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 2024-09-14.

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 8% 5% 4 4 3 5% 7% 32%	100745
	Night	17% 14% 5% 9% 5% 4 4 3 5% 6% 29%	97057
Transparency	Day	50% 8% 12% 19% 10% 1	100557
	Night	55% 7% 11% 16% 10% 1	96915
Seeing	Day	20% 10% 26% 27% 14% 3	14558
	Night	22% 12% 25% 26% 13% 2	24107

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	19% 24% 10% 14% 4 3 3 2 3 5% 13%	2836
	11th to 20th	Day	15% 23% 9% 17% 7% 6% 4 2 3 4 11%	2840
	21st to end	Day	25% 21% 11% 17% 7% 3 3 2 3 2 6%	3124
February	1st to 10th	Day	17% 19% 6% 14% 9% 4 3 3 4 4 18%	1710
	11th to 20th	Day	14% 17% 7% 15% 8% 4 4 3 4 4 19%	1701
	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 6% 4 3 5% 4 6% 9% 43%	2014
	21st to end	Day	20% 7% 2 7% 3 3 5% 3 5% 8% 37%	1980
October	1st to 10th	Day	18% 5% 3 7% 4 4 4 4 5% 8% 38%	1854
	11th to 20th	Day	24% 10% 3 7% 4 5% 4 3 5% 7% 30%	1800
	21st to end	Day	26% 13% 3 7% 5% 4 5% 4 4 5% 24%	1972
November	1st to 10th	Day	15% 14% 4 7% 4 4 4 4 5% 5% 32%	1672
	11th to 20th	Day	18% 22% 4 9% 5% 3 4 2 3 5% 25%	1649
	21st to end	Day	19% 23% 6% 9% 5% 5% 4 3 5% 5% 15%	1520
December	1st to 10th	Day	17% 30% 7% 12% 4 4 3 2 3 3 13%	1520
	11th to 20th	Day	18% 23% 9% 14% 5% 3 4 3 4 5% 12%	1910
	21st to end	Day	24% 24% 9% 13% 5% 4 4 3 3 4 9%	2842
January	1st to 10th	Night	17% 27% 12% 15% 4 3 3 2 3 3 11%	4109
	11th to 20th	Night	13% 23% 11% 19% 5% 3 5% 4 4 3 10%	4120
	21st to end	Night	25% 23% 7% 16% 6% 3 2 2 2 3 11%	4532
February	1st to 10th	Night	20% 18% 5% 14% 6% 5% 4 3 4 3 19%	2470
	11th to 20th	Night	17% 18% 6% 13% 7% 5% 3 2 4 5% 19%	2361
	21st to end	Night	19% 15% 6% 13% 5% 4 4 3 5% 4 23%	1884
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% 3 4 4 4 6% 7% 48%	2024
	21st to end	Night	17% 7% 2 6% 6% 5% 5% 3 5% 6% 38%	1980
October	1st to 10th	Night	17% 6% 3 5% 4 4 5% 4 6% 7% 40%	2106
	11th to 20th	Night	22% 9% 3 8% 5% 5% 4 3 5% 6% 31%	2160
	21st to end	Night	29% 11% 3 8% 4 4 3 3 4 6% 25%	2381
November	1st to 10th	Night	18% 14% 3 7% 4 3 4 3 5% 6% 33%	2406
	11th to 20th	Night	18% 22% 4 10% 5% 4 3 2 4 5% 22%	2527
	21st to end	Night	21% 23% 5% 8% 5% 4 4 3 4 5% 19%	2660
December	1st to 10th	Night	22% 28% 8% 8% 5% 3 3 2 3 4 14%	2660
	11th to 20th	Night	18% 25% 7% 12% 5% 4 3 2 4 4 16%	3285
	21st to end	Night	22% 25% 7% 11% 6% 5% 4 3 4 4 9%	4810

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% 8% 9% 6% 2	2837
	11th to 20th	Day	78% 8% 9% 4 1	2840
	21st to end	Day	83% 6% 5% 4 2	3124
February	1st to 10th	Day	70% 6% 10% 11% 4	1710
	11th to 20th	Day	68% 5% 10% 12% 5% 1	1710
	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	36% 8% 16% 24% 15% 1	2014
	21st to end	Day	45% 8% 11% 22% 14% 1	1980
October	1st to 10th	Day	44% 9% 13% 20% 13% 1	1854
	11th to 20th	Day	52% 7% 13% 18% 8% 1	1800
	21st to end	Day	61% 8% 12% 12% 7% 1	1972
November	1st to 10th	Day	52% 7% 11% 18% 11% 1	1672
	11th to 20th	Day	64% 4 10% 13% 7% 2	1649
	21st to end	Day	70% 6% 9% 10% 4	1520
December	1st to 10th	Day	76% 5% 9% 8% 2	1520
	11th to 20th	Day	75% 6% 9% 9% 2	1906
	21st to end	Day	81% 6% 7% 5% 1	2842
January	1st to 10th	Night	79% 6% 6% 7% 2	4109
	11th to 20th	Night	78% 9% 7% 5% 1	4120
	21st to end	Night	80% 6% 7% 6% 2	4532
February	1st to 10th	Night	69% 7% 9% 11% 4	2470
	11th to 20th	Night	67% 6% 9% 14% 5%	2363
	21st to end	Night	64% 6% 9% 13% 7% 1	1884
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% 14% 25% 19% 1	2024
	21st to end	Night	46% 7% 11% 19% 16% 1	1980
October	1st to 10th	Night	42% 9% 13% 18% 18% 1	2106
	11th to 20th	Night	53% 8% 11% 18% 10%	2160
	21st to end	Night	61% 7% 10% 13% 7% 1	2381
November	1st to 10th	Night	53% 6% 10% 17% 11% 2	2406
	11th to 20th	Night	66% 5% 9% 12% 6% 2	2527
	21st to end	Night	69% 5% 9% 12% 4	2660
December	1st to 10th	Night	77% 7% 7% 7% 3	2660
	11th to 20th	Night	72% 7% 11% 8% 2	3288
	21st to end	Night	78% 8% 8% 5% 1	4810

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	26% 21% 34% 14% 5%	270
	11th to 20th	Day	28% 22% 35% 11% 4	270
	21st to end	Day	27% 18% 35% 17% 2	297
February	1st to 10th	Day	27% 18% 36% 17% 2	270
	11th to 20th	Day	26% 19% 37% 17% 1	270
	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 16% 31% 27% 11%	463
	21st to end	Day	19% 10% 20% 28% 16% 7%	450
October	1st to 10th	Day	15% 10% 24% 26% 21% 5%	450
	11th to 20th	Day	26% 11% 29% 25% 7% 1	450
	21st to end	Day	34% 13% 26% 19% 6%	487
November	1st to 10th	Day	19% 19% 26% 24% 10% 2	270
	11th to 20th	Day	32% 19% 25% 17% 6% 1	241
	21st to end	Day	32% 21% 29% 17% 1	180
December	1st to 10th	Day	25% 24% 29% 18% 2 1	180
	11th to 20th	Day	23% 29% 30% 16% 2	180
	21st to end	Day	30% 21% 32% 15% 1	220
January	1st to 10th	Night	29% 22% 32% 13% 4	760
	11th to 20th	Night	31% 18% 32% 18% 3	760
	21st to end	Night	25% 17% 34% 19% 4	836
February	1st to 10th	Night	29% 16% 31% 20% 3	760
	11th to 20th	Night	27% 17% 31% 22% 3	743
	21st to end	Night	26% 16% 36% 21% 2	628
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% 5% 14% 32% 30% 7%	736
	21st to end	Night	18% 8% 21% 27% 20% 6%	720
October	1st to 10th	Night	19% 9% 22% 27% 19% 3	720
	11th to 20th	Night	26% 13% 26% 25% 9% 1	720
	21st to end	Night	36% 14% 25% 21% 4	792
November	1st to 10th	Night	26% 14% 26% 24% 9% 1	740
	11th to 20th	Night	33% 16% 28% 16% 5% 1	760
	21st to end	Night	34% 19% 27% 16% 5%	760
December	1st to 10th	Night	35% 20% 28% 13% 5%	760
	11th to 20th	Night	29% 23% 32% 14% 3	760
	21st to end	Night	33% 20% 28% 17% 2	836

Page generated at 2024-09-11 10:00:08. Version ac07

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