Fisher Branch
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fisher Branch clear sky chart from 2005-11-06 to 2026-06-16.

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% 8% 3 9% 6% 5% 5% 4 6% 8% 35%	141970
	Night	9% 10% 4 10% 6% 5% 5% 4 6% 7% 33%	138918
Transparency	Day	47% 4 14% 25% 9% 1	141666
	Night	49% 4 13% 23% 10% 1	138807
Seeing	Day	15% 9% 30% 28% 15% 4	18527
	Night	15% 6% 30% 34% 14% 2	28510

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% 14% 7% 13% 6% 7% 8% 6% 8% 6% 19%	4125
	11th to 20th	Day	5% 9% 4 15% 9% 8% 9% 10% 9% 9% 13%	4119
	21st to end	Day	4 10% 6% 12% 7% 7% 9% 6% 7% 9% 24%	5085
February	1st to 10th	Day	8% 13% 5% 14% 9% 8% 6% 6% 6% 7% 19%	1733
	11th to 20th	Day	7% 11% 4 9% 5% 7% 8% 6% 7% 8% 29%	1844
	21st to end	Day	6% 12% 4 10% 8% 7% 6% 6% 6% 7% 28%	1640
March	1st to 10th	Day	8% 10% 4 12% 8% 5% 6% 5% 6% 10% 27%	4658
	11th to 20th	Day	7% 11% 4 13% 8% 6% 6% 4 6% 7% 28%	5088
	21st to end	Day	8% 9% 4 10% 6% 5% 5% 4 5% 7% 37%	5585
April	1st to 10th	Day	9% 10% 3 9% 6% 5% 5% 3 5% 8% 36%	2595
	11th to 20th	Day	12% 9% 4 9% 6% 5% 5% 4 6% 6% 34%	2702
	21st to end	Day	12% 8% 3 7% 5% 5% 5% 4 6% 8% 36%	2730
May	1st to 10th	Day	10% 9% 4 6% 4 4 4 3 5% 7% 44%	8056
	11th to 20th	Day	19% 10% 3 7% 5% 5% 4 4 5% 7% 31%	8786
	21st to end	Day	13% 5% 2 5% 4 4 4 3 6% 7% 47%	9683
June	1st to 10th	Day	16% 8% 2 7% 4 4 5% 5% 6% 7% 35%	3150
	11th to 20th	Day	15% 7% 2 7% 6% 5% 5% 5% 7% 8% 34%	3076
	21st to end	Day	13% 6% 2 6% 6% 5% 5% 5% 7% 8% 36%	3000
July	1st to 10th	Day	9% 5% 2 6% 5% 5% 6% 5% 7% 8% 41%	6800
	11th to 20th	Day	9% 5% 2 6% 4 5% 6% 4 6% 10% 44%	6800
	21st to end	Day	7% 5% 2 6% 3 4 5% 4 6% 10% 48%	7400
August	1st to 10th	Day	7% 4 1 6% 5% 5% 6% 4 8% 10% 43%	4507
	11th to 20th	Day	11% 5% 2 6% 5% 4 5% 4 5% 9% 44%	4171
	21st to end	Day	14% 5% 2 6% 4 4 4 4 6% 9% 42%	4675
September	1st to 10th	Day	11% 6% 2 6% 4 4 5% 4 6% 7% 45%	2502
	11th to 20th	Day	16% 7% 4 8% 5% 5% 4 4 6% 8% 34%	2200
	21st to end	Day	12% 8% 4 6% 5% 4 4 4 6% 8% 39%	2200
October	1st to 10th	Day	13% 7% 3 8% 5% 4 4 3 6% 7% 39%	3333
	11th to 20th	Day	10% 10% 3 8% 5% 5% 5% 5% 7% 9% 33%	3097
	21st to end	Day	13% 12% 4 9% 6% 4 5% 4 6% 7% 29%	3190
November	1st to 10th	Day	16% 14% 5% 11% 8% 4 4 2 5% 5% 25%	1657
	11th to 20th	Day	10% 15% 5% 12% 7% 6% 5% 4 5% 7% 25%	1669
	21st to end	Day	11% 16% 6% 10% 8% 5% 4 4 5% 7% 24%	1470
December	1st to 10th	Day	11% 14% 5% 14% 9% 8% 7% 5% 6% 7% 15%	2360
	11th to 20th	Day	9% 12% 5% 14% 8% 5% 5% 6% 6% 7% 24%	2709
	21st to end	Day	6% 11% 7% 16% 8% 6% 6% 4 5% 6% 27%	3575
January	1st to 10th	Night	6% 14% 7% 15% 7% 7% 6% 5% 7% 7% 20%	8799
	11th to 20th	Night	5% 13% 7% 14% 8% 8% 10% 8% 7% 5% 14%	8809
	21st to end	Night	5% 11% 6% 12% 7% 6% 9% 6% 8% 8% 22%	9128
February	1st to 10th	Night	8% 14% 4 11% 8% 6% 6% 6% 6% 6% 25%	2887
	11th to 20th	Night	5% 10% 4 9% 6% 6% 6% 5% 8% 8% 34%	2663
	21st to end	Night	6% 11% 4 10% 6% 7% 6% 5% 6% 7% 33%	2186
March	1st to 10th	Night	9% 12% 3 11% 5% 6% 6% 4 6% 8% 31%	5433
	11th to 20th	Night	6% 9% 3 9% 6% 5% 5% 4 7% 8% 38%	5090
	21st to end	Night	9% 11% 4 7% 5% 5% 5% 4 5% 6% 39%	5588
April	1st to 10th	Night	9% 7% 3 5% 6% 5% 6% 4 7% 8% 39%	2022
	11th to 20th	Night	13% 9% 3 8% 5% 5% 4 3 6% 6% 37%	1869
	21st to end	Night	11% 7% 3 7% 5% 5% 5% 4 6% 7% 38%	1890
May	1st to 10th	Night	12% 8% 3 8% 4 4 4 3 5% 7% 41%	4888
	11th to 20th	Night	17% 8% 3 7% 5% 4 4 3 5% 7% 35%	4107
	21st to end	Night	11% 7% 3 5% 4 4 4 3 5% 7% 48%	4523
June	1st to 10th	Night	14% 7% 2 7% 5% 4 4 4 6% 8% 38%	1470
	11th to 20th	Night	15% 5% 2 6% 4 5% 5% 4 6% 8% 40%	1435
	21st to end	Night	11% 5% 3 6% 5% 4 5% 5% 7% 10% 39%	1400
July	1st to 10th	Night	7% 3 1 5% 3 4 4 4 6% 9% 53%	3180
	11th to 20th	Night	8% 4 1 5% 4 4 5% 4 6% 9% 48%	3180
	21st to end	Night	6% 3 2 5% 4 4 4 4 7% 10% 51%	3466
August	1st to 10th	Night	9% 5% 2 5% 4 4 4 4 6% 8% 50%	2649
	11th to 20th	Night	8% 4 2 4 3 4 5% 4 7% 9% 50%	2888
	21st to end	Night	10% 6% 2 6% 4 3 4 4 5% 9% 49%	3234
September	1st to 10th	Night	9% 6% 2 5% 4 3 4 3 6% 8% 50%	1893
	11th to 20th	Night	13% 7% 3 7% 4 4 4 3 4 8% 42%	2200
	21st to end	Night	12% 6% 3 6% 5% 5% 4 3 6% 7% 43%	2200
October	1st to 10th	Night	12% 8% 2 5% 3 4 4 4 5% 8% 44%	3813
	11th to 20th	Night	8% 9% 3 7% 4 4 5% 4 8% 9% 38%	4046
	21st to end	Night	11% 9% 3 7% 5% 4 5% 4 7% 7% 37%	4610
November	1st to 10th	Night	13% 13% 4 10% 6% 5% 5% 4 5% 7% 27%	2861
	11th to 20th	Night	11% 16% 6% 11% 6% 5% 5% 4 6% 6% 25%	2948
	21st to end	Night	10% 15% 6% 14% 9% 6% 4 3 6% 7% 21%	3150
December	1st to 10th	Night	8% 17% 6% 14% 12% 8% 5% 4 5% 5% 15%	5050
	11th to 20th	Night	8% 12% 6% 14% 7% 4 5% 6% 6% 6% 26%	5718
	21st to end	Night	7% 11% 5% 16% 8% 7% 5% 4 6% 6% 26%	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	63% 4 10% 15% 7%	4125
	11th to 20th	Day	64% 3 8% 19% 6%	4140
	21st to end	Day	56% 3 11% 24% 6%	5085
February	1st to 10th	Day	62% 6% 11% 13% 7% 1	1733
	11th to 20th	Day	51% 5% 14% 22% 8%	1853
	21st to end	Day	53% 4 12% 21% 9%	1640
March	1st to 10th	Day	52% 5% 15% 18% 10% 1	4658
	11th to 20th	Day	56% 5% 11% 19% 10%	5090
	21st to end	Day	46% 5% 9% 26% 13% 1	5585
April	1st to 10th	Day	47% 5% 13% 22% 12% 1	2595
	11th to 20th	Day	49% 5% 10% 20% 14% 1	2702
	21st to end	Day	45% 6% 13% 27% 8% 2	2730
May	1st to 10th	Day	40% 4 9% 30% 16% 1	8056
	11th to 20th	Day	54% 4 10% 22% 9% 1	8790
	21st to end	Day	37% 4 8% 24% 21% 5%	9683
June	1st to 10th	Day	46% 7% 12% 24% 11% 1	3150
	11th to 20th	Day	47% 6% 13% 22% 11% 1	3076
	21st to end	Day	43% 8% 17% 24% 8%	3000
July	1st to 10th	Day	39% 4 21% 28% 7%	6726
	11th to 20th	Day	36% 3 19% 37% 4	6719
	21st to end	Day	33% 4 23% 34% 6%	7193
August	1st to 10th	Day	35% 5% 19% 33% 8%	4490
	11th to 20th	Day	38% 4 23% 31% 4	4210
	21st to end	Day	39% 4 24% 28% 5%	4674
September	1st to 10th	Day	36% 6% 19% 31% 8% 1	2502
	11th to 20th	Day	49% 6% 17% 25% 4	2200
	21st to end	Day	42% 6% 16% 27% 8%	2200
October	1st to 10th	Day	45% 3 15% 30% 6%	3333
	11th to 20th	Day	47% 5% 11% 28% 8%	3097
	21st to end	Day	54% 3 18% 20% 4	3190
November	1st to 10th	Day	62% 4 12% 18% 4 1	1657
	11th to 20th	Day	59% 6% 14% 16% 5%	1669
	21st to end	Day	60% 6% 15% 15% 4	1470
December	1st to 10th	Day	68% 5% 12% 9% 6%	2360
	11th to 20th	Day	59% 4 14% 16% 6%	2710
	21st to end	Day	59% 3 10% 18% 9% 1	3575
January	1st to 10th	Night	62% 4 8% 17% 8%	8800
	11th to 20th	Night	68% 4 7% 17% 5%	8850
	21st to end	Night	57% 3 10% 22% 7%	9128
February	1st to 10th	Night	57% 5% 11% 18% 9% 1	2887
	11th to 20th	Night	44% 6% 17% 23% 10%	2664
	21st to end	Night	49% 5% 11% 25% 10%	2186
March	1st to 10th	Night	51% 5% 12% 18% 10% 4	5433
	11th to 20th	Night	43% 5% 13% 24% 15% 1	5090
	21st to end	Night	45% 5% 7% 27% 14% 1	5588
April	1st to 10th	Night	40% 5% 11% 25% 16% 3	2022
	11th to 20th	Night	47% 4 11% 19% 17% 3	1869
	21st to end	Night	43% 5% 11% 26% 12% 3	1890
May	1st to 10th	Night	42% 4 9% 30% 14% 1	4888
	11th to 20th	Night	49% 3 11% 26% 10% 1	4107
	21st to end	Night	36% 5% 8% 20% 25% 6%	4526
June	1st to 10th	Night	42% 6% 14% 25% 12% 1	1470
	11th to 20th	Night	41% 5% 17% 23% 11% 2	1435
	21st to end	Night	38% 9% 19% 25% 9% 1	1400
July	1st to 10th	Night	28% 4 22% 37% 9% 1	3145
	11th to 20th	Night	33% 3 18% 39% 6% 1	3138
	21st to end	Night	29% 4 22% 33% 11% 1	3368
August	1st to 10th	Night	32% 4 16% 35% 12%	2642
	11th to 20th	Night	30% 4 25% 33% 7%	2915
	21st to end	Night	35% 3 21% 33% 8%	3234
September	1st to 10th	Night	32% 5% 18% 33% 12% 1	1893
	11th to 20th	Night	41% 6% 17% 27% 9% 1	2200
	21st to end	Night	38% 6% 14% 31% 10% 1	2200
October	1st to 10th	Night	38% 4 14% 31% 13%	3813
	11th to 20th	Night	42% 4 13% 30% 10% 1	4046
	21st to end	Night	46% 3 17% 29% 4	4610
November	1st to 10th	Night	57% 6% 15% 15% 6% 1	2861
	11th to 20th	Night	59% 6% 16% 12% 6%	2948
	21st to end	Night	63% 5% 15% 14% 4	3150
December	1st to 10th	Night	71% 4 11% 9% 4	5050
	11th to 20th	Night	57% 4 11% 14% 13%	5716
	21st to end	Night	59% 4 8% 19% 10% 1	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	9% 8% 36% 31% 11% 5%	330
	11th to 20th	Day	9% 6% 37% 34% 12% 2	330
	21st to end	Day	14% 9% 31% 27% 15% 3	363
February	1st to 10th	Day	15% 5% 34% 33% 11% 2	330
	11th to 20th	Day	10% 8% 32% 30% 16% 4	330
	21st to end	Day	10% 7% 35% 29% 17% 2	273
March	1st to 10th	Day	15% 7% 34% 29% 14% 1	330
	11th to 20th	Day	13% 10% 36% 27% 10% 3	330
	21st to end	Day	12% 8% 35% 28% 15% 1	363
April	1st to 10th	Day	13% 9% 30% 33% 13% 3	615
	11th to 20th	Day	17% 11% 28% 31% 12% 1	740
	21st to end	Day	16% 9% 33% 28% 13% 1	750
May	1st to 10th	Day	15% 11% 31% 27% 14% 2	753
	11th to 20th	Day	20% 9% 31% 24% 13% 4	775
	21st to end	Day	20% 8% 24% 27% 18% 3	844
June	1st to 10th	Day	18% 12% 28% 23% 13% 6%	780
	11th to 20th	Day	14% 11% 33% 25% 13% 4	756
	21st to end	Day	14% 9% 24% 30% 17% 6%	730
July	1st to 10th	Day	9% 7% 28% 30% 17% 8%	721
	11th to 20th	Day	12% 8% 28% 30% 17% 6%	718
	21st to end	Day	6% 8% 27% 31% 21% 8%	794
August	1st to 10th	Day	9% 6% 28% 31% 20% 6%	726
	11th to 20th	Day	12% 5% 25% 28% 21% 9%	715
	21st to end	Day	14% 7% 27% 29% 19% 4	803
September	1st to 10th	Day	14% 8% 30% 31% 15% 3	632
	11th to 20th	Day	18% 8% 36% 26% 11% 2	330
	21st to end	Day	15% 9% 37% 27% 9% 2	330
October	1st to 10th	Day	25% 10% 26% 25% 12% 3	330
	11th to 20th	Day	19% 12% 32% 27% 8% 2	330
	21st to end	Day	25% 8% 29% 25% 11% 2	363
November	1st to 10th	Day	24% 12% 26% 23% 13% 2	330
	11th to 20th	Day	16% 11% 36% 25% 10% 2	330
	21st to end	Day	17% 12% 32% 30% 8%	330
December	1st to 10th	Day	17% 6% 35% 26% 13% 3	330
	11th to 20th	Day	14% 12% 39% 25% 7% 2	330
	21st to end	Day	12% 8% 31% 28% 19% 4	363
January	1st to 10th	Night	13% 6% 33% 32% 14% 2	1050
	11th to 20th	Night	14% 8% 31% 35% 10% 2	1050
	21st to end	Night	14% 6% 33% 34% 13% 1	1155
February	1st to 10th	Night	14% 6% 29% 36% 14% 1	1050
	11th to 20th	Night	10% 6% 29% 36% 17% 3	1029
	21st to end	Night	10% 7% 32% 34% 15% 1	802
March	1st to 10th	Night	15% 5% 31% 31% 15% 3	818
	11th to 20th	Night	11% 7% 39% 32% 11% 1	630
	21st to end	Night	19% 6% 30% 30% 13% 3	693
April	1st to 10th	Night	12% 7% 30% 37% 12% 3	630
	11th to 20th	Night	17% 6% 28% 35% 13% 1	623
	21st to end	Night	16% 7% 31% 36% 10% 1	630
May	1st to 10th	Night	21% 5% 30% 34% 8% 2	630
	11th to 20th	Night	18% 8% 29% 30% 14%	621
	21st to end	Night	18% 6% 28% 34% 14%	683
June	1st to 10th	Night	17% 7% 29% 32% 14% 1	630
	11th to 20th	Night	17% 6% 26% 37% 13% 1	615
	21st to end	Night	14% 5% 21% 42% 18% 1	600
July	1st to 10th	Night	7% 3 23% 45% 21% 2	585
	11th to 20th	Night	10% 5% 25% 41% 19% 2	582
	21st to end	Night	8% 3 25% 37% 24% 3	657
August	1st to 10th	Night	10% 4 18% 46% 21% 1	597
	11th to 20th	Night	9% 3 21% 41% 22% 4	594
	21st to end	Night	13% 4 22% 38% 21% 2	660
September	1st to 10th	Night	13% 4 28% 34% 19% 2	600
	11th to 20th	Night	15% 6% 24% 40% 14% 1	600
	21st to end	Night	15% 5% 31% 36% 13% 1	600
October	1st to 10th	Night	20% 6% 33% 33% 8%	732
	11th to 20th	Night	21% 6% 31% 28% 12% 1	884
	21st to end	Night	22% 8% 31% 29% 8% 1	1100
November	1st to 10th	Night	19% 8% 33% 27% 11% 2	1025
	11th to 20th	Night	19% 8% 34% 26% 9% 3	1050
	21st to end	Night	16% 9% 39% 28% 7% 1	1050
December	1st to 10th	Night	12% 7% 32% 32% 15% 2	1050
	11th to 20th	Night	16% 8% 36% 30% 9% 2	1050
	21st to end	Night	17% 6% 31% 29% 15% 2	1155

Page generated at 2026-06-13 01:31:38. Version ac07

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