Bill Sadowski Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bill Sadowski Park clear sky chart from 2005-11-06 to 2024-05-10.

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	8% 5% 3 6% 7% 4 7% 7% 8% 11% 34%	83918
	Night	7% 5% 2 6% 6% 4 6% 6% 7% 10% 41%	85513
Transparency	Day	36% 14% 20% 18% 10% 2	83641
	Night	36% 12% 19% 20% 11% 2	85309
Seeing	Day	7% 3 14% 29% 28% 19%	15331
	Night	7% 2 12% 31% 33% 14%	25535

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	9% 7% 3 6% 6% 4 6% 6% 7% 10% 36%	2836
	11th to 20th	Day	14% 8% 4 8% 7% 5% 6% 6% 8% 9% 26%	2840
	21st to end	Day	7% 6% 3 8% 8% 5% 6% 6% 6% 8% 38%	3198
February	1st to 10th	Day	9% 5% 2 4 6% 3 6% 6% 7% 10% 43%	1900
	11th to 20th	Day	6% 4 2 3 5% 3 4 6% 6% 11% 49%	1976
	21st to end	Day	5% 3 1 4 5% 3 5% 6% 8% 10% 49%	1727
March	1st to 10th	Day	5% 4 2 6% 7% 4 7% 8% 9% 12% 36%	3435
	11th to 20th	Day	4 2 1 3 4 3 4 5% 7% 11% 54%	3480
	21st to end	Day	8% 4 2 4 5% 3 5% 5% 6% 9% 49%	3815
April	1st to 10th	Day	3 3 2 4 5% 3 5% 5% 8% 11% 51%	2090
	11th to 20th	Day	5% 3 2 4 5% 4 6% 7% 7% 13% 44%	2146
	21st to end	Day	6% 4 2 4 4 4 5% 6% 8% 12% 46%	2280
May	1st to 10th	Day	3 3 1 4 5% 4 5% 6% 8% 12% 50%	2268
	11th to 20th	Day	9% 6% 3 6% 8% 4 7% 8% 9% 11% 28%	2124
	21st to end	Day	9% 6% 3 7% 9% 5% 8% 8% 10% 11% 25%	2518
June	1st to 10th	Day	13% 8% 4 10% 10% 5% 9% 8% 8% 10% 15%	2340
	11th to 20th	Day	7% 6% 3 9% 10% 7% 10% 9% 9% 11% 20%	2340
	21st to end	Day	6% 6% 4 8% 10% 6% 10% 8% 9% 12% 21%	2340
July	1st to 10th	Day	6% 4 3 6% 8% 5% 7% 9% 10% 15% 27%	2340
	11th to 20th	Day	5% 6% 3 6% 8% 6% 7% 10% 11% 14% 23%	2340
	21st to end	Day	5% 4 2 6% 8% 6% 8% 11% 11% 15% 25%	2547
August	1st to 10th	Day	5% 5% 3 8% 9% 6% 8% 9% 8% 11% 26%	2266
	11th to 20th	Day	4 5% 3 7% 7% 5% 8% 10% 12% 15% 25%	2126
	21st to end	Day	8% 6% 3 7% 9% 5% 10% 8% 10% 12% 21%	2195
September	1st to 10th	Day	7% 4 3 8% 8% 6% 10% 10% 11% 12% 21%	1980
	11th to 20th	Day	8% 7% 3 8% 10% 6% 9% 9% 9% 10% 22%	1980
	21st to end	Day	10% 8% 4 8% 10% 5% 8% 8% 8% 9% 21%	1980
October	1st to 10th	Day	8% 8% 3 9% 9% 5% 8% 7% 9% 12% 24%	1897
	11th to 20th	Day	10% 5% 3 6% 7% 5% 7% 7% 9% 11% 29%	1800
	21st to end	Day	11% 7% 3 7% 7% 4 6% 7% 6% 9% 34%	1980
November	1st to 10th	Day	8% 4 3 5% 6% 4 5% 6% 7% 11% 39%	1857
	11th to 20th	Day	9% 6% 3 7% 7% 4 8% 8% 7% 8% 33%	1900
	21st to end	Day	9% 4 2 6% 6% 4 7% 5% 7% 10% 39%	1900
December	1st to 10th	Day	7% 4 3 5% 5% 4 7% 5% 7% 10% 43%	1900
	11th to 20th	Day	9% 6% 3 4 5% 4 6% 6% 7% 10% 40%	2153
	21st to end	Day	13% 6% 2 7% 7% 4 6% 7% 8% 10% 32%	3124
January	1st to 10th	Night	9% 5% 2 6% 6% 4 6% 7% 9% 10% 38%	4109
	11th to 20th	Night	15% 8% 4 7% 7% 5% 6% 6% 5% 8% 28%	4120
	21st to end	Night	8% 7% 3 7% 7% 4 5% 5% 6% 9% 39%	4454
February	1st to 10th	Night	8% 4 3 4 5% 4 4 5% 7% 10% 46%	2280
	11th to 20th	Night	6% 2 2 5% 4 3 4 4 5% 8% 57%	2087
	21st to end	Night	5% 3 2 4 3 3 4 4 6% 11% 57%	1727
March	1st to 10th	Night	6% 4 2 6% 7% 4 6% 6% 8% 10% 40%	3418
	11th to 20th	Night	3 3 1 4 4 3 5% 5% 6% 11% 56%	3480
	21st to end	Night	6% 3 2 3 4 3 4 5% 6% 7% 57%	3817
April	1st to 10th	Night	4 2 1 4 4 2 4 5% 6% 12% 57%	2090
	11th to 20th	Night	5% 3 2 4 4 3 4 5% 6% 10% 53%	1980
	21st to end	Night	6% 4 2 4 5% 3 4 6% 7% 9% 51%	1900
May	1st to 10th	Night	3 2 1 3 4 2 4 4 7% 10% 60%	1897
	11th to 20th	Night	8% 4 2 6% 6% 3 6% 5% 8% 11% 41%	1770
	21st to end	Night	8% 6% 3 5% 6% 4 7% 7% 8% 11% 36%	1768
June	1st to 10th	Night	12% 8% 5% 8% 8% 5% 7% 7% 8% 10% 23%	1620
	11th to 20th	Night	7% 5% 2 5% 6% 4 7% 8% 8% 13% 33%	1620
	21st to end	Night	4 4 3 5% 7% 5% 8% 9% 10% 13% 32%	1620
July	1st to 10th	Night	4 4 3 5% 6% 4 6% 7% 10% 14% 36%	1620
	11th to 20th	Night	4 4 2 5% 6% 4 7% 8% 9% 14% 37%	1620
	21st to end	Night	3 4 1 5% 6% 5% 7% 7% 8% 13% 42%	1771
August	1st to 10th	Night	5% 5% 2 5% 6% 5% 7% 9% 9% 12% 35%	1651
	11th to 20th	Night	2 3 2 4 6% 4 7% 7% 11% 15% 38%	1774
	21st to end	Night	7% 6% 2 8% 8% 5% 7% 8% 9% 12% 29%	2154
September	1st to 10th	Night	5% 4 2 6% 7% 4 8% 9% 9% 12% 33%	1980
	11th to 20th	Night	7% 6% 3 9% 7% 5% 7% 8% 9% 10% 28%	1980
	21st to end	Night	8% 7% 3 9% 9% 4 7% 8% 9% 10% 25%	1980
October	1st to 10th	Night	8% 6% 3 7% 10% 5% 8% 7% 10% 11% 26%	2060
	11th to 20th	Night	9% 6% 2 6% 6% 4 7% 6% 9% 11% 34%	2160
	21st to end	Night	12% 6% 3 7% 6% 3 5% 5% 6% 8% 39%	2376
November	1st to 10th	Night	8% 5% 2 5% 5% 3 5% 6% 7% 9% 44%	2221
	11th to 20th	Night	10% 6% 3 6% 6% 5% 6% 6% 6% 9% 36%	2280
	21st to end	Night	8% 4 2 6% 5% 3 6% 5% 6% 10% 44%	2280
December	1st to 10th	Night	7% 5% 2 4 5% 4 5% 6% 7% 10% 45%	2280
	11th to 20th	Night	11% 5% 2 5% 4 3 4 5% 6% 9% 48%	3037
	21st to end	Night	12% 8% 3 7% 7% 4 6% 6% 7% 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	38% 10% 14% 22% 13% 3	2837
	11th to 20th	Day	49% 12% 16% 14% 7% 2	2840
	21st to end	Day	40% 9% 13% 18% 15% 6%	3198
February	1st to 10th	Day	32% 8% 16% 26% 16% 2	1900
	11th to 20th	Day	26% 7% 16% 27% 20% 5%	1986
	21st to end	Day	22% 9% 16% 25% 22% 6%	1727
March	1st to 10th	Day	29% 16% 19% 22% 11% 2	3435
	11th to 20th	Day	18% 11% 26% 34% 9% 3	3480
	21st to end	Day	27% 9% 14% 30% 17% 4	3815
April	1st to 10th	Day	21% 9% 22% 32% 13% 2	2090
	11th to 20th	Day	26% 12% 20% 24% 16% 2	2146
	21st to end	Day	25% 10% 18% 25% 19% 3	2280
May	1st to 10th	Day	19% 11% 19% 27% 17% 6%	2268
	11th to 20th	Day	40% 14% 21% 19% 6%	2128
	21st to end	Day	43% 15% 17% 16% 8%	2518
June	1st to 10th	Day	55% 17% 17% 9% 2	2340
	11th to 20th	Day	46% 21% 22% 10% 1	2340
	21st to end	Day	44% 21% 24% 9% 1	2340
July	1st to 10th	Day	36% 22% 31% 11%	2275
	11th to 20th	Day	37% 20% 32% 11%	2271
	21st to end	Day	34% 24% 31% 11% 1	2405
August	1st to 10th	Day	39% 22% 26% 11% 2	2253
	11th to 20th	Day	34% 25% 30% 11%	2126
	21st to end	Day	44% 21% 25% 9% 1	2195
September	1st to 10th	Day	42% 24% 22% 11% 1	1980
	11th to 20th	Day	44% 23% 23% 8% 2	1980
	21st to end	Day	49% 20% 16% 10% 5%	1980
October	1st to 10th	Day	44% 15% 21% 13% 6% 1	1897
	11th to 20th	Day	39% 15% 18% 16% 11% 1	1800
	21st to end	Day	41% 9% 14% 19% 12% 5%	1980
November	1st to 10th	Day	35% 11% 17% 16% 16% 5%	1857
	11th to 20th	Day	42% 11% 14% 17% 13% 3	1900
	21st to end	Day	37% 9% 16% 17% 19% 2	1900
December	1st to 10th	Day	32% 11% 16% 23% 17% 2	1900
	11th to 20th	Day	35% 9% 12% 20% 18% 5%	2150
	21st to end	Day	43% 12% 15% 15% 14% 2	3124
January	1st to 10th	Night	37% 11% 16% 19% 14% 2	4109
	11th to 20th	Night	52% 10% 14% 16% 7% 2	4120
	21st to end	Night	40% 10% 12% 18% 15% 5%	4454
February	1st to 10th	Night	32% 7% 15% 25% 18% 3	2280
	11th to 20th	Night	25% 6% 15% 26% 21% 7%	2088
	21st to end	Night	23% 8% 14% 23% 26% 7%	1727
March	1st to 10th	Night	34% 14% 15% 22% 13% 3	3418
	11th to 20th	Night	20% 10% 26% 32% 11% 2	3480
	21st to end	Night	23% 8% 14% 26% 23% 5%	3817
April	1st to 10th	Night	20% 8% 18% 35% 15% 3	2090
	11th to 20th	Night	26% 10% 18% 25% 19% 2	1980
	21st to end	Night	26% 8% 17% 28% 18% 3	1900
May	1st to 10th	Night	20% 7% 18% 33% 17% 4	1897
	11th to 20th	Night	34% 11% 19% 26% 9%	1771
	21st to end	Night	40% 10% 19% 21% 11%	1769
June	1st to 10th	Night	51% 15% 20% 12% 2	1620
	11th to 20th	Night	40% 15% 28% 16% 2	1620
	21st to end	Night	36% 20% 35% 10%	1620
July	1st to 10th	Night	33% 19% 33% 14%	1575
	11th to 20th	Night	32% 18% 35% 14% 1	1566
	21st to end	Night	29% 19% 33% 17% 2	1672
August	1st to 10th	Night	35% 19% 29% 15% 2	1640
	11th to 20th	Night	29% 20% 35% 16%	1774
	21st to end	Night	42% 17% 29% 11% 1	2154
September	1st to 10th	Night	37% 22% 26% 14% 2	1980
	11th to 20th	Night	46% 20% 23% 9% 2	1980
	21st to end	Night	50% 18% 17% 11% 5%	1980
October	1st to 10th	Night	46% 16% 19% 13% 5% 1	2060
	11th to 20th	Night	41% 12% 21% 15% 10% 1	2160
	21st to end	Night	42% 8% 11% 21% 14% 4	2376
November	1st to 10th	Night	37% 9% 16% 19% 16% 4	2221
	11th to 20th	Night	45% 10% 11% 19% 12% 3	2280
	21st to end	Night	35% 10% 16% 20% 17% 3	2280
December	1st to 10th	Night	33% 10% 16% 24% 15% 2	2280
	11th to 20th	Night	34% 8% 12% 22% 18% 7%	3039
	21st to end	Night	44% 11% 15% 14% 13% 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	7% 7% 31% 40% 15% 1	270
	11th to 20th	Day	11% 7% 30% 41% 9% 3	270
	21st to end	Day	8% 10% 36% 36% 9%	297
February	1st to 10th	Day	6% 9% 25% 43% 16% 1	270
	11th to 20th	Day	7% 6% 20% 43% 22% 4	399
	21st to end	Day	4 4 20% 41% 30% 1	382
March	1st to 10th	Day	3 5% 29% 45% 17% 2	460
	11th to 20th	Day	6% 4 26% 38% 24% 2	460
	21st to end	Day	4 4 21% 44% 21% 6%	506
April	1st to 10th	Day	4 3 26% 41% 20% 5%	460
	11th to 20th	Day	4 3 25% 40% 21% 7%	452
	21st to end	Day	5% 3 17% 42% 27% 7%	460
May	1st to 10th	Day	2 1 11% 41% 32% 13%	459
	11th to 20th	Day	9% 3 14% 30% 30% 13%	447
	21st to end	Day	10% 3 6% 25% 34% 22%	485
June	1st to 10th	Day	12% 2 9% 23% 31% 23%	450
	11th to 20th	Day	7% 1 5% 17% 34% 36%	450
	21st to end	Day	4 1 2 12% 32% 49%	450
July	1st to 10th	Day	4 2 8% 36% 50%	445
	11th to 20th	Day	5% 1 2 8% 42% 43%	444
	21st to end	Day	4 1 2 12% 37% 44%	488
August	1st to 10th	Day	8% 1 3 9% 33% 46%	446
	11th to 20th	Day	5% 1 2 13% 34% 45%	439
	21st to end	Day	7% 1 6% 20% 34% 32%	495
September	1st to 10th	Day	7% 4 13% 35% 41%	450
	11th to 20th	Day	7% 2 4 10% 35% 42%	450
	21st to end	Day	9% 4 6% 17% 32% 33%	450
October	1st to 10th	Day	8% 3 7% 35% 34% 13%	450
	11th to 20th	Day	10% 2 13% 29% 32% 16%	450
	21st to end	Day	9% 4 14% 33% 32% 8%	495
November	1st to 10th	Day	6% 5% 21% 33% 28% 7%	455
	11th to 20th	Day	10% 6% 19% 33% 27% 5%	460
	21st to end	Day	9% 3 17% 40% 29% 3	460
December	1st to 10th	Day	10% 3 16% 41% 27% 3	460
	11th to 20th	Day	9% 4 19% 38% 26% 4	270
	21st to end	Day	8% 7% 21% 40% 21% 4	297
January	1st to 10th	Night	6% 4 19% 39% 27% 4	760
	11th to 20th	Night	9% 5% 23% 40% 22% 1	760
	21st to end	Night	8% 5% 25% 44% 18% 1	836
February	1st to 10th	Night	8% 5% 19% 40% 26% 1	760
	11th to 20th	Night	5% 3 23% 42% 24% 2	743
	21st to end	Night	5% 3 16% 47% 28% 1	628
March	1st to 10th	Night	6% 3 23% 44% 22% 2	760
	11th to 20th	Night	6% 2 19% 45% 25% 2	760
	21st to end	Night	5% 3 21% 44% 25% 2	836
April	1st to 10th	Night	3 3 16% 49% 27% 3	760
	11th to 20th	Night	6% 2 18% 45% 27% 2	751
	21st to end	Night	6% 3 13% 47% 29% 3	760
May	1st to 10th	Night	4 12% 41% 38% 4	759
	11th to 20th	Night	10% 1 10% 38% 37% 5%	709
	21st to end	Night	8% 2 6% 23% 45% 16%	608
June	1st to 10th	Night	14% 2 4 21% 40% 18%	540
	11th to 20th	Night	8% 1 2 11% 43% 36%	540
	21st to end	Night	4 1 2 8% 38% 47%	540
July	1st to 10th	Night	4 1 3 5% 42% 45%	525
	11th to 20th	Night	4 1 1 8% 39% 47%	522
	21st to end	Night	4 1 1 8% 34% 52%	591
August	1st to 10th	Night	6% 1 2 7% 45% 40%	577
	11th to 20th	Night	3 2 11% 42% 43%	710
	21st to end	Night	9% 1 4 14% 41% 32%	792
September	1st to 10th	Night	6% 2 3 9% 40% 40%	720
	11th to 20th	Night	7% 1 5% 14% 35% 38%	720
	21st to end	Night	10% 2 5% 15% 38% 30%	720
October	1st to 10th	Night	9% 2 8% 29% 40% 13%	720
	11th to 20th	Night	10% 1 7% 29% 39% 14%	720
	21st to end	Night	13% 2 15% 30% 33% 7%	792
November	1st to 10th	Night	9% 3 19% 35% 30% 4	740
	11th to 20th	Night	11% 3 15% 33% 33% 5%	760
	21st to end	Night	8% 3 14% 42% 30% 3	760
December	1st to 10th	Night	8% 2 12% 39% 34% 4	760
	11th to 20th	Night	10% 5% 15% 37% 30% 4	760
	21st to end	Night	6% 5% 18% 37% 29% 5%	836

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