Netarts Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Netarts Observatory clear sky chart from 2005-11-06 to 2026-02-16.

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	23% 10% 3 7% 4 4 4 3 4 6% 31%	141059
	Night	28% 13% 3 7% 4 3 3 3 4 5% 28%	137124
Transparency	Day	54% 7% 11% 15% 10% 3	135802
	Night	59% 6% 9% 13% 10% 3	133382
Seeing	Day	28% 11% 24% 23% 10% 3	16793
	Night	33% 7% 15% 24% 18% 3	25239

By Month

Percentage Cloud Cover SW (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	45% 16% 4 8% 4 4 3 2 3 3 10%	4722
	11th to 20th	Day	26% 8% 2 5% 3 3 3 2 4 5% 39%	4782
	21st to end	Day	35% 9% 3 6% 4 3 3 2 3 3 29%	5843
February	1st to 10th	Day	37% 13% 3 6% 4 3 4 3 4 5% 18%	1890
	11th to 20th	Day	36% 14% 4 7% 5% 4 3 2 3 4 18%	1801
	21st to end	Day	35% 16% 3 7% 3 4 4 3 4 4 17%	1510
March	1st to 10th	Day	22% 19% 4 8% 6% 5% 5% 4 4 6% 17%	4883
	11th to 20th	Day	32% 16% 3 7% 4 3 3 2 3 4 22%	5000
	21st to end	Day	34% 14% 4 10% 6% 5% 5% 3 4 5% 10%	5486
April	1st to 10th	Day	33% 13% 4 9% 5% 4 4 4 5% 7% 13%	2400
	11th to 20th	Day	28% 13% 3 7% 6% 3 4 3 4 5% 23%	2436
	21st to end	Day	28% 11% 3 7% 6% 4 4 3 5% 6% 21%	2600
May	1st to 10th	Day	22% 10% 2 7% 4 3 3 3 5% 6% 36%	6086
	11th to 20th	Day	21% 12% 3 9% 4 4 5% 4 7% 8% 23%	6277
	21st to end	Day	24% 10% 3 7% 4 5% 4 4 5% 7% 28%	6902
June	1st to 10th	Day	27% 10% 3 7% 5% 4 3 3 5% 6% 28%	2800
	11th to 20th	Day	24% 12% 3 7% 5% 5% 5% 4 6% 7% 22%	2972
	21st to end	Day	17% 9% 3 7% 4 4 4 3 5% 7% 37%	3000
July	1st to 10th	Day	7% 7% 2 5% 3 3 3 3 4 7% 57%	6779
	11th to 20th	Day	6% 6% 3 5% 3 3 3 2 4 7% 58%	6366
	21st to end	Day	8% 8% 3 7% 4 3 3 3 5% 7% 49%	6753
August	1st to 10th	Day	9% 9% 3 7% 4 4 4 3 5% 9% 44%	5777
	11th to 20th	Day	13% 7% 2 7% 5% 5% 5% 4 7% 8% 36%	5796
	21st to end	Day	11% 8% 3 6% 4 4 4 3 6% 9% 42%	6275
September	1st to 10th	Day	11% 7% 2 6% 3 3 3 4 4 7% 49%	2400
	11th to 20th	Day	15% 8% 3 7% 4 5% 5% 3 5% 8% 37%	2325
	21st to end	Day	21% 6% 2 6% 4 3 3 2 4 6% 42%	2150
October	1st to 10th	Day	20% 6% 2 5% 3 3 3 2 5% 6% 46%	3280
	11th to 20th	Day	30% 9% 3 8% 4 4 3 2 5% 6% 26%	3261
	21st to end	Day	33% 7% 3 6% 4 4 4 4 5% 7% 24%	3558
November	1st to 10th	Day	35% 12% 3 8% 5% 4 4 3 4 5% 16%	1689
	11th to 20th	Day	40% 10% 3 6% 4 4 3 3 4 5% 18%	1680
	21st to end	Day	33% 11% 3 8% 4 4 4 2 3 4 23%	1680
December	1st to 10th	Day	26% 8% 3 6% 4 4 3 3 4 5% 35%	2700
	11th to 20th	Day	41% 13% 3 8% 5% 4 3 3 3 4 13%	3108
	21st to end	Day	44% 15% 4 7% 4 3 3 2 3 3 12%	4092
January	1st to 10th	Night	41% 16% 4 9% 5% 4 3 2 3 4 10%	8172
	11th to 20th	Night	24% 11% 3 6% 3 3 2 2 3 5% 39%	8164
	21st to end	Night	35% 10% 3 6% 3 3 2 2 3 4 29%	8371
February	1st to 10th	Night	34% 15% 3 7% 5% 4 4 3 3 5% 17%	2730
	11th to 20th	Night	33% 15% 3 8% 3 4 3 2 3 4 22%	2597
	21st to end	Night	35% 15% 2 7% 5% 3 3 2 3 4 20%	2120
March	1st to 10th	Night	25% 18% 4 8% 5% 5% 5% 3 5% 5% 17%	4996
	11th to 20th	Night	30% 17% 4 8% 4 4 3 2 3 2 24%	5000
	21st to end	Night	37% 18% 4 9% 5% 4 3 3 3 3 10%	5489
April	1st to 10th	Night	33% 16% 3 7% 5% 4 4 3 4 4 17%	2000
	11th to 20th	Night	26% 15% 4 6% 4 4 3 4 4 6% 24%	1910
	21st to end	Night	29% 13% 3 8% 5% 4 3 4 5% 5% 22%	1800
May	1st to 10th	Night	23% 11% 2 6% 4 3 3 3 4 5% 35%	3881
	11th to 20th	Night	26% 18% 5% 8% 5% 4 3 3 4 5% 20%	3616
	21st to end	Night	25% 13% 3 6% 4 4 4 4 5% 7% 26%	3972
June	1st to 10th	Night	24% 11% 3 8% 6% 4 4 2 4 5% 30%	1600
	11th to 20th	Night	23% 12% 4 7% 5% 4 4 5% 5% 6% 25%	1421
	21st to end	Night	17% 11% 2 7% 4 4 3 3 5% 6% 39%	1400
July	1st to 10th	Night	7% 16% 2 5% 2 2 3 2 4 6% 52%	3180
	11th to 20th	Night	6% 11% 2 5% 4 3 3 2 4 5% 55%	3589
	21st to end	Night	10% 14% 4 6% 4 3 3 2 4 6% 44%	4100
August	1st to 10th	Night	11% 16% 5% 8% 5% 3 3 3 3 5% 39%	4035
	11th to 20th	Night	20% 12% 3 6% 3 3 3 3 3 5% 38%	4052
	21st to end	Night	14% 14% 3 6% 4 3 3 2 4 5% 43%	4711
September	1st to 10th	Night	14% 8% 3 5% 2 3 3 3 5% 5% 50%	2000
	11th to 20th	Night	17% 9% 3 8% 4 3 3 3 4 5% 41%	2070
	21st to end	Night	19% 8% 2 6% 3 3 3 3 4 6% 44%	2250
October	1st to 10th	Night	18% 5% 2 5% 3 3 3 2 4 7% 47%	3920
	11th to 20th	Night	27% 11% 3 7% 4 4 4 4 4 7% 26%	3897
	21st to end	Night	32% 9% 3 8% 4 4 4 3 4 5% 24%	4253
November	1st to 10th	Night	37% 10% 3 7% 5% 4 4 3 4 5% 18%	2826
	11th to 20th	Night	40% 10% 3 7% 5% 4 4 2 3 4 19%	2940
	21st to end	Night	31% 11% 3 7% 5% 3 4 3 4 4 25%	2940
December	1st to 10th	Night	24% 8% 3 6% 4 3 3 3 4 6% 36%	4700
	11th to 20th	Night	46% 11% 3 8% 4 3 3 2 3 4 12%	5316
	21st to end	Night	44% 14% 4 7% 4 4 3 2 3 3 12%	7106

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	83% 3 4 6% 3 1	4723
	11th to 20th	Day	48% 3 5% 14% 17% 13%	4782
	21st to end	Day	63% 3 5% 10% 15% 5%	5843
February	1st to 10th	Day	70% 5% 10% 9% 5% 1	1890
	11th to 20th	Day	73% 4 5% 10% 6% 2	1810
	21st to end	Day	72% 6% 7% 8% 6% 1	1510
March	1st to 10th	Day	67% 8% 13% 9% 3	4883
	11th to 20th	Day	66% 7% 6% 14% 7%	5000
	21st to end	Day	77% 7% 9% 5% 2	5486
April	1st to 10th	Day	72% 7% 10% 9% 2	2400
	11th to 20th	Day	65% 7% 8% 12% 7% 2	2439
	21st to end	Day	65% 7% 11% 12% 5% 1	2600
May	1st to 10th	Day	49% 7% 15% 18% 12%	6086
	11th to 20th	Day	55% 11% 16% 12% 5%	6280
	21st to end	Day	54% 10% 21% 13% 1	6904
June	1st to 10th	Day	58% 7% 14% 14% 6%	2800
	11th to 20th	Day	61% 9% 14% 12% 4	2972
	21st to end	Day	45% 8% 18% 19% 8% 2	3000
July	1st to 10th	Day	26% 6% 12% 22% 16% 18%	6706
	11th to 20th	Day	24% 7% 9% 22% 34% 4	6290
	21st to end	Day	31% 7% 17% 30% 14% 1	6556
August	1st to 10th	Day	31% 8% 12% 22% 22% 4	4206
	11th to 20th	Day	40% 10% 18% 20% 9% 3	4195
	21st to end	Day	36% 6% 16% 21% 16% 5%	4518
September	1st to 10th	Day	33% 8% 12% 23% 14% 10%	2400
	11th to 20th	Day	44% 8% 14% 17% 12% 5%	2325
	21st to end	Day	44% 6% 12% 19% 15% 4	2150
October	1st to 10th	Day	39% 5% 7% 28% 20% 1	3280
	11th to 20th	Day	59% 5% 13% 13% 9% 1	3261
	21st to end	Day	60% 4 10% 15% 9% 1	3558
November	1st to 10th	Day	71% 6% 8% 11% 4	1689
	11th to 20th	Day	71% 5% 8% 8% 6% 3	1680
	21st to end	Day	68% 4 7% 8% 11% 3	1680
December	1st to 10th	Day	54% 4 7% 11% 21% 3	2700
	11th to 20th	Day	77% 5% 9% 6% 3	3108
	21st to end	Day	79% 5% 8% 6% 2 1	4092
January	1st to 10th	Night	80% 4 5% 6% 3 2	8172
	11th to 20th	Night	50% 4 6% 15% 14% 11%	8164
	21st to end	Night	62% 2 4 7% 19% 6%	8371
February	1st to 10th	Night	71% 6% 7% 10% 4 2	2730
	11th to 20th	Night	69% 5% 8% 10% 6% 3	2599
	21st to end	Night	70% 5% 9% 9% 6% 2	2120
March	1st to 10th	Night	68% 6% 10% 12% 5%	4996
	11th to 20th	Night	65% 7% 8% 11% 8% 1	5000
	21st to end	Night	77% 7% 8% 6% 2	5489
April	1st to 10th	Night	70% 5% 11% 10% 4	2000
	11th to 20th	Night	61% 7% 10% 14% 6% 3	1910
	21st to end	Night	64% 7% 9% 13% 5% 2	1800
May	1st to 10th	Night	48% 7% 12% 22% 10%	3878
	11th to 20th	Night	58% 14% 13% 8% 6% 1	3616
	21st to end	Night	55% 10% 21% 12% 2	3972
June	1st to 10th	Night	56% 8% 13% 18% 5%	1600
	11th to 20th	Night	56% 9% 15% 17% 2	1421
	21st to end	Night	44% 8% 16% 23% 6% 3	1400
July	1st to 10th	Night	30% 8% 11% 17% 16% 17%	3145
	11th to 20th	Night	27% 8% 10% 22% 25% 8%	3543
	21st to end	Night	37% 7% 16% 23% 13% 3	3985
August	1st to 10th	Night	41% 9% 13% 19% 14% 4	2929
	11th to 20th	Night	44% 6% 16% 21% 9% 4	2929
	21st to end	Night	39% 6% 15% 17% 20% 4	3395
September	1st to 10th	Night	34% 8% 11% 23% 16% 10%	2000
	11th to 20th	Night	44% 6% 13% 16% 14% 6%	2070
	21st to end	Night	41% 6% 12% 17% 17% 7%	2250
October	1st to 10th	Night	37% 6% 9% 28% 18% 2	3920
	11th to 20th	Night	56% 7% 12% 13% 10% 2	3897
	21st to end	Night	62% 5% 7% 15% 9% 2	4253
November	1st to 10th	Night	69% 5% 8% 10% 6% 1	2826
	11th to 20th	Night	71% 5% 7% 7% 6% 3	2940
	21st to end	Night	64% 5% 8% 8% 9% 6%	2940
December	1st to 10th	Night	50% 5% 7% 16% 19% 3	4700
	11th to 20th	Night	78% 5% 6% 6% 5%	5316
	21st to end	Night	78% 6% 7% 6% 2 1	7106

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	49% 15% 19% 11% 5% 1	220
	11th to 20th	Day	38% 8% 18% 19% 13% 3	236
	21st to end	Day	40% 10% 17% 20% 11% 2	473
February	1st to 10th	Day	47% 10% 18% 15% 8% 1	430
	11th to 20th	Day	47% 12% 20% 14% 6%	411
	21st to end	Day	44% 15% 20% 15% 5% 1	344
March	1st to 10th	Day	42% 12% 21% 19% 5%	500
	11th to 20th	Day	39% 13% 20% 18% 7% 2	500
	21st to end	Day	45% 15% 21% 14% 5% 1	550
April	1st to 10th	Day	38% 16% 21% 18% 7% 1	500
	11th to 20th	Day	35% 18% 22% 15% 7% 2	492
	21st to end	Day	33% 19% 24% 16% 7% 1	500
May	1st to 10th	Day	26% 18% 26% 22% 7% 2	503
	11th to 20th	Day	33% 13% 25% 19% 6% 3	528
	21st to end	Day	29% 10% 26% 23% 9% 3	573
June	1st to 10th	Day	29% 10% 28% 19% 11% 3	530
	11th to 20th	Day	24% 15% 33% 21% 6% 1	702
	21st to end	Day	17% 8% 32% 31% 10% 2	730
July	1st to 10th	Day	12% 6% 33% 37% 10% 2	721
	11th to 20th	Day	10% 8% 31% 35% 13% 4	543
	21st to end	Day	5% 7% 25% 42% 15% 5%	575
August	1st to 10th	Day	12% 4 24% 38% 16% 6%	527
	11th to 20th	Day	7% 5% 24% 37% 20% 7%	517
	21st to end	Day	12% 9% 29% 32% 14% 4	583
September	1st to 10th	Day	15% 8% 27% 29% 16% 5%	530
	11th to 20th	Day	19% 8% 24% 31% 13% 4	530
	21st to end	Day	22% 9% 23% 27% 17% 2	530
October	1st to 10th	Day	25% 12% 21% 23% 17% 3	530
	11th to 20th	Day	32% 10% 19% 21% 14% 5%	530
	21st to end	Day	37% 11% 22% 17% 10% 3	583
November	1st to 10th	Day	41% 12% 24% 10% 12% 1	250
	11th to 20th	Day	44% 12% 18% 14% 9% 3	220
	21st to end	Day	40% 11% 15% 17% 14% 4	220
December	1st to 10th	Day	43% 8% 20% 12% 11% 6%	220
	11th to 20th	Day	51% 13% 15% 13% 8%	220
	21st to end	Day	47% 12% 19% 14% 7% 2	242
January	1st to 10th	Night	50% 12% 13% 15% 9% 2	840
	11th to 20th	Night	42% 9% 14% 19% 13% 3	840
	21st to end	Night	40% 7% 15% 24% 13% 2	924
February	1st to 10th	Night	41% 8% 17% 22% 11% 1	840
	11th to 20th	Night	41% 9% 16% 22% 12% 1	804
	21st to end	Night	43% 9% 16% 23% 9%	660
March	1st to 10th	Night	42% 8% 16% 20% 12% 2	800
	11th to 20th	Night	42% 9% 14% 23% 11% 2	800
	21st to end	Night	47% 8% 13% 18% 11% 2	880
April	1st to 10th	Night	41% 8% 14% 23% 12% 2	800
	11th to 20th	Night	33% 10% 19% 24% 13% 2	722
	21st to end	Night	36% 9% 14% 27% 14% 2	600
May	1st to 10th	Night	28% 8% 17% 26% 18% 2	511
	11th to 20th	Night	31% 5% 14% 22% 25% 2	394
	21st to end	Night	29% 8% 15% 23% 21% 3	433
June	1st to 10th	Night	27% 4 16% 29% 22% 2	400
	11th to 20th	Night	25% 7% 16% 33% 17% 3	400
	21st to end	Night	18% 4 16% 32% 29% 2	400
July	1st to 10th	Night	13% 4 14% 32% 33% 4	390
	11th to 20th	Night	12% 2 17% 38% 28% 4	388
	21st to end	Night	9% 3 13% 34% 34% 7%	493
August	1st to 10th	Night	15% 3 9% 29% 36% 8%	597
	11th to 20th	Night	15% 5% 8% 23% 42% 7%	594
	21st to end	Night	16% 4 13% 32% 30% 6%	745
September	1st to 10th	Night	14% 5% 14% 31% 31% 5%	800
	11th to 20th	Night	18% 4 14% 25% 28% 11%	800
	21st to end	Night	21% 3 14% 30% 26% 5%	800
October	1st to 10th	Night	25% 5% 15% 26% 25% 5%	800
	11th to 20th	Night	27% 6% 13% 27% 20% 6%	800
	21st to end	Night	34% 8% 16% 23% 16% 4	880
November	1st to 10th	Night	42% 9% 15% 21% 12% 1	820
	11th to 20th	Night	44% 10% 13% 21% 10% 1	840
	21st to end	Night	37% 7% 16% 26% 12% 3	840
December	1st to 10th	Night	37% 7% 18% 24% 13% 2	840
	11th to 20th	Night	50% 9% 14% 18% 8% 1	840
	21st to end	Night	52% 11% 14% 15% 7% 1	924

Page generated at 2026-02-12 22:42:17. Version ac07

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