Bridgman
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bridgman clear sky chart from 2005-11-06 to 2026-02-01.

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	13% 10% 4 9% 5% 4 4 3 5% 7% 35%	127284
	Night	15% 13% 5% 10% 5% 4 4 3 4 6% 31%	124973
Transparency	Day	49% 3 11% 23% 13% 1	130823
	Night	55% 3 10% 20% 12% 1	129508
Seeing	Day	19% 15% 29% 22% 12% 4	17425
	Night	21% 12% 27% 27% 12% 1	27377

By Month

Percentage Cloud Cover SE (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	11% 22% 10% 21% 5% 3 3 3 3 4 14%	3697
	11th to 20th	Day	11% 18% 9% 17% 12% 8% 9% 2 2 2 9%	3700
	21st to end	Day	18% 19% 6% 14% 4 4 5% 4 4 4 19%	4070
February	1st to 10th	Day	14% 17% 6% 13% 9% 5% 5% 3 5% 5% 19%	1899
	11th to 20th	Day	14% 13% 6% 16% 8% 5% 5% 3 4 4 22%	1948
	21st to end	Day	15% 14% 7% 11% 6% 4 4 3 5% 6% 25%	1650
March	1st to 10th	Day	17% 12% 6% 10% 5% 4 3 3 4 5% 33%	4480
	11th to 20th	Day	9% 9% 8% 8% 4 4 4 3 5% 8% 37%	4746
	21st to end	Day	17% 16% 7% 11% 6% 5% 4 3 4 5% 23%	5815
April	1st to 10th	Day	16% 13% 4 7% 5% 3 4 3 5% 7% 33%	2400
	11th to 20th	Day	14% 10% 3 7% 4 4 4 3 5% 6% 39%	2374
	21st to end	Day	17% 9% 3 7% 4 3 4 4 6% 8% 35%	2593
May	1st to 10th	Day	19% 8% 2 6% 4 4 4 4 6% 8% 35%	5862
	11th to 20th	Day	13% 7% 2 6% 4 4 4 3 6% 8% 41%	5902
	21st to end	Day	15% 7% 2 5% 3 3 3 3 5% 8% 45%	6935
June	1st to 10th	Day	10% 6% 2 6% 5% 3 4 4 6% 8% 46%	2800
	11th to 20th	Day	9% 5% 3 5% 5% 4 5% 5% 6% 7% 47%	2800
	21st to end	Day	11% 5% 2 6% 3 5% 4 4 7% 8% 46%	2800
July	1st to 10th	Day	11% 5% 3 7% 4 4 5% 4 6% 9% 42%	6360
	11th to 20th	Day	9% 5% 2 5% 4 4 4 4 7% 10% 46%	6360
	21st to end	Day	9% 6% 2 6% 4 4 5% 4 6% 9% 44%	6924
August	1st to 10th	Day	10% 5% 2 6% 4 4 4 3 5% 8% 50%	4308
	11th to 20th	Day	11% 5% 2 5% 4 4 4 4 6% 7% 49%	4057
	21st to end	Day	7% 4 2 6% 4 4 5% 4 6% 9% 50%	4312
September	1st to 10th	Day	10% 5% 2 6% 4 3 5% 3 6% 8% 48%	2400
	11th to 20th	Day	12% 4 1 5% 4 4 4 4 6% 7% 49%	2202
	21st to end	Day	13% 7% 2 6% 4 4 4 4 6% 8% 41%	2200
October	1st to 10th	Day	15% 6% 2 6% 4 4 4 4 4 6% 45%	2200
	11th to 20th	Day	22% 8% 3 6% 4 4 4 3 6% 7% 33%	1961
	21st to end	Day	23% 12% 3 8% 4 4 5% 4 5% 7% 26%	1980
November	1st to 10th	Day	15% 13% 3 7% 4 3 4 4 5% 7% 36%	1852
	11th to 20th	Day	17% 20% 5% 9% 4 3 4 3 4 5% 25%	1890
	21st to end	Day	20% 19% 6% 10% 5% 4 3 3 3 4 22%	1890
December	1st to 10th	Day	11% 21% 11% 18% 5% 3 2 2 3 5% 20%	2759
	11th to 20th	Day	15% 21% 11% 14% 7% 5% 4 3 4 5% 13%	3088
	21st to end	Day	23% 21% 8% 15% 6% 4 4 2 3 4 10%	4070
January	1st to 10th	Night	15% 22% 10% 21% 5% 4 3 2 3 4 10%	6488
	11th to 20th	Night	13% 21% 9% 20% 8% 8% 6% 2 2 2 8%	6500
	21st to end	Night	19% 18% 8% 13% 6% 4 6% 3 3 3 17%	7150
February	1st to 10th	Night	16% 16% 6% 11% 9% 4 4 3 4 5% 22%	2500
	11th to 20th	Night	14% 16% 4 14% 7% 5% 5% 3 4 5% 23%	2338
	21st to end	Night	19% 14% 6% 12% 5% 3 3 2 5% 4 26%	1980
March	1st to 10th	Night	15% 12% 5% 10% 4 4 3 3 4 5% 33%	5373
	11th to 20th	Night	11% 9% 4 7% 5% 4 4 3 5% 6% 42%	5212
	21st to end	Night	19% 13% 6% 8% 4 4 4 3 4 5% 30%	5156
April	1st to 10th	Night	15% 11% 3 7% 5% 5% 4 4 5% 6% 34%	2000
	11th to 20th	Night	19% 10% 2 6% 4 4 4 4 5% 6% 36%	1975
	21st to end	Night	18% 8% 3 7% 5% 5% 3 4 5% 6% 36%	1805
May	1st to 10th	Night	19% 9% 4 8% 5% 4 4 4 4 6% 34%	4033
	11th to 20th	Night	15% 7% 3 7% 4 4 3 4 5% 7% 42%	3990
	21st to end	Night	17% 8% 3 7% 4 4 4 3 5% 6% 40%	3942
June	1st to 10th	Night	10% 5% 2 5% 4 4 3 5% 6% 9% 47%	1600
	11th to 20th	Night	9% 7% 2 6% 5% 5% 4 5% 6% 8% 43%	1600
	21st to end	Night	9% 5% 2 7% 6% 4 5% 5% 7% 10% 42%	1600
July	1st to 10th	Night	10% 5% 2 6% 5% 5% 5% 4 7% 10% 42%	3618
	11th to 20th	Night	8% 5% 2 5% 4 4 5% 4 5% 8% 50%	3617
	21st to end	Night	9% 6% 2 6% 4 5% 5% 4 7% 8% 45%	3947
August	1st to 10th	Night	8% 5% 2 6% 4 5% 5% 4 7% 9% 46%	2842
	11th to 20th	Night	10% 4 2 5% 5% 4 4 4 6% 7% 49%	2989
	21st to end	Night	9% 5% 2 6% 5% 4 4 4 6% 7% 49%	3586
September	1st to 10th	Night	10% 6% 2 6% 4 4 3 3 4 8% 49%	2000
	11th to 20th	Night	11% 5% 2 4 3 3 3 3 5% 8% 54%	2177
	21st to end	Night	13% 6% 3 7% 4 5% 4 3 5% 8% 43%	2200
October	1st to 10th	Night	15% 6% 2 5% 4 4 3 3 5% 6% 47%	2200
	11th to 20th	Night	21% 9% 3 8% 4 3 4 3 4 6% 36%	2433
	21st to end	Night	25% 10% 3 8% 4 3 4 3 4 5% 32%	2860
November	1st to 10th	Night	16% 14% 4 6% 4 3 4 3 4 5% 36%	2666
	11th to 20th	Night	15% 19% 5% 11% 5% 5% 3 3 5% 5% 25%	2730
	21st to end	Night	20% 20% 6% 9% 4 3 3 3 3 5% 23%	2730
December	1st to 10th	Night	12% 19% 9% 17% 6% 5% 4 3 4 4 16%	4647
	11th to 20th	Night	16% 23% 12% 15% 7% 4 3 3 3 4 11%	5339
	21st to end	Night	23% 22% 7% 13% 5% 4 4 3 4 4 10%	7150

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	76% 1 10% 11% 2	3698
	11th to 20th	Day	84% 2 6% 5% 2	3700
	21st to end	Day	71% 2 10% 14% 3	4070
February	1st to 10th	Day	68% 3 10% 12% 6% 1	1899
	11th to 20th	Day	65% 3 9% 16% 7%	1958
	21st to end	Day	62% 3 10% 14% 8% 1	1650
March	1st to 10th	Day	56% 2 10% 22% 10%	4480
	11th to 20th	Day	46% 2 12% 31% 8% 1	4746
	21st to end	Day	66% 2 9% 16% 6% 1	5817
April	1st to 10th	Day	53% 3 9% 22% 12%	2400
	11th to 20th	Day	47% 3 9% 24% 14% 3	2374
	21st to end	Day	49% 3 11% 22% 13% 3	2593
May	1st to 10th	Day	49% 3 10% 24% 14% 1	5897
	11th to 20th	Day	43% 3 12% 27% 14% 1	5906
	21st to end	Day	40% 3 9% 28% 19% 1	6949
June	1st to 10th	Day	37% 4 10% 27% 20% 2	2800
	11th to 20th	Day	36% 5% 11% 26% 19% 3	2800
	21st to end	Day	36% 5% 15% 24% 17% 3	2800
July	1st to 10th	Day	39% 4 11% 26% 17% 2	6291
	11th to 20th	Day	32% 6% 14% 31% 16% 1	6285
	21st to end	Day	36% 6% 14% 25% 17% 2	6728
August	1st to 10th	Day	33% 4 14% 32% 15% 1	4293
	11th to 20th	Day	34% 6% 12% 33% 15% 1	4096
	21st to end	Day	32% 5% 12% 28% 20% 3	4311
September	1st to 10th	Day	35% 5% 13% 27% 17% 3	2400
	11th to 20th	Day	34% 4 10% 31% 19% 2	2202
	21st to end	Day	41% 5% 9% 27% 17% 1	2200
October	1st to 10th	Day	30% 3 8% 36% 22% 1	3590
	11th to 20th	Day	40% 4 10% 22% 23%	3164
	21st to end	Day	51% 2 9% 24% 11% 2	3180
November	1st to 10th	Day	48% 3 13% 21% 13% 1	1852
	11th to 20th	Day	63% 2 9% 18% 7% 1	1890
	21st to end	Day	68% 2 9% 17% 4	1890
December	1st to 10th	Day	69% 2 15% 11% 3	2759
	11th to 20th	Day	74% 3 11% 10% 1	3085
	21st to end	Day	81% 2 7% 9% 2	4070
January	1st to 10th	Night	79% 1 6% 11% 2	6488
	11th to 20th	Night	85% 2 7% 5% 2	6500
	21st to end	Night	72% 2 13% 10% 3	7150
February	1st to 10th	Night	66% 3 9% 14% 7% 1	2500
	11th to 20th	Night	64% 2 10% 17% 7% 1	2339
	21st to end	Night	63% 2 9% 17% 7% 2	1980
March	1st to 10th	Night	55% 2 11% 24% 7% 1	5373
	11th to 20th	Night	45% 2 11% 29% 11% 2	5212
	21st to end	Night	58% 2 10% 20% 10% 1	5156
April	1st to 10th	Night	50% 4 11% 21% 13% 1	2000
	11th to 20th	Night	49% 3 8% 22% 16% 3	1975
	21st to end	Night	49% 4 9% 21% 15% 2	1805
May	1st to 10th	Night	52% 2 10% 19% 13% 4	4060
	11th to 20th	Night	43% 4 12% 23% 16% 2	3991
	21st to end	Night	46% 3 8% 21% 20% 1	3950
June	1st to 10th	Night	34% 4 11% 30% 18% 3	1600
	11th to 20th	Night	38% 4 12% 24% 19% 2	1600
	21st to end	Night	37% 4 18% 24% 15% 2	1600
July	1st to 10th	Night	37% 4 12% 29% 13% 4	3580
	11th to 20th	Night	33% 5% 13% 22% 24% 2	3572
	21st to end	Night	36% 5% 15% 22% 20% 2	3832
August	1st to 10th	Night	34% 5% 13% 30% 17% 1	2833
	11th to 20th	Night	33% 5% 11% 29% 20% 1	3016
	21st to end	Night	34% 4 9% 30% 20% 3	3586
September	1st to 10th	Night	36% 4 11% 25% 19% 5%	2000
	11th to 20th	Night	30% 3 8% 32% 26% 2	2177
	21st to end	Night	41% 3 10% 27% 18% 2	2200
October	1st to 10th	Night	28% 3 9% 33% 26% 2	3590
	11th to 20th	Night	45% 2 7% 21% 23% 1	3969
	21st to end	Night	45% 2 8% 27% 17% 1	4610
November	1st to 10th	Night	51% 3 8% 22% 14% 2	2666
	11th to 20th	Night	61% 3 10% 17% 8% 1	2730
	21st to end	Night	66% 2 10% 17% 5%	2730
December	1st to 10th	Night	71% 3 12% 11% 3	4647
	11th to 20th	Night	79% 2 9% 8% 2	5341
	21st to end	Night	79% 2 9% 8% 2	7150

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	22% 21% 36% 15% 5% 1	330
	11th to 20th	Day	24% 25% 35% 11% 4 1	330
	21st to end	Day	26% 24% 31% 16% 2	363
February	1st to 10th	Day	30% 23% 31% 12% 3 1	300
	11th to 20th	Day	26% 29% 32% 11% 1	300
	21st to end	Day	29% 30% 31% 7% 2	249
March	1st to 10th	Day	24% 27% 36% 11% 2	300
	11th to 20th	Day	26% 20% 31% 17% 5% 1	396
	21st to end	Day	31% 19% 29% 15% 6% 1	550
April	1st to 10th	Day	27% 21% 28% 19% 3 1	500
	11th to 20th	Day	24% 24% 28% 15% 7% 2	492
	21st to end	Day	25% 18% 31% 17% 6% 2	500
May	1st to 10th	Day	26% 16% 29% 19% 8% 2	503
	11th to 20th	Day	22% 14% 29% 23% 9% 4	542
	21st to end	Day	14% 13% 31% 24% 13% 4	789
June	1st to 10th	Day	12% 13% 31% 28% 12% 4	730
	11th to 20th	Day	13% 9% 30% 32% 14% 3	730
	21st to end	Day	13% 10% 32% 28% 13% 4	730
July	1st to 10th	Day	9% 7% 27% 27% 21% 9%	721
	11th to 20th	Day	11% 6% 31% 28% 18% 7%	718
	21st to end	Day	8% 5% 27% 35% 19% 6%	794
August	1st to 10th	Day	8% 4 22% 30% 25% 11%	575
	11th to 20th	Day	12% 6% 23% 26% 24% 8%	519
	21st to end	Day	9% 5% 22% 33% 23% 8%	583
September	1st to 10th	Day	15% 6% 22% 28% 21% 7%	530
	11th to 20th	Day	10% 6% 18% 29% 26% 11%	530
	21st to end	Day	18% 12% 20% 25% 16% 8%	530
October	1st to 10th	Day	17% 10% 27% 26% 18% 2	530
	11th to 20th	Day	24% 17% 30% 22% 6%	385
	21st to end	Day	34% 14% 36% 14% 1 1	363
November	1st to 10th	Day	18% 19% 38% 18% 5% 2	330
	11th to 20th	Day	29% 25% 26% 14% 5%	330
	21st to end	Day	34% 20% 33% 11% 1	330
December	1st to 10th	Day	24% 30% 29% 12% 5% 1	330
	11th to 20th	Day	23% 31% 32% 12% 2 1	330
	21st to end	Day	25% 29% 33% 12% 1	363
January	1st to 10th	Night	25% 17% 36% 18% 4	1050
	11th to 20th	Night	26% 18% 35% 17% 3	1050
	21st to end	Night	24% 17% 35% 21% 3	1155
February	1st to 10th	Night	27% 16% 33% 22% 3	855
	11th to 20th	Night	23% 19% 33% 21% 4	783
	21st to end	Night	28% 18% 34% 17% 4	660
March	1st to 10th	Night	23% 17% 31% 22% 7% 1	800
	11th to 20th	Night	20% 13% 34% 26% 6%	800
	21st to end	Night	25% 13% 26% 29% 6%	750
April	1st to 10th	Night	20% 16% 33% 25% 6% 1	600
	11th to 20th	Night	24% 13% 30% 25% 7% 1	593
	21st to end	Night	21% 12% 30% 27% 9% 1	600
May	1st to 10th	Night	22% 7% 29% 30% 11% 1	600
	11th to 20th	Night	19% 7% 23% 36% 14% 1	591
	21st to end	Night	14% 4 23% 38% 19% 1	650
June	1st to 10th	Night	12% 5% 24% 41% 17% 2	600
	11th to 20th	Night	14% 3 28% 38% 16% 1	600
	21st to end	Night	11% 6% 23% 39% 21% 2	600
July	1st to 10th	Night	8% 3 16% 40% 29% 4	585
	11th to 20th	Night	10% 5% 18% 37% 26% 4	582
	21st to end	Night	8% 3 14% 43% 30% 2	657
August	1st to 10th	Night	9% 2 13% 44% 29% 3	597
	11th to 20th	Night	10% 3 14% 38% 30% 5%	594
	21st to end	Night	11% 3 13% 41% 29% 3	660
September	1st to 10th	Night	13% 5% 17% 36% 24% 5%	600
	11th to 20th	Night	12% 4 15% 37% 27% 4	777
	21st to end	Night	15% 7% 23% 29% 22% 3	800
October	1st to 10th	Night	18% 6% 25% 31% 19% 1	800
	11th to 20th	Night	26% 15% 22% 28% 7% 1	800
	21st to end	Night	29% 15% 27% 23% 5%	880
November	1st to 10th	Night	26% 12% 31% 21% 9% 1	820
	11th to 20th	Night	27% 19% 30% 20% 4	840
	21st to end	Night	32% 14% 29% 20% 4	840
December	1st to 10th	Night	29% 20% 31% 16% 4	1003
	11th to 20th	Night	27% 16% 35% 18% 3	1050
	21st to end	Night	32% 17% 32% 17% 2	1155

Page generated at 2026-01-29 01:21:46. Version ac07

Copyright © 2026 Attilla Danko.