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 2024-02-10.

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	9% 8% 4 7% 7% 4 5% 5% 6% 8% 35%	77659
	Night	7% 8% 4 8% 8% 4 6% 6% 6% 8% 35%	81268
Transparency	Day	44% 8% 17% 22% 8% 1	77361
	Night	44% 8% 15% 21% 10% 1	81146
Seeing	Day	12% 8% 27% 31% 17% 5%	14426
	Night	11% 7% 31% 35% 14% 2	23776

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	5% 11% 6% 12% 10% 5% 5% 4 6% 9% 27%	2219
	11th to 20th	Day	4 7% 5% 9% 7% 6% 6% 10% 9% 9% 28%	2199
	21st to end	Day	4 11% 5% 9% 9% 3 5% 6% 6% 8% 33%	2575
February	1st to 10th	Day	7% 13% 7% 9% 9% 5% 6% 5% 6% 7% 25%	1577
	11th to 20th	Day	7% 11% 6% 11% 8% 6% 5% 6% 6% 8% 26%	1575
	21st to end	Day	5% 12% 5% 12% 8% 4 6% 7% 7% 11% 23%	1332
March	1st to 10th	Day	7% 11% 5% 10% 13% 5% 8% 5% 5% 6% 25%	1840
	11th to 20th	Day	7% 10% 5% 9% 9% 3 6% 5% 5% 7% 34%	1979
	21st to end	Day	9% 11% 5% 13% 8% 4 4 4 6% 8% 27%	2178
April	1st to 10th	Day	9% 11% 4 9% 7% 5% 5% 5% 6% 7% 32%	2231
	11th to 20th	Day	11% 11% 5% 8% 7% 3 5% 5% 5% 7% 31%	2310
	21st to end	Day	13% 11% 4 7% 6% 3 5% 5% 6% 9% 32%	2340
May	1st to 10th	Day	12% 10% 3 7% 7% 5% 6% 6% 7% 8% 29%	2523
	11th to 20th	Day	8% 6% 3 6% 7% 4 6% 7% 6% 9% 38%	2654
	21st to end	Day	17% 7% 3 7% 6% 3 6% 6% 6% 7% 31%	2917
June	1st to 10th	Day	16% 8% 2 5% 6% 3 5% 5% 7% 9% 33%	2700
	11th to 20th	Day	19% 7% 4 8% 7% 4 5% 5% 6% 9% 26%	2700
	21st to end	Day	10% 5% 3 5% 6% 4 6% 7% 8% 11% 38%	2700
July	1st to 10th	Day	8% 4 2 5% 5% 4 5% 6% 7% 9% 42%	2700
	11th to 20th	Day	11% 5% 2 5% 5% 3 6% 6% 8% 9% 42%	2700
	21st to end	Day	6% 4 2 5% 5% 3 4 5% 6% 9% 52%	2938
August	1st to 10th	Day	9% 5% 3 5% 5% 4 5% 5% 7% 10% 44%	2572
	11th to 20th	Day	9% 4 2 4 5% 3 5% 5% 6% 9% 48%	2299
	21st to end	Day	9% 4 2 4 5% 3 5% 6% 8% 9% 46%	2574
September	1st to 10th	Day	11% 7% 3 5% 5% 3 4 4 5% 8% 45%	2255
	11th to 20th	Day	16% 7% 3 4 5% 3 4 4 5% 6% 44%	2012
	21st to end	Day	9% 7% 2 5% 5% 3 4 4 5% 8% 48%	1980
October	1st to 10th	Day	9% 10% 4 6% 6% 3 5% 4 5% 5% 42%	1818
	11th to 20th	Day	9% 7% 4 7% 6% 3 6% 5% 5% 7% 41%	1754
	21st to end	Day	5% 11% 4 9% 7% 4 5% 6% 6% 8% 34%	1720
November	1st to 10th	Day	9% 13% 6% 9% 8% 4 6% 5% 5% 8% 26%	1488
	11th to 20th	Day	6% 10% 5% 13% 10% 3 6% 5% 5% 6% 31%	1516
	21st to end	Day	6% 10% 5% 12% 8% 5% 5% 6% 5% 9% 30%	1330
December	1st to 10th	Day	7% 10% 5% 10% 12% 5% 8% 6% 6% 9% 22%	1330
	11th to 20th	Day	5% 9% 5% 12% 10% 6% 7% 7% 6% 8% 25%	1682
	21st to end	Day	5% 8% 4 7% 7% 3 4 4 6% 8% 44%	2442
January	1st to 10th	Night	4 9% 5% 11% 10% 5% 7% 8% 8% 9% 25%	4726
	11th to 20th	Night	3 6% 3 9% 12% 5% 7% 8% 7% 8% 29%	4699
	21st to end	Night	5% 10% 4 10% 8% 4 6% 5% 6% 8% 35%	5109
February	1st to 10th	Night	6% 9% 5% 11% 9% 4 6% 6% 6% 8% 28%	2587
	11th to 20th	Night	6% 11% 5% 9% 10% 5% 7% 7% 7% 9% 24%	2272
	21st to end	Night	5% 7% 4 9% 9% 5% 6% 7% 7% 10% 31%	1924
March	1st to 10th	Night	5% 10% 4 10% 10% 5% 6% 7% 6% 9% 29%	2117
	11th to 20th	Night	7% 9% 4 9% 7% 4 7% 6% 7% 9% 31%	1980
	21st to end	Night	9% 10% 5% 11% 7% 3 6% 6% 7% 9% 28%	2178
April	1st to 10th	Night	7% 10% 4 8% 7% 4 5% 6% 6% 8% 37%	1727
	11th to 20th	Night	10% 10% 3 8% 9% 4 7% 6% 7% 7% 30%	1601
	21st to end	Night	12% 9% 4 6% 7% 4 6% 5% 5% 8% 35%	1620
May	1st to 10th	Night	12% 10% 4 7% 6% 4 6% 5% 6% 8% 33%	1434
	11th to 20th	Night	8% 6% 3 7% 6% 5% 6% 7% 6% 8% 38%	1239
	21st to end	Night	17% 6% 3 6% 6% 3 5% 6% 5% 9% 33%	1358
June	1st to 10th	Night	14% 6% 4 7% 7% 3 7% 6% 6% 7% 32%	1260
	11th to 20th	Night	18% 6% 2 6% 5% 4 7% 5% 8% 9% 30%	1260
	21st to end	Night	8% 4 3 6% 6% 4 5% 6% 7% 9% 43%	1260
July	1st to 10th	Night	8% 5% 3 5% 5% 5% 4 5% 6% 10% 44%	1260
	11th to 20th	Night	8% 4 2 4 5% 3 5% 6% 8% 13% 43%	1260
	21st to end	Night	6% 3 2 4 4 4 5% 4 6% 9% 53%	1379
August	1st to 10th	Night	7% 4 3 5% 6% 4 6% 6% 8% 10% 41%	1364
	11th to 20th	Night	10% 5% 3 5% 6% 3 6% 4 6% 8% 44%	1602
	21st to end	Night	6% 5% 2 5% 5% 3 5% 5% 7% 9% 47%	1782
September	1st to 10th	Night	9% 5% 2 5% 5% 3 5% 5% 6% 7% 47%	1705
	11th to 20th	Night	14% 7% 2 3 5% 2 4 4 5% 7% 47%	1945
	21st to end	Night	7% 6% 3 5% 5% 3 4 4 7% 8% 47%	1980
October	1st to 10th	Night	10% 8% 3 6% 4 4 4 5% 6% 8% 41%	2142
	11th to 20th	Night	8% 6% 3 8% 7% 4 5% 6% 6% 7% 41%	2204
	21st to end	Night	7% 9% 4 8% 8% 4 6% 5% 7% 9% 34%	2618
November	1st to 10th	Night	10% 13% 6% 7% 7% 4 5% 5% 6% 8% 30%	2590
	11th to 20th	Night	6% 9% 5% 9% 10% 5% 6% 5% 6% 8% 31%	2662
	21st to end	Night	5% 10% 6% 10% 9% 4 5% 6% 6% 9% 32%	2850
December	1st to 10th	Night	7% 9% 6% 12% 10% 5% 7% 6% 5% 8% 26%	2850
	11th to 20th	Night	5% 10% 5% 11% 10% 5% 7% 6% 7% 9% 27%	3510
	21st to end	Night	4 6% 3 7% 6% 4 6% 5% 6% 7% 45%	5214

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	53% 6% 13% 19% 7% 1	2219
	11th to 20th	Day	45% 8% 17% 15% 15% 1	2220
	21st to end	Day	46% 8% 18% 21% 6%	2575
February	1st to 10th	Day	56% 6% 14% 18% 6% 1	1577
	11th to 20th	Day	54% 8% 14% 16% 9%	1584
	21st to end	Day	53% 6% 16% 17% 8%	1332
March	1st to 10th	Day	57% 9% 16% 14% 4	1840
	11th to 20th	Day	48% 7% 14% 21% 9% 1	1980
	21st to end	Day	53% 9% 17% 16% 5%	2178
April	1st to 10th	Day	49% 7% 16% 19% 8% 1	2231
	11th to 20th	Day	50% 6% 14% 21% 8%	2310
	21st to end	Day	47% 8% 16% 20% 7% 1	2340
May	1st to 10th	Day	50% 9% 15% 18% 8%	2523
	11th to 20th	Day	39% 8% 14% 27% 11% 1	2658
	21st to end	Day	49% 8% 15% 19% 9%	2918
June	1st to 10th	Day	45% 9% 16% 22% 7%	2700
	11th to 20th	Day	53% 10% 16% 17% 4 1	2700
	21st to end	Day	37% 12% 24% 20% 7% 1	2700
July	1st to 10th	Day	34% 10% 22% 26% 7% 1	2626
	11th to 20th	Day	36% 11% 21% 26% 7%	2619
	21st to end	Day	28% 9% 23% 30% 9% 1	2775
August	1st to 10th	Day	33% 11% 22% 27% 6% 1	2554
	11th to 20th	Day	31% 10% 24% 25% 10% 1	2299
	21st to end	Day	32% 8% 20% 29% 10% 1	2574
September	1st to 10th	Day	37% 6% 18% 24% 10% 4	2255
	11th to 20th	Day	41% 5% 17% 28% 8% 1	2012
	21st to end	Day	34% 8% 16% 30% 11% 2	1980
October	1st to 10th	Day	42% 6% 17% 24% 10%	1818
	11th to 20th	Day	42% 7% 17% 24% 10% 1	1754
	21st to end	Day	46% 8% 15% 21% 9%	1720
November	1st to 10th	Day	55% 8% 12% 18% 6% 1	1488
	11th to 20th	Day	50% 9% 17% 19% 5%	1516
	21st to end	Day	50% 7% 18% 18% 6%	1330
December	1st to 10th	Day	58% 7% 11% 16% 6% 1	1330
	11th to 20th	Day	54% 9% 16% 17% 4	1684
	21st to end	Day	38% 5% 11% 27% 15% 3	2442
January	1st to 10th	Night	49% 10% 16% 19% 5% 1	4726
	11th to 20th	Night	49% 6% 13% 18% 11% 1	4740
	21st to end	Night	46% 8% 14% 25% 7%	5109
February	1st to 10th	Night	52% 7% 12% 18% 10%	2587
	11th to 20th	Night	52% 8% 15% 16% 9%	2273
	21st to end	Night	46% 8% 14% 21% 10% 1	1924
March	1st to 10th	Night	49% 10% 15% 19% 8%	2117
	11th to 20th	Night	47% 8% 12% 23% 9% 1	1980
	21st to end	Night	50% 9% 15% 18% 8% 1	2178
April	1st to 10th	Night	43% 7% 15% 20% 13% 1	1727
	11th to 20th	Night	49% 8% 12% 21% 10% 1	1601
	21st to end	Night	44% 8% 13% 22% 11% 2	1620
May	1st to 10th	Night	47% 8% 12% 23% 11% 1	1434
	11th to 20th	Night	39% 8% 13% 24% 14% 2	1239
	21st to end	Night	45% 8% 15% 21% 10% 1	1358
June	1st to 10th	Night	47% 10% 14% 20% 8% 1	1260
	11th to 20th	Night	48% 11% 15% 18% 8%	1260
	21st to end	Night	34% 11% 24% 23% 7% 1	1260
July	1st to 10th	Night	33% 10% 22% 26% 8% 1	1225
	11th to 20th	Night	30% 13% 25% 22% 8% 1	1218
	21st to end	Night	25% 9% 22% 32% 11% 1	1302
August	1st to 10th	Night	35% 11% 19% 26% 8% 1	1357
	11th to 20th	Night	36% 8% 20% 27% 8% 1	1602
	21st to end	Night	31% 8% 16% 29% 14% 2	1782
September	1st to 10th	Night	33% 8% 20% 19% 14% 6%	1705
	11th to 20th	Night	35% 7% 15% 28% 12% 2	1945
	21st to end	Night	32% 8% 16% 26% 15% 2	1980
October	1st to 10th	Night	40% 7% 16% 25% 11% 1	2142
	11th to 20th	Night	40% 8% 15% 25% 11% 1	2204
	21st to end	Night	44% 10% 15% 23% 6% 1	2618
November	1st to 10th	Night	51% 7% 14% 18% 9% 1	2590
	11th to 20th	Night	49% 8% 16% 18% 8% 1	2662
	21st to end	Night	48% 8% 17% 19% 7%	2850
December	1st to 10th	Night	55% 6% 12% 16% 8% 1	2850
	11th to 20th	Night	52% 9% 20% 14% 5%	3507
	21st to end	Night	37% 7% 13% 22% 17% 4	5214

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	6% 6% 34% 34% 16% 4	180
	11th to 20th	Day	6% 11% 34% 31% 16% 2	180
	21st to end	Day	11% 10% 36% 27% 13% 3	198
February	1st to 10th	Day	16% 12% 32% 28% 11% 1	208
	11th to 20th	Day	15% 6% 37% 28% 12% 2	240
	21st to end	Day	7% 4 34% 31% 20% 5%	198
March	1st to 10th	Day	10% 10% 33% 30% 15% 2	410
	11th to 20th	Day	9% 9% 35% 30% 13% 5%	420
	21st to end	Day	12% 8% 29% 34% 15% 3	462
April	1st to 10th	Day	11% 11% 33% 30% 11% 4	420
	11th to 20th	Day	12% 10% 31% 32% 11% 4	412
	21st to end	Day	18% 11% 28% 26% 14% 3	420
May	1st to 10th	Day	15% 9% 22% 31% 18% 5%	598
	11th to 20th	Day	11% 7% 23% 32% 22% 7%	625
	21st to end	Day	18% 6% 21% 29% 18% 8%	679
June	1st to 10th	Day	16% 8% 24% 34% 14% 4	630
	11th to 20th	Day	19% 7% 28% 27% 15% 4	630
	21st to end	Day	11% 5% 22% 33% 22% 8%	630
July	1st to 10th	Day	9% 4 21% 35% 25% 6%	621
	11th to 20th	Day	14% 5% 24% 31% 21% 6%	618
	21st to end	Day	6% 4 22% 32% 25% 10%	684
August	1st to 10th	Day	11% 5% 22% 32% 24% 7%	550
	11th to 20th	Day	8% 6% 22% 34% 24% 6%	437
	21st to end	Day	10% 8% 18% 32% 25% 7%	495
September	1st to 10th	Day	13% 8% 30% 32% 14% 2	450
	11th to 20th	Day	19% 7% 23% 32% 16% 4	450
	21st to end	Day	14% 12% 29% 30% 12% 3	450
October	1st to 10th	Day	17% 6% 31% 27% 16% 3	288
	11th to 20th	Day	12% 11% 34% 26% 16% 1	270
	21st to end	Day	11% 12% 41% 25% 9% 3	297
November	1st to 10th	Day	16% 8% 34% 29% 11% 2	270
	11th to 20th	Day	12% 11% 37% 30% 10% 1	268
	21st to end	Day	6% 9% 38% 29% 11% 7%	180
December	1st to 10th	Day	11% 7% 36% 33% 11% 3	180
	11th to 20th	Day	9% 11% 34% 32% 12% 1	180
	21st to end	Day	12% 6% 25% 39% 13% 6%	198
January	1st to 10th	Night	9% 9% 37% 33% 11% 1	950
	11th to 20th	Night	10% 10% 34% 35% 11% 1	950
	21st to end	Night	11% 12% 35% 31% 10% 2	979
February	1st to 10th	Night	8% 11% 28% 34% 16% 3	758
	11th to 20th	Night	10% 6% 39% 31% 13% 1	704
	21st to end	Night	7% 4 26% 39% 19% 5%	592
March	1st to 10th	Night	8% 5% 32% 38% 15% 3	720
	11th to 20th	Night	9% 5% 35% 36% 11% 3	720
	21st to end	Night	14% 6% 29% 33% 14% 4	792
April	1st to 10th	Night	8% 8% 33% 30% 17% 3	580
	11th to 20th	Night	14% 8% 30% 34% 12% 1	533
	21st to end	Night	17% 6% 23% 40% 12% 1	540
May	1st to 10th	Night	14% 8% 24% 38% 13% 2	529
	11th to 20th	Night	10% 7% 26% 38% 18% 1	354
	21st to end	Night	18% 6% 21% 29% 23% 3	389
June	1st to 10th	Night	15% 8% 26% 34% 16% 2	360
	11th to 20th	Night	20% 5% 22% 34% 17% 2	360
	21st to end	Night	10% 3 22% 39% 24% 3	360
July	1st to 10th	Night	11% 3 21% 42% 21% 2	350
	11th to 20th	Night	10% 3 26% 42% 18% 1	348
	21st to end	Night	5% 5% 24% 40% 24% 4	394
August	1st to 10th	Night	9% 3 20% 39% 23% 5%	395
	11th to 20th	Night	13% 4 19% 39% 23% 1	534
	21st to end	Night	9% 5% 24% 37% 24% 1	594
September	1st to 10th	Night	11% 3 26% 39% 18% 2	540
	11th to 20th	Night	18% 4 21% 40% 15% 1	685
	21st to end	Night	10% 4 31% 40% 13% 1	720
October	1st to 10th	Night	14% 4 31% 35% 14% 2	720
	11th to 20th	Night	10% 5% 35% 34% 14% 3	720
	21st to end	Night	11% 9% 35% 33% 12%	836
November	1st to 10th	Night	15% 8% 35% 32% 9% 1	925
	11th to 20th	Night	9% 9% 40% 29% 10% 3	950
	21st to end	Night	9% 7% 41% 31% 11% 1	950
December	1st to 10th	Night	11% 7% 33% 31% 13% 3	950
	11th to 20th	Night	9% 9% 39% 30% 11% 1	950
	21st to end	Night	10% 4 38% 32% 13% 3	1045

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