Eastlake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Eastlake clear sky chart from 2005-11-06 to 2026-06-16.

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% 12% 4 10% 5% 4 4 3 5% 7% 31%	137507
	Night	16% 14% 5% 10% 5% 4 4 3 5% 6% 28%	134437
Transparency	Day	51% 7% 12% 19% 11% 1	141140
	Night	56% 6% 10% 17% 10% 1	138875
Seeing	Day	20% 11% 26% 26% 13% 3	16797
	Night	23% 12% 25% 25% 12% 2	26402

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	16% 21% 9% 27% 5% 3 2 2 3 4 9%	5258
	11th to 20th	Day	11% 21% 10% 21% 10% 6% 5% 2 3 3 9%	5280
	21st to end	Day	17% 18% 8% 17% 9% 6% 5% 3 3 3 10%	5780
February	1st to 10th	Day	16% 19% 5% 14% 9% 4 3 3 4 4 19%	1890
	11th to 20th	Day	14% 17% 8% 16% 8% 4 4 3 4 5% 19%	1885
	21st to end	Day	18% 15% 5% 13% 5% 4 5% 4 5% 6% 21%	1730
March	1st to 10th	Day	16% 14% 6% 11% 5% 3 4 3 4 6% 28%	4940
	11th to 20th	Day	12% 14% 5% 10% 5% 4 4 3 4 6% 34%	5090
	21st to end	Day	19% 15% 5% 10% 5% 4 4 3 4 5% 27%	5586
April	1st to 10th	Day	17% 12% 4 8% 5% 4 4 3 6% 6% 32%	2361
	11th to 20th	Day	18% 12% 3 6% 4 4 5% 4 5% 6% 34%	2670
	21st to end	Day	19% 11% 3 7% 4 4 3 3 4 6% 36%	2730
May	1st to 10th	Day	19% 10% 3 8% 5% 5% 4 3 5% 5% 31%	7616
	11th to 20th	Day	15% 9% 3 7% 4 4 4 4 6% 8% 35%	7626
	21st to end	Day	16% 8% 3 6% 4 4 4 4 5% 7% 39%	8648
June	1st to 10th	Day	15% 7% 2 6% 4 4 5% 5% 6% 8% 40%	2940
	11th to 20th	Day	13% 6% 2 8% 4 4 5% 4 6% 8% 40%	2870
	21st to end	Day	12% 5% 2 5% 4 5% 5% 4 6% 10% 41%	2955
July	1st to 10th	Day	9% 5% 2 5% 5% 4 4 4 6% 10% 45%	6104
	11th to 20th	Day	12% 6% 2 6% 3 4 4 4 6% 10% 42%	5900
	21st to end	Day	12% 5% 2 6% 4 4 4 4 6% 9% 44%	6424
August	1st to 10th	Day	12% 7% 2 7% 5% 5% 4 4 7% 9% 39%	4234
	11th to 20th	Day	12% 6% 3 7% 5% 4 5% 5% 8% 9% 36%	4174
	21st to end	Day	11% 5% 2 6% 4 5% 5% 4 6% 10% 42%	4591
September	1st to 10th	Day	15% 6% 2 6% 3 3 4 4 6% 9% 43%	2308
	11th to 20th	Day	11% 6% 2 5% 4 3 5% 4 6% 9% 46%	2200
	21st to end	Day	20% 8% 3 7% 4 3 5% 3 5% 7% 36%	2200
October	1st to 10th	Day	17% 5% 3 7% 4 4 3 4 5% 8% 40%	2060
	11th to 20th	Day	22% 10% 3 6% 4 4 4 3 5% 7% 32%	2000
	21st to end	Day	25% 12% 3 7% 5% 4 5% 4 4 6% 26%	2190
November	1st to 10th	Day	16% 14% 4 7% 4 4 4 4 5% 6% 32%	1852
	11th to 20th	Day	18% 22% 4 9% 6% 3 4 3 3 5% 24%	1822
	21st to end	Day	19% 24% 6% 9% 5% 5% 4 3 4 5% 14%	1680
December	1st to 10th	Day	16% 24% 10% 14% 5% 4 4 2 4 4 13%	2680
	11th to 20th	Day	21% 25% 7% 13% 7% 3 4 3 3 5% 9%	3070
	21st to end	Day	23% 23% 8% 15% 5% 4 4 3 4 4 8%	4163
January	1st to 10th	Night	16% 23% 11% 24% 4 3 3 2 2 3 9%	7635
	11th to 20th	Night	9% 21% 11% 21% 9% 4 5% 3 3 3 10%	7680
	21st to end	Night	17% 19% 7% 15% 7% 4 5% 3 3 4 17%	8401
February	1st to 10th	Night	19% 18% 5% 14% 6% 5% 4 3 4 3 19%	2730
	11th to 20th	Night	17% 18% 6% 13% 7% 5% 4 3 5% 5% 18%	2616
	21st to end	Night	18% 16% 6% 13% 5% 4 4 3 5% 4 23%	2076
March	1st to 10th	Night	19% 17% 3 8% 4 3 3 2 4 4 31%	5132
	11th to 20th	Night	13% 13% 4 7% 3 4 4 3 5% 7% 37%	5090
	21st to end	Night	17% 14% 5% 10% 4 3 3 3 4 5% 30%	5588
April	1st to 10th	Night	19% 15% 4 7% 5% 3 3 3 5% 6% 29%	2258
	11th to 20th	Night	17% 11% 2 8% 4 5% 4 4 7% 7% 32%	1917
	21st to end	Night	16% 9% 2 7% 4 4 5% 5% 6% 7% 36%	1890
May	1st to 10th	Night	22% 9% 3 8% 5% 5% 5% 4 5% 6% 28%	5237
	11th to 20th	Night	15% 8% 3 7% 4 4 4 4 5% 8% 37%	5234
	21st to end	Night	21% 8% 2 5% 3 4 4 4 6% 7% 37%	5487
June	1st to 10th	Night	10% 8% 3 7% 5% 4 4 4 5% 7% 43%	1680
	11th to 20th	Night	10% 5% 3 6% 5% 6% 5% 4 6% 8% 41%	1640
	21st to end	Night	10% 5% 2 6% 5% 5% 5% 4 6% 10% 41%	1428
July	1st to 10th	Night	9% 6% 2 7% 4 4 5% 4 7% 9% 45%	3800
	11th to 20th	Night	10% 5% 2 7% 4 4 5% 4 6% 8% 44%	4057
	21st to end	Night	9% 6% 2 6% 4 4 4 4 5% 8% 48%	4427
August	1st to 10th	Night	10% 6% 3 7% 5% 5% 4 4 6% 8% 41%	2915
	11th to 20th	Night	15% 8% 3 7% 4 4 4 3 4 6% 41%	2875
	21st to end	Night	9% 6% 2 6% 5% 5% 6% 4 7% 8% 43%	3272
September	1st to 10th	Night	12% 6% 2 5% 4 4 4 4 5% 8% 44%	2089
	11th to 20th	Night	10% 5% 2 5% 3 4 4 4 6% 6% 51%	2200
	21st to end	Night	18% 7% 3 6% 6% 5% 5% 3 5% 6% 37%	2200
October	1st to 10th	Night	16% 6% 3 5% 4 4 4 3 5% 7% 43%	2340
	11th to 20th	Night	21% 9% 3 8% 5% 4 4 3 5% 6% 33%	2400
	21st to end	Night	28% 10% 3 7% 4 4 3 3 4 6% 27%	2647
November	1st to 10th	Night	17% 14% 3 7% 4 3 4 3 5% 6% 34%	2666
	11th to 20th	Night	19% 22% 4 10% 5% 4 3 3 4 5% 22%	2794
	21st to end	Night	22% 23% 5% 8% 5% 4 4 3 4 4 18%	2940
December	1st to 10th	Night	17% 24% 12% 12% 6% 4 4 3 4 4 12%	4720
	11th to 20th	Night	19% 27% 7% 12% 5% 4 3 2 4 4 14%	5345
	21st to end	Night	20% 24% 7% 12% 6% 5% 4 3 4 4 11%	7031

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	81% 5% 7% 4 2 1	5259
	11th to 20th	Day	82% 6% 6% 4 2	5280
	21st to end	Day	78% 5% 6% 7% 3	5780
February	1st to 10th	Day	69% 5% 9% 12% 4	1890
	11th to 20th	Day	68% 5% 10% 12% 5% 1	1894
	21st to end	Day	61% 8% 13% 11% 5% 2	1730
March	1st to 10th	Day	54% 6% 14% 20% 6%	4940
	11th to 20th	Day	49% 8% 15% 21% 6% 1	5090
	21st to end	Day	56% 8% 9% 17% 9% 1	5586
April	1st to 10th	Day	51% 6% 13% 17% 12% 1	2361
	11th to 20th	Day	48% 7% 12% 17% 13% 2	2670
	21st to end	Day	48% 7% 12% 21% 10% 2	2730
May	1st to 10th	Day	51% 7% 9% 20% 11% 2	7651
	11th to 20th	Day	45% 8% 13% 21% 11% 2	7630
	21st to end	Day	43% 8% 10% 18% 17% 4	8663
June	1st to 10th	Day	39% 9% 12% 25% 14% 1	2940
	11th to 20th	Day	39% 9% 15% 21% 14% 2	2870
	21st to end	Day	36% 8% 13% 25% 16% 2	2955
July	1st to 10th	Day	34% 6% 13% 27% 18% 2	6039
	11th to 20th	Day	35% 6% 14% 26% 17% 1	5831
	21st to end	Day	34% 7% 14% 24% 20% 1	6240
August	1st to 10th	Day	38% 8% 16% 25% 13%	4221
	11th to 20th	Day	39% 9% 13% 31% 7% 1	4213
	21st to end	Day	35% 7% 15% 29% 12% 1	4591
September	1st to 10th	Day	38% 7% 15% 23% 15% 2	2308
	11th to 20th	Day	34% 8% 16% 26% 16% 1	2200
	21st to end	Day	47% 7% 11% 21% 13% 1	2200
October	1st to 10th	Day	35% 6% 14% 26% 18% 1	3359
	11th to 20th	Day	46% 6% 12% 20% 16% 1	3240
	21st to end	Day	45% 6% 13% 24% 11% 1	3516
November	1st to 10th	Day	52% 7% 11% 19% 11% 1	1852
	11th to 20th	Day	64% 5% 9% 13% 7% 2	1822
	21st to end	Day	71% 6% 8% 10% 4	1680
December	1st to 10th	Day	75% 7% 11% 6% 1	2680
	11th to 20th	Day	79% 5% 7% 8% 1	3066
	21st to end	Day	80% 5% 7% 6% 1	4163
January	1st to 10th	Night	82% 4 5% 7% 2	7636
	11th to 20th	Night	79% 6% 6% 6% 2	7680
	21st to end	Night	71% 5% 8% 12% 4	8401
February	1st to 10th	Night	68% 6% 9% 12% 4	2730
	11th to 20th	Night	67% 6% 9% 13% 5%	2618
	21st to end	Night	64% 6% 9% 13% 8% 1	2076
March	1st to 10th	Night	56% 4 13% 17% 9%	5132
	11th to 20th	Night	45% 7% 14% 24% 10% 1	5090
	21st to end	Night	53% 7% 10% 17% 12% 1	5588
April	1st to 10th	Night	56% 6% 10% 15% 11% 2	2258
	11th to 20th	Night	50% 6% 11% 19% 12% 2	1917
	21st to end	Night	45% 7% 13% 19% 13% 3	1890
May	1st to 10th	Night	55% 7% 8% 16% 10% 4	5264
	11th to 20th	Night	44% 8% 11% 23% 13% 1	5235
	21st to end	Night	44% 7% 12% 20% 16% 2	5495
June	1st to 10th	Night	40% 8% 10% 22% 17% 4	1680
	11th to 20th	Night	38% 8% 13% 21% 18% 2	1640
	21st to end	Night	36% 11% 11% 24% 17% 1	1428
July	1st to 10th	Night	34% 6% 14% 23% 19% 4	3757
	11th to 20th	Night	37% 6% 11% 25% 17% 3	4006
	21st to end	Night	33% 6% 12% 20% 26% 2	4297
August	1st to 10th	Night	38% 8% 12% 27% 14% 2	2904
	11th to 20th	Night	42% 7% 10% 28% 12% 1	2902
	21st to end	Night	37% 7% 12% 28% 15% 2	3272
September	1st to 10th	Night	36% 8% 12% 26% 14% 3	2089
	11th to 20th	Night	32% 7% 14% 27% 19% 2	2200
	21st to end	Night	48% 6% 11% 18% 16% 1	2200
October	1st to 10th	Night	33% 6% 9% 26% 25% 1	3821
	11th to 20th	Night	48% 6% 9% 20% 17% 1	3899
	21st to end	Night	46% 5% 11% 23% 14% 1	4271
November	1st to 10th	Night	52% 6% 10% 18% 12% 2	2666
	11th to 20th	Night	66% 5% 9% 12% 6% 2	2794
	21st to end	Night	70% 5% 9% 12% 4	2940
December	1st to 10th	Night	77% 7% 9% 5% 2	4720
	11th to 20th	Night	75% 6% 9% 8% 1	5348
	21st to end	Night	75% 7% 9% 8% 1	7031

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	28% 25% 32% 11% 4	330
	11th to 20th	Day	32% 25% 31% 9% 3	330
	21st to end	Day	28% 20% 33% 16% 2	363
February	1st to 10th	Day	25% 21% 34% 18% 3	330
	11th to 20th	Day	28% 18% 35% 18% 1	330
	21st to end	Day	25% 25% 38% 11% 1	273
March	1st to 10th	Day	24% 18% 33% 19% 5% 1	483
	11th to 20th	Day	24% 19% 33% 20% 3 1	540
	21st to end	Day	28% 13% 34% 20% 4	594
April	1st to 10th	Day	22% 16% 32% 23% 6% 1	540
	11th to 20th	Day	24% 15% 30% 20% 9% 2	532
	21st to end	Day	23% 12% 32% 25% 8% 1	540
May	1st to 10th	Day	25% 8% 34% 25% 6% 2	543
	11th to 20th	Day	17% 7% 30% 29% 15% 2	567
	21st to end	Day	17% 5% 24% 31% 20% 4	617
June	1st to 10th	Day	15% 5% 25% 38% 14% 3	570
	11th to 20th	Day	16% 7% 22% 34% 19% 2	550
	21st to end	Day	13% 4 25% 36% 19% 3	685
July	1st to 10th	Day	11% 4 19% 35% 24% 7%	575
	11th to 20th	Day	14% 4 18% 35% 23% 6%	524
	21st to end	Day	10% 4 19% 38% 23% 6%	576
August	1st to 10th	Day	9% 4 19% 34% 25% 8%	526
	11th to 20th	Day	13% 4 16% 35% 24% 7%	519
	21st to end	Day	12% 4 21% 33% 23% 8%	583
September	1st to 10th	Day	16% 7% 16% 29% 23% 8%	530
	11th to 20th	Day	10% 3 14% 32% 27% 13%	530
	21st to end	Day	19% 11% 21% 28% 15% 6%	530
October	1st to 10th	Day	14% 10% 24% 27% 20% 6%	530
	11th to 20th	Day	24% 12% 30% 24% 8% 2	530
	21st to end	Day	31% 15% 27% 19% 7%	573
November	1st to 10th	Day	22% 20% 26% 22% 8% 2	330
	11th to 20th	Day	34% 19% 26% 15% 5% 1	294
	21st to end	Day	36% 19% 28% 16% 1	220
December	1st to 10th	Day	27% 24% 29% 17% 2 1	220
	11th to 20th	Day	29% 27% 27% 15% 2	220
	21st to end	Day	33% 21% 30% 14% 1	270
January	1st to 10th	Night	29% 23% 31% 13% 4	840
	11th to 20th	Night	31% 20% 31% 16% 2	840
	21st to end	Night	26% 19% 33% 19% 4	924
February	1st to 10th	Night	29% 16% 30% 21% 4	840
	11th to 20th	Night	27% 17% 31% 22% 3	823
	21st to end	Night	26% 17% 36% 20% 2	692
March	1st to 10th	Night	23% 14% 34% 24% 5%	840
	11th to 20th	Night	24% 14% 32% 22% 6% 1	840
	21st to end	Night	24% 13% 29% 25% 8% 1	924
April	1st to 10th	Night	25% 12% 27% 29% 7%	840
	11th to 20th	Night	21% 10% 33% 24% 10% 1	673
	21st to end	Night	20% 7% 29% 35% 9% 1	630
May	1st to 10th	Night	23% 7% 23% 34% 13% 1	630
	11th to 20th	Night	17% 8% 24% 33% 16% 2	621
	21st to end	Night	15% 4 17% 38% 24% 3	589
June	1st to 10th	Night	13% 2 27% 37% 19% 2	420
	11th to 20th	Night	13% 4 23% 36% 24%	410
	21st to end	Night	10% 5% 22% 40% 22% 1	400
July	1st to 10th	Night	9% 4 13% 37% 32% 6%	529
	11th to 20th	Night	11% 4 18% 32% 29% 5%	582
	21st to end	Night	10% 5% 15% 36% 31% 3	657
August	1st to 10th	Night	9% 4 14% 40% 29% 5%	597
	11th to 20th	Night	12% 4 11% 36% 31% 5%	594
	21st to end	Night	12% 5% 17% 31% 29% 5%	683
September	1st to 10th	Night	15% 6% 16% 31% 26% 6%	800
	11th to 20th	Night	12% 4 13% 32% 32% 7%	800
	21st to end	Night	19% 8% 21% 27% 20% 5%	800
October	1st to 10th	Night	18% 9% 22% 29% 20% 3	800
	11th to 20th	Night	26% 14% 26% 25% 9% 1	800
	21st to end	Night	35% 14% 25% 21% 4	880
November	1st to 10th	Night	27% 15% 26% 23% 8% 1	820
	11th to 20th	Night	34% 16% 28% 16% 5% 1	840
	21st to end	Night	35% 18% 27% 15% 4	840
December	1st to 10th	Night	35% 20% 28% 13% 4	840
	11th to 20th	Night	30% 23% 31% 13% 2	840
	21st to end	Night	33% 20% 28% 18% 2	924

Page generated at 2026-06-13 02:31:39. Version ac07

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