Bridgewater
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bridgewater clear sky chart from 2005-11-06 to 2026-07-16.

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	10% 7% 3 7% 4 4 5% 4 6% 7% 43%	146481
	Night	9% 7% 3 7% 5% 4 4 4 5% 7% 46%	143577
Transparency	Day	39% 5% 14% 25% 14% 2	141159
	Night	37% 5% 14% 26% 16% 2	139911
Seeing	Day	14% 10% 32% 30% 13% 2	18285
	Night	12% 9% 36% 34% 9% 1	28160

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	9% 13% 4 16% 8% 6% 7% 4 5% 5% 23%	4702
	11th to 20th	Day	4 10% 5% 12% 7% 6% 8% 4 8% 8% 30%	4740
	21st to end	Day	4 8% 5% 12% 6% 6% 6% 5% 5% 6% 35%	5787
February	1st to 10th	Day	9% 12% 4 11% 6% 7% 7% 4 6% 6% 29%	1890
	11th to 20th	Day	8% 10% 5% 10% 6% 5% 5% 5% 5% 7% 35%	1910
	21st to end	Day	9% 9% 3 9% 6% 5% 5% 3 6% 6% 38%	1730
March	1st to 10th	Day	10% 8% 4 9% 4 3 3 3 4 7% 47%	4780
	11th to 20th	Day	7% 6% 3 6% 3 4 4 3 6% 8% 50%	5090
	21st to end	Day	21% 11% 4 10% 5% 4 4 4 5% 6% 25%	5585
April	1st to 10th	Day	16% 8% 3 7% 4 3 4 3 5% 7% 38%	2395
	11th to 20th	Day	17% 9% 3 6% 5% 4 4 4 5% 6% 38%	2699
	21st to end	Day	19% 8% 2 6% 4 3 4 3 5% 7% 39%	2730
May	1st to 10th	Day	9% 4 2 5% 3 4 5% 4 6% 8% 52%	7655
	11th to 20th	Day	15% 7% 2 5% 3 4 4 3 4 6% 47%	7627
	21st to end	Day	18% 8% 2 7% 4 4 4 3 6% 7% 37%	8817
June	1st to 10th	Day	11% 5% 2 5% 4 4 5% 4 6% 8% 47%	3134
	11th to 20th	Day	12% 5% 2 6% 4 3 5% 4 6% 8% 45%	3150
	21st to end	Day	9% 4 2 5% 4 4 5% 4 6% 9% 48%	3150
July	1st to 10th	Day	8% 4 2 5% 4 4 5% 5% 6% 9% 48%	6762
	11th to 20th	Day	8% 5% 2 5% 3 4 4 3 5% 7% 54%	6411
	21st to end	Day	5% 5% 2 6% 4 5% 4 5% 7% 9% 48%	6494
August	1st to 10th	Day	9% 6% 3 7% 4 4 6% 5% 7% 9% 42%	5801
	11th to 20th	Day	13% 6% 2 6% 4 4 4 4 6% 8% 44%	5821
	21st to end	Day	8% 5% 2 5% 3 3 3 3 5% 6% 55%	6490
September	1st to 10th	Day	12% 5% 1 4 3 3 3 2 5% 7% 54%	2310
	11th to 20th	Day	9% 5% 1 5% 3 3 3 4 5% 7% 55%	2200
	21st to end	Day	10% 5% 2 4 3 3 3 3 5% 5% 57%	2200
October	1st to 10th	Day	8% 4 2 4 2 2 3 3 4 5% 64%	3407
	11th to 20th	Day	8% 5% 2 5% 3 3 4 3 5% 7% 54%	3240
	21st to end	Day	12% 7% 2 6% 4 4 5% 4 5% 7% 44%	3325
November	1st to 10th	Day	8% 8% 3 6% 3 4 5% 4 7% 7% 45%	1853
	11th to 20th	Day	7% 8% 2 10% 6% 3 4 3 6% 7% 44%	1801
	21st to end	Day	9% 10% 3 8% 4 3 4 3 7% 7% 42%	1680
December	1st to 10th	Day	4 9% 4 10% 7% 7% 6% 4 6% 7% 36%	2690
	11th to 20th	Day	8% 11% 5% 11% 6% 6% 5% 5% 6% 7% 30%	2850
	21st to end	Day	13% 8% 4 15% 6% 4 4 4 7% 6% 28%	3575
January	1st to 10th	Night	7% 11% 5% 13% 9% 7% 6% 4 5% 6% 27%	8201
	11th to 20th	Night	3 8% 4 11% 7% 6% 7% 4 8% 8% 35%	8250
	21st to end	Night	3 8% 4 10% 5% 5% 5% 4 6% 6% 44%	8424
February	1st to 10th	Night	9% 11% 4 8% 6% 5% 5% 3 6% 7% 36%	2730
	11th to 20th	Night	7% 10% 4 8% 5% 4 4 5% 6% 6% 41%	2616
	21st to end	Night	7% 8% 3 7% 5% 4 4 4 6% 8% 44%	2076
March	1st to 10th	Night	10% 8% 2 5% 3 3 3 3 4 7% 51%	5306
	11th to 20th	Night	10% 6% 2 5% 3 3 3 3 6% 8% 52%	5090
	21st to end	Night	16% 11% 3 8% 5% 4 4 3 5% 6% 36%	5588
April	1st to 10th	Night	14% 8% 3 6% 4 4 4 4 5% 6% 41%	2219
	11th to 20th	Night	14% 8% 3 7% 5% 3 3 3 5% 6% 44%	1869
	21st to end	Night	17% 8% 2 5% 3 4 4 4 5% 7% 42%	1890
May	1st to 10th	Night	10% 4 2 4 3 3 4 3 5% 8% 53%	5292
	11th to 20th	Night	12% 7% 2 5% 3 3 3 3 5% 7% 51%	5265
	21st to end	Night	17% 7% 2 6% 4 4 5% 4 5% 7% 39%	5385
June	1st to 10th	Night	7% 5% 2 5% 3 3 4 3 5% 8% 55%	1482
	11th to 20th	Night	8% 6% 2 4 4 3 4 3 6% 8% 53%	1470
	21st to end	Night	8% 3 1 4 3 4 4 3 6% 10% 55%	1470
July	1st to 10th	Night	7% 4 1 5% 3 4 4 4 6% 9% 52%	3432
	11th to 20th	Night	7% 4 2 5% 3 3 3 4 5% 7% 59%	3680
	21st to end	Night	5% 4 2 4 4 3 4 4 6% 9% 56%	4362
August	1st to 10th	Night	7% 5% 2 6% 5% 4 5% 5% 7% 10% 45%	4011
	11th to 20th	Night	7% 5% 2 6% 4 4 4 5% 6% 8% 49%	4028
	21st to end	Night	7% 3 2 5% 4 3 4 4 5% 8% 55%	4487
September	1st to 10th	Night	8% 4 2 4 3 4 3 2 4 6% 60%	2086
	11th to 20th	Night	7% 4 2 4 3 3 5% 4 6% 6% 56%	2200
	21st to end	Night	7% 5% 1 4 3 3 3 3 4 7% 60%	2200
October	1st to 10th	Night	8% 3 1 2 2 2 2 2 3 5% 70%	3740
	11th to 20th	Night	8% 5% 1 5% 3 2 2 2 5% 7% 59%	3899
	21st to end	Night	11% 6% 2 7% 3 3 4 4 5% 8% 46%	4470
November	1st to 10th	Night	8% 6% 2 6% 4 3 4 3 5% 7% 52%	2665
	11th to 20th	Night	7% 7% 2 7% 5% 4 4 3 6% 8% 46%	2817
	21st to end	Night	8% 7% 3 7% 4 4 4 4 5% 7% 47%	2940
December	1st to 10th	Night	4 7% 4 10% 5% 5% 5% 4 5% 6% 45%	4720
	11th to 20th	Night	8% 9% 3 9% 6% 7% 5% 5% 5% 6% 36%	5572
	21st to end	Night	14% 11% 4 12% 5% 4 4 3 5% 6% 30%	7645

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% 5% 13% 13% 5% 1	4705
	11th to 20th	Day	51% 4 13% 18% 14%	4740
	21st to end	Day	48% 5% 17% 20% 10%	5787
February	1st to 10th	Day	54% 7% 15% 16% 9%	1890
	11th to 20th	Day	47% 6% 13% 20% 11% 1	1919
	21st to end	Day	45% 6% 14% 21% 12% 1	1730
March	1st to 10th	Day	38% 4 12% 31% 12% 2	4780
	11th to 20th	Day	31% 5% 10% 30% 21% 3	5090
	21st to end	Day	59% 6% 14% 16% 4 1	5585
April	1st to 10th	Day	45% 5% 13% 25% 11% 1	2395
	11th to 20th	Day	45% 7% 11% 22% 13% 2	2702
	21st to end	Day	45% 6% 13% 24% 12%	2730
May	1st to 10th	Day	29% 5% 9% 28% 28%	7655
	11th to 20th	Day	39% 4 10% 22% 18% 7%	7631
	21st to end	Day	45% 5% 11% 26% 12% 1	8818
June	1st to 10th	Day	32% 8% 17% 29% 12% 2	3134
	11th to 20th	Day	36% 6% 16% 24% 15% 3	3150
	21st to end	Day	32% 7% 16% 28% 15% 3	3150
July	1st to 10th	Day	33% 5% 19% 31% 12% 1	6692
	11th to 20th	Day	30% 4 13% 33% 17% 3	6336
	21st to end	Day	31% 6% 19% 26% 17% 1	6308
August	1st to 10th	Day	33% 7% 16% 28% 14% 2	4220
	11th to 20th	Day	44% 5% 16% 24% 10% 1	4210
	21st to end	Day	29% 6% 18% 27% 17% 3	4674
September	1st to 10th	Day	31% 5% 14% 30% 19% 2	2310
	11th to 20th	Day	29% 5% 18% 31% 15% 1	2200
	21st to end	Day	29% 6% 9% 31% 22% 2	2200
October	1st to 10th	Day	24% 3 8% 27% 33% 4	3407
	11th to 20th	Day	30% 3 13% 29% 20% 4	3240
	21st to end	Day	40% 3 13% 22% 19% 2	3325
November	1st to 10th	Day	35% 7% 17% 26% 13% 3	1853
	11th to 20th	Day	39% 6% 15% 25% 13% 1	1801
	21st to end	Day	41% 5% 16% 26% 12% 1	1680
December	1st to 10th	Day	47% 5% 16% 23% 7% 1	2690
	11th to 20th	Day	52% 5% 19% 18% 6%	2847
	21st to end	Day	54% 6% 14% 21% 5%	3575
January	1st to 10th	Night	56% 5% 13% 18% 8% 1	8202
	11th to 20th	Night	44% 5% 15% 20% 16% 1	8250
	21st to end	Night	39% 5% 16% 26% 13%	8424
February	1st to 10th	Night	46% 6% 15% 21% 11% 1	2730
	11th to 20th	Night	42% 6% 13% 23% 13% 3	2617
	21st to end	Night	37% 6% 14% 25% 14% 3	2076
March	1st to 10th	Night	33% 5% 11% 31% 19% 2	5306
	11th to 20th	Night	30% 4 10% 29% 24% 2	5090
	21st to end	Night	50% 5% 13% 24% 7% 1	5588
April	1st to 10th	Night	42% 7% 15% 23% 13% 1	2219
	11th to 20th	Night	42% 4 10% 23% 19% 2	1869
	21st to end	Night	42% 7% 12% 25% 13% 2	1890
May	1st to 10th	Night	28% 5% 11% 30% 23% 2	5293
	11th to 20th	Night	33% 5% 10% 19% 24% 8%	5266
	21st to end	Night	44% 6% 12% 25% 13% 1	5387
June	1st to 10th	Night	28% 6% 16% 30% 17% 3	1482
	11th to 20th	Night	28% 6% 15% 25% 20% 4	1470
	21st to end	Night	25% 6% 17% 29% 20% 3	1470
July	1st to 10th	Night	29% 4 19% 32% 13% 2	3394
	11th to 20th	Night	26% 4 12% 38% 16% 3	3632
	21st to end	Night	25% 5% 22% 29% 16% 3	4235
August	1st to 10th	Night	30% 7% 16% 29% 15% 2	2916
	11th to 20th	Night	35% 6% 16% 28% 13% 1	2915
	21st to end	Night	26% 6% 18% 24% 22% 4	3234
September	1st to 10th	Night	26% 6% 15% 28% 22% 4	2086
	11th to 20th	Night	26% 7% 16% 32% 18% 2	2200
	21st to end	Night	25% 5% 9% 32% 25% 4	2200
October	1st to 10th	Night	19% 3 7% 22% 44% 5%	3740
	11th to 20th	Night	26% 3 12% 31% 25% 4	3899
	21st to end	Night	37% 4 13% 27% 18% 1	4470
November	1st to 10th	Night	31% 5% 15% 26% 19% 4	2665
	11th to 20th	Night	35% 6% 16% 24% 17% 2	2817
	21st to end	Night	36% 5% 16% 28% 15% 1	2940
December	1st to 10th	Night	39% 5% 15% 31% 9%	4720
	11th to 20th	Night	47% 5% 18% 23% 7%	5574
	21st to end	Night	55% 5% 13% 20% 6%	7645

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	17% 10% 33% 29% 9% 1	330
	11th to 20th	Day	15% 16% 35% 27% 6%	330
	21st to end	Day	12% 12% 39% 29% 7% 1	363
February	1st to 10th	Day	11% 19% 41% 23% 5%	330
	11th to 20th	Day	14% 12% 41% 25% 6% 1	330
	21st to end	Day	16% 13% 42% 25% 3	273
March	1st to 10th	Day	13% 15% 45% 22% 4 1	330
	11th to 20th	Day	18% 11% 37% 22% 10% 2	330
	21st to end	Day	20% 15% 37% 23% 4 1	363
April	1st to 10th	Day	25% 17% 35% 19% 5%	415
	11th to 20th	Day	23% 15% 33% 23% 6%	740
	21st to end	Day	24% 15% 29% 21% 9% 1	750
May	1st to 10th	Day	16% 13% 34% 26% 11% 2	753
	11th to 20th	Day	20% 10% 30% 23% 15% 2	775
	21st to end	Day	19% 9% 29% 30% 11% 2	844
June	1st to 10th	Day	8% 9% 26% 33% 19% 5%	780
	11th to 20th	Day	14% 7% 35% 29% 12% 2	780
	21st to end	Day	10% 6% 32% 36% 14% 2	780
July	1st to 10th	Day	7% 3 21% 40% 23% 6%	771
	11th to 20th	Day	6% 4 29% 39% 21% 3	744
	21st to end	Day	6% 2 27% 43% 20% 3	794
August	1st to 10th	Day	9% 5% 23% 40% 20% 3	726
	11th to 20th	Day	10% 4 26% 35% 21% 4	715
	21st to end	Day	7% 5% 27% 37% 20% 3	803
September	1st to 10th	Day	13% 8% 27% 33% 16% 3	440
	11th to 20th	Day	9% 4 37% 31% 16% 3	330
	21st to end	Day	13% 12% 28% 30% 12% 5%	330
October	1st to 10th	Day	16% 8% 31% 27% 15% 2	330
	11th to 20th	Day	17% 15% 35% 23% 9% 1	330
	21st to end	Day	22% 15% 33% 23% 6% 1	363
November	1st to 10th	Day	18% 12% 36% 23% 9% 1	330
	11th to 20th	Day	13% 16% 38% 27% 6%	330
	21st to end	Day	18% 16% 32% 26% 7% 2	330
December	1st to 10th	Day	13% 10% 37% 29% 11% 1	330
	11th to 20th	Day	15% 15% 40% 24% 5%	330
	21st to end	Day	20% 10% 39% 27% 3 1	363
January	1st to 10th	Night	12% 9% 38% 32% 8% 1	1050
	11th to 20th	Night	10% 14% 37% 31% 7% 1	1050
	21st to end	Night	11% 11% 41% 30% 7%	1155
February	1st to 10th	Night	14% 12% 40% 30% 5%	1050
	11th to 20th	Night	13% 11% 38% 31% 6% 1	982
	21st to end	Night	12% 8% 40% 32% 7% 1	692
March	1st to 10th	Night	14% 9% 41% 31% 4 1	756
	11th to 20th	Night	16% 11% 37% 30% 5%	630
	21st to end	Night	18% 10% 39% 25% 7%	693
April	1st to 10th	Night	17% 13% 43% 24% 3	630
	11th to 20th	Night	20% 12% 36% 24% 7%	623
	21st to end	Night	19% 13% 35% 27% 6% 1	630
May	1st to 10th	Night	16% 8% 37% 29% 10%	630
	11th to 20th	Night	17% 8% 35% 30% 10%	621
	21st to end	Night	18% 5% 35% 32% 10%	683
June	1st to 10th	Night	9% 6% 28% 41% 16%	630
	11th to 20th	Night	11% 4 34% 42% 8% 1	630
	21st to end	Night	9% 5% 29% 45% 13%	630
July	1st to 10th	Night	6% 2 23% 47% 21% 1	615
	11th to 20th	Night	5% 2 26% 50% 17%	597
	21st to end	Night	5% 2 27% 51% 14% 1	657
August	1st to 10th	Night	5% 3 27% 49% 15% 1	597
	11th to 20th	Night	8% 2 26% 45% 18% 1	594
	21st to end	Night	6% 4 29% 45% 17% 1	660
September	1st to 10th	Night	9% 5% 29% 40% 15% 2	600
	11th to 20th	Night	7% 4 35% 39% 13% 2	600
	21st to end	Night	9% 6% 35% 36% 14% 1	600
October	1st to 10th	Night	15% 11% 32% 31% 11%	685
	11th to 20th	Night	16% 11% 37% 27% 8%	800
	21st to end	Night	16% 12% 35% 30% 7%	1010
November	1st to 10th	Night	11% 8% 41% 31% 8% 1	1025
	11th to 20th	Night	11% 11% 42% 28% 7% 1	1050
	21st to end	Night	12% 10% 36% 35% 8%	1050
December	1st to 10th	Night	12% 11% 40% 30% 6% 1	1050
	11th to 20th	Night	15% 9% 37% 32% 7%	1050
	21st to end	Night	20% 11% 35% 27% 7%	1155

Page generated at 2026-07-13 02:14:47. Version ac07

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