Bartole Observing Platform
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bartole Observing Platform clear sky chart from 2005-11-06 to 2024-01-15.

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	15% 9% 4 7% 6% 4 5% 5% 6% 7% 32%	75073
	Night	15% 10% 4 8% 6% 4 5% 5% 5% 7% 31%	74674
Transparency	Day	51% 5% 12% 21% 10% 1	74785
	Night	53% 5% 12% 20% 10% 1	74498
Seeing	Day	17% 7% 26% 26% 16% 6%	13660
	Night	19% 8% 29% 30% 13% 2	22775

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	13% 14% 5% 10% 8% 6% 8% 6% 6% 5% 19%	1517
	11th to 20th	Day	15% 15% 7% 10% 9% 5% 5% 5% 6% 5% 16%	1585
	21st to end	Day	11% 13% 7% 12% 11% 5% 6% 5% 5% 6% 17%	1782
February	1st to 10th	Day	13% 14% 6% 12% 9% 5% 7% 6% 5% 5% 17%	1620
	11th to 20th	Day	12% 11% 6% 12% 8% 5% 6% 6% 4 6% 24%	1573
	21st to end	Day	16% 13% 6% 9% 8% 4 5% 5% 5% 5% 22%	1368
March	1st to 10th	Day	13% 10% 5% 9% 8% 3 6% 6% 4 6% 30%	1977
	11th to 20th	Day	12% 13% 5% 8% 7% 5% 6% 4 5% 5% 32%	1980
	21st to end	Day	18% 8% 3 8% 6% 3 5% 3 5% 6% 36%	2178
April	1st to 10th	Day	17% 11% 4 7% 7% 3 6% 5% 5% 5% 30%	2124
	11th to 20th	Day	18% 8% 3 6% 5% 3 5% 4 5% 7% 37%	2220
	21st to end	Day	20% 7% 4 6% 6% 3 4 4 4 7% 35%	2340
May	1st to 10th	Day	16% 7% 3 7% 6% 4 4 4 5% 7% 36%	2340
	11th to 20th	Day	13% 6% 3 6% 5% 4 4 5% 6% 7% 42%	2478
	21st to end	Day	12% 4 2 5% 5% 3 5% 5% 6% 8% 44%	2725
June	1st to 10th	Day	16% 5% 3 5% 5% 3 5% 5% 6% 7% 39%	2520
	11th to 20th	Day	13% 5% 2 5% 4 3 5% 5% 7% 9% 42%	2601
	21st to end	Day	14% 5% 2 5% 5% 4 5% 5% 6% 8% 41%	2700
July	1st to 10th	Day	9% 4 2 4 5% 3 5% 5% 7% 8% 46%	2661
	11th to 20th	Day	10% 6% 2 6% 5% 4 5% 6% 6% 9% 42%	2520
	21st to end	Day	10% 5% 3 6% 6% 4 6% 5% 7% 10% 38%	2595
August	1st to 10th	Day	10% 5% 3 5% 6% 3 6% 6% 6% 9% 42%	2327
	11th to 20th	Day	8% 6% 3 5% 5% 3 6% 6% 8% 9% 41%	2303
	21st to end	Day	12% 5% 2 5% 6% 3 5% 5% 7% 9% 40%	2491
September	1st to 10th	Day	14% 6% 3 6% 4 4 5% 5% 6% 7% 41%	2160
	11th to 20th	Day	13% 5% 3 6% 5% 3 5% 4 5% 8% 43%	2052
	21st to end	Day	14% 6% 2 7% 5% 5% 5% 5% 6% 7% 37%	1945
October	1st to 10th	Day	20% 7% 3 7% 7% 3 6% 5% 5% 6% 33%	1800
	11th to 20th	Day	20% 10% 4 8% 7% 3 6% 5% 5% 6% 25%	1800
	21st to end	Day	26% 12% 4 8% 7% 3 4 5% 5% 6% 20%	1980
November	1st to 10th	Day	15% 12% 4 8% 6% 4 5% 5% 6% 7% 28%	1573
	11th to 20th	Day	13% 16% 4 8% 9% 5% 6% 6% 5% 7% 21%	1520
	21st to end	Day	18% 17% 5% 9% 8% 5% 6% 4 5% 6% 17%	1520
December	1st to 10th	Day	16% 17% 8% 14% 9% 4 5% 5% 4 6% 12%	1520
	11th to 20th	Day	17% 13% 6% 10% 7% 4 7% 6% 5% 6% 19%	1906
	21st to end	Day	27% 17% 7% 12% 7% 4 4 4 4 4 11%	2772
January	1st to 10th	Night	15% 15% 6% 9% 9% 4 6% 5% 6% 6% 18%	2649
	11th to 20th	Night	17% 15% 6% 11% 10% 6% 7% 5% 4 5% 15%	2460
	21st to end	Night	12% 13% 6% 12% 10% 5% 6% 7% 5% 6% 19%	2574
February	1st to 10th	Night	12% 15% 6% 11% 9% 6% 5% 6% 6% 5% 18%	2340
	11th to 20th	Night	13% 14% 6% 10% 7% 4 5% 6% 5% 6% 23%	2273
	21st to end	Night	15% 11% 6% 11% 8% 4 5% 5% 5% 7% 25%	1881
March	1st to 10th	Night	12% 11% 4 9% 8% 4 5% 4 4 6% 33%	1970
	11th to 20th	Night	14% 10% 5% 7% 7% 4 4 4 5% 5% 35%	1979
	21st to end	Night	16% 8% 3 7% 6% 3 5% 4 4 6% 37%	2178
April	1st to 10th	Night	19% 10% 4 7% 6% 3 5% 5% 5% 6% 31%	1835
	11th to 20th	Night	17% 7% 3 6% 4 3 5% 5% 5% 7% 38%	1705
	21st to end	Night	17% 8% 4 8% 6% 3 4 5% 4 6% 35%	1620
May	1st to 10th	Night	17% 6% 2 5% 5% 3 5% 4 6% 9% 39%	1620
	11th to 20th	Night	14% 6% 3 5% 4 3 4 5% 5% 7% 45%	1415
	21st to end	Night	10% 4 2 5% 4 3 4 5% 5% 8% 51%	1550
June	1st to 10th	Night	13% 5% 3 6% 4 4 5% 6% 5% 8% 41%	1440
	11th to 20th	Night	10% 4 2 5% 5% 4 6% 5% 6% 9% 43%	1351
	21st to end	Night	10% 6% 2 6% 6% 4 5% 5% 5% 7% 44%	1260
July	1st to 10th	Night	6% 4 3 5% 4 2 4 5% 5% 7% 56%	1292
	11th to 20th	Night	9% 5% 2 4 5% 3 5% 5% 6% 8% 48%	1440
	21st to end	Night	8% 4 2 5% 5% 3 6% 5% 6% 8% 48%	1720
August	1st to 10th	Night	9% 5% 1 4 4 3 4 5% 6% 9% 49%	1611
	11th to 20th	Night	7% 4 1 5% 4 3 4 5% 7% 10% 50%	1598
	21st to end	Night	11% 5% 2 4 5% 3 6% 6% 6% 8% 44%	1846
September	1st to 10th	Night	12% 5% 2 5% 5% 3 4 5% 7% 7% 46%	1800
	11th to 20th	Night	13% 4 2 4 4 3 4 5% 5% 8% 49%	1906
	21st to end	Night	15% 7% 3 5% 7% 2 4 4 5% 6% 42%	2014
October	1st to 10th	Night	18% 7% 3 6% 6% 3 4 4 6% 6% 35%	2160
	11th to 20th	Night	18% 10% 4 7% 7% 4 6% 5% 4 6% 30%	2160
	21st to end	Night	23% 11% 4 6% 8% 4 4 5% 6% 6% 23%	2376
November	1st to 10th	Night	18% 9% 3 6% 6% 3 6% 5% 5% 7% 32%	2499
	11th to 20th	Night	16% 14% 6% 9% 6% 4 5% 5% 5% 7% 24%	2660
	21st to end	Night	19% 15% 5% 8% 7% 4 5% 5% 6% 6% 21%	2660
December	1st to 10th	Night	18% 16% 7% 12% 8% 4 5% 4 4 5% 16%	2660
	11th to 20th	Night	16% 15% 6% 12% 8% 4 6% 5% 5% 6% 18%	3288
	21st to end	Night	27% 17% 6% 14% 7% 3 4 3 3 5% 10%	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	64% 6% 13% 13% 5%	1518
	11th to 20th	Day	68% 7% 9% 9% 6% 1	1585
	21st to end	Day	66% 4 9% 13% 7% 1	1782
February	1st to 10th	Day	67% 6% 8% 14% 4	1620
	11th to 20th	Day	61% 3 10% 17% 7% 1	1582
	21st to end	Day	63% 4 10% 17% 7%	1368
March	1st to 10th	Day	54% 5% 13% 18% 10% 1	1980
	11th to 20th	Day	55% 4 10% 17% 12% 2	1980
	21st to end	Day	51% 3 9% 19% 16% 2	2178
April	1st to 10th	Day	55% 5% 8% 20% 10% 1	2124
	11th to 20th	Day	48% 5% 9% 23% 15% 1	2220
	21st to end	Day	51% 4 11% 19% 12% 3	2340
May	1st to 10th	Day	48% 4 9% 23% 14% 2	2340
	11th to 20th	Day	41% 6% 9% 27% 15% 1	2482
	21st to end	Day	37% 5% 15% 25% 14% 3	2725
June	1st to 10th	Day	42% 5% 12% 24% 15% 1	2520
	11th to 20th	Day	38% 6% 13% 26% 16% 1	2601
	21st to end	Day	41% 5% 13% 25% 15% 1	2700
July	1st to 10th	Day	35% 5% 14% 26% 18% 2	2589
	11th to 20th	Day	38% 7% 13% 30% 11% 1	2445
	21st to end	Day	41% 7% 13% 25% 13% 1	2450
August	1st to 10th	Day	37% 6% 16% 26% 12% 2	2314
	11th to 20th	Day	36% 7% 18% 28% 10% 1	2303
	21st to end	Day	39% 6% 15% 27% 12% 1	2491
September	1st to 10th	Day	42% 6% 12% 29% 11% 2	2160
	11th to 20th	Day	40% 4 13% 29% 12% 1	2052
	21st to end	Day	46% 6% 13% 27% 8%	1945
October	1st to 10th	Day	51% 4 13% 20% 11% 1	1800
	11th to 20th	Day	59% 4 13% 18% 5% 1	1800
	21st to end	Day	65% 4 13% 12% 5%	1980
November	1st to 10th	Day	55% 5% 14% 20% 6% 1	1573
	11th to 20th	Day	61% 6% 13% 13% 6% 1	1520
	21st to end	Day	68% 6% 11% 13% 2	1520
December	1st to 10th	Day	73% 4 11% 10% 2	1520
	11th to 20th	Day	67% 6% 11% 12% 3	1906
	21st to end	Day	79% 2 9% 8% 1	2772
January	1st to 10th	Night	66% 5% 11% 14% 4	2649
	11th to 20th	Night	71% 6% 9% 9% 4 1	2460
	21st to end	Night	63% 5% 10% 15% 6% 1	2574
February	1st to 10th	Night	65% 5% 10% 16% 3 1	2340
	11th to 20th	Night	60% 5% 11% 18% 6%	2275
	21st to end	Night	60% 3 11% 17% 8%	1881
March	1st to 10th	Night	55% 3 13% 18% 10% 1	1980
	11th to 20th	Night	52% 3 10% 22% 11% 2	1980
	21st to end	Night	48% 4 10% 21% 15% 2	2178
April	1st to 10th	Night	55% 4 9% 19% 12% 1	1835
	11th to 20th	Night	46% 5% 10% 20% 17% 2	1705
	21st to end	Night	52% 3 10% 18% 15% 2	1620
May	1st to 10th	Night	42% 4 11% 21% 17% 3	1620
	11th to 20th	Night	39% 4 11% 25% 19% 3	1416
	21st to end	Night	32% 5% 17% 27% 17% 3	1551
June	1st to 10th	Night	41% 5% 11% 26% 15% 2	1440
	11th to 20th	Night	37% 5% 11% 25% 21% 1	1351
	21st to end	Night	39% 6% 13% 27% 15% 1	1260
July	1st to 10th	Night	29% 5% 11% 31% 22% 2	1256
	11th to 20th	Night	34% 4 13% 33% 15% 1	1392
	21st to end	Night	33% 6% 13% 31% 15% 2	1624
August	1st to 10th	Night	32% 4 19% 31% 14% 1	1600
	11th to 20th	Night	29% 6% 19% 30% 16% 1	1598
	21st to end	Night	37% 7% 15% 26% 14% 1	1846
September	1st to 10th	Night	37% 5% 15% 29% 13% 2	1800
	11th to 20th	Night	34% 4 13% 33% 15% 1	1906
	21st to end	Night	44% 4 13% 28% 10%	2014
October	1st to 10th	Night	48% 5% 12% 21% 13% 1	2160
	11th to 20th	Night	55% 5% 13% 21% 7%	2160
	21st to end	Night	61% 6% 11% 15% 8%	2376
November	1st to 10th	Night	51% 6% 12% 23% 8% 1	2499
	11th to 20th	Night	60% 5% 13% 15% 6% 1	2660
	21st to end	Night	64% 5% 15% 15% 1	2660
December	1st to 10th	Night	70% 4 13% 10% 3	2660
	11th to 20th	Night	67% 5% 13% 12% 2	3288
	21st to end	Night	79% 3 9% 8% 2	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	15% 11% 39% 23% 10% 2	180
	11th to 20th	Day	21% 10% 39% 21% 7% 2	219
	21st to end	Day	20% 8% 37% 27% 7% 1	264
February	1st to 10th	Day	19% 14% 45% 16% 5%	240
	11th to 20th	Day	19% 14% 40% 25% 2	240
	21st to end	Day	25% 20% 31% 23% 2	203
March	1st to 10th	Day	18% 10% 38% 25% 9%	420
	11th to 20th	Day	17% 11% 35% 27% 9% 1	420
	21st to end	Day	26% 7% 31% 23% 12% 2	462
April	1st to 10th	Day	19% 14% 30% 25% 10% 2	420
	11th to 20th	Day	25% 9% 27% 20% 13% 6%	412
	21st to end	Day	23% 9% 25% 27% 13% 4	420
May	1st to 10th	Day	18% 7% 24% 30% 15% 5%	423
	11th to 20th	Day	16% 5% 22% 32% 18% 7%	447
	21st to end	Day	15% 3 21% 31% 22% 8%	485
June	1st to 10th	Day	16% 5% 25% 29% 22% 4	450
	11th to 20th	Day	14% 6% 23% 29% 23% 5%	531
	21st to end	Day	16% 5% 23% 32% 18% 5%	630
July	1st to 10th	Day	10% 4 18% 31% 29% 8%	584
	11th to 20th	Day	13% 2 20% 27% 27% 11%	444
	21st to end	Day	12% 2 15% 39% 22% 10%	488
August	1st to 10th	Day	10% 2 17% 27% 29% 15%	446
	11th to 20th	Day	9% 3 16% 28% 29% 15%	439
	21st to end	Day	14% 3 21% 27% 24% 11%	495
September	1st to 10th	Day	14% 4 20% 26% 24% 12%	450
	11th to 20th	Day	11% 4 19% 27% 23% 16%	450
	21st to end	Day	14% 6% 25% 25% 21% 8%	450
October	1st to 10th	Day	20% 7% 24% 24% 16% 9%	450
	11th to 20th	Day	23% 10% 34% 23% 8% 1	450
	21st to end	Day	31% 9% 31% 21% 7%	495
November	1st to 10th	Day	21% 16% 29% 21% 11% 1	235
	11th to 20th	Day	21% 18% 32% 21% 6% 2	180
	21st to end	Day	27% 13% 37% 19% 4	180
December	1st to 10th	Day	19% 17% 38% 21% 4 1	180
	11th to 20th	Day	21% 18% 37% 17% 6% 1	180
	21st to end	Day	27% 8% 41% 21% 4	198
January	1st to 10th	Night	22% 10% 40% 20% 7% 1	760
	11th to 20th	Night	25% 8% 32% 27% 7%	737
	21st to end	Night	18% 5% 33% 33% 10% 1	792
February	1st to 10th	Night	20% 8% 42% 26% 4	720
	11th to 20th	Night	19% 9% 37% 29% 6%	703
	21st to end	Night	20% 9% 36% 30% 5%	592
March	1st to 10th	Night	17% 9% 36% 30% 7%	720
	11th to 20th	Night	17% 10% 35% 29% 7% 1	720
	21st to end	Night	20% 7% 30% 30% 12%	792
April	1st to 10th	Night	22% 9% 31% 30% 7%	720
	11th to 20th	Night	19% 7% 30% 30% 11% 2	641
	21st to end	Night	21% 7% 26% 32% 13%	540
May	1st to 10th	Night	19% 2 24% 36% 17% 2	540
	11th to 20th	Night	17% 4 25% 39% 14% 1	354
	21st to end	Night	10% 5% 20% 43% 21% 2	389
June	1st to 10th	Night	15% 5% 25% 40% 14% 1	360
	11th to 20th	Night	9% 7% 19% 46% 17% 1	360
	21st to end	Night	13% 2 19% 43% 20% 2	360
July	1st to 10th	Night	6% 5% 16% 47% 25% 1	350
	11th to 20th	Night	11% 4 21% 41% 22% 2	348
	21st to end	Night	10% 3 17% 44% 25% 1	540
August	1st to 10th	Night	10% 3 13% 42% 30% 2	537
	11th to 20th	Night	5% 2 14% 38% 36% 4	534
	21st to end	Night	12% 3 20% 34% 28% 3	658
September	1st to 10th	Night	13% 5% 18% 35% 23% 6%	720
	11th to 20th	Night	14% 4 19% 32% 23% 7%	720
	21st to end	Night	18% 6% 21% 30% 19% 5%	720
October	1st to 10th	Night	20% 5% 28% 28% 17% 3	720
	11th to 20th	Night	22% 11% 30% 27% 9% 1	720
	21st to end	Night	29% 10% 30% 25% 6%	792
November	1st to 10th	Night	22% 10% 28% 27% 12% 1	740
	11th to 20th	Night	23% 14% 34% 21% 8% 1	760
	21st to end	Night	26% 13% 32% 24% 4	760
December	1st to 10th	Night	27% 13% 37% 18% 5% 1	760
	11th to 20th	Night	22% 12% 38% 21% 5% 1	760
	21st to end	Night	28% 10% 34% 24% 3	836

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