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 2025-02-06.

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 7% 5% 4 4 4 5% 6% 32%	108086
	Night	19% 10% 3 7% 5% 4 4 3 5% 6% 33%	110251
Transparency	Day	50% 6% 12% 20% 10% 1	111632
	Night	49% 6% 12% 21% 11% 1	114870
Seeing	Day	28% 16% 30% 18% 7% 1	16507
	Night	26% 15% 30% 23% 6%	24570

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% 17% 7% 12% 7% 4 5% 4 4 4 24%	3157
	11th to 20th	Day	12% 14% 6% 13% 7% 6% 4 3 4 5% 26%	3505
	21st to end	Day	9% 9% 2 8% 5% 6% 6% 5% 6% 8% 36%	4190
February	1st to 10th	Day	15% 12% 4 8% 6% 6% 5% 3 5% 6% 30%	1755
	11th to 20th	Day	15% 13% 4 9% 6% 5% 5% 4 5% 6% 28%	1663
	21st to end	Day	11% 15% 4 8% 6% 4 5% 3 4 6% 33%	1536
March	1st to 10th	Day	24% 14% 3 6% 4 3 3 3 5% 6% 29%	3263
	11th to 20th	Day	17% 19% 4 10% 6% 5% 4 3 4 5% 22%	3480
	21st to end	Day	28% 12% 4 8% 4 4 3 3 5% 6% 22%	3816
April	1st to 10th	Day	22% 15% 3 7% 4 4 4 3 5% 5% 28%	2237
	11th to 20th	Day	21% 10% 3 7% 4 4 3 3 5% 7% 34%	2442
	21st to end	Day	25% 10% 2 6% 4 4 4 4 4 5% 31%	2470
May	1st to 10th	Day	19% 11% 3 8% 5% 5% 5% 4 5% 6% 29%	4106
	11th to 20th	Day	21% 8% 3 8% 6% 4 4 4 5% 7% 30%	4297
	21st to end	Day	18% 8% 2 7% 5% 5% 5% 4 6% 8% 32%	5054
June	1st to 10th	Day	26% 8% 3 7% 5% 4 4 4 5% 6% 27%	2850
	11th to 20th	Day	22% 7% 3 6% 5% 4 4 4 4 7% 34%	2850
	21st to end	Day	28% 8% 3 6% 5% 4 5% 4 5% 6% 27%	2850
July	1st to 10th	Day	16% 7% 3 7% 6% 5% 6% 5% 7% 9% 31%	4760
	11th to 20th	Day	20% 6% 2 5% 4 5% 5% 4 6% 8% 35%	4741
	21st to end	Day	19% 7% 3 6% 5% 4 5% 4 6% 7% 36%	4657
August	1st to 10th	Day	21% 6% 3 7% 5% 5% 5% 4 6% 7% 31%	4105
	11th to 20th	Day	15% 9% 3 9% 5% 5% 5% 4 6% 8% 31%	4045
	21st to end	Day	14% 6% 2 5% 4 4 4 4 6% 8% 42%	4532
September	1st to 10th	Day	14% 5% 2 6% 5% 4 5% 4 5% 9% 43%	2264
	11th to 20th	Day	19% 6% 2 5% 3 3 4 3 4 6% 45%	2090
	21st to end	Day	21% 5% 2 7% 4 4 3 3 4 6% 42%	2090
October	1st to 10th	Day	18% 8% 3 6% 5% 4 4 3 5% 7% 38%	1948
	11th to 20th	Day	22% 7% 2 7% 4 4 4 3 5% 6% 36%	1900
	21st to end	Day	22% 10% 3 8% 6% 5% 3 3 4 6% 30%	1943
November	1st to 10th	Day	20% 10% 3 7% 4 4 3 4 4 7% 34%	1703
	11th to 20th	Day	21% 9% 3 7% 4 4 3 3 8% 7% 32%	1600
	21st to end	Day	21% 11% 3 10% 4 4 4 4 3 6% 30%	1600
December	1st to 10th	Day	20% 11% 3 8% 4 5% 4 4 5% 8% 29%	2493
	11th to 20th	Day	22% 12% 2 7% 5% 4 4 3 4 4 33%	2618
	21st to end	Day	18% 14% 5% 7% 5% 5% 4 2 3 4 33%	3476
January	1st to 10th	Night	13% 14% 6% 10% 5% 5% 5% 4 6% 7% 25%	6808
	11th to 20th	Night	15% 11% 5% 10% 7% 5% 5% 3 5% 6% 26%	6379
	21st to end	Night	9% 11% 3 7% 4 4 4 4 6% 8% 39%	6750
February	1st to 10th	Night	14% 14% 3 8% 5% 4 4 4 6% 6% 32%	2536
	11th to 20th	Night	15% 12% 4 9% 5% 6% 5% 4 6% 6% 28%	2403
	21st to end	Night	14% 13% 3 7% 6% 5% 5% 4 5% 5% 33%	1914
March	1st to 10th	Night	21% 12% 4 9% 5% 5% 6% 3 4 4 27%	3576
	11th to 20th	Night	20% 14% 4 7% 5% 5% 4 3 6% 6% 24%	3479
	21st to end	Night	30% 10% 3 7% 4 4 3 3 5% 6% 26%	3816
April	1st to 10th	Night	24% 12% 2 6% 4 5% 3 3 4 4 31%	1938
	11th to 20th	Night	23% 8% 3 6% 4 4 4 3 4 6% 37%	1688
	21st to end	Night	25% 9% 2 6% 4 4 3 3 4 7% 32%	1710
May	1st to 10th	Night	21% 9% 3 7% 5% 4 4 4 6% 7% 31%	2834
	11th to 20th	Night	19% 8% 3 6% 4 5% 5% 3 5% 7% 35%	2604
	21st to end	Night	17% 7% 2 6% 5% 5% 4 4 7% 8% 35%	2559
June	1st to 10th	Night	26% 7% 3 6% 5% 5% 4 4 4 7% 29%	1330
	11th to 20th	Night	18% 7% 3 6% 5% 4 5% 3 6% 7% 35%	1330
	21st to end	Night	28% 6% 2 7% 6% 4 3 3 5% 6% 32%	1330
July	1st to 10th	Night	17% 6% 2 5% 5% 5% 5% 4 7% 8% 36%	2210
	11th to 20th	Night	20% 6% 2 6% 5% 5% 4 3 6% 8% 35%	2225
	21st to end	Night	18% 6% 3 5% 4 4 4 4 6% 6% 40%	2865
August	1st to 10th	Night	19% 6% 2 9% 5% 6% 5% 4 6% 7% 31%	2825
	11th to 20th	Night	14% 8% 3 8% 5% 5% 5% 4 6% 9% 34%	2782
	21st to end	Night	16% 6% 2 5% 3 3 4 4 5% 7% 46%	3124
September	1st to 10th	Night	17% 5% 2 4 3 3 4 3 6% 7% 45%	1913
	11th to 20th	Night	16% 6% 2 6% 2 3 4 3 4 6% 48%	2090
	21st to end	Night	21% 4 2 4 4 4 4 3 5% 5% 44%	2090
October	1st to 10th	Night	20% 7% 2 6% 4 3 3 3 4 6% 42%	2232
	11th to 20th	Night	19% 7% 2 8% 4 4 4 4 5% 6% 37%	2280
	21st to end	Night	23% 10% 2 6% 4 4 4 3 4 6% 35%	2650
November	1st to 10th	Night	21% 8% 3 5% 4 4 3 4 5% 6% 37%	2593
	11th to 20th	Night	20% 8% 3 6% 5% 4 4 4 6% 6% 34%	2800
	21st to end	Night	21% 10% 3 8% 5% 4 4 3 6% 7% 29%	2800
December	1st to 10th	Night	18% 10% 4 8% 5% 3 4 4 5% 7% 32%	4695
	11th to 20th	Night	24% 10% 3 6% 4 4 4 3 5% 6% 33%	5591
	21st to end	Night	20% 14% 4 9% 4 4 4 3 4 4 32%	7502

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	59% 7% 12% 14% 6%	3158
	11th to 20th	Day	58% 5% 13% 18% 7% 1	3535
	21st to end	Day	44% 7% 9% 19% 19% 2	4190
February	1st to 10th	Day	53% 5% 10% 19% 11% 2	1755
	11th to 20th	Day	56% 5% 11% 18% 10% 1	1671
	21st to end	Day	51% 4 11% 22% 10% 3	1536
March	1st to 10th	Day	58% 4 10% 16% 9% 4	3267
	11th to 20th	Day	64% 5% 10% 13% 7% 2	3480
	21st to end	Day	63% 4 6% 17% 9% 2	3816
April	1st to 10th	Day	59% 3 8% 15% 12% 2	2237
	11th to 20th	Day	50% 4 10% 23% 11% 1	2442
	21st to end	Day	54% 4 9% 16% 12% 5%	2470
May	1st to 10th	Day	54% 7% 7% 22% 8% 1	4120
	11th to 20th	Day	51% 8% 12% 21% 7% 1	4301
	21st to end	Day	48% 9% 11% 18% 14%	5054
June	1st to 10th	Day	57% 6% 10% 17% 10% 1	2850
	11th to 20th	Day	49% 6% 12% 19% 13% 1	2850
	21st to end	Day	57% 7% 9% 16% 9% 1	2850
July	1st to 10th	Day	46% 8% 17% 19% 10%	4685
	11th to 20th	Day	45% 8% 13% 25% 8%	4660
	21st to end	Day	45% 7% 14% 25% 8%	4509
August	1st to 10th	Day	52% 6% 13% 23% 6%	4092
	11th to 20th	Day	48% 8% 15% 23% 6%	4084
	21st to end	Day	38% 6% 14% 26% 15%	4532
September	1st to 10th	Day	38% 8% 14% 27% 14%	2264
	11th to 20th	Day	40% 5% 10% 29% 14% 1	2090
	21st to end	Day	43% 6% 9% 26% 15% 1	2090
October	1st to 10th	Day	48% 5% 13% 26% 8%	3234
	11th to 20th	Day	45% 5% 12% 29% 8%	3140
	21st to end	Day	41% 5% 15% 22% 17%	3180
November	1st to 10th	Day	51% 5% 12% 20% 12% 1	1703
	11th to 20th	Day	49% 5% 15% 17% 13% 1	1600
	21st to end	Day	56% 5% 14% 19% 6%	1600
December	1st to 10th	Day	52% 5% 18% 17% 7%	2493
	11th to 20th	Day	54% 4 8% 18% 11% 4	2618
	21st to end	Day	53% 5% 11% 15% 12% 3	3476
January	1st to 10th	Night	55% 7% 15% 18% 5% 1	6808
	11th to 20th	Night	55% 6% 13% 19% 7%	6424
	21st to end	Night	42% 6% 8% 24% 18% 2	6750
February	1st to 10th	Night	51% 6% 12% 18% 12% 2	2536
	11th to 20th	Night	55% 5% 11% 17% 11% 2	2406
	21st to end	Night	52% 6% 9% 19% 11% 3	1914
March	1st to 10th	Night	61% 5% 7% 17% 9% 1	3585
	11th to 20th	Night	58% 8% 11% 15% 8% 1	3480
	21st to end	Night	60% 3 6% 17% 12% 2	3816
April	1st to 10th	Night	56% 5% 8% 17% 11% 4	1938
	11th to 20th	Night	48% 5% 9% 20% 15% 2	1688
	21st to end	Night	53% 5% 9% 18% 12% 2	1710
May	1st to 10th	Night	49% 9% 13% 19% 9% 1	2840
	11th to 20th	Night	46% 8% 14% 24% 7% 1	2605
	21st to end	Night	44% 10% 14% 22% 9% 1	2560
June	1st to 10th	Night	56% 6% 10% 18% 9% 1	1330
	11th to 20th	Night	47% 7% 11% 23% 10% 2	1330
	21st to end	Night	54% 6% 12% 19% 8% 1	1330
July	1st to 10th	Night	43% 8% 16% 23% 10%	2175
	11th to 20th	Night	46% 7% 14% 27% 6%	2183
	21st to end	Night	43% 9% 13% 27% 8%	2773
August	1st to 10th	Night	52% 8% 13% 21% 7%	2813
	11th to 20th	Night	44% 9% 18% 23% 6%	2809
	21st to end	Night	37% 7% 15% 23% 17% 1	3124
September	1st to 10th	Night	37% 6% 13% 29% 13% 1	1913
	11th to 20th	Night	39% 5% 12% 29% 15% 1	2090
	21st to end	Night	42% 5% 12% 27% 14% 1	2090
October	1st to 10th	Night	47% 5% 12% 24% 12%	3726
	11th to 20th	Night	40% 6% 12% 29% 12%	3779
	21st to end	Night	42% 5% 17% 22% 14%	4363
November	1st to 10th	Night	47% 6% 13% 22% 10% 1	2593
	11th to 20th	Night	49% 5% 13% 21% 11% 1	2800
	21st to end	Night	54% 6% 15% 16% 9% 1	2800
December	1st to 10th	Night	49% 5% 13% 26% 7%	4695
	11th to 20th	Night	51% 5% 10% 21% 13% 1	5592
	21st to end	Night	56% 4 9% 18% 10% 3	7502

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	31% 20% 34% 13% 2	200
	11th to 20th	Day	35% 22% 29% 9% 5% 1	200
	21st to end	Day	22% 21% 35% 16% 4 1	320
February	1st to 10th	Day	29% 20% 31% 15% 4 1	385
	11th to 20th	Day	31% 23% 29% 14% 3 1	366
	21st to end	Day	27% 22% 30% 17% 4	366
March	1st to 10th	Day	31% 21% 33% 12% 2 1	460
	11th to 20th	Day	31% 19% 31% 14% 4 1	460
	21st to end	Day	34% 20% 27% 12% 6% 1	506
April	1st to 10th	Day	40% 22% 23% 12% 2	460
	11th to 20th	Day	33% 20% 30% 11% 4 1	452
	21st to end	Day	34% 20% 28% 11% 5% 1	460
May	1st to 10th	Day	35% 18% 29% 14% 4 1	463
	11th to 20th	Day	31% 17% 27% 19% 6% 1	612
	21st to end	Day	26% 19% 34% 14% 7%	735
June	1st to 10th	Day	33% 17% 28% 16% 6% 1	680
	11th to 20th	Day	28% 14% 28% 21% 8% 1	680
	21st to end	Day	30% 12% 31% 18% 8% 1	680
July	1st to 10th	Day	23% 12% 35% 20% 9% 1	670
	11th to 20th	Day	21% 9% 33% 25% 11% 1	662
	21st to end	Day	19% 10% 36% 25% 8% 1	532
August	1st to 10th	Day	18% 11% 34% 26% 9% 2	486
	11th to 20th	Day	18% 11% 28% 28% 13% 2	479
	21st to end	Day	21% 13% 27% 26% 11% 3	539
September	1st to 10th	Day	14% 13% 36% 24% 10% 3	490
	11th to 20th	Day	23% 11% 29% 23% 11% 3	490
	21st to end	Day	22% 17% 28% 18% 12% 4	490
October	1st to 10th	Day	22% 17% 22% 24% 11% 3	415
	11th to 20th	Day	28% 17% 26% 17% 9% 3	390
	21st to end	Day	31% 18% 32% 13% 6%	429
November	1st to 10th	Day	29% 15% 32% 17% 7% 1	395
	11th to 20th	Day	32% 20% 27% 15% 6%	400
	21st to end	Day	35% 20% 27% 15% 3 1	400
December	1st to 10th	Day	33% 17% 28% 19% 2	335
	11th to 20th	Day	43% 24% 22% 11% 2	200
	21st to end	Day	32% 22% 25% 16% 4	220
January	1st to 10th	Night	25% 21% 30% 20% 3	900
	11th to 20th	Night	28% 17% 29% 22% 3	813
	21st to end	Night	20% 22% 34% 20% 4	880
February	1st to 10th	Night	24% 22% 30% 19% 4	781
	11th to 20th	Night	27% 22% 31% 16% 4	743
	21st to end	Night	23% 19% 32% 22% 4	628
March	1st to 10th	Night	26% 19% 34% 19% 2	760
	11th to 20th	Night	25% 17% 31% 21% 5%	760
	21st to end	Night	26% 16% 34% 19% 5%	836
April	1st to 10th	Night	34% 18% 29% 17% 3	683
	11th to 20th	Night	29% 18% 33% 15% 5%	564
	21st to end	Night	33% 13% 30% 19% 5%	570
May	1st to 10th	Night	29% 13% 30% 24% 4	570
	11th to 20th	Night	29% 14% 32% 21% 4	562
	21st to end	Night	20% 14% 36% 25% 4	504
June	1st to 10th	Night	27% 7% 31% 28% 6%	380
	11th to 20th	Night	21% 10% 30% 32% 7% 1	380
	21st to end	Night	30% 6% 26% 32% 6% 1	380
July	1st to 10th	Night	18% 6% 39% 29% 7%	370
	11th to 20th	Night	19% 5% 27% 36% 12% 1	368
	21st to end	Night	22% 5% 29% 36% 9%	492
August	1st to 10th	Night	18% 5% 26% 38% 12%	568
	11th to 20th	Night	17% 7% 28% 34% 14%	562
	21st to end	Night	16% 7% 28% 30% 17% 1	627
September	1st to 10th	Night	19% 8% 36% 27% 10%	615
	11th to 20th	Night	20% 9% 24% 32% 14% 1	760
	21st to end	Night	24% 11% 27% 28% 10% 1	760
October	1st to 10th	Night	23% 10% 28% 28% 9% 1	760
	11th to 20th	Night	23% 13% 29% 24% 10% 1	760
	21st to end	Night	28% 17% 31% 20% 4	836
November	1st to 10th	Night	29% 15% 28% 23% 5%	808
	11th to 20th	Night	29% 16% 30% 18% 6% 1	900
	21st to end	Night	30% 19% 27% 20% 4 1	900
December	1st to 10th	Night	33% 15% 28% 20% 4 1	900
	11th to 20th	Night	32% 20% 28% 17% 2	900
	21st to end	Night	30% 20% 28% 18% 4 1	990

Page generated at 2025-02-03 04:05:50. Version ac07

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