AUGO
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the AUGO clear sky chart from 2005-11-06 to 2025-07-06.

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% 9% 3 9% 6% 5% 5% 4 6% 8% 33%	124084
	Night	8% 10% 4 10% 6% 6% 6% 4 6% 8% 32%	123364
Transparency	Day	47% 6% 17% 22% 7%	123820
	Night	49% 5% 16% 21% 8% 1	123274
Seeing	Day	14% 7% 25% 30% 19% 6%	17005
	Night	13% 5% 27% 37% 17% 2	25441

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	4 15% 6% 14% 9% 6% 5% 7% 6% 6% 22%	2947
	11th to 20th	Day	4 9% 3 12% 7% 6% 6% 7% 8% 10% 29%	3159
	21st to end	Day	6% 12% 6% 11% 5% 5% 4 4 6% 8% 32%	3618
February	1st to 10th	Day	6% 14% 4 10% 7% 7% 8% 5% 8% 8% 25%	1600
	11th to 20th	Day	6% 11% 5% 13% 8% 6% 5% 4 7% 8% 27%	1676
	21st to end	Day	4 10% 5% 12% 8% 7% 7% 6% 7% 8% 25%	1510
March	1st to 10th	Day	4 9% 4 11% 9% 7% 8% 5% 7% 8% 27%	4518
	11th to 20th	Day	5% 12% 5% 12% 7% 5% 5% 4 6% 8% 32%	4951
	21st to end	Day	10% 16% 6% 15% 5% 5% 4 3 5% 7% 23%	5568
April	1st to 10th	Day	7% 12% 4 9% 7% 7% 6% 5% 6% 7% 30%	2520
	11th to 20th	Day	11% 11% 3 8% 6% 7% 5% 5% 7% 7% 31%	2570
	21st to end	Day	12% 11% 4 10% 5% 6% 6% 4 8% 8% 27%	2611
May	1st to 10th	Day	14% 7% 3 7% 5% 5% 4 4 6% 7% 39%	6780
	11th to 20th	Day	16% 11% 3 9% 6% 5% 5% 4 5% 7% 29%	6734
	21st to end	Day	10% 7% 2 7% 5% 6% 6% 5% 7% 8% 37%	7405
June	1st to 10th	Day	15% 7% 3 8% 6% 6% 5% 4 7% 8% 31%	3060
	11th to 20th	Day	20% 10% 3 7% 6% 5% 7% 5% 7% 8% 23%	3200
	21st to end	Day	11% 5% 2 8% 6% 5% 7% 6% 7% 9% 35%	3200
July	1st to 10th	Day	8% 5% 3 6% 4 4 6% 5% 7% 9% 43%	5141
	11th to 20th	Day	9% 4 1 5% 4 5% 5% 5% 7% 9% 46%	4782
	21st to end	Day	14% 5% 2 6% 3 4 5% 4 7% 9% 42%	5138
August	1st to 10th	Day	12% 7% 2 6% 4 4 4 4 6% 7% 43%	4625
	11th to 20th	Day	10% 6% 2 6% 5% 4 5% 4 6% 10% 42%	4190
	21st to end	Day	11% 5% 2 7% 5% 5% 5% 5% 6% 9% 41%	4521
September	1st to 10th	Day	12% 7% 3 7% 5% 4 4 4 5% 8% 40%	2442
	11th to 20th	Day	14% 7% 2 7% 3 5% 5% 4 6% 9% 37%	2090
	21st to end	Day	8% 7% 2 7% 5% 4 5% 4 7% 8% 43%	2090
October	1st to 10th	Day	10% 9% 3 8% 5% 5% 5% 5% 8% 8% 34%	3271
	11th to 20th	Day	13% 11% 3 8% 5% 4 5% 4 5% 7% 35%	2873
	21st to end	Day	9% 14% 5% 10% 5% 5% 5% 4 5% 7% 31%	2989
November	1st to 10th	Day	10% 16% 4 9% 6% 4 5% 5% 6% 8% 26%	1563
	11th to 20th	Day	5% 14% 5% 13% 7% 6% 5% 4 6% 8% 28%	1400
	21st to end	Day	4 13% 5% 13% 10% 5% 5% 3 7% 6% 30%	1400
December	1st to 10th	Day	9% 12% 4 13% 7% 7% 7% 5% 7% 8% 21%	2290
	11th to 20th	Day	10% 15% 5% 9% 5% 6% 6% 4 7% 7% 27%	2642
	21st to end	Day	4 7% 4 11% 8% 7% 7% 5% 7% 7% 33%	3010
January	1st to 10th	Night	4 12% 6% 16% 9% 7% 7% 5% 5% 6% 23%	6980
	11th to 20th	Night	4 11% 4 8% 7% 6% 7% 5% 6% 7% 36%	6739
	21st to end	Night	6% 12% 5% 10% 7% 6% 5% 4 5% 7% 33%	7369
February	1st to 10th	Night	7% 11% 5% 11% 8% 6% 7% 5% 7% 8% 26%	2800
	11th to 20th	Night	7% 10% 4 11% 8% 7% 6% 5% 7% 6% 29%	2610
	21st to end	Night	3 10% 4 10% 7% 6% 7% 6% 8% 8% 31%	2118
March	1st to 10th	Night	4 9% 4 10% 6% 7% 7% 5% 7% 9% 32%	5376
	11th to 20th	Night	5% 10% 4 11% 6% 6% 5% 4 7% 9% 33%	5047
	21st to end	Night	11% 18% 7% 13% 5% 4 4 3 4 6% 25%	5406
April	1st to 10th	Night	8% 10% 3 7% 6% 6% 5% 4 7% 8% 34%	1880
	11th to 20th	Night	9% 11% 3 9% 6% 6% 7% 5% 6% 7% 31%	1781
	21st to end	Night	11% 12% 3 8% 5% 5% 5% 4 6% 7% 33%	1785
May	1st to 10th	Night	15% 6% 2 6% 4 4 5% 4 5% 8% 40%	3180
	11th to 20th	Night	16% 9% 3 9% 6% 6% 6% 5% 6% 6% 28%	3159
	21st to end	Night	12% 7% 3 6% 6% 5% 5% 5% 7% 9% 36%	3470
June	1st to 10th	Night	16% 6% 3 8% 6% 5% 6% 5% 5% 8% 31%	1335
	11th to 20th	Night	18% 9% 2 7% 5% 6% 5% 5% 7% 8% 28%	1200
	21st to end	Night	10% 6% 2 7% 5% 4 6% 4 8% 10% 37%	1200
July	1st to 10th	Night	8% 5% 2 6% 4 5% 5% 4 7% 9% 45%	1930
	11th to 20th	Night	7% 4 2 6% 4 5% 5% 5% 6% 10% 46%	2175
	21st to end	Night	14% 5% 2 3 4 4 4 3 7% 9% 45%	2414
August	1st to 10th	Night	9% 5% 2 7% 5% 5% 5% 4 5% 8% 44%	2303
	11th to 20th	Night	14% 7% 2 6% 4 4 4 4 5% 9% 41%	2643
	21st to end	Night	12% 5% 2 6% 4 5% 6% 4 7% 8% 41%	3146
September	1st to 10th	Night	12% 6% 3 5% 4 5% 5% 4 6% 8% 43%	1735
	11th to 20th	Night	12% 7% 3 6% 4 3 4 4 5% 8% 43%	2090
	21st to end	Night	10% 6% 2 6% 4 5% 5% 4 6% 8% 45%	2090
October	1st to 10th	Night	8% 8% 3 7% 5% 6% 5% 5% 8% 10% 36%	3701
	11th to 20th	Night	9% 8% 3 8% 5% 5% 6% 4 7% 9% 35%	4053
	21st to end	Night	9% 10% 4 8% 5% 5% 5% 5% 8% 8% 31%	4537
November	1st to 10th	Night	12% 14% 5% 11% 7% 5% 5% 3 5% 6% 27%	2731
	11th to 20th	Night	8% 14% 5% 12% 7% 6% 6% 5% 5% 7% 26%	3000
	21st to end	Night	6% 13% 5% 13% 9% 6% 5% 4 6% 8% 26%	3000
December	1st to 10th	Night	10% 14% 5% 13% 7% 7% 5% 5% 5% 7% 22%	4890
	11th to 20th	Night	8% 16% 5% 14% 7% 6% 6% 5% 7% 7% 19%	5550
	21st to end	Night	3 8% 4 11% 7% 7% 6% 5% 7% 8% 35%	7941

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	61% 5% 12% 13% 9%	2947
	11th to 20th	Day	49% 5% 15% 15% 15% 1	3180
	21st to end	Day	50% 5% 23% 16% 6%	3618
February	1st to 10th	Day	55% 7% 12% 16% 10%	1600
	11th to 20th	Day	53% 7% 15% 17% 8%	1684
	21st to end	Day	53% 8% 18% 15% 7%	1510
March	1st to 10th	Day	53% 4 16% 20% 7%	4518
	11th to 20th	Day	50% 5% 17% 23% 6%	4952
	21st to end	Day	60% 5% 10% 19% 6%	5568
April	1st to 10th	Day	49% 8% 16% 18% 8% 1	2520
	11th to 20th	Day	49% 6% 14% 21% 9% 1	2570
	21st to end	Day	52% 7% 13% 20% 7% 1	2611
May	1st to 10th	Day	44% 5% 9% 26% 15% 1	6780
	11th to 20th	Day	54% 5% 10% 24% 7%	6738
	21st to end	Day	43% 7% 18% 22% 9% 1	7406
June	1st to 10th	Day	49% 7% 15% 22% 8%	3060
	11th to 20th	Day	57% 8% 14% 17% 5%	3200
	21st to end	Day	44% 9% 20% 21% 7%	3200
July	1st to 10th	Day	36% 6% 22% 26% 9% 1	5062
	11th to 20th	Day	34% 7% 17% 31% 12%	4699
	21st to end	Day	39% 6% 22% 28% 5%	4976
August	1st to 10th	Day	41% 6% 20% 30% 2	4607
	11th to 20th	Day	38% 6% 24% 25% 8%	4232
	21st to end	Day	39% 5% 30% 22% 3	4520
September	1st to 10th	Day	41% 8% 19% 24% 7% 1	2442
	11th to 20th	Day	42% 8% 22% 22% 5%	2090
	21st to end	Day	38% 8% 20% 24% 9% 1	2090
October	1st to 10th	Day	46% 4 23% 23% 4	3271
	11th to 20th	Day	50% 4 18% 24% 5%	2873
	21st to end	Day	54% 4 18% 21% 3	2989
November	1st to 10th	Day	55% 8% 15% 17% 4	1563
	11th to 20th	Day	54% 7% 20% 15% 5%	1400
	21st to end	Day	54% 8% 15% 18% 4 1	1400
December	1st to 10th	Day	59% 6% 18% 12% 5%	2290
	11th to 20th	Day	56% 6% 20% 14% 4	2644
	21st to end	Day	48% 4 13% 26% 8% 1	3010
January	1st to 10th	Night	60% 5% 13% 13% 8% 1	6980
	11th to 20th	Night	46% 5% 14% 18% 16% 1	6780
	21st to end	Night	51% 5% 22% 17% 5%	7369
February	1st to 10th	Night	54% 7% 13% 16% 10% 1	2800
	11th to 20th	Night	54% 6% 12% 19% 9%	2612
	21st to end	Night	46% 9% 15% 21% 9%	2118
March	1st to 10th	Night	46% 5% 18% 23% 8%	5376
	11th to 20th	Night	46% 5% 17% 24% 8%	5047
	21st to end	Night	60% 6% 9% 15% 10%	5406
April	1st to 10th	Night	45% 6% 13% 21% 13% 1	1880
	11th to 20th	Night	50% 7% 10% 18% 13% 2	1781
	21st to end	Night	49% 6% 11% 22% 12% 1	1785
May	1st to 10th	Night	42% 5% 10% 22% 18% 3	3180
	11th to 20th	Night	55% 6% 11% 21% 8% 1	3159
	21st to end	Night	43% 7% 20% 22% 8% 1	3470
June	1st to 10th	Night	50% 6% 15% 19% 9% 1	1335
	11th to 20th	Night	52% 7% 15% 20% 6%	1200
	21st to end	Night	39% 8% 22% 23% 6% 1	1200
July	1st to 10th	Night	34% 7% 21% 25% 11% 1	1900
	11th to 20th	Night	33% 7% 16% 35% 10%	2135
	21st to end	Night	36% 5% 23% 29% 7%	2337
August	1st to 10th	Night	39% 6% 19% 34% 1	2296
	11th to 20th	Night	41% 5% 20% 23% 9%	2667
	21st to end	Night	40% 4 27% 24% 4	3146
September	1st to 10th	Night	38% 7% 21% 26% 6% 2	1735
	11th to 20th	Night	38% 6% 20% 28% 9%	2090
	21st to end	Night	36% 8% 17% 26% 11% 2	2090
October	1st to 10th	Night	43% 4 22% 24% 7%	3701
	11th to 20th	Night	45% 4 17% 30% 4	4053
	21st to end	Night	48% 4 22% 21% 5%	4537
November	1st to 10th	Night	58% 6% 12% 20% 5%	2731
	11th to 20th	Night	57% 8% 15% 15% 5%	3000
	21st to end	Night	56% 7% 17% 16% 4 1	3000
December	1st to 10th	Night	62% 6% 13% 14% 5%	4890
	11th to 20th	Night	63% 6% 16% 11% 3	5547
	21st to end	Night	46% 4 15% 23% 11% 1	7941

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	9% 5% 27% 37% 19% 4	200
	11th to 20th	Day	11% 7% 33% 30% 16% 5%	200
	21st to end	Day	10% 9% 39% 25% 13% 4	220
February	1st to 10th	Day	12% 8% 37% 29% 13% 4	200
	11th to 20th	Day	11% 7% 31% 32% 16% 4	260
	21st to end	Day	8% 7% 35% 32% 13% 5%	274
March	1st to 10th	Day	8% 9% 32% 32% 16% 3	500
	11th to 20th	Day	8% 9% 33% 30% 16% 4	500
	21st to end	Day	18% 5% 29% 28% 15% 4	550
April	1st to 10th	Day	9% 11% 34% 30% 11% 4	500
	11th to 20th	Day	15% 9% 28% 28% 15% 5%	492
	21st to end	Day	16% 9% 31% 29% 12% 2	506
May	1st to 10th	Day	13% 11% 24% 30% 18% 5%	703
	11th to 20th	Day	14% 7% 23% 31% 19% 6%	725
	21st to end	Day	16% 7% 19% 31% 20% 7%	789
June	1st to 10th	Day	19% 8% 25% 30% 14% 4	790
	11th to 20th	Day	21% 6% 18% 25% 23% 6%	930
	21st to end	Day	12% 3 18% 32% 25% 10%	930
July	1st to 10th	Day	12% 3 17% 33% 25% 9%	887
	11th to 20th	Day	14% 4 19% 30% 25% 8%	695
	21st to end	Day	11% 5% 19% 29% 26% 10%	739
August	1st to 10th	Day	14% 4 16% 28% 24% 15%	620
	11th to 20th	Day	10% 4 27% 30% 23% 6%	477
	21st to end	Day	11% 6% 22% 31% 23% 6%	539
September	1st to 10th	Day	17% 11% 25% 24% 17% 6%	490
	11th to 20th	Day	20% 7% 24% 30% 15% 4	490
	21st to end	Day	12% 11% 30% 28% 16% 4	490
October	1st to 10th	Day	14% 10% 30% 27% 15% 4	362
	11th to 20th	Day	16% 4 33% 31% 14% 2	300
	21st to end	Day	18% 12% 31% 24% 12% 4	330
November	1st to 10th	Day	19% 5% 29% 32% 14% 1	297
	11th to 20th	Day	11% 6% 41% 26% 14% 3	200
	21st to end	Day	9% 7% 40% 29% 12% 4	200
December	1st to 10th	Day	8% 8% 33% 32% 16% 5%	200
	11th to 20th	Day	13% 8% 32% 35% 10% 3	200
	21st to end	Day	9% 3 23% 36% 23% 6%	220
January	1st to 10th	Night	12% 6% 29% 37% 14% 1	1047
	11th to 20th	Night	11% 6% 33% 37% 12% 2	1000
	21st to end	Night	14% 7% 35% 32% 10% 2	1063
February	1st to 10th	Night	12% 7% 26% 34% 19% 2	800
	11th to 20th	Night	11% 3 27% 39% 18% 1	784
	21st to end	Night	6% 4 30% 38% 19% 4	660
March	1st to 10th	Night	9% 5% 27% 41% 15% 2	800
	11th to 20th	Night	12% 5% 27% 40% 15% 1	800
	21st to end	Night	15% 4 27% 35% 17% 2	880
April	1st to 10th	Night	11% 5% 25% 38% 18% 3	680
	11th to 20th	Night	12% 5% 27% 38% 16% 2	593
	21st to end	Night	15% 7% 21% 39% 17% 1	592
May	1st to 10th	Night	12% 7% 21% 39% 19% 3	400
	11th to 20th	Night	13% 5% 19% 40% 21% 3	394
	21st to end	Night	19% 4 18% 34% 23% 2	433
June	1st to 10th	Night	19% 5% 19% 39% 17% 2	400
	11th to 20th	Night	21% 5% 14% 36% 22% 3	400
	21st to end	Night	11% 4 13% 42% 27% 4	400
July	1st to 10th	Night	12% 2 17% 39% 29%	380
	11th to 20th	Night	12% 4 18% 41% 23% 2	368
	21st to end	Night	10% 3 14% 40% 30% 4	416
August	1st to 10th	Night	9% 3 15% 37% 31% 6%	378
	11th to 20th	Night	12% 2 19% 40% 26% 1	457
	21st to end	Night	14% 3 17% 43% 22% 1	627
September	1st to 10th	Night	16% 3 21% 36% 23% 2	589
	11th to 20th	Night	15% 3 17% 43% 20% 1	760
	21st to end	Night	12% 4 29% 37% 16% 1	760
October	1st to 10th	Night	16% 4 26% 37% 17% 1	760
	11th to 20th	Night	14% 4 30% 37% 12% 3	760
	21st to end	Night	16% 7% 30% 34% 11% 1	880
November	1st to 10th	Night	17% 5% 30% 35% 11% 2	975
	11th to 20th	Night	14% 7% 34% 32% 11% 3	1000
	21st to end	Night	12% 5% 36% 33% 12% 2	1000
December	1st to 10th	Night	13% 6% 33% 32% 12% 3	1000
	11th to 20th	Night	12% 7% 30% 36% 14% 2	1000
	21st to end	Night	9% 3 30% 36% 18% 3	1205

Page generated at 2025-07-02 23:30:16. Version ac07

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