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 2026-10-14.

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% 3 9% 6% 5% 5% 4 6% 8% 35%	154346
	Night	9% 10% 4 10% 6% 5% 5% 4 6% 7% 33%	146274
Transparency	Day	48% 3 14% 26% 9% 1	154043
	Night	51% 3 13% 23% 9% 1	146163
Seeing	Day	15% 9% 31% 29% 13% 4	19004
	Night	15% 7% 31% 33% 13% 1	28815

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	6% 15% 7% 15% 8% 7% 7% 5% 5% 5% 19%	4125
	11th to 20th	Day	5% 11% 5% 16% 10% 10% 10% 8% 8% 7% 11%	4119
	21st to end	Day	4 14% 6% 14% 9% 8% 8% 4 6% 8% 19%	5105
February	1st to 10th	Day	8% 12% 6% 12% 9% 7% 9% 5% 8% 6% 19%	1827
	11th to 20th	Day	7% 10% 4 9% 7% 9% 7% 7% 9% 7% 23%	1844
	21st to end	Day	5% 12% 4 13% 8% 9% 8% 5% 6% 6% 24%	1614
March	1st to 10th	Day	8% 13% 4 11% 9% 5% 5% 5% 5% 8% 27%	4752
	11th to 20th	Day	8% 10% 5% 14% 10% 7% 6% 4 5% 7% 24%	5088
	21st to end	Day	9% 13% 5% 12% 6% 5% 5% 4 5% 6% 30%	5585
April	1st to 10th	Day	10% 11% 4 9% 6% 4 4 4 6% 8% 35%	2553
	11th to 20th	Day	13% 10% 4 9% 6% 4 4 3 6% 6% 34%	2702
	21st to end	Day	15% 9% 3 7% 5% 4 5% 5% 6% 6% 35%	2730
May	1st to 10th	Day	11% 10% 3 6% 4 4 4 3 5% 6% 45%	7988
	11th to 20th	Day	19% 10% 3 7% 5% 4 4 4 5% 7% 32%	8537
	21st to end	Day	12% 6% 2 6% 4 4 4 3 5% 7% 46%	9683
June	1st to 10th	Day	14% 8% 3 7% 5% 6% 5% 4 6% 7% 35%	3150
	11th to 20th	Day	15% 7% 3 7% 5% 5% 5% 5% 6% 8% 36%	3150
	21st to end	Day	12% 6% 3 6% 6% 6% 5% 5% 8% 9% 34%	3150
July	1st to 10th	Day	8% 5% 2 6% 4 4 5% 5% 7% 10% 43%	8850
	11th to 20th	Day	12% 5% 2 5% 4 4 4 4 6% 9% 45%	8850
	21st to end	Day	8% 4 2 6% 4 4 5% 4 6% 9% 49%	9605
August	1st to 10th	Day	8% 4 1 6% 4 5% 5% 4 7% 10% 45%	6195
	11th to 20th	Day	12% 5% 2 7% 4 5% 5% 4 6% 9% 42%	5948
	21st to end	Day	12% 4 2 6% 4 4 5% 4 6% 9% 44%	6593
September	1st to 10th	Day	11% 5% 2 6% 4 4 4 4 6% 8% 46%	2613
	11th to 20th	Day	16% 7% 3 7% 4 4 5% 4 6% 8% 36%	2315
	21st to end	Day	16% 7% 3 6% 4 4 4 3 5% 7% 42%	2310
October	1st to 10th	Day	12% 7% 2 6% 4 4 5% 3 5% 7% 44%	3380
	11th to 20th	Day	13% 10% 3 7% 4 4 4 3 5% 7% 39%	3244
	21st to end	Day	15% 12% 3 9% 4 4 5% 4 6% 8% 30%	3190
November	1st to 10th	Day	16% 15% 4 9% 5% 3 6% 3 5% 6% 27%	1649
	11th to 20th	Day	10% 17% 6% 13% 8% 4 4 3 4 6% 25%	1680
	21st to end	Day	12% 14% 5% 14% 11% 6% 4 3 4 5% 21%	1578
December	1st to 10th	Day	11% 15% 6% 16% 9% 7% 7% 4 5% 6% 14%	2360
	11th to 20th	Day	9% 14% 6% 14% 7% 4 5% 4 7% 9% 20%	2709
	21st to end	Day	8% 15% 7% 19% 7% 8% 6% 5% 7% 5% 14%	3575
January	1st to 10th	Night	5% 13% 7% 16% 8% 8% 7% 5% 6% 6% 18%	8799
	11th to 20th	Night	5% 14% 6% 13% 10% 8% 10% 9% 7% 5% 13%	8809
	21st to end	Night	6% 14% 6% 11% 6% 6% 7% 5% 7% 9% 21%	9104
February	1st to 10th	Night	7% 14% 5% 11% 8% 6% 8% 5% 6% 6% 25%	2792
	11th to 20th	Night	6% 11% 3 8% 6% 7% 7% 6% 6% 7% 33%	2663
	21st to end	Night	6% 12% 5% 12% 7% 7% 6% 4 5% 7% 29%	2212
March	1st to 10th	Night	8% 12% 4 11% 7% 6% 5% 4 5% 6% 31%	5321
	11th to 20th	Night	6% 10% 4 9% 6% 5% 5% 4 6% 7% 38%	5090
	21st to end	Night	12% 12% 4 9% 6% 4 4 3 6% 6% 34%	5588
April	1st to 10th	Night	12% 9% 3 6% 4 5% 5% 4 6% 7% 40%	2065
	11th to 20th	Night	13% 12% 4 7% 4 4 4 3 6% 5% 38%	1869
	21st to end	Night	12% 9% 3 8% 6% 6% 5% 4 5% 6% 37%	1890
May	1st to 10th	Night	11% 7% 3 6% 3 4 4 4 6% 7% 45%	4959
	11th to 20th	Night	16% 7% 2 5% 4 4 4 4 6% 7% 40%	4339
	21st to end	Night	12% 6% 2 6% 3 4 3 3 5% 7% 49%	4523
June	1st to 10th	Night	12% 6% 2 6% 5% 4 5% 4 6% 8% 42%	1470
	11th to 20th	Night	13% 7% 2 6% 5% 4 5% 3 7% 8% 42%	1470
	21st to end	Night	11% 7% 1 6% 4 4 6% 4 6% 7% 42%	1470
July	1st to 10th	Night	7% 4 2 5% 4 4 5% 5% 7% 8% 50%	4140
	11th to 20th	Night	9% 4 1 5% 3 4 4 4 7% 10% 49%	4140
	21st to end	Night	5% 4 1 5% 4 4 5% 4 7% 9% 50%	4497
August	1st to 10th	Night	7% 4 1 5% 4 4 5% 4 6% 8% 51%	3971
	11th to 20th	Night	10% 4 2 6% 4 4 5% 4 6% 8% 48%	4118
	21st to end	Night	11% 4 2 6% 4 4 5% 4 5% 7% 48%	4555
September	1st to 10th	Night	10% 4 1 5% 4 4 4 3 5% 8% 51%	2006
	11th to 20th	Night	15% 6% 2 6% 4 4 4 4 5% 7% 42%	2303
	21st to end	Night	16% 6% 2 5% 5% 4 4 4 4 6% 43%	2310
October	1st to 10th	Night	15% 7% 2 5% 4 3 3 3 4 7% 47%	3972
	11th to 20th	Night	11% 11% 3 8% 4 5% 4 4 5% 6% 39%	3958
	21st to end	Night	11% 10% 3 8% 5% 5% 5% 3 6% 6% 37%	4610
November	1st to 10th	Night	13% 14% 5% 10% 6% 5% 5% 4 5% 5% 29%	2868
	11th to 20th	Night	12% 16% 6% 11% 7% 5% 4 4 5% 5% 26%	2940
	21st to end	Night	11% 14% 6% 15% 8% 6% 6% 3 4 5% 22%	3040
December	1st to 10th	Night	9% 17% 6% 18% 12% 7% 5% 3 4 4 13%	5050
	11th to 20th	Night	8% 13% 6% 14% 6% 5% 6% 5% 7% 7% 22%	5718
	21st to end	Night	8% 12% 6% 19% 9% 8% 6% 4 5% 5% 18%	7645

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	69% 2 7% 16% 6%	4125
	11th to 20th	Day	71% 3 8% 15% 4	4140
	21st to end	Day	65% 2 7% 21% 5%	5105
February	1st to 10th	Day	62% 5% 12% 14% 7% 1	1827
	11th to 20th	Day	54% 4 13% 22% 7%	1853
	21st to end	Day	59% 5% 12% 15% 9%	1614
March	1st to 10th	Day	56% 3 14% 16% 10% 1	4752
	11th to 20th	Day	59% 4 13% 17% 7%	5090
	21st to end	Day	55% 3 10% 23% 8% 1	5585
April	1st to 10th	Day	48% 3 11% 25% 12%	2553
	11th to 20th	Day	49% 4 12% 22% 12% 1	2702
	21st to end	Day	49% 4 14% 24% 8% 1	2730
May	1st to 10th	Day	41% 2 10% 30% 16%	7988
	11th to 20th	Day	52% 2 8% 27% 10% 1	8541
	21st to end	Day	39% 3 8% 26% 21% 3	9683
June	1st to 10th	Day	47% 4 13% 24% 11% 1	3150
	11th to 20th	Day	46% 4 15% 24% 10% 1	3150
	21st to end	Day	45% 5% 19% 22% 8%	3150
July	1st to 10th	Day	37% 3 23% 31% 6%	8776
	11th to 20th	Day	37% 2 18% 36% 6%	8769
	21st to end	Day	34% 2 19% 36% 9%	9398
August	1st to 10th	Day	34% 3 21% 34% 8%	6179
	11th to 20th	Day	41% 3 24% 28% 4	5987
	21st to end	Day	39% 2 22% 32% 5%	6592
September	1st to 10th	Day	36% 5% 18% 31% 8% 1	2613
	11th to 20th	Day	47% 5% 19% 25% 4	2315
	21st to end	Day	43% 4 14% 31% 7%	2310
October	1st to 10th	Day	42% 3 15% 31% 8%	3380
	11th to 20th	Day	46% 3 11% 26% 14%	3244
	21st to end	Day	52% 3 18% 22% 5%	3190
November	1st to 10th	Day	59% 4 15% 17% 4 1	1649
	11th to 20th	Day	61% 6% 15% 14% 5%	1680
	21st to end	Day	67% 4 14% 13% 2	1578
December	1st to 10th	Day	72% 5% 10% 7% 5%	2360
	11th to 20th	Day	59% 3 13% 16% 8%	2710
	21st to end	Day	70% 3 8% 16% 3	3575
January	1st to 10th	Night	67% 2 11% 14% 7%	8800
	11th to 20th	Night	71% 2 6% 16% 4	8850
	21st to end	Night	59% 2 11% 21% 7%	9104
February	1st to 10th	Night	57% 6% 12% 17% 9%	2792
	11th to 20th	Night	48% 4 15% 24% 9%	2664
	21st to end	Night	55% 4 11% 19% 11%	2212
March	1st to 10th	Night	54% 3 13% 16% 10% 4	5321
	11th to 20th	Night	45% 3 15% 25% 12% 1	5090
	21st to end	Night	52% 2 8% 24% 12% 1	5588
April	1st to 10th	Night	43% 3 11% 25% 16% 2	2065
	11th to 20th	Night	48% 3 9% 22% 15% 2	1869
	21st to end	Night	48% 4 9% 27% 12% 1	1890
May	1st to 10th	Night	39% 2 8% 33% 17%	4959
	11th to 20th	Night	44% 2 9% 30% 13% 2	4339
	21st to end	Night	37% 2 8% 25% 25% 4	4526
June	1st to 10th	Night	39% 7% 16% 24% 13% 1	1470
	11th to 20th	Night	40% 5% 15% 25% 14% 2	1470
	21st to end	Night	39% 6% 20% 26% 8% 1	1470
July	1st to 10th	Night	33% 4 23% 32% 7% 1	4105
	11th to 20th	Night	32% 3 17% 39% 8% 1	4098
	21st to end	Night	31% 2 20% 34% 12%	4399
August	1st to 10th	Night	31% 3 17% 40% 9%	3964
	11th to 20th	Night	35% 2 27% 30% 6%	4145
	21st to end	Night	37% 2 19% 35% 6%	4555
September	1st to 10th	Night	34% 3 19% 32% 12%	2006
	11th to 20th	Night	42% 4 18% 25% 9% 1	2303
	21st to end	Night	43% 4 13% 30% 10% 1	2310
October	1st to 10th	Night	39% 3 12% 33% 12% 1	3972
	11th to 20th	Night	47% 3 13% 29% 9%	3958
	21st to end	Night	49% 3 15% 28% 5%	4610
November	1st to 10th	Night	58% 4 15% 16% 6% 1	2868
	11th to 20th	Night	61% 5% 15% 14% 5%	2940
	21st to end	Night	66% 5% 14% 11% 4	3040
December	1st to 10th	Night	75% 3 11% 8% 3	5050
	11th to 20th	Night	60% 4 12% 13% 11%	5716
	21st to end	Night	68% 3 8% 16% 4	7645

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	12% 5% 35% 31% 15% 3	330
	11th to 20th	Day	10% 7% 32% 38% 12% 2	330
	21st to end	Day	13% 8% 32% 31% 11% 4	363
February	1st to 10th	Day	14% 11% 34% 31% 9% 2	330
	11th to 20th	Day	11% 8% 32% 31% 13% 5%	330
	21st to end	Day	10% 5% 43% 30% 11% 1	273
March	1st to 10th	Day	12% 10% 36% 28% 13% 1	330
	11th to 20th	Day	12% 11% 35% 26% 14% 2	330
	21st to end	Day	14% 9% 34% 28% 13% 2	363
April	1st to 10th	Day	15% 6% 32% 33% 10% 4	573
	11th to 20th	Day	18% 12% 31% 26% 12% 1	740
	21st to end	Day	17% 9% 33% 27% 12% 2	750
May	1st to 10th	Day	16% 14% 29% 27% 12% 2	753
	11th to 20th	Day	22% 11% 26% 26% 12% 2	775
	21st to end	Day	19% 9% 23% 30% 15% 4	844
June	1st to 10th	Day	17% 12% 28% 26% 11% 6%	780
	11th to 20th	Day	16% 10% 33% 29% 10% 3	780
	21st to end	Day	13% 8% 29% 28% 17% 4	780
July	1st to 10th	Day	8% 5% 30% 28% 19% 9%	771
	11th to 20th	Day	12% 8% 32% 28% 16% 5%	768
	21st to end	Day	7% 5% 31% 32% 18% 7%	849
August	1st to 10th	Day	8% 7% 27% 31% 21% 6%	776
	11th to 20th	Day	11% 5% 25% 33% 18% 8%	765
	21st to end	Day	13% 7% 29% 29% 18% 4	858
September	1st to 10th	Day	12% 7% 31% 32% 16% 3	663
	11th to 20th	Day	17% 10% 36% 27% 8% 2	365
	21st to end	Day	21% 8% 29% 29% 10% 2	360
October	1st to 10th	Day	17% 13% 27% 33% 8% 4	360
	11th to 20th	Day	20% 9% 34% 29% 7% 1	339
	21st to end	Day	26% 9% 30% 23% 10% 2	363
November	1st to 10th	Day	24% 9% 29% 27% 10% 2	330
	11th to 20th	Day	18% 10% 39% 23% 9% 2	330
	21st to end	Day	16% 12% 35% 30% 6%	330
December	1st to 10th	Day	16% 6% 33% 29% 13% 2	330
	11th to 20th	Day	15% 8% 42% 25% 9% 1	330
	21st to end	Day	13% 8% 31% 29% 15% 4	363
January	1st to 10th	Night	13% 7% 32% 32% 14% 3	1050
	11th to 20th	Night	16% 7% 31% 34% 11% 1	1050
	21st to end	Night	14% 8% 33% 33% 12% 1	1155
February	1st to 10th	Night	14% 8% 28% 35% 14% 1	1050
	11th to 20th	Night	11% 5% 30% 37% 14% 3	1029
	21st to end	Night	11% 7% 35% 32% 14% 2	828
March	1st to 10th	Night	14% 8% 31% 31% 14% 2	771
	11th to 20th	Night	12% 7% 39% 30% 12% 1	630
	21st to end	Night	19% 7% 28% 30% 14% 2	693
April	1st to 10th	Night	16% 6% 28% 36% 12% 1	630
	11th to 20th	Night	18% 6% 30% 34% 12%	623
	21st to end	Night	16% 8% 30% 34% 11% 1	630
May	1st to 10th	Night	18% 6% 35% 30% 10%	630
	11th to 20th	Night	18% 8% 30% 32% 12% 1	621
	21st to end	Night	18% 6% 31% 33% 11%	683
June	1st to 10th	Night	14% 6% 30% 34% 15%	630
	11th to 20th	Night	15% 5% 31% 35% 14%	630
	21st to end	Night	13% 5% 22% 40% 19% 1	630
July	1st to 10th	Night	6% 4 25% 40% 23% 1	615
	11th to 20th	Night	9% 5% 25% 41% 19% 2	612
	21st to end	Night	8% 2 23% 43% 20% 3	690
August	1st to 10th	Night	8% 3 21% 46% 20% 1	627
	11th to 20th	Night	11% 4 21% 40% 23% 2	624
	21st to end	Night	12% 5% 24% 40% 19% 1	693
September	1st to 10th	Night	12% 4 29% 36% 17% 2	630
	11th to 20th	Night	17% 5% 27% 39% 12%	630
	21st to end	Night	18% 7% 31% 30% 12% 1	630
October	1st to 10th	Night	19% 8% 34% 31% 8%	798
	11th to 20th	Night	21% 8% 33% 29% 8% 1	823
	21st to end	Night	23% 8% 29% 30% 8% 1	1100
November	1st to 10th	Night	19% 9% 35% 27% 10%	1025
	11th to 20th	Night	21% 8% 32% 28% 9% 2	1050
	21st to end	Night	19% 8% 39% 26% 6% 1	1050
December	1st to 10th	Night	13% 6% 32% 36% 12% 2	1050
	11th to 20th	Night	16% 8% 35% 30% 9% 1	1050
	21st to end	Night	18% 8% 30% 30% 13% 1	1155

Page generated at 2026-10-11 04:06:29. Version ac07

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