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 2024-11-30.

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	14% 9% 3 8% 5% 5% 5% 4 6% 7% 33%	102196
	Night	15% 10% 4 9% 6% 5% 5% 4 5% 7% 31%	97381
Transparency	Day	50% 4 13% 22% 10% 1	105797
	Night	52% 4 13% 21% 10% 1	101870
Seeing	Day	17% 8% 27% 26% 16% 6%	14865
	Night	19% 8% 29% 30% 13% 2	23851

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	15% 13% 4 10% 6% 6% 6% 4 5% 5% 25%	2517
	11th to 20th	Day	9% 15% 7% 18% 9% 7% 4 4 6% 5% 15%	2717
	21st to end	Day	17% 19% 6% 13% 8% 6% 5% 3 4 5% 15%	3124
February	1st to 10th	Day	12% 15% 6% 13% 8% 8% 7% 5% 5% 5% 18%	1710
	11th to 20th	Day	12% 12% 6% 13% 8% 6% 5% 5% 4 6% 24%	1663
	21st to end	Day	15% 14% 5% 11% 7% 5% 4 4 6% 6% 22%	1452
March	1st to 10th	Day	17% 12% 4 8% 6% 4 5% 4 4 5% 31%	3432
	11th to 20th	Day	10% 14% 5% 10% 6% 6% 6% 4 6% 5% 28%	3480
	21st to end	Day	15% 8% 3 10% 5% 5% 5% 4 5% 5% 36%	3815
April	1st to 10th	Day	17% 12% 4 9% 6% 5% 5% 4 5% 5% 30%	2243
	11th to 20th	Day	19% 9% 2 6% 4 4 4 3 5% 7% 36%	2345
	21st to end	Day	19% 9% 3 7% 6% 4 3 3 4 6% 35%	2470
May	1st to 10th	Day	15% 8% 3 8% 5% 5% 4 4 6% 7% 36%	4108
	11th to 20th	Day	15% 8% 3 7% 5% 4 4 4 6% 8% 36%	4398
	21st to end	Day	12% 5% 2 6% 4 4 4 4 5% 7% 46%	4837
June	1st to 10th	Day	16% 6% 3 7% 4 4 5% 4 6% 7% 38%	2660
	11th to 20th	Day	12% 5% 2 6% 4 4 5% 4 7% 9% 41%	2746
	21st to end	Day	14% 6% 2 6% 5% 5% 5% 4 6% 8% 40%	2850
July	1st to 10th	Day	11% 5% 2 6% 6% 5% 6% 5% 7% 9% 37%	4679
	11th to 20th	Day	10% 5% 2 5% 5% 5% 5% 4 6% 9% 44%	4440
	21st to end	Day	8% 5% 3 6% 5% 5% 5% 4 7% 9% 44%	4542
August	1st to 10th	Day	13% 8% 3 6% 5% 4 5% 4 6% 7% 39%	4104
	11th to 20th	Day	12% 7% 3 7% 4 4 5% 4 7% 10% 37%	4044
	21st to end	Day	10% 5% 2 6% 4 4 5% 4 6% 9% 44%	4379
September	1st to 10th	Day	14% 6% 2 6% 4 5% 5% 3 6% 7% 42%	2280
	11th to 20th	Day	12% 6% 2 6% 4 4 4 3 5% 8% 44%	2165
	21st to end	Day	15% 6% 2 8% 5% 6% 6% 4 6% 7% 37%	2053
October	1st to 10th	Day	19% 7% 3 8% 5% 5% 5% 4 5% 6% 34%	1900
	11th to 20th	Day	19% 10% 4 9% 6% 4 5% 4 6% 6% 27%	1900
	21st to end	Day	25% 12% 4 10% 5% 5% 4 4 5% 6% 20%	2090
November	1st to 10th	Day	14% 13% 4 9% 5% 5% 4 4 6% 7% 28%	1657
	11th to 20th	Day	13% 17% 4 9% 7% 6% 5% 5% 5% 6% 22%	1600
	21st to end	Day	18% 19% 4 11% 6% 6% 6% 3 5% 6% 16%	1598
December	1st to 10th	Day	16% 18% 7% 15% 8% 6% 5% 4 5% 5% 12%	1520
	11th to 20th	Day	17% 14% 4 11% 6% 7% 6% 5% 5% 6% 19%	1906
	21st to end	Day	26% 18% 6% 14% 6% 5% 4 3 4 4 11%	2772
January	1st to 10th	Night	15% 18% 6% 12% 7% 5% 6% 4 5% 5% 16%	4429
	11th to 20th	Night	13% 12% 6% 15% 11% 8% 7% 4 5% 5% 15%	4239
	21st to end	Night	18% 15% 7% 12% 8% 6% 5% 5% 5% 5% 15%	4532
February	1st to 10th	Night	12% 16% 5% 13% 8% 7% 5% 5% 6% 5% 19%	2470
	11th to 20th	Night	12% 14% 5% 12% 7% 6% 5% 4 6% 6% 23%	2403
	21st to end	Night	14% 11% 5% 12% 6% 5% 5% 4 5% 6% 26%	1995
March	1st to 10th	Night	16% 10% 4 9% 6% 5% 4 4 5% 6% 31%	3408
	11th to 20th	Night	12% 11% 4 9% 5% 5% 5% 4 6% 6% 33%	3479
	21st to end	Night	15% 7% 4 10% 6% 5% 5% 4 5% 7% 33%	3817
April	1st to 10th	Night	18% 12% 3 8% 5% 5% 5% 4 5% 6% 30%	1936
	11th to 20th	Night	18% 8% 3 7% 4 4 4 4 5% 7% 37%	1800
	21st to end	Night	17% 9% 4 9% 5% 4 4 4 4 6% 36%	1710
May	1st to 10th	Night	17% 6% 2 6% 5% 4 4 3 5% 7% 40%	2833
	11th to 20th	Night	15% 7% 2 6% 4 4 5% 4 6% 8% 39%	2495
	21st to end	Night	10% 5% 2 6% 3 4 5% 4 5% 8% 50%	2738
June	1st to 10th	Night	14% 6% 2 7% 3 5% 5% 4 6% 8% 40%	1520
	11th to 20th	Night	9% 4 2 6% 5% 6% 5% 5% 6% 9% 43%	1426
	21st to end	Night	10% 7% 2 7% 5% 5% 4 4 5% 8% 43%	1330
July	1st to 10th	Night	6% 5% 3 6% 4 4 5% 5% 5% 7% 50%	2268
	11th to 20th	Night	12% 5% 2 4 4 3 4 3 5% 8% 50%	2520
	21st to end	Night	8% 5% 2 5% 4 4 5% 4 6% 9% 48%	3008
August	1st to 10th	Night	10% 6% 2 5% 4 5% 3 4 6% 8% 46%	2825
	11th to 20th	Night	13% 5% 2 5% 3 3 3 3 6% 8% 47%	2785
	21st to end	Night	10% 5% 2 6% 4 4 5% 4 6% 8% 46%	3244
September	1st to 10th	Night	12% 5% 2 6% 4 4 4 3 7% 8% 46%	1900
	11th to 20th	Night	12% 4 2 5% 3 3 4 4 5% 7% 50%	2012
	21st to end	Night	16% 7% 2 6% 5% 4 3 4 6% 6% 41%	2126
October	1st to 10th	Night	17% 7% 2 7% 5% 4 4 4 6% 6% 37%	2280
	11th to 20th	Night	18% 10% 4 7% 6% 5% 5% 4 4 6% 31%	2280
	21st to end	Night	22% 11% 3 7% 7% 5% 4 4 6% 6% 24%	2508
November	1st to 10th	Night	17% 10% 3 8% 5% 4 5% 4 5% 7% 32%	2635
	11th to 20th	Night	16% 15% 5% 10% 6% 5% 4 4 6% 7% 24%	2800
	21st to end	Night	18% 16% 5% 9% 6% 5% 5% 4 6% 6% 20%	2798
December	1st to 10th	Night	18% 18% 6% 14% 7% 5% 5% 3 4 5% 16%	2660
	11th to 20th	Night	16% 16% 5% 13% 7% 6% 5% 4 5% 6% 17%	3288
	21st to end	Night	27% 18% 6% 15% 6% 4 4 2 4 4 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	62% 4 16% 14% 5%	2518
	11th to 20th	Day	71% 4 11% 10% 4	2717
	21st to end	Day	73% 3 10% 10% 4 1	3124
February	1st to 10th	Day	67% 6% 8% 15% 4	1710
	11th to 20th	Day	62% 3 10% 17% 7% 1	1672
	21st to end	Day	62% 3 11% 16% 7%	1452
March	1st to 10th	Day	56% 3 13% 18% 10%	3435
	11th to 20th	Day	59% 3 11% 18% 8% 1	3480
	21st to end	Day	51% 3 9% 20% 15% 2	3815
April	1st to 10th	Day	56% 5% 8% 20% 10% 1	2243
	11th to 20th	Day	48% 4 9% 22% 15% 1	2345
	21st to end	Day	51% 4 11% 19% 13% 3	2470
May	1st to 10th	Day	47% 3 11% 24% 14% 2	4120
	11th to 20th	Day	47% 5% 14% 23% 10% 1	4402
	21st to end	Day	38% 4 14% 24% 17% 3	4837
June	1st to 10th	Day	44% 5% 12% 24% 14% 1	2660
	11th to 20th	Day	38% 5% 13% 27% 16% 1	2746
	21st to end	Day	42% 5% 13% 24% 15% 1	2850
July	1st to 10th	Day	42% 4 16% 22% 15% 1	4607
	11th to 20th	Day	36% 5% 13% 34% 11% 1	4365
	21st to end	Day	37% 5% 12% 28% 17% 1	4397
August	1st to 10th	Day	44% 4 14% 25% 12% 1	4091
	11th to 20th	Day	41% 5% 18% 26% 10%	4083
	21st to end	Day	36% 5% 14% 33% 12% 1	4379
September	1st to 10th	Day	41% 6% 12% 29% 11% 1	2280
	11th to 20th	Day	39% 5% 13% 30% 13% 1	2165
	21st to end	Day	46% 5% 13% 26% 9%	2053
October	1st to 10th	Day	44% 4 13% 26% 13% 1	3160
	11th to 20th	Day	45% 5% 15% 22% 12%	3140
	21st to end	Day	58% 3 16% 17% 5%	3428
November	1st to 10th	Day	55% 5% 13% 20% 6% 1	1657
	11th to 20th	Day	61% 6% 13% 14% 7% 1	1600
	21st to end	Day	69% 6% 10% 13% 2	1598
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	69% 4 14% 10% 3	4429
	11th to 20th	Night	71% 4 12% 10% 3	4239
	21st to end	Night	71% 3 11% 10% 3 1	4532
February	1st to 10th	Night	64% 5% 10% 17% 3 1	2470
	11th to 20th	Night	60% 5% 11% 18% 6%	2405
	21st to end	Night	59% 3 12% 17% 8% 1	1995
March	1st to 10th	Night	55% 2 11% 22% 8% 1	3418
	11th to 20th	Night	51% 3 14% 23% 8% 1	3480
	21st to end	Night	51% 3 9% 22% 13% 1	3817
April	1st to 10th	Night	55% 4 9% 20% 12% 1	1936
	11th to 20th	Night	47% 5% 9% 21% 16% 2	1800
	21st to end	Night	51% 3 10% 18% 16% 2	1710
May	1st to 10th	Night	45% 3 13% 20% 17% 3	2840
	11th to 20th	Night	43% 4 14% 25% 12% 2	2496
	21st to end	Night	34% 4 14% 27% 19% 2	2739
June	1st to 10th	Night	42% 5% 11% 25% 15% 2	1520
	11th to 20th	Night	37% 5% 12% 24% 21% 1	1426
	21st to end	Night	39% 5% 13% 26% 15% 1	1330
July	1st to 10th	Night	33% 3 16% 27% 18% 2	2232
	11th to 20th	Night	33% 4 12% 35% 15% 1	2472
	21st to end	Night	33% 5% 13% 32% 16% 1	2912
August	1st to 10th	Night	36% 3 15% 29% 16% 1	2814
	11th to 20th	Night	35% 5% 19% 28% 13% 1	2812
	21st to end	Night	36% 5% 14% 32% 12% 1	3244
September	1st to 10th	Night	36% 5% 15% 30% 13% 1	1900
	11th to 20th	Night	33% 4 13% 33% 17% 1	2012
	21st to end	Night	44% 4 13% 28% 11%	2126
October	1st to 10th	Night	36% 5% 11% 27% 21% 1	3800
	11th to 20th	Night	46% 5% 15% 22% 12%	3779
	21st to end	Night	48% 6% 16% 24% 7%	4120
November	1st to 10th	Night	51% 5% 13% 22% 8% 1	2635
	11th to 20th	Night	60% 5% 13% 15% 7% 1	2800
	21st to end	Night	64% 5% 15% 14% 1	2798
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	19% 11% 40% 22% 7% 2	237
	21st to end	Day	21% 8% 35% 28% 7% 1	297
February	1st to 10th	Day	17% 14% 44% 16% 7% 1	270
	11th to 20th	Day	18% 16% 39% 24% 2	270
	21st to end	Day	24% 19% 32% 23% 2	231
March	1st to 10th	Day	18% 10% 37% 25% 9%	460
	11th to 20th	Day	17% 12% 35% 26% 8% 1	460
	21st to end	Day	25% 8% 32% 23% 11% 1	506
April	1st to 10th	Day	19% 15% 30% 25% 9% 2	460
	11th to 20th	Day	26% 10% 28% 19% 12% 5%	452
	21st to end	Day	23% 10% 25% 26% 12% 4	460
May	1st to 10th	Day	17% 7% 25% 30% 16% 5%	463
	11th to 20th	Day	15% 6% 21% 31% 20% 7%	487
	21st to end	Day	15% 4 22% 31% 21% 7%	529
June	1st to 10th	Day	16% 6% 24% 29% 22% 3	490
	11th to 20th	Day	13% 6% 23% 31% 23% 5%	576
	21st to end	Day	17% 5% 25% 31% 17% 5%	680
July	1st to 10th	Day	11% 3 19% 31% 28% 7%	631
	11th to 20th	Day	13% 2 20% 26% 26% 11%	484
	21st to end	Day	11% 2 15% 38% 22% 11%	532
August	1st to 10th	Day	11% 2 18% 26% 29% 14%	486
	11th to 20th	Day	10% 3 17% 27% 27% 16%	479
	21st to end	Day	14% 3 20% 27% 25% 11%	539
September	1st to 10th	Day	14% 5% 20% 25% 24% 12%	490
	11th to 20th	Day	10% 4 17% 25% 23% 20%	490
	21st to end	Day	14% 6% 24% 26% 22% 9%	490
October	1st to 10th	Day	19% 7% 26% 24% 16% 8%	490
	11th to 20th	Day	21% 10% 34% 23% 9% 2	490
	21st to end	Day	30% 9% 31% 22% 8%	539
November	1st to 10th	Day	21% 15% 31% 22% 11% 1	259
	11th to 20th	Day	22% 17% 32% 22% 6% 2	200
	21st to end	Day	28% 12% 36% 19% 5%	200
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% 33% 27% 7%	760
	21st to end	Night	19% 6% 33% 32% 9% 1	836
February	1st to 10th	Night	19% 9% 41% 27% 4	760
	11th to 20th	Night	19% 10% 37% 29% 6%	743
	21st to end	Night	19% 10% 36% 29% 5%	628
March	1st to 10th	Night	18% 9% 36% 31% 7%	760
	11th to 20th	Night	17% 10% 36% 29% 7% 1	760
	21st to end	Night	20% 8% 31% 29% 11%	836
April	1st to 10th	Night	23% 9% 31% 30% 6%	760
	11th to 20th	Night	20% 7% 31% 30% 10% 2	676
	21st to end	Night	21% 7% 27% 31% 13%	570
May	1st to 10th	Night	18% 2 23% 38% 17% 2	570
	11th to 20th	Night	17% 4 24% 40% 14% 1	374
	21st to end	Night	10% 5% 20% 43% 21% 1	411
June	1st to 10th	Night	16% 5% 24% 40% 14% 1	380
	11th to 20th	Night	9% 6% 20% 47% 17% 1	380
	21st to end	Night	14% 3 20% 42% 19% 2	380
July	1st to 10th	Night	6% 5% 16% 49% 24% 1	370
	11th to 20th	Night	11% 4 20% 41% 22% 2	368
	21st to end	Night	10% 3 17% 43% 26% 2	571
August	1st to 10th	Night	10% 3 13% 43% 29% 2	567
	11th to 20th	Night	6% 2 15% 37% 35% 4	564
	21st to end	Night	12% 4 20% 34% 28% 2	695
September	1st to 10th	Night	13% 5% 19% 34% 23% 6%	760
	11th to 20th	Night	13% 4 18% 31% 25% 9%	760
	21st to end	Night	18% 6% 20% 30% 20% 5%	760
October	1st to 10th	Night	19% 5% 29% 28% 17% 3	760
	11th to 20th	Night	21% 11% 29% 27% 9% 2	760
	21st to end	Night	28% 10% 31% 25% 7%	836
November	1st to 10th	Night	22% 11% 29% 27% 11% 1	780
	11th to 20th	Night	22% 13% 34% 21% 8% 1	800
	21st to end	Night	27% 13% 32% 24% 4	800
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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