Deer Run Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Deer Run Observatory clear sky chart from 2005-11-06 to 2024-11-02.

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	11% 6% 2 6% 5% 5% 5% 4 6% 8% 41%	100905
	Night	12% 6% 2 6% 4 4 4 4 6% 8% 43%	98021
Transparency	Day	39% 7% 11% 19% 17% 6%	100715
	Night	38% 7% 11% 18% 19% 8%	97881
Seeing	Day	14% 9% 23% 25% 20% 9%	14913
	Night	14% 8% 23% 30% 21% 4	24900

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	16% 7% 3 6% 4 3 3 3 5% 7% 44%	2836
	11th to 20th	Day	13% 6% 2 4 3 3 3 3 4 6% 55%	2840
	21st to end	Day	20% 8% 3 6% 4 4 3 3 4 5% 41%	3389
February	1st to 10th	Day	15% 8% 2 7% 4 4 4 3 5% 7% 40%	1900
	11th to 20th	Day	18% 7% 2 6% 3 3 3 3 5% 7% 43%	1848
	21st to end	Day	16% 7% 2 6% 5% 4 4 4 5% 7% 42%	1570
March	1st to 10th	Day	22% 8% 3 7% 4 4 3 4 6% 6% 34%	3213
	11th to 20th	Day	10% 5% 2 5% 4 4 5% 4 6% 8% 47%	3480
	21st to end	Day	17% 6% 2 6% 4 4 3 4 5% 7% 43%	3815
April	1st to 10th	Day	11% 6% 2 6% 5% 4 5% 4 5% 6% 45%	2130
	11th to 20th	Day	12% 5% 2 4 4 3 4 4 5% 7% 49%	2254
	21st to end	Day	7% 4 1 5% 4 3 4 3 5% 7% 56%	2375
May	1st to 10th	Day	9% 4 2 6% 5% 5% 5% 4 7% 8% 46%	4082
	11th to 20th	Day	15% 7% 3 7% 5% 4 4 4 6% 7% 38%	4081
	21st to end	Day	6% 4 2 6% 5% 5% 6% 4 6% 10% 47%	4476
June	1st to 10th	Day	10% 6% 3 7% 6% 7% 7% 6% 9% 9% 31%	2470
	11th to 20th	Day	5% 5% 2 6% 5% 5% 6% 6% 8% 12% 40%	2470
	21st to end	Day	5% 5% 2 7% 7% 8% 8% 6% 10% 9% 33%	2470
July	1st to 10th	Day	11% 8% 4 9% 8% 8% 8% 7% 10% 10% 19%	4120
	11th to 20th	Day	6% 5% 3 8% 8% 8% 7% 6% 8% 10% 31%	4120
	21st to end	Day	6% 7% 3 10% 8% 9% 9% 7% 10% 12% 20%	4466
August	1st to 10th	Day	9% 5% 3 7% 6% 6% 7% 6% 8% 13% 31%	3990
	11th to 20th	Day	6% 4 2 6% 5% 5% 6% 4 6% 10% 47%	3729
	21st to end	Day	8% 5% 2 5% 5% 6% 6% 5% 8% 10% 40%	4163
September	1st to 10th	Day	9% 8% 3 7% 6% 6% 7% 5% 7% 9% 34%	2090
	11th to 20th	Day	14% 6% 2 7% 5% 5% 4 4 7% 8% 38%	2090
	21st to end	Day	12% 6% 2 7% 5% 4 4 4 5% 6% 45%	2090
October	1st to 10th	Day	11% 6% 2 6% 4 3 3 3 4 6% 52%	2090
	11th to 20th	Day	10% 4 2 4 3 3 3 2 5% 7% 57%	2024
	21st to end	Day	10% 5% 2 6% 3 4 3 3 4 6% 56%	2090
November	1st to 10th	Day	11% 5% 1 5% 4 3 5% 3 4 5% 55%	1737
	11th to 20th	Day	13% 5% 2 4 3 3 3 3 4 6% 55%	1710
	21st to end	Day	15% 5% 3 5% 3 4 4 3 5% 6% 47%	1710
December	1st to 10th	Day	16% 6% 2 5% 5% 4 5% 3 6% 6% 42%	1710
	11th to 20th	Day	17% 8% 3 6% 4 3 3 4 4 5% 44%	2153
	21st to end	Day	19% 8% 3 7% 4 3 3 3 3 5% 42%	3124
January	1st to 10th	Night	17% 7% 2 4 3 4 5% 3 6% 7% 41%	4109
	11th to 20th	Night	10% 6% 2 6% 4 4 4 4 5% 7% 49%	4120
	21st to end	Night	21% 10% 3 6% 3 3 3 2 4 5% 41%	4264
February	1st to 10th	Night	15% 7% 3 6% 5% 4 4 3 5% 6% 43%	2280
	11th to 20th	Night	19% 6% 2 5% 4 3 3 2 4 6% 46%	2218
	21st to end	Night	15% 7% 2 5% 3 4 4 4 5% 7% 43%	1884
March	1st to 10th	Night	23% 10% 2 7% 4 4 3 2 4 5% 37%	3637
	11th to 20th	Night	11% 5% 2 5% 5% 4 4 4 5% 7% 48%	3480
	21st to end	Night	15% 6% 2 5% 4 4 5% 3 5% 6% 44%	3817
April	1st to 10th	Night	10% 6% 2 5% 4 4 4 3 7% 7% 48%	2065
	11th to 20th	Night	12% 5% 1 4 4 3 4 4 5% 8% 50%	1875
	21st to end	Night	7% 4 1 5% 3 3 4 3 5% 7% 57%	1803
May	1st to 10th	Night	6% 4 2 6% 5% 5% 4 5% 6% 11% 46%	2813
	11th to 20th	Night	14% 6% 2 6% 4 4 4 4 6% 7% 43%	2812
	21st to end	Night	7% 3 1 4 4 4 4 4 6% 11% 51%	3079
June	1st to 10th	Night	8% 7% 3 7% 6% 6% 5% 5% 7% 12% 33%	1710
	11th to 20th	Night	3 3 2 5% 5% 5% 6% 6% 8% 14% 42%	1710
	21st to end	Night	5% 5% 2 7% 6% 6% 6% 6% 8% 12% 36%	1710
July	1st to 10th	Night	10% 8% 3 9% 7% 7% 8% 7% 9% 11% 21%	2840
	11th to 20th	Night	4 4 2 8% 6% 6% 7% 6% 11% 13% 34%	2840
	21st to end	Night	8% 8% 3 10% 6% 7% 7% 7% 9% 11% 25%	3087
August	1st to 10th	Night	9% 6% 3 8% 5% 7% 6% 5% 9% 12% 30%	2934
	11th to 20th	Night	6% 3 1 6% 4 4 6% 5% 8% 12% 46%	3100
	21st to end	Night	7% 5% 2 5% 5% 5% 5% 4 8% 10% 45%	3476
September	1st to 10th	Night	11% 7% 3 7% 5% 6% 5% 4 5% 12% 37%	2072
	11th to 20th	Night	13% 7% 3 6% 4 4 4 4 5% 8% 40%	2090
	21st to end	Night	9% 5% 2 7% 4 5% 5% 4 6% 8% 45%	2090
October	1st to 10th	Night	10% 5% 2 5% 4 3 4 3 5% 7% 51%	2090
	11th to 20th	Night	10% 3 2 4 3 3 3 3 5% 5% 59%	2154
	21st to end	Night	10% 5% 1 5% 3 4 4 3 4 5% 57%	2508
November	1st to 10th	Night	10% 5% 2 4 3 3 4 3 5% 5% 56%	2370
	11th to 20th	Night	14% 5% 2 4 3 3 3 2 5% 5% 55%	2470
	21st to end	Night	14% 6% 2 5% 4 3 4 3 4 6% 47%	2470
December	1st to 10th	Night	15% 6% 3 5% 4 3 4 3 5% 7% 45%	2470
	11th to 20th	Night	16% 6% 2 6% 4 3 3 3 4 6% 47%	3042
	21st to end	Night	20% 9% 3 7% 4 4 4 3 5% 6% 36%	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	40% 3 5% 19% 23% 10%	2837
	11th to 20th	Day	31% 3 4 17% 31% 13%	2840
	21st to end	Day	46% 4 5% 13% 21% 12%	3389
February	1st to 10th	Day	45% 4 7% 16% 19% 9%	1900
	11th to 20th	Day	42% 5% 5% 15% 25% 9%	1858
	21st to end	Day	43% 4 6% 17% 19% 11%	1570
March	1st to 10th	Day	49% 6% 8% 15% 15% 7%	3213
	11th to 20th	Day	35% 5% 10% 15% 23% 12%	3480
	21st to end	Day	41% 5% 10% 18% 17% 9%	3815
April	1st to 10th	Day	38% 6% 8% 20% 17% 11%	2130
	11th to 20th	Day	34% 4 8% 19% 23% 11%	2254
	21st to end	Day	27% 5% 8% 26% 26% 8%	2375
May	1st to 10th	Day	34% 7% 11% 24% 20% 4	4120
	11th to 20th	Day	43% 7% 11% 22% 15% 2	4085
	21st to end	Day	31% 8% 15% 26% 19% 2	4489
June	1st to 10th	Day	44% 9% 16% 19% 11% 2	2470
	11th to 20th	Day	32% 10% 17% 23% 16% 2	2470
	21st to end	Day	40% 13% 16% 17% 12% 2	2470
July	1st to 10th	Day	50% 16% 21% 9% 3 1	4055
	11th to 20th	Day	41% 14% 21% 19% 4 1	4051
	21st to end	Day	50% 16% 18% 12% 4	4324
August	1st to 10th	Day	40% 11% 19% 23% 7%	3977
	11th to 20th	Day	31% 8% 15% 29% 15% 1	3765
	21st to end	Day	34% 11% 18% 25% 11% 1	4163
September	1st to 10th	Day	43% 10% 16% 14% 14% 3	2090
	11th to 20th	Day	42% 8% 9% 19% 17% 4	2090
	21st to end	Day	40% 5% 8% 20% 20% 6%	2090
October	1st to 10th	Day	34% 4 10% 18% 23% 11%	2090
	11th to 20th	Day	27% 4 6% 23% 26% 13%	2024
	21st to end	Day	31% 3 5% 13% 31% 17%	2090
November	1st to 10th	Day	31% 4 7% 15% 27% 16%	1737
	11th to 20th	Day	32% 3 6% 16% 28% 14%	1710
	21st to end	Day	37% 4 7% 19% 22% 11%	1710
December	1st to 10th	Day	41% 5% 12% 15% 19% 9%	1710
	11th to 20th	Day	42% 3 5% 15% 25% 9%	2150
	21st to end	Day	47% 3 5% 17% 24% 5%	3124
January	1st to 10th	Night	40% 4 6% 14% 24% 11%	4109
	11th to 20th	Night	34% 4 5% 20% 25% 11%	4120
	21st to end	Night	47% 3 4 12% 25% 8%	4264
February	1st to 10th	Night	42% 3 7% 16% 20% 12%	2280
	11th to 20th	Night	41% 3 5% 15% 22% 14%	2219
	21st to end	Night	39% 5% 8% 16% 17% 15%	1884
March	1st to 10th	Night	51% 5% 8% 14% 15% 8%	3637
	11th to 20th	Night	34% 6% 9% 15% 25% 11%	3480
	21st to end	Night	42% 4 8% 16% 20% 10%	3817
April	1st to 10th	Night	34% 5% 11% 17% 19% 13%	2065
	11th to 20th	Night	33% 4 8% 21% 22% 12%	1875
	21st to end	Night	27% 5% 10% 26% 24% 9%	1803
May	1st to 10th	Night	29% 10% 14% 23% 19% 5%	2840
	11th to 20th	Night	39% 7% 15% 23% 13% 3	2813
	21st to end	Night	25% 7% 17% 28% 20% 3	3087
June	1st to 10th	Night	43% 10% 15% 19% 13% 1	1710
	11th to 20th	Night	28% 10% 19% 27% 13% 2	1710
	21st to end	Night	36% 12% 19% 17% 12% 3	1710
July	1st to 10th	Night	51% 17% 20% 9% 3 1	2795
	11th to 20th	Night	34% 16% 27% 17% 5% 1	2786
	21st to end	Night	49% 15% 18% 14% 4 1	2988
August	1st to 10th	Night	40% 12% 20% 22% 6%	2923
	11th to 20th	Night	28% 10% 19% 29% 13% 1	3130
	21st to end	Night	30% 10% 20% 28% 11% 1	3476
September	1st to 10th	Night	40% 9% 17% 16% 14% 5%	2072
	11th to 20th	Night	42% 8% 13% 16% 18% 4	2090
	21st to end	Night	36% 8% 11% 17% 21% 7%	2090
October	1st to 10th	Night	32% 6% 8% 19% 22% 13%	2090
	11th to 20th	Night	27% 3 8% 18% 29% 14%	2154
	21st to end	Night	30% 4 4 15% 29% 17%	2508
November	1st to 10th	Night	31% 4 7% 15% 27% 16%	2370
	11th to 20th	Night	33% 3 5% 15% 28% 16%	2470
	21st to end	Night	38% 4 7% 18% 22% 11%	2470
December	1st to 10th	Night	39% 4 9% 18% 22% 7%	2470
	11th to 20th	Night	39% 3 5% 15% 28% 9%	3044
	21st to end	Night	49% 4 5% 17% 20% 4	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	20% 23% 43% 10% 4	270
	11th to 20th	Day	19% 21% 38% 15% 6% 1	270
	21st to end	Day	23% 28% 38% 8% 2	297
February	1st to 10th	Day	20% 26% 39% 11% 4	270
	11th to 20th	Day	28% 18% 39% 14% 1	270
	21st to end	Day	23% 22% 44% 9% 2	225
March	1st to 10th	Day	18% 20% 32% 23% 6% 1	324
	11th to 20th	Day	16% 16% 41% 18% 9% 1	460
	21st to end	Day	19% 16% 37% 20% 7% 1	506
April	1st to 10th	Day	17% 17% 30% 25% 10% 1	460
	11th to 20th	Day	16% 13% 33% 24% 12% 2	452
	21st to end	Day	11% 10% 29% 31% 16% 3	460
May	1st to 10th	Day	8% 12% 25% 31% 19% 5%	463
	11th to 20th	Day	10% 3 24% 31% 22% 10%	487
	21st to end	Day	11% 4 18% 31% 26% 11%	529
June	1st to 10th	Day	11% 2 15% 32% 27% 12%	490
	11th to 20th	Day	8% 3 15% 27% 27% 21%	490
	21st to end	Day	5% 2 15% 31% 30% 16%	490
July	1st to 10th	Day	8% 2 7% 24% 33% 26%	485
	11th to 20th	Day	7% 1 5% 19% 36% 31%	484
	21st to end	Day	5% 2 7% 24% 38% 24%	532
August	1st to 10th	Day	10% 1 9% 28% 33% 19%	486
	11th to 20th	Day	8% 1 7% 26% 34% 23%	479
	21st to end	Day	12% 3 9% 28% 31% 17%	539
September	1st to 10th	Day	9% 4 14% 26% 33% 14%	490
	11th to 20th	Day	16% 3 14% 34% 24% 9%	490
	21st to end	Day	16% 4 14% 27% 28% 12%	490
October	1st to 10th	Day	14% 6% 28% 28% 19% 6%	490
	11th to 20th	Day	11% 7% 23% 33% 19% 6%	490
	21st to end	Day	14% 9% 26% 29% 20% 3	539
November	1st to 10th	Day	17% 8% 25% 32% 14% 4	329
	11th to 20th	Day	14% 17% 39% 23% 6% 2	270
	21st to end	Day	14% 13% 39% 24% 9% 1	270
December	1st to 10th	Day	23% 18% 32% 22% 4 1	270
	11th to 20th	Day	25% 19% 34% 16% 6%	270
	21st to end	Day	26% 14% 32% 23% 5% 1	297
January	1st to 10th	Night	19% 16% 35% 24% 5%	760
	11th to 20th	Night	19% 14% 28% 29% 9%	760
	21st to end	Night	21% 16% 37% 23% 4	836
February	1st to 10th	Night	18% 11% 33% 30% 8%	760
	11th to 20th	Night	22% 13% 33% 27% 5%	743
	21st to end	Night	18% 14% 39% 27% 3	628
March	1st to 10th	Night	15% 14% 31% 32% 7%	760
	11th to 20th	Night	15% 13% 34% 27% 11% 1	760
	21st to end	Night	14% 14% 32% 29% 11%	836
April	1st to 10th	Night	14% 10% 32% 32% 12%	735
	11th to 20th	Night	15% 10% 29% 30% 16% 1	563
	21st to end	Night	8% 7% 29% 36% 20% 1	570
May	1st to 10th	Night	8% 7% 26% 36% 20% 2	570
	11th to 20th	Night	10% 3 24% 35% 22% 5%	561
	21st to end	Night	9% 1 15% 35% 35% 5%	617
June	1st to 10th	Night	8% 2 14% 37% 34% 5%	570
	11th to 20th	Night	4 2 10% 33% 38% 13%	570
	21st to end	Night	6% 2 8% 35% 39% 10%	570
July	1st to 10th	Night	8% 2 5% 27% 41% 17%	555
	11th to 20th	Night	8% 1 3 23% 47% 17%	552
	21st to end	Night	4 2 6% 28% 48% 12%	624
August	1st to 10th	Night	8% 2 9% 27% 41% 14%	567
	11th to 20th	Night	10% 1 5% 25% 46% 12%	564
	21st to end	Night	14% 2 12% 23% 36% 14%	627
September	1st to 10th	Night	12% 2 12% 27% 38% 9%	742
	11th to 20th	Night	15% 2 14% 33% 30% 5%	760
	21st to end	Night	11% 2 15% 33% 35% 4	760
October	1st to 10th	Night	13% 3 23% 35% 22% 4	760
	11th to 20th	Night	12% 4 24% 31% 26% 3	760
	21st to end	Night	14% 8% 21% 33% 23% 1	836
November	1st to 10th	Night	12% 8% 24% 34% 20% 2	748
	11th to 20th	Night	15% 10% 31% 31% 12% 1	760
	21st to end	Night	16% 10% 29% 31% 13% 1	760
December	1st to 10th	Night	17% 10% 32% 29% 11% 1	760
	11th to 20th	Night	19% 10% 32% 29% 9% 1	760
	21st to end	Night	25% 12% 26% 28% 8%	836

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