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 2025-09-19.

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	6% 5% 2 6% 5% 6% 6% 6% 9% 12% 37%	125537
	Night	6% 5% 2 6% 5% 5% 5% 5% 8% 10% 43%	123524
Transparency	Day	19% 43% 15% 15% 6% 1	129203
	Night	21% 42% 14% 15% 7% 2	127927
Seeing	Day	7% 3 15% 30% 28% 18%	17254
	Night	7% 3 12% 31% 32% 14%	27364

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	6% 5% 2 5% 4 4 5% 5% 7% 11% 45%	4056
	11th to 20th	Day	15% 8% 3 8% 6% 6% 5% 4 7% 9% 29%	4060
	21st to end	Day	8% 7% 3 8% 6% 5% 5% 4 6% 8% 41%	4582
February	1st to 10th	Day	8% 6% 1 5% 5% 5% 5% 5% 7% 10% 44%	2000
	11th to 20th	Day	6% 4 1 4 4 4 4 5% 7% 10% 50%	2083
	21st to end	Day	5% 3 2 4 5% 4 6% 5% 8% 10% 48%	1815
March	1st to 10th	Day	4 3 1 5% 5% 5% 6% 6% 8% 10% 47%	4935
	11th to 20th	Day	3 2 1 3 3 3 4 3 6% 10% 61%	4980
	21st to end	Day	6% 4 2 6% 5% 5% 5% 4 7% 10% 46%	5465
April	1st to 10th	Day	3 3 1 4 4 4 5% 4 8% 11% 51%	2200
	11th to 20th	Day	5% 3 1 5% 5% 6% 5% 6% 7% 13% 45%	2261
	21st to end	Day	6% 4 1 4 4 4 5% 5% 8% 11% 47%	2400
May	1st to 10th	Day	2 2 1 3 3 3 5% 4 7% 13% 58%	5405
	11th to 20th	Day	6% 4 1 5% 4 4 5% 4 7% 10% 49%	5404
	21st to end	Day	4 4 1 5% 5% 6% 7% 7% 11% 13% 36%	6420
June	1st to 10th	Day	13% 9% 4 11% 8% 8% 7% 7% 8% 10% 16%	2600
	11th to 20th	Day	8% 6% 2 10% 9% 9% 8% 7% 9% 11% 22%	2600
	21st to end	Day	6% 6% 3 10% 8% 8% 9% 7% 10% 12% 21%	2600
July	1st to 10th	Day	4 5% 3 8% 6% 7% 7% 7% 10% 15% 28%	5900
	11th to 20th	Day	4 5% 3 8% 7% 7% 7% 7% 10% 14% 29%	5900
	21st to end	Day	2 3 1 4 4 5% 6% 6% 10% 17% 41%	6424
August	1st to 10th	Day	3 4 2 9% 8% 9% 9% 8% 11% 13% 23%	4114
	11th to 20th	Day	4 4 3 7% 5% 7% 9% 6% 12% 15% 28%	3850
	21st to end	Day	5% 4 2 7% 8% 8% 9% 7% 13% 16% 22%	3967
September	1st to 10th	Day	7% 5% 3 9% 8% 8% 10% 8% 11% 12% 21%	2200
	11th to 20th	Day	8% 7% 3 10% 9% 9% 9% 6% 9% 10% 21%	2178
	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% 5% 6% 5% 5% 7% 10% 40%	1957
	11th to 20th	Day	9% 6% 3 8% 6% 6% 7% 6% 7% 8% 34%	2000
	21st to end	Day	8% 5% 2 7% 5% 6% 5% 4 8% 9% 41%	2000
December	1st to 10th	Day	5% 3 2 5% 3 4 5% 3 7% 10% 53%	3260
	11th to 20th	Day	8% 6% 2 6% 5% 5% 6% 5% 8% 12% 37%	3373
	21st to end	Day	11% 7% 2 9% 7% 6% 6% 5% 8% 9% 29%	4466
January	1st to 10th	Night	6% 4 2 6% 5% 5% 6% 5% 8% 10% 43%	5889
	11th to 20th	Night	15% 8% 3 8% 5% 5% 5% 4 5% 7% 34%	5900
	21st to end	Night	9% 8% 3 8% 5% 5% 4 3 5% 8% 42%	6370
February	1st to 10th	Night	8% 5% 2 5% 5% 5% 4 4 7% 10% 47%	2400
	11th to 20th	Night	6% 3 2 6% 3 4 4 4 5% 8% 57%	2199
	21st to end	Night	5% 3 1 4 3 4 4 3 6% 11% 56%	1815
March	1st to 10th	Night	4 3 2 6% 4 4 5% 4 7% 9% 52%	4918
	11th to 20th	Night	3 3 1 4 3 3 4 3 5% 8% 62%	4980
	21st to end	Night	5% 3 2 5% 4 5% 6% 4 7% 8% 52%	5467
April	1st to 10th	Night	4 2 1 4 3 3 3 4 6% 11% 57%	2200
	11th to 20th	Night	5% 4 2 4 4 4 4 4 6% 10% 53%	2085
	21st to end	Night	6% 4 2 4 4 4 4 5% 7% 9% 52%	2000
May	1st to 10th	Night	2 1 1 2 2 3 3 3 7% 11% 64%	4490
	11th to 20th	Night	6% 3 2 5% 4 4 4 3 6% 9% 56%	4490
	21st to end	Night	3 4 1 4 4 5% 6% 6% 9% 12% 46%	4473
June	1st to 10th	Night	11% 8% 4 9% 7% 6% 6% 6% 8% 11% 25%	1800
	11th to 20th	Night	8% 6% 2 6% 5% 6% 7% 6% 9% 13% 33%	1800
	21st to end	Night	4 5% 2 6% 6% 7% 8% 7% 11% 14% 31%	1800
July	1st to 10th	Night	3 4 3 7% 6% 6% 6% 6% 10% 14% 35%	4058
	11th to 20th	Night	3 4 2 6% 6% 6% 6% 6% 9% 14% 38%	4057
	21st to end	Night	2 3 1 4 4 5% 5% 4 8% 14% 49%	4427
August	1st to 10th	Night	3 4 2 7% 6% 8% 8% 7% 9% 13% 34%	2999
	11th to 20th	Night	3 3 2 6% 5% 5% 7% 6% 11% 14% 38%	3197
	21st to end	Night	4 4 2 7% 6% 7% 8% 8% 12% 16% 26%	3910
September	1st to 10th	Night	5% 4 2 8% 6% 6% 9% 7% 10% 12% 32%	2200
	11th to 20th	Night	7% 7% 3 10% 6% 7% 8% 6% 10% 10% 27%	2179
	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 5% 6% 5% 7% 9% 43%	2341
	11th to 20th	Night	10% 6% 3 7% 6% 6% 6% 5% 6% 9% 37%	2400
	21st to end	Night	7% 5% 2 6% 4 5% 5% 5% 6% 9% 46%	2400
December	1st to 10th	Night	5% 4 2 5% 3 4 4 4 6% 9% 54%	3920
	11th to 20th	Night	10% 7% 3 7% 5% 5% 5% 4 7% 8% 41%	4817
	21st to end	Night	10% 8% 3 9% 7% 6% 6% 5% 7% 8% 30%	6490

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	22% 30% 9% 24% 11% 4	4057
	11th to 20th	Day	37% 32% 12% 15% 4	4060
	21st to end	Day	29% 31% 6% 22% 10% 3	4582
February	1st to 10th	Day	9% 64% 9% 12% 5% 1	2000
	11th to 20th	Day	10% 61% 5% 10% 11% 3	2093
	21st to end	Day	9% 64% 7% 9% 7% 3	1815
March	1st to 10th	Day	18% 37% 12% 16% 16% 1	4935
	11th to 20th	Day	8% 32% 15% 22% 14% 10%	4980
	21st to end	Day	22% 33% 10% 22% 11% 2	5465
April	1st to 10th	Day	7% 63% 7% 14% 8% 1	2200
	11th to 20th	Day	7% 64% 7% 9% 9% 3	2261
	21st to end	Day	7% 63% 6% 13% 10% 1	2400
May	1st to 10th	Day	9% 33% 16% 30% 11% 2	5437
	11th to 20th	Day	14% 33% 16% 30% 6%	5408
	21st to end	Day	14% 36% 18% 27% 5%	6434
June	1st to 10th	Day	20% 67% 8% 5%	2600
	11th to 20th	Day	17% 69% 8% 5% 1	2600
	21st to end	Day	12% 68% 15% 5%	2600
July	1st to 10th	Day	26% 36% 29% 10%	5835
	11th to 20th	Day	26% 35% 30% 8% 1	5831
	21st to end	Day	14% 33% 33% 19% 1	6240
August	1st to 10th	Day	26% 47% 20% 6% 1	4101
	11th to 20th	Day	19% 45% 25% 11% 1	3886
	21st to end	Day	22% 46% 28% 4	3967
September	1st to 10th	Day	16% 66% 13% 5%	2200
	11th to 20th	Day	17% 65% 11% 5% 1	2178
	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% 60% 10% 11% 5% 1	1957
	11th to 20th	Day	18% 60% 6% 9% 5% 2	2000
	21st to end	Day	16% 59% 6% 7% 9% 3	2000
December	1st to 10th	Day	14% 39% 8% 24% 13% 3	3260
	11th to 20th	Day	22% 35% 10% 16% 14% 3	3370
	21st to end	Day	37% 33% 12% 10% 8%	4466
January	1st to 10th	Night	25% 31% 11% 19% 12% 1	5889
	11th to 20th	Night	39% 31% 13% 13% 5%	5900
	21st to end	Night	31% 31% 7% 18% 10% 2	6370
February	1st to 10th	Night	10% 63% 9% 11% 6% 1	2400
	11th to 20th	Night	8% 61% 4 10% 12% 5%	2200
	21st to end	Night	10% 63% 7% 8% 9% 4	1815
March	1st to 10th	Night	18% 35% 10% 16% 18% 3	4918
	11th to 20th	Night	11% 32% 14% 19% 14% 9%	4980
	21st to end	Night	20% 32% 10% 20% 15% 3	5467
April	1st to 10th	Night	7% 63% 6% 15% 9% 1	2200
	11th to 20th	Night	8% 64% 8% 7% 10% 3	2085
	21st to end	Night	9% 62% 6% 11% 10% 1	2000
May	1st to 10th	Night	7% 32% 20% 31% 8% 2	4520
	11th to 20th	Night	15% 31% 11% 33% 9% 1	4491
	21st to end	Night	14% 35% 24% 22% 5%	4481
June	1st to 10th	Night	16% 65% 12% 7% 1	1800
	11th to 20th	Night	15% 68% 9% 8%	1800
	21st to end	Night	9% 65% 20% 6%	1800
July	1st to 10th	Night	25% 32% 33% 9%	4015
	11th to 20th	Night	24% 34% 34% 9%	4006
	21st to end	Night	17% 31% 33% 17% 2	4297
August	1st to 10th	Night	24% 44% 21% 9% 2	2988
	11th to 20th	Night	18% 43% 25% 14% 1	3227
	21st to end	Night	21% 48% 28% 3	3910
September	1st to 10th	Night	16% 63% 14% 6% 1	2200
	11th to 20th	Night	17% 65% 13% 5% 1	2179
	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	15% 58% 9% 12% 5% 1	2341
	11th to 20th	Night	18% 60% 5% 10% 5% 2	2400
	21st to end	Night	16% 59% 6% 8% 8% 3	2400
December	1st to 10th	Night	16% 38% 8% 25% 11% 2	3920
	11th to 20th	Night	25% 36% 8% 14% 13% 4	4819
	21st to end	Night	39% 33% 10% 11% 7%	6490

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	6% 6% 34% 39% 14% 1	300
	11th to 20th	Day	12% 8% 30% 39% 8% 3	300
	21st to end	Day	9% 10% 36% 35% 9%	330
February	1st to 10th	Day	5% 8% 24% 46% 16% 1	300
	11th to 20th	Day	6% 6% 21% 44% 21% 3	436
	21st to end	Day	4 5% 23% 39% 28% 1	414
March	1st to 10th	Day	3 5% 31% 43% 16% 2	500
	11th to 20th	Day	5% 5% 28% 36% 23% 2	500
	21st to end	Day	4 5% 23% 43% 20% 5%	550
April	1st to 10th	Day	4 3 27% 43% 19% 5%	500
	11th to 20th	Day	4 3 27% 39% 20% 7%	492
	21st to end	Day	4 3 17% 44% 26% 6%	500
May	1st to 10th	Day	3 1 13% 42% 29% 12%	503
	11th to 20th	Day	8% 3 17% 32% 28% 12%	527
	21st to end	Day	9% 3 6% 28% 33% 21%	573
June	1st to 10th	Day	12% 3 9% 25% 30% 21%	530
	11th to 20th	Day	8% 2 6% 20% 33% 31%	530
	21st to end	Day	5% 1 4 15% 31% 44%	530
July	1st to 10th	Day	5% 3 13% 35% 44%	525
	11th to 20th	Day	4 2 2 12% 42% 39%	524
	21st to end	Day	4 1 2 15% 38% 39%	576
August	1st to 10th	Day	7% 1 5% 13% 32% 42%	526
	11th to 20th	Day	4 1 2 16% 35% 42%	519
	21st to end	Day	6% 1 6% 21% 34% 33%	583
September	1st to 10th	Day	7% 1 4 14% 35% 39%	530
	11th to 20th	Day	8% 3 4 12% 35% 39%	522
	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% 20% 36% 26% 7%	495
	11th to 20th	Day	10% 5% 19% 34% 27% 5%	500
	21st to end	Day	8% 3 18% 40% 28% 3	500
December	1st to 10th	Day	9% 4 18% 41% 25% 3	500
	11th to 20th	Day	8% 4 23% 38% 23% 4	300
	21st to end	Day	10% 7% 21% 39% 19% 4	330
January	1st to 10th	Night	6% 4 20% 40% 26% 4	800
	11th to 20th	Night	9% 5% 23% 40% 22% 2	800
	21st to end	Night	9% 5% 25% 44% 18% 1	880
February	1st to 10th	Night	8% 5% 18% 39% 28% 2	800
	11th to 20th	Night	5% 3 23% 42% 24% 2	783
	21st to end	Night	5% 3 17% 47% 27% 1	660
March	1st to 10th	Night	6% 3 24% 44% 21% 2	800
	11th to 20th	Night	6% 2 20% 46% 25% 2	800
	21st to end	Night	5% 3 22% 44% 24% 2	880
April	1st to 10th	Night	3 3 16% 49% 27% 3	800
	11th to 20th	Night	6% 2 18% 45% 27% 2	791
	21st to end	Night	6% 3 13% 48% 28% 3	800
May	1st to 10th	Night	4 1 12% 42% 38% 4	800
	11th to 20th	Night	9% 2 12% 38% 35% 4	789
	21st to end	Night	7% 2 6% 24% 45% 16%	676
June	1st to 10th	Night	14% 2 4 23% 41% 17%	600
	11th to 20th	Night	9% 1 3 12% 43% 33%	600
	21st to end	Night	4 1 2 8% 40% 45%	600
July	1st to 10th	Night	4 1 3 5% 43% 44%	585
	11th to 20th	Night	3 1 1 9% 40% 46%	582
	21st to end	Night	4 1 1 9% 35% 50%	657
August	1st to 10th	Night	5% 1 3 9% 43% 39%	642
	11th to 20th	Night	3 1 1 11% 42% 43%	790
	21st to end	Night	8% 1 4 14% 41% 32%	880
September	1st to 10th	Night	6% 2 3 10% 40% 39%	800
	11th to 20th	Night	7% 2 5% 14% 35% 36%	793
	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% 29% 4	780
	11th to 20th	Night	11% 3 14% 33% 34% 5%	800
	21st to end	Night	8% 3 14% 42% 29% 3	800
December	1st to 10th	Night	8% 3 13% 39% 33% 4	800
	11th to 20th	Night	10% 5% 15% 38% 29% 4	800
	21st to end	Night	7% 5% 18% 38% 28% 5%	880

Page generated at 2025-09-16 01:49:12. Version ac07

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