Keivers Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Keivers Lake clear sky chart from 2005-11-06 to 2026-04-17.

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	9% 9% 3 8% 5% 5% 5% 4 6% 8% 37%	135411
	Night	7% 9% 4 10% 6% 6% 6% 4 6% 8% 35%	135454
Transparency	Day	45% 3 15% 26% 10% 1	135109
	Night	47% 3 14% 24% 10% 2	135335
Seeing	Day	12% 6% 25% 31% 19% 6%	17188
	Night	12% 5% 29% 36% 16% 2	26433

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	3 11% 6% 14% 8% 7% 5% 4 5% 7% 28%	4125
	11th to 20th	Day	3 7% 3 10% 6% 6% 7% 5% 7% 7% 39%	4119
	21st to end	Day	3 9% 3 10% 5% 5% 4 4 6% 8% 42%	5126
February	1st to 10th	Day	5% 13% 5% 11% 7% 6% 6% 4 7% 8% 27%	1680
	11th to 20th	Day	7% 13% 4 10% 8% 6% 6% 6% 8% 8% 26%	1835
	21st to end	Day	4 13% 6% 12% 8% 6% 6% 5% 7% 7% 27%	1651
March	1st to 10th	Day	2 11% 4 11% 7% 6% 6% 4 7% 10% 32%	4618
	11th to 20th	Day	5% 11% 4 11% 5% 5% 4 3 6% 9% 36%	5081
	21st to end	Day	9% 19% 7% 14% 6% 5% 5% 4 6% 6% 21%	5651
April	1st to 10th	Day	8% 12% 4 8% 5% 6% 5% 6% 7% 8% 30%	2602
	11th to 20th	Day	11% 14% 4 9% 5% 5% 5% 5% 7% 8% 29%	2649
	21st to end	Day	12% 10% 3 8% 5% 5% 5% 5% 5% 9% 33%	2600
May	1st to 10th	Day	15% 9% 3 6% 4 4 5% 4 5% 7% 38%	6316
	11th to 20th	Day	13% 11% 4 8% 5% 6% 6% 5% 7% 9% 26%	6734
	21st to end	Day	12% 7% 2 7% 5% 6% 5% 4 6% 7% 38%	7405
June	1st to 10th	Day	15% 6% 2 6% 5% 5% 5% 5% 7% 10% 32%	3000
	11th to 20th	Day	17% 8% 3 8% 6% 6% 6% 5% 7% 7% 27%	3000
	21st to end	Day	9% 5% 2 6% 5% 5% 6% 5% 8% 10% 39%	3000
July	1st to 10th	Day	7% 4 2 5% 4 4 5% 4 6% 9% 50%	6780
	11th to 20th	Day	11% 5% 2 5% 3 4 5% 5% 7% 10% 43%	6780
	21st to end	Day	9% 5% 2 6% 4 4 4 4 6% 8% 47%	7336
August	1st to 10th	Day	9% 6% 3 6% 4 5% 6% 5% 7% 9% 41%	4541
	11th to 20th	Day	7% 5% 2 6% 4 4 6% 5% 8% 11% 41%	4199
	21st to end	Day	10% 4 2 4 3 4 4 4 6% 8% 50%	4664
September	1st to 10th	Day	11% 5% 2 6% 4 4 4 4 6% 8% 48%	2501
	11th to 20th	Day	15% 7% 2 6% 3 3 4 3 4 7% 47%	2200
	21st to end	Day	9% 8% 2 5% 4 5% 4 3 6% 9% 45%	2200
October	1st to 10th	Day	7% 7% 2 6% 5% 5% 5% 4 7% 8% 43%	3417
	11th to 20th	Day	6% 7% 3 8% 5% 5% 4 4 6% 10% 41%	3015
	21st to end	Day	8% 8% 3 8% 6% 5% 5% 3 6% 6% 42%	3200
November	1st to 10th	Day	9% 16% 6% 11% 4 5% 5% 4 6% 7% 28%	1678
	11th to 20th	Day	7% 13% 3 10% 6% 4 6% 4 6% 7% 34%	1591
	21st to end	Day	5% 12% 3 12% 6% 6% 5% 5% 7% 7% 31%	1470
December	1st to 10th	Day	7% 12% 5% 10% 7% 7% 5% 4 6% 8% 28%	2360
	11th to 20th	Day	6% 12% 5% 11% 9% 7% 6% 4 5% 7% 28%	2712
	21st to end	Day	3 8% 4 10% 6% 5% 5% 4 5% 8% 42%	3575
January	1st to 10th	Night	4 13% 6% 14% 8% 7% 6% 4 6% 7% 25%	8768
	11th to 20th	Night	2 7% 4 11% 6% 6% 6% 5% 6% 8% 37%	8779
	21st to end	Night	3 9% 4 11% 6% 6% 5% 5% 7% 8% 37%	9100
February	1st to 10th	Night	5% 11% 5% 13% 8% 7% 5% 5% 6% 8% 27%	2940
	11th to 20th	Night	5% 12% 5% 12% 6% 6% 7% 5% 7% 7% 28%	2672
	21st to end	Night	3 11% 4 10% 8% 6% 5% 5% 8% 9% 31%	2153
March	1st to 10th	Night	3 9% 3 12% 8% 6% 6% 5% 8% 9% 31%	5496
	11th to 20th	Night	5% 9% 4 11% 6% 5% 7% 5% 8% 10% 30%	5138
	21st to end	Night	8% 18% 6% 15% 6% 5% 5% 5% 6% 7% 19%	5553
April	1st to 10th	Night	10% 11% 4 9% 7% 4 6% 4 6% 9% 31%	2017
	11th to 20th	Night	8% 12% 4 11% 7% 6% 5% 5% 6% 7% 29%	1835
	21st to end	Night	11% 9% 4 9% 5% 5% 6% 4 6% 8% 31%	1800
May	1st to 10th	Night	15% 9% 3 8% 5% 4 4 4 5% 7% 36%	3650
	11th to 20th	Night	12% 10% 3 8% 6% 6% 6% 5% 6% 9% 28%	3159
	21st to end	Night	13% 8% 3 9% 5% 5% 6% 4 6% 7% 34%	3470
June	1st to 10th	Night	16% 8% 3 8% 6% 5% 5% 5% 7% 7% 30%	1400
	11th to 20th	Night	16% 8% 4 8% 8% 6% 7% 5% 6% 7% 26%	1400
	21st to end	Night	11% 6% 2 6% 5% 6% 5% 6% 6% 9% 39%	1400
July	1st to 10th	Night	6% 5% 2 7% 6% 6% 6% 5% 6% 9% 43%	3180
	11th to 20th	Night	8% 4 3 7% 5% 4 5% 5% 7% 10% 42%	3180
	21st to end	Night	10% 5% 2 5% 4 4 4 4 5% 11% 46%	3505
August	1st to 10th	Night	10% 6% 3 6% 4 5% 4 4 6% 9% 44%	2609
	11th to 20th	Night	6% 5% 2 7% 6% 5% 5% 4 8% 12% 40%	2857
	21st to end	Night	8% 5% 2 6% 4 4 5% 4 7% 10% 47%	3245
September	1st to 10th	Night	9% 5% 2 5% 3 4 5% 4 6% 8% 49%	1895
	11th to 20th	Night	14% 7% 2 6% 3 4 4 4 5% 8% 44%	2200
	21st to end	Night	9% 6% 2 6% 3 4 4 3 7% 8% 47%	2200
October	1st to 10th	Night	8% 7% 2 5% 4 4 5% 4 7% 9% 46%	3777
	11th to 20th	Night	7% 8% 3 7% 5% 5% 5% 4 6% 9% 43%	4120
	21st to end	Night	6% 9% 4 8% 5% 5% 6% 4 6% 7% 41%	4600
November	1st to 10th	Night	9% 15% 4 8% 5% 5% 5% 4 6% 8% 31%	2817
	11th to 20th	Night	5% 10% 4 10% 7% 6% 5% 5% 7% 9% 32%	3026
	21st to end	Night	4 11% 4 11% 7% 7% 5% 4 8% 9% 32%	3150
December	1st to 10th	Night	6% 12% 4 11% 7% 6% 7% 5% 6% 8% 27%	5040
	11th to 20th	Night	6% 12% 5% 13% 8% 7% 6% 4 6% 8% 24%	5700
	21st to end	Night	3 8% 3 10% 6% 5% 5% 4 6% 8% 42%	7623

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% 2 8% 21% 12% 1	4125
	11th to 20th	Day	45% 2 14% 17% 18% 4	4140
	21st to end	Day	42% 1 14% 32% 10%	5127
February	1st to 10th	Day	53% 4 13% 18% 11% 1	1680
	11th to 20th	Day	53% 5% 13% 18% 10% 1	1844
	21st to end	Day	55% 3 10% 20% 11%	1651
March	1st to 10th	Day	48% 2 14% 23% 13%	4618
	11th to 20th	Day	46% 3 12% 24% 14%	5082
	21st to end	Day	65% 2 9% 16% 7% 1	5651
April	1st to 10th	Day	49% 5% 15% 20% 9% 1	2602
	11th to 20th	Day	52% 4 10% 23% 10% 1	2649
	21st to end	Day	50% 3 13% 24% 9% 1	2600
May	1st to 10th	Day	47% 2 9% 25% 15% 3	6316
	11th to 20th	Day	54% 2 12% 25% 7%	6738
	21st to end	Day	45% 2 15% 27% 10%	7406
June	1st to 10th	Day	45% 4 17% 23% 10% 2	3000
	11th to 20th	Day	54% 4 14% 22% 5% 1	3000
	21st to end	Day	37% 5% 21% 29% 7% 1	3000
July	1st to 10th	Day	31% 3 19% 33% 13% 1	6706
	11th to 20th	Day	36% 2 22% 31% 8%	6699
	21st to end	Day	35% 3 18% 28% 14% 3	7129
August	1st to 10th	Day	38% 3 19% 32% 7% 1	4524
	11th to 20th	Day	36% 3 25% 29% 6% 1	4238
	21st to end	Day	32% 3 21% 32% 11% 1	4663
September	1st to 10th	Day	35% 3 17% 29% 11% 4	2501
	11th to 20th	Day	39% 3 14% 31% 11% 2	2200
	21st to end	Day	37% 4 16% 27% 12% 3	2200
October	1st to 10th	Day	39% 2 21% 30% 7% 1	3417
	11th to 20th	Day	39% 3 19% 25% 13% 2	3015
	21st to end	Day	42% 3 8% 35% 11% 1	3200
November	1st to 10th	Day	56% 4 11% 20% 8% 2	1678
	11th to 20th	Day	50% 3 13% 24% 9% 1	1591
	21st to end	Day	50% 4 16% 21% 8% 1	1470
December	1st to 10th	Day	56% 2 15% 19% 6% 1	2360
	11th to 20th	Day	56% 2 16% 20% 5% 1	2714
	21st to end	Day	42% 2 10% 27% 16% 3	3575
January	1st to 10th	Night	60% 2 10% 17% 9% 2	8769
	11th to 20th	Night	45% 2 15% 20% 14% 3	8820
	21st to end	Night	46% 2 17% 26% 9% 1	9100
February	1st to 10th	Night	54% 3 9% 20% 12% 1	2940
	11th to 20th	Night	53% 3 10% 20% 12% 2	2673
	21st to end	Night	47% 4 13% 23% 13% 1	2153
March	1st to 10th	Night	49% 3 16% 21% 11% 1	5496
	11th to 20th	Night	47% 4 14% 24% 10% 1	5138
	21st to end	Night	65% 2 10% 15% 7% 1	5553
April	1st to 10th	Night	50% 5% 13% 19% 13% 1	2017
	11th to 20th	Night	52% 4 11% 23% 9% 1	1835
	21st to end	Night	49% 3 13% 25% 8% 2	1800
May	1st to 10th	Night	49% 2 8% 25% 13% 3	3647
	11th to 20th	Night	52% 2 12% 26% 8%	3159
	21st to end	Night	51% 2 14% 25% 7% 1	3470
June	1st to 10th	Night	51% 6% 13% 20% 10% 1	1400
	11th to 20th	Night	57% 4 13% 19% 6% 2	1400
	21st to end	Night	39% 6% 19% 27% 8% 1	1400
July	1st to 10th	Night	39% 3 17% 26% 14% 1	3145
	11th to 20th	Night	37% 4 19% 33% 5% 3	3138
	21st to end	Night	35% 3 20% 27% 13% 1	3407
August	1st to 10th	Night	38% 3 18% 32% 9%	2601
	11th to 20th	Night	36% 3 24% 31% 6% 1	2884
	21st to end	Night	33% 3 21% 33% 9% 2	3245
September	1st to 10th	Night	34% 3 16% 28% 14% 5%	1895
	11th to 20th	Night	38% 4 15% 28% 11% 4	2200
	21st to end	Night	35% 4 15% 29% 15% 3	2200
October	1st to 10th	Night	36% 2 18% 29% 14% 1	3777
	11th to 20th	Night	39% 3 17% 28% 12% 2	4120
	21st to end	Night	43% 3 13% 30% 11% 1	4600
November	1st to 10th	Night	51% 4 10% 24% 10% 1	2817
	11th to 20th	Night	48% 3 16% 21% 11% 1	3026
	21st to end	Night	49% 4 16% 20% 9% 2	3150
December	1st to 10th	Night	56% 2 17% 18% 6% 1	5040
	11th to 20th	Night	59% 3 18% 16% 5%	5697
	21st to end	Night	41% 2 9% 28% 17% 4	7623

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	7% 5% 25% 38% 18% 7%	220
	11th to 20th	Day	9% 6% 35% 31% 17% 3	220
	21st to end	Day	8% 9% 27% 28% 22% 6%	242
February	1st to 10th	Day	13% 8% 24% 35% 12% 7%	220
	11th to 20th	Day	9% 6% 26% 36% 19% 3	325
	21st to end	Day	7% 8% 26% 35% 21% 5%	367
March	1st to 10th	Day	8% 6% 29% 33% 19% 5%	540
	11th to 20th	Day	8% 4 29% 35% 19% 6%	540
	21st to end	Day	12% 8% 27% 30% 16% 7%	594
April	1st to 10th	Day	14% 9% 27% 30% 15% 6%	540
	11th to 20th	Day	17% 11% 27% 26% 15% 5%	517
	21st to end	Day	15% 8% 25% 30% 18% 4	500
May	1st to 10th	Day	18% 9% 23% 26% 18% 6%	591
	11th to 20th	Day	14% 6% 22% 33% 19% 6%	725
	21st to end	Day	16% 5% 20% 29% 22% 8%	789
June	1st to 10th	Day	16% 8% 23% 34% 15% 5%	730
	11th to 20th	Day	18% 8% 22% 31% 17% 4	730
	21st to end	Day	8% 4 24% 32% 23% 9%	730
July	1st to 10th	Day	11% 4 19% 33% 24% 9%	721
	11th to 20th	Day	12% 3 19% 33% 25% 8%	718
	21st to end	Day	8% 3 20% 31% 28% 11%	779
August	1st to 10th	Day	11% 4 22% 30% 23% 10%	527
	11th to 20th	Day	8% 5% 21% 32% 27% 7%	517
	21st to end	Day	10% 6% 20% 31% 25% 9%	583
September	1st to 10th	Day	12% 6% 27% 29% 19% 7%	530
	11th to 20th	Day	17% 6% 21% 27% 22% 7%	530
	21st to end	Day	13% 12% 30% 28% 13% 5%	530
October	1st to 10th	Day	16% 7% 24% 30% 17% 7%	425
	11th to 20th	Day	10% 9% 35% 27% 15% 4	330
	21st to end	Day	15% 13% 30% 30% 11% 2	363
November	1st to 10th	Day	16% 5% 30% 34% 12% 4	330
	11th to 20th	Day	14% 8% 30% 32% 14% 2	283
	21st to end	Day	8% 5% 32% 30% 17% 8%	220
December	1st to 10th	Day	11% 3 34% 31% 15% 5%	220
	11th to 20th	Day	10% 7% 35% 31% 14% 4	220
	21st to end	Day	9% 3 24% 34% 22% 8%	242
January	1st to 10th	Night	11% 5% 32% 36% 14% 2	1050
	11th to 20th	Night	11% 7% 34% 34% 12% 2	1050
	21st to end	Night	10% 8% 30% 36% 13% 2	965
February	1st to 10th	Night	10% 7% 27% 37% 17% 2	840
	11th to 20th	Night	10% 5% 33% 38% 13% 1	824
	21st to end	Night	8% 2 27% 37% 21% 5%	692
March	1st to 10th	Night	9% 4 29% 40% 16% 3	840
	11th to 20th	Night	9% 4 31% 39% 14% 3	840
	21st to end	Night	13% 6% 27% 35% 16% 3	924
April	1st to 10th	Night	15% 6% 27% 34% 15% 3	757
	11th to 20th	Night	15% 7% 31% 36% 11% 1	611
	21st to end	Night	15% 8% 28% 35% 14% 1	600
May	1st to 10th	Night	16% 9% 26% 33% 15% 1	500
	11th to 20th	Night	11% 7% 30% 35% 17% 1	394
	21st to end	Night	20% 5% 22% 32% 19% 2	433
June	1st to 10th	Night	18% 7% 26% 35% 11% 3	400
	11th to 20th	Night	18% 4 31% 29% 18% 1	400
	21st to end	Night	12% 4 21% 40% 22% 2	400
July	1st to 10th	Night	12% 2 16% 45% 25% 2	390
	11th to 20th	Night	11% 2 19% 47% 20% 2	388
	21st to end	Night	6% 3 18% 40% 29% 3	438
August	1st to 10th	Night	12% 3 16% 38% 27% 4	398
	11th to 20th	Night	10% 4 19% 40% 25% 2	562
	21st to end	Night	9% 4 21% 41% 24%	660
September	1st to 10th	Night	11% 3 24% 41% 19% 2	670
	11th to 20th	Night	16% 3 20% 38% 22% 2	800
	21st to end	Night	11% 4 30% 36% 18% 2	800
October	1st to 10th	Night	15% 4 25% 36% 17% 2	800
	11th to 20th	Night	11% 6% 30% 37% 14% 2	800
	21st to end	Night	11% 9% 32% 34% 14% 1	880
November	1st to 10th	Night	15% 7% 32% 34% 10% 2	972
	11th to 20th	Night	9% 7% 39% 32% 12% 2	1050
	21st to end	Night	10% 5% 34% 37% 12% 2	1050
December	1st to 10th	Night	12% 7% 32% 32% 14% 3	1050
	11th to 20th	Night	9% 6% 34% 36% 12% 2	1050
	21st to end	Night	11% 3 31% 37% 15% 3	1155

Page generated at 2026-04-14 00:44:26. Version ac07

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