Bridgeport Lake Private Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bridgeport Lake Private Observatory clear sky chart from 2005-11-06 to 2024-12-09.

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	2 4 2 4 3 3 4 3 5% 6% 64%	105354
	Night	1 3 2 4 3 3 3 3 5% 7% 67%	103157
Transparency	Day	18% 6% 9% 19% 26% 22%	105098
	Night	16% 6% 10% 22% 28% 18%	103003
Seeing	Day	7% 15% 26% 29% 17% 6%	15218
	Night	3 7% 26% 37% 22% 5%	24682

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	1 2 1 4 4 4 4 5% 7% 11% 57%	2539
	11th to 20th	Day	4 2 5% 4 4 5% 5% 8% 10% 52%	2603
	21st to end	Day	2 7% 3 6% 4 5% 5% 4 6% 9% 47%	3146
February	1st to 10th	Day	4 2 6% 3 3 3 3 7% 7% 60%	1789
	11th to 20th	Day	1 4 2 6% 4 3 4 4 7% 10% 55%	1850
	21st to end	Day	4 1 4 4 3 4 5% 6% 7% 59%	1570
March	1st to 10th	Day	4 3 8% 5% 6% 6% 7% 7% 8% 46%	3138
	11th to 20th	Day	3 1 6% 3 3 3 3 6% 8% 63%	3359
	21st to end	Day	1 7% 3 6% 4 4 5% 4 6% 8% 52%	4124
April	1st to 10th	Day	2 5% 2 5% 4 3 5% 4 5% 7% 58%	2280
	11th to 20th	Day	1 5% 2 4 4 4 4 3 5% 7% 62%	2249
	21st to end	Day	2 6% 2 4 2 4 4 3 5% 5% 63%	2280
May	1st to 10th	Day	2 3 1 3 2 3 3 3 5% 6% 70%	4010
	11th to 20th	Day	3 3 2 4 3 3 4 3 4 6% 66%	4132
	21st to end	Day	3 5% 2 5% 3 3 3 3 4 6% 63%	4813
June	1st to 10th	Day	4 4 1 5% 4 4 4 4 5% 7% 59%	2660
	11th to 20th	Day	2 2 1 3 2 2 3 2 4 5% 74%	2660
	21st to end	Day	3 2 1 4 3 3 3 3 3 4 71%	2660
July	1st to 10th	Day	2 2 1 2 2 2 3 2 3 3 78%	4420
	11th to 20th	Day	6% 5% 2 6% 4 4 4 3 4 5% 56%	4420
	21st to end	Day	4 4 1 4 3 3 3 3 4 5% 65%	4705
August	1st to 10th	Day	4 3 2 5% 3 3 4 3 4 4 64%	3916
	11th to 20th	Day	2 2 1 3 2 2 2 2 3 3 79%	3724
	21st to end	Day	2 2 1 2 2 2 2 2 2 3 81%	4180
September	1st to 10th	Day	3 2 1 3 3 3 3 2 3 3 74%	2280
	11th to 20th	Day	3 3 1 4 3 3 3 2 3 5% 70%	2214
	21st to end	Day	2 2 1 3 2 2 2 1 4 4 77%	2090
October	1st to 10th	Day	3 4 2 4 2 3 3 2 3 4 70%	3337
	11th to 20th	Day	2 3 2 2 1 1 2 1 3 4 80%	3161
	21st to end	Day	1 2 2 3 2 2 3 3 5% 7% 71%	3330
November	1st to 10th	Day	1 3 2 4 3 3 4 3 5% 6% 67%	1764
	11th to 20th	Day	1 2 1 3 2 3 3 3 4 9% 69%	1800
	21st to end	Day	1 3 1 3 3 2 3 3 7% 9% 65%	1800
December	1st to 10th	Day	1 4 1 4 3 2 3 3 5% 10% 63%	1629
	11th to 20th	Day	2 6% 2 7% 5% 5% 6% 5% 7% 8% 46%	1928
	21st to end	Day	1 7% 3 7% 4 4 5% 5% 8% 9% 48%	2794
January	1st to 10th	Night	1 3 3 6% 4 4 5% 4 6% 8% 57%	4406
	11th to 20th	Night	4 2 5% 4 5% 5% 5% 9% 9% 52%	4358
	21st to end	Night	1 7% 2 6% 4 4 5% 4 7% 9% 50%	4521
February	1st to 10th	Night	4 2 6% 4 4 4 4 6% 8% 59%	2390
	11th to 20th	Night	4 2 5% 4 4 3 3 6% 10% 60%	2218
	21st to end	Night	4 2 5% 3 3 3 4 7% 8% 62%	1884
March	1st to 10th	Night	4 3 7% 5% 4 5% 5% 7% 8% 53%	3736
	11th to 20th	Night	5% 4 5% 2 3 3 3 5% 8% 61%	3618
	21st to end	Night	5% 2 6% 4 4 5% 4 6% 9% 55%	3529
April	1st to 10th	Night	1 4 2 3 3 3 4 4 6% 8% 60%	1900
	11th to 20th	Night	1 4 1 4 4 3 4 3 5% 5% 66%	1879
	21st to end	Night	2 5% 1 3 2 3 3 3 4 5% 69%	1900
May	1st to 10th	Night	1 2 1 3 2 2 2 2 3 5% 76%	2961
	11th to 20th	Night	2 3 1 3 2 2 2 2 4 6% 74%	2753
	21st to end	Night	2 3 1 4 3 2 3 2 3 5% 71%	2762
June	1st to 10th	Night	5% 3 1 3 2 3 3 3 4 7% 66%	1520
	11th to 20th	Night	2 1 1 1 1 1 2 2 3 4 82%	1520
	21st to end	Night	2 2 2 2 2 3 2 2 3 80%	1520
July	1st to 10th	Night	1 1 1 1 1 1 2 3 88%	2540
	11th to 20th	Night	2 3 2 4 3 4 4 3 5% 6% 64%	2540
	21st to end	Night	2 2 1 2 2 3 3 3 4 4 76%	2844
August	1st to 10th	Night	2 2 1 3 2 2 2 2 4 5% 75%	3028
	11th to 20th	Night	1 1 2 1 1 1 2 2 3 85%	3126
	21st to end	Night	1 1 1 1 1 1 1 2 3 87%	3498
September	1st to 10th	Night	1 1 1 1 1 1 1 2 2 3 85%	1900
	11th to 20th	Night	2 3 1 2 2 3 2 2 3 4 78%	1966
	21st to end	Night	2 3 1 2 2 2 2 1 3 4 79%	2090
October	1st to 10th	Night	3 3 1 2 2 2 2 2 3 4 76%	3640
	11th to 20th	Night	1 1 1 2 1 2 3 2 3 5% 79%	3777
	21st to end	Night	1 2 2 3 2 2 3 2 3 6% 74%	4232
November	1st to 10th	Night	1 2 1 2 2 3 3 3 5% 7% 71%	2535
	11th to 20th	Night	1 2 2 3 2 3 3 3 5% 7% 71%	2600
	21st to end	Night	3 2 3 3 3 3 3 5% 7% 68%	2600
December	1st to 10th	Night	1 3 2 5% 3 3 3 4 5% 7% 64%	2728
	11th to 20th	Night	1 5% 2 6% 5% 3 5% 5% 7% 10% 52%	3276
	21st to end	Night	1 6% 2 7% 5% 5% 6% 5% 8% 10% 45%	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	19% 9% 19% 28% 21% 4	2539
	11th to 20th	Day	24% 10% 16% 22% 21% 7%	2603
	21st to end	Day	29% 10% 15% 22% 19% 5%	3146
February	1st to 10th	Day	20% 7% 13% 25% 24% 11%	1789
	11th to 20th	Day	22% 6% 13% 26% 25% 9%	1860
	21st to end	Day	20% 8% 14% 27% 25% 6%	1570
March	1st to 10th	Day	27% 8% 18% 23% 17% 8%	3138
	11th to 20th	Day	17% 9% 18% 37% 16% 4	3359
	21st to end	Day	25% 10% 16% 30% 17% 3	4124
April	1st to 10th	Day	24% 8% 15% 27% 18% 8%	2280
	11th to 20th	Day	20% 8% 12% 30% 22% 9%	2252
	21st to end	Day	20% 7% 15% 30% 23% 6%	2280
May	1st to 10th	Day	14% 5% 8% 28% 34% 11%	4010
	11th to 20th	Day	16% 6% 6% 24% 36% 12%	4135
	21st to end	Day	19% 7% 7% 22% 38% 7%	4814
June	1st to 10th	Day	22% 7% 9% 21% 30% 10%	2660
	11th to 20th	Day	12% 5% 6% 19% 34% 24%	2660
	21st to end	Day	16% 4 3 10% 32% 35%	2660
July	1st to 10th	Day	10% 3 2 6% 13% 65%	4351
	11th to 20th	Day	25% 6% 4 8% 15% 41%	4345
	21st to end	Day	20% 5% 4 11% 18% 42%	4556
August	1st to 10th	Day	21% 5% 4 9% 21% 41%	3901
	11th to 20th	Day	11% 3 2 6% 16% 62%	3760
	21st to end	Day	10% 2 2 7% 30% 49%	4179
September	1st to 10th	Day	15% 3 2 9% 29% 41%	2280
	11th to 20th	Day	15% 4 4 19% 30% 27%	2214
	21st to end	Day	13% 3 3 18% 34% 29%	2090
October	1st to 10th	Day	16% 5% 4 11% 34% 30%	3337
	11th to 20th	Day	11% 3 3 13% 45% 25%	3161
	21st to end	Day	11% 6% 5% 21% 41% 17%	3330
November	1st to 10th	Day	16% 6% 9% 25% 29% 15%	1764
	11th to 20th	Day	12% 6% 11% 27% 33% 12%	1800
	21st to end	Day	14% 7% 12% 25% 29% 14%	1800
December	1st to 10th	Day	16% 8% 14% 25% 25% 12%	1629
	11th to 20th	Day	30% 12% 13% 20% 17% 8%	1928
	21st to end	Day	26% 11% 15% 22% 20% 5%	2794
January	1st to 10th	Night	22% 8% 15% 31% 20% 4	4406
	11th to 20th	Night	22% 10% 18% 26% 18% 6%	4358
	21st to end	Night	27% 10% 16% 24% 17% 5%	4521
February	1st to 10th	Night	23% 8% 12% 25% 22% 11%	2390
	11th to 20th	Night	19% 5% 12% 28% 27% 8%	2219
	21st to end	Night	19% 7% 13% 31% 24% 7%	1884
March	1st to 10th	Night	26% 7% 16% 23% 21% 7%	3736
	11th to 20th	Night	18% 7% 14% 38% 18% 4	3618
	21st to end	Night	21% 8% 16% 33% 19% 2	3529
April	1st to 10th	Night	19% 9% 16% 31% 18% 7%	1900
	11th to 20th	Night	18% 6% 14% 28% 24% 9%	1879
	21st to end	Night	17% 6% 15% 36% 23% 3	1900
May	1st to 10th	Night	12% 4 7% 34% 36% 6%	2961
	11th to 20th	Night	13% 4 8% 26% 40% 10%	2754
	21st to end	Night	16% 6% 7% 26% 41% 4	2762
June	1st to 10th	Night	17% 5% 10% 26% 34% 7%	1520
	11th to 20th	Night	9% 3 7% 20% 39% 22%	1520
	21st to end	Night	11% 3 4 15% 31% 36%	1520
July	1st to 10th	Night	4 2 2 7% 17% 69%	2500
	11th to 20th	Night	19% 6% 5% 9% 22% 40%	2492
	21st to end	Night	12% 4 4 15% 22% 44%	2755
August	1st to 10th	Night	12% 4 4 12% 29% 39%	3019
	11th to 20th	Night	7% 3 2 9% 18% 61%	3156
	21st to end	Night	6% 3 2 11% 33% 45%	3498
September	1st to 10th	Night	6% 3 2 12% 38% 39%	1900
	11th to 20th	Night	11% 5% 4 18% 36% 26%	1966
	21st to end	Night	10% 2 4 18% 39% 26%	2090
October	1st to 10th	Night	12% 5% 5% 15% 39% 24%	3640
	11th to 20th	Night	7% 3 5% 16% 50% 18%	3777
	21st to end	Night	11% 6% 4 20% 38% 21%	4232
November	1st to 10th	Night	13% 6% 9% 28% 30% 13%	2535
	11th to 20th	Night	13% 7% 10% 27% 33% 11%	2600
	21st to end	Night	15% 6% 12% 25% 30% 12%	2600
December	1st to 10th	Night	18% 8% 14% 24% 27% 10%	2728
	11th to 20th	Night	25% 11% 15% 23% 21% 5%	3276
	21st to end	Night	28% 13% 13% 18% 22% 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	9% 17% 33% 26% 12% 2	180
	11th to 20th	Day	5% 19% 28% 24% 17% 7%	217
	21st to end	Day	7% 13% 24% 35% 17% 5%	407
February	1st to 10th	Day	7% 16% 29% 29% 13% 6%	408
	11th to 20th	Day	5% 19% 30% 30% 15% 2	455
	21st to end	Day	6% 20% 30% 29% 14% 2	382
March	1st to 10th	Day	5% 19% 35% 28% 10% 3	460
	11th to 20th	Day	7% 22% 27% 23% 15% 5%	460
	21st to end	Day	8% 22% 31% 29% 9%	506
April	1st to 10th	Day	10% 19% 30% 26% 13% 2	460
	11th to 20th	Day	11% 19% 27% 26% 12% 5%	452
	21st to end	Day	10% 19% 24% 27% 14% 6%	460
May	1st to 10th	Day	11% 15% 34% 24% 12% 4	463
	11th to 20th	Day	13% 19% 25% 23% 13% 8%	488
	21st to end	Day	12% 18% 19% 24% 19% 8%	529
June	1st to 10th	Day	9% 16% 24% 27% 16% 7%	490
	11th to 20th	Day	8% 19% 27% 25% 16% 5%	490
	21st to end	Day	4 14% 26% 32% 18% 6%	490
July	1st to 10th	Day	4 11% 25% 32% 20% 9%	486
	11th to 20th	Day	6% 8% 21% 33% 24% 7%	484
	21st to end	Day	7% 7% 21% 34% 22% 8%	531
August	1st to 10th	Day	7% 10% 24% 29% 23% 7%	487
	11th to 20th	Day	5% 10% 27% 30% 18% 9%	477
	21st to end	Day	4 7% 27% 35% 21% 6%	539
September	1st to 10th	Day	5% 9% 23% 36% 18% 8%	490
	11th to 20th	Day	8% 15% 24% 30% 20% 4	490
	21st to end	Day	6% 11% 23% 38% 19% 4	490
October	1st to 10th	Day	8% 15% 25% 25% 20% 7%	490
	11th to 20th	Day	7% 11% 26% 30% 21% 6%	490
	21st to end	Day	6% 14% 28% 26% 20% 5%	470
November	1st to 10th	Day	5% 13% 27% 26% 20% 9%	300
	11th to 20th	Day	5% 10% 27% 26% 23% 9%	300
	21st to end	Day	4 12% 23% 30% 24% 6%	300
December	1st to 10th	Day	8% 9% 27% 26% 19% 12%	219
	11th to 20th	Day	7% 13% 26% 28% 22% 4	180
	21st to end	Day	9% 18% 29% 26% 14% 5%	198
January	1st to 10th	Night	4 9% 33% 28% 16% 9%	760
	11th to 20th	Night	3 9% 29% 38% 16% 7%	760
	21st to end	Night	5% 6% 31% 33% 18% 7%	836
February	1st to 10th	Night	3 9% 28% 36% 19% 5%	760
	11th to 20th	Night	3 9% 31% 32% 18% 6%	744
	21st to end	Night	4 11% 33% 35% 12% 4	628
March	1st to 10th	Night	4 11% 36% 31% 13% 5%	760
	11th to 20th	Night	3 13% 30% 30% 18% 7%	760
	21st to end	Night	3 13% 37% 32% 13% 2	836
April	1st to 10th	Night	5% 10% 32% 35% 16% 3	760
	11th to 20th	Night	4 12% 30% 33% 16% 5%	751
	21st to end	Night	5% 10% 28% 34% 19% 5%	760
May	1st to 10th	Night	6% 9% 32% 33% 16% 5%	632
	11th to 20th	Night	5% 7% 26% 36% 23% 3	520
	21st to end	Night	5% 6% 23% 34% 28% 4	411
June	1st to 10th	Night	5% 4 22% 38% 28% 2	380
	11th to 20th	Night	3 3 24% 44% 24% 3	380
	21st to end	Night	3 1 21% 50% 22% 3	380
July	1st to 10th	Night	1 1 12% 50% 32% 4	370
	11th to 20th	Night	2 2 10% 51% 32% 2	368
	21st to end	Night	2 2 8% 45% 37% 6%	463
August	1st to 10th	Night	3 2 13% 41% 35% 6%	669
	11th to 20th	Night	2 2 15% 43% 31% 6%	752
	21st to end	Night	3 1 15% 44% 33% 5%	836
September	1st to 10th	Night	1 3 16% 40% 35% 6%	760
	11th to 20th	Night	3 4 18% 42% 28% 6%	760
	21st to end	Night	3 4 20% 37% 28% 9%	760
October	1st to 10th	Night	3 5% 21% 39% 26% 7%	760
	11th to 20th	Night	3 6% 16% 41% 27% 7%	760
	21st to end	Night	3 4 25% 32% 25% 11%	836
November	1st to 10th	Night	2 5% 27% 34% 24% 7%	780
	11th to 20th	Night	3 7% 30% 35% 20% 6%	800
	21st to end	Night	4 7% 28% 33% 23% 5%	800
December	1st to 10th	Night	2 7% 33% 34% 19% 6%	794
	11th to 20th	Night	3 8% 34% 34% 17% 4	760
	21st to end	Night	3 13% 34% 35% 12% 3	836

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