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 2024-02-20.

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 6% 5% 3 5% 5% 5% 7% 42%	78248
	Night	9% 7% 3 6% 6% 3 4 5% 5% 7% 44%	80961
Transparency	Day	40% 7% 15% 24% 12% 2	77959
	Night	39% 6% 14% 24% 14% 2	80773
Seeing	Day	14% 9% 31% 30% 13% 2	14866
	Night	12% 9% 35% 34% 10% 1	24979

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% 12% 5% 12% 10% 4 8% 7% 6% 5% 23%	2520
	11th to 20th	Day	5% 12% 6% 10% 7% 4 8% 5% 7% 8% 26%	2540
	21st to end	Day	6% 11% 7% 13% 8% 5% 7% 5% 5% 5% 26%	3110
February	1st to 10th	Day	9% 10% 5% 8% 8% 5% 7% 6% 6% 6% 30%	1710
	11th to 20th	Day	9% 9% 4 8% 7% 4 5% 6% 6% 7% 35%	1713
	21st to end	Day	10% 10% 4 8% 7% 5% 6% 4 6% 7% 34%	1480
March	1st to 10th	Day	12% 9% 5% 10% 5% 3 3 3 4 8% 39%	1872
	11th to 20th	Day	12% 9% 5% 8% 5% 4 5% 4 5% 8% 36%	1980
	21st to end	Day	16% 11% 5% 7% 6% 3 5% 5% 6% 7% 29%	2178
April	1st to 10th	Day	16% 6% 3 7% 5% 3 4 5% 5% 7% 39%	2052
	11th to 20th	Day	19% 9% 3 5% 5% 3 4 4 4 7% 37%	2309
	21st to end	Day	19% 8% 3 5% 5% 2 4 4 4 7% 40%	2340
May	1st to 10th	Day	16% 7% 3 5% 5% 3 4 4 6% 7% 40%	2340
	11th to 20th	Day	15% 7% 3 6% 5% 3 5% 4 5% 8% 40%	2302
	21st to end	Day	17% 6% 3 6% 5% 3 4 4 5% 9% 38%	2650
June	1st to 10th	Day	11% 4 2 4 4 3 5% 5% 5% 9% 48%	2686
	11th to 20th	Day	12% 4 2 6% 4 3 4 5% 6% 8% 46%	2700
	21st to end	Day	8% 4 2 5% 4 3 5% 5% 5% 9% 50%	2700
July	1st to 10th	Day	5% 4 2 4 4 3 4 5% 6% 10% 53%	2629
	11th to 20th	Day	6% 2 1 3 4 2 3 4 5% 8% 61%	2520
	21st to end	Day	5% 3 1 3 4 3 4 5% 6% 9% 55%	2577
August	1st to 10th	Day	9% 5% 3 5% 4 3 5% 6% 7% 10% 43%	2328
	11th to 20th	Day	9% 4 2 4 4 3 5% 5% 7% 8% 50%	2301
	21st to end	Day	7% 3 2 4 4 2 4 4 6% 7% 58%	2574
September	1st to 10th	Day	13% 5% 2 4 4 2 3 3 5% 7% 52%	2080
	11th to 20th	Day	9% 4 2 4 4 2 3 5% 5% 7% 55%	1980
	21st to end	Day	11% 5% 2 4 4 2 3 3 4 6% 54%	1980
October	1st to 10th	Day	15% 6% 2 4 4 2 3 3 4 6% 50%	1886
	11th to 20th	Day	14% 7% 2 4 3 2 3 3 5% 6% 52%	1800
	21st to end	Day	15% 7% 3 5% 4 2 4 3 4 6% 47%	1862
November	1st to 10th	Day	8% 7% 3 5% 4 3 5% 5% 7% 7% 47%	1673
	11th to 20th	Day	7% 8% 2 9% 8% 3 4 4 6% 7% 43%	1630
	21st to end	Day	9% 9% 3 6% 4 3 4 4 6% 8% 44%	1520
December	1st to 10th	Day	8% 8% 3 8% 7% 4 5% 5% 5% 8% 38%	1520
	11th to 20th	Day	8% 10% 6% 8% 8% 5% 5% 5% 5% 8% 34%	1764
	21st to end	Day	16% 9% 5% 13% 7% 3 4 5% 6% 5% 27%	2442
January	1st to 10th	Night	9% 11% 4 10% 13% 6% 7% 6% 5% 5% 24%	4417
	11th to 20th	Night	4 9% 5% 9% 8% 4 8% 6% 9% 9% 29%	4430
	21st to end	Night	5% 10% 6% 11% 8% 4 6% 6% 5% 6% 32%	4554
February	1st to 10th	Night	9% 10% 4 8% 6% 4 5% 4 6% 7% 38%	2470
	11th to 20th	Night	8% 9% 4 7% 6% 3 4 5% 6% 6% 42%	2355
	21st to end	Night	9% 9% 3 6% 7% 3 5% 5% 6% 8% 41%	1776
March	1st to 10th	Night	10% 8% 4 6% 5% 2 5% 4 5% 8% 42%	2088
	11th to 20th	Night	11% 9% 3 7% 6% 3 4 4 5% 6% 42%	1980
	21st to end	Night	14% 10% 4 7% 5% 3 4 4 4 7% 39%	2178
April	1st to 10th	Night	14% 7% 3 5% 5% 3 5% 5% 6% 7% 41%	1903
	11th to 20th	Night	16% 8% 3 7% 5% 3 3 3 4 6% 42%	1599
	21st to end	Night	16% 7% 2 4 4 2 5% 5% 5% 7% 43%	1620
May	1st to 10th	Night	14% 5% 3 5% 4 3 3 5% 6% 9% 43%	1620
	11th to 20th	Night	15% 5% 2 5% 4 3 4 4 4 7% 47%	1593
	21st to end	Night	14% 6% 3 6% 5% 3 4 5% 6% 9% 39%	1621
June	1st to 10th	Night	7% 5% 3 4 3 2 4 4 6% 8% 55%	1271
	11th to 20th	Night	7% 5% 2 4 4 2 4 5% 5% 9% 52%	1260
	21st to end	Night	6% 3 2 2 4 2 4 3 5% 10% 59%	1260
July	1st to 10th	Night	4 3 2 4 3 2 4 4 6% 9% 59%	1326
	11th to 20th	Night	4 2 1 2 4 2 3 5% 6% 7% 64%	1440
	21st to end	Night	3 3 1 3 4 2 4 5% 5% 10% 59%	1737
August	1st to 10th	Night	6% 4 2 5% 4 3 4 5% 9% 10% 49%	1611
	11th to 20th	Night	6% 4 1 4 3 3 2 5% 6% 7% 59%	1600
	21st to end	Night	5% 2 1 3 3 1 3 4 6% 8% 63%	1782
September	1st to 10th	Night	8% 4 2 3 4 3 3 3 4 6% 59%	1876
	11th to 20th	Night	7% 3 2 3 4 2 4 5% 5% 6% 58%	1980
	21st to end	Night	8% 5% 2 4 4 2 3 3 4 7% 59%	1980
October	1st to 10th	Night	15% 5% 3 4 3 2 3 3 4 6% 51%	2056
	11th to 20th	Night	12% 6% 2 5% 4 2 3 3 5% 6% 53%	2160
	21st to end	Night	13% 6% 2 5% 4 2 3 4 4 7% 50%	2492
November	1st to 10th	Night	8% 5% 2 5% 4 2 4 4 5% 7% 53%	2405
	11th to 20th	Night	7% 7% 3 6% 6% 3 5% 4 6% 8% 45%	2548
	21st to end	Night	8% 7% 2 6% 4 3 4 5% 5% 7% 48%	2660
December	1st to 10th	Night	7% 8% 4 7% 7% 3 5% 5% 5% 7% 41%	2660
	11th to 20th	Night	7% 8% 3 7% 6% 3 4 6% 5% 7% 44%	3428
	21st to end	Night	17% 11% 5% 12% 6% 3 4 4 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	1722
	21st to end	Day	49% 7% 14% 19% 10% 1	1480
March	1st to 10th	Day	47% 6% 14% 24% 8% 1	1872
	11th to 20th	Day	45% 7% 13% 23% 11%	1980
	21st to end	Day	53% 8% 17% 16% 5% 1	2178
April	1st to 10th	Day	44% 6% 14% 25% 11% 1	2052
	11th to 20th	Day	47% 7% 11% 21% 11% 2	2312
	21st to end	Day	45% 6% 14% 25% 11%	2340
May	1st to 10th	Day	44% 7% 13% 22% 13%	2340
	11th to 20th	Day	43% 7% 16% 21% 12%	2306
	21st to end	Day	43% 8% 14% 23% 12%	2650
June	1st to 10th	Day	32% 8% 18% 29% 12% 1	2686
	11th to 20th	Day	35% 7% 17% 24% 15% 3	2700
	21st to end	Day	29% 8% 16% 29% 14% 2	2700
July	1st to 10th	Day	26% 8% 17% 34% 14% 1	2558
	11th to 20th	Day	22% 6% 14% 29% 22% 7%	2445
	21st to end	Day	24% 8% 16% 29% 20% 3	2434
August	1st to 10th	Day	33% 10% 17% 26% 11% 2	2314
	11th to 20th	Day	30% 8% 16% 32% 13% 1	2301
	21st to end	Day	25% 8% 13% 32% 18% 4	2574
September	1st to 10th	Day	33% 5% 13% 27% 20% 3	2080
	11th to 20th	Day	29% 5% 18% 31% 16% 1	1980
	21st to end	Day	31% 7% 10% 31% 19% 1	1980
October	1st to 10th	Day	36% 5% 13% 27% 17% 1	1886
	11th to 20th	Day	33% 4 12% 30% 17% 3	1800
	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% 12% 3	2356
	21st to end	Night	41% 7% 13% 23% 13% 3	1776
March	1st to 10th	Night	40% 7% 17% 25% 10% 2	2088
	11th to 20th	Night	43% 5% 10% 26% 14% 1	1980
	21st to end	Night	46% 6% 15% 23% 8% 1	2178
April	1st to 10th	Night	41% 8% 15% 23% 13% 1	1903
	11th to 20th	Night	45% 4 11% 21% 17% 2	1599
	21st to end	Night	40% 8% 12% 26% 12% 2	1620
May	1st to 10th	Night	37% 6% 16% 25% 14% 1	1620
	11th to 20th	Night	37% 7% 14% 24% 18% 1	1594
	21st to end	Night	40% 8% 16% 21% 14% 1	1622
June	1st to 10th	Night	28% 7% 16% 29% 18% 2	1271
	11th to 20th	Night	27% 7% 16% 25% 19% 5%	1260
	21st to end	Night	22% 6% 17% 30% 22% 3	1260
July	1st to 10th	Night	21% 8% 16% 34% 19% 3	1288
	11th to 20th	Night	18% 7% 14% 29% 24% 8%	1392
	21st to end	Night	20% 6% 15% 31% 22% 5%	1640
August	1st to 10th	Night	27% 9% 18% 27% 16% 3	1601
	11th to 20th	Night	23% 7% 16% 32% 19% 3	1600
	21st to end	Night	19% 6% 16% 29% 24% 6%	1782
September	1st to 10th	Night	27% 7% 14% 27% 22% 4	1876
	11th to 20th	Night	24% 7% 15% 33% 19% 2	1980
	21st to end	Night	26% 5% 10% 32% 24% 3	1980
October	1st to 10th	Night	34% 5% 12% 26% 21% 1	2056
	11th to 20th	Night	32% 5% 10% 29% 20% 4	2160
	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% 21% 6% 1	267
	21st to end	Day	18% 13% 40% 25% 3 1	198
March	1st to 10th	Day	14% 17% 41% 23% 5% 1	240
	11th to 20th	Day	19% 9% 37% 23% 10% 2	240
	21st to end	Day	22% 11% 34% 26% 6% 1	264
April	1st to 10th	Day	25% 17% 35% 18% 5%	312
	11th to 20th	Day	24% 13% 32% 23% 7% 1	590
	21st to end	Day	23% 15% 29% 22% 10% 2	600
May	1st to 10th	Day	18% 12% 34% 26% 9% 1	603
	11th to 20th	Day	20% 9% 31% 24% 14% 2	625
	21st to end	Day	20% 8% 28% 30% 12% 2	679
June	1st to 10th	Day	7% 8% 24% 35% 21% 5%	630
	11th to 20th	Day	13% 6% 34% 31% 13% 3	630
	21st to end	Day	8% 6% 30% 39% 16% 2	630
July	1st to 10th	Day	6% 3 20% 40% 25% 6%	621
	11th to 20th	Day	5% 4 32% 38% 19% 2	618
	21st to end	Day	5% 2 26% 43% 21% 2	684
August	1st to 10th	Day	9% 4 21% 40% 22% 3	626
	11th to 20th	Day	9% 4 25% 35% 23% 4	615
	21st to end	Day	7% 5% 26% 37% 21% 4	693
September	1st to 10th	Day	14% 7% 29% 31% 15% 4	370
	11th to 20th	Day	9% 4 35% 33% 17% 3	270
	21st to end	Day	15% 13% 31% 30% 10% 1	270
October	1st to 10th	Day	19% 8% 30% 27% 13% 3	270
	11th to 20th	Day	17% 14% 33% 25% 10% 1	270
	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	885
	21st to end	Night	13% 7% 38% 33% 8% 1	592
March	1st to 10th	Night	13% 9% 40% 33% 4 1	648
	11th to 20th	Night	16% 9% 38% 32% 6%	540
	21st to end	Night	19% 9% 36% 27% 8% 1	594
April	1st to 10th	Night	16% 12% 43% 25% 3	540
	11th to 20th	Night	22% 12% 34% 24% 8%	533
	21st to end	Night	17% 12% 36% 27% 7% 1	540
May	1st to 10th	Night	16% 9% 37% 28% 10%	540
	11th to 20th	Night	17% 8% 35% 29% 11%	531
	21st to end	Night	18% 5% 34% 33% 10%	584
June	1st to 10th	Night	9% 4 29% 40% 17%	540
	11th to 20th	Night	10% 3 34% 43% 9% 1	540
	21st to end	Night	6% 5% 28% 48% 14%	540
July	1st to 10th	Night	5% 2 22% 47% 22% 1	525
	11th to 20th	Night	4 2 26% 50% 17%	522
	21st to end	Night	4 2 26% 53% 14%	591
August	1st to 10th	Night	5% 3 25% 50% 16% 1	537
	11th to 20th	Night	8% 2 26% 43% 20% 1	534
	21st to end	Night	5% 4 29% 44% 17% 1	594
September	1st to 10th	Night	9% 5% 30% 39% 14% 2	540
	11th to 20th	Night	6% 4 35% 39% 13% 3	540
	21st to end	Night	9% 6% 36% 36% 11% 1	540
October	1st to 10th	Night	16% 11% 32% 30% 10%	616
	11th to 20th	Night	16% 11% 37% 27% 9%	720
	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 2024-02-17 05:28:38. Version ac07

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