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 2026-08-30.

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	15% 9% 3 7% 4 4 4 3 5% 6% 40%	153304
	Night	17% 10% 3 7% 4 4 4 3 4 6% 37%	146299
Transparency	Day	45% 6% 11% 19% 14% 5%	148080
	Night	50% 5% 11% 17% 12% 5%	142523
Seeing	Day	24% 12% 24% 24% 12% 3	17074
	Night	26% 7% 16% 30% 19% 2	25956

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	33% 18% 5% 12% 7% 5% 4 3 3 3 8%	4722
	11th to 20th	Day	20% 8% 3 5% 3 3 3 3 4 6% 43%	4897
	21st to end	Day	23% 10% 3 9% 6% 5% 5% 4 4 4 27%	5843
February	1st to 10th	Day	28% 15% 4 9% 7% 5% 5% 4 4 6% 14%	1890
	11th to 20th	Day	27% 15% 5% 10% 5% 4 4 4 5% 5% 16%	1845
	21st to end	Day	28% 18% 5% 9% 5% 4 3 4 4 3 18%	1615
March	1st to 10th	Day	19% 17% 4 9% 6% 6% 6% 4 5% 6% 17%	4976
	11th to 20th	Day	26% 16% 4 9% 5% 4 3 2 3 3 25%	5110
	21st to end	Day	24% 16% 5% 12% 7% 6% 5% 4 5% 5% 11%	5636
April	1st to 10th	Day	26% 16% 5% 10% 7% 5% 4 3 5% 4 15%	2520
	11th to 20th	Day	24% 14% 3 9% 6% 4 4 3 4 5% 23%	2505
	21st to end	Day	20% 12% 3 8% 6% 5% 5% 3 6% 7% 25%	2730
May	1st to 10th	Day	11% 7% 3 8% 5% 5% 5% 4 6% 8% 41%	7810
	11th to 20th	Day	10% 7% 3 8% 5% 5% 5% 4 7% 8% 38%	8160
	21st to end	Day	11% 7% 3 6% 5% 5% 6% 5% 7% 8% 38%	8992
June	1st to 10th	Day	19% 10% 3 7% 5% 4 4 4 5% 6% 34%	2940
	11th to 20th	Day	13% 9% 3 8% 5% 5% 6% 4 7% 8% 33%	2940
	21st to end	Day	9% 6% 2 5% 4 3 4 3 6% 7% 51%	2940
July	1st to 10th	Day	2 2 1 2 2 2 2 2 4 6% 75%	8219
	11th to 20th	Day	3 3 1 2 2 2 2 2 3 5% 75%	8220
	21st to end	Day	3 3 1 3 2 2 2 2 4 7% 70%	8645
August	1st to 10th	Day	2 3 1 4 3 3 3 3 4 8% 66%	5907
	11th to 20th	Day	5% 4 2 4 3 4 4 4 6% 8% 56%	5926
	21st to end	Day	6% 4 2 4 3 4 4 4 6% 8% 55%	6318
September	1st to 10th	Day	5% 3 2 4 3 2 3 3 5% 7% 63%	2400
	11th to 20th	Day	10% 6% 2 6% 4 4 4 4 6% 8% 46%	2343
	21st to end	Day	14% 6% 2 6% 4 3 4 3 4 6% 47%	2137
October	1st to 10th	Day	12% 8% 3 6% 4 4 3 2 4 5% 50%	3280
	11th to 20th	Day	15% 8% 3 8% 5% 6% 5% 5% 6% 8% 31%	3261
	21st to end	Day	21% 11% 4 10% 5% 5% 6% 4 6% 8% 21%	3558
November	1st to 10th	Day	29% 10% 6% 10% 5% 4 4 3 6% 6% 17%	1759
	11th to 20th	Day	30% 12% 5% 9% 5% 6% 4 3 5% 5% 16%	1680
	21st to end	Day	26% 11% 4 10% 6% 4 4 4 5% 6% 20%	1680
December	1st to 10th	Day	21% 9% 3 8% 5% 4 3 4 4 7% 34%	2700
	11th to 20th	Day	31% 15% 5% 12% 5% 4 5% 3 5% 5% 10%	3108
	21st to end	Day	33% 19% 4 13% 6% 5% 4 3 3 4 7%	4092
January	1st to 10th	Night	35% 17% 4 12% 6% 4 3 2 3 3 10%	8172
	11th to 20th	Night	19% 10% 3 7% 4 3 3 2 3 4 40%	8068
	21st to end	Night	25% 12% 4 8% 4 3 3 2 3 4 31%	8371
February	1st to 10th	Night	23% 16% 4 10% 6% 5% 4 4 5% 5% 18%	2730
	11th to 20th	Night	23% 15% 4 7% 6% 5% 4 3 4 5% 24%	2662
	21st to end	Night	25% 16% 4 9% 5% 5% 4 3 5% 4 21%	2190
March	1st to 10th	Night	19% 16% 4 10% 5% 6% 5% 4 5% 5% 20%	5123
	11th to 20th	Night	22% 17% 4 9% 5% 4 3 2 3 4 28%	5110
	21st to end	Night	24% 19% 4 10% 5% 4 4 3 5% 5% 16%	5580
April	1st to 10th	Night	22% 15% 4 10% 5% 6% 4 3 5% 6% 22%	2100
	11th to 20th	Night	17% 12% 4 8% 4 3 4 5% 5% 6% 31%	2058
	21st to end	Night	17% 9% 3 8% 5% 5% 5% 4 5% 7% 32%	1890
May	1st to 10th	Night	13% 5% 2 5% 4 4 4 3 6% 9% 45%	5125
	11th to 20th	Night	9% 9% 3 9% 6% 5% 4 4 6% 6% 39%	4700
	21st to end	Night	8% 8% 3 7% 4 4 4 4 7% 9% 43%	5181
June	1st to 10th	Night	15% 9% 3 4 4 5% 3 3 6% 6% 41%	1680
	11th to 20th	Night	10% 5% 3 5% 4 3 3 5% 6% 8% 49%	1680
	21st to end	Night	8% 4 2 4 3 3 3 3 4 6% 59%	1680
July	1st to 10th	Night	1 1 1 1 1 1 2 2 4 7% 78%	4740
	11th to 20th	Night	2 2 1 2 2 2 2 2 3 5% 76%	4740
	21st to end	Night	2 3 1 3 3 2 3 2 4 8% 68%	5442
August	1st to 10th	Night	2 3 1 3 3 3 4 3 6% 7% 66%	4125
	11th to 20th	Night	6% 4 2 4 4 4 4 4 5% 8% 57%	4142
	21st to end	Night	4 3 1 5% 3 3 3 3 5% 7% 62%	4870
September	1st to 10th	Night	5% 3 1 3 2 3 3 2 5% 7% 66%	2000
	11th to 20th	Night	8% 4 2 5% 4 3 4 3 5% 7% 55%	2054
	21st to end	Night	10% 6% 2 5% 3 3 3 3 5% 7% 54%	2262
October	1st to 10th	Night	7% 5% 2 6% 3 4 4 3 4 6% 54%	3920
	11th to 20th	Night	14% 7% 3 8% 5% 5% 5% 4 7% 9% 34%	3897
	21st to end	Night	23% 10% 4 9% 5% 5% 4 4 5% 5% 26%	4253
November	1st to 10th	Night	27% 11% 3 8% 5% 4 5% 3 4 6% 24%	2752
	11th to 20th	Night	30% 12% 4 10% 5% 4 4 3 4 5% 19%	2940
	21st to end	Night	21% 10% 3 8% 5% 6% 6% 4 5% 5% 27%	2940
December	1st to 10th	Night	18% 9% 3 6% 4 4 4 4 5% 6% 36%	4700
	11th to 20th	Night	33% 15% 5% 11% 6% 5% 4 2 3 4 12%	5316
	21st to end	Night	32% 16% 4 11% 7% 5% 4 3 3 3 11%	7106

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	81% 5% 5% 5% 4 1	4723
	11th to 20th	Day	43% 4 5% 14% 20% 14%	4897
	21st to end	Day	60% 4 5% 9% 14% 7%	5843
February	1st to 10th	Day	71% 6% 8% 10% 5% 1	1890
	11th to 20th	Day	69% 7% 9% 7% 5% 2	1854
	21st to end	Day	71% 4 7% 8% 7% 2	1615
March	1st to 10th	Day	65% 6% 11% 13% 4	4976
	11th to 20th	Day	66% 4 5% 16% 8% 1	5110
	21st to end	Day	74% 7% 9% 7% 3	5636
April	1st to 10th	Day	71% 5% 10% 10% 4	2520
	11th to 20th	Day	64% 6% 9% 13% 7% 2	2508
	21st to end	Day	58% 7% 11% 16% 7% 1	2730
May	1st to 10th	Day	40% 6% 10% 30% 13%	7810
	11th to 20th	Day	42% 7% 17% 24% 8% 1	8163
	21st to end	Day	40% 9% 24% 23% 4	8994
June	1st to 10th	Day	51% 6% 14% 21% 7% 1	2940
	11th to 20th	Day	47% 8% 16% 21% 8% 1	2940
	21st to end	Day	33% 5% 17% 28% 14% 3	2940
July	1st to 10th	Day	13% 4 12% 31% 24% 17%	8151
	11th to 20th	Day	15% 2 7% 16% 40% 20%	8145
	21st to end	Day	17% 4 13% 35% 27% 5%	8451
August	1st to 10th	Day	17% 5% 10% 27% 29% 11%	4336
	11th to 20th	Day	25% 8% 15% 33% 15% 3	4325
	21st to end	Day	27% 5% 12% 26% 22% 9%	4585
September	1st to 10th	Day	22% 4 11% 31% 20% 12%	2400
	11th to 20th	Day	35% 8% 13% 22% 17% 6%	2343
	21st to end	Day	38% 6% 11% 23% 18% 5%	2137
October	1st to 10th	Day	37% 5% 6% 17% 26% 9%	3280
	11th to 20th	Day	51% 8% 12% 16% 12% 1	3261
	21st to end	Day	59% 6% 8% 15% 11% 1	3558
November	1st to 10th	Day	68% 6% 7% 13% 5%	1759
	11th to 20th	Day	69% 8% 8% 7% 5% 3	1680
	21st to end	Day	64% 6% 7% 8% 12% 3	1680
December	1st to 10th	Day	51% 4 7% 12% 20% 5%	2700
	11th to 20th	Day	75% 6% 9% 7% 2	3108
	21st to end	Day	81% 6% 5% 5% 2 1	4092
January	1st to 10th	Night	80% 4 5% 6% 4 1	8172
	11th to 20th	Night	48% 3 6% 12% 16% 15%	8068
	21st to end	Night	59% 2 4 8% 16% 10%	8371
February	1st to 10th	Night	68% 6% 9% 11% 5% 1	2730
	11th to 20th	Night	64% 6% 10% 11% 7% 2	2664
	21st to end	Night	66% 4 9% 11% 7% 2	2190
March	1st to 10th	Night	65% 5% 11% 13% 4 2	5123
	11th to 20th	Night	62% 5% 8% 16% 7% 1	5110
	21st to end	Night	70% 6% 11% 10% 2	5580
April	1st to 10th	Night	65% 6% 11% 13% 4	2100
	11th to 20th	Night	53% 7% 14% 17% 6% 3	2058
	21st to end	Night	52% 6% 13% 19% 8% 2	1890
May	1st to 10th	Night	37% 8% 12% 28% 14% 1	5123
	11th to 20th	Night	46% 6% 14% 25% 7% 2	4700
	21st to end	Night	36% 8% 29% 23% 4	5182
June	1st to 10th	Night	43% 8% 14% 29% 6% 1	1680
	11th to 20th	Night	33% 7% 21% 29% 10% 1	1680
	21st to end	Night	28% 6% 17% 31% 15% 4	1680
July	1st to 10th	Night	10% 5% 14% 31% 22% 19%	4700
	11th to 20th	Night	14% 3 10% 15% 31% 27%	4692
	21st to end	Night	19% 6% 14% 29% 26% 6%	5324
August	1st to 10th	Night	13% 5% 13% 27% 28% 14%	3019
	11th to 20th	Night	25% 7% 16% 33% 14% 5%	3019
	21st to end	Night	22% 5% 10% 31% 24% 8%	3528
September	1st to 10th	Night	21% 5% 10% 28% 23% 12%	2000
	11th to 20th	Night	31% 5% 13% 26% 16% 9%	2054
	21st to end	Night	32% 5% 14% 23% 18% 9%	2262
October	1st to 10th	Night	32% 5% 7% 24% 25% 7%	3920
	11th to 20th	Night	47% 7% 14% 19% 11% 2	3897
	21st to end	Night	60% 5% 7% 16% 8% 3	4253
November	1st to 10th	Night	62% 7% 8% 14% 8% 1	2752
	11th to 20th	Night	68% 5% 8% 9% 7% 2	2940
	21st to end	Night	58% 7% 10% 10% 11% 5%	2940
December	1st to 10th	Night	47% 5% 8% 14% 22% 4	4700
	11th to 20th	Night	76% 6% 7% 7% 4	5316
	21st to end	Night	77% 7% 7% 6% 2 1	7106

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	46% 17% 20% 10% 7%	220
	11th to 20th	Day	37% 11% 23% 18% 11% 1	273
	21st to end	Day	37% 13% 19% 19% 10% 2	473
February	1st to 10th	Day	39% 15% 18% 20% 7% 1	430
	11th to 20th	Day	42% 16% 21% 16% 5% 1	425
	21st to end	Day	43% 14% 20% 17% 5% 1	386
March	1st to 10th	Day	41% 16% 20% 17% 6%	540
	11th to 20th	Day	39% 13% 21% 17% 8% 2	540
	21st to end	Day	40% 16% 20% 15% 7% 1	594
April	1st to 10th	Day	36% 15% 20% 18% 9% 2	540
	11th to 20th	Day	34% 18% 23% 16% 6% 3	532
	21st to end	Day	28% 17% 26% 20% 7% 2	540
May	1st to 10th	Day	20% 15% 30% 21% 11% 3	543
	11th to 20th	Day	31% 14% 21% 24% 8% 3	568
	21st to end	Day	21% 11% 26% 25% 15% 3	617
June	1st to 10th	Day	24% 11% 27% 24% 12% 2	570
	11th to 20th	Day	18% 18% 32% 23% 9% 1	570
	21st to end	Day	10% 9% 28% 36% 15% 2	570
July	1st to 10th	Day	6% 6% 32% 34% 19% 3	566
	11th to 20th	Day	5% 9% 32% 35% 16% 3	564
	21st to end	Day	3 6% 28% 38% 20% 5%	619
August	1st to 10th	Day	3 5% 30% 37% 19% 6%	567
	11th to 20th	Day	5% 5% 23% 35% 27% 5%	557
	21st to end	Day	9% 8% 28% 34% 17% 4	620
September	1st to 10th	Day	7% 8% 31% 32% 20% 3	530
	11th to 20th	Day	16% 8% 26% 30% 16% 4	530
	21st to end	Day	18% 13% 24% 32% 10% 3	530
October	1st to 10th	Day	21% 12% 27% 22% 15% 4	530
	11th to 20th	Day	23% 13% 20% 23% 17% 3	530
	21st to end	Day	31% 14% 23% 20% 8% 4	583
November	1st to 10th	Day	37% 14% 20% 20% 7% 2	295
	11th to 20th	Day	37% 11% 23% 18% 8% 2	220
	21st to end	Day	37% 14% 17% 17% 14%	220
December	1st to 10th	Day	38% 10% 16% 22% 9% 5%	220
	11th to 20th	Day	49% 10% 19% 15% 7%	220
	21st to end	Day	42% 15% 18% 17% 8%	242
January	1st to 10th	Night	46% 9% 14% 18% 10% 2	840
	11th to 20th	Night	36% 8% 16% 22% 15% 3	840
	21st to end	Night	35% 5% 14% 30% 15% 2	924
February	1st to 10th	Night	34% 8% 15% 29% 13% 1	840
	11th to 20th	Night	35% 7% 17% 28% 13% 1	824
	21st to end	Night	39% 10% 15% 23% 13%	692
March	1st to 10th	Night	34% 9% 20% 26% 10% 1	840
	11th to 20th	Night	34% 9% 16% 26% 14% 1	840
	21st to end	Night	37% 10% 16% 23% 12% 1	924
April	1st to 10th	Night	33% 8% 16% 25% 16% 1	840
	11th to 20th	Night	26% 11% 21% 26% 15% 2	810
	21st to end	Night	22% 7% 21% 30% 18% 1	630
May	1st to 10th	Night	18% 5% 23% 33% 19% 2	562
	11th to 20th	Night	18% 7% 17% 35% 22% 2	414
	21st to end	Night	16% 4 19% 36% 22% 2	455
June	1st to 10th	Night	20% 5% 17% 33% 24% 2	420
	11th to 20th	Night	14% 4 22% 43% 16% 1	420
	21st to end	Night	13% 3 14% 45% 25%	420
July	1st to 10th	Night	3 2 13% 48% 33%	410
	11th to 20th	Night	6% 2 15% 53% 23%	408
	21st to end	Night	3 2 10% 47% 36% 1	557
August	1st to 10th	Night	3 3 10% 44% 35% 5%	627
	11th to 20th	Night	5% 1 9% 40% 41% 4	624
	21st to end	Night	7% 3 17% 42% 28% 3	811
September	1st to 10th	Night	8% 4 17% 39% 30% 2	800
	11th to 20th	Night	11% 3 16% 33% 32% 5%	800
	21st to end	Night	14% 5% 14% 40% 24% 3	800
October	1st to 10th	Night	17% 6% 18% 31% 24% 3	800
	11th to 20th	Night	23% 5% 12% 32% 23% 5%	800
	21st to end	Night	30% 7% 18% 25% 16% 4	880
November	1st to 10th	Night	35% 7% 14% 28% 15% 1	820
	11th to 20th	Night	38% 9% 17% 21% 13% 1	840
	21st to end	Night	27% 9% 18% 28% 16% 3	840
December	1st to 10th	Night	31% 6% 17% 27% 18% 2	840
	11th to 20th	Night	43% 7% 14% 21% 14% 1	840
	21st to end	Night	42% 11% 16% 22% 8% 1	924

Page generated at 2026-08-27 01:07:16. Version ac07

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