Prairie Grass Stargaze
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Prairie Grass Stargaze clear sky chart from 2005-11-06 to 2026-07-16.

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	12% 8% 3 8% 5% 4 5% 4 5% 7% 40%	139344
	Night	11% 8% 3 8% 5% 5% 5% 4 5% 6% 41%	133647
Transparency	Day	43% 6% 13% 24% 13% 1	142927
	Night	42% 6% 13% 24% 14% 2	138144
Seeing	Day	16% 11% 32% 26% 12% 3	18321
	Night	14% 11% 36% 29% 9% 1	28184

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% 13% 6% 20% 10% 7% 6% 4 4 5% 19%	4691
	11th to 20th	Day	5% 11% 5% 11% 7% 7% 10% 6% 9% 7% 23%	5267
	21st to end	Day	3 9% 7% 11% 6% 6% 7% 4 6% 6% 35%	5812
February	1st to 10th	Day	7% 13% 4 11% 9% 7% 7% 5% 6% 6% 26%	1890
	11th to 20th	Day	9% 10% 5% 10% 7% 6% 6% 4 7% 6% 30%	1844
	21st to end	Day	12% 11% 3 10% 6% 4 5% 4 6% 6% 33%	1641
March	1st to 10th	Day	13% 7% 3 7% 4 4 4 3 5% 7% 43%	5014
	11th to 20th	Day	9% 11% 3 6% 3 3 4 3 5% 8% 45%	5090
	21st to end	Day	23% 12% 5% 10% 5% 4 4 3 4 6% 25%	5583
April	1st to 10th	Day	19% 10% 3 7% 4 4 4 3 6% 7% 34%	2449
	11th to 20th	Day	19% 10% 4 7% 4 4 4 4 4 6% 34%	2613
	21st to end	Day	23% 10% 3 6% 4 4 4 3 4 5% 34%	2730
May	1st to 10th	Day	10% 5% 2 5% 4 4 4 3 6% 7% 50%	7617
	11th to 20th	Day	17% 8% 2 5% 3 3 3 3 4 6% 46%	8062
	21st to end	Day	17% 7% 3 7% 5% 4 5% 4 5% 7% 36%	9047
June	1st to 10th	Day	12% 5% 2 5% 4 4 4 4 6% 8% 46%	2940
	11th to 20th	Day	15% 5% 2 6% 5% 4 5% 4 6% 8% 40%	3109
	21st to end	Day	11% 5% 2 6% 4 4 4 4 6% 8% 45%	3150
July	1st to 10th	Day	8% 5% 2 6% 5% 4 5% 5% 7% 10% 44%	6950
	11th to 20th	Day	9% 4 2 5% 3 3 4 3 5% 7% 55%	6441
	21st to end	Day	8% 4 2 5% 4 4 5% 4 6% 9% 49%	6422
August	1st to 10th	Day	13% 6% 3 6% 4 4 5% 4 5% 6% 43%	4234
	11th to 20th	Day	13% 7% 2 6% 5% 4 5% 4 7% 8% 39%	4171
	21st to end	Day	9% 4 2 5% 4 4 4 3 6% 8% 52%	4586
September	1st to 10th	Day	11% 5% 2 4 4 4 4 4 5% 7% 51%	2400
	11th to 20th	Day	10% 5% 1 5% 4 4 4 3 5% 7% 50%	2231
	21st to end	Day	13% 5% 2 4 3 3 4 4 5% 7% 51%	2190
October	1st to 10th	Day	14% 7% 2 5% 4 4 4 2 4 6% 48%	2000
	11th to 20th	Day	14% 9% 2 6% 4 3 4 3 4 5% 45%	2000
	21st to end	Day	16% 8% 2 8% 3 3 3 3 4 7% 42%	2195
November	1st to 10th	Day	13% 9% 2 7% 3 4 3 3 5% 7% 42%	1767
	11th to 20th	Day	10% 11% 4 11% 6% 4 4 3 5% 5% 36%	1680
	21st to end	Day	11% 10% 4 10% 6% 5% 3 3 6% 6% 36%	1680
December	1st to 10th	Day	6% 10% 5% 11% 9% 8% 4 4 6% 8% 30%	2690
	11th to 20th	Day	10% 12% 6% 11% 8% 8% 6% 4 5% 6% 23%	3088
	21st to end	Day	15% 12% 4 21% 6% 4 4 3 5% 6% 20%	4070
January	1st to 10th	Night	7% 10% 5% 16% 10% 7% 6% 5% 5% 5% 23%	8232
	11th to 20th	Night	3 9% 4 12% 8% 8% 12% 6% 7% 7% 23%	7708
	21st to end	Night	4 10% 6% 11% 5% 6% 6% 4 6% 5% 37%	8402
February	1st to 10th	Night	8% 12% 4 10% 7% 5% 5% 4 5% 7% 32%	2730
	11th to 20th	Night	8% 9% 4 9% 5% 5% 5% 5% 6% 6% 37%	2663
	21st to end	Night	9% 8% 3 8% 6% 6% 5% 4 5% 7% 38%	2185
March	1st to 10th	Night	10% 8% 3 6% 4 3 3 3 4 5% 52%	5060
	11th to 20th	Night	10% 7% 2 6% 4 4 5% 4 6% 8% 44%	5090
	21st to end	Night	23% 10% 3 9% 4 3 4 3 4 5% 31%	5588
April	1st to 10th	Night	15% 10% 3 7% 5% 3 4 4 5% 6% 39%	2170
	11th to 20th	Night	16% 9% 3 6% 4 4 4 3 5% 6% 40%	1954
	21st to end	Night	19% 9% 3 6% 3 3 4 3 5% 7% 39%	1890
May	1st to 10th	Night	11% 5% 2 5% 3 3 3 3 5% 6% 54%	5266
	11th to 20th	Night	15% 6% 2 4 3 3 3 2 4 5% 51%	4815
	21st to end	Night	19% 8% 3 6% 4 4 4 3 5% 6% 40%	5139
June	1st to 10th	Night	9% 4 1 4 3 3 4 4 6% 8% 55%	1680
	11th to 20th	Night	10% 5% 2 4 4 3 5% 5% 6% 8% 48%	1504
	21st to end	Night	8% 4 2 4 3 4 4 3 6% 7% 55%	1470
July	1st to 10th	Night	7% 3 1 5% 4 4 5% 4 7% 9% 51%	3248
	11th to 20th	Night	6% 3 2 4 3 4 4 3 6% 8% 56%	3637
	21st to end	Night	8% 5% 2 4 4 3 5% 3 5% 8% 53%	4449
August	1st to 10th	Night	13% 5% 2 4 3 3 4 3 4 7% 50%	2926
	11th to 20th	Night	12% 5% 2 5% 3 3 3 3 6% 8% 52%	2888
	21st to end	Night	8% 4 2 5% 4 3 4 3 5% 8% 54%	3319
September	1st to 10th	Night	8% 4 2 5% 3 3 4 2 4 6% 58%	2000
	11th to 20th	Night	9% 4 2 4 3 4 3 3 5% 7% 55%	2165
	21st to end	Night	10% 4 2 5% 2 3 4 3 5% 7% 56%	2200
October	1st to 10th	Night	14% 5% 2 4 3 3 3 3 4 6% 52%	2390
	11th to 20th	Night	15% 9% 2 6% 3 2 3 3 4 6% 48%	2400
	21st to end	Night	15% 9% 3 7% 3 3 3 3 4 7% 43%	2641
November	1st to 10th	Night	11% 7% 2 8% 4 5% 4 4 5% 5% 46%	2749
	11th to 20th	Night	10% 10% 4 9% 5% 4 4 4 4 5% 41%	2940
	21st to end	Night	11% 9% 3 9% 4 4 4 3 5% 6% 40%	2940
December	1st to 10th	Night	5% 8% 4 12% 8% 7% 5% 4 5% 7% 34%	4720
	11th to 20th	Night	11% 10% 5% 12% 8% 6% 5% 4 5% 6% 29%	5339
	21st to end	Night	16% 12% 5% 16% 6% 5% 5% 4 5% 5% 21%	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	67% 4 10% 12% 7%	4692
	11th to 20th	Day	55% 4 10% 19% 12%	5267
	21st to end	Day	48% 5% 16% 22% 9%	5812
February	1st to 10th	Day	56% 6% 15% 15% 8% 1	1890
	11th to 20th	Day	52% 7% 12% 19% 8% 2	1853
	21st to end	Day	49% 8% 13% 19% 10% 2	1641
March	1st to 10th	Day	40% 5% 16% 26% 12% 1	5014
	11th to 20th	Day	37% 5% 12% 30% 13% 2	5090
	21st to end	Day	61% 5% 11% 16% 6%	5585
April	1st to 10th	Day	49% 6% 15% 20% 9% 1	2449
	11th to 20th	Day	50% 6% 12% 20% 10% 1	2613
	21st to end	Day	52% 6% 11% 22% 9%	2730
May	1st to 10th	Day	31% 6% 12% 28% 22%	7655
	11th to 20th	Day	39% 5% 9% 22% 19% 6%	8066
	21st to end	Day	46% 6% 10% 25% 11% 1	9061
June	1st to 10th	Day	34% 8% 16% 27% 13% 1	2940
	11th to 20th	Day	41% 7% 13% 22% 16% 2	3109
	21st to end	Day	36% 8% 15% 26% 13% 2	3150
July	1st to 10th	Day	33% 8% 20% 28% 10% 1	6876
	11th to 20th	Day	28% 6% 14% 34% 17% 2	6364
	21st to end	Day	30% 7% 17% 29% 15% 1	6240
August	1st to 10th	Day	40% 7% 12% 27% 12% 2	4220
	11th to 20th	Day	40% 9% 15% 27% 8% 1	4210
	21st to end	Day	31% 6% 18% 28% 15% 2	4585
September	1st to 10th	Day	33% 6% 14% 29% 18% 1	2400
	11th to 20th	Day	32% 6% 17% 29% 13% 1	2231
	21st to end	Day	33% 6% 11% 31% 17% 2	2190
October	1st to 10th	Day	28% 4 8% 30% 29% 1	3260
	11th to 20th	Day	38% 4 13% 23% 20% 2	3240
	21st to end	Day	41% 4 13% 28% 13% 1	3522
November	1st to 10th	Day	41% 5% 15% 20% 16% 3	1767
	11th to 20th	Day	50% 5% 12% 21% 10% 1	1680
	21st to end	Day	48% 5% 16% 20% 10% 1	1680
December	1st to 10th	Day	52% 6% 15% 20% 7% 1	2690
	11th to 20th	Day	62% 5% 14% 14% 5%	3085
	21st to end	Day	65% 5% 11% 12% 6% 1	4070
January	1st to 10th	Night	61% 6% 10% 17% 6% 1	8233
	11th to 20th	Night	57% 5% 13% 14% 10% 1	7708
	21st to end	Night	45% 6% 13% 24% 13%	8402
February	1st to 10th	Night	50% 6% 13% 20% 9% 2	2730
	11th to 20th	Night	44% 7% 13% 22% 13% 2	2664
	21st to end	Night	45% 7% 13% 21% 11% 3	2185
March	1st to 10th	Night	36% 4 9% 35% 15% 2	5060
	11th to 20th	Night	35% 6% 12% 31% 15% 1	5090
	21st to end	Night	56% 5% 12% 19% 7% 1	5588
April	1st to 10th	Night	44% 7% 13% 24% 11% 1	2170
	11th to 20th	Night	44% 6% 10% 22% 17% 2	1954
	21st to end	Night	44% 7% 10% 24% 13% 2	1890
May	1st to 10th	Night	31% 5% 10% 32% 22% 1	5293
	11th to 20th	Night	35% 5% 7% 20% 23% 9%	4816
	21st to end	Night	44% 6% 10% 27% 12% 2	5149
June	1st to 10th	Night	27% 8% 18% 28% 17% 3	1680
	11th to 20th	Night	32% 8% 15% 22% 19% 3	1504
	21st to end	Night	26% 7% 17% 31% 18% 2	1470
July	1st to 10th	Night	28% 7% 20% 29% 15% 2	3215
	11th to 20th	Night	25% 6% 15% 34% 18% 2	3594
	21st to end	Night	30% 7% 16% 31% 15% 1	4320
August	1st to 10th	Night	35% 6% 14% 27% 16% 3	2916
	11th to 20th	Night	32% 7% 15% 34% 12% 1	2915
	21st to end	Night	29% 7% 18% 27% 17% 2	3319
September	1st to 10th	Night	27% 5% 14% 31% 21% 2	2000
	11th to 20th	Night	28% 6% 15% 33% 16% 2	2165
	21st to end	Night	28% 6% 11% 30% 23% 2	2200
October	1st to 10th	Night	23% 3 7% 29% 35% 3	3910
	11th to 20th	Night	28% 3 13% 29% 22% 4	3899
	21st to end	Night	41% 4 12% 28% 14% 1	4265
November	1st to 10th	Night	39% 5% 14% 22% 17% 3	2749
	11th to 20th	Night	45% 6% 12% 22% 13% 2	2940
	21st to end	Night	44% 6% 16% 22% 11% 1	2940
December	1st to 10th	Night	49% 5% 16% 22% 8%	4720
	11th to 20th	Night	55% 6% 15% 19% 4	5341
	21st to end	Night	63% 6% 10% 16% 4	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	15% 13% 38% 22% 10% 2	330
	11th to 20th	Day	18% 15% 38% 23% 4 1	330
	21st to end	Day	12% 16% 39% 24% 9% 1	363
February	1st to 10th	Day	15% 18% 44% 19% 4 1	330
	11th to 20th	Day	14% 15% 40% 25% 5% 1	330
	21st to end	Day	18% 16% 44% 19% 2	273
March	1st to 10th	Day	20% 14% 42% 20% 3	330
	11th to 20th	Day	24% 12% 35% 21% 8% 1	330
	21st to end	Day	27% 15% 30% 21% 6% 1	363
April	1st to 10th	Day	26% 18% 33% 18% 5%	469
	11th to 20th	Day	25% 16% 32% 20% 6% 1	651
	21st to end	Day	25% 17% 28% 20% 9% 2	750
May	1st to 10th	Day	19% 14% 32% 24% 9% 2	753
	11th to 20th	Day	22% 11% 29% 24% 11% 3	775
	21st to end	Day	17% 10% 29% 30% 13% 2	844
June	1st to 10th	Day	10% 8% 28% 31% 19% 4	780
	11th to 20th	Day	15% 9% 36% 26% 10% 3	780
	21st to end	Day	11% 9% 33% 30% 14% 2	780
July	1st to 10th	Day	7% 6% 23% 33% 25% 6%	771
	11th to 20th	Day	7% 4 31% 32% 20% 6%	744
	21st to end	Day	7% 3 27% 40% 19% 5%	794
August	1st to 10th	Day	10% 5% 22% 37% 22% 4	726
	11th to 20th	Day	12% 4 25% 33% 22% 4	715
	21st to end	Day	8% 5% 29% 35% 18% 5%	753
September	1st to 10th	Day	14% 7% 29% 28% 18% 4	530
	11th to 20th	Day	9% 5% 34% 35% 14% 3	361
	21st to end	Day	15% 12% 30% 22% 15% 5%	330
October	1st to 10th	Day	18% 11% 32% 23% 12% 4	330
	11th to 20th	Day	17% 16% 41% 18% 7% 1	330
	21st to end	Day	22% 17% 37% 19% 5%	363
November	1st to 10th	Day	21% 14% 36% 22% 5% 3	330
	11th to 20th	Day	15% 23% 41% 16% 4	330
	21st to end	Day	19% 18% 38% 19% 5%	330
December	1st to 10th	Day	14% 14% 43% 22% 8%	330
	11th to 20th	Day	16% 18% 39% 22% 5%	330
	21st to end	Day	25% 17% 37% 20% 2	363
January	1st to 10th	Night	11% 12% 45% 24% 7% 1	1050
	11th to 20th	Night	12% 15% 41% 26% 5% 1	1050
	21st to end	Night	15% 14% 40% 26% 5%	1155
February	1st to 10th	Night	14% 14% 43% 24% 5% 1	1050
	11th to 20th	Night	12% 16% 42% 23% 6%	1029
	21st to end	Night	13% 14% 41% 23% 7% 1	801
March	1st to 10th	Night	15% 13% 42% 24% 7%	648
	11th to 20th	Night	17% 14% 40% 23% 5%	630
	21st to end	Night	23% 12% 30% 26% 8% 1	693
April	1st to 10th	Night	20% 14% 40% 22% 4	630
	11th to 20th	Night	20% 14% 35% 25% 6% 1	623
	21st to end	Night	21% 12% 34% 24% 7% 1	630
May	1st to 10th	Night	16% 10% 35% 31% 8%	630
	11th to 20th	Night	18% 9% 33% 30% 9% 1	621
	21st to end	Night	18% 8% 29% 34% 11%	683
June	1st to 10th	Night	9% 6% 30% 42% 13%	630
	11th to 20th	Night	11% 6% 34% 40% 9%	630
	21st to end	Night	10% 5% 27% 46% 12%	630
July	1st to 10th	Night	5% 2 26% 40% 25% 1	615
	11th to 20th	Night	3 2 28% 44% 21% 1	597
	21st to end	Night	5% 2 24% 47% 20% 2	657
August	1st to 10th	Night	9% 3 22% 45% 21% 1	597
	11th to 20th	Night	8% 4 23% 42% 21% 3	594
	21st to end	Night	8% 3 27% 40% 20% 2	660
September	1st to 10th	Night	9% 5% 27% 42% 15% 2	600
	11th to 20th	Night	10% 5% 33% 38% 13% 2	600
	21st to end	Night	11% 11% 32% 31% 14% 1	600
October	1st to 10th	Night	16% 9% 33% 31% 10% 1	790
	11th to 20th	Night	17% 14% 36% 25% 7%	800
	21st to end	Night	21% 13% 33% 26% 7%	881
November	1st to 10th	Night	15% 13% 38% 26% 8%	1025
	11th to 20th	Night	15% 16% 41% 23% 5% 1	1050
	21st to end	Night	16% 14% 41% 23% 6%	1050
December	1st to 10th	Night	13% 13% 43% 25% 6%	1050
	11th to 20th	Night	19% 13% 37% 25% 6% 1	1050
	21st to end	Night	22% 14% 38% 23% 4	1155

Page generated at 2026-07-13 02:14:52. Version ac07

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