Clearview Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Clearview Observatory clear sky chart from 2005-11-06 to 2024-11-08.

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	22% 9% 3 7% 5% 4 4 3 5% 6% 32%	105692
	Night	25% 10% 3 7% 4 4 4 3 4 5% 30%	101959
Transparency	Day	53% 6% 13% 18% 8% 1	105449
	Night	57% 6% 12% 17% 7% 1	101848
Seeing	Day	27% 6% 18% 26% 17% 6%	15094
	Night	33% 5% 12% 26% 21% 4	23445

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	40% 15% 4 9% 5% 4 3 2 3 4 11%	2251
	11th to 20th	Day	27% 12% 4 8% 5% 4 4 4 5% 7% 21%	2516
	21st to end	Day	40% 15% 4 8% 4 4 3 3 3 4 11%	2840
February	1st to 10th	Day	33% 13% 4 8% 5% 4 4 4 5% 4 16%	1710
	11th to 20th	Day	28% 14% 5% 8% 5% 4 4 3 4 4 20%	1665
	21st to end	Day	29% 15% 4 7% 6% 5% 3 3 3 5% 20%	1479
March	1st to 10th	Day	21% 14% 3 9% 6% 5% 6% 4 6% 6% 20%	3195
	11th to 20th	Day	20% 10% 3 7% 5% 4 4 3 5% 6% 33%	3490
	21st to end	Day	27% 13% 4 10% 6% 5% 5% 4 5% 6% 15%	3967
April	1st to 10th	Day	28% 13% 3 7% 6% 5% 4 3 6% 6% 17%	2280
	11th to 20th	Day	25% 11% 3 7% 6% 5% 5% 4 4 7% 24%	2271
	21st to end	Day	22% 11% 4 9% 6% 6% 5% 5% 5% 6% 21%	2526
May	1st to 10th	Day	19% 8% 2 6% 4 4 4 3 6% 6% 38%	4420
	11th to 20th	Day	18% 7% 2 6% 4 4 5% 4 6% 9% 35%	4377
	21st to end	Day	30% 11% 3 8% 5% 5% 4 3 5% 6% 20%	4813
June	1st to 10th	Day	25% 8% 2 6% 5% 5% 5% 3 5% 6% 28%	2707
	11th to 20th	Day	26% 9% 3 8% 5% 4 5% 5% 5% 6% 23%	2850
	21st to end	Day	14% 8% 3 7% 5% 4 5% 4 6% 7% 38%	2850
July	1st to 10th	Day	8% 5% 2 4 2 3 3 3 4 5% 62%	4740
	11th to 20th	Day	7% 3 1 3 3 2 2 2 4 5% 68%	4530
	21st to end	Day	12% 4 1 5% 3 3 3 2 4 5% 57%	4790
August	1st to 10th	Day	6% 3 1 3 2 3 3 3 5% 7% 63%	4351
	11th to 20th	Day	11% 6% 3 7% 5% 5% 5% 4 6% 8% 41%	4026
	21st to end	Day	17% 8% 2 6% 4 4 3 3 4 6% 42%	4321
September	1st to 10th	Day	12% 6% 3 6% 4 3 3 3 4 7% 48%	2280
	11th to 20th	Day	16% 8% 3 8% 5% 5% 5% 3 5% 7% 37%	2280
	21st to end	Day	20% 8% 3 6% 4 5% 4 3 5% 6% 36%	2013
October	1st to 10th	Day	17% 7% 2 7% 5% 5% 5% 4 7% 10% 34%	3180
	11th to 20th	Day	33% 9% 3 8% 4 4 3 3 4 6% 24%	3161
	21st to end	Day	30% 11% 4 9% 5% 5% 4 3 5% 6% 17%	3234
November	1st to 10th	Day	38% 11% 3 6% 4 3 5% 4 4 5% 17%	1588
	11th to 20th	Day	35% 11% 4 6% 4 4 4 3 3 4 22%	1520
	21st to end	Day	36% 11% 3 7% 4 4 3 3 5% 5% 19%	1520
December	1st to 10th	Day	31% 12% 3 8% 5% 4 3 2 3 5% 22%	1520
	11th to 20th	Day	33% 14% 4 9% 4 5% 4 4 5% 5% 14%	1925
	21st to end	Day	28% 13% 5% 12% 7% 5% 5% 3 4 5% 13%	2506
January	1st to 10th	Night	39% 14% 4 9% 5% 4 4 3 4 3 11%	4689
	11th to 20th	Night	29% 12% 5% 7% 4 3 3 3 5% 7% 23%	4382
	21st to end	Night	37% 14% 3 9% 5% 5% 4 3 4 4 12%	4802
February	1st to 10th	Night	33% 11% 4 8% 6% 4 4 3 4 6% 18%	2470
	11th to 20th	Night	28% 15% 3 7% 4 5% 4 3 4 4 22%	2402
	21st to end	Night	29% 16% 3 6% 4 3 4 3 5% 5% 22%	1974
March	1st to 10th	Night	20% 15% 5% 9% 7% 6% 6% 5% 6% 6% 17%	3676
	11th to 20th	Night	20% 10% 3 5% 4 3 3 2 5% 6% 38%	3489
	21st to end	Night	30% 15% 4 9% 5% 4 4 4 4 4 16%	3685
April	1st to 10th	Night	27% 11% 3 8% 6% 4 6% 5% 5% 6% 18%	1900
	11th to 20th	Night	23% 10% 2 9% 5% 5% 5% 4 5% 5% 29%	1855
	21st to end	Night	25% 12% 3 8% 5% 5% 5% 4 4 6% 24%	1653
May	1st to 10th	Night	19% 9% 3 6% 4 4 4 2 3 4 42%	2540
	11th to 20th	Night	19% 7% 3 6% 4 3 4 3 4 6% 40%	2516
	21st to end	Night	31% 10% 3 7% 6% 5% 5% 2 4 4 21%	2762
June	1st to 10th	Night	22% 9% 4 6% 6% 4 5% 3 5% 6% 31%	1468
	11th to 20th	Night	26% 11% 4 8% 5% 4 3 3 6% 5% 25%	1330
	21st to end	Night	15% 5% 2 7% 5% 4 3 3 6% 7% 42%	1330
July	1st to 10th	Night	10% 6% 2 5% 3 2 2 2 3 4 61%	2220
	11th to 20th	Night	5% 3 1 3 2 1 2 2 4 4 73%	2426
	21st to end	Night	12% 5% 2 4 2 3 4 3 4 5% 56%	2762
August	1st to 10th	Night	5% 2 1 3 3 3 2 2 4 6% 68%	2578
	11th to 20th	Night	14% 6% 2 6% 3 3 3 2 4 6% 50%	2812
	21st to end	Night	19% 6% 2 5% 3 3 3 2 3 5% 48%	3338
September	1st to 10th	Night	10% 6% 2 5% 3 3 3 3 4 6% 53%	1900
	11th to 20th	Night	17% 8% 3 6% 5% 3 4 3 5% 5% 40%	1900
	21st to end	Night	19% 8% 2 7% 4 4 4 3 5% 5% 38%	2163
October	1st to 10th	Night	16% 7% 3 6% 5% 4 5% 4 6% 8% 37%	3800
	11th to 20th	Night	30% 8% 3 6% 4 4 4 3 4 5% 29%	3777
	21st to end	Night	34% 12% 4 7% 4 4 3 3 4 5% 21%	4327
November	1st to 10th	Night	35% 10% 4 6% 4 4 4 3 4 5% 21%	2646
	11th to 20th	Night	35% 10% 3 7% 4 3 4 3 4 4 22%	2660
	21st to end	Night	34% 10% 3 8% 5% 4 4 3 4 5% 21%	2660
December	1st to 10th	Night	31% 11% 3 8% 5% 3 3 3 4 5% 24%	2660
	11th to 20th	Night	30% 15% 5% 9% 6% 4 4 3 5% 4 15%	3280
	21st to end	Night	29% 15% 5% 10% 5% 5% 4 3 5% 4 14%	5127

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	79% 5% 5% 8% 2 1	2251
	11th to 20th	Day	61% 5% 10% 16% 6% 1	2540
	21st to end	Day	78% 4 7% 9% 2	2840
February	1st to 10th	Day	71% 6% 10% 9% 3 1	1710
	11th to 20th	Day	69% 5% 9% 10% 7%	1674
	21st to end	Day	69% 5% 9% 12% 5%	1479
March	1st to 10th	Day	62% 6% 12% 15% 5%	3195
	11th to 20th	Day	52% 7% 14% 24% 2 1	3490
	21st to end	Day	68% 8% 13% 10% 1	3967
April	1st to 10th	Day	68% 7% 14% 10% 1	2280
	11th to 20th	Day	63% 4 12% 13% 6% 1	2271
	21st to end	Day	64% 6% 11% 13% 5% 1	2526
May	1st to 10th	Day	48% 5% 14% 22% 11%	4420
	11th to 20th	Day	44% 8% 23% 20% 4	4380
	21st to end	Day	66% 7% 17% 9% 1	4814
June	1st to 10th	Day	58% 5% 17% 14% 5% 1	2707
	11th to 20th	Day	63% 6% 15% 12% 4	2850
	21st to end	Day	46% 6% 20% 20% 7% 1	2850
July	1st to 10th	Day	26% 5% 9% 22% 24% 13%	4666
	11th to 20th	Day	22% 3 9% 31% 32% 3	4451
	21st to end	Day	30% 5% 17% 33% 14% 2	4639
August	1st to 10th	Day	22% 5% 14% 41% 17% 1	4334
	11th to 20th	Day	40% 8% 21% 22% 7% 2	4065
	21st to end	Day	44% 5% 13% 27% 11% 1	4320
September	1st to 10th	Day	38% 4 15% 26% 13% 4	2280
	11th to 20th	Day	48% 5% 13% 19% 14% 2	2280
	21st to end	Day	48% 6% 17% 17% 10% 2	2013
October	1st to 10th	Day	44% 6% 17% 27% 6%	3180
	11th to 20th	Day	64% 4 10% 15% 7%	3161
	21st to end	Day	66% 6% 10% 9% 7% 1	3234
November	1st to 10th	Day	70% 5% 11% 11% 4	1588
	11th to 20th	Day	68% 4 9% 10% 7% 2	1520
	21st to end	Day	69% 4 6% 12% 8% 1	1520
December	1st to 10th	Day	67% 4 7% 12% 9% 1	1520
	11th to 20th	Day	70% 5% 12% 11% 2 1	1928
	21st to end	Day	72% 7% 10% 9% 2	2506
January	1st to 10th	Night	78% 6% 6% 7% 2 1	4689
	11th to 20th	Night	62% 4 9% 17% 7% 1	4420
	21st to end	Night	76% 6% 7% 8% 3	4802
February	1st to 10th	Night	69% 5% 10% 10% 4 1	2470
	11th to 20th	Night	66% 5% 10% 11% 7% 1	2404
	21st to end	Night	66% 5% 10% 15% 4 1	1974
March	1st to 10th	Night	64% 8% 11% 13% 5%	3676
	11th to 20th	Night	49% 6% 20% 23% 2 1	3490
	21st to end	Night	70% 8% 12% 9% 1	3685
April	1st to 10th	Night	66% 7% 13% 12% 2	1900
	11th to 20th	Night	58% 6% 14% 13% 8% 2	1855
	21st to end	Night	64% 6% 11% 13% 5% 1	1653
May	1st to 10th	Night	48% 4 12% 26% 8% 1	2540
	11th to 20th	Night	46% 6% 22% 21% 4	2516
	21st to end	Night	66% 8% 15% 9% 1	2762
June	1st to 10th	Night	55% 6% 16% 18% 5%	1468
	11th to 20th	Night	62% 7% 13% 15% 3	1330
	21st to end	Night	43% 5% 21% 22% 5% 3	1330
July	1st to 10th	Night	29% 4 9% 21% 20% 17%	2185
	11th to 20th	Night	18% 3 9% 27% 41% 2	2382
	21st to end	Night	30% 5% 13% 30% 19% 3	2674
August	1st to 10th	Night	19% 4 14% 41% 21% 2	2570
	11th to 20th	Night	37% 6% 22% 24% 8% 2	2839
	21st to end	Night	41% 5% 14% 30% 9%	3338
September	1st to 10th	Night	34% 4 16% 28% 13% 4	1900
	11th to 20th	Night	47% 5% 10% 20% 13% 4	1900
	21st to end	Night	47% 5% 14% 21% 10% 2	2163
October	1st to 10th	Night	44% 8% 18% 26% 4	3800
	11th to 20th	Night	57% 5% 13% 18% 7%	3777
	21st to end	Night	68% 4 11% 11% 6%	4327
November	1st to 10th	Night	66% 5% 13% 12% 3 1	2646
	11th to 20th	Night	67% 4 10% 12% 5% 2	2660
	21st to end	Night	67% 4 8% 11% 9% 1	2660
December	1st to 10th	Night	65% 5% 10% 12% 8% 1	2660
	11th to 20th	Night	72% 6% 10% 9% 3	3276
	21st to end	Night	71% 9% 9% 9% 3	5127

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	41% 6% 13% 14% 18% 9%	180
	11th to 20th	Day	37% 8% 13% 21% 14% 7%	180
	21st to end	Day	46% 5% 13% 18% 12% 6%	231
February	1st to 10th	Day	48% 5% 16% 19% 9% 3	370
	11th to 20th	Day	45% 6% 19% 17% 11% 2	365
	21st to end	Day	41% 6% 19% 23% 9% 2	339
March	1st to 10th	Day	35% 9% 24% 17% 13% 2	460
	11th to 20th	Day	32% 9% 18% 22% 15% 5%	460
	21st to end	Day	39% 9% 22% 19% 10% 1	506
April	1st to 10th	Day	35% 9% 23% 19% 10% 3	460
	11th to 20th	Day	29% 12% 24% 20% 9% 6%	452
	21st to end	Day	27% 11% 24% 23% 12% 3	460
May	1st to 10th	Day	21% 7% 21% 32% 16% 3	463
	11th to 20th	Day	28% 4 16% 26% 18% 8%	488
	21st to end	Day	31% 5% 14% 27% 16% 7%	529
June	1st to 10th	Day	26% 4 24% 27% 15% 5%	537
	11th to 20th	Day	25% 7% 21% 29% 15% 3	680
	21st to end	Day	15% 6% 19% 34% 21% 5%	680
July	1st to 10th	Day	12% 3 18% 36% 26% 4	671
	11th to 20th	Day	9% 5% 18% 34% 27% 8%	551
	21st to end	Day	10% 2 15% 39% 25% 9%	531
August	1st to 10th	Day	12% 2 12% 36% 25% 13%	487
	11th to 20th	Day	9% 2 13% 38% 27% 12%	477
	21st to end	Day	16% 3 20% 34% 18% 10%	539
September	1st to 10th	Day	17% 5% 19% 33% 18% 7%	490
	11th to 20th	Day	20% 6% 17% 27% 24% 6%	490
	21st to end	Day	22% 5% 20% 30% 16% 7%	490
October	1st to 10th	Day	26% 7% 16% 25% 18% 8%	490
	11th to 20th	Day	34% 5% 15% 21% 18% 7%	490
	21st to end	Day	38% 7% 16% 19% 15% 6%	413
November	1st to 10th	Day	46% 6% 13% 19% 12% 4	217
	11th to 20th	Day	45% 4 12% 12% 16% 12%	180
	21st to end	Day	37% 8% 17% 16% 8% 14%	180
December	1st to 10th	Day	46% 5% 9% 12% 16% 12%	180
	11th to 20th	Day	43% 5% 17% 20% 13% 2	180
	21st to end	Day	43% 5% 13% 22% 14% 4	198
January	1st to 10th	Night	49% 7% 11% 17% 14% 3	838
	11th to 20th	Night	42% 5% 11% 19% 19% 3	760
	21st to end	Night	40% 6% 11% 25% 16% 3	836
February	1st to 10th	Night	41% 4 12% 28% 11% 3	760
	11th to 20th	Night	41% 3 10% 26% 17% 2	744
	21st to end	Night	38% 5% 14% 28% 13% 2	628
March	1st to 10th	Night	36% 5% 15% 26% 15% 2	760
	11th to 20th	Night	36% 7% 12% 25% 16% 3	760
	21st to end	Night	39% 6% 14% 27% 12% 1	836
April	1st to 10th	Night	35% 6% 14% 27% 17% 2	760
	11th to 20th	Night	29% 6% 16% 30% 17% 3	727
	21st to end	Night	32% 5% 16% 30% 14% 3	513
May	1st to 10th	Night	24% 5% 12% 34% 23% 2	380
	11th to 20th	Night	24% 3 10% 30% 28% 5%	374
	21st to end	Night	28% 2 11% 28% 25% 6%	411
June	1st to 10th	Night	28% 3 15% 32% 19% 4	380
	11th to 20th	Night	32% 5% 13% 29% 19% 3	380
	21st to end	Night	18% 4 13% 33% 27% 5%	380
July	1st to 10th	Night	15% 3 11% 31% 36% 4	370
	11th to 20th	Night	10% 2 14% 33% 37% 5%	368
	21st to end	Night	10% 2 9% 33% 39% 6%	416
August	1st to 10th	Night	11% 1 4 30% 44% 10%	401
	11th to 20th	Night	10% 2 5% 24% 45% 14%	564
	21st to end	Night	16% 2 10% 31% 33% 7%	741
September	1st to 10th	Night	13% 3 8% 32% 37% 7%	760
	11th to 20th	Night	21% 4 7% 24% 33% 11%	760
	21st to end	Night	24% 5% 10% 27% 27% 7%	760
October	1st to 10th	Night	24% 3 9% 29% 28% 7%	760
	11th to 20th	Night	33% 4 13% 23% 21% 6%	760
	21st to end	Night	37% 5% 13% 24% 16% 4	836
November	1st to 10th	Night	42% 6% 14% 24% 13% 1	770
	11th to 20th	Night	41% 5% 14% 22% 14% 3	760
	21st to end	Night	42% 5% 11% 22% 16% 5%	760
December	1st to 10th	Night	36% 5% 10% 26% 19% 4	760
	11th to 20th	Night	47% 4 11% 24% 12% 2	760
	21st to end	Night	49% 5% 13% 21% 11% 1	912

Page generated at 2024-11-05 05:15:53. Version ac07

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