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 2024-10-25.

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	21% 11% 3 8% 5% 4 4 3 5% 6% 30%	101952
	Night	21% 10% 3 8% 5% 4 4 3 5% 6% 30%	96919
Transparency	Day	53% 5% 12% 19% 10% 1	101714
	Night	54% 5% 12% 20% 9% 1	96778
Seeing	Day	30% 16% 32% 16% 5% 1	17244
	Night	27% 15% 32% 20% 6%	24685

By Month

Percentage Cloud Cover NE (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	17% 11% 5% 10% 6% 6% 5% 3 5% 6% 25%	2526
	11th to 20th	Day	17% 12% 5% 15% 8% 7% 5% 4 4 5% 17%	2716
	21st to end	Day	19% 11% 5% 9% 6% 5% 5% 4 5% 5% 26%	3124
February	1st to 10th	Day	20% 14% 5% 10% 7% 5% 4 4 4 5% 22%	1710
	11th to 20th	Day	18% 12% 4 11% 8% 5% 5% 4 5% 4 24%	1663
	21st to end	Day	13% 14% 4 8% 6% 4 4 3 4 7% 32%	1449
March	1st to 10th	Day	27% 14% 3 7% 6% 5% 3 3 3 4 25%	3430
	11th to 20th	Day	17% 17% 4 10% 5% 4 4 3 4 6% 26%	3480
	21st to end	Day	31% 15% 4 10% 4 3 3 2 3 4 22%	3816
April	1st to 10th	Day	25% 15% 4 8% 4 3 3 3 4 4 26%	2246
	11th to 20th	Day	21% 12% 2 6% 4 3 3 3 6% 6% 34%	2342
	21st to end	Day	23% 11% 3 6% 4 3 4 3 4 6% 34%	2470
May	1st to 10th	Day	25% 13% 3 9% 5% 4 4 3 5% 6% 23%	4124
	11th to 20th	Day	24% 11% 3 7% 4 4 4 3 4 6% 30%	4398
	21st to end	Day	19% 9% 3 6% 4 4 4 4 6% 8% 33%	4836
June	1st to 10th	Day	26% 10% 3 7% 4 4 3 4 5% 7% 26%	2660
	11th to 20th	Day	22% 8% 3 7% 4 4 4 3 4 6% 34%	2766
	21st to end	Day	25% 10% 3 7% 6% 5% 4 3 5% 7% 26%	2850
July	1st to 10th	Day	21% 9% 2 6% 5% 4 4 4 6% 8% 30%	4664
	11th to 20th	Day	17% 10% 3 8% 4 4 4 4 6% 8% 32%	4440
	21st to end	Day	20% 9% 3 6% 4 4 4 4 5% 8% 33%	4564
August	1st to 10th	Day	22% 10% 3 8% 4 4 4 4 6% 8% 27%	4105
	11th to 20th	Day	16% 8% 3 7% 5% 5% 5% 4 6% 8% 34%	4045
	21st to end	Day	10% 5% 2 6% 4 4 5% 4 7% 8% 46%	4378
September	1st to 10th	Day	16% 7% 2 5% 4 4 4 4 5% 7% 43%	2280
	11th to 20th	Day	19% 6% 2 6% 4 4 4 3 4 6% 43%	2171
	21st to end	Day	18% 8% 3 7% 3 3 4 3 4 6% 41%	2052
October	1st to 10th	Day	19% 7% 2 6% 4 4 4 4 6% 8% 37%	1900
	11th to 20th	Day	20% 8% 2 6% 4 4 4 4 6% 8% 34%	1900
	21st to end	Day	21% 11% 3 7% 5% 4 4 3 4 6% 32%	2028
November	1st to 10th	Day	21% 11% 3 7% 5% 4 3 2 5% 6% 32%	1570
	11th to 20th	Day	22% 12% 4 7% 4 4 4 4 5% 7% 27%	1520
	21st to end	Day	21% 10% 4 8% 6% 5% 4 4 5% 5% 27%	1520
December	1st to 10th	Day	26% 12% 4 9% 5% 5% 4 4 5% 5% 20%	1520
	11th to 20th	Day	30% 12% 4 7% 6% 5% 5% 4 5% 6% 18%	1906
	21st to end	Day	22% 11% 6% 8% 5% 5% 4 3 5% 7% 23%	2783
January	1st to 10th	Night	15% 11% 4 14% 6% 5% 7% 4 5% 6% 23%	4429
	11th to 20th	Night	18% 13% 5% 14% 7% 6% 5% 3 4 6% 19%	4246
	21st to end	Night	17% 14% 4 10% 5% 5% 5% 4 6% 7% 22%	4532
February	1st to 10th	Night	20% 12% 5% 9% 5% 6% 6% 4 6% 5% 22%	2470
	11th to 20th	Night	17% 10% 5% 10% 7% 5% 5% 4 6% 6% 23%	2403
	21st to end	Night	13% 12% 4 9% 6% 5% 5% 4 6% 6% 30%	1999
March	1st to 10th	Night	24% 13% 3 6% 6% 5% 4 3 4 5% 27%	3410
	11th to 20th	Night	18% 14% 4 9% 6% 5% 5% 4 5% 6% 23%	3479
	21st to end	Night	32% 11% 5% 10% 4 2 2 2 3 4 25%	3816
April	1st to 10th	Night	25% 13% 3 7% 4 3 4 4 4 5% 28%	1933
	11th to 20th	Night	24% 9% 3 6% 4 4 3 4 4 7% 32%	1784
	21st to end	Night	25% 10% 2 7% 4 4 4 3 4 5% 32%	1710
May	1st to 10th	Night	20% 16% 4 7% 4 4 4 3 5% 6% 28%	2817
	11th to 20th	Night	26% 11% 3 6% 4 4 4 3 5% 6% 28%	2506
	21st to end	Night	20% 11% 4 7% 5% 4 3 3 5% 6% 31%	2749
June	1st to 10th	Night	26% 9% 2 6% 4 4 4 3 5% 7% 30%	1520
	11th to 20th	Night	20% 8% 3 7% 5% 4 3 3 5% 6% 36%	1425
	21st to end	Night	27% 9% 3 7% 4 5% 3 3 6% 5% 27%	1330
July	1st to 10th	Night	20% 10% 3 7% 5% 5% 5% 4 6% 8% 28%	2269
	11th to 20th	Night	19% 9% 3 6% 5% 4 4 3 6% 8% 32%	2530
	21st to end	Night	18% 7% 3 6% 4 4 4 4 6% 7% 38%	2989
August	1st to 10th	Night	21% 10% 3 7% 4 4 4 2 5% 6% 35%	2825
	11th to 20th	Night	17% 9% 3 7% 4 4 4 3 5% 7% 37%	2782
	21st to end	Night	10% 5% 2 4 4 3 4 3 5% 7% 52%	3276
September	1st to 10th	Night	15% 7% 2 6% 3 3 3 3 5% 7% 46%	1900
	11th to 20th	Night	18% 7% 2 4 3 3 4 3 5% 6% 46%	2007
	21st to end	Night	20% 9% 2 7% 3 4 3 3 4 6% 39%	2128
October	1st to 10th	Night	18% 6% 3 6% 5% 3 3 3 5% 6% 42%	2280
	11th to 20th	Night	20% 6% 2 5% 4 4 4 4 5% 7% 40%	2280
	21st to end	Night	24% 9% 2 5% 4 3 3 4 4 6% 35%	2434
November	1st to 10th	Night	20% 9% 2 6% 4 4 4 4 6% 6% 34%	2504
	11th to 20th	Night	21% 9% 3 8% 5% 4 5% 4 6% 6% 29%	2660
	21st to end	Night	21% 9% 3 8% 6% 4 4 4 5% 7% 28%	2660
December	1st to 10th	Night	24% 13% 3 8% 6% 4 4 3 5% 7% 22%	2660
	11th to 20th	Night	30% 11% 3 8% 4 4 3 4 5% 6% 22%	3293
	21st to end	Night	24% 9% 4 9% 5% 4 5% 3 5% 6% 26%	4884

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% 3 18% 16% 5%	2527
	11th to 20th	Day	65% 4 12% 15% 4	2716
	21st to end	Day	57% 4 11% 19% 9%	3124
February	1st to 10th	Day	63% 3 11% 15% 7% 1	1710
	11th to 20th	Day	62% 4 10% 16% 7% 1	1671
	21st to end	Day	53% 3 12% 20% 9% 3	1449
March	1st to 10th	Day	63% 3 8% 17% 7% 2	3434
	11th to 20th	Day	57% 4 13% 17% 8% 1	3480
	21st to end	Day	68% 3 5% 13% 10% 2	3816
April	1st to 10th	Day	61% 3 7% 14% 12% 2	2246
	11th to 20th	Day	50% 5% 8% 23% 13% 1	2342
	21st to end	Day	53% 3 10% 18% 13% 3	2470
May	1st to 10th	Day	60% 5% 12% 16% 7% 1	4138
	11th to 20th	Day	56% 6% 11% 19% 8% 1	4402
	21st to end	Day	46% 7% 15% 20% 11% 1	4836
June	1st to 10th	Day	57% 5% 10% 19% 9%	2660
	11th to 20th	Day	51% 4 11% 20% 13% 2	2766
	21st to end	Day	58% 6% 11% 15% 9% 1	2850
July	1st to 10th	Day	51% 5% 13% 17% 12% 2	4592
	11th to 20th	Day	49% 5% 13% 22% 9% 1	4364
	21st to end	Day	48% 6% 15% 20% 10% 1	4418
August	1st to 10th	Day	55% 6% 13% 18% 9% 1	4092
	11th to 20th	Day	46% 6% 14% 25% 9%	4084
	21st to end	Day	33% 5% 14% 27% 20% 1	4378
September	1st to 10th	Day	40% 4 13% 25% 16% 2	2280
	11th to 20th	Day	43% 4 8% 25% 18% 2	2171
	21st to end	Day	44% 5% 7% 26% 17% 1	2052
October	1st to 10th	Day	45% 4 10% 26% 13% 2	1900
	11th to 20th	Day	47% 5% 12% 23% 12% 1	1900
	21st to end	Day	54% 3 10% 22% 10% 1	2028
November	1st to 10th	Day	53% 4 11% 21% 10% 1	1570
	11th to 20th	Day	55% 4 13% 19% 8% 1	1520
	21st to end	Day	58% 4 13% 18% 6%	1520
December	1st to 10th	Day	63% 5% 10% 18% 4 1	1520
	11th to 20th	Day	65% 5% 9% 15% 7%	1905
	21st to end	Day	59% 3 18% 14% 6%	2783
January	1st to 10th	Night	58% 5% 13% 19% 4	4429
	11th to 20th	Night	65% 5% 12% 13% 5%	4246
	21st to end	Night	59% 4 13% 17% 6%	4532
February	1st to 10th	Night	60% 5% 11% 16% 8% 1	2470
	11th to 20th	Night	58% 4 13% 17% 8% 1	2406
	21st to end	Night	53% 4 12% 20% 9% 2	1999
March	1st to 10th	Night	60% 3 8% 18% 10% 1	3419
	11th to 20th	Night	59% 4 12% 15% 8% 1	3480
	21st to end	Night	65% 2 7% 14% 9% 2	3816
April	1st to 10th	Night	57% 4 8% 15% 12% 3	1933
	11th to 20th	Night	52% 4 7% 21% 14% 2	1784
	21st to end	Night	55% 3 9% 19% 12% 3	1710
May	1st to 10th	Night	58% 4 13% 17% 7%	2823
	11th to 20th	Night	57% 5% 9% 20% 7% 1	2507
	21st to end	Night	52% 6% 12% 21% 8% 1	2750
June	1st to 10th	Night	55% 4 11% 21% 9%	1520
	11th to 20th	Night	50% 5% 11% 22% 12% 1	1425
	21st to end	Night	58% 6% 11% 15% 10% 1	1330
July	1st to 10th	Night	53% 6% 12% 18% 10% 1	2233
	11th to 20th	Night	50% 6% 14% 19% 10% 1	2482
	21st to end	Night	46% 6% 12% 22% 13% 1	2895
August	1st to 10th	Night	51% 5% 13% 22% 9%	2813
	11th to 20th	Night	46% 6% 16% 24% 8%	2809
	21st to end	Night	31% 6% 14% 28% 21%	3275
September	1st to 10th	Night	38% 6% 10% 27% 17% 2	1900
	11th to 20th	Night	39% 4 8% 29% 17% 2	2007
	21st to end	Night	46% 5% 7% 25% 15% 1	2128
October	1st to 10th	Night	43% 4 12% 25% 15% 2	2280
	11th to 20th	Night	43% 5% 13% 27% 12%	2280
	21st to end	Night	49% 4 12% 21% 13% 1	2434
November	1st to 10th	Night	49% 5% 14% 21% 11% 1	2504
	11th to 20th	Night	53% 5% 12% 21% 9% 1	2660
	21st to end	Night	53% 5% 16% 19% 7%	2660
December	1st to 10th	Night	61% 4 12% 19% 4	2660
	11th to 20th	Night	62% 4 10% 17% 7% 1	3295
	21st to end	Night	57% 4 14% 19% 6%	4884

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	35% 18% 33% 11% 3	370
	11th to 20th	Day	36% 18% 30% 12% 3	370
	21st to end	Day	27% 21% 35% 14% 3	407
February	1st to 10th	Day	33% 21% 30% 14% 2	370
	11th to 20th	Day	37% 24% 26% 11% 2	366
	21st to end	Day	32% 20% 30% 14% 3 1	321
March	1st to 10th	Day	35% 24% 30% 8% 3	460
	11th to 20th	Day	34% 24% 27% 10% 3 1	460
	21st to end	Day	38% 20% 27% 11% 4	506
April	1st to 10th	Day	41% 22% 27% 8% 2	460
	11th to 20th	Day	32% 23% 32% 10% 2	452
	21st to end	Day	34% 16% 32% 13% 4	460
May	1st to 10th	Day	37% 22% 29% 10% 2 1	468
	11th to 20th	Day	29% 19% 29% 18% 4 1	674
	21st to end	Day	31% 14% 35% 16% 3 1	735
June	1st to 10th	Day	32% 15% 31% 17% 4	680
	11th to 20th	Day	26% 15% 34% 20% 5% 1	680
	21st to end	Day	33% 12% 30% 19% 5% 1	680
July	1st to 10th	Day	24% 9% 36% 24% 7%	670
	11th to 20th	Day	21% 7% 39% 22% 9% 1	668
	21st to end	Day	24% 9% 38% 22% 7% 1	590
August	1st to 10th	Day	18% 10% 39% 24% 8% 1	486
	11th to 20th	Day	20% 9% 38% 21% 11% 2	479
	21st to end	Day	19% 11% 35% 25% 7% 3	539
September	1st to 10th	Day	20% 13% 37% 21% 7% 1	490
	11th to 20th	Day	26% 14% 29% 20% 8% 3	490
	21st to end	Day	23% 14% 35% 18% 7% 2	470
October	1st to 10th	Day	23% 13% 34% 20% 8% 3	390
	11th to 20th	Day	28% 16% 33% 15% 5% 4	390
	21st to end	Day	31% 16% 33% 13% 6% 1	411
November	1st to 10th	Day	27% 18% 30% 16% 7% 2	365
	11th to 20th	Day	40% 17% 24% 13% 5% 1	370
	21st to end	Day	34% 19% 33% 10% 4 1	370
December	1st to 10th	Day	40% 17% 28% 12% 3	370
	11th to 20th	Day	44% 21% 22% 12% 1	370
	21st to end	Day	37% 23% 25% 13% 2	407
January	1st to 10th	Night	32% 19% 32% 15% 3	850
	11th to 20th	Night	31% 18% 30% 18% 3	794
	21st to end	Night	27% 21% 32% 15% 4	836
February	1st to 10th	Night	32% 18% 32% 17% 2	760
	11th to 20th	Night	30% 23% 33% 13% 1	743
	21st to end	Night	22% 21% 35% 18% 4	628
March	1st to 10th	Night	28% 21% 34% 15% 2	760
	11th to 20th	Night	26% 21% 30% 19% 4 1	760
	21st to end	Night	29% 21% 31% 14% 4	836
April	1st to 10th	Night	36% 15% 32% 14% 3	603
	11th to 20th	Night	28% 20% 32% 16% 3	564
	21st to end	Night	31% 18% 28% 19% 4 1	570
May	1st to 10th	Night	31% 15% 33% 16% 5% 1	570
	11th to 20th	Night	29% 12% 32% 20% 6% 1	562
	21st to end	Night	23% 14% 40% 18% 5% 1	616
June	1st to 10th	Night	32% 10% 34% 20% 4	570
	11th to 20th	Night	23% 12% 38% 21% 6%	475
	21st to end	Night	31% 7% 31% 23% 7% 1	380
July	1st to 10th	Night	20% 7% 38% 25% 10%	402
	11th to 20th	Night	19% 7% 38% 26% 10%	552
	21st to end	Night	21% 6% 30% 33% 9%	623
August	1st to 10th	Night	18% 7% 32% 32% 11% 1	568
	11th to 20th	Night	21% 7% 31% 28% 12% 1	562
	21st to end	Night	16% 7% 31% 32% 12% 1	627
September	1st to 10th	Night	19% 7% 35% 28% 10%	570
	11th to 20th	Night	22% 9% 30% 23% 13% 2	677
	21st to end	Night	26% 10% 32% 22% 9% 2	760
October	1st to 10th	Night	23% 9% 32% 26% 9% 1	760
	11th to 20th	Night	23% 15% 32% 20% 9% 1	760
	21st to end	Night	30% 14% 32% 19% 5%	812
November	1st to 10th	Night	28% 14% 29% 22% 6% 1	800
	11th to 20th	Night	29% 18% 28% 20% 5%	850
	21st to end	Night	28% 21% 28% 17% 5%	850
December	1st to 10th	Night	33% 16% 32% 13% 5%	850
	11th to 20th	Night	36% 21% 28% 13% 3	850
	21st to end	Night	32% 20% 28% 17% 3	935

Page generated at 2024-10-22 21:21:06. Version ac07

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