Anola
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Anola clear sky chart from 2005-11-06 to 2025-06-10.

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	11% 9% 4 9% 6% 5% 5% 4 6% 7% 34%	123335
	Night	9% 11% 4 10% 6% 5% 5% 4 6% 7% 32%	123621
Transparency	Day	49% 4 14% 24% 9% 1	123077
	Night	52% 3 13% 22% 9% 1	123527
Seeing	Day	14% 9% 31% 29% 14% 4	17041
	Night	15% 7% 30% 33% 13% 1	27046

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% 16% 6% 15% 8% 7% 7% 6% 5% 6% 18%	3179
	11th to 20th	Day	5% 11% 6% 16% 10% 11% 9% 8% 8% 7% 10%	3159
	21st to end	Day	5% 17% 7% 17% 10% 7% 8% 4 6% 5% 13%	3935
February	1st to 10th	Day	8% 12% 6% 12% 8% 7% 9% 5% 8% 6% 19%	1740
	11th to 20th	Day	7% 10% 4 9% 7% 10% 8% 6% 8% 7% 24%	1754
	21st to end	Day	5% 12% 5% 13% 8% 9% 8% 4 6% 6% 25%	1539
March	1st to 10th	Day	8% 12% 4 11% 9% 5% 5% 5% 5% 8% 27%	4649
	11th to 20th	Day	8% 10% 5% 14% 11% 7% 6% 4 5% 7% 23%	4978
	21st to end	Day	9% 13% 5% 12% 6% 5% 5% 4 5% 6% 30%	5464
April	1st to 10th	Day	10% 11% 4 9% 5% 4 4 4 6% 7% 35%	2432
	11th to 20th	Day	13% 10% 4 9% 6% 4 4 3 6% 7% 35%	2572
	21st to end	Day	16% 9% 3 7% 5% 4 5% 5% 5% 6% 35%	2600
May	1st to 10th	Day	12% 8% 2 5% 4 4 4 3 5% 6% 46%	6165
	11th to 20th	Day	19% 9% 2 7% 5% 4 4 4 6% 8% 33%	6569
	21st to end	Day	14% 7% 3 6% 4 4 4 3 5% 6% 46%	7428
June	1st to 10th	Day	14% 8% 3 7% 5% 6% 5% 4 6% 8% 35%	2987
	11th to 20th	Day	16% 7% 3 7% 5% 5% 4 5% 6% 8% 35%	2850
	21st to end	Day	12% 6% 3 7% 6% 6% 5% 5% 8% 9% 35%	2850
July	1st to 10th	Day	9% 4 2 5% 5% 5% 6% 5% 7% 10% 41%	4750
	11th to 20th	Day	9% 4 2 5% 4 3 4 4 7% 9% 51%	4750
	21st to end	Day	7% 4 2 5% 5% 4 5% 4 6% 9% 51%	5150
August	1st to 10th	Day	8% 5% 2 6% 4 4 5% 4 6% 9% 46%	4229
	11th to 20th	Day	11% 5% 2 6% 4 5% 4 4 5% 8% 46%	4041
	21st to end	Day	14% 5% 2 5% 4 4 5% 4 5% 9% 44%	4532
September	1st to 10th	Day	10% 5% 2 6% 4 4 4 4 6% 8% 48%	2365
	11th to 20th	Day	14% 7% 3 6% 4 4 4 4 6% 8% 38%	2095
	21st to end	Day	16% 7% 3 6% 4 4 4 3 5% 7% 41%	2090
October	1st to 10th	Day	12% 8% 2 7% 4 4 5% 3 5% 7% 43%	3178
	11th to 20th	Day	12% 10% 3 7% 4 4 4 3 5% 7% 40%	3115
	21st to end	Day	15% 12% 3 9% 4 4 5% 4 6% 8% 30%	3091
November	1st to 10th	Day	16% 15% 4 9% 5% 3 6% 3 5% 6% 27%	1569
	11th to 20th	Day	10% 18% 6% 13% 8% 4 4 4 4 6% 23%	1600
	21st to end	Day	12% 14% 5% 14% 11% 6% 5% 3 3 6% 21%	1503
December	1st to 10th	Day	10% 15% 6% 16% 9% 7% 7% 4 5% 6% 14%	2290
	11th to 20th	Day	9% 14% 6% 14% 7% 4 5% 5% 7% 10% 21%	2639
	21st to end	Day	8% 15% 7% 19% 7% 8% 6% 5% 7% 5% 14%	3498
January	1st to 10th	Night	4 13% 7% 15% 8% 9% 8% 5% 6% 7% 18%	6787
	11th to 20th	Night	5% 14% 6% 13% 10% 9% 9% 9% 8% 5% 11%	6759
	21st to end	Night	8% 19% 8% 14% 7% 6% 5% 4 6% 6% 18%	7038
February	1st to 10th	Night	7% 13% 5% 11% 8% 6% 8% 5% 6% 6% 25%	2659
	11th to 20th	Night	6% 10% 2 8% 6% 7% 7% 6% 6% 7% 33%	2533
	21st to end	Night	6% 11% 5% 13% 7% 7% 5% 4 5% 7% 29%	2110
March	1st to 10th	Night	8% 12% 4 11% 7% 6% 5% 4 5% 6% 31%	5204
	11th to 20th	Night	6% 10% 4 9% 6% 5% 5% 4 6% 7% 38%	4980
	21st to end	Night	12% 12% 4 9% 6% 4 4 3 6% 6% 34%	5467
April	1st to 10th	Night	12% 9% 3 6% 4 5% 5% 4 6% 7% 40%	1966
	11th to 20th	Night	13% 12% 4 7% 4 4 4 3 6% 5% 37%	1779
	21st to end	Night	12% 9% 3 8% 6% 6% 5% 4 5% 6% 37%	1800
May	1st to 10th	Night	13% 8% 3 7% 3 3 4 3 5% 6% 44%	3814
	11th to 20th	Night	16% 7% 2 5% 4 4 5% 4 7% 8% 37%	3343
	21st to end	Night	13% 7% 2 5% 3 3 3 3 5% 6% 50%	3470
June	1st to 10th	Night	12% 6% 2 6% 5% 4 5% 4 6% 8% 42%	1397
	11th to 20th	Night	13% 7% 2 6% 5% 3 5% 3 7% 7% 42%	1330
	21st to end	Night	10% 7% 1 6% 4 4 5% 4 6% 8% 44%	1330
July	1st to 10th	Night	8% 3 1 4 3 4 4 5% 7% 9% 51%	2220
	11th to 20th	Night	6% 3 1 3 3 3 4 4 7% 10% 56%	2220
	21st to end	Night	5% 3 1 4 4 4 5% 4 8% 10% 51%	2414
August	1st to 10th	Night	7% 5% 1 6% 4 4 5% 5% 6% 8% 49%	2707
	11th to 20th	Night	9% 4 2 5% 4 4 4 4 6% 8% 51%	2798
	21st to end	Night	10% 4 2 6% 4 4 5% 4 6% 7% 47%	3135
September	1st to 10th	Night	10% 4 1 5% 4 4 4 3 5% 7% 53%	1814
	11th to 20th	Night	14% 6% 2 6% 4 4 5% 4 5% 7% 43%	2083
	21st to end	Night	16% 6% 2 6% 5% 5% 4 4 5% 7% 41%	2090
October	1st to 10th	Night	15% 7% 2 5% 4 3 3 3 4 7% 46%	3736
	11th to 20th	Night	10% 11% 3 8% 4 5% 4 4 5% 6% 40%	3800
	21st to end	Night	11% 10% 3 8% 5% 5% 5% 3 6% 7% 37%	4467
November	1st to 10th	Night	14% 14% 5% 10% 6% 5% 5% 4 5% 5% 29%	2728
	11th to 20th	Night	12% 16% 6% 11% 7% 5% 4 4 5% 5% 25%	2800
	21st to end	Night	12% 14% 6% 15% 8% 6% 6% 3 4 5% 22%	2895
December	1st to 10th	Night	9% 18% 6% 18% 12% 7% 5% 3 4 4 13%	4900
	11th to 20th	Night	8% 14% 6% 14% 6% 5% 5% 5% 7% 7% 22%	5568
	21st to end	Night	8% 12% 6% 19% 9% 7% 6% 4 5% 5% 18%	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	67% 2 9% 16% 6%	3179
	11th to 20th	Day	70% 3 7% 16% 4	3180
	21st to end	Day	74% 2 9% 12% 3	3935
February	1st to 10th	Day	61% 5% 12% 14% 8% 1	1740
	11th to 20th	Day	54% 4 13% 21% 7%	1763
	21st to end	Day	58% 5% 12% 16% 8% 1	1539
March	1st to 10th	Day	56% 3 14% 16% 10% 1	4649
	11th to 20th	Day	59% 4 13% 17% 7%	4980
	21st to end	Day	55% 3 10% 23% 8% 1	5464
April	1st to 10th	Day	48% 4 11% 25% 12%	2432
	11th to 20th	Day	48% 4 11% 23% 12% 1	2572
	21st to end	Day	49% 4 14% 24% 9% 1	2600
May	1st to 10th	Day	39% 3 11% 28% 19% 1	6165
	11th to 20th	Day	50% 2 9% 27% 11% 1	6573
	21st to end	Day	40% 3 8% 24% 21% 4	7428
June	1st to 10th	Day	47% 5% 13% 24% 11% 1	2987
	11th to 20th	Day	47% 5% 15% 23% 10% 1	2850
	21st to end	Day	44% 5% 19% 23% 8%	2850
July	1st to 10th	Day	37% 5% 23% 28% 7%	4676
	11th to 20th	Day	30% 3 21% 38% 7%	4669
	21st to end	Day	32% 3 20% 37% 8%	4988
August	1st to 10th	Day	35% 3 19% 34% 9%	4213
	11th to 20th	Day	38% 3 22% 32% 5%	4080
	21st to end	Day	40% 3 22% 30% 6%	4531
September	1st to 10th	Day	34% 5% 18% 32% 9% 1	2365
	11th to 20th	Day	44% 5% 20% 26% 4	2095
	21st to end	Day	44% 4 15% 31% 7%	2090
October	1st to 10th	Day	43% 3 15% 31% 8%	3178
	11th to 20th	Day	45% 3 11% 27% 14%	3115
	21st to end	Day	52% 3 18% 22% 5%	3091
November	1st to 10th	Day	59% 4 16% 17% 3 1	1569
	11th to 20th	Day	62% 6% 14% 14% 4	1600
	21st to end	Day	68% 4 14% 13% 2	1503
December	1st to 10th	Day	72% 5% 10% 7% 5%	2290
	11th to 20th	Day	59% 3 14% 17% 8%	2640
	21st to end	Day	70% 3 8% 16% 3	3498
January	1st to 10th	Night	66% 2 11% 13% 8%	6787
	11th to 20th	Night	71% 3 6% 16% 4	6800
	21st to end	Night	66% 3 12% 15% 4	7038
February	1st to 10th	Night	57% 6% 12% 16% 9%	2659
	11th to 20th	Night	48% 4 15% 24% 9%	2534
	21st to end	Night	55% 4 12% 19% 10%	2110
March	1st to 10th	Night	54% 3 13% 16% 10% 4	5204
	11th to 20th	Night	45% 3 15% 25% 12%	4980
	21st to end	Night	52% 2 8% 25% 12% 1	5467
April	1st to 10th	Night	42% 4 11% 26% 16% 2	1966
	11th to 20th	Night	48% 3 8% 23% 16% 3	1779
	21st to end	Night	48% 4 9% 26% 12% 1	1800
May	1st to 10th	Night	41% 3 9% 27% 20%	3814
	11th to 20th	Night	45% 2 10% 29% 12% 2	3343
	21st to end	Night	37% 3 8% 25% 23% 5%	3470
June	1st to 10th	Night	38% 7% 17% 24% 13% 1	1397
	11th to 20th	Night	40% 5% 15% 23% 14% 2	1330
	21st to end	Night	37% 6% 20% 27% 8% 1	1330
July	1st to 10th	Night	29% 6% 23% 34% 8% 1	2185
	11th to 20th	Night	24% 4 23% 40% 9% 1	2178
	21st to end	Night	28% 2 23% 37% 8% 1	2337
August	1st to 10th	Night	32% 3 16% 36% 12% 1	2700
	11th to 20th	Night	32% 3 26% 31% 8%	2825
	21st to end	Night	37% 2 20% 32% 9%	3135
September	1st to 10th	Night	33% 3 18% 32% 13%	1814
	11th to 20th	Night	41% 4 18% 26% 10% 1	2083
	21st to end	Night	44% 4 13% 29% 9% 1	2090
October	1st to 10th	Night	39% 3 12% 34% 12%	3736
	11th to 20th	Night	45% 3 13% 30% 9%	3800
	21st to end	Night	48% 3 14% 29% 5%	4467
November	1st to 10th	Night	58% 4 16% 16% 6% 1	2728
	11th to 20th	Night	62% 5% 14% 14% 4	2800
	21st to end	Night	66% 5% 14% 11% 4	2895
December	1st to 10th	Night	76% 3 11% 8% 2	4900
	11th to 20th	Night	60% 4 12% 13% 11%	5566
	21st to end	Night	68% 3 8% 16% 5%	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	11% 4 34% 32% 16% 3	300
	11th to 20th	Day	10% 7% 30% 38% 13% 2	300
	21st to end	Day	14% 9% 31% 30% 11% 5%	330
February	1st to 10th	Day	14% 10% 32% 33% 9% 2	300
	11th to 20th	Day	11% 8% 34% 30% 13% 5%	300
	21st to end	Day	9% 6% 44% 30% 10% 1	249
March	1st to 10th	Day	11% 9% 34% 31% 14% 1	300
	11th to 20th	Day	12% 11% 34% 27% 15% 2	300
	21st to end	Day	13% 8% 34% 29% 14% 2	330
April	1st to 10th	Day	14% 7% 31% 33% 11% 4	532
	11th to 20th	Day	17% 12% 31% 26% 13% 1	690
	21st to end	Day	18% 9% 32% 27% 12% 2	700
May	1st to 10th	Day	15% 14% 30% 27% 12% 2	703
	11th to 20th	Day	21% 11% 26% 26% 13% 2	725
	21st to end	Day	19% 9% 23% 30% 15% 3	789
June	1st to 10th	Day	17% 12% 28% 26% 11% 6%	726
	11th to 20th	Day	18% 10% 33% 28% 9% 3	680
	21st to end	Day	12% 8% 28% 30% 18% 5%	680
July	1st to 10th	Day	8% 6% 31% 27% 20% 9%	671
	11th to 20th	Day	11% 7% 31% 28% 18% 5%	668
	21st to end	Day	7% 5% 31% 30% 19% 8%	739
August	1st to 10th	Day	8% 7% 26% 32% 21% 6%	676
	11th to 20th	Day	10% 6% 23% 34% 18% 9%	665
	21st to end	Day	14% 7% 30% 28% 17% 4	748
September	1st to 10th	Day	10% 6% 31% 34% 16% 2	575
	11th to 20th	Day	15% 10% 37% 26% 8% 3	305
	21st to end	Day	21% 9% 30% 29% 10% 1	300
October	1st to 10th	Day	19% 13% 24% 32% 8% 4	300
	11th to 20th	Day	16% 9% 35% 32% 8% 1	300
	21st to end	Day	26% 9% 31% 22% 10% 2	330
November	1st to 10th	Day	23% 8% 28% 29% 11% 2	300
	11th to 20th	Day	18% 9% 40% 22% 9% 2	300
	21st to end	Day	17% 13% 34% 30% 6%	300
December	1st to 10th	Day	15% 6% 32% 31% 13% 2	300
	11th to 20th	Day	15% 7% 42% 26% 9% 1	300
	21st to end	Day	12% 7% 30% 30% 15% 5%	330
January	1st to 10th	Night	13% 7% 32% 32% 14% 3	1000
	11th to 20th	Night	16% 7% 30% 35% 11% 1	1000
	21st to end	Night	15% 8% 32% 33% 11% 1	1100
February	1st to 10th	Night	14% 7% 27% 36% 14% 1	1000
	11th to 20th	Night	11% 5% 30% 36% 15% 3	979
	21st to end	Night	11% 7% 35% 32% 14% 2	790
March	1st to 10th	Night	14% 7% 31% 31% 14% 2	734
	11th to 20th	Night	12% 7% 38% 30% 12% 1	600
	21st to end	Night	19% 7% 27% 30% 15% 2	660
April	1st to 10th	Night	15% 6% 29% 37% 12% 1	600
	11th to 20th	Night	18% 6% 30% 34% 12% 1	593
	21st to end	Night	16% 8% 31% 34% 11% 1	600
May	1st to 10th	Night	19% 6% 36% 30% 10% 1	600
	11th to 20th	Night	18% 7% 30% 31% 13% 1	591
	21st to end	Night	18% 6% 31% 33% 12%	650
June	1st to 10th	Night	13% 6% 30% 35% 16%	599
	11th to 20th	Night	15% 6% 32% 33% 14%	570
	21st to end	Night	13% 5% 21% 40% 20% 1	570
July	1st to 10th	Night	6% 4 25% 40% 23% 2	555
	11th to 20th	Night	9% 5% 25% 40% 20% 2	552
	21st to end	Night	8% 3 23% 42% 22% 3	624
August	1st to 10th	Night	8% 3 21% 45% 21% 1	567
	11th to 20th	Night	10% 4 21% 38% 23% 3	564
	21st to end	Night	12% 5% 24% 41% 18% 1	627
September	1st to 10th	Night	12% 4 29% 36% 17% 2	570
	11th to 20th	Night	16% 5% 27% 39% 13%	570
	21st to end	Night	18% 7% 32% 31% 12% 1	570
October	1st to 10th	Night	21% 7% 32% 31% 8%	722
	11th to 20th	Night	19% 8% 34% 29% 8% 1	769
	21st to end	Night	22% 8% 30% 30% 9% 1	1045
November	1st to 10th	Night	19% 8% 35% 27% 10%	975
	11th to 20th	Night	21% 8% 32% 29% 9% 2	1000
	21st to end	Night	19% 8% 39% 26% 7% 1	1000
December	1st to 10th	Night	13% 6% 32% 36% 12% 2	1000
	11th to 20th	Night	16% 8% 35% 31% 9% 1	1000
	21st to end	Night	18% 7% 30% 30% 13% 1	1100

Page generated at 2025-06-07 09:28:15. Version ac07

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