Powder River
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Powder River clear sky chart from 2005-11-06 to 2024-03-06.

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	5% 5% 2 4 4 3 4 5% 6% 8% 54%	78549
	Night	5% 6% 3 5% 4 3 4 5% 6% 8% 53%	81037
Transparency	Day	27% 6% 14% 26% 20% 7%	78254
	Night	28% 7% 14% 27% 18% 6%	80854
Seeing	Day	8% 9% 27% 29% 20% 6%	14765
	Night	8% 8% 32% 36% 15% 1	25012

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	1 4 3 7% 6% 4 4 5% 5% 8% 52%	2538
	11th to 20th	Day	2 5% 2 5% 8% 4 6% 6% 7% 9% 44%	2576
	21st to end	Day	2 4 2 4 3 2 3 4 5% 7% 64%	3146
February	1st to 10th	Day	2 8% 4 7% 5% 3 5% 7% 6% 9% 44%	1710
	11th to 20th	Day	3 8% 3 6% 6% 3 4 4 6% 7% 51%	1665
	21st to end	Day	2 6% 3 5% 6% 3 3 5% 7% 7% 53%	1560
March	1st to 10th	Day	4 6% 3 5% 5% 2 3 5% 5% 9% 53%	1917
	11th to 20th	Day	4 6% 3 4 4 2 4 6% 6% 10% 51%	1980
	21st to end	Day	7% 8% 4 5% 5% 3 5% 6% 6% 8% 43%	2240
April	1st to 10th	Day	6% 8% 2 4 5% 3 4 5% 6% 10% 47%	2160
	11th to 20th	Day	9% 9% 3 7% 5% 3 5% 4 6% 8% 42%	2131
	21st to end	Day	11% 9% 3 5% 5% 3 4 5% 5% 7% 42%	2222
May	1st to 10th	Day	12% 7% 2 5% 5% 3 5% 5% 6% 9% 41%	2443
	11th to 20th	Day	13% 7% 2 4 4 2 5% 5% 5% 10% 42%	2478
	21st to end	Day	10% 5% 2 5% 4 3 6% 5% 7% 10% 42%	2724
June	1st to 10th	Day	5% 3 2 4 4 3 4 5% 6% 9% 54%	2520
	11th to 20th	Day	5% 3 1 3 3 3 4 5% 6% 9% 57%	2520
	21st to end	Day	3 2 1 2 3 2 3 5% 6% 8% 65%	2520
July	1st to 10th	Day	4 3 1 3 4 3 5% 5% 6% 9% 59%	2520
	11th to 20th	Day	3 2 1 2 3 2 4 4 6% 8% 65%	2520
	21st to end	Day	4 3 1 3 3 2 4 6% 6% 8% 61%	2709
August	1st to 10th	Day	3 3 1 4 4 3 4 6% 6% 8% 58%	2328
	11th to 20th	Day	3 3 1 3 4 3 4 4 6% 8% 62%	2295
	21st to end	Day	2 2 1 3 4 2 4 4 5% 7% 65%	2376
September	1st to 10th	Day	5% 2 2 3 4 2 3 3 5% 7% 64%	2160
	11th to 20th	Day	5% 3 1 3 4 2 2 3 5% 8% 63%	2160
	21st to end	Day	7% 4 2 3 2 2 3 3 4 6% 64%	1914
October	1st to 10th	Day	10% 7% 2 4 4 2 4 4 4 6% 54%	1800
	11th to 20th	Day	7% 5% 2 3 3 3 4 4 5% 6% 60%	1800
	21st to end	Day	4 6% 2 4 4 2 4 4 5% 8% 55%	1940
November	1st to 10th	Day	4 5% 2 5% 3 2 4 5% 5% 8% 56%	1673
	11th to 20th	Day	2 5% 3 4 5% 2 5% 5% 7% 8% 54%	1544
	21st to end	Day	3 7% 3 4 3 3 4 6% 6% 9% 52%	1520
December	1st to 10th	Day	1 6% 4 7% 6% 3 3 5% 7% 9% 49%	1520
	11th to 20th	Day	2 5% 2 4 3 3 4 5% 6% 9% 57%	1926
	21st to end	Day	2 6% 3 6% 6% 3 5% 5% 5% 8% 51%	2794
January	1st to 10th	Night	1 5% 4 7% 6% 4 6% 6% 6% 8% 46%	4417
	11th to 20th	Night	1 5% 4 8% 6% 4 5% 4 7% 10% 46%	4421
	21st to end	Night	2 5% 3 5% 4 2 4 5% 5% 7% 58%	4521
February	1st to 10th	Night	2 7% 4 7% 6% 4 5% 5% 5% 8% 47%	2470
	11th to 20th	Night	3 7% 4 7% 6% 3 4 5% 5% 7% 49%	2402
	21st to end	Night	2 7% 3 7% 6% 3 5% 4 6% 9% 48%	1893
March	1st to 10th	Night	4 7% 3 5% 5% 2 4 5% 6% 8% 51%	2156
	11th to 20th	Night	4 7% 2 6% 4 3 4 4 6% 9% 50%	1980
	21st to end	Night	7% 9% 3 5% 5% 3 5% 5% 7% 9% 41%	2116
April	1st to 10th	Night	8% 8% 3 5% 3 2 4 4 5% 9% 48%	1800
	11th to 20th	Night	10% 11% 4 6% 6% 3 5% 4 5% 8% 38%	1777
	21st to end	Night	11% 8% 3 5% 4 3 5% 4 6% 7% 45%	1737
May	1st to 10th	Night	11% 7% 3 3 5% 2 4 5% 6% 8% 47%	1515
	11th to 20th	Night	15% 6% 2 4 5% 3 5% 5% 4 9% 43%	1417
	21st to end	Night	10% 6% 3 4 4 3 4 5% 7% 9% 46%	1552
June	1st to 10th	Night	5% 4 2 4 5% 3 4 5% 7% 9% 53%	1440
	11th to 20th	Night	8% 3 1 2 3 2 4 3 5% 8% 60%	1440
	21st to end	Night	4 2 1 3 3 2 4 3 6% 7% 66%	1440
July	1st to 10th	Night	4 3 1 3 3 3 4 5% 7% 10% 58%	1440
	11th to 20th	Night	3 1 1 2 2 3 3 5% 5% 8% 67%	1440
	21st to end	Night	4 1 1 2 3 2 3 4 6% 9% 64%	1605
August	1st to 10th	Night	2 2 1 3 4 3 4 6% 6% 12% 56%	1611
	11th to 20th	Night	3 2 1 2 3 2 4 5% 6% 8% 63%	1604
	21st to end	Night	2 2 1 3 3 2 3 4 6% 9% 63%	1980
September	1st to 10th	Night	6% 4 1 2 3 2 3 3 5% 7% 64%	1800
	11th to 20th	Night	6% 4 1 2 3 2 4 4 5% 7% 63%	1800
	21st to end	Night	8% 4 1 3 3 1 2 3 3 5% 66%	2042
October	1st to 10th	Night	10% 8% 2 4 4 2 4 4 6% 5% 52%	2160
	11th to 20th	Night	8% 6% 2 4 4 2 3 3 4 6% 58%	2160
	21st to end	Night	5% 6% 2 4 4 3 4 4 5% 6% 57%	2398
November	1st to 10th	Night	4 6% 2 5% 4 3 4 5% 6% 9% 53%	2405
	11th to 20th	Night	3 5% 3 5% 6% 3 5% 4 6% 7% 53%	2634
	21st to end	Night	4 7% 3 4 4 3 4 5% 6% 7% 54%	2660
December	1st to 10th	Night	2 7% 3 6% 5% 3 4 5% 6% 8% 51%	2660
	11th to 20th	Night	3 6% 2 4 4 3 5% 5% 7% 8% 54%	3271
	21st to end	Night	3 7% 3 6% 5% 3 4 5% 6% 9% 48%	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	28% 9% 15% 30% 18% 1	2539
	11th to 20th	Day	32% 10% 20% 22% 15% 1	2576
	21st to end	Day	19% 8% 23% 34% 14% 2	3146
February	1st to 10th	Day	34% 9% 18% 27% 10% 1	1710
	11th to 20th	Day	33% 8% 17% 25% 15% 3	1674
	21st to end	Day	28% 7% 19% 25% 18% 3	1560
March	1st to 10th	Day	27% 6% 16% 33% 15% 2	1917
	11th to 20th	Day	27% 7% 17% 31% 16% 2	1980
	21st to end	Day	37% 8% 16% 28% 10% 1	2240
April	1st to 10th	Day	32% 7% 19% 24% 15% 3	2160
	11th to 20th	Day	40% 5% 14% 26% 14% 1	2134
	21st to end	Day	41% 7% 10% 29% 13% 1	2222
May	1st to 10th	Day	37% 8% 15% 26% 12% 2	2443
	11th to 20th	Day	38% 7% 14% 26% 13% 1	2482
	21st to end	Day	34% 9% 16% 27% 13% 2	2724
June	1st to 10th	Day	26% 8% 16% 27% 19% 5%	2520
	11th to 20th	Day	22% 7% 13% 23% 22% 13%	2520
	21st to end	Day	16% 5% 9% 25% 29% 16%	2520
July	1st to 10th	Day	19% 5% 10% 23% 29% 14%	2451
	11th to 20th	Day	17% 4 8% 21% 28% 22%	2445
	21st to end	Day	19% 6% 9% 20% 27% 20%	2558
August	1st to 10th	Day	22% 6% 9% 24% 25% 15%	2313
	11th to 20th	Day	19% 5% 8% 24% 28% 16%	2295
	21st to end	Day	18% 4 8% 19% 32% 19%	2376
September	1st to 10th	Day	20% 4 7% 18% 30% 21%	2160
	11th to 20th	Day	21% 5% 8% 23% 28% 16%	2160
	21st to end	Day	22% 4 9% 25% 31% 8%	1914
October	1st to 10th	Day	32% 5% 11% 26% 21% 6%	1800
	11th to 20th	Day	26% 6% 13% 30% 20% 5%	1800
	21st to end	Day	26% 6% 16% 30% 18% 4	1940
November	1st to 10th	Day	27% 7% 13% 28% 21% 4	1673
	11th to 20th	Day	25% 6% 17% 29% 18% 4	1544
	21st to end	Day	27% 7% 15% 28% 19% 3	1520
December	1st to 10th	Day	31% 7% 20% 24% 16% 2	1520
	11th to 20th	Day	22% 6% 24% 33% 14%	1924
	21st to end	Day	30% 7% 12% 30% 18% 3	2794
January	1st to 10th	Night	33% 7% 15% 29% 15% 1	4417
	11th to 20th	Night	32% 8% 22% 20% 16% 4	4421
	21st to end	Night	25% 7% 25% 30% 12% 1	4521
February	1st to 10th	Night	35% 7% 17% 28% 11% 2	2470
	11th to 20th	Night	34% 6% 15% 26% 15% 4	2403
	21st to end	Night	32% 7% 16% 23% 19% 3	1893
March	1st to 10th	Night	30% 6% 14% 30% 17% 2	2156
	11th to 20th	Night	30% 6% 16% 29% 16% 3	1980
	21st to end	Night	37% 7% 16% 27% 11% 1	2116
April	1st to 10th	Night	33% 8% 17% 24% 15% 4	1800
	11th to 20th	Night	45% 7% 11% 22% 14% 2	1777
	21st to end	Night	38% 7% 11% 28% 15% 2	1737
May	1st to 10th	Night	35% 8% 13% 29% 14% 2	1515
	11th to 20th	Night	38% 8% 12% 27% 12% 3	1418
	21st to end	Night	33% 7% 16% 27% 14% 2	1552
June	1st to 10th	Night	26% 9% 19% 25% 17% 5%	1440
	11th to 20th	Night	23% 6% 13% 22% 24% 12%	1440
	21st to end	Night	17% 5% 9% 25% 29% 16%	1440
July	1st to 10th	Night	19% 7% 10% 27% 26% 11%	1400
	11th to 20th	Night	14% 5% 10% 23% 25% 23%	1392
	21st to end	Night	16% 6% 10% 23% 26% 18%	1516
August	1st to 10th	Night	20% 7% 12% 30% 19% 12%	1602
	11th to 20th	Night	18% 6% 11% 25% 27% 14%	1604
	21st to end	Night	17% 5% 8% 22% 29% 18%	1980
September	1st to 10th	Night	21% 4 8% 20% 28% 19%	1800
	11th to 20th	Night	22% 5% 10% 22% 26% 16%	1800
	21st to end	Night	23% 3 9% 26% 30% 10%	2042
October	1st to 10th	Night	33% 7% 10% 24% 19% 8%	2160
	11th to 20th	Night	28% 5% 10% 28% 20% 8%	2160
	21st to end	Night	27% 5% 14% 29% 19% 5%	2398
November	1st to 10th	Night	26% 8% 14% 26% 21% 5%	2405
	11th to 20th	Night	29% 8% 12% 30% 18% 3	2634
	21st to end	Night	28% 6% 14% 28% 20% 4	2660
December	1st to 10th	Night	30% 8% 17% 26% 15% 3	2660
	11th to 20th	Night	26% 7% 19% 34% 12% 1	3272
	21st to end	Night	31% 7% 13% 29% 16% 4	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	6% 14% 30% 29% 15% 6%	270
	11th to 20th	Day	7% 10% 36% 31% 14% 2	270
	21st to end	Day	4 7% 38% 37% 12% 2	297
February	1st to 10th	Day	6% 17% 47% 23% 6%	270
	11th to 20th	Day	4 15% 44% 27% 10% 1	270
	21st to end	Day	7% 12% 39% 28% 12% 1	225
March	1st to 10th	Day	8% 15% 39% 27% 11%	322
	11th to 20th	Day	7% 12% 32% 31% 14% 4	420
	21st to end	Day	11% 11% 32% 30% 13% 3	462
April	1st to 10th	Day	10% 14% 31% 32% 11% 3	420
	11th to 20th	Day	13% 13% 35% 28% 9% 1	412
	21st to end	Day	18% 12% 22% 30% 13% 5%	420
May	1st to 10th	Day	17% 10% 25% 27% 16% 5%	526
	11th to 20th	Day	19% 7% 20% 26% 22% 6%	625
	21st to end	Day	12% 9% 24% 24% 22% 8%	679
June	1st to 10th	Day	5% 8% 22% 25% 27% 12%	630
	11th to 20th	Day	7% 10% 31% 30% 20% 3	630
	21st to end	Day	5% 5% 23% 31% 29% 7%	630
July	1st to 10th	Day	5% 3 18% 30% 35% 10%	621
	11th to 20th	Day	3 3 17% 35% 32% 10%	618
	21st to end	Day	4 3 13% 33% 37% 10%	651
August	1st to 10th	Day	4 4 19% 32% 32% 9%	447
	11th to 20th	Day	4 3 16% 35% 28% 13%	437
	21st to end	Day	3 7% 19% 33% 24% 14%	495
September	1st to 10th	Day	4 5% 23% 32% 24% 12%	450
	11th to 20th	Day	7% 7% 26% 27% 22% 10%	450
	21st to end	Day	9% 7% 26% 30% 20% 8%	334
October	1st to 10th	Day	11% 7% 24% 27% 21% 9%	270
	11th to 20th	Day	10% 12% 29% 27% 18% 4	270
	21st to end	Day	8% 12% 34% 32% 11% 3	297
November	1st to 10th	Day	9% 13% 33% 30% 12% 3	270
	11th to 20th	Day	7% 13% 41% 24% 12% 3	270
	21st to end	Day	10% 10% 36% 30% 11% 3	270
December	1st to 10th	Day	3 10% 44% 30% 11% 2	270
	11th to 20th	Day	6% 17% 44% 24% 7% 1	270
	21st to end	Day	11% 16% 30% 28% 12% 3	297
January	1st to 10th	Night	4 13% 35% 33% 14% 2	950
	11th to 20th	Night	5% 14% 40% 29% 11% 1	941
	21st to end	Night	6% 8% 44% 31% 11% 1	836
February	1st to 10th	Night	6% 9% 42% 33% 9% 1	760
	11th to 20th	Night	7% 10% 38% 34% 11% 1	744
	21st to end	Night	6% 13% 38% 32% 10% 1	628
March	1st to 10th	Night	8% 11% 36% 32% 11% 1	742
	11th to 20th	Night	8% 8% 32% 37% 15% 1	720
	21st to end	Night	12% 8% 29% 36% 14% 2	730
April	1st to 10th	Night	14% 10% 31% 36% 8%	540
	11th to 20th	Night	14% 8% 33% 35% 9%	533
	21st to end	Night	13% 9% 25% 35% 17% 1	540
May	1st to 10th	Night	14% 8% 25% 32% 18% 3	540
	11th to 20th	Night	18% 4 22% 33% 21% 2	531
	21st to end	Night	12% 8% 24% 36% 19% 1	584
June	1st to 10th	Night	5% 7% 24% 38% 24% 2	540
	11th to 20th	Night	9% 7% 33% 39% 11%	540
	21st to end	Night	4 3 24% 46% 23%	540
July	1st to 10th	Night	6% 1 21% 42% 30% 1	525
	11th to 20th	Night	3 3 23% 45% 25% 1	522
	21st to end	Night	4 1 14% 50% 30% 1	591
August	1st to 10th	Night	3 2 19% 49% 27% 1	537
	11th to 20th	Night	3 3 18% 46% 29% 1	534
	21st to end	Night	3 3 20% 46% 26% 2	594
September	1st to 10th	Night	7% 3 23% 40% 24% 2	540
	11th to 20th	Night	7% 5% 25% 39% 21% 3	540
	21st to end	Night	11% 4 22% 38% 23% 3	666
October	1st to 10th	Night	14% 6% 27% 34% 18% 2	720
	11th to 20th	Night	12% 6% 29% 38% 14% 1	720
	21st to end	Night	9% 8% 31% 36% 13% 2	814
November	1st to 10th	Night	6% 9% 37% 35% 12% 1	925
	11th to 20th	Night	6% 12% 43% 30% 8%	950
	21st to end	Night	7% 9% 38% 34% 11% 1	950
December	1st to 10th	Night	7% 12% 40% 31% 10%	950
	11th to 20th	Night	7% 10% 42% 34% 7%	950
	21st to end	Night	8% 14% 39% 29% 9% 1	1045

Page generated at 2024-03-03 04:28:57. Version ac07

Copyright © 2024 Attilla Danko.