Haliburton Forest Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Haliburton Forest Observatory clear sky chart from 2005-11-06 to 2025-09-04.

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	16% 12% 4 9% 5% 4 4 3 5% 6% 30%	127089
	Night	16% 14% 5% 10% 5% 4 4 3 4 6% 28%	121583
Transparency	Day	55% 4 10% 20% 10% 1	130656
	Night	57% 4 10% 19% 10% 1	126105
Seeing	Day	25% 16% 31% 19% 8% 2	15783
	Night	24% 14% 29% 23% 9% 1	24597

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	12% 18% 7% 16% 7% 6% 4 3 4 4 20%	3597
	11th to 20th	Day	9% 21% 11% 18% 7% 6% 5% 3 4 3 13%	3616
	21st to end	Day	12% 19% 9% 17% 7% 6% 3 3 3 3 17%	4466
February	1st to 10th	Day	12% 19% 8% 17% 8% 5% 4 3 3 4 18%	1800
	11th to 20th	Day	12% 16% 7% 15% 6% 5% 3 3 4 6% 22%	1753
	21st to end	Day	15% 19% 6% 11% 6% 6% 5% 3 3 5% 20%	1525
March	1st to 10th	Day	17% 16% 4 12% 6% 4 3 3 4 6% 24%	4860
	11th to 20th	Day	12% 15% 6% 11% 6% 5% 6% 4 5% 6% 24%	4980
	21st to end	Day	17% 17% 5% 9% 4 3 3 2 3 4 33%	5500
April	1st to 10th	Day	20% 16% 4 8% 5% 3 4 3 4 6% 27%	2400
	11th to 20th	Day	23% 13% 3 6% 4 3 4 3 4 5% 33%	2430
	21st to end	Day	21% 14% 4 7% 4 3 3 2 4 5% 33%	2600
May	1st to 10th	Day	19% 9% 3 8% 5% 4 5% 3 5% 7% 31%	6115
	11th to 20th	Day	17% 9% 3 7% 5% 4 4 3 5% 7% 36%	6318
	21st to end	Day	21% 10% 2 7% 4 4 4 4 5% 6% 32%	6949
June	1st to 10th	Day	21% 9% 3 6% 5% 5% 4 4 6% 7% 30%	2800
	11th to 20th	Day	15% 8% 2 6% 5% 5% 4 5% 7% 8% 35%	2871
	21st to end	Day	19% 8% 3 7% 5% 5% 5% 4 6% 7% 32%	3000
July	1st to 10th	Day	15% 6% 2 6% 5% 5% 5% 4 7% 10% 35%	6645
	11th to 20th	Day	12% 6% 2 6% 4 4 4 4 5% 7% 44%	6360
	21st to end	Day	8% 6% 2 6% 5% 4 4 4 6% 9% 47%	6836
August	1st to 10th	Day	15% 9% 3 9% 5% 6% 6% 4 6% 7% 31%	4234
	11th to 20th	Day	17% 7% 3 7% 4 5% 5% 5% 7% 7% 33%	4174
	21st to end	Day	10% 6% 2 6% 5% 5% 6% 5% 7% 10% 39%	4461
September	1st to 10th	Day	17% 8% 3 6% 5% 4 4 4 5% 7% 37%	2316
	11th to 20th	Day	15% 6% 2 6% 5% 3 4 3 5% 7% 43%	2233
	21st to end	Day	20% 9% 3 6% 4 3 5% 4 5% 5% 35%	2010
October	1st to 10th	Day	21% 9% 3 8% 5% 4 4 3 5% 6% 32%	1900
	11th to 20th	Day	28% 14% 3 8% 5% 4 4 3 5% 5% 22%	1900
	21st to end	Day	30% 14% 5% 8% 4 3 4 3 3 5% 20%	2076
November	1st to 10th	Day	19% 16% 3 7% 5% 4 4 4 4 6% 28%	1618
	11th to 20th	Day	17% 19% 6% 11% 5% 5% 4 3 5% 4 21%	1600
	21st to end	Day	20% 25% 7% 11% 5% 4 4 3 4 4 14%	1600
December	1st to 10th	Day	16% 24% 10% 14% 6% 5% 4 3 5% 4 10%	2600
	11th to 20th	Day	17% 25% 8% 15% 5% 2 2 2 3 3 18%	2986
	21st to end	Day	21% 21% 8% 14% 5% 3 3 2 3 4 16%	3960
January	1st to 10th	Night	13% 18% 9% 17% 7% 5% 4 3 4 5% 16%	6349
	11th to 20th	Night	11% 18% 7% 24% 10% 6% 4 3 3 4 10%	6251
	21st to end	Night	12% 19% 9% 17% 6% 7% 5% 3 4 3 14%	6490
February	1st to 10th	Night	11% 19% 7% 14% 9% 5% 5% 3 5% 5% 18%	2600
	11th to 20th	Night	13% 15% 7% 14% 6% 5% 4 4 4 4 24%	2533
	21st to end	Night	14% 18% 6% 13% 7% 5% 5% 3 5% 5% 20%	2103
March	1st to 10th	Night	16% 16% 5% 12% 5% 4 4 2 4 5% 27%	4965
	11th to 20th	Night	8% 15% 6% 11% 6% 5% 5% 4 6% 8% 25%	4979
	21st to end	Night	18% 12% 5% 8% 6% 4 4 3 5% 5% 29%	5431
April	1st to 10th	Night	20% 16% 4 8% 3 4 4 3 4 6% 28%	2000
	11th to 20th	Night	18% 12% 4 6% 4 4 3 3 4 5% 35%	1937
	21st to end	Night	20% 10% 4 9% 6% 4 4 4 4 5% 31%	1800
May	1st to 10th	Night	21% 8% 2 7% 5% 4 4 4 6% 6% 32%	3823
	11th to 20th	Night	16% 8% 2 5% 3 4 3 4 5% 8% 42%	3575
	21st to end	Night	19% 10% 3 6% 4 4 4 3 5% 7% 35%	3926
June	1st to 10th	Night	17% 10% 3 7% 5% 5% 4 4 5% 7% 34%	1600
	11th to 20th	Night	14% 7% 3 5% 4 4 4 4 6% 7% 43%	1520
	21st to end	Night	17% 8% 2 6% 5% 5% 3 3 7% 7% 36%	1400
July	1st to 10th	Night	14% 7% 3 8% 5% 5% 5% 4 5% 8% 37%	3309
	11th to 20th	Night	15% 8% 2 5% 4 3 4 3 4 6% 45%	3600
	21st to end	Night	10% 7% 2 5% 3 3 4 3 4 7% 51%	4013
August	1st to 10th	Night	11% 5% 2 5% 4 4 4 4 6% 8% 47%	2915
	11th to 20th	Night	17% 8% 3 7% 4 4 4 4 5% 5% 41%	2875
	21st to end	Night	14% 4 2 5% 3 3 4 3 5% 9% 47%	3402
September	1st to 10th	Night	11% 7% 2 6% 4 4 5% 4 6% 6% 45%	1931
	11th to 20th	Night	14% 6% 1 5% 3 4 4 3 4 7% 47%	1943
	21st to end	Night	20% 8% 2 6% 4 4 3 3 4 5% 41%	2169
October	1st to 10th	Night	19% 8% 3 7% 4 4 4 3 4 6% 37%	2280
	11th to 20th	Night	24% 14% 4 7% 5% 4 4 3 4 5% 27%	2280
	21st to end	Night	25% 16% 5% 7% 5% 4 4 2 4 5% 23%	2520
November	1st to 10th	Night	20% 15% 4 8% 4 4 3 3 5% 5% 28%	2680
	11th to 20th	Night	18% 16% 5% 8% 5% 4 4 3 4 6% 26%	2800
	21st to end	Night	21% 20% 5% 10% 6% 4 4 3 4 5% 17%	2800
December	1st to 10th	Night	18% 26% 8% 13% 6% 4 3 3 4 4 10%	4580
	11th to 20th	Night	17% 24% 8% 15% 6% 4 3 2 3 4 15%	5208
	21st to end	Night	22% 21% 8% 13% 6% 4 3 2 3 4 15%	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	68% 3 7% 15% 7%	3598
	11th to 20th	Day	77% 2 5% 9% 6% 1	3646
	21st to end	Day	74% 3 5% 9% 8% 1	4466
February	1st to 10th	Day	72% 3 6% 13% 6% 1	1800
	11th to 20th	Day	65% 3 9% 12% 9% 2	1762
	21st to end	Day	68% 4 7% 12% 9%	1525
March	1st to 10th	Day	63% 3 11% 9% 13% 1	4863
	11th to 20th	Day	60% 4 12% 16% 7% 2	4980
	21st to end	Day	56% 3 6% 19% 13% 2	5500
April	1st to 10th	Day	58% 4 8% 19% 10% 2	2400
	11th to 20th	Day	55% 3 6% 22% 13% 1	2430
	21st to end	Day	56% 3 7% 19% 12% 3	2600
May	1st to 10th	Day	53% 4 8% 21% 9% 5%	6124
	11th to 20th	Day	48% 3 9% 22% 16% 1	6322
	21st to end	Day	52% 4 11% 18% 12% 3	6949
June	1st to 10th	Day	53% 4 9% 21% 12%	2800
	11th to 20th	Day	44% 5% 11% 25% 13% 2	2871
	21st to end	Day	49% 5% 13% 21% 10% 1	3000
July	1st to 10th	Day	43% 5% 15% 27% 10% 1	6575
	11th to 20th	Day	38% 4 12% 33% 12%	6285
	21st to end	Day	34% 4 15% 34% 13%	6640
August	1st to 10th	Day	50% 5% 13% 24% 8% 1	4221
	11th to 20th	Day	48% 5% 14% 26% 7%	4213
	21st to end	Day	37% 6% 14% 33% 9%	4461
September	1st to 10th	Day	45% 4 12% 26% 11% 1	2316
	11th to 20th	Day	40% 5% 13% 29% 13% 1	2233
	21st to end	Day	50% 5% 10% 25% 9%	2010
October	1st to 10th	Day	50% 5% 11% 26% 8% 1	3160
	11th to 20th	Day	56% 4 10% 20% 10%	3140
	21st to end	Day	64% 4 11% 17% 4	3402
November	1st to 10th	Day	57% 3 13% 20% 6%	1618
	11th to 20th	Day	65% 4 10% 13% 6% 1	1600
	21st to end	Day	75% 3 8% 9% 4 1	1600
December	1st to 10th	Day	78% 3 9% 8% 2	2600
	11th to 20th	Day	74% 2 4 13% 6% 1	2986
	21st to end	Day	73% 3 4 12% 7%	3960
January	1st to 10th	Night	71% 3 6% 13% 5%	6349
	11th to 20th	Night	79% 2 6% 7% 6% 1	6296
	21st to end	Night	75% 3 5% 8% 8% 1	6490
February	1st to 10th	Night	67% 4 9% 13% 6% 1	2600
	11th to 20th	Night	64% 3 7% 18% 8%	2535
	21st to end	Night	66% 3 7% 15% 7% 1	2103
March	1st to 10th	Night	61% 3 8% 12% 12% 4	4975
	11th to 20th	Night	57% 4 14% 16% 8% 1	4980
	21st to end	Night	55% 4 6% 20% 12% 2	5431
April	1st to 10th	Night	58% 3 7% 18% 11% 2	2000
	11th to 20th	Night	51% 4 6% 23% 15% 1	1937
	21st to end	Night	56% 3 7% 17% 15% 2	1800
May	1st to 10th	Night	51% 4 9% 20% 12% 4	3830
	11th to 20th	Night	41% 4 12% 25% 17% 2	3576
	21st to end	Night	49% 4 10% 23% 13% 1	3927
June	1st to 10th	Night	49% 5% 11% 20% 14% 2	1600
	11th to 20th	Night	39% 4 13% 27% 16% 1	1520
	21st to end	Night	46% 6% 14% 23% 11% 1	1400
July	1st to 10th	Night	45% 6% 13% 24% 12%	3271
	11th to 20th	Night	40% 4 11% 33% 12%	3552
	21st to end	Night	34% 4 9% 39% 13%	3895
August	1st to 10th	Night	35% 5% 17% 27% 15% 1	2904
	11th to 20th	Night	44% 5% 16% 25% 10% 1	2902
	21st to end	Night	35% 5% 13% 34% 11% 2	3402
September	1st to 10th	Night	37% 6% 15% 28% 12% 1	1931
	11th to 20th	Night	38% 4 14% 31% 14%	1943
	21st to end	Night	46% 4 11% 28% 11%	2169
October	1st to 10th	Night	41% 5% 10% 29% 16%	3800
	11th to 20th	Night	52% 4 13% 21% 10%	3779
	21st to end	Night	58% 4 16% 16% 6%	4144
November	1st to 10th	Night	57% 4 12% 19% 7%	2680
	11th to 20th	Night	60% 4 11% 17% 7% 1	2800
	21st to end	Night	71% 4 9% 12% 4	2800
December	1st to 10th	Night	77% 4 10% 8% 2	4580
	11th to 20th	Night	75% 3 6% 10% 7%	5208
	21st to end	Night	76% 2 5% 10% 7%	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	22% 23% 38% 14% 3 1	200
	11th to 20th	Day	29% 13% 40% 14% 3 1	210
	21st to end	Day	25% 20% 36% 14% 4	330
February	1st to 10th	Day	30% 28% 32% 7% 2 1	300
	11th to 20th	Day	30% 28% 35% 6% 1	300
	21st to end	Day	37% 20% 31% 10%	289
March	1st to 10th	Day	26% 20% 35% 16% 2	500
	11th to 20th	Day	27% 21% 32% 16% 4 1	500
	21st to end	Day	33% 16% 31% 14% 5% 1	550
April	1st to 10th	Day	30% 20% 29% 15% 5% 1	500
	11th to 20th	Day	37% 18% 21% 14% 7% 3	492
	21st to end	Day	31% 16% 34% 11% 7% 1	500
May	1st to 10th	Day	25% 15% 31% 20% 6% 3	503
	11th to 20th	Day	23% 15% 30% 19% 10% 2	527
	21st to end	Day	22% 17% 29% 21% 9% 2	573
June	1st to 10th	Day	26% 14% 32% 22% 5% 1	530
	11th to 20th	Day	19% 14% 34% 22% 8% 2	601
	21st to end	Day	23% 14% 33% 21% 7% 2	730
July	1st to 10th	Day	16% 9% 33% 31% 9% 2	654
	11th to 20th	Day	16% 12% 32% 23% 13% 3	524
	21st to end	Day	14% 13% 33% 28% 10% 3	576
August	1st to 10th	Day	17% 7% 28% 29% 13% 5%	526
	11th to 20th	Day	16% 8% 26% 29% 15% 5%	519
	21st to end	Day	18% 10% 31% 23% 12% 5%	583
September	1st to 10th	Day	19% 11% 31% 19% 14% 6%	502
	11th to 20th	Day	17% 9% 24% 23% 17% 10%	490
	21st to end	Day	23% 13% 26% 22% 11% 4	490
October	1st to 10th	Day	27% 15% 26% 17% 12% 3	490
	11th to 20th	Day	33% 19% 30% 14% 3 2	490
	21st to end	Day	38% 17% 29% 13% 3	532
November	1st to 10th	Day	35% 17% 30% 14% 3	252
	11th to 20th	Day	31% 22% 32% 13% 3 1	200
	21st to end	Day	35% 21% 36% 7% 3	200
December	1st to 10th	Day	31% 19% 36% 12% 3	200
	11th to 20th	Day	37% 28% 22% 12% 2 1	200
	21st to end	Day	32% 22% 28% 12% 5% 1	220
January	1st to 10th	Night	27% 17% 36% 16% 4	800
	11th to 20th	Night	29% 16% 32% 18% 4 1	800
	21st to end	Night	21% 16% 35% 21% 7% 1	880
February	1st to 10th	Night	23% 21% 33% 19% 3	800
	11th to 20th	Night	22% 21% 36% 18% 3	783
	21st to end	Night	24% 23% 30% 20% 3	660
March	1st to 10th	Night	23% 20% 35% 18% 4	800
	11th to 20th	Night	21% 18% 37% 19% 4 1	800
	21st to end	Night	21% 15% 34% 21% 8%	880
April	1st to 10th	Night	29% 16% 31% 20% 5%	800
	11th to 20th	Night	26% 16% 29% 20% 9%	753
	21st to end	Night	27% 9% 31% 23% 11%	600
May	1st to 10th	Night	24% 7% 29% 28% 11% 1	500
	11th to 20th	Night	19% 9% 34% 28% 9%	394
	21st to end	Night	15% 11% 31% 32% 11% 1	433
June	1st to 10th	Night	20% 11% 31% 30% 8% 1	400
	11th to 20th	Night	18% 8% 27% 36% 10% 1	400
	21st to end	Night	22% 7% 20% 39% 12% 1	400
July	1st to 10th	Night	9% 6% 28% 38% 18% 1	390
	11th to 20th	Night	14% 6% 25% 34% 20% 1	388
	21st to end	Night	12% 7% 25% 39% 17%	475
August	1st to 10th	Night	12% 4 20% 38% 23% 2	597
	11th to 20th	Night	14% 7% 18% 36% 23% 3	594
	21st to end	Night	16% 7% 26% 29% 20% 2	761
September	1st to 10th	Night	14% 7% 28% 30% 18% 3	773
	11th to 20th	Night	18% 6% 21% 28% 22% 4	760
	21st to end	Night	25% 9% 20% 28% 15% 2	760
October	1st to 10th	Night	23% 11% 29% 23% 12% 1	760
	11th to 20th	Night	31% 13% 28% 19% 8% 1	760
	21st to end	Night	36% 14% 26% 19% 4	836
November	1st to 10th	Night	31% 14% 27% 21% 7%	780
	11th to 20th	Night	29% 18% 31% 16% 6% 1	800
	21st to end	Night	34% 16% 28% 18% 3 1	800
December	1st to 10th	Night	35% 18% 30% 13% 4	800
	11th to 20th	Night	26% 22% 34% 14% 3 1	800
	21st to end	Night	34% 17% 30% 16% 3 1	880

Page generated at 2025-09-01 01:51:04. Version ac07

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