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 2025-02-21.

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	16% 12% 4 9% 5% 4 4 3 5% 7% 30%	108853
	Night	16% 15% 5% 10% 5% 4 4 3 5% 6% 28%	109693
Transparency	Day	51% 7% 12% 18% 10% 1	112530
	Night	56% 7% 10% 16% 10% 1	114155
Seeing	Day	20% 11% 26% 27% 13% 3	15042
	Night	23% 12% 25% 26% 13% 2	24744

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	15% 22% 10% 25% 4 3 2 1 2 4 11%	4056
	11th to 20th	Day	12% 23% 9% 19% 9% 6% 4 2 3 3 9%	4060
	21st to end	Day	21% 20% 10% 16% 8% 5% 3 2 3 2 11%	4466
February	1st to 10th	Day	17% 19% 6% 14% 9% 4 3 3 4 4 18%	1800
	11th to 20th	Day	15% 17% 8% 15% 8% 4 4 3 4 4 19%	1793
	21st to end	Day	19% 15% 4 12% 5% 4 5% 4 5% 6% 22%	1570
March	1st to 10th	Day	20% 15% 6% 7% 4 3 4 3 5% 7% 26%	3361
	11th to 20th	Day	13% 17% 5% 10% 5% 4 3 2 4 5% 32%	3480
	21st to end	Day	20% 14% 4 9% 5% 3 4 3 4 5% 28%	3815
April	1st to 10th	Day	16% 12% 4 8% 4 4 4 3 6% 6% 33%	2136
	11th to 20th	Day	19% 12% 3 6% 4 4 5% 4 5% 6% 34%	2413
	21st to end	Day	20% 11% 3 7% 4 4 3 3 4 6% 35%	2470
May	1st to 10th	Day	18% 10% 3 9% 6% 4 4 3 5% 6% 32%	4082
	11th to 20th	Day	17% 9% 3 7% 4 4 4 3 6% 7% 36%	4081
	21st to end	Day	11% 6% 3 6% 5% 4 5% 4 6% 8% 41%	4621
June	1st to 10th	Day	15% 7% 2 6% 4 4 5% 5% 7% 8% 38%	2660
	11th to 20th	Day	12% 6% 2 7% 4 4 5% 4 6% 8% 41%	2660
	21st to end	Day	13% 6% 2 5% 4 5% 5% 4 6% 10% 41%	2807
July	1st to 10th	Day	9% 5% 2 6% 5% 5% 4 4 6% 11% 43%	4268
	11th to 20th	Day	11% 5% 2 5% 3 4 4 4 6% 10% 47%	4120
	21st to end	Day	10% 5% 2 6% 4 5% 4 4 7% 9% 42%	4466
August	1st to 10th	Day	12% 7% 2 7% 5% 5% 4 4 7% 9% 39%	4104
	11th to 20th	Day	12% 6% 3 7% 5% 4 5% 5% 8% 9% 36%	4044
	21st to end	Day	11% 5% 2 6% 4 5% 5% 4 7% 10% 42%	4450
September	1st to 10th	Day	16% 6% 3 6% 3 3 4 4 6% 9% 42%	2193
	11th to 20th	Day	12% 6% 2 5% 4 3 5% 4 6% 9% 44%	2090
	21st to end	Day	20% 8% 3 7% 3 3 5% 3 5% 7% 35%	2090
October	1st to 10th	Day	17% 5% 3 7% 4 4 4 4 5% 8% 39%	1957
	11th to 20th	Day	23% 10% 3 7% 4 4 4 3 4 7% 31%	1900
	21st to end	Day	25% 12% 3 7% 5% 4 5% 4 4 6% 25%	2081
November	1st to 10th	Day	16% 14% 4 7% 4 4 4 4 5% 6% 32%	1762
	11th to 20th	Day	18% 22% 4 9% 5% 3 4 3 3 5% 24%	1735
	21st to end	Day	20% 24% 6% 9% 5% 5% 4 3 5% 5% 15%	1600
December	1st to 10th	Day	16% 24% 10% 14% 5% 4 4 2 3 4 13%	2600
	11th to 20th	Day	21% 25% 7% 12% 7% 3 4 3 3 5% 9%	2990
	21st to end	Day	23% 23% 8% 15% 5% 4 4 3 4 4 7%	4072
January	1st to 10th	Night	15% 23% 12% 24% 4 3 2 2 2 3 10%	5889
	11th to 20th	Night	10% 23% 12% 20% 8% 4 5% 3 3 3 9%	5900
	21st to end	Night	21% 21% 7% 16% 5% 3 4 2 3 3 14%	6490
February	1st to 10th	Night	20% 18% 5% 14% 6% 5% 4 3 4 3 18%	2600
	11th to 20th	Night	17% 18% 6% 13% 7% 5% 3 2 4 5% 18%	2488
	21st to end	Night	19% 15% 6% 13% 5% 4 4 3 5% 4 23%	1885
March	1st to 10th	Night	21% 16% 3 7% 3 3 3 2 4 4 32%	3491
	11th to 20th	Night	16% 15% 5% 7% 4 4 3 3 4 6% 33%	3480
	21st to end	Night	18% 15% 5% 10% 3 3 3 3 5% 4 32%	3817
April	1st to 10th	Night	18% 15% 4 7% 5% 3 3 3 5% 6% 30%	2043
	11th to 20th	Night	18% 10% 2 8% 4 5% 4 4 6% 7% 33%	1733
	21st to end	Night	16% 9% 2 6% 5% 4 5% 5% 5% 7% 35%	1710
May	1st to 10th	Night	23% 9% 3 7% 5% 4 4 4 5% 7% 30%	2813
	11th to 20th	Night	15% 9% 3 7% 5% 4 4 4 5% 8% 36%	2812
	21st to end	Night	13% 5% 2 4 3 4 4 4 7% 9% 45%	2930
June	1st to 10th	Night	11% 8% 3 7% 5% 4 5% 4 6% 6% 41%	1520
	11th to 20th	Night	10% 5% 3 7% 5% 6% 5% 4 6% 8% 42%	1520
	21st to end	Night	10% 5% 2 6% 5% 5% 6% 4 6% 10% 40%	1357
July	1st to 10th	Night	10% 6% 2 6% 3 3 3 3 6% 9% 47%	2663
	11th to 20th	Night	10% 5% 2 6% 3 4 4 4 7% 8% 48%	2840
	21st to end	Night	8% 6% 2 6% 4 5% 5% 4 6% 9% 45%	3087
August	1st to 10th	Night	10% 6% 3 7% 5% 5% 4 4 6% 8% 41%	2825
	11th to 20th	Night	15% 8% 3 7% 4 4 4 3 4 6% 41%	2785
	21st to end	Night	9% 6% 2 6% 5% 5% 6% 4 6% 8% 43%	3172
September	1st to 10th	Night	13% 6% 2 5% 4 4 5% 4 5% 8% 43%	1984
	11th to 20th	Night	11% 5% 2 5% 4 4 4 4 6% 6% 49%	2090
	21st to end	Night	18% 7% 3 6% 6% 5% 5% 3 5% 6% 37%	2090
October	1st to 10th	Night	16% 6% 3 5% 4 4 4 3 6% 7% 41%	2223
	11th to 20th	Night	22% 9% 3 8% 5% 4 4 3 5% 5% 32%	2280
	21st to end	Night	28% 11% 3 7% 4 4 4 3 5% 6% 26%	2514
November	1st to 10th	Night	17% 14% 3 7% 4 3 4 3 5% 6% 33%	2536
	11th to 20th	Night	19% 22% 4 10% 4 4 3 3 4 5% 22%	2661
	21st to end	Night	22% 23% 5% 8% 5% 4 4 3 4 4 18%	2800
December	1st to 10th	Night	17% 24% 12% 12% 6% 4 4 3 4 4 12%	4580
	11th to 20th	Night	19% 27% 7% 11% 5% 4 3 2 4 4 14%	5205
	21st to end	Night	20% 24% 6% 12% 6% 5% 4 3 5% 5% 11%	6880

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	79% 6% 7% 5% 2 1	4057
	11th to 20th	Day	81% 7% 8% 3 1	4060
	21st to end	Day	79% 6% 6% 8% 2	4466
February	1st to 10th	Day	70% 5% 10% 11% 4	1800
	11th to 20th	Day	68% 5% 9% 12% 5% 1	1802
	21st to end	Day	61% 8% 13% 11% 6% 2	1570
March	1st to 10th	Day	55% 7% 12% 22% 4	3361
	11th to 20th	Day	51% 10% 16% 17% 6% 1	3480
	21st to end	Day	53% 10% 11% 16% 9% 1	3815
April	1st to 10th	Day	50% 6% 13% 17% 13% 1	2136
	11th to 20th	Day	48% 7% 13% 17% 13% 2	2413
	21st to end	Day	49% 7% 12% 20% 9% 3	2470
May	1st to 10th	Day	50% 8% 10% 21% 9% 1	4120
	11th to 20th	Day	45% 10% 15% 20% 8% 2	4085
	21st to end	Day	36% 10% 13% 19% 15% 6%	4635
June	1st to 10th	Day	40% 9% 12% 24% 13% 1	2660
	11th to 20th	Day	37% 10% 15% 21% 14% 2	2660
	21st to end	Day	37% 8% 12% 26% 15% 2	2807
July	1st to 10th	Day	35% 6% 14% 24% 17% 3	4203
	11th to 20th	Day	32% 6% 14% 28% 19% 1	4051
	21st to end	Day	35% 8% 16% 21% 19% 1	4324
August	1st to 10th	Day	39% 8% 15% 25% 13%	4091
	11th to 20th	Day	39% 9% 13% 30% 7% 1	4083
	21st to end	Day	35% 7% 15% 28% 13% 1	4450
September	1st to 10th	Day	39% 7% 16% 21% 15% 2	2193
	11th to 20th	Day	35% 8% 16% 24% 17% 1	2090
	21st to end	Day	47% 7% 11% 21% 13% 1	2090
October	1st to 10th	Day	35% 7% 15% 25% 17% 1	3256
	11th to 20th	Day	47% 6% 12% 19% 15% 1	3140
	21st to end	Day	45% 6% 14% 24% 11% 1	3407
November	1st to 10th	Day	52% 7% 11% 19% 11% 1	1762
	11th to 20th	Day	64% 4 10% 13% 8% 2	1735
	21st to end	Day	71% 6% 9% 10% 4	1600
December	1st to 10th	Day	76% 7% 11% 5% 1	2600
	11th to 20th	Day	79% 5% 7% 8% 1	2986
	21st to end	Day	80% 5% 7% 6% 1	4072
January	1st to 10th	Night	81% 4 5% 7% 2	5889
	11th to 20th	Night	81% 7% 6% 5% 1	5900
	21st to end	Night	76% 6% 8% 7% 3	6490
February	1st to 10th	Night	69% 7% 9% 11% 4	2600
	11th to 20th	Night	67% 5% 9% 13% 5%	2490
	21st to end	Night	64% 6% 9% 13% 7% 1	1885
March	1st to 10th	Night	55% 5% 13% 18% 8%	3491
	11th to 20th	Night	49% 8% 16% 17% 9% 1	3480
	21st to end	Night	52% 8% 12% 18% 10% 1	3817
April	1st to 10th	Night	53% 7% 11% 15% 12% 2	2043
	11th to 20th	Night	48% 6% 12% 19% 12% 3	1733
	21st to end	Night	45% 7% 13% 18% 13% 3	1710
May	1st to 10th	Night	52% 7% 10% 18% 10% 3	2840
	11th to 20th	Night	43% 10% 12% 20% 12% 3	2813
	21st to end	Night	31% 10% 14% 24% 19% 3	2937
June	1st to 10th	Night	40% 8% 10% 23% 15% 3	1520
	11th to 20th	Night	38% 8% 13% 21% 18% 3	1520
	21st to end	Night	36% 11% 11% 24% 16% 1	1357
July	1st to 10th	Night	34% 5% 13% 24% 19% 5%	2618
	11th to 20th	Night	33% 6% 12% 27% 19% 4	2786
	21st to end	Night	35% 8% 14% 20% 22% 2	2988
August	1st to 10th	Night	38% 8% 12% 27% 13% 2	2814
	11th to 20th	Night	43% 7% 10% 28% 11% 1	2812
	21st to end	Night	36% 7% 12% 28% 16% 2	3172
September	1st to 10th	Night	37% 9% 12% 25% 14% 3	1984
	11th to 20th	Night	34% 7% 13% 25% 19% 2	2090
	21st to end	Night	48% 7% 11% 19% 16% 1	2090
October	1st to 10th	Night	33% 6% 9% 26% 24% 1	3704
	11th to 20th	Night	49% 6% 9% 20% 16% 1	3779
	21st to end	Night	46% 5% 12% 23% 14% 1	4138
November	1st to 10th	Night	52% 6% 10% 18% 11% 2	2536
	11th to 20th	Night	66% 5% 9% 12% 6% 2	2661
	21st to end	Night	70% 5% 9% 12% 4	2800
December	1st to 10th	Night	78% 7% 9% 5% 2	4580
	11th to 20th	Night	76% 6% 9% 8% 1	5208
	21st to end	Night	75% 8% 9% 8% 1	6880

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	27% 23% 33% 12% 5%	300
	11th to 20th	Day	29% 25% 33% 10% 3	300
	21st to end	Day	27% 21% 35% 15% 2	330
February	1st to 10th	Day	26% 20% 36% 16% 2	300
	11th to 20th	Day	29% 19% 35% 16% 1	300
	21st to end	Day	24% 24% 40% 12% 1	225
March	1st to 10th	Day	24% 16% 32% 22% 5% 1	408
	11th to 20th	Day	23% 16% 34% 22% 3 1	460
	21st to end	Day	30% 10% 33% 22% 4	506
April	1st to 10th	Day	20% 13% 34% 25% 7% 1	460
	11th to 20th	Day	24% 13% 31% 21% 10% 2	452
	21st to end	Day	23% 11% 32% 26% 7% 1	460
May	1st to 10th	Day	24% 7% 32% 28% 7% 2	463
	11th to 20th	Day	17% 6% 30% 29% 16% 2	487
	21st to end	Day	13% 4 22% 34% 23% 5%	529
June	1st to 10th	Day	15% 5% 23% 39% 14% 3	490
	11th to 20th	Day	15% 6% 20% 36% 21% 2	490
	21st to end	Day	14% 5% 25% 35% 19% 2	637
July	1st to 10th	Day	11% 4 19% 35% 25% 7%	533
	11th to 20th	Day	14% 4 18% 35% 24% 6%	484
	21st to end	Day	10% 4 18% 38% 24% 5%	532
August	1st to 10th	Day	10% 5% 19% 34% 24% 8%	486
	11th to 20th	Day	13% 4 17% 35% 24% 6%	479
	21st to end	Day	12% 3 20% 33% 24% 8%	539
September	1st to 10th	Day	16% 7% 16% 30% 24% 7%	490
	11th to 20th	Day	11% 3 15% 32% 27% 12%	490
	21st to end	Day	20% 11% 21% 27% 15% 6%	490
October	1st to 10th	Day	14% 10% 24% 26% 20% 5%	490
	11th to 20th	Day	25% 12% 29% 24% 8% 2	490
	21st to end	Day	32% 15% 26% 20% 7%	530
November	1st to 10th	Day	20% 20% 26% 23% 9% 2	300
	11th to 20th	Day	33% 19% 27% 16% 5% 1	267
	21st to end	Day	34% 20% 29% 16% 1	200
December	1st to 10th	Day	27% 24% 29% 18% 2 1	200
	11th to 20th	Day	26% 27% 29% 16% 2	200
	21st to end	Day	30% 22% 31% 16% 1	245
January	1st to 10th	Night	29% 23% 32% 13% 4	800
	11th to 20th	Night	31% 19% 32% 17% 2	800
	21st to end	Night	25% 18% 34% 19% 4	880
February	1st to 10th	Night	30% 16% 31% 20% 3	800
	11th to 20th	Night	27% 17% 31% 22% 3	783
	21st to end	Night	26% 16% 36% 21% 2	629
March	1st to 10th	Night	22% 14% 34% 26% 5%	760
	11th to 20th	Night	23% 14% 32% 23% 7% 1	760
	21st to end	Night	25% 11% 28% 26% 8% 1	836
April	1st to 10th	Night	22% 12% 28% 30% 7%	760
	11th to 20th	Night	21% 9% 33% 25% 10% 1	609
	21st to end	Night	20% 6% 29% 35% 9% 1	570
May	1st to 10th	Night	22% 6% 23% 35% 14% 1	570
	11th to 20th	Night	17% 7% 23% 33% 18% 2	561
	21st to end	Night	12% 3 17% 38% 26% 3	532
June	1st to 10th	Night	13% 1 27% 37% 20% 2	380
	11th to 20th	Night	13% 3 21% 37% 26% 1	380
	21st to end	Night	11% 4 22% 39% 23% 1	380
July	1st to 10th	Night	9% 3 14% 35% 32% 6%	502
	11th to 20th	Night	11% 4 18% 32% 29% 5%	552
	21st to end	Night	10% 5% 15% 36% 30% 3	624
August	1st to 10th	Night	10% 4 14% 39% 29% 5%	567
	11th to 20th	Night	12% 4 11% 37% 30% 5%	564
	21st to end	Night	12% 5% 16% 31% 30% 6%	649
September	1st to 10th	Night	16% 5% 17% 31% 26% 6%	760
	11th to 20th	Night	13% 4 13% 32% 31% 7%	760
	21st to end	Night	19% 8% 22% 26% 19% 5%	760
October	1st to 10th	Night	19% 9% 22% 28% 19% 3	760
	11th to 20th	Night	27% 13% 25% 25% 10% 1	760
	21st to end	Night	34% 14% 25% 22% 5%	836
November	1st to 10th	Night	26% 14% 26% 23% 9% 1	780
	11th to 20th	Night	34% 16% 28% 16% 5% 1	800
	21st to end	Night	35% 18% 27% 15% 4	800
December	1st to 10th	Night	35% 20% 28% 13% 4	800
	11th to 20th	Night	30% 23% 31% 14% 2	800
	21st to end	Night	33% 20% 28% 18% 2	880

Page generated at 2025-02-18 03:26:28. Version ac07

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