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 2024-11-01.

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	19% 18% 4 8% 4 4 3 3 4 5% 29%	101716
	Night	19% 20% 5% 8% 4 4 3 3 4 4 27%	97276
Transparency	Day	58% 6% 9% 14% 10% 2	101471
	Night	60% 6% 9% 13% 9% 3	97165
Seeing	Day	29% 15% 25% 21% 9% 2	15093
	Night	32% 11% 23% 23% 11% 1	23398

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	22% 33% 9% 10% 4 3 2 2 2 3 10%	2219
	11th to 20th	Day	17% 21% 5% 14% 4 4 2 2 3 6% 22%	2418
	21st to end	Day	25% 34% 7% 9% 3 2 2 2 2 3 11%	2794
February	1st to 10th	Day	25% 26% 4 10% 4 3 3 2 4 4 15%	1686
	11th to 20th	Day	18% 29% 6% 9% 5% 4 3 3 3 3 17%	1665
	21st to end	Day	14% 30% 11% 11% 5% 3 3 2 2 3 15%	1484
March	1st to 10th	Day	14% 26% 12% 13% 4 3 3 2 3 4 16%	3154
	11th to 20th	Day	13% 29% 6% 6% 3 3 2 2 2 4 31%	3490
	21st to end	Day	17% 33% 7% 10% 5% 4 3 2 2 3 14%	4000
April	1st to 10th	Day	18% 34% 8% 9% 5% 4 3 2 3 4 10%	2280
	11th to 20th	Day	20% 29% 5% 8% 4 4 3 3 3 4 17%	2273
	21st to end	Day	21% 29% 5% 8% 5% 4 4 2 3 5% 14%	2570
May	1st to 10th	Day	12% 23% 4 9% 5% 4 3 3 4 4 29%	4420
	11th to 20th	Day	16% 15% 4 7% 5% 5% 5% 4 5% 7% 27%	4377
	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	25% 13% 2 6% 3 4 3 3 4 6% 31%	1900
	11th to 20th	Day	31% 14% 3 6% 3 4 3 3 4 5% 24%	1900
	21st to end	Day	31% 17% 4 7% 4 3 3 2 3 3 22%	1924
November	1st to 10th	Day	37% 21% 4 7% 3 3 3 2 3 3 14%	1520
	11th to 20th	Day	31% 27% 5% 7% 2 2 1 1 3 2 19%	1520
	21st to end	Day	29% 25% 4 7% 3 3 2 3 4 3 18%	1520
December	1st to 10th	Day	21% 27% 6% 7% 4 2 2 2 3 3 23%	1520
	11th to 20th	Day	20% 29% 6% 9% 3 3 2 2 2 3 19%	1831
	21st to end	Day	19% 30% 6% 11% 6% 4 4 2 3 3 10%	2442
January	1st to 10th	Night	22% 31% 7% 9% 4 4 3 2 3 2 13%	4726
	11th to 20th	Night	19% 20% 6% 10% 4 3 4 2 4 6% 21%	4477
	21st to end	Night	23% 34% 6% 8% 4 3 3 2 3 3 11%	4862
February	1st to 10th	Night	25% 22% 5% 10% 6% 3 4 3 3 4 15%	2491
	11th to 20th	Night	17% 29% 6% 10% 5% 3 2 3 2 3 20%	2402
	21st to end	Night	17% 29% 7% 10% 4 4 3 3 4 3 17%	1970
March	1st to 10th	Night	12% 23% 12% 12% 5% 3 3 3 4 4 20%	3719
	11th to 20th	Night	13% 24% 4 7% 3 3 3 3 3 5% 32%	3489
	21st to end	Night	17% 30% 7% 11% 5% 4 3 2 2 3 17%	3653
April	1st to 10th	Night	17% 28% 6% 9% 6% 4 4 3 4 4 15%	1900
	11th to 20th	Night	18% 23% 5% 9% 6% 4 4 3 4 4 21%	1855
	21st to end	Night	22% 24% 5% 7% 5% 5% 3 3 4 4 17%	1609
May	1st to 10th	Night	13% 17% 5% 8% 4 3 2 2 4 4 38%	2540
	11th to 20th	Night	12% 14% 4 8% 6% 5% 4 3 5% 7% 34%	2516
	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	21% 10% 3 7% 4 5% 4 3 4 6% 33%	2280
	11th to 20th	Night	30% 13% 3 7% 4 4 3 2 4 4 27%	2280
	21st to end	Night	29% 17% 4 7% 4 3 3 2 4 5% 23%	2673
November	1st to 10th	Night	35% 20% 4 7% 5% 4 3 2 4 4 13%	2560
	11th to 20th	Night	31% 24% 3 6% 3 3 3 2 3 3 18%	2660
	21st to end	Night	28% 24% 5% 8% 4 3 3 2 2 3 17%	2660
December	1st to 10th	Night	21% 22% 5% 8% 4 3 3 3 4 4 23%	2660
	11th to 20th	Night	25% 28% 5% 8% 4 3 3 2 3 3 14%	3358
	21st to end	Night	20% 28% 7% 11% 4 4 4 3 4 4 11%	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	80% 5% 4 8% 3 1	2219
	11th to 20th	Day	65% 4 8% 10% 8% 4	2442
	21st to end	Day	80% 5% 4 5% 5% 1	2794
February	1st to 10th	Day	74% 5% 6% 7% 6% 2	1686
	11th to 20th	Day	71% 7% 6% 7% 6% 3	1674
	21st to end	Day	76% 5% 6% 8% 4 2	1484
March	1st to 10th	Day	72% 5% 8% 7% 7% 1	3154
	11th to 20th	Day	60% 4 10% 21% 5% 1	3490
	21st to end	Day	77% 5% 7% 6% 5%	4000
April	1st to 10th	Day	79% 6% 8% 6% 1	2280
	11th to 20th	Day	72% 5% 7% 7% 7% 1	2273
	21st to end	Day	75% 6% 7% 6% 5% 1	2570
May	1st to 10th	Day	60% 6% 11% 17% 6%	4420
	11th to 20th	Day	56% 10% 20% 13% 2	4380
	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	55% 7% 10% 19% 9% 1	1900
	11th to 20th	Day	63% 6% 8% 14% 8% 1	1900
	21st to end	Day	68% 5% 6% 10% 10% 1	1924
November	1st to 10th	Day	77% 5% 5% 8% 5% 1	1520
	11th to 20th	Day	75% 3 4 9% 7% 3	1520
	21st to end	Day	72% 4 5% 8% 8% 3	1520
December	1st to 10th	Day	68% 4 7% 9% 10% 2	1520
	11th to 20th	Day	71% 7% 7% 10% 4 1	1833
	21st to end	Day	77% 7% 5% 6% 4	2442
January	1st to 10th	Night	80% 4 4 8% 3 2	4726
	11th to 20th	Night	63% 6% 7% 11% 9% 5%	4515
	21st to end	Night	80% 5% 4 5% 5% 1	4862
February	1st to 10th	Night	74% 5% 6% 7% 5% 2	2491
	11th to 20th	Night	71% 5% 5% 9% 7% 3	2404
	21st to end	Night	71% 5% 7% 11% 6% 1	1970
March	1st to 10th	Night	67% 6% 9% 7% 9% 2	3719
	11th to 20th	Night	56% 6% 12% 19% 7% 1	3490
	21st to end	Night	74% 6% 8% 9% 3	3653
April	1st to 10th	Night	73% 7% 9% 9% 2	1900
	11th to 20th	Night	66% 6% 9% 9% 8% 1	1855
	21st to end	Night	70% 8% 7% 9% 5% 1	1609
May	1st to 10th	Night	50% 7% 10% 22% 10%	2540
	11th to 20th	Night	47% 11% 19% 19% 4	2516
	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	53% 7% 11% 19% 9% 1	2280
	11th to 20th	Night	62% 6% 8% 13% 10% 1	2280
	21st to end	Night	66% 5% 6% 11% 12% 1	2673
November	1st to 10th	Night	76% 5% 6% 7% 4 1	2560
	11th to 20th	Night	73% 5% 5% 7% 7% 2	2660
	21st to end	Night	74% 4 5% 7% 8% 3	2660
December	1st to 10th	Night	65% 6% 8% 9% 9% 3	2660
	11th to 20th	Night	76% 6% 5% 7% 5% 2	3354
	21st to end	Night	74% 8% 6% 6% 5% 1	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	33% 20% 22% 16% 8% 1	180
	11th to 20th	Day	34% 18% 21% 18% 9% 1	180
	21st to end	Day	33% 22% 20% 17% 7% 1	198
February	1st to 10th	Day	41% 20% 24% 12% 3 1	346
	11th to 20th	Day	35% 20% 26% 15% 2 1	365
	21st to end	Day	31% 20% 27% 18% 3	341
March	1st to 10th	Day	33% 23% 26% 13% 5%	460
	11th to 20th	Day	33% 18% 21% 17% 8% 2	460
	21st to end	Day	37% 20% 23% 14% 5% 1	506
April	1st to 10th	Day	37% 21% 21% 15% 5% 1	460
	11th to 20th	Day	35% 19% 21% 14% 8% 3	452
	21st to end	Day	36% 20% 21% 15% 8% 2	460
May	1st to 10th	Day	23% 16% 25% 24% 10% 1	463
	11th to 20th	Day	25% 13% 22% 23% 15% 3	488
	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	42% 16% 20% 15% 6% 1	196
	11th to 20th	Day	43% 13% 19% 14% 8% 2	180
	21st to end	Day	41% 13% 24% 9% 7% 6%	180
December	1st to 10th	Day	39% 14% 19% 14% 12% 2	180
	11th to 20th	Day	33% 23% 24% 14% 6% 1	180
	21st to end	Day	28% 21% 30% 17% 4	198
January	1st to 10th	Night	44% 15% 21% 15% 5%	850
	11th to 20th	Night	37% 13% 24% 20% 6%	786
	21st to end	Night	35% 15% 26% 18% 5% 1	836
February	1st to 10th	Night	37% 14% 29% 16% 4 1	760
	11th to 20th	Night	32% 12% 33% 19% 4	744
	21st to end	Night	34% 13% 29% 19% 5%	628
March	1st to 10th	Night	32% 15% 25% 19% 9%	760
	11th to 20th	Night	35% 16% 22% 21% 6%	760
	21st to end	Night	35% 14% 26% 17% 6% 1	836
April	1st to 10th	Night	33% 13% 23% 20% 8% 2	760
	11th to 20th	Night	30% 13% 25% 22% 8% 2	727
	21st to end	Night	36% 7% 24% 21% 11% 1	469
May	1st to 10th	Night	24% 10% 23% 28% 12% 3	380
	11th to 20th	Night	23% 3 17% 37% 17% 2	374
	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	46% 14% 21% 17% 3	742
	11th to 20th	Night	45% 14% 22% 14% 6%	760
	21st to end	Night	43% 13% 23% 15% 5% 1	760
December	1st to 10th	Night	33% 12% 31% 18% 5%	760
	11th to 20th	Night	42% 15% 29% 13% 1	784
	21st to end	Night	36% 21% 28% 13% 2	935

Page generated at 2024-10-29 08:20:49. Version ac07

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