Kirkland
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Kirkland clear sky chart from 2005-11-06 to 2026-04-02.

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% 5% 5% 4 6% 7% 36%	131437
	Night	13% 10% 4 8% 5% 4 4 4 5% 6% 38%	130682
Transparency	Day	44% 6% 12% 23% 13% 1	134944
	Night	45% 6% 11% 22% 14% 2	135250
Seeing	Day	16% 11% 29% 25% 14% 5%	17682
	Night	17% 10% 32% 30% 11% 1	27683

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	10% 13% 7% 15% 7% 6% 5% 4 6% 6% 22%	4691
	11th to 20th	Day	7% 11% 6% 13% 5% 5% 5% 6% 7% 6% 30%	4710
	21st to end	Day	11% 13% 6% 9% 5% 5% 4 3 5% 6% 32%	5431
February	1st to 10th	Day	12% 13% 5% 10% 6% 6% 7% 4 5% 6% 25%	1890
	11th to 20th	Day	12% 11% 3 9% 6% 5% 4 3 5% 5% 36%	2035
	21st to end	Day	12% 13% 4 11% 5% 4 4 4 5% 5% 32%	1730
March	1st to 10th	Day	16% 11% 3 6% 3 3 3 3 4 5% 43%	4580
	11th to 20th	Day	11% 6% 2 8% 4 5% 5% 3 6% 8% 42%	4843
	21st to end	Day	18% 13% 5% 13% 6% 5% 5% 3 5% 5% 22%	6088
April	1st to 10th	Day	18% 12% 3 8% 6% 4 4 4 4 6% 30%	2412
	11th to 20th	Day	16% 9% 2 7% 5% 6% 5% 4 6% 6% 33%	2374
	21st to end	Day	18% 8% 3 8% 5% 5% 5% 4 5% 6% 33%	2470
May	1st to 10th	Day	15% 8% 3 6% 5% 4 5% 4 6% 8% 36%	5878
	11th to 20th	Day	13% 6% 2 6% 5% 5% 5% 4 6% 7% 41%	6319
	21st to end	Day	14% 7% 3 6% 4 5% 5% 4 7% 9% 37%	6935
June	1st to 10th	Day	9% 5% 2 6% 4 5% 4 4 7% 8% 45%	2800
	11th to 20th	Day	9% 6% 2 5% 4 4 5% 4 7% 10% 45%	2800
	21st to end	Day	10% 7% 2 7% 4 5% 5% 5% 7% 9% 40%	2800
July	1st to 10th	Day	9% 7% 3 7% 5% 5% 5% 5% 7% 10% 36%	6360
	11th to 20th	Day	8% 6% 2 6% 4 4 5% 4 7% 10% 42%	6360
	21st to end	Day	9% 7% 3 8% 5% 5% 5% 4 7% 9% 38%	6924
August	1st to 10th	Day	9% 6% 2 6% 4 4 5% 4 7% 9% 43%	4502
	11th to 20th	Day	11% 5% 2 5% 4 4 5% 4 7% 10% 44%	3849
	21st to end	Day	8% 5% 2 5% 4 5% 5% 4 6% 9% 47%	4312
September	1st to 10th	Day	11% 5% 2 5% 3 4 5% 3 5% 8% 47%	2400
	11th to 20th	Day	12% 4 1 4 3 4 3 3 5% 8% 53%	2308
	21st to end	Day	11% 6% 2 6% 5% 3 4 3 6% 7% 46%	2200
October	1st to 10th	Day	12% 6% 2 6% 3 4 4 3 5% 6% 48%	2090
	11th to 20th	Day	18% 9% 3 6% 4 4 4 4 5% 6% 36%	2000
	21st to end	Day	19% 9% 3 7% 4 3 3 3 5% 5% 38%	2003
November	1st to 10th	Day	12% 8% 3 7% 4 4 4 4 5% 6% 44%	1852
	11th to 20th	Day	15% 13% 4 9% 6% 4 4 4 5% 7% 30%	1890
	21st to end	Day	16% 13% 5% 10% 4 3 3 2 4 5% 35%	1753
December	1st to 10th	Day	8% 9% 4 9% 5% 4 4 3 4 7% 42%	2690
	11th to 20th	Day	11% 16% 5% 12% 7% 6% 5% 4 5% 6% 23%	3088
	21st to end	Day	21% 23% 8% 13% 5% 4 4 3 3 4 12%	4070
January	1st to 10th	Night	10% 14% 6% 14% 6% 5% 4 3 4 4 31%	8232
	11th to 20th	Night	10% 13% 6% 15% 7% 6% 5% 5% 7% 5% 21%	8280
	21st to end	Night	12% 14% 6% 9% 5% 4 4 3 5% 6% 32%	8781
February	1st to 10th	Night	14% 14% 5% 9% 5% 5% 4 3 4 5% 32%	2730
	11th to 20th	Night	13% 10% 4 8% 5% 4 4 3 5% 6% 38%	2469
	21st to end	Night	16% 12% 4 8% 4 3 3 3 4 7% 35%	2076
March	1st to 10th	Night	16% 10% 4 7% 4 4 4 3 4 5% 42%	5493
	11th to 20th	Night	9% 7% 2 6% 4 4 4 3 5% 7% 48%	5382
	21st to end	Night	19% 12% 6% 11% 5% 4 4 3 4 5% 28%	5082
April	1st to 10th	Night	17% 10% 3 5% 4 4 4 4 4 5% 39%	2010
	11th to 20th	Night	17% 10% 3 6% 5% 4 4 3 4 6% 39%	1975
	21st to end	Night	17% 9% 3 7% 4 4 4 4 5% 7% 38%	1927
May	1st to 10th	Night	18% 7% 3 6% 4 4 4 4 6% 7% 37%	4002
	11th to 20th	Night	11% 6% 2 5% 4 4 4 4 7% 9% 43%	3596
	21st to end	Night	14% 9% 2 6% 4 4 5% 4 6% 7% 39%	3942
June	1st to 10th	Night	10% 4 1 5% 5% 4 5% 4 7% 8% 47%	1600
	11th to 20th	Night	9% 6% 2 6% 4 4 4 5% 7% 8% 46%	1600
	21st to end	Night	9% 6% 2 6% 4 6% 5% 4 7% 7% 44%	1600
July	1st to 10th	Night	11% 7% 2 7% 5% 4 4 4 6% 9% 41%	3618
	11th to 20th	Night	6% 5% 3 6% 4 4 4 4 6% 8% 49%	3617
	21st to end	Night	9% 6% 2 6% 5% 5% 5% 5% 6% 8% 43%	3947
August	1st to 10th	Night	5% 4 2 6% 4 5% 4 4 6% 9% 50%	2654
	11th to 20th	Night	8% 5% 2 6% 4 4 4 4 6% 8% 48%	3200
	21st to end	Night	8% 4 2 5% 4 4 4 3 6% 9% 51%	3586
September	1st to 10th	Night	9% 6% 2 5% 4 3 3 3 5% 6% 55%	2000
	11th to 20th	Night	9% 4 1 5% 3 4 4 3 5% 7% 54%	2071
	21st to end	Night	10% 6% 2 5% 3 5% 4 3 5% 7% 49%	2200
October	1st to 10th	Night	11% 6% 3 5% 4 4 4 3 4 5% 52%	2307
	11th to 20th	Night	16% 8% 2 6% 3 3 4 3 4 6% 45%	2400
	21st to end	Night	19% 9% 3 6% 4 4 4 3 5% 6% 38%	2835
November	1st to 10th	Night	12% 8% 2 6% 3 4 4 3 4 6% 48%	2666
	11th to 20th	Night	14% 11% 4 8% 4 4 4 3 5% 6% 36%	2730
	21st to end	Night	16% 12% 4 8% 4 3 4 3 5% 5% 35%	2865
December	1st to 10th	Night	10% 9% 3 7% 5% 5% 5% 4 5% 6% 41%	4720
	11th to 20th	Night	15% 16% 5% 10% 5% 4 4 3 4 5% 29%	5339
	21st to end	Night	21% 19% 7% 11% 5% 5% 5% 4 4 4 16%	7150

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	62% 4 13% 15% 6%	4692
	11th to 20th	Day	51% 5% 11% 16% 14% 3	4710
	21st to end	Day	52% 4 14% 21% 8%	5431
February	1st to 10th	Day	57% 6% 12% 15% 9% 1	1890
	11th to 20th	Day	49% 6% 11% 23% 9% 2	2045
	21st to end	Day	53% 6% 10% 20% 10% 1	1730
March	1st to 10th	Day	44% 5% 10% 27% 11% 4	4580
	11th to 20th	Day	39% 5% 12% 32% 11% 1	4843
	21st to end	Day	62% 7% 10% 14% 6% 1	6090
April	1st to 10th	Day	54% 6% 10% 21% 9%	2412
	11th to 20th	Day	48% 7% 10% 21% 11% 2	2374
	21st to end	Day	51% 6% 12% 18% 12% 1	2470
May	1st to 10th	Day	44% 7% 11% 22% 16% 1	5913
	11th to 20th	Day	39% 8% 10% 26% 16% 1	6323
	21st to end	Day	40% 7% 12% 25% 12% 3	6949
June	1st to 10th	Day	34% 7% 14% 27% 16% 2	2800
	11th to 20th	Day	33% 7% 13% 25% 19% 2	2800
	21st to end	Day	39% 9% 13% 24% 14% 2	2800
July	1st to 10th	Day	40% 7% 14% 25% 12% 1	6291
	11th to 20th	Day	35% 8% 15% 27% 15% 1	6285
	21st to end	Day	38% 9% 17% 19% 14% 2	6728
August	1st to 10th	Day	35% 8% 16% 29% 11% 1	4487
	11th to 20th	Day	32% 7% 13% 33% 14% 1	3885
	21st to end	Day	32% 7% 12% 30% 17% 2	4311
September	1st to 10th	Day	35% 7% 11% 27% 17% 3	2400
	11th to 20th	Day	29% 6% 12% 31% 21% 2	2308
	21st to end	Day	36% 5% 11% 27% 19% 1	2200
October	1st to 10th	Day	25% 4 7% 33% 30% 1	3402
	11th to 20th	Day	33% 5% 11% 26% 25% 2	3240
	21st to end	Day	43% 4 9% 28% 14% 3	3215
November	1st to 10th	Day	40% 4 14% 25% 15% 2	1852
	11th to 20th	Day	53% 4 11% 21% 10% 1	1890
	21st to end	Day	54% 4 12% 22% 8%	1753
December	1st to 10th	Day	43% 4 17% 27% 8% 1	2690
	11th to 20th	Day	60% 5% 11% 17% 6% 1	3085
	21st to end	Day	77% 4 6% 8% 5%	4070
January	1st to 10th	Night	56% 5% 11% 18% 9%	8233
	11th to 20th	Night	61% 4 10% 11% 12% 1	8280
	21st to end	Night	53% 4 11% 21% 10%	8781
February	1st to 10th	Night	54% 4 10% 18% 12% 1	2730
	11th to 20th	Night	47% 4 11% 23% 13% 1	2470
	21st to end	Night	49% 4 12% 21% 11% 3	2076
March	1st to 10th	Night	46% 4 11% 23% 11% 5%	5493
	11th to 20th	Night	35% 5% 11% 32% 13% 3	5382
	21st to end	Night	59% 5% 9% 18% 9% 1	5082
April	1st to 10th	Night	46% 6% 10% 22% 14% 2	2010
	11th to 20th	Night	46% 6% 7% 21% 16% 4	1975
	21st to end	Night	44% 7% 11% 24% 11% 3	1927
May	1st to 10th	Night	45% 7% 12% 17% 17% 2	4029
	11th to 20th	Night	34% 9% 15% 24% 14% 4	3597
	21st to end	Night	41% 8% 11% 23% 15% 2	3950
June	1st to 10th	Night	32% 7% 14% 26% 19% 3	1600
	11th to 20th	Night	34% 7% 11% 24% 22% 3	1600
	21st to end	Night	37% 8% 13% 21% 18% 2	1600
July	1st to 10th	Night	39% 8% 13% 23% 14% 2	3580
	11th to 20th	Night	30% 7% 13% 29% 19% 1	3572
	21st to end	Night	35% 9% 14% 22% 17% 2	3832
August	1st to 10th	Night	28% 8% 14% 30% 18% 2	2645
	11th to 20th	Night	31% 8% 14% 30% 17% 1	3230
	21st to end	Night	28% 6% 13% 31% 18% 3	3586
September	1st to 10th	Night	29% 6% 10% 28% 24% 3	2000
	11th to 20th	Night	29% 6% 9% 33% 22% 2	2071
	21st to end	Night	34% 6% 11% 29% 19% 2	2200
October	1st to 10th	Night	23% 4 7% 35% 29% 2	3775
	11th to 20th	Night	35% 4 8% 24% 27% 3	3899
	21st to end	Night	42% 4 9% 25% 18% 3	4573
November	1st to 10th	Night	39% 5% 9% 27% 18% 3	2666
	11th to 20th	Night	47% 5% 11% 22% 12% 2	2730
	21st to end	Night	51% 4 11% 22% 11%	2865
December	1st to 10th	Night	42% 6% 14% 27% 10% 2	4720
	11th to 20th	Night	57% 4 12% 16% 10% 1	5341
	21st to end	Night	70% 5% 8% 11% 5%	7150

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	19% 12% 36% 25% 7%	330
	11th to 20th	Day	21% 14% 43% 18% 3 1	330
	21st to end	Day	21% 14% 37% 23% 3 1	363
February	1st to 10th	Day	17% 19% 38% 21% 5% 1	330
	11th to 20th	Day	22% 16% 36% 21% 4	330
	21st to end	Day	22% 21% 40% 15% 1	273
March	1st to 10th	Day	18% 22% 38% 19% 3	330
	11th to 20th	Day	25% 17% 36% 14% 7% 1	330
	21st to end	Day	26% 15% 34% 18% 6% 2	583
April	1st to 10th	Day	25% 13% 34% 23% 5%	504
	11th to 20th	Day	22% 21% 26% 20% 10% 2	492
	21st to end	Day	23% 14% 31% 22% 9% 2	500
May	1st to 10th	Day	19% 14% 30% 24% 9% 3	506
	11th to 20th	Day	20% 10% 29% 25% 13% 3	725
	21st to end	Day	16% 10% 29% 25% 15% 6%	789
June	1st to 10th	Day	9% 8% 31% 28% 18% 5%	730
	11th to 20th	Day	10% 6% 32% 31% 15% 5%	730
	21st to end	Day	11% 8% 30% 32% 15% 5%	730
July	1st to 10th	Day	9% 3 20% 29% 25% 14%	721
	11th to 20th	Day	9% 5% 23% 33% 20% 10%	718
	21st to end	Day	8% 3 21% 37% 23% 8%	794
August	1st to 10th	Day	9% 3 19% 33% 25% 12%	726
	11th to 20th	Day	11% 5% 17% 27% 23% 17%	519
	21st to end	Day	8% 4 16% 32% 28% 12%	583
September	1st to 10th	Day	12% 7% 20% 29% 24% 8%	530
	11th to 20th	Day	8% 3 20% 29% 26% 14%	530
	21st to end	Day	13% 11% 25% 24% 19% 8%	530
October	1st to 10th	Day	13% 9% 29% 25% 19% 5%	420
	11th to 20th	Day	21% 19% 31% 22% 8% 1	330
	21st to end	Day	28% 13% 31% 22% 5% 1	363
November	1st to 10th	Day	15% 17% 35% 20% 10% 2	330
	11th to 20th	Day	22% 19% 34% 16% 7% 1	330
	21st to end	Day	22% 12% 39% 20% 6%	330
December	1st to 10th	Day	16% 15% 43% 19% 6% 1	330
	11th to 20th	Day	17% 13% 41% 21% 8%	330
	21st to end	Day	27% 17% 38% 14% 3	363
January	1st to 10th	Night	19% 13% 38% 24% 5%	1050
	11th to 20th	Night	19% 14% 40% 21% 5% 1	1050
	21st to end	Night	20% 12% 36% 28% 5%	1155
February	1st to 10th	Night	23% 10% 40% 23% 5%	1050
	11th to 20th	Night	19% 12% 37% 27% 4	834
	21st to end	Night	21% 12% 42% 22% 4	692
March	1st to 10th	Night	21% 11% 38% 24% 5%	840
	11th to 20th	Night	16% 12% 37% 28% 6%	766
	21st to end	Night	22% 13% 35% 24% 6% 1	693
April	1st to 10th	Night	22% 13% 36% 25% 4	603
	11th to 20th	Night	22% 13% 31% 27% 6%	593
	21st to end	Night	20% 10% 35% 28% 8%	600
May	1st to 10th	Night	18% 9% 33% 31% 8% 1	600
	11th to 20th	Night	17% 7% 33% 31% 12%	591
	21st to end	Night	15% 5% 28% 35% 17%	650
June	1st to 10th	Night	9% 5% 28% 42% 15%	600
	11th to 20th	Night	10% 4 31% 44% 11% 1	600
	21st to end	Night	9% 4 30% 38% 18% 1	600
July	1st to 10th	Night	9% 2 16% 39% 30% 3	585
	11th to 20th	Night	8% 3 22% 40% 23% 4	582
	21st to end	Night	7% 1 19% 46% 25% 2	657
August	1st to 10th	Night	5% 3 14% 47% 28% 4	597
	11th to 20th	Night	7% 3 14% 41% 30% 4	594
	21st to end	Night	9% 2 17% 41% 29% 2	660
September	1st to 10th	Night	10% 3 21% 35% 27% 4	600
	11th to 20th	Night	10% 5% 18% 35% 29% 3	671
	21st to end	Night	12% 8% 24% 33% 21% 3	800
October	1st to 10th	Night	13% 6% 28% 35% 17% 1	800
	11th to 20th	Night	20% 11% 32% 27% 9%	800
	21st to end	Night	24% 12% 31% 25% 8%	880
November	1st to 10th	Night	17% 11% 39% 23% 10% 1	820
	11th to 20th	Night	20% 14% 35% 24% 7%	840
	21st to end	Night	20% 14% 37% 23% 5%	975
December	1st to 10th	Night	20% 13% 38% 24% 5%	1050
	11th to 20th	Night	22% 13% 36% 25% 4 1	1050
	21st to end	Night	28% 14% 34% 21% 3	1155

Page generated at 2026-03-30 01:18:39. Version ac07

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