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 2024-11-28.

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 6% 2 5% 4 4 4 4 6% 8% 54%	105362
	Night	6% 8% 2 5% 4 4 4 3 5% 7% 53%	102932
Transparency	Day	28% 7% 10% 22% 22% 11%	105119
	Night	31% 7% 11% 22% 20% 9%	102764
Seeing	Day	8% 8% 24% 34% 21% 5%	15443
	Night	8% 3 22% 43% 22% 2	25599

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	5% 6% 4 10% 6% 4 5% 3 6% 9% 42%	2700
	11th to 20th	Day	7% 13% 3 10% 5% 4 4 4 5% 7% 40%	2860
	21st to end	Day	6% 10% 3 7% 3 4 3 2 4 6% 51%	3146
February	1st to 10th	Day	7% 12% 3 7% 5% 5% 4 3 6% 6% 43%	1710
	11th to 20th	Day	5% 12% 4 8% 4 3 4 4 4 8% 43%	1692
	21st to end	Day	6% 15% 5% 7% 5% 4 4 4 4 6% 41%	1570
March	1st to 10th	Day	4 15% 3 8% 4 4 4 4 6% 8% 40%	3428
	11th to 20th	Day	3 7% 3 7% 5% 5% 5% 5% 6% 8% 45%	3490
	21st to end	Day	7% 16% 4 9% 6% 5% 5% 3 5% 6% 35%	3845
April	1st to 10th	Day	7% 7% 2 7% 4 4 4 3 5% 7% 50%	2280
	11th to 20th	Day	6% 8% 4 6% 5% 5% 5% 4 6% 7% 44%	2251
	21st to end	Day	5% 7% 2 6% 5% 4 5% 3 6% 7% 51%	2280
May	1st to 10th	Day	7% 9% 3 7% 5% 5% 5% 4 6% 7% 42%	4070
	11th to 20th	Day	4 4 1 5% 4 4 5% 5% 7% 10% 50%	4188
	21st to end	Day	6% 5% 1 4 3 4 4 4 5% 7% 59%	4825
June	1st to 10th	Day	2 3 1 4 3 3 4 4 7% 8% 62%	2660
	11th to 20th	Day	2 2 1 3 3 3 4 3 5% 6% 67%	2660
	21st to end	Day	2 2 1 2 3 3 4 3 6% 7% 67%	2660
July	1st to 10th	Day	2 2 1 3 2 3 3 3 4 6% 71%	4430
	11th to 20th	Day	1 2 1 3 3 3 6% 6% 10% 13% 53%	4180
	21st to end	Day	2 2 1 4 3 4 5% 4 7% 8% 59%	4454
August	1st to 10th	Day	3 3 1 4 4 5% 6% 6% 9% 12% 49%	4092
	11th to 20th	Day	3 2 1 4 4 4 4 5% 7% 10% 56%	3935
	21st to end	Day	3 2 1 4 3 4 4 5% 7% 11% 57%	4180
September	1st to 10th	Day	5% 3 1 3 3 3 3 4 5% 7% 62%	2280
	11th to 20th	Day	4 3 1 3 2 3 4 4 5% 6% 64%	2273
	21st to end	Day	5% 2 1 4 3 2 3 3 3 5% 68%	2001
October	1st to 10th	Day	4 2 1 2 2 2 2 2 3 4 76%	3170
	11th to 20th	Day	4 3 1 3 3 4 5% 4 7% 9% 57%	3150
	21st to end	Day	6% 4 2 4 3 3 3 2 4 5% 65%	3438
November	1st to 10th	Day	4 6% 2 3 3 2 3 3 5% 6% 64%	1902
	11th to 20th	Day	7% 5% 1 4 3 3 3 3 4 6% 61%	1746
	21st to end	Day	6% 9% 3 5% 5% 2 3 2 4 5% 58%	1576
December	1st to 10th	Day	9% 11% 3 5% 4 3 3 2 4 5% 51%	1520
	11th to 20th	Day	6% 11% 3 8% 5% 4 4 3 4 7% 44%	1926
	21st to end	Day	6% 11% 4 7% 5% 4 4 3 5% 7% 46%	2794
January	1st to 10th	Night	4 11% 5% 10% 6% 5% 5% 3 5% 5% 40%	4285
	11th to 20th	Night	6% 19% 4 7% 4 3 3 2 4 7% 41%	4110
	21st to end	Night	7% 15% 4 8% 4 4 3 3 4 5% 45%	4521
February	1st to 10th	Night	6% 12% 3 7% 4 4 4 3 4 5% 47%	2470
	11th to 20th	Night	6% 11% 3 7% 4 4 4 4 5% 6% 46%	2374
	21st to end	Night	7% 13% 3 8% 4 3 3 2 4 6% 46%	1884
March	1st to 10th	Night	6% 14% 3 8% 4 4 4 3 5% 5% 44%	3444
	11th to 20th	Night	5% 11% 3 6% 4 4 4 3 5% 6% 49%	3490
	21st to end	Night	10% 17% 4 8% 4 4 4 3 5% 6% 35%	3805
April	1st to 10th	Night	8% 10% 3 5% 4 4 5% 3 5% 6% 47%	1900
	11th to 20th	Night	8% 11% 3 5% 4 3 4 3 5% 6% 47%	1877
	21st to end	Night	8% 8% 2 5% 4 4 4 3 5% 7% 51%	1900
May	1st to 10th	Night	11% 11% 2 6% 4 3 4 3 5% 7% 43%	2896
	11th to 20th	Night	6% 4 2 5% 4 4 5% 5% 6% 8% 52%	2715
	21st to end	Night	9% 4 1 4 2 3 3 3 5% 7% 59%	2762
June	1st to 10th	Night	2 4 1 3 3 4 3 4 6% 7% 64%	1520
	11th to 20th	Night	3 3 1 3 2 4 3 3 3 6% 68%	1520
	21st to end	Night	2 2 2 3 3 4 3 6% 6% 68%	1520
July	1st to 10th	Night	2 1 1 3 3 4 4 3 5% 5% 70%	2540
	11th to 20th	Night	1 1 1 3 3 4 5% 4 8% 11% 58%	2786
	21st to end	Night	2 2 1 4 3 4 4 4 6% 9% 60%	3109
August	1st to 10th	Night	3 3 1 5% 5% 7% 7% 6% 9% 12% 42%	2847
	11th to 20th	Night	3 2 1 5% 4 5% 5% 4 6% 9% 55%	2903
	21st to end	Night	3 2 1 5% 4 5% 5% 4 8% 9% 53%	3487
September	1st to 10th	Night	3 3 1 4 3 3 3 3 6% 8% 63%	1900
	11th to 20th	Night	5% 3 1 4 3 3 4 3 5% 7% 62%	1904
	21st to end	Night	5% 3 1 3 2 3 3 2 3 5% 69%	2177
October	1st to 10th	Night	5% 2 1 2 2 1 2 2 3 5% 76%	3800
	11th to 20th	Night	4 3 1 4 3 4 5% 4 5% 8% 59%	3778
	21st to end	Night	6% 6% 2 4 3 3 3 2 3 4 65%	4120
November	1st to 10th	Night	5% 6% 2 4 3 3 3 2 4 6% 63%	2375
	11th to 20th	Night	7% 5% 1 4 3 2 3 2 4 5% 64%	2650
	21st to end	Night	7% 8% 3 4 3 2 2 2 4 5% 59%	2759
December	1st to 10th	Night	8% 11% 2 6% 3 3 3 2 4 5% 52%	2660
	11th to 20th	Night	6% 12% 3 6% 4 5% 4 3 5% 7% 43%	3271
	21st to end	Night	7% 13% 3 8% 4 3 4 3 4 6% 46%	4873

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% 11% 20% 22% 9% 1	2701
	11th to 20th	Day	41% 12% 19% 20% 8% 1	2860
	21st to end	Day	35% 7% 18% 29% 9% 2	3146
February	1st to 10th	Day	43% 8% 16% 20% 11% 2	1710
	11th to 20th	Day	43% 7% 9% 24% 14% 3	1701
	21st to end	Day	46% 7% 7% 20% 17% 3	1570
March	1st to 10th	Day	38% 11% 11% 21% 18% 1	3428
	11th to 20th	Day	31% 10% 15% 32% 9% 2	3490
	21st to end	Day	47% 10% 10% 20% 12% 1	3845
April	1st to 10th	Day	35% 7% 10% 22% 20% 6%	2280
	11th to 20th	Day	38% 9% 9% 20% 20% 4	2254
	21st to end	Day	34% 8% 8% 25% 22% 3	2280
May	1st to 10th	Day	36% 12% 9% 17% 23% 3	4070
	11th to 20th	Day	23% 12% 12% 26% 21% 6%	4191
	21st to end	Day	24% 7% 7% 19% 37% 7%	4825
June	1st to 10th	Day	19% 6% 7% 21% 30% 16%	2660
	11th to 20th	Day	19% 5% 6% 12% 28% 30%	2660
	21st to end	Day	16% 5% 6% 16% 27% 29%	2660
July	1st to 10th	Day	15% 5% 6% 9% 22% 43%	4361
	11th to 20th	Day	20% 5% 8% 28% 26% 13%	4108
	21st to end	Day	21% 6% 10% 19% 20% 24%	4314
August	1st to 10th	Day	27% 5% 17% 23% 15% 12%	4078
	11th to 20th	Day	26% 5% 10% 18% 25% 16%	3974
	21st to end	Day	23% 6% 12% 20% 24% 16%	4179
September	1st to 10th	Day	23% 5% 8% 15% 28% 21%	2280
	11th to 20th	Day	20% 7% 9% 19% 28% 17%	2273
	21st to end	Day	20% 5% 5% 18% 39% 12%	2001
October	1st to 10th	Day	15% 3 5% 16% 39% 22%	3170
	11th to 20th	Day	24% 3 5% 33% 29% 6%	3150
	21st to end	Day	24% 3 6% 36% 28% 5%	3438
November	1st to 10th	Day	23% 6% 9% 27% 31% 4	1902
	11th to 20th	Day	26% 5% 10% 32% 22% 4	1746
	21st to end	Day	31% 5% 9% 29% 21% 5%	1576
December	1st to 10th	Day	37% 8% 17% 22% 13% 3	1520
	11th to 20th	Day	41% 6% 10% 27% 15%	1924
	21st to end	Day	39% 8% 12% 20% 19% 1	2794
January	1st to 10th	Night	41% 11% 14% 22% 12% 1	4285
	11th to 20th	Night	44% 8% 19% 20% 8% 1	4110
	21st to end	Night	41% 8% 17% 22% 10% 2	4521
February	1st to 10th	Night	41% 6% 14% 24% 13% 1	2470
	11th to 20th	Night	40% 7% 10% 26% 16% 1	2375
	21st to end	Night	40% 6% 6% 26% 19% 3	1884
March	1st to 10th	Night	38% 10% 10% 22% 20% 1	3444
	11th to 20th	Night	33% 9% 13% 31% 12% 3	3490
	21st to end	Night	48% 9% 11% 21% 10% 2	3805
April	1st to 10th	Night	38% 6% 8% 21% 21% 6%	1900
	11th to 20th	Night	38% 7% 9% 20% 20% 7%	1877
	21st to end	Night	33% 7% 9% 23% 24% 4	1900
May	1st to 10th	Night	35% 11% 8% 20% 22% 4	2896
	11th to 20th	Night	25% 10% 12% 32% 17% 4	2716
	21st to end	Night	23% 8% 8% 16% 35% 10%	2762
June	1st to 10th	Night	17% 7% 9% 19% 30% 18%	1520
	11th to 20th	Night	20% 4 6% 15% 20% 35%	1520
	21st to end	Night	14% 4 7% 19% 24% 31%	1520
July	1st to 10th	Night	17% 5% 9% 8% 15% 46%	2500
	11th to 20th	Night	18% 5% 9% 33% 17% 18%	2735
	21st to end	Night	20% 6% 14% 19% 19% 21%	3011
August	1st to 10th	Night	31% 7% 20% 15% 14% 12%	2838
	11th to 20th	Night	26% 4 19% 15% 18% 18%	2930
	21st to end	Night	28% 7% 11% 17% 22% 16%	3487
September	1st to 10th	Night	21% 5% 8% 17% 26% 24%	1900
	11th to 20th	Night	22% 6% 11% 16% 26% 19%	1904
	21st to end	Night	19% 4 5% 18% 37% 16%	2177
October	1st to 10th	Night	15% 3 5% 16% 41% 21%	3800
	11th to 20th	Night	24% 3 8% 31% 27% 7%	3778
	21st to end	Night	26% 3 5% 34% 30% 3	4120
November	1st to 10th	Night	24% 5% 9% 29% 28% 4	2375
	11th to 20th	Night	25% 5% 10% 32% 25% 4	2650
	21st to end	Night	30% 5% 8% 28% 26% 4	2759
December	1st to 10th	Night	37% 5% 15% 24% 17% 2	2660
	11th to 20th	Night	40% 7% 12% 24% 16% 1	3272
	21st to end	Night	41% 6% 12% 20% 20% 1	4873

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	15% 4 20% 37% 19% 5%	270
	11th to 20th	Day	9% 10% 28% 36% 16% 1	270
	21st to end	Day	10% 5% 21% 44% 15% 5%	297
February	1st to 10th	Day	13% 8% 33% 36% 9% 2	270
	11th to 20th	Day	13% 10% 34% 29% 13% 1	270
	21st to end	Day	12% 13% 33% 32% 8% 2	225
March	1st to 10th	Day	13% 17% 26% 29% 12% 3	444
	11th to 20th	Day	9% 13% 27% 32% 16% 2	460
	21st to end	Day	14% 17% 33% 25% 9% 1	506
April	1st to 10th	Day	12% 17% 32% 26% 11% 3	460
	11th to 20th	Day	14% 18% 33% 23% 10% 1	452
	21st to end	Day	11% 15% 34% 27% 12%	460
May	1st to 10th	Day	14% 17% 32% 23% 12% 2	463
	11th to 20th	Day	8% 7% 28% 32% 19% 5%	553
	21st to end	Day	6% 12% 25% 32% 21% 4	734
June	1st to 10th	Day	4 8% 23% 34% 26% 5%	680
	11th to 20th	Day	5% 9% 25% 36% 22% 3	680
	21st to end	Day	2 6% 22% 41% 27% 2	680
July	1st to 10th	Day	1 2 16% 41% 34% 6%	671
	11th to 20th	Day	2 2 11% 40% 35% 10%	525
	21st to end	Day	5% 1 15% 36% 34% 10%	531
August	1st to 10th	Day	5% 3 16% 38% 29% 9%	487
	11th to 20th	Day	3 3 14% 40% 30% 10%	477
	21st to end	Day	3 2 15% 40% 32% 8%	539
September	1st to 10th	Day	5% 4 18% 36% 26% 11%	490
	11th to 20th	Day	5% 5% 26% 36% 23% 5%	490
	21st to end	Day	6% 7% 20% 29% 27% 9%	401
October	1st to 10th	Day	8% 7% 21% 21% 28% 15%	300
	11th to 20th	Day	4 11% 24% 31% 22% 9%	300
	21st to end	Day	10% 5% 22% 36% 20% 6%	330
November	1st to 10th	Day	7% 10% 24% 38% 18% 4	300
	11th to 20th	Day	5% 5% 26% 40% 17% 7%	300
	21st to end	Day	13% 4 22% 38% 15% 7%	291
December	1st to 10th	Day	10% 7% 31% 34% 13% 5%	270
	11th to 20th	Day	9% 4 27% 37% 17% 5%	270
	21st to end	Day	14% 6% 27% 37% 12% 4	297
January	1st to 10th	Night	11% 3 22% 44% 18% 3	870
	11th to 20th	Night	10% 3 26% 42% 17% 2	760
	21st to end	Night	12% 4 20% 47% 14% 3	836
February	1st to 10th	Night	11% 3 28% 46% 11% 1	760
	11th to 20th	Night	9% 4 31% 44% 12% 1	744
	21st to end	Night	13% 4 33% 42% 9%	628
March	1st to 10th	Night	10% 5% 31% 43% 10% 1	760
	11th to 20th	Night	6% 4 25% 47% 17% 1	760
	21st to end	Night	11% 4 30% 43% 11%	825
April	1st to 10th	Night	10% 5% 34% 42% 9%	570
	11th to 20th	Night	12% 7% 24% 43% 12% 1	563
	21st to end	Night	11% 4 33% 37% 15% 1	570
May	1st to 10th	Night	12% 5% 27% 42% 13% 1	570
	11th to 20th	Night	9% 4 18% 45% 21% 2	561
	21st to end	Night	9% 6% 22% 40% 21% 2	617
June	1st to 10th	Night	4 3 18% 46% 28% 1	570
	11th to 20th	Night	4 4 21% 47% 22% 1	570
	21st to end	Night	3 2 12% 50% 32% 1	570
July	1st to 10th	Night	3 1 10% 43% 41% 3	555
	11th to 20th	Night	2 1 6% 39% 48% 4	552
	21st to end	Night	3 1 8% 37% 49% 2	624
August	1st to 10th	Night	4 1 10% 39% 44% 3	567
	11th to 20th	Night	4 1 11% 45% 37% 3	564
	21st to end	Night	3 1 10% 44% 39% 3	627
September	1st to 10th	Night	3 1 14% 45% 34% 3	570
	11th to 20th	Night	5% 2 15% 46% 30% 2	574
	21st to end	Night	6% 2 18% 38% 31% 5%	760
October	1st to 10th	Night	10% 2 19% 42% 26% 2	760
	11th to 20th	Night	5% 2 25% 43% 23% 3	760
	21st to end	Night	9% 3 21% 43% 21% 3	836
November	1st to 10th	Night	7% 3 22% 46% 20% 1	815
	11th to 20th	Night	8% 3 24% 45% 18% 2	1000
	21st to end	Night	10% 4 21% 42% 20% 2	986
December	1st to 10th	Night	12% 2 24% 46% 15% 1	950
	11th to 20th	Night	14% 3 25% 40% 17% 1	950
	21st to end	Night	15% 5% 25% 42% 12% 1	1045

Page generated at 2024-11-24 22:22:20. Version ac07

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