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 2025-02-21.

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% 34%	112123
	Night	9% 10% 4 10% 6% 5% 5% 4 6% 7% 33%	115195
Transparency	Day	48% 5% 15% 24% 8%	111864
	Night	49% 5% 13% 23% 9% 1	115101
Seeing	Day	15% 9% 30% 28% 15% 4	16626
	Night	15% 6% 30% 34% 14% 2	26760

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% 14% 6% 8% 7% 6% 8% 6% 18%	3179
	11th to 20th	Day	5% 10% 4 16% 9% 8% 7% 9% 11% 9% 12%	3159
	21st to end	Day	5% 12% 8% 14% 8% 7% 7% 5% 6% 7% 20%	3929
February	1st to 10th	Day	8% 12% 5% 13% 8% 8% 6% 6% 7% 7% 19%	1650
	11th to 20th	Day	7% 10% 3 9% 6% 7% 8% 6% 7% 8% 29%	1754
	21st to end	Day	6% 13% 4 10% 8% 6% 6% 6% 6% 7% 29%	1488
March	1st to 10th	Day	10% 11% 4 11% 8% 5% 6% 5% 6% 9% 25%	3174
	11th to 20th	Day	7% 11% 5% 14% 8% 6% 5% 4 5% 6% 28%	3478
	21st to end	Day	6% 10% 4 11% 7% 6% 6% 4 6% 6% 35%	3814
April	1st to 10th	Day	9% 10% 3 9% 5% 5% 5% 3 5% 8% 37%	2348
	11th to 20th	Day	12% 9% 4 8% 6% 5% 5% 5% 6% 6% 34%	2442
	21st to end	Day	13% 8% 3 7% 5% 5% 5% 4 5% 8% 37%	2470
May	1st to 10th	Day	15% 9% 3 6% 4 4 4 3 6% 8% 38%	4344
	11th to 20th	Day	20% 9% 3 7% 4 4 4 4 4 6% 34%	4705
	21st to end	Day	19% 7% 3 7% 4 4 4 4 6% 6% 36%	5173
June	1st to 10th	Day	17% 8% 2 7% 4 4 5% 5% 5% 7% 36%	2850
	11th to 20th	Day	15% 7% 2 7% 6% 5% 5% 4 6% 7% 34%	2850
	21st to end	Day	13% 7% 3 6% 6% 5% 5% 5% 7% 8% 36%	2850
July	1st to 10th	Day	11% 6% 3 6% 5% 5% 6% 5% 7% 8% 37%	4750
	11th to 20th	Day	7% 4 2 5% 4 4 5% 4 6% 10% 49%	4750
	21st to end	Day	5% 4 2 5% 3 4 5% 4 7% 10% 50%	5150
August	1st to 10th	Day	7% 4 1 6% 5% 5% 6% 4 8% 10% 43%	4369
	11th to 20th	Day	11% 5% 2 6% 5% 4 5% 4 5% 9% 44%	4041
	21st to end	Day	14% 5% 2 6% 4 4 4 4 6% 9% 42%	4532
September	1st to 10th	Day	11% 6% 2 6% 3 4 5% 4 6% 7% 46%	2377
	11th to 20th	Day	15% 6% 4 8% 5% 5% 4 4 6% 7% 36%	2090
	21st to end	Day	13% 8% 4 6% 5% 5% 4 4 6% 8% 38%	2090
October	1st to 10th	Day	13% 7% 3 8% 5% 4 4 3 6% 7% 39%	3231
	11th to 20th	Day	10% 9% 3 8% 5% 5% 5% 5% 7% 8% 33%	3001
	21st to end	Day	13% 12% 4 9% 6% 4 5% 4 6% 7% 29%	3091
November	1st to 10th	Day	17% 14% 5% 11% 7% 4 4 2 5% 6% 25%	1577
	11th to 20th	Day	10% 16% 5% 13% 7% 6% 5% 4 5% 6% 24%	1590
	21st to end	Day	12% 16% 6% 10% 8% 5% 4 4 5% 7% 24%	1400
December	1st to 10th	Day	11% 14% 5% 14% 10% 8% 7% 5% 6% 7% 14%	2290
	11th to 20th	Day	9% 12% 5% 13% 8% 5% 5% 6% 6% 7% 24%	2639
	21st to end	Day	6% 11% 7% 16% 8% 6% 5% 3 5% 6% 27%	3498
January	1st to 10th	Night	5% 12% 6% 15% 8% 7% 7% 5% 7% 7% 20%	6787
	11th to 20th	Night	5% 12% 7% 15% 9% 9% 10% 8% 7% 5% 14%	6759
	21st to end	Night	7% 14% 7% 14% 7% 6% 6% 5% 7% 7% 19%	7048
February	1st to 10th	Night	8% 14% 4 11% 8% 6% 6% 6% 6% 7% 25%	2750
	11th to 20th	Night	5% 10% 4 9% 6% 6% 6% 5% 8% 8% 33%	2533
	21st to end	Night	6% 11% 3 10% 7% 7% 6% 5% 6% 7% 34%	1985
March	1st to 10th	Night	11% 11% 3 11% 5% 6% 6% 4 6% 8% 30%	3688
	11th to 20th	Night	5% 9% 3 9% 6% 4 5% 4 7% 8% 40%	3480
	21st to end	Night	8% 12% 4 7% 5% 5% 5% 4 6% 6% 38%	3817
April	1st to 10th	Night	9% 8% 2 5% 5% 5% 6% 5% 8% 8% 40%	1829
	11th to 20th	Night	14% 10% 3 7% 5% 5% 5% 4 6% 6% 37%	1689
	21st to end	Night	11% 7% 3 7% 6% 5% 5% 4 7% 7% 38%	1710
May	1st to 10th	Night	18% 10% 3 7% 4 4 5% 3 5% 6% 34%	2622
	11th to 20th	Night	17% 8% 3 7% 5% 4 4 3 5% 7% 38%	2201
	21st to end	Night	15% 7% 2 6% 4 4 5% 4 5% 7% 39%	2414
June	1st to 10th	Night	15% 8% 2 7% 4 4 5% 4 6% 8% 38%	1330
	11th to 20th	Night	15% 5% 2 5% 4 5% 5% 4 7% 8% 40%	1330
	21st to end	Night	11% 5% 2 6% 5% 4 5% 5% 7% 10% 39%	1330
July	1st to 10th	Night	8% 3 1 5% 3 4 4 3 6% 9% 54%	2220
	11th to 20th	Night	7% 3 1 3 3 4 4 4 6% 9% 56%	2220
	21st to end	Night	5% 3 1 5% 4 4 4 3 8% 10% 53%	2414
August	1st to 10th	Night	9% 5% 2 5% 4 4 4 4 6% 8% 50%	2567
	11th to 20th	Night	8% 4 2 4 3 4 5% 4 7% 9% 50%	2798
	21st to end	Night	10% 6% 2 6% 4 3 4 4 5% 9% 48%	3135
September	1st to 10th	Night	9% 6% 2 5% 4 3 4 3 6% 8% 50%	1798
	11th to 20th	Night	12% 7% 3 7% 4 4 4 3 4 8% 44%	2090
	21st to end	Night	12% 6% 3 6% 5% 5% 4 3 7% 8% 41%	2090
October	1st to 10th	Night	12% 8% 2 5% 4 4 4 4 5% 8% 44%	3696
	11th to 20th	Night	8% 9% 3 8% 4 4 5% 4 8% 9% 39%	3922
	21st to end	Night	10% 10% 3 7% 5% 4 5% 4 7% 7% 38%	4467
November	1st to 10th	Night	14% 13% 4 10% 7% 5% 5% 4 5% 7% 27%	2721
	11th to 20th	Night	11% 16% 6% 12% 6% 6% 5% 4 5% 6% 24%	2807
	21st to end	Night	11% 16% 6% 14% 9% 6% 4 3 6% 7% 20%	3000
December	1st to 10th	Night	8% 17% 6% 15% 12% 8% 5% 4 5% 5% 14%	4900
	11th to 20th	Night	8% 12% 6% 14% 7% 4 4 6% 6% 6% 26%	5568
	21st to end	Night	7% 11% 5% 16% 8% 7% 5% 4 6% 6% 26%	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	63% 5% 10% 17% 5%	3179
	11th to 20th	Day	63% 4 7% 19% 7%	3180
	21st to end	Day	62% 4 13% 17% 4	3929
February	1st to 10th	Day	61% 6% 12% 13% 8% 1	1650
	11th to 20th	Day	51% 5% 14% 21% 8%	1763
	21st to end	Day	52% 5% 12% 22% 9%	1488
March	1st to 10th	Day	54% 7% 13% 21% 5%	3174
	11th to 20th	Day	55% 6% 12% 18% 9%	3480
	21st to end	Day	47% 7% 11% 25% 9% 1	3814
April	1st to 10th	Day	46% 6% 13% 23% 12% 1	2348
	11th to 20th	Day	49% 5% 9% 20% 15% 1	2442
	21st to end	Day	44% 6% 13% 27% 8% 2	2470
May	1st to 10th	Day	43% 7% 11% 27% 11% 1	4344
	11th to 20th	Day	49% 6% 9% 22% 12% 2	4709
	21st to end	Day	47% 7% 11% 24% 11% 1	5173
June	1st to 10th	Day	46% 7% 12% 23% 11% 1	2850
	11th to 20th	Day	47% 7% 12% 21% 12% 1	2850
	21st to end	Day	43% 8% 17% 24% 8%	2850
July	1st to 10th	Day	43% 5% 20% 25% 7%	4676
	11th to 20th	Day	31% 4 21% 38% 6% 1	4669
	21st to end	Day	29% 5% 23% 35% 8%	4988
August	1st to 10th	Day	35% 5% 19% 33% 7%	4352
	11th to 20th	Day	37% 4 22% 32% 4	4080
	21st to end	Day	40% 4 24% 28% 5%	4531
September	1st to 10th	Day	35% 6% 19% 31% 8% 1	2377
	11th to 20th	Day	47% 6% 17% 26% 4	2090
	21st to end	Day	43% 6% 16% 26% 8%	2090
October	1st to 10th	Day	45% 3 15% 30% 6%	3231
	11th to 20th	Day	47% 5% 11% 28% 8%	3001
	21st to end	Day	54% 3 18% 20% 4	3091
November	1st to 10th	Day	61% 4 13% 18% 4 1	1577
	11th to 20th	Day	60% 6% 14% 16% 4	1590
	21st to end	Day	60% 6% 16% 14% 4	1400
December	1st to 10th	Day	69% 6% 12% 8% 5%	2290
	11th to 20th	Day	58% 4 14% 17% 6%	2640
	21st to end	Day	58% 3 10% 18% 9% 1	3498
January	1st to 10th	Night	61% 5% 9% 16% 9%	6787
	11th to 20th	Night	68% 5% 6% 17% 5%	6800
	21st to end	Night	62% 4 11% 16% 6%	7048
February	1st to 10th	Night	56% 6% 11% 18% 9% 1	2750
	11th to 20th	Night	43% 7% 16% 23% 10%	2534
	21st to end	Night	47% 5% 11% 26% 10%	1985
March	1st to 10th	Night	50% 7% 11% 23% 9% 1	3688
	11th to 20th	Night	40% 6% 14% 24% 14% 1	3480
	21st to end	Night	44% 7% 10% 26% 12% 1	3817
April	1st to 10th	Night	38% 5% 12% 25% 17% 3	1829
	11th to 20th	Night	47% 4 10% 19% 17% 3	1689
	21st to end	Night	43% 6% 11% 26% 12% 3	1710
May	1st to 10th	Night	48% 7% 9% 25% 11%	2622
	11th to 20th	Night	45% 6% 12% 25% 10% 2	2201
	21st to end	Night	41% 8% 12% 26% 11% 1	2414
June	1st to 10th	Night	42% 7% 15% 25% 12% 1	1330
	11th to 20th	Night	41% 6% 17% 22% 12% 2	1330
	21st to end	Night	38% 9% 19% 24% 8% 1	1330
July	1st to 10th	Night	28% 5% 24% 34% 8% 1	2185
	11th to 20th	Night	25% 4 21% 41% 8% 1	2178
	21st to end	Night	26% 6% 20% 35% 12% 1	2337
August	1st to 10th	Night	32% 4 16% 35% 12%	2560
	11th to 20th	Night	30% 4 25% 33% 8%	2825
	21st to end	Night	35% 3 21% 33% 8%	3135
September	1st to 10th	Night	32% 5% 18% 33% 12% 1	1798
	11th to 20th	Night	39% 6% 17% 27% 9% 1	2090
	21st to end	Night	40% 6% 15% 30% 10% 1	2090
October	1st to 10th	Night	38% 4 14% 31% 13%	3696
	11th to 20th	Night	41% 4 14% 31% 10% 1	3922
	21st to end	Night	46% 3 17% 29% 4	4467
November	1st to 10th	Night	57% 6% 16% 15% 5% 1	2721
	11th to 20th	Night	60% 7% 16% 12% 5%	2807
	21st to end	Night	63% 5% 15% 12% 4	3000
December	1st to 10th	Night	72% 4 11% 9% 4	4900
	11th to 20th	Night	56% 5% 11% 15% 13%	5566
	21st to end	Night	59% 4 8% 19% 10% 1	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	8% 8% 35% 32% 10% 6%	300
	11th to 20th	Day	10% 5% 35% 34% 14% 2	300
	21st to end	Day	15% 10% 29% 26% 15% 3	330
February	1st to 10th	Day	15% 4 34% 34% 12% 2	300
	11th to 20th	Day	10% 8% 33% 30% 15% 4	300
	21st to end	Day	8% 8% 35% 28% 19% 3	225
March	1st to 10th	Day	15% 8% 29% 31% 16% 1	270
	11th to 20th	Day	12% 12% 36% 26% 11% 3	270
	21st to end	Day	11% 7% 34% 29% 18% 1	297
April	1st to 10th	Day	12% 9% 32% 32% 12% 3	528
	11th to 20th	Day	18% 11% 26% 31% 13% 2	640
	21st to end	Day	16% 9% 34% 28% 12% 1	650
May	1st to 10th	Day	16% 11% 31% 26% 13% 3	653
	11th to 20th	Day	19% 9% 29% 24% 14% 4	675
	21st to end	Day	21% 9% 24% 26% 18% 2	734
June	1st to 10th	Day	18% 11% 27% 23% 14% 7%	680
	11th to 20th	Day	15% 11% 33% 23% 13% 4	680
	21st to end	Day	15% 9% 22% 31% 18% 6%	680
July	1st to 10th	Day	9% 7% 28% 30% 17% 8%	671
	11th to 20th	Day	12% 8% 28% 30% 17% 6%	668
	21st to end	Day	6% 8% 26% 29% 22% 8%	739
August	1st to 10th	Day	9% 6% 28% 30% 21% 7%	676
	11th to 20th	Day	12% 5% 24% 28% 21% 9%	665
	21st to end	Day	15% 7% 27% 29% 19% 3	748
September	1st to 10th	Day	13% 9% 29% 32% 15% 2	587
	11th to 20th	Day	17% 8% 37% 24% 12% 2	300
	21st to end	Day	17% 9% 37% 27% 8% 2	300
October	1st to 10th	Day	26% 10% 24% 23% 13% 4	300
	11th to 20th	Day	16% 12% 32% 29% 8% 3	300
	21st to end	Day	24% 8% 31% 25% 11% 2	330
November	1st to 10th	Day	24% 11% 25% 24% 15% 2	300
	11th to 20th	Day	17% 11% 36% 25% 10% 2	300
	21st to end	Day	18% 13% 33% 29% 7%	300
December	1st to 10th	Day	16% 7% 34% 27% 13% 3	300
	11th to 20th	Day	14% 9% 41% 27% 8% 2	300
	21st to end	Day	12% 6% 31% 28% 19% 4	330
January	1st to 10th	Night	12% 6% 34% 32% 15% 2	1000
	11th to 20th	Night	14% 8% 30% 37% 10% 2	1000
	21st to end	Night	14% 6% 32% 34% 13% 1	1100
February	1st to 10th	Night	13% 6% 29% 37% 14% 1	1000
	11th to 20th	Night	9% 6% 29% 36% 17% 3	979
	21st to end	Night	10% 6% 32% 35% 16% 1	729
March	1st to 10th	Night	14% 5% 30% 31% 16% 3	740
	11th to 20th	Night	11% 7% 38% 31% 12% 1	570
	21st to end	Night	19% 5% 29% 30% 14% 3	627
April	1st to 10th	Night	12% 7% 30% 36% 12% 3	570
	11th to 20th	Night	18% 6% 27% 35% 14% 1	563
	21st to end	Night	15% 6% 31% 36% 10% 1	570
May	1st to 10th	Night	22% 5% 29% 34% 8% 2	570
	11th to 20th	Night	17% 8% 29% 31% 15% 1	561
	21st to end	Night	19% 6% 28% 33% 14%	617
June	1st to 10th	Night	17% 6% 26% 34% 15% 1	570
	11th to 20th	Night	16% 6% 26% 36% 14% 1	570
	21st to end	Night	14% 5% 20% 41% 18% 1	570
July	1st to 10th	Night	7% 3 23% 44% 21% 2	555
	11th to 20th	Night	9% 5% 25% 40% 19% 2	552
	21st to end	Night	8% 3 25% 36% 25% 3	624
August	1st to 10th	Night	10% 5% 19% 44% 21% 1	567
	11th to 20th	Night	9% 3 21% 41% 22% 4	564
	21st to end	Night	14% 4 22% 39% 20% 2	627
September	1st to 10th	Night	13% 4 28% 34% 19% 2	570
	11th to 20th	Night	14% 6% 25% 40% 14% 1	570
	21st to end	Night	15% 4 31% 37% 11% 1	570
October	1st to 10th	Night	20% 6% 32% 34% 9%	695
	11th to 20th	Night	20% 6% 31% 29% 13% 1	840
	21st to end	Night	21% 9% 31% 29% 8% 1	1045
November	1st to 10th	Night	19% 7% 33% 27% 12% 2	975
	11th to 20th	Night	19% 8% 34% 27% 9% 3	1000
	21st to end	Night	17% 9% 39% 27% 7% 1	1000
December	1st to 10th	Night	12% 7% 31% 32% 15% 2	1000
	11th to 20th	Night	16% 8% 35% 31% 9% 2	1000
	21st to end	Night	17% 6% 30% 29% 16% 2	1100

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