Fanny Bay
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fanny Bay clear sky chart from 2005-11-06 to 2025-03-12.

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	18% 10% 3 8% 5% 5% 5% 4 5% 6% 30%	112240
	Night	21% 11% 3 8% 5% 5% 5% 4 5% 6% 28%	115420
Transparency	Day	51% 11% 13% 17% 7% 1	111982
	Night	55% 10% 13% 15% 6% 1	115324
Seeing	Day	23% 10% 22% 23% 16% 5%	16011
	Night	25% 6% 19% 26% 19% 4	24215

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	29% 21% 5% 10% 5% 5% 4 3 4 5% 11%	3179
	11th to 20th	Day	17% 10% 3 8% 8% 5% 6% 4 6% 8% 24%	3159
	21st to end	Day	34% 13% 3 7% 4 4 4 3 3 3 21%	3880
February	1st to 10th	Day	24% 16% 6% 10% 5% 5% 5% 4 5% 5% 14%	1800
	11th to 20th	Day	22% 16% 5% 10% 5% 4 4 3 4 5% 23%	1755
	21st to end	Day	23% 13% 4 9% 7% 7% 5% 5% 5% 6% 16%	1485
March	1st to 10th	Day	19% 16% 5% 9% 7% 6% 6% 4 5% 6% 17%	3392
	11th to 20th	Day	17% 11% 3 9% 6% 6% 5% 4 5% 5% 30%	3503
	21st to end	Day	23% 15% 4 9% 6% 5% 5% 4 5% 5% 20%	3825
April	1st to 10th	Day	22% 15% 3 10% 7% 5% 6% 4 4 5% 18%	2279
	11th to 20th	Day	20% 13% 4 9% 7% 5% 5% 4 5% 5% 22%	2438
	21st to end	Day	22% 13% 4 8% 6% 5% 5% 4 5% 6% 22%	2470
May	1st to 10th	Day	14% 9% 3 7% 5% 5% 5% 4 6% 6% 35%	4403
	11th to 20th	Day	13% 8% 3 7% 6% 5% 6% 4 6% 9% 32%	4377
	21st to end	Day	21% 12% 4 9% 6% 6% 5% 4 5% 6% 21%	5144
June	1st to 10th	Day	20% 10% 3 9% 7% 5% 6% 4 6% 6% 23%	2850
	11th to 20th	Day	15% 11% 4 10% 8% 6% 7% 5% 6% 8% 20%	2850
	21st to end	Day	17% 8% 3 8% 5% 5% 5% 5% 6% 6% 32%	2850
July	1st to 10th	Day	7% 4 2 4 3 3 3 3 5% 7% 59%	4740
	11th to 20th	Day	4 3 1 3 3 2 3 3 4 5% 69%	4740
	21st to end	Day	7% 5% 2 6% 5% 5% 5% 5% 8% 8% 46%	5083
August	1st to 10th	Day	6% 2 1 3 2 2 3 3 5% 7% 66%	4221
	11th to 20th	Day	11% 7% 2 7% 4 5% 6% 5% 8% 9% 36%	4026
	21st to end	Day	13% 7% 2 6% 4 4 4 4 6% 7% 42%	4521
September	1st to 10th	Day	10% 6% 2 6% 4 4 5% 4 5% 7% 48%	2293
	11th to 20th	Day	17% 8% 3 7% 4 4 4 3 4 7% 38%	2182
	21st to end	Day	21% 7% 3 6% 5% 4 4 4 5% 5% 35%	2063
October	1st to 10th	Day	19% 10% 5% 10% 4 4 6% 5% 5% 7% 24%	3180
	11th to 20th	Day	25% 8% 3 9% 6% 5% 5% 4 5% 4 25%	3161
	21st to end	Day	22% 12% 3 10% 7% 6% 7% 5% 5% 5% 17%	3147
November	1st to 10th	Day	30% 14% 4 8% 7% 7% 4 2 4 5% 15%	1568
	11th to 20th	Day	25% 14% 4 9% 7% 5% 5% 4 3 5% 19%	1600
	21st to end	Day	30% 12% 4 8% 5% 5% 5% 4 4 5% 18%	1600
December	1st to 10th	Day	18% 16% 6% 10% 8% 6% 5% 4 5% 5% 18%	2333
	11th to 20th	Day	34% 18% 4 9% 5% 5% 5% 3 3 3 10%	2645
	21st to end	Day	35% 17% 5% 9% 6% 4 4 4 5% 3 8%	3498
January	1st to 10th	Night	27% 19% 5% 12% 6% 4 4 3 4 4 11%	6766
	11th to 20th	Night	18% 9% 3 8% 6% 4 5% 4 5% 7% 31%	6739
	21st to end	Night	31% 12% 3 7% 4 4 4 3 4 3 25%	7069
February	1st to 10th	Night	23% 15% 4 9% 6% 4 5% 4 5% 5% 20%	2600
	11th to 20th	Night	20% 15% 4 8% 4 5% 4 3 4 6% 27%	2532
	21st to end	Night	20% 14% 4 9% 6% 5% 5% 3 4 6% 22%	2145
March	1st to 10th	Night	21% 13% 3 9% 5% 5% 5% 4 5% 6% 22%	3698
	11th to 20th	Night	12% 7% 3 6% 5% 6% 7% 5% 8% 8% 33%	3504
	21st to end	Night	22% 15% 4 8% 6% 5% 4 4 5% 5% 23%	3828
April	1st to 10th	Night	18% 12% 3 8% 5% 6% 6% 5% 6% 7% 24%	1898
	11th to 20th	Night	18% 11% 5% 7% 5% 5% 4 5% 6% 6% 29%	1691
	21st to end	Night	21% 9% 3 8% 6% 5% 4 4 6% 8% 26%	1710
May	1st to 10th	Night	14% 6% 3 7% 5% 5% 4 3 5% 6% 41%	2555
	11th to 20th	Night	14% 6% 2 5% 5% 5% 5% 5% 7% 8% 39%	2516
	21st to end	Night	20% 13% 4 8% 5% 5% 5% 4 5% 7% 25%	2427
June	1st to 10th	Night	15% 10% 3 8% 6% 6% 6% 4 5% 7% 30%	1330
	11th to 20th	Night	15% 8% 5% 8% 7% 6% 7% 4 7% 7% 27%	1330
	21st to end	Night	13% 8% 4 6% 5% 4 4 4 7% 9% 37%	1330
July	1st to 10th	Night	7% 4 2 4 3 3 3 2 5% 6% 62%	2220
	11th to 20th	Night	4 2 1 2 3 2 3 3 4 6% 70%	2220
	21st to end	Night	8% 4 1 5% 4 4 4 5% 7% 7% 50%	2467
August	1st to 10th	Night	5% 3 1 3 2 2 2 2 4 5% 70%	2712
	11th to 20th	Night	13% 6% 2 6% 4 5% 5% 4 6% 9% 41%	2812
	21st to end	Night	15% 6% 2 7% 4 4 4 4 4 4 45%	3146
September	1st to 10th	Night	9% 5% 2 5% 3 3 4 4 5% 8% 53%	1886
	11th to 20th	Night	17% 8% 3 6% 4 4 5% 4 6% 6% 38%	1995
	21st to end	Night	20% 6% 3 8% 4 3 4 3 4 6% 38%	2116
October	1st to 10th	Night	17% 9% 4 11% 6% 6% 5% 3 4 6% 30%	3800
	11th to 20th	Night	23% 8% 4 10% 6% 5% 5% 4 5% 6% 24%	3777
	21st to end	Night	22% 10% 3 11% 6% 5% 5% 4 5% 5% 24%	4410
November	1st to 10th	Night	29% 12% 4 9% 5% 5% 5% 4 5% 5% 18%	2730
	11th to 20th	Night	26% 12% 3 8% 6% 5% 5% 5% 4 5% 20%	2800
	21st to end	Night	27% 11% 4 9% 6% 5% 4 4 4 4 22%	2800
December	1st to 10th	Night	21% 14% 5% 11% 6% 7% 5% 3 4 5% 18%	4843
	11th to 20th	Night	32% 18% 5% 11% 6% 4 4 3 4 3 9%	5560
	21st to end	Night	36% 14% 4 8% 5% 5% 5% 4 5% 4 12%	7458

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	77% 8% 6% 8% 1	3179
	11th to 20th	Day	54% 17% 14% 13% 2	3180
	21st to end	Day	67% 7% 9% 12% 5%	3880
February	1st to 10th	Day	71% 10% 7% 7% 4 1	1800
	11th to 20th	Day	66% 9% 9% 12% 4	1764
	21st to end	Day	66% 9% 12% 8% 4 1	1485
March	1st to 10th	Day	64% 11% 10% 9% 6%	3392
	11th to 20th	Day	55% 10% 10% 20% 5%	3503
	21st to end	Day	62% 13% 12% 11% 2	3825
April	1st to 10th	Day	66% 12% 9% 10% 4	2279
	11th to 20th	Day	60% 11% 8% 12% 7% 2	2438
	21st to end	Day	60% 10% 10% 14% 6% 1	2470
May	1st to 10th	Day	45% 14% 15% 19% 8%	4403
	11th to 20th	Day	40% 15% 19% 21% 4	4380
	21st to end	Day	57% 14% 11% 12% 6%	5145
June	1st to 10th	Day	56% 12% 12% 13% 6% 2	2850
	11th to 20th	Day	53% 14% 15% 13% 4	2850
	21st to end	Day	45% 12% 16% 19% 8% 1	2850
July	1st to 10th	Day	23% 6% 11% 28% 24% 8%	4666
	11th to 20th	Day	16% 7% 15% 41% 20% 1	4659
	21st to end	Day	26% 10% 22% 26% 15% 2	4922
August	1st to 10th	Day	18% 6% 13% 44% 18% 1	4204
	11th to 20th	Day	36% 14% 25% 17% 8% 1	4065
	21st to end	Day	37% 12% 21% 22% 7%	4520
September	1st to 10th	Day	32% 11% 17% 26% 12% 2	2293
	11th to 20th	Day	45% 9% 14% 18% 13% 1	2182
	21st to end	Day	49% 11% 14% 17% 9% 1	2063
October	1st to 10th	Day	54% 8% 16% 17% 5%	3180
	11th to 20th	Day	60% 9% 11% 16% 4	3161
	21st to end	Day	60% 12% 12% 11% 4	3147
November	1st to 10th	Day	73% 10% 6% 7% 5%	1568
	11th to 20th	Day	66% 10% 9% 9% 5% 1	1600
	21st to end	Day	70% 11% 7% 7% 5%	1600
December	1st to 10th	Day	67% 10% 10% 11% 3	2333
	11th to 20th	Day	77% 9% 6% 5% 2	2648
	21st to end	Day	76% 8% 9% 6% 2	3498
January	1st to 10th	Night	78% 8% 5% 7% 2	6766
	11th to 20th	Night	50% 14% 16% 15% 4 1	6780
	21st to end	Night	64% 8% 10% 13% 5%	7069
February	1st to 10th	Night	66% 9% 8% 10% 6% 1	2600
	11th to 20th	Night	59% 10% 11% 13% 6% 1	2534
	21st to end	Night	63% 7% 10% 14% 5% 1	2145
March	1st to 10th	Night	59% 10% 11% 14% 5%	3698
	11th to 20th	Night	45% 17% 10% 23% 5%	3505
	21st to end	Night	63% 13% 10% 12% 2	3828
April	1st to 10th	Night	56% 13% 12% 14% 5%	1898
	11th to 20th	Night	53% 11% 10% 16% 8% 2	1691
	21st to end	Night	54% 13% 10% 15% 7% 1	1710
May	1st to 10th	Night	39% 9% 19% 26% 8%	2555
	11th to 20th	Night	35% 16% 24% 19% 5% 1	2516
	21st to end	Night	56% 10% 15% 17% 3	2427
June	1st to 10th	Night	51% 9% 18% 15% 6% 2	1330
	11th to 20th	Night	48% 11% 21% 15% 5%	1330
	21st to end	Night	40% 10% 21% 20% 7% 2	1330
July	1st to 10th	Night	22% 6% 13% 28% 22% 8%	2185
	11th to 20th	Night	14% 5% 17% 43% 19% 2	2178
	21st to end	Night	23% 11% 22% 29% 13% 2	2389
August	1st to 10th	Night	16% 5% 12% 41% 24% 1	2704
	11th to 20th	Night	35% 12% 27% 15% 8% 1	2839
	21st to end	Night	37% 10% 23% 24% 5%	3146
September	1st to 10th	Night	26% 10% 18% 30% 13% 2	1886
	11th to 20th	Night	44% 10% 13% 17% 14% 3	1995
	21st to end	Night	46% 10% 16% 18% 9% 2	2116
October	1st to 10th	Night	53% 10% 15% 15% 7%	3800
	11th to 20th	Night	58% 9% 12% 17% 3	3777
	21st to end	Night	58% 10% 15% 13% 4	4410
November	1st to 10th	Night	68% 11% 8% 8% 4 1	2730
	11th to 20th	Night	67% 12% 9% 7% 4 1	2800
	21st to end	Night	67% 9% 10% 10% 4 1	2800
December	1st to 10th	Night	68% 10% 10% 10% 2	4843
	11th to 20th	Night	79% 8% 6% 5% 1	5556
	21st to end	Night	71% 10% 10% 7% 2	7458

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	40% 10% 25% 17% 4 5%	200
	11th to 20th	Day	37% 7% 25% 18% 11% 3	200
	21st to end	Day	36% 11% 19% 19% 12% 3	321
February	1st to 10th	Day	33% 14% 28% 15% 9% 2	400
	11th to 20th	Day	31% 12% 25% 20% 10% 2	395
	21st to end	Day	29% 20% 24% 16% 8% 3	331
March	1st to 10th	Day	26% 17% 23% 20% 12% 2	470
	11th to 20th	Day	28% 14% 21% 21% 13% 3	465
	21st to end	Day	28% 13% 26% 20% 10% 3	506
April	1st to 10th	Day	30% 15% 24% 19% 9% 3	460
	11th to 20th	Day	25% 14% 27% 19% 11% 4	452
	21st to end	Day	28% 15% 23% 18% 11% 5%	460
May	1st to 10th	Day	16% 11% 23% 28% 18% 3	463
	11th to 20th	Day	23% 6% 20% 28% 17% 6%	488
	21st to end	Day	18% 7% 23% 31% 16% 4	718
June	1st to 10th	Day	25% 10% 23% 22% 16% 3	680
	11th to 20th	Day	18% 13% 29% 23% 14% 3	680
	21st to end	Day	16% 10% 23% 27% 20% 4	680
July	1st to 10th	Day	15% 6% 21% 29% 24% 5%	671
	11th to 20th	Day	7% 6% 24% 36% 22% 5%	668
	21st to end	Day	6% 8% 19% 31% 28% 8%	708
August	1st to 10th	Day	11% 4 15% 30% 26% 13%	487
	11th to 20th	Day	10% 6% 15% 30% 30% 9%	477
	21st to end	Day	13% 8% 23% 29% 19% 7%	539
September	1st to 10th	Day	14% 6% 23% 32% 18% 7%	490
	11th to 20th	Day	24% 7% 21% 24% 18% 6%	490
	21st to end	Day	26% 11% 22% 19% 17% 5%	490
October	1st to 10th	Day	28% 10% 19% 18% 18% 7%	490
	11th to 20th	Day	32% 10% 22% 15% 15% 6%	490
	21st to end	Day	32% 14% 22% 17% 9% 5%	422
November	1st to 10th	Day	36% 16% 21% 14% 12% 3	200
	11th to 20th	Day	34% 12% 15% 15% 17% 9%	200
	21st to end	Day	41% 5% 20% 16% 11% 9%	200
December	1st to 10th	Day	29% 11% 21% 19% 10% 11%	200
	11th to 20th	Day	36% 9% 20% 19% 14% 4	200
	21st to end	Day	42% 9% 18% 19% 11% 1	220
January	1st to 10th	Night	39% 11% 21% 18% 8% 3	900
	11th to 20th	Night	34% 7% 20% 23% 15% 1	900
	21st to end	Night	35% 5% 21% 21% 14% 4	959
February	1st to 10th	Night	31% 8% 21% 26% 12% 1	800
	11th to 20th	Night	28% 7% 21% 28% 16% 1	784
	21st to end	Night	28% 10% 21% 25% 13% 3	660
March	1st to 10th	Night	24% 9% 25% 23% 16% 3	800
	11th to 20th	Night	24% 10% 24% 25% 15% 3	766
	21st to end	Night	27% 7% 21% 24% 17% 3	836
April	1st to 10th	Night	23% 10% 18% 29% 18% 3	753
	11th to 20th	Night	22% 3 26% 33% 14% 2	563
	21st to end	Night	22% 6% 22% 31% 16% 4	570
May	1st to 10th	Night	16% 4 21% 33% 24% 2	395
	11th to 20th	Night	17% 4 15% 35% 24% 5%	374
	21st to end	Night	17% 3 19% 33% 26% 2	411
June	1st to 10th	Night	17% 7% 19% 33% 23% 1	380
	11th to 20th	Night	15% 6% 26% 29% 23% 1	380
	21st to end	Night	14% 5% 18% 36% 22% 4	380
July	1st to 10th	Night	10% 1 15% 34% 36% 4	370
	11th to 20th	Night	6% 5% 11% 40% 35% 3	368
	21st to end	Night	7% 3 8% 36% 40% 6%	416
August	1st to 10th	Night	11% 2 8% 27% 43% 9%	483
	11th to 20th	Night	7% 2 9% 30% 44% 8%	564
	21st to end	Night	13% 3 15% 31% 34% 5%	627
September	1st to 10th	Night	11% 1 13% 34% 32% 8%	746
	11th to 20th	Night	19% 5% 14% 21% 28% 13%	760
	21st to end	Night	23% 6% 17% 27% 21% 6%	760
October	1st to 10th	Night	23% 5% 16% 27% 24% 5%	760
	11th to 20th	Night	30% 4 17% 23% 19% 6%	760
	21st to end	Night	29% 7% 23% 24% 14% 3	836
November	1st to 10th	Night	36% 8% 20% 25% 10% 1	780
	11th to 20th	Night	33% 8% 23% 22% 12% 3	800
	21st to end	Night	32% 8% 20% 22% 14% 4	800
December	1st to 10th	Night	29% 7% 19% 24% 16% 4	884
	11th to 20th	Night	39% 7% 21% 21% 9% 2	900
	21st to end	Night	38% 9% 24% 21% 8% 1	990

Page generated at 2025-03-09 05:08:46. Version ac07

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