Goodsell Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Goodsell Observatory clear sky chart from 2005-11-06 to 2025-11-18.

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	13% 8% 3 8% 5% 4 4 4 5% 7% 39%	127389
	Night	12% 9% 4 8% 5% 4 4 4 5% 6% 39%	123270
Transparency	Day	44% 6% 13% 25% 12% 1	130966
	Night	45% 5% 12% 24% 13% 2	127769
Seeing	Day	16% 10% 31% 27% 13% 4	17433
	Night	15% 9% 33% 31% 10% 1	27283

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	7% 15% 6% 19% 8% 7% 5% 3 4 5% 21%	3617
	11th to 20th	Day	6% 13% 7% 12% 7% 6% 8% 9% 10% 5% 19%	3689
	21st to end	Day	7% 15% 7% 14% 6% 5% 5% 3 4 5% 29%	4488
February	1st to 10th	Day	9% 10% 5% 11% 8% 6% 6% 6% 6% 6% 27%	1800
	11th to 20th	Day	9% 11% 5% 10% 6% 5% 5% 4 6% 6% 33%	1754
	21st to end	Day	13% 10% 4 9% 6% 5% 5% 4 4 7% 33%	1558
March	1st to 10th	Day	12% 7% 3 5% 3 3 3 4 5% 7% 46%	4837
	11th to 20th	Day	11% 9% 3 7% 4 3 4 4 6% 8% 42%	4980
	21st to end	Day	24% 11% 4 10% 5% 4 4 3 4 6% 27%	5525
April	1st to 10th	Day	17% 11% 4 7% 4 3 4 4 6% 7% 33%	2400
	11th to 20th	Day	20% 12% 3 7% 5% 5% 4 3 4 5% 33%	2374
	21st to end	Day	21% 11% 3 8% 5% 4 5% 4 5% 5% 30%	2590
May	1st to 10th	Day	14% 5% 2 4 3 3 3 3 5% 6% 50%	6087
	11th to 20th	Day	16% 7% 2 5% 4 4 3 3 5% 7% 44%	6319
	21st to end	Day	19% 7% 2 6% 4 4 4 4 5% 6% 39%	6935
June	1st to 10th	Day	11% 5% 2 5% 4 4 4 4 6% 8% 47%	2800
	11th to 20th	Day	14% 6% 3 7% 5% 4 4 4 7% 9% 36%	2800
	21st to end	Day	11% 6% 2 6% 5% 5% 6% 5% 7% 9% 39%	2800
July	1st to 10th	Day	9% 5% 2 6% 4 4 5% 5% 6% 10% 45%	6360
	11th to 20th	Day	9% 3 1 4 3 3 4 3 5% 7% 57%	6360
	21st to end	Day	8% 4 2 5% 4 4 5% 5% 6% 9% 48%	6799
August	1st to 10th	Day	12% 6% 2 6% 4 5% 5% 4 7% 7% 41%	4234
	11th to 20th	Day	13% 5% 2 5% 4 5% 5% 4 6% 9% 44%	4171
	21st to end	Day	9% 5% 2 6% 4 4 4 4 5% 8% 47%	4447
September	1st to 10th	Day	13% 6% 1 5% 3 4 4 4 6% 8% 47%	2400
	11th to 20th	Day	11% 6% 2 6% 3 4 4 4 6% 6% 48%	2376
	21st to end	Day	14% 7% 2 5% 4 4 4 4 5% 7% 45%	2100
October	1st to 10th	Day	15% 6% 2 5% 4 5% 4 3 5% 6% 45%	2000
	11th to 20th	Day	15% 9% 2 7% 4 5% 4 3 5% 6% 41%	2000
	21st to end	Day	17% 12% 4 7% 4 3 4 3 4 7% 36%	2183
November	1st to 10th	Day	11% 11% 4 6% 6% 4 4 3 5% 7% 39%	1750
	11th to 20th	Day	10% 13% 6% 10% 6% 4 5% 3 5% 5% 31%	1656
	21st to end	Day	12% 11% 4 9% 6% 4 4 4 4 6% 36%	1600
December	1st to 10th	Day	7% 10% 4 14% 10% 7% 5% 4 6% 7% 26%	2610
	11th to 20th	Day	11% 14% 6% 10% 9% 6% 5% 4 5% 6% 24%	3008
	21st to end	Day	19% 19% 8% 18% 5% 4 3 2 4 4 14%	3982
January	1st to 10th	Night	7% 12% 5% 17% 7% 6% 5% 4 5% 6% 26%	6348
	11th to 20th	Night	7% 11% 5% 13% 8% 7% 9% 8% 8% 5% 20%	6286
	21st to end	Night	9% 15% 6% 10% 6% 5% 4 3 4 5% 33%	6490
February	1st to 10th	Night	7% 13% 6% 10% 6% 6% 4 4 4 6% 34%	2600
	11th to 20th	Night	7% 10% 4 9% 6% 6% 5% 3 5% 6% 39%	2533
	21st to end	Night	12% 9% 4 9% 6% 5% 4 3 5% 6% 37%	2071
March	1st to 10th	Night	11% 7% 2 7% 4 4 4 3 5% 6% 48%	5060
	11th to 20th	Night	10% 6% 2 7% 5% 5% 5% 4 6% 9% 42%	4980
	21st to end	Night	25% 12% 4 10% 4 3 3 3 4 5% 29%	5390
April	1st to 10th	Night	14% 12% 3 7% 5% 4 4 3 5% 6% 38%	2000
	11th to 20th	Night	20% 10% 3 6% 5% 4 4 3 4 6% 35%	1975
	21st to end	Night	19% 9% 3 7% 5% 4 4 3 4 6% 36%	1806
May	1st to 10th	Night	12% 7% 2 5% 4 3 4 3 4 5% 50%	3826
	11th to 20th	Night	15% 5% 1 4 2 3 4 3 5% 7% 51%	3596
	21st to end	Night	17% 8% 3 7% 4 4 4 3 4 6% 41%	3942
June	1st to 10th	Night	10% 5% 1 6% 4 4 4 4 6% 7% 50%	1600
	11th to 20th	Night	11% 6% 2 6% 4 5% 5% 4 6% 8% 43%	1600
	21st to end	Night	8% 5% 2 5% 4 3 3 4 6% 8% 53%	1600
July	1st to 10th	Night	8% 4 1 5% 4 4 4 5% 7% 10% 48%	3618
	11th to 20th	Night	7% 4 1 4 3 4 4 4 5% 9% 56%	3617
	21st to end	Night	9% 4 2 5% 3 4 4 4 6% 8% 51%	4069
August	1st to 10th	Night	12% 6% 1 6% 4 4 5% 3 4 7% 47%	2926
	11th to 20th	Night	14% 4 2 4 2 3 3 3 5% 7% 52%	2888
	21st to end	Night	10% 5% 2 6% 4 4 4 4 5% 6% 51%	3453
September	1st to 10th	Night	9% 4 2 6% 3 3 4 3 4 7% 55%	2000
	11th to 20th	Night	12% 4 2 5% 3 2 4 4 5% 7% 53%	2020
	21st to end	Night	13% 6% 2 5% 3 3 3 3 4 6% 54%	2280
October	1st to 10th	Night	14% 5% 2 5% 3 3 3 3 5% 6% 52%	2400
	11th to 20th	Night	15% 8% 3 6% 4 4 4 3 5% 6% 43%	2400
	21st to end	Night	18% 11% 3 6% 4 3 3 3 5% 6% 38%	2656
November	1st to 10th	Night	12% 10% 4 6% 4 3 4 4 5% 6% 42%	2766
	11th to 20th	Night	12% 11% 5% 10% 5% 4 3 3 5% 5% 36%	2899
	21st to end	Night	14% 10% 4 9% 6% 4 3 3 4 6% 37%	2800
December	1st to 10th	Night	6% 9% 4 14% 7% 8% 5% 4 5% 7% 31%	4580
	11th to 20th	Night	11% 16% 7% 13% 7% 5% 4 4 4 6% 25%	5199
	21st to end	Night	22% 15% 8% 15% 5% 4 4 3 4 4 17%	6996

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	66% 5% 9% 16% 5%	3618
	11th to 20th	Day	59% 5% 8% 16% 11%	3689
	21st to end	Day	57% 6% 14% 15% 7%	4488
February	1st to 10th	Day	55% 6% 13% 15% 9% 1	1800
	11th to 20th	Day	51% 6% 11% 23% 8% 1	1763
	21st to end	Day	52% 6% 13% 18% 11%	1558
March	1st to 10th	Day	38% 4 17% 27% 12% 2	4837
	11th to 20th	Day	41% 4 15% 28% 10% 1	4980
	21st to end	Day	61% 5% 10% 16% 7%	5527
April	1st to 10th	Day	51% 5% 11% 20% 11% 1	2400
	11th to 20th	Day	54% 5% 11% 18% 11% 2	2374
	21st to end	Day	55% 6% 11% 19% 8% 1	2590
May	1st to 10th	Day	35% 5% 12% 30% 16% 2	6125
	11th to 20th	Day	40% 5% 9% 25% 15% 5%	6323
	21st to end	Day	46% 5% 9% 31% 9% 1	6949
June	1st to 10th	Day	34% 8% 13% 30% 14% 1	2800
	11th to 20th	Day	43% 7% 14% 22% 14% 1	2800
	21st to end	Day	39% 9% 16% 24% 10% 2	2800
July	1st to 10th	Day	34% 8% 16% 33% 9% 1	6291
	11th to 20th	Day	27% 5% 15% 35% 16% 1	6285
	21st to end	Day	31% 8% 14% 30% 15% 1	6605
August	1st to 10th	Day	39% 7% 12% 28% 13% 1	4220
	11th to 20th	Day	37% 7% 13% 32% 11%	4210
	21st to end	Day	34% 7% 15% 29% 14% 1	4446
September	1st to 10th	Day	35% 6% 14% 30% 15%	2400
	11th to 20th	Day	36% 7% 16% 31% 10% 1	2376
	21st to end	Day	39% 5% 11% 32% 12% 1	2100
October	1st to 10th	Day	30% 3 7% 37% 23%	3260
	11th to 20th	Day	39% 4 12% 24% 20% 1	3240
	21st to end	Day	44% 4 13% 30% 9%	3509
November	1st to 10th	Day	45% 5% 14% 19% 14% 2	1750
	11th to 20th	Day	54% 6% 11% 18% 10% 1	1656
	21st to end	Day	49% 6% 17% 21% 7% 1	1600
December	1st to 10th	Day	57% 6% 17% 13% 6% 1	2610
	11th to 20th	Day	61% 5% 15% 14% 5%	3005
	21st to end	Day	75% 4 8% 9% 3	3982
January	1st to 10th	Night	59% 4 10% 20% 6%	6348
	11th to 20th	Night	60% 5% 10% 14% 10%	6286
	21st to end	Night	54% 5% 11% 22% 8%	6490
February	1st to 10th	Night	52% 4 12% 21% 10% 1	2600
	11th to 20th	Night	47% 5% 13% 25% 9% 1	2534
	21st to end	Night	49% 5% 11% 21% 12% 2	2071
March	1st to 10th	Night	37% 4 12% 29% 16% 2	5060
	11th to 20th	Night	38% 4 14% 28% 15% 1	4980
	21st to end	Night	59% 3 9% 17% 10% 1	5390
April	1st to 10th	Night	48% 5% 10% 22% 15% 1	2000
	11th to 20th	Night	50% 5% 9% 18% 16% 2	1975
	21st to end	Night	49% 4 10% 20% 15% 2	1806
May	1st to 10th	Night	35% 5% 10% 26% 22% 2	3853
	11th to 20th	Night	33% 5% 10% 23% 21% 7%	3597
	21st to end	Night	44% 5% 9% 28% 12% 1	3950
June	1st to 10th	Night	31% 7% 12% 30% 17% 2	1600
	11th to 20th	Night	38% 7% 14% 21% 18% 3	1600
	21st to end	Night	28% 7% 16% 30% 17% 3	1600
July	1st to 10th	Night	29% 7% 20% 30% 13% 1	3580
	11th to 20th	Night	25% 6% 14% 39% 15% 2	3572
	21st to end	Night	32% 6% 16% 27% 17% 2	3952
August	1st to 10th	Night	36% 6% 11% 29% 14% 4	2916
	11th to 20th	Night	32% 6% 14% 32% 15% 1	2915
	21st to end	Night	33% 7% 16% 27% 15% 2	3453
September	1st to 10th	Night	29% 6% 12% 34% 19% 1	2000
	11th to 20th	Night	30% 6% 15% 31% 16% 1	2020
	21st to end	Night	33% 4 12% 31% 19% 2	2280
October	1st to 10th	Night	24% 3 6% 34% 28% 4	3920
	11th to 20th	Night	32% 5% 12% 26% 22% 4	3899
	21st to end	Night	43% 4 10% 28% 14% 1	4280
November	1st to 10th	Night	41% 6% 13% 24% 14% 2	2766
	11th to 20th	Night	51% 5% 11% 20% 12% 1	2899
	21st to end	Night	50% 5% 15% 22% 8% 1	2800
December	1st to 10th	Night	52% 6% 18% 19% 5%	4580
	11th to 20th	Night	61% 5% 11% 17% 5% 1	5201
	21st to end	Night	71% 4 9% 12% 4	6996

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	11% 12% 36% 27% 10% 4	300
	11th to 20th	Day	14% 16% 36% 28% 5% 1	300
	21st to end	Day	15% 12% 37% 24% 10% 2	330
February	1st to 10th	Day	14% 15% 41% 26% 4 1	300
	11th to 20th	Day	14% 13% 41% 24% 8% 1	300
	21st to end	Day	17% 13% 40% 28% 2	249
March	1st to 10th	Day	17% 11% 43% 22% 5% 1	300
	11th to 20th	Day	21% 11% 37% 23% 8% 1	300
	21st to end	Day	30% 12% 29% 20% 8% 2	355
April	1st to 10th	Day	25% 14% 36% 20% 6% 1	500
	11th to 20th	Day	27% 16% 24% 22% 9% 1	492
	21st to end	Day	26% 13% 30% 20% 9% 2	690
May	1st to 10th	Day	19% 12% 31% 25% 11% 2	703
	11th to 20th	Day	19% 12% 28% 24% 14% 4	725
	21st to end	Day	19% 9% 26% 28% 14% 3	789
June	1st to 10th	Day	10% 10% 27% 30% 20% 4	730
	11th to 20th	Day	16% 7% 34% 31% 9% 3	730
	21st to end	Day	13% 9% 32% 27% 14% 5%	730
July	1st to 10th	Day	7% 6% 22% 31% 24% 10%	721
	11th to 20th	Day	10% 5% 28% 31% 19% 8%	718
	21st to end	Day	7% 3 23% 41% 20% 6%	794
August	1st to 10th	Day	10% 4 23% 35% 23% 6%	726
	11th to 20th	Day	15% 3 19% 33% 24% 5%	715
	21st to end	Day	10% 5% 27% 34% 18% 6%	666
September	1st to 10th	Day	14% 9% 29% 28% 14% 6%	530
	11th to 20th	Day	11% 6% 29% 32% 18% 4	506
	21st to end	Day	16% 10% 29% 22% 15% 8%	330
October	1st to 10th	Day	16% 9% 33% 25% 14% 4	330
	11th to 20th	Day	18% 19% 38% 18% 5% 1	330
	21st to end	Day	25% 16% 36% 15% 9% 1	363
November	1st to 10th	Day	19% 14% 39% 18% 9% 1	330
	11th to 20th	Day	16% 20% 40% 20% 5%	321
	21st to end	Day	22% 13% 41% 19% 4	300
December	1st to 10th	Day	15% 11% 40% 25% 7% 1	300
	11th to 20th	Day	20% 15% 35% 22% 8%	300
	21st to end	Day	26% 15% 34% 21% 3 1	330
January	1st to 10th	Night	11% 12% 38% 30% 8% 1	1000
	11th to 20th	Night	16% 12% 38% 27% 6% 1	1000
	21st to end	Night	17% 10% 38% 28% 6% 1	1100
February	1st to 10th	Night	13% 12% 41% 27% 6% 1	1000
	11th to 20th	Night	12% 12% 44% 25% 6% 1	979
	21st to end	Night	16% 11% 38% 26% 8% 1	751
March	1st to 10th	Night	17% 10% 38% 27% 8% 1	668
	11th to 20th	Night	16% 11% 38% 29% 6% 1	600
	21st to end	Night	22% 11% 31% 25% 10% 2	660
April	1st to 10th	Night	21% 12% 37% 25% 6%	600
	11th to 20th	Night	23% 10% 31% 28% 7%	593
	21st to end	Night	22% 10% 32% 26% 8% 2	600
May	1st to 10th	Night	19% 10% 33% 31% 7% 1	600
	11th to 20th	Night	17% 7% 30% 35% 10% 1	591
	21st to end	Night	17% 6% 26% 36% 13% 1	650
June	1st to 10th	Night	11% 5% 31% 39% 14% 1	600
	11th to 20th	Night	14% 4 32% 41% 10%	600
	21st to end	Night	10% 4 24% 46% 15% 1	600
July	1st to 10th	Night	7% 2 20% 42% 27% 3	585
	11th to 20th	Night	6% 3 24% 45% 19% 2	582
	21st to end	Night	5% 3 20% 50% 20% 2	657
August	1st to 10th	Night	7% 2 20% 45% 24% 2	597
	11th to 20th	Night	11% 3 20% 37% 24% 4	594
	21st to end	Night	9% 2 26% 38% 23% 2	660
September	1st to 10th	Night	11% 5% 26% 38% 17% 4	600
	11th to 20th	Night	13% 5% 31% 32% 18% 2	600
	21st to end	Night	13% 9% 31% 30% 17% 1	680
October	1st to 10th	Night	17% 9% 29% 31% 14% 1	800
	11th to 20th	Night	19% 11% 37% 26% 7% 1	800
	21st to end	Night	25% 10% 30% 27% 7%	880
November	1st to 10th	Night	17% 13% 36% 27% 6% 1	920
	11th to 20th	Night	17% 14% 39% 24% 6%	1036
	21st to end	Night	16% 15% 38% 23% 7%	1000
December	1st to 10th	Night	15% 10% 41% 28% 6% 1	1000
	11th to 20th	Night	19% 11% 38% 25% 7% 1	1000
	21st to end	Night	24% 11% 34% 26% 4	1100

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