Pierre
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Pierre clear sky chart from 2005-11-06 to 2026-01-02.

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	10% 6% 2 6% 4 4 4 3 5% 7% 48%	135292
	Night	8% 7% 3 7% 4 4 4 4 6% 7% 47%	133408
Transparency	Day	35% 6% 14% 27% 16% 2	129999
	Night	35% 6% 14% 26% 16% 2	129708
Seeing	Day	13% 8% 28% 31% 17% 4	17531
	Night	12% 7% 31% 39% 11% 1	27532

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	6% 11% 6% 15% 8% 5% 3 3 5% 6% 31%	3646
	11th to 20th	Day	3 8% 4 11% 7% 8% 6% 5% 10% 7% 30%	3640
	21st to end	Day	3 6% 4 12% 7% 6% 5% 4 5% 6% 44%	4004
February	1st to 10th	Day	8% 14% 4 8% 5% 6% 4 4 5% 6% 36%	1741
	11th to 20th	Day	7% 9% 3 8% 7% 4 4 4 6% 7% 42%	1949
	21st to end	Day	8% 10% 3 7% 5% 4 5% 3 6% 6% 42%	1650
March	1st to 10th	Day	7% 7% 2 6% 4 4 4 3 4 6% 52%	4500
	11th to 20th	Day	6% 6% 2 5% 3 4 4 4 6% 8% 52%	4865
	21st to end	Day	19% 11% 3 7% 5% 4 4 4 6% 8% 29%	5599
April	1st to 10th	Day	14% 9% 3 5% 4 4 4 3 6% 6% 42%	2400
	11th to 20th	Day	15% 8% 3 8% 5% 4 4 3 5% 6% 39%	2469
	21st to end	Day	16% 8% 2 7% 5% 4 4 3 5% 6% 41%	2600
May	1st to 10th	Day	12% 4 2 4 3 4 4 3 5% 7% 51%	5900
	11th to 20th	Day	18% 6% 2 5% 3 3 3 3 5% 6% 48%	5990
	21st to end	Day	18% 7% 2 5% 4 3 4 3 5% 7% 42%	6925
June	1st to 10th	Day	10% 4 2 5% 4 3 4 4 6% 8% 51%	2800
	11th to 20th	Day	9% 5% 2 5% 4 4 4 5% 7% 9% 48%	2800
	21st to end	Day	6% 4 2 5% 4 2 4 3 5% 8% 57%	2800
July	1st to 10th	Day	7% 4 2 5% 4 4 4 4 6% 9% 52%	6339
	11th to 20th	Day	7% 5% 2 5% 4 4 4 3 5% 7% 55%	6340
	21st to end	Day	6% 4 2 5% 4 4 5% 4 7% 9% 52%	6903
August	1st to 10th	Day	8% 5% 2 6% 4 4 3 3 5% 7% 52%	5939
	11th to 20th	Day	9% 5% 2 6% 4 4 5% 4 5% 7% 49%	5821
	21st to end	Day	7% 5% 2 4 2 3 3 3 5% 7% 59%	6197
September	1st to 10th	Day	8% 3 1 4 3 3 4 3 4 6% 62%	2385
	11th to 20th	Day	10% 3 2 4 3 2 3 3 5% 7% 59%	2200
	21st to end	Day	11% 3 1 3 3 2 2 2 5% 6% 61%	2200
October	1st to 10th	Day	8% 3 1 2 2 2 2 2 4 6% 67%	3590
	11th to 20th	Day	9% 6% 2 6% 4 3 3 2 4 6% 56%	3075
	21st to end	Day	11% 7% 2 6% 4 4 4 3 5% 7% 46%	3190
November	1st to 10th	Day	10% 6% 3 5% 4 3 4 4 5% 7% 49%	1853
	11th to 20th	Day	5% 7% 3 7% 6% 4 4 4 5% 7% 48%	1890
	21st to end	Day	6% 10% 3 6% 5% 4 4 3 5% 7% 46%	1856
December	1st to 10th	Day	7% 12% 4 11% 5% 6% 5% 4 5% 5% 37%	2360
	11th to 20th	Day	5% 9% 4 10% 6% 5% 5% 4 6% 6% 38%	2784
	21st to end	Day	12% 9% 3 9% 4 5% 4 3 5% 7% 38%	4092
January	1st to 10th	Night	6% 12% 5% 13% 6% 6% 5% 5% 5% 7% 30%	6342
	11th to 20th	Night	3 8% 3 9% 6% 7% 7% 5% 9% 7% 36%	6340
	21st to end	Night	3 6% 4 11% 5% 4 4 3 5% 6% 48%	6974
February	1st to 10th	Night	8% 12% 4 9% 5% 6% 6% 4 5% 7% 34%	2664
	11th to 20th	Night	5% 9% 4 8% 4 6% 5% 5% 6% 7% 41%	2348
	21st to end	Night	8% 8% 3 6% 4 4 4 4 6% 7% 45%	1980
March	1st to 10th	Night	8% 7% 3 6% 4 4 4 3 6% 7% 47%	5374
	11th to 20th	Night	9% 6% 2 6% 3 3 4 3 6% 8% 50%	5085
	21st to end	Night	16% 10% 3 8% 5% 4 4 4 5% 7% 34%	5323
April	1st to 10th	Night	14% 7% 2 6% 4 4 4 3 5% 8% 43%	2000
	11th to 20th	Night	15% 7% 2 5% 4 5% 4 4 4 7% 43%	1878
	21st to end	Night	15% 8% 3 6% 5% 3 4 2 5% 7% 42%	1800
May	1st to 10th	Night	9% 5% 2 5% 4 3 4 4 6% 7% 52%	4080
	11th to 20th	Night	16% 5% 2 4 3 3 4 3 5% 6% 49%	3923
	21st to end	Night	17% 7% 2 6% 4 4 4 3 6% 7% 40%	3972
June	1st to 10th	Night	9% 4 1 4 3 3 4 4 5% 9% 53%	1600
	11th to 20th	Night	7% 5% 2 5% 4 4 4 5% 8% 8% 47%	1600
	21st to end	Night	6% 3 1 4 4 4 4 3 5% 8% 58%	1600
July	1st to 10th	Night	4 3 2 4 4 5% 5% 4 7% 10% 51%	3640
	11th to 20th	Night	6% 3 1 4 3 2 3 3 5% 7% 63%	3640
	21st to end	Night	6% 3 2 5% 4 4 5% 5% 7% 10% 50%	3970
August	1st to 10th	Night	7% 4 2 5% 4 5% 6% 4 7% 9% 48%	3871
	11th to 20th	Night	6% 4 2 5% 3 4 4 4 6% 9% 53%	4028
	21st to end	Night	7% 5% 2 5% 4 3 4 3 5% 7% 56%	4763
September	1st to 10th	Night	6% 4 1 4 2 3 3 3 4 7% 63%	2015
	11th to 20th	Night	8% 4 1 5% 3 3 3 4 5% 7% 56%	2200
	21st to end	Night	10% 4 1 4 3 3 3 2 5% 5% 60%	2200
October	1st to 10th	Night	9% 3 1 3 2 2 2 2 4 5% 69%	3590
	11th to 20th	Night	9% 5% 2 5% 3 4 4 3 5% 8% 53%	4032
	21st to end	Night	9% 7% 2 6% 4 3 4 4 5% 8% 48%	4610
November	1st to 10th	Night	7% 7% 2 6% 4 4 4 4 5% 7% 49%	2665
	11th to 20th	Night	7% 8% 2 7% 5% 5% 4 3 5% 7% 47%	2730
	21st to end	Night	6% 8% 3 6% 5% 4 4 3 6% 8% 48%	2755
December	1st to 10th	Night	4 7% 3 9% 6% 6% 4 4 6% 6% 45%	5050
	11th to 20th	Night	5% 9% 3 8% 5% 5% 5% 4 7% 8% 40%	5638
	21st to end	Night	13% 10% 3 8% 4 4 4 4 5% 7% 38%	7128

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	54% 5% 15% 20% 6%	3647
	11th to 20th	Day	47% 6% 16% 15% 15% 1	3640
	21st to end	Day	40% 7% 17% 23% 13%	4004
February	1st to 10th	Day	47% 7% 14% 20% 11%	1741
	11th to 20th	Day	41% 7% 16% 21% 14% 3	1959
	21st to end	Day	40% 7% 17% 22% 12% 2	1650
March	1st to 10th	Day	34% 5% 11% 30% 18% 2	4500
	11th to 20th	Day	29% 5% 14% 31% 20%	4865
	21st to end	Day	52% 7% 16% 18% 7% 1	5599
April	1st to 10th	Day	41% 6% 13% 26% 12% 2	2400
	11th to 20th	Day	45% 6% 12% 23% 12% 2	2472
	21st to end	Day	43% 6% 13% 27% 10% 1	2600
May	1st to 10th	Day	31% 6% 10% 32% 20% 2	5900
	11th to 20th	Day	37% 6% 13% 23% 18% 4	5994
	21st to end	Day	41% 6% 12% 27% 14%	6926
June	1st to 10th	Day	29% 8% 18% 29% 12% 3	2800
	11th to 20th	Day	31% 9% 17% 27% 14% 2	2800
	21st to end	Day	25% 7% 15% 29% 20% 4	2800
July	1st to 10th	Day	28% 7% 14% 33% 16% 2	6271
	11th to 20th	Day	30% 5% 11% 27% 24% 4	6265
	21st to end	Day	27% 7% 16% 27% 19% 4	6705
August	1st to 10th	Day	31% 6% 12% 25% 22% 5%	4320
	11th to 20th	Day	37% 6% 15% 26% 14% 2	4210
	21st to end	Day	21% 5% 15% 30% 23% 6%	4459
September	1st to 10th	Day	24% 5% 11% 30% 25% 5%	2385
	11th to 20th	Day	26% 5% 16% 28% 22% 2	2200
	21st to end	Day	25% 4 10% 34% 25% 3	2200
October	1st to 10th	Day	21% 3 9% 25% 35% 7%	3590
	11th to 20th	Day	31% 3 12% 37% 15% 2	3075
	21st to end	Day	37% 5% 13% 27% 16% 2	3190
November	1st to 10th	Day	34% 5% 15% 27% 15% 4	1853
	11th to 20th	Day	34% 4 18% 28% 14% 2	1890
	21st to end	Day	37% 6% 15% 28% 13% 2	1856
December	1st to 10th	Day	47% 5% 14% 25% 8%	2360
	11th to 20th	Day	43% 7% 16% 23% 10% 1	2781
	21st to end	Day	45% 6% 12% 32% 5% 1	4092
January	1st to 10th	Night	52% 5% 13% 21% 9% 1	6342
	11th to 20th	Night	42% 6% 18% 19% 14% 1	6340
	21st to end	Night	36% 6% 19% 25% 14% 1	6974
February	1st to 10th	Night	48% 6% 14% 19% 12% 1	2664
	11th to 20th	Night	40% 6% 14% 22% 14% 3	2348
	21st to end	Night	36% 6% 15% 26% 13% 4	1980
March	1st to 10th	Night	36% 5% 13% 27% 18% 2	5374
	11th to 20th	Night	31% 5% 11% 33% 19% 1	5085
	21st to end	Night	49% 7% 12% 24% 8% 1	5323
April	1st to 10th	Night	41% 5% 13% 25% 14% 3	2000
	11th to 20th	Night	39% 6% 13% 23% 16% 4	1878
	21st to end	Night	42% 6% 12% 26% 13% 1	1800
May	1st to 10th	Night	30% 6% 12% 26% 24% 3	4080
	11th to 20th	Night	35% 5% 10% 23% 23% 3	3924
	21st to end	Night	42% 7% 13% 26% 11%	3972
June	1st to 10th	Night	27% 7% 15% 30% 17% 3	1600
	11th to 20th	Night	31% 8% 17% 24% 17% 3	1600
	21st to end	Night	23% 6% 15% 32% 20% 3	1600
July	1st to 10th	Night	25% 7% 20% 28% 19% 2	3600
	11th to 20th	Night	22% 4 13% 33% 24% 4	3592
	21st to end	Night	27% 7% 21% 27% 14% 3	3856
August	1st to 10th	Night	29% 7% 16% 28% 14% 6%	2814
	11th to 20th	Night	31% 7% 19% 26% 15% 2	2915
	21st to end	Night	25% 5% 13% 28% 24% 5%	3432
September	1st to 10th	Night	23% 5% 12% 29% 25% 6%	2015
	11th to 20th	Night	26% 6% 14% 30% 20% 4	2200
	21st to end	Night	27% 5% 9% 29% 27% 4	2200
October	1st to 10th	Night	20% 3 7% 19% 43% 7%	3590
	11th to 20th	Night	30% 4 9% 33% 21% 3	4032
	21st to end	Night	34% 5% 13% 24% 20% 4	4610
November	1st to 10th	Night	33% 5% 14% 26% 18% 5%	2665
	11th to 20th	Night	35% 5% 15% 23% 17% 4	2730
	21st to end	Night	34% 5% 17% 28% 14% 2	2755
December	1st to 10th	Night	37% 5% 16% 28% 12% 1	5050
	11th to 20th	Night	39% 6% 18% 27% 8% 1	5640
	21st to end	Night	45% 5% 13% 27% 9%	7128

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	9% 9% 27% 36% 14% 6%	303
	11th to 20th	Day	11% 10% 36% 28% 12% 3	300
	21st to end	Day	12% 10% 35% 28% 12% 4	330
February	1st to 10th	Day	15% 11% 38% 27% 8%	300
	11th to 20th	Day	14% 7% 36% 30% 12% 1	300
	21st to end	Day	16% 10% 31% 31% 12% 1	249
March	1st to 10th	Day	19% 7% 33% 27% 10% 4	300
	11th to 20th	Day	11% 12% 27% 37% 10% 4	300
	21st to end	Day	19% 12% 29% 23% 12% 4	388
April	1st to 10th	Day	21% 14% 33% 21% 11%	500
	11th to 20th	Day	21% 16% 28% 27% 8% 1	590
	21st to end	Day	19% 9% 30% 27% 13% 2	700
May	1st to 10th	Day	18% 8% 26% 28% 17% 3	703
	11th to 20th	Day	18% 6% 25% 31% 13% 5%	725
	21st to end	Day	16% 8% 28% 27% 15% 5%	789
June	1st to 10th	Day	9% 6% 22% 31% 21% 10%	730
	11th to 20th	Day	12% 5% 30% 35% 16% 2	730
	21st to end	Day	9% 6% 25% 37% 20% 2	730
July	1st to 10th	Day	7% 2 20% 40% 27% 4	721
	11th to 20th	Day	7% 4 24% 42% 20% 2	718
	21st to end	Day	5% 3 24% 43% 21% 4	794
August	1st to 10th	Day	10% 4 23% 35% 23% 6%	726
	11th to 20th	Day	9% 3 22% 38% 23% 4	715
	21st to end	Day	9% 4 22% 35% 24% 6%	679
September	1st to 10th	Day	9% 4 24% 34% 22% 7%	515
	11th to 20th	Day	12% 6% 20% 31% 25% 7%	330
	21st to end	Day	15% 7% 26% 28% 21% 3	330
October	1st to 10th	Day	17% 8% 25% 26% 20% 5%	330
	11th to 20th	Day	17% 11% 36% 19% 15% 2	330
	21st to end	Day	16% 14% 30% 26% 12% 2	363
November	1st to 10th	Day	16% 10% 30% 27% 14% 3	330
	11th to 20th	Day	12% 13% 30% 29% 15% 2	330
	21st to end	Day	13% 10% 33% 27% 15% 2	330
December	1st to 10th	Day	14% 11% 35% 28% 11% 2	330
	11th to 20th	Day	15% 10% 42% 24% 8% 1	330
	21st to end	Day	15% 10% 36% 26% 11% 1	363
January	1st to 10th	Night	11% 7% 32% 40% 9% 2	1006
	11th to 20th	Night	10% 12% 31% 38% 9% 1	1000
	21st to end	Night	10% 8% 36% 34% 11% 1	1100
February	1st to 10th	Night	14% 9% 35% 33% 8% 1	1000
	11th to 20th	Night	9% 7% 36% 37% 11% 1	794
	21st to end	Night	13% 5% 33% 38% 9% 1	660
March	1st to 10th	Night	12% 8% 34% 37% 9% 1	800
	11th to 20th	Night	12% 9% 30% 40% 8% 1	653
	21st to end	Night	16% 9% 30% 34% 10% 1	660
April	1st to 10th	Night	18% 9% 33% 34% 7%	600
	11th to 20th	Night	19% 11% 30% 36% 4	593
	21st to end	Night	18% 8% 28% 36% 10% 1	600
May	1st to 10th	Night	11% 6% 31% 37% 14% 1	600
	11th to 20th	Night	18% 4 27% 38% 12% 1	591
	21st to end	Night	13% 6% 32% 35% 13% 1	650
June	1st to 10th	Night	9% 4 25% 42% 19% 2	600
	11th to 20th	Night	9% 5% 35% 42% 9% 1	600
	21st to end	Night	6% 3 27% 49% 15%	600
July	1st to 10th	Night	5% 3 23% 50% 18% 1	585
	11th to 20th	Night	6% 2 27% 51% 15%	582
	21st to end	Night	5% 1 27% 51% 14% 1	657
August	1st to 10th	Night	6% 3 27% 49% 14%	597
	11th to 20th	Night	7% 2 26% 46% 19%	594
	21st to end	Night	7% 3 28% 45% 17%	660
September	1st to 10th	Night	8% 5% 26% 45% 15% 2	600
	11th to 20th	Night	10% 4 29% 42% 16% 1	600
	21st to end	Night	12% 6% 29% 37% 16% 1	600
October	1st to 10th	Night	16% 6% 29% 35% 14%	600
	11th to 20th	Night	15% 9% 30% 34% 12%	870
	21st to end	Night	15% 9% 31% 36% 8% 1	1100
November	1st to 10th	Night	11% 7% 35% 35% 12%	1025
	11th to 20th	Night	12% 9% 32% 37% 10%	1050
	21st to end	Night	10% 8% 33% 38% 11%	1050
December	1st to 10th	Night	11% 9% 36% 34% 10%	1050
	11th to 20th	Night	12% 8% 34% 37% 9%	1050
	21st to end	Night	17% 8% 33% 33% 9%	1155

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