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 2026-05-02.

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% 4 4 5% 4 6% 8% 43%	131868
	Night	12% 6% 2 6% 4 4 5% 4 6% 8% 44%	130616
Transparency	Day	37% 7% 12% 19% 17% 8%	135631
	Night	36% 6% 11% 18% 19% 9%	134923
Seeing	Day	13% 7% 21% 25% 22% 13%	17063
	Night	13% 6% 23% 32% 22% 4	27156

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	12% 6% 2 7% 4 3 4 3 4 6% 49%	5258
	11th to 20th	Day	14% 5% 2 4 2 2 3 2 5% 7% 54%	5280
	21st to end	Day	13% 8% 3 7% 4 3 4 4 6% 7% 42%	5958
February	1st to 10th	Day	15% 7% 2 6% 5% 4 4 3 5% 7% 42%	2100
	11th to 20th	Day	17% 7% 2 5% 4 3 4 3 5% 6% 45%	2048
	21st to end	Day	15% 7% 2 5% 4 3 4 3 6% 7% 44%	1730
March	1st to 10th	Day	18% 9% 3 6% 4 4 4 3 5% 7% 38%	4925
	11th to 20th	Day	8% 4 2 4 3 4 4 4 5% 7% 55%	5090
	21st to end	Day	14% 7% 3 6% 4 4 4 3 4 5% 47%	5586
April	1st to 10th	Day	10% 6% 2 6% 5% 4 5% 3 6% 6% 47%	2310
	11th to 20th	Day	9% 5% 2 5% 4 3 4 3 5% 7% 52%	2378
	21st to end	Day	6% 4 2 5% 4 4 5% 4 6% 7% 53%	2727
May	1st to 10th	Day	11% 6% 2 7% 5% 5% 5% 4 5% 8% 42%	5875
	11th to 20th	Day	14% 6% 2 7% 4 4 5% 4 7% 9% 38%	5861
	21st to end	Day	6% 3 2 6% 5% 5% 5% 5% 7% 10% 47%	6433
June	1st to 10th	Day	12% 5% 2 7% 6% 5% 6% 5% 7% 10% 34%	2600
	11th to 20th	Day	6% 5% 1 6% 5% 5% 5% 6% 9% 11% 43%	2600
	21st to end	Day	5% 5% 2 7% 7% 7% 8% 5% 9% 11% 34%	2600
July	1st to 10th	Day	10% 7% 3 8% 6% 6% 8% 7% 10% 13% 23%	5900
	11th to 20th	Day	3 3 2 5% 5% 6% 6% 5% 9% 14% 43%	5900
	21st to end	Day	6% 6% 2 7% 6% 6% 8% 6% 10% 13% 29%	6424
August	1st to 10th	Day	13% 6% 2 7% 6% 7% 7% 6% 8% 11% 27%	4234
	11th to 20th	Day	6% 4 2 6% 5% 5% 6% 4 7% 11% 44%	3988
	21st to end	Day	8% 5% 2 6% 5% 5% 6% 5% 7% 11% 38%	4158
September	1st to 10th	Day	9% 7% 3 7% 6% 6% 5% 5% 6% 9% 38%	2200
	11th to 20th	Day	12% 7% 3 7% 5% 4 5% 4 6% 8% 40%	2200
	21st to end	Day	12% 7% 2 7% 5% 5% 5% 4 5% 5% 43%	2200
October	1st to 10th	Day	12% 7% 1 6% 4 3 4 2 5% 6% 50%	2200
	11th to 20th	Day	10% 5% 1 3 2 4 2 3 6% 6% 58%	2041
	21st to end	Day	9% 4 2 5% 3 3 4 3 5% 5% 57%	2200
November	1st to 10th	Day	11% 6% 2 5% 3 3 3 3 5% 6% 53%	2036
	11th to 20th	Day	12% 6% 2 5% 3 3 2 2 4 6% 56%	1890
	21st to end	Day	12% 6% 2 5% 4 3 3 4 5% 8% 47%	1890
December	1st to 10th	Day	11% 7% 2 6% 4 3 3 3 5% 5% 51%	3020
	11th to 20th	Day	14% 6% 2 5% 4 4 3 3 5% 6% 48%	3463
	21st to end	Day	18% 8% 3 6% 4 3 3 3 4 5% 43%	4565
January	1st to 10th	Night	10% 6% 1 5% 4 4 4 4 6% 7% 49%	7635
	11th to 20th	Night	12% 5% 2 6% 4 4 4 3 4 6% 49%	7680
	21st to end	Night	17% 8% 3 6% 3 4 4 3 5% 7% 40%	8207
February	1st to 10th	Night	13% 7% 2 5% 4 4 4 4 5% 6% 46%	2520
	11th to 20th	Night	16% 7% 2 6% 4 3 3 3 5% 5% 45%	2458
	21st to end	Night	14% 7% 2 5% 4 3 4 3 5% 7% 48%	2076
March	1st to 10th	Night	20% 8% 2 5% 3 3 4 3 4 6% 42%	5147
	11th to 20th	Night	8% 5% 2 4 3 4 5% 4 6% 8% 52%	5090
	21st to end	Night	14% 5% 2 5% 3 4 4 3 5% 7% 48%	5588
April	1st to 10th	Night	11% 5% 2 6% 4 4 4 4 6% 8% 48%	2310
	11th to 20th	Night	9% 4 1 4 4 4 4 3 5% 8% 53%	2206
	21st to end	Night	6% 4 1 5% 3 5% 5% 4 6% 7% 53%	1890
May	1st to 10th	Night	9% 6% 3 7% 5% 5% 5% 4 6% 10% 41%	4042
	11th to 20th	Night	16% 4 2 5% 4 4 5% 4 7% 10% 38%	4032
	21st to end	Night	7% 4 2 6% 3 4 4 5% 7% 11% 45%	4421
June	1st to 10th	Night	8% 7% 3 8% 5% 5% 6% 5% 9% 9% 35%	1800
	11th to 20th	Night	6% 4 2 6% 5% 6% 5% 5% 9% 11% 42%	1800
	21st to end	Night	5% 6% 3 8% 6% 5% 6% 7% 8% 11% 35%	1800
July	1st to 10th	Night	13% 8% 3 9% 6% 7% 7% 5% 9% 11% 22%	4058
	11th to 20th	Night	4 3 2 6% 6% 6% 7% 6% 9% 15% 34%	4057
	21st to end	Night	8% 6% 3 8% 7% 6% 8% 6% 10% 13% 26%	4427
August	1st to 10th	Night	13% 6% 2 8% 6% 7% 7% 6% 8% 11% 27%	2915
	11th to 20th	Night	6% 4 2 7% 5% 5% 5% 5% 8% 11% 42%	3055
	21st to end	Night	7% 5% 2 5% 4 4 4 5% 7% 11% 47%	3704
September	1st to 10th	Night	9% 7% 3 7% 5% 4 5% 5% 6% 11% 38%	2200
	11th to 20th	Night	10% 6% 3 7% 4 6% 5% 4 5% 8% 41%	2200
	21st to end	Night	11% 6% 2 7% 4 5% 6% 5% 6% 9% 40%	2200
October	1st to 10th	Night	11% 5% 2 6% 3 3 3 4 5% 7% 51%	2200
	11th to 20th	Night	11% 5% 1 3 3 2 3 3 3 5% 60%	2356
	21st to end	Night	10% 5% 2 4 3 3 4 2 5% 5% 58%	2640
November	1st to 10th	Night	10% 6% 2 5% 3 4 4 3 4 5% 55%	2477
	11th to 20th	Night	12% 5% 2 5% 3 3 3 3 4 6% 55%	2730
	21st to end	Night	12% 6% 2 5% 4 3 4 3 5% 6% 49%	2730
December	1st to 10th	Night	12% 5% 2 5% 3 3 3 3 4 5% 55%	4380
	11th to 20th	Night	15% 6% 3 6% 3 3 3 3 4 5% 50%	4952
	21st to end	Night	17% 8% 3 6% 4 4 3 3 4 5% 43%	6633

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	37% 4 6% 19% 27% 8%	5259
	11th to 20th	Day	31% 3 5% 15% 28% 18%	5280
	21st to end	Day	42% 3 6% 17% 19% 12%	5958
February	1st to 10th	Day	42% 4 7% 17% 21% 9%	2100
	11th to 20th	Day	40% 4 6% 16% 25% 8%	2058
	21st to end	Day	39% 4 8% 17% 20% 12%	1730
March	1st to 10th	Day	45% 4 8% 13% 20% 9%	4925
	11th to 20th	Day	28% 5% 9% 15% 21% 22%	5090
	21st to end	Day	40% 4 7% 19% 18% 11%	5586
April	1st to 10th	Day	37% 5% 9% 20% 18% 11%	2310
	11th to 20th	Day	32% 4 7% 21% 24% 12%	2378
	21st to end	Day	28% 5% 11% 24% 25% 6%	2727
May	1st to 10th	Day	39% 6% 14% 23% 16% 2	5910
	11th to 20th	Day	41% 7% 16% 23% 11% 2	5865
	21st to end	Day	30% 8% 17% 24% 19% 1	6447
June	1st to 10th	Day	42% 9% 15% 19% 14% 1	2600
	11th to 20th	Day	31% 11% 18% 23% 15% 2	2600
	21st to end	Day	39% 12% 18% 18% 11% 2	2600
July	1st to 10th	Day	47% 15% 22% 12% 2 1	5835
	11th to 20th	Day	28% 14% 32% 23% 2	5831
	21st to end	Day	41% 16% 21% 19% 2	6240
August	1st to 10th	Day	47% 11% 19% 20% 3	4221
	11th to 20th	Day	32% 9% 17% 29% 12%	4027
	21st to end	Day	37% 10% 18% 27% 7% 1	4158
September	1st to 10th	Day	41% 9% 15% 18% 14% 4	2200
	11th to 20th	Day	41% 7% 11% 19% 18% 4	2200
	21st to end	Day	42% 6% 10% 19% 17% 6%	2200
October	1st to 10th	Day	37% 4 7% 13% 24% 16%	3590
	11th to 20th	Day	17% 3 4 16% 26% 34%	3307
	21st to end	Day	21% 2 5% 19% 37% 16%	3538
November	1st to 10th	Day	33% 4 8% 14% 25% 15%	2036
	11th to 20th	Day	31% 2 7% 18% 27% 15%	1890
	21st to end	Day	36% 4 9% 18% 23% 11%	1890
December	1st to 10th	Day	36% 4 7% 15% 27% 10%	3020
	11th to 20th	Day	39% 3 5% 22% 23% 7%	3460
	21st to end	Day	45% 3 5% 19% 24% 4	4565
January	1st to 10th	Night	32% 4 8% 19% 28% 9%	7636
	11th to 20th	Night	38% 3 4 15% 27% 13%	7680
	21st to end	Night	45% 4 5% 14% 23% 9%	8207
February	1st to 10th	Night	39% 4 7% 17% 21% 12%	2520
	11th to 20th	Night	42% 4 7% 16% 20% 12%	2459
	21st to end	Night	37% 5% 7% 17% 19% 15%	2076
March	1st to 10th	Night	44% 4 9% 16% 17% 11%	5147
	11th to 20th	Night	28% 5% 9% 14% 25% 19%	5090
	21st to end	Night	36% 4 8% 17% 22% 13%	5588
April	1st to 10th	Night	34% 6% 11% 17% 19% 13%	2310
	11th to 20th	Night	29% 4 8% 22% 25% 12%	2206
	21st to end	Night	28% 6% 12% 24% 22% 8%	1890
May	1st to 10th	Night	37% 8% 15% 22% 14% 4	4069
	11th to 20th	Night	39% 8% 19% 22% 10% 2	4033
	21st to end	Night	30% 8% 16% 25% 19% 3	4429
June	1st to 10th	Night	40% 11% 18% 17% 13% 1	1800
	11th to 20th	Night	32% 11% 21% 23% 13% 1	1800
	21st to end	Night	38% 13% 18% 17% 12% 3	1800
July	1st to 10th	Night	52% 13% 21% 11% 3 1	4015
	11th to 20th	Night	35% 13% 32% 18% 2	4006
	21st to end	Night	45% 16% 20% 16% 2	4297
August	1st to 10th	Night	46% 11% 23% 17% 2	2904
	11th to 20th	Night	32% 10% 20% 27% 9% 1	3082
	21st to end	Night	31% 9% 23% 30% 6% 1	3704
September	1st to 10th	Night	40% 10% 17% 17% 13% 3	2200
	11th to 20th	Night	40% 9% 13% 18% 16% 4	2200
	21st to end	Night	39% 7% 13% 18% 19% 5%	2200
October	1st to 10th	Night	35% 4 10% 12% 23% 15%	3590
	11th to 20th	Night	18% 2 4 12% 29% 34%	3829
	21st to end	Night	20% 3 4 18% 34% 21%	4252
November	1st to 10th	Night	32% 4 8% 13% 27% 15%	2477
	11th to 20th	Night	32% 3 6% 16% 28% 15%	2730
	21st to end	Night	35% 4 9% 18% 21% 12%	2730
December	1st to 10th	Night	33% 4 7% 17% 30% 9%	4380
	11th to 20th	Night	39% 4 9% 17% 23% 9%	4954
	21st to end	Night	44% 4 5% 19% 25% 3	6633

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% 46% 18% 5% 1	330
	11th to 20th	Day	17% 19% 32% 20% 9% 2	330
	21st to end	Day	22% 18% 40% 15% 5%	363
February	1st to 10th	Day	19% 14% 40% 21% 6%	330
	11th to 20th	Day	25% 15% 35% 21% 3	330
	21st to end	Day	20% 17% 38% 21% 4 1	273
March	1st to 10th	Day	13% 15% 27% 31% 13% 1	481
	11th to 20th	Day	14% 9% 33% 31% 11% 1	540
	21st to end	Day	15% 11% 33% 28% 11% 2	594
April	1st to 10th	Day	17% 13% 27% 27% 14% 3	540
	11th to 20th	Day	11% 8% 28% 27% 20% 5%	532
	21st to end	Day	8% 8% 22% 32% 22% 8%	540
May	1st to 10th	Day	9% 9% 22% 31% 20% 10%	507
	11th to 20th	Day	12% 3 18% 26% 25% 16%	527
	21st to end	Day	12% 3 12% 27% 28% 17%	573
June	1st to 10th	Day	13% 2 11% 25% 31% 19%	530
	11th to 20th	Day	7% 3 12% 21% 28% 29%	530
	21st to end	Day	7% 1 9% 27% 31% 25%	530
July	1st to 10th	Day	9% 1 6% 17% 33% 34%	525
	11th to 20th	Day	7% 1 4 13% 34% 41%	524
	21st to end	Day	5% 1 6% 20% 38% 30%	576
August	1st to 10th	Day	13% 2 9% 19% 30% 27%	526
	11th to 20th	Day	7% 2 6% 15% 36% 34%	519
	21st to end	Day	16% 2 9% 21% 30% 22%	583
September	1st to 10th	Day	11% 2 12% 23% 28% 24%	530
	11th to 20th	Day	14% 2 10% 31% 31% 13%	530
	21st to end	Day	13% 3 12% 26% 30% 15%	530
October	1st to 10th	Day	14% 3 22% 32% 20% 10%	530
	11th to 20th	Day	10% 4 20% 31% 25% 9%	530
	21st to end	Day	11% 8% 24% 30% 24% 4	583
November	1st to 10th	Day	18% 6% 21% 29% 19% 6%	514
	11th to 20th	Day	15% 7% 37% 25% 14% 2	330
	21st to end	Day	12% 16% 27% 28% 15% 2	330
December	1st to 10th	Day	21% 14% 36% 16% 11% 2	330
	11th to 20th	Day	21% 12% 30% 23% 13% 2	330
	21st to end	Day	23% 10% 30% 25% 9% 2	363
January	1st to 10th	Night	16% 12% 37% 29% 6% 1	840
	11th to 20th	Night	17% 10% 32% 32% 9%	840
	21st to end	Night	19% 10% 40% 27% 4	924
February	1st to 10th	Night	16% 10% 33% 35% 6%	840
	11th to 20th	Night	19% 11% 35% 30% 5%	823
	21st to end	Night	16% 10% 35% 35% 3	692
March	1st to 10th	Night	14% 10% 30% 37% 8%	840
	11th to 20th	Night	13% 11% 33% 32% 11% 1	840
	21st to end	Night	12% 10% 35% 33% 10%	924
April	1st to 10th	Night	13% 8% 31% 34% 13% 1	840
	11th to 20th	Night	10% 8% 29% 35% 18%	754
	21st to end	Night	7% 5% 24% 43% 20% 1	630
May	1st to 10th	Night	9% 4 26% 40% 20% 1	603
	11th to 20th	Night	10% 2 22% 37% 24% 4	591
	21st to end	Night	9% 2 11% 37% 35% 5%	650
June	1st to 10th	Night	9% 2 12% 39% 33% 6%	600
	11th to 20th	Night	7% 2 11% 31% 36% 13%	600
	21st to end	Night	7% 2 8% 33% 42% 9%	600
July	1st to 10th	Night	10% 1 6% 27% 44% 13%	585
	11th to 20th	Night	8% 1 3 23% 50% 15%	582
	21st to end	Night	7% 1 5% 28% 48% 11%	657
August	1st to 10th	Night	9% 1 7% 25% 46% 11%	597
	11th to 20th	Night	10% 1 5% 24% 50% 11%	594
	21st to end	Night	12% 2 8% 27% 39% 12%	726
September	1st to 10th	Night	12% 2 9% 29% 38% 10%	800
	11th to 20th	Night	12% 2 10% 32% 39% 5%	800
	21st to end	Night	13% 2 14% 30% 37% 4	800
October	1st to 10th	Night	13% 2 20% 35% 26% 5%	800
	11th to 20th	Night	14% 5% 18% 33% 26% 4	800
	21st to end	Night	12% 4 21% 36% 25% 2	880
November	1st to 10th	Night	14% 5% 22% 36% 22% 1	820
	11th to 20th	Night	15% 9% 25% 35% 15% 1	840
	21st to end	Night	15% 10% 28% 33% 14% 1	840
December	1st to 10th	Night	17% 8% 31% 30% 12% 2	840
	11th to 20th	Night	18% 7% 30% 32% 13% 1	840
	21st to end	Night	20% 9% 27% 34% 10%	924

Page generated at 2026-04-29 02:21:43. Version ac07

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