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 2025-01-07.

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% 42%	105076
	Night	12% 6% 2 6% 4 4 5% 4 6% 8% 44%	103909
Transparency	Day	37% 7% 12% 19% 18% 7%	108883
	Night	36% 7% 11% 18% 19% 9%	108241
Seeing	Day	13% 6% 20% 25% 22% 14%	15313
	Night	13% 6% 22% 32% 23% 4	25385

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 3 4 6% 45%	2890
	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	11% 7% 3 9% 6% 7% 8% 7% 10% 13% 20%	4120
	11th to 20th	Day	5% 3 2 7% 6% 7% 7% 6% 9% 13% 36%	4120
	21st to end	Day	7% 6% 3 8% 7% 7% 8% 6% 10% 13% 23%	4466
August	1st to 10th	Day	13% 5% 2 7% 6% 7% 7% 6% 8% 11% 28%	4104
	11th to 20th	Day	6% 4 2 6% 5% 5% 6% 4 7% 11% 44%	3864
	21st to end	Day	8% 5% 2 6% 5% 5% 7% 5% 8% 11% 38%	4031
September	1st to 10th	Day	10% 7% 3 7% 6% 6% 5% 5% 7% 9% 36%	2090
	11th to 20th	Day	12% 7% 3 7% 6% 4 5% 5% 6% 8% 38%	2090
	21st to end	Day	12% 7% 2 7% 5% 5% 5% 4 5% 5% 43%	2090
October	1st to 10th	Day	11% 6% 1 6% 3 3 4 2 5% 6% 51%	2090
	11th to 20th	Day	10% 4 1 3 2 4 2 3 6% 6% 57%	1939
	21st to end	Day	8% 4 2 5% 3 3 4 3 5% 5% 58%	2090
November	1st to 10th	Day	11% 6% 2 5% 4 3 3 3 5% 6% 52%	1937
	11th to 20th	Day	12% 6% 2 5% 3 3 3 2 5% 6% 54%	1800
	21st to end	Day	13% 6% 2 5% 4 3 3 4 5% 7% 47%	1800
December	1st to 10th	Day	11% 7% 2 5% 4 3 3 3 5% 5% 52%	2930
	11th to 20th	Day	15% 6% 2 5% 4 4 3 3 5% 6% 47%	3373
	21st to end	Day	18% 8% 3 6% 4 3 3 3 4 5% 42%	4466
January	1st to 10th	Night	15% 6% 2 5% 4 4 4 4 6% 7% 42%	4188
	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	13% 9% 3 9% 6% 6% 7% 6% 8% 11% 22%	2840
	11th to 20th	Night	5% 4 2 6% 6% 7% 7% 6% 10% 14% 33%	2840
	21st to end	Night	9% 6% 3 8% 7% 6% 9% 7% 10% 13% 24%	3087
August	1st to 10th	Night	13% 6% 2 7% 6% 7% 7% 6% 8% 12% 28%	2825
	11th to 20th	Night	6% 4 2 7% 5% 5% 5% 5% 8% 11% 43%	2960
	21st to end	Night	6% 5% 2 5% 4 4 4 5% 7% 11% 47%	3590
September	1st to 10th	Night	10% 7% 3 7% 5% 4 5% 5% 6% 11% 37%	2090
	11th to 20th	Night	10% 7% 3 8% 4 6% 6% 4 5% 8% 40%	2090
	21st to end	Night	11% 6% 2 7% 4 5% 6% 5% 6% 8% 40%	2090
October	1st to 10th	Night	11% 5% 2 6% 3 3 3 3 5% 7% 52%	2090
	11th to 20th	Night	12% 5% 1 3 3 2 3 3 3 5% 59%	2238
	21st to end	Night	9% 5% 2 4 3 3 4 2 5% 5% 58%	2508
November	1st to 10th	Night	10% 6% 2 5% 3 4 4 3 5% 5% 54%	2356
	11th to 20th	Night	13% 5% 2 5% 3 3 3 3 4 6% 53%	2600
	21st to end	Night	12% 7% 2 5% 3 3 4 3 5% 6% 50%	2600
December	1st to 10th	Night	11% 5% 2 5% 3 3 3 3 4 5% 56%	4250
	11th to 20th	Night	15% 6% 3 6% 3 3 3 3 4 5% 49%	4822
	21st to end	Night	18% 8% 3 6% 4 4 3 3 4 5% 42%	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	40% 5% 5% 16% 23% 10%	2891
	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	50% 15% 22% 10% 3 1	4055
	11th to 20th	Day	35% 14% 27% 20% 3 1	4051
	21st to end	Day	45% 18% 20% 13% 3	4324
August	1st to 10th	Day	46% 11% 20% 21% 3	4091
	11th to 20th	Day	32% 9% 16% 30% 12%	3903
	21st to end	Day	36% 10% 18% 27% 7% 1	4031
September	1st to 10th	Day	42% 9% 16% 16% 13% 4	2090
	11th to 20th	Day	43% 7% 11% 17% 17% 4	2090
	21st to end	Day	42% 6% 9% 19% 18% 6%	2090
October	1st to 10th	Day	36% 4 7% 12% 24% 17%	3480
	11th to 20th	Day	17% 3 4 16% 26% 35%	3205
	21st to end	Day	21% 3 5% 19% 37% 16%	3428
November	1st to 10th	Day	34% 4 8% 15% 25% 15%	1937
	11th to 20th	Day	33% 2 7% 18% 25% 16%	1800
	21st to end	Day	36% 4 8% 18% 23% 11%	1800
December	1st to 10th	Day	35% 4 7% 15% 28% 11%	2930
	11th to 20th	Day	39% 4 5% 23% 23% 7%	3370
	21st to end	Day	46% 3 5% 19% 23% 4	4466
January	1st to 10th	Night	39% 6% 5% 15% 23% 12%	4188
	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	51% 14% 20% 10% 4 1	2795
	11th to 20th	Night	36% 14% 27% 19% 3	2786
	21st to end	Night	47% 17% 19% 13% 3	2988
August	1st to 10th	Night	45% 11% 24% 17% 3	2814
	11th to 20th	Night	32% 10% 19% 28% 10% 1	2987
	21st to end	Night	30% 9% 23% 30% 6% 1	3590
September	1st to 10th	Night	41% 10% 17% 15% 13% 3	2090
	11th to 20th	Night	41% 10% 13% 17% 15% 4	2090
	21st to end	Night	39% 7% 12% 17% 19% 5%	2090
October	1st to 10th	Night	35% 4 10% 11% 24% 16%	3480
	11th to 20th	Night	18% 2 4 11% 29% 35%	3711
	21st to end	Night	19% 3 5% 18% 34% 21%	4120
November	1st to 10th	Night	33% 4 8% 13% 26% 15%	2356
	11th to 20th	Night	34% 3 6% 15% 28% 15%	2600
	21st to end	Night	36% 4 8% 19% 22% 12%	2600
December	1st to 10th	Night	32% 4 7% 18% 30% 9%	4250
	11th to 20th	Night	39% 4 9% 17% 23% 9%	4824
	21st to end	Night	45% 4 5% 18% 26% 3	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	14% 16% 45% 18% 6% 1	288
	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% 20% 37% 31%	532
August	1st to 10th	Day	11% 1 9% 19% 31% 29%	486
	11th to 20th	Day	8% 2 6% 15% 34% 36%	479
	21st to end	Day	15% 2 8% 21% 32% 23%	539
September	1st to 10th	Day	12% 2 11% 21% 29% 24%	490
	11th to 20th	Day	15% 3 9% 29% 31% 13%	490
	21st to end	Day	13% 2 12% 25% 31% 17%	490
October	1st to 10th	Day	13% 3 21% 31% 21% 10%	490
	11th to 20th	Day	10% 4 21% 31% 24% 10%	490
	21st to end	Day	10% 7% 22% 31% 26% 4	539
November	1st to 10th	Day	19% 5% 21% 28% 20% 6%	475
	11th to 20th	Day	17% 8% 36% 24% 13% 3	300
	21st to end	Day	12% 14% 26% 29% 16% 3	300
December	1st to 10th	Day	19% 13% 37% 18% 12% 2	300
	11th to 20th	Day	21% 11% 31% 24% 12% 1	300
	21st to end	Day	24% 11% 29% 25% 10% 2	330
January	1st to 10th	Night	16% 12% 36% 29% 6% 1	785
	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% 29% 48% 11%	624
August	1st to 10th	Night	8% 1 6% 25% 48% 12%	567
	11th to 20th	Night	10% 1 5% 24% 50% 10%	564
	21st to end	Night	11% 2 7% 27% 40% 12%	689
September	1st to 10th	Night	13% 2 9% 27% 39% 11%	760
	11th to 20th	Night	13% 2 11% 30% 39% 5%	760
	21st to end	Night	13% 2 14% 31% 37% 4	760
October	1st to 10th	Night	13% 2 19% 35% 27% 5%	760
	11th to 20th	Night	15% 4 18% 32% 26% 4	760
	21st to end	Night	11% 4 20% 37% 26% 2	836
November	1st to 10th	Night	14% 5% 22% 35% 23% 1	780
	11th to 20th	Night	15% 9% 25% 35% 15% 1	800
	21st to end	Night	15% 9% 27% 33% 15% 1	800
December	1st to 10th	Night	16% 8% 32% 31% 13% 2	800
	11th to 20th	Night	18% 6% 30% 32% 13% 1	800
	21st to end	Night	21% 9% 27% 33% 9%	880

Page generated at 2025-01-04 03:24:03. Version ac07

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