Birdton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Birdton clear sky chart from 2005-11-06 to 2026-06-01.

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% 10% 3 8% 5% 4 4 4 5% 7% 31%	131875
	Night	19% 10% 3 7% 5% 4 4 4 5% 6% 33%	131401
Transparency	Day	51% 6% 12% 20% 10% 1	135374
	Night	50% 6% 12% 21% 11% 1	135990
Seeing	Day	28% 17% 30% 17% 7% 1	18303
	Night	26% 15% 30% 23% 6%	26276

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	11% 17% 6% 12% 7% 5% 5% 4 5% 5% 24%	4093
	11th to 20th	Day	14% 15% 6% 14% 7% 6% 4 3 4 4 23%	4572
	21st to end	Day	8% 9% 3 8% 5% 6% 6% 5% 7% 9% 34%	5423
February	1st to 10th	Day	14% 11% 4 9% 7% 6% 5% 4 4 6% 30%	1890
	11th to 20th	Day	15% 13% 4 9% 6% 5% 5% 4 5% 6% 28%	1843
	21st to end	Day	11% 14% 4 9% 6% 4 5% 4 4 6% 33%	1693
March	1st to 10th	Day	25% 13% 3 9% 6% 3 3 3 4 5% 26%	4797
	11th to 20th	Day	19% 16% 4 9% 5% 4 4 3 5% 5% 25%	5090
	21st to end	Day	26% 13% 4 9% 4 5% 4 3 5% 6% 21%	5587
April	1st to 10th	Day	22% 15% 3 7% 4 4 4 3 5% 5% 28%	2473
	11th to 20th	Day	22% 11% 3 7% 4 4 3 3 5% 6% 32%	2702
	21st to end	Day	25% 10% 2 7% 4 4 4 4 4 5% 32%	2730
May	1st to 10th	Day	24% 12% 3 8% 5% 4 5% 4 5% 5% 24%	6016
	11th to 20th	Day	25% 9% 3 8% 5% 4 4 4 5% 6% 28%	6312
	21st to end	Day	21% 9% 2 7% 5% 4 5% 4 6% 7% 29%	7425
June	1st to 10th	Day	26% 8% 3 7% 5% 4 4 4 5% 7% 27%	3000
	11th to 20th	Day	22% 7% 3 6% 5% 4 4 4 5% 7% 33%	3000
	21st to end	Day	28% 8% 3 6% 5% 4 5% 4 5% 6% 27%	3000
July	1st to 10th	Day	16% 7% 3 7% 6% 5% 6% 5% 7% 9% 29%	6820
	11th to 20th	Day	18% 6% 2 6% 4 4 5% 4 6% 8% 37%	6787
	21st to end	Day	15% 6% 2 6% 5% 4 5% 4 6% 8% 39%	6699
August	1st to 10th	Day	20% 6% 3 7% 5% 5% 5% 4 6% 7% 33%	4235
	11th to 20th	Day	15% 8% 3 9% 5% 5% 5% 4 6% 8% 32%	4175
	21st to end	Day	14% 6% 2 5% 4 4 4 4 6% 8% 42%	4675
September	1st to 10th	Day	14% 5% 2 5% 4 4 5% 4 5% 9% 44%	2382
	11th to 20th	Day	18% 6% 2 5% 3 3 4 3 4 6% 46%	2200
	21st to end	Day	20% 5% 2 7% 4 4 3 3 4 6% 42%	2200
October	1st to 10th	Day	17% 8% 2 6% 4 4 4 3 5% 7% 40%	2050
	11th to 20th	Day	21% 7% 3 7% 4 4 4 3 5% 6% 36%	2000
	21st to end	Day	22% 10% 3 8% 5% 5% 3 3 4 6% 30%	2045
November	1st to 10th	Day	20% 11% 3 7% 4 4 3 4 5% 7% 33%	1790
	11th to 20th	Day	20% 9% 3 7% 4 4 3 3 7% 6% 32%	1680
	21st to end	Day	21% 11% 3 10% 4 4 4 4 4 6% 29%	1680
December	1st to 10th	Day	20% 11% 3 8% 4 5% 4 4 5% 7% 29%	2570
	11th to 20th	Day	22% 12% 2 8% 5% 4 4 3 4 4 32%	2688
	21st to end	Day	18% 13% 5% 7% 5% 5% 4 2 3 4 34%	3553
January	1st to 10th	Night	13% 15% 5% 9% 5% 5% 5% 4 6% 7% 27%	8831
	11th to 20th	Night	18% 14% 5% 10% 7% 5% 5% 3 5% 6% 23%	8313
	21st to end	Night	8% 11% 4 8% 5% 6% 5% 5% 6% 7% 36%	8742
February	1st to 10th	Night	13% 13% 3 9% 5% 4 4 4 6% 6% 33%	2730
	11th to 20th	Night	15% 12% 4 9% 5% 6% 5% 4 6% 6% 29%	2663
	21st to end	Night	14% 13% 3 7% 6% 5% 5% 4 5% 5% 34%	2108
March	1st to 10th	Night	23% 12% 5% 9% 5% 5% 5% 3 4 4 26%	5262
	11th to 20th	Night	21% 12% 3 7% 5% 5% 4 4 6% 7% 27%	5089
	21st to end	Night	30% 11% 3 6% 3 4 3 3 4 6% 28%	5587
April	1st to 10th	Night	24% 12% 3 6% 4 5% 3 3 4 5% 31%	2142
	11th to 20th	Night	24% 8% 3 6% 3 4 3 3 4 6% 35%	1868
	21st to end	Night	24% 10% 2 6% 5% 3 4 4 4 7% 31%	1890
May	1st to 10th	Night	24% 11% 3 7% 5% 4 4 4 5% 6% 26%	4144
	11th to 20th	Night	22% 8% 2 6% 4 5% 5% 4 4 7% 33%	3816
	21st to end	Night	19% 9% 2 6% 4 4 4 3 6% 7% 35%	3756
June	1st to 10th	Night	26% 6% 3 6% 5% 5% 4 4 4 7% 30%	1400
	11th to 20th	Night	18% 7% 3 6% 5% 4 6% 3 6% 7% 35%	1400
	21st to end	Night	27% 6% 2 7% 6% 4 3 3 5% 6% 32%	1400
July	1st to 10th	Night	19% 7% 2 6% 5% 5% 5% 3 6% 7% 33%	3160
	11th to 20th	Night	18% 5% 2 6% 5% 5% 5% 3 6% 8% 36%	3175
	21st to end	Night	14% 5% 2 5% 4 5% 5% 5% 6% 8% 41%	4108
August	1st to 10th	Night	19% 6% 2 9% 5% 6% 5% 4 5% 8% 32%	2915
	11th to 20th	Night	14% 7% 3 8% 5% 4 5% 4 6% 9% 35%	2872
	21st to end	Night	16% 6% 2 5% 3 3 4 4 5% 7% 45%	3223
September	1st to 10th	Night	17% 5% 2 4 3 3 3 3 6% 7% 46%	2015
	11th to 20th	Night	16% 6% 2 6% 2 3 4 3 5% 6% 49%	2200
	21st to end	Night	20% 4 2 4 4 4 4 3 5% 5% 45%	2200
October	1st to 10th	Night	19% 6% 2 6% 4 3 3 3 4 6% 44%	2350
	11th to 20th	Night	19% 7% 2 8% 4 4 4 4 5% 7% 37%	2400
	21st to end	Night	22% 10% 2 7% 4 4 4 3 4 5% 34%	2790
November	1st to 10th	Night	21% 8% 3 5% 4 4 3 3 5% 6% 36%	2726
	11th to 20th	Night	20% 8% 3 6% 5% 4 4 4 6% 6% 34%	2940
	21st to end	Night	21% 10% 3 8% 5% 4 4 4 5% 7% 29%	2940
December	1st to 10th	Night	18% 10% 4 8% 5% 3 4 4 5% 7% 32%	4838
	11th to 20th	Night	24% 10% 3 6% 4 4 4 3 5% 6% 32%	5741
	21st to end	Night	19% 14% 4 9% 4 4 4 3 4 4 32%	7667

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% 7% 11% 15% 9%	4094
	11th to 20th	Day	62% 5% 12% 14% 7% 1	4602
	21st to end	Day	42% 7% 9% 23% 17% 2	5423
February	1st to 10th	Day	53% 5% 11% 19% 10% 2	1890
	11th to 20th	Day	54% 5% 11% 20% 9% 1	1851
	21st to end	Day	50% 4 11% 22% 10% 2	1693
March	1st to 10th	Day	60% 4 9% 12% 12% 3	4801
	11th to 20th	Day	60% 5% 12% 14% 7% 2	5090
	21st to end	Day	61% 4 5% 18% 9% 2	5587
April	1st to 10th	Day	58% 3 9% 16% 12% 2	2473
	11th to 20th	Day	51% 5% 10% 22% 11% 1	2702
	21st to end	Day	54% 4 9% 16% 12% 5%	2730
May	1st to 10th	Day	60% 6% 7% 18% 8% 1	6027
	11th to 20th	Day	55% 7% 11% 19% 6% 2	6316
	21st to end	Day	52% 7% 10% 17% 14%	7425
June	1st to 10th	Day	56% 6% 10% 17% 10% 1	3000
	11th to 20th	Day	49% 6% 12% 20% 13% 1	3000
	21st to end	Day	57% 7% 9% 17% 9% 1	3000
July	1st to 10th	Day	48% 8% 16% 19% 8%	6745
	11th to 20th	Day	42% 8% 15% 27% 9%	6706
	21st to end	Day	41% 7% 14% 30% 9%	6507
August	1st to 10th	Day	50% 6% 13% 24% 6%	4222
	11th to 20th	Day	47% 8% 15% 23% 6%	4214
	21st to end	Day	38% 6% 14% 26% 15%	4675
September	1st to 10th	Day	37% 7% 14% 28% 14%	2382
	11th to 20th	Day	39% 5% 10% 29% 15% 1	2200
	21st to end	Day	42% 6% 9% 27% 15% 1	2200
October	1st to 10th	Day	47% 5% 13% 27% 8%	3336
	11th to 20th	Day	45% 5% 12% 29% 8%	3240
	21st to end	Day	42% 5% 15% 23% 16%	3282
November	1st to 10th	Day	51% 5% 12% 20% 11% 1	1790
	11th to 20th	Day	49% 5% 15% 17% 12% 1	1680
	21st to end	Day	56% 5% 13% 19% 6%	1680
December	1st to 10th	Day	52% 5% 18% 17% 7%	2570
	11th to 20th	Day	55% 4 8% 18% 10% 4	2688
	21st to end	Day	53% 5% 11% 16% 12% 3	3553
January	1st to 10th	Night	54% 6% 13% 19% 8%	8831
	11th to 20th	Night	59% 5% 11% 17% 7% 1	8358
	21st to end	Night	44% 6% 8% 24% 17% 2	8742
February	1st to 10th	Night	50% 6% 12% 20% 12% 2	2730
	11th to 20th	Night	53% 5% 11% 19% 11% 1	2666
	21st to end	Night	51% 6% 8% 21% 12% 2	2108
March	1st to 10th	Night	62% 4 6% 13% 12% 3	5271
	11th to 20th	Night	55% 7% 16% 14% 7% 1	5090
	21st to end	Night	58% 3 6% 18% 13% 1	5587
April	1st to 10th	Night	56% 4 8% 17% 11% 4	2142
	11th to 20th	Night	50% 5% 9% 20% 14% 1	1868
	21st to end	Night	53% 5% 9% 18% 13% 2	1890
May	1st to 10th	Night	56% 7% 10% 16% 10% 1	4150
	11th to 20th	Night	50% 7% 11% 22% 7% 2	3817
	21st to end	Night	46% 9% 14% 20% 9% 1	3757
June	1st to 10th	Night	55% 6% 10% 19% 10% 1	1400
	11th to 20th	Night	47% 7% 11% 24% 10% 2	1400
	21st to end	Night	54% 6% 12% 19% 9% 1	1400
July	1st to 10th	Night	48% 7% 14% 22% 9%	3125
	11th to 20th	Night	44% 8% 14% 29% 5%	3133
	21st to end	Night	38% 9% 15% 27% 10%	3986
August	1st to 10th	Night	50% 8% 13% 22% 7%	2903
	11th to 20th	Night	43% 9% 19% 23% 6%	2899
	21st to end	Night	37% 7% 15% 23% 17% 1	3223
September	1st to 10th	Night	36% 6% 13% 30% 13% 1	2015
	11th to 20th	Night	38% 5% 12% 30% 16% 1	2200
	21st to end	Night	41% 5% 11% 26% 15% 1	2200
October	1st to 10th	Night	46% 5% 12% 24% 13%	3844
	11th to 20th	Night	40% 6% 12% 29% 12%	3899
	21st to end	Night	43% 5% 17% 22% 13%	4503
November	1st to 10th	Night	48% 6% 13% 22% 10% 1	2726
	11th to 20th	Night	49% 5% 13% 21% 10% 1	2940
	21st to end	Night	54% 6% 14% 16% 9% 1	2940
December	1st to 10th	Night	49% 5% 12% 25% 7%	4838
	11th to 20th	Night	51% 5% 10% 20% 13% 1	5742
	21st to end	Night	55% 4 9% 18% 10% 3	7667

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	32% 20% 33% 13% 3	220
	11th to 20th	Day	36% 22% 29% 8% 4	220
	21st to end	Day	23% 21% 35% 16% 4 1	347
February	1st to 10th	Day	27% 19% 32% 16% 4 1	430
	11th to 20th	Day	31% 22% 30% 14% 3 1	426
	21st to end	Day	27% 23% 30% 17% 3	427
March	1st to 10th	Day	32% 22% 32% 11% 2 1	540
	11th to 20th	Day	33% 21% 29% 13% 4 1	540
	21st to end	Day	35% 21% 26% 12% 5% 1	594
April	1st to 10th	Day	41% 23% 23% 10% 2	540
	11th to 20th	Day	36% 20% 29% 10% 4 1	532
	21st to end	Day	32% 19% 30% 12% 6% 1	540
May	1st to 10th	Day	36% 19% 27% 13% 3 1	543
	11th to 20th	Day	30% 18% 28% 18% 5% 1	706
	21st to end	Day	27% 19% 33% 14% 7%	845
June	1st to 10th	Day	32% 16% 28% 17% 6% 1	730
	11th to 20th	Day	29% 14% 28% 20% 8% 1	730
	21st to end	Day	31% 12% 31% 18% 8% 1	730
July	1st to 10th	Day	22% 13% 36% 20% 9% 1	720
	11th to 20th	Day	21% 9% 33% 25% 11% 1	711
	21st to end	Day	19% 10% 38% 24% 8% 1	576
August	1st to 10th	Day	17% 10% 34% 26% 10% 2	526
	11th to 20th	Day	18% 10% 27% 29% 13% 3	519
	21st to end	Day	20% 13% 28% 25% 11% 3	583
September	1st to 10th	Day	14% 13% 35% 24% 11% 3	530
	11th to 20th	Day	23% 11% 29% 23% 11% 3	530
	21st to end	Day	21% 17% 28% 18% 12% 4	530
October	1st to 10th	Day	21% 17% 22% 26% 11% 3	447
	11th to 20th	Day	27% 16% 28% 17% 9% 3	420
	21st to end	Day	30% 19% 32% 13% 6%	462
November	1st to 10th	Day	30% 16% 31% 16% 6%	425
	11th to 20th	Day	32% 20% 27% 15% 6%	430
	21st to end	Day	34% 20% 27% 14% 3	430
December	1st to 10th	Day	33% 17% 28% 18% 2	362
	11th to 20th	Day	41% 23% 24% 10% 1	220
	21st to end	Day	33% 22% 26% 16% 4	242
January	1st to 10th	Night	25% 21% 30% 20% 3	950
	11th to 20th	Night	29% 17% 29% 21% 3	854
	21st to end	Night	21% 21% 35% 19% 4	924
February	1st to 10th	Night	23% 21% 32% 20% 4	840
	11th to 20th	Night	27% 22% 31% 16% 4	823
	21st to end	Night	23% 20% 32% 21% 4	692
March	1st to 10th	Night	26% 20% 33% 19% 2	840
	11th to 20th	Night	26% 17% 31% 21% 5%	840
	21st to end	Night	27% 16% 33% 19% 5%	924
April	1st to 10th	Night	34% 19% 28% 16% 3	755
	11th to 20th	Night	31% 17% 32% 15% 4	624
	21st to end	Night	32% 13% 30% 20% 6%	630
May	1st to 10th	Night	29% 14% 30% 23% 3	630
	11th to 20th	Night	29% 14% 32% 20% 4	622
	21st to end	Night	21% 15% 35% 25% 4	558
June	1st to 10th	Night	28% 7% 30% 30% 6%	400
	11th to 20th	Night	21% 10% 30% 31% 7% 1	400
	21st to end	Night	30% 6% 27% 32% 5% 1	400
July	1st to 10th	Night	18% 6% 39% 30% 7%	390
	11th to 20th	Night	19% 5% 27% 38% 11% 1	388
	21st to end	Night	21% 5% 30% 35% 9%	518
August	1st to 10th	Night	17% 5% 26% 38% 13%	598
	11th to 20th	Night	17% 7% 28% 34% 15%	592
	21st to end	Night	16% 7% 29% 30% 17% 1	660
September	1st to 10th	Night	19% 8% 35% 27% 10%	648
	11th to 20th	Night	19% 10% 24% 32% 15% 1	800
	21st to end	Night	23% 11% 27% 28% 10% 1	800
October	1st to 10th	Night	22% 11% 29% 28% 9% 1	800
	11th to 20th	Night	23% 12% 29% 25% 10% 1	800
	21st to end	Night	28% 17% 30% 20% 5%	880
November	1st to 10th	Night	30% 15% 27% 22% 5%	851
	11th to 20th	Night	29% 16% 30% 19% 6% 1	950
	21st to end	Night	30% 18% 27% 20% 5% 1	950
December	1st to 10th	Night	33% 15% 27% 21% 3 1	950
	11th to 20th	Night	32% 20% 29% 17% 2	950
	21st to end	Night	30% 20% 28% 18% 3	1045

Page generated at 2026-05-29 02:53:32. Version ac07

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