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 2024-09-29.

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% 9% 3 9% 6% 5% 5% 4 6% 8% 37%	101621
	Night	7% 8% 4 9% 6% 6% 6% 5% 6% 8% 35%	96706
Transparency	Day	42% 8% 16% 23% 9% 1	101362
	Night	44% 8% 15% 22% 9% 1	96611
Seeing	Day	12% 8% 27% 31% 17% 5%	15432
	Night	11% 7% 31% 35% 14% 2	24454

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% 12% 5% 13% 9% 6% 5% 4 6% 9% 27%	2219
	11th to 20th	Day	4 8% 4 11% 6% 7% 6% 9% 9% 9% 28%	2199
	21st to end	Day	4 12% 5% 11% 7% 5% 5% 5% 6% 8% 33%	2575
February	1st to 10th	Day	6% 15% 5% 11% 7% 6% 6% 4 6% 8% 24%	1586
	11th to 20th	Day	6% 12% 6% 12% 7% 7% 5% 5% 6% 8% 27%	1665
	21st to end	Day	5% 14% 3 13% 7% 6% 6% 5% 7% 11% 23%	1413
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%	2069
October	1st to 10th	Day	9% 11% 4 7% 5% 4 5% 3 5% 5% 42%	1818
	11th to 20th	Day	8% 7% 3 8% 6% 4 6% 4 5% 7% 41%	1754
	21st to end	Day	5% 12% 4 11% 5% 6% 5% 4 6% 8% 34%	1720
November	1st to 10th	Day	9% 15% 4 11% 7% 5% 6% 4 6% 7% 26%	1488
	11th to 20th	Day	6% 11% 4 14% 8% 5% 5% 4 6% 6% 31%	1516
	21st to end	Day	5% 11% 4 13% 7% 6% 5% 5% 6% 9% 29%	1330
December	1st to 10th	Day	7% 11% 5% 13% 9% 8% 6% 5% 7% 9% 22%	1330
	11th to 20th	Day	5% 10% 4 14% 8% 8% 7% 5% 6% 8% 25%	1682
	21st to end	Day	4 9% 4 9% 5% 4 4 3 6% 8% 44%	2442
January	1st to 10th	Night	3 9% 5% 13% 8% 7% 7% 6% 8% 9% 25%	4726
	11th to 20th	Night	3 7% 3 11% 10% 7% 7% 7% 8% 8% 29%	4699
	21st to end	Night	4 10% 4 12% 7% 5% 6% 4 6% 7% 35%	5109
February	1st to 10th	Night	6% 10% 4 13% 8% 5% 6% 5% 7% 8% 27%	2594
	11th to 20th	Night	5% 11% 4 11% 8% 7% 7% 5% 7% 9% 26%	2402
	21st to end	Night	5% 8% 4 11% 7% 7% 6% 6% 7% 9% 30%	2041
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 6% 4 5% 4 4 7% 8% 47%	2079
October	1st to 10th	Night	10% 8% 3 7% 4 4 5% 4 6% 8% 41%	2142
	11th to 20th	Night	8% 6% 3 9% 6% 5% 5% 5% 6% 7% 41%	2204
	21st to end	Night	7% 10% 4 9% 6% 5% 6% 4 7% 9% 33%	2618
November	1st to 10th	Night	9% 14% 5% 8% 5% 5% 5% 4 6% 8% 30%	2590
	11th to 20th	Night	6% 11% 5% 10% 8% 7% 5% 4 6% 8% 31%	2662
	21st to end	Night	5% 11% 4 12% 7% 6% 5% 4 6% 8% 31%	2850
December	1st to 10th	Night	7% 10% 5% 13% 9% 7% 6% 4 5% 8% 26%	2850
	11th to 20th	Night	5% 11% 5% 13% 8% 6% 6% 5% 7% 9% 26%	3510
	21st to end	Night	4 7% 3 8% 5% 5% 6% 4 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% 13% 18% 5% 1	1586
	11th to 20th	Day	53% 8% 13% 16% 9% 1	1674
	21st to end	Day	53% 7% 16% 16% 8%	1413
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	33% 8% 16% 30% 11% 2	2069
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%	2594
	11th to 20th	Night	51% 8% 14% 16% 10% 1	2403
	21st to end	Night	46% 8% 14% 21% 10% 1	2041
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	33% 8% 16% 26% 15% 2	2079
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% 11% 31% 29% 11% 2	211
	11th to 20th	Day	14% 6% 35% 29% 13% 4	270
	21st to end	Day	7% 5% 34% 30% 19% 4	225
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	13% 12% 30% 29% 13% 3	483
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	760
	11th to 20th	Night	9% 6% 38% 32% 14% 1	744
	21st to end	Night	7% 4 26% 38% 19% 5%	628
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	756
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

Page generated at 2024-09-26 07:52:25. Version ac07

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