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 2024-11-05.

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	7% 5% 2 7% 6% 6% 7% 6% 9% 12% 35%	100531
	Night	7% 5% 2 6% 5% 5% 6% 5% 8% 11% 41%	98452
Transparency	Day	18% 52% 14% 12% 4 1	104241
	Night	19% 51% 13% 11% 5% 1	102881
Seeing	Day	7% 3 14% 29% 28% 18%	16048
	Night	7% 2 12% 31% 33% 15%	26174

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% 5% 6% 5% 7% 10% 36%	2836
	11th to 20th	Day	14% 8% 4 9% 6% 7% 5% 5% 8% 9% 26%	2840
	21st to end	Day	7% 7% 3 9% 7% 6% 6% 5% 6% 8% 38%	3198
February	1st to 10th	Day	8% 6% 2 5% 5% 5% 5% 5% 7% 10% 42%	1900
	11th to 20th	Day	6% 4 1 4 5% 4 4 5% 7% 11% 49%	1976
	21st to end	Day	5% 3 1 4 5% 4 6% 5% 8% 10% 49%	1727
March	1st to 10th	Day	5% 4 2 6% 6% 6% 7% 6% 9% 12% 36%	3435
	11th to 20th	Day	4 3 1 4 3 4 4 4 8% 11% 53%	3480
	21st to end	Day	8% 5% 2 5% 4 4 4 4 6% 9% 48%	3815
April	1st to 10th	Day	3 3 1 4 5% 4 5% 4 8% 11% 51%	2090
	11th to 20th	Day	5% 4 1 5% 5% 6% 5% 6% 8% 13% 43%	2146
	21st to end	Day	6% 4 1 4 4 5% 5% 5% 8% 11% 46%	2280
May	1st to 10th	Day	2 2 1 3 3 3 4 4 7% 11% 59%	3765
	11th to 20th	Day	6% 4 2 5% 5% 5% 6% 5% 9% 11% 42%	3764
	21st to end	Day	6% 5% 2 6% 6% 6% 6% 6% 9% 11% 37%	4463
June	1st to 10th	Day	13% 9% 4 11% 8% 8% 7% 7% 8% 10% 16%	2470
	11th to 20th	Day	8% 7% 2 10% 9% 9% 8% 7% 9% 10% 20%	2470
	21st to end	Day	6% 6% 3 10% 9% 8% 9% 7% 10% 12% 20%	2470
July	1st to 10th	Day	5% 5% 3 6% 6% 6% 7% 6% 10% 16% 31%	4120
	11th to 20th	Day	4 5% 2 7% 6% 6% 7% 8% 12% 16% 27%	4120
	21st to end	Day	3 3 1 5% 5% 6% 7% 7% 11% 17% 34%	4466
August	1st to 10th	Day	3 4 2 9% 8% 9% 9% 8% 11% 13% 23%	3988
	11th to 20th	Day	4 4 3 8% 5% 7% 9% 7% 13% 14% 26%	3730
	21st to end	Day	5% 4 2 7% 8% 8% 9% 7% 13% 16% 22%	3845
September	1st to 10th	Day	7% 5% 3 8% 7% 8% 10% 8% 11% 12% 21%	2090
	11th to 20th	Day	8% 7% 3 10% 9% 9% 9% 6% 9% 10% 21%	2090
	21st to end	Day	10% 8% 4 10% 8% 8% 8% 6% 8% 9% 22%	2090
October	1st to 10th	Day	8% 8% 3 10% 7% 6% 7% 5% 9% 11% 24%	2002
	11th to 20th	Day	10% 5% 3 8% 6% 7% 7% 5% 10% 11% 28%	1900
	21st to end	Day	10% 6% 3 9% 5% 5% 6% 6% 6% 9% 34%	2090
November	1st to 10th	Day	8% 5% 3 6% 6% 6% 5% 5% 7% 11% 39%	1898
	11th to 20th	Day	9% 7% 3 8% 6% 6% 7% 6% 6% 8% 33%	1900
	21st to end	Day	8% 5% 2 7% 5% 6% 5% 4 8% 9% 39%	1900
December	1st to 10th	Day	7% 5% 2 6% 5% 5% 6% 4 7% 10% 43%	1900
	11th to 20th	Day	9% 7% 2 5% 5% 5% 6% 5% 7% 10% 40%	2153
	21st to end	Day	13% 6% 2 8% 6% 5% 6% 5% 8% 9% 32%	3124
January	1st to 10th	Night	9% 5% 2 6% 5% 5% 6% 5% 9% 9% 38%	4109
	11th to 20th	Night	15% 9% 4 9% 6% 6% 6% 4 6% 7% 28%	4120
	21st to end	Night	8% 7% 3 8% 6% 5% 5% 4 6% 9% 39%	4454
February	1st to 10th	Night	8% 5% 2 5% 5% 5% 4 4 7% 10% 46%	2280
	11th to 20th	Night	6% 3 2 6% 3 4 4 3 5% 8% 57%	2087
	21st to end	Night	4 3 1 4 3 4 4 3 6% 11% 56%	1727
March	1st to 10th	Night	6% 4 2 8% 6% 6% 6% 5% 8% 10% 40%	3418
	11th to 20th	Night	3 3 1 4 3 4 5% 4 6% 11% 56%	3480
	21st to end	Night	6% 3 2 4 3 4 4 4 6% 7% 57%	3817
April	1st to 10th	Night	4 2 1 4 3 3 3 4 7% 11% 57%	2090
	11th to 20th	Night	5% 4 2 4 4 4 4 4 6% 10% 52%	1980
	21st to end	Night	6% 4 2 4 4 4 4 5% 7% 9% 51%	1900
May	1st to 10th	Night	3 1 1 3 3 3 3 3 7% 10% 64%	3130
	11th to 20th	Night	6% 3 1 5% 4 4 4 4 7% 10% 52%	3130
	21st to end	Night	5% 5% 2 5% 4 5% 5% 5% 8% 10% 47%	3117
June	1st to 10th	Night	11% 9% 4 9% 7% 6% 6% 6% 8% 11% 24%	1710
	11th to 20th	Night	8% 6% 2 6% 5% 6% 7% 6% 8% 13% 32%	1710
	21st to end	Night	4 5% 2 6% 6% 7% 8% 7% 11% 14% 31%	1710
July	1st to 10th	Night	3 4 3 6% 5% 6% 7% 6% 11% 14% 35%	2840
	11th to 20th	Night	3 4 2 5% 5% 6% 7% 6% 10% 15% 37%	2840
	21st to end	Night	2 3 1 5% 5% 6% 7% 5% 9% 15% 42%	3087
August	1st to 10th	Night	3 4 2 7% 6% 8% 8% 7% 9% 13% 34%	2907
	11th to 20th	Night	3 3 2 6% 5% 5% 8% 6% 11% 15% 37%	3097
	21st to end	Night	4 4 2 7% 6% 7% 8% 8% 13% 16% 26%	3790
September	1st to 10th	Night	5% 4 2 7% 6% 6% 9% 6% 10% 12% 32%	2090
	11th to 20th	Night	7% 7% 3 10% 6% 7% 8% 6% 10% 10% 27%	2090
	21st to end	Night	8% 7% 3 10% 8% 6% 7% 6% 9% 10% 26%	2090
October	1st to 10th	Night	8% 6% 3 9% 8% 7% 7% 6% 10% 10% 26%	2175
	11th to 20th	Night	10% 6% 2 7% 5% 6% 6% 5% 9% 11% 33%	2280
	21st to end	Night	11% 6% 3 8% 5% 5% 5% 4 6% 8% 39%	2508
November	1st to 10th	Night	8% 5% 2 6% 4 4 5% 5% 7% 9% 43%	2280
	11th to 20th	Night	10% 7% 3 7% 6% 6% 6% 5% 6% 9% 36%	2280
	21st to end	Night	8% 5% 2 7% 5% 5% 5% 5% 6% 10% 44%	2280
December	1st to 10th	Night	7% 5% 2 5% 4 5% 5% 5% 7% 10% 45%	2280
	11th to 20th	Night	10% 6% 2 5% 4 4 4 4 6% 8% 48%	3037
	21st to end	Night	11% 8% 3 8% 6% 6% 5% 5% 7% 8% 32%	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	28% 41% 8% 14% 7% 1	2837
	11th to 20th	Day	36% 42% 10% 8% 4	2840
	21st to end	Day	27% 43% 6% 11% 10% 4	3198
February	1st to 10th	Day	9% 67% 8% 11% 4 1	1900
	11th to 20th	Day	9% 64% 4 9% 11% 3	1986
	21st to end	Day	7% 67% 7% 8% 7% 3	1727
March	1st to 10th	Day	20% 51% 13% 12% 3 1	3435
	11th to 20th	Day	7% 45% 20% 23% 3 1	3480
	21st to end	Day	18% 44% 8% 19% 10% 2	3815
April	1st to 10th	Day	7% 66% 7% 14% 5% 1	2090
	11th to 20th	Day	7% 68% 8% 9% 7% 1	2146
	21st to end	Day	8% 66% 6% 11% 8% 1	2280
May	1st to 10th	Day	6% 43% 11% 25% 12% 3	3800
	11th to 20th	Day	12% 46% 19% 20% 2	3768
	21st to end	Day	11% 47% 11% 25% 7%	4476
June	1st to 10th	Day	18% 71% 7% 4	2470
	11th to 20th	Day	18% 72% 7% 3	2470
	21st to end	Day	11% 71% 14% 5%	2470
July	1st to 10th	Day	16% 44% 27% 13%	4055
	11th to 20th	Day	19% 44% 32% 5%	4051
	21st to end	Day	14% 45% 30% 11%	4324
August	1st to 10th	Day	26% 48% 19% 6% 1	3975
	11th to 20th	Day	19% 46% 25% 10%	3766
	21st to end	Day	22% 47% 27% 4	3845
September	1st to 10th	Day	14% 68% 12% 5%	2090
	11th to 20th	Day	16% 67% 11% 5% 1	2090
	21st to end	Day	15% 69% 7% 7% 2	2090
October	1st to 10th	Day	27% 44% 15% 11% 3	3327
	11th to 20th	Day	31% 43% 10% 10% 5% 1	3140
	21st to end	Day	22% 39% 7% 21% 9% 2	3428
November	1st to 10th	Day	13% 61% 10% 11% 4 1	1898
	11th to 20th	Day	17% 63% 6% 8% 4 1	1900
	21st to end	Day	16% 62% 6% 7% 7% 2	1900
December	1st to 10th	Day	14% 63% 6% 10% 6% 1	1900
	11th to 20th	Day	17% 50% 6% 9% 13% 4	2150
	21st to end	Day	32% 43% 10% 8% 6%	3124
January	1st to 10th	Night	28% 43% 10% 10% 8% 1	4109
	11th to 20th	Night	39% 42% 8% 9% 3	4120
	21st to end	Night	28% 43% 7% 8% 10% 3	4454
February	1st to 10th	Night	10% 66% 9% 10% 5%	2280
	11th to 20th	Night	7% 63% 4 9% 11% 5%	2088
	21st to end	Night	9% 66% 6% 7% 9% 4	1727
March	1st to 10th	Night	24% 49% 10% 12% 4 1	3418
	11th to 20th	Night	10% 45% 19% 21% 4 1	3480
	21st to end	Night	14% 43% 9% 15% 15% 4	3817
April	1st to 10th	Night	6% 66% 6% 15% 7% 1	2090
	11th to 20th	Night	8% 67% 8% 7% 9% 1	1980
	21st to end	Night	9% 65% 6% 10% 8% 1	1900
May	1st to 10th	Night	6% 44% 14% 27% 7% 3	3160
	11th to 20th	Night	11% 44% 13% 27% 6%	3131
	21st to end	Night	10% 46% 15% 23% 6%	3125
June	1st to 10th	Night	15% 68% 11% 6% 1	1710
	11th to 20th	Night	15% 71% 8% 6%	1710
	21st to end	Night	8% 68% 19% 5%	1710
July	1st to 10th	Night	18% 41% 28% 13%	2795
	11th to 20th	Night	17% 42% 34% 7%	2786
	21st to end	Night	18% 42% 29% 11%	2988
August	1st to 10th	Night	24% 45% 21% 8% 2	2896
	11th to 20th	Night	18% 44% 25% 13% 1	3127
	21st to end	Night	21% 49% 28% 3	3790
September	1st to 10th	Night	14% 65% 13% 6% 1	2090
	11th to 20th	Night	16% 67% 12% 4 1	2090
	21st to end	Night	16% 66% 10% 6% 2	2090
October	1st to 10th	Night	29% 44% 13% 12% 2	3630
	11th to 20th	Night	35% 40% 11% 7% 6% 1	3779
	21st to end	Night	24% 40% 7% 18% 10% 2	4120
November	1st to 10th	Night	14% 59% 9% 12% 5% 1	2280
	11th to 20th	Night	18% 63% 5% 9% 4 2	2280
	21st to end	Night	16% 62% 6% 8% 7% 1	2280
December	1st to 10th	Night	17% 62% 6% 9% 6%	2280
	11th to 20th	Night	16% 50% 5% 10% 12% 6%	3039
	21st to end	Night	33% 44% 9% 8% 6%	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% 31% 13%	463
	11th to 20th	Day	8% 3 17% 31% 29% 12%	487
	21st to end	Day	9% 3 6% 26% 34% 22%	529
June	1st to 10th	Day	11% 2 9% 25% 30% 22%	490
	11th to 20th	Day	9% 1 6% 19% 32% 33%	490
	21st to end	Day	5% 1 3 13% 31% 47%	490
July	1st to 10th	Day	4 3 11% 35% 46%	485
	11th to 20th	Day	4 2 2 10% 42% 40%	484
	21st to end	Day	4 2 2 13% 38% 41%	532
August	1st to 10th	Day	8% 1 5% 11% 32% 43%	486
	11th to 20th	Day	4 1 2 15% 34% 43%	479
	21st to end	Day	7% 1 6% 21% 34% 32%	539
September	1st to 10th	Day	7% 4 14% 37% 39%	490
	11th to 20th	Day	8% 2 4 11% 34% 41%	490
	21st to end	Day	9% 3 7% 19% 30% 31%	490
October	1st to 10th	Day	9% 3 8% 34% 33% 13%	490
	11th to 20th	Day	11% 2 13% 29% 30% 15%	490
	21st to end	Day	9% 4 17% 34% 29% 8%	539
November	1st to 10th	Day	6% 5% 21% 35% 27% 7%	472
	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	760
	11th to 20th	Night	9% 1 11% 38% 35% 5%	749
	21st to end	Night	7% 2 6% 24% 45% 15%	642
June	1st to 10th	Night	14% 2 4 23% 41% 17%	570
	11th to 20th	Night	10% 1 3 11% 41% 34%	570
	21st to end	Night	4 1 2 8% 39% 46%	570
July	1st to 10th	Night	4 1 3 5% 43% 44%	555
	11th to 20th	Night	4 1 1 8% 39% 47%	552
	21st to end	Night	4 1 1 8% 34% 52%	624
August	1st to 10th	Night	6% 3 9% 44% 38%	610
	11th to 20th	Night	3 1 1 11% 42% 43%	750
	21st to end	Night	8% 1 4 14% 41% 31%	836
September	1st to 10th	Night	6% 2 3 10% 41% 39%	760
	11th to 20th	Night	7% 2 5% 14% 35% 37%	760
	21st to end	Night	10% 2 6% 15% 37% 30%	760
October	1st to 10th	Night	9% 3 8% 28% 40% 13%	760
	11th to 20th	Night	11% 1 8% 30% 38% 13%	760
	21st to end	Night	13% 3 17% 30% 31% 7%	836
November	1st to 10th	Night	8% 3 19% 36% 30% 4	760
	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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