Keene
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Keene clear sky chart from 2005-11-06 to 2025-08-05.

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	18% 8% 3 7% 5% 4 4 4 5% 7% 35%	125594
	Night	18% 9% 3 7% 5% 4 4 3 5% 6% 36%	122442
Transparency	Day	47% 6% 11% 21% 13% 2	129101
	Night	47% 6% 12% 21% 13% 2	127022
Seeing	Day	25% 18% 29% 18% 7% 2	15844
	Night	22% 17% 29% 24% 8% 1	24750

By Month

Percentage Cloud Cover NE (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% 9% 5% 14% 6% 6% 4 4 5% 5% 30%	3597
	11th to 20th	Day	13% 9% 4 9% 4 5% 4 4 6% 6% 35%	3570
	21st to end	Day	14% 12% 5% 8% 5% 4 3 2 4 5% 38%	3960
February	1st to 10th	Day	15% 11% 4 7% 5% 6% 6% 5% 6% 6% 29%	1821
	11th to 20th	Day	13% 9% 4 10% 6% 5% 4 4 5% 7% 33%	1948
	21st to end	Day	18% 10% 4 9% 5% 5% 3 3 5% 5% 33%	1650
March	1st to 10th	Day	20% 12% 4 10% 5% 4 3 3 4 4 30%	4476
	11th to 20th	Day	16% 11% 4 7% 5% 4 4 3 4 6% 37%	4672
	21st to end	Day	25% 9% 3 7% 3 4 4 3 4 6% 33%	5922
April	1st to 10th	Day	20% 10% 4 8% 5% 4 3 3 5% 6% 34%	2400
	11th to 20th	Day	17% 9% 2 7% 4 4 5% 4 5% 6% 37%	2374
	21st to end	Day	20% 9% 4 7% 5% 4 4 3 4 5% 34%	2575
May	1st to 10th	Day	32% 9% 3 7% 5% 4 4 3 4 5% 23%	5886
	11th to 20th	Day	20% 10% 4 9% 5% 5% 4 3 5% 6% 30%	6198
	21st to end	Day	20% 7% 3 7% 5% 4 4 4 6% 8% 34%	6949
June	1st to 10th	Day	18% 7% 2 7% 6% 5% 5% 4 6% 8% 32%	2800
	11th to 20th	Day	18% 7% 2 7% 5% 4 4 4 5% 8% 36%	2800
	21st to end	Day	18% 7% 3 6% 6% 5% 5% 4 6% 8% 33%	2800
July	1st to 10th	Day	14% 7% 3 7% 5% 4 5% 5% 7% 10% 32%	6360
	11th to 20th	Day	11% 6% 3 7% 5% 5% 5% 5% 8% 11% 34%	6360
	21st to end	Day	16% 6% 2 5% 4 4 4 4 6% 8% 41%	6926
August	1st to 10th	Day	15% 7% 3 7% 4 5% 5% 4 6% 9% 35%	4334
	11th to 20th	Day	14% 7% 3 8% 4 5% 5% 4 7% 9% 35%	3900
	21st to end	Day	9% 5% 2 7% 5% 4 6% 4 8% 9% 41%	4180
September	1st to 10th	Day	13% 7% 2 5% 4 5% 3 5% 5% 9% 44%	2280
	11th to 20th	Day	15% 6% 2 5% 4 3 3 3 4 6% 49%	2129
	21st to end	Day	17% 6% 2 6% 4 4 3 3 5% 8% 42%	2090
October	1st to 10th	Day	22% 8% 2 6% 4 4 5% 3 4 5% 36%	2081
	11th to 20th	Day	15% 7% 2 7% 4 4 4 4 5% 6% 42%	1833
	21st to end	Day	21% 10% 3 6% 6% 4 4 3 4 7% 33%	1881
November	1st to 10th	Day	13% 8% 2 6% 4 4 3 3 4 7% 45%	1761
	11th to 20th	Day	18% 9% 2 7% 3 3 4 3 4 5% 42%	1800
	21st to end	Day	20% 9% 3 7% 4 3 4 2 5% 7% 36%	1735
December	1st to 10th	Day	14% 11% 5% 9% 4 4 4 3 5% 6% 33%	2600
	11th to 20th	Day	21% 12% 4 5% 4 4 4 2 4 4 37%	2986
	21st to end	Day	20% 11% 4 8% 5% 3 3 3 4 5% 34%	3960
January	1st to 10th	Night	13% 9% 6% 13% 6% 5% 4 3 4 5% 33%	6349
	11th to 20th	Night	12% 12% 4 10% 7% 5% 5% 4 5% 6% 30%	6315
	21st to end	Night	15% 10% 4 8% 5% 5% 4 4 6% 6% 33%	6996
February	1st to 10th	Night	15% 10% 3 8% 5% 5% 5% 4 5% 6% 34%	2574
	11th to 20th	Night	11% 10% 4 7% 6% 6% 5% 4 7% 7% 34%	2338
	21st to end	Night	15% 10% 3 8% 5% 4 5% 4 5% 6% 35%	1980
March	1st to 10th	Night	21% 10% 2 8% 5% 4 5% 3 5% 6% 31%	5364
	11th to 20th	Night	16% 10% 3 7% 5% 4 4 3 5% 5% 36%	5285
	21st to end	Night	24% 11% 3 7% 3 4 3 3 5% 5% 31%	4994
April	1st to 10th	Night	20% 9% 3 7% 4 4 4 3 6% 6% 34%	2000
	11th to 20th	Night	21% 10% 3 5% 4 3 4 2 5% 6% 38%	1975
	21st to end	Night	20% 9% 3 7% 4 3 4 2 5% 6% 37%	1823
May	1st to 10th	Night	32% 10% 3 6% 4 4 4 4 5% 5% 23%	4054
	11th to 20th	Night	19% 10% 3 8% 6% 5% 4 4 6% 6% 28%	3725
	21st to end	Night	22% 9% 3 7% 5% 4 4 3 5% 6% 31%	3926
June	1st to 10th	Night	19% 8% 2 6% 4 3 4 4 4 7% 38%	1600
	11th to 20th	Night	19% 7% 2 6% 5% 5% 4 3 6% 7% 38%	1600
	21st to end	Night	16% 7% 2 6% 4 5% 4 5% 7% 7% 38%	1600
July	1st to 10th	Night	14% 6% 2 6% 4 4 5% 4 6% 9% 40%	3600
	11th to 20th	Night	15% 7% 3 7% 5% 5% 6% 4 6% 7% 36%	3600
	21st to end	Night	13% 6% 2 5% 4 4 3 4 5% 5% 50%	3926
August	1st to 10th	Night	23% 7% 2 7% 4 4 4 3 4 6% 36%	2652
	11th to 20th	Night	15% 8% 3 8% 4 4 4 3 6% 7% 38%	2910
	21st to end	Night	8% 5% 1 4 3 3 4 3 6% 8% 55%	3476
September	1st to 10th	Night	13% 6% 2 5% 3 3 3 4 5% 7% 48%	1900
	11th to 20th	Night	14% 5% 1 5% 2 3 4 3 5% 6% 52%	2050
	21st to end	Night	17% 5% 2 6% 4 3 4 3 5% 6% 47%	2090
October	1st to 10th	Night	22% 7% 2 6% 4 3 3 2 4 6% 38%	2095
	11th to 20th	Night	16% 7% 2 6% 4 4 4 4 6% 6% 42%	2346
	21st to end	Night	22% 9% 2 6% 4 3 4 3 5% 6% 34%	2717
November	1st to 10th	Night	16% 7% 2 6% 4 4 4 3 5% 5% 45%	2537
	11th to 20th	Night	17% 8% 3 6% 4 3 3 3 4 6% 42%	2600
	21st to end	Night	15% 10% 3 7% 4 4 4 4 5% 6% 39%	2661
December	1st to 10th	Night	18% 11% 4 9% 5% 4 4 3 5% 6% 30%	4580
	11th to 20th	Night	25% 10% 3 6% 3 3 3 3 4 4 36%	5208
	21st to end	Night	20% 12% 5% 8% 4 3 3 3 4 5% 33%	6996

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	55% 4 8% 24% 9% 1	3598
	11th to 20th	Day	47% 5% 12% 19% 14% 3	3600
	21st to end	Day	49% 4 8% 20% 17% 2	3960
February	1st to 10th	Day	51% 7% 12% 18% 11% 2	1821
	11th to 20th	Day	50% 6% 10% 19% 13% 2	1957
	21st to end	Day	54% 4 9% 19% 13% 2	1650
March	1st to 10th	Day	58% 3 10% 12% 10% 7%	4479
	11th to 20th	Day	46% 6% 15% 21% 9% 3	4672
	21st to end	Day	52% 4 6% 15% 18% 5%	5922
April	1st to 10th	Day	52% 5% 8% 19% 13% 3	2400
	11th to 20th	Day	47% 6% 10% 18% 16% 2	2374
	21st to end	Day	52% 5% 8% 17% 15% 3	2575
May	1st to 10th	Day	62% 7% 9% 13% 8% 1	5897
	11th to 20th	Day	56% 6% 13% 16% 9% 1	6202
	21st to end	Day	47% 7% 11% 23% 11% 1	6949
June	1st to 10th	Day	48% 7% 12% 21% 11% 1	2800
	11th to 20th	Day	47% 6% 12% 20% 14% 2	2800
	21st to end	Day	48% 8% 12% 20% 12% 1	2800
July	1st to 10th	Day	46% 7% 13% 21% 13% 1	6290
	11th to 20th	Day	40% 8% 16% 23% 12% 1	6285
	21st to end	Day	41% 6% 12% 27% 14% 1	6728
August	1st to 10th	Day	45% 7% 15% 21% 11% 1	4320
	11th to 20th	Day	44% 7% 15% 27% 7% 1	3939
	21st to end	Day	35% 7% 14% 29% 14% 1	4180
September	1st to 10th	Day	37% 6% 13% 26% 17% 1	2280
	11th to 20th	Day	36% 5% 9% 25% 22% 2	2129
	21st to end	Day	41% 6% 10% 24% 16% 3	2090
October	1st to 10th	Day	48% 5% 7% 23% 15% 2	3458
	11th to 20th	Day	39% 4 11% 26% 17% 3	3023
	21st to end	Day	38% 4 10% 31% 14% 3	3081
November	1st to 10th	Day	39% 5% 15% 25% 15% 2	1761
	11th to 20th	Day	44% 5% 9% 20% 19% 3	1800
	21st to end	Day	48% 6% 15% 21% 9% 1	1735
December	1st to 10th	Day	50% 6% 12% 25% 7% 1	2600
	11th to 20th	Day	51% 4 10% 17% 17% 1	2986
	21st to end	Day	53% 4 7% 18% 13% 5%	3960
January	1st to 10th	Night	51% 6% 11% 21% 10% 2	6349
	11th to 20th	Night	52% 6% 13% 16% 10% 2	6360
	21st to end	Night	49% 5% 10% 16% 16% 4	6996
February	1st to 10th	Night	49% 5% 13% 20% 10% 2	2574
	11th to 20th	Night	46% 6% 12% 20% 13% 2	2340
	21st to end	Night	48% 6% 11% 23% 10% 4	1980
March	1st to 10th	Night	52% 5% 11% 16% 14% 3	5374
	11th to 20th	Night	48% 6% 16% 18% 10% 2	5286
	21st to end	Night	52% 5% 6% 13% 20% 3	4994
April	1st to 10th	Night	50% 6% 10% 19% 14% 2	2000
	11th to 20th	Night	47% 7% 9% 19% 16% 2	1975
	21st to end	Night	48% 5% 10% 18% 16% 4	1823
May	1st to 10th	Night	60% 7% 11% 13% 8% 1	4060
	11th to 20th	Night	54% 8% 12% 16% 9% 2	3726
	21st to end	Night	53% 7% 12% 18% 10% 1	3927
June	1st to 10th	Night	46% 7% 12% 24% 11% 1	1600
	11th to 20th	Night	45% 7% 13% 21% 12% 1	1600
	21st to end	Night	41% 8% 15% 21% 13% 1	1600
July	1st to 10th	Night	41% 6% 14% 25% 13%	3560
	11th to 20th	Night	45% 8% 13% 19% 14% 1	3552
	21st to end	Night	36% 5% 13% 31% 14% 1	3809
August	1st to 10th	Night	49% 6% 13% 21% 10% 1	2642
	11th to 20th	Night	45% 6% 17% 23% 9%	2937
	21st to end	Night	27% 5% 17% 35% 15% 1	3476
September	1st to 10th	Night	35% 6% 12% 27% 18% 1	1900
	11th to 20th	Night	33% 5% 11% 27% 21% 2	2050
	21st to end	Night	38% 5% 11% 27% 17% 2	2090
October	1st to 10th	Night	42% 4 16% 24% 13% 1	3498
	11th to 20th	Night	35% 4 12% 25% 21% 3	3895
	21st to end	Night	39% 5% 11% 33% 12% 1	4467
November	1st to 10th	Night	40% 5% 12% 23% 17% 3	2537
	11th to 20th	Night	42% 6% 11% 22% 16% 3	2600
	21st to end	Night	45% 6% 14% 23% 11% 1	2661
December	1st to 10th	Night	54% 5% 10% 24% 6%	4580
	11th to 20th	Night	51% 5% 12% 13% 18% 1	5208
	21st to end	Night	54% 4 8% 17% 13% 4	6996

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	30% 26% 27% 14% 3	200
	11th to 20th	Day	35% 21% 34% 9% 3 1	200
	21st to end	Day	25% 30% 31% 10% 3	220
February	1st to 10th	Day	33% 31% 26% 9% 1	341
	11th to 20th	Day	34% 25% 28% 11% 1	496
	21st to end	Day	32% 25% 28% 12% 2	414
March	1st to 10th	Day	32% 22% 33% 11% 3	500
	11th to 20th	Day	30% 28% 27% 10% 4 1	500
	21st to end	Day	33% 23% 28% 10% 4 3	550
April	1st to 10th	Day	37% 21% 24% 10% 5% 1	500
	11th to 20th	Day	32% 27% 24% 11% 5% 2	492
	21st to end	Day	30% 19% 31% 13% 6% 1	500
May	1st to 10th	Day	36% 21% 24% 12% 6% 1	503
	11th to 20th	Day	22% 21% 35% 15% 6% 2	527
	21st to end	Day	21% 14% 33% 24% 6% 1	573
June	1st to 10th	Day	22% 16% 34% 18% 9% 2	530
	11th to 20th	Day	21% 15% 32% 23% 7% 2	530
	21st to end	Day	20% 17% 34% 19% 8% 2	530
July	1st to 10th	Day	17% 12% 30% 27% 12% 2	525
	11th to 20th	Day	15% 10% 31% 31% 10% 2	524
	21st to end	Day	16% 13% 34% 26% 9% 3	576
August	1st to 10th	Day	12% 12% 28% 30% 12% 5%	502
	11th to 20th	Day	15% 11% 28% 27% 15% 5%	479
	21st to end	Day	13% 12% 29% 28% 12% 6%	539
September	1st to 10th	Day	19% 12% 25% 25% 14% 6%	490
	11th to 20th	Day	17% 15% 25% 20% 14% 10%	490
	21st to end	Day	19% 13% 33% 18% 11% 6%	490
October	1st to 10th	Day	29% 15% 21% 21% 11% 4	490
	11th to 20th	Day	23% 17% 28% 21% 9% 2	454
	21st to end	Day	34% 13% 27% 21% 4 2	429
November	1st to 10th	Day	24% 18% 28% 19% 10% 1	395
	11th to 20th	Day	31% 22% 26% 17% 3 1	400
	21st to end	Day	34% 18% 28% 15% 4 1	335
December	1st to 10th	Day	27% 28% 29% 13% 4 1	200
	11th to 20th	Day	41% 24% 24% 10% 2	200
	21st to end	Day	31% 22% 30% 12% 5%	220
January	1st to 10th	Night	21% 25% 34% 17% 2	800
	11th to 20th	Night	26% 22% 30% 19% 2	800
	21st to end	Night	19% 23% 34% 21% 3	880
February	1st to 10th	Night	23% 23% 33% 18% 2	800
	11th to 20th	Night	24% 24% 35% 15% 1	783
	21st to end	Night	27% 24% 29% 18% 2	660
March	1st to 10th	Night	25% 22% 32% 18% 2	800
	11th to 20th	Night	23% 25% 29% 19% 4	800
	21st to end	Night	27% 20% 30% 18% 5%	880
April	1st to 10th	Night	28% 18% 30% 20% 4	800
	11th to 20th	Night	26% 21% 27% 20% 6%	791
	21st to end	Night	27% 19% 28% 21% 5%	623
May	1st to 10th	Night	30% 12% 31% 22% 5%	600
	11th to 20th	Night	20% 17% 33% 25% 5%	466
	21st to end	Night	20% 8% 28% 33% 9% 1	433
June	1st to 10th	Night	20% 9% 27% 33% 10% 1	400
	11th to 20th	Night	20% 10% 30% 32% 9% 1	400
	21st to end	Night	18% 8% 28% 38% 9% 1	400
July	1st to 10th	Night	14% 5% 28% 40% 12% 1	390
	11th to 20th	Night	15% 4 27% 37% 16% 2	388
	21st to end	Night	12% 5% 29% 39% 13% 1	438
August	1st to 10th	Night	14% 6% 24% 36% 19% 1	448
	11th to 20th	Night	16% 7% 26% 32% 18% 2	638
	21st to end	Night	15% 7% 23% 35% 19% 2	836
September	1st to 10th	Night	16% 7% 28% 30% 17% 2	760
	11th to 20th	Night	16% 8% 24% 29% 19% 4	760
	21st to end	Night	18% 9% 27% 29% 15% 1	760
October	1st to 10th	Night	26% 12% 21% 27% 12% 2	760
	11th to 20th	Night	20% 14% 30% 25% 10% 1	760
	21st to end	Night	28% 17% 27% 22% 6% 1	836
November	1st to 10th	Night	20% 18% 30% 24% 8%	780
	11th to 20th	Night	23% 24% 26% 21% 7% 1	800
	21st to end	Night	23% 20% 33% 18% 6% 1	800
December	1st to 10th	Night	27% 20% 30% 19% 5%	800
	11th to 20th	Night	27% 21% 31% 17% 4	800
	21st to end	Night	26% 21% 33% 16% 3	880

Page generated at 2025-08-02 01:32:24. Version ac07

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