Banks
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Banks clear sky chart from 2005-11-06 to 2024-11-25.

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	17% 8% 3 7% 5% 4 4 3 5% 6% 37%	106016
	Night	19% 9% 3 7% 5% 4 4 3 4 5% 38%	102123
Transparency	Day	47% 8% 12% 17% 12% 4	105758
	Night	48% 8% 13% 18% 11% 3	101970
Seeing	Day	21% 11% 24% 26% 15% 4	15027
	Night	22% 6% 22% 33% 15% 1	23623

By Month

Percentage Cloud Cover SW (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	35% 14% 4 10% 6% 6% 5% 4 4 4 8%	2539
	11th to 20th	Day	35% 12% 5% 9% 6% 3 3 3 3 3 18%	2540
	21st to end	Day	33% 13% 4 11% 6% 5% 4 3 4 4 13%	3081
February	1st to 10th	Day	29% 14% 4 9% 5% 5% 5% 3 5% 5% 17%	1710
	11th to 20th	Day	28% 14% 4 9% 7% 5% 5% 3 4 3 18%	1665
	21st to end	Day	26% 14% 5% 10% 7% 5% 4 3 5% 4 18%	1470
March	1st to 10th	Day	19% 16% 4 11% 7% 6% 6% 4 6% 6% 17%	3318
	11th to 20th	Day	21% 9% 3 9% 6% 4 3 2 3 4 36%	3490
	21st to end	Day	23% 13% 5% 11% 7% 6% 5% 4 5% 6% 16%	3881
April	1st to 10th	Day	25% 12% 4 10% 7% 5% 5% 4 5% 5% 19%	2280
	11th to 20th	Day	22% 12% 3 8% 6% 5% 4 3 5% 5% 25%	2267
	21st to end	Day	20% 10% 4 8% 7% 6% 6% 4 6% 7% 23%	2470
May	1st to 10th	Day	18% 8% 3 8% 5% 4 4 3 5% 5% 36%	4327
	11th to 20th	Day	9% 6% 2 6% 4 4 5% 4 6% 8% 47%	4377
	21st to end	Day	18% 8% 3 9% 7% 6% 7% 5% 5% 6% 25%	4813
June	1st to 10th	Day	20% 9% 3 8% 6% 5% 4 3 5% 6% 33%	2660
	11th to 20th	Day	15% 9% 3 9% 6% 5% 6% 5% 6% 8% 28%	2712
	21st to end	Day	8% 5% 2 6% 4 5% 4 3 5% 7% 51%	2850
July	1st to 10th	Day	4 3 1 4 3 2 3 2 3 4 70%	4585
	11th to 20th	Day	4 2 1 2 2 2 2 2 3 4 75%	4420
	21st to end	Day	6% 2 1 3 2 2 2 2 3 6% 70%	4790
August	1st to 10th	Day	3 3 1 4 3 2 3 2 4 6% 69%	4101
	11th to 20th	Day	6% 4 2 5% 4 4 5% 4 6% 9% 51%	4026
	21st to end	Day	8% 6% 2 6% 3 4 3 3 4 6% 54%	4335
September	1st to 10th	Day	6% 3 2 4 4 3 4 3 4 7% 61%	2280
	11th to 20th	Day	11% 6% 2 7% 4 5% 4 4 5% 8% 44%	2262
	21st to end	Day	16% 5% 2 5% 4 3 4 3 4 7% 46%	2009
October	1st to 10th	Day	13% 6% 2 4 3 3 3 3 5% 7% 49%	3180
	11th to 20th	Day	17% 8% 3 10% 6% 5% 6% 4 7% 6% 29%	3161
	21st to end	Day	25% 11% 3 7% 5% 4 4 4 5% 6% 25%	3393
November	1st to 10th	Day	28% 12% 4 10% 7% 5% 4 4 4 6% 17%	1630
	11th to 20th	Day	31% 12% 5% 7% 5% 4 5% 3 4 5% 20%	1600
	21st to end	Day	26% 12% 4 10% 5% 5% 4 3 5% 4 23%	1552
December	1st to 10th	Day	26% 14% 5% 8% 5% 4 4 3 4 3 24%	1520
	11th to 20th	Day	29% 13% 3 9% 6% 5% 5% 3 5% 5% 16%	1928
	21st to end	Day	30% 14% 5% 13% 7% 5% 5% 3 4 4 11%	2794
January	1st to 10th	Night	32% 12% 4 10% 7% 5% 5% 4 5% 4 12%	4406
	11th to 20th	Night	34% 13% 4 8% 5% 4 4 2 3 4 18%	4420
	21st to end	Night	36% 14% 3 9% 5% 4 3 3 4 4 16%	4583
February	1st to 10th	Night	25% 13% 3 8% 7% 5% 5% 3 5% 5% 21%	2470
	11th to 20th	Night	25% 12% 4 8% 5% 4 4 4 4 4 27%	2402
	21st to end	Night	24% 14% 4 9% 6% 4 5% 4 4 5% 22%	1984
March	1st to 10th	Night	16% 18% 4 9% 5% 7% 6% 3 4 5% 23%	3554
	11th to 20th	Night	15% 10% 2 7% 4 4 4 3 4 5% 42%	3490
	21st to end	Night	23% 14% 4 10% 7% 6% 6% 4 4 5% 18%	3771
April	1st to 10th	Night	22% 12% 4 9% 5% 5% 5% 4 5% 4 25%	1900
	11th to 20th	Night	16% 12% 3 8% 5% 5% 4 3 6% 6% 31%	1855
	21st to end	Night	19% 10% 3 6% 5% 4 4 4 5% 7% 33%	1710
May	1st to 10th	Night	19% 7% 2 5% 4 3 4 3 4 5% 44%	2621
	11th to 20th	Night	7% 4 2 4 3 3 4 4 5% 7% 58%	2516
	21st to end	Night	11% 6% 3 7% 5% 6% 6% 4 6% 7% 39%	2762
June	1st to 10th	Night	13% 7% 2 6% 7% 6% 4 4 3 6% 41%	1520
	11th to 20th	Night	12% 7% 3 7% 5% 4 4 3 5% 6% 45%	1459
	21st to end	Night	6% 4 2 4 4 2 3 2 4 6% 62%	1330
July	1st to 10th	Night	2 1 1 2 2 2 2 2 3 3 81%	2367
	11th to 20th	Night	3 2 1 3 2 2 2 1 3 4 77%	2540
	21st to end	Night	2 2 1 2 2 2 2 2 2 3 80%	2761
August	1st to 10th	Night	2 2 1 2 1 1 2 2 4 4 80%	2835
	11th to 20th	Night	6% 4 2 4 2 3 3 3 5% 6% 63%	2812
	21st to end	Night	9% 3 2 5% 3 3 3 2 4 4 63%	3337
September	1st to 10th	Night	5% 2 1 3 3 3 3 2 4 5% 68%	1900
	11th to 20th	Night	9% 6% 2 5% 5% 4 5% 3 4 6% 52%	1914
	21st to end	Night	10% 5% 2 5% 4 4 4 3 5% 6% 55%	2171
October	1st to 10th	Night	10% 4 1 4 3 3 3 3 4 6% 58%	3800
	11th to 20th	Night	16% 7% 3 7% 4 4 4 4 6% 8% 37%	3777
	21st to end	Night	23% 10% 3 7% 4 5% 4 3 4 5% 32%	4172
November	1st to 10th	Night	27% 10% 3 8% 5% 5% 5% 3 5% 5% 24%	2664
	11th to 20th	Night	33% 10% 3 8% 5% 5% 4 3 4 5% 22%	2800
	21st to end	Night	24% 10% 3 7% 6% 5% 4 4 4 4 28%	2722
December	1st to 10th	Night	25% 13% 4 7% 6% 4 4 3 5% 5% 25%	2660
	11th to 20th	Night	28% 12% 4 9% 6% 5% 5% 3 4 5% 19%	3276
	21st to end	Night	29% 13% 4 10% 5% 5% 4 3 5% 4 18%	4862

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% 9% 5% 4 2	2539
	11th to 20th	Day	72% 6% 7% 10% 3 2	2540
	21st to end	Day	74% 8% 7% 7% 4	3081
February	1st to 10th	Day	69% 8% 10% 9% 3	1710
	11th to 20th	Day	70% 9% 7% 10% 4 1	1674
	21st to end	Day	69% 7% 9% 9% 5% 1	1470
March	1st to 10th	Day	65% 9% 13% 10% 3	3318
	11th to 20th	Day	52% 6% 8% 25% 8%	3490
	21st to end	Day	67% 11% 11% 8% 3	3881
April	1st to 10th	Day	66% 8% 13% 11% 2	2280
	11th to 20th	Day	59% 9% 10% 12% 8% 2	2270
	21st to end	Day	58% 10% 12% 12% 7% 1	2470
May	1st to 10th	Day	48% 9% 12% 18% 12% 1	4327
	11th to 20th	Day	31% 11% 22% 26% 10% 1	4380
	21st to end	Day	54% 15% 16% 13% 2	4814
June	1st to 10th	Day	52% 8% 15% 17% 7% 1	2660
	11th to 20th	Day	51% 11% 16% 15% 6%	2712
	21st to end	Day	32% 8% 17% 27% 11% 4	2850
July	1st to 10th	Day	18% 5% 9% 16% 22% 30%	4515
	11th to 20th	Day	15% 4 7% 20% 38% 16%	4345
	21st to end	Day	17% 5% 12% 28% 34% 5%	4639
August	1st to 10th	Day	17% 5% 11% 27% 28% 13%	4085
	11th to 20th	Day	26% 9% 21% 27% 13% 4	4065
	21st to end	Day	31% 6% 12% 25% 20% 6%	4334
September	1st to 10th	Day	23% 7% 14% 26% 19% 11%	2280
	11th to 20th	Day	39% 9% 14% 18% 14% 6%	2262
	21st to end	Day	39% 8% 14% 20% 15% 4	2009
October	1st to 10th	Day	35% 6% 9% 29% 19% 2	3180
	11th to 20th	Day	53% 9% 13% 14% 11% 1	3161
	21st to end	Day	57% 7% 9% 17% 9% 1	3393
November	1st to 10th	Day	68% 9% 9% 11% 3	1630
	11th to 20th	Day	67% 8% 9% 9% 6% 1	1600
	21st to end	Day	64% 7% 7% 9% 11% 1	1552
December	1st to 10th	Day	66% 6% 6% 11% 9% 1	1520
	11th to 20th	Day	69% 8% 11% 11% 2	1928
	21st to end	Day	76% 10% 7% 5% 2	2794
January	1st to 10th	Night	73% 10% 8% 5% 3 1	4406
	11th to 20th	Night	70% 7% 7% 11% 4 2	4420
	21st to end	Night	72% 7% 8% 7% 5% 1	4583
February	1st to 10th	Night	64% 10% 10% 12% 4	2470
	11th to 20th	Night	60% 8% 12% 13% 5% 2	2404
	21st to end	Night	63% 8% 12% 10% 6% 1	1984
March	1st to 10th	Night	61% 9% 12% 15% 3	3554
	11th to 20th	Night	42% 10% 14% 25% 9% 1	3490
	21st to end	Night	65% 11% 12% 11% 1	3771
April	1st to 10th	Night	61% 8% 15% 12% 5%	1900
	11th to 20th	Night	52% 9% 14% 15% 8% 3	1855
	21st to end	Night	50% 9% 15% 17% 6% 2	1710
May	1st to 10th	Night	41% 9% 14% 26% 9% 1	2621
	11th to 20th	Night	25% 7% 19% 33% 14% 2	2516
	21st to end	Night	39% 15% 29% 13% 4	2762
June	1st to 10th	Night	45% 7% 17% 23% 7% 1	1520
	11th to 20th	Night	40% 8% 20% 25% 7%	1459
	21st to end	Night	24% 6% 20% 33% 12% 4	1330
July	1st to 10th	Night	11% 4 9% 22% 22% 32%	2328
	11th to 20th	Night	14% 3 7% 20% 33% 22%	2492
	21st to end	Night	11% 3 12% 30% 36% 7%	2674
August	1st to 10th	Night	10% 3 11% 31% 31% 13%	2827
	11th to 20th	Night	22% 7% 23% 31% 12% 5%	2839
	21st to end	Night	26% 5% 15% 27% 21% 5%	3337
September	1st to 10th	Night	19% 7% 13% 29% 21% 11%	1900
	11th to 20th	Night	33% 8% 15% 23% 13% 8%	1914
	21st to end	Night	31% 7% 16% 21% 18% 7%	2171
October	1st to 10th	Night	29% 6% 11% 33% 20% 2	3800
	11th to 20th	Night	43% 8% 18% 19% 11% 2	3777
	21st to end	Night	53% 8% 9% 18% 10% 1	4172
November	1st to 10th	Night	60% 9% 10% 14% 6%	2664
	11th to 20th	Night	65% 8% 10% 10% 6% 1	2800
	21st to end	Night	58% 9% 9% 11% 12% 2	2722
December	1st to 10th	Night	61% 7% 9% 12% 9%	2660
	11th to 20th	Night	68% 8% 9% 10% 5%	3276
	21st to end	Night	68% 12% 10% 8% 2	4862

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	46% 13% 17% 12% 9% 3	180
	11th to 20th	Day	42% 4 20% 15% 13% 6%	180
	21st to end	Day	35% 10% 17% 20% 15% 3	368
February	1st to 10th	Day	38% 8% 23% 19% 10% 2	370
	11th to 20th	Day	35% 13% 27% 15% 9% 1	365
	21st to end	Day	35% 16% 22% 19% 6% 2	334
March	1st to 10th	Day	31% 16% 24% 21% 7% 1	460
	11th to 20th	Day	27% 16% 24% 20% 10% 3	460
	21st to end	Day	33% 14% 23% 18% 11% 1	506
April	1st to 10th	Day	30% 15% 20% 23% 8% 4	460
	11th to 20th	Day	26% 19% 26% 17% 7% 4	452
	21st to end	Day	22% 17% 27% 21% 12% 2	460
May	1st to 10th	Day	16% 18% 28% 22% 12% 4	463
	11th to 20th	Day	22% 11% 27% 22% 14% 5%	488
	21st to end	Day	18% 12% 24% 26% 16% 4	529
June	1st to 10th	Day	21% 10% 25% 26% 15% 2	490
	11th to 20th	Day	13% 17% 32% 27% 9% 2	542
	21st to end	Day	6% 10% 33% 32% 17% 3	680
July	1st to 10th	Day	8% 7% 30% 34% 16% 6%	585
	11th to 20th	Day	5% 9% 26% 36% 18% 5%	484
	21st to end	Day	3 5% 25% 40% 22% 5%	531
August	1st to 10th	Day	6% 4 21% 37% 24% 8%	487
	11th to 20th	Day	5% 4 20% 37% 25% 10%	477
	21st to end	Day	8% 7% 27% 33% 19% 6%	539
September	1st to 10th	Day	7% 7% 26% 34% 22% 4	490
	11th to 20th	Day	14% 6% 20% 32% 22% 6%	490
	21st to end	Day	17% 9% 24% 30% 16% 4	490
October	1st to 10th	Day	20% 10% 22% 24% 19% 4	490
	11th to 20th	Day	21% 9% 23% 24% 18% 6%	490
	21st to end	Day	30% 11% 25% 18% 11% 4	508
November	1st to 10th	Day	31% 11% 23% 22% 12% 2	233
	11th to 20th	Day	38% 10% 19% 18% 10% 6%	200
	21st to end	Day	28% 13% 24% 19% 11% 6%	188
December	1st to 10th	Day	36% 8% 18% 21% 13% 4	180
	11th to 20th	Day	41% 6% 23% 18% 9% 2	180
	21st to end	Day	35% 13% 18% 22% 11% 2	198
January	1st to 10th	Night	37% 7% 18% 22% 14% 3	760
	11th to 20th	Night	36% 7% 13% 25% 18% 1	760
	21st to end	Night	31% 5% 13% 31% 17% 3	836
February	1st to 10th	Night	30% 8% 19% 27% 15% 2	760
	11th to 20th	Night	30% 9% 18% 26% 17% 1	744
	21st to end	Night	29% 8% 21% 29% 13%	628
March	1st to 10th	Night	28% 8% 20% 30% 13% 1	760
	11th to 20th	Night	25% 6% 18% 36% 13% 1	760
	21st to end	Night	28% 10% 20% 29% 12% 1	836
April	1st to 10th	Night	25% 11% 22% 28% 14% 1	760
	11th to 20th	Night	21% 8% 27% 32% 11% 1	727
	21st to end	Night	22% 7% 25% 33% 12% 1	570
May	1st to 10th	Night	15% 6% 34% 30% 14% 1	435
	11th to 20th	Night	14% 5% 27% 38% 15% 1	374
	21st to end	Night	14% 7% 27% 35% 15%	411
June	1st to 10th	Night	16% 5% 31% 37% 10%	380
	11th to 20th	Night	10% 9% 34% 37% 10% 1	380
	21st to end	Night	8% 4 37% 41% 9%	380
July	1st to 10th	Night	3 4 34% 48% 11% 1	370
	11th to 20th	Night	4 7% 40% 39% 10%	368
	21st to end	Night	3 3 36% 47% 11%	416
August	1st to 10th	Night	3 3 24% 44% 24% 1	554
	11th to 20th	Night	6% 2 17% 49% 24% 2	564
	21st to end	Night	7% 4 29% 40% 19% 1	740
September	1st to 10th	Night	6% 4 26% 46% 16% 2	760
	11th to 20th	Night	11% 3 21% 35% 27% 4	760
	21st to end	Night	11% 6% 22% 41% 19% 2	760
October	1st to 10th	Night	16% 4 23% 37% 18% 2	760
	11th to 20th	Night	20% 4 16% 34% 23% 4	760
	21st to end	Night	26% 7% 19% 30% 17% 2	836
November	1st to 10th	Night	30% 6% 15% 34% 14%	780
	11th to 20th	Night	37% 7% 16% 26% 13% 1	800
	21st to end	Night	29% 5% 16% 31% 17% 2	778
December	1st to 10th	Night	28% 6% 19% 30% 15% 2	760
	11th to 20th	Night	37% 6% 17% 26% 13% 1	760
	21st to end	Night	37% 8% 18% 25% 11% 1	836

Page generated at 2024-11-22 05:02:26. Version ac07

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