Esther
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Esther clear sky chart from 2005-11-06 to 2026-07-01.

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	8% 8% 3 9% 5% 5% 5% 4 6% 8% 38%	141908
	Night	7% 8% 3 10% 6% 6% 5% 5% 7% 8% 36%	139169
Transparency	Day	42% 6% 15% 25% 10% 1	141605
	Night	44% 6% 15% 23% 11% 1	139058
Seeing	Day	12% 8% 28% 30% 17% 5%	17766
	Night	11% 7% 30% 36% 14% 2	26926

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	7% 12% 5% 14% 8% 7% 6% 4 6% 5% 25%	4125
	11th to 20th	Day	3 8% 5% 11% 7% 6% 6% 8% 7% 9% 31%	4119
	21st to end	Day	4 9% 4 10% 8% 6% 5% 5% 7% 9% 34%	4688
February	1st to 10th	Day	8% 14% 5% 11% 7% 6% 5% 4 6% 7% 27%	1827
	11th to 20th	Day	7% 12% 4 11% 6% 6% 7% 5% 7% 7% 28%	1845
	21st to end	Day	6% 11% 5% 11% 8% 7% 7% 6% 7% 8% 25%	1557
March	1st to 10th	Day	5% 9% 4 11% 7% 6% 6% 4 7% 10% 32%	4737
	11th to 20th	Day	4 11% 7% 13% 6% 5% 5% 4 6% 9% 32%	5109
	21st to end	Day	7% 14% 6% 15% 6% 5% 4 3 5% 7% 27%	5607
April	1st to 10th	Day	7% 10% 4 9% 6% 6% 6% 4 6% 7% 34%	2580
	11th to 20th	Day	9% 13% 4 9% 5% 4 6% 5% 7% 7% 32%	2700
	21st to end	Day	12% 11% 4 8% 4 5% 4 4 7% 8% 33%	2762
May	1st to 10th	Day	10% 8% 3 8% 5% 5% 5% 4 6% 7% 40%	8224
	11th to 20th	Day	13% 9% 3 9% 7% 6% 7% 4 7% 7% 28%	8563
	21st to end	Day	10% 6% 2 7% 5% 5% 5% 5% 7% 9% 39%	9649
June	1st to 10th	Day	15% 7% 3 7% 5% 5% 5% 4 7% 9% 34%	3150
	11th to 20th	Day	17% 8% 3 7% 6% 6% 5% 5% 7% 8% 28%	3150
	21st to end	Day	10% 5% 2 6% 5% 5% 6% 5% 8% 9% 39%	3150
July	1st to 10th	Day	7% 5% 2 6% 4 5% 5% 5% 7% 9% 46%	6781
	11th to 20th	Day	9% 5% 2 7% 5% 4 5% 4 7% 9% 43%	6780
	21st to end	Day	6% 3 1 4 4 4 4 4 7% 9% 53%	7376
August	1st to 10th	Day	8% 6% 3 5% 4 4 5% 4 6% 7% 47%	4605
	11th to 20th	Day	6% 4 1 5% 4 4 4 5% 6% 10% 50%	4158
	21st to end	Day	8% 4 2 4 4 4 4 4 7% 9% 52%	4664
September	1st to 10th	Day	10% 6% 2 6% 4 4 4 4 4 7% 49%	2459
	11th to 20th	Day	14% 6% 2 6% 4 4 4 3 4 7% 45%	2290
	21st to end	Day	9% 4 2 6% 3 3 3 3 6% 7% 53%	2180
October	1st to 10th	Day	6% 6% 2 6% 4 4 5% 3 6% 7% 50%	3270
	11th to 20th	Day	5% 5% 3 8% 4 5% 5% 4 6% 10% 46%	3250
	21st to end	Day	6% 8% 2 7% 4 5% 5% 4 7% 9% 43%	3029
November	1st to 10th	Day	10% 15% 3 10% 7% 7% 5% 4 6% 7% 26%	1648
	11th to 20th	Day	6% 11% 5% 12% 7% 6% 5% 4 6% 7% 32%	1680
	21st to end	Day	6% 12% 5% 12% 6% 6% 5% 4 7% 8% 28%	1549
December	1st to 10th	Day	8% 14% 6% 13% 7% 5% 6% 4 5% 7% 25%	2360
	11th to 20th	Day	7% 13% 5% 13% 8% 9% 6% 4 6% 7% 22%	2712
	21st to end	Day	3 7% 4 13% 7% 6% 4 4 5% 7% 41%	3575
January	1st to 10th	Night	5% 8% 5% 14% 10% 8% 7% 6% 7% 7% 24%	8768
	11th to 20th	Night	2 8% 5% 12% 7% 7% 7% 6% 6% 8% 32%	8779
	21st to end	Night	4 9% 4 11% 8% 7% 7% 4 6% 8% 31%	9548
February	1st to 10th	Night	6% 10% 5% 12% 8% 6% 6% 5% 7% 7% 28%	2792
	11th to 20th	Night	5% 10% 4 11% 7% 7% 7% 6% 7% 7% 28%	2662
	21st to end	Night	4 10% 3 9% 8% 6% 7% 5% 9% 8% 30%	2249
March	1st to 10th	Night	4 8% 4 13% 8% 7% 6% 4 7% 9% 31%	5370
	11th to 20th	Night	4 9% 4 10% 7% 6% 6% 5% 7% 10% 33%	5110
	21st to end	Night	8% 11% 5% 16% 7% 7% 5% 4 6% 6% 24%	5610
April	1st to 10th	Night	8% 10% 3 8% 5% 6% 5% 5% 6% 8% 36%	2037
	11th to 20th	Night	9% 12% 4 10% 7% 4 6% 5% 6% 7% 31%	1871
	21st to end	Night	11% 9% 3 8% 5% 5% 5% 3 6% 9% 35%	1857
May	1st to 10th	Night	13% 8% 3 6% 4 4 4 3 6% 7% 42%	4724
	11th to 20th	Night	11% 8% 2 8% 5% 6% 6% 5% 8% 9% 31%	4292
	21st to end	Night	10% 6% 2 7% 4 5% 6% 4 7% 9% 39%	4522
June	1st to 10th	Night	13% 9% 3 7% 5% 5% 6% 5% 7% 6% 33%	1470
	11th to 20th	Night	15% 7% 3 7% 4 4 6% 5% 7% 8% 33%	1470
	21st to end	Night	10% 5% 2 5% 4 4 6% 4 8% 9% 44%	1470
July	1st to 10th	Night	5% 4 2 5% 4 5% 5% 5% 7% 8% 51%	3180
	11th to 20th	Night	6% 5% 3 6% 4 4 5% 5% 7% 10% 45%	3180
	21st to end	Night	7% 4 1 4 4 4 4 4 7% 10% 52%	3467
August	1st to 10th	Night	8% 5% 2 6% 4 4 5% 4 7% 7% 47%	2532
	11th to 20th	Night	6% 4 2 6% 4 4 4 4 6% 10% 50%	2901
	21st to end	Night	10% 4 1 5% 3 3 4 4 6% 9% 50%	3245
September	1st to 10th	Night	9% 4 2 6% 4 4 4 3 5% 7% 53%	1940
	11th to 20th	Night	12% 7% 2 6% 5% 4 3 3 5% 7% 49%	2106
	21st to end	Night	7% 6% 2 5% 4 4 5% 4 7% 9% 49%	2220
October	1st to 10th	Night	7% 8% 3 7% 4 3 4 3 6% 8% 46%	3920
	11th to 20th	Night	4 5% 2 6% 4 5% 4 5% 6% 9% 50%	3898
	21st to end	Night	6% 8% 3 9% 6% 5% 5% 4 7% 9% 38%	4736
November	1st to 10th	Night	10% 14% 5% 9% 6% 5% 4 3 6% 7% 32%	2870
	11th to 20th	Night	6% 10% 3 11% 7% 6% 5% 5% 5% 8% 34%	2940
	21st to end	Night	5% 13% 5% 11% 7% 6% 5% 4 6% 8% 30%	3070
December	1st to 10th	Night	10% 13% 5% 14% 9% 7% 6% 4 6% 7% 20%	5040
	11th to 20th	Night	6% 13% 5% 14% 8% 7% 7% 5% 8% 8% 20%	5700
	21st to end	Night	3 6% 3 10% 8% 5% 5% 4 6% 6% 43%	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	59% 5% 11% 17% 8%	4125
	11th to 20th	Day	46% 6% 16% 17% 15% 1	4140
	21st to end	Day	46% 6% 21% 21% 5%	4689
February	1st to 10th	Day	55% 5% 11% 18% 9%	1827
	11th to 20th	Day	52% 7% 12% 17% 12% 1	1854
	21st to end	Day	53% 7% 14% 17% 9%	1557
March	1st to 10th	Day	47% 6% 20% 20% 7%	4737
	11th to 20th	Day	50% 6% 16% 19% 9%	5110
	21st to end	Day	55% 6% 12% 22% 5%	5607
April	1st to 10th	Day	47% 7% 15% 22% 9% 1	2580
	11th to 20th	Day	48% 6% 14% 23% 8% 1	2700
	21st to end	Day	47% 8% 12% 23% 9% 1	2762
May	1st to 10th	Day	42% 6% 10% 24% 15% 4	8224
	11th to 20th	Day	51% 6% 10% 22% 11%	8567
	21st to end	Day	38% 7% 13% 29% 11% 1	9650
June	1st to 10th	Day	45% 7% 15% 22% 10% 1	3150
	11th to 20th	Day	51% 8% 12% 21% 7% 1	3150
	21st to end	Day	38% 10% 21% 22% 8% 1	3150
July	1st to 10th	Day	31% 7% 19% 29% 12% 1	6707
	11th to 20th	Day	37% 6% 15% 31% 11% 1	6699
	21st to end	Day	26% 6% 19% 31% 15% 3	7169
August	1st to 10th	Day	35% 7% 17% 33% 9% 1	4587
	11th to 20th	Day	28% 7% 20% 36% 9% 1	4197
	21st to end	Day	28% 6% 18% 35% 13%	4663
September	1st to 10th	Day	35% 5% 14% 27% 12% 6%	2459
	11th to 20th	Day	40% 5% 14% 30% 9% 2	2290
	21st to end	Day	30% 6% 16% 34% 12% 3	2180
October	1st to 10th	Day	34% 5% 17% 34% 10%	3270
	11th to 20th	Day	34% 5% 17% 34% 10%	3250
	21st to end	Day	37% 5% 15% 36% 7%	3029
November	1st to 10th	Day	57% 6% 12% 17% 7% 1	1648
	11th to 20th	Day	50% 8% 16% 20% 6%	1680
	21st to end	Day	52% 7% 16% 19% 5%	1549
December	1st to 10th	Day	58% 7% 19% 12% 4 1	2360
	11th to 20th	Day	60% 6% 17% 14% 3	2714
	21st to end	Day	43% 5% 9% 27% 15% 2	3575
January	1st to 10th	Night	56% 6% 13% 14% 10%	8769
	11th to 20th	Night	47% 5% 18% 15% 13% 1	8820
	21st to end	Night	50% 6% 16% 21% 7%	9548
February	1st to 10th	Night	52% 6% 13% 18% 11% 1	2792
	11th to 20th	Night	50% 7% 13% 17% 12% 1	2663
	21st to end	Night	46% 7% 14% 23% 9% 1	2249
March	1st to 10th	Night	47% 6% 20% 19% 7%	5370
	11th to 20th	Night	43% 7% 18% 25% 6%	5110
	21st to end	Night	58% 6% 11% 17% 7%	5610
April	1st to 10th	Night	44% 7% 13% 22% 13% 1	2037
	11th to 20th	Night	50% 6% 12% 20% 11% 1	1871
	21st to end	Night	45% 7% 10% 24% 13% 1	1857
May	1st to 10th	Night	41% 5% 7% 26% 19% 3	4724
	11th to 20th	Night	44% 8% 12% 24% 12% 1	4292
	21st to end	Night	38% 8% 16% 27% 11%	4526
June	1st to 10th	Night	46% 9% 13% 19% 11% 1	1470
	11th to 20th	Night	44% 8% 15% 21% 11% 1	1470
	21st to end	Night	32% 10% 21% 27% 9% 1	1470
July	1st to 10th	Night	29% 7% 23% 26% 15%	3145
	11th to 20th	Night	33% 6% 17% 31% 12% 1	3138
	21st to end	Night	28% 5% 18% 31% 16% 2	3369
August	1st to 10th	Night	34% 6% 18% 32% 9% 1	2525
	11th to 20th	Night	29% 6% 17% 39% 8% 1	2928
	21st to end	Night	29% 6% 16% 33% 15% 1	3245
September	1st to 10th	Night	30% 6% 15% 25% 16% 7%	1940
	11th to 20th	Night	36% 5% 14% 29% 14% 2	2106
	21st to end	Night	30% 6% 16% 29% 17% 2	2220
October	1st to 10th	Night	36% 4 19% 28% 12% 1	3920
	11th to 20th	Night	30% 5% 16% 35% 13% 1	3898
	21st to end	Night	42% 6% 13% 34% 5%	4736
November	1st to 10th	Night	52% 5% 12% 20% 9% 1	2870
	11th to 20th	Night	48% 7% 18% 19% 8%	2940
	21st to end	Night	50% 8% 16% 19% 7%	3070
December	1st to 10th	Night	62% 6% 15% 12% 5%	5040
	11th to 20th	Night	59% 7% 18% 12% 4	5697
	21st to end	Night	40% 5% 13% 23% 17% 2	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	10% 7% 30% 32% 18% 5%	220
	11th to 20th	Day	9% 10% 29% 32% 18% 2	220
	21st to end	Day	10% 10% 38% 30% 9% 4	242
February	1st to 10th	Day	14% 9% 35% 25% 13% 2	297
	11th to 20th	Day	9% 5% 31% 36% 14% 5%	330
	21st to end	Day	6% 8% 35% 30% 16% 5%	273
March	1st to 10th	Day	9% 12% 36% 30% 12% 2	481
	11th to 20th	Day	10% 12% 37% 26% 11% 4	540
	21st to end	Day	14% 10% 31% 32% 11% 2	594
April	1st to 10th	Day	11% 11% 36% 26% 13% 3	540
	11th to 20th	Day	13% 13% 33% 29% 11% 2	532
	21st to end	Day	15% 11% 26% 29% 15% 4	572
May	1st to 10th	Day	14% 10% 23% 32% 16% 5%	753
	11th to 20th	Day	12% 7% 26% 31% 18% 6%	775
	21st to end	Day	16% 7% 22% 27% 20% 8%	844
June	1st to 10th	Day	15% 11% 25% 29% 16% 4	780
	11th to 20th	Day	18% 9% 29% 27% 14% 4	780
	21st to end	Day	12% 6% 22% 29% 24% 7%	780
July	1st to 10th	Day	10% 3 20% 38% 23% 7%	722
	11th to 20th	Day	12% 5% 24% 30% 22% 8%	718
	21st to end	Day	5% 5% 21% 32% 27% 10%	794
August	1st to 10th	Day	11% 6% 18% 35% 22% 9%	683
	11th to 20th	Day	9% 6% 21% 32% 25% 8%	517
	21st to end	Day	7% 7% 24% 30% 26% 7%	583
September	1st to 10th	Day	12% 10% 26% 28% 19% 5%	530
	11th to 20th	Day	16% 6% 24% 30% 20% 5%	530
	21st to end	Day	13% 10% 33% 27% 14% 4	510
October	1st to 10th	Day	15% 5% 28% 31% 15% 6%	330
	11th to 20th	Day	9% 11% 32% 29% 15% 3	330
	21st to end	Day	10% 10% 40% 25% 12% 1	363
November	1st to 10th	Day	18% 8% 35% 27% 11% 1	330
	11th to 20th	Day	10% 8% 41% 27% 13% 1	330
	21st to end	Day	7% 10% 33% 32% 12% 5%	261
December	1st to 10th	Day	10% 8% 36% 34% 10% 3	220
	11th to 20th	Day	11% 14% 35% 31% 10%	220
	21st to end	Day	11% 6% 29% 33% 17% 4	242
January	1st to 10th	Night	7% 10% 34% 36% 12% 1	1050
	11th to 20th	Night	9% 9% 38% 33% 10% 1	1050
	21st to end	Night	10% 12% 36% 31% 10% 1	1118
February	1st to 10th	Night	10% 9% 25% 38% 16% 2	840
	11th to 20th	Night	9% 6% 33% 38% 12% 2	824
	21st to end	Night	7% 5% 25% 38% 21% 4	692
March	1st to 10th	Night	9% 6% 32% 39% 12% 2	840
	11th to 20th	Night	10% 8% 34% 36% 11% 2	840
	21st to end	Night	14% 6% 29% 33% 15% 3	924
April	1st to 10th	Night	10% 9% 35% 33% 11% 2	635
	11th to 20th	Night	13% 8% 34% 34% 10% 1	623
	21st to end	Night	16% 7% 24% 38% 14% 1	630
May	1st to 10th	Night	14% 7% 23% 39% 17% 1	630
	11th to 20th	Night	9% 7% 24% 40% 19% 1	486
	21st to end	Night	16% 5% 19% 36% 22% 3	455
June	1st to 10th	Night	15% 8% 28% 32% 15% 3	420
	11th to 20th	Night	18% 6% 25% 34% 16% 1	420
	21st to end	Night	12% 4 20% 40% 22% 2	420
July	1st to 10th	Night	8% 5% 20% 47% 20%	390
	11th to 20th	Night	10% 3 24% 40% 22% 1	388
	21st to end	Night	5% 4 23% 42% 23% 3	438
August	1st to 10th	Night	7% 4 19% 40% 25% 4	507
	11th to 20th	Night	11% 4 20% 42% 21% 2	594
	21st to end	Night	7% 5% 25% 39% 23% 1	660
September	1st to 10th	Night	11% 5% 23% 42% 18% 2	600
	11th to 20th	Night	14% 4 24% 37% 19% 1	706
	21st to end	Night	9% 5% 33% 37% 14% 2	800
October	1st to 10th	Night	13% 5% 31% 35% 15% 1	800
	11th to 20th	Night	10% 5% 33% 38% 12% 2	800
	21st to end	Night	12% 9% 35% 33% 10% 1	966
November	1st to 10th	Night	16% 8% 35% 33% 7% 1	1025
	11th to 20th	Night	10% 8% 36% 33% 10% 3	1050
	21st to end	Night	9% 7% 37% 35% 10% 1	1050
December	1st to 10th	Night	12% 7% 33% 33% 12% 3	1050
	11th to 20th	Night	11% 10% 35% 34% 10% 1	1050
	21st to end	Night	10% 5% 35% 34% 14% 3	1155

Page generated at 2026-06-28 00:10:45. Version ac07

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