SMSU Planetarium
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the SMSU Planetarium clear sky chart from 2005-11-06 to 2026-03-18.

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	11% 8% 3 8% 5% 5% 5% 4 6% 7% 39%	131460
	Night	10% 8% 3 8% 5% 5% 5% 4 5% 6% 40%	130275
Transparency	Day	42% 6% 13% 24% 13% 1	135017
	Night	42% 5% 13% 24% 13% 2	134785
Seeing	Day	16% 10% 31% 28% 13% 3	17787
	Night	14% 10% 34% 31% 10% 1	27854

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	6% 13% 5% 17% 10% 8% 7% 4 4 5% 20%	4124
	11th to 20th	Day	4 11% 5% 12% 7% 8% 10% 6% 9% 7% 22%	5082
	21st to end	Day	3 9% 7% 11% 6% 5% 6% 5% 6% 7% 35%	5812
February	1st to 10th	Day	8% 13% 5% 10% 9% 7% 6% 5% 6% 6% 27%	1890
	11th to 20th	Day	8% 12% 5% 10% 7% 6% 5% 5% 5% 6% 30%	1844
	21st to end	Day	10% 11% 4 12% 7% 5% 4 4 5% 7% 32%	1667
March	1st to 10th	Day	11% 9% 3 7% 4 4 4 3 5% 7% 42%	4949
	11th to 20th	Day	9% 9% 3 7% 4 4 4 3 5% 8% 43%	5057
	21st to end	Day	23% 12% 4 10% 5% 5% 4 3 4 6% 24%	5462
April	1st to 10th	Day	18% 9% 3 6% 4 3 4 3 6% 7% 36%	2310
	11th to 20th	Day	18% 11% 4 6% 4 5% 4 3 4 7% 34%	2532
	21st to end	Day	22% 10% 3 7% 4 3 4 3 5% 6% 35%	2600
May	1st to 10th	Day	11% 6% 2 5% 3 4 3 4 5% 7% 50%	5862
	11th to 20th	Day	18% 8% 2 5% 3 3 3 3 4 6% 44%	6153
	21st to end	Day	16% 7% 3 7% 4 5% 5% 4 6% 7% 36%	6935
June	1st to 10th	Day	12% 5% 2 5% 4 5% 4 4 6% 7% 46%	2883
	11th to 20th	Day	15% 7% 3 6% 4 4 5% 4 6% 7% 40%	3000
	21st to end	Day	9% 5% 2 6% 4 4 4 5% 7% 8% 46%	3000
July	1st to 10th	Day	8% 4 2 5% 4 4 5% 5% 7% 11% 45%	6800
	11th to 20th	Day	7% 4 2 5% 3 3 3 3 5% 8% 56%	6564
	21st to end	Day	7% 5% 2 5% 4 4 5% 4 7% 9% 47%	6422
August	1st to 10th	Day	14% 6% 2 5% 4 4 4 4 5% 8% 43%	4234
	11th to 20th	Day	12% 6% 2 6% 4 5% 5% 4 6% 8% 40%	4171
	21st to end	Day	8% 5% 2 5% 4 4 5% 3 6% 8% 51%	4645
September	1st to 10th	Day	11% 5% 2 4 4 4 3 3 5% 7% 51%	2397
	11th to 20th	Day	10% 5% 2 5% 4 3 3 3 6% 8% 49%	2200
	21st to end	Day	13% 5% 2 4 3 3 3 3 4 6% 53%	2200
October	1st to 10th	Day	14% 7% 2 5% 5% 3 4 3 4 6% 47%	2010
	11th to 20th	Day	14% 9% 2 5% 3 3 4 3 5% 5% 46%	2000
	21st to end	Day	17% 10% 3 6% 3 3 3 3 4 5% 43%	2150
November	1st to 10th	Day	12% 10% 3 7% 5% 4 3 3 5% 6% 42%	1790
	11th to 20th	Day	10% 11% 4 11% 6% 4 4 4 4 6% 36%	1680
	21st to end	Day	12% 12% 3 9% 6% 4 5% 3 6% 7% 34%	1680
December	1st to 10th	Day	6% 10% 4 12% 10% 7% 5% 3 6% 7% 30%	2690
	11th to 20th	Day	9% 15% 6% 11% 7% 7% 6% 4 5% 7% 23%	3088
	21st to end	Day	16% 12% 5% 19% 4 4 4 3 5% 6% 21%	3577
January	1st to 10th	Night	6% 10% 5% 16% 10% 8% 6% 4 6% 5% 23%	8784
	11th to 20th	Night	3 9% 4 13% 8% 8% 11% 6% 8% 6% 22%	7891
	21st to end	Night	4 10% 6% 9% 5% 6% 5% 4 6% 6% 38%	8402
February	1st to 10th	Night	7% 12% 4 9% 7% 6% 6% 4 6% 6% 33%	2730
	11th to 20th	Night	7% 9% 5% 8% 5% 6% 6% 5% 6% 6% 38%	2663
	21st to end	Night	9% 9% 4 8% 7% 6% 4 4 6% 7% 37%	2156
March	1st to 10th	Night	10% 7% 3 6% 4 3 3 3 5% 7% 49%	5128
	11th to 20th	Night	10% 7% 3 6% 4 4 4 4 6% 9% 44%	5057
	21st to end	Night	21% 11% 4 10% 4 4 3 2 4 5% 31%	5467
April	1st to 10th	Night	15% 10% 3 5% 4 4 4 3 5% 7% 40%	2089
	11th to 20th	Night	16% 9% 4 6% 3 4 4 4 4 6% 40%	1814
	21st to end	Night	19% 8% 3 8% 4 4 3 3 4 5% 39%	1800
May	1st to 10th	Night	13% 5% 2 4 3 3 3 2 4 5% 56%	4053
	11th to 20th	Night	14% 8% 2 4 3 3 4 3 5% 6% 48%	3747
	21st to end	Night	18% 7% 2 6% 4 4 3 3 4 7% 41%	3942
June	1st to 10th	Night	9% 4 1 5% 4 3 4 3 6% 7% 54%	1511
	11th to 20th	Night	9% 4 3 5% 5% 5% 3 4 6% 9% 49%	1400
	21st to end	Night	8% 4 1 4 3 2 4 4 5% 7% 56%	1400
July	1st to 10th	Night	8% 4 2 5% 4 3 5% 4 7% 9% 50%	3178
	11th to 20th	Night	6% 4 2 5% 4 4 4 3 5% 7% 57%	3392
	21st to end	Night	9% 5% 2 5% 3 4 4 4 6% 9% 50%	4449
August	1st to 10th	Night	12% 5% 2 5% 4 3 4 3 5% 7% 50%	2926
	11th to 20th	Night	11% 5% 2 4 3 3 4 3 4 7% 53%	2888
	21st to end	Night	8% 4 2 5% 3 3 4 3 5% 7% 56%	3261
September	1st to 10th	Night	8% 4 2 4 3 4 3 3 6% 6% 57%	2000
	11th to 20th	Night	8% 5% 1 4 4 3 4 3 5% 7% 56%	2200
	21st to end	Night	10% 5% 2 4 3 4 3 3 5% 6% 56%	2200
October	1st to 10th	Night	15% 6% 2 4 3 2 3 3 5% 6% 52%	2369
	11th to 20th	Night	15% 7% 2 6% 3 3 4 3 4 5% 48%	2400
	21st to end	Night	15% 8% 3 7% 4 3 3 3 5% 6% 42%	2688
November	1st to 10th	Night	10% 8% 3 7% 5% 4 4 3 5% 6% 45%	2728
	11th to 20th	Night	11% 10% 3 10% 5% 4 4 3 4 5% 41%	2940
	21st to end	Night	9% 11% 3 9% 6% 4 4 3 5% 7% 39%	2940
December	1st to 10th	Night	5% 8% 5% 13% 8% 6% 5% 3 6% 7% 35%	4720
	11th to 20th	Night	11% 11% 4 12% 8% 6% 5% 4 6% 7% 27%	5339
	21st to end	Night	16% 14% 5% 15% 6% 5% 5% 3 4 5% 22%	7623

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% 4 11% 12% 6%	4125
	11th to 20th	Day	56% 4 11% 18% 10%	5082
	21st to end	Day	48% 5% 16% 21% 10%	5812
February	1st to 10th	Day	57% 6% 14% 15% 8%	1890
	11th to 20th	Day	53% 5% 12% 20% 9% 1	1853
	21st to end	Day	52% 6% 13% 18% 11% 1	1667
March	1st to 10th	Day	40% 6% 15% 26% 12% 1	4949
	11th to 20th	Day	40% 4 11% 30% 13% 2	5057
	21st to end	Day	61% 5% 10% 17% 6%	5464
April	1st to 10th	Day	46% 7% 13% 22% 11% 1	2310
	11th to 20th	Day	50% 4 12% 21% 12% 1	2532
	21st to end	Day	50% 6% 13% 22% 9%	2600
May	1st to 10th	Day	33% 6% 11% 27% 21% 1	5900
	11th to 20th	Day	41% 5% 10% 20% 15% 9%	6157
	21st to end	Day	45% 7% 11% 26% 11% 1	6949
June	1st to 10th	Day	35% 7% 15% 28% 13% 1	2883
	11th to 20th	Day	42% 8% 13% 22% 14% 2	3000
	21st to end	Day	33% 9% 16% 26% 15% 2	3000
July	1st to 10th	Day	31% 8% 20% 29% 11% 1	6726
	11th to 20th	Day	27% 5% 14% 36% 16% 2	6483
	21st to end	Day	31% 7% 18% 27% 16% 2	6240
August	1st to 10th	Day	39% 6% 12% 29% 12% 2	4220
	11th to 20th	Day	40% 7% 15% 30% 7% 1	4210
	21st to end	Day	31% 7% 18% 27% 15% 2	4644
September	1st to 10th	Day	31% 6% 13% 31% 17% 1	2397
	11th to 20th	Day	32% 8% 17% 30% 13% 1	2200
	21st to end	Day	33% 5% 11% 30% 20% 2	2200
October	1st to 10th	Day	29% 4 8% 29% 29% 1	3270
	11th to 20th	Day	38% 5% 11% 23% 21% 2	3240
	21st to end	Day	41% 4 15% 26% 13% 1	3455
November	1st to 10th	Day	42% 5% 13% 23% 14% 3	1790
	11th to 20th	Day	48% 6% 12% 22% 10% 1	1680
	21st to end	Day	49% 5% 15% 20% 10% 1	1680
December	1st to 10th	Day	53% 6% 14% 19% 7% 1	2690
	11th to 20th	Day	60% 6% 15% 14% 5%	3085
	21st to end	Day	62% 5% 11% 14% 7% 1	3577
January	1st to 10th	Night	61% 5% 10% 17% 6%	8785
	11th to 20th	Night	57% 5% 12% 16% 9% 1	7891
	21st to end	Night	45% 5% 14% 24% 12%	8402
February	1st to 10th	Night	50% 6% 13% 19% 10% 2	2730
	11th to 20th	Night	45% 6% 14% 22% 12% 2	2664
	21st to end	Night	45% 6% 13% 20% 12% 3	2156
March	1st to 10th	Night	35% 5% 9% 34% 15% 2	5128
	11th to 20th	Night	36% 5% 13% 32% 13% 1	5057
	21st to end	Night	56% 5% 13% 19% 7%	5467
April	1st to 10th	Night	43% 6% 14% 25% 11% 1	2089
	11th to 20th	Night	44% 5% 11% 22% 15% 2	1814
	21st to end	Night	47% 5% 11% 23% 12% 2	1800
May	1st to 10th	Night	30% 5% 12% 28% 22% 3	4080
	11th to 20th	Night	36% 6% 9% 18% 21% 9%	3748
	21st to end	Night	43% 6% 10% 27% 13% 1	3950
June	1st to 10th	Night	29% 7% 15% 29% 17% 3	1511
	11th to 20th	Night	33% 6% 16% 24% 19% 3	1400
	21st to end	Night	26% 6% 17% 30% 19% 2	1400
July	1st to 10th	Night	29% 6% 18% 30% 15% 2	3145
	11th to 20th	Night	27% 5% 15% 35% 16% 2	3353
	21st to end	Night	30% 7% 18% 30% 14% 1	4320
August	1st to 10th	Night	34% 6% 15% 26% 16% 3	2916
	11th to 20th	Night	32% 6% 16% 34% 12% 1	2915
	21st to end	Night	27% 6% 18% 29% 17% 3	3261
September	1st to 10th	Night	26% 5% 13% 34% 20% 1	2000
	11th to 20th	Night	28% 8% 13% 33% 18% 2	2200
	21st to end	Night	29% 5% 10% 31% 22% 2	2200
October	1st to 10th	Night	22% 3 7% 30% 34% 4	3876
	11th to 20th	Night	30% 3 12% 28% 23% 3	3899
	21st to end	Night	39% 5% 12% 29% 14% 1	4336
November	1st to 10th	Night	39% 6% 14% 22% 17% 3	2728
	11th to 20th	Night	45% 5% 12% 22% 14% 2	2940
	21st to end	Night	43% 6% 17% 22% 11% 1	2940
December	1st to 10th	Night	48% 5% 17% 22% 7%	4720
	11th to 20th	Night	55% 7% 15% 19% 4	5341
	21st to end	Night	62% 6% 10% 17% 4	7623

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	15% 12% 33% 26% 12% 2	330
	11th to 20th	Day	14% 15% 41% 22% 7% 1	330
	21st to end	Day	12% 14% 39% 25% 8% 2	363
February	1st to 10th	Day	17% 16% 43% 20% 3 1	330
	11th to 20th	Day	12% 16% 38% 26% 7% 1	330
	21st to end	Day	17% 14% 41% 25% 3	273
March	1st to 10th	Day	18% 14% 38% 24% 5% 1	330
	11th to 20th	Day	25% 9% 35% 25% 5% 1	321
	21st to end	Day	27% 13% 27% 23% 8% 2	330
April	1st to 10th	Day	25% 15% 31% 24% 4	410
	11th to 20th	Day	26% 16% 30% 21% 6% 1	650
	21st to end	Day	24% 15% 29% 20% 10% 1	700
May	1st to 10th	Day	18% 13% 32% 23% 11% 2	703
	11th to 20th	Day	22% 9% 31% 22% 14% 2	725
	21st to end	Day	18% 8% 29% 30% 13% 2	789
June	1st to 10th	Day	10% 10% 25% 31% 19% 4	730
	11th to 20th	Day	17% 8% 35% 27% 10% 3	730
	21st to end	Day	11% 8% 31% 33% 15% 2	730
July	1st to 10th	Day	9% 4 22% 35% 24% 6%	721
	11th to 20th	Day	6% 6% 31% 32% 19% 6%	718
	21st to end	Day	7% 3 24% 39% 22% 5%	794
August	1st to 10th	Day	13% 2 21% 38% 22% 4	726
	11th to 20th	Day	13% 4 23% 31% 23% 5%	715
	21st to end	Day	8% 5% 28% 34% 22% 4	786
September	1st to 10th	Day	13% 6% 29% 29% 18% 4	527
	11th to 20th	Day	10% 4 35% 33% 14% 5%	330
	21st to end	Day	15% 13% 27% 25% 14% 5%	330
October	1st to 10th	Day	16% 12% 29% 25% 14% 3	330
	11th to 20th	Day	18% 16% 37% 18% 9% 1	330
	21st to end	Day	22% 17% 34% 21% 6%	363
November	1st to 10th	Day	21% 17% 33% 21% 7% 2	330
	11th to 20th	Day	16% 18% 43% 18% 5%	330
	21st to end	Day	19% 18% 32% 24% 7% 1	330
December	1st to 10th	Day	12% 12% 42% 26% 8%	330
	11th to 20th	Day	16% 20% 37% 23% 4	330
	21st to end	Day	25% 12% 36% 23% 3 1	363
January	1st to 10th	Night	10% 12% 42% 28% 7% 1	1050
	11th to 20th	Night	12% 15% 40% 28% 6% 1	1050
	21st to end	Night	17% 14% 36% 27% 6%	1155
February	1st to 10th	Night	13% 12% 42% 28% 5%	1050
	11th to 20th	Night	13% 13% 42% 25% 6%	1029
	21st to end	Night	12% 14% 39% 27% 8% 1	772
March	1st to 10th	Night	14% 12% 38% 29% 6% 1	681
	11th to 20th	Night	18% 13% 37% 27% 6%	621
	21st to end	Night	23% 10% 29% 28% 9% 1	660
April	1st to 10th	Night	20% 13% 38% 25% 5% 1	600
	11th to 20th	Night	21% 12% 33% 26% 8% 1	593
	21st to end	Night	21% 12% 34% 25% 9% 1	600
May	1st to 10th	Night	19% 9% 33% 30% 9%	600
	11th to 20th	Night	17% 6% 35% 31% 10% 1	591
	21st to end	Night	15% 6% 32% 35% 11% 1	650
June	1st to 10th	Night	10% 7% 25% 41% 18%	600
	11th to 20th	Night	11% 4 37% 39% 9%	600
	21st to end	Night	10% 4 26% 48% 12%	600
July	1st to 10th	Night	5% 3 24% 43% 23% 2	585
	11th to 20th	Night	5% 2 27% 46% 20% 1	582
	21st to end	Night	5% 2 22% 48% 21% 2	657
August	1st to 10th	Night	10% 3 20% 47% 19% 2	597
	11th to 20th	Night	10% 4 19% 43% 23% 2	594
	21st to end	Night	6% 3 24% 43% 21% 2	660
September	1st to 10th	Night	9% 4 27% 42% 17% 2	600
	11th to 20th	Night	10% 5% 29% 36% 18% 1	600
	21st to end	Night	11% 10% 32% 32% 14% 1	600
October	1st to 10th	Night	17% 10% 32% 30% 11%	769
	11th to 20th	Night	17% 13% 38% 25% 6% 1	800
	21st to end	Night	21% 13% 32% 28% 7%	928
November	1st to 10th	Night	14% 11% 38% 29% 8%	1025
	11th to 20th	Night	14% 14% 40% 24% 7%	1050
	21st to end	Night	14% 13% 40% 27% 5%	1050
December	1st to 10th	Night	13% 11% 41% 29% 5%	1050
	11th to 20th	Night	20% 11% 36% 27% 6% 1	1050
	21st to end	Night	22% 13% 37% 23% 5% 1	1155

Page generated at 2026-03-15 01:23:54. Version ac07

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