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 2026-09-14.

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	16% 17% 4 7% 4 4 4 3 4 5% 31%	153625
	Night	16% 19% 5% 8% 4 4 4 3 4 5% 30%	146157
Transparency	Day	54% 8% 11% 16% 10% 2	153339
	Night	56% 7% 10% 14% 10% 2	146023
Seeing	Day	29% 15% 25% 21% 8% 2	17483
	Night	31% 11% 24% 23% 11% 1	25702

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	15% 37% 9% 11% 4 3 3 2 3 3 9%	4125
	11th to 20th	Day	11% 14% 4 9% 3 4 3 3 4 5% 40%	4534
	21st to end	Day	15% 24% 5% 8% 4 3 4 3 4 3 27%	5186
February	1st to 10th	Day	23% 24% 5% 11% 4 3 3 2 4 4 16%	1864
	11th to 20th	Day	17% 29% 6% 10% 5% 4 3 3 3 3 18%	1845
	21st to end	Day	14% 31% 10% 10% 5% 3 3 3 2 3 15%	1636
March	1st to 10th	Day	11% 25% 11% 12% 4 4 4 2 4 4 19%	4634
	11th to 20th	Day	11% 32% 8% 9% 4 3 3 3 2 3 22%	5110
	21st to end	Day	16% 33% 7% 11% 5% 4 3 2 3 3 13%	5865
April	1st to 10th	Day	17% 33% 8% 9% 4 3 3 2 3 4 12%	2520
	11th to 20th	Day	18% 28% 5% 8% 4 3 3 3 3 4 19%	2515
	21st to end	Day	20% 28% 5% 7% 5% 4 3 2 3 5% 18%	2841
May	1st to 10th	Day	10% 15% 3 7% 4 4 4 5% 6% 6% 36%	8195
	11th to 20th	Day	17% 22% 4 8% 5% 5% 5% 4 4 6% 20%	8160
	21st to end	Day	19% 17% 4 7% 5% 4 4 3 4 7% 24%	8993
June	1st to 10th	Day	28% 15% 3 7% 5% 5% 5% 4 4 5% 20%	3063
	11th to 20th	Day	31% 15% 4 8% 6% 5% 4 4 4 5% 15%	3150
	21st to end	Day	23% 10% 3 7% 5% 4 5% 3 5% 6% 28%	3150
July	1st to 10th	Day	11% 5% 1 4 3 3 4 3 5% 7% 53%	8820
	11th to 20th	Day	6% 5% 2 3 3 3 3 3 4 5% 63%	8604
	21st to end	Day	12% 5% 1 4 3 5% 4 4 6% 7% 49%	8916
August	1st to 10th	Day	7% 4 1 3 3 4 4 2 4 7% 61%	6441
	11th to 20th	Day	11% 5% 2 5% 3 4 6% 5% 7% 8% 44%	5996
	21st to end	Day	19% 10% 3 7% 4 4 4 4 4 6% 36%	6286
September	1st to 10th	Day	15% 7% 2 7% 4 3 4 3 5% 6% 44%	2520
	11th to 20th	Day	21% 9% 3 7% 4 3 3 3 4 5% 38%	2437
	21st to end	Day	27% 9% 2 6% 3 3 3 3 4 5% 35%	2125
October	1st to 10th	Day	23% 12% 2 5% 3 4 4 4 5% 7% 32%	3280
	11th to 20th	Day	33% 15% 3 5% 3 4 3 3 4 5% 23%	3261
	21st to end	Day	24% 22% 7% 9% 4 4 4 4 4 3 15%	3269
November	1st to 10th	Day	35% 22% 4 7% 3 3 3 2 3 3 15%	1683
	11th to 20th	Day	32% 27% 5% 7% 2 2 1 1 3 2 18%	1680
	21st to end	Day	27% 26% 5% 7% 3 3 2 3 3 4 17%	1680
December	1st to 10th	Day	16% 19% 4 6% 3 2 4 4 4 4 31%	2700
	11th to 20th	Day	18% 34% 8% 9% 4 3 3 2 2 3 13%	2966
	21st to end	Day	16% 34% 7% 12% 6% 4 4 3 4 4 8%	3575
January	1st to 10th	Night	16% 32% 8% 10% 5% 4 4 3 3 3 13%	8770
	11th to 20th	Night	15% 13% 5% 8% 3 3 3 2 4 7% 38%	8347
	21st to end	Night	14% 24% 5% 7% 3 3 4 4 4 4 29%	8994
February	1st to 10th	Night	23% 22% 6% 11% 6% 4 4 3 3 4 16%	2753
	11th to 20th	Night	15% 27% 6% 11% 5% 3 2 3 2 4 20%	2662
	21st to end	Night	16% 30% 7% 9% 5% 4 3 3 4 4 17%	2170
March	1st to 10th	Night	10% 21% 11% 10% 4 3 3 3 5% 6% 24%	5479
	11th to 20th	Night	11% 28% 8% 10% 3 3 3 3 3 4 23%	5109
	21st to end	Night	20% 30% 7% 11% 4 3 3 2 2 3 14%	5352
April	1st to 10th	Night	17% 27% 6% 8% 6% 4 4 3 4 5% 17%	2100
	11th to 20th	Night	17% 22% 4 9% 6% 4 4 3 4 5% 22%	2053
	21st to end	Night	20% 23% 5% 7% 5% 5% 3 3 4 5% 21%	1778
May	1st to 10th	Night	9% 13% 3 6% 3 4 5% 4 5% 6% 42%	4724
	11th to 20th	Night	13% 20% 3 7% 6% 5% 5% 3 5% 7% 25%	4700
	21st to end	Night	14% 15% 3 7% 3 4 6% 4 7% 8% 28%	5178
June	1st to 10th	Night	25% 12% 4 7% 5% 4 4 4 4 6% 25%	1553
	11th to 20th	Night	23% 14% 3 9% 4 4 4 4 5% 7% 23%	1470
	21st to end	Night	19% 9% 2 7% 4 5% 4 4 5% 6% 35%	1470
July	1st to 10th	Night	9% 5% 1 4 2 3 3 3 4 7% 58%	4140
	11th to 20th	Night	5% 4 1 3 2 2 2 2 3 5% 70%	4354
	21st to end	Night	10% 4 2 4 3 3 4 3 4 7% 57%	5152
August	1st to 10th	Night	4 4 1 2 2 2 2 2 4 6% 71%	3709
	11th to 20th	Night	7% 7% 2 5% 3 3 3 3 5% 8% 54%	4051
	21st to end	Night	15% 10% 2 5% 3 3 4 3 6% 7% 42%	4861
September	1st to 10th	Night	13% 6% 3 6% 4 4 3 3 5% 6% 47%	2100
	11th to 20th	Night	22% 8% 4 6% 4 3 3 3 3 6% 38%	2030
	21st to end	Night	24% 9% 2 6% 4 4 4 3 3 5% 35%	2273
October	1st to 10th	Night	17% 11% 2 5% 4 5% 4 4 6% 8% 33%	3920
	11th to 20th	Night	30% 14% 3 5% 3 3 2 2 4 6% 28%	3897
	21st to end	Night	25% 22% 5% 8% 3 2 3 2 3 5% 21%	4532
November	1st to 10th	Night	33% 21% 4 7% 4 4 3 2 4 4 13%	2830
	11th to 20th	Night	32% 24% 4 6% 3 3 3 2 3 3 17%	2940
	21st to end	Night	26% 24% 6% 9% 4 4 4 2 2 3 16%	2940
December	1st to 10th	Night	16% 17% 3 6% 4 4 4 3 4 6% 32%	4700
	11th to 20th	Night	22% 28% 6% 9% 5% 5% 5% 3 3 3 12%	5443
	21st to end	Night	18% 32% 7% 12% 5% 4 4 2 3 4 9%	7623

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% 6% 4 6% 4 1	4125
	11th to 20th	Day	46% 6% 8% 15% 19% 5%	4558
	21st to end	Day	61% 7% 4 12% 14% 2	5187
February	1st to 10th	Day	72% 6% 6% 8% 7% 2	1864
	11th to 20th	Day	69% 7% 6% 9% 7% 3	1854
	21st to end	Day	76% 5% 5% 9% 4 1	1636
March	1st to 10th	Day	67% 7% 7% 9% 9% 1	4634
	11th to 20th	Day	69% 5% 7% 15% 3 1	5110
	21st to end	Day	77% 6% 7% 7% 4	5865
April	1st to 10th	Day	77% 6% 9% 7% 1	2520
	11th to 20th	Day	69% 6% 8% 8% 7% 1	2515
	21st to end	Day	71% 6% 8% 9% 6% 1	2841
May	1st to 10th	Day	46% 9% 16% 22% 6%	8195
	11th to 20th	Day	64% 10% 15% 10% 1	8163
	21st to end	Day	59% 10% 17% 11% 2	8994
June	1st to 10th	Day	65% 8% 11% 10% 5% 1	3063
	11th to 20th	Day	72% 6% 7% 11% 3	3150
	21st to end	Day	56% 8% 11% 18% 6% 1	3150
July	1st to 10th	Day	30% 9% 15% 20% 19% 8%	8746
	11th to 20th	Day	22% 6% 11% 28% 26% 6%	8523
	21st to end	Day	30% 9% 17% 27% 15% 2	8723
August	1st to 10th	Day	23% 6% 12% 23% 30% 6%	6424
	11th to 20th	Day	32% 13% 22% 24% 8% 1	6036
	21st to end	Day	49% 8% 8% 26% 8% 1	6285
September	1st to 10th	Day	40% 7% 11% 22% 16% 4	2520
	11th to 20th	Day	49% 6% 8% 18% 17% 2	2437
	21st to end	Day	52% 6% 13% 15% 11% 2	2125
October	1st to 10th	Day	50% 8% 12% 21% 9%	3280
	11th to 20th	Day	64% 6% 9% 12% 9% 1	3261
	21st to end	Day	71% 9% 6% 7% 7%	3269
November	1st to 10th	Day	75% 5% 6% 9% 4 1	1683
	11th to 20th	Day	75% 3 4 8% 7% 2	1680
	21st to end	Day	72% 4 6% 7% 8% 3	1680
December	1st to 10th	Day	55% 7% 9% 16% 9% 4	2700
	11th to 20th	Day	77% 6% 6% 7% 3 1	2968
	21st to end	Day	78% 7% 6% 5% 3	3575
January	1st to 10th	Night	77% 5% 4 8% 4 1	8770
	11th to 20th	Night	47% 5% 9% 13% 20% 6%	8385
	21st to end	Night	58% 6% 7% 13% 13% 3	8994
February	1st to 10th	Night	72% 5% 6% 8% 6% 3	2753
	11th to 20th	Night	70% 5% 5% 9% 7% 3	2664
	21st to end	Night	71% 5% 7% 11% 6% 1	2170
March	1st to 10th	Night	60% 7% 9% 11% 10% 2	5479
	11th to 20th	Night	65% 7% 9% 14% 5% 1	5110
	21st to end	Night	76% 6% 8% 8% 2	5352
April	1st to 10th	Night	71% 7% 10% 10% 2	2100
	11th to 20th	Night	64% 6% 11% 10% 8% 1	2053
	21st to end	Night	66% 8% 8% 12% 5% 1	1778
May	1st to 10th	Night	42% 9% 13% 27% 9%	4721
	11th to 20th	Night	56% 13% 16% 12% 3	4700
	21st to end	Night	50% 13% 20% 14% 2	5182
June	1st to 10th	Night	58% 8% 12% 13% 7% 1	1553
	11th to 20th	Night	60% 10% 12% 13% 5%	1470
	21st to end	Night	48% 9% 14% 18% 8% 1	1470
July	1st to 10th	Night	26% 10% 17% 19% 20% 9%	4105
	11th to 20th	Night	18% 6% 12% 24% 29% 10%	4312
	21st to end	Night	27% 8% 17% 27% 16% 5%	5040
August	1st to 10th	Night	16% 5% 11% 34% 28% 6%	3701
	11th to 20th	Night	27% 12% 24% 26% 9% 2	4076
	21st to end	Night	41% 9% 14% 26% 9% 2	4861
September	1st to 10th	Night	37% 8% 12% 21% 17% 4	2100
	11th to 20th	Night	49% 7% 8% 16% 16% 4	2030
	21st to end	Night	52% 7% 10% 17% 10% 3	2273
October	1st to 10th	Night	47% 9% 15% 21% 7%	3920
	11th to 20th	Night	59% 6% 8% 14% 12% 1	3897
	21st to end	Night	67% 6% 6% 10% 10% 1	4532
November	1st to 10th	Night	75% 6% 7% 7% 4 1	2830
	11th to 20th	Night	74% 5% 5% 7% 7% 2	2940
	21st to end	Night	74% 4 4 7% 7% 3	2940
December	1st to 10th	Night	54% 8% 9% 15% 11% 3	4700
	11th to 20th	Night	77% 6% 5% 8% 3 1	5439
	21st to end	Night	78% 8% 5% 5% 3 1	7623

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% 16% 7%	220
	11th to 20th	Day	30% 17% 25% 18% 11%	220
	21st to end	Day	29% 21% 22% 19% 9%	242
February	1st to 10th	Day	37% 19% 25% 14% 4	404
	11th to 20th	Day	32% 20% 27% 16% 3 1	425
	21st to end	Day	34% 19% 26% 18% 3 1	397
March	1st to 10th	Day	33% 23% 26% 14% 5%	540
	11th to 20th	Day	36% 20% 20% 15% 7% 1	540
	21st to end	Day	36% 22% 23% 14% 4 1	594
April	1st to 10th	Day	34% 22% 21% 16% 5% 1	540
	11th to 20th	Day	32% 19% 22% 17% 8% 3	532
	21st to end	Day	33% 18% 22% 16% 9% 2	540
May	1st to 10th	Day	21% 16% 25% 27% 10% 1	543
	11th to 20th	Day	27% 14% 21% 21% 13% 3	568
	21st to end	Day	31% 14% 22% 21% 9% 3	617
June	1st to 10th	Day	31% 13% 24% 23% 8% 1	693
	11th to 20th	Day	37% 15% 26% 17% 5% 1	780
	21st to end	Day	26% 13% 24% 26% 10% 2	780
July	1st to 10th	Day	19% 13% 29% 29% 8% 1	771
	11th to 20th	Day	17% 11% 32% 27% 9% 3	695
	21st to end	Day	13% 9% 31% 30% 12% 6%	619
August	1st to 10th	Day	14% 9% 29% 29% 14% 5%	567
	11th to 20th	Day	13% 7% 31% 31% 14% 5%	557
	21st to end	Day	19% 13% 30% 23% 12% 3	627
September	1st to 10th	Day	19% 16% 26% 25% 11% 3	570
	11th to 20th	Day	27% 14% 25% 22% 10% 2	543
	21st to end	Day	33% 13% 26% 17% 9% 2	530
October	1st to 10th	Day	31% 14% 24% 19% 9% 2	530
	11th to 20th	Day	40% 15% 17% 16% 10% 2	530
	21st to end	Day	39% 14% 24% 15% 6% 1	408
November	1st to 10th	Day	43% 18% 19% 15% 5% 1	239
	11th to 20th	Day	46% 14% 19% 13% 7% 1	220
	21st to end	Day	39% 14% 26% 9% 7% 5%	220
December	1st to 10th	Day	38% 13% 18% 15% 14% 2	220
	11th to 20th	Day	38% 23% 22% 12% 5%	220
	21st to end	Day	31% 18% 29% 17% 5%	242
January	1st to 10th	Night	42% 15% 23% 15% 4	950
	11th to 20th	Night	34% 13% 26% 21% 5%	871
	21st to end	Night	33% 15% 27% 19% 5% 1	924
February	1st to 10th	Night	35% 14% 30% 16% 4 1	840
	11th to 20th	Night	30% 12% 34% 20% 4	824
	21st to end	Night	35% 13% 30% 18% 4	692
March	1st to 10th	Night	30% 15% 26% 20% 8%	840
	11th to 20th	Night	36% 16% 23% 20% 5%	840
	21st to end	Night	34% 14% 27% 17% 6% 1	924
April	1st to 10th	Night	32% 13% 23% 22% 8% 2	840
	11th to 20th	Night	29% 12% 26% 23% 8% 2	805
	21st to end	Night	34% 7% 24% 23% 10% 1	518
May	1st to 10th	Night	23% 10% 24% 29% 11% 3	420
	11th to 20th	Night	24% 5% 18% 35% 15% 2	414
	21st to end	Night	30% 4 19% 29% 17% 1	455
June	1st to 10th	Night	28% 8% 20% 29% 14% 1	420
	11th to 20th	Night	25% 10% 23% 28% 13% 1	420
	21st to end	Night	21% 5% 20% 35% 17% 1	420
July	1st to 10th	Night	18% 2 17% 32% 29% 2	410
	11th to 20th	Night	11% 6% 19% 36% 25% 2	408
	21st to end	Night	10% 3 11% 41% 32% 2	460
August	1st to 10th	Night	10% 2 14% 35% 36% 2	418
	11th to 20th	Night	11% 3 11% 38% 32% 5%	583
	21st to end	Night	17% 5% 19% 35% 23% 1	819
September	1st to 10th	Night	17% 3 25% 33% 21% 2	840
	11th to 20th	Night	25% 6% 18% 27% 22% 3	812
	21st to end	Night	30% 6% 20% 30% 13% 1	800
October	1st to 10th	Night	27% 8% 22% 27% 16% 1	800
	11th to 20th	Night	39% 8% 20% 22% 10% 1	800
	21st to end	Night	39% 12% 26% 18% 4 1	880
November	1st to 10th	Night	44% 14% 23% 17% 2	820
	11th to 20th	Night	45% 13% 22% 14% 5%	840
	21st to end	Night	41% 13% 25% 15% 5% 1	840
December	1st to 10th	Night	33% 11% 30% 20% 5%	840
	11th to 20th	Night	43% 15% 28% 13% 1	870
	21st to end	Night	36% 21% 28% 14% 1	1045

Page generated at 2026-09-11 01:11:55. Version ac07

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