Chico Community Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Chico Community Observatory clear sky chart from 2005-11-06 to 2024-11-04.

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	10% 3 1 3 2 2 2 2 4 5% 65%	105206
	Night	12% 4 1 3 2 2 3 2 4 5% 60%	102515
Transparency	Day	22% 4 7% 18% 24% 26%	104960
	Night	26% 5% 8% 17% 21% 23%	102350
Seeing	Day	10% 7% 18% 28% 27% 10%	15126
	Night	12% 4 17% 36% 27% 3	24330

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	29% 7% 2 5% 3 3 2 2 4 5% 37%	2539
	11th to 20th	Day	28% 8% 2 7% 4 3 3 2 3 5% 34%	2776
	21st to end	Day	29% 7% 3 5% 3 3 3 3 5% 6% 34%	3146
February	1st to 10th	Day	20% 5% 1 3 3 4 3 4 5% 5% 48%	1710
	11th to 20th	Day	18% 6% 2 5% 2 3 4 3 4 6% 48%	1727
	21st to end	Day	19% 5% 2 4 2 4 3 3 4 7% 48%	1570
March	1st to 10th	Day	27% 10% 3 7% 4 4 3 3 4 6% 31%	3293
	11th to 20th	Day	17% 4 1 3 2 2 2 2 3 6% 57%	3490
	21st to end	Day	20% 8% 2 6% 4 4 4 4 6% 7% 36%	3934
April	1st to 10th	Day	15% 6% 2 4 4 3 3 3 5% 8% 47%	2280
	11th to 20th	Day	14% 4 1 4 3 3 3 3 4 5% 56%	2249
	21st to end	Day	6% 3 2 3 3 3 3 3 5% 8% 62%	2280
May	1st to 10th	Day	7% 2 1 2 2 2 2 2 3 6% 71%	4012
	11th to 20th	Day	3 2 1 2 2 2 1 2 3 5% 79%	4377
	21st to end	Day	3 2 1 2 2 2 2 2 4 6% 75%	4813
June	1st to 10th	Day	5% 3 1 2 3 2 3 3 5% 8% 64%	2660
	11th to 20th	Day	2 1 1 2 2 1 2 2 3 5% 78%	2660
	21st to end	Day	2 1 1 1 1 1 2 2 2 3 84%	2660
July	1st to 10th	Day	1 1 1 1 1 2 93%	4420
	11th to 20th	Day	1 1 1 1 1 2 1 2 3 86%	4420
	21st to end	Day	1 1 1 1 1 1 2 3 90%	4466
August	1st to 10th	Day	2 2 1 2 1 1 2 3 4 5% 77%	4091
	11th to 20th	Day	1 1 1 1 1 1 2 3 90%	3880
	21st to end	Day	1 1 1 1 1 1 1 2 2 89%	4180
September	1st to 10th	Day	1 1 1 1 2 1 2 3 87%	2280
	11th to 20th	Day	3 2 1 2 2 1 2 2 3 5% 76%	2280
	21st to end	Day	3 1 1 1 1 1 2 3 5% 80%	2027
October	1st to 10th	Day	3 2 1 2 2 2 2 2 3 4 77%	3180
	11th to 20th	Day	6% 3 1 3 2 2 2 3 4 6% 70%	3161
	21st to end	Day	7% 3 1 4 3 4 4 4 6% 7% 57%	3448
November	1st to 10th	Day	15% 3 1 4 3 3 3 3 6% 6% 53%	1753
	11th to 20th	Day	15% 3 2 5% 3 3 4 3 5% 7% 50%	1682
	21st to end	Day	14% 5% 1 4 3 3 4 4 5% 5% 54%	1520
December	1st to 10th	Day	22% 4 1 3 2 2 4 2 3 5% 51%	1520
	11th to 20th	Day	32% 8% 2 5% 4 3 3 2 4 5% 31%	1928
	21st to end	Day	23% 7% 2 5% 4 4 4 3 5% 7% 37%	2794
January	1st to 10th	Night	19% 7% 2 6% 3 3 3 3 5% 7% 41%	4406
	11th to 20th	Night	28% 6% 2 5% 3 4 3 3 4 6% 36%	4189
	21st to end	Night	29% 8% 3 6% 4 4 3 2 4 5% 32%	4521
February	1st to 10th	Night	19% 5% 2 4 3 3 3 3 5% 6% 49%	2470
	11th to 20th	Night	17% 6% 2 4 4 3 4 3 5% 5% 47%	2338
	21st to end	Night	18% 5% 2 3 3 3 4 3 4 5% 49%	1884
March	1st to 10th	Night	24% 9% 3 6% 4 3 3 4 4 5% 34%	3564
	11th to 20th	Night	19% 5% 1 3 1 1 2 2 3 5% 56%	3490
	21st to end	Night	20% 8% 2 6% 4 4 4 4 6% 7% 36%	3719
April	1st to 10th	Night	11% 5% 2 5% 4 3 4 3 6% 8% 48%	1900
	11th to 20th	Night	12% 5% 1 4 3 3 3 2 5% 7% 56%	1879
	21st to end	Night	7% 4 1 3 2 2 3 3 4 6% 65%	1900
May	1st to 10th	Night	6% 4 2 4 3 2 3 3 4 5% 66%	2940
	11th to 20th	Night	3 2 1 2 2 3 2 3 4 5% 74%	2516
	21st to end	Night	3 3 1 2 2 2 3 2 3 5% 74%	2762
June	1st to 10th	Night	5% 3 1 4 3 3 3 4 5% 9% 61%	1520
	11th to 20th	Night	2 1 2 2 1 2 1 4 7% 77%	1520
	21st to end	Night	2 1 1 2 2 1 2 2 3 3 81%	1520
July	1st to 10th	Night	1 1 1 1 1 2 93%	2540
	11th to 20th	Night	1 1 1 2 2 2 1 1 2 2 84%	2540
	21st to end	Night	1 1 1 1 1 1 1 3 3 87%	3095
August	1st to 10th	Night	3 3 1 2 2 2 2 3 4 4 75%	2848
	11th to 20th	Night	1 1 1 1 1 2 2 90%	2962
	21st to end	Night	2 1 1 1 1 1 2 2 88%	3498
September	1st to 10th	Night	1 1 1 1 1 1 1 2 3 88%	1900
	11th to 20th	Night	4 2 1 2 2 2 3 2 3 5% 76%	1900
	21st to end	Night	3 1 1 1 1 1 2 2 4 5% 80%	2150
October	1st to 10th	Night	3 2 2 2 2 2 1 3 3 80%	3800
	11th to 20th	Night	4 2 1 2 1 2 3 2 3 5% 75%	3777
	21st to end	Night	9% 2 1 3 3 3 3 3 5% 7% 63%	4121
November	1st to 10th	Night	14% 4 1 3 2 3 4 4 5% 6% 54%	2395
	11th to 20th	Night	14% 3 1 3 3 3 3 4 6% 7% 53%	2493
	21st to end	Night	14% 4 2 4 2 3 3 3 4 6% 56%	2660
December	1st to 10th	Night	22% 4 1 3 2 2 3 2 5% 7% 49%	2660
	11th to 20th	Night	35% 5% 2 3 3 3 3 3 5% 6% 33%	3276
	21st to end	Night	24% 6% 2 6% 4 4 4 3 4 5% 37%	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	49% 6% 10% 26% 7% 3	2539
	11th to 20th	Day	53% 6% 8% 14% 10% 8%	2776
	21st to end	Day	51% 7% 12% 13% 12% 5%	3146
February	1st to 10th	Day	37% 6% 12% 18% 20% 8%	1710
	11th to 20th	Day	36% 6% 9% 20% 22% 7%	1736
	21st to end	Day	35% 5% 11% 26% 17% 6%	1570
March	1st to 10th	Day	50% 9% 9% 15% 13% 4	3293
	11th to 20th	Day	30% 4 9% 24% 21% 12%	3490
	21st to end	Day	41% 10% 13% 20% 12% 3	3934
April	1st to 10th	Day	35% 6% 11% 23% 19% 6%	2280
	11th to 20th	Day	29% 5% 11% 23% 23% 9%	2252
	21st to end	Day	20% 5% 13% 29% 24% 9%	2280
May	1st to 10th	Day	15% 4 11% 24% 25% 21%	4012
	11th to 20th	Day	11% 3 7% 22% 35% 23%	4380
	21st to end	Day	11% 4 12% 31% 28% 13%	4814
June	1st to 10th	Day	18% 6% 11% 25% 26% 15%	2660
	11th to 20th	Day	8% 3 9% 20% 32% 27%	2660
	21st to end	Day	8% 2 4 13% 32% 42%	2660
July	1st to 10th	Day	3 1 2 6% 16% 73%	4351
	11th to 20th	Day	7% 1 2 7% 18% 65%	4345
	21st to end	Day	3 1 1 6% 28% 60%	4325
August	1st to 10th	Day	10% 2 2 7% 26% 52%	4076
	11th to 20th	Day	4 1 1 10% 41% 43%	3919
	21st to end	Day	5% 1 3 14% 38% 39%	4179
September	1st to 10th	Day	4 1 3 8% 26% 57%	2280
	11th to 20th	Day	12% 3 6% 21% 36% 22%	2280
	21st to end	Day	10% 2 6% 20% 30% 33%	2027
October	1st to 10th	Day	12% 3 3 12% 23% 47%	3180
	11th to 20th	Day	17% 3 5% 24% 30% 22%	3161
	21st to end	Day	23% 4 7% 22% 30% 14%	3448
November	1st to 10th	Day	29% 5% 11% 23% 19% 14%	1753
	11th to 20th	Day	32% 8% 11% 22% 18% 9%	1682
	21st to end	Day	30% 6% 10% 20% 21% 13%	1520
December	1st to 10th	Day	36% 6% 9% 19% 20% 11%	1520
	11th to 20th	Day	58% 4 7% 13% 13% 5%	1928
	21st to end	Day	46% 9% 14% 17% 11% 3	2794
January	1st to 10th	Night	41% 9% 16% 22% 9% 3	4406
	11th to 20th	Night	48% 9% 11% 11% 13% 8%	4189
	21st to end	Night	55% 6% 10% 11% 13% 6%	4521
February	1st to 10th	Night	35% 5% 9% 21% 17% 13%	2470
	11th to 20th	Night	35% 6% 9% 19% 23% 9%	2340
	21st to end	Night	36% 5% 9% 23% 19% 8%	1884
March	1st to 10th	Night	43% 12% 15% 13% 14% 3	3564
	11th to 20th	Night	30% 5% 7% 23% 22% 12%	3490
	21st to end	Night	40% 10% 15% 20% 11% 4	3719
April	1st to 10th	Night	32% 6% 14% 21% 19% 9%	1900
	11th to 20th	Night	26% 6% 12% 25% 20% 11%	1879
	21st to end	Night	20% 6% 13% 27% 26% 8%	1900
May	1st to 10th	Night	16% 7% 11% 17% 29% 20%	2940
	11th to 20th	Night	12% 4 9% 19% 32% 25%	2516
	21st to end	Night	12% 6% 10% 33% 24% 16%	2762
June	1st to 10th	Night	19% 7% 12% 25% 25% 12%	1520
	11th to 20th	Night	9% 4 9% 19% 30% 29%	1520
	21st to end	Night	9% 2 4 13% 29% 42%	1520
July	1st to 10th	Night	3 1 2 7% 14% 74%	2500
	11th to 20th	Night	9% 1 2 6% 17% 65%	2492
	21st to end	Night	5% 1 1 7% 26% 60%	2998
August	1st to 10th	Night	14% 2 2 8% 24% 51%	2839
	11th to 20th	Night	4 2 2 9% 36% 48%	2989
	21st to end	Night	6% 1 2 11% 35% 44%	3498
September	1st to 10th	Night	5% 2 2 7% 27% 58%	1900
	11th to 20th	Night	12% 3 6% 17% 36% 26%	1900
	21st to end	Night	9% 2 5% 16% 31% 37%	2150
October	1st to 10th	Night	12% 2 3 10% 18% 54%	3800
	11th to 20th	Night	14% 3 7% 23% 30% 24%	3777
	21st to end	Night	20% 3 5% 23% 28% 20%	4121
November	1st to 10th	Night	28% 6% 10% 23% 17% 15%	2395
	11th to 20th	Night	28% 7% 13% 22% 19% 10%	2493
	21st to end	Night	30% 5% 7% 22% 22% 13%	2660
December	1st to 10th	Night	36% 5% 11% 18% 18% 12%	2660
	11th to 20th	Night	51% 5% 8% 14% 17% 5%	3276
	21st to end	Night	47% 8% 11% 17% 12% 4	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	42% 8% 13% 22% 14% 1	180
	11th to 20th	Day	25% 9% 18% 28% 14% 6%	325
	21st to end	Day	23% 5% 20% 23% 22% 7%	407
February	1st to 10th	Day	23% 9% 18% 26% 19% 5%	370
	11th to 20th	Day	22% 13% 21% 24% 16% 4	395
	21st to end	Day	16% 12% 25% 27% 16% 3	382
March	1st to 10th	Day	25% 17% 25% 20% 10% 2	460
	11th to 20th	Day	24% 10% 22% 23% 16% 5%	460
	21st to end	Day	21% 16% 24% 25% 12% 2	506
April	1st to 10th	Day	17% 14% 24% 25% 15% 4	460
	11th to 20th	Day	15% 13% 23% 24% 19% 6%	452
	21st to end	Day	6% 12% 21% 31% 24% 6%	460
May	1st to 10th	Day	8% 9% 34% 25% 20% 5%	463
	11th to 20th	Day	8% 9% 21% 25% 25% 12%	488
	21st to end	Day	4 8% 19% 27% 30% 12%	529
June	1st to 10th	Day	5% 7% 18% 28% 32% 10%	490
	11th to 20th	Day	4 6% 20% 34% 29% 7%	490
	21st to end	Day	1 3 15% 35% 33% 13%	490
July	1st to 10th	Day	1 2 10% 36% 39% 12%	486
	11th to 20th	Day	1 8% 33% 43% 14%	484
	21st to end	Day	1 6% 34% 45% 14%	531
August	1st to 10th	Day	2 1 12% 30% 40% 15%	487
	11th to 20th	Day	1 2 10% 27% 41% 18%	477
	21st to end	Day	2 1 9% 29% 45% 15%	539
September	1st to 10th	Day	1 2 10% 31% 43% 14%	490
	11th to 20th	Day	4 4 18% 28% 32% 14%	490
	21st to end	Day	3 4 19% 34% 30% 11%	490
October	1st to 10th	Day	4 7% 20% 25% 30% 15%	490
	11th to 20th	Day	8% 6% 18% 24% 31% 14%	490
	21st to end	Day	12% 7% 20% 27% 24% 10%	539
November	1st to 10th	Day	17% 7% 18% 22% 24% 12%	331
	11th to 20th	Day	14% 5% 14% 30% 25% 12%	257
	21st to end	Day	12% 6% 19% 29% 27% 7%	180
December	1st to 10th	Day	25% 6% 21% 22% 14% 13%	180
	11th to 20th	Day	27% 4 20% 24% 17% 8%	180
	21st to end	Day	20% 9% 20% 25% 22% 4	198
January	1st to 10th	Night	22% 5% 17% 34% 20% 2	760
	11th to 20th	Night	22% 5% 14% 39% 18% 2	760
	21st to end	Night	20% 4 19% 34% 20% 3	836
February	1st to 10th	Night	20% 4 17% 38% 19% 2	760
	11th to 20th	Night	18% 7% 18% 33% 21% 2	744
	21st to end	Night	18% 6% 24% 36% 14% 1	628
March	1st to 10th	Night	22% 10% 20% 29% 16% 3	760
	11th to 20th	Night	20% 7% 19% 29% 23% 2	760
	21st to end	Night	19% 9% 24% 32% 16% 1	836
April	1st to 10th	Night	12% 8% 28% 34% 18% 2	760
	11th to 20th	Night	12% 7% 23% 33% 21% 3	751
	21st to end	Night	8% 6% 22% 37% 24% 3	760
May	1st to 10th	Night	7% 7% 29% 32% 23% 1	624
	11th to 20th	Night	5% 3 22% 40% 28% 2	374
	21st to end	Night	5% 8% 18% 40% 27% 1	411
June	1st to 10th	Night	7% 3 19% 43% 27% 2	380
	11th to 20th	Night	1 4 22% 48% 24% 1	380
	21st to end	Night	2 2 17% 46% 31% 2	380
July	1st to 10th	Night	1 11% 48% 36% 2	370
	11th to 20th	Night	1 1 13% 50% 34% 2	368
	21st to end	Night	1 7% 40% 49% 4	610
August	1st to 10th	Night	2 2 9% 38% 47% 3	567
	11th to 20th	Night	1 1 9% 42% 44% 5%	649
	21st to end	Night	1 1 6% 38% 51% 3	836
September	1st to 10th	Night	1 1 8% 38% 48% 4	760
	11th to 20th	Night	4 2 11% 39% 38% 7%	760
	21st to end	Night	4 3 14% 36% 36% 8%	760
October	1st to 10th	Night	5% 4 17% 35% 33% 6%	760
	11th to 20th	Night	7% 3 15% 34% 36% 5%	760
	21st to end	Night	9% 4 15% 36% 29% 7%	836
November	1st to 10th	Night	14% 6% 14% 32% 30% 4	754
	11th to 20th	Night	14% 2 18% 39% 25% 2	760
	21st to end	Night	13% 4 17% 40% 23% 3	760
December	1st to 10th	Night	22% 4 15% 35% 21% 4	760
	11th to 20th	Night	28% 4 16% 30% 20% 2	760
	21st to end	Night	23% 6% 20% 34% 17% 1	836

Page generated at 2024-11-01 19:47:34. Version ac07

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