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 2024-01-31.

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% 9% 3 6% 5% 3 4 4 5% 6% 33%	74785
	Night	20% 9% 3 6% 5% 3 4 4 5% 6% 34%	75344
Transparency	Day	51% 6% 12% 20% 10% 1	74485
	Night	50% 6% 11% 21% 11% 1	75179
Seeing	Day	28% 16% 30% 18% 7% 1	15152
	Night	26% 15% 30% 23% 6%	23237

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	16% 14% 5% 9% 7% 3 5% 5% 5% 5% 28%	1327
	11th to 20th	Day	20% 14% 5% 8% 6% 3 4 4 3 5% 27%	1492
	21st to end	Day	13% 10% 4 7% 6% 4 5% 4 4 7% 36%	1758
February	1st to 10th	Day	15% 10% 4 7% 7% 4 6% 5% 4 7% 30%	1620
	11th to 20th	Day	16% 13% 5% 7% 7% 4 5% 5% 5% 6% 28%	1573
	21st to end	Day	11% 14% 5% 7% 7% 4 5% 4 4 6% 33%	1448
March	1st to 10th	Day	18% 14% 4 7% 6% 3 4 4 5% 6% 29%	1874
	11th to 20th	Day	16% 12% 4 6% 7% 4 4 4 4 6% 31%	1980
	21st to end	Day	20% 11% 5% 9% 6% 3 4 3 4 5% 31%	2178
April	1st to 10th	Day	22% 14% 4 6% 5% 3 4 4 5% 5% 27%	2119
	11th to 20th	Day	21% 10% 3 6% 5% 3 3 4 5% 7% 34%	2312
	21st to end	Day	27% 10% 3 6% 4 3 4 4 4 5% 30%	2340
May	1st to 10th	Day	25% 10% 3 6% 5% 3 4 4 4 5% 30%	2340
	11th to 20th	Day	26% 7% 3 6% 6% 3 3 4 4 5% 34%	2419
	21st to end	Day	20% 8% 2 6% 5% 3 4 4 6% 8% 33%	2844
June	1st to 10th	Day	27% 8% 4 6% 6% 3 5% 5% 5% 6% 26%	2700
	11th to 20th	Day	23% 7% 4 5% 5% 2 5% 4 4 7% 34%	2700
	21st to end	Day	28% 7% 4 6% 5% 3 5% 5% 5% 6% 27%	2700
July	1st to 10th	Day	18% 6% 3 5% 6% 4 5% 5% 5% 8% 35%	2700
	11th to 20th	Day	17% 7% 2 5% 5% 4 5% 6% 7% 8% 34%	2695
	21st to end	Day	18% 6% 4 5% 6% 3 5% 6% 7% 8% 31%	2654
August	1st to 10th	Day	20% 5% 3 5% 5% 4 5% 6% 6% 7% 34%	2327
	11th to 20th	Day	17% 7% 3 7% 6% 3 6% 5% 6% 8% 33%	2304
	21st to end	Day	15% 5% 3 5% 5% 4 5% 5% 5% 7% 41%	2574
September	1st to 10th	Day	13% 5% 2 5% 6% 3 5% 5% 5% 9% 42%	2146
	11th to 20th	Day	20% 6% 2 4 3 3 4 5% 4 6% 44%	1980
	21st to end	Day	22% 4 2 5% 4 2 3 4 4 6% 43%	1980
October	1st to 10th	Day	17% 8% 3 6% 5% 2 4 4 5% 7% 39%	1846
	11th to 20th	Day	22% 7% 2 6% 5% 3 4 3 5% 6% 36%	1800
	21st to end	Day	23% 10% 3 7% 7% 4 4 4 4 5% 29%	1841
November	1st to 10th	Day	20% 10% 3 6% 4 3 3 5% 5% 7% 34%	1616
	11th to 20th	Day	20% 8% 3 6% 5% 3 5% 4 7% 7% 33%	1520
	21st to end	Day	22% 10% 3 8% 5% 3 4 5% 3 6% 31%	1520
December	1st to 10th	Day	24% 10% 4 5% 6% 4 5% 5% 4 6% 27%	1459
	11th to 20th	Day	23% 12% 4 7% 7% 4 4 4 3 5% 27%	1668
	21st to end	Day	21% 13% 5% 6% 6% 3 3 3 3 4 35%	2431
January	1st to 10th	Night	15% 12% 6% 8% 6% 3 5% 5% 6% 7% 26%	2838
	11th to 20th	Night	19% 12% 4 7% 7% 3 5% 5% 6% 6% 26%	2684
	21st to end	Night	12% 10% 4 7% 6% 3 5% 6% 6% 7% 34%	2823
February	1st to 10th	Night	14% 13% 3 6% 6% 3 5% 5% 6% 6% 32%	2340
	11th to 20th	Night	16% 12% 5% 8% 5% 4 5% 5% 5% 6% 28%	2273
	21st to end	Night	14% 12% 4 7% 7% 4 6% 5% 5% 5% 33%	1804
March	1st to 10th	Night	15% 12% 4 8% 6% 3 4 4 5% 5% 33%	2072
	11th to 20th	Night	18% 10% 4 6% 5% 4 5% 5% 5% 7% 32%	1979
	21st to end	Night	17% 11% 4 8% 5% 4 4 4 4 5% 35%	2178
April	1st to 10th	Night	25% 11% 3 5% 5% 3 4 4 4 5% 31%	1837
	11th to 20th	Night	22% 7% 3 5% 4 3 4 4 4 6% 37%	1598
	21st to end	Night	27% 9% 3 5% 4 3 4 4 4 7% 31%	1620
May	1st to 10th	Night	23% 8% 3 5% 5% 3 4 5% 5% 7% 32%	1620
	11th to 20th	Night	25% 8% 3 5% 4 3 5% 4 3 5% 34%	1475
	21st to end	Night	19% 7% 2 6% 7% 4 5% 5% 6% 7% 34%	1444
June	1st to 10th	Night	27% 6% 3 5% 6% 4 4 5% 3 7% 29%	1260
	11th to 20th	Night	19% 6% 3 5% 5% 3 6% 4 6% 7% 35%	1260
	21st to end	Night	28% 5% 2 6% 6% 2 4 3 4 7% 33%	1260
July	1st to 10th	Night	17% 6% 3 4 5% 4 5% 5% 5% 8% 38%	1260
	11th to 20th	Night	18% 5% 2 5% 5% 4 5% 4 7% 9% 36%	1262
	21st to end	Night	21% 6% 3 5% 5% 3 4 5% 6% 6% 35%	1646
August	1st to 10th	Night	16% 5% 2 5% 5% 4 4 4 5% 7% 41%	1612
	11th to 20th	Night	18% 7% 3 5% 6% 3 5% 5% 5% 8% 36%	1596
	21st to end	Night	14% 5% 3 5% 3 2 4 5% 5% 8% 46%	1782
September	1st to 10th	Night	17% 5% 2 4 4 2 4 4 6% 7% 45%	1811
	11th to 20th	Night	17% 6% 2 5% 3 2 4 4 4 6% 47%	1980
	21st to end	Night	21% 4 1 3 4 3 4 3 5% 5% 46%	1980
October	1st to 10th	Night	19% 6% 3 5% 5% 2 3 4 4 7% 42%	2114
	11th to 20th	Night	20% 6% 2 7% 5% 3 4 5% 5% 7% 37%	2160
	21st to end	Night	24% 10% 2 6% 5% 3 4 4 4 6% 34%	2510
November	1st to 10th	Night	22% 7% 4 5% 5% 3 3 4 5% 6% 37%	2460
	11th to 20th	Night	21% 7% 3 5% 6% 3 4 4 5% 7% 35%	2660
	21st to end	Night	21% 9% 3 8% 6% 3 5% 4 6% 7% 30%	2660
December	1st to 10th	Night	27% 9% 4 6% 5% 3 4 4 4 5% 28%	2719
	11th to 20th	Night	27% 9% 3 5% 6% 3 4 5% 5% 6% 27%	3531
	21st to end	Night	21% 14% 4 6% 5% 3 3 4 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	56% 6% 13% 16% 9% 1	1328
	11th to 20th	Day	61% 4 9% 17% 9% 1	1492
	21st to end	Day	48% 4 11% 22% 14% 2	1758
February	1st to 10th	Day	54% 5% 11% 19% 9% 1	1620
	11th to 20th	Day	57% 5% 11% 17% 9% 1	1581
	21st to end	Day	51% 4 11% 21% 10% 2	1448
March	1st to 10th	Day	57% 4 10% 17% 11% 2	1878
	11th to 20th	Day	53% 4 11% 17% 11% 3	1980
	21st to end	Day	56% 4 8% 19% 10% 4	2178
April	1st to 10th	Day	60% 3 9% 14% 12% 2	2119
	11th to 20th	Day	50% 4 10% 23% 12% 2	2312
	21st to end	Day	57% 4 9% 15% 11% 5%	2340
May	1st to 10th	Day	55% 6% 7% 19% 11% 2	2340
	11th to 20th	Day	52% 5% 9% 20% 12% 2	2423
	21st to end	Day	49% 7% 13% 22% 9% 1	2844
June	1st to 10th	Day	57% 6% 10% 16% 10% 1	2700
	11th to 20th	Day	50% 5% 12% 19% 13% 1	2700
	21st to end	Day	57% 7% 10% 16% 9% 1	2700
July	1st to 10th	Day	45% 8% 16% 21% 9% 1	2625
	11th to 20th	Day	44% 9% 14% 23% 9% 1	2614
	21st to end	Day	48% 8% 15% 20% 9%	2506
August	1st to 10th	Day	48% 7% 15% 24% 6%	2314
	11th to 20th	Day	47% 8% 14% 24% 7%	2304
	21st to end	Day	42% 6% 14% 26% 12%	2574
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	56% 5% 12% 17% 9% 1	2838
	11th to 20th	Night	57% 6% 11% 16% 8% 1	2684
	21st to end	Night	46% 6% 11% 23% 12% 2	2823
February	1st to 10th	Night	51% 5% 12% 19% 12% 1	2340
	11th to 20th	Night	55% 5% 11% 17% 10% 2	2276
	21st to end	Night	53% 6% 8% 19% 12% 2	1804
March	1st to 10th	Night	54% 4 7% 20% 13% 2	2081
	11th to 20th	Night	52% 6% 11% 17% 13% 2	1980
	21st to end	Night	53% 4 8% 19% 13% 2	2178
April	1st to 10th	Night	56% 5% 8% 16% 11% 4	1837
	11th to 20th	Night	48% 6% 9% 20% 15% 2	1598
	21st to end	Night	55% 5% 10% 17% 11% 2	1620
May	1st to 10th	Night	52% 5% 9% 19% 12% 2	1620
	11th to 20th	Night	54% 5% 9% 20% 11% 2	1476
	21st to end	Night	51% 7% 11% 18% 11% 1	1445
June	1st to 10th	Night	57% 6% 9% 19% 9% 1	1260
	11th to 20th	Night	48% 7% 10% 23% 10% 1	1260
	21st to end	Night	53% 6% 12% 19% 9% 1	1260
July	1st to 10th	Night	43% 9% 15% 24% 9%	1225
	11th to 20th	Night	43% 8% 15% 23% 10%	1220
	21st to end	Night	48% 8% 13% 20% 10% 1	1554
August	1st to 10th	Night	41% 8% 16% 27% 8%	1600
	11th to 20th	Night	45% 8% 17% 24% 6%	1596
	21st to end	Night	36% 7% 15% 27% 14% 1	1782
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	24% 20% 34% 17% 4 1	290
February	1st to 10th	Day	29% 19% 33% 16% 3	340
	11th to 20th	Day	31% 23% 27% 15% 3 1	336
	21st to end	Day	26% 23% 30% 17% 4	332
March	1st to 10th	Day	30% 22% 33% 12% 2 1	420
	11th to 20th	Day	30% 20% 31% 14% 4 1	420
	21st to end	Day	32% 21% 26% 13% 7% 1	462
April	1st to 10th	Day	40% 22% 23% 12% 2	420
	11th to 20th	Day	33% 19% 30% 12% 5% 1	412
	21st to end	Day	36% 18% 28% 11% 6% 1	420
May	1st to 10th	Day	35% 18% 28% 14% 3 1	423
	11th to 20th	Day	33% 17% 27% 16% 5% 1	565
	21st to end	Day	27% 19% 33% 14% 7%	680
June	1st to 10th	Day	34% 16% 28% 17% 6% 1	630
	11th to 20th	Day	29% 14% 28% 21% 7% 1	630
	21st to end	Day	30% 11% 31% 20% 9% 1	630
July	1st to 10th	Day	24% 12% 34% 20% 10% 1	620
	11th to 20th	Day	21% 8% 32% 25% 12% 1	613
	21st to end	Day	19% 10% 36% 25% 8% 1	488
August	1st to 10th	Day	17% 10% 35% 26% 9% 2	446
	11th to 20th	Day	20% 10% 28% 28% 13% 2	439
	21st to end	Day	21% 13% 27% 25% 11% 3	495
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	835
February	1st to 10th	Night	25% 22% 31% 19% 3	720
	11th to 20th	Night	28% 21% 31% 15% 4	703
	21st to end	Night	23% 19% 32% 21% 4	592
March	1st to 10th	Night	25% 19% 35% 19% 2	720
	11th to 20th	Night	25% 17% 32% 21% 5%	720
	21st to end	Night	24% 17% 34% 20% 5%	792
April	1st to 10th	Night	34% 18% 29% 17% 3	648
	11th to 20th	Night	28% 18% 33% 15% 5%	534
	21st to end	Night	34% 14% 28% 19% 6%	540
May	1st to 10th	Night	29% 13% 30% 24% 4	540
	11th to 20th	Night	30% 14% 32% 20% 4	532
	21st to end	Night	21% 14% 35% 25% 4	477
June	1st to 10th	Night	28% 7% 30% 29% 6%	360
	11th to 20th	Night	22% 10% 29% 31% 6% 1	360
	21st to end	Night	30% 5% 26% 33% 6% 1	360
July	1st to 10th	Night	19% 6% 39% 29% 8%	350
	11th to 20th	Night	19% 5% 28% 36% 12% 1	348
	21st to end	Night	22% 4 29% 35% 9%	466
August	1st to 10th	Night	17% 5% 26% 38% 13%	538
	11th to 20th	Night	18% 7% 28% 34% 14%	532
	21st to end	Night	16% 7% 28% 30% 16% 1	594
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 2024-01-28 06:26:37. Version ac07

Copyright 2024 Attilla Danko