Rosebud
Clear Sky Chart
History

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

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	12% 8% 3 6% 4 4 4 4 5% 7% 43%	113533
	Night	13% 8% 3 7% 4 4 4 3 5% 6% 44%	114935
Transparency	Day	38% 6% 11% 24% 17% 3	117170
	Night	40% 5% 11% 23% 18% 3	119440
Seeing	Day	17% 13% 28% 25% 13% 3	16106
	Night	18% 13% 30% 27% 11% 1	26094

By Month

Percentage Cloud Cover SE (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	12% 13% 6% 13% 4 4 3 3 5% 5% 32%	3659
	11th to 20th	Day	9% 11% 4 8% 5% 6% 3 3 5% 6% 41%	4080
	21st to end	Day	16% 11% 5% 8% 3 4 4 3 4 6% 37%	4488
February	1st to 10th	Day	14% 13% 5% 8% 5% 4 4 3 5% 5% 33%	1800
	11th to 20th	Day	15% 10% 3 7% 4 4 4 3 4 5% 38%	1873
	21st to end	Day	13% 10% 3 8% 4 4 4 3 4 6% 40%	1650
March	1st to 10th	Day	15% 11% 3 5% 3 3 3 2 3 4 48%	4742
	11th to 20th	Day	9% 6% 2 5% 4 3 4 3 4 7% 52%	4980
	21st to end	Day	13% 10% 3 7% 5% 5% 5% 4 5% 8% 35%	5640
April	1st to 10th	Day	12% 7% 3 6% 5% 4 4 4 5% 7% 43%	2400
	11th to 20th	Day	17% 8% 2 6% 4 4 3 3 5% 5% 41%	2254
	21st to end	Day	19% 8% 3 7% 5% 4 4 3 6% 6% 35%	2280
May	1st to 10th	Day	15% 9% 3 7% 5% 5% 6% 4 7% 9% 32%	3829
	11th to 20th	Day	18% 8% 2 7% 4 4 4 4 5% 7% 38%	4353
	21st to end	Day	11% 7% 3 6% 5% 5% 5% 4 6% 7% 44%	4824
June	1st to 10th	Day	9% 4 2 5% 4 5% 4 5% 8% 8% 45%	2660
	11th to 20th	Day	8% 4 2 5% 4 4 4 4 6% 10% 50%	2660
	21st to end	Day	5% 4 1 5% 5% 4 5% 5% 7% 10% 48%	2660
July	1st to 10th	Day	13% 5% 2 6% 4 5% 5% 4 7% 9% 41%	4440
	11th to 20th	Day	5% 4 2 5% 4 4 5% 4 7% 10% 50%	4361
	21st to end	Day	8% 5% 2 6% 5% 5% 7% 5% 7% 10% 39%	4465
August	1st to 10th	Day	6% 3 2 4 4 4 5% 5% 8% 9% 51%	4104
	11th to 20th	Day	13% 5% 2 6% 4 5% 5% 4 6% 7% 43%	3796
	21st to end	Day	7% 4 2 5% 4 4 4 3 5% 8% 52%	4180
September	1st to 10th	Day	13% 5% 1 4 4 3 4 4 5% 8% 50%	2280
	11th to 20th	Day	11% 6% 2 5% 4 3 4 3 5% 7% 50%	2280
	21st to end	Day	9% 5% 2 5% 4 4 4 3 5% 7% 52%	2025
October	1st to 10th	Day	10% 4 2 6% 4 3 3 2 4 7% 56%	1900
	11th to 20th	Day	14% 6% 2 4 3 3 3 2 4 5% 53%	1900
	21st to end	Day	17% 9% 2 5% 3 3 3 2 3 6% 46%	2090
November	1st to 10th	Day	12% 7% 1 4 3 3 3 3 4 6% 53%	1815
	11th to 20th	Day	13% 7% 2 6% 4 3 3 4 5% 6% 47%	1800
	21st to end	Day	15% 11% 3 6% 2 3 3 3 4 5% 44%	1665
December	1st to 10th	Day	10% 10% 2 7% 4 3 3 2 4 5% 51%	2610
	11th to 20th	Day	12% 10% 4 7% 5% 4 4 3 4 7% 41%	3008
	21st to end	Day	19% 20% 5% 10% 4 4 4 2 3 4 24%	3982
January	1st to 10th	Night	15% 10% 7% 13% 5% 4 4 3 3 4 31%	6302
	11th to 20th	Night	11% 9% 4 14% 6% 6% 5% 3 3 4 36%	5900
	21st to end	Night	18% 12% 4 7% 4 4 4 3 3 4 38%	6490
February	1st to 10th	Night	15% 11% 5% 8% 4 4 4 3 5% 6% 35%	2600
	11th to 20th	Night	15% 9% 4 8% 5% 3 3 3 5% 5% 39%	2412
	21st to end	Night	15% 10% 3 7% 4 4 3 2 5% 5% 41%	1980
March	1st to 10th	Night	17% 12% 3 5% 4 3 3 2 4 5% 43%	5153
	11th to 20th	Night	12% 9% 2 5% 3 3 3 3 4 6% 49%	4980
	21st to end	Night	17% 10% 4 7% 5% 5% 5% 4 5% 6% 33%	5287
April	1st to 10th	Night	12% 6% 3 6% 4 4 3 3 5% 7% 48%	2000
	11th to 20th	Night	14% 9% 3 5% 3 3 3 3 5% 7% 45%	1881
	21st to end	Night	18% 7% 3 6% 4 4 4 3 5% 6% 40%	1900
May	1st to 10th	Night	16% 8% 2 6% 4 4 4 4 5% 9% 40%	3051
	11th to 20th	Night	14% 7% 3 6% 5% 4 5% 3 5% 7% 43%	2548
	21st to end	Night	9% 7% 2 6% 4 5% 5% 4 5% 8% 43%	2743
June	1st to 10th	Night	8% 5% 2 5% 5% 3 4 4 6% 9% 50%	1520
	11th to 20th	Night	6% 4 1 4 4 3 4 4 5% 11% 52%	1520
	21st to end	Night	4 3 1 5% 4 3 4 4 6% 10% 57%	1520
July	1st to 10th	Night	12% 5% 2 6% 5% 3 4 4 6% 8% 45%	2530
	11th to 20th	Night	4 4 2 4 3 3 4 3 6% 9% 58%	2591
	21st to end	Night	6% 6% 3 6% 5% 4 6% 4 7% 9% 44%	3098
August	1st to 10th	Night	5% 3 1 4 3 3 3 3 6% 8% 61%	2836
	11th to 20th	Night	11% 5% 2 5% 4 3 4 3 6% 7% 49%	3033
	21st to end	Night	6% 3 1 4 3 3 4 3 6% 8% 58%	3476
September	1st to 10th	Night	12% 5% 2 5% 3 3 3 2 4 6% 55%	1900
	11th to 20th	Night	9% 5% 2 6% 4 4 4 3 4 8% 51%	1900
	21st to end	Night	9% 5% 2 5% 4 4 3 3 5% 5% 56%	2130
October	1st to 10th	Night	8% 4 1 4 3 3 3 2 4 7% 60%	2280
	11th to 20th	Night	13% 6% 1 5% 2 3 3 2 5% 6% 53%	2280
	21st to end	Night	19% 7% 1 4 3 3 3 2 4 5% 49%	2508
November	1st to 10th	Night	10% 7% 2 5% 3 3 3 2 4 5% 56%	2481
	11th to 20th	Night	14% 7% 2 5% 4 3 4 2 4 6% 49%	2600
	21st to end	Night	16% 10% 3 5% 4 3 3 2 4 5% 45%	2730
December	1st to 10th	Night	11% 9% 3 7% 4 3 3 3 5% 5% 47%	4580
	11th to 20th	Night	15% 9% 4 6% 4 4 4 3 4 6% 41%	5199
	21st to end	Night	23% 17% 5% 9% 5% 4 4 3 3 4 23%	6996

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	53% 5% 10% 19% 11% 2	3660
	11th to 20th	Day	43% 4 9% 24% 16% 4	4080
	21st to end	Day	49% 4 9% 15% 18% 5%	4488
February	1st to 10th	Day	53% 4 10% 21% 11% 1	1800
	11th to 20th	Day	48% 5% 10% 18% 14% 5%	1882
	21st to end	Day	44% 5% 8% 23% 15% 5%	1650
March	1st to 10th	Day	41% 3 6% 21% 22% 7%	4742
	11th to 20th	Day	32% 4 8% 24% 25% 7%	4980
	21st to end	Day	45% 8% 13% 26% 8%	5642
April	1st to 10th	Day	39% 6% 12% 23% 19% 1	2400
	11th to 20th	Day	44% 4 11% 22% 16% 3	2254
	21st to end	Day	49% 6% 12% 20% 13% 1	2280
May	1st to 10th	Day	44% 10% 13% 21% 12% 1	3864
	11th to 20th	Day	45% 8% 10% 24% 13% 1	4357
	21st to end	Day	38% 8% 10% 23% 20% 1	4837
June	1st to 10th	Day	33% 10% 14% 26% 15% 2	2660
	11th to 20th	Day	29% 7% 13% 28% 19% 3	2660
	21st to end	Day	28% 9% 17% 26% 15% 5%	2660
July	1st to 10th	Day	38% 7% 13% 27% 12% 2	4371
	11th to 20th	Day	27% 8% 15% 32% 16% 2	4286
	21st to end	Day	36% 9% 17% 27% 9% 1	4325
August	1st to 10th	Day	26% 8% 17% 34% 15%	4090
	11th to 20th	Day	38% 7% 13% 24% 17% 2	3833
	21st to end	Day	28% 7% 16% 33% 14% 3	4179
September	1st to 10th	Day	31% 7% 11% 26% 20% 5%	2280
	11th to 20th	Day	34% 4 9% 26% 25% 2	2280
	21st to end	Day	32% 6% 9% 27% 23% 3	2025
October	1st to 10th	Day	18% 3 6% 19% 45% 9%	3160
	11th to 20th	Day	23% 3 6% 22% 37% 10%	3140
	21st to end	Day	32% 4 7% 28% 26% 3	3428
November	1st to 10th	Day	33% 4 12% 24% 22% 5%	1815
	11th to 20th	Day	38% 4 9% 22% 22% 5%	1800
	21st to end	Day	44% 5% 8% 27% 16% 1	1665
December	1st to 10th	Day	37% 4 10% 33% 15% 1	2610
	11th to 20th	Day	44% 4 12% 22% 17% 1	3005
	21st to end	Day	64% 5% 11% 12% 7% 1	3982
January	1st to 10th	Night	57% 4 8% 20% 10% 1	6302
	11th to 20th	Night	53% 4 6% 22% 12% 2	5900
	21st to end	Night	51% 4 9% 19% 15% 3	6490
February	1st to 10th	Night	51% 5% 10% 19% 13% 2	2600
	11th to 20th	Night	47% 4 10% 21% 16% 3	2413
	21st to end	Night	45% 4 10% 22% 15% 4	1980
March	1st to 10th	Night	45% 4 6% 21% 20% 3	5153
	11th to 20th	Night	36% 4 9% 23% 22% 7%	4980
	21st to end	Night	49% 8% 10% 22% 9% 1	5287
April	1st to 10th	Night	35% 5% 12% 26% 18% 3	2000
	11th to 20th	Night	39% 6% 10% 23% 17% 5%	1881
	21st to end	Night	44% 5% 10% 23% 17% 1	1900
May	1st to 10th	Night	40% 8% 16% 20% 14% 2	3081
	11th to 20th	Night	40% 8% 12% 25% 13% 1	2549
	21st to end	Night	36% 10% 14% 21% 16% 2	2751
June	1st to 10th	Night	31% 8% 14% 27% 17% 3	1520
	11th to 20th	Night	24% 8% 13% 27% 24% 3	1520
	21st to end	Night	21% 8% 16% 29% 19% 7%	1520
July	1st to 10th	Night	36% 6% 12% 28% 15% 3	2490
	11th to 20th	Night	22% 6% 12% 38% 21% 2	2543
	21st to end	Night	33% 8% 19% 26% 13% 1	2999
August	1st to 10th	Night	20% 7% 19% 31% 20% 1	2826
	11th to 20th	Night	34% 6% 15% 26% 16% 3	3062
	21st to end	Night	22% 6% 17% 35% 16% 3	3476
September	1st to 10th	Night	31% 5% 10% 26% 23% 6%	1900
	11th to 20th	Night	31% 6% 10% 23% 27% 3	1900
	21st to end	Night	30% 6% 9% 25% 27% 3	2130
October	1st to 10th	Night	15% 3 7% 18% 48% 9%	3800
	11th to 20th	Night	22% 3 7% 22% 34% 13%	3779
	21st to end	Night	32% 4 8% 26% 27% 3	4120
November	1st to 10th	Night	31% 5% 11% 26% 21% 6%	2481
	11th to 20th	Night	36% 4 8% 24% 23% 5%	2600
	21st to end	Night	43% 4 10% 25% 17% 2	2730
December	1st to 10th	Night	39% 4 9% 33% 15% 1	4580
	11th to 20th	Night	44% 4 12% 22% 18% 1	5201
	21st to end	Night	64% 5% 11% 13% 5% 1	6996

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	27% 26% 31% 14% 3	300
	11th to 20th	Day	30% 25% 37% 9%	300
	21st to end	Day	18% 30% 40% 11% 2	330
February	1st to 10th	Day	27% 25% 35% 12% 1	300
	11th to 20th	Day	31% 27% 29% 10% 2 1	300
	21st to end	Day	29% 24% 37% 8% 1	249
March	1st to 10th	Day	24% 28% 39% 8% 1	300
	11th to 20th	Day	33% 21% 33% 11% 1 1	300
	21st to end	Day	35% 22% 29% 12% 1	405
April	1st to 10th	Day	23% 18% 37% 16% 4 1	500
	11th to 20th	Day	27% 19% 31% 17% 6%	452
	21st to end	Day	25% 18% 35% 17% 5% 1	460
May	1st to 10th	Day	22% 16% 36% 20% 5% 1	501
	11th to 20th	Day	17% 16% 28% 26% 11% 2	675
	21st to end	Day	14% 10% 34% 25% 13% 4	734
June	1st to 10th	Day	10% 6% 26% 34% 20% 5%	680
	11th to 20th	Day	9% 5% 28% 37% 19% 3	680
	21st to end	Day	6% 8% 35% 35% 14% 3	680
July	1st to 10th	Day	13% 3 17% 31% 28% 9%	671
	11th to 20th	Day	6% 5% 24% 37% 24% 5%	668
	21st to end	Day	9% 3 20% 35% 27% 6%	739
August	1st to 10th	Day	9% 3 19% 40% 24% 5%	676
	11th to 20th	Day	12% 5% 21% 34% 24% 5%	522
	21st to end	Day	10% 2 19% 31% 31% 7%	539
September	1st to 10th	Day	12% 4 19% 33% 25% 7%	490
	11th to 20th	Day	10% 3 20% 32% 24% 11%	490
	21st to end	Day	12% 10% 23% 32% 18% 5%	405
October	1st to 10th	Day	13% 12% 31% 28% 13% 3	300
	11th to 20th	Day	20% 19% 31% 23% 5% 1	300
	21st to end	Day	30% 24% 28% 16% 2	330
November	1st to 10th	Day	18% 14% 40% 18% 8% 2	300
	11th to 20th	Day	23% 23% 30% 17% 6% 1	300
	21st to end	Day	27% 19% 30% 20% 3 1	300
December	1st to 10th	Day	19% 27% 31% 15% 6% 2	300
	11th to 20th	Day	25% 20% 37% 14% 3	300
	21st to end	Day	28% 25% 33% 10% 3	330
January	1st to 10th	Night	21% 21% 35% 19% 4	1000
	11th to 20th	Night	23% 24% 33% 18% 3	1000
	21st to end	Night	20% 20% 39% 19% 1	1100
February	1st to 10th	Night	24% 18% 38% 17% 2	1000
	11th to 20th	Night	23% 21% 37% 18% 2	857
	21st to end	Night	24% 21% 37% 17% 2	660
March	1st to 10th	Night	24% 18% 36% 19% 2	710
	11th to 20th	Night	24% 15% 37% 21% 4	600
	21st to end	Night	25% 19% 35% 18% 3	660
April	1st to 10th	Night	17% 20% 38% 23% 3	600
	11th to 20th	Night	20% 15% 35% 25% 5%	565
	21st to end	Night	22% 14% 36% 22% 6%	570
May	1st to 10th	Night	17% 12% 33% 29% 9%	570
	11th to 20th	Night	17% 9% 28% 32% 13% 1	561
	21st to end	Night	12% 6% 29% 32% 18% 2	617
June	1st to 10th	Night	10% 3 21% 41% 23% 2	570
	11th to 20th	Night	7% 3 27% 42% 20% 1	570
	21st to end	Night	5% 3 26% 45% 19% 2	570
July	1st to 10th	Night	11% 2 12% 40% 30% 5%	555
	11th to 20th	Night	3 3 20% 41% 30% 3	552
	21st to end	Night	7% 1 17% 44% 28% 2	624
August	1st to 10th	Night	7% 2 15% 44% 32% 1	567
	11th to 20th	Night	7% 2 18% 39% 30% 3	564
	21st to end	Night	7% 2 16% 40% 33% 3	627
September	1st to 10th	Night	14% 3 15% 37% 27% 4	570
	11th to 20th	Night	11% 4 15% 38% 28% 5%	570
	21st to end	Night	10% 6% 25% 33% 22% 4	719
October	1st to 10th	Night	10% 5% 29% 30% 23% 3	760
	11th to 20th	Night	16% 14% 34% 26% 10% 1	760
	21st to end	Night	23% 14% 34% 23% 6%	836
November	1st to 10th	Night	14% 12% 38% 26% 9%	780
	11th to 20th	Night	19% 17% 33% 24% 7%	800
	21st to end	Night	23% 17% 35% 20% 5%	930
December	1st to 10th	Night	22% 17% 35% 20% 4 1	1000
	11th to 20th	Night	25% 14% 33% 24% 3	1000
	21st to end	Night	28% 19% 34% 18% 2	1100

Page generated at 2025-04-08 08:17:28. Version ac07

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