Prairie Peak
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Prairie Peak clear sky chart from 2005-11-06 to 2025-04-26.

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	18% 10% 3 7% 4 4 4 3 5% 6% 36%	117877
	Night	19% 11% 3 8% 4 4 4 3 4 5% 35%	119564
Transparency	Day	49% 6% 10% 17% 13% 5%	117625
	Night	52% 5% 10% 16% 12% 5%	119405
Seeing	Day	25% 12% 24% 24% 12% 3	15300
	Night	26% 6% 15% 30% 20% 2	24403

By Month

Percentage Cloud Cover SW (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	36% 17% 5% 11% 7% 4 4 2 3 3 8%	3639
	11th to 20th	Day	26% 10% 3 7% 4 3 3 2 4 5% 32%	3755
	21st to end	Day	26% 9% 3 7% 5% 4 4 4 4 5% 29%	4510
February	1st to 10th	Day	28% 16% 4 9% 7% 5% 5% 4 4 5% 13%	1800
	11th to 20th	Day	27% 15% 5% 10% 5% 4 4 4 5% 5% 16%	1755
	21st to end	Day	27% 18% 5% 9% 5% 4 3 4 4 3 17%	1540
March	1st to 10th	Day	19% 17% 4 9% 6% 6% 6% 4 5% 6% 18%	4868
	11th to 20th	Day	26% 16% 4 9% 5% 4 3 2 3 3 25%	5000
	21st to end	Day	24% 16% 5% 12% 7% 6% 5% 4 5% 5% 10%	5515
April	1st to 10th	Day	27% 17% 5% 10% 7% 5% 4 3 5% 4 15%	2400
	11th to 20th	Day	24% 14% 3 8% 6% 4 4 3 4 5% 24%	2384
	21st to end	Day	21% 12% 4 8% 7% 4 5% 3 6% 7% 24%	2538
May	1st to 10th	Day	18% 10% 4 9% 5% 4 4 4 5% 6% 32%	4217
	11th to 20th	Day	11% 6% 2 5% 3 2 3 3 6% 7% 51%	4377
	21st to end	Day	15% 8% 3 7% 5% 6% 7% 5% 8% 7% 28%	4813
June	1st to 10th	Day	21% 10% 3 7% 5% 4 4 3 5% 6% 32%	2660
	11th to 20th	Day	14% 10% 3 8% 5% 5% 6% 4 7% 8% 31%	2660
	21st to end	Day	8% 5% 2 5% 4 3 4 3 6% 7% 53%	2660
July	1st to 10th	Day	3 2 1 3 2 2 2 2 4 5% 75%	4420
	11th to 20th	Day	4 3 1 3 2 2 2 2 3 5% 73%	4420
	21st to end	Day	3 3 1 2 2 2 2 2 3 5% 76%	4643
August	1st to 10th	Day	2 3 1 3 3 3 3 3 4 7% 68%	4091
	11th to 20th	Day	5% 4 2 4 3 4 5% 4 7% 8% 54%	4026
	21st to end	Day	7% 4 1 4 3 4 4 4 5% 7% 57%	4335
September	1st to 10th	Day	5% 3 1 3 3 2 3 3 5% 7% 65%	2280
	11th to 20th	Day	10% 6% 2 7% 4 4 4 4 6% 8% 45%	2226
	21st to end	Day	14% 7% 2 6% 4 3 4 3 4 6% 46%	2030
October	1st to 10th	Day	12% 8% 2 6% 4 3 3 2 4 5% 51%	3180
	11th to 20th	Day	16% 8% 3 8% 6% 6% 5% 5% 6% 8% 30%	3161
	21st to end	Day	21% 11% 4 9% 5% 5% 6% 4 6% 8% 21%	3448
November	1st to 10th	Day	28% 10% 6% 10% 5% 4 4 3 5% 6% 17%	1674
	11th to 20th	Day	30% 11% 4 8% 5% 6% 4 4 5% 5% 17%	1600
	21st to end	Day	26% 11% 4 10% 6% 4 4 4 5% 6% 21%	1600
December	1st to 10th	Day	20% 9% 3 8% 5% 4 3 4 4 7% 35%	2620
	11th to 20th	Day	31% 15% 5% 12% 5% 4 5% 3 5% 5% 10%	3028
	21st to end	Day	34% 19% 5% 13% 6% 5% 4 2 3 3 7%	4004
January	1st to 10th	Night	37% 16% 4 12% 6% 4 3 2 2 3 10%	6306
	11th to 20th	Night	25% 13% 4 9% 4 3 3 2 3 4 29%	6207
	21st to end	Night	29% 12% 3 6% 3 2 2 2 3 4 33%	6468
February	1st to 10th	Night	23% 16% 4 10% 6% 5% 5% 4 5% 5% 17%	2600
	11th to 20th	Night	23% 15% 4 8% 6% 5% 3 3 4 5% 24%	2532
	21st to end	Night	24% 16% 4 9% 5% 5% 4 3 5% 4 21%	2089
March	1st to 10th	Night	18% 16% 4 10% 5% 6% 5% 4 5% 5% 21%	5011
	11th to 20th	Night	21% 17% 4 8% 5% 4 3 3 3 4 28%	5000
	21st to end	Night	24% 19% 4 10% 5% 4 4 3 5% 5% 16%	5459
April	1st to 10th	Night	23% 14% 4 10% 5% 6% 4 2 5% 5% 21%	2000
	11th to 20th	Night	17% 12% 4 8% 4 3 4 5% 5% 6% 32%	1959
	21st to end	Night	18% 9% 3 8% 6% 5% 5% 4 5% 7% 32%	1758
May	1st to 10th	Night	20% 8% 3 7% 4 3 3 3 4 4 40%	2746
	11th to 20th	Night	8% 5% 2 5% 4 3 3 3 4 6% 56%	2516
	21st to end	Night	10% 9% 3 7% 4 5% 5% 4 7% 8% 40%	2762
June	1st to 10th	Night	16% 9% 3 4 4 5% 3 4 6% 6% 39%	1520
	11th to 20th	Night	10% 5% 3 6% 4 3 3 5% 6% 8% 47%	1520
	21st to end	Night	7% 4 2 4 3 3 3 3 4 6% 61%	1520
July	1st to 10th	Night	1 2 1 2 1 1 1 1 2 5% 82%	2540
	11th to 20th	Night	3 3 1 2 2 1 2 2 4 6% 75%	2540
	21st to end	Night	2 2 1 2 2 2 2 2 3 5% 77%	2910
August	1st to 10th	Night	1 2 1 2 2 2 3 3 6% 8% 72%	2848
	11th to 20th	Night	3 2 1 4 4 4 4 4 6% 9% 59%	2812
	21st to end	Night	4 4 1 5% 2 3 3 2 4 6% 65%	3338
September	1st to 10th	Night	5% 3 1 3 2 2 2 2 4 6% 68%	1900
	11th to 20th	Night	8% 5% 2 5% 4 3 4 3 5% 7% 54%	1951
	21st to end	Night	10% 6% 2 5% 3 3 3 3 5% 7% 53%	2149
October	1st to 10th	Night	7% 5% 2 6% 3 4 4 3 4 6% 55%	3800
	11th to 20th	Night	14% 7% 3 7% 5% 5% 5% 4 7% 9% 34%	3777
	21st to end	Night	24% 10% 4 9% 5% 5% 4 4 5% 5% 26%	4121
November	1st to 10th	Night	27% 11% 3 8% 5% 4 5% 3 4 6% 25%	2617
	11th to 20th	Night	30% 12% 4 10% 5% 4 4 3 4 5% 19%	2800
	21st to end	Night	21% 10% 3 8% 5% 6% 5% 4 5% 5% 27%	2800
December	1st to 10th	Night	17% 9% 3 6% 5% 4 4 4 5% 6% 36%	4560
	11th to 20th	Night	33% 15% 5% 11% 6% 5% 4 2 3 4 12%	5176
	21st to end	Night	33% 16% 4 11% 7% 5% 4 3 3 3 11%	6952

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	80% 6% 4 5% 4 1	3639
	11th to 20th	Day	54% 5% 6% 16% 17% 3	3755
	21st to end	Day	58% 5% 5% 10% 16% 6%	4510
February	1st to 10th	Day	72% 6% 7% 9% 5%	1800
	11th to 20th	Day	69% 7% 10% 7% 5% 2	1764
	21st to end	Day	72% 4 8% 9% 6% 2	1540
March	1st to 10th	Day	65% 6% 11% 13% 4	4868
	11th to 20th	Day	66% 4 6% 17% 8%	5000
	21st to end	Day	74% 7% 9% 7% 3	5515
April	1st to 10th	Day	72% 5% 9% 10% 4	2400
	11th to 20th	Day	63% 5% 9% 13% 7% 2	2387
	21st to end	Day	59% 7% 11% 15% 7% 1	2538
May	1st to 10th	Day	52% 7% 12% 17% 12%	4217
	11th to 20th	Day	32% 5% 16% 31% 15% 1	4380
	21st to end	Day	49% 11% 24% 15% 2	4814
June	1st to 10th	Day	53% 6% 14% 20% 6%	2660
	11th to 20th	Day	49% 8% 18% 18% 6%	2660
	21st to end	Day	31% 5% 17% 29% 14% 3	2660
July	1st to 10th	Day	15% 3 10% 14% 27% 31%	4351
	11th to 20th	Day	16% 2 6% 19% 33% 23%	4345
	21st to end	Day	13% 3 10% 27% 39% 9%	4496
August	1st to 10th	Day	17% 5% 9% 28% 29% 11%	4076
	11th to 20th	Day	25% 8% 15% 33% 15% 3	4065
	21st to end	Day	27% 5% 12% 25% 22% 8%	4334
September	1st to 10th	Day	21% 4 10% 32% 21% 13%	2280
	11th to 20th	Day	36% 8% 13% 21% 17% 6%	2226
	21st to end	Day	39% 6% 11% 23% 17% 5%	2030
October	1st to 10th	Day	37% 5% 6% 17% 27% 9%	3180
	11th to 20th	Day	51% 8% 13% 16% 11% 1	3161
	21st to end	Day	59% 6% 8% 15% 11% 1	3448
November	1st to 10th	Day	68% 6% 7% 13% 5%	1674
	11th to 20th	Day	68% 8% 8% 7% 6% 3	1600
	21st to end	Day	64% 6% 7% 8% 12% 3	1600
December	1st to 10th	Day	50% 4 7% 12% 20% 6%	2620
	11th to 20th	Day	76% 6% 9% 7% 2	3028
	21st to end	Day	82% 6% 5% 4 2 1	4004
January	1st to 10th	Night	80% 4 4 5% 5% 1	6306
	11th to 20th	Night	58% 4 7% 15% 13% 3	6207
	21st to end	Night	58% 2 4 10% 16% 9%	6468
February	1st to 10th	Night	69% 6% 9% 11% 4 1	2600
	11th to 20th	Night	64% 6% 11% 10% 7% 2	2534
	21st to end	Night	67% 4 9% 11% 7% 2	2089
March	1st to 10th	Night	65% 5% 11% 13% 4 2	5011
	11th to 20th	Night	62% 5% 8% 16% 7% 1	5000
	21st to end	Night	70% 6% 12% 10% 1	5459
April	1st to 10th	Night	66% 6% 11% 12% 5%	2000
	11th to 20th	Night	52% 8% 14% 17% 6% 3	1959
	21st to end	Night	53% 6% 13% 18% 7% 2	1758
May	1st to 10th	Night	47% 6% 13% 22% 10% 1	2746
	11th to 20th	Night	31% 4 15% 33% 14% 4	2516
	21st to end	Night	40% 10% 30% 17% 3	2762
June	1st to 10th	Night	45% 8% 14% 29% 4 1	1520
	11th to 20th	Night	34% 7% 22% 28% 8% 1	1520
	21st to end	Night	26% 5% 18% 32% 14% 4	1520
July	1st to 10th	Night	11% 3 11% 17% 24% 35%	2500
	11th to 20th	Night	15% 3 8% 18% 25% 32%	2492
	21st to end	Night	14% 3 10% 27% 37% 10%	2819
August	1st to 10th	Night	13% 5% 13% 27% 28% 13%	2839
	11th to 20th	Night	25% 8% 16% 33% 15% 5%	2839
	21st to end	Night	22% 5% 10% 31% 24% 8%	3338
September	1st to 10th	Night	20% 4 10% 28% 25% 13%	1900
	11th to 20th	Night	32% 5% 13% 25% 16% 9%	1951
	21st to end	Night	32% 5% 14% 23% 17% 9%	2149
October	1st to 10th	Night	31% 5% 7% 24% 25% 7%	3800
	11th to 20th	Night	47% 7% 14% 19% 10% 2	3777
	21st to end	Night	61% 5% 7% 15% 8% 3	4121
November	1st to 10th	Night	61% 8% 8% 14% 9% 1	2617
	11th to 20th	Night	68% 6% 8% 9% 7% 3	2800
	21st to end	Night	58% 7% 10% 9% 11% 6%	2800
December	1st to 10th	Night	46% 5% 8% 15% 22% 5%	4560
	11th to 20th	Night	76% 6% 7% 7% 3	5176
	21st to end	Night	77% 7% 6% 6% 2 1	6952

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	48% 16% 19% 11% 8%	200
	11th to 20th	Day	40% 12% 22% 15% 11% 1	250
	21st to end	Day	38% 12% 18% 19% 11% 2	440
February	1st to 10th	Day	40% 15% 18% 19% 7% 1	400
	11th to 20th	Day	43% 15% 20% 16% 5% 1	395
	21st to end	Day	42% 14% 20% 18% 6% 1	359
March	1st to 10th	Day	40% 16% 20% 17% 6%	500
	11th to 20th	Day	39% 12% 21% 18% 8% 2	500
	21st to end	Day	41% 16% 19% 16% 7% 1	550
April	1st to 10th	Day	38% 16% 19% 18% 8% 1	500
	11th to 20th	Day	34% 18% 23% 17% 6% 3	492
	21st to end	Day	29% 17% 25% 19% 7% 2	481
May	1st to 10th	Day	22% 16% 30% 19% 10% 3	463
	11th to 20th	Day	30% 11% 21% 25% 9% 3	488
	21st to end	Day	22% 11% 24% 25% 16% 3	529
June	1st to 10th	Day	24% 10% 26% 24% 13% 2	490
	11th to 20th	Day	20% 19% 29% 22% 10% 1	490
	21st to end	Day	9% 9% 28% 37% 16% 2	490
July	1st to 10th	Day	7% 7% 32% 34% 17% 3	486
	11th to 20th	Day	5% 8% 30% 36% 17% 3	484
	21st to end	Day	4 5% 27% 40% 20% 4	531
August	1st to 10th	Day	3 4 30% 38% 20% 6%	487
	11th to 20th	Day	5% 5% 22% 34% 29% 6%	477
	21st to end	Day	8% 8% 28% 33% 18% 4	539
September	1st to 10th	Day	7% 8% 30% 32% 20% 3	490
	11th to 20th	Day	17% 8% 24% 31% 16% 4	490
	21st to end	Day	18% 13% 24% 32% 10% 4	490
October	1st to 10th	Day	20% 12% 26% 23% 15% 4	490
	11th to 20th	Day	22% 12% 20% 23% 18% 4	490
	21st to end	Day	32% 14% 22% 20% 9% 4	539
November	1st to 10th	Day	36% 13% 20% 20% 7% 3	270
	11th to 20th	Day	38% 12% 22% 19% 9% 2	200
	21st to end	Day	38% 15% 16% 18% 14% 1	200
December	1st to 10th	Day	35% 11% 17% 24% 10% 5%	200
	11th to 20th	Day	48% 9% 21% 15% 7% 1	200
	21st to end	Day	42% 15% 18% 17% 8%	220
January	1st to 10th	Night	46% 9% 15% 18% 11% 2	800
	11th to 20th	Night	38% 8% 15% 21% 15% 3	800
	21st to end	Night	35% 4 13% 29% 16% 3	880
February	1st to 10th	Night	34% 9% 14% 28% 14% 2	800
	11th to 20th	Night	35% 7% 16% 28% 14% 1	784
	21st to end	Night	38% 10% 15% 23% 13%	660
March	1st to 10th	Night	33% 9% 20% 27% 10% 1	800
	11th to 20th	Night	33% 9% 16% 26% 15% 2	800
	21st to end	Night	37% 10% 16% 23% 13% 1	880
April	1st to 10th	Night	34% 9% 16% 25% 15% 1	800
	11th to 20th	Night	25% 11% 21% 26% 15% 2	771
	21st to end	Night	23% 8% 20% 29% 19% 2	586
May	1st to 10th	Night	19% 5% 21% 33% 19% 2	508
	11th to 20th	Night	17% 5% 16% 36% 24% 2	374
	21st to end	Night	17% 4 18% 36% 22% 2	411
June	1st to 10th	Night	21% 4 16% 32% 26% 1	380
	11th to 20th	Night	14% 4 20% 43% 18% 2	380
	21st to end	Night	12% 2 14% 45% 27% 1	380
July	1st to 10th	Night	4 3 12% 48% 33%	370
	11th to 20th	Night	6% 2 13% 53% 24% 1	368
	21st to end	Night	3 2 10% 47% 37% 2	503
August	1st to 10th	Night	3 2 9% 44% 37% 6%	567
	11th to 20th	Night	5% 1 9% 38% 43% 5%	564
	21st to end	Night	7% 3 17% 40% 30% 3	741
September	1st to 10th	Night	7% 4 16% 40% 31% 2	760
	11th to 20th	Night	11% 3 16% 32% 32% 5%	760
	21st to end	Night	14% 5% 13% 39% 25% 3	760
October	1st to 10th	Night	16% 6% 18% 31% 25% 3	760
	11th to 20th	Night	23% 5% 12% 33% 24% 5%	760
	21st to end	Night	30% 7% 17% 24% 16% 4	836
November	1st to 10th	Night	34% 7% 14% 29% 15% 1	780
	11th to 20th	Night	39% 9% 16% 21% 13% 1	800
	21st to end	Night	27% 9% 17% 28% 16% 3	800
December	1st to 10th	Night	29% 6% 17% 27% 19% 3	800
	11th to 20th	Night	42% 7% 14% 22% 14% 1	800
	21st to end	Night	42% 11% 15% 22% 9% 1	880

Page generated at 2025-04-23 06:25:07. Version ac07

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