Bancroft
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bancroft clear sky chart from 2005-11-06 to 2024-02-05.

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% 11% 4 8% 6% 3 5% 4 5% 6% 30%	78122
	Night	16% 12% 5% 8% 6% 3 4 4 5% 6% 30%	80726
Transparency	Day	54% 6% 10% 18% 10% 1	77827
	Night	54% 6% 11% 18% 10% 1	80555
Seeing	Day	24% 16% 31% 18% 8% 3	13336
	Night	22% 14% 31% 23% 9% 1	22728

By Month

Percentage Cloud Cover NE (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	16% 19% 6% 15% 6% 3 3 3 3 3 21%	2517
	11th to 20th	Day	13% 17% 10% 16% 11% 4 5% 3 3 4 15%	2520
	21st to end	Day	19% 20% 8% 13% 7% 3 4 3 3 3 18%	3096
February	1st to 10th	Day	13% 17% 6% 14% 8% 4 5% 4 5% 4 19%	1656
	11th to 20th	Day	13% 16% 6% 11% 7% 4 4 4 4 6% 27%	1573
	21st to end	Day	18% 15% 6% 10% 7% 3 5% 4 4 5% 23%	1401
March	1st to 10th	Day	14% 13% 5% 10% 9% 4 4 5% 4 6% 27%	1908
	11th to 20th	Day	13% 15% 5% 10% 8% 4 5% 4 4 5% 27%	1980
	21st to end	Day	18% 11% 4 7% 5% 3 4 4 4 4 37%	2214
April	1st to 10th	Day	20% 14% 4 7% 5% 3 4 4 4 6% 28%	2160
	11th to 20th	Day	21% 11% 3 6% 5% 2 4 4 4 5% 37%	2139
	21st to end	Day	22% 10% 4 7% 6% 3 4 3 4 5% 33%	2340
May	1st to 10th	Day	19% 9% 3 6% 6% 3 5% 4 4 6% 34%	2460
	11th to 20th	Day	17% 8% 4 7% 5% 3 4 4 5% 6% 37%	2478
	21st to end	Day	14% 7% 3 6% 6% 3 5% 5% 5% 7% 39%	2725
June	1st to 10th	Day	21% 8% 3 6% 6% 3 5% 5% 6% 7% 30%	2520
	11th to 20th	Day	16% 6% 3 5% 5% 3 6% 5% 6% 8% 36%	2520
	21st to end	Day	16% 7% 3 6% 5% 3 6% 6% 6% 8% 34%	2520
July	1st to 10th	Day	13% 5% 3 6% 6% 4 5% 5% 6% 8% 39%	2520
	11th to 20th	Day	12% 7% 3 5% 5% 4 5% 5% 7% 9% 38%	2520
	21st to end	Day	12% 6% 2 6% 6% 4 7% 6% 7% 9% 35%	2744
August	1st to 10th	Day	12% 7% 3 7% 7% 4 6% 6% 6% 8% 34%	2330
	11th to 20th	Day	13% 7% 3 7% 7% 4 6% 5% 8% 7% 35%	2303
	21st to end	Day	15% 7% 3 6% 5% 3 5% 6% 6% 8% 35%	2430
September	1st to 10th	Day	15% 6% 3 5% 6% 4 4 4 6% 9% 39%	2160
	11th to 20th	Day	13% 6% 3 6% 5% 3 4 4 5% 7% 43%	2160
	21st to end	Day	18% 7% 3 6% 6% 4 5% 6% 5% 6% 36%	1878
October	1st to 10th	Day	21% 10% 4 6% 5% 3 4 4 5% 6% 33%	1800
	11th to 20th	Day	25% 12% 3 7% 6% 3 5% 5% 4 5% 24%	1800
	21st to end	Day	29% 13% 4 7% 6% 3 4 3 4 6% 21%	1936
November	1st to 10th	Day	16% 12% 3 8% 6% 4 5% 5% 4 6% 32%	1576
	11th to 20th	Day	16% 15% 6% 9% 7% 3 3 4 5% 7% 25%	1520
	21st to end	Day	21% 18% 7% 9% 7% 4 4 4 3 4 18%	1520
December	1st to 10th	Day	19% 20% 8% 11% 9% 3 3 4 4 5% 14%	1520
	11th to 20th	Day	18% 17% 5% 11% 6% 3 4 4 4 6% 22%	1906
	21st to end	Day	25% 22% 7% 12% 6% 3 2 2 2 3 17%	2772
January	1st to 10th	Night	17% 18% 9% 12% 8% 4 4 4 5% 5% 15%	4429
	11th to 20th	Night	12% 14% 7% 15% 13% 5% 6% 5% 4 5% 14%	4440
	21st to end	Night	18% 15% 8% 12% 7% 5% 6% 4 4 5% 16%	4556
February	1st to 10th	Night	12% 17% 7% 10% 8% 4 6% 5% 5% 6% 20%	2399
	11th to 20th	Night	13% 13% 7% 10% 7% 4 5% 5% 4 6% 28%	2273
	21st to end	Night	14% 16% 4 9% 7% 3 4 4 5% 6% 27%	1853
March	1st to 10th	Night	14% 11% 6% 10% 6% 4 4 4 4 4 33%	2038
	11th to 20th	Night	13% 12% 5% 8% 6% 3 4 4 5% 5% 33%	1979
	21st to end	Night	13% 11% 4 6% 5% 4 4 4 4 6% 39%	2141
April	1st to 10th	Night	19% 12% 4 6% 6% 3 4 4 4 5% 32%	1800
	11th to 20th	Night	18% 9% 3 7% 5% 3 4 4 4 6% 38%	1775
	21st to end	Night	18% 10% 4 5% 7% 3 5% 4 5% 7% 32%	1630
May	1st to 10th	Night	19% 7% 3 5% 5% 2 3 5% 5% 8% 37%	1499
	11th to 20th	Night	15% 6% 3 5% 5% 3 4 4 6% 8% 41%	1415
	21st to end	Night	12% 5% 2 4 5% 3 5% 4 6% 8% 47%	1550
June	1st to 10th	Night	17% 6% 3 6% 6% 2 5% 6% 6% 8% 35%	1440
	11th to 20th	Night	11% 5% 2 6% 6% 3 5% 5% 5% 8% 45%	1440
	21st to end	Night	14% 8% 3 6% 5% 4 5% 5% 5% 8% 37%	1440
July	1st to 10th	Night	8% 5% 2 5% 6% 5% 4 4 6% 7% 47%	1440
	11th to 20th	Night	12% 5% 2 5% 5% 3 5% 6% 5% 9% 44%	1440
	21st to end	Night	9% 5% 2 4 6% 2 4 4 7% 10% 46%	1574
August	1st to 10th	Night	9% 5% 2 5% 5% 3 5% 5% 7% 8% 45%	1604
	11th to 20th	Night	9% 6% 2 5% 5% 3 5% 5% 5% 8% 47%	1598
	21st to end	Night	11% 5% 3 6% 4 4 4 4 6% 7% 46%	1907
September	1st to 10th	Night	11% 5% 2 6% 5% 3 4 5% 7% 7% 47%	1800
	11th to 20th	Night	14% 5% 2 4 4 3 4 4 4 7% 48%	1800
	21st to end	Night	18% 8% 3 5% 4 3 4 4 5% 5% 41%	2078
October	1st to 10th	Night	19% 9% 3 5% 5% 3 4 5% 4 7% 36%	2160
	11th to 20th	Night	22% 12% 3 7% 7% 3 4 4 4 6% 28%	2160
	21st to end	Night	23% 13% 4 8% 6% 3 4 5% 4 5% 25%	2419
November	1st to 10th	Night	17% 12% 3 6% 7% 3 5% 4 4 6% 33%	2497
	11th to 20th	Night	18% 13% 5% 8% 6% 3 5% 4 5% 6% 27%	2660
	21st to end	Night	19% 16% 5% 9% 7% 4 6% 5% 5% 5% 20%	2660
December	1st to 10th	Night	20% 19% 7% 9% 7% 4 5% 5% 5% 5% 15%	2660
	11th to 20th	Night	17% 19% 6% 10% 7% 3 4 4 3 5% 23%	3288
	21st to end	Night	26% 19% 7% 11% 7% 3 3 3 3 4 13%	4884

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	67% 5% 12% 9% 6% 1	2518
	11th to 20th	Day	73% 6% 7% 7% 6% 1	2520
	21st to end	Day	73% 4 6% 10% 6% 2	3096
February	1st to 10th	Day	67% 5% 8% 13% 5% 1	1656
	11th to 20th	Day	61% 5% 10% 13% 10% 2	1582
	21st to end	Day	64% 4 7% 13% 10% 1	1401
March	1st to 10th	Day	58% 5% 14% 13% 9% 2	1911
	11th to 20th	Day	58% 5% 11% 14% 10% 2	1980
	21st to end	Day	51% 5% 7% 18% 14% 5%	2214
April	1st to 10th	Day	58% 4 7% 17% 11% 3	2160
	11th to 20th	Day	50% 5% 8% 21% 14% 1	2139
	21st to end	Day	55% 5% 7% 17% 13% 3	2340
May	1st to 10th	Day	49% 6% 9% 18% 13% 4	2460
	11th to 20th	Day	48% 5% 8% 23% 15% 2	2482
	21st to end	Day	43% 8% 12% 19% 14% 3	2725
June	1st to 10th	Day	52% 6% 10% 19% 12% 1	2520
	11th to 20th	Day	43% 7% 12% 22% 13% 2	2520
	21st to end	Day	46% 7% 14% 20% 12% 1	2520
July	1st to 10th	Day	40% 7% 11% 26% 14% 1	2450
	11th to 20th	Day	40% 9% 14% 26% 11% 1	2445
	21st to end	Day	43% 9% 13% 24% 10%	2591
August	1st to 10th	Day	46% 8% 13% 21% 11% 1	2316
	11th to 20th	Day	45% 8% 14% 23% 9% 1	2303
	21st to end	Day	44% 8% 14% 24% 10% 1	2430
September	1st to 10th	Day	42% 6% 12% 28% 12% 1	2160
	11th to 20th	Day	40% 6% 12% 28% 14% 1	2160
	21st to end	Day	47% 7% 13% 23% 10%	1878
October	1st to 10th	Day	52% 6% 11% 19% 12% 1	1800
	11th to 20th	Day	61% 7% 12% 13% 6% 1	1800
	21st to end	Day	65% 6% 9% 13% 7%	1936
November	1st to 10th	Day	52% 7% 14% 19% 7% 1	1576
	11th to 20th	Day	59% 6% 12% 13% 8% 1	1520
	21st to end	Day	69% 6% 9% 10% 6% 1	1520
December	1st to 10th	Day	73% 6% 8% 9% 4	1520
	11th to 20th	Day	64% 6% 10% 11% 8% 1	1906
	21st to end	Day	75% 3 5% 13% 4	2772
January	1st to 10th	Night	69% 5% 11% 11% 4	4429
	11th to 20th	Night	70% 8% 8% 8% 5% 1	4440
	21st to end	Night	69% 7% 9% 8% 7% 1	4556
February	1st to 10th	Night	62% 6% 11% 13% 7% 1	2399
	11th to 20th	Night	58% 5% 10% 18% 9%	2275
	21st to end	Night	57% 5% 9% 19% 10% 1	1853
March	1st to 10th	Night	54% 5% 10% 16% 13% 2	2048
	11th to 20th	Night	51% 5% 11% 20% 11% 2	1980
	21st to end	Night	47% 5% 8% 20% 16% 3	2141
April	1st to 10th	Night	54% 5% 9% 19% 12% 2	1800
	11th to 20th	Night	48% 5% 8% 23% 15% 2	1775
	21st to end	Night	51% 7% 9% 16% 14% 2	1630
May	1st to 10th	Night	45% 6% 10% 19% 17% 3	1499
	11th to 20th	Night	40% 6% 11% 24% 17% 3	1416
	21st to end	Night	34% 8% 15% 22% 19% 3	1551
June	1st to 10th	Night	45% 8% 11% 24% 12% 1	1440
	11th to 20th	Night	38% 8% 12% 24% 18% 1	1440
	21st to end	Night	44% 7% 14% 21% 12% 1	1440
July	1st to 10th	Night	34% 8% 12% 24% 20% 3	1400
	11th to 20th	Night	36% 8% 12% 31% 13%	1392
	21st to end	Night	32% 9% 17% 30% 12% 1	1486
August	1st to 10th	Night	34% 9% 18% 27% 12% 1	1594
	11th to 20th	Night	34% 9% 17% 27% 11% 1	1598
	21st to end	Night	37% 7% 14% 29% 12% 1	1907
September	1st to 10th	Night	34% 9% 16% 26% 14% 1	1800
	11th to 20th	Night	35% 7% 13% 33% 11% 1	1800
	21st to end	Night	43% 7% 11% 29% 10%	2078
October	1st to 10th	Night	48% 7% 12% 19% 14%	2160
	11th to 20th	Night	57% 6% 12% 18% 7%	2160
	21st to end	Night	60% 6% 11% 13% 9%	2419
November	1st to 10th	Night	51% 6% 14% 20% 9% 1	2497
	11th to 20th	Night	57% 7% 11% 16% 8% 1	2660
	21st to end	Night	64% 6% 12% 13% 5%	2660
December	1st to 10th	Night	69% 7% 9% 11% 3	2660
	11th to 20th	Night	65% 5% 9% 13% 7% 1	3288
	21st to end	Night	76% 4 6% 10% 4	4884

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	26% 21% 35% 14% 4 1	180
	11th to 20th	Day	28% 23% 31% 13% 4 1	180
	21st to end	Day	28% 19% 35% 15% 3	290
February	1st to 10th	Day	31% 27% 32% 7% 2	252
	11th to 20th	Day	31% 28% 34% 6%	240
	21st to end	Day	36% 22% 29% 11% 1	267
March	1st to 10th	Day	24% 21% 34% 17% 3	420
	11th to 20th	Day	28% 22% 30% 15% 5% 1	420
	21st to end	Day	32% 19% 29% 13% 6% 1	462
April	1st to 10th	Day	29% 19% 33% 13% 6%	420
	11th to 20th	Day	33% 21% 22% 14% 9% 2	412
	21st to end	Day	30% 19% 32% 14% 4 2	420
May	1st to 10th	Day	28% 15% 31% 17% 4 4	423
	11th to 20th	Day	21% 16% 35% 17% 7% 3	447
	21st to end	Day	19% 18% 33% 19% 9% 2	485
June	1st to 10th	Day	24% 14% 35% 19% 7% 1	450
	11th to 20th	Day	18% 14% 32% 22% 11% 2	450
	21st to end	Day	19% 15% 34% 20% 10% 2	450
July	1st to 10th	Day	12% 8% 35% 29% 13% 2	445
	11th to 20th	Day	15% 13% 30% 25% 13% 4	444
	21st to end	Day	14% 11% 37% 24% 10% 3	488
August	1st to 10th	Day	15% 8% 33% 27% 12% 6%	446
	11th to 20th	Day	13% 8% 26% 32% 15% 6%	439
	21st to end	Day	16% 12% 30% 23% 12% 7%	495
September	1st to 10th	Day	16% 10% 33% 20% 14% 7%	450
	11th to 20th	Day	15% 12% 27% 22% 16% 10%	450
	21st to end	Day	20% 15% 26% 23% 11% 5%	450
October	1st to 10th	Day	25% 17% 24% 18% 13% 3	450
	11th to 20th	Day	28% 22% 31% 14% 5% 1	450
	21st to end	Day	34% 19% 30% 14% 4	473
November	1st to 10th	Day	27% 16% 34% 18% 5%	270
	11th to 20th	Day	31% 22% 32% 10% 6% 1	180
	21st to end	Day	31% 23% 35% 8% 2 1	180
December	1st to 10th	Day	36% 18% 31% 13% 2	180
	11th to 20th	Day	35% 24% 28% 10% 1 1	180
	21st to end	Day	35% 21% 29% 11% 3 1	198
January	1st to 10th	Night	27% 21% 32% 15% 4	760
	11th to 20th	Night	28% 18% 32% 17% 5%	760
	21st to end	Night	20% 16% 35% 22% 7% 1	836
February	1st to 10th	Night	23% 22% 37% 16% 2	739
	11th to 20th	Night	22% 19% 40% 16% 3	703
	21st to end	Night	24% 21% 34% 18% 3	592
March	1st to 10th	Night	23% 21% 35% 18% 3	720
	11th to 20th	Night	23% 18% 34% 20% 4 1	720
	21st to end	Night	21% 15% 35% 21% 8% 1	792
April	1st to 10th	Night	25% 16% 34% 20% 5%	720
	11th to 20th	Night	24% 18% 29% 20% 8% 1	711
	21st to end	Night	23% 11% 31% 24% 10% 1	550
May	1st to 10th	Night	25% 9% 27% 27% 11% 1	419
	11th to 20th	Night	17% 13% 34% 29% 8%	354
	21st to end	Night	13% 8% 37% 29% 12% 1	389
June	1st to 10th	Night	18% 9% 35% 29% 8% 1	360
	11th to 20th	Night	14% 11% 31% 32% 12% 1	360
	21st to end	Night	16% 9% 28% 35% 11%	360
July	1st to 10th	Night	7% 6% 33% 37% 15% 2	350
	11th to 20th	Night	12% 5% 29% 36% 17%	348
	21st to end	Night	10% 5% 32% 40% 12% 1	394
August	1st to 10th	Night	13% 4 22% 35% 25% 2	530
	11th to 20th	Night	11% 4 22% 39% 22% 3	534
	21st to end	Night	13% 7% 30% 28% 19% 2	719
September	1st to 10th	Night	12% 7% 33% 28% 18% 2	720
	11th to 20th	Night	15% 6% 26% 29% 19% 4	720
	21st to end	Night	22% 11% 21% 25% 17% 3	720
October	1st to 10th	Night	24% 11% 28% 22% 12% 3	720
	11th to 20th	Night	28% 14% 32% 18% 8% 1	720
	21st to end	Night	30% 15% 29% 20% 5%	792
November	1st to 10th	Night	24% 15% 29% 25% 7%	740
	11th to 20th	Night	26% 17% 34% 15% 7% 2	760
	21st to end	Night	29% 17% 28% 20% 6%	760
December	1st to 10th	Night	31% 19% 32% 15% 4	760
	11th to 20th	Night	27% 19% 35% 16% 3 1	760
	21st to end	Night	34% 15% 32% 16% 2	836

Page generated at 2024-02-02 05:20:31. Version ac07

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