Killarney Provincial Park Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Killarney Provincial Park Observatory clear sky chart from 2005-11-06 to 2025-11-03.

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	15% 10% 4 8% 5% 4 4 3 5% 7% 35%	126860
	Night	15% 11% 4 8% 5% 4 4 4 5% 6% 33%	123274
Transparency	Day	31% 38% 7% 15% 8% 1	130360
	Night	33% 38% 7% 14% 8% 1	127862
Seeing	Day	21% 15% 32% 21% 8% 2	16606
	Night	22% 12% 29% 26% 10% 1	25728

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% 17% 7% 10% 4 4 3 3 4 5% 31%	3158
	11th to 20th	Day	9% 15% 7% 16% 8% 6% 5% 4 6% 5% 18%	3475
	21st to end	Day	13% 20% 8% 13% 7% 5% 4 3 5% 4 19%	4290
February	1st to 10th	Day	11% 17% 6% 10% 7% 5% 5% 4 5% 5% 26%	1800
	11th to 20th	Day	11% 15% 5% 10% 6% 5% 4 3 4 6% 29%	1753
	21st to end	Day	12% 18% 7% 12% 7% 4 5% 3 3 6% 25%	1595
March	1st to 10th	Day	18% 13% 4 8% 4 4 4 3 5% 5% 32%	4740
	11th to 20th	Day	14% 13% 5% 10% 5% 5% 4 4 5% 7% 28%	4980
	21st to end	Day	15% 14% 6% 9% 5% 3 3 3 4 6% 32%	5465
April	1st to 10th	Day	18% 12% 4 8% 4 4 5% 4 4 7% 31%	2348
	11th to 20th	Day	19% 10% 2 6% 4 4 3 3 5% 5% 37%	2572
	21st to end	Day	22% 8% 3 6% 4 3 4 3 5% 7% 36%	2600
May	1st to 10th	Day	18% 7% 2 6% 5% 4 4 3 5% 7% 39%	5888
	11th to 20th	Day	15% 7% 2 7% 4 3 5% 3 5% 7% 42%	6224
	21st to end	Day	19% 8% 2 7% 4 4 4 3 5% 7% 38%	7129
June	1st to 10th	Day	15% 7% 3 6% 5% 4 4 4 6% 8% 38%	3000
	11th to 20th	Day	12% 7% 2 6% 5% 4 4 3 5% 8% 42%	3000
	21st to end	Day	16% 7% 3 7% 4 5% 5% 3 5% 8% 37%	3000
July	1st to 10th	Day	14% 7% 3 7% 4 4 4 4 6% 8% 40%	6819
	11th to 20th	Day	10% 5% 2 5% 4 4 4 3 5% 7% 51%	6820
	21st to end	Day	9% 4 2 5% 4 4 4 4 6% 9% 50%	6686
August	1st to 10th	Day	10% 6% 3 7% 4 4 5% 4 6% 9% 41%	4234
	11th to 20th	Day	15% 6% 2 5% 4 4 4 3 6% 9% 42%	4174
	21st to end	Day	10% 5% 2 6% 4 4 5% 4 5% 8% 47%	4675
September	1st to 10th	Day	12% 6% 2 8% 6% 4 5% 4 6% 6% 41%	2387
	11th to 20th	Day	13% 5% 2 5% 4 4 4 4 6% 8% 47%	2200
	21st to end	Day	19% 8% 2 6% 5% 4 4 3 5% 7% 38%	2200
October	1st to 10th	Day	17% 6% 3 7% 5% 4 5% 4 5% 6% 39%	2030
	11th to 20th	Day	25% 9% 3 7% 5% 5% 4 3 5% 6% 27%	2000
	21st to end	Day	25% 12% 3 8% 5% 5% 3 3 5% 6% 26%	2070
November	1st to 10th	Day	17% 11% 4 8% 5% 4 5% 4 6% 7% 29%	1700
	11th to 20th	Day	16% 17% 4 9% 5% 5% 4 4 6% 6% 25%	1600
	21st to end	Day	20% 20% 5% 10% 6% 4 4 3 4 5% 19%	1600
December	1st to 10th	Day	13% 20% 6% 10% 5% 4 4 5% 7% 6% 19%	2551
	11th to 20th	Day	18% 16% 7% 11% 5% 4 4 3 4 5% 23%	2621
	21st to end	Day	27% 21% 5% 9% 4 3 3 3 3 4 17%	3476
January	1st to 10th	Night	10% 14% 6% 10% 5% 5% 5% 4 6% 7% 28%	6808
	11th to 20th	Night	11% 17% 5% 12% 5% 5% 5% 4 5% 6% 24%	6426
	21st to end	Night	11% 18% 7% 13% 5% 5% 5% 4 5% 5% 20%	6658
February	1st to 10th	Night	12% 14% 6% 11% 6% 4 5% 4 5% 5% 27%	2600
	11th to 20th	Night	11% 13% 5% 10% 6% 5% 5% 5% 5% 5% 29%	2533
	21st to end	Night	12% 17% 5% 10% 6% 5% 5% 4 6% 5% 26%	2031
March	1st to 10th	Night	16% 10% 3 9% 5% 4 4 3 5% 5% 36%	5099
	11th to 20th	Night	12% 11% 5% 9% 5% 5% 5% 4 6% 8% 31%	4979
	21st to end	Night	18% 10% 6% 9% 5% 4 3 3 4 5% 34%	5467
April	1st to 10th	Night	19% 10% 3 7% 4 4 4 4 5% 6% 34%	2069
	11th to 20th	Night	18% 10% 3 6% 4 3 4 3 4 7% 39%	1777
	21st to end	Night	19% 9% 3 9% 5% 5% 3 3 4 6% 33%	1800
May	1st to 10th	Night	16% 7% 2 7% 5% 4 4 4 5% 6% 39%	4053
	11th to 20th	Night	12% 7% 3 7% 4 5% 4 4 5% 8% 42%	3667
	21st to end	Night	16% 9% 3 7% 5% 5% 4 3 4 7% 37%	3750
June	1st to 10th	Night	13% 8% 2 5% 4 6% 5% 5% 8% 7% 38%	1400
	11th to 20th	Night	11% 5% 2 5% 6% 5% 5% 5% 6% 10% 42%	1400
	21st to end	Night	14% 6% 3 7% 4 4 4 4 6% 8% 40%	1400
July	1st to 10th	Night	13% 7% 2 7% 4 3 3 4 5% 8% 44%	3160
	11th to 20th	Night	11% 4 2 4 3 3 4 3 5% 8% 52%	3160
	21st to end	Night	9% 5% 2 5% 4 4 4 4 5% 8% 51%	4158
August	1st to 10th	Night	10% 6% 3 6% 4 4 4 5% 7% 8% 43%	2915
	11th to 20th	Night	14% 6% 2 5% 4 4 3 3 5% 7% 47%	2875
	21st to end	Night	10% 6% 2 5% 3 4 4 3 5% 7% 51%	3223
September	1st to 10th	Night	12% 5% 2 5% 5% 4 4 3 5% 6% 47%	1989
	11th to 20th	Night	12% 4 1 5% 3 4 4 4 4 8% 52%	2200
	21st to end	Night	17% 7% 2 6% 4 4 3 3 5% 8% 41%	2200
October	1st to 10th	Night	18% 8% 2 6% 4 3 4 3 5% 6% 40%	2369
	11th to 20th	Night	23% 9% 3 7% 5% 4 4 4 6% 6% 30%	2400
	21st to end	Night	23% 11% 3 8% 5% 4 4 3 5% 6% 28%	2765
November	1st to 10th	Night	18% 11% 3 7% 5% 4 5% 4 5% 8% 32%	2642
	11th to 20th	Night	18% 13% 4 10% 6% 4 6% 4 5% 6% 25%	2800
	21st to end	Night	20% 18% 4 8% 5% 5% 4 3 5% 6% 21%	2800
December	1st to 10th	Night	15% 19% 4 9% 5% 5% 5% 3 5% 6% 22%	4613
	11th to 20th	Night	16% 15% 5% 13% 6% 4 4 3 4 5% 24%	5586
	21st to end	Night	25% 19% 6% 10% 5% 3 3 2 3 5% 18%	7502

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	41% 28% 6% 17% 5% 2	3159
	11th to 20th	Day	51% 28% 7% 8% 5% 1	3506
	21st to end	Day	51% 30% 4 8% 7%	4290
February	1st to 10th	Day	24% 61% 4 9% 3	1800
	11th to 20th	Day	23% 60% 4 7% 5%	1762
	21st to end	Day	25% 61% 2 8% 4	1595
March	1st to 10th	Day	42% 29% 6% 6% 13% 4	4743
	11th to 20th	Day	42% 29% 11% 10% 7% 1	4980
	21st to end	Day	41% 28% 9% 12% 9% 1	5465
April	1st to 10th	Day	21% 61% 3 9% 5%	2348
	11th to 20th	Day	20% 61% 2 10% 5% 1	2572
	21st to end	Day	19% 62% 4 9% 5% 1	2600
May	1st to 10th	Day	33% 30% 5% 18% 10% 3	5897
	11th to 20th	Day	30% 30% 8% 17% 13% 2	6228
	21st to end	Day	38% 28% 7% 13% 11% 3	7129
June	1st to 10th	Day	16% 62% 4 10% 7% 1	3000
	11th to 20th	Day	17% 61% 4 10% 7% 1	3000
	21st to end	Day	19% 60% 4 10% 6% 1	3000
July	1st to 10th	Day	35% 26% 13% 19% 7%	6746
	11th to 20th	Day	24% 26% 10% 33% 6%	6739
	21st to end	Day	22% 25% 11% 27% 13%	6495
August	1st to 10th	Day	23% 37% 9% 22% 7% 1	4221
	11th to 20th	Day	28% 36% 11% 17% 7%	4213
	21st to end	Day	23% 36% 10% 23% 7%	4674
September	1st to 10th	Day	19% 58% 7% 11% 4	2387
	11th to 20th	Day	12% 56% 6% 17% 8%	2200
	21st to end	Day	18% 57% 7% 12% 5%	2200
October	1st to 10th	Day	24% 36% 6% 22% 13%	3303
	11th to 20th	Day	27% 36% 10% 21% 6%	3240
	21st to end	Day	40% 35% 7% 12% 5%	3320
November	1st to 10th	Day	28% 55% 5% 9% 4	1700
	11th to 20th	Day	28% 57% 4 8% 4	1600
	21st to end	Day	28% 56% 4 8% 4	1600
December	1st to 10th	Day	43% 36% 13% 6% 2	2551
	11th to 20th	Day	45% 32% 4 10% 8% 1	2621
	21st to end	Day	56% 27% 3 10% 5%	3476
January	1st to 10th	Night	39% 30% 8% 15% 7% 1	6808
	11th to 20th	Night	44% 28% 10% 10% 8%	6470
	21st to end	Night	49% 30% 4 8% 7% 1	6658
February	1st to 10th	Night	22% 62% 3 10% 4	2600
	11th to 20th	Night	22% 60% 4 9% 5%	2535
	21st to end	Night	22% 62% 3 8% 5%	2031
March	1st to 10th	Night	38% 30% 6% 11% 11% 4	5109
	11th to 20th	Night	39% 29% 12% 13% 6% 1	4980
	21st to end	Night	42% 29% 4 13% 11% 2	5467
April	1st to 10th	Night	22% 61% 2 8% 6%	2069
	11th to 20th	Night	18% 62% 2 9% 8% 1	1777
	21st to end	Night	21% 62% 4 7% 6% 1	1800
May	1st to 10th	Night	33% 30% 6% 17% 12% 3	4060
	11th to 20th	Night	29% 30% 6% 18% 15% 2	3668
	21st to end	Night	37% 30% 5% 17% 8% 3	3751
June	1st to 10th	Night	15% 61% 3 12% 7% 2	1400
	11th to 20th	Night	14% 62% 5% 11% 8% 1	1400
	21st to end	Night	15% 60% 4 12% 8% 1	1400
July	1st to 10th	Night	33% 26% 10% 21% 9% 1	3125
	11th to 20th	Night	25% 25% 11% 32% 8%	3118
	21st to end	Night	24% 25% 9% 28% 14%	4036
August	1st to 10th	Night	24% 37% 10% 19% 10%	2904
	11th to 20th	Night	25% 37% 14% 17% 6%	2902
	21st to end	Night	20% 37% 9% 25% 9%	3223
September	1st to 10th	Night	16% 57% 8% 14% 5%	1989
	11th to 20th	Night	12% 56% 7% 17% 8%	2200
	21st to end	Night	18% 57% 6% 12% 7%	2200
October	1st to 10th	Night	23% 35% 6% 24% 12%	3876
	11th to 20th	Night	25% 36% 10% 22% 7%	3899
	21st to end	Night	32% 36% 15% 13% 5%	4465
November	1st to 10th	Night	25% 56% 6% 9% 4	2642
	11th to 20th	Night	26% 57% 5% 8% 4	2800
	21st to end	Night	28% 58% 4 6% 4	2800
December	1st to 10th	Night	42% 36% 11% 9% 3	4613
	11th to 20th	Night	44% 32% 5% 8% 10% 1	5585
	21st to end	Night	54% 26% 5% 10% 5%	7502

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	23% 20% 32% 22% 4 1	200
	11th to 20th	Day	20% 16% 38% 19% 7%	276
	21st to end	Day	24% 17% 33% 18% 7% 1	330
February	1st to 10th	Day	28% 26% 29% 12% 4	300
	11th to 20th	Day	24% 24% 36% 14% 1 1	300
	21st to end	Day	32% 24% 34% 10%	249
March	1st to 10th	Day	25% 24% 31% 15% 4	407
	11th to 20th	Day	23% 18% 35% 19% 5% 1	500
	21st to end	Day	27% 19% 31% 18% 4 1	550
April	1st to 10th	Day	26% 17% 30% 19% 7% 1	500
	11th to 20th	Day	31% 19% 24% 15% 8% 3	492
	21st to end	Day	31% 17% 28% 15% 7% 1	500
May	1st to 10th	Day	21% 15% 37% 18% 6% 2	503
	11th to 20th	Day	20% 15% 31% 19% 12% 2	527
	21st to end	Day	19% 12% 35% 23% 9% 2	649
June	1st to 10th	Day	17% 16% 37% 24% 5% 1	730
	11th to 20th	Day	16% 17% 37% 22% 6% 2	730
	21st to end	Day	22% 14% 34% 21% 7% 2	730
July	1st to 10th	Day	11% 14% 36% 29% 10% 2	721
	11th to 20th	Day	12% 14% 34% 26% 10% 3	718
	21st to end	Day	12% 10% 36% 27% 11% 4	677
August	1st to 10th	Day	15% 8% 27% 29% 15% 5%	526
	11th to 20th	Day	13% 6% 33% 27% 13% 8%	519
	21st to end	Day	15% 11% 30% 25% 13% 6%	583
September	1st to 10th	Day	17% 10% 31% 26% 11% 5%	530
	11th to 20th	Day	14% 7% 29% 30% 13% 7%	530
	21st to end	Day	25% 12% 25% 25% 11% 3	530
October	1st to 10th	Day	23% 14% 29% 22% 10% 2	530
	11th to 20th	Day	28% 16% 36% 16% 4 1	530
	21st to end	Day	32% 18% 31% 15% 2 1	453
November	1st to 10th	Day	29% 18% 36% 12% 5%	266
	11th to 20th	Day	27% 24% 32% 14% 3 1	200
	21st to end	Day	33% 20% 29% 14% 6%	200
December	1st to 10th	Day	25% 18% 34% 16% 8%	200
	11th to 20th	Day	31% 21% 32% 15% 1 1	200
	21st to end	Day	33% 19% 34% 10% 5%	220
January	1st to 10th	Night	22% 15% 33% 22% 6% 1	1000
	11th to 20th	Night	25% 16% 29% 23% 7% 1	1000
	21st to end	Night	20% 11% 31% 28% 8% 1	957
February	1st to 10th	Night	20% 16% 37% 22% 5%	800
	11th to 20th	Night	20% 16% 34% 24% 5% 1	783
	21st to end	Night	21% 17% 34% 22% 5%	660
March	1st to 10th	Night	19% 18% 35% 22% 6%	800
	11th to 20th	Night	21% 15% 35% 22% 7% 1	800
	21st to end	Night	22% 12% 32% 27% 6% 1	880
April	1st to 10th	Night	25% 12% 33% 24% 5%	768
	11th to 20th	Night	24% 13% 26% 24% 11% 2	593
	21st to end	Night	24% 14% 26% 26% 10%	600
May	1st to 10th	Night	16% 9% 29% 35% 11% 1	600
	11th to 20th	Night	15% 9% 31% 34% 11% 1	434
	21st to end	Night	14% 9% 30% 33% 13%	433
June	1st to 10th	Night	17% 7% 34% 32% 10%	400
	11th to 20th	Night	14% 8% 28% 38% 12% 1	400
	21st to end	Night	17% 7% 29% 34% 13% 2	400
July	1st to 10th	Night	11% 6% 25% 47% 11% 1	390
	11th to 20th	Night	9% 5% 27% 41% 19%	388
	21st to end	Night	11% 6% 22% 41% 19% 1	636
August	1st to 10th	Night	12% 4 24% 38% 21% 2	597
	11th to 20th	Night	15% 4 23% 31% 22% 4	594
	21st to end	Night	15% 7% 23% 30% 23% 2	660
September	1st to 10th	Night	16% 7% 27% 29% 18% 2	766
	11th to 20th	Night	13% 7% 26% 29% 21% 4	800
	21st to end	Night	21% 8% 26% 25% 17% 3	800
October	1st to 10th	Night	25% 10% 25% 28% 12% 2	800
	11th to 20th	Night	30% 14% 28% 22% 6% 1	800
	21st to end	Night	30% 15% 28% 22% 4 1	880
November	1st to 10th	Night	26% 14% 29% 24% 7%	789
	11th to 20th	Night	27% 17% 27% 23% 6%	800
	21st to end	Night	31% 16% 31% 17% 5%	800
December	1st to 10th	Night	27% 17% 31% 18% 6%	820
	11th to 20th	Night	28% 18% 33% 17% 4 1	1000
	21st to end	Night	32% 15% 27% 19% 6%	1100

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