Bridgetown
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bridgetown clear sky chart from 2005-11-06 to 2026-04-02.

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	18% 13% 4 10% 6% 4 4 3 4 5% 28%	131635
	Night	18% 15% 5% 13% 7% 4 3 3 4 5% 23%	130284
Transparency	Day	57% 6% 11% 17% 9% 1	135194
	Night	62% 6% 10% 15% 7% 1	134812
Seeing	Day	29% 20% 30% 15% 4 1	18630
	Night	28% 19% 29% 18% 4	26454

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	13% 23% 10% 19% 13% 5% 2 2 2 2 10%	4093
	11th to 20th	Day	16% 23% 11% 26% 5% 5% 2 2 2 2 6%	4928
	21st to end	Day	13% 14% 7% 19% 18% 9% 4 2 2 2 10%	5781
February	1st to 10th	Day	16% 18% 9% 16% 11% 6% 4 2 4 3 11%	1890
	11th to 20th	Day	15% 16% 6% 17% 11% 6% 3 2 3 4 16%	1843
	21st to end	Day	11% 17% 7% 12% 8% 5% 4 3 3 5% 26%	1630
March	1st to 10th	Day	20% 19% 5% 15% 7% 6% 3 2 3 3 17%	4981
	11th to 20th	Day	15% 16% 4 10% 5% 4 4 2 4 5% 29%	5090
	21st to end	Day	23% 19% 7% 10% 5% 4 4 2 3 4 20%	5587
April	1st to 10th	Day	22% 16% 4 7% 4 3 3 3 5% 4 27%	2345
	11th to 20th	Day	20% 13% 3 6% 3 3 3 2 5% 6% 36%	2527
	21st to end	Day	21% 12% 3 6% 5% 3 3 3 4 6% 34%	2600
May	1st to 10th	Day	23% 16% 4 9% 6% 5% 4 3 4 5% 21%	5886
	11th to 20th	Day	18% 11% 3 8% 5% 5% 5% 3 5% 6% 29%	6267
	21st to end	Day	16% 11% 3 8% 5% 4 4 3 5% 7% 33%	6948
June	1st to 10th	Day	23% 9% 2 6% 5% 4 4 4 5% 6% 31%	2888
	11th to 20th	Day	19% 8% 2 6% 4 4 4 4 6% 7% 37%	3000
	21st to end	Day	22% 9% 3 8% 5% 5% 4 3 5% 6% 30%	3000
July	1st to 10th	Day	21% 9% 3 6% 4 4 5% 4 6% 7% 32%	6820
	11th to 20th	Day	19% 8% 3 5% 3 3 4 3 5% 8% 39%	6592
	21st to end	Day	13% 7% 2 6% 4 4 5% 4 6% 9% 40%	6481
August	1st to 10th	Day	21% 10% 3 8% 4 4 5% 4 5% 5% 32%	4235
	11th to 20th	Day	12% 7% 3 7% 4 5% 5% 4 6% 7% 40%	4175
	21st to end	Day	11% 5% 2 5% 3 3 4 4 5% 7% 50%	4586
September	1st to 10th	Day	17% 7% 2 5% 3 3 4 3 4 6% 46%	2400
	11th to 20th	Day	16% 6% 2 6% 3 3 4 2 4 6% 47%	2235
	21st to end	Day	19% 7% 3 5% 3 2 3 3 5% 6% 45%	2190
October	1st to 10th	Day	19% 8% 3 5% 4 4 4 3 5% 7% 40%	2000
	11th to 20th	Day	19% 11% 3 8% 4 3 4 3 5% 7% 34%	2000
	21st to end	Day	20% 15% 2 9% 4 4 4 3 4 5% 30%	2169
November	1st to 10th	Day	21% 15% 4 8% 4 4 3 3 4 5% 27%	1742
	11th to 20th	Day	19% 21% 8% 8% 5% 4 4 2 3 5% 20%	1680
	21st to end	Day	19% 22% 7% 13% 6% 4 3 3 4 4 16%	1680
December	1st to 10th	Day	18% 20% 9% 22% 4 3 3 2 4 3 11%	2690
	11th to 20th	Day	23% 18% 6% 18% 7% 4 3 2 3 3 13%	3076
	21st to end	Day	18% 18% 9% 17% 8% 3 3 3 4 4 14%	3600
January	1st to 10th	Night	12% 21% 10% 23% 11% 5% 2 2 2 2 10%	8831
	11th to 20th	Night	19% 22% 10% 24% 5% 4 2 2 2 3 8%	7930
	21st to end	Night	11% 14% 6% 20% 19% 7% 4 2 3 4 9%	8400
February	1st to 10th	Night	17% 18% 7% 20% 9% 5% 3 3 3 3 11%	2730
	11th to 20th	Night	17% 15% 7% 17% 11% 5% 3 3 3 4 16%	2663
	21st to end	Night	11% 16% 7% 12% 8% 6% 4 4 5% 5% 23%	2175
March	1st to 10th	Night	19% 19% 7% 14% 9% 4 3 2 3 3 17%	5078
	11th to 20th	Night	17% 17% 6% 10% 5% 4 4 3 4 5% 24%	5089
	21st to end	Night	24% 15% 6% 10% 5% 3 3 2 3 4 24%	5587
April	1st to 10th	Night	25% 16% 3 7% 4 4 4 3 4 4 27%	2077
	11th to 20th	Night	22% 13% 3 6% 4 4 3 3 6% 7% 30%	1818
	21st to end	Night	21% 14% 3 7% 5% 4 3 3 4 5% 30%	1800
May	1st to 10th	Night	22% 18% 5% 9% 5% 4 4 2 4 5% 23%	4054
	11th to 20th	Night	21% 10% 3 7% 5% 5% 5% 4 5% 6% 29%	3644
	21st to end	Night	16% 13% 3 8% 5% 4 4 3 5% 7% 32%	3948
June	1st to 10th	Night	24% 9% 2 6% 4 5% 3 4 6% 7% 29%	1527
	11th to 20th	Night	21% 6% 3 6% 4 4 4 4 6% 7% 36%	1400
	21st to end	Night	21% 7% 3 7% 6% 6% 5% 4 5% 8% 29%	1400
July	1st to 10th	Night	22% 11% 3 8% 4 4 4 4 5% 7% 26%	3160
	11th to 20th	Night	19% 8% 3 6% 4 4 4 5% 6% 7% 35%	3339
	21st to end	Night	14% 6% 2 6% 4 4 4 4 7% 8% 40%	4371
August	1st to 10th	Night	23% 9% 3 7% 4 4 4 3 5% 7% 33%	2915
	11th to 20th	Night	15% 7% 3 7% 5% 5% 4 4 7% 8% 35%	2872
	21st to end	Night	11% 7% 2 6% 4 3 4 4 6% 8% 46%	3312
September	1st to 10th	Night	14% 6% 2 5% 5% 5% 4 3 5% 7% 45%	2000
	11th to 20th	Night	19% 6% 2 5% 3 3 3 3 5% 6% 44%	2161
	21st to end	Night	17% 7% 2 6% 4 4 4 4 5% 7% 39%	2209
October	1st to 10th	Night	19% 7% 3 7% 3 4 4 3 4 6% 40%	2400
	11th to 20th	Night	17% 10% 3 7% 4 4 4 3 5% 7% 35%	2400
	21st to end	Night	24% 13% 3 7% 5% 4 3 3 4 4 29%	2670
November	1st to 10th	Night	21% 14% 4 7% 5% 5% 3 3 4 5% 29%	2774
	11th to 20th	Night	18% 24% 6% 9% 5% 4 4 3 4 5% 20%	2940
	21st to end	Night	18% 21% 7% 10% 5% 3 3 3 4 4 20%	2940
December	1st to 10th	Night	16% 20% 9% 22% 6% 4 3 3 4 4 10%	4720
	11th to 20th	Night	17% 18% 6% 20% 7% 4 3 2 3 4 17%	5353
	21st to end	Night	21% 19% 7% 15% 8% 3 3 2 3 3 17%	7597

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	81% 5% 9% 5% 1	4094
	11th to 20th	Day	85% 5% 5% 4 1	4961
	21st to end	Day	79% 6% 8% 4 3 1	5781
February	1st to 10th	Day	78% 5% 8% 6% 3	1890
	11th to 20th	Day	74% 6% 7% 9% 4	1851
	21st to end	Day	62% 5% 11% 15% 7% 1	1630
March	1st to 10th	Day	72% 4 7% 10% 6% 1	4985
	11th to 20th	Day	56% 7% 13% 18% 7% 1	5090
	21st to end	Day	70% 3 5% 12% 9% 1	5587
April	1st to 10th	Day	60% 6% 8% 12% 12% 2	2345
	11th to 20th	Day	50% 5% 10% 22% 12% 1	2527
	21st to end	Day	52% 5% 11% 18% 12% 3	2600
May	1st to 10th	Day	62% 8% 10% 15% 5% 1	5897
	11th to 20th	Day	52% 9% 13% 18% 7% 1	6271
	21st to end	Day	49% 8% 13% 16% 12%	6948
June	1st to 10th	Day	53% 7% 10% 19% 10%	2888
	11th to 20th	Day	46% 7% 14% 19% 12% 1	3000
	21st to end	Day	56% 7% 9% 17% 10% 1	3000
July	1st to 10th	Day	52% 5% 14% 18% 10% 1	6745
	11th to 20th	Day	45% 5% 12% 26% 12%	6511
	21st to end	Day	41% 7% 15% 26% 11%	6296
August	1st to 10th	Day	53% 7% 9% 19% 11%	4222
	11th to 20th	Day	42% 7% 15% 24% 11%	4214
	21st to end	Day	33% 6% 14% 27% 19% 1	4586
September	1st to 10th	Day	39% 5% 12% 27% 15% 2	2400
	11th to 20th	Day	40% 5% 11% 25% 18% 1	2235
	21st to end	Day	42% 5% 9% 25% 17% 2	2190
October	1st to 10th	Day	45% 6% 11% 26% 12%	3260
	11th to 20th	Day	48% 5% 9% 25% 14%	3240
	21st to end	Day	49% 3 13% 21% 13% 1	3483
November	1st to 10th	Day	59% 6% 12% 16% 7%	1742
	11th to 20th	Day	67% 6% 11% 12% 4 1	1680
	21st to end	Day	72% 6% 10% 10% 2	1680
December	1st to 10th	Day	78% 5% 6% 9% 1	2690
	11th to 20th	Day	76% 5% 6% 9% 3	3075
	21st to end	Day	74% 6% 9% 5% 5%	3600
January	1st to 10th	Night	81% 5% 7% 6% 1	8831
	11th to 20th	Night	82% 5% 6% 5% 1	7972
	21st to end	Night	79% 5% 7% 7% 2	8400
February	1st to 10th	Night	78% 5% 7% 6% 4	2730
	11th to 20th	Night	73% 5% 8% 10% 3	2666
	21st to end	Night	63% 6% 10% 14% 6% 1	2175
March	1st to 10th	Night	73% 5% 6% 9% 7% 1	5087
	11th to 20th	Night	58% 8% 13% 16% 5%	5090
	21st to end	Night	65% 4 6% 16% 9% 1	5587
April	1st to 10th	Night	61% 4 9% 13% 10% 2	2077
	11th to 20th	Night	53% 6% 10% 19% 11% 1	1818
	21st to end	Night	56% 6% 9% 15% 12% 1	1800
May	1st to 10th	Night	63% 7% 9% 13% 7%	4060
	11th to 20th	Night	52% 9% 11% 20% 5% 2	3645
	21st to end	Night	50% 10% 15% 17% 8%	3949
June	1st to 10th	Night	53% 8% 12% 20% 7%	1527
	11th to 20th	Night	46% 8% 14% 22% 10% 1	1400
	21st to end	Night	53% 8% 12% 16% 9% 2	1400
July	1st to 10th	Night	56% 7% 13% 16% 8%	3125
	11th to 20th	Night	47% 7% 16% 18% 13% 1	3297
	21st to end	Night	40% 7% 15% 25% 13%	4242
August	1st to 10th	Night	51% 7% 12% 22% 7%	2903
	11th to 20th	Night	45% 8% 18% 22% 7%	2899
	21st to end	Night	33% 8% 16% 26% 16% 1	3311
September	1st to 10th	Night	38% 8% 12% 27% 15% 1	2000
	11th to 20th	Night	39% 6% 11% 28% 15% 1	2161
	21st to end	Night	44% 7% 10% 23% 14% 2	2209
October	1st to 10th	Night	47% 5% 12% 24% 11% 1	3920
	11th to 20th	Night	45% 6% 12% 23% 15%	3899
	21st to end	Night	49% 4 10% 23% 13% 1	4306
November	1st to 10th	Night	57% 7% 11% 17% 8%	2774
	11th to 20th	Night	66% 7% 10% 12% 4	2940
	21st to end	Night	67% 7% 13% 11% 2	2940
December	1st to 10th	Night	77% 5% 8% 9% 1	4720
	11th to 20th	Night	71% 5% 8% 13% 2	5355
	21st to end	Night	72% 6% 7% 10% 5% 1	7597

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	40% 29% 25% 6%	220
	11th to 20th	Day	39% 25% 24% 9% 3	369
	21st to end	Day	29% 27% 34% 8% 2	473
February	1st to 10th	Day	32% 24% 30% 12% 2	430
	11th to 20th	Day	37% 27% 24% 10% 2	426
	21st to end	Day	31% 27% 28% 12% 2	394
March	1st to 10th	Day	34% 28% 30% 7% 1	540
	11th to 20th	Day	35% 28% 26% 9% 2	540
	21st to end	Day	38% 28% 22% 9% 2 1	594
April	1st to 10th	Day	40% 29% 23% 6% 2	504
	11th to 20th	Day	34% 27% 25% 11% 2	492
	21st to end	Day	32% 23% 28% 13% 4	500
May	1st to 10th	Day	31% 25% 30% 10% 3 1	503
	11th to 20th	Day	26% 19% 30% 18% 5% 1	699
	21st to end	Day	28% 19% 32% 16% 3 1	790
June	1st to 10th	Day	34% 16% 28% 18% 5%	730
	11th to 20th	Day	23% 17% 36% 18% 6% 1	730
	21st to end	Day	28% 16% 33% 18% 5% 1	730
July	1st to 10th	Day	22% 11% 39% 20% 6% 1	720
	11th to 20th	Day	20% 10% 36% 24% 9% 1	718
	21st to end	Day	20% 11% 41% 22% 6%	606
August	1st to 10th	Day	16% 11% 40% 26% 6% 1	526
	11th to 20th	Day	19% 14% 33% 22% 10% 2	519
	21st to end	Day	18% 15% 32% 25% 8% 2	583
September	1st to 10th	Day	19% 14% 38% 22% 6% 1	530
	11th to 20th	Day	21% 17% 31% 21% 8% 2	530
	21st to end	Day	21% 19% 30% 20% 8% 1	524
October	1st to 10th	Day	25% 15% 28% 22% 9% 2	420
	11th to 20th	Day	26% 20% 31% 16% 5% 2	420
	21st to end	Day	30% 24% 27% 13% 4 1	462
November	1st to 10th	Day	33% 23% 27% 13% 2 1	425
	11th to 20th	Day	40% 23% 21% 11% 3 1	430
	21st to end	Day	38% 25% 28% 6% 3	430
December	1st to 10th	Day	37% 26% 27% 10% 1	430
	11th to 20th	Day	46% 25% 21% 7% 1	430
	21st to end	Day	40% 24% 28% 6% 1 1	263
January	1st to 10th	Night	33% 25% 29% 12% 1	950
	11th to 20th	Night	37% 23% 26% 12% 3	867
	21st to end	Night	28% 28% 30% 11% 3	924
February	1st to 10th	Night	33% 24% 28% 13% 2	840
	11th to 20th	Night	36% 25% 26% 12% 1	823
	21st to end	Night	24% 27% 30% 17% 2	692
March	1st to 10th	Night	31% 25% 31% 12% 1	840
	11th to 20th	Night	29% 23% 29% 16% 3	840
	21st to end	Night	31% 23% 28% 14% 3	924
April	1st to 10th	Night	38% 20% 27% 14% 1	670
	11th to 20th	Night	29% 23% 32% 14% 2	594
	21st to end	Night	29% 22% 26% 19% 4	600
May	1st to 10th	Night	26% 19% 33% 18% 4 1	600
	11th to 20th	Night	26% 15% 32% 23% 4	592
	21st to end	Night	21% 15% 41% 19% 4 1	649
June	1st to 10th	Night	27% 15% 29% 24% 5%	527
	11th to 20th	Night	22% 10% 38% 25% 5%	400
	21st to end	Night	22% 11% 36% 24% 8%	400
July	1st to 10th	Night	17% 9% 43% 25% 5%	390
	11th to 20th	Night	20% 10% 35% 26% 9%	463
	21st to end	Night	17% 8% 36% 33% 5%	656
August	1st to 10th	Night	17% 10% 32% 32% 8% 1	598
	11th to 20th	Night	18% 8% 32% 30% 11% 1	592
	21st to end	Night	17% 10% 32% 31% 10%	660
September	1st to 10th	Night	17% 12% 33% 28% 10%	600
	11th to 20th	Night	20% 11% 28% 27% 11% 1	761
	21st to end	Night	21% 14% 31% 25% 9% 1	800
October	1st to 10th	Night	22% 12% 30% 28% 8%	800
	11th to 20th	Night	24% 20% 29% 19% 7% 1	800
	21st to end	Night	33% 23% 23% 17% 4	880
November	1st to 10th	Night	34% 19% 27% 16% 4 1	877
	11th to 20th	Night	36% 22% 23% 14% 5%	950
	21st to end	Night	35% 23% 24% 15% 2	950
December	1st to 10th	Night	34% 23% 28% 13% 2	950
	11th to 20th	Night	37% 27% 25% 9% 2	950
	21st to end	Night	36% 26% 24% 11% 2	1045

Page generated at 2026-03-30 03:18:43. Version ac07

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