Newton/Godin Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Newton/Godin Observatory clear sky chart from 2005-11-06 to 2024-01-16.

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	13% 8% 3 7% 6% 3 5% 5% 5% 8% 36%	74763
	Night	16% 9% 4 7% 6% 3 5% 5% 5% 7% 32%	75058
Transparency	Day	32% 36% 13% 14% 5% 1	74453
	Night	35% 36% 12% 13% 4 1	74887
Seeing	Day	15% 6% 17% 30% 25% 7%	14278
	Night	19% 7% 18% 30% 21% 6%	22662

By Month

Percentage Cloud Cover NW (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	27% 12% 6% 10% 6% 3 6% 6% 3 7% 14%	1329
	11th to 20th	Day	19% 14% 6% 10% 8% 4 6% 6% 5% 6% 15%	1297
	21st to end	Day	22% 12% 7% 11% 8% 4 7% 5% 6% 5% 13%	1660
February	1st to 10th	Day	25% 11% 4 8% 8% 4 5% 5% 5% 8% 15%	1620
	11th to 20th	Day	21% 11% 4 9% 6% 5% 6% 4 5% 7% 23%	1575
	21st to end	Day	16% 12% 4 8% 8% 4 7% 6% 7% 6% 22%	1336
March	1st to 10th	Day	14% 11% 5% 7% 8% 4 7% 7% 7% 7% 23%	1894
	11th to 20th	Day	16% 12% 6% 9% 7% 4 6% 6% 5% 7% 22%	1980
	21st to end	Day	15% 11% 5% 9% 7% 4 7% 6% 7% 7% 22%	2209
April	1st to 10th	Day	16% 9% 4 7% 7% 4 6% 7% 6% 9% 24%	2160
	11th to 20th	Day	13% 10% 4 8% 6% 4 6% 7% 7% 8% 28%	2230
	21st to end	Day	13% 8% 4 6% 6% 4 5% 6% 7% 9% 32%	2344
May	1st to 10th	Day	11% 5% 3 6% 7% 5% 6% 5% 6% 8% 39%	2520
	11th to 20th	Day	10% 6% 3 6% 5% 4 6% 7% 6% 10% 38%	2477
	21st to end	Day	12% 7% 3 6% 5% 3 6% 5% 5% 8% 40%	2750
June	1st to 10th	Day	12% 6% 3 6% 6% 4 5% 5% 6% 9% 38%	2700
	11th to 20th	Day	8% 5% 3 6% 6% 3 6% 6% 6% 10% 41%	2700
	21st to end	Day	8% 5% 2 5% 5% 3 5% 5% 6% 8% 49%	2700
July	1st to 10th	Day	6% 4 2 4 4 2 4 4 4 8% 58%	2700
	11th to 20th	Day	5% 3 1 4 3 2 4 4 6% 7% 61%	2700
	21st to end	Day	4 2 1 2 2 1 2 4 4 8% 72%	2776
August	1st to 10th	Day	5% 3 1 3 3 2 2 3 4 8% 66%	2426
	11th to 20th	Day	4 3 1 3 3 2 3 5% 5% 7% 62%	2298
	21st to end	Day	6% 3 2 4 4 3 4 5% 6% 10% 52%	2525
September	1st to 10th	Day	7% 4 2 5% 4 3 4 4 6% 9% 53%	2160
	11th to 20th	Day	10% 8% 3 5% 4 3 6% 5% 5% 8% 45%	2127
	21st to end	Day	14% 6% 2 5% 5% 3 5% 5% 5% 8% 42%	1915
October	1st to 10th	Day	16% 7% 3 5% 7% 3 6% 5% 6% 7% 36%	1800
	11th to 20th	Day	19% 9% 4 8% 7% 5% 5% 6% 6% 7% 25%	1800
	21st to end	Day	21% 11% 3 7% 6% 3 5% 5% 6% 8% 26%	1870
November	1st to 10th	Day	25% 12% 5% 10% 7% 4 5% 4 5% 6% 17%	1488
	11th to 20th	Day	21% 13% 4 9% 8% 4 6% 4 3 5% 24%	1520
	21st to end	Day	23% 11% 5% 9% 7% 5% 6% 5% 4 5% 19%	1520
December	1st to 10th	Day	20% 12% 5% 8% 8% 4 6% 4 5% 6% 23%	1520
	11th to 20th	Day	23% 13% 5% 11% 7% 5% 6% 5% 5% 6% 13%	1695
	21st to end	Day	21% 16% 6% 11% 8% 3 6% 5% 4 5% 13%	2442
January	1st to 10th	Night	26% 12% 4 10% 7% 4 6% 5% 5% 6% 15%	2836
	11th to 20th	Night	23% 12% 5% 9% 7% 4 6% 5% 5% 6% 19%	2789
	21st to end	Night	22% 12% 5% 8% 7% 4 5% 5% 6% 7% 20%	2691
February	1st to 10th	Night	24% 11% 4 8% 7% 4 6% 6% 4 6% 21%	2340
	11th to 20th	Night	18% 11% 4 8% 7% 4 5% 5% 4 7% 27%	2272
	21st to end	Night	21% 11% 5% 7% 6% 3 6% 5% 6% 7% 23%	1920
March	1st to 10th	Night	16% 10% 3 7% 7% 4 7% 6% 7% 7% 26%	2064
	11th to 20th	Night	17% 11% 4 7% 7% 4 5% 6% 7% 7% 24%	1979
	21st to end	Night	16% 12% 4 9% 8% 4 6% 5% 6% 7% 23%	2147
April	1st to 10th	Night	17% 9% 4 7% 6% 4 6% 5% 6% 7% 28%	1800
	11th to 20th	Night	14% 8% 3 7% 6% 4 5% 6% 8% 8% 31%	1678
	21st to end	Night	15% 9% 3 8% 5% 3 5% 5% 5% 9% 33%	1615
May	1st to 10th	Night	9% 7% 2 5% 5% 4 6% 6% 6% 8% 42%	1440
	11th to 20th	Night	9% 5% 4 6% 5% 3 6% 7% 7% 10% 38%	1416
	21st to end	Night	10% 6% 3 5% 6% 3 5% 5% 7% 11% 39%	1521
June	1st to 10th	Night	12% 6% 4 6% 7% 3 5% 5% 6% 6% 41%	1260
	11th to 20th	Night	10% 6% 2 5% 4 3 5% 7% 8% 11% 40%	1260
	21st to end	Night	6% 3 2 3 4 2 4 5% 6% 11% 53%	1260
July	1st to 10th	Night	5% 3 1 4 4 2 3 6% 4 10% 57%	1260
	11th to 20th	Night	3 2 1 3 3 2 4 4 4 10% 61%	1260
	21st to end	Night	2 1 1 2 2 1 3 3 4 10% 72%	1539
August	1st to 10th	Night	3 2 1 3 3 2 3 3 6% 7% 66%	1511
	11th to 20th	Night	3 2 1 2 2 2 3 3 4 8% 70%	1602
	21st to end	Night	7% 3 2 3 3 2 4 5% 8% 11% 53%	1830
September	1st to 10th	Night	6% 3 2 4 3 2 3 4 5% 9% 60%	1800
	11th to 20th	Night	10% 7% 3 5% 5% 2 4 4 6% 7% 47%	1831
	21st to end	Night	11% 6% 3 5% 5% 3 4 4 5% 8% 45%	2044
October	1st to 10th	Night	13% 7% 3 6% 7% 3 4 4 5% 6% 41%	2160
	11th to 20th	Night	18% 8% 3 6% 7% 4 4 4 5% 7% 33%	2160
	21st to end	Night	22% 9% 3 6% 5% 3 5% 4 5% 6% 33%	2484
November	1st to 10th	Night	24% 11% 4 7% 7% 4 6% 5% 5% 6% 22%	2590
	11th to 20th	Night	23% 10% 4 9% 6% 4 5% 5% 6% 6% 23%	2660
	21st to end	Night	21% 11% 5% 10% 7% 4 6% 5% 5% 5% 20%	2660
December	1st to 10th	Night	22% 11% 4 8% 7% 4 6% 5% 5% 6% 23%	2660
	11th to 20th	Night	23% 14% 6% 9% 8% 4 6% 6% 4 5% 14%	3505
	21st to end	Night	24% 14% 5% 9% 7% 4 5% 5% 5% 6% 16%	5214

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	48% 39% 5% 6% 1	1329
	11th to 20th	Day	43% 40% 9% 6% 2	1297
	21st to end	Day	47% 36% 8% 7% 1	1660
February	1st to 10th	Day	44% 38% 9% 6% 2	1620
	11th to 20th	Day	40% 37% 10% 10% 4	1584
	21st to end	Day	44% 36% 9% 9% 3	1336
March	1st to 10th	Day	39% 36% 10% 11% 3 1	1894
	11th to 20th	Day	42% 35% 10% 10% 3	1980
	21st to end	Day	40% 36% 12% 10% 2	2209
April	1st to 10th	Day	37% 37% 14% 10% 2	2160
	11th to 20th	Day	32% 36% 10% 15% 7% 1	2230
	21st to end	Day	33% 36% 12% 14% 4	2344
May	1st to 10th	Day	30% 37% 13% 15% 5%	2520
	11th to 20th	Day	27% 37% 14% 17% 5%	2480
	21st to end	Day	33% 36% 15% 13% 3	2751
June	1st to 10th	Day	30% 36% 15% 14% 4 1	2700
	11th to 20th	Day	28% 36% 19% 14% 2	2700
	21st to end	Day	22% 36% 19% 14% 7% 1	2700
July	1st to 10th	Day	16% 38% 15% 21% 8% 2	2626
	11th to 20th	Day	16% 36% 14% 24% 9%	2619
	21st to end	Day	9% 35% 15% 26% 11% 3	2622
August	1st to 10th	Day	14% 36% 19% 24% 7%	2409
	11th to 20th	Day	17% 34% 17% 21% 9% 2	2298
	21st to end	Day	17% 37% 17% 24% 5% 1	2525
September	1st to 10th	Day	17% 35% 16% 20% 10% 2	2160
	11th to 20th	Day	24% 36% 13% 17% 9% 1	2127
	21st to end	Day	30% 36% 11% 16% 7% 1	1915
October	1st to 10th	Day	31% 35% 12% 16% 5%	1800
	11th to 20th	Day	40% 36% 13% 8% 3	1800
	21st to end	Day	38% 37% 10% 10% 5%	1870
November	1st to 10th	Day	44% 39% 7% 7% 2 1	1488
	11th to 20th	Day	44% 38% 8% 7% 3	1520
	21st to end	Day	47% 39% 5% 8% 1	1520
December	1st to 10th	Day	41% 39% 9% 9% 3	1520
	11th to 20th	Day	52% 31% 11% 5% 1	1698
	21st to end	Day	59% 24% 8% 6% 3	2442
January	1st to 10th	Night	47% 39% 8% 6% 1	2836
	11th to 20th	Night	42% 41% 7% 8% 2 1	2789
	21st to end	Night	42% 37% 7% 11% 2 1	2691
February	1st to 10th	Night	42% 37% 11% 8% 2	2340
	11th to 20th	Night	35% 37% 11% 12% 5%	2274
	21st to end	Night	42% 35% 8% 11% 3 1	1920
March	1st to 10th	Night	38% 36% 11% 13% 3	2064
	11th to 20th	Night	39% 36% 12% 10% 2 1	1980
	21st to end	Night	40% 36% 12% 11% 1	2147
April	1st to 10th	Night	36% 36% 13% 11% 4	1800
	11th to 20th	Night	29% 36% 12% 17% 4 2	1678
	21st to end	Night	35% 36% 11% 13% 5%	1615
May	1st to 10th	Night	27% 37% 15% 15% 7%	1440
	11th to 20th	Night	26% 37% 16% 15% 6% 1	1416
	21st to end	Night	31% 37% 17% 12% 3	1521
June	1st to 10th	Night	31% 36% 13% 14% 5% 1	1260
	11th to 20th	Night	26% 37% 21% 14% 2	1260
	21st to end	Night	18% 36% 21% 15% 7% 3	1260
July	1st to 10th	Night	15% 37% 16% 21% 8% 3	1225
	11th to 20th	Night	13% 37% 15% 25% 10% 1	1218
	21st to end	Night	6% 37% 11% 27% 14% 4	1454
August	1st to 10th	Night	14% 36% 17% 24% 8% 2	1503
	11th to 20th	Night	10% 35% 17% 22% 12% 4	1602
	21st to end	Night	17% 36% 14% 25% 8% 1	1830
September	1st to 10th	Night	13% 35% 13% 24% 11% 4	1800
	11th to 20th	Night	22% 36% 12% 15% 11% 4	1831
	21st to end	Night	26% 36% 12% 16% 9% 1	2044
October	1st to 10th	Night	30% 34% 11% 15% 9%	2160
	11th to 20th	Night	32% 35% 14% 14% 4	2160
	21st to end	Night	35% 36% 9% 15% 5%	2484
November	1st to 10th	Night	41% 40% 6% 9% 3	2590
	11th to 20th	Night	40% 40% 10% 8% 2	2660
	21st to end	Night	42% 40% 9% 8% 2	2660
December	1st to 10th	Night	40% 39% 10% 8% 2	2660
	11th to 20th	Night	52% 32% 11% 3 1	3501
	21st to end	Night	56% 24% 10% 8% 2	5214

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	33% 8% 22% 25% 12% 1	180
	11th to 20th	Day	25% 11% 20% 26% 17% 1	171
	21st to end	Day	28% 8% 17% 27% 17% 3	252
February	1st to 10th	Day	29% 14% 20% 24% 13%	340
	11th to 20th	Day	27% 11% 16% 31% 15% 1	335
	21st to end	Day	20% 16% 20% 28% 15% 1	282
March	1st to 10th	Day	20% 10% 18% 29% 19% 4	420
	11th to 20th	Day	20% 10% 18% 28% 19% 5%	420
	21st to end	Day	18% 9% 21% 31% 19% 3	462
April	1st to 10th	Day	18% 12% 20% 25% 20% 5%	420
	11th to 20th	Day	17% 8% 16% 32% 20% 8%	412
	21st to end	Day	17% 8% 22% 27% 23% 4	420
May	1st to 10th	Day	12% 7% 15% 31% 30% 5%	423
	11th to 20th	Day	14% 4 13% 29% 33% 7%	448
	21st to end	Day	12% 4 20% 31% 26% 8%	512
June	1st to 10th	Day	15% 5% 22% 33% 21% 5%	630
	11th to 20th	Day	9% 7% 29% 35% 16% 4	630
	21st to end	Day	7% 4 22% 32% 24% 11%	630
July	1st to 10th	Day	8% 2 16% 34% 30% 9%	621
	11th to 20th	Day	4 4 21% 32% 30% 9%	618
	21st to end	Day	2 2 15% 31% 31% 19%	522
August	1st to 10th	Day	6% 2 11% 24% 38% 19%	447
	11th to 20th	Day	2 1 9% 25% 44% 19%	437
	21st to end	Day	7% 3 13% 31% 33% 13%	495
September	1st to 10th	Day	10% 2 9% 34% 37% 8%	450
	11th to 20th	Day	13% 3 10% 24% 36% 13%	450
	21st to end	Day	14% 4 14% 30% 30% 8%	450
October	1st to 10th	Day	18% 5% 12% 27% 27% 10%	450
	11th to 20th	Day	23% 8% 8% 30% 25% 6%	450
	21st to end	Day	22% 10% 19% 31% 15% 3	403
November	1st to 10th	Day	31% 8% 19% 26% 16%	180
	11th to 20th	Day	23% 8% 20% 22% 25% 2	180
	21st to end	Day	24% 12% 18% 27% 15% 4	180
December	1st to 10th	Day	24% 9% 13% 34% 17% 2	180
	11th to 20th	Day	31% 8% 20% 27% 14% 1	180
	21st to end	Day	34% 7% 21% 30% 8% 1	198
January	1st to 10th	Night	29% 12% 19% 25% 13% 1	850
	11th to 20th	Night	27% 11% 14% 27% 20% 2	829
	21st to end	Night	25% 8% 15% 29% 20% 4	792
February	1st to 10th	Night	26% 13% 17% 28% 14% 3	720
	11th to 20th	Night	23% 9% 18% 29% 18% 4	704
	21st to end	Night	26% 11% 18% 24% 17% 4	592
March	1st to 10th	Night	17% 12% 16% 31% 18% 6%	720
	11th to 20th	Night	20% 9% 23% 25% 19% 4	720
	21st to end	Night	18% 9% 20% 31% 18% 5%	792
April	1st to 10th	Night	21% 7% 20% 27% 21% 3	720
	11th to 20th	Night	16% 9% 22% 30% 19% 5%	610
	21st to end	Night	15% 8% 26% 32% 15% 4	535
May	1st to 10th	Night	11% 5% 24% 33% 25% 3	360
	11th to 20th	Night	11% 5% 18% 34% 27% 6%	354
	21st to end	Night	12% 4 22% 35% 26% 2	389
June	1st to 10th	Night	14% 4 24% 34% 21% 3	360
	11th to 20th	Night	11% 3 30% 37% 16% 3	360
	21st to end	Night	7% 3 27% 30% 26% 7%	360
July	1st to 10th	Night	7% 2 19% 39% 29% 4	350
	11th to 20th	Night	4 2 21% 42% 28% 3	348
	21st to end	Night	3 1 22% 36% 32% 7%	394
August	1st to 10th	Night	4 3 12% 34% 39% 9%	437
	11th to 20th	Night	4 1 7% 35% 38% 16%	534
	21st to end	Night	7% 3 18% 32% 31% 8%	642
September	1st to 10th	Night	8% 2 13% 33% 32% 12%	720
	11th to 20th	Night	13% 2 9% 27% 31% 18%	720
	21st to end	Night	13% 2 14% 31% 28% 11%	720
October	1st to 10th	Night	16% 4 10% 28% 29% 13%	720
	11th to 20th	Night	19% 6% 11% 29% 23% 12%	720
	21st to end	Night	25% 7% 14% 29% 20% 5%	792
November	1st to 10th	Night	28% 7% 18% 28% 17% 2	740
	11th to 20th	Night	23% 12% 20% 25% 17% 4	760
	21st to end	Night	25% 9% 20% 25% 16% 5%	760
December	1st to 10th	Night	24% 9% 17% 28% 19% 3	760
	11th to 20th	Night	27% 11% 19% 30% 12% 1	843
	21st to end	Night	28% 12% 24% 26% 9% 1	935

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