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 2024-12-09.

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	19% 12% 4 9% 5% 4 4 3 4 6% 29%	101976
	Night	19% 14% 5% 11% 6% 4 4 3 4 5% 25%	97850
Transparency	Day	55% 7% 11% 17% 9% 1	105546
	Night	59% 7% 11% 15% 7% 1	102369
Seeing	Day	29% 20% 30% 16% 5% 1	16915
	Night	28% 19% 29% 18% 5%	24639

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	15% 21% 7% 16% 12% 4 3 2 2 3 15%	2207
	11th to 20th	Day	16% 19% 8% 26% 6% 5% 3 2 3 2 9%	2656
	21st to end	Day	17% 15% 8% 18% 11% 6% 3 2 3 3 13%	3124
February	1st to 10th	Day	17% 18% 9% 15% 11% 5% 4 2 3 3 11%	1710
	11th to 20th	Day	15% 17% 6% 16% 12% 6% 4 2 3 3 15%	1663
	21st to end	Day	11% 17% 7% 12% 8% 5% 4 3 3 5% 27%	1479
March	1st to 10th	Day	23% 19% 5% 9% 7% 5% 3 2 3 4 20%	3387
	11th to 20th	Day	14% 21% 5% 12% 6% 4 4 3 4 4 24%	3480
	21st to end	Day	27% 16% 6% 11% 5% 3 3 2 3 3 21%	3816
April	1st to 10th	Day	21% 17% 4 8% 4 3 3 3 5% 5% 27%	2217
	11th to 20th	Day	19% 13% 2 6% 3 3 3 2 5% 6% 37%	2399
	21st to end	Day	21% 13% 3 6% 5% 4 3 3 4 6% 33%	2470
May	1st to 10th	Day	21% 17% 3 7% 5% 4 4 3 5% 6% 25%	4106
	11th to 20th	Day	18% 9% 3 8% 5% 5% 4 3 6% 7% 32%	4361
	21st to end	Day	16% 8% 3 7% 4 4 4 4 6% 8% 37%	4836
June	1st to 10th	Day	24% 9% 2 6% 5% 4 4 4 5% 6% 30%	2743
	11th to 20th	Day	20% 8% 2 6% 4 4 4 4 6% 7% 36%	2850
	21st to end	Day	23% 10% 3 8% 5% 5% 4 3 5% 6% 30%	2850
July	1st to 10th	Day	20% 8% 3 6% 4 4 4 4 6% 7% 35%	4760
	11th to 20th	Day	21% 8% 3 5% 4 3 4 3 5% 8% 35%	4602
	21st to end	Day	15% 8% 3 6% 4 4 5% 4 6% 8% 35%	4509
August	1st to 10th	Day	21% 10% 3 8% 4 4 5% 4 5% 5% 31%	4105
	11th to 20th	Day	13% 7% 3 7% 4 5% 5% 4 6% 7% 40%	4045
	21st to end	Day	11% 5% 2 5% 3 3 4 4 5% 7% 50%	4446
September	1st to 10th	Day	18% 6% 2 5% 3 3 4 3 4 6% 47%	2280
	11th to 20th	Day	16% 6% 2 7% 3 3 4 2 4 6% 47%	2123
	21st to end	Day	20% 7% 3 5% 3 2 3 3 4 6% 44%	2081
October	1st to 10th	Day	19% 8% 3 5% 4 4 4 3 5% 7% 38%	1900
	11th to 20th	Day	20% 11% 3 8% 3 3 4 3 5% 7% 34%	1900
	21st to end	Day	21% 14% 2 8% 4 4 4 3 3 5% 31%	2061
November	1st to 10th	Day	20% 15% 4 9% 4 4 3 3 4 5% 28%	1657
	11th to 20th	Day	19% 20% 8% 8% 6% 4 4 2 3 5% 21%	1600
	21st to end	Day	19% 22% 7% 13% 5% 4 3 3 4 4 16%	1600
December	1st to 10th	Day	22% 24% 7% 14% 4 3 2 2 4 4 14%	1584
	11th to 20th	Day	25% 18% 7% 16% 8% 4 3 2 3 3 10%	1906
	21st to end	Day	22% 19% 10% 17% 7% 3 2 2 3 3 11%	2463
January	1st to 10th	Night	15% 17% 9% 20% 9% 4 3 3 3 2 14%	4748
	11th to 20th	Night	16% 21% 7% 21% 7% 5% 3 2 3 4 11%	4300
	21st to end	Night	17% 14% 7% 17% 11% 5% 4 3 5% 5% 12%	4532
February	1st to 10th	Night	18% 18% 7% 19% 9% 5% 3 3 3 3 11%	2470
	11th to 20th	Night	18% 15% 6% 17% 12% 5% 3 3 3 4 14%	2403
	21st to end	Night	11% 16% 7% 12% 8% 6% 4 4 5% 5% 23%	1975
March	1st to 10th	Night	21% 17% 5% 13% 8% 5% 3 2 3 4 20%	3452
	11th to 20th	Night	14% 22% 7% 12% 6% 5% 5% 3 4 4 17%	3479
	21st to end	Night	24% 14% 7% 12% 6% 4 3 2 3 3 23%	3816
April	1st to 10th	Night	24% 16% 3 7% 5% 4 4 3 4 4 27%	1962
	11th to 20th	Night	22% 13% 3 5% 4 4 4 3 6% 6% 30%	1726
	21st to end	Night	21% 14% 3 7% 5% 4 4 3 4 5% 30%	1710
May	1st to 10th	Night	19% 18% 4 7% 5% 4 4 3 5% 6% 26%	2834
	11th to 20th	Night	19% 9% 3 7% 5% 5% 5% 4 6% 7% 30%	2541
	21st to end	Night	14% 10% 3 9% 5% 5% 5% 4 5% 8% 31%	2749
June	1st to 10th	Night	25% 9% 2 6% 4 5% 3 4 6% 7% 29%	1451
	11th to 20th	Night	22% 6% 3 6% 4 4 3 4 6% 6% 35%	1330
	21st to end	Night	20% 7% 3 7% 6% 6% 5% 4 5% 8% 29%	1330
July	1st to 10th	Night	20% 11% 3 8% 4 4 5% 4 6% 7% 28%	2210
	11th to 20th	Night	21% 9% 3 6% 4 4 4 5% 7% 7% 30%	2333
	21st to end	Night	13% 7% 3 8% 5% 4 5% 4 7% 7% 38%	3043
August	1st to 10th	Night	23% 9% 3 7% 4 4 4 3 5% 7% 32%	2825
	11th to 20th	Night	15% 7% 3 7% 5% 5% 5% 4 7% 7% 34%	2782
	21st to end	Night	11% 7% 2 6% 4 3 4 3 6% 8% 46%	3210
September	1st to 10th	Night	14% 6% 2 4 5% 5% 4 3 5% 7% 44%	1900
	11th to 20th	Night	19% 6% 2 4 3 3 3 3 5% 6% 44%	2053
	21st to end	Night	17% 7% 2 6% 5% 4 4 4 5% 6% 39%	2098
October	1st to 10th	Night	20% 7% 3 7% 3 4 4 3 5% 6% 39%	2280
	11th to 20th	Night	17% 10% 3 7% 5% 4 4 3 5% 7% 36%	2280
	21st to end	Night	25% 13% 3 7% 4 4 3 3 4 4 29%	2536
November	1st to 10th	Night	21% 13% 4 7% 5% 5% 3 3 4 5% 30%	2639
	11th to 20th	Night	18% 23% 6% 9% 5% 4 4 3 4 5% 21%	2800
	21st to end	Night	19% 22% 7% 10% 5% 4 3 3 4 4 20%	2800
December	1st to 10th	Night	23% 21% 7% 15% 5% 3 3 3 3 4 12%	2779
	11th to 20th	Night	22% 20% 7% 17% 8% 4 3 2 3 3 12%	3293
	21st to end	Night	25% 20% 8% 13% 5% 3 2 2 3 3 17%	5181

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	72% 8% 14% 5% 1	2208
	11th to 20th	Day	79% 7% 7% 5% 1	2656
	21st to end	Day	69% 10% 13% 6% 2	3124
February	1st to 10th	Day	78% 5% 8% 5% 3	1710
	11th to 20th	Day	75% 6% 7% 8% 3	1671
	21st to end	Day	62% 5% 11% 15% 6% 1	1479
March	1st to 10th	Day	68% 5% 8% 13% 4 1	3391
	11th to 20th	Day	60% 8% 12% 12% 6% 1	3480
	21st to end	Day	70% 4 5% 11% 8% 1	3816
April	1st to 10th	Day	60% 6% 8% 13% 11% 2	2217
	11th to 20th	Day	49% 5% 10% 22% 12% 1	2399
	21st to end	Day	53% 5% 11% 17% 12% 3	2470
May	1st to 10th	Day	56% 9% 11% 17% 6% 1	4120
	11th to 20th	Day	47% 10% 16% 18% 8% 1	4365
	21st to end	Day	43% 10% 17% 17% 13%	4836
June	1st to 10th	Day	54% 7% 10% 20% 9%	2743
	11th to 20th	Day	47% 7% 14% 18% 12% 1	2850
	21st to end	Day	57% 8% 9% 16% 10% 1	2850
July	1st to 10th	Day	49% 6% 13% 19% 12% 1	4685
	11th to 20th	Day	47% 6% 13% 24% 9%	4521
	21st to end	Day	45% 8% 14% 22% 10% 1	4365
August	1st to 10th	Day	55% 8% 9% 18% 10%	4092
	11th to 20th	Day	43% 7% 15% 23% 11%	4084
	21st to end	Day	33% 6% 14% 26% 19% 1	4446
September	1st to 10th	Day	39% 6% 12% 26% 14% 2	2280
	11th to 20th	Day	40% 5% 11% 25% 17% 1	2123
	21st to end	Day	42% 5% 9% 25% 16% 2	2081
October	1st to 10th	Day	46% 6% 11% 26% 11%	3160
	11th to 20th	Day	47% 5% 9% 25% 14%	3140
	21st to end	Day	48% 3 13% 21% 13% 1	3375
November	1st to 10th	Day	58% 6% 12% 16% 7%	1657
	11th to 20th	Day	66% 6% 11% 13% 4 1	1600
	21st to end	Day	72% 6% 10% 10% 2	1600
December	1st to 10th	Day	76% 6% 8% 7% 2	1584
	11th to 20th	Day	79% 7% 6% 6% 2	1905
	21st to end	Day	77% 7% 10% 4 2	2463
January	1st to 10th	Night	73% 9% 9% 8% 1	4748
	11th to 20th	Night	75% 8% 8% 6% 2	4300
	21st to end	Night	71% 8% 11% 8% 2	4532
February	1st to 10th	Night	78% 5% 7% 6% 4	2470
	11th to 20th	Night	74% 6% 8% 8% 3	2406
	21st to end	Night	63% 6% 11% 13% 6% 1	1975
March	1st to 10th	Night	69% 7% 7% 11% 6% 1	3461
	11th to 20th	Night	64% 10% 10% 9% 5% 1	3480
	21st to end	Night	67% 5% 7% 12% 7% 1	3816
April	1st to 10th	Night	61% 5% 9% 13% 10% 2	1962
	11th to 20th	Night	52% 6% 10% 19% 12% 1	1726
	21st to end	Night	55% 7% 9% 15% 13% 1	1710
May	1st to 10th	Night	57% 9% 13% 16% 6%	2840
	11th to 20th	Night	49% 12% 15% 19% 6% 1	2542
	21st to end	Night	48% 13% 17% 17% 6%	2750
June	1st to 10th	Night	53% 8% 12% 19% 7%	1451
	11th to 20th	Night	47% 8% 13% 21% 9% 1	1330
	21st to end	Night	54% 9% 12% 15% 8% 2	1330
July	1st to 10th	Night	53% 8% 13% 16% 11%	2175
	11th to 20th	Night	51% 8% 17% 15% 9%	2291
	21st to end	Night	43% 8% 13% 23% 12% 1	2947
August	1st to 10th	Night	52% 7% 12% 21% 7%	2813
	11th to 20th	Night	45% 8% 17% 22% 7%	2809
	21st to end	Night	33% 8% 16% 25% 16% 1	3209
September	1st to 10th	Night	39% 8% 12% 26% 14% 1	1900
	11th to 20th	Night	40% 6% 11% 27% 15% 1	2053
	21st to end	Night	44% 7% 10% 23% 14% 2	2098
October	1st to 10th	Night	48% 5% 12% 23% 11% 1	3800
	11th to 20th	Night	44% 6% 12% 23% 15%	3779
	21st to end	Night	49% 4 10% 23% 13% 1	4172
November	1st to 10th	Night	56% 7% 12% 17% 8%	2639
	11th to 20th	Night	65% 8% 10% 12% 5%	2800
	21st to end	Night	67% 7% 13% 11% 2	2800
December	1st to 10th	Night	76% 6% 9% 8% 1	2779
	11th to 20th	Night	77% 5% 7% 9% 2	3295
	21st to end	Night	72% 6% 8% 10% 2	5181

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	39% 28% 26% 7%	180
	11th to 20th	Day	39% 25% 25% 8% 3	314
	21st to end	Day	26% 28% 35% 9% 2	407
February	1st to 10th	Day	33% 23% 31% 11% 1 1	370
	11th to 20th	Day	37% 29% 22% 10% 2	366
	21st to end	Day	29% 27% 30% 13% 2	339
March	1st to 10th	Day	33% 27% 30% 8% 1	460
	11th to 20th	Day	34% 28% 26% 9% 2	460
	21st to end	Day	36% 28% 23% 10% 3 1	506
April	1st to 10th	Day	38% 29% 24% 7% 2	460
	11th to 20th	Day	32% 28% 26% 12% 2	452
	21st to end	Day	32% 22% 28% 14% 4	460
May	1st to 10th	Day	31% 25% 29% 10% 4 1	463
	11th to 20th	Day	26% 19% 30% 20% 6%	650
	21st to end	Day	27% 19% 33% 17% 3 1	735
June	1st to 10th	Day	34% 16% 28% 18% 5%	680
	11th to 20th	Day	23% 16% 36% 18% 6% 1	680
	21st to end	Day	28% 15% 33% 18% 5% 1	680
July	1st to 10th	Day	22% 11% 39% 21% 6% 1	670
	11th to 20th	Day	20% 9% 38% 23% 9% 1	668
	21st to end	Day	20% 11% 40% 23% 6%	561
August	1st to 10th	Day	17% 11% 39% 26% 6% 1	486
	11th to 20th	Day	20% 15% 33% 20% 10% 2	479
	21st to end	Day	17% 14% 32% 27% 8% 2	539
September	1st to 10th	Day	19% 14% 38% 22% 7% 1	490
	11th to 20th	Day	22% 17% 30% 21% 8% 2	490
	21st to end	Day	22% 19% 29% 20% 8% 1	485
October	1st to 10th	Day	25% 15% 27% 22% 9% 2	390
	11th to 20th	Day	27% 21% 29% 17% 5% 2	390
	21st to end	Day	30% 25% 27% 14% 4 1	429
November	1st to 10th	Day	31% 24% 28% 14% 2 1	395
	11th to 20th	Day	41% 23% 21% 12% 3 1	400
	21st to end	Day	37% 25% 29% 6% 3	400
December	1st to 10th	Day	36% 27% 26% 11% 1	394
	11th to 20th	Day	46% 26% 21% 6% 1	370
	21st to end	Day	41% 25% 27% 6% 1 1	217
January	1st to 10th	Night	34% 24% 29% 12% 1	850
	11th to 20th	Night	36% 24% 26% 12% 3	783
	21st to end	Night	27% 27% 31% 12% 3	836
February	1st to 10th	Night	34% 24% 28% 13% 2	760
	11th to 20th	Night	36% 26% 26% 11% 1	743
	21st to end	Night	23% 27% 31% 17% 2	628
March	1st to 10th	Night	30% 25% 31% 13% 1	760
	11th to 20th	Night	29% 23% 29% 16% 3	760
	21st to end	Night	30% 23% 28% 15% 4	836
April	1st to 10th	Night	37% 20% 28% 14% 2	632
	11th to 20th	Night	28% 23% 32% 15% 2	564
	21st to end	Night	29% 22% 26% 19% 4	570
May	1st to 10th	Night	26% 18% 33% 18% 4 1	570
	11th to 20th	Night	26% 15% 32% 23% 4	562
	21st to end	Night	20% 16% 41% 19% 4 1	616
June	1st to 10th	Night	27% 15% 30% 23% 5%	501
	11th to 20th	Night	23% 10% 37% 25% 5%	380
	21st to end	Night	22% 11% 36% 23% 8%	380
July	1st to 10th	Night	16% 9% 43% 26% 6%	370
	11th to 20th	Night	20% 11% 35% 25% 9%	439
	21st to end	Night	17% 8% 36% 34% 6%	623
August	1st to 10th	Night	17% 10% 33% 31% 8% 1	568
	11th to 20th	Night	19% 9% 32% 29% 11% 1	562
	21st to end	Night	17% 9% 32% 31% 11%	627
September	1st to 10th	Night	18% 12% 33% 28% 10%	570
	11th to 20th	Night	21% 11% 28% 27% 11% 1	723
	21st to end	Night	21% 14% 31% 25% 9% 1	760
October	1st to 10th	Night	23% 11% 29% 28% 9%	760
	11th to 20th	Night	22% 21% 30% 19% 7% 1	760
	21st to end	Night	33% 23% 23% 17% 3	836
November	1st to 10th	Night	32% 19% 27% 17% 5% 1	832
	11th to 20th	Night	35% 23% 22% 14% 5%	900
	21st to end	Night	35% 22% 25% 16% 2	900
December	1st to 10th	Night	34% 23% 28% 13% 2	893
	11th to 20th	Night	37% 27% 25% 8% 2	850
	21st to end	Night	37% 26% 24% 10% 2	935

Page generated at 2024-12-06 04:54:54. Version ac07

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