Eastman
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Eastman clear sky chart from 2005-11-06 to 2024-07-31.

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% 4 5% 4 6% 8% 42%	90054
	Night	12% 6% 2 6% 4 4 5% 4 6% 8% 44%	89727
Transparency	Day	39% 7% 11% 18% 18% 7%	89828
	Night	37% 7% 11% 17% 19% 8%	89557
Seeing	Day	13% 6% 20% 24% 23% 14%	14732
	Night	13% 6% 22% 32% 23% 4	24775

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	13% 7% 2 7% 4 4 4 4 4 6% 44%	2836
	11th to 20th	Day	13% 7% 2 4 2 3 3 3 5% 7% 53%	2840
	21st to end	Day	15% 8% 3 5% 4 3 3 3 5% 6% 45%	3218
February	1st to 10th	Day	15% 7% 3 6% 5% 4 4 3 6% 7% 41%	1900
	11th to 20th	Day	16% 7% 2 5% 4 3 4 3 5% 6% 46%	1848
	21st to end	Day	15% 7% 2 5% 4 3 4 3 6% 7% 44%	1570
March	1st to 10th	Day	19% 11% 3 7% 4 3 4 3 5% 6% 35%	3360
	11th to 20th	Day	9% 4 2 5% 4 4 5% 4 6% 8% 50%	3480
	21st to end	Day	16% 7% 2 6% 4 4 4 3 4 6% 43%	3815
April	1st to 10th	Day	10% 6% 2 6% 5% 4 5% 3 6% 6% 47%	2090
	11th to 20th	Day	10% 6% 2 6% 4 4 4 3 5% 7% 50%	2149
	21st to end	Day	6% 4 1 5% 4 4 4 4 6% 7% 55%	2467
May	1st to 10th	Day	8% 5% 2 6% 5% 5% 5% 4 5% 8% 47%	4082
	11th to 20th	Day	15% 7% 3 7% 4 4 5% 4 6% 7% 38%	4081
	21st to end	Day	5% 3 2 6% 4 4 5% 5% 7% 9% 49%	4476
June	1st to 10th	Day	12% 5% 2 7% 6% 5% 6% 5% 7% 11% 34%	2470
	11th to 20th	Day	6% 4 1 6% 5% 5% 5% 6% 9% 10% 43%	2470
	21st to end	Day	5% 5% 2 7% 7% 7% 8% 5% 9% 11% 33%	2470
July	1st to 10th	Day	8% 6% 2 9% 6% 6% 7% 6% 10% 12% 27%	2470
	11th to 20th	Day	7% 4 3 9% 7% 7% 7% 6% 9% 12% 29%	2470
	21st to end	Day	6% 6% 3 8% 7% 7% 8% 6% 9% 11% 30%	2679
August	1st to 10th	Day	8% 6% 2 8% 7% 8% 8% 7% 9% 11% 26%	2327
	11th to 20th	Day	10% 6% 3 8% 7% 7% 8% 6% 8% 11% 27%	2207
	21st to end	Day	12% 7% 3 9% 6% 6% 8% 5% 8% 9% 26%	2297
September	1st to 10th	Day	8% 7% 3 7% 6% 6% 5% 5% 7% 9% 37%	1980
	11th to 20th	Day	11% 7% 3 7% 6% 4 5% 5% 6% 8% 39%	1980
	21st to end	Day	12% 7% 3 7% 5% 5% 5% 4 5% 5% 42%	1980
October	1st to 10th	Day	11% 6% 1 5% 3 3 4 2 5% 7% 52%	1980
	11th to 20th	Day	11% 5% 1 4 2 4 2 3 6% 7% 55%	1837
	21st to end	Day	9% 4 2 5% 4 3 4 3 6% 5% 56%	1980
November	1st to 10th	Day	10% 6% 2 5% 4 3 3 3 5% 5% 53%	1838
	11th to 20th	Day	12% 6% 2 5% 3 3 3 2 5% 6% 54%	1710
	21st to end	Day	13% 6% 2 5% 4 3 3 4 5% 7% 47%	1710
December	1st to 10th	Day	15% 7% 2 5% 4 4 5% 4 6% 6% 42%	1710
	11th to 20th	Day	17% 7% 1 5% 4 4 3 4 4 6% 45%	2153
	21st to end	Day	17% 9% 4 8% 4 3 4 2 3 5% 42%	3124
January	1st to 10th	Night	15% 6% 2 6% 4 4 4 4 6% 7% 42%	4109
	11th to 20th	Night	9% 5% 2 6% 5% 4 5% 4 5% 7% 48%	4120
	21st to end	Night	17% 8% 3 6% 4 5% 4 3 4 6% 41%	4436
February	1st to 10th	Night	13% 7% 3 5% 5% 4 4 4 5% 6% 44%	2280
	11th to 20th	Night	17% 7% 2 6% 4 3 3 3 5% 5% 46%	2218
	21st to end	Night	14% 6% 2 5% 4 3 4 3 5% 7% 47%	1884
March	1st to 10th	Night	22% 10% 3 6% 3 3 3 2 4 5% 38%	3492
	11th to 20th	Night	10% 5% 2 5% 4 4 5% 3 6% 8% 49%	3480
	21st to end	Night	17% 5% 2 5% 4 4 5% 3 6% 7% 43%	3817
April	1st to 10th	Night	11% 5% 2 6% 4 3 3 3 6% 8% 48%	2090
	11th to 20th	Night	10% 4 2 4 5% 4 5% 4 5% 8% 50%	1994
	21st to end	Night	6% 4 1 4 3 5% 5% 4 6% 8% 55%	1710
May	1st to 10th	Night	6% 6% 2 6% 5% 4 5% 4 6% 10% 46%	2813
	11th to 20th	Night	13% 5% 2 6% 4 5% 5% 4 6% 8% 42%	2812
	21st to end	Night	6% 4 2 5% 3 4 4 4 6% 11% 51%	3079
June	1st to 10th	Night	8% 7% 2 8% 5% 5% 7% 5% 9% 9% 35%	1710
	11th to 20th	Night	5% 4 2 6% 5% 6% 5% 5% 9% 11% 42%	1710
	21st to end	Night	5% 6% 3 8% 6% 5% 7% 7% 9% 11% 34%	1710
July	1st to 10th	Night	7% 7% 2 6% 5% 6% 8% 7% 10% 13% 29%	1710
	11th to 20th	Night	7% 5% 2 6% 6% 7% 7% 6% 10% 13% 31%	1710
	21st to end	Night	6% 5% 2 6% 6% 5% 7% 6% 10% 13% 35%	1870
August	1st to 10th	Night	4 5% 2 7% 5% 6% 8% 7% 9% 13% 33%	1611
	11th to 20th	Night	8% 6% 2 9% 6% 6% 6% 6% 9% 11% 32%	1689
	21st to end	Night	9% 7% 3 7% 5% 6% 6% 6% 8% 10% 33%	2038
September	1st to 10th	Night	9% 7% 2 7% 6% 4 5% 5% 6% 11% 37%	1980
	11th to 20th	Night	9% 7% 3 7% 5% 6% 6% 4 5% 8% 41%	1980
	21st to end	Night	10% 6% 2 8% 4 4 6% 5% 6% 8% 40%	1980
October	1st to 10th	Night	11% 5% 2 6% 3 3 3 3 5% 7% 52%	1980
	11th to 20th	Night	13% 5% 1 3 3 2 4 3 3 5% 57%	2120
	21st to end	Night	9% 5% 2 4 3 3 4 2 5% 6% 57%	2376
November	1st to 10th	Night	10% 6% 2 5% 3 3 4 3 4 5% 55%	2235
	11th to 20th	Night	13% 5% 2 5% 3 3 3 3 4 6% 54%	2470
	21st to end	Night	13% 7% 2 5% 3 3 4 3 5% 6% 49%	2470
December	1st to 10th	Night	13% 5% 2 5% 4 4 4 4 5% 7% 45%	2470
	11th to 20th	Night	16% 6% 2 6% 3 3 3 3 4 5% 49%	3042
	21st to end	Night	17% 9% 3 7% 4 4 4 3 5% 6% 37%	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% 5% 6% 16% 23% 10%	2837
	11th to 20th	Day	32% 4 6% 18% 27% 14%	2840
	21st to end	Day	41% 4 6% 13% 23% 14%	3218
February	1st to 10th	Day	43% 4 7% 17% 20% 9%	1900
	11th to 20th	Day	40% 5% 6% 15% 26% 8%	1858
	21st to end	Day	39% 4 8% 17% 20% 11%	1570
March	1st to 10th	Day	49% 5% 8% 15% 16% 7%	3360
	11th to 20th	Day	31% 7% 11% 16% 21% 14%	3480
	21st to end	Day	43% 5% 8% 20% 16% 8%	3815
April	1st to 10th	Day	37% 5% 9% 20% 18% 12%	2090
	11th to 20th	Day	34% 4 8% 20% 22% 12%	2149
	21st to end	Day	27% 5% 10% 25% 27% 7%	2467
May	1st to 10th	Day	34% 7% 11% 26% 19% 3	4120
	11th to 20th	Day	43% 7% 10% 22% 15% 2	4085
	21st to end	Day	28% 6% 18% 26% 20% 2	4489
June	1st to 10th	Day	42% 9% 15% 18% 14% 1	2470
	11th to 20th	Day	31% 10% 18% 24% 15% 2	2470
	21st to end	Day	39% 12% 18% 17% 11% 2	2470
July	1st to 10th	Day	43% 13% 22% 15% 5% 2	2405
	11th to 20th	Day	42% 13% 24% 15% 4 1	2401
	21st to end	Day	40% 14% 21% 19% 5% 1	2537
August	1st to 10th	Day	46% 13% 19% 17% 4	2314
	11th to 20th	Day	46% 13% 20% 15% 6%	2207
	21st to end	Day	50% 12% 17% 12% 8% 2	2297
September	1st to 10th	Day	41% 9% 15% 17% 13% 4	1980
	11th to 20th	Day	43% 7% 12% 16% 18% 4	1980
	21st to end	Day	43% 6% 9% 18% 18% 6%	1980
October	1st to 10th	Day	34% 4 9% 19% 23% 11%	1980
	11th to 20th	Day	29% 5% 7% 22% 27% 10%	1837
	21st to end	Day	29% 4 6% 15% 28% 17%	1980
November	1st to 10th	Day	33% 4 7% 15% 25% 16%	1838
	11th to 20th	Day	33% 2 7% 18% 25% 15%	1710
	21st to end	Day	37% 4 9% 18% 22% 10%	1710
December	1st to 10th	Day	41% 5% 11% 15% 19% 8%	1710
	11th to 20th	Day	41% 4 5% 15% 27% 8%	2150
	21st to end	Day	47% 4 5% 16% 24% 5%	3124
January	1st to 10th	Night	39% 6% 5% 15% 22% 13%	4109
	11th to 20th	Night	35% 4 6% 19% 26% 11%	4120
	21st to end	Night	45% 5% 5% 11% 25% 9%	4436
February	1st to 10th	Night	40% 4 8% 17% 20% 11%	2280
	11th to 20th	Night	41% 4 6% 15% 21% 13%	2219
	21st to end	Night	38% 5% 8% 17% 18% 15%	1884
March	1st to 10th	Night	49% 5% 10% 14% 14% 8%	3492
	11th to 20th	Night	32% 6% 9% 15% 25% 13%	3480
	21st to end	Night	39% 5% 8% 17% 19% 11%	3817
April	1st to 10th	Night	33% 5% 10% 17% 20% 13%	2090
	11th to 20th	Night	31% 5% 8% 21% 22% 12%	1994
	21st to end	Night	26% 5% 12% 25% 23% 9%	1710
May	1st to 10th	Night	32% 9% 15% 23% 17% 5%	2840
	11th to 20th	Night	38% 8% 14% 23% 14% 3	2813
	21st to end	Night	26% 8% 15% 27% 21% 4	3087
June	1st to 10th	Night	41% 11% 18% 18% 12% 1	1710
	11th to 20th	Night	31% 10% 21% 24% 13% 1	1710
	21st to end	Night	38% 13% 18% 16% 11% 3	1710
July	1st to 10th	Night	40% 16% 21% 16% 6% 1	1665
	11th to 20th	Night	38% 13% 26% 17% 5%	1656
	21st to end	Night	35% 14% 24% 21% 5% 1	1771
August	1st to 10th	Night	36% 14% 25% 20% 4	1600
	11th to 20th	Night	40% 13% 23% 18% 6%	1689
	21st to end	Night	44% 13% 19% 15% 8% 2	2038
September	1st to 10th	Night	40% 11% 17% 15% 14% 3	1980
	11th to 20th	Night	40% 10% 13% 17% 16% 5%	1980
	21st to end	Night	40% 7% 12% 16% 20% 5%	1980
October	1st to 10th	Night	32% 6% 10% 18% 24% 11%	1980
	11th to 20th	Night	31% 3 7% 18% 29% 10%	2120
	21st to end	Night	29% 4 6% 17% 26% 18%	2376
November	1st to 10th	Night	32% 4 8% 13% 27% 16%	2235
	11th to 20th	Night	34% 3 6% 15% 27% 15%	2470
	21st to end	Night	37% 4 8% 19% 21% 12%	2470
December	1st to 10th	Night	38% 6% 11% 16% 23% 7%	2470
	11th to 20th	Night	39% 4 6% 14% 27% 10%	3044
	21st to end	Night	48% 5% 5% 17% 22% 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	13% 16% 46% 19% 6% 1	270
	11th to 20th	Day	14% 17% 34% 22% 11% 3	270
	21st to end	Day	22% 17% 40% 15% 5%	297
February	1st to 10th	Day	20% 14% 37% 21% 7%	270
	11th to 20th	Day	23% 13% 37% 24% 3	270
	21st to end	Day	17% 18% 37% 22% 4 1	225
March	1st to 10th	Day	12% 14% 29% 32% 13% 1	407
	11th to 20th	Day	14% 8% 34% 32% 11% 1	460
	21st to end	Day	16% 11% 32% 29% 11% 2	506
April	1st to 10th	Day	17% 13% 27% 27% 14% 3	460
	11th to 20th	Day	12% 8% 29% 25% 19% 6%	452
	21st to end	Day	8% 7% 22% 32% 23% 8%	460
May	1st to 10th	Day	8% 9% 22% 30% 21% 11%	463
	11th to 20th	Day	11% 3 16% 26% 27% 17%	487
	21st to end	Day	11% 2 12% 26% 30% 19%	529
June	1st to 10th	Day	13% 1 10% 24% 32% 20%	490
	11th to 20th	Day	7% 3 13% 20% 27% 30%	490
	21st to end	Day	7% 1 9% 29% 29% 24%	490
July	1st to 10th	Day	9% 1 6% 17% 32% 35%	485
	11th to 20th	Day	7% 1 5% 12% 32% 43%	484
	21st to end	Day	5% 1 6% 19% 37% 32%	529
August	1st to 10th	Day	10% 1 9% 18% 31% 30%	446
	11th to 20th	Day	8% 2 5% 14% 33% 38%	439
	21st to end	Day	16% 2 7% 19% 33% 24%	495
September	1st to 10th	Day	9% 2 10% 22% 31% 26%	450
	11th to 20th	Day	13% 2 9% 29% 33% 14%	450
	21st to end	Day	12% 2 12% 25% 31% 18%	450
October	1st to 10th	Day	13% 2 20% 32% 22% 11%	450
	11th to 20th	Day	11% 3 18% 31% 26% 10%	450
	21st to end	Day	11% 7% 23% 28% 26% 5%	495
November	1st to 10th	Day	18% 5% 22% 28% 21% 6%	436
	11th to 20th	Day	17% 7% 36% 24% 13% 2	270
	21st to end	Day	11% 14% 25% 31% 16% 3	270
December	1st to 10th	Day	19% 11% 36% 18% 13% 2	270
	11th to 20th	Day	22% 10% 31% 24% 13% 1	270
	21st to end	Day	22% 11% 30% 25% 10% 2	297
January	1st to 10th	Night	17% 11% 36% 29% 6% 1	760
	11th to 20th	Night	16% 11% 30% 33% 10%	760
	21st to end	Night	19% 9% 39% 28% 4	836
February	1st to 10th	Night	16% 10% 33% 35% 6%	760
	11th to 20th	Night	19% 10% 35% 32% 5%	743
	21st to end	Night	16% 9% 36% 36% 4	628
March	1st to 10th	Night	14% 10% 32% 37% 7%	760
	11th to 20th	Night	13% 11% 32% 32% 12% 1	760
	21st to end	Night	12% 10% 35% 32% 10%	836
April	1st to 10th	Night	12% 8% 31% 34% 13% 1	760
	11th to 20th	Night	11% 8% 29% 34% 17%	682
	21st to end	Night	7% 5% 24% 43% 20% 1	570
May	1st to 10th	Night	8% 4 26% 39% 21% 1	570
	11th to 20th	Night	9% 2 22% 37% 25% 4	561
	21st to end	Night	9% 2 9% 37% 37% 5%	617
June	1st to 10th	Night	9% 2 11% 39% 34% 6%	570
	11th to 20th	Night	7% 2 11% 31% 35% 13%	570
	21st to end	Night	7% 2 8% 33% 41% 9%	570
July	1st to 10th	Night	10% 1 6% 27% 43% 13%	555
	11th to 20th	Night	8% 1 3 23% 50% 15%	552
	21st to end	Night	7% 1 5% 28% 48% 11%	624
August	1st to 10th	Night	7% 1 6% 26% 48% 13%	537
	11th to 20th	Night	10% 1 5% 23% 51% 10%	534
	21st to end	Night	12% 2 7% 26% 41% 13%	652
September	1st to 10th	Night	11% 2 9% 27% 41% 11%	720
	11th to 20th	Night	12% 2 10% 31% 40% 5%	720
	21st to end	Night	13% 2 14% 31% 38% 4	720
October	1st to 10th	Night	12% 2 19% 35% 27% 5%	720
	11th to 20th	Night	15% 4 17% 32% 28% 4	720
	21st to end	Night	12% 4 20% 36% 26% 2	792
November	1st to 10th	Night	13% 5% 23% 35% 23% 1	740
	11th to 20th	Night	15% 9% 25% 36% 15% 1	760
	21st to end	Night	16% 7% 28% 34% 15% 1	760
December	1st to 10th	Night	16% 7% 31% 31% 13% 2	760
	11th to 20th	Night	18% 7% 30% 31% 14% 1	760
	21st to end	Night	22% 9% 26% 34% 10%	836

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