Godin-Goff Memorial Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Godin-Goff Memorial Observatory clear sky chart from 2005-11-06 to 2026-02-01.

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	4 5% 2 5% 4 4 4 4 6% 8% 56%	136305
	Night	5% 7% 2 5% 4 4 4 3 5% 7% 54%	133229
Transparency	Day	28% 6% 10% 23% 23% 11%	131187
	Night	30% 5% 10% 24% 21% 8%	129350
Seeing	Day	7% 8% 23% 35% 21% 5%	16998
	Night	8% 3 22% 44% 21% 2	27241

By Month

Percentage Cloud Cover SW (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	4 7% 3 9% 6% 5% 5% 3 5% 8% 44%	3969
	11th to 20th	Day	4 9% 3 9% 4 3 3 3 5% 7% 48%	4190
	21st to end	Day	4 8% 3 6% 4 4 3 2 4 6% 57%	4609
February	1st to 10th	Day	6% 11% 3 7% 4 5% 4 3 6% 7% 44%	1800
	11th to 20th	Day	5% 12% 4 8% 4 3 4 4 4 8% 42%	1784
	21st to end	Day	6% 14% 4 6% 5% 4 4 3 4 5% 43%	1650
March	1st to 10th	Day	3 13% 3 7% 4 4 4 3 5% 8% 47%	4924
	11th to 20th	Day	3 9% 3 7% 5% 5% 5% 4 7% 8% 43%	5000
	21st to end	Day	6% 12% 3 7% 5% 5% 5% 4 6% 7% 41%	5519
April	1st to 10th	Day	7% 7% 2 6% 4 4 4 3 5% 6% 51%	2400
	11th to 20th	Day	6% 7% 4 6% 5% 5% 5% 5% 6% 7% 45%	2371
	21st to end	Day	5% 7% 2 6% 4 4 5% 3 6% 7% 52%	2400
May	1st to 10th	Day	6% 7% 2 6% 4 5% 5% 4 7% 9% 45%	5827
	11th to 20th	Day	3 4 2 6% 4 4 5% 4 7% 9% 52%	6014
	21st to end	Day	4 4 1 3 2 3 4 4 6% 8% 61%	6925
June	1st to 10th	Day	3 3 1 4 3 3 4 4 7% 8% 62%	2800
	11th to 20th	Day	2 2 1 3 3 3 4 3 5% 6% 68%	2800
	21st to end	Day	2 2 1 2 3 3 4 3 6% 7% 68%	2800
July	1st to 10th	Day	2 1 1 3 3 3 3 3 4 6% 72%	6339
	11th to 20th	Day	1 1 2 3 3 5% 5% 10% 13% 56%	5978
	21st to end	Day	2 2 1 3 3 4 4 5% 8% 10% 58%	6401
August	1st to 10th	Day	2 2 1 3 3 4 5% 5% 8% 12% 57%	5779
	11th to 20th	Day	2 2 1 3 3 3 4 4 6% 9% 62%	5666
	21st to end	Day	4 3 1 4 3 4 5% 5% 7% 11% 52%	5984
September	1st to 10th	Day	5% 3 1 3 3 3 3 4 5% 7% 62%	2400
	11th to 20th	Day	4 3 1 3 3 3 4 4 6% 6% 64%	2392
	21st to end	Day	5% 2 1 4 3 2 3 3 4 5% 67%	2106
October	1st to 10th	Day	4 2 1 2 2 2 2 2 3 4 76%	3270
	11th to 20th	Day	4 3 1 3 3 4 5% 4 7% 9% 57%	3250
	21st to end	Day	5% 4 2 4 3 3 3 2 4 5% 65%	3548
November	1st to 10th	Day	4 5% 2 3 3 2 3 3 5% 5% 65%	1999
	11th to 20th	Day	6% 5% 1 4 3 3 3 3 4 7% 61%	1833
	21st to end	Day	5% 9% 2 5% 4 2 3 2 4 5% 59%	1680
December	1st to 10th	Day	6% 7% 2 4 3 2 2 2 4 5% 65%	2700
	11th to 20th	Day	4 8% 2 6% 4 3 3 2 4 8% 56%	3106
	21st to end	Day	5% 9% 3 6% 5% 4 4 3 5% 8% 47%	4092
January	1st to 10th	Night	3 9% 5% 10% 6% 5% 5% 3 5% 6% 42%	6260
	11th to 20th	Night	4 14% 3 7% 3 3 3 2 4 6% 51%	6010
	21st to end	Night	5% 13% 4 7% 4 3 3 2 3 4 53%	6611
February	1st to 10th	Night	6% 12% 3 7% 4 4 4 3 5% 6% 46%	2600
	11th to 20th	Night	6% 12% 3 7% 4 4 4 4 5% 6% 45%	2502
	21st to end	Night	7% 13% 3 7% 4 3 3 2 4 6% 48%	1980
March	1st to 10th	Night	4 13% 3 8% 4 4 4 3 5% 5% 46%	4954
	11th to 20th	Night	5% 10% 3 6% 4 3 4 4 5% 6% 50%	5000
	21st to end	Night	8% 14% 3 7% 4 4 4 3 5% 5% 42%	5452
April	1st to 10th	Night	8% 10% 3 5% 4 4 5% 3 5% 6% 48%	2000
	11th to 20th	Night	8% 11% 3 5% 4 4 4 3 5% 6% 47%	1977
	21st to end	Night	8% 8% 2 5% 4 4 4 3 5% 7% 51%	2000
May	1st to 10th	Night	8% 9% 2 6% 4 4 5% 4 6% 8% 45%	4149
	11th to 20th	Night	5% 5% 2 5% 4 4 5% 5% 5% 7% 52%	3899
	21st to end	Night	6% 3 1 3 2 3 3 3 5% 7% 63%	3972
June	1st to 10th	Night	2 4 1 3 3 4 3 4 6% 7% 64%	1600
	11th to 20th	Night	3 3 1 3 2 4 3 3 3 6% 69%	1600
	21st to end	Night	2 2 3 3 3 4 3 6% 6% 68%	1600
July	1st to 10th	Night	2 1 1 3 4 4 5% 4 6% 5% 66%	3640
	11th to 20th	Night	1 2 1 4 3 4 5% 5% 9% 13% 54%	3998
	21st to end	Night	2 3 1 4 3 4 5% 4 7% 9% 58%	4472
August	1st to 10th	Night	2 2 1 5% 4 5% 6% 5% 8% 11% 51%	4033
	11th to 20th	Night	2 2 1 4 3 4 4 4 6% 9% 61%	4182
	21st to end	Night	4 3 2 6% 5% 5% 6% 5% 8% 9% 46%	4993
September	1st to 10th	Night	3 3 1 4 3 3 3 3 6% 8% 63%	2000
	11th to 20th	Night	5% 3 1 4 3 3 3 3 5% 7% 62%	2004
	21st to end	Night	5% 3 1 3 2 3 3 2 4 6% 68%	2292
October	1st to 10th	Night	5% 2 1 2 2 2 2 2 3 5% 76%	3920
	11th to 20th	Night	4 3 1 4 3 4 4 4 5% 8% 59%	3898
	21st to end	Night	6% 6% 1 4 3 3 3 2 3 5% 65%	4252
November	1st to 10th	Night	4 5% 2 3 3 3 3 2 4 6% 65%	2497
	11th to 20th	Night	7% 5% 1 4 3 3 3 2 4 5% 64%	2783
	21st to end	Night	7% 8% 3 4 3 2 3 2 4 6% 58%	2940
December	1st to 10th	Night	5% 7% 2 4 2 2 2 2 4 6% 65%	4710
	11th to 20th	Night	4 9% 2 5% 4 4 4 3 5% 6% 54%	5321
	21st to end	Night	5% 11% 4 8% 4 4 4 4 5% 6% 45%	7128

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	38% 8% 18% 25% 11% 1	3970
	11th to 20th	Day	34% 10% 13% 21% 20% 2	4190
	21st to end	Day	32% 5% 12% 27% 20% 3	4609
February	1st to 10th	Day	42% 8% 15% 20% 11% 3	1800
	11th to 20th	Day	44% 7% 8% 24% 14% 3	1793
	21st to end	Day	44% 6% 7% 21% 18% 3	1650
March	1st to 10th	Day	35% 8% 8% 22% 22% 5%	4924
	11th to 20th	Day	37% 7% 11% 30% 13% 2	5000
	21st to end	Day	42% 7% 12% 27% 11% 1	5519
April	1st to 10th	Day	34% 7% 10% 23% 21% 6%	2400
	11th to 20th	Day	37% 9% 9% 20% 21% 4	2374
	21st to end	Day	33% 8% 8% 25% 23% 3	2400
May	1st to 10th	Day	32% 8% 12% 23% 22% 3	5827
	11th to 20th	Day	26% 8% 9% 24% 26% 7%	6017
	21st to end	Day	21% 5% 6% 22% 38% 8%	6926
June	1st to 10th	Day	20% 6% 7% 22% 30% 15%	2800
	11th to 20th	Day	18% 5% 6% 12% 28% 32%	2800
	21st to end	Day	16% 5% 6% 15% 27% 31%	2800
July	1st to 10th	Day	17% 4 5% 9% 19% 47%	6271
	11th to 20th	Day	19% 4 8% 26% 30% 14%	5906
	21st to end	Day	21% 4 10% 18% 27% 20%	6217
August	1st to 10th	Day	27% 5% 16% 23% 16% 13%	4208
	11th to 20th	Day	25% 5% 10% 17% 26% 16%	4101
	21st to end	Day	23% 6% 12% 20% 23% 16%	4311
September	1st to 10th	Day	22% 5% 9% 16% 27% 21%	2400
	11th to 20th	Day	21% 6% 9% 19% 29% 16%	2392
	21st to end	Day	21% 5% 5% 19% 38% 12%	2106
October	1st to 10th	Day	16% 3 5% 16% 39% 22%	3270
	11th to 20th	Day	24% 3 5% 33% 29% 6%	3250
	21st to end	Day	23% 3 6% 35% 28% 5%	3548
November	1st to 10th	Day	23% 5% 9% 28% 31% 4	1999
	11th to 20th	Day	26% 5% 10% 33% 21% 4	1833
	21st to end	Day	31% 4 10% 30% 20% 4	1680
December	1st to 10th	Day	26% 4 14% 40% 14% 1	2700
	11th to 20th	Day	31% 4 16% 34% 16%	3104
	21st to end	Day	36% 6% 17% 24% 17% 1	4092
January	1st to 10th	Night	42% 8% 13% 23% 12% 2	6260
	11th to 20th	Night	36% 6% 13% 21% 22% 2	6010
	21st to end	Night	35% 6% 12% 21% 22% 4	6611
February	1st to 10th	Night	41% 6% 14% 24% 13% 2	2600
	11th to 20th	Night	41% 7% 9% 25% 16% 2	2503
	21st to end	Night	39% 6% 6% 26% 20% 4	1980
March	1st to 10th	Night	38% 7% 7% 21% 24% 3	4954
	11th to 20th	Night	34% 6% 9% 29% 19% 2	5000
	21st to end	Night	44% 6% 12% 27% 10% 1	5452
April	1st to 10th	Night	38% 6% 7% 22% 22% 6%	2000
	11th to 20th	Night	39% 7% 8% 20% 20% 7%	1977
	21st to end	Night	33% 7% 8% 22% 26% 4	2000
May	1st to 10th	Night	34% 8% 12% 24% 20% 3	4146
	11th to 20th	Night	28% 7% 9% 30% 22% 4	3900
	21st to end	Night	20% 5% 8% 20% 38% 9%	3972
June	1st to 10th	Night	18% 6% 10% 20% 29% 17%	1600
	11th to 20th	Night	20% 4 6% 15% 20% 36%	1600
	21st to end	Night	14% 4 7% 18% 23% 33%	1600
July	1st to 10th	Night	21% 4 7% 9% 12% 47%	3600
	11th to 20th	Night	21% 3 10% 32% 18% 17%	3947
	21st to end	Night	22% 5% 12% 21% 21% 19%	4344
August	1st to 10th	Night	31% 7% 20% 15% 15% 12%	2928
	11th to 20th	Night	25% 4 19% 15% 19% 19%	3023
	21st to end	Night	28% 6% 11% 17% 22% 16%	3597
September	1st to 10th	Night	20% 5% 8% 18% 25% 23%	2000
	11th to 20th	Night	22% 6% 10% 17% 26% 18%	2004
	21st to end	Night	19% 4 5% 19% 37% 16%	2292
October	1st to 10th	Night	15% 3 4 16% 42% 21%	3920
	11th to 20th	Night	25% 3 8% 31% 27% 7%	3898
	21st to end	Night	25% 2 5% 34% 30% 3	4252
November	1st to 10th	Night	23% 5% 9% 31% 29% 4	2497
	11th to 20th	Night	25% 4 10% 33% 24% 4	2783
	21st to end	Night	31% 4 9% 28% 24% 4	2940
December	1st to 10th	Night	23% 3 15% 42% 15% 1	4710
	11th to 20th	Night	33% 5% 12% 37% 13%	5322
	21st to end	Night	42% 4 12% 25% 16% 1	7128

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% 5% 20% 40% 17% 4	330
	11th to 20th	Day	8% 8% 25% 39% 17% 2	330
	21st to end	Day	9% 4 21% 47% 14% 4	363
February	1st to 10th	Day	12% 9% 34% 36% 8% 2	300
	11th to 20th	Day	13% 11% 33% 30% 12% 1	300
	21st to end	Day	11% 12% 31% 35% 10% 2	249
March	1st to 10th	Day	13% 16% 26% 29% 12% 3	483
	11th to 20th	Day	9% 13% 27% 32% 15% 2	500
	21st to end	Day	13% 17% 33% 26% 10% 1	550
April	1st to 10th	Day	11% 16% 31% 27% 11% 3	500
	11th to 20th	Day	14% 18% 34% 23% 10% 1	492
	21st to end	Day	10% 15% 34% 28% 13%	500
May	1st to 10th	Day	14% 17% 30% 24% 13% 2	503
	11th to 20th	Day	8% 8% 29% 32% 18% 4	597
	21st to end	Day	6% 12% 24% 32% 22% 4	789
June	1st to 10th	Day	4 8% 23% 34% 27% 5%	730
	11th to 20th	Day	5% 9% 24% 36% 23% 3	730
	21st to end	Day	2 7% 22% 39% 27% 3	730
July	1st to 10th	Day	1 2 16% 41% 33% 6%	721
	11th to 20th	Day	2 2 11% 40% 34% 10%	567
	21st to end	Day	5% 1 15% 36% 34% 10%	575
August	1st to 10th	Day	5% 3 18% 38% 28% 9%	527
	11th to 20th	Day	3 3 13% 39% 31% 12%	517
	21st to end	Day	4 2 15% 40% 33% 8%	583
September	1st to 10th	Day	5% 4 17% 36% 27% 11%	530
	11th to 20th	Day	5% 5% 25% 37% 24% 5%	530
	21st to end	Day	6% 7% 20% 30% 28% 9%	436
October	1st to 10th	Day	8% 7% 20% 23% 28% 14%	330
	11th to 20th	Day	4 11% 25% 31% 21% 8%	330
	21st to end	Day	9% 5% 22% 36% 21% 6%	363
November	1st to 10th	Day	6% 10% 22% 39% 18% 4	330
	11th to 20th	Day	5% 5% 25% 40% 18% 8%	330
	21st to end	Day	12% 5% 21% 40% 17% 6%	330
December	1st to 10th	Day	9% 7% 27% 37% 15% 5%	330
	11th to 20th	Day	8% 3 25% 40% 18% 6%	330
	21st to end	Day	13% 7% 25% 39% 12% 4	363
January	1st to 10th	Night	11% 3 23% 44% 17% 3	960
	11th to 20th	Night	9% 3 25% 44% 18% 2	840
	21st to end	Night	11% 4 22% 47% 14% 2	924
February	1st to 10th	Night	11% 3 30% 44% 11% 1	800
	11th to 20th	Night	9% 4 32% 43% 11% 1	784
	21st to end	Night	12% 4 33% 42% 9%	660
March	1st to 10th	Night	10% 5% 31% 43% 10% 1	800
	11th to 20th	Night	6% 4 26% 46% 17% 1	800
	21st to end	Night	11% 4 30% 43% 12%	868
April	1st to 10th	Night	10% 5% 33% 44% 8%	600
	11th to 20th	Night	12% 7% 25% 43% 12% 1	593
	21st to end	Night	10% 4 33% 38% 14% 1	600
May	1st to 10th	Night	12% 5% 27% 43% 13% 1	600
	11th to 20th	Night	9% 4 20% 45% 20% 2	591
	21st to end	Night	8% 6% 22% 40% 22% 2	650
June	1st to 10th	Night	4 3 18% 46% 28% 1	600
	11th to 20th	Night	4 4 21% 49% 22% 1	600
	21st to end	Night	3 2 13% 50% 32% 1	600
July	1st to 10th	Night	2 1 10% 45% 39% 3	585
	11th to 20th	Night	2 1 6% 41% 47% 4	582
	21st to end	Night	3 1 8% 39% 47% 2	657
August	1st to 10th	Night	4 1 11% 40% 42% 3	597
	11th to 20th	Night	4 1 10% 46% 37% 3	594
	21st to end	Night	3 1 10% 44% 39% 3	660
September	1st to 10th	Night	3 1 13% 46% 34% 3	600
	11th to 20th	Night	5% 2 16% 46% 29% 2	604
	21st to end	Night	6% 2 18% 38% 32% 5%	800
October	1st to 10th	Night	10% 2 19% 43% 25% 2	800
	11th to 20th	Night	6% 2 26% 41% 22% 3	800
	21st to end	Night	9% 3 21% 44% 21% 3	880
November	1st to 10th	Night	6% 3 23% 46% 20% 1	857
	11th to 20th	Night	8% 3 25% 46% 17% 2	1050
	21st to end	Night	9% 5% 22% 43% 20% 2	1050
December	1st to 10th	Night	11% 2 24% 46% 16% 1	1050
	11th to 20th	Night	13% 3 26% 40% 17% 1	1050
	21st to end	Night	14% 5% 26% 42% 12% 1	1155

Page generated at 2026-01-28 23:21:44. Version ac07

Copyright © 2026 Attilla Danko.