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 2025-02-25.

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% 9% 3 9% 6% 5% 5% 4 6% 8% 36%	112067
	Night	7% 9% 4 10% 7% 6% 6% 5% 6% 8% 34%	115268
Transparency	Day	43% 8% 16% 23% 9% 1	111808
	Night	45% 8% 15% 22% 9% 1	115173
Seeing	Day	12% 8% 28% 31% 17% 5%	15802
	Night	11% 7% 31% 35% 14% 2	25139

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% 10% 5% 14% 9% 6% 6% 4 6% 7% 27%	3179
	11th to 20th	Day	3 9% 5% 12% 6% 7% 5% 7% 8% 9% 28%	3159
	21st to end	Day	4 11% 4 11% 6% 5% 5% 4 6% 9% 35%	3701
February	1st to 10th	Day	6% 16% 5% 12% 7% 6% 6% 4 6% 7% 24%	1670
	11th to 20th	Day	6% 11% 6% 12% 7% 8% 5% 5% 6% 8% 27%	1755
	21st to end	Day	5% 13% 3 13% 7% 6% 6% 5% 8% 11% 23%	1449
March	1st to 10th	Day	4 11% 5% 11% 9% 7% 7% 5% 6% 7% 29%	3217
	11th to 20th	Day	5% 12% 4 10% 6% 3 4 3 5% 9% 38%	3489
	21st to end	Day	6% 11% 6% 17% 7% 5% 5% 4 5% 6% 27%	3825
April	1st to 10th	Day	9% 12% 3 9% 6% 6% 5% 4 6% 7% 33%	2356
	11th to 20th	Day	11% 12% 5% 9% 6% 4 5% 4 6% 7% 31%	2440
	21st to end	Day	12% 12% 4 7% 6% 4 5% 4 6% 9% 31%	2470
May	1st to 10th	Day	17% 11% 4 9% 5% 5% 5% 4 5% 6% 28%	4446
	11th to 20th	Day	11% 10% 3 9% 7% 6% 6% 6% 7% 8% 30%	4694
	21st to end	Day	13% 8% 3 10% 6% 6% 6% 5% 7% 8% 27%	5161
June	1st to 10th	Day	16% 8% 2 6% 5% 4 5% 4 7% 9% 32%	2850
	11th to 20th	Day	18% 8% 3 8% 6% 4 5% 4 6% 9% 27%	2850
	21st to end	Day	9% 5% 2 6% 5% 5% 5% 6% 8% 10% 38%	2850
July	1st to 10th	Day	6% 4 2 6% 4 5% 5% 4 7% 9% 48%	4740
	11th to 20th	Day	8% 4 2 5% 4 4 6% 5% 7% 9% 46%	4740
	21st to end	Day	5% 3 1 5% 4 4 4 4 6% 10% 55%	5138
August	1st to 10th	Day	9% 6% 3 6% 4 5% 5% 4 6% 8% 45%	4497
	11th to 20th	Day	6% 4 2 5% 5% 4 5% 4 6% 9% 49%	4028
	21st to end	Day	8% 4 2 5% 4 4 5% 4 7% 9% 48%	4521
September	1st to 10th	Day	11% 7% 3 6% 4 4 4 3 5% 8% 47%	2380
	11th to 20th	Day	16% 7% 3 5% 4 4 4 3 5% 6% 43%	2123
	21st to end	Day	8% 7% 2 6% 4 4 4 3 6% 8% 48%	2090
October	1st to 10th	Day	5% 8% 3 7% 5% 5% 5% 3 5% 7% 46%	3202
	11th to 20th	Day	5% 6% 3 8% 6% 5% 6% 5% 6% 9% 42%	3067
	21st to end	Day	6% 8% 3 8% 4 5% 6% 4 6% 8% 41%	2987
November	1st to 10th	Day	9% 15% 4 11% 7% 5% 6% 4 6% 7% 26%	1568
	11th to 20th	Day	6% 12% 4 14% 8% 5% 5% 4 6% 7% 30%	1595
	21st to end	Day	6% 12% 4 14% 7% 6% 5% 5% 5% 8% 28%	1400
December	1st to 10th	Day	9% 15% 6% 13% 7% 6% 5% 5% 6% 8% 22%	2290
	11th to 20th	Day	7% 13% 4 14% 8% 8% 8% 5% 7% 7% 21%	2642
	21st to end	Day	3 7% 3 11% 9% 5% 5% 3 6% 8% 41%	3498
January	1st to 10th	Night	3 8% 5% 14% 9% 8% 7% 6% 7% 8% 24%	6766
	11th to 20th	Night	3 8% 4 11% 9% 6% 6% 6% 7% 7% 33%	6739
	21st to end	Night	4 9% 4 13% 7% 6% 6% 4 6% 7% 35%	7297
February	1st to 10th	Night	6% 10% 4 13% 8% 6% 6% 5% 7% 8% 27%	2730
	11th to 20th	Night	5% 10% 4 11% 8% 7% 6% 5% 8% 10% 26%	2532
	21st to end	Night	4 8% 4 10% 7% 7% 6% 6% 7% 9% 30%	2099
March	1st to 10th	Night	3 11% 4 13% 10% 7% 6% 5% 6% 8% 27%	3654
	11th to 20th	Night	4 9% 4 8% 5% 6% 6% 6% 7% 9% 38%	3490
	21st to end	Night	6% 11% 6% 17% 7% 6% 5% 5% 6% 8% 22%	3828
April	1st to 10th	Night	7% 12% 3 8% 7% 5% 5% 5% 6% 8% 35%	1822
	11th to 20th	Night	10% 10% 4 9% 8% 5% 6% 5% 7% 7% 29%	1691
	21st to end	Night	12% 10% 3 7% 6% 5% 4 4 5% 8% 35%	1710
May	1st to 10th	Night	21% 12% 4 9% 5% 5% 5% 4 5% 5% 25%	2520
	11th to 20th	Night	9% 7% 3 8% 6% 6% 6% 6% 7% 10% 31%	2199
	21st to end	Night	14% 9% 3 9% 6% 5% 6% 5% 6% 8% 28%	2414
June	1st to 10th	Night	13% 7% 4 8% 5% 6% 6% 5% 6% 8% 32%	1330
	11th to 20th	Night	17% 7% 2 7% 5% 5% 6% 5% 8% 9% 29%	1330
	21st to end	Night	9% 5% 2 6% 5% 5% 5% 5% 7% 9% 43%	1330
July	1st to 10th	Night	8% 4 3 6% 4 6% 5% 5% 6% 9% 45%	2220
	11th to 20th	Night	5% 3 1 4 4 4 6% 5% 8% 11% 48%	2220
	21st to end	Night	4 3 2 5% 4 4 5% 4 6% 9% 53%	2414
August	1st to 10th	Night	11% 5% 3 5% 4 4 5% 4 7% 8% 45%	2433
	11th to 20th	Night	7% 4 3 7% 5% 5% 5% 4 7% 8% 47%	2811
	21st to end	Night	8% 5% 2 7% 4 4 5% 4 7% 9% 45%	3146
September	1st to 10th	Night	9% 5% 2 6% 4 4 4 4 6% 7% 48%	1800
	11th to 20th	Night	14% 7% 2 5% 4 4 4 3 5% 7% 47%	2054
	21st to end	Night	7% 7% 3 5% 4 5% 4 4 7% 8% 46%	2090
October	1st to 10th	Night	9% 8% 2 7% 4 5% 5% 4 6% 8% 43%	3769
	11th to 20th	Night	5% 5% 2 7% 5% 4 5% 5% 7% 9% 46%	3859
	21st to end	Night	6% 9% 3 8% 6% 5% 5% 4 7% 9% 37%	4540
November	1st to 10th	Night	9% 14% 5% 9% 5% 5% 5% 4 6% 8% 30%	2730
	11th to 20th	Night	5% 11% 5% 10% 8% 7% 5% 4 6% 8% 31%	2803
	21st to end	Night	5% 12% 4 12% 7% 6% 5% 4 6% 8% 30%	3000
December	1st to 10th	Night	9% 13% 5% 15% 8% 7% 6% 5% 5% 7% 22%	4890
	11th to 20th	Night	5% 13% 5% 14% 9% 6% 6% 5% 7% 8% 20%	5550
	21st to end	Night	3 6% 3 9% 8% 6% 6% 4 6% 7% 42%	7458

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	55% 5% 11% 21% 7%	3179
	11th to 20th	Day	48% 6% 14% 13% 18% 1	3180
	21st to end	Day	45% 7% 20% 23% 5%	3701
February	1st to 10th	Day	57% 6% 13% 17% 6% 1	1670
	11th to 20th	Day	52% 8% 13% 16% 10% 1	1764
	21st to end	Day	52% 7% 16% 17% 9% 1	1449
March	1st to 10th	Day	51% 9% 16% 17% 8%	3217
	11th to 20th	Day	42% 8% 20% 19% 11%	3490
	21st to end	Day	53% 10% 14% 17% 6%	3825
April	1st to 10th	Day	49% 7% 16% 19% 9% 1	2356
	11th to 20th	Day	49% 6% 14% 22% 8%	2440
	21st to end	Day	47% 9% 16% 19% 8% 1	2470
May	1st to 10th	Day	54% 9% 12% 20% 5%	4446
	11th to 20th	Day	46% 11% 13% 21% 9%	4698
	21st to end	Day	46% 13% 18% 16% 7%	5162
June	1st to 10th	Day	44% 9% 16% 22% 8% 1	2850
	11th to 20th	Day	52% 10% 15% 18% 5% 1	2850
	21st to end	Day	36% 12% 23% 21% 8% 1	2850
July	1st to 10th	Day	29% 9% 19% 26% 15% 1	4666
	11th to 20th	Day	32% 9% 15% 31% 13% 1	4659
	21st to end	Day	24% 7% 18% 31% 18% 2	4976
August	1st to 10th	Day	35% 9% 16% 33% 7%	4479
	11th to 20th	Day	29% 9% 24% 30% 8%	4067
	21st to end	Day	30% 7% 22% 32% 8%	4520
September	1st to 10th	Day	36% 6% 18% 24% 11% 5%	2380
	11th to 20th	Day	41% 5% 18% 28% 7% 1	2123
	21st to end	Day	34% 8% 15% 30% 11% 2	2090
October	1st to 10th	Day	37% 6% 18% 30% 8%	3202
	11th to 20th	Day	38% 6% 15% 31% 9% 1	3067
	21st to end	Day	39% 7% 15% 33% 7%	2987
November	1st to 10th	Day	55% 7% 13% 18% 5% 1	1568
	11th to 20th	Day	50% 9% 17% 19% 5%	1595
	21st to end	Day	52% 7% 17% 18% 6%	1400
December	1st to 10th	Day	59% 7% 17% 13% 4 1	2290
	11th to 20th	Day	60% 8% 17% 12% 3	2644
	21st to end	Day	41% 5% 9% 27% 15% 2	3498
January	1st to 10th	Night	52% 8% 15% 16% 7% 1	6766
	11th to 20th	Night	48% 6% 13% 16% 15% 1	6780
	21st to end	Night	47% 7% 16% 24% 5%	7297
February	1st to 10th	Night	52% 7% 12% 18% 11%	2730
	11th to 20th	Night	50% 8% 14% 16% 11% 1	2533
	21st to end	Night	46% 8% 14% 21% 10% 1	2099
March	1st to 10th	Night	51% 9% 14% 18% 7%	3654
	11th to 20th	Night	37% 10% 21% 23% 8% 1	3490
	21st to end	Night	54% 11% 13% 16% 6%	3828
April	1st to 10th	Night	44% 7% 15% 20% 13% 1	1822
	11th to 20th	Night	50% 8% 12% 20% 10% 1	1691
	21st to end	Night	44% 8% 13% 21% 12% 2	1710
May	1st to 10th	Night	57% 8% 9% 19% 6% 1	2520
	11th to 20th	Night	40% 12% 17% 22% 9% 1	2199
	21st to end	Night	48% 12% 14% 19% 6% 1	2414
June	1st to 10th	Night	46% 9% 14% 20% 9% 1	1330
	11th to 20th	Night	47% 11% 15% 18% 8%	1330
	21st to end	Night	34% 11% 24% 24% 8% 1	1330
July	1st to 10th	Night	34% 10% 19% 20% 17% 1	2185
	11th to 20th	Night	25% 11% 19% 32% 11% 2	2178
	21st to end	Night	25% 7% 17% 32% 16% 3	2337
August	1st to 10th	Night	35% 8% 16% 34% 6%	2426
	11th to 20th	Night	32% 7% 19% 35% 6% 1	2838
	21st to end	Night	33% 8% 17% 30% 11% 1	3146
September	1st to 10th	Night	33% 8% 19% 19% 15% 6%	1800
	11th to 20th	Night	37% 6% 15% 28% 12% 2	2054
	21st to end	Night	32% 8% 16% 27% 15% 2	2090
October	1st to 10th	Night	39% 6% 19% 26% 10% 1	3769
	11th to 20th	Night	33% 6% 16% 34% 10% 1	3859
	21st to end	Night	41% 8% 16% 30% 4	4540
November	1st to 10th	Night	51% 7% 14% 19% 8% 1	2730
	11th to 20th	Night	50% 8% 16% 18% 8%	2803
	21st to end	Night	50% 8% 17% 18% 6%	3000
December	1st to 10th	Night	62% 7% 14% 12% 5% 1	4890
	11th to 20th	Night	58% 8% 18% 12% 4	5547
	21st to end	Night	39% 6% 12% 23% 17% 3	7458

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	7% 6% 35% 35% 15% 4	200
	11th to 20th	Day	6% 12% 35% 31% 15% 2	200
	21st to end	Day	11% 10% 40% 25% 12% 2	220
February	1st to 10th	Day	14% 11% 31% 30% 12% 2	235
	11th to 20th	Day	13% 5% 35% 31% 13% 3	300
	21st to end	Day	6% 6% 33% 30% 19% 4	237
March	1st to 10th	Day	9% 11% 32% 31% 15% 3	450
	11th to 20th	Day	9% 8% 35% 30% 13% 6%	460
	21st to end	Day	11% 9% 30% 33% 14% 3	506
April	1st to 10th	Day	13% 12% 34% 28% 10% 3	460
	11th to 20th	Day	12% 11% 33% 31% 11% 4	452
	21st to end	Day	18% 11% 27% 27% 14% 3	460
May	1st to 10th	Day	16% 9% 23% 31% 17% 5%	648
	11th to 20th	Day	11% 8% 24% 30% 21% 6%	675
	21st to end	Day	16% 6% 21% 28% 20% 9%	734
June	1st to 10th	Day	16% 9% 24% 33% 14% 4	680
	11th to 20th	Day	19% 7% 28% 27% 16% 4	680
	21st to end	Day	10% 5% 23% 33% 21% 8%	680
July	1st to 10th	Day	9% 4 20% 36% 26% 6%	671
	11th to 20th	Day	14% 4 22% 31% 22% 6%	668
	21st to end	Day	6% 5% 21% 31% 26% 11%	739
August	1st to 10th	Day	10% 5% 22% 31% 25% 7%	595
	11th to 20th	Day	8% 6% 22% 34% 24% 7%	477
	21st to end	Day	10% 9% 19% 31% 24% 6%	539
September	1st to 10th	Day	12% 8% 29% 31% 17% 3	490
	11th to 20th	Day	18% 7% 24% 32% 15% 3	490
	21st to end	Day	14% 13% 29% 28% 13% 3	490
October	1st to 10th	Day	15% 6% 33% 27% 16% 3	319
	11th to 20th	Day	11% 11% 35% 25% 17% 1	300
	21st to end	Day	12% 11% 40% 25% 9% 3	330
November	1st to 10th	Day	16% 9% 34% 29% 11% 2	300
	11th to 20th	Day	10% 12% 37% 30% 10% 1	297
	21st to end	Day	8% 9% 36% 31% 11% 7%	200
December	1st to 10th	Day	11% 8% 37% 32% 10% 3	200
	11th to 20th	Day	9% 11% 36% 31% 12% 2	200
	21st to end	Day	10% 6% 24% 39% 15% 5%	220
January	1st to 10th	Night	8% 9% 37% 33% 11% 1	1000
	11th to 20th	Night	9% 11% 35% 35% 10% 1	1000
	21st to end	Night	11% 12% 36% 30% 10% 2	1030
February	1st to 10th	Night	7% 11% 28% 35% 16% 3	800
	11th to 20th	Night	9% 6% 37% 33% 14% 1	784
	21st to end	Night	7% 4 27% 38% 19% 5%	646
March	1st to 10th	Night	8% 6% 32% 37% 14% 3	760
	11th to 20th	Night	9% 5% 36% 36% 11% 3	760
	21st to end	Night	13% 6% 30% 33% 13% 4	836
April	1st to 10th	Night	9% 9% 33% 30% 16% 3	612
	11th to 20th	Night	14% 9% 30% 34% 12% 1	563
	21st to end	Night	17% 7% 23% 40% 13% 1	570
May	1st to 10th	Night	16% 9% 24% 37% 13% 2	558
	11th to 20th	Night	9% 7% 26% 38% 18% 1	374
	21st to end	Night	17% 7% 22% 29% 23% 2	411
June	1st to 10th	Night	14% 9% 27% 33% 15% 2	380
	11th to 20th	Night	19% 5% 23% 34% 17% 2	380
	21st to end	Night	10% 4 22% 38% 23% 3	380
July	1st to 10th	Night	11% 3 20% 44% 21% 2	370
	11th to 20th	Night	10% 2 26% 42% 19% 2	368
	21st to end	Night	5% 5% 24% 39% 24% 3	416
August	1st to 10th	Night	9% 4 20% 39% 23% 5%	418
	11th to 20th	Night	13% 4 19% 40% 23% 1	564
	21st to end	Night	9% 6% 24% 37% 23% 1	627
September	1st to 10th	Night	10% 4 25% 40% 18% 2	570
	11th to 20th	Night	18% 4 21% 40% 15% 1	724
	21st to end	Night	10% 5% 31% 40% 13% 1	760
October	1st to 10th	Night	13% 5% 32% 34% 14% 1	760
	11th to 20th	Night	10% 6% 35% 34% 13% 3	760
	21st to end	Night	11% 9% 35% 33% 12%	883
November	1st to 10th	Night	15% 8% 35% 32% 9% 1	975
	11th to 20th	Night	9% 9% 41% 29% 9% 3	1000
	21st to end	Night	9% 7% 40% 31% 11% 1	1000
December	1st to 10th	Night	12% 8% 34% 31% 13% 3	1000
	11th to 20th	Night	10% 9% 39% 30% 11% 1	1000
	21st to end	Night	10% 4 38% 32% 14% 3	1100

Page generated at 2025-02-22 04:51:33. Version ac07

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