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 2024-04-10.

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	10% 10% 3 5% 5% 3 4 4 5% 6% 44%	83062
	Night	12% 10% 3 5% 5% 3 4 4 5% 6% 43%	85799
Transparency	Day	39% 7% 12% 19% 16% 8%	82766
	Night	40% 7% 12% 19% 14% 6%	85616
Seeing	Day	14% 11% 28% 30% 15% 3	13614
	Night	16% 4 18% 39% 22% 2	23089

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	13% 22% 7% 7% 6% 4 5% 5% 4 6% 21%	2539
	11th to 20th	Day	15% 18% 8% 7% 6% 4 4 4 5% 5% 24%	2540
	21st to end	Day	19% 19% 5% 7% 5% 2 4 4 4 7% 24%	2794
February	1st to 10th	Day	16% 16% 6% 9% 5% 3 4 3 4 5% 28%	1649
	11th to 20th	Day	13% 19% 5% 6% 7% 3 5% 4 5% 6% 29%	1850
	21st to end	Day	14% 17% 6% 9% 7% 3 4 6% 4 5% 23%	1570
March	1st to 10th	Day	11% 17% 9% 8% 7% 3 4 4 4 5% 27%	3138
	11th to 20th	Day	9% 11% 3 5% 4 2 3 4 3 4 51%	3360
	21st to end	Day	13% 14% 5% 9% 8% 5% 7% 5% 6% 7% 21%	3998
April	1st to 10th	Day	13% 13% 4 7% 6% 4 5% 5% 5% 6% 31%	2270
	11th to 20th	Day	11% 11% 4 6% 4 3 6% 5% 4 8% 37%	2181
	21st to end	Day	12% 10% 3 5% 6% 3 4 4 5% 7% 40%	2340
May	1st to 10th	Day	8% 8% 3 5% 5% 3 5% 6% 6% 7% 44%	2340
	11th to 20th	Day	12% 8% 3 5% 6% 3 4 5% 6% 8% 40%	2387
	21st to end	Day	10% 9% 4 7% 7% 4 5% 5% 8% 7% 34%	2723
June	1st to 10th	Day	12% 7% 3 5% 6% 3 6% 6% 6% 8% 38%	2520
	11th to 20th	Day	11% 5% 2 4 5% 3 4 4 6% 8% 48%	2520
	21st to end	Day	4 3 1 3 3 2 3 4 3 5% 67%	2520
July	1st to 10th	Day	3 2 1 2 2 2 3 4 4 6% 70%	2520
	11th to 20th	Day	2 1 1 2 2 1 3 3 3 5% 78%	2520
	21st to end	Day	3 2 1 3 3 2 3 3 4 5% 72%	2741
August	1st to 10th	Day	4 3 1 3 4 3 3 4 4 6% 65%	2420
	11th to 20th	Day	2 1 1 2 3 2 3 3 4 6% 74%	2299
	21st to end	Day	3 3 1 2 2 2 3 4 4 5% 71%	2408
September	1st to 10th	Day	4 2 1 2 3 2 3 3 3 4 73%	2160
	11th to 20th	Day	6% 3 2 3 3 3 3 4 4 6% 62%	1994
	21st to end	Day	8% 4 2 3 4 2 3 4 4 5% 60%	1980
October	1st to 10th	Day	10% 6% 2 4 4 2 4 4 5% 7% 50%	1980
	11th to 20th	Day	11% 6% 2 4 4 2 3 4 5% 6% 52%	1730
	21st to end	Day	12% 9% 2 6% 5% 3 4 4 5% 7% 43%	1782
November	1st to 10th	Day	18% 12% 3 5% 5% 3 3 4 6% 6% 35%	1674
	11th to 20th	Day	16% 14% 3 6% 4 3 4 4 5% 7% 34%	1710
	21st to end	Day	14% 10% 4 7% 6% 3 5% 4 5% 7% 36%	1663
December	1st to 10th	Day	20% 13% 5% 6% 4 2 3 4 6% 7% 31%	1520
	11th to 20th	Day	18% 15% 6% 8% 5% 3 4 4 6% 6% 25%	1928
	21st to end	Day	14% 13% 5% 7% 4 3 5% 4 5% 6% 35%	2794
January	1st to 10th	Night	15% 17% 5% 7% 6% 4 5% 5% 5% 6% 24%	4406
	11th to 20th	Night	21% 19% 7% 6% 5% 3 4 3 3 5% 24%	4420
	21st to end	Night	20% 17% 4 7% 6% 3 5% 4 5% 5% 24%	4862
February	1st to 10th	Night	16% 16% 5% 6% 6% 2 4 3 4 5% 32%	2525
	11th to 20th	Night	14% 15% 4 6% 5% 3 4 3 4 5% 35%	2218
	21st to end	Night	15% 16% 6% 6% 5% 3 5% 4 4 6% 29%	1884
March	1st to 10th	Night	13% 16% 5% 6% 6% 3 3 4 4 6% 34%	3736
	11th to 20th	Night	10% 13% 3 4 4 2 3 3 3 4 50%	3619
	21st to end	Night	11% 11% 3 8% 6% 4 6% 6% 7% 9% 29%	3653
April	1st to 10th	Night	13% 11% 3 4 4 3 4 4 5% 7% 41%	1900
	11th to 20th	Night	13% 7% 3 6% 6% 3 4 5% 5% 5% 44%	1727
	21st to end	Night	9% 6% 2 5% 4 3 5% 4 5% 6% 51%	1620
May	1st to 10th	Night	8% 5% 2 3 4 3 5% 5% 5% 8% 53%	1620
	11th to 20th	Night	9% 5% 2 6% 5% 3 5% 6% 5% 10% 44%	1504
	21st to end	Night	10% 7% 3 6% 6% 3 5% 5% 6% 9% 40%	1552
June	1st to 10th	Night	12% 5% 2 4 5% 4 4 5% 6% 8% 45%	1440
	11th to 20th	Night	9% 5% 1 4 4 3 3 4 4 6% 57%	1440
	21st to end	Night	3 3 1 2 3 2 4 5% 6% 5% 65%	1440
July	1st to 10th	Night	1 2 1 3 2 2 3 4 6% 7% 68%	1440
	11th to 20th	Night	2 1 1 3 2 3 3 4 5% 77%	1440
	21st to end	Night	2 3 1 2 2 2 3 4 4 6% 71%	1576
August	1st to 10th	Night	3 3 1 4 3 2 4 5% 4 6% 65%	1517
	11th to 20th	Night	1 1 1 2 2 1 3 4 5% 5% 75%	1602
	21st to end	Night	3 3 1 3 2 3 2 3 3 5% 71%	1946
September	1st to 10th	Night	3 2 1 3 3 2 2 3 4 4 75%	1800
	11th to 20th	Night	6% 4 1 4 3 2 3 4 4 6% 63%	1966
	21st to end	Night	8% 4 1 3 3 1 3 3 4 5% 65%	1980
October	1st to 10th	Night	9% 5% 1 4 4 2 3 3 4 7% 56%	1980
	11th to 20th	Night	11% 5% 1 4 4 3 4 4 4 6% 55%	2226
	21st to end	Night	12% 8% 2 5% 4 3 4 5% 6% 7% 45%	2574
November	1st to 10th	Night	18% 9% 3 5% 4 3 3 4 5% 7% 40%	2405
	11th to 20th	Night	20% 8% 3 5% 5% 3 4 5% 5% 6% 36%	2470
	21st to end	Night	14% 10% 3 5% 5% 3 5% 4 4 6% 40%	2513
December	1st to 10th	Night	16% 14% 3 5% 6% 4 4 5% 5% 6% 32%	2660
	11th to 20th	Night	18% 15% 4 8% 7% 3 5% 5% 4 5% 25%	3276
	21st to end	Night	15% 13% 4 7% 5% 3 5% 4 5% 7% 33%	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	61% 12% 16% 10% 1	2539
	11th to 20th	Day	61% 8% 13% 14% 4	2540
	21st to end	Day	59% 10% 18% 11% 2	2794
February	1st to 10th	Day	57% 8% 15% 16% 3 1	1649
	11th to 20th	Day	55% 9% 15% 16% 6%	1860
	21st to end	Day	59% 8% 11% 15% 6% 1	1570
March	1st to 10th	Day	54% 9% 11% 17% 9%	3138
	11th to 20th	Day	35% 7% 9% 35% 13% 1	3360
	21st to end	Day	52% 13% 16% 13% 5%	3998
April	1st to 10th	Day	50% 7% 16% 18% 8% 2	2270
	11th to 20th	Day	44% 6% 14% 21% 13% 2	2184
	21st to end	Day	42% 6% 13% 23% 14%	2340
May	1st to 10th	Day	35% 7% 14% 26% 16% 2	2340
	11th to 20th	Day	39% 7% 12% 27% 12% 3	2390
	21st to end	Day	44% 9% 15% 19% 11% 2	2724
June	1st to 10th	Day	41% 8% 13% 22% 15% 1	2520
	11th to 20th	Day	32% 6% 10% 22% 22% 7%	2520
	21st to end	Day	19% 4 8% 18% 34% 17%	2520
July	1st to 10th	Day	14% 4 7% 17% 29% 30%	2451
	11th to 20th	Day	11% 2 5% 9% 31% 43%	2445
	21st to end	Day	14% 3 5% 10% 26% 42%	2589
August	1st to 10th	Day	20% 5% 9% 14% 27% 25%	2403
	11th to 20th	Day	12% 3 6% 17% 37% 25%	2299
	21st to end	Day	16% 4 6% 17% 36% 22%	2408
September	1st to 10th	Day	15% 4 6% 18% 30% 27%	2160
	11th to 20th	Day	22% 5% 10% 20% 29% 14%	1994
	21st to end	Day	24% 4 9% 26% 27% 10%	1980
October	1st to 10th	Day	34% 6% 12% 22% 21% 5%	1980
	11th to 20th	Day	32% 5% 12% 28% 21% 3	1730
	21st to end	Day	39% 8% 14% 21% 16% 2	1782
November	1st to 10th	Day	48% 7% 13% 20% 12% 1	1674
	11th to 20th	Day	49% 8% 17% 20% 6%	1710
	21st to end	Day	48% 6% 16% 18% 10% 1	1663
December	1st to 10th	Day	51% 9% 19% 16% 5% 1	1520
	11th to 20th	Day	59% 11% 15% 13% 3	1928
	21st to end	Day	49% 7% 18% 19% 6%	2794
January	1st to 10th	Night	57% 11% 17% 13% 1 1	4406
	11th to 20th	Night	63% 7% 13% 12% 5%	4420
	21st to end	Night	57% 12% 15% 13% 3	4862
February	1st to 10th	Night	54% 7% 16% 18% 4 1	2525
	11th to 20th	Night	50% 7% 14% 19% 9% 1	2219
	21st to end	Night	54% 8% 11% 17% 8% 1	1884
March	1st to 10th	Night	47% 8% 12% 21% 11% 1	3736
	11th to 20th	Night	37% 6% 8% 30% 18% 1	3619
	21st to end	Night	43% 13% 19% 18% 7%	3653
April	1st to 10th	Night	41% 7% 13% 24% 13% 2	1900
	11th to 20th	Night	41% 7% 12% 22% 16% 2	1727
	21st to end	Night	33% 6% 15% 26% 19% 1	1620
May	1st to 10th	Night	28% 6% 12% 30% 23% 1	1620
	11th to 20th	Night	34% 7% 13% 28% 16% 1	1504
	21st to end	Night	39% 8% 14% 25% 13% 1	1552
June	1st to 10th	Night	35% 9% 14% 28% 14% 1	1440
	11th to 20th	Night	29% 5% 10% 24% 25% 7%	1440
	21st to end	Night	18% 5% 8% 19% 33% 17%	1440
July	1st to 10th	Night	13% 4 7% 15% 31% 29%	1400
	11th to 20th	Night	11% 2 5% 12% 27% 42%	1392
	21st to end	Night	14% 3 6% 9% 28% 40%	1488
August	1st to 10th	Night	19% 4 9% 13% 28% 28%	1509
	11th to 20th	Night	11% 3 6% 15% 32% 33%	1602
	21st to end	Night	16% 3 6% 14% 32% 28%	1946
September	1st to 10th	Night	15% 3 6% 15% 30% 31%	1800
	11th to 20th	Night	22% 4 8% 17% 29% 20%	1966
	21st to end	Night	22% 4 6% 23% 30% 15%	1980
October	1st to 10th	Night	28% 4 10% 25% 24% 8%	1980
	11th to 20th	Night	31% 5% 11% 28% 22% 4	2226
	21st to end	Night	36% 7% 13% 23% 19% 3	2574
November	1st to 10th	Night	43% 6% 13% 21% 15% 2	2405
	11th to 20th	Night	48% 7% 13% 24% 9%	2470
	21st to end	Night	45% 6% 13% 23% 10% 2	2513
December	1st to 10th	Night	50% 8% 18% 14% 9% 1	2660
	11th to 20th	Night	58% 8% 13% 17% 4	3276
	21st to end	Night	49% 9% 20% 16% 6%	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	20% 15% 27% 23% 14% 2	180
	11th to 20th	Day	22% 9% 22% 24% 14% 8%	180
	21st to end	Day	20% 9% 25% 28% 13% 6%	198
February	1st to 10th	Day	25% 10% 32% 18% 13% 2	261
	11th to 20th	Day	23% 13% 30% 24% 9% 1	455
	21st to end	Day	22% 17% 28% 25% 8% 1	382
March	1st to 10th	Day	20% 19% 32% 24% 5%	460
	11th to 20th	Day	19% 13% 28% 25% 13% 2	460
	21st to end	Day	21% 17% 31% 23% 8% 1	506
April	1st to 10th	Day	21% 18% 26% 21% 13% 1	457
	11th to 20th	Day	18% 19% 30% 22% 8% 1	412
	21st to end	Day	15% 19% 30% 25% 10% 1	420
May	1st to 10th	Day	11% 15% 34% 26% 12% 2	423
	11th to 20th	Day	22% 11% 27% 25% 14% 2	448
	21st to end	Day	12% 12% 24% 29% 17% 5%	485
June	1st to 10th	Day	12% 13% 27% 28% 17% 4	450
	11th to 20th	Day	14% 17% 32% 24% 12% 2	450
	21st to end	Day	5% 8% 33% 31% 20% 3	450
July	1st to 10th	Day	3 5% 34% 40% 15% 3	446
	11th to 20th	Day	1 9% 32% 41% 14% 2	444
	21st to end	Day	3 4 29% 41% 20% 3	487
August	1st to 10th	Day	5% 6% 31% 37% 18% 3	447
	11th to 20th	Day	2 4 26% 39% 24% 4	437
	21st to end	Day	5% 8% 25% 37% 23% 2	495
September	1st to 10th	Day	6% 6% 24% 39% 22% 3	450
	11th to 20th	Day	9% 7% 25% 35% 22% 2	450
	21st to end	Day	8% 8% 28% 34% 19% 3	450
October	1st to 10th	Day	11% 10% 22% 30% 23% 3	450
	11th to 20th	Day	14% 8% 25% 30% 17% 7%	338
	21st to end	Day	19% 10% 21% 33% 13% 4	297
November	1st to 10th	Day	21% 10% 23% 29% 14% 2	270
	11th to 20th	Day	17% 8% 24% 31% 16% 3	270
	21st to end	Day	16% 7% 24% 30% 19% 4	248
December	1st to 10th	Day	34% 7% 17% 17% 18% 7%	180
	11th to 20th	Day	28% 7% 24% 28% 12% 2	180
	21st to end	Day	19% 13% 24% 29% 14% 3	198
January	1st to 10th	Night	26% 5% 19% 32% 16% 3	760
	11th to 20th	Night	25% 6% 18% 28% 19% 4	760
	21st to end	Night	22% 3 18% 33% 21% 3	836
February	1st to 10th	Night	23% 6% 27% 31% 12% 1	760
	11th to 20th	Night	22% 4 23% 34% 16% 2	744
	21st to end	Night	21% 7% 21% 36% 14% 2	628
March	1st to 10th	Night	22% 6% 24% 34% 13% 2	760
	11th to 20th	Night	17% 6% 19% 39% 18% 1	760
	21st to end	Night	20% 6% 23% 38% 12% 1	836
April	1st to 10th	Night	18% 7% 20% 36% 17% 2	760
	11th to 20th	Night	15% 7% 26% 36% 14% 1	659
	21st to end	Night	12% 5% 22% 43% 17% 1	540
May	1st to 10th	Night	9% 6% 21% 43% 21%	540
	11th to 20th	Night	10% 5% 16% 36% 31% 2	442
	21st to end	Night	11% 3 17% 36% 29% 3	389
June	1st to 10th	Night	13% 4 12% 42% 26% 3	360
	11th to 20th	Night	11% 3 17% 42% 26% 1	360
	21st to end	Night	4 1 11% 50% 33% 1	360
July	1st to 10th	Night	1 1 12% 47% 36% 3	350
	11th to 20th	Night	2 1 10% 60% 26% 1	348
	21st to end	Night	4 1 7% 52% 36% 1	394
August	1st to 10th	Night	5% 2 8% 50% 33% 2	443
	11th to 20th	Night	1 1 7% 47% 40% 3	534
	21st to end	Night	4 1 11% 46% 34% 3	758
September	1st to 10th	Night	4 1 8% 52% 33% 2	720
	11th to 20th	Night	7% 2 10% 42% 35% 4	720
	21st to end	Night	9% 2 15% 38% 30% 6%	720
October	1st to 10th	Night	11% 2 16% 42% 27% 2	720
	11th to 20th	Night	12% 3 16% 40% 26% 3	720
	21st to end	Night	15% 2 20% 39% 20% 3	792
November	1st to 10th	Night	21% 3 19% 38% 17% 2	740
	11th to 20th	Night	25% 4 18% 35% 16% 1	760
	21st to end	Night	18% 4 21% 37% 16% 4	760
December	1st to 10th	Night	22% 5% 21% 34% 16% 2	760
	11th to 20th	Night	27% 4 19% 34% 14% 2	760
	21st to end	Night	30% 4 23% 31% 10% 2	836

Page generated at 2024-04-07 07:28:13. Version ac07

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