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 2025-02-21.

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% 37%	112090
	Night	9% 10% 4 10% 6% 5% 5% 4 6% 7% 34%	115219
Transparency	Day	26% 44% 10% 15% 4	111834
	Night	29% 42% 8% 14% 6%	115122
Seeing	Day	14% 9% 30% 29% 15% 4	16599
	Night	14% 7% 30% 33% 13% 2	26732

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% 7% 13% 7% 9% 7% 6% 7% 9% 17%	3179
	11th to 20th	Day	5% 11% 4 15% 10% 9% 7% 8% 10% 8% 14%	3182
	21st to end	Day	5% 14% 6% 12% 7% 6% 8% 5% 7% 7% 23%	4004
February	1st to 10th	Day	9% 10% 5% 12% 8% 8% 8% 6% 8% 5% 22%	1649
	11th to 20th	Day	6% 10% 3 10% 7% 7% 8% 6% 9% 8% 28%	1754
	21st to end	Day	7% 12% 4 9% 7% 5% 7% 5% 7% 8% 29%	1516
March	1st to 10th	Day	10% 11% 3 9% 7% 5% 6% 5% 6% 8% 30%	3151
	11th to 20th	Day	7% 9% 4 12% 8% 6% 6% 4 6% 9% 28%	3478
	21st to end	Day	6% 8% 4 12% 6% 5% 5% 4 6% 6% 37%	3814
April	1st to 10th	Day	9% 9% 3 8% 5% 4 4 4 6% 9% 38%	2340
	11th to 20th	Day	13% 10% 4 7% 4 6% 4 4 6% 7% 37%	2442
	21st to end	Day	11% 8% 3 8% 4 4 5% 4 6% 7% 39%	2470
May	1st to 10th	Day	15% 9% 2 6% 4 4 4 3 5% 6% 43%	4263
	11th to 20th	Day	18% 8% 3 7% 5% 4 5% 4 6% 6% 36%	4705
	21st to end	Day	18% 6% 2 6% 4 4 4 4 5% 7% 39%	5173
June	1st to 10th	Day	13% 7% 2 6% 5% 4 4 4 6% 8% 39%	2850
	11th to 20th	Day	13% 6% 3 6% 5% 5% 4 5% 5% 8% 40%	2850
	21st to end	Day	11% 6% 2 6% 5% 4 5% 5% 7% 9% 40%	2850
July	1st to 10th	Day	8% 4 2 5% 4 4 4 4 7% 9% 49%	4750
	11th to 20th	Day	8% 3 1 4 4 3 4 4 6% 9% 53%	4750
	21st to end	Day	5% 3 1 5% 4 4 4 4 7% 10% 53%	5068
August	1st to 10th	Day	7% 4 2 5% 4 5% 5% 4 7% 10% 48%	4361
	11th to 20th	Day	10% 5% 2 6% 4 4 4 4 5% 8% 47%	4041
	21st to end	Day	12% 6% 2 6% 4 3 4 3 5% 8% 48%	4532
September	1st to 10th	Day	10% 5% 2 6% 4 3 4 3 6% 8% 50%	2358
	11th to 20th	Day	14% 7% 2 7% 4 5% 3 4 5% 8% 40%	2090
	21st to end	Day	12% 7% 2 8% 4 3 5% 4 6% 8% 40%	2090
October	1st to 10th	Day	13% 8% 3 6% 4 4 4 3 5% 7% 44%	3261
	11th to 20th	Day	10% 10% 4 8% 5% 5% 4 3 6% 8% 36%	2992
	21st to end	Day	14% 14% 4 8% 4 3 4 4 6% 7% 32%	3091
November	1st to 10th	Day	17% 16% 5% 11% 5% 5% 4 4 5% 6% 24%	1612
	11th to 20th	Day	9% 14% 5% 15% 8% 8% 4 3 5% 7% 23%	1597
	21st to end	Day	11% 15% 6% 13% 8% 6% 5% 3 4 6% 25%	1400
December	1st to 10th	Day	10% 14% 5% 13% 9% 11% 7% 5% 6% 5% 15%	2290
	11th to 20th	Day	9% 12% 4 10% 6% 5% 5% 6% 10% 11% 23%	2639
	21st to end	Day	5% 11% 5% 16% 8% 7% 5% 4 5% 6% 29%	3498
January	1st to 10th	Night	4 12% 6% 15% 8% 7% 7% 4 6% 7% 23%	6787
	11th to 20th	Night	4 13% 6% 14% 9% 10% 9% 8% 7% 5% 16%	6732
	21st to end	Night	6% 15% 7% 15% 7% 6% 5% 4 6% 7% 21%	6974
February	1st to 10th	Night	8% 12% 5% 11% 6% 6% 7% 5% 6% 7% 27%	2750
	11th to 20th	Night	5% 8% 3 8% 6% 6% 6% 6% 8% 7% 36%	2533
	21st to end	Night	6% 10% 4 11% 7% 5% 4 4 6% 7% 36%	1957
March	1st to 10th	Night	11% 11% 3 10% 5% 6% 5% 4 7% 7% 31%	3712
	11th to 20th	Night	5% 8% 3 7% 5% 4 5% 5% 6% 8% 44%	3480
	21st to end	Night	8% 11% 4 10% 6% 5% 5% 4 6% 7% 34%	3817
April	1st to 10th	Night	9% 6% 2 7% 5% 4 5% 5% 7% 8% 42%	1835
	11th to 20th	Night	14% 9% 3 9% 6% 4 5% 4 4 7% 34%	1689
	21st to end	Night	12% 9% 4 7% 6% 5% 4 4 6% 6% 39%	1710
May	1st to 10th	Night	16% 10% 3 8% 3 4 4 4 6% 7% 35%	2705
	11th to 20th	Night	16% 5% 2 6% 4 4 5% 3 6% 7% 41%	2201
	21st to end	Night	16% 5% 2 6% 4 4 4 4 5% 6% 44%	2414
June	1st to 10th	Night	12% 7% 3 7% 4 4 4 5% 5% 8% 41%	1330
	11th to 20th	Night	16% 6% 2 6% 4 4 4 4 5% 9% 41%	1330
	21st to end	Night	10% 5% 2 7% 5% 5% 5% 5% 7% 9% 41%	1330
July	1st to 10th	Night	8% 3 1 4 3 4 4 5% 6% 9% 53%	2220
	11th to 20th	Night	7% 3 1 4 3 4 4 4 6% 10% 53%	2220
	21st to end	Night	5% 4 1 5% 3 4 5% 5% 8% 10% 52%	2493
August	1st to 10th	Night	8% 5% 2 7% 4 4 5% 4 7% 9% 46%	2577
	11th to 20th	Night	8% 4 2 5% 3 4 4 5% 7% 9% 49%	2798
	21st to end	Night	10% 5% 2 5% 4 3 4 3 5% 9% 49%	3135
September	1st to 10th	Night	9% 5% 2 4 4 4 4 4 6% 9% 50%	1818
	11th to 20th	Night	11% 7% 3 6% 4 5% 4 3 6% 8% 43%	2090
	21st to end	Night	13% 8% 2 8% 4 4 4 4 6% 7% 41%	2090
October	1st to 10th	Night	15% 9% 2 5% 3 3 3 3 5% 6% 45%	3666
	11th to 20th	Night	9% 10% 3 7% 5% 5% 4 4 5% 8% 40%	3928
	21st to end	Night	8% 12% 5% 9% 5% 4 5% 3 5% 6% 38%	4467
November	1st to 10th	Night	13% 15% 5% 13% 5% 5% 4 3 6% 6% 26%	2683
	11th to 20th	Night	11% 16% 6% 14% 7% 6% 4 4 5% 5% 22%	2800
	21st to end	Night	11% 14% 5% 15% 7% 5% 5% 4 5% 6% 23%	3000
December	1st to 10th	Night	7% 17% 6% 15% 10% 7% 5% 4 5% 6% 18%	4900
	11th to 20th	Night	7% 13% 6% 13% 6% 5% 6% 7% 7% 6% 26%	5568
	21st to end	Night	6% 10% 5% 13% 8% 7% 6% 4 5% 6% 30%	7480

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	47% 26% 8% 14% 5%	3179
	11th to 20th	Day	48% 27% 6% 13% 7%	3203
	21st to end	Day	44% 29% 11% 14% 2	4004
February	1st to 10th	Day	25% 64% 4 5% 2	1649
	11th to 20th	Day	21% 62% 6% 10% 2	1763
	21st to end	Day	16% 66% 4 8% 6%	1516
March	1st to 10th	Day	29% 42% 11% 15% 3	3151
	11th to 20th	Day	34% 44% 8% 11% 3	3480
	21st to end	Day	29% 41% 10% 13% 6%	3814
April	1st to 10th	Day	15% 66% 5% 10% 4	2340
	11th to 20th	Day	16% 66% 4 8% 5% 1	2442
	21st to end	Day	13% 65% 7% 11% 2 1	2470
May	1st to 10th	Day	26% 41% 7% 20% 6%	4263
	11th to 20th	Day	32% 41% 6% 13% 7% 1	4709
	21st to end	Day	28% 41% 9% 17% 6%	5173
June	1st to 10th	Day	14% 66% 6% 10% 3	2850
	11th to 20th	Day	16% 65% 5% 8% 6%	2850
	21st to end	Day	15% 65% 8% 9% 3	2850
July	1st to 10th	Day	22% 38% 21% 16% 3	4676
	11th to 20th	Day	16% 37% 16% 27% 3	4669
	21st to end	Day	15% 36% 18% 26% 5%	4908
August	1st to 10th	Day	20% 38% 14% 23% 5%	4345
	11th to 20th	Day	23% 38% 17% 20% 2	4080
	21st to end	Day	23% 37% 19% 18% 3	4531
September	1st to 10th	Day	13% 61% 10% 14% 2 1	2358
	11th to 20th	Day	18% 62% 7% 11% 2	2090
	21st to end	Day	18% 61% 8% 10% 3	2090
October	1st to 10th	Day	26% 37% 8% 24% 5%	3261
	11th to 20th	Day	24% 38% 9% 20% 8%	2992
	21st to end	Day	32% 37% 12% 15% 4	3091
November	1st to 10th	Day	28% 56% 7% 7% 1	1612
	11th to 20th	Day	24% 59% 8% 7% 1	1597
	21st to end	Day	28% 58% 6% 6% 2	1400
December	1st to 10th	Day	47% 39% 7% 5% 2	2290
	11th to 20th	Day	35% 32% 13% 13% 8%	2640
	21st to end	Day	39% 27% 8% 18% 8%	3498
January	1st to 10th	Night	45% 28% 7% 13% 7%	6787
	11th to 20th	Night	52% 27% 6% 12% 3	6773
	21st to end	Night	46% 30% 10% 12% 3	6974
February	1st to 10th	Night	22% 63% 6% 7% 3	2750
	11th to 20th	Night	17% 61% 7% 12% 2	2534
	21st to end	Night	16% 65% 4 10% 5%	1957
March	1st to 10th	Night	29% 43% 7% 16% 5%	3712
	11th to 20th	Night	21% 42% 11% 17% 8%	3480
	21st to end	Night	28% 43% 4 18% 6%	3817
April	1st to 10th	Night	13% 66% 6% 8% 7% 1	1835
	11th to 20th	Night	17% 65% 2 8% 5% 2	1689
	21st to end	Night	14% 65% 4 10% 5% 2	1710
May	1st to 10th	Night	28% 43% 8% 13% 8%	2705
	11th to 20th	Night	26% 41% 10% 16% 5% 2	2201
	21st to end	Night	23% 41% 9% 21% 6%	2414
June	1st to 10th	Night	14% 66% 5% 10% 5%	1330
	11th to 20th	Night	15% 64% 4 9% 7%	1330
	21st to end	Night	14% 65% 6% 12% 2	1330
July	1st to 10th	Night	20% 39% 18% 20% 3	2185
	11th to 20th	Night	16% 37% 14% 29% 4	2178
	21st to end	Night	15% 36% 17% 24% 6% 1	2414
August	1st to 10th	Night	19% 37% 11% 23% 9%	2569
	11th to 20th	Night	17% 39% 18% 21% 5%	2825
	21st to end	Night	24% 37% 13% 21% 4	3135
September	1st to 10th	Night	13% 61% 7% 14% 4 1	1818
	11th to 20th	Night	16% 61% 10% 11% 3	2090
	21st to end	Night	18% 60% 6% 11% 5% 1	2090
October	1st to 10th	Night	24% 38% 5% 23% 10%	3666
	11th to 20th	Night	22% 37% 9% 21% 10% 1	3928
	21st to end	Night	27% 38% 10% 23% 3	4467
November	1st to 10th	Night	28% 56% 9% 5% 1	2683
	11th to 20th	Night	26% 58% 8% 6% 2	2800
	21st to end	Night	28% 58% 4 7% 3	3000
December	1st to 10th	Night	48% 36% 8% 6% 2	4900
	11th to 20th	Night	36% 33% 9% 10% 12%	5566
	21st to end	Night	38% 28% 8% 17% 9% 1	7480

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% 34% 34% 11% 5%	300
	11th to 20th	Day	12% 8% 34% 32% 13% 1	300
	21st to end	Day	15% 8% 32% 27% 14% 3	330
February	1st to 10th	Day	14% 7% 35% 34% 8% 2	300
	11th to 20th	Day	9% 11% 34% 27% 13% 5%	300
	21st to end	Day	6% 10% 35% 28% 19% 2	225
March	1st to 10th	Day	13% 10% 29% 31% 16%	270
	11th to 20th	Day	10% 14% 34% 24% 16% 2	270
	21st to end	Day	13% 8% 29% 35% 10% 4	297
April	1st to 10th	Day	14% 9% 29% 33% 12% 3	520
	11th to 20th	Day	16% 12% 29% 30% 12% 1	640
	21st to end	Day	14% 10% 36% 25% 14% 2	650
May	1st to 10th	Day	16% 10% 29% 29% 14% 2	653
	11th to 20th	Day	19% 9% 29% 24% 16% 4	675
	21st to end	Day	21% 9% 24% 25% 18% 3	734
June	1st to 10th	Day	15% 11% 30% 24% 13% 7%	680
	11th to 20th	Day	16% 11% 31% 27% 11% 3	680
	21st to end	Day	14% 7% 24% 31% 19% 5%	680
July	1st to 10th	Day	8% 7% 27% 30% 20% 8%	671
	11th to 20th	Day	11% 7% 28% 30% 17% 6%	668
	21st to end	Day	7% 5% 28% 29% 23% 9%	739
August	1st to 10th	Day	7% 5% 30% 29% 21% 8%	676
	11th to 20th	Day	11% 7% 20% 30% 23% 8%	665
	21st to end	Day	14% 7% 25% 31% 18% 4	748
September	1st to 10th	Day	11% 9% 33% 32% 13% 3	568
	11th to 20th	Day	16% 9% 36% 28% 9% 3	300
	21st to end	Day	19% 8% 34% 28% 11% 1	300
October	1st to 10th	Day	23% 11% 27% 27% 10% 3	300
	11th to 20th	Day	12% 11% 37% 31% 8% 1	300
	21st to end	Day	22% 9% 32% 25% 11% 2	330
November	1st to 10th	Day	25% 11% 24% 28% 11% 1	300
	11th to 20th	Day	16% 11% 36% 25% 10% 2	300
	21st to end	Day	17% 12% 37% 28% 6%	300
December	1st to 10th	Day	14% 10% 32% 26% 14% 3	300
	11th to 20th	Day	16% 10% 38% 26% 8% 2	300
	21st to end	Day	11% 8% 33% 30% 15% 4	330
January	1st to 10th	Night	11% 7% 37% 32% 12% 2	1000
	11th to 20th	Night	15% 8% 32% 34% 10% 1	1000
	21st to end	Night	14% 9% 32% 34% 11% 1	1100
February	1st to 10th	Night	14% 5% 30% 36% 13% 1	1000
	11th to 20th	Night	10% 6% 29% 37% 15% 3	979
	21st to end	Night	11% 6% 34% 33% 14% 2	701
March	1st to 10th	Night	16% 6% 29% 31% 16% 2	751
	11th to 20th	Night	10% 8% 38% 31% 12% 1	570
	21st to end	Night	16% 6% 29% 31% 15% 3	627
April	1st to 10th	Night	11% 7% 32% 35% 12% 2	570
	11th to 20th	Night	18% 7% 26% 36% 12% 1	563
	21st to end	Night	16% 6% 31% 36% 11% 1	570
May	1st to 10th	Night	20% 6% 27% 36% 9% 1	570
	11th to 20th	Night	15% 8% 29% 30% 16% 2	561
	21st to end	Night	18% 8% 25% 36% 12% 1	617
June	1st to 10th	Night	16% 5% 29% 31% 18% 1	570
	11th to 20th	Night	17% 7% 27% 33% 15% 1	570
	21st to end	Night	10% 6% 21% 42% 19% 1	570
July	1st to 10th	Night	7% 5% 23% 41% 23% 2	555
	11th to 20th	Night	10% 4 24% 42% 19% 2	552
	21st to end	Night	8% 3 20% 40% 24% 4	624
August	1st to 10th	Night	8% 4 20% 45% 20% 2	567
	11th to 20th	Night	9% 3 21% 40% 22% 5%	564
	21st to end	Night	13% 5% 22% 37% 21% 1	627
September	1st to 10th	Night	11% 5% 30% 35% 17% 2	570
	11th to 20th	Night	14% 6% 29% 38% 12% 1	570
	21st to end	Night	14% 7% 33% 33% 12% 1	570
October	1st to 10th	Night	21% 7% 32% 30% 9% 1	678
	11th to 20th	Night	18% 7% 34% 29% 11% 1	846
	21st to end	Night	20% 9% 32% 27% 9% 1	1045
November	1st to 10th	Night	18% 11% 32% 26% 11% 2	975
	11th to 20th	Night	18% 9% 37% 26% 8% 3	1000
	21st to end	Night	17% 11% 38% 27% 7% 1	1000
December	1st to 10th	Night	11% 8% 31% 35% 13% 2	1000
	11th to 20th	Night	14% 9% 36% 31% 8% 2	1000
	21st to end	Night	17% 7% 30% 30% 14% 2	1100

Page generated at 2025-02-18 02:26:26. Version ac07

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