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 2024-03-01.

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	22% 18% 5% 7% 5% 3 4 3 4 5% 25%	78209
	Night	22% 19% 5% 7% 5% 3 4 3 4 4 24%	81137
Transparency	Day	63% 6% 9% 13% 7% 1	77924
	Night	64% 6% 8% 12% 8% 2	81001
Seeing	Day	30% 15% 24% 21% 9% 2	14081
	Night	32% 11% 23% 22% 11% 1	22657

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% 31% 9% 9% 5% 2 2 2 2 3 10%	2219
	11th to 20th	Day	18% 20% 5% 12% 6% 3 3 3 2 6% 22%	2418
	21st to end	Day	25% 34% 7% 8% 4 2 2 2 2 3 11%	2794
February	1st to 10th	Day	26% 24% 5% 9% 5% 2 3 3 4 4 15%	1686
	11th to 20th	Day	18% 28% 7% 7% 6% 3 3 3 3 4 17%	1665
	21st to end	Day	15% 28% 12% 9% 6% 2 4 3 2 3 15%	1484
March	1st to 10th	Day	23% 25% 10% 8% 5% 2 4 3 3 3 15%	1804
	11th to 20th	Day	22% 32% 7% 6% 5% 3 2 3 2 4 14%	1980
	21st to end	Day	22% 31% 7% 9% 5% 3 4 2 3 3 10%	2276
April	1st to 10th	Day	20% 32% 9% 9% 4 3 4 3 3 4 10%	2160
	11th to 20th	Day	22% 28% 6% 7% 5% 3 4 4 3 3 15%	2151
	21st to end	Day	22% 27% 5% 7% 6% 3 4 3 3 5% 14%	2434
May	1st to 10th	Day	17% 20% 4 8% 7% 4 5% 4 3 5% 22%	2520
	11th to 20th	Day	20% 15% 4 7% 6% 3 6% 6% 5% 6% 22%	2477
	21st to end	Day	28% 14% 4 7% 6% 3 4 4 4 5% 21%	2723
June	1st to 10th	Day	31% 14% 3 6% 6% 3 4 5% 4 4 19%	2625
	11th to 20th	Day	35% 15% 4 8% 6% 4 4 4 4 4 12%	2700
	21st to end	Day	24% 9% 3 6% 6% 3 5% 4 5% 6% 29%	2700
July	1st to 10th	Day	17% 8% 3 5% 5% 3 4 5% 5% 5% 40%	2700
	11th to 20th	Day	15% 8% 3 5% 4 3 4 4 4 5% 45%	2638
	21st to end	Day	11% 6% 2 4 3 2 4 3 5% 5% 55%	2741
August	1st to 10th	Day	12% 6% 2 5% 5% 3 4 3 5% 7% 48%	2507
	11th to 20th	Day	13% 4 2 4 3 3 5% 5% 6% 7% 50%	2331
	21st to end	Day	19% 8% 3 6% 5% 3 4 5% 4 7% 37%	2466
September	1st to 10th	Day	17% 7% 2 6% 5% 3 4 4 4 6% 43%	2160
	11th to 20th	Day	24% 8% 3 6% 6% 2 3 3 4 5% 37%	2160
	21st to end	Day	28% 9% 3 6% 4 2 3 3 4 5% 35%	1914
October	1st to 10th	Day	26% 12% 2 5% 4 3 4 4 4 6% 31%	1800
	11th to 20th	Day	31% 14% 3 5% 4 3 3 4 4 5% 24%	1800
	21st to end	Day	33% 16% 4 6% 5% 2 3 2 3 4 23%	1823
November	1st to 10th	Day	37% 20% 4 7% 3 2 3 3 3 3 14%	1520
	11th to 20th	Day	33% 25% 5% 6% 3 1 2 1 3 2 19%	1520
	21st to end	Day	29% 23% 5% 7% 4 2 2 3 3 3 18%	1520
December	1st to 10th	Day	22% 25% 8% 7% 4 1 2 3 3 3 23%	1520
	11th to 20th	Day	20% 28% 7% 8% 4 2 2 3 2 4 19%	1831
	21st to end	Day	20% 29% 7% 10% 7% 3 4 3 3 3 10%	2442
January	1st to 10th	Night	23% 30% 8% 8% 6% 3 3 3 3 2 13%	4726
	11th to 20th	Night	19% 19% 6% 10% 5% 2 4 3 4 6% 21%	4477
	21st to end	Night	23% 33% 6% 7% 5% 2 3 3 3 3 11%	4862
February	1st to 10th	Night	25% 21% 6% 8% 6% 3 4 4 3 4 16%	2491
	11th to 20th	Night	17% 28% 6% 9% 6% 2 3 3 2 3 20%	2402
	21st to end	Night	18% 27% 7% 8% 5% 3 3 4 4 4 18%	1970
March	1st to 10th	Night	21% 24% 6% 7% 6% 2 3 3 4 4 20%	2161
	11th to 20th	Night	23% 26% 5% 7% 4 3 3 3 3 4 17%	1979
	21st to end	Night	23% 26% 7% 7% 6% 3 4 4 2 3 15%	2080
April	1st to 10th	Night	18% 27% 6% 7% 7% 3 5% 3 4 5% 15%	1800
	11th to 20th	Night	20% 22% 5% 9% 7% 3 4 4 3 4 19%	1757
	21st to end	Night	23% 23% 5% 7% 6% 4 4 4 4 4 18%	1525
May	1st to 10th	Night	20% 15% 4 7% 6% 3 3 4 5% 6% 29%	1440
	11th to 20th	Night	17% 13% 3 7% 8% 4 5% 5% 5% 8% 25%	1416
	21st to end	Night	26% 11% 3 6% 5% 3 5% 5% 5% 6% 25%	1552
June	1st to 10th	Night	27% 11% 4 7% 6% 4 5% 4 3 6% 23%	1332
	11th to 20th	Night	26% 13% 3 7% 6% 4 5% 5% 5% 6% 19%	1260
	21st to end	Night	19% 7% 2 6% 5% 3 5% 5% 5% 7% 37%	1260
July	1st to 10th	Night	15% 8% 3 5% 6% 3 4 3 4 6% 44%	1260
	11th to 20th	Night	11% 6% 3 6% 5% 2 3 4 4 6% 51%	1320
	21st to end	Night	9% 3 2 4 4 2 3 3 5% 6% 60%	1576
August	1st to 10th	Night	9% 6% 2 3 4 3 3 3 5% 6% 56%	1432
	11th to 20th	Night	8% 5% 1 4 3 2 2 4 5% 6% 60%	1567
	21st to end	Night	12% 7% 3 5% 4 3 5% 5% 7% 7% 42%	1890
September	1st to 10th	Night	14% 6% 3 5% 5% 3 3 4 5% 5% 46%	1800
	11th to 20th	Night	23% 8% 4 5% 5% 3 3 4 3 4 38%	1800
	21st to end	Night	24% 10% 2 5% 5% 3 4 4 3 5% 35%	2044
October	1st to 10th	Night	22% 10% 3 6% 5% 4 4 5% 4 5% 33%	2160
	11th to 20th	Night	30% 13% 3 6% 5% 3 4 3 3 4 27%	2160
	21st to end	Night	29% 16% 4 6% 5% 2 3 3 3 5% 23%	2532
November	1st to 10th	Night	35% 19% 5% 6% 5% 3 3 3 4 4 13%	2554
	11th to 20th	Night	33% 22% 4 5% 4 2 3 3 3 3 18%	2660
	21st to end	Night	29% 22% 5% 8% 5% 2 3 3 2 3 17%	2660
December	1st to 10th	Night	22% 21% 6% 7% 5% 2 3 3 4 5% 23%	2660
	11th to 20th	Night	25% 27% 6% 7% 5% 3 3 3 3 3 14%	3358
	21st to end	Night	20% 28% 7% 10% 5% 3 4 4 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	75% 5% 6% 8% 5% 1	1804
	11th to 20th	Day	77% 4 6% 8% 3 2	1980
	21st to end	Day	80% 6% 6% 6% 1	2276
April	1st to 10th	Day	80% 5% 8% 6% 1	2160
	11th to 20th	Day	74% 5% 6% 6% 7% 1	2151
	21st to end	Day	75% 6% 7% 6% 5% 1	2434
May	1st to 10th	Day	66% 7% 9% 12% 5%	2520
	11th to 20th	Day	61% 9% 14% 12% 3	2480
	21st to end	Day	67% 8% 11% 11% 3	2724
June	1st to 10th	Day	68% 8% 10% 9% 5% 1	2625
	11th to 20th	Day	77% 6% 8% 8% 2	2700
	21st to end	Day	56% 8% 12% 19% 5% 1	2700
July	1st to 10th	Day	45% 9% 10% 23% 11% 1	2626
	11th to 20th	Day	40% 7% 11% 27% 13% 1	2557
	21st to end	Day	29% 6% 11% 32% 18% 4	2589
August	1st to 10th	Day	36% 8% 15% 23% 15% 3	2490
	11th to 20th	Day	31% 8% 16% 27% 15% 3	2331
	21st to end	Day	46% 8% 11% 26% 8% 1	2466
September	1st to 10th	Day	42% 7% 11% 21% 15% 4	2160
	11th to 20th	Day	51% 6% 7% 16% 18% 2	2160
	21st to end	Day	53% 6% 12% 15% 12% 2	1914
October	1st to 10th	Day	55% 6% 10% 19% 9% 1	1800
	11th to 20th	Day	62% 6% 9% 14% 8% 1	1800
	21st to end	Day	68% 4 6% 10% 11% 1	1823
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	70% 5% 7% 11% 6% 1	1970
March	1st to 10th	Night	69% 5% 10% 9% 6% 1	2161
	11th to 20th	Night	72% 6% 7% 9% 5% 1	1980
	21st to end	Night	76% 7% 8% 8% 1	2080
April	1st to 10th	Night	73% 6% 9% 9% 2	1800
	11th to 20th	Night	69% 6% 9% 9% 7% 1	1757
	21st to end	Night	70% 8% 7% 10% 5% 1	1525
May	1st to 10th	Night	57% 10% 11% 16% 6%	1440
	11th to 20th	Night	56% 10% 16% 12% 6%	1416
	21st to end	Night	59% 10% 12% 16% 3	1552
June	1st to 10th	Night	62% 7% 12% 13% 5% 2	1332
	11th to 20th	Night	64% 10% 13% 10% 3	1260
	21st to end	Night	47% 10% 16% 18% 8% 2	1260
July	1st to 10th	Night	42% 7% 13% 21% 14% 3	1225
	11th to 20th	Night	34% 8% 14% 29% 12% 3	1278
	21st to end	Night	23% 7% 13% 28% 23% 6%	1488
August	1st to 10th	Night	29% 6% 17% 23% 20% 4	1424
	11th to 20th	Night	25% 8% 19% 26% 18% 4	1567
	21st to end	Night	40% 6% 14% 27% 12% 1	1890
September	1st to 10th	Night	40% 7% 12% 21% 17% 4	1800
	11th to 20th	Night	50% 6% 7% 16% 17% 4	1800
	21st to end	Night	53% 6% 10% 17% 11% 4	2044
October	1st to 10th	Night	54% 7% 10% 19% 10% 1	2160
	11th to 20th	Night	62% 6% 8% 13% 10% 1	2160
	21st to end	Night	65% 5% 6% 11% 12% 1	2532
November	1st to 10th	Night	76% 5% 6% 7% 4 1	2554
	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	32% 20% 27% 18% 3	341
March	1st to 10th	Day	34% 24% 26% 12% 5%	421
	11th to 20th	Day	36% 19% 21% 17% 7%	420
	21st to end	Day	38% 19% 23% 14% 5% 1	462
April	1st to 10th	Day	38% 21% 20% 15% 5% 1	420
	11th to 20th	Day	36% 19% 19% 14% 9% 3	412
	21st to end	Day	35% 20% 21% 15% 8% 2	420
May	1st to 10th	Day	23% 15% 26% 24% 11% 1	423
	11th to 20th	Day	24% 11% 22% 23% 16% 4	448
	21st to end	Day	31% 10% 22% 23% 11% 3	485
June	1st to 10th	Day	32% 13% 23% 23% 8% 1	555
	11th to 20th	Day	38% 13% 26% 18% 5% 1	630
	21st to end	Day	24% 11% 23% 29% 11% 2	630
July	1st to 10th	Day	21% 11% 28% 31% 8% 1	621
	11th to 20th	Day	18% 10% 31% 28% 10% 3	556
	21st to end	Day	13% 7% 30% 32% 13% 6%	487
August	1st to 10th	Day	15% 9% 28% 29% 14% 5%	447
	11th to 20th	Day	13% 6% 30% 32% 14% 5%	437
	21st to end	Day	19% 12% 30% 25% 11% 3	495
September	1st to 10th	Day	22% 17% 28% 24% 8% 1	450
	11th to 20th	Day	30% 14% 22% 23% 10% 1	450
	21st to end	Day	33% 12% 25% 18% 10% 2	450
October	1st to 10th	Day	31% 14% 24% 19% 10% 3	450
	11th to 20th	Day	39% 15% 17% 17% 11% 2	450
	21st to end	Day	40% 13% 22% 15% 8% 1	338
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	35% 13% 29% 19% 5%	628
March	1st to 10th	Night	33% 15% 25% 19% 9%	722
	11th to 20th	Night	37% 16% 22% 19% 6%	720
	21st to end	Night	36% 14% 25% 17% 7% 1	792
April	1st to 10th	Night	34% 12% 23% 20% 8% 2	720
	11th to 20th	Night	32% 13% 24% 21% 9% 2	689
	21st to end	Night	37% 6% 24% 21% 11% 1	445
May	1st to 10th	Night	24% 10% 23% 28% 11% 4	360
	11th to 20th	Night	23% 3 17% 36% 17% 3	354
	21st to end	Night	33% 3 19% 27% 18% 1	389
June	1st to 10th	Night	29% 8% 19% 28% 15% 1	360
	11th to 20th	Night	28% 8% 22% 28% 13% 1	360
	21st to end	Night	21% 4 20% 35% 19% 2	360
July	1st to 10th	Night	19% 2 17% 30% 30% 2	350
	11th to 20th	Night	12% 7% 17% 36% 26% 2	348
	21st to end	Night	10% 1 12% 43% 32% 3	394
August	1st to 10th	Night	11% 3 13% 33% 39% 2	358
	11th to 20th	Night	11% 2 12% 36% 34% 5%	499
	21st to end	Night	17% 4 19% 34% 24% 1	702
September	1st to 10th	Night	18% 3 26% 32% 19% 2	720
	11th to 20th	Night	27% 6% 16% 25% 23% 3	720
	21st to end	Night	31% 5% 20% 29% 14% 1	720
October	1st to 10th	Night	28% 8% 20% 28% 16% 1	720
	11th to 20th	Night	39% 7% 21% 22% 10% 1	720
	21st to end	Night	39% 11% 26% 18% 4 1	792
November	1st to 10th	Night	46% 14% 21% 17% 2	740
	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 2024-02-27 03:30:15. Version ac07

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