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 2024-08-30.

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	20% 10% 3 7% 5% 4 4 4 5% 6% 32%	95781
	Night	20% 9% 3 7% 4 4 4 4 5% 6% 33%	93322
Transparency	Day	51% 6% 12% 20% 10% 1	95495
	Night	50% 6% 12% 21% 10% 1	93163
Seeing	Day	28% 16% 30% 18% 7% 1	16045
	Night	26% 15% 30% 23% 6%	23876

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% 12% 5% 9% 6% 4 4 4 5% 5% 32%	2207
	11th to 20th	Day	16% 12% 5% 12% 6% 6% 4 3 4 4 28%	2468
	21st to end	Day	12% 10% 2 8% 5% 6% 5% 4 5% 8% 35%	2932
February	1st to 10th	Day	15% 11% 4 8% 7% 6% 5% 3 5% 6% 30%	1710
	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	20% 6% 3 6% 4 5% 4 5% 6% 7% 34%	2457
	11th to 20th	Day	16% 7% 3 8% 5% 5% 5% 4 6% 8% 34%	2434
	21st to end	Day	15% 6% 3 5% 5% 4 5% 4 5% 7% 41%	2694
September	1st to 10th	Day	13% 5% 2 6% 5% 4 5% 4 5% 9% 42%	2146
	11th to 20th	Day	20% 6% 2 4 3 3 4 3 4 6% 44%	1980
	21st to end	Day	22% 5% 2 6% 4 3 3 3 4 6% 43%	1980
October	1st to 10th	Day	17% 8% 3 6% 5% 4 4 3 5% 6% 39%	1846
	11th to 20th	Day	22% 7% 2 7% 4 4 4 2 5% 6% 36%	1800
	21st to end	Day	23% 10% 3 8% 6% 5% 3 3 4 5% 29%	1841
November	1st to 10th	Day	20% 10% 3 7% 4 4 3 4 5% 7% 34%	1616
	11th to 20th	Day	20% 8% 3 7% 4 4 3 3 8% 7% 33%	1520
	21st to end	Day	21% 11% 3 9% 4 4 4 4 3 6% 31%	1520
December	1st to 10th	Day	24% 11% 4 7% 5% 5% 4 3 4 6% 27%	1459
	11th to 20th	Day	23% 13% 2 8% 6% 5% 5% 3 3 5% 27%	1668
	21st to end	Day	20% 13% 4 7% 5% 3 3 2 3 3 35%	2431
January	1st to 10th	Night	12% 11% 5% 8% 4 4 5% 4 6% 8% 32%	4748
	11th to 20th	Night	16% 12% 4 10% 7% 5% 5% 4 6% 6% 26%	4490
	21st to end	Night	12% 13% 4 8% 5% 5% 5% 4 6% 7% 32%	4722
February	1st to 10th	Night	14% 14% 3 8% 5% 4 4 4 6% 6% 32%	2470
	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	17% 6% 2 7% 4 5% 4 3 5% 8% 40%	1702
	11th to 20th	Night	17% 7% 2 6% 5% 5% 4 4 5% 9% 36%	1686
	21st to end	Night	14% 5% 3 6% 3 3 4 5% 5% 7% 46%	1872
September	1st to 10th	Night	17% 5% 2 5% 3 3 4 3 5% 7% 45%	1811
	11th to 20th	Night	17% 6% 2 5% 2 3 4 3 5% 6% 47%	1980
	21st to end	Night	21% 4 1 3 4 4 4 3 5% 5% 46%	1980
October	1st to 10th	Night	19% 6% 2 6% 4 3 3 3 5% 6% 42%	2114
	11th to 20th	Night	20% 7% 2 7% 4 4 4 4 5% 6% 37%	2160
	21st to end	Night	23% 10% 2 7% 4 4 3 3 4 5% 34%	2510
November	1st to 10th	Night	22% 8% 3 5% 4 4 3 3 5% 5% 37%	2460
	11th to 20th	Night	21% 8% 3 6% 5% 4 4 4 6% 6% 35%	2660
	21st to end	Night	21% 10% 3 8% 5% 4 4 4 6% 7% 29%	2660
December	1st to 10th	Night	27% 10% 3 7% 5% 3 4 3 4 5% 28%	2719
	11th to 20th	Night	26% 10% 2 6% 5% 4 4 4 5% 6% 27%	3531
	21st to end	Night	21% 14% 4 7% 4 4 3 3 4 4 33%	5236

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	51% 8% 15% 17% 9%	2208
	11th to 20th	Day	57% 3 10% 19% 9% 1	2468
	21st to end	Day	46% 9% 11% 20% 14% 1	2932
February	1st to 10th	Day	54% 5% 11% 19% 10% 2	1710
	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	48% 7% 15% 24% 6%	2444
	11th to 20th	Day	47% 8% 13% 25% 7%	2434
	21st to end	Day	41% 6% 14% 27% 12%	2694
September	1st to 10th	Day	38% 8% 14% 27% 13%	2146
	11th to 20th	Day	41% 5% 10% 28% 14% 1	1980
	21st to end	Day	42% 6% 9% 26% 15% 1	1980
October	1st to 10th	Day	45% 5% 12% 27% 11%	1846
	11th to 20th	Day	49% 5% 15% 24% 7% 1	1800
	21st to end	Day	56% 5% 11% 18% 10%	1841
November	1st to 10th	Day	50% 5% 12% 20% 12% 1	1616
	11th to 20th	Day	48% 5% 15% 18% 13% 1	1520
	21st to end	Day	55% 5% 14% 19% 6%	1520
December	1st to 10th	Day	58% 5% 12% 17% 8% 1	1459
	11th to 20th	Day	61% 4 8% 17% 9% 1	1668
	21st to end	Day	55% 4 12% 17% 10% 3	2431
January	1st to 10th	Night	48% 6% 17% 21% 8% 1	4748
	11th to 20th	Night	54% 6% 12% 19% 8% 1	4490
	21st to end	Night	48% 7% 10% 21% 12% 1	4722
February	1st to 10th	Night	50% 6% 12% 19% 12% 1	2470
	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	42% 8% 15% 26% 8%	1690
	11th to 20th	Night	45% 8% 17% 24% 6%	1686
	21st to end	Night	36% 7% 15% 27% 14% 1	1872
September	1st to 10th	Night	37% 6% 14% 29% 13% 1	1811
	11th to 20th	Night	39% 5% 12% 28% 16% 1	1980
	21st to end	Night	40% 5% 11% 27% 15% 1	1980
October	1st to 10th	Night	43% 5% 12% 25% 16% 1	2114
	11th to 20th	Night	47% 6% 12% 25% 10%	2160
	21st to end	Night	52% 6% 11% 20% 11%	2510
November	1st to 10th	Night	48% 6% 13% 21% 11% 1	2460
	11th to 20th	Night	49% 5% 13% 22% 10% 1	2660
	21st to end	Night	53% 7% 15% 16% 9% 1	2660
December	1st to 10th	Night	58% 5% 10% 20% 7%	2719
	11th to 20th	Night	57% 5% 9% 19% 9%	3532
	21st to end	Night	56% 4 11% 19% 6% 4	5236

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	29% 19% 34% 14% 2	180
	11th to 20th	Day	38% 23% 28% 8% 2 1	180
	21st to end	Day	23% 19% 34% 18% 5% 1	293
February	1st to 10th	Day	28% 19% 32% 15% 4 1	370
	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% 25% 11% 3	532
September	1st to 10th	Day	14% 12% 37% 25% 10% 3	450
	11th to 20th	Day	25% 12% 30% 21% 10% 3	450
	21st to end	Day	23% 17% 29% 15% 11% 4	450
October	1st to 10th	Day	22% 17% 23% 23% 11% 3	383
	11th to 20th	Day	27% 16% 27% 17% 9% 3	360
	21st to end	Day	32% 18% 31% 13% 6%	396
November	1st to 10th	Day	28% 15% 32% 17% 7% 1	365
	11th to 20th	Day	31% 19% 28% 15% 6%	370
	21st to end	Day	34% 20% 27% 15% 3 1	370
December	1st to 10th	Day	34% 17% 27% 19% 2	309
	11th to 20th	Day	42% 24% 23% 10% 1	180
	21st to end	Day	33% 24% 26% 14% 3	198
January	1st to 10th	Night	25% 20% 30% 21% 3	850
	11th to 20th	Night	29% 18% 30% 21% 3	772
	21st to end	Night	20% 22% 34% 20% 4	836
February	1st to 10th	Night	24% 22% 31% 19% 4	760
	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	17% 7% 28% 30% 17% 1	624
September	1st to 10th	Night	19% 8% 36% 26% 10% 1	582
	11th to 20th	Night	21% 10% 25% 31% 13% 1	720
	21st to end	Night	24% 11% 26% 28% 10% 1	720
October	1st to 10th	Night	23% 10% 29% 27% 10% 1	720
	11th to 20th	Night	23% 12% 30% 24% 10% 1	720
	21st to end	Night	29% 17% 31% 19% 5%	792
November	1st to 10th	Night	29% 14% 27% 23% 6% 1	765
	11th to 20th	Night	29% 16% 29% 19% 6% 1	850
	21st to end	Night	28% 19% 27% 21% 4 1	850
December	1st to 10th	Night	34% 15% 28% 18% 4 1	850
	11th to 20th	Night	32% 20% 29% 16% 2	850
	21st to end	Night	30% 21% 28% 17% 3 1	935

Page generated at 2024-08-27 10:49:37. Version ac07

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