Our Prairie Sky
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Our Prairie Sky clear sky chart from 2005-11-06 to 2026-01-17.

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 5% 4 6% 7% 36%	127271
	Night	14% 10% 4 8% 5% 4 4 3 5% 6% 38%	124648
Transparency	Day	46% 5% 11% 23% 14% 2	130808
	Night	46% 4 11% 22% 15% 2	129185
Seeing	Day	17% 12% 30% 24% 12% 4	17375
	Night	18% 11% 31% 28% 11% 1	27294

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	12% 11% 8% 13% 6% 5% 5% 4 6% 6% 24%	3697
	11th to 20th	Day	10% 13% 6% 14% 6% 5% 4 5% 6% 4 25%	3668
	21st to end	Day	17% 19% 5% 9% 4 3 3 2 5% 6% 27%	4074
February	1st to 10th	Day	16% 13% 6% 9% 6% 5% 5% 3 5% 7% 25%	1882
	11th to 20th	Day	14% 12% 5% 8% 6% 5% 3 3 5% 6% 32%	1948
	21st to end	Day	15% 12% 6% 10% 5% 4 4 3 6% 6% 29%	1650
March	1st to 10th	Day	18% 12% 4 6% 4 3 3 3 4 5% 39%	4480
	11th to 20th	Day	8% 8% 4 7% 5% 5% 5% 4 6% 8% 41%	4662
	21st to end	Day	18% 14% 7% 12% 6% 5% 5% 4 5% 6% 19%	5967
April	1st to 10th	Day	17% 13% 3 8% 5% 5% 4 3 5% 6% 31%	2400
	11th to 20th	Day	16% 9% 2 6% 5% 5% 5% 4 6% 7% 35%	2374
	21st to end	Day	19% 8% 3 6% 4 5% 4 4 5% 7% 34%	2520
May	1st to 10th	Day	18% 8% 3 6% 5% 5% 5% 4 6% 8% 32%	5862
	11th to 20th	Day	14% 6% 2 6% 5% 5% 5% 4 6% 8% 39%	6057
	21st to end	Day	14% 6% 3 7% 5% 4 5% 4 5% 9% 39%	6935
June	1st to 10th	Day	10% 5% 3 6% 5% 4 5% 4 6% 8% 45%	2800
	11th to 20th	Day	10% 5% 2 6% 4 5% 5% 5% 6% 8% 45%	2800
	21st to end	Day	9% 6% 2 6% 5% 6% 6% 5% 7% 9% 38%	2800
July	1st to 10th	Day	10% 6% 2 7% 5% 6% 6% 5% 7% 10% 36%	6360
	11th to 20th	Day	9% 5% 2 6% 5% 5% 5% 4 8% 10% 41%	6360
	21st to end	Day	10% 6% 2 7% 5% 5% 5% 5% 7% 9% 39%	6924
August	1st to 10th	Day	8% 5% 2 6% 4 5% 5% 4 6% 8% 48%	4403
	11th to 20th	Day	9% 5% 2 6% 4 4 5% 4 6% 9% 44%	3888
	21st to end	Day	6% 4 2 6% 4 5% 5% 4 7% 9% 48%	4312
September	1st to 10th	Day	11% 5% 2 4 4 4 5% 4 5% 7% 48%	2400
	11th to 20th	Day	11% 5% 1 4 4 2 4 3 5% 8% 51%	2251
	21st to end	Day	11% 6% 2 5% 5% 4 4 4 6% 9% 43%	2200
October	1st to 10th	Day	12% 6% 2 6% 4 4 4 4 5% 5% 48%	2181
	11th to 20th	Day	17% 8% 2 7% 5% 4 4 4 5% 7% 37%	1972
	21st to end	Day	18% 10% 3 8% 4 4 3 3 6% 6% 34%	1980
November	1st to 10th	Day	12% 9% 3 5% 4 3 3 3 5% 7% 45%	1852
	11th to 20th	Day	17% 9% 4 8% 4 3 4 3 5% 7% 35%	1890
	21st to end	Day	17% 12% 4 9% 5% 4 4 3 3 5% 34%	1874
December	1st to 10th	Day	9% 11% 3 9% 5% 4 4 3 4 6% 41%	2690
	11th to 20th	Day	12% 16% 6% 12% 5% 5% 5% 4 6% 6% 24%	3088
	21st to end	Day	23% 23% 6% 13% 6% 4 4 3 3 4 11%	4070
January	1st to 10th	Night	14% 14% 6% 12% 6% 4 4 3 5% 4 28%	6488
	11th to 20th	Night	14% 15% 6% 13% 7% 6% 5% 4 6% 4 21%	6445
	21st to end	Night	18% 14% 6% 8% 4 4 3 3 4 4 31%	6886
February	1st to 10th	Night	16% 15% 4 9% 5% 5% 4 3 4 5% 31%	2515
	11th to 20th	Night	15% 11% 4 8% 5% 5% 5% 3 4 6% 35%	2338
	21st to end	Night	18% 12% 4 8% 4 3 4 3 4 6% 34%	1980
March	1st to 10th	Night	16% 11% 4 7% 4 4 3 2 4 5% 40%	5373
	11th to 20th	Night	11% 7% 2 6% 4 4 4 3 5% 7% 46%	5330
	21st to end	Night	17% 10% 6% 10% 6% 5% 5% 4 4 5% 28%	4972
April	1st to 10th	Night	14% 9% 3 7% 4 5% 4 3 6% 8% 38%	2000
	11th to 20th	Night	18% 8% 3 7% 4 4 3 3 6% 7% 38%	1975
	21st to end	Night	17% 8% 3 8% 4 5% 4 4 5% 6% 36%	1878
May	1st to 10th	Night	19% 9% 3 7% 5% 4 4 4 5% 7% 34%	4033
	11th to 20th	Night	13% 7% 2 5% 3 4 4 4 6% 9% 42%	3842
	21st to end	Night	15% 9% 3 7% 5% 4 4 3 6% 6% 40%	3942
June	1st to 10th	Night	10% 5% 3 6% 4 4 4 3 5% 7% 50%	1600
	11th to 20th	Night	9% 6% 2 7% 4 4 4 4 6% 9% 45%	1600
	21st to end	Night	9% 6% 2 6% 6% 4 5% 4 6% 8% 43%	1600
July	1st to 10th	Night	9% 5% 3 7% 5% 5% 6% 4 7% 9% 41%	3618
	11th to 20th	Night	7% 5% 2 6% 4 4 4 4 6% 8% 50%	3617
	21st to end	Night	8% 5% 2 7% 5% 5% 5% 4 7% 9% 44%	3947
August	1st to 10th	Night	7% 4 2 6% 5% 4 6% 4 7% 8% 48%	2748
	11th to 20th	Night	8% 4 2 5% 4 4 5% 4 5% 8% 51%	3158
	21st to end	Night	7% 5% 2 5% 4 3 4 3 5% 8% 53%	3586
September	1st to 10th	Night	10% 5% 2 6% 3 3 4 3 5% 6% 53%	2000
	11th to 20th	Night	8% 4 2 5% 2 4 3 3 6% 8% 55%	2128
	21st to end	Night	10% 5% 2 7% 5% 5% 5% 3 5% 6% 47%	2200
October	1st to 10th	Night	10% 5% 2 6% 4 3 4 3 4 5% 53%	2215
	11th to 20th	Night	17% 7% 2 6% 3 3 3 3 4 6% 45%	2426
	21st to end	Night	20% 8% 3 6% 5% 3 3 3 5% 6% 38%	2860
November	1st to 10th	Night	12% 9% 3 5% 4 3 3 3 5% 7% 46%	2666
	11th to 20th	Night	13% 9% 4 9% 5% 4 5% 3 5% 6% 37%	2730
	21st to end	Night	17% 11% 4 8% 5% 4 4 3 4 6% 35%	2743
December	1st to 10th	Night	11% 10% 3 8% 5% 4 4 3 5% 5% 43%	4720
	11th to 20th	Night	16% 14% 5% 9% 5% 4 4 3 4 5% 30%	5339
	21st to end	Night	23% 19% 6% 11% 5% 4 4 3 4 5% 16%	7150

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	61% 4 12% 15% 7% 1	3698
	11th to 20th	Day	62% 3 9% 10% 12% 4	3668
	21st to end	Day	60% 3 11% 17% 8% 1	4074
February	1st to 10th	Day	59% 4 12% 15% 8% 2	1882
	11th to 20th	Day	53% 4 9% 22% 9% 2	1958
	21st to end	Day	56% 4 9% 20% 7% 2	1650
March	1st to 10th	Day	50% 3 7% 24% 13% 3	4480
	11th to 20th	Day	40% 4 12% 33% 11% 1	4662
	21st to end	Day	65% 4 11% 12% 6% 1	5969
April	1st to 10th	Day	53% 4 10% 20% 12%	2400
	11th to 20th	Day	48% 5% 11% 22% 12% 3	2374
	21st to end	Day	50% 5% 13% 19% 11% 2	2520
May	1st to 10th	Day	48% 6% 11% 22% 12% 2	5897
	11th to 20th	Day	43% 5% 11% 26% 13% 1	6061
	21st to end	Day	42% 5% 10% 24% 16% 3	6949
June	1st to 10th	Day	36% 6% 12% 25% 18% 2	2800
	11th to 20th	Day	36% 5% 12% 25% 19% 3	2800
	21st to end	Day	38% 8% 15% 21% 15% 3	2800
July	1st to 10th	Day	41% 6% 12% 23% 15% 2	6291
	11th to 20th	Day	36% 7% 15% 27% 14% 1	6285
	21st to end	Day	40% 6% 15% 22% 14% 2	6728
August	1st to 10th	Day	33% 6% 15% 30% 15% 1	4388
	11th to 20th	Day	34% 6% 11% 33% 16% 1	3925
	21st to end	Day	31% 6% 13% 27% 19% 3	4311
September	1st to 10th	Day	34% 6% 12% 27% 17% 4	2400
	11th to 20th	Day	31% 5% 10% 27% 23% 4	2251
	21st to end	Day	37% 6% 9% 26% 20% 2	2200
October	1st to 10th	Day	26% 4 7% 30% 31% 2	3558
	11th to 20th	Day	36% 4 12% 24% 24% 1	3188
	21st to end	Day	43% 4 9% 25% 17% 2	3180
November	1st to 10th	Day	38% 5% 14% 26% 16% 2	1852
	11th to 20th	Day	50% 4 12% 22% 12% 1	1890
	21st to end	Day	54% 3 10% 23% 10%	1874
December	1st to 10th	Day	46% 3 15% 26% 9%	2690
	11th to 20th	Day	60% 4 12% 18% 6% 1	3085
	21st to end	Day	78% 4 6% 8% 4	4070
January	1st to 10th	Night	60% 3 9% 18% 10%	6488
	11th to 20th	Night	66% 2 10% 9% 11% 2	6445
	21st to end	Night	59% 2 10% 17% 11% 1	6886
February	1st to 10th	Night	57% 3 10% 18% 10% 2	2515
	11th to 20th	Night	51% 4 9% 21% 13% 2	2339
	21st to end	Night	53% 3 11% 19% 11% 3	1980
March	1st to 10th	Night	49% 3 9% 26% 11% 3	5373
	11th to 20th	Night	38% 4 12% 28% 15% 3	5330
	21st to end	Night	58% 4 9% 20% 8%	4972
April	1st to 10th	Night	44% 5% 13% 24% 13% 2	2000
	11th to 20th	Night	47% 3 8% 21% 16% 4	1975
	21st to end	Night	48% 5% 10% 21% 14% 3	1878
May	1st to 10th	Night	51% 4 11% 17% 14% 4	4060
	11th to 20th	Night	38% 6% 14% 26% 13% 3	3843
	21st to end	Night	45% 4 10% 20% 17% 4	3950
June	1st to 10th	Night	34% 4 13% 26% 20% 4	1600
	11th to 20th	Night	35% 4 12% 23% 22% 3	1600
	21st to end	Night	37% 7% 14% 22% 16% 3	1600
July	1st to 10th	Night	39% 5% 12% 27% 13% 4	3580
	11th to 20th	Night	32% 5% 15% 24% 21% 1	3572
	21st to end	Night	37% 6% 15% 23% 16% 4	3832
August	1st to 10th	Night	31% 6% 17% 29% 16% 1	2739
	11th to 20th	Night	31% 5% 14% 29% 20% 1	3187
	21st to end	Night	29% 5% 11% 33% 18% 3	3586
September	1st to 10th	Night	31% 5% 11% 26% 23% 4	2000
	11th to 20th	Night	28% 4 9% 28% 28% 3	2128
	21st to end	Night	37% 5% 9% 28% 19% 3	2200
October	1st to 10th	Night	22% 4 7% 34% 31% 3	3618
	11th to 20th	Night	33% 4 8% 24% 29% 2	3949
	21st to end	Night	40% 3 8% 24% 21% 4	4610
November	1st to 10th	Night	39% 3 10% 27% 18% 3	2666
	11th to 20th	Night	47% 3 11% 23% 14% 2	2730
	21st to end	Night	52% 3 10% 23% 11%	2743
December	1st to 10th	Night	44% 3 14% 27% 12% 1	4720
	11th to 20th	Night	57% 3 11% 16% 11% 1	5341
	21st to end	Night	72% 4 8% 10% 6%	7150

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	21% 16% 37% 21% 4	330
	11th to 20th	Day	26% 22% 35% 12% 4 1	318
	21st to end	Day	22% 21% 38% 15% 5%	330
February	1st to 10th	Day	25% 20% 41% 13% 2	300
	11th to 20th	Day	25% 20% 37% 16% 3	300
	21st to end	Day	25% 22% 40% 11% 2	249
March	1st to 10th	Day	24% 22% 38% 15% 1	300
	11th to 20th	Day	26% 19% 35% 15% 5%	345
	21st to end	Day	29% 19% 31% 16% 5% 1	550
April	1st to 10th	Day	28% 15% 28% 21% 6%	500
	11th to 20th	Day	25% 20% 27% 17% 10% 1	492
	21st to end	Day	23% 19% 34% 15% 7% 2	500
May	1st to 10th	Day	23% 15% 31% 20% 8% 2	503
	11th to 20th	Day	20% 10% 33% 22% 12% 3	606
	21st to end	Day	14% 11% 35% 24% 12% 5%	789
June	1st to 10th	Day	12% 9% 31% 31% 12% 5%	730
	11th to 20th	Day	13% 6% 33% 30% 15% 3	730
	21st to end	Day	13% 9% 33% 29% 12% 5%	730
July	1st to 10th	Day	9% 5% 25% 29% 20% 12%	721
	11th to 20th	Day	10% 6% 28% 30% 17% 9%	718
	21st to end	Day	8% 3 28% 35% 20% 6%	794
August	1st to 10th	Day	8% 2 21% 34% 24% 11%	631
	11th to 20th	Day	10% 5% 20% 31% 24% 11%	519
	21st to end	Day	7% 3 20% 39% 21% 10%	583
September	1st to 10th	Day	13% 5% 23% 30% 22% 7%	530
	11th to 20th	Day	9% 5% 17% 30% 27% 11%	530
	21st to end	Day	15% 9% 25% 26% 18% 7%	530
October	1st to 10th	Day	15% 9% 27% 28% 17% 4	511
	11th to 20th	Day	21% 19% 31% 22% 7%	330
	21st to end	Day	29% 14% 36% 17% 4	363
November	1st to 10th	Day	18% 18% 36% 19% 7% 2	330
	11th to 20th	Day	25% 18% 34% 16% 6% 1	330
	21st to end	Day	25% 15% 38% 19% 3	330
December	1st to 10th	Day	18% 22% 39% 15% 5% 1	330
	11th to 20th	Day	21% 19% 39% 17% 3	330
	21st to end	Day	29% 19% 38% 12% 1	363
January	1st to 10th	Night	21% 17% 37% 23% 3	1050
	11th to 20th	Night	22% 19% 36% 19% 3 1	1031
	21st to end	Night	21% 16% 36% 24% 4	1100
February	1st to 10th	Night	24% 14% 37% 21% 3	915
	11th to 20th	Night	21% 16% 34% 26% 3	783
	21st to end	Night	24% 17% 38% 18% 3	660
March	1st to 10th	Night	22% 16% 38% 20% 5%	800
	11th to 20th	Night	17% 14% 39% 23% 7% 1	800
	21st to end	Night	24% 11% 35% 22% 7%	670
April	1st to 10th	Night	20% 14% 38% 24% 5% 1	600
	11th to 20th	Night	21% 14% 34% 23% 7%	593
	21st to end	Night	21% 10% 34% 27% 7% 1	600
May	1st to 10th	Night	19% 8% 34% 30% 9%	600
	11th to 20th	Night	18% 7% 30% 33% 12% 1	591
	21st to end	Night	14% 4 28% 37% 17% 1	650
June	1st to 10th	Night	10% 5% 25% 46% 14%	600
	11th to 20th	Night	11% 5% 32% 38% 14% 1	600
	21st to end	Night	12% 4 28% 37% 19% 1	600
July	1st to 10th	Night	8% 2 20% 43% 23% 3	585
	11th to 20th	Night	7% 2 23% 38% 27% 3	582
	21st to end	Night	5% 2 18% 47% 26% 2	657
August	1st to 10th	Night	5% 1 16% 45% 30% 4	597
	11th to 20th	Night	8% 3 14% 40% 31% 4	594
	21st to end	Night	7% 2 20% 39% 29% 3	660
September	1st to 10th	Night	12% 3 19% 35% 27% 4	600
	11th to 20th	Night	9% 5% 16% 40% 27% 4	728
	21st to end	Night	11% 6% 25% 34% 21% 3	800
October	1st to 10th	Night	13% 7% 25% 36% 18% 2	800
	11th to 20th	Night	20% 13% 32% 27% 8%	800
	21st to end	Night	24% 14% 32% 22% 7%	880
November	1st to 10th	Night	19% 12% 37% 23% 8% 1	820
	11th to 20th	Night	18% 19% 35% 22% 5%	840
	21st to end	Night	23% 15% 36% 20% 6%	853
December	1st to 10th	Night	22% 15% 38% 21% 4	1050
	11th to 20th	Night	23% 14% 37% 22% 3	1050
	21st to end	Night	30% 15% 35% 19% 1	1155

Page generated at 2026-01-14 00:14:27. Version ac07

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