Prairie Skies Star Party
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Prairie Skies Star Party 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 4 4 6% 8% 36%	127308
	Night	14% 9% 3 8% 5% 4 4 3 5% 6% 38%	124631
Transparency	Day	45% 5% 12% 23% 14% 2	130843
	Night	46% 5% 11% 22% 15% 2	129170
Seeing	Day	17% 10% 28% 25% 15% 5%	17364
	Night	18% 9% 30% 30% 12% 1	27282

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% 13% 7% 13% 6% 5% 5% 4 5% 7% 23%	3697
	11th to 20th	Day	11% 13% 6% 14% 7% 7% 4 5% 6% 4 24%	3668
	21st to end	Day	17% 18% 5% 10% 5% 3 3 2 4 5% 27%	4141
February	1st to 10th	Day	17% 13% 4 9% 6% 6% 5% 3 5% 5% 26%	1870
	11th to 20th	Day	14% 11% 5% 9% 7% 5% 3 3 5% 6% 33%	1948
	21st to end	Day	16% 13% 5% 9% 5% 5% 3 4 5% 7% 30%	1650
March	1st to 10th	Day	19% 12% 3 7% 3 3 3 2 3 5% 39%	4480
	11th to 20th	Day	9% 8% 4 6% 4 4 5% 4 6% 9% 41%	4682
	21st to end	Day	19% 13% 5% 11% 5% 5% 5% 3 5% 6% 22%	5967
April	1st to 10th	Day	17% 12% 3 8% 4 4 4 3 5% 7% 33%	2400
	11th to 20th	Day	16% 10% 3 7% 5% 5% 4 4 5% 7% 36%	2374
	21st to end	Day	19% 7% 3 8% 4 4 5% 4 5% 7% 34%	2498
May	1st to 10th	Day	20% 7% 2 7% 5% 4 5% 4 7% 8% 31%	5862
	11th to 20th	Day	14% 6% 2 6% 5% 5% 5% 4 6% 8% 40%	6081
	21st to end	Day	14% 6% 2 7% 4 4 4 4 6% 9% 39%	6935
June	1st to 10th	Day	11% 5% 2 6% 5% 4 5% 4 6% 8% 45%	2800
	11th to 20th	Day	10% 5% 2 5% 5% 5% 5% 4 6% 9% 45%	2800
	21st to end	Day	10% 6% 2 7% 5% 5% 6% 5% 7% 8% 40%	2800
July	1st to 10th	Day	9% 6% 2 7% 4 5% 6% 5% 7% 11% 37%	6360
	11th to 20th	Day	9% 5% 2 6% 5% 5% 5% 5% 7% 10% 40%	6360
	21st to end	Day	11% 6% 2 7% 5% 6% 5% 5% 7% 9% 39%	6924
August	1st to 10th	Day	7% 5% 2 6% 4 5% 4 4 6% 9% 48%	4395
	11th to 20th	Day	9% 5% 2 6% 4 4 5% 4 7% 10% 44%	3849
	21st to end	Day	7% 4 2 6% 4 4 5% 4 7% 10% 48%	4312
September	1st to 10th	Day	10% 6% 2 5% 4 4 5% 4 6% 7% 48%	2400
	11th to 20th	Day	12% 5% 1 4 3 4 4 4 5% 8% 52%	2265
	21st to end	Day	10% 7% 2 5% 4 5% 4 3 6% 9% 45%	2200
October	1st to 10th	Day	12% 7% 2 6% 4 3 4 4 5% 6% 47%	2164
	11th to 20th	Day	18% 7% 2 6% 4 5% 4 3 5% 6% 39%	1992
	21st to end	Day	19% 8% 2 8% 4 4 4 3 5% 6% 36%	1980
November	1st to 10th	Day	13% 8% 2 5% 4 3 4 3 5% 7% 46%	1852
	11th to 20th	Day	17% 10% 4 7% 5% 3 4 3 5% 6% 35%	1890
	21st to end	Day	18% 12% 4 9% 4 4 3 3 4 5% 34%	1864
December	1st to 10th	Day	9% 12% 4 9% 4 4 4 3 3 5% 42%	2690
	11th to 20th	Day	13% 16% 4 11% 6% 6% 5% 3 6% 7% 23%	3088
	21st to end	Day	26% 21% 7% 13% 6% 3 4 3 3 4 11%	4070
January	1st to 10th	Night	14% 13% 6% 12% 5% 4 4 3 5% 5% 28%	6488
	11th to 20th	Night	13% 15% 7% 14% 8% 5% 5% 3 5% 4 21%	6445
	21st to end	Night	19% 14% 6% 9% 4 4 4 3 3 4 30%	6835
February	1st to 10th	Night	16% 15% 4 8% 5% 4 4 4 4 5% 31%	2528
	11th to 20th	Night	14% 11% 4 8% 5% 4 4 3 5% 7% 34%	2338
	21st to end	Night	18% 11% 4 8% 4 3 4 3 4 5% 34%	1980
March	1st to 10th	Night	17% 11% 4 6% 4 4 3 3 4 5% 40%	5373
	11th to 20th	Night	11% 6% 2 6% 4 4 4 3 6% 7% 46%	5321
	21st to end	Night	19% 10% 5% 9% 6% 5% 5% 3 5% 5% 27%	4962
April	1st to 10th	Night	15% 8% 3 6% 5% 4 4 3 6% 6% 40%	2000
	11th to 20th	Night	19% 9% 2 5% 4 4 4 3 5% 6% 40%	1975
	21st to end	Night	18% 8% 2 7% 5% 4 5% 4 6% 6% 36%	1900
May	1st to 10th	Night	20% 8% 3 7% 4 4 4 3 5% 7% 34%	4033
	11th to 20th	Night	13% 6% 2 6% 4 4 4 4 6% 9% 42%	3820
	21st to end	Night	15% 8% 2 7% 4 4 5% 4 5% 7% 39%	3942
June	1st to 10th	Night	10% 5% 2 5% 4 3 4 3 5% 8% 50%	1600
	11th to 20th	Night	9% 5% 3 6% 4 4 4 3 7% 9% 46%	1600
	21st to end	Night	10% 6% 3 6% 4 4 5% 5% 6% 9% 43%	1600
July	1st to 10th	Night	10% 6% 2 7% 4 5% 5% 5% 7% 9% 40%	3618
	11th to 20th	Night	7% 5% 2 7% 4 5% 5% 4 5% 8% 48%	3617
	21st to end	Night	8% 6% 2 8% 5% 5% 5% 4 7% 8% 43%	3947
August	1st to 10th	Night	5% 4 2 5% 5% 5% 5% 4 7% 9% 49%	2753
	11th to 20th	Night	8% 5% 1 5% 4 5% 4 4 6% 9% 51%	3200
	21st to end	Night	8% 4 2 5% 4 3 4 3 5% 9% 53%	3586
September	1st to 10th	Night	9% 5% 2 5% 3 4 3 3 5% 7% 55%	2000
	11th to 20th	Night	9% 4 1 4 3 3 3 3 6% 8% 56%	2115
	21st to end	Night	9% 5% 2 7% 5% 5% 5% 4 6% 7% 45%	2200
October	1st to 10th	Night	10% 5% 2 6% 4 3 4 3 5% 6% 53%	2233
	11th to 20th	Night	15% 7% 2 6% 3 3 3 3 5% 7% 46%	2406
	21st to end	Night	19% 8% 3 7% 4 3 3 3 4 6% 39%	2860
November	1st to 10th	Night	12% 8% 2 5% 3 4 3 3 5% 6% 47%	2666
	11th to 20th	Night	14% 10% 4 7% 4 5% 4 3 5% 6% 38%	2730
	21st to end	Night	18% 11% 3 7% 6% 4 3 2 4 6% 36%	2751
December	1st to 10th	Night	12% 9% 3 7% 4 4 4 4 5% 6% 43%	4720
	11th to 20th	Night	18% 14% 4 9% 5% 4 4 3 4 4 31%	5339
	21st to end	Night	25% 18% 6% 11% 5% 4 4 3 4 4 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	60% 5% 13% 15% 7% 1	3698
	11th to 20th	Day	61% 4 9% 10% 13% 4	3668
	21st to end	Day	60% 3 12% 18% 7%	4141
February	1st to 10th	Day	59% 6% 11% 15% 7% 2	1870
	11th to 20th	Day	53% 5% 11% 22% 8% 2	1958
	21st to end	Day	54% 6% 11% 20% 7% 2	1650
March	1st to 10th	Day	49% 4 8% 23% 13% 2	4480
	11th to 20th	Day	39% 4 12% 34% 11% 1	4682
	21st to end	Day	61% 7% 11% 13% 7% 1	5969
April	1st to 10th	Day	51% 5% 12% 20% 13%	2400
	11th to 20th	Day	48% 6% 11% 21% 11% 3	2374
	21st to end	Day	49% 7% 13% 18% 11% 2	2498
May	1st to 10th	Day	48% 6% 12% 20% 13% 1	5897
	11th to 20th	Day	41% 6% 12% 26% 13% 2	6085
	21st to end	Day	41% 5% 11% 24% 15% 3	6949
June	1st to 10th	Day	35% 8% 13% 24% 17% 3	2800
	11th to 20th	Day	35% 7% 12% 24% 20% 3	2800
	21st to end	Day	38% 9% 14% 21% 15% 3	2800
July	1st to 10th	Day	41% 4 12% 25% 16% 2	6291
	11th to 20th	Day	39% 4 15% 27% 14% 1	6285
	21st to end	Day	42% 4 18% 22% 13% 2	6728
August	1st to 10th	Day	32% 6% 17% 31% 13% 1	4380
	11th to 20th	Day	34% 5% 12% 33% 16% 1	3885
	21st to end	Day	31% 6% 12% 29% 18% 3	4311
September	1st to 10th	Day	34% 6% 13% 26% 18% 4	2400
	11th to 20th	Day	30% 5% 12% 26% 23% 4	2265
	21st to end	Day	36% 5% 10% 26% 20% 2	2200
October	1st to 10th	Day	26% 4 7% 28% 33% 2	3528
	11th to 20th	Day	34% 3 11% 24% 26% 1	3220
	21st to end	Day	41% 3 9% 27% 18% 2	3180
November	1st to 10th	Day	38% 5% 14% 26% 16% 2	1852
	11th to 20th	Day	50% 4 12% 21% 12% 1	1890
	21st to end	Day	53% 4 10% 22% 10%	1864
December	1st to 10th	Day	46% 3 13% 28% 8%	2690
	11th to 20th	Day	61% 4 12% 18% 5%	3085
	21st to end	Day	79% 3 6% 7% 4	4070
January	1st to 10th	Night	59% 5% 10% 17% 9%	6488
	11th to 20th	Night	67% 3 10% 9% 11% 1	6445
	21st to end	Night	59% 4 10% 17% 10% 1	6835
February	1st to 10th	Night	55% 5% 11% 17% 10% 2	2528
	11th to 20th	Night	49% 6% 11% 21% 12% 1	2339
	21st to end	Night	51% 6% 10% 20% 10% 3	1980
March	1st to 10th	Night	47% 4 9% 25% 10% 4	5373
	11th to 20th	Night	38% 4 13% 27% 15% 3	5321
	21st to end	Night	58% 6% 8% 19% 8% 1	4962
April	1st to 10th	Night	44% 6% 13% 22% 13% 2	2000
	11th to 20th	Night	45% 5% 10% 20% 16% 4	1975
	21st to end	Night	46% 8% 11% 20% 12% 3	1900
May	1st to 10th	Night	50% 5% 12% 16% 14% 4	4060
	11th to 20th	Night	38% 7% 15% 25% 13% 3	3821
	21st to end	Night	43% 7% 11% 20% 16% 4	3950
June	1st to 10th	Night	32% 7% 12% 26% 20% 4	1600
	11th to 20th	Night	33% 6% 13% 24% 21% 3	1600
	21st to end	Night	35% 9% 15% 22% 15% 4	1600
July	1st to 10th	Night	41% 4 12% 26% 14% 4	3580
	11th to 20th	Night	35% 3 15% 25% 20% 2	3572
	21st to end	Night	38% 4 16% 23% 15% 4	3832
August	1st to 10th	Night	31% 4 19% 29% 16% 1	2744
	11th to 20th	Night	30% 4 16% 28% 20% 2	3230
	21st to end	Night	29% 4 12% 33% 19% 3	3586
September	1st to 10th	Night	29% 6% 11% 26% 23% 5%	2000
	11th to 20th	Night	27% 6% 9% 28% 27% 4	2115
	21st to end	Night	36% 7% 11% 24% 19% 3	2200
October	1st to 10th	Night	21% 4 7% 32% 33% 2	3649
	11th to 20th	Night	32% 3 8% 24% 30% 2	3917
	21st to end	Night	39% 2 9% 25% 21% 4	4610
November	1st to 10th	Night	38% 5% 10% 27% 18% 3	2666
	11th to 20th	Night	46% 4 12% 22% 13% 2	2730
	21st to end	Night	52% 4 11% 22% 11%	2751
December	1st to 10th	Night	44% 3 14% 27% 11% 1	4720
	11th to 20th	Night	57% 3 12% 17% 10% 1	5341
	21st to end	Night	72% 4 8% 10% 5%	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	23% 12% 34% 23% 7% 1	330
	11th to 20th	Day	26% 17% 37% 15% 5%	318
	21st to end	Day	23% 19% 30% 24% 5%	330
February	1st to 10th	Day	23% 18% 40% 15% 4	300
	11th to 20th	Day	24% 16% 36% 20% 4	300
	21st to end	Day	26% 15% 43% 13% 3	249
March	1st to 10th	Day	22% 22% 37% 17% 2	300
	11th to 20th	Day	23% 20% 33% 18% 5%	330
	21st to end	Day	30% 14% 32% 16% 6% 1	550
April	1st to 10th	Day	24% 14% 33% 21% 7% 1	500
	11th to 20th	Day	21% 19% 28% 20% 10% 2	492
	21st to end	Day	21% 15% 33% 20% 8% 2	500
May	1st to 10th	Day	22% 11% 29% 26% 9% 3	503
	11th to 20th	Day	21% 9% 28% 24% 14% 4	617
	21st to end	Day	14% 8% 33% 22% 15% 8%	789
June	1st to 10th	Day	11% 9% 27% 28% 19% 5%	730
	11th to 20th	Day	11% 4 29% 32% 19% 5%	730
	21st to end	Day	12% 7% 32% 29% 15% 5%	730
July	1st to 10th	Day	9% 3 19% 30% 24% 15%	721
	11th to 20th	Day	9% 3 21% 32% 22% 12%	718
	21st to end	Day	10% 3 21% 33% 25% 8%	794
August	1st to 10th	Day	7% 2 15% 33% 29% 12%	641
	11th to 20th	Day	11% 4 17% 29% 25% 14%	519
	21st to end	Day	9% 2 16% 33% 28% 12%	583
September	1st to 10th	Day	12% 5% 19% 27% 28% 9%	530
	11th to 20th	Day	10% 3 14% 28% 31% 13%	530
	21st to end	Day	14% 7% 25% 25% 20% 9%	530
October	1st to 10th	Day	14% 6% 28% 28% 18% 5%	494
	11th to 20th	Day	19% 19% 28% 25% 8% 1	330
	21st to end	Day	28% 14% 33% 20% 4 1	363
November	1st to 10th	Day	17% 13% 35% 22% 10% 4	330
	11th to 20th	Day	24% 16% 34% 16% 9% 1	330
	21st to end	Day	26% 12% 36% 19% 6%	330
December	1st to 10th	Day	16% 17% 40% 19% 7% 1	330
	11th to 20th	Day	23% 15% 36% 22% 5% 1	330
	21st to end	Day	29% 20% 35% 13% 3	363
January	1st to 10th	Night	21% 14% 38% 22% 5%	1050
	11th to 20th	Night	22% 16% 36% 21% 4	1031
	21st to end	Night	22% 13% 36% 26% 3	1100
February	1st to 10th	Night	25% 11% 38% 22% 3	928
	11th to 20th	Night	19% 14% 36% 26% 4	783
	21st to end	Night	23% 14% 40% 20% 3	660
March	1st to 10th	Night	21% 15% 37% 23% 5%	800
	11th to 20th	Night	18% 12% 38% 27% 5% 1	790
	21st to end	Night	27% 10% 34% 23% 6%	660
April	1st to 10th	Night	18% 13% 39% 25% 6%	600
	11th to 20th	Night	22% 12% 34% 26% 6% 1	593
	21st to end	Night	21% 9% 34% 28% 7%	600
May	1st to 10th	Night	19% 7% 33% 33% 8%	600
	11th to 20th	Night	17% 6% 31% 34% 11% 1	591
	21st to end	Night	12% 5% 29% 36% 17% 1	650
June	1st to 10th	Night	12% 4 26% 45% 13%	600
	11th to 20th	Night	12% 4 27% 44% 13% 1	600
	21st to end	Night	11% 4 27% 41% 17% 1	600
July	1st to 10th	Night	10% 1 15% 42% 27% 4	585
	11th to 20th	Night	7% 2 18% 43% 28% 2	582
	21st to end	Night	6% 1 17% 46% 29% 1	657
August	1st to 10th	Night	6% 1 11% 47% 31% 3	597
	11th to 20th	Night	7% 3 11% 44% 31% 4	594
	21st to end	Night	8% 1 15% 39% 33% 3	660
September	1st to 10th	Night	11% 4 16% 39% 27% 3	600
	11th to 20th	Night	9% 4 15% 38% 31% 3	715
	21st to end	Night	11% 6% 24% 34% 23% 3	800
October	1st to 10th	Night	12% 6% 24% 38% 19% 1	800
	11th to 20th	Night	20% 12% 31% 28% 10%	800
	21st to end	Night	24% 12% 32% 25% 7%	880
November	1st to 10th	Night	16% 10% 39% 25% 9% 1	820
	11th to 20th	Night	19% 15% 35% 25% 5%	840
	21st to end	Night	23% 13% 34% 24% 6%	861
December	1st to 10th	Night	22% 13% 36% 24% 5%	1050
	11th to 20th	Night	25% 12% 34% 25% 5%	1050
	21st to end	Night	30% 13% 34% 21% 2	1155

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

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