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 2024-01-13.

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% 3 5% 5% 3 4 4 5% 7% 48%	74444
	Night	9% 7% 3 5% 5% 3 4 5% 5% 8% 47%	75317
Transparency	Day	35% 6% 15% 27% 15% 3	74147
	Night	35% 6% 14% 26% 16% 3	75136
Seeing	Day	12% 7% 27% 32% 18% 4	14780
	Night	11% 7% 31% 39% 12% 1	24856

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	5% 8% 4 8% 7% 4 4 5% 7% 8% 40%	1518
	11th to 20th	Day	5% 9% 5% 9% 7% 4 5% 5% 6% 7% 38%	1460
	21st to end	Day	7% 12% 5% 8% 7% 4 5% 4 5% 7% 35%	1584
February	1st to 10th	Day	7% 11% 5% 6% 7% 4 5% 5% 5% 7% 38%	1567
	11th to 20th	Day	7% 8% 4 6% 8% 3 4 5% 7% 7% 42%	1749
	21st to end	Day	8% 10% 4 7% 6% 3 4 4 6% 7% 41%	1480
March	1st to 10th	Day	11% 9% 2 6% 6% 3 4 5% 5% 7% 43%	1800
	11th to 20th	Day	9% 6% 3 6% 5% 3 4 5% 6% 8% 44%	1930
	21st to end	Day	14% 10% 4 5% 6% 3 4 5% 6% 9% 34%	2230
April	1st to 10th	Day	14% 8% 3 5% 5% 3 4 5% 5% 6% 42%	2160
	11th to 20th	Day	17% 8% 3 7% 6% 2 4 4 4 6% 38%	2219
	21st to end	Day	15% 7% 2 6% 5% 3 5% 4 5% 6% 42%	2340
May	1st to 10th	Day	16% 5% 2 4 4 3 5% 4 5% 8% 44%	2340
	11th to 20th	Day	15% 6% 2 4 5% 2 4 4 6% 8% 44%	2352
	21st to end	Day	15% 6% 2 5% 4 2 4 5% 5% 8% 43%	2724
June	1st to 10th	Day	10% 4 2 4 4 2 4 5% 5% 9% 51%	2520
	11th to 20th	Day	8% 4 2 4 4 2 4 5% 7% 9% 49%	2520
	21st to end	Day	6% 3 2 4 5% 2 4 4 5% 8% 58%	2520
July	1st to 10th	Day	4 2 2 4 4 2 5% 5% 6% 10% 56%	2520
	11th to 20th	Day	4 2 1 3 3 2 3 3 4 7% 67%	2520
	21st to end	Day	4 2 1 3 4 3 4 4 6% 9% 60%	2742
August	1st to 10th	Day	8% 5% 2 4 5% 3 4 5% 6% 9% 49%	2389
	11th to 20th	Day	7% 3 2 4 3 2 5% 4 5% 8% 58%	2301
	21st to end	Day	7% 3 1 3 3 2 3 4 5% 7% 62%	2463
September	1st to 10th	Day	8% 3 1 3 4 2 4 4 3 6% 61%	2147
	11th to 20th	Day	10% 3 2 3 3 1 3 3 4 7% 60%	1980
	21st to end	Day	12% 4 2 3 3 2 2 3 5% 7% 58%	1980
October	1st to 10th	Day	15% 5% 2 3 4 2 3 3 4 6% 52%	1980
	11th to 20th	Day	14% 7% 2 5% 4 2 3 3 4 6% 51%	1716
	21st to end	Day	12% 8% 2 4 4 2 3 4 4 6% 50%	1782
November	1st to 10th	Day	10% 6% 3 4 5% 2 5% 4 5% 7% 49%	1673
	11th to 20th	Day	6% 7% 3 7% 6% 3 4 5% 5% 7% 48%	1710
	21st to end	Day	6% 9% 4 6% 5% 2 5% 4 5% 8% 47%	1680
December	1st to 10th	Day	7% 9% 4 7% 6% 3 7% 5% 6% 8% 38%	1330
	11th to 20th	Day	4 8% 5% 7% 6% 4 5% 5% 7% 8% 41%	1724
	21st to end	Day	15% 12% 3 7% 6% 3 5% 4 4 6% 34%	2794
January	1st to 10th	Night	5% 8% 4 7% 6% 4 6% 7% 7% 9% 38%	2647
	11th to 20th	Night	5% 10% 4 9% 6% 3 5% 4 6% 9% 40%	2562
	21st to end	Night	6% 10% 5% 8% 6% 4 5% 6% 5% 7% 36%	2772
February	1st to 10th	Night	9% 10% 5% 8% 6% 4 6% 5% 5% 7% 36%	2398
	11th to 20th	Night	6% 8% 5% 7% 5% 4 5% 6% 6% 7% 42%	2107
	21st to end	Night	9% 8% 3 6% 5% 3 5% 5% 6% 6% 44%	1776
March	1st to 10th	Night	9% 8% 4 7% 4 3 5% 4 6% 8% 43%	2160
	11th to 20th	Night	11% 8% 3 5% 4 3 4 5% 6% 8% 44%	2029
	21st to end	Night	12% 9% 3 6% 5% 3 4 5% 6% 7% 40%	2124
April	1st to 10th	Night	13% 7% 2 5% 6% 3 4 4 5% 8% 43%	1800
	11th to 20th	Night	17% 7% 3 3 4 3 5% 5% 5% 7% 42%	1689
	21st to end	Night	14% 7% 2 5% 5% 3 4 3 5% 8% 43%	1620
May	1st to 10th	Night	10% 5% 2 5% 6% 3 5% 5% 6% 8% 45%	1620
	11th to 20th	Night	15% 5% 2 4 4 2 4 5% 6% 7% 46%	1541
	21st to end	Night	12% 6% 2 6% 5% 4 6% 4 6% 9% 41%	1552
June	1st to 10th	Night	10% 3 2 3 4 2 4 5% 5% 10% 53%	1440
	11th to 20th	Night	7% 4 3 4 5% 3 5% 5% 7% 8% 48%	1440
	21st to end	Night	5% 3 1 3 5% 3 4 4 5% 9% 60%	1440
July	1st to 10th	Night	5% 2 1 3 4 3 5% 5% 6% 10% 55%	1440
	11th to 20th	Night	5% 2 1 4 2 1 4 4 6% 7% 64%	1440
	21st to end	Night	4 2 1 4 4 2 4 6% 6% 9% 58%	1576
August	1st to 10th	Night	5% 3 1 4 5% 3 5% 5% 7% 8% 52%	1548
	11th to 20th	Night	5% 3 1 3 2 2 4 5% 6% 9% 60%	1600
	21st to end	Night	5% 2 1 3 3 2 4 3 5% 8% 65%	1890
September	1st to 10th	Night	7% 4 1 4 3 2 3 4 3 7% 62%	1813
	11th to 20th	Night	8% 3 1 4 3 3 3 4 5% 7% 58%	1980
	21st to end	Night	11% 4 2 4 4 2 4 3 4 5% 58%	1980
October	1st to 10th	Night	16% 4 2 4 4 2 4 3 5% 6% 50%	1980
	11th to 20th	Night	12% 5% 2 4 4 3 4 4 4 7% 52%	2222
	21st to end	Night	11% 7% 2 5% 4 2 3 4 5% 7% 49%	2574
November	1st to 10th	Night	7% 7% 3 4 5% 3 5% 4 5% 7% 50%	2405
	11th to 20th	Night	7% 6% 3 6% 6% 4 4 4 5% 7% 47%	2470
	21st to end	Night	6% 7% 3 4 5% 2 5% 4 5% 8% 50%	2491
December	1st to 10th	Night	7% 9% 4 7% 6% 5% 5% 4 5% 6% 42%	2850
	11th to 20th	Night	5% 8% 3 6% 5% 3 4 5% 6% 9% 46%	3468
	21st to end	Night	16% 11% 3 8% 4 2 4 4 4 6% 37%	4873

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	41% 6% 18% 22% 12% 1	1519
	11th to 20th	Day	44% 6% 19% 20% 9% 2	1460
	21st to end	Day	48% 7% 15% 20% 10%	1584
February	1st to 10th	Day	45% 8% 15% 21% 11%	1567
	11th to 20th	Day	40% 7% 17% 20% 13% 2	1759
	21st to end	Day	43% 7% 16% 20% 11% 2	1480
March	1st to 10th	Day	41% 7% 15% 25% 11% 1	1800
	11th to 20th	Day	38% 7% 14% 25% 16% 1	1930
	21st to end	Day	46% 8% 17% 21% 7% 1	2230
April	1st to 10th	Day	42% 6% 13% 26% 11% 2	2160
	11th to 20th	Day	47% 6% 13% 22% 11% 2	2222
	21st to end	Day	42% 6% 14% 28% 10%	2340
May	1st to 10th	Day	38% 6% 14% 27% 13% 1	2340
	11th to 20th	Day	38% 7% 17% 25% 13% 1	2356
	21st to end	Day	38% 8% 18% 23% 12% 1	2724
June	1st to 10th	Day	29% 8% 17% 31% 12% 2	2520
	11th to 20th	Day	30% 9% 17% 28% 14% 2	2520
	21st to end	Day	24% 7% 16% 30% 19% 4	2520
July	1st to 10th	Day	23% 8% 14% 33% 18% 4	2451
	11th to 20th	Day	18% 5% 12% 30% 25% 10%	2445
	21st to end	Day	21% 6% 13% 29% 24% 7%	2590
August	1st to 10th	Day	31% 8% 13% 26% 19% 4	2373
	11th to 20th	Day	25% 6% 16% 31% 19% 3	2301
	21st to end	Day	23% 6% 12% 29% 24% 6%	2463
September	1st to 10th	Day	26% 5% 10% 28% 25% 6%	2147
	11th to 20th	Day	25% 5% 15% 29% 23% 2	1980
	21st to end	Day	27% 4 11% 34% 22% 2	1980
October	1st to 10th	Day	34% 5% 12% 26% 21% 2	1980
	11th to 20th	Day	35% 4 11% 30% 17% 4	1716
	21st to end	Day	36% 5% 15% 29% 13% 3	1782
November	1st to 10th	Day	34% 5% 16% 24% 16% 4	1673
	11th to 20th	Day	35% 5% 17% 28% 13% 2	1710
	21st to end	Day	36% 6% 15% 27% 14% 2	1680
December	1st to 10th	Day	42% 8% 15% 24% 10% 1	1330
	11th to 20th	Day	37% 8% 20% 28% 6% 1	1721
	21st to end	Day	50% 7% 11% 26% 6% 1	2794
January	1st to 10th	Night	40% 7% 17% 22% 12% 1	2647
	11th to 20th	Night	42% 6% 19% 23% 9% 1	2562
	21st to end	Night	45% 7% 17% 20% 9% 1	2772
February	1st to 10th	Night	46% 6% 15% 20% 12% 1	2398
	11th to 20th	Night	40% 7% 14% 23% 13% 3	2107
	21st to end	Night	39% 6% 15% 23% 12% 4	1776
March	1st to 10th	Night	40% 6% 17% 22% 12% 2	2160
	11th to 20th	Night	38% 5% 12% 27% 16% 2	2029
	21st to end	Night	42% 8% 15% 24% 10% 2	2124
April	1st to 10th	Night	41% 5% 13% 24% 14% 3	1800
	11th to 20th	Night	40% 6% 13% 22% 15% 3	1689
	21st to end	Night	40% 6% 13% 27% 12% 1	1620
May	1st to 10th	Night	37% 6% 15% 25% 16% 1	1620
	11th to 20th	Night	37% 7% 14% 26% 16%	1542
	21st to end	Night	39% 8% 17% 24% 11% 1	1552
June	1st to 10th	Night	28% 8% 16% 30% 17% 3	1440
	11th to 20th	Night	30% 8% 17% 25% 16% 4	1440
	21st to end	Night	22% 6% 16% 33% 20% 3	1440
July	1st to 10th	Night	22% 8% 15% 30% 21% 4	1400
	11th to 20th	Night	19% 5% 10% 30% 26% 10%	1392
	21st to end	Night	21% 7% 12% 31% 22% 8%	1488
August	1st to 10th	Night	27% 8% 17% 25% 18% 5%	1540
	11th to 20th	Night	20% 7% 16% 31% 23% 4	1600
	21st to end	Night	19% 5% 12% 31% 25% 8%	1890
September	1st to 10th	Night	24% 5% 11% 27% 26% 7%	1813
	11th to 20th	Night	24% 6% 13% 31% 21% 4	1980
	21st to end	Night	29% 5% 10% 29% 25% 3	1980
October	1st to 10th	Night	35% 6% 11% 24% 21% 3	1980
	11th to 20th	Night	32% 5% 9% 29% 20% 5%	2222
	21st to end	Night	34% 6% 14% 22% 19% 4	2574
November	1st to 10th	Night	33% 5% 14% 25% 18% 5%	2405
	11th to 20th	Night	36% 6% 14% 24% 18% 4	2470
	21st to end	Night	33% 5% 16% 28% 15% 2	2491
December	1st to 10th	Night	42% 5% 13% 27% 11% 2	2850
	11th to 20th	Night	35% 6% 18% 31% 9% 1	3470
	21st to end	Night	48% 6% 13% 24% 9% 1	4873

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	7% 10% 30% 36% 13% 5%	270
	11th to 20th	Day	10% 9% 34% 29% 15% 3	248
	21st to end	Day	13% 10% 40% 27% 7% 3	264
February	1st to 10th	Day	13% 8% 40% 29% 10%	240
	11th to 20th	Day	15% 7% 38% 28% 11% 1	240
	21st to end	Day	17% 10% 32% 30% 11% 1	198
March	1st to 10th	Day	20% 8% 31% 28% 8% 5%	240
	11th to 20th	Day	12% 8% 27% 37% 12% 5%	240
	21st to end	Day	17% 10% 30% 23% 14% 5%	316
April	1st to 10th	Day	20% 13% 33% 21% 12%	420
	11th to 20th	Day	21% 14% 29% 27% 8% 1	500
	21st to end	Day	17% 9% 30% 28% 14% 2	600
May	1st to 10th	Day	18% 8% 27% 27% 17% 3	603
	11th to 20th	Day	17% 6% 26% 31% 14% 5%	625
	21st to end	Day	15% 8% 29% 27% 16% 5%	679
June	1st to 10th	Day	8% 6% 22% 31% 22% 11%	630
	11th to 20th	Day	10% 5% 29% 36% 17% 3	630
	21st to end	Day	8% 5% 23% 39% 23% 3	630
July	1st to 10th	Day	5% 2 19% 42% 27% 4	621
	11th to 20th	Day	6% 4 24% 43% 20% 2	618
	21st to end	Day	5% 3 22% 44% 23% 3	684
August	1st to 10th	Day	9% 2 22% 37% 23% 7%	626
	11th to 20th	Day	8% 3 20% 39% 25% 5%	615
	21st to end	Day	8% 4 19% 36% 26% 6%	582
September	1st to 10th	Day	10% 4 24% 34% 22% 7%	437
	11th to 20th	Day	10% 4 17% 34% 27% 8%	270
	21st to end	Day	17% 8% 26% 29% 19% 1	270
October	1st to 10th	Day	19% 8% 24% 25% 19% 6%	270
	11th to 20th	Day	17% 10% 33% 20% 18% 2	270
	21st to end	Day	15% 12% 32% 27% 12% 2	297
November	1st to 10th	Day	16% 9% 27% 29% 17% 3	270
	11th to 20th	Day	11% 12% 29% 30% 15% 2	270
	21st to end	Day	13% 11% 33% 26% 16% 3	270
December	1st to 10th	Day	13% 10% 33% 30% 11% 2	270
	11th to 20th	Day	11% 9% 41% 27% 10% 1	270
	21st to end	Day	17% 11% 35% 25% 11% 1	297
January	1st to 10th	Night	11% 7% 32% 40% 9% 1	950
	11th to 20th	Night	10% 11% 30% 40% 10% 1	915
	21st to end	Night	11% 8% 37% 34% 10%	990
February	1st to 10th	Night	12% 8% 35% 34% 9% 1	900
	11th to 20th	Night	9% 7% 36% 35% 11% 1	713
	21st to end	Night	14% 5% 32% 38% 10% 1	592
March	1st to 10th	Night	12% 7% 34% 36% 10% 1	720
	11th to 20th	Night	13% 8% 30% 41% 7% 1	589
	21st to end	Night	15% 9% 29% 35% 11% 1	594
April	1st to 10th	Night	17% 9% 33% 34% 7%	540
	11th to 20th	Night	20% 10% 28% 38% 4	533
	21st to end	Night	17% 8% 27% 36% 11% 1	540
May	1st to 10th	Night	11% 5% 31% 38% 14% 1	540
	11th to 20th	Night	18% 4 27% 38% 12% 1	531
	21st to end	Night	13% 6% 32% 35% 13% 1	584
June	1st to 10th	Night	10% 4 25% 41% 19% 2	540
	11th to 20th	Night	8% 5% 34% 43% 10% 1	540
	21st to end	Night	4 2 26% 51% 16%	540
July	1st to 10th	Night	5% 2 23% 52% 18% 1	525
	11th to 20th	Night	5% 2 26% 52% 14%	522
	21st to end	Night	5% 1 26% 52% 15% 1	591
August	1st to 10th	Night	5% 2 25% 52% 15%	537
	11th to 20th	Night	6% 2 25% 47% 19%	534
	21st to end	Night	6% 3 27% 46% 18%	594
September	1st to 10th	Night	8% 5% 26% 44% 15% 1	540
	11th to 20th	Night	9% 3 28% 43% 16% 1	540
	21st to end	Night	13% 6% 30% 37% 14% 1	540
October	1st to 10th	Night	18% 5% 30% 34% 13%	540
	11th to 20th	Night	14% 8% 28% 36% 13%	782
	21st to end	Night	15% 9% 30% 36% 9% 1	990
November	1st to 10th	Night	11% 7% 34% 35% 13% 1	925
	11th to 20th	Night	11% 10% 31% 37% 11%	950
	21st to end	Night	9% 8% 34% 38% 11%	950
December	1st to 10th	Night	11% 9% 36% 34% 10%	950
	11th to 20th	Night	11% 7% 34% 39% 10%	950
	21st to end	Night	18% 8% 32% 33% 10%	1045

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