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 2024-01-14.

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	5% 6% 2 4 4 3 4 5% 5% 7% 54%	74695
	Night	6% 7% 2 4 4 3 4 4 5% 7% 55%	75086
Transparency	Day	30% 7% 10% 22% 21% 9%	74412
	Night	31% 6% 11% 23% 21% 8%	74890
Seeing	Day	8% 8% 24% 34% 21% 5%	14220
	Night	8% 3 21% 43% 22% 2	24480

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	8% 7% 3 6% 6% 3 5% 4 5% 7% 46%	1615
	11th to 20th	Day	5% 10% 3 5% 4 2 4 4 5% 7% 52%	1647
	21st to end	Day	8% 10% 3 6% 4 3 3 3 4 6% 48%	1782
February	1st to 10th	Day	6% 10% 4 7% 5% 3 4 4 5% 7% 45%	1620
	11th to 20th	Day	5% 11% 5% 7% 6% 2 5% 5% 4 8% 43%	1601
	21st to end	Day	8% 13% 5% 6% 6% 3 4 4 4 6% 41%	1480
March	1st to 10th	Day	6% 11% 3 6% 4 2 4 5% 5% 8% 45%	1964
	11th to 20th	Day	4 7% 3 5% 4 3 4 5% 5% 8% 52%	1980
	21st to end	Day	6% 9% 3 7% 6% 3 6% 4 5% 7% 44%	2186
April	1st to 10th	Day	8% 7% 3 6% 5% 3 4 4 5% 7% 49%	2160
	11th to 20th	Day	6% 8% 4 6% 5% 3 5% 6% 6% 7% 44%	2131
	21st to end	Day	5% 6% 2 5% 6% 3 4 4 5% 7% 51%	2160
May	1st to 10th	Day	6% 6% 3 5% 6% 4 5% 6% 6% 8% 45%	2313
	11th to 20th	Day	6% 4 2 4 5% 3 5% 5% 6% 9% 51%	2362
	21st to end	Day	5% 3 1 4 5% 3 5% 5% 6% 8% 56%	2724
June	1st to 10th	Day	3 3 1 3 3 2 4 4 6% 8% 62%	2520
	11th to 20th	Day	3 2 1 3 3 2 4 4 5% 6% 67%	2520
	21st to end	Day	1 2 1 2 3 2 4 4 6% 7% 68%	2520
July	1st to 10th	Day	3 2 1 3 4 4 4 6% 6% 9% 59%	2520
	11th to 20th	Day	2 2 1 3 4 3 7% 6% 7% 11% 54%	2382
	21st to end	Day	4 4 2 4 6% 4 7% 6% 9% 10% 44%	2545
August	1st to 10th	Day	4 3 1 5% 5% 4 5% 7% 8% 9% 48%	2328
	11th to 20th	Day	3 2 1 4 4 2 3 5% 6% 10% 59%	2245
	21st to end	Day	3 2 1 4 4 3 5% 7% 7% 10% 55%	2376
September	1st to 10th	Day	6% 3 2 2 4 2 3 5% 5% 7% 61%	2160
	11th to 20th	Day	4 3 2 3 3 2 4 4 5% 6% 64%	2154
	21st to end	Day	5% 2 1 3 4 1 3 4 4 5% 67%	1896
October	1st to 10th	Day	8% 3 2 3 3 2 4 4 5% 7% 60%	1800
	11th to 20th	Day	5% 3 1 3 2 1 3 3 4 6% 70%	1800
	21st to end	Day	6% 5% 2 4 3 2 3 3 4 5% 62%	1980
November	1st to 10th	Day	4 5% 1 2 3 1 3 4 5% 5% 66%	1805
	11th to 20th	Day	7% 5% 2 3 4 2 4 3 3 6% 61%	1659
	21st to end	Day	5% 8% 3 4 5% 1 3 2 3 5% 59%	1520
December	1st to 10th	Day	9% 10% 4 4 4 3 3 3 4 5% 51%	1520
	11th to 20th	Day	7% 10% 4 7% 6% 3 4 4 5% 7% 44%	1926
	21st to end	Day	6% 10% 4 6% 6% 3 4 4 5% 7% 46%	2794
January	1st to 10th	Night	7% 11% 4 5% 5% 2 3 3 5% 6% 48%	2567
	11th to 20th	Night	6% 11% 3 5% 4 3 3 2 3 5% 54%	2391
	21st to end	Night	9% 11% 3 5% 5% 2 3 3 3 5% 51%	2574
February	1st to 10th	Night	6% 11% 4 5% 5% 3 4 4 4 6% 49%	2340
	11th to 20th	Night	7% 11% 3 6% 5% 3 4 5% 5% 6% 46%	2245
	21st to end	Night	7% 12% 4 7% 5% 3 3 3 4 6% 47%	1776
March	1st to 10th	Night	8% 9% 3 6% 4 3 4 4 4 6% 49%	1994
	11th to 20th	Night	5% 7% 3 4 4 2 4 4 4 5% 56%	1980
	21st to end	Night	8% 10% 3 6% 5% 3 5% 4 5% 6% 45%	2168
April	1st to 10th	Night	8% 10% 3 5% 4 3 5% 4 5% 6% 47%	1800
	11th to 20th	Night	8% 10% 4 4 5% 3 4 4 5% 6% 47%	1777
	21st to end	Night	8% 8% 2 4 4 2 4 4 5% 7% 52%	1800
May	1st to 10th	Night	8% 6% 2 4 5% 3 4 5% 6% 8% 48%	1643
	11th to 20th	Night	8% 4 2 4 4 2 5% 5% 6% 6% 55%	1531
	21st to end	Night	7% 4 1 4 3 2 4 6% 6% 8% 54%	1552
June	1st to 10th	Night	2 3 1 2 3 3 3 5% 5% 7% 65%	1440
	11th to 20th	Night	4 3 2 3 2 2 4 4 3 6% 69%	1440
	21st to end	Night	2 2 2 3 2 4 4 6% 6% 69%	1440
July	1st to 10th	Night	2 2 2 3 3 3 5% 6% 7% 8% 59%	1440
	11th to 20th	Night	2 1 1 3 3 3 6% 6% 7% 10% 57%	1574
	21st to end	Night	4 2 2 4 5% 4 6% 7% 8% 12% 46%	1773
August	1st to 10th	Night	3 3 1 4 5% 4 5% 5% 7% 10% 53%	1611
	11th to 20th	Night	4 3 1 4 3 2 4 4 5% 9% 61%	1655
	21st to end	Night	3 3 1 4 4 3 5% 5% 7% 9% 55%	1980
September	1st to 10th	Night	4 3 1 3 4 2 4 4 6% 8% 62%	1800
	11th to 20th	Night	5% 3 1 4 3 2 3 4 5% 7% 62%	1803
	21st to end	Night	5% 3 2 3 3 2 3 3 3 5% 68%	2062
October	1st to 10th	Night	8% 4 1 3 4 2 3 4 3 6% 61%	2160
	11th to 20th	Night	5% 3 1 2 3 2 2 3 4 5% 70%	2160
	21st to end	Night	8% 6% 2 3 2 2 2 2 3 5% 65%	2376
November	1st to 10th	Night	5% 5% 1 3 3 1 3 3 4 6% 65%	2253
	11th to 20th	Night	7% 5% 1 4 3 2 3 3 4 5% 64%	2517
	21st to end	Night	7% 7% 3 4 3 2 2 3 4 6% 59%	2660
December	1st to 10th	Night	9% 10% 3 5% 4 3 3 3 4 5% 52%	2660
	11th to 20th	Night	7% 11% 4 6% 5% 3 5% 4 5% 7% 43%	3271
	21st to end	Night	7% 12% 4 7% 5% 3 3 4 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	40% 6% 18% 26% 9% 1	1616
	11th to 20th	Day	34% 7% 18% 26% 13% 1	1647
	21st to end	Day	39% 8% 15% 26% 9% 3	1782
February	1st to 10th	Day	42% 8% 16% 21% 11% 2	1620
	11th to 20th	Day	43% 7% 8% 25% 14% 3	1610
	21st to end	Day	47% 6% 7% 21% 15% 3	1480
March	1st to 10th	Day	40% 6% 9% 25% 19% 1	1964
	11th to 20th	Day	32% 7% 12% 31% 15% 3	1980
	21st to end	Day	40% 9% 10% 24% 15% 2	2186
April	1st to 10th	Day	36% 7% 10% 20% 20% 6%	2160
	11th to 20th	Day	38% 9% 9% 20% 19% 4	2134
	21st to end	Day	34% 8% 8% 25% 21% 3	2160
May	1st to 10th	Day	37% 7% 10% 21% 21% 4	2313
	11th to 20th	Day	30% 9% 11% 25% 21% 5%	2365
	21st to end	Day	27% 8% 9% 18% 29% 9%	2724
June	1st to 10th	Day	20% 6% 7% 21% 30% 17%	2520
	11th to 20th	Day	19% 5% 7% 11% 28% 31%	2520
	21st to end	Day	15% 5% 6% 16% 27% 30%	2520
July	1st to 10th	Day	22% 9% 9% 14% 21% 26%	2451
	11th to 20th	Day	22% 9% 13% 21% 19% 15%	2310
	21st to end	Day	32% 10% 17% 19% 14% 8%	2404
August	1st to 10th	Day	30% 10% 14% 18% 16% 13%	2313
	11th to 20th	Day	22% 8% 9% 19% 25% 17%	2245
	21st to end	Day	23% 9% 11% 21% 22% 14%	2376
September	1st to 10th	Day	23% 5% 9% 14% 26% 23%	2160
	11th to 20th	Day	21% 7% 10% 19% 28% 16%	2154
	21st to end	Day	21% 6% 4 19% 39% 11%	1896
October	1st to 10th	Day	27% 5% 9% 25% 27% 8%	1800
	11th to 20th	Day	19% 5% 5% 28% 34% 9%	1800
	21st to end	Day	26% 5% 10% 31% 23% 5%	1980
November	1st to 10th	Day	22% 6% 9% 27% 32% 4	1805
	11th to 20th	Day	27% 6% 10% 32% 21% 3	1659
	21st to end	Day	31% 5% 9% 29% 21% 5%	1520
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	38% 6% 15% 28% 12% 1	2567
	11th to 20th	Night	36% 6% 17% 27% 13% 1	2391
	21st to end	Night	39% 7% 13% 26% 12% 3	2574
February	1st to 10th	Night	40% 6% 15% 25% 13% 1	2340
	11th to 20th	Night	41% 7% 9% 26% 17% 1	2246
	21st to end	Night	40% 6% 6% 27% 18% 2	1776
March	1st to 10th	Night	37% 6% 10% 25% 22% 1	1994
	11th to 20th	Night	30% 7% 9% 30% 19% 5%	1980
	21st to end	Night	40% 7% 9% 26% 16% 3	2168
April	1st to 10th	Night	39% 6% 7% 20% 21% 7%	1800
	11th to 20th	Night	38% 7% 9% 20% 19% 7%	1777
	21st to end	Night	34% 7% 9% 23% 24% 4	1800
May	1st to 10th	Night	32% 8% 11% 21% 22% 5%	1643
	11th to 20th	Night	30% 8% 11% 25% 22% 4	1532
	21st to end	Night	25% 8% 12% 18% 26% 11%	1552
June	1st to 10th	Night	17% 6% 9% 19% 30% 18%	1440
	11th to 20th	Night	19% 4 7% 15% 20% 35%	1440
	21st to end	Night	13% 5% 7% 19% 24% 33%	1440
July	1st to 10th	Night	20% 9% 13% 12% 19% 27%	1400
	11th to 20th	Night	20% 8% 16% 21% 17% 18%	1523
	21st to end	Night	26% 11% 22% 19% 14% 8%	1674
August	1st to 10th	Night	23% 11% 18% 19% 16% 13%	1602
	11th to 20th	Night	19% 6% 15% 17% 21% 21%	1655
	21st to end	Night	24% 8% 12% 18% 20% 18%	1980
September	1st to 10th	Night	21% 6% 8% 16% 23% 25%	1800
	11th to 20th	Night	22% 6% 11% 17% 25% 19%	1803
	21st to end	Night	20% 5% 5% 18% 38% 15%	2062
October	1st to 10th	Night	25% 5% 8% 25% 24% 13%	2160
	11th to 20th	Night	20% 5% 7% 23% 34% 12%	2160
	21st to end	Night	25% 4 7% 31% 27% 5%	2376
November	1st to 10th	Night	23% 5% 10% 29% 29% 4	2253
	11th to 20th	Night	25% 5% 10% 32% 24% 4	2517
	21st to end	Night	30% 5% 8% 28% 26% 4	2660
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% 8% 28% 37% 16% 2	249
	21st to end	Day	10% 6% 22% 44% 14% 4	264
February	1st to 10th	Day	12% 8% 34% 36% 8% 2	240
	11th to 20th	Day	12% 10% 34% 29% 14% 1	240
	21st to end	Day	11% 14% 34% 33% 7% 2	198
March	1st to 10th	Day	12% 18% 26% 29% 12% 2	404
	11th to 20th	Day	10% 14% 26% 33% 15% 2	420
	21st to end	Day	13% 18% 34% 26% 8% 1	462
April	1st to 10th	Day	12% 17% 32% 25% 10% 3	420
	11th to 20th	Day	15% 18% 33% 22% 10% 1	412
	21st to end	Day	11% 16% 34% 26% 12%	420
May	1st to 10th	Day	13% 17% 33% 23% 12% 2	423
	11th to 20th	Day	9% 7% 29% 31% 19% 5%	509
	21st to end	Day	6% 12% 25% 32% 21% 4	679
June	1st to 10th	Day	4 8% 24% 33% 27% 4	630
	11th to 20th	Day	5% 10% 23% 36% 23% 3	630
	21st to end	Day	2 6% 23% 40% 27% 2	630
July	1st to 10th	Day	1 2 15% 41% 35% 6%	621
	11th to 20th	Day	2 2 12% 41% 34% 9%	483
	21st to end	Day	5% 1 14% 36% 34% 10%	487
August	1st to 10th	Day	5% 3 17% 38% 28% 9%	447
	11th to 20th	Day	2 3 14% 41% 30% 11%	437
	21st to end	Day	4 2 15% 39% 32% 8%	495
September	1st to 10th	Day	5% 5% 18% 37% 25% 10%	450
	11th to 20th	Day	5% 5% 25% 36% 24% 5%	450
	21st to end	Day	6% 8% 21% 29% 27% 9%	366
October	1st to 10th	Day	9% 8% 23% 21% 26% 13%	270
	11th to 20th	Day	4 11% 24% 30% 21% 9%	270
	21st to end	Day	11% 5% 23% 36% 20% 6%	297
November	1st to 10th	Day	7% 10% 24% 37% 18% 4	270
	11th to 20th	Day	5% 4 27% 40% 17% 7%	270
	21st to end	Day	11% 4 23% 39% 15% 8%	270
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 25% 42% 18% 2	736
	21st to end	Night	13% 4 20% 48% 13% 2	792
February	1st to 10th	Night	11% 2 27% 47% 12% 1	720
	11th to 20th	Night	9% 3 30% 45% 12% 1	704
	21st to end	Night	13% 3 32% 43% 9%	592
March	1st to 10th	Night	10% 5% 31% 44% 10% 1	720
	11th to 20th	Night	6% 3 25% 47% 17% 1	720
	21st to end	Night	10% 4 29% 44% 12% 1	782
April	1st to 10th	Night	11% 5% 32% 43% 9%	540
	11th to 20th	Night	13% 7% 24% 44% 13% 1	533
	21st to end	Night	11% 4 33% 36% 15% 1	540
May	1st to 10th	Night	12% 5% 26% 44% 14% 1	540
	11th to 20th	Night	10% 4 19% 44% 22% 2	531
	21st to end	Night	8% 6% 22% 40% 22% 2	584
June	1st to 10th	Night	4 3 18% 45% 29% 1	540
	11th to 20th	Night	4 4 21% 47% 23% 1	540
	21st to end	Night	2 2 12% 49% 34% 1	540
July	1st to 10th	Night	2 1 9% 42% 42% 3	525
	11th to 20th	Night	2 1 6% 39% 48% 4	522
	21st to end	Night	3 1 7% 36% 51% 3	591
August	1st to 10th	Night	4 1 10% 39% 43% 3	537
	11th to 20th	Night	4 1 10% 44% 38% 3	534
	21st to end	Night	3 1 10% 43% 40% 3	594
September	1st to 10th	Night	3 1 14% 45% 34% 4	540
	11th to 20th	Night	5% 2 14% 45% 31% 2	543
	21st to end	Night	6% 2 19% 36% 32% 6%	720
October	1st to 10th	Night	10% 2 20% 43% 24% 2	720
	11th to 20th	Night	6% 2 25% 42% 23% 3	720
	21st to end	Night	9% 3 21% 43% 22% 3	792
November	1st to 10th	Night	7% 3 22% 45% 21% 2	773
	11th to 20th	Night	8% 3 23% 45% 19% 2	950
	21st to end	Night	9% 4 20% 43% 21% 3	950
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 2024-01-11 11:31:57. Version ac07

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