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 2024-11-11.

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% 9% 3 7% 5% 4 4 3 5% 7% 34%	101613
	Night	17% 10% 3 8% 5% 4 4 4 5% 6% 34%	97562
Transparency	Day	48% 6% 13% 22% 11% 1	105173
	Night	48% 6% 13% 21% 11% 1	102091
Seeing	Day	23% 16% 31% 19% 9% 3	14489
	Night	22% 14% 30% 24% 9% 1	23708

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	16% 17% 4 9% 5% 4 3 3 4 5% 30%	2517
	11th to 20th	Day	13% 18% 6% 12% 7% 5% 5% 3 4 4 22%	2520
	21st to end	Day	20% 19% 7% 12% 5% 5% 4 3 3 3 19%	3101
February	1st to 10th	Day	14% 15% 5% 12% 6% 4 5% 4 5% 6% 23%	1710
	11th to 20th	Day	13% 15% 6% 11% 6% 5% 4 3 4 4 29%	1663
	21st to end	Day	18% 15% 4 10% 6% 5% 5% 3 4 4 25%	1513
March	1st to 10th	Day	22% 12% 4 7% 5% 4 3 3 4 6% 30%	3295
	11th to 20th	Day	11% 17% 4 9% 5% 4 4 3 5% 6% 31%	3480
	21st to end	Day	15% 9% 2 6% 4 3 3 3 5% 6% 45%	3905
April	1st to 10th	Day	21% 13% 3 6% 4 4 4 3 4 6% 31%	2280
	11th to 20th	Day	23% 9% 2 6% 3 4 4 2 4 6% 38%	2254
	21st to end	Day	22% 10% 3 7% 5% 4 4 3 4 5% 33%	2436
May	1st to 10th	Day	20% 8% 2 7% 5% 4 5% 3 5% 6% 34%	4326
	11th to 20th	Day	17% 9% 3 8% 5% 4 4 4 6% 8% 33%	4398
	21st to end	Day	14% 5% 2 7% 5% 4 4 3 6% 8% 43%	4837
June	1st to 10th	Day	18% 7% 3 7% 6% 5% 6% 4 6% 7% 31%	2660
	11th to 20th	Day	14% 6% 3 5% 5% 5% 5% 4 7% 8% 38%	2660
	21st to end	Day	18% 7% 3 7% 4 5% 4 4 6% 7% 35%	2660
July	1st to 10th	Day	12% 5% 2 6% 5% 5% 6% 4 7% 10% 38%	4440
	11th to 20th	Day	12% 5% 2 5% 4 4 5% 4 6% 9% 44%	4440
	21st to end	Day	8% 5% 2 7% 5% 6% 5% 5% 7% 9% 42%	4814
August	1st to 10th	Day	17% 8% 3 6% 4 4 5% 4 7% 8% 36%	4104
	11th to 20th	Day	17% 6% 2 6% 5% 4 4 3 6% 9% 36%	4044
	21st to end	Day	12% 5% 2 7% 4 4 5% 5% 6% 9% 40%	4222
September	1st to 10th	Day	14% 5% 2 5% 5% 5% 4 4 5% 7% 43%	2280
	11th to 20th	Day	11% 5% 2 5% 4 4 4 3 5% 7% 50%	2280
	21st to end	Day	17% 7% 2 6% 4 4 4 4 5% 8% 40%	1991
October	1st to 10th	Day	20% 8% 3 7% 4 3 5% 3 4 7% 34%	1900
	11th to 20th	Day	22% 7% 3 8% 5% 4 4 4 6% 6% 31%	1900
	21st to end	Day	26% 10% 3 7% 4 6% 4 3 4 6% 27%	2039
November	1st to 10th	Day	15% 8% 3 8% 6% 5% 5% 4 6% 6% 35%	1706
	11th to 20th	Day	18% 11% 3 9% 5% 4 4 4 5% 6% 30%	1520
	21st to end	Day	22% 14% 4 9% 5% 3 4 3 5% 6% 24%	1520
December	1st to 10th	Day	20% 17% 5% 9% 6% 5% 5% 3 4 5% 21%	1520
	11th to 20th	Day	19% 16% 5% 9% 5% 5% 3 3 4 5% 28%	1906
	21st to end	Day	29% 16% 4 10% 5% 3 4 2 3 4 20%	2772
January	1st to 10th	Night	19% 15% 6% 10% 5% 5% 4 3 5% 5% 22%	4429
	11th to 20th	Night	15% 14% 5% 13% 7% 6% 5% 4 5% 5% 21%	4440
	21st to end	Night	19% 15% 7% 10% 5% 5% 5% 3 4 5% 21%	4550
February	1st to 10th	Night	15% 14% 5% 10% 7% 5% 5% 4 5% 5% 26%	2470
	11th to 20th	Night	13% 15% 4 9% 5% 5% 5% 3 5% 5% 28%	2403
	21st to end	Night	16% 11% 4 8% 6% 4 4 4 6% 6% 31%	1940
March	1st to 10th	Night	19% 11% 4 8% 5% 5% 4 3 4 5% 31%	3542
	11th to 20th	Night	17% 15% 4 9% 5% 4 4 3 5% 6% 28%	3479
	21st to end	Night	17% 9% 3 6% 4 3 3 3 4 6% 42%	3727
April	1st to 10th	Night	20% 10% 3 7% 5% 4 3 4 5% 6% 34%	1900
	11th to 20th	Night	18% 9% 3 7% 4 4 4 4 4 5% 38%	1875
	21st to end	Night	19% 8% 3 6% 5% 4 5% 5% 5% 7% 34%	1762
May	1st to 10th	Night	21% 8% 3 6% 5% 4 4 3 5% 6% 35%	2615
	11th to 20th	Night	19% 8% 3 6% 4 3 4 4 6% 6% 37%	2495
	21st to end	Night	12% 6% 2 6% 4 4 4 3 5% 6% 46%	2738
June	1st to 10th	Night	15% 6% 2 6% 5% 5% 5% 5% 6% 8% 37%	1520
	11th to 20th	Night	12% 6% 2 5% 5% 5% 4 3 6% 8% 44%	1520
	21st to end	Night	15% 6% 2 6% 4 5% 4 4 6% 7% 41%	1520
July	1st to 10th	Night	9% 5% 2 7% 5% 6% 5% 4 7% 7% 43%	2520
	11th to 20th	Night	14% 5% 2 5% 3 4 4 3 5% 7% 48%	2520
	21st to end	Night	11% 4 2 5% 3 4 4 3 6% 8% 50%	2739
August	1st to 10th	Night	12% 5% 2 6% 4 4 4 3 6% 7% 46%	2822
	11th to 20th	Night	14% 6% 2 5% 3 5% 4 4 6% 7% 46%	2785
	21st to end	Night	9% 4 2 6% 4 4 4 4 7% 9% 47%	3402
September	1st to 10th	Night	12% 6% 2 5% 4 4 4 4 6% 7% 47%	1900
	11th to 20th	Night	13% 3 1 4 3 4 4 4 5% 6% 53%	1900
	21st to end	Night	18% 6% 2 6% 4 4 4 4 5% 5% 42%	2186
October	1st to 10th	Night	18% 7% 2 7% 5% 5% 4 3 5% 6% 39%	2280
	11th to 20th	Night	22% 8% 2 8% 5% 5% 4 3 4 6% 32%	2280
	21st to end	Night	23% 10% 2 8% 4 4 5% 4 6% 5% 29%	2557
November	1st to 10th	Night	19% 8% 3 5% 5% 4 4 4 5% 6% 38%	2587
	11th to 20th	Night	19% 10% 4 6% 5% 5% 5% 3 5% 7% 31%	2667
	21st to end	Night	21% 12% 3 8% 5% 4 4 4 6% 6% 27%	2660
December	1st to 10th	Night	21% 15% 4 9% 5% 4 4 5% 6% 7% 19%	2660
	11th to 20th	Night	19% 16% 4 9% 5% 4 4 3 4 4 28%	3288
	21st to end	Night	30% 17% 3 9% 5% 4 4 3 4 4 16%	4884

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	56% 5% 16% 14% 7% 2	2518
	11th to 20th	Day	66% 4 12% 10% 7%	2520
	21st to end	Day	71% 4 9% 10% 5% 1	3101
February	1st to 10th	Day	61% 5% 12% 16% 5% 1	1710
	11th to 20th	Day	60% 4 10% 15% 11% 1	1672
	21st to end	Day	62% 4 10% 12% 10% 1	1513
March	1st to 10th	Day	55% 5% 13% 16% 10% 1	3298
	11th to 20th	Day	52% 6% 15% 15% 10% 2	3480
	21st to end	Day	40% 5% 9% 27% 16% 4	3905
April	1st to 10th	Day	55% 4 8% 20% 11% 3	2280
	11th to 20th	Day	47% 5% 8% 22% 16% 1	2254
	21st to end	Day	54% 4 8% 18% 14% 2	2436
May	1st to 10th	Day	49% 6% 10% 21% 12% 2	4339
	11th to 20th	Day	48% 7% 14% 21% 9% 1	4402
	21st to end	Day	38% 6% 14% 24% 15% 3	4837
June	1st to 10th	Day	49% 8% 12% 18% 13% 1	2660
	11th to 20th	Day	41% 7% 12% 25% 14% 2	2660
	21st to end	Day	45% 7% 14% 21% 12% 1	2660
July	1st to 10th	Day	39% 7% 16% 25% 13% 1	4370
	11th to 20th	Day	34% 7% 16% 33% 10%	4365
	21st to end	Day	36% 8% 15% 29% 11%	4661
August	1st to 10th	Day	44% 7% 15% 22% 11% 1	4091
	11th to 20th	Day	42% 6% 16% 26% 9%	4083
	21st to end	Day	37% 7% 14% 31% 10% 1	4222
September	1st to 10th	Day	38% 7% 14% 28% 12% 1	2280
	11th to 20th	Day	33% 5% 15% 31% 15% 1	2280
	21st to end	Day	43% 7% 13% 27% 10%	1991
October	1st to 10th	Day	41% 6% 13% 30% 10% 1	3160
	11th to 20th	Day	44% 5% 16% 24% 10% 1	3140
	21st to end	Day	52% 6% 13% 21% 8%	3341
November	1st to 10th	Day	47% 7% 16% 21% 9% 1	1706
	11th to 20th	Day	53% 6% 13% 17% 10% 1	1520
	21st to end	Day	60% 7% 13% 13% 7%	1520
December	1st to 10th	Day	64% 6% 13% 11% 5%	1520
	11th to 20th	Day	60% 6% 14% 13% 7%	1906
	21st to end	Day	68% 4 8% 15% 5%	2772
January	1st to 10th	Night	63% 6% 14% 13% 5%	4429
	11th to 20th	Night	63% 6% 15% 11% 4 1	4440
	21st to end	Night	65% 6% 11% 12% 6%	4550
February	1st to 10th	Night	59% 6% 12% 18% 6%	2470
	11th to 20th	Night	56% 6% 10% 20% 9% 1	2405
	21st to end	Night	52% 5% 12% 20% 9% 1	1940
March	1st to 10th	Night	53% 6% 9% 21% 10% 1	3552
	11th to 20th	Night	54% 7% 14% 17% 8% 1	3480
	21st to end	Night	40% 6% 9% 25% 18% 2	3727
April	1st to 10th	Night	50% 5% 8% 21% 13% 2	1900
	11th to 20th	Night	48% 5% 9% 19% 17% 1	1875
	21st to end	Night	47% 7% 11% 17% 15% 3	1762
May	1st to 10th	Night	50% 5% 11% 18% 14% 2	2621
	11th to 20th	Night	44% 7% 13% 25% 9% 2	2496
	21st to end	Night	37% 7% 13% 21% 20% 2	2739
June	1st to 10th	Night	43% 6% 14% 22% 14% 1	1520
	11th to 20th	Night	37% 6% 13% 22% 20% 2	1520
	21st to end	Night	41% 7% 14% 23% 14% 2	1520
July	1st to 10th	Night	37% 8% 13% 23% 17% 2	2480
	11th to 20th	Night	35% 6% 13% 33% 13%	2472
	21st to end	Night	32% 7% 18% 30% 11% 1	2651
August	1st to 10th	Night	37% 5% 14% 28% 14% 1	2812
	11th to 20th	Night	36% 6% 17% 28% 11% 1	2812
	21st to end	Night	31% 8% 14% 35% 11% 1	3402
September	1st to 10th	Night	36% 7% 15% 27% 14% 1	1900
	11th to 20th	Night	31% 6% 16% 31% 16% 1	1900
	21st to end	Night	41% 7% 12% 27% 12% 1	2186
October	1st to 10th	Night	36% 5% 11% 28% 19% 1	3800
	11th to 20th	Night	43% 6% 15% 28% 8%	3779
	21st to end	Night	47% 6% 14% 25% 9%	4205
November	1st to 10th	Night	46% 6% 13% 23% 11% 1	2587
	11th to 20th	Night	50% 6% 13% 20% 9% 2	2667
	21st to end	Night	55% 8% 16% 16% 6%	2660
December	1st to 10th	Night	61% 7% 13% 15% 5%	2660
	11th to 20th	Night	59% 5% 12% 16% 7% 1	3288
	21st to end	Night	69% 6% 10% 11% 4	4884

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	26% 24% 29% 17% 3 1	180
	11th to 20th	Day	29% 20% 33% 15% 2 1	180
	21st to end	Day	27% 23% 33% 13% 4 1	292
February	1st to 10th	Day	31% 27% 30% 10% 2	270
	11th to 20th	Day	29% 27% 38% 6% 1	270
	21st to end	Day	37% 21% 33% 7% 2	325
March	1st to 10th	Day	27% 18% 36% 15% 4	460
	11th to 20th	Day	28% 22% 31% 15% 4	460
	21st to end	Day	33% 19% 28% 13% 6% 1	506
April	1st to 10th	Day	32% 19% 33% 10% 6%	460
	11th to 20th	Day	31% 23% 21% 15% 7% 3	452
	21st to end	Day	32% 20% 30% 11% 6% 2	460
May	1st to 10th	Day	25% 17% 30% 17% 7% 4	463
	11th to 20th	Day	19% 15% 35% 21% 8% 3	487
	21st to end	Day	16% 14% 37% 19% 11% 4	529
June	1st to 10th	Day	21% 14% 35% 21% 7% 2	490
	11th to 20th	Day	14% 15% 33% 22% 12% 2	490
	21st to end	Day	23% 14% 30% 20% 10% 2	490
July	1st to 10th	Day	12% 10% 30% 30% 15% 3	485
	11th to 20th	Day	15% 10% 30% 26% 15% 4	484
	21st to end	Day	11% 9% 37% 28% 11% 4	532
August	1st to 10th	Day	14% 9% 29% 27% 15% 6%	486
	11th to 20th	Day	12% 8% 31% 27% 16% 6%	479
	21st to end	Day	14% 12% 31% 24% 12% 7%	539
September	1st to 10th	Day	13% 12% 31% 24% 11% 8%	490
	11th to 20th	Day	11% 9% 26% 23% 18% 12%	490
	21st to end	Day	20% 12% 27% 23% 13% 5%	490
October	1st to 10th	Day	23% 19% 25% 17% 12% 5%	490
	11th to 20th	Day	24% 19% 32% 16% 7% 2	490
	21st to end	Day	30% 18% 29% 20% 3	512
November	1st to 10th	Day	28% 16% 27% 19% 8% 1	340
	11th to 20th	Day	32% 22% 28% 14% 3 1	180
	21st to end	Day	28% 21% 32% 14% 3 1	180
December	1st to 10th	Day	31% 18% 34% 14% 3	180
	11th to 20th	Day	37% 22% 27% 11% 2 1	180
	21st to end	Day	38% 18% 33% 9% 2	198
January	1st to 10th	Night	27% 20% 29% 19% 4	760
	11th to 20th	Night	28% 17% 30% 19% 5%	760
	21st to end	Night	21% 17% 33% 24% 4 1	836
February	1st to 10th	Night	22% 22% 36% 19% 2	760
	11th to 20th	Night	23% 20% 36% 17% 4	743
	21st to end	Night	25% 20% 34% 18% 3	628
March	1st to 10th	Night	22% 18% 35% 21% 3	760
	11th to 20th	Night	26% 19% 31% 19% 4 1	760
	21st to end	Night	21% 17% 32% 22% 7% 1	836
April	1st to 10th	Night	26% 16% 33% 21% 4	760
	11th to 20th	Night	24% 21% 28% 19% 8% 1	751
	21st to end	Night	23% 12% 31% 23% 10%	622
May	1st to 10th	Night	22% 10% 28% 26% 11% 2	442
	11th to 20th	Night	16% 9% 34% 32% 10%	374
	21st to end	Night	12% 8% 36% 30% 12% 1	411
June	1st to 10th	Night	16% 7% 34% 32% 11%	380
	11th to 20th	Night	13% 9% 34% 31% 13% 1	380
	21st to end	Night	17% 7% 27% 36% 13% 1	380
July	1st to 10th	Night	6% 7% 32% 38% 16% 1	370
	11th to 20th	Night	11% 2 31% 36% 19% 1	368
	21st to end	Night	11% 2 30% 41% 15% 1	416
August	1st to 10th	Night	12% 4 24% 35% 24% 2	564
	11th to 20th	Night	11% 5% 22% 36% 24% 2	564
	21st to end	Night	11% 5% 30% 34% 19% 2	788
September	1st to 10th	Night	14% 6% 31% 30% 18% 3	760
	11th to 20th	Night	13% 5% 24% 27% 27% 4	760
	21st to end	Night	19% 10% 22% 29% 18% 3	760
October	1st to 10th	Night	20% 13% 26% 24% 16% 2	760
	11th to 20th	Night	24% 13% 30% 23% 8% 1	760
	21st to end	Night	27% 15% 30% 22% 5%	836
November	1st to 10th	Night	26% 13% 26% 26% 9% 1	780
	11th to 20th	Night	25% 18% 31% 20% 6% 1	763
	21st to end	Night	29% 17% 28% 21% 6%	760
December	1st to 10th	Night	31% 19% 28% 20% 3	760
	11th to 20th	Night	27% 18% 34% 18% 3	760
	21st to end	Night	35% 15% 33% 15% 2	836

Page generated at 2024-11-08 06:44:51. Version ac07

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