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 2024-09-29.

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 8% 6% 5% 5% 4 6% 8% 34%	101633
	Night	10% 10% 4 9% 6% 5% 5% 4 6% 7% 34%	96737
Transparency	Day	47% 6% 15% 24% 8% 1	101374
	Night	48% 6% 14% 23% 9% 1	96643
Seeing	Day	14% 9% 30% 28% 15% 4	16191
	Night	15% 6% 29% 34% 14% 2	26059

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% 16% 7% 11% 6% 9% 8% 5% 9% 6% 18%	2219
	11th to 20th	Day	5% 9% 5% 21% 12% 10% 7% 6% 7% 8% 11%	2199
	21st to end	Day	7% 14% 8% 15% 8% 6% 6% 4 6% 7% 18%	2733
February	1st to 10th	Day	8% 12% 5% 13% 8% 8% 6% 6% 7% 7% 20%	1567
	11th to 20th	Day	7% 11% 4 9% 6% 7% 8% 5% 6% 8% 28%	1664
	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%	2068
October	1st to 10th	Day	18% 9% 3 9% 5% 4 4 3 6% 7% 31%	1843
	11th to 20th	Day	13% 13% 4 9% 6% 5% 5% 4 6% 7% 27%	1724
	21st to end	Day	15% 15% 5% 11% 6% 5% 6% 4 6% 5% 23%	1782
November	1st to 10th	Day	17% 14% 5% 11% 7% 4 4 2 5% 6% 24%	1497
	11th to 20th	Day	9% 15% 5% 13% 7% 6% 5% 4 5% 6% 24%	1511
	21st to end	Day	12% 15% 6% 10% 8% 5% 4 4 5% 6% 24%	1330
December	1st to 10th	Day	8% 15% 5% 13% 9% 8% 8% 5% 6% 7% 17%	1330
	11th to 20th	Day	8% 14% 7% 15% 7% 5% 6% 5% 7% 7% 21%	1679
	21st to end	Day	8% 10% 4 10% 7% 5% 6% 4 6% 7% 33%	2442
January	1st to 10th	Night	6% 13% 5% 13% 8% 8% 8% 5% 7% 8% 20%	4737
	11th to 20th	Night	5% 12% 7% 17% 11% 10% 8% 5% 6% 5% 14%	4709
	21st to end	Night	8% 14% 8% 14% 7% 6% 6% 5% 6% 6% 19%	4933
February	1st to 10th	Night	8% 14% 4 11% 8% 5% 6% 6% 6% 7% 26%	2613
	11th to 20th	Night	5% 10% 4 10% 6% 6% 6% 5% 8% 8% 32%	2403
	21st to end	Night	6% 11% 3 10% 7% 7% 6% 5% 6% 7% 34%	1984
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% 7% 41%	2079
October	1st to 10th	Night	15% 10% 3 6% 5% 4 5% 5% 5% 7% 37%	2098
	11th to 20th	Night	13% 12% 3 8% 4 4 5% 4 6% 6% 33%	2235
	21st to end	Night	16% 14% 4 8% 5% 3 4 3 5% 6% 31%	2574
November	1st to 10th	Night	14% 14% 4 10% 7% 5% 5% 4 5% 7% 25%	2581
	11th to 20th	Night	10% 16% 6% 12% 6% 6% 5% 4 6% 6% 24%	2666
	21st to end	Night	11% 16% 6% 13% 9% 6% 4 3 6% 7% 21%	2850
December	1st to 10th	Night	6% 12% 5% 13% 10% 8% 6% 5% 6% 7% 21%	2850
	11th to 20th	Night	8% 15% 6% 13% 6% 5% 5% 4 6% 7% 25%	3518
	21st to end	Night	7% 10% 4 12% 7% 6% 5% 4 6% 7% 31%	5225

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	62% 7% 14% 15% 2	2219
	11th to 20th	Day	69% 5% 10% 13% 3	2220
	21st to end	Day	63% 5% 12% 15% 5%	2733
February	1st to 10th	Day	60% 7% 12% 13% 7% 1	1567
	11th to 20th	Day	51% 5% 14% 20% 9%	1673
	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%	2068
October	1st to 10th	Day	52% 6% 16% 21% 5%	1843
	11th to 20th	Day	55% 8% 13% 20% 4 1	1724
	21st to end	Day	62% 6% 14% 15% 3	1782
November	1st to 10th	Day	62% 4 12% 17% 4 1	1497
	11th to 20th	Day	60% 7% 14% 15% 4	1511
	21st to end	Day	60% 6% 15% 15% 4	1330
December	1st to 10th	Day	65% 7% 13% 12% 4	1330
	11th to 20th	Day	60% 7% 15% 13% 4	1680
	21st to end	Day	49% 5% 14% 18% 13% 1	2442
January	1st to 10th	Night	58% 7% 12% 17% 5%	4737
	11th to 20th	Night	70% 6% 8% 13% 3	4750
	21st to end	Night	62% 5% 11% 16% 5%	4933
February	1st to 10th	Night	56% 6% 11% 17% 9% 1	2613
	11th to 20th	Night	44% 7% 15% 22% 11%	2404
	21st to end	Night	47% 5% 11% 26% 10%	1984
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% 29% 10% 1	2079
October	1st to 10th	Night	46% 6% 16% 22% 9%	2098
	11th to 20th	Night	49% 7% 13% 26% 5%	2235
	21st to end	Night	54% 6% 15% 21% 4	2574
November	1st to 10th	Night	58% 6% 15% 15% 5% 1	2581
	11th to 20th	Night	60% 7% 16% 12% 5%	2666
	21st to end	Night	62% 6% 15% 13% 4	2850
December	1st to 10th	Night	61% 7% 16% 12% 5%	2850
	11th to 20th	Night	56% 7% 14% 15% 8%	3516
	21st to end	Night	52% 5% 10% 18% 14% 1	5225

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% 10% 6%	270
	11th to 20th	Day	9% 4 35% 34% 15% 3	270
	21st to end	Day	16% 8% 27% 28% 17% 4	297
February	1st to 10th	Day	15% 4 33% 36% 11% 2	270
	11th to 20th	Day	11% 9% 35% 28% 13% 4	270
	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	16% 9% 36% 28% 9% 2	294
October	1st to 10th	Day	27% 10% 23% 22% 14% 4	270
	11th to 20th	Day	16% 12% 31% 29% 9% 3	270
	21st to end	Day	25% 8% 29% 24% 11% 2	297
November	1st to 10th	Day	24% 11% 26% 25% 13% 1	270
	11th to 20th	Day	13% 11% 37% 26% 10% 2	270
	21st to end	Day	19% 14% 34% 27% 6%	270
December	1st to 10th	Day	14% 7% 34% 27% 14% 4	270
	11th to 20th	Day	13% 9% 41% 26% 8% 2	270
	21st to end	Day	12% 5% 30% 29% 19% 4	297
January	1st to 10th	Night	13% 6% 34% 32% 14% 2	950
	11th to 20th	Night	14% 7% 30% 37% 10% 2	950
	21st to end	Night	15% 6% 31% 35% 13% 1	1045
February	1st to 10th	Night	13% 6% 29% 37% 15% 1	950
	11th to 20th	Night	10% 6% 30% 35% 17% 3	929
	21st to end	Night	10% 6% 32% 35% 16% 1	728
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% 38% 11% 1	567
October	1st to 10th	Night	20% 6% 31% 34% 9%	658
	11th to 20th	Night	21% 6% 29% 29% 13% 1	795
	21st to end	Night	22% 9% 30% 29% 8% 1	990
November	1st to 10th	Night	20% 7% 32% 27% 11% 2	925
	11th to 20th	Night	18% 8% 34% 27% 9% 3	950
	21st to end	Night	17% 9% 39% 27% 7% 1	950
December	1st to 10th	Night	11% 7% 31% 33% 16% 3	950
	11th to 20th	Night	16% 8% 34% 31% 10% 2	950
	21st to end	Night	17% 6% 31% 29% 15% 2	1045

Page generated at 2024-09-26 08:52:18. Version ac07

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