Bella Bella
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bella Bella clear sky chart from 2005-11-06 to 2025-02-06.

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	35% 11% 3 7% 4 4 3 3 4 5% 21%	111962
	Night	39% 12% 3 7% 4 3 3 2 3 4 20%	114958
Transparency	Day	67% 4 12% 12% 4 1	111702
	Night	70% 3 11% 11% 4 1	114864
Seeing	Day	37% 9% 16% 20% 14% 4	16381
	Night	43% 8% 10% 18% 16% 5%	24143

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	41% 18% 4 7% 4 3 3 2 4 4 9%	3179
	11th to 20th	Day	38% 10% 2 4 3 3 3 3 4 5% 24%	3159
	21st to end	Day	49% 11% 2 5% 2 2 3 2 3 5% 16%	3820
February	1st to 10th	Day	46% 11% 3 7% 3 2 2 2 3 3 18%	1561
	11th to 20th	Day	35% 13% 3 6% 4 3 3 2 3 6% 23%	1660
	21st to end	Day	34% 16% 3 6% 4 3 3 3 2 2 25%	1475
March	1st to 10th	Day	32% 16% 3 7% 4 4 4 2 3 4 22%	3126
	11th to 20th	Day	35% 20% 4 8% 5% 4 3 2 3 3 14%	3486
	21st to end	Day	26% 12% 3 6% 4 4 4 3 5% 5% 28%	3841
April	1st to 10th	Day	36% 16% 4 8% 5% 4 3 3 4 4 15%	2374
	11th to 20th	Day	33% 12% 3 7% 4 4 3 3 5% 6% 21%	2438
	21st to end	Day	36% 11% 3 7% 6% 3 4 2 4 5% 19%	2470
May	1st to 10th	Day	29% 10% 3 6% 4 3 4 3 5% 6% 27%	4472
	11th to 20th	Day	34% 10% 3 6% 4 4 4 3 5% 6% 21%	4696
	21st to end	Day	32% 12% 3 7% 4 3 4 3 4 5% 21%	5161
June	1st to 10th	Day	37% 11% 3 6% 5% 4 4 3 4 5% 18%	2850
	11th to 20th	Day	37% 11% 4 8% 4 4 4 3 4 5% 16%	2850
	21st to end	Day	38% 11% 3 6% 4 4 3 2 4 6% 20%	2850
July	1st to 10th	Day	17% 6% 2 5% 4 4 4 3 5% 8% 43%	4740
	11th to 20th	Day	20% 10% 3 7% 4 4 5% 4 6% 7% 29%	4740
	21st to end	Day	37% 8% 3 7% 5% 4 4 3 5% 6% 19%	5138
August	1st to 10th	Day	14% 6% 3 5% 3 4 4 3 5% 7% 45%	4450
	11th to 20th	Day	26% 12% 4 9% 4 4 3 3 4 6% 26%	4065
	21st to end	Day	30% 10% 3 7% 4 4 4 3 5% 7% 22%	4521
September	1st to 10th	Day	33% 10% 4 6% 4 4 4 3 4 7% 23%	2391
	11th to 20th	Day	31% 10% 4 8% 4 4 3 3 5% 5% 23%	2090
	21st to end	Day	42% 11% 3 7% 5% 4 3 2 4 5% 15%	2090
October	1st to 10th	Day	41% 11% 3 8% 4 4 3 3 4 4 15%	3288
	11th to 20th	Day	42% 9% 4 9% 6% 5% 4 3 3 5% 10%	2948
	21st to end	Day	35% 11% 3 8% 5% 4 4 3 3 5% 19%	3101
November	1st to 10th	Day	50% 10% 3 6% 4 2 2 2 2 3 15%	1587
	11th to 20th	Day	49% 14% 4 6% 4 3 3 2 3 2 12%	1512
	21st to end	Day	46% 11% 3 6% 4 4 2 3 3 2 16%	1400
December	1st to 10th	Day	49% 11% 3 5% 3 3 2 2 3 4 15%	2290
	11th to 20th	Day	50% 15% 3 6% 4 3 3 2 3 2 11%	2645
	21st to end	Day	49% 16% 4 9% 4 3 2 2 2 2 8%	3498
January	1st to 10th	Night	46% 16% 4 7% 4 3 3 2 3 3 10%	6766
	11th to 20th	Night	37% 9% 2 6% 3 4 4 3 5% 5% 23%	6739
	21st to end	Night	53% 11% 3 5% 2 2 2 1 2 4 17%	7136
February	1st to 10th	Night	46% 12% 2 5% 4 2 3 2 3 3 19%	2730
	11th to 20th	Night	37% 13% 3 6% 3 2 3 2 3 4 24%	2407
	21st to end	Night	32% 15% 2 6% 4 3 2 3 3 5% 24%	1979
March	1st to 10th	Night	31% 14% 4 7% 4 4 4 3 4 5% 21%	3738
	11th to 20th	Night	34% 19% 4 8% 5% 3 4 3 3 2 13%	3492
	21st to end	Night	27% 13% 3 8% 4 4 3 3 4 6% 26%	3809
April	1st to 10th	Night	33% 16% 3 8% 4 3 3 3 4 4 20%	1806
	11th to 20th	Night	33% 14% 3 6% 4 2 2 3 4 4 23%	1691
	21st to end	Night	34% 12% 3 7% 3 4 2 2 3 4 26%	1710
May	1st to 10th	Night	22% 10% 3 6% 4 4 5% 3 5% 7% 30%	2490
	11th to 20th	Night	32% 10% 3 7% 4 5% 4 4 5% 5% 22%	2199
	21st to end	Night	35% 9% 3 7% 5% 4 3 3 4 4 24%	2414
June	1st to 10th	Night	38% 10% 3 5% 4 4 3 2 4 4 23%	1330
	11th to 20th	Night	35% 9% 3 6% 3 4 4 4 6% 6% 21%	1330
	21st to end	Night	36% 10% 2 7% 4 3 3 3 4 6% 23%	1330
July	1st to 10th	Night	17% 7% 2 6% 3 3 3 2 5% 5% 47%	2220
	11th to 20th	Night	22% 12% 3 6% 4 3 3 3 5% 7% 31%	2220
	21st to end	Night	32% 9% 3 7% 5% 4 4 2 5% 5% 26%	2414
August	1st to 10th	Night	14% 8% 2 6% 3 3 3 3 5% 7% 46%	2488
	11th to 20th	Night	26% 10% 3 7% 4 3 3 3 5% 6% 29%	2773
	21st to end	Night	30% 8% 3 7% 5% 5% 5% 3 3 5% 26%	3146
September	1st to 10th	Night	29% 9% 3 7% 5% 3 3 3 4 5% 28%	1786
	11th to 20th	Night	30% 9% 3 6% 4 3 3 2 3 5% 31%	2090
	21st to end	Night	44% 10% 3 7% 4 4 3 2 3 4 15%	2090
October	1st to 10th	Night	50% 10% 3 6% 3 3 2 2 3 3 15%	3691
	11th to 20th	Night	47% 13% 4 8% 5% 3 2 2 3 3 10%	3982
	21st to end	Night	36% 10% 3 7% 3 3 4 3 4 7% 20%	4458
November	1st to 10th	Night	48% 13% 3 6% 4 3 2 2 2 2 13%	2711
	11th to 20th	Night	47% 14% 3 7% 4 3 2 2 3 3 12%	2885
	21st to end	Night	46% 13% 3 7% 4 3 2 2 2 3 16%	3000
December	1st to 10th	Night	50% 11% 2 6% 3 2 2 2 2 4 15%	4890
	11th to 20th	Night	45% 15% 4 7% 4 3 3 2 3 3 12%	5560
	21st to end	Night	46% 17% 3 8% 3 3 3 2 3 3 9%	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	80% 2 5% 10% 2	3179
	11th to 20th	Day	64% 2 7% 15% 6% 6%	3180
	21st to end	Day	74% 2 10% 10% 3 1	3820
February	1st to 10th	Day	73% 1 5% 5% 9% 6%	1561
	11th to 20th	Day	67% 3 7% 14% 7% 2	1669
	21st to end	Day	67% 3 7% 11% 9% 4	1475
March	1st to 10th	Day	68% 4 6% 10% 10% 1	3126
	11th to 20th	Day	78% 1 6% 8% 5% 1	3486
	21st to end	Day	59% 3 13% 16% 7% 1	3841
April	1st to 10th	Day	77% 2 8% 8% 4 1	2374
	11th to 20th	Day	67% 3 8% 12% 9% 2	2438
	21st to end	Day	71% 2 9% 12% 5% 1	2470
May	1st to 10th	Day	60% 3 18% 15% 2	4472
	11th to 20th	Day	67% 3 17% 11% 2	4699
	21st to end	Day	70% 3 11% 10% 5% 1	5162
June	1st to 10th	Day	71% 4 13% 9% 2 2	2850
	11th to 20th	Day	74% 4 13% 8% 1	2850
	21st to end	Day	70% 3 15% 10% 2	2850
July	1st to 10th	Day	42% 6% 17% 21% 11% 2	4666
	11th to 20th	Day	52% 9% 28% 11% 1	4659
	21st to end	Day	67% 7% 15% 10% 1	4976
August	1st to 10th	Day	37% 4 17% 39% 3	4432
	11th to 20th	Day	64% 5% 15% 13% 2	4104
	21st to end	Day	63% 9% 16% 11% 1	4520
September	1st to 10th	Day	64% 4 17% 10% 3 1	2391
	11th to 20th	Day	63% 4 11% 16% 5%	2090
	21st to end	Day	76% 3 9% 9% 3	2090
October	1st to 10th	Day	75% 3 10% 9% 2 1	3288
	11th to 20th	Day	77% 4 9% 8% 2	2948
	21st to end	Day	70% 4 7% 12% 8%	3101
November	1st to 10th	Day	78% 2 5% 10% 5% 1	1587
	11th to 20th	Day	82% 2 5% 5% 5% 1	1512
	21st to end	Day	76% 2 5% 9% 6% 2	1400
December	1st to 10th	Day	74% 3 8% 9% 4 1	2290
	11th to 20th	Day	82% 2 5% 6% 3 2	2648
	21st to end	Day	86% 2 4 4 2 1	3498
January	1st to 10th	Night	82% 2 5% 8% 3	6766
	11th to 20th	Night	64% 4 9% 12% 6% 5%	6780
	21st to end	Night	76% 2 9% 10% 3	7136
February	1st to 10th	Night	74% 2 4 7% 8% 5%	2730
	11th to 20th	Night	68% 2 7% 13% 8% 3	2409
	21st to end	Night	65% 2 10% 13% 7% 3	1979
March	1st to 10th	Night	66% 3 8% 14% 7% 2	3738
	11th to 20th	Night	78% 3 6% 9% 3 1	3493
	21st to end	Night	63% 4 12% 13% 5% 3	3809
April	1st to 10th	Night	70% 4 12% 9% 5% 1	1806
	11th to 20th	Night	65% 2 8% 14% 9% 2	1691
	21st to end	Night	66% 2 11% 17% 3 1	1710
May	1st to 10th	Night	54% 5% 22% 16% 3	2490
	11th to 20th	Night	67% 4 16% 10% 2	2199
	21st to end	Night	67% 3 13% 10% 5% 2	2414
June	1st to 10th	Night	67% 4 14% 11% 1 2	1330
	11th to 20th	Night	67% 5% 18% 9% 1	1330
	21st to end	Night	65% 3 18% 12% 2	1330
July	1st to 10th	Night	40% 4 18% 27% 11%	2185
	11th to 20th	Night	54% 7% 29% 9% 1	2178
	21st to end	Night	61% 8% 20% 10% 1	2337
August	1st to 10th	Night	39% 4 21% 35% 2	2481
	11th to 20th	Night	58% 7% 19% 14% 2	2800
	21st to end	Night	63% 6% 18% 12% 1	3146
September	1st to 10th	Night	59% 4 21% 12% 3 1	1786
	11th to 20th	Night	57% 4 14% 18% 6%	2090
	21st to end	Night	77% 3 7% 9% 3 1	2090
October	1st to 10th	Night	78% 2 9% 8% 2 1	3691
	11th to 20th	Night	82% 3 7% 6% 1	3982
	21st to end	Night	65% 5% 12% 12% 7%	4458
November	1st to 10th	Night	80% 2 6% 7% 5% 1	2711
	11th to 20th	Night	80% 2 5% 8% 5% 2	2885
	21st to end	Night	76% 1 6% 9% 6% 1	3000
December	1st to 10th	Night	75% 3 8% 7% 5% 1	4890
	11th to 20th	Night	79% 3 5% 8% 4 1	5556
	21st to end	Night	82% 3 6% 5% 2 1	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	50% 14% 18% 10% 6% 3	200
	11th to 20th	Day	53% 13% 12% 14% 8% 1	200
	21st to end	Day	53% 7% 14% 14% 8% 3	360
February	1st to 10th	Day	48% 11% 21% 13% 6% 1	386
	11th to 20th	Day	37% 15% 19% 16% 11% 2	365
	21st to end	Day	46% 16% 18% 10% 9% 2	307
March	1st to 10th	Day	35% 12% 21% 18% 10% 3	370
	11th to 20th	Day	41% 15% 14% 18% 10% 2	459
	21st to end	Day	39% 8% 17% 18% 14% 3	506
April	1st to 10th	Day	43% 12% 18% 17% 8% 2	460
	11th to 20th	Day	31% 9% 20% 22% 14% 4	452
	21st to end	Day	37% 10% 19% 17% 14% 4	460
May	1st to 10th	Day	31% 9% 17% 25% 16% 3	557
	11th to 20th	Day	29% 7% 19% 28% 14% 3	675
	21st to end	Day	32% 10% 22% 25% 9% 2	735
June	1st to 10th	Day	39% 10% 16% 21% 12% 3	680
	11th to 20th	Day	35% 9% 20% 20% 13% 3	680
	21st to end	Day	36% 6% 15% 25% 14% 4	680
July	1st to 10th	Day	24% 7% 15% 27% 21% 6%	671
	11th to 20th	Day	28% 7% 17% 24% 18% 5%	668
	21st to end	Day	31% 6% 12% 24% 20% 6%	739
August	1st to 10th	Day	23% 4 13% 25% 28% 7%	676
	11th to 20th	Day	27% 7% 13% 29% 19% 6%	504
	21st to end	Day	40% 7% 14% 20% 15% 4	539
September	1st to 10th	Day	37% 6% 14% 20% 15% 8%	490
	11th to 20th	Day	33% 8% 14% 20% 19% 5%	490
	21st to end	Day	43% 9% 19% 15% 10% 4	490
October	1st to 10th	Day	38% 11% 12% 18% 15% 7%	490
	11th to 20th	Day	43% 11% 16% 17% 8% 5%	424
	21st to end	Day	41% 12% 17% 16% 11% 2	429
November	1st to 10th	Day	50% 11% 16% 13% 10%	219
	11th to 20th	Day	49% 14% 14% 12% 6% 6%	200
	21st to end	Day	49% 14% 13% 11% 9% 5%	200
December	1st to 10th	Day	42% 13% 11% 18% 12% 5%	200
	11th to 20th	Day	53% 8% 10% 20% 9% 2	200
	21st to end	Day	56% 8% 12% 16% 6% 1	220
January	1st to 10th	Night	53% 12% 13% 12% 9% 2	900
	11th to 20th	Night	55% 9% 13% 15% 7% 1	900
	21st to end	Night	52% 7% 11% 16% 11% 3	990
February	1st to 10th	Night	51% 11% 13% 18% 6% 1	875
	11th to 20th	Night	44% 10% 12% 19% 12% 3	747
	21st to end	Night	44% 11% 13% 20% 10% 2	628
March	1st to 10th	Night	39% 10% 17% 20% 13% 1	760
	11th to 20th	Night	46% 11% 11% 20% 11% 1	760
	21st to end	Night	44% 8% 10% 18% 16% 3	829
April	1st to 10th	Night	40% 7% 9% 21% 18% 4	570
	11th to 20th	Night	38% 6% 12% 24% 16% 4	563
	21st to end	Night	39% 7% 9% 24% 18% 3	570
May	1st to 10th	Night	35% 6% 7% 21% 24% 6%	451
	11th to 20th	Night	30% 5% 10% 27% 22% 5%	374
	21st to end	Night	32% 4 5% 26% 27% 5%	411
June	1st to 10th	Night	38% 4 6% 17% 27% 7%	380
	11th to 20th	Night	37% 5% 5% 20% 23% 10%	380
	21st to end	Night	39% 3 5% 22% 23% 7%	380
July	1st to 10th	Night	30% 2 4 19% 31% 13%	370
	11th to 20th	Night	31% 4 5% 17% 31% 13%	368
	21st to end	Night	28% 6% 3 17% 34% 12%	416
August	1st to 10th	Night	25% 4 3 14% 33% 21%	538
	11th to 20th	Night	29% 2 4 16% 36% 13%	564
	21st to end	Night	39% 4 5% 19% 28% 5%	627
September	1st to 10th	Night	32% 6% 7% 20% 23% 11%	603
	11th to 20th	Night	32% 7% 6% 19% 24% 13%	760
	21st to end	Night	48% 8% 9% 18% 15% 3	760
October	1st to 10th	Night	42% 6% 9% 20% 18% 5%	760
	11th to 20th	Night	48% 7% 10% 17% 14% 5%	760
	21st to end	Night	46% 7% 11% 22% 10% 3	836
November	1st to 10th	Night	55% 9% 13% 17% 6% 1	780
	11th to 20th	Night	53% 11% 11% 16% 7% 2	843
	21st to end	Night	52% 11% 10% 15% 9% 2	900
December	1st to 10th	Night	44% 9% 13% 19% 12% 3	900
	11th to 20th	Night	47% 13% 13% 17% 8% 3	900
	21st to end	Night	53% 11% 12% 17% 6% 1	990

Page generated at 2025-02-03 00:05:50. Version ac07

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