Warman Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Warman 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	12% 9% 3 8% 5% 4 5% 4 6% 7% 37%	128550
	Night	12% 9% 3 9% 5% 5% 5% 4 6% 7% 37%	122763
Transparency	Day	44% 6% 13% 25% 11% 1	132095
	Night	45% 6% 13% 23% 12% 1	127295
Seeing	Day	16% 10% 30% 27% 13% 3	17607
	Night	16% 9% 31% 32% 11% 1	27532

By Month

Percentage Cloud Cover SE (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	8% 12% 4 14% 9% 6% 5% 4 5% 6% 29%	3617
	11th to 20th	Day	4 10% 5% 14% 8% 8% 8% 7% 10% 6% 20%	3620
	21st to end	Day	5% 15% 8% 13% 6% 5% 5% 4 6% 6% 28%	4420
February	1st to 10th	Day	9% 12% 4 10% 7% 6% 5% 3 5% 7% 33%	1800
	11th to 20th	Day	7% 10% 4 9% 7% 5% 5% 3 5% 8% 37%	1754
	21st to end	Day	8% 13% 4 9% 6% 5% 5% 4 5% 7% 35%	1525
March	1st to 10th	Day	11% 9% 3 6% 4 4 4 3 6% 8% 42%	4802
	11th to 20th	Day	9% 8% 3 9% 5% 5% 5% 4 6% 8% 38%	4980
	21st to end	Day	21% 11% 4 9% 5% 4 4 4 4 6% 29%	5539
April	1st to 10th	Day	17% 10% 3 9% 5% 5% 4 3 5% 6% 33%	2400
	11th to 20th	Day	18% 11% 4 8% 5% 4 4 4 5% 5% 31%	2418
	21st to end	Day	21% 10% 3 8% 4 4 4 3 4 6% 33%	2600
May	1st to 10th	Day	14% 6% 2 6% 4 4 3 3 4 5% 49%	6183
	11th to 20th	Day	16% 8% 2 6% 4 4 4 3 5% 6% 41%	6319
	21st to end	Day	15% 8% 3 7% 5% 4 4 4 6% 8% 35%	6935
June	1st to 10th	Day	11% 6% 2 5% 4 4 5% 4 7% 8% 45%	2800
	11th to 20th	Day	14% 6% 3 7% 5% 5% 5% 4 6% 8% 37%	2974
	21st to end	Day	10% 5% 2 6% 5% 5% 6% 5% 7% 10% 38%	3000
July	1st to 10th	Day	8% 4 2 6% 4 4 5% 5% 7% 11% 45%	6800
	11th to 20th	Day	9% 5% 2 5% 3 3 4 4 6% 9% 51%	6404
	21st to end	Day	8% 5% 2 5% 4 4 4 4 6% 10% 48%	6924
August	1st to 10th	Day	12% 5% 2 5% 4 4 5% 4 7% 8% 44%	4249
	11th to 20th	Day	12% 5% 2 7% 5% 5% 5% 4 6% 9% 40%	4171
	21st to end	Day	13% 7% 2 7% 5% 4 4 3 5% 7% 42%	4510
September	1st to 10th	Day	9% 6% 2 6% 4 5% 4 4 7% 10% 44%	2400
	11th to 20th	Day	12% 6% 3 6% 4 4 5% 3 6% 7% 45%	2368
	21st to end	Day	13% 8% 2 6% 4 5% 3 3 6% 7% 44%	2105
October	1st to 10th	Day	17% 7% 2 7% 4 4 4 4 6% 8% 39%	2000
	11th to 20th	Day	16% 11% 2 8% 5% 5% 4 4 4 6% 36%	2000
	21st to end	Day	18% 12% 3 8% 4 3 4 3 4 6% 33%	2150
November	1st to 10th	Day	13% 12% 4 11% 6% 4 4 3 5% 5% 32%	1687
	11th to 20th	Day	11% 15% 7% 12% 6% 5% 4 4 5% 5% 26%	1680
	21st to end	Day	13% 13% 4 9% 7% 4 5% 4 6% 7% 28%	1680
December	1st to 10th	Day	8% 13% 5% 14% 12% 7% 6% 4 6% 6% 19%	2690
	11th to 20th	Day	9% 18% 7% 11% 6% 4 4 4 6% 7% 26%	3064
	21st to end	Day	19% 20% 6% 17% 7% 4 4 3 3 3 13%	3982
January	1st to 10th	Night	8% 8% 4 14% 10% 6% 4 3 5% 6% 32%	6348
	11th to 20th	Night	6% 9% 4 11% 7% 7% 9% 8% 9% 7% 23%	6360
	21st to end	Night	6% 15% 6% 12% 5% 5% 4 4 6% 6% 30%	6554
February	1st to 10th	Night	7% 10% 5% 10% 6% 5% 5% 4 5% 7% 37%	2600
	11th to 20th	Night	6% 9% 4 9% 6% 6% 4 4 6% 7% 38%	2533
	21st to end	Night	11% 10% 4 8% 5% 5% 5% 4 6% 7% 35%	2104
March	1st to 10th	Night	11% 7% 2 6% 4 4 4 3 4 6% 49%	5080
	11th to 20th	Night	10% 8% 3 9% 6% 5% 6% 4 8% 8% 35%	4980
	21st to end	Night	21% 12% 3 11% 5% 4 4 3 4 5% 28%	5389
April	1st to 10th	Night	16% 11% 3 6% 4 4 4 3 5% 5% 38%	2000
	11th to 20th	Night	18% 10% 4 7% 4 4 3 2 5% 5% 36%	1927
	21st to end	Night	19% 9% 3 7% 4 4 4 5% 5% 6% 33%	1800
May	1st to 10th	Night	12% 7% 2 5% 4 3 3 2 5% 6% 51%	3732
	11th to 20th	Night	13% 6% 2 6% 3 3 3 3 5% 7% 48%	3596
	21st to end	Night	14% 9% 3 7% 5% 4 4 4 6% 7% 38%	3942
June	1st to 10th	Night	11% 5% 2 5% 4 5% 5% 3 7% 8% 44%	1600
	11th to 20th	Night	11% 5% 2 6% 4 5% 5% 4 6% 7% 44%	1420
	21st to end	Night	10% 4 2 6% 4 5% 3 4 6% 8% 48%	1400
July	1st to 10th	Night	8% 4 1 4 4 4 5% 4 6% 10% 51%	3178
	11th to 20th	Night	8% 4 2 4 4 3 3 3 5% 8% 56%	3568
	21st to end	Night	9% 6% 3 7% 4 4 3 4 5% 8% 47%	3947
August	1st to 10th	Night	10% 5% 2 6% 3 4 4 4 5% 8% 51%	2907
	11th to 20th	Night	13% 6% 2 5% 3 3 3 4 6% 7% 48%	2888
	21st to end	Night	13% 7% 3 6% 4 4 4 4 6% 8% 42%	3392
September	1st to 10th	Night	9% 4 2 5% 3 4 3 4 5% 8% 53%	2000
	11th to 20th	Night	9% 5% 1 4 4 4 4 3 6% 8% 51%	2030
	21st to end	Night	14% 5% 1 5% 4 4 4 2 5% 7% 50%	2275
October	1st to 10th	Night	14% 7% 2 5% 4 3 4 3 4 6% 47%	2400
	11th to 20th	Night	14% 11% 3 7% 4 4 4 3 5% 6% 39%	2400
	21st to end	Night	17% 11% 4 9% 4 4 3 3 5% 6% 34%	2689
November	1st to 10th	Night	14% 9% 3 9% 5% 5% 4 4 5% 7% 35%	2830
	11th to 20th	Night	14% 12% 4 10% 6% 5% 5% 4 5% 6% 31%	2940
	21st to end	Night	12% 9% 4 9% 6% 5% 5% 5% 6% 7% 32%	2940
December	1st to 10th	Night	7% 9% 4 16% 9% 9% 8% 5% 6% 7% 22%	4720
	11th to 20th	Night	10% 16% 6% 13% 6% 5% 5% 4 7% 7% 21%	5298
	21st to end	Night	21% 19% 6% 15% 5% 3 3 2 4 4 18%	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	55% 5% 8% 18% 14%	3618
	11th to 20th	Day	57% 6% 9% 19% 9%	3620
	21st to end	Day	55% 6% 14% 18% 7%	4420
February	1st to 10th	Day	51% 4 11% 22% 10% 2	1800
	11th to 20th	Day	46% 6% 13% 25% 9% 1	1763
	21st to end	Day	47% 6% 13% 21% 12% 1	1525
March	1st to 10th	Day	40% 5% 16% 25% 11% 4	4802
	11th to 20th	Day	42% 5% 14% 28% 10% 1	4980
	21st to end	Day	55% 6% 10% 20% 9% 1	5541
April	1st to 10th	Day	51% 5% 11% 19% 13% 1	2400
	11th to 20th	Day	54% 5% 9% 18% 12% 1	2418
	21st to end	Day	53% 6% 10% 20% 10%	2600
May	1st to 10th	Day	36% 5% 14% 27% 17% 1	6222
	11th to 20th	Day	42% 6% 12% 22% 12% 6%	6323
	21st to end	Day	43% 7% 11% 28% 11% 1	6949
June	1st to 10th	Day	35% 7% 16% 31% 10% 1	2800
	11th to 20th	Day	43% 8% 14% 21% 13% 1	2974
	21st to end	Day	36% 9% 18% 26% 10% 1	3000
July	1st to 10th	Day	31% 8% 19% 32% 10%	6726
	11th to 20th	Day	28% 6% 18% 35% 12% 1	6328
	21st to end	Day	31% 7% 17% 32% 13% 1	6728
August	1st to 10th	Day	35% 7% 14% 28% 14% 1	4234
	11th to 20th	Day	39% 6% 14% 32% 9%	4210
	21st to end	Day	40% 6% 17% 25% 11% 1	4509
September	1st to 10th	Day	35% 7% 14% 34% 9%	2400
	11th to 20th	Day	38% 7% 18% 29% 7%	2368
	21st to end	Day	39% 6% 12% 33% 9% 1	2105
October	1st to 10th	Day	34% 5% 12% 33% 16% 1	3260
	11th to 20th	Day	39% 5% 12% 25% 17% 2	3240
	21st to end	Day	50% 4 15% 24% 7%	3452
November	1st to 10th	Day	53% 7% 10% 19% 10% 1	1687
	11th to 20th	Day	59% 5% 13% 16% 6% 1	1680
	21st to end	Day	54% 6% 16% 17% 5% 2	1680
December	1st to 10th	Day	63% 6% 13% 14% 4 1	2690
	11th to 20th	Day	57% 5% 12% 18% 8%	3061
	21st to end	Day	76% 4 6% 8% 5%	3982
January	1st to 10th	Night	52% 5% 11% 18% 13% 1	6348
	11th to 20th	Night	53% 6% 13% 15% 12% 1	6360
	21st to end	Night	52% 6% 13% 22% 6%	6554
February	1st to 10th	Night	47% 5% 12% 22% 12% 1	2600
	11th to 20th	Night	43% 7% 13% 25% 11% 2	2534
	21st to end	Night	47% 6% 12% 21% 12% 1	2104
March	1st to 10th	Night	37% 5% 15% 22% 18% 4	5080
	11th to 20th	Night	44% 5% 13% 24% 13%	4980
	21st to end	Night	59% 4 10% 16% 11% 1	5389
April	1st to 10th	Night	47% 6% 9% 20% 16% 1	2000
	11th to 20th	Night	49% 5% 8% 21% 15% 2	1927
	21st to end	Night	50% 6% 10% 20% 13% 2	1800
May	1st to 10th	Night	34% 5% 12% 29% 18% 2	3758
	11th to 20th	Night	36% 5% 11% 23% 18% 7%	3597
	21st to end	Night	44% 6% 10% 26% 13% 1	3950
June	1st to 10th	Night	36% 7% 15% 28% 12% 3	1600
	11th to 20th	Night	37% 7% 15% 23% 16% 2	1420
	21st to end	Night	33% 8% 15% 29% 13% 3	1400
July	1st to 10th	Night	28% 8% 19% 31% 13% 1	3145
	11th to 20th	Night	26% 6% 15% 38% 13% 2	3525
	21st to end	Night	35% 6% 15% 30% 13% 2	3832
August	1st to 10th	Night	32% 6% 14% 29% 16% 3	2898
	11th to 20th	Night	34% 6% 14% 35% 11% 1	2915
	21st to end	Night	38% 7% 15% 28% 10% 1	3392
September	1st to 10th	Night	28% 7% 15% 35% 14% 1	2000
	11th to 20th	Night	32% 6% 19% 31% 13%	2030
	21st to end	Night	34% 5% 13% 33% 13% 1	2275
October	1st to 10th	Night	26% 3 8% 36% 23% 4	3920
	11th to 20th	Night	36% 4 12% 27% 19% 1	3899
	21st to end	Night	47% 4 13% 24% 12%	4337
November	1st to 10th	Night	48% 6% 12% 24% 9% 2	2830
	11th to 20th	Night	54% 5% 14% 17% 9% 1	2940
	21st to end	Night	50% 8% 16% 19% 6% 1	2940
December	1st to 10th	Night	58% 8% 14% 15% 4	4720
	11th to 20th	Night	60% 6% 10% 16% 6% 1	5300
	21st to end	Night	71% 4 7% 13% 5%	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	15% 13% 33% 26% 11% 2	300
	11th to 20th	Day	14% 10% 40% 30% 6%	300
	21st to end	Day	15% 9% 37% 24% 13% 1	330
February	1st to 10th	Day	17% 14% 44% 19% 6% 1	300
	11th to 20th	Day	11% 21% 41% 19% 6% 2	300
	21st to end	Day	18% 11% 43% 24% 4	249
March	1st to 10th	Day	18% 14% 40% 21% 6% 2	300
	11th to 20th	Day	18% 11% 38% 21% 10% 1	300
	21st to end	Day	27% 12% 28% 22% 9% 2	356
April	1st to 10th	Day	23% 14% 31% 25% 5% 1	500
	11th to 20th	Day	26% 13% 29% 23% 8% 1	536
	21st to end	Day	26% 8% 32% 22% 9% 2	700
May	1st to 10th	Day	20% 11% 29% 27% 11% 2	703
	11th to 20th	Day	19% 13% 26% 27% 12% 4	725
	21st to end	Day	18% 8% 26% 28% 16% 4	789
June	1st to 10th	Day	12% 7% 28% 31% 17% 4	730
	11th to 20th	Day	15% 9% 34% 29% 11% 2	730
	21st to end	Day	14% 7% 30% 29% 13% 7%	730
July	1st to 10th	Day	8% 4 22% 34% 23% 9%	721
	11th to 20th	Day	9% 7% 26% 30% 20% 8%	718
	21st to end	Day	8% 5% 28% 33% 20% 7%	794
August	1st to 10th	Day	12% 5% 22% 34% 22% 5%	726
	11th to 20th	Day	15% 7% 20% 29% 24% 5%	715
	21st to end	Day	13% 8% 23% 30% 21% 4	703
September	1st to 10th	Day	11% 8% 29% 30% 18% 4	530
	11th to 20th	Day	11% 5% 30% 31% 20% 3	498
	21st to end	Day	18% 13% 26% 23% 14% 6%	330
October	1st to 10th	Day	17% 9% 32% 25% 11% 6%	330
	11th to 20th	Day	18% 19% 34% 24% 5%	330
	21st to end	Day	26% 13% 37% 17% 7%	363
November	1st to 10th	Day	21% 14% 35% 22% 7% 1	330
	11th to 20th	Day	20% 15% 38% 20% 5% 1	330
	21st to end	Day	21% 15% 37% 24% 3	330
December	1st to 10th	Day	15% 14% 40% 22% 9%	330
	11th to 20th	Day	20% 16% 36% 23% 4	321
	21st to end	Day	30% 10% 32% 24% 2 1	330
January	1st to 10th	Night	13% 11% 37% 31% 8% 1	1000
	11th to 20th	Night	15% 8% 38% 30% 8% 1	1000
	21st to end	Night	15% 11% 38% 29% 7% 1	1100
February	1st to 10th	Night	12% 10% 39% 29% 9% 1	1000
	11th to 20th	Night	10% 13% 42% 26% 8% 1	979
	21st to end	Night	15% 11% 36% 28% 9% 1	784
March	1st to 10th	Night	15% 12% 37% 26% 8% 1	675
	11th to 20th	Night	17% 11% 40% 26% 6%	600
	21st to end	Night	22% 11% 28% 27% 9% 3	660
April	1st to 10th	Night	21% 11% 35% 27% 6%	600
	11th to 20th	Night	24% 9% 31% 28% 8% 1	593
	21st to end	Night	25% 6% 30% 30% 9% 1	600
May	1st to 10th	Night	18% 9% 33% 31% 9% 1	600
	11th to 20th	Night	16% 7% 33% 31% 10% 2	591
	21st to end	Night	16% 6% 27% 36% 15%	650
June	1st to 10th	Night	13% 6% 25% 39% 16% 1	600
	11th to 20th	Night	13% 5% 32% 39% 11%	600
	21st to end	Night	12% 6% 22% 41% 18% 1	600
July	1st to 10th	Night	5% 3 21% 44% 25% 3	585
	11th to 20th	Night	8% 4 24% 40% 22% 2	582
	21st to end	Night	5% 4 21% 46% 22% 2	657
August	1st to 10th	Night	8% 3 16% 51% 20% 2	597
	11th to 20th	Night	14% 3 19% 35% 26% 3	594
	21st to end	Night	12% 4 22% 36% 23% 2	660
September	1st to 10th	Night	11% 4 24% 39% 21% 3	600
	11th to 20th	Night	11% 4 27% 37% 19% 2	600
	21st to end	Night	15% 8% 30% 31% 16% 1	675
October	1st to 10th	Night	18% 8% 29% 31% 13% 1	800
	11th to 20th	Night	20% 12% 33% 29% 6% 1	800
	21st to end	Night	22% 11% 30% 29% 6%	880
November	1st to 10th	Night	20% 11% 30% 31% 8%	984
	11th to 20th	Night	19% 13% 32% 27% 8% 1	1050
	21st to end	Night	16% 14% 37% 26% 7%	1050
December	1st to 10th	Night	16% 11% 35% 30% 8% 1	1050
	11th to 20th	Night	20% 12% 34% 27% 7% 1	1036
	21st to end	Night	25% 10% 33% 25% 6% 1	1100

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