Stargazer Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stargazer Observatory clear sky chart from 2005-11-06 to 2024-11-05.

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	19% 9% 3 7% 5% 4 4 4 5% 6% 34%	105541
	Night	22% 11% 3 8% 5% 4 4 3 5% 6% 30%	102095
Transparency	Day	50% 9% 14% 17% 8% 1	105295
	Night	55% 8% 13% 16% 7% 1	101987
Seeing	Day	24% 9% 20% 26% 17% 5%	15203
	Night	30% 9% 14% 24% 19% 4	23495

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	32% 18% 4 9% 5% 5% 4 4 4 4 12%	2219
	11th to 20th	Day	25% 12% 3 8% 4 5% 4 4 5% 7% 23%	2388
	21st to end	Day	33% 16% 4 10% 7% 5% 5% 3 4 5% 9%	2840
February	1st to 10th	Day	30% 14% 4 9% 5% 4 4 4 5% 6% 17%	1710
	11th to 20th	Day	27% 14% 3 10% 5% 5% 4 4 4 5% 20%	1665
	21st to end	Day	25% 16% 5% 7% 5% 4 5% 3 6% 4 20%	1461
March	1st to 10th	Day	18% 13% 4 10% 6% 5% 6% 4 6% 8% 20%	3219
	11th to 20th	Day	17% 11% 3 6% 4 4 5% 3 5% 6% 34%	3490
	21st to end	Day	23% 12% 4 10% 6% 6% 5% 4 5% 6% 19%	3945
April	1st to 10th	Day	23% 14% 3 7% 7% 5% 5% 4 6% 6% 20%	2280
	11th to 20th	Day	20% 10% 4 8% 6% 5% 5% 4 5% 6% 26%	2296
	21st to end	Day	22% 10% 3 8% 5% 5% 5% 4 7% 6% 26%	2522
May	1st to 10th	Day	18% 8% 3 6% 4 4 4 3 5% 6% 40%	4420
	11th to 20th	Day	14% 6% 2 6% 4 4 5% 4 6% 9% 40%	4377
	21st to end	Day	28% 9% 3 8% 5% 4 4 3 5% 6% 25%	4813
June	1st to 10th	Day	21% 8% 3 7% 5% 4 5% 4 5% 6% 33%	2779
	11th to 20th	Day	20% 9% 3 7% 5% 5% 5% 5% 6% 7% 29%	2850
	21st to end	Day	12% 7% 2 7% 5% 4 5% 4 7% 8% 41%	2850
July	1st to 10th	Day	6% 4 1 4 3 2 2 3 3 5% 68%	4740
	11th to 20th	Day	5% 3 2 3 2 3 2 3 4 5% 68%	4647
	21st to end	Day	11% 4 2 5% 3 3 3 2 3 6% 58%	4790
August	1st to 10th	Day	6% 3 1 4 3 3 3 3 4 7% 63%	4350
	11th to 20th	Day	10% 7% 2 6% 4 4 5% 4 6% 7% 45%	4026
	21st to end	Day	14% 8% 3 8% 4 4 4 3 5% 6% 42%	4352
September	1st to 10th	Day	11% 6% 3 5% 4 3 3 3 4 7% 50%	2280
	11th to 20th	Day	13% 8% 3 7% 4 5% 4 4 5% 6% 40%	2280
	21st to end	Day	17% 8% 3 7% 5% 5% 4 3 4 7% 36%	2008
October	1st to 10th	Day	17% 8% 3 8% 5% 5% 5% 5% 6% 10% 30%	3180
	11th to 20th	Day	28% 12% 3 8% 4 4 3 3 4 6% 24%	3161
	21st to end	Day	24% 11% 5% 10% 5% 6% 5% 3 5% 6% 19%	3237
November	1st to 10th	Day	32% 10% 4 8% 5% 4 5% 4 5% 5% 17%	1537
	11th to 20th	Day	31% 10% 4 7% 6% 4 4 3 4 5% 21%	1520
	21st to end	Day	31% 12% 4 7% 6% 4 5% 4 4 6% 17%	1520
December	1st to 10th	Day	26% 14% 3 8% 5% 5% 5% 3 3 6% 23%	1520
	11th to 20th	Day	28% 14% 5% 10% 7% 4 4 4 4 5% 14%	1827
	21st to end	Day	24% 17% 5% 12% 6% 6% 5% 4 4 5% 14%	2442
January	1st to 10th	Night	30% 16% 4 10% 6% 5% 4 3 4 4 13%	4726
	11th to 20th	Night	27% 13% 4 7% 4 4 4 3 4 8% 23%	4508
	21st to end	Night	31% 16% 4 9% 6% 6% 4 3 4 5% 12%	4803
February	1st to 10th	Night	29% 14% 3 8% 5% 4 4 3 4 5% 20%	2470
	11th to 20th	Night	26% 13% 4 9% 5% 4 3 3 4 5% 23%	2402
	21st to end	Night	26% 14% 4 7% 5% 5% 4 4 5% 5% 21%	1992
March	1st to 10th	Night	19% 13% 5% 12% 7% 6% 6% 4 6% 6% 18%	3653
	11th to 20th	Night	18% 11% 2 7% 4 3 4 4 4 7% 36%	3489
	21st to end	Night	28% 14% 4 9% 5% 4 5% 4 5% 5% 17%	3707
April	1st to 10th	Night	24% 12% 4 8% 6% 5% 4 5% 7% 6% 20%	1900
	11th to 20th	Night	20% 10% 3 8% 7% 6% 4 4 4 5% 28%	1832
	21st to end	Night	25% 12% 4 9% 5% 4 4 3 5% 5% 23%	1657
May	1st to 10th	Night	17% 9% 3 6% 3 3 3 3 4 5% 44%	2540
	11th to 20th	Night	12% 7% 2 6% 4 5% 5% 4 5% 7% 43%	2516
	21st to end	Night	25% 10% 4 8% 5% 4 5% 3 5% 6% 25%	2762
June	1st to 10th	Night	21% 8% 4 7% 6% 4 4 4 5% 7% 31%	1397
	11th to 20th	Night	22% 11% 2 7% 5% 5% 5% 4 5% 6% 28%	1330
	21st to end	Night	15% 6% 2 5% 5% 5% 4 4 6% 7% 42%	1330
July	1st to 10th	Night	8% 4 1 3 2 2 2 2 2 4 69%	2220
	11th to 20th	Night	5% 3 1 2 2 2 2 2 3 4 74%	2311
	21st to end	Night	11% 4 1 4 2 3 4 3 4 5% 58%	2762
August	1st to 10th	Night	6% 2 1 2 2 2 3 3 5% 6% 68%	2579
	11th to 20th	Night	13% 7% 2 5% 3 3 3 2 4 5% 52%	2812
	21st to end	Night	16% 6% 2 6% 3 3 3 3 4 6% 48%	3320
September	1st to 10th	Night	9% 5% 2 5% 3 3 3 3 5% 6% 55%	1900
	11th to 20th	Night	17% 8% 2 7% 4 4 4 4 4 5% 41%	1900
	21st to end	Night	16% 7% 3 7% 4 4 4 3 4 7% 41%	2170
October	1st to 10th	Night	15% 7% 2 7% 5% 5% 4 4 6% 8% 36%	3800
	11th to 20th	Night	27% 9% 3 7% 4 3 3 3 5% 6% 31%	3777
	21st to end	Night	25% 13% 4 9% 5% 4 4 3 5% 6% 22%	4323
November	1st to 10th	Night	33% 10% 4 7% 5% 4 4 2 4 5% 20%	2639
	11th to 20th	Night	30% 12% 3 7% 5% 4 4 3 4 5% 21%	2660
	21st to end	Night	32% 10% 3 8% 6% 5% 4 3 5% 5% 20%	2660
December	1st to 10th	Night	26% 13% 4 8% 4 4 4 3 5% 6% 24%	2660
	11th to 20th	Night	28% 14% 4 11% 6% 5% 4 3 5% 5% 15%	3374
	21st to end	Night	27% 16% 5% 11% 6% 5% 5% 3 4 5% 13%	5214

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	76% 10% 5% 7% 2 1	2219
	11th to 20th	Day	60% 9% 10% 15% 5% 1	2412
	21st to end	Day	77% 8% 7% 5% 2	2840
February	1st to 10th	Day	69% 9% 10% 8% 3 1	1710
	11th to 20th	Day	66% 8% 9% 9% 7% 1	1674
	21st to end	Day	66% 9% 10% 10% 4 1	1461
March	1st to 10th	Day	58% 12% 14% 11% 4	3219
	11th to 20th	Day	51% 9% 14% 23% 2	3490
	21st to end	Day	64% 12% 12% 11% 1	3945
April	1st to 10th	Day	64% 11% 14% 9% 1	2280
	11th to 20th	Day	61% 8% 10% 12% 7% 1	2296
	21st to end	Day	61% 10% 11% 13% 5%	2522
May	1st to 10th	Day	46% 9% 11% 23% 10%	4420
	11th to 20th	Day	39% 15% 23% 19% 4	4380
	21st to end	Day	61% 11% 16% 10% 1	4814
June	1st to 10th	Day	54% 9% 17% 13% 6% 1	2779
	11th to 20th	Day	57% 12% 16% 12% 4	2850
	21st to end	Day	43% 10% 19% 20% 7% 1	2850
July	1st to 10th	Day	22% 7% 10% 24% 25% 12%	4666
	11th to 20th	Day	20% 5% 10% 33% 30% 3	4566
	21st to end	Day	30% 7% 19% 30% 13% 2	4639
August	1st to 10th	Day	21% 7% 17% 37% 18% 1	4333
	11th to 20th	Day	38% 10% 20% 24% 6% 2	4065
	21st to end	Day	43% 7% 13% 26% 11%	4351
September	1st to 10th	Day	35% 8% 16% 23% 13% 4	2280
	11th to 20th	Day	44% 8% 14% 17% 15% 1	2280
	21st to end	Day	46% 9% 17% 17% 9% 2	2008
October	1st to 10th	Day	46% 8% 18% 22% 4	3180
	11th to 20th	Day	60% 6% 13% 13% 7%	3161
	21st to end	Day	65% 8% 11% 10% 6%	3237
November	1st to 10th	Day	68% 8% 13% 7% 4	1537
	11th to 20th	Day	66% 9% 8% 10% 5% 2	1520
	21st to end	Day	68% 6% 9% 10% 8% 1	1520
December	1st to 10th	Day	64% 7% 10% 11% 8% 1	1520
	11th to 20th	Day	69% 10% 10% 8% 3 1	1829
	21st to end	Day	71% 11% 10% 6% 2	2442
January	1st to 10th	Night	74% 10% 7% 7% 2 1	4726
	11th to 20th	Night	59% 7% 11% 17% 5% 1	4546
	21st to end	Night	73% 9% 8% 7% 2	4803
February	1st to 10th	Night	68% 6% 11% 9% 4 2	2470
	11th to 20th	Night	65% 7% 11% 10% 6% 1	2404
	21st to end	Night	65% 7% 9% 14% 4 1	1992
March	1st to 10th	Night	64% 10% 9% 11% 5%	3653
	11th to 20th	Night	46% 11% 17% 23% 2 1	3490
	21st to end	Night	68% 10% 11% 10%	3707
April	1st to 10th	Night	64% 10% 13% 12% 2	1900
	11th to 20th	Night	58% 8% 13% 12% 7% 2	1832
	21st to end	Night	63% 8% 11% 12% 6%	1657
May	1st to 10th	Night	41% 9% 13% 28% 8% 1	2540
	11th to 20th	Night	38% 13% 23% 20% 6%	2516
	21st to end	Night	60% 10% 18% 10% 1	2762
June	1st to 10th	Night	53% 7% 17% 16% 5% 1	1397
	11th to 20th	Night	56% 8% 18% 14% 2	1330
	21st to end	Night	41% 7% 23% 21% 5% 3	1330
July	1st to 10th	Night	23% 5% 10% 25% 21% 16%	2185
	11th to 20th	Night	17% 5% 10% 29% 38% 1	2269
	21st to end	Night	28% 7% 14% 30% 19% 2	2674
August	1st to 10th	Night	16% 5% 17% 42% 19% 2	2571
	11th to 20th	Night	35% 7% 23% 25% 9% 2	2839
	21st to end	Night	38% 7% 18% 27% 9%	3320
September	1st to 10th	Night	31% 7% 16% 29% 13% 4	1900
	11th to 20th	Night	46% 8% 10% 19% 15% 3	1900
	21st to end	Night	45% 7% 14% 22% 10% 1	2170
October	1st to 10th	Night	45% 8% 19% 23% 4	3800
	11th to 20th	Night	55% 5% 16% 17% 7%	3777
	21st to end	Night	64% 8% 10% 12% 5%	4323
November	1st to 10th	Night	67% 7% 10% 11% 3 1	2639
	11th to 20th	Night	66% 7% 10% 10% 5% 2	2660
	21st to end	Night	67% 6% 10% 9% 7% 1	2660
December	1st to 10th	Night	61% 8% 10% 13% 7% 1	2660
	11th to 20th	Night	70% 10% 11% 6% 3 1	3371
	21st to end	Night	71% 13% 7% 7% 2	5214

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	38% 12% 16% 16% 12% 7%	180
	11th to 20th	Day	34% 15% 15% 16% 14% 5%	180
	21st to end	Day	43% 11% 15% 16% 12% 3	231
February	1st to 10th	Day	41% 12% 18% 19% 9% 2	370
	11th to 20th	Day	38% 12% 20% 19% 10% 1	365
	21st to end	Day	35% 14% 21% 20% 9% 1	331
March	1st to 10th	Day	31% 15% 23% 19% 10% 2	460
	11th to 20th	Day	32% 13% 14% 20% 16% 5%	460
	21st to end	Day	33% 13% 24% 20% 9% 1	506
April	1st to 10th	Day	29% 15% 23% 19% 11% 3	460
	11th to 20th	Day	22% 17% 25% 21% 11% 5%	452
	21st to end	Day	27% 13% 24% 21% 13% 2	460
May	1st to 10th	Day	19% 8% 24% 32% 14% 2	463
	11th to 20th	Day	24% 7% 19% 26% 19% 5%	488
	21st to end	Day	25% 9% 20% 25% 16% 6%	529
June	1st to 10th	Day	21% 9% 26% 28% 14% 2	609
	11th to 20th	Day	22% 9% 27% 27% 13% 3	680
	21st to end	Day	12% 7% 25% 30% 21% 5%	680
July	1st to 10th	Day	12% 4 20% 36% 24% 4	671
	11th to 20th	Day	8% 6% 20% 37% 24% 6%	614
	21st to end	Day	8% 2 16% 36% 28% 9%	531
August	1st to 10th	Day	11% 3 13% 35% 29% 10%	487
	11th to 20th	Day	8% 3 15% 35% 29% 11%	477
	21st to end	Day	12% 7% 20% 31% 21% 8%	539
September	1st to 10th	Day	16% 7% 19% 34% 19% 5%	490
	11th to 20th	Day	15% 8% 21% 30% 22% 4	490
	21st to end	Day	22% 8% 23% 24% 17% 5%	490
October	1st to 10th	Day	24% 10% 17% 26% 16% 7%	490
	11th to 20th	Day	33% 8% 19% 18% 17% 5%	490
	21st to end	Day	33% 12% 19% 19% 12% 5%	416
November	1st to 10th	Day	39% 12% 21% 17% 9% 2	196
	11th to 20th	Day	36% 13% 14% 14% 12% 10%	180
	21st to end	Day	36% 12% 18% 12% 11% 11%	180
December	1st to 10th	Day	45% 12% 10% 11% 11% 11%	180
	11th to 20th	Day	42% 14% 17% 18% 9% 1	180
	21st to end	Day	42% 9% 18% 22% 7% 3	198
January	1st to 10th	Night	45% 12% 14% 16% 12% 2	850
	11th to 20th	Night	40% 11% 11% 19% 17% 2	794
	21st to end	Night	38% 9% 16% 20% 14% 3	836
February	1st to 10th	Night	39% 10% 13% 26% 10% 2	760
	11th to 20th	Night	35% 10% 13% 26% 15% 1	744
	21st to end	Night	36% 10% 16% 24% 12% 3	628
March	1st to 10th	Night	34% 14% 15% 22% 13% 2	760
	11th to 20th	Night	36% 12% 14% 21% 14% 3	760
	21st to end	Night	36% 12% 19% 23% 9% 1	836
April	1st to 10th	Night	31% 11% 17% 24% 14% 3	760
	11th to 20th	Night	26% 10% 21% 25% 15% 3	704
	21st to end	Night	31% 10% 16% 29% 12% 2	517
May	1st to 10th	Night	19% 7% 17% 31% 24% 2	380
	11th to 20th	Night	21% 6% 13% 25% 30% 4	374
	21st to end	Night	25% 6% 14% 26% 25% 5%	411
June	1st to 10th	Night	24% 6% 17% 29% 22% 2	380
	11th to 20th	Night	24% 7% 13% 34% 19% 2	380
	21st to end	Night	17% 4 12% 35% 28% 5%	380
July	1st to 10th	Night	12% 4 8% 36% 38% 3	370
	11th to 20th	Night	9% 3 13% 36% 35% 5%	368
	21st to end	Night	8% 2 9% 33% 41% 7%	416
August	1st to 10th	Night	10% 2 6% 26% 45% 11%	402
	11th to 20th	Night	10% 1 6% 23% 46% 14%	564
	21st to end	Night	14% 4 10% 30% 36% 7%	723
September	1st to 10th	Night	12% 3 11% 36% 32% 7%	760
	11th to 20th	Night	20% 5% 11% 22% 32% 9%	760
	21st to end	Night	22% 6% 13% 26% 27% 5%	760
October	1st to 10th	Night	22% 6% 13% 26% 26% 7%	760
	11th to 20th	Night	31% 8% 13% 23% 20% 5%	760
	21st to end	Night	32% 10% 17% 24% 14% 4	836
November	1st to 10th	Night	39% 11% 17% 23% 10%	760
	11th to 20th	Night	39% 11% 17% 18% 13% 3	760
	21st to end	Night	39% 9% 16% 19% 12% 5%	760
December	1st to 10th	Night	35% 8% 14% 24% 15% 4	760
	11th to 20th	Night	42% 12% 15% 21% 9% 1	787
	21st to end	Night	42% 13% 18% 17% 9%	935

Page generated at 2024-11-02 23:11:07. Version ac07

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