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 2024-01-14.

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	19% 8% 3 7% 6% 3 5% 4 5% 6% 34%	75066
	Night	19% 8% 3 6% 6% 3 4 4 4 5% 36%	74688
Transparency	Day	51% 8% 12% 17% 10% 2	74768
	Night	49% 8% 12% 17% 10% 3	74507
Seeing	Day	21% 11% 24% 26% 15% 4	13845
	Night	22% 6% 21% 33% 16% 1	22578

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	38% 13% 4 8% 7% 4 4 4 4 3 11%	1519
	11th to 20th	Day	33% 10% 6% 7% 6% 2 4 3 4 4 21%	1464
	21st to end	Day	26% 11% 4 10% 7% 3 5% 4 4 5% 21%	1745
February	1st to 10th	Day	30% 13% 4 8% 6% 4 5% 4 4 5% 17%	1620
	11th to 20th	Day	28% 13% 5% 8% 8% 4 5% 4 4 3 19%	1575
	21st to end	Day	26% 13% 5% 9% 8% 4 5% 4 4 4 19%	1386
March	1st to 10th	Day	27% 11% 5% 9% 7% 4 5% 5% 6% 5% 17%	1902
	11th to 20th	Day	29% 10% 4 8% 7% 3 5% 4 4 5% 20%	1980
	21st to end	Day	26% 12% 5% 10% 8% 4 6% 6% 5% 5% 13%	2209
April	1st to 10th	Day	25% 11% 4 9% 8% 4 6% 4 5% 6% 18%	2160
	11th to 20th	Day	24% 11% 4 7% 7% 4 5% 4 5% 5% 24%	2146
	21st to end	Day	20% 10% 4 7% 7% 4 6% 6% 6% 7% 24%	2340
May	1st to 10th	Day	14% 7% 4 8% 7% 4 4 5% 5% 7% 36%	2466
	11th to 20th	Day	16% 9% 3 7% 6% 3 5% 5% 6% 7% 31%	2477
	21st to end	Day	20% 7% 3 7% 6% 4 5% 6% 6% 7% 28%	2723
June	1st to 10th	Day	20% 8% 4 7% 7% 3 4 4 5% 6% 32%	2520
	11th to 20th	Day	16% 8% 4 8% 7% 4 6% 6% 6% 8% 28%	2569
	21st to end	Day	8% 5% 3 5% 5% 3 5% 4 4 7% 51%	2700
July	1st to 10th	Day	7% 3 2 5% 5% 3 4 4 4 6% 57%	2615
	11th to 20th	Day	7% 4 1 3 4 2 3 3 4 6% 63%	2520
	21st to end	Day	5% 2 1 2 2 1 2 2 3 5% 74%	2741
August	1st to 10th	Day	5% 3 2 4 4 2 3 3 4 7% 64%	2338
	11th to 20th	Day	6% 3 1 3 3 2 4 4 5% 7% 64%	2298
	21st to end	Day	7% 4 2 4 4 3 4 4 5% 7% 55%	2466
September	1st to 10th	Day	6% 3 2 3 4 2 3 4 4 7% 62%	2160
	11th to 20th	Day	11% 6% 3 6% 5% 3 5% 5% 5% 8% 44%	2143
	21st to end	Day	16% 6% 2 4 5% 2 4 4 4 6% 45%	1904
October	1st to 10th	Day	18% 8% 3 5% 5% 4 5% 4 5% 6% 38%	1800
	11th to 20th	Day	18% 8% 3 7% 7% 3 5% 4 6% 6% 32%	1800
	21st to end	Day	26% 11% 4 7% 5% 3 4 4 3 4 32%	1951
November	1st to 10th	Day	28% 11% 4 8% 8% 4 4 5% 4 6% 17%	1547
	11th to 20th	Day	31% 10% 5% 7% 5% 3 5% 4 4 5% 20%	1520
	21st to end	Day	26% 11% 4 9% 6% 3 4 3 5% 4 24%	1520
December	1st to 10th	Day	26% 13% 5% 8% 6% 3 5% 4 4 4 24%	1520
	11th to 20th	Day	29% 13% 4 8% 8% 4 5% 4 5% 5% 16%	1928
	21st to end	Day	30% 13% 6% 11% 9% 4 5% 5% 4 4 11%	2794
January	1st to 10th	Night	33% 10% 4 7% 7% 3 5% 4 4 5% 17%	2646
	11th to 20th	Night	32% 11% 4 6% 6% 3 4 4 4 6% 20%	2568
	21st to end	Night	25% 11% 4 8% 6% 3 4 4 4 5% 27%	2610
February	1st to 10th	Night	25% 12% 3 7% 8% 4 5% 4 6% 5% 21%	2340
	11th to 20th	Night	25% 11% 4 7% 6% 3 4 4 4 5% 27%	2272
	21st to end	Night	24% 12% 5% 8% 7% 3 4 5% 4 5% 23%	1870
March	1st to 10th	Night	23% 13% 4 7% 6% 4 6% 4 3 4 26%	2056
	11th to 20th	Night	22% 9% 4 8% 6% 4 5% 5% 5% 6% 25%	1980
	21st to end	Night	24% 10% 4 9% 7% 4 6% 5% 5% 6% 20%	2146
April	1st to 10th	Night	23% 11% 5% 8% 6% 4 5% 5% 5% 5% 25%	1800
	11th to 20th	Night	17% 10% 5% 7% 6% 4 5% 4 6% 6% 30%	1757
	21st to end	Night	19% 9% 3 6% 5% 3 4 5% 5% 8% 34%	1620
May	1st to 10th	Night	10% 6% 3 6% 6% 3 6% 5% 5% 7% 43%	1493
	11th to 20th	Night	13% 5% 3 5% 6% 3 6% 6% 6% 8% 39%	1416
	21st to end	Night	13% 6% 3 5% 6% 4 6% 5% 6% 7% 39%	1552
June	1st to 10th	Night	13% 7% 3 5% 7% 5% 5% 5% 3 7% 41%	1440
	11th to 20th	Night	13% 7% 3 6% 6% 3 4 4 5% 7% 43%	1383
	21st to end	Night	6% 4 2 4 4 2 2 3 3 6% 63%	1260
July	1st to 10th	Night	4 2 2 3 3 2 3 4 4 5% 68%	1337
	11th to 20th	Night	4 3 1 2 3 1 3 2 4 6% 70%	1440
	21st to end	Night	2 1 1 1 2 1 2 2 2 3 83%	1576
August	1st to 10th	Night	3 2 1 2 2 1 2 3 4 6% 74%	1598
	11th to 20th	Night	4 1 1 2 2 2 2 3 3 5% 75%	1602
	21st to end	Night	6% 3 2 4 3 2 4 3 4 5% 66%	1889
September	1st to 10th	Night	5% 2 1 3 4 2 3 3 4 5% 69%	1800
	11th to 20th	Night	8% 6% 2 5% 5% 3 4 5% 4 6% 51%	1813
	21st to end	Night	10% 5% 2 4 5% 3 4 4 5% 6% 54%	2056
October	1st to 10th	Night	15% 6% 2 5% 5% 3 3 3 4 5% 49%	2160
	11th to 20th	Night	17% 6% 3 5% 5% 3 4 4 5% 7% 41%	2160
	21st to end	Night	22% 8% 3 5% 5% 3 3 4 3 5% 40%	2403
November	1st to 10th	Night	27% 9% 3 7% 6% 4 5% 4 5% 5% 25%	2527
	11th to 20th	Night	31% 9% 3 7% 6% 3 4 4 4 5% 23%	2660
	21st to end	Night	23% 9% 3 7% 6% 4 5% 5% 4 4 29%	2660
December	1st to 10th	Night	25% 12% 5% 6% 6% 3 4 4 4 6% 25%	2660
	11th to 20th	Night	29% 12% 4 8% 7% 4 5% 4 4 5% 19%	3276
	21st to end	Night	29% 13% 4 9% 7% 4 4 4 4 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	79% 6% 5% 5% 4 1	1519
	11th to 20th	Day	69% 5% 9% 9% 5% 3	1464
	21st to end	Day	65% 8% 9% 11% 7%	1745
February	1st to 10th	Day	70% 8% 10% 9% 3	1620
	11th to 20th	Day	69% 9% 7% 10% 4 1	1584
	21st to end	Day	69% 7% 8% 9% 5% 1	1386
March	1st to 10th	Day	67% 8% 10% 9% 5%	1902
	11th to 20th	Day	67% 7% 9% 13% 4 1	1980
	21st to end	Day	72% 10% 9% 8% 1	2209
April	1st to 10th	Day	67% 8% 12% 11% 3	2160
	11th to 20th	Day	61% 8% 10% 12% 7% 2	2149
	21st to end	Day	58% 10% 12% 12% 8% 1	2340
May	1st to 10th	Day	48% 8% 15% 19% 9% 1	2466
	11th to 20th	Day	50% 10% 14% 18% 6% 1	2480
	21st to end	Day	53% 11% 15% 17% 3	2724
June	1st to 10th	Day	53% 8% 15% 17% 6% 1	2520
	11th to 20th	Day	52% 11% 17% 14% 5%	2569
	21st to end	Day	33% 8% 17% 27% 11% 4	2700
July	1st to 10th	Day	29% 8% 13% 23% 22% 5%	2545
	11th to 20th	Day	24% 6% 10% 29% 25% 6%	2445
	21st to end	Day	14% 4 11% 32% 32% 6%	2589
August	1st to 10th	Day	20% 8% 17% 31% 19% 5%	2321
	11th to 20th	Day	20% 7% 15% 29% 21% 7%	2298
	21st to end	Day	27% 8% 12% 30% 19% 3	2466
September	1st to 10th	Day	22% 7% 14% 27% 20% 11%	2160
	11th to 20th	Day	39% 9% 14% 17% 15% 6%	2143
	21st to end	Day	40% 8% 13% 19% 16% 5%	1904
October	1st to 10th	Day	47% 9% 8% 20% 14% 3	1800
	11th to 20th	Day	52% 9% 12% 14% 11% 1	1800
	21st to end	Day	59% 7% 8% 13% 13% 1	1951
November	1st to 10th	Day	68% 9% 9% 10% 3	1547
	11th to 20th	Day	66% 8% 10% 9% 6% 1	1520
	21st to end	Day	64% 7% 8% 10% 11% 1	1520
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	70% 7% 9% 7% 5% 1	2646
	11th to 20th	Night	66% 6% 9% 9% 7% 3	2568
	21st to end	Night	60% 7% 10% 12% 9% 1	2610
February	1st to 10th	Night	64% 10% 10% 12% 4	2340
	11th to 20th	Night	60% 8% 12% 13% 5% 2	2274
	21st to end	Night	63% 8% 11% 10% 6% 1	1870
March	1st to 10th	Night	62% 7% 11% 15% 5%	2056
	11th to 20th	Night	57% 10% 13% 14% 6% 1	1980
	21st to end	Night	63% 11% 13% 12% 1	2146
April	1st to 10th	Night	61% 8% 13% 12% 5%	1800
	11th to 20th	Night	53% 8% 14% 15% 7% 3	1757
	21st to end	Night	50% 9% 15% 17% 7% 2	1620
May	1st to 10th	Night	39% 8% 18% 25% 8% 1	1493
	11th to 20th	Night	41% 9% 20% 20% 6% 3	1416
	21st to end	Night	42% 12% 20% 19% 7%	1552
June	1st to 10th	Night	45% 6% 18% 24% 6% 1	1440
	11th to 20th	Night	42% 8% 21% 23% 6%	1383
	21st to end	Night	25% 6% 20% 33% 12% 5%	1260
July	1st to 10th	Night	19% 7% 16% 29% 21% 8%	1298
	11th to 20th	Night	18% 6% 12% 28% 29% 8%	1392
	21st to end	Night	8% 3 11% 36% 30% 12%	1488
August	1st to 10th	Night	13% 5% 18% 35% 24% 6%	1590
	11th to 20th	Night	14% 4 16% 36% 21% 8%	1602
	21st to end	Night	20% 6% 12% 36% 21% 4	1889
September	1st to 10th	Night	19% 7% 12% 29% 21% 11%	1800
	11th to 20th	Night	33% 8% 15% 22% 13% 9%	1813
	21st to end	Night	31% 7% 16% 20% 19% 7%	2056
October	1st to 10th	Night	39% 6% 10% 25% 17% 3	2160
	11th to 20th	Night	41% 9% 13% 20% 16% 3	2160
	21st to end	Night	48% 8% 9% 17% 15% 2	2403
November	1st to 10th	Night	60% 9% 10% 14% 6%	2527
	11th to 20th	Night	64% 8% 10% 10% 6% 1	2660
	21st to end	Night	57% 9% 9% 11% 12% 2	2660
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	43% 5% 19% 14% 13% 6%	166
	21st to end	Day	34% 10% 15% 21% 16% 3	337
February	1st to 10th	Day	39% 9% 21% 19% 10% 2	340
	11th to 20th	Day	35% 11% 28% 16% 9% 1	335
	21st to end	Day	34% 17% 22% 19% 7% 1	304
March	1st to 10th	Day	32% 16% 24% 21% 7% 1	420
	11th to 20th	Day	29% 16% 24% 19% 10% 1	420
	21st to end	Day	34% 13% 22% 19% 11% 1	462
April	1st to 10th	Day	31% 14% 20% 22% 8% 4	420
	11th to 20th	Day	28% 18% 24% 18% 8% 5%	412
	21st to end	Day	22% 17% 27% 20% 12% 2	420
May	1st to 10th	Day	15% 18% 26% 23% 13% 4	423
	11th to 20th	Day	23% 10% 25% 22% 14% 5%	448
	21st to end	Day	18% 12% 23% 27% 16% 4	485
June	1st to 10th	Day	22% 10% 25% 25% 16% 2	450
	11th to 20th	Day	13% 17% 32% 27% 8% 2	499
	21st to end	Day	7% 10% 33% 32% 17% 3	630
July	1st to 10th	Day	8% 6% 29% 35% 17% 6%	540
	11th to 20th	Day	6% 10% 27% 34% 18% 5%	444
	21st to end	Day	2 4 24% 41% 22% 6%	487
August	1st to 10th	Day	6% 4 21% 38% 23% 8%	447
	11th to 20th	Day	5% 3 19% 38% 26% 9%	437
	21st to end	Day	7% 7% 27% 34% 19% 5%	495
September	1st to 10th	Day	8% 7% 27% 35% 19% 4	450
	11th to 20th	Day	14% 5% 19% 33% 23% 6%	450
	21st to end	Day	18% 10% 24% 30% 16% 4	450
October	1st to 10th	Day	20% 9% 22% 24% 20% 4	450
	11th to 20th	Day	22% 8% 22% 25% 17% 6%	450
	21st to end	Day	30% 11% 24% 19% 12% 5%	466
November	1st to 10th	Day	30% 10% 23% 24% 11% 1	210
	11th to 20th	Day	34% 9% 20% 18% 11% 7%	180
	21st to end	Day	27% 12% 25% 19% 12% 6%	180
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	734
	21st to end	Night	30% 5% 13% 32% 18% 3	792
February	1st to 10th	Night	30% 7% 19% 27% 14% 2	720
	11th to 20th	Night	29% 9% 18% 27% 17% 1	704
	21st to end	Night	29% 9% 20% 29% 13%	592
March	1st to 10th	Night	28% 7% 20% 29% 14% 1	720
	11th to 20th	Night	26% 6% 17% 37% 13% 1	720
	21st to end	Night	28% 9% 20% 29% 13% 2	792
April	1st to 10th	Night	26% 11% 22% 27% 14% 1	720
	11th to 20th	Night	22% 7% 26% 32% 11% 1	689
	21st to end	Night	23% 7% 23% 33% 13% 1	540
May	1st to 10th	Night	14% 6% 33% 31% 14% 1	413
	11th to 20th	Night	15% 4 26% 39% 15% 1	354
	21st to end	Night	15% 7% 27% 34% 16%	389
June	1st to 10th	Night	16% 5% 30% 38% 11%	360
	11th to 20th	Night	10% 8% 33% 37% 11% 1	360
	21st to end	Night	8% 4 35% 42% 10%	360
July	1st to 10th	Night	3 3 32% 50% 11% 1	350
	11th to 20th	Night	4 7% 39% 40% 11%	348
	21st to end	Night	3 2 36% 48% 11%	394
August	1st to 10th	Night	3 3 23% 44% 25% 2	524
	11th to 20th	Night	5% 2 16% 50% 25% 2	534
	21st to end	Night	7% 3 30% 40% 19% 1	701
September	1st to 10th	Night	6% 4 27% 45% 16% 2	720
	11th to 20th	Night	11% 3 19% 36% 28% 4	720
	21st to end	Night	11% 6% 20% 41% 20% 2	720
October	1st to 10th	Night	17% 4 23% 37% 18% 2	720
	11th to 20th	Night	20% 4 16% 32% 23% 4	720
	21st to end	Night	26% 6% 18% 30% 18% 2	792
November	1st to 10th	Night	30% 6% 15% 35% 14%	740
	11th to 20th	Night	35% 7% 16% 27% 14% 1	760
	21st to end	Night	28% 4 17% 31% 18% 2	760
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 2024-01-11 01:22:38. Version ac07

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