Kelsar Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Kelsar Observatory clear sky chart from 2005-11-06 to 2026-03-03.

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	18% 9% 3 8% 5% 5% 4 4 5% 6% 32%	135294
	Night	20% 10% 3 8% 5% 4 4 3 5% 6% 32%	134594
Transparency	Day	50% 8% 15% 18% 8% 1	135009
	Night	53% 8% 14% 17% 7% 1	134457
Seeing	Day	21% 11% 21% 25% 17% 5%	16735
	Night	23% 9% 19% 28% 18% 2	25242

By Month

Percentage Cloud Cover NW (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	33% 13% 4 10% 6% 6% 5% 4 5% 4 11%	4125
	11th to 20th	Day	18% 10% 5% 13% 6% 5% 4 3 5% 6% 26%	4712
	21st to end	Day	30% 11% 4 9% 6% 5% 4 3 4 5% 21%	5422
February	1st to 10th	Day	26% 13% 4 9% 7% 6% 5% 3 6% 6% 15%	1890
	11th to 20th	Day	25% 15% 4 9% 5% 5% 4 3 4 5% 21%	1845
	21st to end	Day	24% 13% 4 8% 6% 5% 6% 4 5% 5% 21%	1614
March	1st to 10th	Day	18% 14% 4 11% 7% 6% 6% 4 6% 6% 17%	4703
	11th to 20th	Day	20% 13% 4 9% 5% 4 4 3 4 5% 28%	5000
	21st to end	Day	22% 11% 4 11% 8% 6% 6% 5% 6% 6% 16%	5634
April	1st to 10th	Day	23% 12% 4 9% 6% 6% 5% 5% 6% 7% 19%	2400
	11th to 20th	Day	18% 11% 4 7% 7% 5% 4 4 5% 6% 28%	2410
	21st to end	Day	17% 9% 4 10% 6% 5% 5% 5% 6% 7% 26%	2622
May	1st to 10th	Day	13% 8% 3 7% 5% 4 5% 4 5% 7% 40%	6320
	11th to 20th	Day	19% 10% 4 8% 6% 5% 5% 4 6% 6% 29%	6277
	21st to end	Day	15% 10% 3 8% 5% 5% 5% 5% 6% 8% 30%	6903
June	1st to 10th	Day	16% 8% 3 8% 6% 6% 4 5% 7% 8% 29%	2863
	11th to 20th	Day	13% 12% 4 9% 9% 7% 6% 5% 6% 7% 21%	3000
	21st to end	Day	12% 8% 3 7% 5% 5% 5% 5% 6% 7% 38%	3000
July	1st to 10th	Day	7% 5% 2 5% 3 3 3 3 4 6% 60%	6780
	11th to 20th	Day	4 4 1 3 3 3 3 3 4 5% 68%	6514
	21st to end	Day	9% 6% 2 5% 3 3 3 3 5% 7% 54%	6874
August	1st to 10th	Day	5% 5% 2 6% 4 4 3 3 5% 6% 58%	4418
	11th to 20th	Day	13% 6% 3 7% 4 4 5% 3 6% 8% 40%	4156
	21st to end	Day	14% 9% 3 7% 4 4 4 3 4 6% 42%	4485
September	1st to 10th	Day	9% 6% 2 6% 5% 4 4 3 5% 7% 49%	2400
	11th to 20th	Day	12% 8% 2 8% 5% 4 5% 4 6% 7% 39%	2400
	21st to end	Day	16% 7% 3 6% 4 4 6% 4 5% 8% 37%	2107
October	1st to 10th	Day	13% 8% 2 6% 4 5% 6% 4 7% 10% 35%	3280
	11th to 20th	Day	26% 8% 3 7% 5% 4 4 4 6% 7% 26%	3261
	21st to end	Day	28% 11% 3 9% 6% 4 4 3 5% 6% 21%	3396
November	1st to 10th	Day	29% 12% 3 8% 5% 4 4 4 6% 6% 18%	1678
	11th to 20th	Day	30% 11% 3 8% 6% 5% 4 3 4 6% 19%	1680
	21st to end	Day	28% 11% 3 10% 6% 5% 5% 3 5% 6% 18%	1680
December	1st to 10th	Day	21% 8% 3 12% 8% 7% 6% 4 5% 7% 19%	2700
	11th to 20th	Day	35% 11% 4 12% 6% 5% 4 3 5% 4 10%	3105
	21st to end	Day	31% 15% 5% 12% 7% 5% 5% 3 5% 4 10%	3640
January	1st to 10th	Night	32% 14% 5% 10% 6% 5% 4 3 4 4 13%	8756
	11th to 20th	Night	19% 10% 4 9% 4 4 3 3 4 6% 35%	8182
	21st to end	Night	26% 11% 3 9% 5% 5% 4 3 4 5% 25%	8767
February	1st to 10th	Night	25% 14% 4 9% 5% 5% 4 3 5% 7% 21%	2730
	11th to 20th	Night	22% 12% 4 8% 6% 5% 4 3 5% 6% 25%	2662
	21st to end	Night	23% 12% 3 9% 6% 4 5% 4 5% 6% 24%	2191
March	1st to 10th	Night	17% 14% 4 10% 6% 6% 6% 5% 6% 8% 20%	5234
	11th to 20th	Night	22% 12% 3 6% 4 4 4 3 5% 6% 32%	4999
	21st to end	Night	27% 13% 4 9% 6% 5% 4 4 6% 5% 17%	5341
April	1st to 10th	Night	20% 9% 4 9% 6% 5% 5% 4 7% 7% 24%	2000
	11th to 20th	Night	14% 9% 3 9% 5% 5% 5% 4 6% 7% 32%	1935
	21st to end	Night	16% 9% 3 8% 7% 5% 4 4 6% 7% 31%	1776
May	1st to 10th	Night	14% 8% 3 6% 4 4 5% 3 4 5% 44%	3640
	11th to 20th	Night	12% 8% 3 8% 5% 5% 5% 4 6% 7% 37%	3616
	21st to end	Night	7% 7% 3 8% 6% 6% 6% 5% 8% 9% 35%	3972
June	1st to 10th	Night	12% 6% 3 8% 5% 5% 5% 4 6% 8% 39%	1532
	11th to 20th	Night	11% 8% 2 7% 7% 7% 6% 5% 6% 9% 33%	1400
	21st to end	Night	5% 6% 2 8% 6% 4 4 5% 6% 6% 48%	1400
July	1st to 10th	Night	6% 4 1 5% 3 3 3 2 4 4 63%	3180
	11th to 20th	Night	2 2 1 2 2 2 3 2 3 5% 76%	3443
	21st to end	Night	4 4 1 4 3 3 3 3 5% 7% 62%	3969
August	1st to 10th	Night	3 2 1 4 2 3 3 2 4 6% 70%	2733
	11th to 20th	Night	10% 6% 2 6% 3 4 3 3 4 8% 53%	2902
	21st to end	Night	13% 6% 2 5% 4 3 4 3 4 6% 50%	3429
September	1st to 10th	Night	7% 4 2 4 3 3 4 3 5% 6% 59%	2000
	11th to 20th	Night	12% 7% 3 6% 5% 4 4 3 5% 6% 45%	2000
	21st to end	Night	14% 6% 3 7% 4 5% 5% 3 5% 7% 42%	2289
October	1st to 10th	Night	14% 6% 2 6% 4 4 4 3 5% 9% 42%	3920
	11th to 20th	Night	23% 8% 2 6% 4 4 5% 3 5% 7% 32%	3897
	21st to end	Night	27% 10% 3 8% 5% 4 4 3 5% 5% 27%	4410
November	1st to 10th	Night	31% 10% 3 7% 5% 5% 5% 3 4 5% 23%	2836
	11th to 20th	Night	29% 11% 3 7% 5% 5% 4 3 4 4 23%	2940
	21st to end	Night	26% 10% 4 9% 6% 5% 4 4 5% 6% 21%	2940
December	1st to 10th	Night	21% 9% 3 11% 6% 5% 5% 4 5% 6% 24%	4700
	11th to 20th	Night	34% 14% 5% 11% 6% 5% 4 3 4 4 11%	5320
	21st to end	Night	32% 16% 5% 10% 5% 4 4 3 4 4 12%	7553

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	75% 9% 7% 7% 2	4125
	11th to 20th	Day	61% 6% 8% 16% 9% 1	4736
	21st to end	Day	65% 5% 9% 14% 7%	5423
February	1st to 10th	Day	67% 11% 9% 8% 4 1	1890
	11th to 20th	Day	66% 8% 10% 10% 6%	1854
	21st to end	Day	62% 11% 12% 11% 5%	1614
March	1st to 10th	Day	59% 11% 15% 12% 3	4703
	11th to 20th	Day	57% 7% 13% 19% 3	5000
	21st to end	Day	65% 10% 14% 9% 1	5634
April	1st to 10th	Day	60% 12% 16% 11% 1	2400
	11th to 20th	Day	53% 9% 14% 15% 6% 2	2410
	21st to end	Day	54% 12% 16% 13% 5% 1	2622
May	1st to 10th	Day	39% 9% 17% 24% 10% 1	6320
	11th to 20th	Day	50% 10% 19% 17% 4	6280
	21st to end	Day	46% 11% 22% 18% 3	6904
June	1st to 10th	Day	48% 12% 20% 14% 6% 1	2863
	11th to 20th	Day	56% 12% 16% 12% 4	3000
	21st to end	Day	41% 11% 21% 19% 7% 2	3000
July	1st to 10th	Day	26% 6% 17% 23% 18% 10%	6706
	11th to 20th	Day	20% 4 14% 29% 29% 4	6434
	21st to end	Day	30% 4 21% 33% 10% 2	6681
August	1st to 10th	Day	25% 5% 13% 35% 20% 2	4401
	11th to 20th	Day	41% 6% 20% 23% 9% 2	4195
	21st to end	Day	43% 6% 13% 27% 11% 1	4484
September	1st to 10th	Day	33% 8% 18% 23% 13% 5%	2400
	11th to 20th	Day	41% 11% 15% 17% 14% 2	2400
	21st to end	Day	45% 9% 18% 17% 10% 2	2107
October	1st to 10th	Day	44% 6% 18% 27% 5%	3280
	11th to 20th	Day	57% 8% 12% 15% 7%	3261
	21st to end	Day	63% 6% 11% 12% 6% 1	3396
November	1st to 10th	Day	65% 8% 13% 10% 4	1678
	11th to 20th	Day	66% 9% 8% 10% 5% 1	1680
	21st to end	Day	64% 9% 10% 11% 6%	1680
December	1st to 10th	Day	65% 5% 8% 15% 7%	2700
	11th to 20th	Day	74% 9% 8% 7% 1	3108
	21st to end	Day	73% 9% 10% 6% 2	3640
January	1st to 10th	Night	76% 7% 7% 7% 2	8756
	11th to 20th	Night	54% 7% 9% 19% 11% 1	8220
	21st to end	Night	64% 6% 8% 17% 6%	8767
February	1st to 10th	Night	63% 9% 13% 10% 5%	2730
	11th to 20th	Night	58% 11% 12% 11% 7% 1	2664
	21st to end	Night	59% 10% 14% 11% 5%	2191
March	1st to 10th	Night	55% 12% 16% 13% 5%	5234
	11th to 20th	Night	51% 9% 15% 22% 3 1	5000
	21st to end	Night	65% 12% 12% 10% 1	5341
April	1st to 10th	Night	56% 13% 17% 12% 2	2000
	11th to 20th	Night	47% 13% 16% 14% 9% 1	1935
	21st to end	Night	51% 12% 16% 15% 6% 1	1776
May	1st to 10th	Night	40% 9% 13% 29% 10% 1	3637
	11th to 20th	Night	43% 11% 22% 18% 6%	3616
	21st to end	Night	43% 18% 20% 18% 1	3972
June	1st to 10th	Night	43% 9% 21% 20% 6% 1	1532
	11th to 20th	Night	44% 15% 21% 17% 3	1400
	21st to end	Night	36% 9% 24% 21% 8% 3	1400
July	1st to 10th	Night	27% 5% 18% 22% 16% 12%	3145
	11th to 20th	Night	13% 4 17% 28% 35% 3	3400
	21st to end	Night	23% 5% 22% 31% 15% 3	3857
August	1st to 10th	Night	18% 5% 12% 38% 25% 2	2725
	11th to 20th	Night	33% 5% 27% 22% 10% 2	2929
	21st to end	Night	37% 7% 16% 27% 13% 1	3429
September	1st to 10th	Night	25% 9% 20% 27% 15% 5%	2000
	11th to 20th	Night	39% 10% 13% 18% 16% 4	2000
	21st to end	Night	42% 9% 14% 23% 10% 2	2289
October	1st to 10th	Night	41% 5% 19% 29% 5%	3920
	11th to 20th	Night	52% 6% 15% 21% 5%	3897
	21st to end	Night	60% 5% 11% 15% 8% 1	4410
November	1st to 10th	Night	62% 9% 13% 12% 3 1	2836
	11th to 20th	Night	64% 8% 11% 10% 6% 2	2940
	21st to end	Night	61% 11% 12% 9% 7% 1	2940
December	1st to 10th	Night	65% 7% 8% 15% 6%	4700
	11th to 20th	Night	76% 8% 9% 5% 2	5316
	21st to end	Night	73% 8% 10% 7% 2	7553

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	38% 12% 21% 15% 10% 4	220
	11th to 20th	Day	27% 14% 22% 18% 15% 4	220
	21st to end	Day	33% 14% 20% 18% 12% 3	323
February	1st to 10th	Day	34% 15% 17% 21% 9% 3	430
	11th to 20th	Day	35% 16% 23% 17% 7% 2	425
	21st to end	Day	31% 17% 26% 17% 8% 1	386
March	1st to 10th	Day	26% 16% 26% 21% 9% 2	509
	11th to 20th	Day	27% 15% 22% 20% 11% 5%	500
	21st to end	Day	26% 17% 26% 20% 10% 2	550
April	1st to 10th	Day	28% 15% 23% 21% 10% 3	500
	11th to 20th	Day	22% 16% 29% 20% 8% 5%	492
	21st to end	Day	19% 14% 27% 25% 13% 2	500
May	1st to 10th	Day	15% 11% 26% 30% 15% 4	503
	11th to 20th	Day	23% 8% 21% 25% 16% 7%	528
	21st to end	Day	17% 8% 24% 28% 16% 7%	573
June	1st to 10th	Day	19% 9% 23% 26% 17% 6%	593
	11th to 20th	Day	18% 13% 23% 29% 14% 3	730
	21st to end	Day	13% 7% 20% 34% 20% 6%	730
July	1st to 10th	Day	10% 4 19% 34% 26% 8%	721
	11th to 20th	Day	5% 4 16% 38% 29% 9%	609
	21st to end	Day	8% 3 10% 29% 38% 13%	575
August	1st to 10th	Day	9% 4 14% 30% 32% 10%	527
	11th to 20th	Day	10% 3 14% 30% 31% 12%	517
	21st to end	Day	14% 8% 18% 32% 22% 7%	583
September	1st to 10th	Day	13% 6% 21% 35% 20% 5%	530
	11th to 20th	Day	16% 8% 20% 28% 22% 7%	530
	21st to end	Day	17% 11% 23% 29% 16% 4	530
October	1st to 10th	Day	21% 10% 24% 22% 18% 6%	530
	11th to 20th	Day	26% 12% 19% 24% 14% 5%	530
	21st to end	Day	33% 14% 20% 19% 11% 3	483
November	1st to 10th	Day	33% 18% 22% 16% 11% 1	236
	11th to 20th	Day	35% 13% 25% 13% 10% 5%	220
	21st to end	Day	32% 13% 20% 17% 11% 7%	220
December	1st to 10th	Day	39% 13% 17% 15% 12% 5%	220
	11th to 20th	Day	42% 16% 20% 14% 7% 1	220
	21st to end	Day	38% 14% 19% 17% 10% 2	242
January	1st to 10th	Night	40% 13% 17% 16% 12% 2	949
	11th to 20th	Night	31% 10% 17% 23% 17% 2	840
	21st to end	Night	27% 11% 19% 26% 15% 2	924
February	1st to 10th	Night	32% 14% 20% 23% 11% 2	840
	11th to 20th	Night	26% 12% 23% 25% 13% 1	824
	21st to end	Night	27% 14% 22% 24% 10% 2	692
March	1st to 10th	Night	25% 13% 22% 25% 13% 1	808
	11th to 20th	Night	25% 15% 21% 25% 13% 2	800
	21st to end	Night	26% 15% 22% 26% 9% 1	880
April	1st to 10th	Night	23% 11% 25% 26% 14% 2	800
	11th to 20th	Night	17% 11% 27% 30% 13% 3	747
	21st to end	Night	19% 11% 22% 34% 14% 2	576
May	1st to 10th	Night	14% 11% 22% 35% 17% 1	400
	11th to 20th	Night	15% 5% 20% 33% 25% 2	394
	21st to end	Night	11% 6% 18% 38% 24% 3	433
June	1st to 10th	Night	12% 8% 22% 35% 22% 1	400
	11th to 20th	Night	12% 10% 26% 35% 16% 2	400
	21st to end	Night	8% 7% 19% 39% 25% 2	400
July	1st to 10th	Night	7% 3 14% 38% 35% 2	390
	11th to 20th	Night	5% 2 17% 41% 33% 2	388
	21st to end	Night	5% 2 11% 38% 39% 4	438
August	1st to 10th	Night	5% 3 11% 32% 41% 9%	470
	11th to 20th	Night	7% 2 10% 29% 45% 7%	594
	21st to end	Night	10% 3 15% 36% 33% 4	766
September	1st to 10th	Night	9% 3 15% 39% 30% 4	800
	11th to 20th	Night	14% 5% 16% 29% 32% 5%	800
	21st to end	Night	17% 7% 18% 34% 21% 3	800
October	1st to 10th	Night	17% 5% 20% 29% 25% 4	800
	11th to 20th	Night	25% 8% 17% 27% 20% 3	800
	21st to end	Night	27% 9% 22% 27% 14% 2	880
November	1st to 10th	Night	33% 11% 19% 26% 11%	820
	11th to 20th	Night	33% 12% 22% 20% 12% 1	840
	21st to end	Night	29% 10% 21% 23% 14% 2	840
December	1st to 10th	Night	30% 9% 16% 28% 16% 1	840
	11th to 20th	Night	36% 11% 22% 21% 9% 1	840
	21st to end	Night	39% 14% 19% 19% 9% 1	1029

Page generated at 2026-02-27 22:40:23. Version ac07

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