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 2024-10-20.

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	11% 7% 3 7% 4 4 4 4 6% 7% 43%	101146
	Night	9% 7% 3 7% 5% 4 4 4 5% 7% 45%	97687
Transparency	Day	39% 7% 15% 25% 13% 2	100896
	Night	38% 6% 15% 25% 15% 2	97527
Seeing	Day	14% 9% 31% 30% 13% 2	15891
	Night	12% 9% 35% 34% 10% 1	25739

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	8% 13% 4 15% 7% 6% 8% 4 6% 5% 22%	2520
	11th to 20th	Day	5% 13% 6% 12% 6% 4 9% 4 8% 8% 26%	2540
	21st to end	Day	6% 12% 7% 15% 6% 7% 7% 4 5% 5% 26%	3110
February	1st to 10th	Day	9% 11% 4 10% 6% 7% 7% 4 6% 6% 30%	1710
	11th to 20th	Day	9% 10% 4 9% 6% 5% 5% 5% 5% 7% 35%	1723
	21st to end	Day	10% 10% 3 9% 6% 6% 5% 3 6% 6% 35%	1570
March	1st to 10th	Day	9% 9% 4 10% 3 3 3 3 4 8% 44%	3254
	11th to 20th	Day	9% 7% 3 7% 4 4 4 3 5% 7% 47%	3480
	21st to end	Day	24% 11% 4 11% 5% 4 4 3 5% 6% 24%	3814
April	1st to 10th	Day	16% 7% 2 7% 5% 3 4 3 5% 7% 39%	2167
	11th to 20th	Day	18% 9% 3 6% 4 4 4 4 5% 6% 38%	2439
	21st to end	Day	18% 9% 3 6% 4 3 4 3 5% 7% 39%	2470
May	1st to 10th	Day	15% 7% 2 6% 4 5% 5% 3 6% 7% 39%	4120
	11th to 20th	Day	12% 6% 2 5% 4 4 4 3 5% 7% 48%	4082
	21st to end	Day	17% 6% 2 7% 4 3 4 3 6% 8% 40%	4706
June	1st to 10th	Day	11% 5% 2 4 4 4 5% 4 6% 9% 48%	2836
	11th to 20th	Day	13% 5% 2 6% 4 4 5% 4 6% 8% 45%	2850
	21st to end	Day	8% 4 2 5% 4 4 5% 4 6% 9% 49%	2850
July	1st to 10th	Day	11% 5% 2 6% 4 4 4 5% 6% 9% 45%	4623
	11th to 20th	Day	6% 3 1 4 3 4 4 3 5% 7% 59%	4430
	21st to end	Day	4 3 1 5% 4 4 4 5% 7% 9% 54%	4510
August	1st to 10th	Day	8% 5% 2 6% 4 4 5% 4 7% 9% 47%	4103
	11th to 20th	Day	17% 8% 2 6% 4 4 4 4 6% 7% 37%	4041
	21st to end	Day	7% 5% 2 5% 4 3 4 3 6% 7% 54%	4532
September	1st to 10th	Day	12% 5% 1 4 3 3 3 2 5% 7% 54%	2195
	11th to 20th	Day	8% 4 1 5% 3 3 3 4 5% 6% 56%	2090
	21st to end	Day	10% 5% 2 5% 3 3 3 3 5% 5% 56%	2090
October	1st to 10th	Day	14% 5% 2 5% 3 3 3 3 4 6% 52%	1990
	11th to 20th	Day	13% 7% 2 4 2 3 4 2 5% 6% 52%	1890
	21st to end	Day	15% 7% 2 6% 3 3 4 3 4 6% 47%	1862
November	1st to 10th	Day	8% 7% 3 6% 3 4 5% 4 7% 7% 47%	1673
	11th to 20th	Day	7% 8% 2 10% 6% 3 4 3 6% 7% 43%	1630
	21st to end	Day	9% 10% 2 7% 4 4 4 3 6% 7% 44%	1520
December	1st to 10th	Day	7% 10% 2 9% 5% 6% 5% 4 6% 8% 38%	1520
	11th to 20th	Day	8% 11% 5% 10% 6% 5% 5% 4 5% 7% 33%	1764
	21st to end	Day	16% 10% 4 14% 6% 4 4 4 6% 5% 27%	2442
January	1st to 10th	Night	9% 11% 4 13% 11% 8% 6% 4 5% 5% 24%	4417
	11th to 20th	Night	4 10% 4 11% 7% 6% 8% 4 9% 8% 29%	4430
	21st to end	Night	5% 11% 6% 13% 6% 6% 6% 5% 5% 6% 32%	4554
February	1st to 10th	Night	9% 11% 4 8% 6% 4 5% 3 6% 6% 37%	2470
	11th to 20th	Night	8% 10% 3 8% 5% 4 4 5% 6% 6% 41%	2361
	21st to end	Night	8% 9% 3 7% 6% 4 4 4 6% 8% 42%	1884
March	1st to 10th	Night	8% 8% 3 6% 4 3 4 3 5% 7% 49%	3606
	11th to 20th	Night	8% 7% 2 6% 4 4 4 3 5% 7% 50%	3480
	21st to end	Night	20% 12% 4 8% 6% 4 4 3 4 6% 30%	3817
April	1st to 10th	Night	14% 8% 3 6% 5% 4 4 4 6% 7% 41%	2007
	11th to 20th	Night	16% 8% 3 7% 5% 3 3 2 4 6% 43%	1689
	21st to end	Night	16% 8% 2 5% 3 4 5% 4 5% 7% 42%	1710
May	1st to 10th	Night	17% 5% 2 5% 3 4 3 4 5% 7% 45%	2850
	11th to 20th	Night	10% 4 2 5% 4 3 4 3 5% 8% 52%	2823
	21st to end	Night	15% 6% 2 6% 4 4 3 4 6% 8% 43%	2876
June	1st to 10th	Night	6% 6% 2 5% 3 3 4 3 5% 8% 55%	1341
	11th to 20th	Night	8% 6% 2 5% 4 3 4 3 6% 8% 52%	1330
	21st to end	Night	7% 3 1 3 3 4 4 3 6% 10% 57%	1330
July	1st to 10th	Night	9% 5% 2 5% 3 3 4 3 6% 8% 51%	2342
	11th to 20th	Night	4 2 1 3 3 2 3 4 5% 7% 65%	2540
	21st to end	Night	2 2 1 3 4 3 3 4 6% 10% 61%	3036
August	1st to 10th	Night	6% 5% 2 5% 4 3 5% 4 7% 9% 50%	2836
	11th to 20th	Night	9% 6% 2 6% 4 4 4 4 6% 6% 49%	2798
	21st to end	Night	8% 3 2 4 4 3 3 4 6% 9% 56%	3135
September	1st to 10th	Night	8% 4 2 3 3 4 3 2 4 6% 60%	1981
	11th to 20th	Night	7% 3 2 4 3 3 4 4 5% 6% 58%	2090
	21st to end	Night	8% 5% 1 4 3 3 3 3 4 7% 60%	2090
October	1st to 10th	Night	14% 5% 2 4 3 3 2 3 4 6% 53%	2171
	11th to 20th	Night	11% 6% 2 5% 3 2 3 3 5% 6% 54%	2275
	21st to end	Night	13% 6% 2 6% 3 3 4 3 4 7% 50%	2492
November	1st to 10th	Night	8% 6% 2 5% 4 3 4 3 5% 7% 53%	2405
	11th to 20th	Night	7% 7% 2 7% 5% 4 5% 3 6% 8% 45%	2548
	21st to end	Night	8% 7% 2 6% 4 4 4 4 6% 7% 48%	2660
December	1st to 10th	Night	7% 8% 3 9% 6% 5% 5% 4 6% 7% 41%	2660
	11th to 20th	Night	7% 9% 2 8% 5% 4 5% 4 5% 7% 43%	3428
	21st to end	Night	17% 11% 5% 14% 5% 4 3 3 4 5% 29%	5225

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	58% 9% 14% 14% 6%	2521
	11th to 20th	Day	53% 6% 12% 22% 6%	2540
	21st to end	Day	57% 8% 16% 13% 7%	3110
February	1st to 10th	Day	53% 7% 15% 16% 9%	1710
	11th to 20th	Day	47% 7% 15% 20% 10% 2	1732
	21st to end	Day	47% 7% 14% 20% 11% 1	1570
March	1st to 10th	Day	39% 6% 13% 28% 12% 1	3254
	11th to 20th	Day	35% 7% 11% 29% 15% 3	3480
	21st to end	Day	61% 7% 15% 13% 3 1	3814
April	1st to 10th	Day	44% 6% 14% 25% 11% 1	2167
	11th to 20th	Day	46% 7% 11% 21% 12% 2	2442
	21st to end	Day	45% 6% 13% 24% 11%	2470
May	1st to 10th	Day	40% 8% 13% 23% 16%	4120
	11th to 20th	Day	34% 7% 12% 28% 16% 3	4086
	21st to end	Day	40% 7% 13% 25% 13% 1	4706
June	1st to 10th	Day	32% 8% 17% 29% 12% 2	2836
	11th to 20th	Day	36% 7% 16% 23% 15% 3	2850
	21st to end	Day	30% 8% 16% 29% 14% 2	2850
July	1st to 10th	Day	35% 6% 20% 27% 11% 1	4552
	11th to 20th	Day	25% 5% 14% 34% 19% 4	4355
	21st to end	Day	24% 7% 17% 28% 22% 2	4367
August	1st to 10th	Day	33% 7% 16% 29% 14% 2	4090
	11th to 20th	Day	45% 5% 16% 24% 9% 1	4080
	21st to end	Day	29% 6% 18% 27% 16% 3	4531
September	1st to 10th	Day	31% 5% 12% 29% 20% 2	2195
	11th to 20th	Day	28% 5% 18% 32% 16% 1	2090
	21st to end	Day	30% 6% 10% 31% 21% 2	2090
October	1st to 10th	Day	35% 5% 12% 28% 19% 1	1990
	11th to 20th	Day	33% 4 12% 30% 18% 3	1890
	21st to end	Day	39% 5% 13% 26% 16% 2	1862
November	1st to 10th	Day	34% 7% 17% 25% 14% 3	1673
	11th to 20th	Day	40% 6% 15% 24% 13% 1	1630
	21st to end	Day	39% 5% 17% 25% 13% 1	1520
December	1st to 10th	Day	43% 7% 18% 21% 9% 1	1520
	11th to 20th	Day	49% 6% 19% 20% 5%	1761
	21st to end	Day	55% 7% 12% 19% 5% 1	2442
January	1st to 10th	Night	59% 7% 11% 16% 7%	4417
	11th to 20th	Night	48% 7% 15% 21% 9% 1	4430
	21st to end	Night	49% 9% 17% 17% 7%	4554
February	1st to 10th	Night	46% 7% 14% 21% 11% 1	2470
	11th to 20th	Night	42% 6% 13% 23% 13% 3	2362
	21st to end	Night	39% 7% 14% 24% 13% 3	1884
March	1st to 10th	Night	33% 7% 12% 25% 21% 2	3606
	11th to 20th	Night	32% 6% 11% 29% 19% 2	3480
	21st to end	Night	55% 7% 15% 17% 6% 1	3817
April	1st to 10th	Night	41% 8% 15% 23% 13% 1	2007
	11th to 20th	Night	44% 4 11% 21% 18% 2	1689
	21st to end	Night	40% 8% 12% 26% 12% 2	1710
May	1st to 10th	Night	36% 7% 15% 22% 17% 3	2850
	11th to 20th	Night	29% 8% 13% 24% 23% 3	2824
	21st to end	Night	38% 7% 13% 26% 15% 1	2877
June	1st to 10th	Night	28% 6% 16% 29% 17% 4	1341
	11th to 20th	Night	28% 7% 16% 25% 19% 5%	1330
	21st to end	Night	23% 6% 17% 30% 21% 3	1330
July	1st to 10th	Night	31% 5% 22% 26% 13% 4	2304
	11th to 20th	Night	18% 5% 15% 38% 20% 4	2492
	21st to end	Night	18% 6% 19% 32% 22% 4	2940
August	1st to 10th	Night	30% 6% 16% 30% 16% 2	2826
	11th to 20th	Night	35% 6% 16% 28% 13% 1	2825
	21st to end	Night	26% 6% 18% 24% 22% 4	3135
September	1st to 10th	Night	26% 6% 13% 28% 23% 4	1981
	11th to 20th	Night	24% 7% 15% 33% 19% 2	2090
	21st to end	Night	26% 5% 10% 31% 24% 4	2090
October	1st to 10th	Night	33% 4 11% 26% 23% 2	2171
	11th to 20th	Night	32% 4 10% 29% 21% 4	2275
	21st to end	Night	35% 6% 13% 24% 20% 2	2492
November	1st to 10th	Night	30% 5% 15% 25% 20% 4	2405
	11th to 20th	Night	36% 6% 15% 24% 17% 2	2548
	21st to end	Night	35% 5% 15% 27% 16% 1	2660
December	1st to 10th	Night	42% 7% 17% 25% 9% 1	2660
	11th to 20th	Night	39% 6% 21% 26% 7%	3430
	21st to end	Night	57% 5% 12% 19% 6% 1	5225

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% 33% 30% 10% 1	270
	11th to 20th	Day	14% 16% 34% 29% 7%	270
	21st to end	Day	13% 12% 36% 29% 8% 1	297
February	1st to 10th	Day	10% 17% 42% 26% 5%	270
	11th to 20th	Day	16% 12% 43% 22% 6% 1	270
	21st to end	Day	16% 13% 42% 25% 3	225
March	1st to 10th	Day	13% 17% 43% 23% 4 1	270
	11th to 20th	Day	19% 9% 38% 23% 10% 2	270
	21st to end	Day	22% 12% 35% 25% 5% 1	297
April	1st to 10th	Day	25% 17% 35% 18% 5%	347
	11th to 20th	Day	23% 14% 33% 23% 6%	640
	21st to end	Day	23% 16% 29% 21% 10% 2	650
May	1st to 10th	Day	18% 13% 35% 25% 9% 1	653
	11th to 20th	Day	19% 9% 31% 24% 15% 2	675
	21st to end	Day	19% 10% 29% 30% 11% 2	734
June	1st to 10th	Day	7% 9% 24% 35% 21% 5%	680
	11th to 20th	Day	15% 6% 35% 30% 12% 3	680
	21st to end	Day	9% 6% 31% 38% 15% 2	680
July	1st to 10th	Day	7% 3 20% 39% 24% 6%	671
	11th to 20th	Day	5% 4 30% 38% 21% 2	668
	21st to end	Day	5% 2 26% 43% 21% 3	739
August	1st to 10th	Day	9% 4 22% 41% 21% 3	676
	11th to 20th	Day	10% 4 26% 35% 22% 3	665
	21st to end	Day	7% 5% 27% 37% 20% 3	748
September	1st to 10th	Day	13% 7% 28% 33% 16% 4	405
	11th to 20th	Day	8% 4 37% 32% 16% 3	300
	21st to end	Day	14% 13% 30% 30% 11% 3	300
October	1st to 10th	Day	18% 8% 30% 26% 15% 3	300
	11th to 20th	Day	16% 14% 34% 25% 10% 1	297
	21st to end	Day	21% 17% 32% 23% 7% 1	297
November	1st to 10th	Day	18% 12% 35% 24% 10% 1	270
	11th to 20th	Day	14% 16% 37% 28% 6%	270
	21st to end	Day	17% 17% 30% 28% 6% 1	270
December	1st to 10th	Day	12% 9% 39% 28% 11% 1	270
	11th to 20th	Day	14% 14% 39% 26% 6%	270
	21st to end	Day	22% 12% 38% 25% 3	297
January	1st to 10th	Night	12% 10% 37% 32% 8% 1	950
	11th to 20th	Night	11% 13% 36% 32% 7% 1	950
	21st to end	Night	12% 11% 39% 30% 7%	1045
February	1st to 10th	Night	14% 11% 39% 30% 5%	950
	11th to 20th	Night	13% 12% 36% 32% 7% 1	887
	21st to end	Night	13% 7% 39% 33% 7% 1	628
March	1st to 10th	Night	13% 9% 41% 33% 4 1	684
	11th to 20th	Night	15% 11% 38% 31% 5%	570
	21st to end	Night	19% 10% 37% 26% 8%	627
April	1st to 10th	Night	17% 14% 42% 25% 3	570
	11th to 20th	Night	22% 12% 34% 24% 7%	563
	21st to end	Night	17% 12% 36% 27% 7% 1	570
May	1st to 10th	Night	17% 9% 37% 27% 10%	570
	11th to 20th	Night	16% 8% 35% 30% 11%	561
	21st to end	Night	18% 5% 35% 33% 9%	617
June	1st to 10th	Night	9% 5% 29% 40% 17%	570
	11th to 20th	Night	11% 3 34% 43% 9% 1	570
	21st to end	Night	6% 5% 28% 48% 13%	570
July	1st to 10th	Night	6% 2 23% 46% 22% 1	555
	11th to 20th	Night	4 3 26% 50% 17%	552
	21st to end	Night	4 2 27% 52% 15% 1	624
August	1st to 10th	Night	5% 3 26% 50% 16% 1	567
	11th to 20th	Night	8% 2 27% 44% 19% 1	564
	21st to end	Night	6% 4 29% 44% 17% 1	627
September	1st to 10th	Night	9% 5% 29% 40% 15% 2	570
	11th to 20th	Night	6% 4 36% 38% 13% 2	570
	21st to end	Night	9% 6% 36% 36% 12% 1	570
October	1st to 10th	Night	16% 11% 32% 30% 11%	651
	11th to 20th	Night	15% 11% 37% 28% 9%	759
	21st to end	Night	16% 11% 34% 31% 8%	908
November	1st to 10th	Night	10% 9% 39% 32% 9% 1	925
	11th to 20th	Night	11% 11% 41% 29% 8% 1	950
	21st to end	Night	12% 10% 37% 34% 8%	950
December	1st to 10th	Night	12% 11% 40% 30% 6% 1	950
	11th to 20th	Night	14% 8% 36% 33% 8%	950
	21st to end	Night	20% 12% 33% 27% 7%	1045

Page generated at 2024-10-17 12:09:40. Version ac07

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