Henry Coe State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Henry Coe State Park 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	7% 4 1 4 3 3 3 2 4 6% 64%	104979
	Night	8% 5% 2 4 3 3 3 3 4 7% 58%	102784
Transparency	Day	21% 5% 8% 18% 23% 24%	104735
	Night	24% 6% 10% 19% 20% 21%	102617
Seeing	Day	9% 9% 22% 33% 21% 6%	15416
	Night	10% 4 15% 33% 30% 8%	24797

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	15% 11% 4 6% 4 3 4 3 4 5% 42%	2667
	11th to 20th	Day	15% 8% 3 8% 6% 5% 6% 3 5% 6% 36%	2860
	21st to end	Day	21% 9% 3 6% 5% 4 4 3 5% 8% 33%	3146
February	1st to 10th	Day	18% 8% 2 5% 3 2 2 3 5% 6% 46%	1710
	11th to 20th	Day	12% 8% 2 5% 4 4 5% 4 4 6% 46%	1798
	21st to end	Day	17% 7% 2 5% 4 4 4 3 4 5% 46%	1570
March	1st to 10th	Day	12% 13% 4 11% 6% 6% 6% 4 6% 6% 26%	3319
	11th to 20th	Day	10% 6% 2 4 3 3 3 3 5% 7% 55%	3490
	21st to end	Day	12% 9% 3 8% 6% 5% 6% 5% 5% 7% 34%	3934
April	1st to 10th	Day	13% 7% 2 6% 4 4 3 3 4 6% 47%	2280
	11th to 20th	Day	9% 5% 1 4 3 3 3 3 5% 7% 55%	2249
	21st to end	Day	6% 4 1 3 3 3 3 2 4 8% 61%	2280
May	1st to 10th	Day	6% 3 1 3 2 2 2 2 3 6% 71%	3800
	11th to 20th	Day	3 2 1 2 2 3 2 2 4 6% 74%	4212
	21st to end	Day	2 2 1 3 3 3 2 2 4 6% 71%	4813
June	1st to 10th	Day	3 4 1 3 3 2 2 3 5% 7% 66%	2660
	11th to 20th	Day	1 1 1 2 1 1 2 2 3 6% 80%	2660
	21st to end	Day	2 2 1 2 2 1 2 2 2 3 83%	2660
July	1st to 10th	Day	1 1 1 1 1 2 3 90%	4420
	11th to 20th	Day	1 1 2 1 2 2 1 2 3 84%	4182
	21st to end	Day	1 1 1 1 2 5% 87%	4455
August	1st to 10th	Day	1 1 1 2 1 2 2 2 4 6% 78%	4091
	11th to 20th	Day	1 1 1 1 1 2 4 90%	3753
	21st to end	Day	1 1 1 1 1 1 2 2 4 85%	4180
September	1st to 10th	Day	1 1 1 1 1 1 1 1 2 3 86%	2280
	11th to 20th	Day	1 2 1 3 2 2 3 2 4 7% 75%	2280
	21st to end	Day	3 1 2 1 2 1 1 4 5% 80%	2040
October	1st to 10th	Day	1 3 1 3 2 2 2 2 4 6% 74%	3180
	11th to 20th	Day	3 2 1 2 2 2 2 2 3 5% 77%	3161
	21st to end	Day	3 3 1 4 3 3 4 3 5% 6% 65%	3448
November	1st to 10th	Day	7% 5% 1 3 4 4 5% 3 5% 8% 55%	1824
	11th to 20th	Day	9% 4 2 4 3 4 4 4 6% 7% 55%	1710
	21st to end	Day	11% 6% 1 3 2 3 2 3 5% 7% 57%	1625
December	1st to 10th	Day	14% 5% 2 6% 4 3 4 3 4 7% 46%	1520
	11th to 20th	Day	28% 10% 3 5% 4 2 3 3 4 5% 33%	1928
	21st to end	Day	14% 11% 3 7% 4 4 4 4 6% 6% 36%	2794
January	1st to 10th	Night	12% 7% 2 6% 4 4 4 4 5% 6% 46%	4278
	11th to 20th	Night	19% 9% 3 6% 4 4 5% 4 5% 7% 35%	4110
	21st to end	Night	20% 9% 3 7% 5% 4 4 3 5% 6% 34%	4521
February	1st to 10th	Night	17% 7% 2 4 3 3 3 3 4 6% 49%	2470
	11th to 20th	Night	12% 6% 2 4 4 4 4 4 6% 7% 47%	2270
	21st to end	Night	13% 7% 2 5% 4 2 3 3 4 6% 50%	1884
March	1st to 10th	Night	16% 13% 3 8% 5% 4 4 3 6% 6% 32%	3550
	11th to 20th	Night	10% 7% 2 5% 3 3 2 2 3 6% 57%	3490
	21st to end	Night	13% 13% 2 9% 5% 4 4 3 5% 7% 35%	3719
April	1st to 10th	Night	11% 7% 1 3 4 4 3 4 6% 6% 50%	1900
	11th to 20th	Night	7% 7% 2 4 4 3 3 3 4 7% 56%	1879
	21st to end	Night	4 4 2 4 3 3 4 3 6% 7% 59%	1900
May	1st to 10th	Night	2 3 2 4 3 3 3 2 4 5% 70%	3164
	11th to 20th	Night	2 2 1 4 3 5% 4 3 7% 14% 55%	2682
	21st to end	Night	1 2 1 3 2 5% 4 2 6% 10% 62%	2762
June	1st to 10th	Night	3 2 1 4 4 3 2 3 5% 8% 65%	1520
	11th to 20th	Night	1 1 1 3 3 3 3 3 5% 7% 71%	1520
	21st to end	Night	1 1 1 3 3 2 3 2 4 6% 75%	1520
July	1st to 10th	Night	1 1 1 1 2 3 6% 85%	2540
	11th to 20th	Night	1 2 1 2 2 2 3 8% 78%	2782
	21st to end	Night	1 1 2 2 4 4 3 5% 14% 64%	3109
August	1st to 10th	Night	1 1 1 2 3 2 3 3 5% 8% 71%	2848
	11th to 20th	Night	1 1 1 2 2 1 3 6% 82%	3095
	21st to end	Night	1 2 2 1 2 2 1 3 6% 79%	3498
September	1st to 10th	Night	1 1 2 1 2 2 1 3 6% 80%	1900
	11th to 20th	Night	3 2 1 3 2 2 3 2 4 7% 71%	1900
	21st to end	Night	2 2 1 3 1 2 1 2 2 5% 79%	2134
October	1st to 10th	Night	2 2 1 2 2 2 2 2 3 6% 77%	3800
	11th to 20th	Night	2 2 1 3 2 2 2 2 3 7% 73%	3777
	21st to end	Night	4 3 2 4 3 2 3 3 4 6% 66%	4121
November	1st to 10th	Night	6% 6% 1 4 3 3 3 3 4 7% 60%	2323
	11th to 20th	Night	8% 5% 2 4 3 3 3 3 6% 9% 55%	2470
	21st to end	Night	8% 6% 1 4 3 3 4 3 4 6% 58%	2550
December	1st to 10th	Night	15% 6% 2 5% 3 3 3 3 4 6% 50%	2660
	11th to 20th	Night	27% 9% 2 6% 4 2 3 3 5% 6% 33%	3276
	21st to end	Night	17% 7% 3 7% 5% 5% 5% 4 5% 6% 36%	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	39% 9% 11% 28% 9% 3	2667
	11th to 20th	Day	47% 9% 11% 15% 11% 7%	2860
	21st to end	Day	48% 9% 9% 16% 13% 4	3146
February	1st to 10th	Day	38% 5% 8% 20% 19% 11%	1710
	11th to 20th	Day	37% 5% 10% 18% 22% 8%	1808
	21st to end	Day	39% 6% 8% 21% 20% 6%	1570
March	1st to 10th	Day	49% 13% 10% 11% 14% 3	3319
	11th to 20th	Day	27% 7% 11% 30% 14% 11%	3490
	21st to end	Day	40% 14% 15% 19% 10% 2	3934
April	1st to 10th	Day	36% 6% 12% 21% 19% 6%	2280
	11th to 20th	Day	27% 7% 13% 25% 21% 7%	2252
	21st to end	Day	20% 7% 13% 29% 25% 5%	2280
May	1st to 10th	Day	15% 4 13% 28% 27% 14%	3800
	11th to 20th	Day	10% 3 10% 30% 37% 10%	4215
	21st to end	Day	12% 6% 13% 32% 31% 5%	4814
June	1st to 10th	Day	16% 6% 12% 26% 28% 11%	2660
	11th to 20th	Day	8% 3 9% 22% 37% 21%	2660
	21st to end	Day	9% 2 4 15% 29% 41%	2660
July	1st to 10th	Day	3 1 2 7% 15% 72%	4351
	11th to 20th	Day	8% 2 3 8% 14% 65%	4110
	21st to end	Day	3 1 3 7% 27% 58%	4315
August	1st to 10th	Day	9% 2 4 9% 24% 52%	4076
	11th to 20th	Day	3 1 2 9% 29% 55%	3789
	21st to end	Day	6% 2 4 11% 31% 46%	4179
September	1st to 10th	Day	6% 2 3 10% 29% 50%	2280
	11th to 20th	Day	10% 4 8% 23% 34% 20%	2280
	21st to end	Day	10% 2 4 20% 38% 26%	2040
October	1st to 10th	Day	12% 3 5% 11% 24% 45%	3180
	11th to 20th	Day	12% 3 6% 22% 34% 24%	3161
	21st to end	Day	19% 3 7% 18% 32% 20%	3448
November	1st to 10th	Day	25% 6% 10% 21% 24% 14%	1824
	11th to 20th	Day	28% 7% 9% 22% 26% 9%	1710
	21st to end	Day	27% 5% 11% 17% 29% 11%	1625
December	1st to 10th	Day	35% 7% 12% 17% 18% 11%	1520
	11th to 20th	Day	53% 5% 8% 14% 14% 6%	1928
	21st to end	Day	43% 9% 12% 21% 11% 4	2794
January	1st to 10th	Night	33% 10% 17% 24% 12% 3	4278
	11th to 20th	Night	45% 9% 13% 15% 9% 8%	4110
	21st to end	Night	47% 9% 10% 15% 12% 6%	4521
February	1st to 10th	Night	36% 4 9% 19% 20% 12%	2470
	11th to 20th	Night	32% 6% 12% 19% 22% 9%	2271
	21st to end	Night	32% 5% 11% 27% 18% 7%	1884
March	1st to 10th	Night	46% 12% 12% 12% 13% 4	3550
	11th to 20th	Night	29% 5% 11% 23% 20% 11%	3490
	21st to end	Night	39% 14% 13% 19% 11% 4	3719
April	1st to 10th	Night	32% 7% 14% 21% 19% 7%	1900
	11th to 20th	Night	27% 6% 12% 28% 18% 8%	1879
	21st to end	Night	19% 7% 14% 29% 25% 7%	1900
May	1st to 10th	Night	13% 8% 14% 23% 27% 16%	3164
	11th to 20th	Night	10% 4 15% 39% 18% 14%	2682
	21st to end	Night	10% 6% 16% 31% 29% 9%	2762
June	1st to 10th	Night	18% 8% 11% 23% 26% 14%	1520
	11th to 20th	Night	12% 4 9% 20% 29% 28%	1520
	21st to end	Night	11% 3 6% 19% 22% 40%	1520
July	1st to 10th	Night	4 1 3 10% 13% 69%	2500
	11th to 20th	Night	8% 3 3 11% 15% 60%	2731
	21st to end	Night	9% 2 7% 16% 26% 40%	3011
August	1st to 10th	Night	13% 3 4 13% 16% 52%	2839
	11th to 20th	Night	5% 2 4 11% 23% 56%	3125
	21st to end	Night	8% 2 5% 14% 27% 44%	3498
September	1st to 10th	Night	8% 2 4 11% 23% 53%	1900
	11th to 20th	Night	13% 5% 7% 21% 29% 25%	1900
	21st to end	Night	11% 2 7% 15% 36% 29%	2134
October	1st to 10th	Night	12% 2 5% 11% 17% 52%	3800
	11th to 20th	Night	13% 3 6% 22% 33% 23%	3777
	21st to end	Night	17% 4 6% 19% 30% 25%	4121
November	1st to 10th	Night	23% 5% 10% 22% 22% 18%	2323
	11th to 20th	Night	25% 6% 11% 20% 28% 10%	2470
	21st to end	Night	26% 5% 9% 20% 24% 15%	2550
December	1st to 10th	Night	34% 6% 10% 18% 18% 14%	2660
	11th to 20th	Night	50% 6% 10% 14% 16% 5%	3276
	21st to end	Night	44% 10% 13% 16% 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	29% 13% 21% 23% 14% 1	256
	11th to 20th	Day	19% 9% 22% 31% 16% 5%	370
	21st to end	Day	18% 9% 20% 28% 21% 4	407
February	1st to 10th	Day	22% 11% 23% 22% 17% 5%	370
	11th to 20th	Day	16% 17% 26% 27% 13% 1	430
	21st to end	Day	18% 15% 25% 29% 12% 2	382
March	1st to 10th	Day	23% 15% 27% 25% 7% 2	460
	11th to 20th	Day	22% 15% 21% 24% 14% 4	460
	21st to end	Day	18% 15% 35% 21% 11% 1	506
April	1st to 10th	Day	18% 13% 30% 24% 14% 2	460
	11th to 20th	Day	13% 17% 28% 26% 13% 3	452
	21st to end	Day	7% 16% 30% 27% 14% 6%	460
May	1st to 10th	Day	9% 13% 33% 30% 12% 3	463
	11th to 20th	Day	7% 10% 31% 31% 16% 4	488
	21st to end	Day	6% 12% 27% 32% 18% 5%	529
June	1st to 10th	Day	5% 9% 28% 31% 19% 8%	490
	11th to 20th	Day	2 9% 29% 38% 17% 5%	490
	21st to end	Day	1 4 21% 40% 25% 8%	490
July	1st to 10th	Day	1 1 16% 43% 31% 8%	486
	11th to 20th	Day	1 11% 44% 34% 11%	484
	21st to end	Day	1 10% 45% 29% 15%	531
August	1st to 10th	Day	3 1 18% 41% 28% 10%	487
	11th to 20th	Day	2 3 18% 38% 27% 12%	477
	21st to end	Day	1 1 11% 42% 33% 11%	539
September	1st to 10th	Day	2 3 14% 40% 31% 10%	490
	11th to 20th	Day	3 6% 22% 38% 21% 9%	490
	21st to end	Day	3 7% 16% 40% 27% 8%	490
October	1st to 10th	Day	3 8% 22% 33% 29% 6%	490
	11th to 20th	Day	5% 8% 21% 31% 27% 8%	490
	21st to end	Day	8% 6% 23% 33% 24% 5%	539
November	1st to 10th	Day	8% 11% 19% 26% 30% 6%	402
	11th to 20th	Day	7% 7% 18% 31% 26% 10%	270
	21st to end	Day	10% 6% 23% 30% 26% 4	230
December	1st to 10th	Day	14% 11% 18% 32% 19% 7%	180
	11th to 20th	Day	17% 13% 15% 29% 20% 6%	180
	21st to end	Day	20% 14% 19% 25% 17% 5%	198
January	1st to 10th	Night	17% 5% 16% 32% 21% 8%	760
	11th to 20th	Night	15% 4 13% 36% 23% 9%	760
	21st to end	Night	20% 5% 13% 32% 24% 6%	836
February	1st to 10th	Night	20% 6% 14% 32% 22% 7%	760
	11th to 20th	Night	15% 8% 17% 32% 20% 7%	744
	21st to end	Night	15% 7% 19% 37% 19% 3	628
March	1st to 10th	Night	19% 8% 18% 30% 21% 4	760
	11th to 20th	Night	18% 6% 18% 28% 24% 5%	760
	21st to end	Night	14% 9% 23% 33% 18% 3	836
April	1st to 10th	Night	13% 7% 21% 33% 22% 3	760
	11th to 20th	Night	11% 10% 21% 34% 20% 5%	751
	21st to end	Night	6% 8% 27% 30% 23% 7%	760
May	1st to 10th	Night	6% 4 25% 36% 23% 6%	757
	11th to 20th	Night	6% 2 16% 36% 34% 7%	475
	21st to end	Night	4 5% 19% 36% 30% 6%	411
June	1st to 10th	Night	4 4 17% 37% 33% 5%	380
	11th to 20th	Night	1 4 16% 42% 33% 4	380
	21st to end	Night	2 1 8% 39% 45% 6%	380
July	1st to 10th	Night	1 8% 35% 49% 7%	370
	11th to 20th	Night	1 2 27% 55% 14%	503
	21st to end	Night	1 6% 28% 50% 14%	624
August	1st to 10th	Night	1 1 10% 32% 47% 10%	567
	11th to 20th	Night	1 1 10% 38% 40% 10%	733
	21st to end	Night	1 1 5% 31% 50% 12%	836
September	1st to 10th	Night	1 1 6% 33% 47% 11%	760
	11th to 20th	Night	4 1 11% 35% 39% 10%	760
	21st to end	Night	3 2 12% 31% 40% 12%	760
October	1st to 10th	Night	5% 3 12% 36% 35% 11%	760
	11th to 20th	Night	7% 3 13% 31% 34% 11%	760
	21st to end	Night	6% 3 14% 32% 27% 17%	836
November	1st to 10th	Night	8% 5% 15% 30% 31% 11%	754
	11th to 20th	Night	10% 3 13% 36% 30% 8%	760
	21st to end	Night	11% 4 15% 36% 27% 8%	760
December	1st to 10th	Night	17% 5% 15% 33% 23% 6%	760
	11th to 20th	Night	22% 6% 16% 31% 22% 5%	760
	21st to end	Night	18% 8% 20% 31% 19% 4	836

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