Old Broadwell Mill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Old Broadwell Mill Observatory clear sky chart from 2005-11-06 to 2024-11-04.

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	13% 6% 2 6% 5% 5% 5% 4 6% 8% 41%	100867
	Night	13% 7% 2 6% 4 4 4 4 5% 7% 44%	98111
Transparency	Day	39% 7% 11% 19% 19% 5%	104685
	Night	37% 6% 10% 20% 20% 7%	102431
Seeing	Day	15% 10% 22% 24% 19% 10%	14667
	Night	15% 8% 22% 30% 21% 4	24646

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	17% 13% 3 6% 3 4 4 3 5% 5% 36%	2836
	11th to 20th	Day	14% 8% 3 6% 4 4 3 3 4 4 48%	2840
	21st to end	Day	23% 10% 3 6% 3 3 3 2 3 6% 39%	3453
February	1st to 10th	Day	19% 9% 3 5% 5% 4 3 3 5% 5% 38%	1900
	11th to 20th	Day	22% 9% 2 6% 4 3 3 2 4 5% 39%	1848
	21st to end	Day	20% 8% 3 7% 5% 4 3 4 4 6% 37%	1570
March	1st to 10th	Day	23% 8% 3 7% 4 4 3 4 5% 6% 33%	3120
	11th to 20th	Day	15% 8% 2 5% 4 4 3 4 5% 7% 43%	3434
	21st to end	Day	18% 6% 3 7% 4 4 4 4 6% 7% 38%	3843
April	1st to 10th	Day	13% 6% 2 6% 5% 4 4 3 5% 7% 45%	2280
	11th to 20th	Day	14% 6% 2 5% 4 4 4 4 5% 6% 46%	2254
	21st to end	Day	10% 4 2 5% 5% 4 5% 4 6% 8% 49%	2321
May	1st to 10th	Day	11% 5% 2 6% 5% 5% 5% 4 6% 8% 43%	4082
	11th to 20th	Day	16% 8% 2 5% 4 4 4 4 5% 8% 38%	4081
	21st to end	Day	8% 5% 2 6% 4 5% 5% 5% 7% 9% 45%	4476
June	1st to 10th	Day	11% 6% 2 8% 6% 6% 6% 5% 8% 9% 32%	2470
	11th to 20th	Day	5% 4 2 6% 5% 5% 5% 4 8% 11% 44%	2470
	21st to end	Day	8% 5% 2 6% 5% 6% 7% 6% 9% 10% 37%	2470
July	1st to 10th	Day	8% 6% 2 7% 6% 7% 8% 6% 10% 12% 28%	4120
	11th to 20th	Day	7% 5% 2 7% 5% 6% 6% 5% 8% 12% 36%	4120
	21st to end	Day	10% 9% 4 10% 7% 7% 7% 6% 8% 10% 20%	4466
August	1st to 10th	Day	4 2 1 5% 4 5% 6% 5% 8% 13% 48%	3882
	11th to 20th	Day	7% 4 2 5% 4 5% 5% 5% 7% 11% 45%	3729
	21st to end	Day	6% 4 2 5% 5% 5% 5% 5% 6% 8% 49%	4180
September	1st to 10th	Day	9% 5% 3 7% 6% 5% 5% 5% 6% 8% 40%	2180
	11th to 20th	Day	13% 6% 2 7% 4 5% 4 4 6% 6% 42%	2090
	21st to end	Day	12% 5% 2 6% 4 5% 3 3 5% 7% 48%	2090
October	1st to 10th	Day	11% 4 2 5% 3 4 4 3 5% 5% 54%	2090
	11th to 20th	Day	11% 5% 2 4 3 2 2 3 4 6% 57%	2085
	21st to end	Day	13% 5% 1 5% 3 3 4 3 4 5% 54%	1981
November	1st to 10th	Day	14% 6% 2 4 4 3 3 2 3 4 56%	1699
	11th to 20th	Day	13% 6% 2 4 3 3 3 3 4 6% 52%	1710
	21st to end	Day	14% 6% 2 6% 4 3 3 4 5% 7% 45%	1710
December	1st to 10th	Day	21% 7% 3 6% 4 3 3 3 5% 5% 39%	1710
	11th to 20th	Day	18% 6% 3 6% 5% 4 4 3 4 5% 42%	2153
	21st to end	Day	20% 9% 5% 6% 5% 4 4 2 4 6% 35%	3124
January	1st to 10th	Night	17% 12% 2 5% 3 4 4 3 4 6% 39%	4109
	11th to 20th	Night	16% 10% 3 5% 4 3 3 3 4 5% 44%	4120
	21st to end	Night	21% 14% 2 5% 3 3 3 2 3 4 39%	4198
February	1st to 10th	Night	17% 8% 3 6% 4 4 3 3 5% 6% 41%	2280
	11th to 20th	Night	22% 8% 2 6% 4 3 3 2 4 4 43%	2218
	21st to end	Night	19% 8% 3 6% 4 4 4 4 5% 7% 38%	1884
March	1st to 10th	Night	23% 10% 3 6% 4 4 4 3 4 5% 34%	3733
	11th to 20th	Night	13% 6% 2 5% 3 3 4 4 6% 8% 47%	3525
	21st to end	Night	17% 7% 3 7% 5% 5% 4 3 4 6% 41%	3803
April	1st to 10th	Night	12% 5% 2 4 4 5% 4 5% 6% 7% 47%	1900
	11th to 20th	Night	14% 5% 2 4 3 3 3 3 6% 6% 50%	1875
	21st to end	Night	9% 6% 2 6% 4 4 4 3 5% 5% 53%	1857
May	1st to 10th	Night	10% 6% 2 7% 5% 5% 5% 4 5% 8% 43%	2813
	11th to 20th	Night	15% 8% 2 6% 4 4 4 3 6% 7% 39%	2812
	21st to end	Night	6% 4 2 5% 4 5% 5% 5% 8% 11% 47%	3079
June	1st to 10th	Night	5% 5% 2 7% 5% 6% 6% 6% 9% 12% 37%	1710
	11th to 20th	Night	3 3 2 3 4 4 5% 5% 7% 12% 51%	1710
	21st to end	Night	5% 5% 1 6% 4 4 5% 5% 7% 13% 46%	1710
July	1st to 10th	Night	7% 5% 2 7% 6% 6% 6% 6% 9% 13% 33%	2840
	11th to 20th	Night	6% 5% 2 6% 5% 4 5% 5% 10% 12% 39%	2840
	21st to end	Night	8% 9% 4 11% 7% 7% 7% 6% 8% 10% 24%	3087
August	1st to 10th	Night	4 3 1 5% 3 4 4 4 7% 12% 53%	3042
	11th to 20th	Night	7% 5% 2 6% 4 3 5% 4 5% 9% 51%	3100
	21st to end	Night	7% 4 2 4 3 4 4 3 5% 8% 55%	3476
September	1st to 10th	Night	7% 4 3 6% 5% 5% 6% 5% 7% 8% 44%	1978
	11th to 20th	Night	11% 5% 3 7% 4 4 4 4 5% 8% 46%	2090
	21st to end	Night	8% 4 2 5% 3 4 3 4 6% 8% 52%	2090
October	1st to 10th	Night	9% 4 1 4 3 3 3 2 4 6% 61%	2090
	11th to 20th	Night	11% 5% 2 4 3 4 3 3 4 6% 55%	2094
	21st to end	Night	13% 5% 1 5% 4 3 3 3 3 4 55%	2612
November	1st to 10th	Night	11% 4 1 4 3 3 3 3 5% 6% 56%	2452
	11th to 20th	Night	12% 7% 2 4 3 3 3 2 4 6% 54%	2470
	21st to end	Night	14% 7% 2 6% 4 3 4 3 4 6% 48%	2470
December	1st to 10th	Night	18% 8% 2 6% 4 4 4 4 5% 6% 40%	2470
	11th to 20th	Night	17% 9% 2 5% 3 3 4 2 3 4 48%	3042
	21st to end	Night	17% 10% 4 7% 4 4 4 4 6% 8% 33%	4532

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	50% 4 7% 14% 21% 4	2837
	11th to 20th	Day	40% 4 7% 23% 23% 3	2840
	21st to end	Day	49% 2 7% 17% 19% 5%	3453
February	1st to 10th	Day	48% 3 8% 18% 19% 3	1900
	11th to 20th	Day	49% 3 5% 18% 19% 6%	1858
	21st to end	Day	49% 5% 6% 12% 21% 7%	1570
March	1st to 10th	Day	52% 5% 9% 11% 14% 9%	3120
	11th to 20th	Day	41% 4 8% 18% 23% 7%	3434
	21st to end	Day	44% 6% 12% 16% 18% 4	3843
April	1st to 10th	Day	38% 5% 10% 21% 18% 8%	2280
	11th to 20th	Day	39% 5% 8% 18% 24% 7%	2254
	21st to end	Day	33% 6% 10% 25% 23% 3	2321
May	1st to 10th	Day	36% 8% 13% 23% 17% 3	4120
	11th to 20th	Day	43% 6% 13% 26% 12% 1	4085
	21st to end	Day	33% 9% 12% 26% 18% 2	4489
June	1st to 10th	Day	44% 11% 14% 17% 13% 1	2470
	11th to 20th	Day	31% 8% 20% 22% 17% 1	2470
	21st to end	Day	37% 11% 16% 22% 12% 3	2470
July	1st to 10th	Day	42% 13% 21% 17% 6% 1	4055
	11th to 20th	Day	37% 12% 22% 22% 6% 1	4051
	21st to end	Day	56% 13% 14% 13% 5%	4324
August	1st to 10th	Day	26% 8% 14% 36% 15%	3869
	11th to 20th	Day	31% 9% 18% 26% 14% 2	3765
	21st to end	Day	31% 9% 15% 17% 25% 3	4179
September	1st to 10th	Day	39% 10% 14% 16% 15% 6%	2180
	11th to 20th	Day	41% 8% 11% 19% 18% 3	2090
	21st to end	Day	36% 5% 12% 20% 21% 6%	2090
October	1st to 10th	Day	25% 4 7% 10% 36% 18%	3480
	11th to 20th	Day	20% 3 4 16% 29% 28%	3441
	21st to end	Day	23% 3 7% 21% 35% 10%	3244
November	1st to 10th	Day	34% 3 7% 16% 29% 10%	1699
	11th to 20th	Day	34% 4 7% 18% 26% 10%	1710
	21st to end	Day	38% 5% 7% 19% 25% 6%	1710
December	1st to 10th	Day	46% 6% 8% 16% 19% 5%	1710
	11th to 20th	Day	46% 3 6% 17% 21% 6%	2150
	21st to end	Day	51% 4 8% 17% 17% 2	3124
January	1st to 10th	Night	46% 3 6% 17% 24% 3	4109
	11th to 20th	Night	43% 4 6% 22% 19% 6%	4120
	21st to end	Night	51% 3 5% 14% 23% 5%	4198
February	1st to 10th	Night	44% 4 7% 18% 20% 7%	2280
	11th to 20th	Night	47% 4 5% 16% 20% 8%	2219
	21st to end	Night	46% 6% 7% 13% 19% 9%	1884
March	1st to 10th	Night	52% 5% 9% 13% 15% 6%	3733
	11th to 20th	Night	33% 5% 10% 18% 24% 10%	3525
	21st to end	Night	45% 4 7% 19% 20% 5%	3803
April	1st to 10th	Night	35% 6% 11% 20% 20% 7%	1900
	11th to 20th	Night	35% 4 7% 20% 22% 12%	1875
	21st to end	Night	33% 5% 10% 26% 21% 6%	1857
May	1st to 10th	Night	36% 10% 12% 21% 19% 2	2840
	11th to 20th	Night	42% 7% 13% 25% 12% 1	2813
	21st to end	Night	27% 11% 14% 29% 18% 2	3087
June	1st to 10th	Night	35% 12% 15% 22% 15% 2	1710
	11th to 20th	Night	23% 11% 23% 23% 17% 2	1710
	21st to end	Night	29% 10% 18% 22% 17% 5%	1710
July	1st to 10th	Night	38% 13% 23% 18% 7% 1	2795
	11th to 20th	Night	32% 13% 24% 24% 6% 2	2786
	21st to end	Night	53% 13% 14% 14% 6% 1	2988
August	1st to 10th	Night	23% 8% 16% 39% 13% 1	3031
	11th to 20th	Night	29% 7% 17% 29% 15% 2	3130
	21st to end	Night	27% 7% 14% 19% 27% 5%	3476
September	1st to 10th	Night	33% 10% 17% 18% 16% 6%	1978
	11th to 20th	Night	36% 9% 10% 21% 21% 3	2090
	21st to end	Night	30% 6% 13% 21% 23% 7%	2090
October	1st to 10th	Night	23% 3 7% 16% 33% 19%	3480
	11th to 20th	Night	19% 2 4 16% 30% 28%	3477
	21st to end	Night	22% 2 5% 24% 33% 15%	4299
November	1st to 10th	Night	30% 4 10% 19% 25% 13%	2452
	11th to 20th	Night	32% 4 7% 19% 27% 12%	2470
	21st to end	Night	38% 4 7% 20% 24% 7%	2470
December	1st to 10th	Night	45% 6% 7% 18% 19% 4	2470
	11th to 20th	Night	41% 3 7% 15% 29% 5%	3044
	21st to end	Night	48% 4 10% 19% 17% 2	4532

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% 37% 13% 3	270
	11th to 20th	Day	26% 22% 31% 16% 4	270
	21st to end	Day	24% 27% 35% 11% 3 1	297
February	1st to 10th	Day	25% 21% 36% 14% 4	270
	11th to 20th	Day	35% 21% 29% 12% 3	270
	21st to end	Day	28% 26% 35% 10%	225
March	1st to 10th	Day	26% 21% 33% 15% 3 1	270
	11th to 20th	Day	22% 18% 33% 18% 7% 1	427
	21st to end	Day	22% 15% 34% 21% 7%	506
April	1st to 10th	Day	22% 14% 32% 20% 11% 2	460
	11th to 20th	Day	18% 14% 29% 26% 12% 1	452
	21st to end	Day	14% 10% 31% 30% 13% 2	460
May	1st to 10th	Day	14% 10% 28% 25% 17% 6%	463
	11th to 20th	Day	12% 6% 21% 32% 20% 10%	487
	21st to end	Day	10% 5% 20% 31% 20% 15%	529
June	1st to 10th	Day	13% 4 15% 31% 23% 13%	490
	11th to 20th	Day	7% 3 16% 24% 28% 23%	490
	21st to end	Day	11% 4 13% 24% 28% 19%	490
July	1st to 10th	Day	9% 2 8% 26% 29% 26%	485
	11th to 20th	Day	7% 1 6% 23% 32% 30%	484
	21st to end	Day	8% 3 10% 23% 33% 24%	532
August	1st to 10th	Day	8% 2 11% 21% 34% 24%	486
	11th to 20th	Day	8% 4 10% 27% 33% 18%	479
	21st to end	Day	15% 2 9% 21% 34% 19%	539
September	1st to 10th	Day	8% 3 10% 30% 35% 14%	490
	11th to 20th	Day	14% 4 13% 24% 32% 13%	490
	21st to end	Day	13% 3 17% 26% 30% 10%	490
October	1st to 10th	Day	10% 4 22% 33% 20% 10%	490
	11th to 20th	Day	11% 8% 23% 31% 23% 3	490
	21st to end	Day	16% 10% 20% 33% 19% 2	430
November	1st to 10th	Day	20% 8% 25% 32% 11% 4	279
	11th to 20th	Day	15% 15% 37% 26% 7%	270
	21st to end	Day	14% 18% 35% 23% 9% 1	270
December	1st to 10th	Day	28% 19% 30% 19% 4 1	270
	11th to 20th	Day	23% 17% 33% 19% 7% 1	270
	21st to end	Day	27% 18% 33% 18% 4	297
January	1st to 10th	Night	22% 16% 31% 26% 5%	760
	11th to 20th	Night	22% 16% 30% 24% 7%	760
	21st to end	Night	23% 15% 33% 26% 3	836
February	1st to 10th	Night	21% 12% 30% 32% 5%	760
	11th to 20th	Night	25% 16% 32% 24% 3	743
	21st to end	Night	23% 17% 34% 24% 2	628
March	1st to 10th	Night	21% 13% 31% 30% 5%	760
	11th to 20th	Night	19% 12% 35% 25% 9% 1	760
	21st to end	Night	20% 13% 29% 29% 9%	834
April	1st to 10th	Night	15% 10% 34% 28% 12% 1	570
	11th to 20th	Night	17% 11% 31% 28% 13% 1	563
	21st to end	Night	12% 7% 25% 40% 16% 1	570
May	1st to 10th	Night	10% 5% 26% 32% 23% 3	570
	11th to 20th	Night	10% 4 19% 34% 27% 5%	561
	21st to end	Night	9% 2 11% 38% 35% 6%	617
June	1st to 10th	Night	7% 2 12% 37% 36% 5%	570
	11th to 20th	Night	3 1 12% 30% 40% 15%	570
	21st to end	Night	7% 1 9% 28% 44% 10%	570
July	1st to 10th	Night	8% 2 6% 24% 45% 15%	555
	11th to 20th	Night	6% 5% 23% 51% 16%	552
	21st to end	Night	7% 1 7% 26% 45% 14%	624
August	1st to 10th	Night	6% 2 6% 27% 45% 14%	567
	11th to 20th	Night	10% 2 7% 28% 44% 9%	564
	21st to end	Night	14% 1 7% 26% 40% 11%	627
September	1st to 10th	Night	9% 2 8% 29% 41% 11%	648
	11th to 20th	Night	13% 3 12% 28% 38% 5%	760
	21st to end	Night	10% 2 15% 34% 36% 3	760
October	1st to 10th	Night	10% 4 20% 35% 26% 5%	760
	11th to 20th	Night	12% 7% 24% 34% 21% 2	760
	21st to end	Night	15% 8% 20% 37% 18% 2	836
November	1st to 10th	Night	13% 7% 19% 37% 22% 2	755
	11th to 20th	Night	16% 9% 28% 33% 12% 1	760
	21st to end	Night	17% 11% 25% 35% 11% 1	760
December	1st to 10th	Night	22% 13% 28% 28% 8% 1	760
	11th to 20th	Night	25% 9% 28% 29% 9% 1	760
	21st to end	Night	25% 13% 27% 28% 7%	836

Page generated at 2024-11-01 21:47:40. Version ac07

Copyright © 2024 Attilla Danko.