Goodwin Mountain Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Goodwin Mountain Observatory clear sky chart from 2005-11-06 to 2024-12-02.

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	2 4 2 5% 4 5% 5% 5% 8% 10% 51%	105577
	Night	1 3 1 4 3 3 4 4 8% 11% 57%	102709
Transparency	Day	23% 15% 17% 21% 17% 7%	105332
	Night	18% 16% 20% 23% 17% 6%	102544
Seeing	Day	12% 24% 35% 20% 7% 1	15802
	Night	8% 19% 35% 27% 10% 1	25860

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	1 5% 4 5% 5% 5% 9% 15% 50%	2538
	11th to 20th	Day	1 1 3 3 6% 7% 6% 10% 12% 51%	2828
	21st to end	Day	1 1 4 2 3 5% 5% 10% 14% 55%	3146
February	1st to 10th	Day	2 1 5% 5% 7% 7% 7% 11% 12% 42%	1710
	11th to 20th	Day	3 2 6% 6% 6% 8% 6% 9% 11% 43%	1665
	21st to end	Day	2 1 5% 6% 7% 8% 10% 10% 12% 39%	1461
March	1st to 10th	Day	2 2 5% 5% 5% 7% 7% 11% 12% 45%	3444
	11th to 20th	Day	2 2 5% 4 4 5% 5% 8% 11% 54%	3490
	21st to end	Day	2 9% 3 8% 6% 6% 8% 7% 12% 12% 28%	3825
April	1st to 10th	Day	1 8% 2 8% 5% 5% 7% 8% 10% 11% 36%	2233
	11th to 20th	Day	1 7% 3 7% 6% 7% 8% 6% 9% 11% 36%	2314
	21st to end	Day	3 11% 4 8% 6% 6% 7% 5% 7% 9% 35%	2470
May	1st to 10th	Day	3 10% 4 10% 7% 7% 7% 6% 8% 9% 28%	4110
	11th to 20th	Day	3 8% 2 6% 5% 5% 5% 5% 7% 9% 43%	4320
	21st to end	Day	5% 7% 2 5% 5% 6% 6% 5% 9% 10% 39%	4825
June	1st to 10th	Day	5% 4 2 6% 5% 6% 6% 6% 8% 10% 43%	2660
	11th to 20th	Day	4 4 1 4 5% 5% 4 5% 8% 9% 51%	2660
	21st to end	Day	2 2 1 4 3 4 4 4 7% 8% 61%	2660
July	1st to 10th	Day	2 2 1 3 3 3 4 4 7% 8% 64%	4430
	11th to 20th	Day	1 2 1 4 4 4 6% 6% 8% 8% 56%	4410
	21st to end	Day	3 3 1 5% 4 5% 6% 5% 8% 9% 52%	4454
August	1st to 10th	Day	2 3 2 5% 4 5% 5% 5% 8% 9% 51%	4092
	11th to 20th	Day	2 2 1 3 3 3 5% 4 7% 9% 60%	4028
	21st to end	Day	2 2 1 3 3 3 4 3 5% 6% 69%	4384
September	1st to 10th	Day	3 4 1 4 4 3 4 3 5% 7% 61%	2280
	11th to 20th	Day	5% 3 1 3 3 3 4 4 5% 8% 62%	2149
	21st to end	Day	3 5% 2 5% 3 3 3 3 5% 7% 62%	2079
October	1st to 10th	Day	2 6% 1 4 2 3 3 4 5% 5% 66%	3170
	11th to 20th	Day	1 4 1 4 3 3 3 3 5% 9% 64%	3150
	21st to end	Day	5% 3 4 3 3 4 3 4 9% 63%	3438
November	1st to 10th	Day	1 3 1 4 4 5% 5% 5% 9% 10% 53%	1706
	11th to 20th	Day	2 1 4 4 4 4 5% 10% 11% 55%	1600
	21st to end	Day	1 2 1 5% 4 4 4 4 7% 11% 57%	1600
December	1st to 10th	Day	2 1 5% 4 3 5% 4 9% 12% 54%	1528
	11th to 20th	Day	2 1 3 3 3 5% 6% 9% 13% 55%	1926
	21st to end	Day	3 2 5% 4 4 5% 6% 9% 12% 49%	2794
January	1st to 10th	Night	1 1 4 4 4 5% 6% 11% 14% 49%	4417
	11th to 20th	Night	1 1 3 6% 6% 6% 6% 11% 15% 46%	4174
	21st to end	Night	2 2 5% 3 3 5% 5% 10% 13% 52%	4521
February	1st to 10th	Night	2 2 6% 3 4 6% 6% 10% 12% 49%	2470
	11th to 20th	Night	3 2 5% 4 4 5% 5% 9% 11% 51%	2402
	21st to end	Night	2 2 6% 5% 4 5% 6% 11% 13% 46%	1990
March	1st to 10th	Night	3 2 5% 4 3 4 5% 10% 13% 50%	3430
	11th to 20th	Night	2 2 5% 3 4 4 4 7% 12% 58%	3490
	21st to end	Night	1 4 3 9% 4 4 6% 6% 11% 11% 41%	3828
April	1st to 10th	Night	1 6% 2 6% 4 4 6% 5% 8% 9% 47%	1946
	11th to 20th	Night	2 5% 3 7% 4 4 5% 6% 8% 11% 45%	1812
	21st to end	Night	3 8% 3 5% 4 5% 4 5% 7% 9% 48%	1710
May	1st to 10th	Night	4 12% 3 7% 5% 5% 5% 5% 7% 10% 37%	2860
	11th to 20th	Night	3 6% 2 5% 4 3 4 4 5% 7% 58%	2581
	21st to end	Night	4 5% 1 4 3 4 5% 5% 8% 12% 50%	2762
June	1st to 10th	Night	2 3 1 4 3 3 4 4 8% 11% 55%	1520
	11th to 20th	Night	3 3 1 4 3 2 3 3 5% 9% 63%	1520
	21st to end	Night	1 1 2 2 2 3 3 6% 7% 72%	1418
July	1st to 10th	Night	2 2 1 1 2 2 3 3 5% 7% 73%	2540
	11th to 20th	Night	1 1 1 1 2 2 3 6% 9% 74%	2557
	21st to end	Night	1 1 2 2 2 4 4 8% 10% 65%	3109
August	1st to 10th	Night	2 5% 2 4 3 3 3 4 5% 8% 61%	2847
	11th to 20th	Night	1 1 1 3 3 4 5% 5% 6% 9% 62%	2811
	21st to end	Night	1 1 1 2 2 2 3 2 4 6% 75%	3270
September	1st to 10th	Night	2 2 1 3 3 3 3 3 5% 7% 69%	1900
	11th to 20th	Night	3 3 1 3 2 2 3 3 7% 9% 63%	2028
	21st to end	Night	3 4 1 3 2 2 3 2 4 7% 68%	2100
October	1st to 10th	Night	2 4 1 4 2 2 3 2 4 5% 70%	3800
	11th to 20th	Night	1 3 2 3 3 3 5% 4 7% 9% 61%	3778
	21st to end	Night	1 4 2 4 2 2 3 3 7% 10% 61%	4120
November	1st to 10th	Night	1 2 1 4 2 3 4 5% 8% 12% 60%	2567
	11th to 20th	Night	2 1 3 2 3 4 4 8% 11% 60%	2800
	21st to end	Night	3 1 4 3 3 4 4 7% 11% 60%	2800
December	1st to 10th	Night	1 1 4 3 3 5% 5% 10% 12% 57%	2687
	11th to 20th	Night	2 1 3 2 4 4 4 8% 14% 58%	3271
	21st to end	Night	3 2 5% 3 4 4 5% 9% 11% 54%	4873

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	19% 23% 24% 19% 12% 2	2539
	11th to 20th	Day	17% 24% 26% 18% 11% 4	2828
	21st to end	Day	16% 26% 22% 20% 12% 3	3146
February	1st to 10th	Day	26% 25% 24% 18% 7% 1	1710
	11th to 20th	Day	28% 20% 23% 20% 6% 3	1674
	21st to end	Day	30% 23% 21% 16% 7% 3	1461
March	1st to 10th	Day	22% 20% 23% 21% 13% 2	3444
	11th to 20th	Day	19% 22% 23% 25% 10% 1	3490
	21st to end	Day	36% 26% 22% 14% 2	3825
April	1st to 10th	Day	35% 20% 19% 18% 7% 1	2233
	11th to 20th	Day	35% 17% 22% 19% 6%	2317
	21st to end	Day	41% 16% 18% 20% 4	2470
May	1st to 10th	Day	39% 14% 21% 19% 5% 1	4110
	11th to 20th	Day	28% 13% 19% 24% 12% 3	4324
	21st to end	Day	32% 15% 20% 24% 9%	4825
June	1st to 10th	Day	31% 16% 20% 21% 10% 1	2660
	11th to 20th	Day	25% 13% 14% 22% 19% 7%	2660
	21st to end	Day	16% 9% 12% 26% 26% 10%	2660
July	1st to 10th	Day	15% 7% 10% 18% 29% 22%	4361
	11th to 20th	Day	18% 8% 9% 17% 23% 26%	4335
	21st to end	Day	23% 8% 10% 16% 33% 11%	4314
August	1st to 10th	Day	21% 10% 11% 18% 25% 14%	4078
	11th to 20th	Day	17% 8% 10% 21% 32% 12%	4067
	21st to end	Day	15% 6% 9% 18% 36% 16%	4383
September	1st to 10th	Day	21% 9% 10% 17% 33% 11%	2280
	11th to 20th	Day	20% 9% 14% 22% 26% 8%	2149
	21st to end	Day	23% 7% 12% 30% 23% 5%	2079
October	1st to 10th	Day	21% 6% 9% 21% 30% 13%	3170
	11th to 20th	Day	15% 9% 16% 35% 19% 6%	3150
	21st to end	Day	18% 11% 15% 36% 19% 2	3438
November	1st to 10th	Day	21% 17% 20% 24% 16% 2	1706
	11th to 20th	Day	18% 21% 21% 25% 12% 3	1600
	21st to end	Day	21% 16% 21% 23% 15% 4	1600
December	1st to 10th	Day	20% 25% 21% 17% 11% 6%	1528
	11th to 20th	Day	18% 29% 22% 23% 8% 1	1924
	21st to end	Day	24% 17% 16% 19% 13% 11%	2794
January	1st to 10th	Night	16% 24% 26% 18% 14% 2	4417
	11th to 20th	Night	20% 22% 30% 14% 9% 5%	4174
	21st to end	Night	18% 23% 24% 20% 12% 2	4521
February	1st to 10th	Night	21% 24% 26% 21% 7% 2	2470
	11th to 20th	Night	22% 20% 24% 19% 10% 3	2403
	21st to end	Night	25% 22% 22% 18% 8% 4	1990
March	1st to 10th	Night	17% 21% 29% 18% 13% 2	3430
	11th to 20th	Night	14% 20% 26% 30% 9% 1	3490
	21st to end	Night	26% 29% 25% 17% 3 1	3828
April	1st to 10th	Night	29% 18% 24% 18% 10% 2	1946
	11th to 20th	Night	26% 20% 24% 22% 7% 1	1812
	21st to end	Night	30% 15% 24% 26% 6%	1710
May	1st to 10th	Night	32% 16% 21% 21% 10% 1	2860
	11th to 20th	Night	23% 9% 20% 33% 11% 3	2582
	21st to end	Night	22% 14% 24% 29% 10% 1	2762
June	1st to 10th	Night	21% 15% 26% 25% 11% 1	1520
	11th to 20th	Night	18% 10% 18% 22% 23% 10%	1520
	21st to end	Night	9% 8% 13% 27% 30% 13%	1418
July	1st to 10th	Night	11% 5% 9% 25% 35% 15%	2500
	11th to 20th	Night	7% 4 7% 22% 36% 25%	2509
	21st to end	Night	10% 6% 8% 27% 33% 15%	3011
August	1st to 10th	Night	18% 7% 11% 22% 30% 11%	2838
	11th to 20th	Night	16% 8% 9% 27% 27% 12%	2838
	21st to end	Night	11% 5% 7% 23% 37% 17%	3270
September	1st to 10th	Night	14% 7% 11% 22% 35% 10%	1900
	11th to 20th	Night	17% 8% 15% 26% 26% 8%	2028
	21st to end	Night	19% 8% 12% 31% 26% 5%	2100
October	1st to 10th	Night	17% 7% 10% 26% 31% 10%	3800
	11th to 20th	Night	17% 11% 16% 31% 21% 3	3778
	21st to end	Night	17% 10% 16% 33% 18% 5%	4120
November	1st to 10th	Night	16% 19% 19% 28% 15% 3	2567
	11th to 20th	Night	14% 19% 27% 25% 12% 3	2800
	21st to end	Night	17% 17% 23% 26% 13% 5%	2800
December	1st to 10th	Night	16% 26% 25% 18% 11% 4	2687
	11th to 20th	Night	17% 24% 27% 20% 12%	3272
	21st to end	Night	21% 18% 18% 19% 11% 13%	4873

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	19% 23% 29% 20% 9% 1	270
	11th to 20th	Day	14% 33% 29% 14% 9% 2	270
	21st to end	Day	9% 28% 41% 16% 5%	297
February	1st to 10th	Day	22% 42% 26% 8% 1	270
	11th to 20th	Day	20% 33% 33% 9% 5%	270
	21st to end	Day	23% 30% 29% 13% 4	262
March	1st to 10th	Day	19% 32% 37% 10% 2	460
	11th to 20th	Day	11% 31% 37% 17% 3	460
	21st to end	Day	16% 30% 37% 14% 2	506
April	1st to 10th	Day	18% 33% 36% 11% 2	460
	11th to 20th	Day	17% 37% 32% 13% 2	452
	21st to end	Day	14% 30% 28% 21% 5% 2	460
May	1st to 10th	Day	16% 26% 34% 16% 7% 1	463
	11th to 20th	Day	15% 18% 32% 22% 10% 2	633
	21st to end	Day	15% 19% 28% 25% 10% 2	734
June	1st to 10th	Day	8% 22% 33% 22% 14% 2	680
	11th to 20th	Day	11% 29% 36% 18% 5% 1	680
	21st to end	Day	4 21% 35% 27% 10% 2	680
July	1st to 10th	Day	4 15% 35% 28% 15% 3	671
	11th to 20th	Day	3 16% 40% 28% 11% 2	661
	21st to end	Day	6% 14% 41% 27% 11% 1	531
August	1st to 10th	Day	6% 15% 43% 27% 9% 1	487
	11th to 20th	Day	4 14% 43% 26% 9% 3	477
	21st to end	Day	6% 18% 40% 24% 9% 2	539
September	1st to 10th	Day	5% 17% 41% 27% 9% 2	490
	11th to 20th	Day	11% 23% 35% 22% 9% 1	490
	21st to end	Day	8% 23% 39% 20% 8% 1	479
October	1st to 10th	Day	8% 23% 35% 23% 11% 1	300
	11th to 20th	Day	18% 20% 33% 17% 10% 2	300
	21st to end	Day	18% 28% 37% 14% 3	330
November	1st to 10th	Day	15% 32% 33% 13% 5% 1	300
	11th to 20th	Day	17% 37% 29% 14% 1 1	300
	21st to end	Day	12% 32% 36% 18% 3	300
December	1st to 10th	Day	21% 28% 28% 17% 5% 1	273
	11th to 20th	Day	21% 26% 32% 16% 6%	270
	21st to end	Day	23% 28% 24% 16% 5% 4	297
January	1st to 10th	Night	12% 23% 34% 25% 5% 1	950
	11th to 20th	Night	10% 29% 35% 16% 8% 3	798
	21st to end	Night	4 23% 45% 21% 5% 1	836
February	1st to 10th	Night	9% 31% 34% 20% 5% 1	760
	11th to 20th	Night	10% 28% 40% 15% 7% 1	744
	21st to end	Night	12% 27% 36% 17% 6% 1	628
March	1st to 10th	Night	8% 25% 40% 22% 5% 1	760
	11th to 20th	Night	6% 24% 36% 26% 7% 1	760
	21st to end	Night	6% 22% 41% 26% 5%	836
April	1st to 10th	Night	10% 22% 43% 19% 6%	616
	11th to 20th	Night	6% 24% 42% 21% 6% 1	563
	21st to end	Night	8% 19% 34% 29% 9% 2	570
May	1st to 10th	Night	14% 15% 31% 26% 11% 2	570
	11th to 20th	Night	12% 11% 30% 30% 15% 2	561
	21st to end	Night	11% 15% 29% 32% 13% 1	617
June	1st to 10th	Night	6% 18% 29% 29% 17% 1	570
	11th to 20th	Night	8% 21% 40% 25% 6%	570
	21st to end	Night	1 7% 31% 41% 19% 1	468
July	1st to 10th	Night	2 6% 27% 40% 24% 1	555
	11th to 20th	Night	2 8% 26% 46% 17% 1	552
	21st to end	Night	2 2 25% 50% 19% 2	624
August	1st to 10th	Night	5% 5% 23% 46% 20% 1	567
	11th to 20th	Night	3 4 25% 46% 21% 2	564
	21st to end	Night	3 6% 28% 40% 22% 1	627
September	1st to 10th	Night	3 5% 30% 41% 18% 3	570
	11th to 20th	Night	6% 9% 28% 40% 13% 4	698
	21st to end	Night	8% 11% 32% 32% 14% 4	760
October	1st to 10th	Night	9% 14% 36% 29% 10% 2	760
	11th to 20th	Night	8% 20% 33% 26% 11% 2	760
	21st to end	Night	8% 21% 42% 20% 7% 2	836
November	1st to 10th	Night	7% 28% 39% 18% 6% 2	855
	11th to 20th	Night	13% 28% 38% 17% 4 1	1000
	21st to end	Night	7% 27% 40% 21% 5% 1	1000
December	1st to 10th	Night	13% 28% 35% 18% 5%	960
	11th to 20th	Night	10% 27% 41% 18% 5% 1	950
	21st to end	Night	13% 25% 36% 17% 6% 2	1045

Page generated at 2024-11-29 08:43:09. Version ac07

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