Broemmelsiek Park Astronomy Area
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Broemmelsiek Park Astronomy Area clear sky chart from 2005-11-06 to 2025-04-26.

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% 7% 3 7% 4 4 4 4 5% 7% 43%	113690
	Night	13% 8% 3 7% 4 4 4 3 5% 6% 43%	115129
Transparency	Day	39% 5% 11% 25% 18% 3	117325
	Night	41% 4 10% 24% 18% 3	119638
Seeing	Day	16% 12% 28% 25% 14% 4	16188
	Night	17% 12% 30% 28% 12% 1	26161

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% 5% 4 4 3 5% 6% 30%	3617
	11th to 20th	Day	9% 9% 3 9% 5% 6% 4 4 4 6% 41%	3968
	21st to end	Day	17% 13% 5% 8% 4 3 3 2 4 4 36%	4488
February	1st to 10th	Day	15% 11% 4 9% 5% 4 4 4 5% 5% 35%	1800
	11th to 20th	Day	15% 10% 4 7% 5% 4 4 4 4 6% 38%	1900
	21st to end	Day	14% 11% 3 8% 4 3 4 3 5% 6% 40%	1650
March	1st to 10th	Day	16% 10% 2 5% 3 3 3 2 3 4 49%	4613
	11th to 20th	Day	9% 6% 2 5% 3 3 4 3 6% 6% 52%	4980
	21st to end	Day	13% 8% 3 7% 6% 5% 5% 4 6% 7% 36%	5725
April	1st to 10th	Day	12% 7% 3 7% 5% 5% 4 3 6% 7% 42%	2400
	11th to 20th	Day	17% 8% 3 7% 4 4 4 3 4 6% 41%	2374
	21st to end	Day	17% 6% 3 8% 5% 4 4 4 6% 7% 36%	2340
May	1st to 10th	Day	14% 8% 3 8% 5% 4 5% 5% 7% 10% 32%	3837
	11th to 20th	Day	17% 8% 2 6% 4 4 4 3 5% 8% 38%	4399
	21st to end	Day	9% 6% 2 6% 5% 4 5% 4 5% 8% 45%	4824
June	1st to 10th	Day	8% 5% 2 5% 5% 4 4 3 6% 9% 48%	2660
	11th to 20th	Day	7% 4 2 4 4 4 4 4 7% 9% 50%	2660
	21st to end	Day	4 4 2 5% 5% 4 6% 5% 8% 11% 46%	2660
July	1st to 10th	Day	13% 6% 2 6% 4 4 5% 4 7% 9% 40%	4440
	11th to 20th	Day	4 4 1 5% 4 5% 5% 5% 7% 10% 50%	4440
	21st to end	Day	7% 5% 2 6% 5% 5% 5% 5% 8% 11% 41%	4528
August	1st to 10th	Day	5% 4 2 5% 4 4 5% 5% 7% 10% 50%	4104
	11th to 20th	Day	13% 5% 2 5% 4 5% 5% 4 6% 9% 42%	3746
	21st to end	Day	6% 4 2 5% 4 4 4 4 6% 9% 52%	4180
September	1st to 10th	Day	12% 4 2 5% 4 3 3 3 5% 8% 50%	2280
	11th to 20th	Day	10% 5% 2 5% 3 3 4 4 5% 9% 50%	2273
	21st to end	Day	9% 5% 2 6% 3 4 4 4 5% 7% 53%	2053
October	1st to 10th	Day	10% 5% 2 5% 3 3 3 3 3 7% 56%	1900
	11th to 20th	Day	14% 6% 3 5% 3 3 3 2 4 6% 53%	1900
	21st to end	Day	18% 8% 2 5% 3 3 3 3 4 4 47%	2090
November	1st to 10th	Day	12% 7% 1 4 3 3 3 3 4 6% 54%	1766
	11th to 20th	Day	13% 8% 2 6% 4 4 3 3 5% 6% 48%	1800
	21st to end	Day	15% 10% 4 7% 4 4 4 2 4 6% 42%	1695
December	1st to 10th	Day	8% 10% 3 6% 4 4 3 2 4 6% 50%	2610
	11th to 20th	Day	12% 9% 4 9% 5% 4 4 3 4 6% 39%	3008
	21st to end	Day	22% 15% 5% 10% 5% 4 4 3 4 4 23%	3982
January	1st to 10th	Night	15% 11% 6% 12% 5% 3 4 3 4 4 32%	6348
	11th to 20th	Night	11% 11% 4 11% 5% 6% 5% 3 3 5% 35%	6010
	21st to end	Night	18% 13% 4 7% 4 4 3 3 4 5% 35%	6490
February	1st to 10th	Night	15% 13% 4 8% 5% 4 4 4 5% 5% 34%	2600
	11th to 20th	Night	16% 9% 3 8% 4 3 4 3 5% 6% 39%	2383
	21st to end	Night	15% 9% 3 9% 4 3 3 2 5% 5% 42%	1980
March	1st to 10th	Night	19% 11% 3 5% 3 3 3 3 3 4 43%	5281
	11th to 20th	Night	12% 7% 2 5% 3 3 3 3 4 7% 50%	4980
	21st to end	Night	16% 10% 3 8% 5% 4 5% 4 5% 6% 35%	5202
April	1st to 10th	Night	12% 7% 2 7% 4 3 4 3 5% 7% 46%	2000
	11th to 20th	Night	13% 6% 2 6% 4 4 4 3 6% 6% 45%	1975
	21st to end	Night	18% 7% 2 6% 4 3 3 3 5% 7% 41%	1956
May	1st to 10th	Night	16% 8% 2 6% 3 3 3 4 6% 8% 40%	3055
	11th to 20th	Night	15% 6% 2 6% 4 4 4 3 5% 7% 43%	2506
	21st to end	Night	9% 5% 2 6% 5% 5% 5% 4 6% 9% 44%	2743
June	1st to 10th	Night	8% 4 2 5% 4 5% 4 4 6% 9% 49%	1520
	11th to 20th	Night	6% 4 2 4 3 4 4 4 5% 11% 54%	1520
	21st to end	Night	4 3 1 5% 3 4 4 4 7% 9% 55%	1520
July	1st to 10th	Night	12% 6% 2 5% 4 4 4 4 5% 9% 44%	2530
	11th to 20th	Night	5% 4 1 4 4 3 3 3 6% 9% 57%	2530
	21st to end	Night	7% 5% 3 7% 5% 6% 5% 4 6% 11% 42%	3030
August	1st to 10th	Night	5% 3 1 4 3 4 4 4 6% 8% 58%	2836
	11th to 20th	Night	11% 6% 2 5% 4 4 4 3 5% 8% 48%	3071
	21st to end	Night	5% 3 1 4 3 4 4 3 5% 10% 58%	3476
September	1st to 10th	Night	12% 4 2 5% 3 4 3 3 5% 6% 53%	1900
	11th to 20th	Night	7% 6% 2 6% 4 4 4 4 5% 6% 52%	1900
	21st to end	Night	9% 4 2 4 4 3 4 4 5% 7% 53%	2109
October	1st to 10th	Night	8% 4 2 4 3 4 3 2 4 5% 60%	2280
	11th to 20th	Night	13% 6% 2 4 3 2 3 3 4 7% 53%	2280
	21st to end	Night	16% 8% 2 5% 3 3 3 3 4 6% 48%	2508
November	1st to 10th	Night	10% 6% 2 5% 3 3 4 3 4 6% 55%	2531
	11th to 20th	Night	12% 7% 2 5% 4 3 4 3 4 7% 49%	2600
	21st to end	Night	17% 8% 3 6% 4 2 4 3 5% 5% 44%	2704
December	1st to 10th	Night	11% 9% 3 7% 4 4 3 2 4 5% 47%	4580
	11th to 20th	Night	14% 8% 3 7% 5% 4 4 4 5% 6% 41%	5199
	21st to end	Night	23% 17% 4 9% 5% 4 4 3 4 4 22%	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	56% 4 10% 19% 10% 2	3618
	11th to 20th	Day	44% 4 11% 20% 16% 5%	3968
	21st to end	Day	53% 3 8% 15% 17% 4	4488
February	1st to 10th	Day	51% 5% 12% 21% 11% 1	1800
	11th to 20th	Day	48% 5% 9% 19% 15% 4	1910
	21st to end	Day	46% 4 8% 23% 15% 4	1650
March	1st to 10th	Day	41% 3 5% 22% 25% 4	4613
	11th to 20th	Day	32% 4 8% 24% 26% 6%	4980
	21st to end	Day	45% 6% 13% 27% 9% 1	5727
April	1st to 10th	Day	42% 5% 10% 25% 17% 1	2400
	11th to 20th	Day	44% 5% 10% 23% 15% 4	2374
	21st to end	Day	46% 6% 11% 22% 14% 1	2340
May	1st to 10th	Day	45% 9% 13% 22% 10% 1	3872
	11th to 20th	Day	44% 7% 10% 25% 13% 1	4403
	21st to end	Day	36% 8% 10% 23% 22% 1	4837
June	1st to 10th	Day	32% 9% 12% 27% 17% 2	2660
	11th to 20th	Day	28% 7% 13% 26% 23% 3	2660
	21st to end	Day	28% 9% 17% 26% 15% 5%	2660
July	1st to 10th	Day	39% 6% 11% 29% 12% 2	4371
	11th to 20th	Day	28% 6% 14% 32% 18% 2	4365
	21st to end	Day	35% 7% 18% 27% 11% 1	4386
August	1st to 10th	Day	27% 7% 15% 36% 15%	4090
	11th to 20th	Day	38% 7% 12% 26% 16% 1	3782
	21st to end	Day	28% 6% 15% 33% 15% 3	4179
September	1st to 10th	Day	33% 5% 10% 26% 21% 5%	2280
	11th to 20th	Day	32% 5% 9% 26% 25% 3	2273
	21st to end	Day	31% 5% 9% 28% 24% 3	2053
October	1st to 10th	Day	19% 3 5% 18% 47% 8%	3160
	11th to 20th	Day	24% 2 7% 21% 37% 9%	3140
	21st to end	Day	33% 3 7% 28% 26% 2	3428
November	1st to 10th	Day	33% 4 11% 26% 21% 5%	1766
	11th to 20th	Day	38% 4 9% 24% 20% 5%	1800
	21st to end	Day	46% 4 8% 27% 15%	1695
December	1st to 10th	Day	38% 3 12% 31% 16%	2610
	11th to 20th	Day	48% 3 12% 22% 13% 1	3005
	21st to end	Day	65% 4 11% 12% 7% 1	3982
January	1st to 10th	Night	57% 3 9% 22% 9% 1	6348
	11th to 20th	Night	54% 3 6% 22% 12% 3	6010
	21st to end	Night	53% 3 7% 19% 16% 2	6490
February	1st to 10th	Night	52% 5% 10% 20% 12% 1	2600
	11th to 20th	Night	47% 4 9% 21% 17% 3	2384
	21st to end	Night	46% 4 9% 23% 15% 3	1980
March	1st to 10th	Night	47% 3 5% 22% 21% 2	5281
	11th to 20th	Night	36% 3 9% 23% 22% 7%	4980
	21st to end	Night	50% 5% 9% 24% 10% 1	5202
April	1st to 10th	Night	39% 4 10% 25% 18% 4	2000
	11th to 20th	Night	38% 5% 10% 23% 19% 5%	1975
	21st to end	Night	44% 4 8% 25% 17% 1	1956
May	1st to 10th	Night	41% 8% 15% 20% 14% 1	3085
	11th to 20th	Night	41% 7% 12% 27% 12% 1	2507
	21st to end	Night	35% 9% 13% 24% 18% 2	2751
June	1st to 10th	Night	29% 9% 14% 26% 18% 4	1520
	11th to 20th	Night	26% 6% 11% 27% 26% 4	1520
	21st to end	Night	25% 6% 16% 27% 20% 6%	1520
July	1st to 10th	Night	37% 6% 11% 30% 14% 3	2490
	11th to 20th	Night	24% 4 11% 37% 21% 3	2482
	21st to end	Night	35% 6% 19% 25% 13% 1	2934
August	1st to 10th	Night	23% 7% 15% 34% 19% 1	2826
	11th to 20th	Night	35% 5% 12% 26% 19% 2	3101
	21st to end	Night	24% 5% 16% 34% 18% 3	3476
September	1st to 10th	Night	32% 5% 9% 23% 24% 6%	1900
	11th to 20th	Night	32% 5% 8% 25% 26% 5%	1900
	21st to end	Night	30% 6% 9% 24% 27% 4	2109
October	1st to 10th	Night	17% 3 6% 18% 49% 8%	3800
	11th to 20th	Night	22% 3 6% 23% 36% 10%	3779
	21st to end	Night	32% 3 8% 26% 27% 5%	4120
November	1st to 10th	Night	32% 4 11% 25% 22% 6%	2531
	11th to 20th	Night	37% 4 8% 25% 23% 4	2600
	21st to end	Night	43% 4 11% 24% 17% 2	2704
December	1st to 10th	Night	41% 3 8% 33% 14% 1	4580
	11th to 20th	Night	44% 3 13% 21% 18% 1	5201
	21st to end	Night	67% 4 11% 12% 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	22% 25% 34% 15% 4	300
	11th to 20th	Day	26% 26% 34% 14%	300
	21st to end	Day	18% 25% 41% 15% 2	330
February	1st to 10th	Day	24% 23% 38% 12% 2	300
	11th to 20th	Day	28% 27% 28% 13% 3	300
	21st to end	Day	30% 22% 37% 9% 2	249
March	1st to 10th	Day	21% 22% 45% 11% 2	300
	11th to 20th	Day	31% 22% 31% 13% 3 1	300
	21st to end	Day	32% 20% 32% 12% 3	438
April	1st to 10th	Day	22% 19% 36% 15% 7% 1	500
	11th to 20th	Day	23% 21% 31% 18% 7%	492
	21st to end	Day	23% 16% 36% 18% 6%	480
May	1st to 10th	Day	18% 18% 34% 23% 6% 2	468
	11th to 20th	Day	19% 13% 30% 23% 13% 2	675
	21st to end	Day	13% 9% 31% 28% 13% 6%	734
June	1st to 10th	Day	9% 6% 25% 33% 22% 6%	680
	11th to 20th	Day	8% 5% 23% 40% 21% 4	680
	21st to end	Day	5% 7% 33% 34% 17% 4	680
July	1st to 10th	Day	11% 4 16% 29% 28% 12%	671
	11th to 20th	Day	6% 3 24% 37% 25% 4	668
	21st to end	Day	10% 4 20% 33% 29% 5%	739
August	1st to 10th	Day	8% 3 17% 39% 25% 7%	676
	11th to 20th	Day	13% 4 18% 31% 26% 7%	496
	21st to end	Day	9% 2 17% 32% 31% 10%	539
September	1st to 10th	Day	11% 5% 17% 35% 25% 8%	490
	11th to 20th	Day	11% 2 17% 30% 30% 11%	490
	21st to end	Day	12% 9% 21% 30% 21% 7%	453
October	1st to 10th	Day	10% 13% 27% 33% 14% 4	300
	11th to 20th	Day	19% 17% 32% 24% 7%	300
	21st to end	Day	28% 21% 29% 18% 4	330
November	1st to 10th	Day	16% 12% 38% 21% 9% 3	300
	11th to 20th	Day	20% 20% 31% 19% 7% 2	300
	21st to end	Day	27% 16% 31% 22% 4 1	300
December	1st to 10th	Day	18% 23% 36% 15% 5% 3	300
	11th to 20th	Day	22% 19% 35% 20% 4	300
	21st to end	Day	24% 25% 37% 11% 3	330
January	1st to 10th	Night	19% 19% 37% 21% 4	1000
	11th to 20th	Night	23% 21% 34% 19% 3	1000
	21st to end	Night	19% 20% 39% 21% 1	1100
February	1st to 10th	Night	23% 17% 38% 20% 2	1000
	11th to 20th	Night	23% 19% 37% 19% 2	828
	21st to end	Night	23% 17% 41% 17% 2	660
March	1st to 10th	Night	23% 17% 38% 19% 3	760
	11th to 20th	Night	25% 12% 35% 23% 5%	600
	21st to end	Night	26% 16% 34% 19% 5%	660
April	1st to 10th	Night	16% 18% 38% 23% 5%	600
	11th to 20th	Night	18% 14% 35% 25% 7%	593
	21st to end	Night	20% 13% 37% 25% 5%	587
May	1st to 10th	Night	17% 10% 33% 31% 8% 1	570
	11th to 20th	Night	17% 8% 29% 30% 14% 1	561
	21st to end	Night	11% 6% 26% 37% 19% 2	617
June	1st to 10th	Night	9% 3 22% 39% 26% 1	570
	11th to 20th	Night	8% 2 25% 45% 19% 1	570
	21st to end	Night	4 2 27% 45% 20% 1	570
July	1st to 10th	Night	12% 2 13% 38% 30% 6%	555
	11th to 20th	Night	5% 1 19% 42% 31% 2	552
	21st to end	Night	7% 1 18% 40% 32% 2	624
August	1st to 10th	Night	8% 2 13% 41% 34% 2	567
	11th to 20th	Night	7% 2 16% 40% 30% 5%	564
	21st to end	Night	6% 1 13% 42% 35% 3	627
September	1st to 10th	Night	14% 3 15% 36% 28% 5%	570
	11th to 20th	Night	9% 4 16% 34% 32% 5%	570
	21st to end	Night	11% 7% 23% 32% 23% 4	746
October	1st to 10th	Night	9% 6% 28% 31% 22% 4	760
	11th to 20th	Night	16% 12% 32% 29% 11%	760
	21st to end	Night	22% 13% 35% 24% 5%	836
November	1st to 10th	Night	14% 10% 38% 27% 10% 1	780
	11th to 20th	Night	17% 17% 34% 26% 6%	800
	21st to end	Night	23% 16% 32% 22% 6%	904
December	1st to 10th	Night	22% 16% 34% 23% 4 1	1000
	11th to 20th	Night	23% 14% 32% 27% 4	1000
	21st to end	Night	28% 18% 33% 20% 2	1100

Page generated at 2025-04-23 08:25:07. Version ac07

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