Ivanhoe Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ivanhoe Observatory clear sky chart from 2005-11-06 to 2025-12-18.

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	17% 10% 3 8% 5% 4 4 3 5% 7% 34%	127564
	Night	17% 10% 3 8% 5% 4 4 4 5% 6% 33%	123462
Transparency	Day	48% 6% 12% 21% 11% 1	131106
	Night	49% 6% 12% 20% 11% 1	128007
Seeing	Day	23% 16% 31% 18% 8% 3	15832
	Night	22% 14% 30% 24% 9% 1	25103

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	13% 13% 4 9% 5% 4 4 4 5% 6% 32%	3597
	11th to 20th	Day	11% 20% 8% 14% 6% 6% 5% 3 4 4 21%	3570
	21st to end	Day	15% 16% 7% 15% 6% 5% 4 3 4 4 21%	4443
February	1st to 10th	Day	14% 15% 5% 12% 6% 4 5% 4 5% 6% 23%	1800
	11th to 20th	Day	13% 15% 6% 11% 7% 5% 4 3 4 4 28%	1753
	21st to end	Day	18% 15% 4 10% 6% 5% 5% 3 4 4 25%	1591
March	1st to 10th	Day	20% 12% 4 9% 5% 4 3 3 4 6% 30%	4739
	11th to 20th	Day	12% 13% 4 9% 5% 5% 5% 4 6% 6% 32%	4980
	21st to end	Day	20% 11% 3 6% 4 3 3 2 4 5% 39%	5597
April	1st to 10th	Day	21% 13% 3 7% 4 4 4 3 4 6% 32%	2400
	11th to 20th	Day	22% 9% 2 6% 3 4 4 3 4 6% 37%	2374
	21st to end	Day	22% 10% 3 7% 5% 4 4 3 4 5% 33%	2564
May	1st to 10th	Day	23% 9% 3 7% 5% 4 4 3 5% 6% 30%	6204
	11th to 20th	Day	19% 8% 3 8% 5% 4 4 3 5% 6% 35%	6318
	21st to end	Day	20% 6% 3 7% 4 4 4 4 5% 7% 36%	6949
June	1st to 10th	Day	18% 7% 3 7% 6% 5% 6% 4 6% 7% 32%	2800
	11th to 20th	Day	14% 6% 3 5% 5% 5% 5% 4 7% 8% 39%	2800
	21st to end	Day	18% 7% 3 7% 4 4 4 4 6% 8% 36%	2800
July	1st to 10th	Day	12% 6% 2 6% 5% 5% 5% 4 6% 9% 39%	6360
	11th to 20th	Day	10% 5% 2 5% 4 5% 5% 4 6% 8% 46%	6360
	21st to end	Day	8% 4 2 6% 4 5% 5% 4 7% 9% 46%	6926
August	1st to 10th	Day	16% 8% 3 6% 4 4 4 4 6% 8% 37%	4234
	11th to 20th	Day	17% 6% 2 6% 5% 4 4 3 6% 9% 36%	4174
	21st to end	Day	12% 5% 2 7% 4 4 5% 5% 6% 9% 40%	4355
September	1st to 10th	Day	13% 5% 2 6% 5% 5% 4 4 5% 7% 44%	2400
	11th to 20th	Day	10% 5% 2 5% 3 4 4 3 5% 7% 51%	2400
	21st to end	Day	17% 7% 2 6% 4 4 4 4 5% 7% 40%	2095
October	1st to 10th	Day	20% 8% 3 7% 4 3 5% 3 4 7% 36%	2000
	11th to 20th	Day	21% 8% 3 8% 5% 4 4 4 6% 6% 31%	2000
	21st to end	Day	26% 10% 3 6% 4 6% 4 3 4 6% 27%	2146
November	1st to 10th	Day	16% 8% 3 8% 5% 4 5% 4 6% 6% 35%	1793
	11th to 20th	Day	17% 12% 3 9% 6% 4 4 4 5% 6% 31%	1680
	21st to end	Day	21% 15% 4 9% 5% 3 4 3 5% 6% 24%	1680
December	1st to 10th	Day	20% 18% 5% 10% 6% 5% 5% 3 4 5% 20%	2680
	11th to 20th	Day	16% 19% 5% 11% 5% 5% 3 2 3 4 26%	3042
	21st to end	Day	25% 15% 4 9% 5% 4 4 2 3 5% 25%	3960
January	1st to 10th	Night	16% 14% 6% 11% 6% 5% 5% 3 5% 5% 25%	6349
	11th to 20th	Night	12% 15% 6% 16% 8% 6% 5% 4 5% 5% 18%	6315
	21st to end	Night	15% 15% 7% 13% 5% 4 5% 4 4 5% 23%	6508
February	1st to 10th	Night	15% 14% 5% 10% 7% 5% 5% 4 5% 5% 26%	2600
	11th to 20th	Night	14% 15% 5% 10% 5% 5% 5% 3 5% 5% 28%	2533
	21st to end	Night	16% 11% 3 9% 6% 4 4 4 6% 6% 31%	2038
March	1st to 10th	Night	19% 12% 4 9% 5% 5% 4 3 4 5% 30%	5098
	11th to 20th	Night	13% 11% 3 8% 5% 5% 5% 4 6% 8% 32%	4979
	21st to end	Night	20% 9% 3 7% 4 4 3 3 4 6% 37%	5335
April	1st to 10th	Night	20% 10% 4 7% 5% 4 3 4 5% 6% 33%	2000
	11th to 20th	Night	19% 9% 3 7% 4 4 4 4 4 5% 37%	1975
	21st to end	Night	19% 8% 3 6% 5% 4 5% 5% 5% 7% 34%	1854
May	1st to 10th	Night	26% 8% 3 7% 4 4 4 3 5% 6% 29%	3737
	11th to 20th	Night	16% 7% 2 6% 3 3 4 4 5% 6% 42%	3575
	21st to end	Night	19% 7% 3 6% 5% 4 4 3 5% 6% 38%	3926
June	1st to 10th	Night	15% 6% 2 6% 5% 5% 5% 5% 6% 8% 38%	1600
	11th to 20th	Night	12% 6% 2 6% 5% 5% 4 3 6% 8% 43%	1600
	21st to end	Night	15% 6% 2 6% 4 5% 4 4 6% 7% 41%	1600
July	1st to 10th	Night	10% 5% 2 7% 5% 5% 5% 4 7% 8% 41%	3600
	11th to 20th	Night	12% 5% 2 6% 4 4 4 3 5% 6% 50%	3600
	21st to end	Night	10% 4 2 5% 4 4 4 3 6% 8% 51%	3926
August	1st to 10th	Night	12% 5% 2 6% 4 4 4 3 6% 7% 46%	2912
	11th to 20th	Night	14% 6% 2 5% 3 4 4 4 5% 7% 46%	2875
	21st to end	Night	9% 4 2 6% 4 4 4 4 7% 9% 47%	3510
September	1st to 10th	Night	11% 6% 2 5% 4 4 4 4 6% 7% 47%	2000
	11th to 20th	Night	12% 3 1 4 3 4 5% 4 5% 6% 54%	2000
	21st to end	Night	18% 6% 2 6% 4 4 4 4 5% 5% 42%	2302
October	1st to 10th	Night	17% 7% 2 6% 4 4 4 3 5% 6% 41%	2400
	11th to 20th	Night	21% 8% 2 8% 5% 5% 4 4 4 6% 32%	2400
	21st to end	Night	22% 10% 2 7% 4 4 5% 4 6% 5% 30%	2692
November	1st to 10th	Night	19% 9% 3 5% 5% 4 4 4 5% 6% 37%	2720
	11th to 20th	Night	18% 10% 4 7% 5% 5% 5% 3 5% 6% 31%	2940
	21st to end	Night	21% 13% 3 8% 5% 4 4 4 6% 6% 26%	2940
December	1st to 10th	Night	19% 16% 4 9% 6% 5% 5% 5% 6% 7% 20%	4720
	11th to 20th	Night	19% 16% 5% 10% 5% 3 4 3 5% 5% 24%	5307
	21st to end	Night	26% 17% 3 10% 4 4 3 3 4 4 21%	6996

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	51% 5% 13% 21% 9% 1	3598
	11th to 20th	Day	67% 4 10% 11% 7%	3600
	21st to end	Day	67% 4 8% 10% 9% 1	4443
February	1st to 10th	Day	61% 5% 11% 16% 6% 1	1800
	11th to 20th	Day	60% 4 9% 15% 10% 1	1762
	21st to end	Day	63% 5% 10% 12% 10% 1	1591
March	1st to 10th	Day	55% 5% 12% 13% 15% 1	4742
	11th to 20th	Day	50% 6% 18% 14% 10% 2	4980
	21st to end	Day	48% 4 7% 22% 16% 3	5597
April	1st to 10th	Day	55% 4 8% 19% 12% 3	2400
	11th to 20th	Day	48% 5% 8% 21% 16% 1	2374
	21st to end	Day	54% 4 8% 19% 14% 2	2564
May	1st to 10th	Day	55% 5% 9% 17% 11% 3	6214
	11th to 20th	Day	49% 6% 11% 17% 16% 1	6322
	21st to end	Day	47% 6% 13% 22% 11% 2	6949
June	1st to 10th	Day	48% 8% 12% 18% 13% 1	2800
	11th to 20th	Day	41% 7% 12% 26% 13% 2	2800
	21st to end	Day	44% 7% 14% 21% 12% 1	2800
July	1st to 10th	Day	39% 6% 15% 26% 13%	6290
	11th to 20th	Day	33% 7% 15% 29% 16%	6285
	21st to end	Day	33% 7% 14% 35% 11%	6728
August	1st to 10th	Day	43% 7% 16% 23% 11% 1	4221
	11th to 20th	Day	42% 6% 15% 27% 9% 1	4213
	21st to end	Day	37% 7% 14% 32% 10% 1	4355
September	1st to 10th	Day	37% 7% 14% 28% 12% 1	2400
	11th to 20th	Day	32% 5% 15% 32% 15% 1	2400
	21st to end	Day	43% 7% 13% 27% 10%	2095
October	1st to 10th	Day	40% 6% 13% 30% 11% 1	3260
	11th to 20th	Day	44% 5% 16% 24% 10% 1	3240
	21st to end	Day	51% 6% 13% 21% 8%	3448
November	1st to 10th	Day	48% 7% 15% 21% 9% 1	1793
	11th to 20th	Day	53% 6% 13% 17% 10% 1	1680
	21st to end	Day	60% 6% 12% 14% 7%	1680
December	1st to 10th	Day	65% 6% 16% 9% 4	2680
	11th to 20th	Day	63% 5% 10% 14% 8%	3042
	21st to end	Day	63% 5% 9% 16% 8%	3960
January	1st to 10th	Night	60% 5% 12% 15% 8%	6349
	11th to 20th	Night	66% 6% 13% 10% 5% 1	6360
	21st to end	Night	62% 6% 10% 10% 11% 1	6508
February	1st to 10th	Night	58% 6% 12% 18% 6% 1	2600
	11th to 20th	Night	56% 5% 10% 19% 9% 1	2535
	21st to end	Night	52% 5% 12% 21% 9% 1	2038
March	1st to 10th	Night	55% 5% 7% 17% 11% 5%	5108
	11th to 20th	Night	47% 6% 18% 19% 8% 2	4980
	21st to end	Night	46% 5% 9% 22% 16% 2	5335
April	1st to 10th	Night	52% 5% 8% 21% 13% 2	2000
	11th to 20th	Night	48% 5% 9% 20% 16% 1	1975
	21st to end	Night	47% 7% 10% 17% 15% 3	1854
May	1st to 10th	Night	56% 5% 9% 15% 11% 4	3743
	11th to 20th	Night	41% 6% 14% 22% 15% 2	3576
	21st to end	Night	45% 6% 13% 19% 15% 2	3927
June	1st to 10th	Night	43% 6% 14% 22% 14% 1	1600
	11th to 20th	Night	38% 6% 13% 22% 19% 2	1600
	21st to end	Night	41% 7% 14% 23% 14% 2	1600
July	1st to 10th	Night	38% 7% 15% 21% 17% 1	3560
	11th to 20th	Night	34% 6% 13% 32% 15% 1	3552
	21st to end	Night	30% 7% 15% 34% 13% 1	3809
August	1st to 10th	Night	36% 5% 14% 28% 14% 1	2902
	11th to 20th	Night	36% 6% 17% 28% 12% 1	2902
	21st to end	Night	31% 7% 14% 35% 11% 1	3510
September	1st to 10th	Night	35% 7% 15% 29% 14% 1	2000
	11th to 20th	Night	30% 6% 15% 32% 16% 1	2000
	21st to end	Night	42% 7% 12% 26% 13% 1	2302
October	1st to 10th	Night	35% 5% 11% 28% 19% 1	3920
	11th to 20th	Night	43% 6% 14% 28% 9%	3899
	21st to end	Night	46% 6% 13% 25% 9%	4340
November	1st to 10th	Night	46% 6% 13% 23% 11% 1	2720
	11th to 20th	Night	50% 6% 12% 21% 9% 2	2940
	21st to end	Night	56% 8% 15% 16% 5%	2940
December	1st to 10th	Night	60% 7% 14% 15% 4	4720
	11th to 20th	Night	61% 6% 11% 13% 8%	5307
	21st to end	Night	65% 6% 9% 11% 9%	6996

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	24% 25% 33% 16% 3 1	200
	11th to 20th	Day	29% 19% 34% 16% 2 1	200
	21st to end	Day	26% 25% 33% 12% 3 1	325
February	1st to 10th	Day	31% 27% 30% 10% 2	300
	11th to 20th	Day	31% 27% 35% 6% 1	300
	21st to end	Day	36% 20% 35% 7% 2	355
March	1st to 10th	Day	28% 18% 35% 15% 4	500
	11th to 20th	Day	28% 23% 31% 14% 4	500
	21st to end	Day	34% 18% 29% 13% 5% 1	550
April	1st to 10th	Day	33% 20% 32% 10% 5%	500
	11th to 20th	Day	31% 24% 22% 14% 7% 3	492
	21st to end	Day	32% 20% 31% 11% 5% 2	500
May	1st to 10th	Day	24% 18% 31% 16% 7% 4	503
	11th to 20th	Day	19% 16% 35% 20% 8% 2	527
	21st to end	Day	18% 14% 35% 19% 11% 3	573
June	1st to 10th	Day	21% 15% 35% 21% 7% 2	530
	11th to 20th	Day	14% 15% 35% 22% 12% 2	530
	21st to end	Day	23% 14% 31% 20% 10% 2	530
July	1st to 10th	Day	12% 10% 32% 29% 14% 3	525
	11th to 20th	Day	15% 10% 31% 26% 15% 4	524
	21st to end	Day	11% 10% 38% 27% 11% 4	576
August	1st to 10th	Day	13% 9% 29% 29% 15% 6%	526
	11th to 20th	Day	13% 8% 31% 26% 16% 6%	519
	21st to end	Day	14% 12% 31% 24% 12% 7%	583
September	1st to 10th	Day	14% 12% 30% 25% 11% 8%	530
	11th to 20th	Day	10% 8% 26% 24% 19% 12%	530
	21st to end	Day	20% 12% 29% 23% 12% 5%	530
October	1st to 10th	Day	22% 18% 25% 17% 13% 5%	530
	11th to 20th	Day	24% 19% 33% 15% 6% 2	530
	21st to end	Day	29% 17% 30% 20% 3	553
November	1st to 10th	Day	30% 17% 27% 18% 8% 1	367
	11th to 20th	Day	30% 21% 31% 12% 5% 1	220
	21st to end	Day	30% 24% 29% 14% 3 1	220
December	1st to 10th	Day	31% 17% 36% 13% 3	220
	11th to 20th	Day	37% 21% 28% 11% 2 1	214
	21st to end	Day	37% 17% 32% 10% 4	220
January	1st to 10th	Night	27% 21% 30% 18% 4	800
	11th to 20th	Night	28% 18% 31% 19% 5%	800
	21st to end	Night	21% 18% 34% 23% 4 1	880
February	1st to 10th	Night	22% 23% 35% 18% 2	800
	11th to 20th	Night	24% 20% 36% 16% 4	783
	21st to end	Night	25% 19% 34% 18% 3	660
March	1st to 10th	Night	23% 18% 35% 21% 3	800
	11th to 20th	Night	25% 19% 31% 19% 4 1	800
	21st to end	Night	22% 18% 32% 21% 6% 1	880
April	1st to 10th	Night	26% 17% 33% 21% 4	800
	11th to 20th	Night	24% 20% 28% 20% 7% 1	791
	21st to end	Night	23% 12% 31% 24% 9%	654
May	1st to 10th	Night	24% 10% 27% 27% 11% 2	465
	11th to 20th	Night	16% 9% 35% 31% 9%	394
	21st to end	Night	14% 8% 36% 30% 12% 1	433
June	1st to 10th	Night	17% 7% 34% 31% 11%	400
	11th to 20th	Night	13% 10% 34% 30% 12% 1	400
	21st to end	Night	17% 8% 28% 35% 12% 1	400
July	1st to 10th	Night	6% 7% 34% 37% 15% 1	390
	11th to 20th	Night	11% 3 30% 37% 19% 1	388
	21st to end	Night	11% 3 30% 40% 15% 1	438
August	1st to 10th	Night	11% 3 24% 36% 24% 2	594
	11th to 20th	Night	11% 5% 22% 36% 24% 2	594
	21st to end	Night	11% 6% 29% 35% 18% 2	830
September	1st to 10th	Night	13% 6% 31% 29% 18% 3	800
	11th to 20th	Night	12% 5% 24% 27% 27% 4	800
	21st to end	Night	19% 10% 23% 29% 17% 3	800
October	1st to 10th	Night	19% 12% 27% 24% 16% 2	800
	11th to 20th	Night	24% 14% 31% 23% 8% 1	800
	21st to end	Night	26% 15% 31% 22% 5%	880
November	1st to 10th	Night	26% 14% 26% 26% 8% 1	820
	11th to 20th	Night	24% 17% 33% 19% 6% 1	840
	21st to end	Night	29% 18% 27% 20% 5%	840
December	1st to 10th	Night	30% 19% 28% 20% 3	840
	11th to 20th	Night	27% 19% 35% 17% 3	829
	21st to end	Night	34% 15% 33% 16% 3	880

Page generated at 2025-12-15 01:13:49. Version ac07

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