August	1st to 10th	Day	1 2 1 3 2 3 3 3 6% 7% 70%	4091
	11th to 20th	Day	1 1 2 1 1 2 1 3 4 84%	3790
	21st to end	Day	1 2 2 2 3 2 4 5% 78%	4180
September	1st to 10th	Day	1 1 1 1 2 1 2 1 2 5% 82%	2280
	11th to 20th	Day	2 3 2 4 3 3 3 2 5% 7% 66%	2280
	21st to end	Day	2 1 1 2 2 2 3 1 3 5% 77%	2024
October	1st to 10th	Day	2 2 1 3 2 2 2 2 4 7% 74%	3180
	11th to 20th	Day	2 3 1 3 2 3 3 3 4 6% 70%	3161
	21st to end	Day	2 3 1 3 2 3 4 3 6% 8% 63%	3448
November	1st to 10th	Day	6% 6% 1 5% 4 4 4 4 5% 7% 55%	1920
	11th to 20th	Day	5% 6% 2 5% 5% 5% 4 4 6% 7% 51%	1800
	21st to end	Day	9% 5% 2 5% 4 3 3 3 6% 8% 52%	1672
December	1st to 10th	Day	8% 5% 2 7% 5% 5% 6% 4 5% 8% 44%	1520
	11th to 20th	Day	15% 10% 4 11% 5% 4 4 4 5% 6% 31%	1928
	21st to end	Day	9% 12% 4 10% 5% 6% 5% 4 6% 7% 32%	2794
January	1st to 10th	Night	11% 10% 3 7% 5% 4 4 4 6% 6% 39%	4222
	11th to 20th	Night	11% 10% 6% 11% 6% 5% 5% 4 5% 6% 31%	4110
	21st to end	Night	14% 13% 4 8% 5% 6% 5% 4 5% 6% 30%	4521
February	1st to 10th	Night	10% 7% 3 6% 5% 4 4 4 5% 6% 48%	2470
	11th to 20th	Night	9% 8% 2 6% 3 5% 4 4 6% 7% 44%	2294
	21st to end	Night	9% 8% 4 5% 4 4 4 4 5% 6% 49%	1884
March	1st to 10th	Night	10% 13% 4 11% 6% 5% 5% 4 6% 6% 30%	3500
	11th to 20th	Night	8% 7% 3 6% 4 4 4 3 4 6% 51%	3490
	21st to end	Night	10% 14% 5% 9% 7% 5% 5% 4 5% 5% 33%	3750
April	1st to 10th	Night	9% 7% 3 5% 4 4 5% 5% 6% 7% 46%	1900
	11th to 20th	Night	7% 6% 3 6% 4 4 4 3 5% 6% 53%	1879
	21st to end	Night	4 4 2 4 3 3 5% 4 5% 9% 57%	1900
May	1st to 10th	Night	2 5% 2 4 2 3 5% 3 4 5% 65%	3102
	11th to 20th	Night	2 3 1 3 4 3 4 4 7% 10% 59%	2743
	21st to end	Night	2 3 1 3 3 3 3 3 4 8% 68%	2762
June	1st to 10th	Night	2 4 1 3 3 2 3 3 5% 9% 64%	1520
	11th to 20th	Night	1 2 1 3 2 1 3 4 5% 7% 72%	1520
	21st to end	Night	1 3 1 3 2 2 3 2 4 6% 75%	1520
July	1st to 10th	Night	1 1 1 2 2 1 3 4 85%	2540
	11th to 20th	Night	1 1 3 2 3 3 2 4 7% 73%	2848
	21st to end	Night	1 1 3 3 6% 3 4 7% 7% 65%	3109
August	1st to 10th	Night	1 3 2 4 4 6% 4 3 6% 9% 60%	2848
	11th to 20th	Night	2 1 3 2 2 2 2 4 6% 75%	3056
	21st to end	Night	1 2 1 3 3 5% 4 3 5% 6% 69%	3498
September	1st to 10th	Night	1 1 1 2 2 2 3 2 5% 7% 74%	1900
	11th to 20th	Night	2 3 2 5% 3 4 4 3 5% 5% 65%	1900
	21st to end	Night	2 3 1 3 2 2 2 2 4 6% 74%	2150
October	1st to 10th	Night	2 1 1 2 2 2 3 3 3 6% 75%	3800
	11th to 20th	Night	3 5% 2 4 3 4 4 3 5% 6% 60%	3777
	21st to end	Night	3 4 2 4 3 4 5% 3 5% 6% 61%	4121
November	1st to 10th	Night	5% 5% 2 5% 4 3 3 3 5% 8% 57%	2375
	11th to 20th	Night	6% 5% 2 6% 3 4 4 4 6% 8% 52%	2600
	21st to end	Night	6% 5% 1 4 5% 4 4 4 4 7% 55%	2720
December	1st to 10th	Night	8% 7% 3 6% 5% 3 4 3 4 7% 48%	2660
	11th to 20th	Night	15% 12% 4 9% 5% 4 4 3 5% 7% 32%	3276
	21st to end	Night	10% 9% 4 9% 6% 6% 7% 5% 6% 6% 31%	4862

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	40% 11% 12% 25% 9% 3	2712
	11th to 20th	Day	47% 10% 11% 13% 11% 8%	2860
	21st to end	Day	49% 10% 9% 15% 13% 5%	3146
February	1st to 10th	Day	38% 6% 9% 19% 18% 11%	1710
	11th to 20th	Day	38% 6% 10% 17% 21% 8%	1781
	21st to end	Day	39% 6% 8% 21% 19% 6%	1570
March	1st to 10th	Day	50% 13% 9% 12% 13% 3	3371
	11th to 20th	Day	28% 7% 10% 28% 15% 11%	3490
	21st to end	Day	43% 12% 16% 17% 10% 2	3902
April	1st to 10th	Day	36% 6% 12% 21% 19% 5%	2280
	11th to 20th	Day	28% 7% 15% 25% 20% 6%	2252
	21st to end	Day	23% 6% 14% 28% 24% 5%	2280
May	1st to 10th	Day	15% 5% 10% 31% 26% 13%	3858
	11th to 20th	Day	11% 3 14% 29% 31% 13%	4159
	21st to end	Day	16% 4 14% 29% 33% 4	4814
June	1st to 10th	Day	19% 6% 12% 27% 26% 9%	2660
	11th to 20th	Day	9% 4 10% 24% 36% 17%	2660
	21st to end	Day	10% 3 6% 15% 31% 36%	2660
July	1st to 10th	Day	4 1 3 8% 16% 68%	4351
	11th to 20th	Day	7% 2 6% 9% 18% 58%	4047
	21st to end	Day	4 2 5% 10% 35% 44%	4315
August	1st to 10th	Day	10% 3 6% 12% 34% 35%	4076
	11th to 20th	Day	5% 2 4 10% 43% 36%	3827
	21st to end	Day	7% 3 6% 14% 34% 36%	4179
September	1st to 10th	Day	8% 2 4 11% 31% 45%	2280
	11th to 20th	Day	15% 4 8% 24% 30% 18%	2280
	21st to end	Day	10% 3 7% 20% 36% 23%	2024
October	1st to 10th	Day	12% 3 6% 11% 29% 39%	3180
	11th to 20th	Day	15% 5% 8% 26% 30% 17%	3161
	21st to end	Day	17% 5% 8% 22% 31% 17%	3448
November	1st to 10th	Day	28% 6% 9% 21% 24% 12%	1920
	11th to 20th	Day	30% 7% 11% 21% 23% 9%	1800
	21st to end	Day	31% 5% 9% 16% 29% 10%	1672
December	1st to 10th	Day	35% 8% 11% 18% 16% 11%	1520
	11th to 20th	Day	52% 7% 10% 13% 13% 6%	1928
	21st to end	Day	46% 9% 12% 19% 11% 3	2794
January	1st to 10th	Night	36% 11% 17% 21% 11% 3	4222
	11th to 20th	Night	47% 11% 14% 11% 9% 8%	4110
	21st to end	Night	49% 11% 9% 12% 11% 7%	4521
February	1st to 10th	Night	36% 5% 9% 18% 20% 12%	2470
	11th to 20th	Night	36% 6% 11% 18% 21% 8%	2296
	21st to end	Night	33% 6% 12% 27% 16% 5%	1884
March	1st to 10th	Night	46% 13% 14% 12% 13% 3	3500
	11th to 20th	Night	29% 7% 14% 20% 21% 11%	3490
	21st to end	Night	42% 12% 15% 17% 10% 4	3750
April	1st to 10th	Night	33% 8% 15% 21% 18% 5%	1900
	11th to 20th	Night	29% 6% 14% 27% 17% 8%	1879
	21st to end	Night	21% 7% 17% 27% 22% 7%	1900
May	1st to 10th	Night	14% 8% 14% 24% 25% 14%	3102
	11th to 20th	Night	12% 5% 34% 22% 16% 11%	2744
	21st to end	Night	13% 6% 20% 29% 28% 5%	2762
June	1st to 10th	Night	17% 6% 16% 26% 25% 10%	1520
	11th to 20th	Night	10% 4 11% 20% 30% 23%	1520
	21st to end	Night	11% 4 8% 17% 25% 35%	1520
July	1st to 10th	Night	4 2 3 10% 16% 65%	2500
	11th to 20th	Night	8% 3 7% 12% 18% 52%	2795
	21st to end	Night	9% 4 12% 14% 28% 33%	3011
August	1st to 10th	Night	15% 4 9% 13% 31% 28%	2839
	11th to 20th	Night	9% 2 6% 10% 38% 35%	3085
	21st to end	Night	10% 4 10% 14% 34% 28%	3498
September	1st to 10th	Night	9% 3 5% 12% 27% 44%	1900
	11th to 20th	Night	16% 5% 9% 23% 27% 19%	1900
	21st to end	Night	11% 3 7% 18% 33% 27%	2150
October	1st to 10th	Night	11% 3 7% 10% 24% 44%	3800
	11th to 20th	Night	19% 5% 10% 23% 25% 18%	3777
	21st to end	Night	19% 6% 8% 21% 26% 20%	4121
November	1st to 10th	Night	24% 7% 10% 23% 22% 15%	2375
	11th to 20th	Night	29% 6% 11% 21% 24% 9%	2600
	21st to end	Night	29% 5% 10% 18% 23% 15%	2720
December	1st to 10th	Night	35% 7% 10% 17% 18% 13%	2660
	11th to 20th	Night	52% 5% 10% 13% 15% 5%	3276
	21st to end	Night	45% 11% 14% 14% 11% 5%	4862

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	24% 16% 23% 20% 15% 1	288
	11th to 20th	Day	14% 14% 26% 30% 13% 4	370
	21st to end	Day	15% 13% 25% 27% 17% 3	407
February	1st to 10th	Day	15% 19% 24% 22% 15% 4	370
	11th to 20th	Day	17% 19% 28% 24% 10% 2	416
	21st to end	Day	11% 20% 30% 25% 12% 2	382
March	1st to 10th	Day	17% 19% 32% 23% 8% 1	460
	11th to 20th	Day	16% 20% 25% 22% 13% 4	460
	21st to end	Day	13% 20% 33% 24% 9% 1	506
April	1st to 10th	Day	13% 17% 31% 24% 13% 3	460
	11th to 20th	Day	12% 19% 29% 24% 14% 3	452
	21st to end	Day	6% 19% 27% 30% 11% 7%	460
May	1st to 10th	Day	7% 16% 33% 27% 13% 4	463
	11th to 20th	Day	8% 12% 30% 28% 16% 6%	488
	21st to end	Day	5% 11% 27% 32% 17% 7%	529
June	1st to 10th	Day	3 11% 28% 30% 20% 8%	490
	11th to 20th	Day	2 9% 29% 36% 18% 5%	490
	21st to end	Day	1 4 22% 37% 27% 9%	490
July	1st to 10th	Day	1 2 16% 40% 33% 8%	486
	11th to 20th	Day	1 11% 45% 31% 12%	484
	21st to end	Day	1 11% 41% 32% 15%	531
August	1st to 10th	Day	1 2 19% 40% 29% 9%	487
	11th to 20th	Day	3 18% 39% 24% 16%	477
	21st to end	Day	2 12% 42% 32% 12%	539
September	1st to 10th	Day	1 4 13% 40% 31% 10%	490
	11th to 20th	Day	2 5% 25% 39% 20% 10%	490
	21st to end	Day	3 6% 17% 36% 30% 8%	490
October	1st to 10th	Day	2 8% 22% 30% 26% 11%	490
	11th to 20th	Day	5% 10% 19% 29% 28% 9%	490
	21st to end	Day	7% 8% 22% 34% 23% 6%	539
November	1st to 10th	Day	7% 13% 21% 25% 28% 7%	456
	11th to 20th	Day	4 11% 23% 28% 26% 9%	300
	21st to end	Day	8% 10% 22% 30% 24% 5%	236
December	1st to 10th	Day	9% 16% 18% 30% 19% 8%	180
	11th to 20th	Day	9% 22% 20% 23% 17% 9%	180
	21st to end	Day	11% 25% 23% 21% 15% 5%	198
January	1st to 10th	Night	16% 7% 18% 30% 23% 6%	760
	11th to 20th	Night	12% 7% 16% 35% 22% 8%	760
	21st to end	Night	16% 6% 15% 33% 24% 6%	836
February	1st to 10th	Night	14% 10% 15% 33% 24% 5%	760
	11th to 20th	Night	13% 10% 20% 32% 20% 5%	744
	21st to end	Night	14% 9% 21% 35% 18% 3	628
March	1st to 10th	Night	14% 12% 21% 30% 20% 3	760
	11th to 20th	Night	14% 9% 19% 28% 25% 4	760
	21st to end	Night	11% 11% 23% 34% 19% 3	836
April	1st to 10th	Night	11% 6% 25% 32% 23% 3	760
	11th to 20th	Night	10% 12% 20% 33% 20% 6%	751
	21st to end	Night	6% 7% 27% 31% 23% 6%	760
May	1st to 10th	Night	5% 4 26% 34% 26% 5%	721
	11th to 20th	Night	5% 3 12% 36% 37% 6%	510
	21st to end	Night	3 4 18% 40% 31% 3	411
June	1st to 10th	Night	3 4 15% 44% 30% 4	380
	11th to 20th	Night	1 3 12% 48% 33% 2	380
	21st to end	Night	1 9% 39% 48% 3	380
July	1st to 10th	Night	1 4 36% 56% 4	370
	11th to 20th	Night	1 1 30% 55% 12%	541
	21st to end	Night	1 1 2 29% 55% 13%	624
August	1st to 10th	Night	3 3 34% 52% 8%	567
	11th to 20th	Night	1 1 8% 39% 44% 8%	706
	21st to end	Night	1 1 7% 32% 50% 10%	836
September	1st to 10th	Night	1 1 8% 30% 49% 11%	760
	11th to 20th	Night	3 2 10% 38% 39% 8%	760
	21st to end	Night	3 2 11% 34% 40% 10%	760
October	1st to 10th	Night	3 3 11% 37% 35% 11%	760
	11th to 20th	Night	6% 4 12% 31% 37% 11%	760
	21st to end	Night	5% 5% 11% 33% 30% 15%	836
November	1st to 10th	Night	6% 5% 16% 30% 34% 9%	780
	11th to 20th	Night	9% 3 17% 34% 31% 7%	800
	21st to end	Night	9% 5% 16% 38% 25% 7%	800
December	1st to 10th	Night	13% 6% 18% 32% 25% 6%	760
	11th to 20th	Night	17% 6% 19% 33% 21% 5%	760
	21st to end	Night	14% 12% 21% 31% 18% 4	836

Page generated at 2024-11-27 14:30:51. Version ac07

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