Coronation
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Coronation 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% 6% 5% 5% 4 6% 8% 37%	142125
	Night	7% 8% 4 10% 7% 6% 6% 5% 6% 8% 34%	138959
Transparency	Day	43% 8% 16% 24% 9% 1	141822
	Night	45% 8% 15% 22% 10% 1	138848
Seeing	Day	12% 8% 28% 30% 17% 5%	17692
	Night	11% 7% 32% 34% 14% 2	26797

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	6% 13% 5% 14% 9% 7% 6% 5% 5% 7% 24%	4125
	11th to 20th	Day	2 7% 4 13% 7% 7% 6% 7% 7% 9% 31%	4119
	21st to end	Day	3 9% 4 10% 7% 6% 6% 5% 6% 10% 35%	4802
February	1st to 10th	Day	6% 15% 5% 11% 7% 6% 6% 4 7% 8% 25%	1754
	11th to 20th	Day	6% 11% 5% 11% 6% 7% 5% 5% 6% 8% 28%	1845
	21st to end	Day	4 13% 4 13% 7% 6% 6% 5% 7% 11% 22%	1557
March	1st to 10th	Day	4 9% 4 11% 8% 7% 6% 4 6% 8% 32%	4738
	11th to 20th	Day	5% 12% 5% 14% 7% 5% 4 3 5% 7% 33%	5109
	21st to end	Day	7% 12% 6% 16% 6% 5% 5% 4 6% 8% 25%	5607
April	1st to 10th	Day	8% 12% 4 9% 6% 6% 5% 4 6% 7% 34%	2604
	11th to 20th	Day	10% 13% 5% 9% 6% 4 5% 4 6% 7% 31%	2700
	21st to end	Day	12% 12% 4 8% 6% 4 5% 4 6% 9% 32%	2730
May	1st to 10th	Day	11% 7% 3 7% 4 5% 5% 4 6% 8% 40%	8253
	11th to 20th	Day	13% 10% 3 9% 7% 6% 6% 5% 6% 7% 27%	8755
	21st to end	Day	11% 7% 3 8% 5% 5% 5% 5% 6% 7% 37%	9649
June	1st to 10th	Day	15% 8% 2 6% 5% 4 5% 4 7% 9% 33%	3150
	11th to 20th	Day	17% 8% 3 9% 7% 4 5% 4 7% 9% 26%	3150
	21st to end	Day	10% 5% 2 6% 5% 5% 5% 6% 9% 10% 37%	3150
July	1st to 10th	Day	6% 5% 2 6% 4 5% 5% 4 6% 9% 48%	6781
	11th to 20th	Day	10% 6% 2 6% 4 4 6% 5% 7% 8% 42%	6780
	21st to end	Day	7% 4 2 6% 4 4 4 4 6% 10% 49%	7376
August	1st to 10th	Day	9% 6% 2 6% 5% 5% 5% 4 6% 8% 45%	4640
	11th to 20th	Day	6% 4 2 5% 4 4 5% 4 7% 9% 49%	4158
	21st to end	Day	8% 4 2 5% 4 4 5% 4 7% 9% 49%	4664
September	1st to 10th	Day	10% 7% 3 6% 4 4 4 3 5% 8% 47%	2505
	11th to 20th	Day	15% 7% 2 5% 4 4 4 3 5% 6% 45%	2235
	21st to end	Day	8% 6% 2 6% 4 4 4 3 6% 8% 49%	2200
October	1st to 10th	Day	5% 8% 3 7% 5% 5% 5% 3 6% 7% 46%	3303
	11th to 20th	Day	5% 6% 3 7% 6% 5% 6% 5% 6% 9% 42%	3164
	21st to end	Day	6% 8% 3 8% 4 5% 5% 4 6% 8% 42%	3082
November	1st to 10th	Day	9% 15% 4 11% 7% 5% 6% 4 6% 7% 26%	1648
	11th to 20th	Day	6% 11% 4 14% 8% 5% 5% 4 6% 6% 31%	1675
	21st to end	Day	5% 11% 4 14% 8% 6% 5% 5% 5% 8% 27%	1470
December	1st to 10th	Day	9% 15% 6% 13% 7% 6% 5% 5% 6% 8% 21%	2360
	11th to 20th	Day	7% 13% 4 14% 8% 8% 8% 5% 7% 7% 21%	2712
	21st to end	Day	3 7% 3 11% 9% 5% 5% 3 6% 8% 40%	3575
January	1st to 10th	Night	5% 9% 5% 14% 9% 8% 7% 6% 7% 7% 23%	8768
	11th to 20th	Night	2 7% 4 11% 8% 6% 6% 5% 7% 8% 36%	8779
	21st to end	Night	4 8% 4 12% 8% 7% 6% 4 6% 8% 32%	9434
February	1st to 10th	Night	6% 10% 4 13% 8% 6% 6% 5% 7% 8% 28%	2866
	11th to 20th	Night	5% 10% 4 11% 8% 7% 6% 5% 7% 9% 26%	2662
	21st to end	Night	4 9% 4 10% 7% 7% 7% 6% 7% 9% 30%	2249
March	1st to 10th	Night	3 9% 4 12% 8% 7% 7% 5% 7% 10% 29%	5372
	11th to 20th	Night	3 10% 4 10% 6% 7% 6% 6% 7% 9% 32%	5110
	21st to end	Night	8% 12% 6% 17% 7% 6% 5% 4 5% 7% 22%	5610
April	1st to 10th	Night	7% 12% 3 9% 7% 5% 4 5% 6% 8% 35%	2013
	11th to 20th	Night	9% 10% 4 9% 8% 5% 6% 5% 8% 7% 29%	1871
	21st to end	Night	11% 11% 3 7% 5% 5% 4 4 5% 8% 36%	1890
May	1st to 10th	Night	12% 9% 3 8% 5% 4 5% 3 5% 6% 39%	4677
	11th to 20th	Night	10% 9% 3 9% 6% 6% 6% 6% 6% 9% 30%	4105
	21st to end	Night	11% 7% 3 8% 6% 5% 6% 5% 6% 9% 35%	4522
June	1st to 10th	Night	13% 7% 4 8% 5% 6% 6% 5% 6% 7% 33%	1470
	11th to 20th	Night	17% 7% 2 7% 5% 6% 6% 5% 8% 8% 29%	1470
	21st to end	Night	11% 5% 2 6% 5% 5% 5% 4 7% 9% 42%	1470
July	1st to 10th	Night	6% 3 2 5% 4 5% 5% 5% 7% 9% 49%	3180
	11th to 20th	Night	8% 4 2 6% 5% 5% 5% 4 7% 10% 43%	3180
	21st to end	Night	7% 5% 2 6% 5% 5% 5% 4 7% 8% 46%	3467
August	1st to 10th	Night	11% 5% 3 6% 4 4 4 4 7% 8% 44%	2509
	11th to 20th	Night	7% 4 3 7% 5% 5% 5% 4 7% 9% 47%	2901
	21st to end	Night	8% 5% 2 6% 4 4 5% 4 7% 9% 46%	3245
September	1st to 10th	Night	9% 5% 2 6% 4 4 4 4 6% 7% 49%	1895
	11th to 20th	Night	13% 7% 2 5% 4 4 4 3 5% 7% 47%	2162
	21st to end	Night	7% 6% 3 5% 4 5% 4 4 7% 8% 47%	2200
October	1st to 10th	Night	9% 8% 2 7% 4 5% 5% 4 6% 8% 43%	3888
	11th to 20th	Night	5% 5% 2 7% 5% 4 5% 5% 7% 9% 47%	3982
	21st to end	Night	6% 9% 3 8% 6% 5% 5% 4 7% 8% 37%	4686
November	1st to 10th	Night	10% 14% 5% 9% 5% 5% 5% 4 6% 8% 30%	2870
	11th to 20th	Night	6% 11% 5% 10% 7% 7% 5% 4 6% 8% 31%	2943
	21st to end	Night	5% 12% 4 12% 7% 6% 6% 4 6% 8% 30%	3150
December	1st to 10th	Night	9% 13% 5% 14% 8% 7% 6% 5% 5% 7% 21%	5040
	11th to 20th	Night	6% 13% 5% 14% 9% 6% 6% 5% 7% 8% 20%	5700
	21st to end	Night	3 6% 3 9% 8% 6% 6% 4 6% 7% 42%	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	58% 5% 10% 18% 9%	4125
	11th to 20th	Day	46% 6% 16% 14% 18% 1	4140
	21st to end	Day	44% 7% 21% 23% 5%	4803
February	1st to 10th	Day	55% 6% 14% 18% 7% 1	1754
	11th to 20th	Day	51% 8% 13% 17% 11% 1	1854
	21st to end	Day	52% 6% 15% 17% 9%	1557
March	1st to 10th	Day	47% 7% 19% 19% 8%	4738
	11th to 20th	Day	49% 6% 15% 18% 11%	5110
	21st to end	Day	53% 9% 12% 20% 6%	5607
April	1st to 10th	Day	48% 7% 16% 20% 9%	2604
	11th to 20th	Day	49% 6% 14% 22% 8% 1	2700
	21st to end	Day	47% 8% 15% 20% 8% 1	2730
May	1st to 10th	Day	40% 7% 10% 27% 13% 3	8253
	11th to 20th	Day	51% 9% 10% 21% 9%	8759
	21st to end	Day	40% 9% 16% 24% 10% 1	9650
June	1st to 10th	Day	44% 9% 15% 22% 9% 1	3150
	11th to 20th	Day	51% 10% 15% 19% 5% 1	3150
	21st to end	Day	37% 11% 22% 21% 7% 1	3150
July	1st to 10th	Day	30% 8% 18% 30% 12% 1	6707
	11th to 20th	Day	37% 8% 15% 28% 11%	6699
	21st to end	Day	29% 8% 18% 30% 13% 1	7169
August	1st to 10th	Day	35% 9% 16% 32% 7%	4622
	11th to 20th	Day	29% 9% 24% 30% 8%	4197
	21st to end	Day	30% 7% 21% 32% 9%	4663
September	1st to 10th	Day	35% 6% 18% 26% 11% 4	2505
	11th to 20th	Day	39% 5% 17% 29% 8% 1	2235
	21st to end	Day	33% 7% 16% 30% 12% 2	2200
October	1st to 10th	Day	37% 6% 19% 30% 9%	3303
	11th to 20th	Day	38% 6% 15% 31% 10% 1	3164
	21st to end	Day	38% 7% 15% 33% 7%	3082
November	1st to 10th	Day	55% 7% 13% 18% 6% 1	1648
	11th to 20th	Day	50% 9% 17% 19% 5%	1675
	21st to end	Day	53% 7% 17% 18% 6%	1470
December	1st to 10th	Day	59% 7% 17% 13% 4 1	2360
	11th to 20th	Day	60% 8% 16% 13% 3	2714
	21st to end	Day	42% 5% 10% 26% 15% 2	3575
January	1st to 10th	Night	55% 8% 13% 14% 10% 1	8769
	11th to 20th	Night	44% 5% 17% 19% 14% 1	8820
	21st to end	Night	48% 7% 17% 20% 7%	9434
February	1st to 10th	Night	51% 7% 12% 19% 11% 1	2866
	11th to 20th	Night	50% 7% 13% 17% 12% 1	2663
	21st to end	Night	47% 8% 14% 21% 10% 1	2249
March	1st to 10th	Night	46% 8% 19% 19% 8%	5372
	11th to 20th	Night	44% 8% 17% 24% 7%	5110
	21st to end	Night	57% 9% 10% 17% 7%	5610
April	1st to 10th	Night	45% 7% 15% 20% 12% 1	2013
	11th to 20th	Night	49% 8% 12% 20% 10% 1	1871
	21st to end	Night	44% 8% 12% 23% 12% 1	1890
May	1st to 10th	Night	43% 6% 8% 25% 16% 2	4677
	11th to 20th	Night	44% 9% 15% 22% 9% 1	4105
	21st to end	Night	41% 10% 15% 25% 8%	4526
June	1st to 10th	Night	46% 9% 14% 20% 11% 1	1470
	11th to 20th	Night	48% 11% 15% 18% 8%	1470
	21st to end	Night	36% 10% 23% 24% 7% 1	1470
July	1st to 10th	Night	29% 9% 24% 24% 15% 1	3145
	11th to 20th	Night	33% 9% 18% 30% 8% 2	3138
	21st to end	Night	32% 9% 18% 28% 12% 2	3369
August	1st to 10th	Night	36% 9% 16% 33% 6%	2502
	11th to 20th	Night	32% 8% 19% 34% 6% 1	2928
	21st to end	Night	32% 8% 17% 30% 12% 1	3245
September	1st to 10th	Night	32% 8% 18% 21% 15% 6%	1895
	11th to 20th	Night	36% 6% 15% 29% 12% 3	2162
	21st to end	Night	32% 8% 16% 28% 15% 2	2200
October	1st to 10th	Night	38% 6% 19% 26% 10% 1	3888
	11th to 20th	Night	32% 6% 16% 34% 11% 1	3982
	21st to end	Night	41% 8% 16% 31% 4	4686
November	1st to 10th	Night	51% 7% 13% 19% 8% 1	2870
	11th to 20th	Night	49% 8% 16% 18% 8%	2943
	21st to end	Night	50% 8% 16% 19% 7%	3150
December	1st to 10th	Night	62% 7% 14% 12% 5% 1	5040
	11th to 20th	Night	58% 8% 18% 12% 4	5697
	21st to end	Night	40% 6% 12% 22% 16% 3	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	8% 5% 35% 34% 15% 3	220
	11th to 20th	Day	6% 13% 37% 29% 14% 2	220
	21st to end	Day	10% 10% 41% 25% 11% 2	242
February	1st to 10th	Day	14% 10% 32% 29% 12% 3	259
	11th to 20th	Day	12% 5% 33% 32% 14% 3	330
	21st to end	Day	6% 7% 36% 30% 18% 4	273
March	1st to 10th	Day	9% 10% 33% 30% 15% 3	529
	11th to 20th	Day	9% 9% 35% 29% 12% 5%	540
	21st to end	Day	11% 10% 29% 33% 14% 2	594
April	1st to 10th	Day	11% 12% 33% 29% 10% 4	540
	11th to 20th	Day	11% 12% 33% 30% 11% 3	532
	21st to end	Day	18% 11% 25% 27% 15% 4	540
May	1st to 10th	Day	15% 9% 25% 30% 17% 5%	748
	11th to 20th	Day	13% 9% 25% 29% 19% 6%	775
	21st to end	Day	16% 6% 21% 30% 19% 8%	844
June	1st to 10th	Day	17% 11% 25% 32% 13% 4	780
	11th to 20th	Day	17% 9% 28% 28% 15% 4	780
	21st to end	Day	11% 6% 22% 32% 22% 7%	780
July	1st to 10th	Day	9% 4 21% 34% 26% 6%	722
	11th to 20th	Day	14% 5% 22% 31% 22% 6%	718
	21st to end	Day	6% 5% 21% 32% 25% 11%	794
August	1st to 10th	Day	10% 5% 22% 32% 24% 7%	640
	11th to 20th	Day	8% 6% 24% 33% 23% 6%	517
	21st to end	Day	9% 9% 18% 32% 25% 7%	583
September	1st to 10th	Day	12% 8% 27% 32% 17% 4	530
	11th to 20th	Day	17% 7% 23% 32% 17% 4	530
	21st to end	Day	13% 12% 31% 28% 13% 3	530
October	1st to 10th	Day	14% 6% 33% 29% 16% 3	350
	11th to 20th	Day	12% 12% 35% 25% 15% 2	330
	21st to end	Day	11% 13% 40% 24% 9% 3	363
November	1st to 10th	Day	15% 10% 35% 28% 10% 2	330
	11th to 20th	Day	10% 12% 36% 31% 10% 1	327
	21st to end	Day	7% 8% 36% 31% 11% 6%	220
December	1st to 10th	Day	10% 9% 38% 31% 9% 3	220
	11th to 20th	Day	10% 12% 35% 31% 10% 2	220
	21st to end	Day	10% 6% 26% 38% 14% 5%	242
January	1st to 10th	Night	9% 9% 37% 33% 11% 1	1050
	11th to 20th	Night	10% 11% 35% 34% 10% 1	1050
	21st to end	Night	11% 13% 36% 30% 10% 1	1081
February	1st to 10th	Night	7% 10% 29% 35% 15% 3	840
	11th to 20th	Night	9% 6% 37% 33% 14% 1	824
	21st to end	Night	7% 5% 28% 38% 17% 4	692
March	1st to 10th	Night	7% 6% 33% 38% 14% 3	840
	11th to 20th	Night	9% 6% 37% 36% 10% 3	840
	21st to end	Night	13% 7% 31% 33% 13% 3	924
April	1st to 10th	Night	9% 9% 33% 30% 15% 3	676
	11th to 20th	Night	14% 9% 32% 32% 11% 1	623
	21st to end	Night	17% 7% 23% 40% 13% 1	630
May	1st to 10th	Night	14% 9% 25% 37% 13% 2	616
	11th to 20th	Night	10% 8% 26% 37% 17% 1	414
	21st to end	Night	17% 7% 21% 31% 22% 2	455
June	1st to 10th	Night	15% 9% 29% 32% 14% 2	420
	11th to 20th	Night	19% 5% 24% 34% 17% 2	420
	21st to end	Night	12% 4 21% 37% 23% 3	420
July	1st to 10th	Night	10% 3 21% 44% 20% 2	390
	11th to 20th	Night	11% 3 26% 41% 18% 2	388
	21st to end	Night	5% 5% 24% 39% 24% 3	438
August	1st to 10th	Night	9% 4 20% 38% 24% 5%	440
	11th to 20th	Night	12% 4 20% 41% 22% 1	594
	21st to end	Night	9% 6% 23% 38% 23% 1	660
September	1st to 10th	Night	10% 4 25% 42% 18% 2	600
	11th to 20th	Night	18% 4 20% 40% 17% 1	762
	21st to end	Night	10% 6% 32% 39% 13% 1	800
October	1st to 10th	Night	13% 5% 32% 35% 14% 1	800
	11th to 20th	Night	10% 6% 36% 34% 13% 2	800
	21st to end	Night	12% 9% 35% 32% 11%	930
November	1st to 10th	Night	15% 9% 35% 31% 8% 1	1025
	11th to 20th	Night	10% 9% 41% 29% 9% 2	1050
	21st to end	Night	9% 6% 40% 32% 11% 1	1050
December	1st to 10th	Night	12% 8% 36% 30% 12% 3	1050
	11th to 20th	Night	10% 10% 39% 29% 11% 1	1050
	21st to end	Night	10% 3 38% 32% 13% 3	1155

Page generated at 2026-06-28 00:10:49. Version ac07

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