Oak Point
Clear Sky Chart
History

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

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	10% 8% 3 8% 5% 5% 5% 4 6% 8% 38%	141870
	Night	8% 10% 4 10% 6% 5% 5% 4 6% 7% 34%	138995
Transparency	Day	29% 36% 11% 17% 6% 1	141569
	Night	32% 36% 9% 16% 7% 1	138881
Seeing	Day	14% 9% 30% 28% 14% 4	18498
	Night	14% 7% 31% 33% 13% 2	28480

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	5% 13% 6% 13% 7% 8% 8% 5% 7% 8% 19%	4125
	11th to 20th	Day	5% 10% 4 13% 10% 8% 9% 8% 10% 8% 14%	4156
	21st to end	Day	4 12% 5% 10% 6% 6% 9% 5% 9% 10% 24%	5188
February	1st to 10th	Day	8% 11% 5% 12% 8% 8% 8% 5% 7% 4 23%	1732
	11th to 20th	Day	6% 10% 3 10% 7% 7% 8% 6% 9% 8% 28%	1844
	21st to end	Day	6% 11% 4 10% 7% 6% 8% 5% 7% 8% 28%	1671
March	1st to 10th	Day	8% 10% 3 9% 6% 5% 6% 4 7% 9% 32%	4634
	11th to 20th	Day	7% 9% 5% 11% 7% 6% 6% 5% 7% 8% 30%	5088
	21st to end	Day	9% 8% 4 11% 5% 5% 5% 4 6% 7% 36%	5585
April	1st to 10th	Day	10% 9% 3 8% 5% 4 4 4 6% 9% 37%	2586
	11th to 20th	Day	12% 10% 3 7% 4 5% 5% 4 6% 7% 36%	2702
	21st to end	Day	11% 8% 3 8% 4 4 5% 4 6% 7% 40%	2730
May	1st to 10th	Day	9% 6% 2 6% 4 4 4 4 5% 7% 50%	7905
	11th to 20th	Day	17% 9% 3 8% 5% 5% 5% 4 6% 6% 33%	8786
	21st to end	Day	12% 5% 2 6% 4 4 4 3 5% 7% 49%	9683
June	1st to 10th	Day	13% 7% 3 6% 5% 4 4 4 6% 8% 39%	3150
	11th to 20th	Day	13% 6% 3 6% 5% 4 4 5% 5% 8% 39%	3076
	21st to end	Day	11% 6% 2 5% 5% 4 5% 5% 7% 9% 40%	3000
July	1st to 10th	Day	7% 4 2 5% 4 4 4 4 7% 9% 49%	6800
	11th to 20th	Day	9% 5% 2 5% 4 4 5% 4 6% 9% 48%	6800
	21st to end	Day	6% 4 2 6% 4 4 4 4 7% 10% 50%	7276
August	1st to 10th	Day	7% 4 2 5% 4 5% 5% 4 7% 10% 47%	4499
	11th to 20th	Day	10% 5% 2 6% 4 4 4 4 5% 8% 47%	4171
	21st to end	Day	11% 6% 2 6% 4 3 4 3 5% 8% 48%	4675
September	1st to 10th	Day	10% 5% 2 6% 4 4 4 3 6% 8% 49%	2482
	11th to 20th	Day	15% 7% 2 7% 4 5% 3 4 5% 8% 39%	2200
	21st to end	Day	12% 7% 2 7% 4 3 5% 4 6% 8% 42%	2200
October	1st to 10th	Day	13% 8% 3 6% 4 4 4 3 4 6% 44%	3364
	11th to 20th	Day	11% 10% 4 8% 5% 5% 5% 3 6% 8% 35%	3087
	21st to end	Day	14% 14% 4 8% 4 3 4 4 6% 7% 32%	3190
November	1st to 10th	Day	17% 16% 5% 11% 5% 5% 4 4 5% 6% 24%	1694
	11th to 20th	Day	9% 14% 5% 15% 7% 7% 4 3 6% 7% 24%	1677
	21st to end	Day	10% 15% 5% 13% 7% 6% 4 4 4 6% 25%	1470
December	1st to 10th	Day	10% 14% 5% 13% 9% 11% 7% 5% 6% 5% 15%	2360
	11th to 20th	Day	9% 12% 4 10% 6% 5% 6% 6% 9% 10% 22%	2709
	21st to end	Day	5% 11% 5% 16% 8% 6% 5% 3 5% 6% 29%	3575
January	1st to 10th	Night	5% 14% 6% 15% 7% 6% 6% 4 5% 7% 24%	8799
	11th to 20th	Night	4 13% 6% 14% 8% 9% 9% 7% 7% 6% 17%	8768
	21st to end	Night	5% 12% 6% 12% 6% 6% 8% 6% 8% 9% 23%	9026
February	1st to 10th	Night	7% 12% 5% 11% 6% 6% 7% 5% 6% 7% 27%	2887
	11th to 20th	Night	6% 9% 3 8% 6% 6% 6% 6% 8% 7% 36%	2663
	21st to end	Night	6% 10% 4 11% 7% 6% 5% 5% 6% 7% 34%	2155
March	1st to 10th	Night	9% 11% 4 10% 5% 6% 6% 4 6% 7% 33%	5458
	11th to 20th	Night	5% 9% 4 8% 5% 5% 5% 5% 6% 7% 41%	5090
	21st to end	Night	10% 10% 4 11% 5% 5% 4 4 5% 6% 35%	5588
April	1st to 10th	Night	9% 7% 2 7% 5% 4 5% 5% 7% 8% 41%	2029
	11th to 20th	Night	14% 9% 3 9% 6% 4 5% 4 5% 7% 35%	1869
	21st to end	Night	12% 9% 4 7% 6% 5% 4 3 6% 6% 39%	1890
May	1st to 10th	Night	11% 8% 2 7% 4 5% 4 4 6% 8% 41%	5041
	11th to 20th	Night	16% 6% 2 7% 5% 5% 5% 4 6% 7% 36%	4107
	21st to end	Night	11% 6% 2 6% 4 4 4 3 5% 7% 48%	4523
June	1st to 10th	Night	11% 7% 3 7% 4 4 4 4 5% 8% 41%	1470
	11th to 20th	Night	16% 6% 2 6% 4 4 4 4 5% 9% 40%	1435
	21st to end	Night	10% 5% 2 7% 5% 6% 5% 4 7% 9% 41%	1400
July	1st to 10th	Night	6% 3 1 4 3 4 4 4 6% 9% 55%	3180
	11th to 20th	Night	8% 4 2 6% 4 4 4 4 7% 10% 48%	3180
	21st to end	Night	6% 4 2 5% 4 4 5% 5% 8% 9% 49%	3573
August	1st to 10th	Night	8% 5% 2 7% 4 4 5% 4 7% 9% 46%	2659
	11th to 20th	Night	8% 4 1 5% 3 4 4 5% 7% 9% 49%	2888
	21st to end	Night	10% 5% 2 5% 4 3 4 3 5% 9% 49%	3234
September	1st to 10th	Night	8% 5% 2 4 4 4 4 4 6% 9% 49%	1914
	11th to 20th	Night	12% 7% 3 6% 5% 5% 4 3 6% 8% 42%	2200
	21st to end	Night	13% 8% 2 8% 4 4 4 4 5% 7% 43%	2200
October	1st to 10th	Night	15% 9% 2 5% 3 3 4 3 5% 7% 45%	3782
	11th to 20th	Night	9% 10% 3 7% 5% 5% 4 4 5% 8% 39%	4053
	21st to end	Night	9% 12% 4 9% 5% 4 5% 4 5% 7% 37%	4610
November	1st to 10th	Night	13% 14% 4 13% 5% 5% 4 3 5% 6% 26%	2821
	11th to 20th	Night	11% 16% 6% 14% 7% 6% 4 4 5% 5% 23%	2940
	21st to end	Night	10% 14% 5% 15% 8% 6% 5% 4 5% 6% 23%	3150
December	1st to 10th	Night	7% 17% 6% 14% 9% 7% 5% 4 5% 6% 19%	5050
	11th to 20th	Night	7% 13% 5% 12% 6% 5% 6% 7% 7% 6% 26%	5718
	21st to end	Night	6% 10% 5% 13% 8% 7% 6% 4 5% 6% 30%	7645

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	50% 21% 9% 14% 6%	4125
	11th to 20th	Day	51% 21% 7% 14% 6%	4177
	21st to end	Day	40% 23% 9% 22% 5%	5188
February	1st to 10th	Day	27% 61% 4 5% 2	1732
	11th to 20th	Day	23% 59% 6% 10% 2	1853
	21st to end	Day	19% 60% 5% 8% 7%	1671
March	1st to 10th	Day	33% 29% 15% 13% 8% 1	4634
	11th to 20th	Day	39% 31% 10% 14% 5%	5090
	21st to end	Day	35% 29% 10% 17% 9%	5585
April	1st to 10th	Day	18% 60% 6% 11% 5%	2586
	11th to 20th	Day	20% 60% 5% 9% 6% 1	2702
	21st to end	Day	16% 59% 8% 13% 3 1	2730
May	1st to 10th	Day	27% 24% 8% 28% 13%	7905
	11th to 20th	Day	44% 24% 8% 18% 6% 1	8790
	21st to end	Day	26% 23% 8% 20% 19% 4	9683
June	1st to 10th	Day	17% 60% 6% 12% 4	3150
	11th to 20th	Day	18% 61% 6% 10% 5%	3076
	21st to end	Day	16% 62% 9% 10% 3	3000
July	1st to 10th	Day	24% 28% 23% 21% 4	6726
	11th to 20th	Day	26% 27% 17% 28% 2	6719
	21st to end	Day	22% 26% 20% 27% 4	7071
August	1st to 10th	Day	20% 37% 14% 23% 5%	4483
	11th to 20th	Day	23% 37% 17% 20% 2	4210
	21st to end	Day	23% 36% 19% 19% 3	4674
September	1st to 10th	Day	14% 58% 10% 15% 3 1	2482
	11th to 20th	Day	21% 59% 8% 10% 2	2200
	21st to end	Day	18% 58% 8% 12% 4	2200
October	1st to 10th	Day	27% 36% 8% 24% 5%	3364
	11th to 20th	Day	25% 37% 9% 20% 8%	3087
	21st to end	Day	33% 36% 12% 15% 4	3190
November	1st to 10th	Day	30% 54% 7% 7% 2	1694
	11th to 20th	Day	25% 56% 9% 8% 2	1677
	21st to end	Day	29% 56% 6% 7% 2	1470
December	1st to 10th	Day	48% 38% 7% 5% 2	2360
	11th to 20th	Day	36% 31% 13% 12% 7%	2710
	21st to end	Day	40% 27% 8% 18% 8%	3575
January	1st to 10th	Night	49% 22% 8% 15% 6%	8800
	11th to 20th	Night	55% 22% 7% 12% 4	8809
	21st to end	Night	43% 24% 9% 19% 5%	9026
February	1st to 10th	Night	24% 60% 7% 7% 2	2887
	11th to 20th	Night	18% 59% 7% 13% 3	2664
	21st to end	Night	20% 60% 4 11% 5%	2155
March	1st to 10th	Night	36% 31% 9% 14% 8% 3	5458
	11th to 20th	Night	30% 30% 10% 19% 11%	5090
	21st to end	Night	35% 30% 4 20% 10%	5588
April	1st to 10th	Night	16% 59% 6% 10% 7% 1	2029
	11th to 20th	Night	20% 59% 4 10% 6% 2	1869
	21st to end	Night	17% 59% 4 11% 6% 2	1890
May	1st to 10th	Night	31% 25% 9% 21% 14% 1	5041
	11th to 20th	Night	37% 24% 10% 20% 7% 1	4107
	21st to end	Night	27% 23% 6% 18% 21% 4	4526
June	1st to 10th	Night	17% 60% 6% 11% 5%	1470
	11th to 20th	Night	17% 60% 5% 11% 7%	1435
	21st to end	Night	16% 62% 6% 13% 3	1400
July	1st to 10th	Night	21% 28% 20% 26% 5%	3145
	11th to 20th	Night	25% 26% 14% 31% 3	3138
	21st to end	Night	22% 27% 20% 24% 6% 1	3473
August	1st to 10th	Night	19% 37% 11% 23% 10%	2651
	11th to 20th	Night	17% 37% 19% 21% 5%	2915
	21st to end	Night	24% 36% 14% 22% 4	3234
September	1st to 10th	Night	14% 58% 7% 16% 4 1	1914
	11th to 20th	Night	18% 58% 10% 10% 3	2200
	21st to end	Night	18% 57% 6% 12% 6% 1	2200
October	1st to 10th	Night	24% 37% 5% 23% 10%	3782
	11th to 20th	Night	23% 36% 9% 20% 10% 1	4053
	21st to end	Night	28% 36% 10% 22% 3	4610
November	1st to 10th	Night	29% 54% 9% 5% 2 1	2821
	11th to 20th	Night	27% 56% 8% 6% 3	2940
	21st to end	Night	29% 55% 5% 8% 3	3150
December	1st to 10th	Night	47% 36% 8% 6% 3	5050
	11th to 20th	Night	36% 32% 9% 10% 12%	5716
	21st to end	Night	39% 27% 8% 16% 9% 1	7645

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	10% 7% 35% 33% 11% 5%	330
	11th to 20th	Day	11% 9% 36% 31% 12% 1	330
	21st to end	Day	14% 8% 33% 28% 14% 3	363
February	1st to 10th	Day	14% 9% 34% 33% 8% 2	330
	11th to 20th	Day	9% 12% 32% 26% 15% 5%	330
	21st to end	Day	7% 11% 36% 27% 17% 1	273
March	1st to 10th	Day	14% 9% 33% 30% 14%	330
	11th to 20th	Day	12% 14% 35% 24% 15% 2	330
	21st to end	Day	13% 9% 32% 32% 9% 4	363
April	1st to 10th	Day	15% 10% 28% 33% 11% 3	606
	11th to 20th	Day	16% 12% 30% 30% 11% 1	740
	21st to end	Day	15% 10% 35% 25% 14% 2	750
May	1st to 10th	Day	16% 10% 29% 29% 14% 2	753
	11th to 20th	Day	20% 9% 30% 23% 14% 3	775
	21st to end	Day	20% 9% 24% 25% 19% 4	844
June	1st to 10th	Day	15% 12% 31% 24% 13% 6%	780
	11th to 20th	Day	15% 11% 32% 28% 12% 3	756
	21st to end	Day	13% 8% 26% 31% 18% 4	730
July	1st to 10th	Day	8% 6% 27% 31% 20% 8%	721
	11th to 20th	Day	11% 7% 29% 30% 17% 6%	718
	21st to end	Day	7% 5% 28% 30% 22% 8%	794
August	1st to 10th	Day	7% 5% 29% 29% 21% 8%	726
	11th to 20th	Day	12% 7% 22% 29% 22% 8%	715
	21st to end	Day	14% 8% 24% 31% 19% 4	803
September	1st to 10th	Day	11% 9% 33% 31% 13% 3	612
	11th to 20th	Day	17% 9% 35% 28% 8% 3	330
	21st to end	Day	18% 8% 33% 29% 12% 1	330
October	1st to 10th	Day	22% 11% 27% 28% 10% 2	330
	11th to 20th	Day	15% 11% 36% 30% 8% 1	330
	21st to end	Day	21% 10% 31% 26% 10% 2	363
November	1st to 10th	Day	25% 12% 26% 27% 10% 1	330
	11th to 20th	Day	15% 12% 36% 25% 11% 2	330
	21st to end	Day	16% 12% 36% 28% 7%	330
December	1st to 10th	Day	15% 10% 34% 25% 13% 3	330
	11th to 20th	Day	17% 12% 38% 24% 8% 2	330
	21st to end	Day	12% 9% 33% 28% 14% 4	363
January	1st to 10th	Night	12% 6% 37% 31% 12% 2	1050
	11th to 20th	Night	14% 8% 34% 33% 10% 1	1050
	21st to end	Night	13% 9% 33% 33% 11% 1	1155
February	1st to 10th	Night	14% 6% 31% 35% 13% 1	1050
	11th to 20th	Night	10% 6% 30% 36% 15% 2	1029
	21st to end	Night	11% 7% 34% 33% 13% 1	771
March	1st to 10th	Night	15% 7% 31% 30% 14% 2	830
	11th to 20th	Night	10% 8% 38% 32% 11% 1	630
	21st to end	Night	17% 7% 30% 30% 14% 3	693
April	1st to 10th	Night	12% 7% 31% 37% 12% 2	630
	11th to 20th	Night	17% 8% 27% 36% 11% 1	623
	21st to end	Night	17% 6% 30% 35% 11% 1	630
May	1st to 10th	Night	19% 6% 28% 37% 9% 1	630
	11th to 20th	Night	17% 8% 29% 29% 15% 1	621
	21st to end	Night	17% 7% 26% 36% 13% 1	683
June	1st to 10th	Night	15% 6% 31% 30% 16% 1	630
	11th to 20th	Night	17% 7% 27% 35% 14% 1	615
	21st to end	Night	10% 6% 22% 42% 19% 1	600
July	1st to 10th	Night	7% 5% 23% 41% 23% 2	585
	11th to 20th	Night	10% 3 24% 43% 19% 2	582
	21st to end	Night	8% 3 20% 40% 24% 4	657
August	1st to 10th	Night	8% 5% 21% 44% 21% 2	597
	11th to 20th	Night	8% 4 22% 39% 22% 5%	594
	21st to end	Night	13% 5% 23% 37% 22% 1	660
September	1st to 10th	Night	10% 5% 30% 35% 18% 2	600
	11th to 20th	Night	15% 5% 29% 38% 12% 1	600
	21st to end	Night	14% 7% 32% 33% 14% 1	600
October	1st to 10th	Night	20% 8% 33% 30% 9% 1	714
	11th to 20th	Night	20% 7% 33% 28% 11% 1	891
	21st to end	Night	21% 9% 32% 28% 9% 1	1100
November	1st to 10th	Night	18% 12% 32% 26% 10% 2	1025
	11th to 20th	Night	17% 10% 37% 25% 8% 3	1050
	21st to end	Night	16% 10% 39% 27% 7% 1	1050
December	1st to 10th	Night	11% 8% 31% 35% 13% 2	1050
	11th to 20th	Night	15% 9% 37% 31% 7% 2	1050
	21st to end	Night	17% 7% 31% 30% 13% 2	1155

Page generated at 2026-06-13 01:31:41. Version ac07

Copyright © 2026 Attilla Danko.