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 2024-11-08.

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% 9% 3 8% 5% 4 4 4 5% 7% 38%	101605
	Night	12% 9% 3 8% 5% 4 4 3 5% 6% 40%	97608
Transparency	Day	44% 6% 13% 24% 11% 1	105224
	Night	44% 5% 12% 24% 13% 2	102129
Seeing	Day	16% 10% 30% 27% 13% 4	16009
	Night	15% 9% 33% 31% 10% 1	25871

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	9% 18% 7% 18% 5% 5% 6% 4 4 5% 19%	2527
	11th to 20th	Day	6% 14% 5% 13% 8% 7% 8% 7% 8% 5% 19%	2571
	21st to end	Day	10% 19% 6% 15% 7% 5% 4 4 4 5% 21%	3135
February	1st to 10th	Day	9% 10% 5% 11% 8% 6% 6% 6% 6% 7% 27%	1710
	11th to 20th	Day	9% 11% 5% 10% 6% 6% 5% 4 6% 6% 33%	1664
	21st to end	Day	13% 11% 4 10% 6% 5% 5% 4 4 7% 32%	1482
March	1st to 10th	Day	13% 9% 3 7% 4 4 3 4 4 7% 42%	3365
	11th to 20th	Day	10% 10% 3 8% 4 4 4 4 6% 8% 40%	3480
	21st to end	Day	25% 12% 4 11% 5% 4 4 3 4 5% 23%	3863
April	1st to 10th	Day	18% 11% 4 7% 4 3 4 3 6% 7% 33%	2280
	11th to 20th	Day	21% 12% 3 7% 5% 4 4 3 4 5% 33%	2254
	21st to end	Day	21% 11% 3 8% 5% 4 5% 4 5% 5% 30%	2460
May	1st to 10th	Day	18% 6% 2 5% 4 4 4 4 6% 7% 40%	4237
	11th to 20th	Day	13% 6% 2 6% 4 4 4 3 5% 8% 44%	4399
	21st to end	Day	18% 6% 2 6% 5% 4 4 4 5% 7% 38%	4824
June	1st to 10th	Day	11% 5% 2 5% 4 4 4 4 6% 8% 47%	2660
	11th to 20th	Day	14% 6% 2 7% 5% 4 4 4 7% 9% 37%	2660
	21st to end	Day	10% 6% 2 6% 5% 5% 6% 5% 7% 9% 40%	2660
July	1st to 10th	Day	11% 5% 2 6% 4 5% 5% 5% 7% 10% 39%	4440
	11th to 20th	Day	6% 3 1 4 3 3 4 4 6% 7% 59%	4440
	21st to end	Day	7% 4 2 5% 4 5% 5% 5% 6% 9% 49%	4730
August	1st to 10th	Day	12% 6% 2 6% 4 5% 5% 4 7% 7% 42%	4104
	11th to 20th	Day	13% 5% 2 5% 4 5% 5% 4 6% 8% 44%	4041
	21st to end	Day	10% 5% 2 6% 4 4 4 4 5% 7% 47%	4311
September	1st to 10th	Day	13% 6% 1 5% 3 4 4 3 5% 8% 47%	2280
	11th to 20th	Day	12% 5% 2 6% 3 4 4 3 6% 6% 49%	2257
	21st to end	Day	15% 7% 2 5% 4 4 4 4 5% 7% 44%	1995
October	1st to 10th	Day	15% 7% 2 5% 4 5% 4 3 5% 6% 44%	1900
	11th to 20th	Day	14% 9% 2 6% 4 5% 4 3 5% 6% 41%	1900
	21st to end	Day	18% 11% 4 7% 4 3 4 3 5% 7% 36%	2074
November	1st to 10th	Day	12% 11% 4 6% 6% 4 4 3 5% 7% 38%	1641
	11th to 20th	Day	11% 13% 6% 10% 7% 4 5% 4 5% 6% 29%	1520
	21st to end	Day	12% 11% 4 9% 6% 3 4 4 4 7% 37%	1520
December	1st to 10th	Day	11% 13% 4 12% 8% 6% 5% 3 5% 6% 27%	1520
	11th to 20th	Day	10% 14% 7% 10% 6% 5% 5% 4 5% 6% 29%	1918
	21st to end	Day	20% 16% 6% 17% 6% 4 3 2 4 5% 18%	2783
January	1st to 10th	Night	10% 15% 7% 18% 5% 4 4 3 4 5% 25%	4428
	11th to 20th	Night	7% 12% 5% 14% 8% 6% 7% 7% 7% 5% 21%	4394
	21st to end	Night	12% 18% 7% 13% 6% 5% 4 3 4 4 26%	4532
February	1st to 10th	Night	6% 13% 6% 10% 6% 6% 4 4 4 6% 34%	2470
	11th to 20th	Night	8% 9% 4 8% 6% 7% 5% 3 5% 6% 39%	2403
	21st to end	Night	13% 9% 4 9% 6% 5% 4 3 5% 6% 36%	1971
March	1st to 10th	Night	10% 7% 3 6% 4 4 4 3 5% 6% 48%	3518
	11th to 20th	Night	9% 7% 2 8% 5% 5% 5% 4 6% 7% 41%	3480
	21st to end	Night	25% 11% 4 10% 4 2 3 3 4 5% 29%	3768
April	1st to 10th	Night	14% 12% 3 7% 5% 4 4 3 5% 6% 37%	1900
	11th to 20th	Night	20% 11% 3 6% 5% 4 4 3 4 6% 34%	1875
	21st to end	Night	18% 9% 3 7% 5% 4 4 3 4 7% 37%	1716
May	1st to 10th	Night	15% 7% 2 6% 5% 4 4 3 5% 6% 42%	2666
	11th to 20th	Night	14% 4 2 5% 3 4 3 3 5% 8% 50%	2506
	21st to end	Night	14% 8% 3 6% 4 4 4 3 4 6% 44%	2743
June	1st to 10th	Night	10% 5% 1 5% 4 4 4 4 6% 7% 50%	1520
	11th to 20th	Night	10% 6% 2 6% 4 5% 5% 4 6% 8% 45%	1520
	21st to end	Night	8% 4 2 4 4 3 3 3 5% 8% 53%	1520
July	1st to 10th	Night	10% 4 1 5% 4 4 4 5% 7% 9% 46%	2530
	11th to 20th	Night	4 2 1 3 3 4 3 4 5% 9% 60%	2530
	21st to end	Night	6% 3 1 4 3 4 4 4 6% 8% 57%	2830
August	1st to 10th	Night	12% 6% 1 6% 4 4 5% 3 4 7% 47%	2836
	11th to 20th	Night	13% 4 2 4 2 3 3 3 5% 7% 52%	2798
	21st to end	Night	10% 6% 2 6% 4 4 4 4 5% 6% 50%	3347
September	1st to 10th	Night	9% 3 2 5% 3 3 4 3 4 7% 57%	1900
	11th to 20th	Night	12% 4 2 5% 3 2 4 4 4 6% 54%	1919
	21st to end	Night	13% 6% 2 5% 3 3 3 3 4 6% 53%	2166
October	1st to 10th	Night	15% 5% 2 5% 3 3 3 3 4 6% 51%	2280
	11th to 20th	Night	15% 8% 3 5% 4 4 4 3 5% 7% 43%	2280
	21st to end	Night	18% 11% 4 6% 4 3 4 3 5% 6% 38%	2523
November	1st to 10th	Night	12% 10% 4 6% 4 3 4 4 5% 5% 42%	2596
	11th to 20th	Night	12% 12% 5% 10% 6% 4 3 3 5% 5% 34%	2660
	21st to end	Night	14% 10% 4 8% 5% 4 3 3 4 6% 38%	2660
December	1st to 10th	Night	9% 13% 5% 11% 6% 5% 5% 4 5% 7% 31%	2660
	11th to 20th	Night	12% 13% 5% 11% 7% 5% 4 4 5% 7% 28%	3279
	21st to end	Night	23% 14% 5% 13% 5% 4 4 3 4 4 21%	4884

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	67% 6% 10% 13% 4	2528
	11th to 20th	Day	62% 6% 10% 16% 6%	2571
	21st to end	Day	65% 7% 12% 12% 4	3135
February	1st to 10th	Day	55% 7% 13% 16% 9% 1	1710
	11th to 20th	Day	51% 7% 12% 22% 7% 1	1673
	21st to end	Day	53% 6% 12% 17% 11%	1482
March	1st to 10th	Day	43% 5% 14% 26% 12% 1	3365
	11th to 20th	Day	42% 6% 10% 30% 10% 2	3480
	21st to end	Day	65% 6% 8% 15% 5%	3863
April	1st to 10th	Day	50% 6% 12% 20% 11% 1	2280
	11th to 20th	Day	53% 5% 10% 19% 11% 2	2254
	21st to end	Day	56% 6% 11% 18% 8% 1	2460
May	1st to 10th	Day	42% 6% 13% 25% 12% 1	4275
	11th to 20th	Day	38% 7% 11% 29% 14% 2	4403
	21st to end	Day	46% 6% 11% 26% 10% 1	4837
June	1st to 10th	Day	34% 9% 13% 29% 14% 1	2660
	11th to 20th	Day	41% 7% 13% 22% 15% 1	2660
	21st to end	Day	38% 9% 17% 24% 10% 2	2660
July	1st to 10th	Day	38% 9% 19% 24% 10% 1	4371
	11th to 20th	Day	23% 6% 16% 34% 19% 2	4365
	21st to end	Day	30% 9% 14% 29% 17% 2	4581
August	1st to 10th	Day	39% 7% 12% 28% 13% 1	4090
	11th to 20th	Day	37% 7% 13% 33% 11%	4080
	21st to end	Day	35% 7% 15% 28% 14% 1	4310
September	1st to 10th	Day	35% 6% 13% 30% 16%	2280
	11th to 20th	Day	35% 7% 15% 32% 11% 1	2257
	21st to end	Day	39% 6% 11% 32% 12% 1	1995
October	1st to 10th	Day	30% 3 7% 36% 23%	3160
	11th to 20th	Day	38% 4 12% 25% 20% 1	3140
	21st to end	Day	43% 3 13% 30% 9%	3400
November	1st to 10th	Day	46% 5% 14% 19% 14% 3	1641
	11th to 20th	Day	55% 6% 12% 17% 10% 1	1520
	21st to end	Day	47% 6% 17% 22% 7% 1	1520
December	1st to 10th	Day	58% 6% 16% 12% 7%	1520
	11th to 20th	Day	56% 6% 18% 14% 6%	1915
	21st to end	Day	70% 5% 9% 11% 4	2783
January	1st to 10th	Night	61% 5% 11% 17% 5%	4428
	11th to 20th	Night	61% 6% 11% 16% 5%	4394
	21st to end	Night	62% 5% 9% 17% 6%	4532
February	1st to 10th	Night	51% 4 12% 21% 10% 1	2470
	11th to 20th	Night	46% 5% 13% 25% 9% 1	2404
	21st to end	Night	50% 5% 10% 21% 12% 2	1971
March	1st to 10th	Night	37% 5% 12% 28% 16% 1	3518
	11th to 20th	Night	39% 5% 11% 28% 16% 1	3480
	21st to end	Night	59% 4 8% 21% 7% 1	3768
April	1st to 10th	Night	48% 5% 10% 21% 14% 1	1900
	11th to 20th	Night	50% 6% 9% 17% 16% 2	1875
	21st to end	Night	48% 4 10% 21% 15% 2	1716
May	1st to 10th	Night	41% 6% 12% 18% 21% 1	2693
	11th to 20th	Night	32% 6% 11% 27% 20% 5%	2507
	21st to end	Night	40% 7% 11% 26% 16% 1	2751
June	1st to 10th	Night	31% 8% 12% 30% 17% 2	1520
	11th to 20th	Night	37% 7% 13% 22% 19% 3	1520
	21st to end	Night	28% 7% 16% 30% 17% 3	1520
July	1st to 10th	Night	31% 8% 21% 26% 13% 2	2490
	11th to 20th	Night	20% 6% 14% 39% 19% 2	2482
	21st to end	Night	24% 7% 17% 29% 21% 2	2740
August	1st to 10th	Night	36% 6% 10% 29% 14% 4	2826
	11th to 20th	Night	31% 6% 14% 32% 16% 1	2825
	21st to end	Night	34% 7% 16% 27% 15% 2	3347
September	1st to 10th	Night	28% 5% 11% 34% 20% 1	1900
	11th to 20th	Night	30% 6% 15% 31% 17% 1	1919
	21st to end	Night	33% 4 12% 31% 18% 2	2166
October	1st to 10th	Night	24% 3 6% 34% 28% 4	3800
	11th to 20th	Night	31% 5% 12% 26% 22% 4	3779
	21st to end	Night	43% 4 11% 28% 14% 1	4147
November	1st to 10th	Night	42% 6% 13% 23% 15% 2	2596
	11th to 20th	Night	52% 5% 11% 19% 12% 1	2660
	21st to end	Night	48% 5% 15% 23% 8% 1	2660
December	1st to 10th	Night	53% 6% 15% 19% 6% 1	2660
	11th to 20th	Night	55% 7% 13% 17% 6% 1	3281
	21st to end	Night	67% 5% 10% 14% 4	4884

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	12% 11% 36% 27% 11% 3	270
	11th to 20th	Day	14% 16% 35% 28% 5% 1	270
	21st to end	Day	15% 11% 35% 25% 11% 3	297
February	1st to 10th	Day	11% 15% 41% 26% 4 1	270
	11th to 20th	Day	15% 13% 40% 24% 7% 1	270
	21st to end	Day	18% 13% 38% 29% 2	225
March	1st to 10th	Day	18% 12% 42% 21% 6% 1	270
	11th to 20th	Day	20% 10% 38% 23% 8% 1	270
	21st to end	Day	30% 12% 26% 21% 9% 2	321
April	1st to 10th	Day	25% 13% 36% 20% 6% 1	460
	11th to 20th	Day	27% 16% 23% 23% 10% 1	452
	21st to end	Day	26% 12% 29% 20% 10% 3	640
May	1st to 10th	Day	19% 13% 33% 25% 9% 2	653
	11th to 20th	Day	18% 12% 29% 23% 13% 4	675
	21st to end	Day	19% 10% 26% 28% 15% 3	734
June	1st to 10th	Day	10% 9% 27% 30% 19% 4	680
	11th to 20th	Day	15% 7% 34% 32% 9% 3	680
	21st to end	Day	12% 9% 31% 28% 15% 5%	680
July	1st to 10th	Day	7% 6% 23% 30% 24% 10%	671
	11th to 20th	Day	9% 5% 28% 31% 20% 8%	668
	21st to end	Day	7% 3 23% 40% 20% 6%	739
August	1st to 10th	Day	10% 3 23% 35% 23% 5%	676
	11th to 20th	Day	14% 3 19% 33% 24% 6%	665
	21st to end	Day	11% 5% 27% 34% 17% 6%	618
September	1st to 10th	Day	14% 8% 29% 29% 14% 6%	490
	11th to 20th	Day	11% 6% 30% 31% 18% 4	467
	21st to end	Day	18% 10% 31% 22% 13% 7%	300
October	1st to 10th	Day	17% 9% 31% 26% 14% 4	300
	11th to 20th	Day	17% 18% 39% 20% 6% 1	300
	21st to end	Day	25% 16% 36% 14% 8% 1	330
November	1st to 10th	Day	18% 13% 38% 19% 11%	291
	11th to 20th	Day	16% 20% 40% 20% 4	270
	21st to end	Day	22% 13% 41% 19% 4	270
December	1st to 10th	Day	16% 10% 39% 26% 8% 1	270
	11th to 20th	Day	19% 15% 34% 23% 9%	270
	21st to end	Day	26% 15% 35% 21% 3	297
January	1st to 10th	Night	11% 12% 38% 29% 8% 1	950
	11th to 20th	Night	16% 12% 38% 27% 6% 1	950
	21st to end	Night	18% 10% 37% 28% 6% 1	1045
February	1st to 10th	Night	12% 11% 41% 28% 6% 1	950
	11th to 20th	Night	12% 12% 43% 25% 6% 1	929
	21st to end	Night	17% 11% 37% 28% 8% 1	715
March	1st to 10th	Night	17% 10% 37% 27% 8% 1	635
	11th to 20th	Night	16% 11% 37% 29% 6% 1	570
	21st to end	Night	22% 11% 30% 26% 10% 2	627
April	1st to 10th	Night	21% 11% 38% 24% 6%	570
	11th to 20th	Night	24% 10% 30% 28% 8%	563
	21st to end	Night	21% 10% 32% 26% 8% 2	570
May	1st to 10th	Night	19% 10% 35% 29% 6% 1	570
	11th to 20th	Night	17% 7% 31% 34% 10% 1	561
	21st to end	Night	17% 6% 27% 35% 14% 1	617
June	1st to 10th	Night	11% 5% 31% 38% 14% 1	570
	11th to 20th	Night	13% 4 32% 41% 10%	570
	21st to end	Night	10% 3 23% 47% 15% 1	570
July	1st to 10th	Night	7% 1 20% 42% 27% 3	555
	11th to 20th	Night	5% 3 25% 44% 20% 3	552
	21st to end	Night	5% 2 20% 51% 20% 2	624
August	1st to 10th	Night	7% 2 20% 46% 23% 2	567
	11th to 20th	Night	10% 3 20% 38% 25% 4	564
	21st to end	Night	10% 2 26% 38% 22% 2	627
September	1st to 10th	Night	10% 4 25% 40% 17% 4	570
	11th to 20th	Night	13% 5% 31% 31% 18% 2	570
	21st to end	Night	13% 9% 32% 29% 16%	646
October	1st to 10th	Night	18% 9% 29% 30% 14% 1	760
	11th to 20th	Night	18% 11% 37% 26% 7% 1	760
	21st to end	Night	25% 11% 29% 27% 7%	836
November	1st to 10th	Night	17% 12% 36% 27% 6% 1	863
	11th to 20th	Night	17% 13% 40% 25% 6%	950
	21st to end	Night	16% 14% 39% 23% 8%	950
December	1st to 10th	Night	15% 10% 40% 28% 6% 1	950
	11th to 20th	Night	20% 9% 39% 26% 7% 1	950
	21st to end	Night	24% 11% 35% 26% 4	1045

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