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 2024-11-30.

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	24% 11% 3 7% 4 4 4 3 4 6% 30%	106357
	Night	28% 13% 3 7% 4 4 3 3 4 5% 27%	101921
Transparency	Day	54% 7% 11% 14% 10% 3	106097
	Night	59% 7% 10% 13% 9% 3	101771
Seeing	Day	29% 11% 24% 23% 11% 3	15317
	Night	33% 7% 14% 24% 18% 3	23688

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	42% 19% 4 8% 4 3 3 2 2 3 10%	2539
	11th to 20th	Day	42% 11% 3 5% 4 3 3 2 3 3 20%	2554
	21st to end	Day	46% 13% 3 6% 4 3 3 2 2 3 14%	3146
February	1st to 10th	Day	39% 13% 3 6% 4 3 3 3 4 5% 18%	1710
	11th to 20th	Day	36% 14% 4 7% 5% 4 3 2 3 4 18%	1665
	21st to end	Day	34% 16% 4 7% 4 4 3 3 4 4 17%	1437
March	1st to 10th	Day	23% 19% 3 8% 6% 5% 5% 4 4 6% 17%	3399
	11th to 20th	Day	27% 13% 3 6% 4 3 3 2 3 5% 31%	3490
	21st to end	Day	32% 17% 4 9% 6% 4 4 3 3 5% 13%	3825
April	1st to 10th	Day	33% 14% 4 9% 5% 3 3 4 5% 6% 13%	2280
	11th to 20th	Day	30% 13% 4 8% 6% 3 4 3 4 5% 21%	2312
	21st to end	Day	30% 11% 3 7% 6% 4 4 3 5% 6% 20%	2470
May	1st to 10th	Day	24% 11% 3 7% 4 3 3 3 4 5% 31%	4251
	11th to 20th	Day	15% 11% 3 7% 4 4 4 4 7% 9% 32%	4377
	21st to end	Day	29% 10% 4 7% 5% 5% 4 4 5% 6% 20%	4813
June	1st to 10th	Day	28% 10% 3 7% 5% 4 4 3 5% 6% 26%	2660
	11th to 20th	Day	25% 12% 3 7% 5% 5% 4 4 5% 7% 22%	2823
	21st to end	Day	17% 9% 3 7% 4 4 4 3 5% 7% 38%	2850
July	1st to 10th	Day	7% 6% 2 5% 3 2 3 3 5% 7% 58%	4740
	11th to 20th	Day	8% 7% 3 5% 3 3 3 2 4 7% 55%	4452
	21st to end	Day	10% 8% 3 6% 4 3 3 3 6% 8% 47%	4702
August	1st to 10th	Day	7% 9% 3 7% 4 4 3 4 5% 9% 45%	4091
	11th to 20th	Day	12% 7% 2 7% 5% 5% 4 4 7% 8% 39%	4026
	21st to end	Day	11% 7% 3 5% 4 3 4 3 6% 9% 45%	4380
September	1st to 10th	Day	11% 7% 2 6% 3 3 4 4 4 7% 51%	2280
	11th to 20th	Day	16% 8% 3 6% 4 4 5% 3 5% 8% 37%	2209
	21st to end	Day	21% 6% 2 6% 4 3 3 2 4 6% 42%	2043
October	1st to 10th	Day	20% 6% 2 4 3 3 3 2 5% 6% 46%	3180
	11th to 20th	Day	30% 9% 3 8% 4 4 4 3 5% 6% 25%	3161
	21st to end	Day	33% 7% 2 6% 4 4 4 4 5% 7% 24%	3448
November	1st to 10th	Day	35% 12% 3 8% 5% 4 4 3 4 5% 16%	1607
	11th to 20th	Day	39% 10% 3 6% 4 4 3 3 4 5% 19%	1600
	21st to end	Day	33% 11% 3 8% 4 4 4 2 3 4 23%	1595
December	1st to 10th	Day	31% 11% 4 7% 4 4 3 3 3 4 26%	1520
	11th to 20th	Day	37% 11% 3 7% 5% 4 4 3 3 5% 18%	1928
	21st to end	Day	40% 16% 4 8% 4 3 3 2 3 3 14%	2794
January	1st to 10th	Night	40% 18% 4 8% 5% 4 3 2 3 3 10%	4406
	11th to 20th	Night	39% 15% 3 7% 3 3 3 2 3 4 19%	4390
	21st to end	Night	49% 12% 3 6% 3 3 3 2 2 3 14%	4521
February	1st to 10th	Night	35% 15% 3 7% 5% 4 3 3 3 5% 16%	2470
	11th to 20th	Night	32% 15% 3 8% 3 4 3 2 3 4 22%	2402
	21st to end	Night	34% 15% 2 8% 5% 4 4 2 3 4 19%	2017
March	1st to 10th	Night	26% 19% 4 6% 4 4 5% 3 4 5% 19%	3473
	11th to 20th	Night	24% 16% 4 6% 3 3 2 2 3 3 34%	3490
	21st to end	Night	34% 22% 3 7% 4 4 3 3 3 3 14%	3828
April	1st to 10th	Night	33% 15% 3 7% 5% 4 4 3 4 4 18%	1900
	11th to 20th	Night	27% 15% 4 6% 4 4 3 4 4 5% 23%	1814
	21st to end	Night	30% 12% 3 8% 5% 5% 3 4 5% 5% 21%	1710
May	1st to 10th	Night	29% 12% 2 6% 4 3 3 2 3 4 32%	2711
	11th to 20th	Night	17% 17% 4 8% 5% 3 4 3 5% 6% 28%	2516
	21st to end	Night	27% 14% 4 7% 4 5% 4 4 5% 6% 20%	2762
June	1st to 10th	Night	25% 10% 3 8% 6% 4 4 3 4 5% 28%	1520
	11th to 20th	Night	23% 12% 4 8% 5% 4 4 4 5% 6% 24%	1350
	21st to end	Night	16% 11% 2 6% 4 4 3 3 4 6% 39%	1330
July	1st to 10th	Night	7% 13% 3 5% 3 3 3 2 4 6% 53%	2220
	11th to 20th	Night	8% 12% 3 5% 4 3 4 3 4 6% 49%	2503
	21st to end	Night	12% 13% 3 6% 3 3 3 2 4 5% 45%	2849
August	1st to 10th	Night	7% 18% 5% 7% 5% 3 3 3 4 6% 38%	2848
	11th to 20th	Night	16% 13% 3 6% 3 3 3 3 4 6% 41%	2812
	21st to end	Night	17% 8% 2 5% 3 3 3 2 4 5% 46%	3292
September	1st to 10th	Night	13% 7% 3 5% 1 3 3 3 5% 5% 53%	1900
	11th to 20th	Night	17% 9% 3 8% 4 3 3 3 4 5% 40%	1966
	21st to end	Night	18% 7% 2 6% 4 3 3 3 4 6% 44%	2137
October	1st to 10th	Night	18% 5% 2 5% 3 3 3 2 4 7% 46%	3800
	11th to 20th	Night	28% 11% 3 7% 4 4 4 4 4 7% 25%	3777
	21st to end	Night	32% 9% 3 7% 4 4 4 3 4 5% 24%	4121
November	1st to 10th	Night	36% 10% 3 7% 5% 4 4 3 4 5% 18%	2688
	11th to 20th	Night	40% 10% 3 7% 5% 4 4 2 4 4 19%	2800
	21st to end	Night	30% 11% 3 7% 5% 3 4 3 4 4 26%	2800
December	1st to 10th	Night	30% 11% 3 7% 5% 4 4 3 4 5% 25%	2660
	11th to 20th	Night	36% 11% 3 7% 5% 4 4 3 4 6% 18%	3276
	21st to end	Night	38% 16% 4 8% 5% 4 4 2 3 3 14%	4862

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	82% 4 6% 4 2 1	2539
	11th to 20th	Day	71% 3 6% 12% 4 4	2554
	21st to end	Day	78% 5% 4 7% 5% 1	3146
February	1st to 10th	Day	71% 5% 10% 8% 5%	1710
	11th to 20th	Day	74% 5% 5% 10% 5% 2	1674
	21st to end	Day	72% 6% 7% 8% 5% 1	1437
March	1st to 10th	Day	67% 9% 12% 9% 3	3399
	11th to 20th	Day	55% 8% 7% 18% 10% 1	3490
	21st to end	Day	74% 8% 9% 6% 2	3825
April	1st to 10th	Day	72% 7% 10% 9% 2	2280
	11th to 20th	Day	67% 7% 8% 10% 6% 2	2315
	21st to end	Day	66% 7% 11% 11% 5% 1	2470
May	1st to 10th	Day	53% 8% 15% 11% 12%	4251
	11th to 20th	Day	44% 12% 20% 17% 8% 1	4380
	21st to end	Day	62% 13% 16% 9%	4814
June	1st to 10th	Day	60% 8% 14% 13% 6%	2660
	11th to 20th	Day	61% 9% 14% 11% 4	2823
	21st to end	Day	44% 8% 18% 19% 8% 3	2850
July	1st to 10th	Day	26% 6% 10% 15% 18% 25%	4666
	11th to 20th	Day	27% 6% 9% 20% 33% 5%	4376
	21st to end	Day	31% 7% 12% 28% 20% 2	4553
August	1st to 10th	Day	31% 8% 12% 22% 23% 4	4076
	11th to 20th	Day	40% 10% 18% 21% 9% 3	4065
	21st to end	Day	35% 6% 17% 21% 16% 5%	4379
September	1st to 10th	Day	32% 7% 12% 24% 15% 10%	2280
	11th to 20th	Day	45% 8% 14% 17% 12% 5%	2209
	21st to end	Day	44% 7% 13% 18% 15% 4	2043
October	1st to 10th	Day	39% 4 7% 28% 20% 2	3180
	11th to 20th	Day	60% 6% 13% 13% 9% 1	3161
	21st to end	Day	60% 5% 10% 15% 9% 1	3448
November	1st to 10th	Day	72% 6% 8% 11% 4	1607
	11th to 20th	Day	70% 5% 8% 7% 7% 3	1600
	21st to end	Day	68% 4 5% 9% 11% 3	1595
December	1st to 10th	Day	63% 6% 8% 9% 12% 3	1520
	11th to 20th	Day	70% 5% 11% 9% 5%	1928
	21st to end	Day	75% 6% 8% 7% 3 1	2794
January	1st to 10th	Night	81% 5% 5% 5% 2 2	4406
	11th to 20th	Night	72% 4 6% 11% 4 3	4390
	21st to end	Night	78% 3 5% 6% 6% 2	4521
February	1st to 10th	Night	73% 6% 6% 9% 3 2	2470
	11th to 20th	Night	68% 5% 8% 10% 6% 2	2404
	21st to end	Night	70% 5% 9% 9% 6% 2	2017
March	1st to 10th	Night	67% 7% 9% 14% 3	3473
	11th to 20th	Night	53% 8% 10% 16% 11% 1	3490
	21st to end	Night	75% 7% 8% 8% 2	3828
April	1st to 10th	Night	70% 5% 11% 9% 4	1900
	11th to 20th	Night	62% 7% 10% 12% 5% 3	1814
	21st to end	Night	64% 8% 9% 12% 5% 2	1710
May	1st to 10th	Night	54% 8% 12% 17% 9% 1	2711
	11th to 20th	Night	44% 18% 16% 11% 9% 1	2516
	21st to end	Night	62% 12% 17% 7% 2	2762
June	1st to 10th	Night	57% 8% 13% 16% 5%	1520
	11th to 20th	Night	57% 9% 15% 16% 2	1350
	21st to end	Night	43% 8% 16% 23% 7% 3	1330
July	1st to 10th	Night	27% 9% 11% 10% 17% 25%	2185
	11th to 20th	Night	32% 8% 11% 17% 23% 10%	2457
	21st to end	Night	36% 6% 12% 23% 18% 5%	2760
August	1st to 10th	Night	41% 9% 13% 18% 15% 4	2839
	11th to 20th	Night	44% 6% 16% 21% 9% 4	2839
	21st to end	Night	39% 6% 15% 18% 20% 3	3292
September	1st to 10th	Night	31% 7% 11% 24% 16% 10%	1900
	11th to 20th	Night	45% 6% 12% 16% 14% 6%	1966
	21st to end	Night	41% 6% 13% 17% 16% 7%	2137
October	1st to 10th	Night	37% 6% 8% 29% 18% 2	3800
	11th to 20th	Night	57% 7% 12% 13% 10% 2	3777
	21st to end	Night	62% 5% 7% 14% 9% 2	4121
November	1st to 10th	Night	68% 5% 8% 11% 7% 1	2688
	11th to 20th	Night	71% 6% 7% 7% 6% 3	2800
	21st to end	Night	63% 5% 8% 9% 10% 6%	2800
December	1st to 10th	Night	63% 6% 8% 10% 10% 3	2660
	11th to 20th	Night	68% 7% 9% 8% 7% 1	3276
	21st to end	Night	75% 7% 7% 7% 3 1	4862

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	47% 17% 18% 12% 6% 1	180
	11th to 20th	Day	45% 8% 17% 15% 11% 3	194
	21st to end	Day	43% 10% 17% 18% 11% 2	407
February	1st to 10th	Day	48% 10% 16% 15% 9% 2	370
	11th to 20th	Day	47% 12% 20% 14% 6%	365
	21st to end	Day	44% 15% 20% 15% 4 1	319
March	1st to 10th	Day	43% 11% 20% 20% 5%	460
	11th to 20th	Day	38% 12% 20% 19% 8% 3	460
	21st to end	Day	44% 15% 21% 14% 5% 1	506
April	1st to 10th	Day	38% 16% 20% 18% 7% 1	460
	11th to 20th	Day	38% 17% 22% 14% 7% 2	452
	21st to end	Day	35% 19% 24% 15% 7%	460
May	1st to 10th	Day	26% 19% 26% 21% 6% 2	463
	11th to 20th	Day	32% 12% 26% 20% 7% 3	488
	21st to end	Day	29% 10% 25% 23% 9% 3	529
June	1st to 10th	Day	31% 9% 28% 19% 11% 2	490
	11th to 20th	Day	25% 16% 32% 21% 6% 1	653
	21st to end	Day	16% 8% 33% 31% 10% 2	680
July	1st to 10th	Day	12% 7% 32% 37% 10% 2	671
	11th to 20th	Day	11% 8% 31% 34% 12% 4	502
	21st to end	Day	5% 8% 25% 42% 15% 5%	531
August	1st to 10th	Day	12% 5% 23% 38% 16% 6%	487
	11th to 20th	Day	7% 5% 23% 38% 20% 7%	477
	21st to end	Day	12% 9% 29% 32% 13% 4	539
September	1st to 10th	Day	15% 8% 27% 30% 15% 5%	490
	11th to 20th	Day	20% 8% 24% 31% 13% 4	490
	21st to end	Day	22% 9% 23% 27% 17% 2	490
October	1st to 10th	Day	26% 11% 20% 22% 18% 3	490
	11th to 20th	Day	32% 9% 19% 21% 15% 5%	490
	21st to end	Day	36% 11% 22% 17% 10% 4	539
November	1st to 10th	Day	40% 13% 24% 9% 14% 1	228
	11th to 20th	Day	44% 11% 19% 15% 9% 3	200
	21st to end	Day	40% 12% 14% 16% 14% 4	199
December	1st to 10th	Day	43% 7% 22% 11% 12% 4	180
	11th to 20th	Day	48% 12% 16% 14% 9% 1	180
	21st to end	Day	47% 10% 20% 15% 7% 2	198
January	1st to 10th	Night	50% 11% 13% 14% 10% 2	760
	11th to 20th	Night	45% 10% 14% 16% 13% 3	760
	21st to end	Night	41% 8% 14% 23% 12% 2	836
February	1st to 10th	Night	42% 8% 16% 21% 12% 2	760
	11th to 20th	Night	40% 9% 15% 21% 13% 1	744
	21st to end	Night	43% 9% 15% 23% 10%	628
March	1st to 10th	Night	42% 8% 16% 20% 12% 2	760
	11th to 20th	Night	41% 9% 14% 23% 12% 2	760
	21st to end	Night	47% 8% 14% 18% 11% 2	836
April	1st to 10th	Night	41% 8% 14% 22% 13% 2	760
	11th to 20th	Night	34% 10% 19% 23% 13% 2	686
	21st to end	Night	35% 9% 14% 27% 14% 2	570
May	1st to 10th	Night	29% 8% 17% 25% 18% 2	486
	11th to 20th	Night	30% 6% 13% 22% 26% 2	374
	21st to end	Night	29% 8% 16% 24% 19% 4	411
June	1st to 10th	Night	27% 4 17% 29% 23% 1	380
	11th to 20th	Night	24% 8% 16% 32% 17% 3	380
	21st to end	Night	17% 4 16% 33% 28% 2	380
July	1st to 10th	Night	13% 4 14% 32% 33% 4	370
	11th to 20th	Night	13% 2 17% 38% 27% 4	368
	21st to end	Night	9% 3 13% 35% 34% 6%	468
August	1st to 10th	Night	14% 3 10% 28% 36% 8%	567
	11th to 20th	Night	15% 4 8% 23% 43% 8%	564
	21st to end	Night	16% 4 14% 32% 29% 6%	708
September	1st to 10th	Night	14% 5% 13% 32% 32% 5%	760
	11th to 20th	Night	19% 4 14% 24% 29% 11%	760
	21st to end	Night	21% 3 15% 30% 26% 5%	760
October	1st to 10th	Night	25% 5% 15% 25% 25% 5%	760
	11th to 20th	Night	28% 6% 12% 27% 21% 6%	760
	21st to end	Night	34% 7% 15% 23% 16% 4	836
November	1st to 10th	Night	41% 8% 15% 22% 12% 1	780
	11th to 20th	Night	44% 10% 13% 22% 10% 1	800
	21st to end	Night	36% 7% 16% 26% 13% 3	800
December	1st to 10th	Night	36% 7% 19% 23% 13% 2	760
	11th to 20th	Night	48% 9% 14% 20% 9% 1	760
	21st to end	Night	53% 11% 13% 16% 7% 1	836

Page generated at 2024-11-27 14:30:49. Version ac07

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