Godfrey Road Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Godfrey Road Observatory clear sky chart from 2005-11-06 to 2026-02-16.

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	16% 9% 4 9% 5% 5% 5% 4 6% 7% 31%	130640
	Night	16% 10% 4 9% 6% 5% 5% 4 5% 6% 30%	130205
Transparency	Day	36% 37% 7% 13% 7% 1	134134
	Night	38% 36% 7% 11% 7% 1	134798
Seeing	Day	26% 17% 28% 18% 9% 2	16346
	Night	24% 15% 26% 25% 9% 1	25395

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	9% 8% 4 22% 9% 6% 5% 4 5% 5% 22%	4661
	11th to 20th	Day	9% 14% 6% 15% 7% 6% 5% 4 5% 5% 24%	4650
	21st to end	Day	8% 12% 6% 10% 6% 6% 6% 4 6% 6% 30%	5124
February	1st to 10th	Day	12% 12% 5% 11% 5% 6% 5% 4 5% 7% 28%	1854
	11th to 20th	Day	10% 12% 5% 12% 8% 5% 5% 4 6% 6% 28%	1998
	21st to end	Day	16% 11% 4 10% 6% 4 4 4 5% 5% 30%	1650
March	1st to 10th	Day	19% 13% 4 13% 5% 5% 4 3 3 3 26%	4476
	11th to 20th	Day	14% 12% 5% 8% 5% 4 5% 4 5% 6% 33%	4674
	21st to end	Day	22% 11% 4 9% 5% 4 4 3 4 6% 29%	5919
April	1st to 10th	Day	20% 13% 3 8% 5% 4 4 3 4 6% 32%	2400
	11th to 20th	Day	17% 11% 3 7% 5% 4 5% 4 5% 6% 34%	2374
	21st to end	Day	22% 10% 4 7% 5% 4 4 3 5% 7% 30%	2598
May	1st to 10th	Day	34% 10% 4 8% 5% 4 3 3 4 5% 21%	5886
	11th to 20th	Day	18% 10% 3 9% 5% 5% 5% 4 6% 7% 27%	6288
	21st to end	Day	17% 8% 3 7% 5% 5% 5% 4 7% 8% 31%	6949
June	1st to 10th	Day	19% 8% 3 8% 5% 6% 6% 5% 6% 7% 29%	2800
	11th to 20th	Day	17% 7% 2 6% 5% 5% 5% 4 5% 8% 36%	2800
	21st to end	Day	19% 8% 2 8% 6% 6% 5% 4 6% 8% 29%	2800
July	1st to 10th	Day	12% 7% 2 7% 5% 5% 6% 4 7% 10% 33%	6360
	11th to 20th	Day	10% 6% 3 7% 6% 6% 6% 5% 8% 10% 34%	6360
	21st to end	Day	14% 6% 2 6% 4 4 6% 4 7% 9% 39%	6926
August	1st to 10th	Day	14% 7% 2 7% 5% 5% 6% 5% 7% 9% 33%	4466
	11th to 20th	Day	14% 8% 4 8% 5% 5% 6% 5% 7% 8% 30%	4086
	21st to end	Day	9% 5% 2 7% 5% 5% 5% 4 7% 10% 40%	4312
September	1st to 10th	Day	12% 5% 2 6% 4 3 5% 4 5% 8% 45%	2400
	11th to 20th	Day	13% 5% 2 6% 4 4 3 3 5% 6% 48%	2244
	21st to end	Day	16% 7% 2 6% 4 4 3 4 6% 7% 42%	2200
October	1st to 10th	Day	21% 7% 3 7% 4 4 4 3 4 6% 36%	2181
	11th to 20th	Day	15% 8% 3 8% 5% 5% 4 3 5% 6% 37%	1911
	21st to end	Day	23% 11% 4 7% 4 4 4 4 5% 6% 28%	1980
November	1st to 10th	Day	13% 9% 4 7% 4 5% 4 4 6% 6% 37%	1851
	11th to 20th	Day	16% 10% 4 8% 4 5% 5% 4 5% 6% 33%	1890
	21st to end	Day	18% 11% 5% 8% 6% 5% 4 3 5% 5% 29%	1778
December	1st to 10th	Day	16% 13% 5% 14% 7% 6% 5% 4 5% 7% 18%	2680
	11th to 20th	Day	21% 13% 3 9% 5% 5% 5% 3 4 5% 28%	3066
	21st to end	Day	19% 13% 5% 12% 5% 4 4 3 3 5% 27%	4048
January	1st to 10th	Night	11% 9% 6% 19% 8% 5% 5% 3 5% 5% 24%	8234
	11th to 20th	Night	10% 13% 5% 16% 9% 7% 6% 5% 5% 6% 18%	8235
	21st to end	Night	11% 9% 4 9% 8% 7% 6% 5% 7% 7% 27%	9057
February	1st to 10th	Night	12% 12% 4 10% 7% 6% 5% 5% 7% 6% 27%	2763
	11th to 20th	Night	10% 9% 5% 12% 8% 7% 5% 4 6% 7% 28%	2399
	21st to end	Night	13% 10% 4 10% 7% 6% 4 4 5% 7% 30%	1980
March	1st to 10th	Night	20% 11% 3 9% 6% 4 5% 4 5% 6% 26%	5364
	11th to 20th	Night	14% 12% 4 10% 6% 5% 4 3 4 6% 32%	5283
	21st to end	Night	21% 13% 3 9% 4 4 4 3 4 5% 30%	5008
April	1st to 10th	Night	20% 10% 2 9% 5% 5% 4 3 5% 6% 32%	2000
	11th to 20th	Night	19% 11% 3 8% 4 4 4 3 5% 5% 34%	1975
	21st to end	Night	20% 10% 3 6% 4 5% 4 3 5% 7% 34%	1800
May	1st to 10th	Night	34% 10% 3 8% 4 4 4 3 4 5% 22%	4054
	11th to 20th	Night	17% 12% 4 9% 5% 6% 4 4 5% 6% 29%	3634
	21st to end	Night	18% 7% 3 8% 5% 5% 6% 4 5% 8% 31%	3926
June	1st to 10th	Night	20% 6% 3 7% 6% 5% 5% 3 6% 7% 33%	1600
	11th to 20th	Night	19% 7% 3 5% 4 4 5% 5% 5% 6% 38%	1600
	21st to end	Night	17% 7% 3 7% 4 5% 5% 4 6% 7% 36%	1600
July	1st to 10th	Night	11% 5% 2 6% 5% 5% 6% 5% 7% 10% 38%	3600
	11th to 20th	Night	14% 7% 3 7% 5% 5% 5% 4 6% 8% 36%	3600
	21st to end	Night	11% 5% 2 5% 4 4 4 4 6% 7% 47%	3926
August	1st to 10th	Night	19% 9% 3 8% 5% 4 4 3 4 6% 35%	2651
	11th to 20th	Night	15% 8% 3 6% 5% 4 5% 4 6% 9% 37%	2958
	21st to end	Night	9% 5% 2 5% 4 3 5% 4 7% 10% 45%	3586
September	1st to 10th	Night	12% 6% 2 5% 3 3 5% 4 5% 7% 48%	2000
	11th to 20th	Night	13% 5% 2 6% 3 3 3 3 6% 7% 50%	2155
	21st to end	Night	15% 6% 2 5% 5% 4 4 3 6% 6% 44%	2200
October	1st to 10th	Night	20% 7% 3 7% 5% 4 2 4 6% 7% 36%	2215
	11th to 20th	Night	16% 9% 3 7% 5% 5% 5% 4 5% 7% 36%	2487
	21st to end	Night	22% 9% 3 7% 5% 4 4 4 6% 6% 30%	2860
November	1st to 10th	Night	15% 9% 3 8% 5% 4 4 3 6% 6% 36%	2667
	11th to 20th	Night	16% 9% 3 6% 5% 5% 5% 4 6% 7% 34%	2730
	21st to end	Night	16% 10% 4 8% 6% 5% 4 3 6% 7% 30%	2840
December	1st to 10th	Night	16% 13% 5% 13% 7% 6% 6% 4 5% 7% 18%	4720
	11th to 20th	Night	23% 10% 3 9% 5% 5% 4 3 4 6% 27%	5348
	21st to end	Night	21% 13% 5% 10% 5% 5% 4 3 5% 6% 23%	7150

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	54% 23% 6% 13% 4	4662
	11th to 20th	Day	53% 22% 5% 11% 8% 2	4680
	21st to end	Day	49% 22% 4 13% 11% 1	5124
February	1st to 10th	Day	23% 60% 5% 7% 5% 1	1854
	11th to 20th	Day	24% 59% 4 8% 5% 1	2007
	21st to end	Day	19% 62% 4 6% 6% 1	1650
March	1st to 10th	Day	50% 29% 3 7% 7% 5%	4479
	11th to 20th	Day	37% 30% 11% 14% 6% 3	4674
	21st to end	Day	46% 28% 3 9% 13% 2	5919
April	1st to 10th	Day	24% 61% 3 7% 4 2	2400
	11th to 20th	Day	20% 63% 3 7% 6% 1	2374
	21st to end	Day	21% 62% 3 7% 6%	2598
May	1st to 10th	Day	52% 31% 5% 9% 3	5897
	11th to 20th	Day	44% 31% 10% 10% 4	6292
	21st to end	Day	40% 30% 8% 16% 6%	6949
June	1st to 10th	Day	20% 63% 4 7% 6%	2800
	11th to 20th	Day	19% 62% 4 9% 6% 1	2800
	21st to end	Day	19% 61% 4 10% 6% 1	2800
July	1st to 10th	Day	36% 26% 12% 17% 9%	6290
	11th to 20th	Day	35% 26% 11% 19% 9%	6285
	21st to end	Day	33% 25% 9% 24% 9%	6728
August	1st to 10th	Day	34% 36% 9% 14% 7%	4452
	11th to 20th	Day	36% 36% 10% 15% 2	4125
	21st to end	Day	26% 35% 12% 17% 10% 1	4312
September	1st to 10th	Day	14% 58% 5% 15% 7% 1	2400
	11th to 20th	Day	16% 56% 4 12% 9% 1	2244
	21st to end	Day	17% 58% 4 14% 6% 1	2200
October	1st to 10th	Day	33% 34% 4 17% 11% 1	3558
	11th to 20th	Day	29% 35% 8% 17% 12%	3088
	21st to end	Day	28% 35% 6% 23% 8% 1	3180
November	1st to 10th	Day	25% 54% 6% 9% 6%	1851
	11th to 20th	Day	25% 54% 5% 6% 9%	1890
	21st to end	Day	27% 54% 9% 6% 3	1778
December	1st to 10th	Day	48% 34% 8% 7% 2	2680
	11th to 20th	Day	43% 31% 4 12% 10% 1	3066
	21st to end	Day	46% 26% 3 10% 11% 3	4048
January	1st to 10th	Night	54% 21% 9% 10% 5%	8234
	11th to 20th	Night	59% 22% 6% 6% 6% 1	8280
	21st to end	Night	51% 22% 5% 11% 9% 2	9057
February	1st to 10th	Night	24% 59% 4 8% 4	2763
	11th to 20th	Night	23% 60% 5% 6% 6%	2401
	21st to end	Night	20% 62% 5% 8% 4 1	1980
March	1st to 10th	Night	48% 29% 6% 7% 10% 2	5374
	11th to 20th	Night	40% 30% 11% 9% 8% 2	5284
	21st to end	Night	47% 28% 2 9% 12% 2	5008
April	1st to 10th	Night	23% 62% 3 6% 6%	2000
	11th to 20th	Night	22% 62% 3 7% 6%	1975
	21st to end	Night	21% 63% 2 6% 7% 1	1800
May	1st to 10th	Night	51% 31% 7% 8% 3	4060
	11th to 20th	Night	44% 31% 8% 12% 4	3635
	21st to end	Night	41% 31% 9% 12% 6% 1	3927
June	1st to 10th	Night	18% 63% 3 8% 7%	1600
	11th to 20th	Night	18% 62% 6% 8% 6%	1600
	21st to end	Night	18% 61% 5% 12% 5% 1	1600
July	1st to 10th	Night	34% 26% 14% 18% 8%	3560
	11th to 20th	Night	40% 26% 7% 18% 9%	3552
	21st to end	Night	31% 25% 9% 27% 7%	3809
August	1st to 10th	Night	38% 36% 7% 13% 6%	2641
	11th to 20th	Night	34% 38% 11% 12% 6%	2985
	21st to end	Night	22% 35% 13% 20% 9%	3586
September	1st to 10th	Night	14% 58% 6% 15% 8%	2000
	11th to 20th	Night	15% 58% 5% 12% 9% 1	2155
	21st to end	Night	16% 57% 5% 13% 8% 1	2200
October	1st to 10th	Night	34% 35% 7% 17% 6% 1	3618
	11th to 20th	Night	29% 36% 7% 14% 13% 1	4049
	21st to end	Night	30% 36% 7% 20% 7%	4610
November	1st to 10th	Night	25% 54% 5% 11% 4 1	2667
	11th to 20th	Night	25% 55% 5% 8% 8%	2730
	21st to end	Night	27% 56% 6% 8% 4	2840
December	1st to 10th	Night	48% 34% 7% 9% 2	4720
	11th to 20th	Night	45% 30% 6% 7% 11%	5348
	21st to end	Night	51% 26% 4 10% 6% 3	7150

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% 20% 31% 13% 4 1	220
	11th to 20th	Day	37% 25% 27% 9% 2 1	220
	21st to end	Day	29% 27% 27% 12% 5%	242
February	1st to 10th	Day	34% 30% 27% 7% 2	329
	11th to 20th	Day	32% 25% 30% 11% 2	516
	21st to end	Day	31% 25% 26% 14% 4	414
March	1st to 10th	Day	30% 20% 33% 14% 3	500
	11th to 20th	Day	34% 24% 26% 11% 4 1	500
	21st to end	Day	34% 22% 24% 11% 6% 2	550
April	1st to 10th	Day	39% 20% 22% 11% 6% 1	500
	11th to 20th	Day	37% 24% 20% 12% 7% 1	492
	21st to end	Day	34% 22% 25% 11% 6% 2	500
May	1st to 10th	Day	35% 22% 24% 12% 6% 2	503
	11th to 20th	Day	24% 18% 31% 18% 7% 2	527
	21st to end	Day	23% 16% 31% 21% 8% 1	573
June	1st to 10th	Day	23% 15% 34% 20% 8% 1	530
	11th to 20th	Day	21% 16% 33% 18% 10% 2	530
	21st to end	Day	22% 16% 31% 19% 9% 2	530
July	1st to 10th	Day	18% 12% 34% 24% 11% 2	525
	11th to 20th	Day	15% 9% 36% 25% 12% 2	524
	21st to end	Day	16% 11% 34% 26% 11% 2	576
August	1st to 10th	Day	13% 12% 28% 27% 17% 2	526
	11th to 20th	Day	18% 10% 25% 24% 15% 7%	519
	21st to end	Day	15% 12% 29% 25% 14% 5%	583
September	1st to 10th	Day	16% 11% 28% 24% 15% 7%	530
	11th to 20th	Day	17% 11% 26% 19% 18% 9%	530
	21st to end	Day	21% 12% 29% 21% 12% 6%	530
October	1st to 10th	Day	26% 13% 23% 21% 14% 4	530
	11th to 20th	Day	27% 15% 25% 19% 12% 2	480
	21st to end	Day	39% 15% 25% 15% 6%	462
November	1st to 10th	Day	29% 17% 22% 20% 11% 1	425
	11th to 20th	Day	30% 22% 23% 17% 7% 1	430
	21st to end	Day	36% 18% 25% 16% 4	318
December	1st to 10th	Day	31% 20% 28% 15% 5%	220
	11th to 20th	Day	38% 22% 28% 10% 3	220
	21st to end	Day	34% 17% 33% 12% 2	242
January	1st to 10th	Night	24% 21% 32% 20% 3	840
	11th to 20th	Night	28% 19% 28% 21% 3	840
	21st to end	Night	20% 21% 35% 19% 4	924
February	1st to 10th	Night	25% 18% 33% 21% 3	840
	11th to 20th	Night	25% 23% 31% 18% 3	804
	21st to end	Night	24% 18% 31% 23% 4	660
March	1st to 10th	Night	28% 16% 30% 22% 3	800
	11th to 20th	Night	27% 21% 25% 21% 6%	800
	21st to end	Night	29% 18% 27% 19% 7% 1	880
April	1st to 10th	Night	30% 20% 25% 22% 4	800
	11th to 20th	Night	25% 22% 25% 21% 7% 1	791
	21st to end	Night	27% 19% 27% 23% 5%	600
May	1st to 10th	Night	31% 14% 26% 22% 7%	600
	11th to 20th	Night	20% 13% 30% 29% 8%	427
	21st to end	Night	20% 8% 27% 32% 12% 1	433
June	1st to 10th	Night	23% 8% 24% 35% 10% 1	400
	11th to 20th	Night	21% 9% 22% 36% 13%	400
	21st to end	Night	21% 6% 23% 39% 12%	400
July	1st to 10th	Night	17% 4 19% 43% 16% 1	390
	11th to 20th	Night	18% 3 21% 37% 20% 2	388
	21st to end	Night	13% 5% 19% 43% 18% 1	438
August	1st to 10th	Night	18% 3 13% 43% 22%	437
	11th to 20th	Night	17% 6% 22% 33% 21% 2	639
	21st to end	Night	18% 6% 17% 35% 22% 2	880
September	1st to 10th	Night	17% 7% 24% 32% 19% 2	800
	11th to 20th	Night	16% 8% 19% 28% 25% 3	800
	21st to end	Night	20% 10% 22% 30% 17% 2	800
October	1st to 10th	Night	24% 11% 19% 28% 17% 2	800
	11th to 20th	Night	25% 13% 23% 27% 12% 1	800
	21st to end	Night	30% 13% 27% 24% 7%	880
November	1st to 10th	Night	24% 17% 24% 26% 8%	820
	11th to 20th	Night	26% 18% 25% 22% 8% 1	840
	21st to end	Night	28% 18% 27% 21% 6% 1	840
December	1st to 10th	Night	27% 20% 29% 20% 4	840
	11th to 20th	Night	30% 18% 29% 20% 3	840
	21st to end	Night	31% 21% 27% 18% 4	924

Page generated at 2026-02-13 01:42:12. Version ac07

Copyright © 2026 Attilla Danko.