Artist Point
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Artist Point clear sky chart from 2005-11-06 to 2025-05-11.

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	18% 19% 5% 8% 4 4 4 3 4 5% 28%	117588
	Night	18% 20% 5% 8% 4 4 3 3 4 5% 27%	120027
Transparency	Day	59% 7% 9% 14% 10% 2	117343
	Night	60% 7% 9% 13% 9% 2	119916
Seeing	Day	29% 15% 25% 21% 9% 2	15650
	Night	31% 11% 23% 23% 11% 1	24150

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	18% 32% 8% 11% 4 4 3 2 3 3 11%	3179
	11th to 20th	Day	12% 17% 5% 11% 3 4 3 3 4 6% 33%	3476
	21st to end	Day	18% 26% 5% 7% 3 3 3 3 3 3 27%	4004
February	1st to 10th	Day	24% 24% 5% 11% 4 3 3 2 4 4 16%	1775
	11th to 20th	Day	17% 29% 6% 9% 5% 4 3 3 3 3 18%	1755
	21st to end	Day	14% 30% 10% 11% 5% 3 4 3 3 3 15%	1560
March	1st to 10th	Day	11% 25% 10% 12% 4 4 4 2 4 4 19%	4534
	11th to 20th	Day	10% 33% 8% 9% 4 4 3 3 2 3 22%	5000
	21st to end	Day	16% 33% 7% 11% 5% 4 3 2 3 3 13%	5739
April	1st to 10th	Day	18% 33% 8% 9% 5% 4 3 2 3 4 11%	2400
	11th to 20th	Day	19% 28% 5% 8% 5% 3 3 3 3 4 19%	2394
	21st to end	Day	20% 29% 5% 7% 5% 4 4 2 3 5% 16%	2706
May	1st to 10th	Day	12% 23% 4 9% 5% 4 3 3 4 4 29%	4560
	11th to 20th	Day	16% 15% 4 7% 5% 5% 5% 4 5% 7% 27%	4380
	21st to end	Day	24% 23% 6% 10% 5% 5% 4 3 3 4 13%	4813
June	1st to 10th	Day	30% 15% 3 7% 5% 5% 4 4 4 5% 19%	2771
	11th to 20th	Day	34% 16% 4 8% 6% 4 4 3 4 4 12%	2850
	21st to end	Day	23% 10% 3 7% 5% 4 4 3 5% 6% 29%	2850
July	1st to 10th	Day	11% 5% 1 4 3 3 3 3 4 4 59%	4740
	11th to 20th	Day	8% 5% 2 4 2 2 2 2 3 4 65%	4622
	21st to end	Day	14% 6% 1 4 3 4 4 3 5% 6% 50%	4790
August	1st to 10th	Day	7% 4 1 4 3 3 3 3 5% 8% 59%	4401
	11th to 20th	Day	15% 6% 2 6% 3 4 5% 5% 7% 8% 39%	4071
	21st to end	Day	18% 9% 3 7% 4 4 5% 4 4 5% 37%	4322
September	1st to 10th	Day	16% 7% 2 7% 4 3 4 3 4 5% 45%	2280
	11th to 20th	Day	22% 9% 3 7% 5% 3 2 3 4 5% 37%	2280
	21st to end	Day	28% 9% 2 7% 4 3 3 3 4 5% 34%	2019
October	1st to 10th	Day	23% 12% 2 5% 3 4 4 4 5% 7% 32%	3180
	11th to 20th	Day	34% 14% 3 5% 3 4 3 3 4 5% 22%	3161
	21st to end	Day	24% 22% 7% 9% 4 4 4 4 4 3 15%	3168
November	1st to 10th	Day	35% 22% 4 7% 3 3 3 2 3 3 14%	1601
	11th to 20th	Day	31% 28% 5% 7% 2 2 1 1 3 2 18%	1600
	21st to end	Day	28% 26% 5% 7% 3 3 2 3 4 4 17%	1600
December	1st to 10th	Day	15% 19% 5% 6% 3 2 4 5% 4 4 32%	2620
	11th to 20th	Day	18% 34% 8% 9% 4 3 3 2 2 3 14%	2889
	21st to end	Day	16% 34% 7% 12% 6% 4 4 3 4 3 8%	3498
January	1st to 10th	Night	18% 29% 6% 10% 5% 4 3 2 3 3 16%	6766
	11th to 20th	Night	13% 15% 5% 9% 4 3 4 3 4 7% 32%	6405
	21st to end	Night	16% 25% 5% 7% 3 3 3 3 4 4 28%	6952
February	1st to 10th	Night	24% 22% 6% 11% 6% 3 4 3 2 4 16%	2622
	11th to 20th	Night	16% 28% 6% 11% 5% 3 2 3 2 3 20%	2532
	21st to end	Night	17% 29% 6% 10% 4 4 3 3 4 3 17%	2070
March	1st to 10th	Night	10% 21% 11% 10% 4 3 3 3 5% 6% 24%	5359
	11th to 20th	Night	10% 28% 8% 10% 3 3 3 3 3 4 24%	4999
	21st to end	Night	20% 30% 7% 11% 4 3 3 2 2 3 15%	5236
April	1st to 10th	Night	17% 28% 6% 9% 6% 4 4 3 4 5% 15%	2000
	11th to 20th	Night	18% 22% 4 9% 6% 4 4 3 4 5% 23%	1954
	21st to end	Night	21% 24% 5% 7% 5% 5% 3 3 4 5% 19%	1693
May	1st to 10th	Night	13% 17% 5% 8% 4 3 3 2 4 4 38%	2620
	11th to 20th	Night	12% 13% 4 8% 6% 5% 4 3 5% 7% 34%	2519
	21st to end	Night	22% 23% 5% 10% 4 4 4 3 3 4 17%	2762
June	1st to 10th	Night	26% 12% 4 8% 5% 4 4 3 4 5% 23%	1405
	11th to 20th	Night	25% 15% 3 9% 5% 5% 4 4 5% 6% 20%	1330
	21st to end	Night	18% 9% 2 7% 4 5% 4 4 5% 6% 36%	1330
July	1st to 10th	Night	9% 5% 2 4 3 2 2 2 3 5% 62%	2220
	11th to 20th	Night	6% 4 1 4 3 2 2 2 3 3 70%	2336
	21st to end	Night	10% 4 2 4 3 3 4 3 4 6% 57%	2762
August	1st to 10th	Night	5% 4 1 2 3 3 3 2 4 6% 67%	2529
	11th to 20th	Night	10% 10% 2 6% 3 3 4 3 5% 7% 48%	2751
	21st to end	Night	15% 8% 2 5% 3 4 4 3 6% 7% 43%	3338
September	1st to 10th	Night	13% 6% 2 7% 4 4 3 3 5% 5% 47%	1900
	11th to 20th	Night	23% 8% 4 6% 4 3 3 3 3 5% 37%	1900
	21st to end	Night	24% 10% 2 6% 4 4 4 3 3 5% 34%	2159
October	1st to 10th	Night	17% 11% 2 5% 4 5% 4 4 6% 8% 33%	3800
	11th to 20th	Night	30% 14% 3 5% 3 3 3 2 4 6% 28%	3777
	21st to end	Night	26% 21% 5% 8% 3 2 3 2 3 5% 22%	4391
November	1st to 10th	Night	33% 21% 4 7% 4 4 3 2 4 4 13%	2692
	11th to 20th	Night	31% 24% 4 6% 3 3 3 2 3 3 17%	2800
	21st to end	Night	27% 24% 6% 9% 4 3 3 2 2 3 16%	2800
December	1st to 10th	Night	15% 17% 3 6% 4 4 4 3 4 6% 33%	4560
	11th to 20th	Night	22% 27% 6% 9% 5% 5% 5% 3 3 3 12%	5300
	21st to end	Night	18% 33% 7% 12% 5% 4 4 2 3 3 8%	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	77% 7% 4 7% 5% 1	3179
	11th to 20th	Day	52% 5% 10% 16% 13% 3	3500
	21st to end	Day	62% 7% 5% 13% 13% 1	4004
February	1st to 10th	Day	73% 6% 6% 7% 6% 2	1775
	11th to 20th	Day	70% 6% 6% 8% 7% 3	1764
	21st to end	Day	76% 5% 6% 8% 4 2	1560
March	1st to 10th	Day	67% 7% 7% 9% 9% 1	4534
	11th to 20th	Day	68% 5% 7% 16% 3 1	5000
	21st to end	Day	77% 6% 7% 6% 4	5739
April	1st to 10th	Day	79% 6% 9% 6% 1	2400
	11th to 20th	Day	70% 5% 8% 8% 7% 1	2394
	21st to end	Day	73% 6% 8% 8% 5% 1	2706
May	1st to 10th	Day	60% 6% 11% 17% 6%	4560
	11th to 20th	Day	56% 10% 20% 13% 2	4383
	21st to end	Day	76% 8% 9% 6% 1	4814
June	1st to 10th	Day	67% 8% 10% 9% 5% 1	2771
	11th to 20th	Day	76% 6% 7% 8% 2	2850
	21st to end	Day	56% 8% 12% 18% 5% 1	2850
July	1st to 10th	Day	29% 7% 6% 19% 25% 14%	4666
	11th to 20th	Day	24% 4 7% 25% 31% 9%	4541
	21st to end	Day	31% 8% 12% 30% 16% 3	4639
August	1st to 10th	Day	24% 6% 11% 27% 31% 2	4384
	11th to 20th	Day	39% 12% 17% 22% 9% 2	4111
	21st to end	Day	48% 9% 8% 24% 10% 1	4321
September	1st to 10th	Day	41% 6% 11% 21% 16% 5%	2280
	11th to 20th	Day	50% 6% 8% 16% 18% 2	2280
	21st to end	Day	53% 6% 13% 14% 12% 2	2019
October	1st to 10th	Day	50% 8% 11% 21% 9%	3180
	11th to 20th	Day	64% 6% 9% 12% 8% 1	3161
	21st to end	Day	70% 9% 6% 8% 7%	3168
November	1st to 10th	Day	76% 5% 6% 8% 4 1	1601
	11th to 20th	Day	75% 3 4 8% 7% 2	1600
	21st to end	Day	72% 4 6% 7% 8% 3	1600
December	1st to 10th	Day	54% 7% 10% 16% 10% 4	2620
	11th to 20th	Day	76% 6% 6% 8% 3 1	2891
	21st to end	Day	79% 7% 5% 5% 3	3498
January	1st to 10th	Night	75% 5% 4 9% 5% 1	6766
	11th to 20th	Night	51% 6% 10% 16% 13% 4	6443
	21st to end	Night	61% 5% 7% 14% 11% 2	6952
February	1st to 10th	Night	73% 5% 6% 7% 6% 2	2622
	11th to 20th	Night	71% 5% 5% 9% 7% 3	2534
	21st to end	Night	71% 5% 7% 11% 6% 1	2070
March	1st to 10th	Night	60% 7% 9% 11% 11% 2	5359
	11th to 20th	Night	64% 7% 9% 14% 5% 1	5000
	21st to end	Night	76% 6% 8% 8% 2	5236
April	1st to 10th	Night	73% 7% 10% 9% 2	2000
	11th to 20th	Night	65% 6% 10% 10% 8% 1	1954
	21st to end	Night	68% 8% 8% 11% 5% 1	1693
May	1st to 10th	Night	50% 7% 11% 22% 10%	2620
	11th to 20th	Night	47% 11% 19% 19% 4	2519
	21st to end	Night	68% 10% 10% 10% 2	2762
June	1st to 10th	Night	61% 8% 12% 13% 6% 1	1405
	11th to 20th	Night	63% 10% 13% 11% 4	1330
	21st to end	Night	48% 10% 15% 17% 9% 1	1330
July	1st to 10th	Night	25% 6% 9% 17% 26% 17%	2185
	11th to 20th	Night	20% 4 8% 22% 30% 17%	2294
	21st to end	Night	27% 8% 14% 24% 20% 8%	2674
August	1st to 10th	Night	19% 5% 12% 31% 30% 2	2521
	11th to 20th	Night	34% 12% 19% 22% 11% 2	2776
	21st to end	Night	40% 8% 14% 27% 10% 2	3338
September	1st to 10th	Night	38% 8% 12% 21% 17% 5%	1900
	11th to 20th	Night	50% 7% 8% 15% 16% 4	1900
	21st to end	Night	53% 6% 11% 16% 10% 3	2159
October	1st to 10th	Night	48% 9% 15% 21% 7%	3800
	11th to 20th	Night	59% 6% 9% 14% 12% 1	3777
	21st to end	Night	67% 6% 6% 10% 10% 1	4391
November	1st to 10th	Night	76% 6% 7% 7% 4 1	2692
	11th to 20th	Night	74% 5% 5% 7% 7% 2	2800
	21st to end	Night	74% 4 5% 6% 7% 3	2800
December	1st to 10th	Night	53% 8% 9% 15% 12% 3	4560
	11th to 20th	Night	77% 6% 5% 8% 3 1	5296
	21st to end	Night	79% 7% 5% 5% 3 1	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	34% 20% 22% 17% 8% 1	200
	11th to 20th	Day	31% 18% 23% 18% 11% 1	200
	21st to end	Day	30% 22% 21% 19% 8%	220
February	1st to 10th	Day	39% 20% 24% 13% 3 1	375
	11th to 20th	Day	34% 20% 28% 15% 3 1	395
	21st to end	Day	32% 20% 27% 18% 3 1	369
March	1st to 10th	Day	33% 22% 26% 14% 5%	500
	11th to 20th	Day	33% 20% 21% 16% 8% 2	500
	21st to end	Day	37% 21% 23% 15% 5% 1	550
April	1st to 10th	Day	36% 22% 21% 15% 4 1	500
	11th to 20th	Day	33% 19% 22% 16% 8% 3	492
	21st to end	Day	34% 19% 20% 15% 9% 2	500
May	1st to 10th	Day	22% 16% 25% 25% 10% 1	503
	11th to 20th	Day	25% 13% 21% 22% 15% 3	489
	21st to end	Day	32% 12% 21% 22% 10% 3	529
June	1st to 10th	Day	32% 13% 23% 23% 8% 1	601
	11th to 20th	Day	39% 13% 25% 18% 5% 1	680
	21st to end	Day	25% 11% 24% 28% 10% 2	680
July	1st to 10th	Day	20% 12% 28% 31% 8% 1	671
	11th to 20th	Day	16% 9% 31% 30% 10% 4	602
	21st to end	Day	14% 8% 30% 31% 12% 5%	531
August	1st to 10th	Day	14% 8% 28% 30% 15% 5%	487
	11th to 20th	Day	13% 6% 31% 31% 13% 5%	477
	21st to end	Day	19% 13% 30% 24% 11% 3	539
September	1st to 10th	Day	20% 17% 27% 24% 9% 2	490
	11th to 20th	Day	29% 14% 24% 22% 10% 1	490
	21st to end	Day	34% 12% 25% 18% 10% 2	490
October	1st to 10th	Day	32% 13% 24% 19% 9% 2	490
	11th to 20th	Day	40% 14% 17% 16% 10% 2	490
	21st to end	Day	39% 14% 24% 16% 7% 1	373
November	1st to 10th	Day	41% 18% 20% 14% 6% 1	217
	11th to 20th	Day	44% 14% 20% 14% 8% 2	200
	21st to end	Day	38% 15% 26% 10% 8% 5%	200
December	1st to 10th	Day	36% 13% 18% 16% 16% 2	200
	11th to 20th	Day	34% 24% 24% 13% 5% 1	200
	21st to end	Day	30% 20% 29% 17% 4	220
January	1st to 10th	Night	43% 15% 23% 15% 5%	900
	11th to 20th	Night	35% 13% 26% 20% 6%	828
	21st to end	Night	33% 16% 27% 19% 5% 1	880
February	1st to 10th	Night	36% 14% 29% 16% 4 1	800
	11th to 20th	Night	31% 12% 34% 19% 4	784
	21st to end	Night	35% 13% 29% 18% 5%	660
March	1st to 10th	Night	31% 15% 26% 20% 9%	800
	11th to 20th	Night	35% 16% 23% 21% 5%	800
	21st to end	Night	35% 14% 26% 17% 6% 1	880
April	1st to 10th	Night	33% 13% 23% 21% 8% 2	800
	11th to 20th	Night	29% 12% 27% 22% 8% 2	766
	21st to end	Night	35% 7% 23% 23% 11% 1	493
May	1st to 10th	Night	24% 10% 23% 29% 11% 3	400
	11th to 20th	Night	23% 3 17% 37% 17% 2	375
	21st to end	Night	32% 4 18% 27% 18% 1	411
June	1st to 10th	Night	29% 8% 19% 29% 14% 1	380
	11th to 20th	Night	27% 9% 22% 27% 13% 1	380
	21st to end	Night	21% 5% 20% 35% 18% 2	380
July	1st to 10th	Night	18% 2 18% 31% 29% 2	370
	11th to 20th	Night	11% 6% 17% 35% 28% 2	368
	21st to end	Night	10% 2 11% 43% 31% 2	416
August	1st to 10th	Night	10% 3 12% 35% 38% 2	378
	11th to 20th	Night	11% 3 11% 36% 33% 5%	527
	21st to end	Night	17% 4 20% 34% 23% 1	741
September	1st to 10th	Night	17% 3 25% 33% 20% 2	760
	11th to 20th	Night	26% 6% 18% 24% 23% 3	760
	21st to end	Night	31% 5% 20% 30% 13% 1	760
October	1st to 10th	Night	27% 8% 21% 28% 16% 1	760
	11th to 20th	Night	39% 7% 20% 23% 10% 1	760
	21st to end	Night	39% 11% 27% 18% 4 1	836
November	1st to 10th	Night	44% 14% 22% 18% 2	780
	11th to 20th	Night	45% 13% 22% 14% 5%	800
	21st to end	Night	42% 13% 24% 16% 5% 1	800
December	1st to 10th	Night	32% 12% 31% 20% 6%	800
	11th to 20th	Night	41% 15% 29% 14% 1	827
	21st to end	Night	36% 21% 28% 13% 2	990

Page generated at 2025-05-08 06:33:55. Version ac07

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