Bertucci's Sky
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bertucci's Sky clear sky chart from 2005-11-06 to 2026-03-18.

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	1 3 1 3 2 3 3 3 5% 6% 70%	139800
	Night	1 3 1 3 2 2 3 3 5% 7% 69%	139127
Transparency	Day	15% 6% 10% 20% 28% 21%	134774
	Night	15% 7% 12% 24% 27% 15%	135134
Seeing	Day	9% 20% 30% 24% 12% 4	16778
	Night	5% 13% 26% 34% 19% 4	26264

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	3 1 3 2 3 4 4 7% 11% 61%	4722
	11th to 20th	Day	1 2 1 3 3 3 4 3 5% 7% 69%	4897
	21st to end	Day	2 7% 2 5% 3 3 4 4 6% 9% 55%	5843
February	1st to 10th	Day	1 5% 2 4 3 3 4 4 7% 9% 59%	1911
	11th to 20th	Day	1 4 2 5% 4 4 4 4 7% 11% 54%	2050
	21st to end	Day	1 4 1 4 3 3 4 4 7% 8% 61%	1730
March	1st to 10th	Day	2 5% 4 7% 4 5% 5% 5% 7% 9% 48%	4618
	11th to 20th	Day	4 1 3 2 2 4 4 6% 8% 66%	4983
	21st to end	Day	1 7% 2 4 3 3 4 4 6% 8% 59%	5837
April	1st to 10th	Day	2 4 1 5% 4 4 4 4 6% 10% 57%	2400
	11th to 20th	Day	2 4 1 4 3 3 4 5% 6% 7% 61%	2369
	21st to end	Day	3 4 2 3 3 3 3 3 5% 8% 64%	2400
May	1st to 10th	Day	3 3 1 3 3 3 3 2 4 5% 70%	5698
	11th to 20th	Day	1 2 2 2 2 2 2 4 6% 76%	6132
	21st to end	Day	2 3 1 3 2 2 3 3 4 5% 72%	6902
June	1st to 10th	Day	3 3 1 3 3 3 3 3 5% 7% 65%	2800
	11th to 20th	Day	1 2 1 2 2 1 2 2 4 5% 79%	2800
	21st to end	Day	2 2 1 2 2 2 3 3 3 4 76%	2800
July	1st to 10th	Day	1 2 1 1 2 2 2 3 86%	6319
	11th to 20th	Day	2 1 1 3 2 2 2 2 3 4 77%	6320
	21st to end	Day	1 2 1 2 2 2 4 4 5% 5% 73%	6712
August	1st to 10th	Day	1 1 2 2 2 2 2 2 3 83%	5675
	11th to 20th	Day	1 1 1 2 1 2 3 88%	5364
	21st to end	Day	1 1 1 3 3 3 3 2 3 4 75%	5984
September	1st to 10th	Day	1 1 2 1 2 2 2 4 5% 79%	2400
	11th to 20th	Day	1 2 1 3 3 3 3 1 4 5% 74%	2360
	21st to end	Day	1 2 1 3 2 2 3 2 3 3 78%	2200
October	1st to 10th	Day	2 2 1 2 2 2 3 3 4 6% 74%	3349
	11th to 20th	Day	1 2 1 2 2 1 2 1 3 3 81%	3261
	21st to end	Day	1 1 1 2 2 2 3 3 5% 7% 74%	3472
November	1st to 10th	Day	1 3 1 3 2 3 4 4 6% 8% 65%	1854
	11th to 20th	Day	2 3 1 3 3 3 3 4 6% 8% 66%	1890
	21st to end	Day	1 2 1 3 2 3 4 3 7% 9% 65%	1848
December	1st to 10th	Day	1 2 1 2 1 2 3 3 6% 8% 71%	2700
	11th to 20th	Day	2 5% 2 5% 3 4 5% 5% 7% 9% 54%	3108
	21st to end	Day	1 4 3 6% 4 4 5% 4 7% 13% 51%	4092
January	1st to 10th	Night	1 4 2 4 2 3 3 3 6% 10% 62%	8172
	11th to 20th	Night	3 2 4 3 2 3 3 5% 7% 69%	8066
	21st to end	Night	2 6% 3 5% 4 4 4 4 6% 8% 54%	8371
February	1st to 10th	Night	1 4 2 5% 4 4 4 4 6% 7% 60%	2708
	11th to 20th	Night	1 4 2 4 2 3 4 4 8% 11% 56%	2458
	21st to end	Night	3 2 4 4 3 3 4 6% 10% 61%	2076
March	1st to 10th	Night	1 7% 4 5% 4 4 5% 4 6% 9% 52%	5496
	11th to 20th	Night	1 4 1 4 3 3 4 3 6% 8% 63%	5167
	21st to end	Night	1 6% 2 5% 4 4 4 4 6% 9% 55%	5124
April	1st to 10th	Night	2 3 1 3 4 3 4 4 7% 10% 60%	2000
	11th to 20th	Night	1 4 1 3 3 3 4 3 6% 8% 64%	1979
	21st to end	Night	3 4 1 3 2 2 2 2 5% 7% 68%	2000
May	1st to 10th	Night	2 3 1 3 2 2 2 2 3 5% 75%	4289
	11th to 20th	Night	1 2 1 2 2 2 3 2 4 5% 77%	3764
	21st to end	Night	2 2 1 2 2 1 2 2 3 5% 79%	3972
June	1st to 10th	Night	3 3 1 3 2 2 3 3 4 5% 70%	1600
	11th to 20th	Night	1 1 1 1 2 2 2 4 4 83%	1600
	21st to end	Night	2 2 1 1 1 2 2 2 2 3 82%	1600
July	1st to 10th	Night	1 1 1 1 2 92%	3640
	11th to 20th	Night	2 2 1 3 2 2 2 2 3 4 80%	3640
	21st to end	Night	1 1 1 2 2 2 3 2 4 6% 77%	4141
August	1st to 10th	Night	1 1 2 2 1 1 1 3 4 83%	4142
	11th to 20th	Night	1 1 1 1 1 1 2 3 88%	4506
	21st to end	Night	2 1 1 3 2 2 2 2 3 3 80%	5015
September	1st to 10th	Night	1 1 1 2 2 1 3 3 86%	2000
	11th to 20th	Night	2 2 1 2 1 2 2 2 3 5% 78%	2038
	21st to end	Night	1 1 1 3 2 2 2 2 3 4 79%	2200
October	1st to 10th	Night	2 2 2 2 2 2 2 2 5% 81%	3846
	11th to 20th	Night	1 2 1 2 1 1 2 2 3 4 83%	3897
	21st to end	Night	1 2 1 3 2 2 3 2 4 7% 74%	4336
November	1st to 10th	Night	1 2 1 2 2 2 3 3 6% 8% 69%	2665
	11th to 20th	Night	1 3 1 2 3 2 4 3 6% 9% 66%	2730
	21st to end	Night	2 3 1 3 2 3 3 3 6% 9% 67%	2767
December	1st to 10th	Night	1 2 1 3 2 3 3 3 5% 8% 69%	4700
	11th to 20th	Night	2 3 1 4 3 3 4 4 7% 13% 56%	5316
	21st to end	Night	1 5% 2 5% 4 5% 6% 5% 9% 12% 47%	7106

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	15% 10% 22% 33% 18% 1	4723
	11th to 20th	Day	15% 7% 10% 20% 36% 12%	4897
	21st to end	Day	26% 7% 11% 22% 28% 6%	5843
February	1st to 10th	Day	21% 10% 15% 26% 20% 8%	1911
	11th to 20th	Day	24% 10% 12% 27% 22% 5%	2060
	21st to end	Day	22% 10% 17% 27% 17% 7%	1730
March	1st to 10th	Day	27% 11% 13% 23% 20% 5%	4618
	11th to 20th	Day	15% 8% 15% 34% 24% 5%	4983
	21st to end	Day	22% 10% 17% 25% 23% 2	5837
April	1st to 10th	Day	24% 9% 17% 24% 20% 5%	2400
	11th to 20th	Day	21% 9% 14% 27% 22% 7%	2372
	21st to end	Day	20% 8% 15% 29% 24% 4	2400
May	1st to 10th	Day	16% 5% 7% 27% 38% 7%	5698
	11th to 20th	Day	11% 4 8% 25% 41% 11%	6135
	21st to end	Day	14% 5% 8% 19% 41% 13%	6904
June	1st to 10th	Day	19% 7% 11% 23% 32% 9%	2800
	11th to 20th	Day	10% 4 7% 21% 36% 23%	2800
	21st to end	Day	12% 4 5% 13% 33% 34%	2800
July	1st to 10th	Day	6% 1 2 5% 18% 67%	6251
	11th to 20th	Day	11% 2 4 8% 11% 64%	6245
	21st to end	Day	10% 4 6% 14% 26% 40%	6516
August	1st to 10th	Day	12% 3 4 8% 24% 49%	4126
	11th to 20th	Day	6% 2 2 6% 19% 65%	3880
	21st to end	Day	7% 2 2 10% 36% 43%	4311
September	1st to 10th	Day	9% 3 4 10% 34% 40%	2400
	11th to 20th	Day	13% 3 6% 20% 35% 22%	2360
	21st to end	Day	13% 3 4 18% 37% 25%	2200
October	1st to 10th	Day	13% 4 7% 12% 33% 32%	3349
	11th to 20th	Day	10% 3 5% 20% 48% 14%	3261
	21st to end	Day	11% 4 9% 27% 35% 15%	3472
November	1st to 10th	Day	17% 8% 12% 25% 28% 10%	1854
	11th to 20th	Day	16% 8% 16% 24% 29% 7%	1890
	21st to end	Day	16% 9% 12% 29% 25% 9%	1848
December	1st to 10th	Day	13% 7% 16% 29% 30% 5%	2700
	11th to 20th	Day	24% 11% 19% 21% 20% 6%	3108
	21st to end	Day	22% 10% 23% 26% 16% 2	4092
January	1st to 10th	Night	17% 8% 22% 35% 16% 2	8172
	11th to 20th	Night	15% 7% 11% 24% 37% 5%	8066
	21st to end	Night	26% 8% 12% 24% 26% 4	8371
February	1st to 10th	Night	23% 10% 13% 26% 20% 9%	2708
	11th to 20th	Night	19% 10% 15% 30% 22% 5%	2459
	21st to end	Night	19% 11% 17% 28% 19% 6%	2076
March	1st to 10th	Night	24% 10% 13% 26% 21% 5%	5496
	11th to 20th	Night	17% 10% 15% 41% 16% 2	5167
	21st to end	Night	22% 14% 21% 28% 12% 3	5124
April	1st to 10th	Night	21% 11% 19% 27% 18% 5%	2000
	11th to 20th	Night	18% 8% 17% 29% 20% 8%	1979
	21st to end	Night	16% 9% 18% 33% 22% 2	2000
May	1st to 10th	Night	13% 6% 8% 34% 34% 5%	4286
	11th to 20th	Night	11% 4 10% 24% 40% 10%	3764
	21st to end	Night	10% 4 9% 24% 46% 6%	3972
June	1st to 10th	Night	16% 8% 11% 26% 31% 9%	1600
	11th to 20th	Night	8% 3 7% 22% 36% 24%	1600
	21st to end	Night	9% 3 4 16% 35% 34%	1600
July	1st to 10th	Night	3 1 2 5% 24% 66%	3600
	11th to 20th	Night	11% 1 4 6% 14% 64%	3592
	21st to end	Night	9% 3 5% 19% 22% 42%	4025
August	1st to 10th	Night	11% 2 4 10% 29% 43%	3012
	11th to 20th	Night	6% 2 2 7% 22% 62%	3256
	21st to end	Night	6% 2 2 12% 40% 38%	3608
September	1st to 10th	Night	6% 2 3 11% 38% 40%	2000
	11th to 20th	Night	10% 3 7% 23% 36% 21%	2038
	21st to end	Night	11% 3 6% 19% 36% 25%	2200
October	1st to 10th	Night	10% 3 4 15% 36% 32%	3846
	11th to 20th	Night	8% 3 6% 21% 48% 14%	3897
	21st to end	Night	11% 3 9% 26% 38% 13%	4336
November	1st to 10th	Night	14% 9% 12% 28% 26% 11%	2665
	11th to 20th	Night	14% 8% 14% 28% 28% 7%	2730
	21st to end	Night	16% 7% 14% 28% 26% 9%	2767
December	1st to 10th	Night	14% 7% 17% 28% 26% 7%	4700
	11th to 20th	Night	19% 12% 18% 28% 19% 4	5316
	21st to end	Night	25% 13% 20% 23% 16% 2	7106

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	18% 26% 26% 19% 9% 2	220
	11th to 20th	Day	13% 20% 24% 26% 14% 4	273
	21st to end	Day	8% 22% 28% 25% 13% 4	473
February	1st to 10th	Day	15% 25% 27% 20% 10% 2	441
	11th to 20th	Day	13% 28% 30% 23% 6%	535
	21st to end	Day	13% 25% 34% 23% 5%	446
March	1st to 10th	Day	15% 31% 31% 16% 7% 1	540
	11th to 20th	Day	15% 29% 28% 17% 10% 1	529
	21st to end	Day	16% 32% 28% 18% 6%	550
April	1st to 10th	Day	13% 29% 31% 17% 9% 1	500
	11th to 20th	Day	15% 30% 29% 16% 8% 2	492
	21st to end	Day	11% 25% 31% 20% 9% 4	500
May	1st to 10th	Day	13% 30% 27% 19% 7% 3	503
	11th to 20th	Day	13% 23% 31% 21% 8% 5%	528
	21st to end	Day	11% 18% 30% 23% 12% 6%	573
June	1st to 10th	Day	8% 19% 30% 25% 12% 6%	530
	11th to 20th	Day	8% 24% 34% 22% 8% 4	530
	21st to end	Day	2 15% 37% 28% 12% 6%	530
July	1st to 10th	Day	2 14% 37% 27% 16% 4	526
	11th to 20th	Day	2 11% 34% 30% 16% 6%	524
	21st to end	Day	2 8% 36% 31% 17% 6%	575
August	1st to 10th	Day	4 13% 32% 31% 15% 6%	527
	11th to 20th	Day	2 13% 37% 26% 15% 7%	517
	21st to end	Day	2 11% 36% 30% 16% 5%	583
September	1st to 10th	Day	3 11% 35% 30% 19% 3	530
	11th to 20th	Day	5% 16% 31% 32% 13% 4	530
	21st to end	Day	5% 15% 32% 34% 12% 3	530
October	1st to 10th	Day	6% 20% 26% 26% 19% 3	530
	11th to 20th	Day	6% 18% 24% 31% 17% 4	530
	21st to end	Day	8% 17% 27% 26% 18% 4	533
November	1st to 10th	Day	11% 15% 25% 21% 23% 5%	330
	11th to 20th	Day	8% 19% 26% 28% 13% 6%	330
	21st to end	Day	6% 21% 25% 25% 18% 4	308
December	1st to 10th	Day	12% 19% 20% 24% 17% 9%	220
	11th to 20th	Day	10% 24% 28% 19% 13% 6%	220
	21st to end	Day	19% 19% 27% 21% 11% 2	242
January	1st to 10th	Night	6% 18% 30% 23% 15% 8%	840
	11th to 20th	Night	4 15% 27% 34% 15% 5%	840
	21st to end	Night	5% 12% 31% 31% 16% 5%	924
February	1st to 10th	Night	7% 14% 29% 31% 15% 3	840
	11th to 20th	Night	5% 19% 30% 27% 15% 5%	824
	21st to end	Night	6% 22% 26% 33% 11% 3	692
March	1st to 10th	Night	7% 20% 34% 26% 11% 3	840
	11th to 20th	Night	6% 20% 28% 24% 18% 4	828
	21st to end	Night	5% 24% 30% 28% 12% 2	880
April	1st to 10th	Night	6% 15% 31% 31% 15% 2	800
	11th to 20th	Night	7% 18% 27% 29% 14% 4	791
	21st to end	Night	6% 14% 28% 31% 16% 5%	800
May	1st to 10th	Night	6% 16% 26% 31% 16% 4	685
	11th to 20th	Night	4 11% 26% 39% 18% 2	464
	21st to end	Night	6% 7% 25% 36% 25% 2	433
June	1st to 10th	Night	5% 9% 22% 42% 20% 3	400
	11th to 20th	Night	2 8% 26% 39% 25% 1	400
	21st to end	Night	2 3 26% 45% 22% 3	400
July	1st to 10th	Night	2 4 20% 48% 25% 2	390
	11th to 20th	Night	2 2 24% 46% 26%	388
	21st to end	Night	3 2 18% 41% 32% 5%	508
August	1st to 10th	Night	3 2 17% 45% 29% 3	641
	11th to 20th	Night	2 4 21% 43% 26% 4	792
	21st to end	Night	2 4 21% 45% 25% 3	880
September	1st to 10th	Night	1 4 21% 39% 30% 5%	800
	11th to 20th	Night	3 7% 21% 35% 28% 6%	800
	21st to end	Night	2 8% 22% 34% 27% 7%	800
October	1st to 10th	Night	4 8% 22% 37% 23% 6%	800
	11th to 20th	Night	6% 8% 18% 39% 25% 5%	800
	21st to end	Night	3 12% 21% 30% 22% 12%	880
November	1st to 10th	Night	5% 13% 22% 30% 23% 7%	820
	11th to 20th	Night	4 14% 28% 33% 14% 6%	840
	21st to end	Night	6% 15% 24% 30% 20% 5%	840
December	1st to 10th	Night	6% 14% 28% 33% 15% 5%	840
	11th to 20th	Night	6% 19% 26% 30% 13% 6%	840
	21st to end	Night	8% 19% 32% 28% 11% 2	924

Page generated at 2026-03-14 23:23:56. Version ac07

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