BlueBirdsKnoll Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the BlueBirdsKnoll Observatory clear sky chart from 2005-11-06 to 2024-11-02.

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	18% 7% 2 6% 4 4 4 4 6% 7% 39%	101252
	Night	18% 8% 2 6% 4 4 4 3 5% 6% 40%	97739
Transparency	Day	43% 7% 13% 22% 14% 2	101007
	Night	44% 6% 12% 22% 14% 2	97604
Seeing	Day	20% 16% 32% 22% 9% 2	15012
	Night	21% 13% 32% 25% 8% 1	24043

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% 7% 2 6% 4 4 3 3 4 5% 45%	2517
	11th to 20th	Day	17% 9% 3 8% 4 5% 5% 4 4 5% 36%	2520
	21st to end	Day	22% 11% 4 8% 4 4 4 3 4 5% 32%	2871
February	1st to 10th	Day	18% 7% 2 6% 5% 4 5% 3 5% 6% 38%	1767
	11th to 20th	Day	15% 7% 2 6% 4 4 4 4 7% 7% 41%	1848
	21st to end	Day	22% 8% 2 6% 3 4 3 4 5% 6% 37%	1570
March	1st to 10th	Day	27% 10% 3 6% 4 4 3 2 3 5% 34%	3116
	11th to 20th	Day	10% 5% 2 5% 4 4 6% 5% 7% 9% 43%	3266
	21st to end	Day	21% 7% 2 6% 4 4 4 3 4 6% 39%	4166
April	1st to 10th	Day	19% 9% 2 6% 4 3 3 3 6% 7% 37%	2280
	11th to 20th	Day	20% 7% 2 5% 4 4 3 3 5% 7% 41%	2254
	21st to end	Day	21% 6% 2 4 4 4 4 3 5% 6% 40%	2375
May	1st to 10th	Day	29% 9% 2 5% 3 3 4 3 5% 7% 30%	4106
	11th to 20th	Day	22% 8% 2 7% 4 4 4 4 6% 7% 31%	4288
	21st to end	Day	16% 5% 2 5% 3 3 4 4 6% 8% 45%	4837
June	1st to 10th	Day	18% 6% 2 6% 4 4 5% 4 7% 8% 36%	2660
	11th to 20th	Day	16% 7% 2 6% 4 4 5% 4 7% 10% 36%	2660
	21st to end	Day	13% 6% 2 7% 5% 4 5% 4 6% 9% 38%	2660
July	1st to 10th	Day	13% 6% 2 7% 5% 6% 6% 4 7% 8% 35%	4440
	11th to 20th	Day	14% 6% 2 5% 4 5% 5% 5% 7% 9% 38%	4440
	21st to end	Day	17% 8% 3 7% 5% 5% 5% 5% 6% 8% 32%	4814
August	1st to 10th	Day	20% 7% 2 7% 5% 5% 5% 4 6% 9% 31%	4270
	11th to 20th	Day	12% 7% 3 6% 4 4 4 4 6% 9% 41%	3730
	21st to end	Day	8% 6% 2 5% 5% 4 5% 3 7% 10% 45%	4180
September	1st to 10th	Day	13% 6% 2 6% 4 4 5% 3 5% 6% 45%	2280
	11th to 20th	Day	13% 5% 2 5% 4 3 4 3 4 6% 50%	2155
	21st to end	Day	20% 6% 2 6% 4 3 4 3 4 6% 40%	2090
October	1st to 10th	Day	21% 7% 2 6% 4 3 3 3 5% 6% 41%	2052
	11th to 20th	Day	15% 5% 2 5% 3 3 3 3 5% 7% 47%	1893
	21st to end	Day	20% 6% 2 6% 3 4 4 4 5% 6% 41%	1881
November	1st to 10th	Day	14% 6% 2 6% 4 3 3 2 5% 5% 49%	1681
	11th to 20th	Day	19% 6% 1 5% 2 3 3 2 5% 7% 46%	1710
	21st to end	Day	17% 6% 2 5% 3 4 4 3 6% 7% 43%	1677
December	1st to 10th	Day	20% 6% 3 6% 4 4 3 5% 5% 6% 38%	1520
	11th to 20th	Day	23% 6% 2 4 4 3 3 2 4 6% 44%	1906
	21st to end	Day	19% 11% 3 7% 5% 5% 3 3 5% 6% 33%	2772
January	1st to 10th	Night	17% 6% 2 5% 3 4 3 3 5% 6% 46%	4429
	11th to 20th	Night	17% 9% 3 7% 4 3 3 2 4 4 43%	4440
	21st to end	Night	25% 11% 3 7% 4 3 4 3 3 5% 33%	4784
February	1st to 10th	Night	17% 10% 3 5% 4 4 4 3 4 6% 41%	2412
	11th to 20th	Night	16% 8% 2 6% 4 4 3 3 4 7% 41%	2218
	21st to end	Night	19% 9% 2 6% 4 4 3 3 3 6% 41%	1884
March	1st to 10th	Night	25% 11% 3 5% 3 3 3 3 4 5% 35%	3724
	11th to 20th	Night	12% 7% 3 7% 4 4 4 4 6% 7% 44%	3687
	21st to end	Night	21% 8% 3 5% 3 3 3 3 5% 5% 41%	3466
April	1st to 10th	Night	19% 8% 2 6% 4 4 5% 4 5% 6% 37%	1900
	11th to 20th	Night	20% 6% 2 6% 4 3 4 3 6% 6% 41%	1875
	21st to end	Night	20% 7% 3 6% 4 3 4 2 4 5% 42%	1805
May	1st to 10th	Night	24% 11% 3 7% 4 4 4 3 5% 6% 28%	2834
	11th to 20th	Night	22% 9% 3 8% 4 4 4 4 4 6% 31%	2634
	21st to end	Night	18% 7% 2 5% 4 4 4 2 5% 7% 42%	2738
June	1st to 10th	Night	18% 7% 2 7% 4 4 4 4 5% 6% 40%	1520
	11th to 20th	Night	16% 6% 2 5% 4 3 4 3 6% 9% 41%	1520
	21st to end	Night	13% 7% 3 5% 4 4 4 3 6% 9% 42%	1520
July	1st to 10th	Night	14% 6% 3 7% 5% 5% 5% 5% 6% 9% 35%	2520
	11th to 20th	Night	17% 6% 2 6% 5% 4 5% 4 7% 8% 36%	2520
	21st to end	Night	21% 8% 2 7% 4 4 4 5% 6% 6% 33%	2739
August	1st to 10th	Night	23% 7% 2 8% 5% 5% 5% 4 6% 6% 29%	2626
	11th to 20th	Night	15% 7% 3 6% 5% 4 4 4 5% 6% 40%	3093
	21st to end	Night	10% 5% 1 4 3 3 3 3 5% 8% 54%	3476
September	1st to 10th	Night	14% 6% 3 6% 5% 3 4 3 4 7% 44%	1900
	11th to 20th	Night	14% 5% 2 4 4 2 4 3 4 7% 52%	2023
	21st to end	Night	17% 7% 3 5% 4 4 4 3 4 6% 43%	2090
October	1st to 10th	Night	19% 8% 2 6% 4 4 3 3 4 6% 40%	2126
	11th to 20th	Night	15% 5% 2 6% 3 3 4 3 5% 6% 49%	2285
	21st to end	Night	22% 7% 2 5% 3 3 3 3 5% 5% 42%	2717
November	1st to 10th	Night	13% 6% 2 5% 4 4 4 3 5% 6% 49%	2431
	11th to 20th	Night	20% 6% 2 5% 4 3 3 2 4 6% 46%	2470
	21st to end	Night	16% 6% 2 5% 4 4 3 4 5% 6% 46%	2501
December	1st to 10th	Night	20% 7% 3 5% 3 3 4 3 5% 5% 40%	2660
	11th to 20th	Night	21% 6% 2 5% 4 4 4 3 5% 5% 41%	3288
	21st to end	Night	22% 10% 3 6% 4 3 3 3 5% 5% 36%	4884

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	38% 5% 10% 32% 11% 2	2518
	11th to 20th	Day	47% 6% 11% 23% 11% 1	2520
	21st to end	Day	51% 9% 8% 20% 10% 2	2871
February	1st to 10th	Day	45% 5% 14% 20% 13% 2	1767
	11th to 20th	Day	39% 6% 12% 23% 17% 3	1857
	21st to end	Day	47% 6% 11% 20% 13% 3	1570
March	1st to 10th	Day	52% 5% 12% 18% 11% 2	3119
	11th to 20th	Day	31% 8% 16% 30% 13% 1	3266
	21st to end	Day	45% 5% 7% 17% 21% 5%	4166
April	1st to 10th	Day	46% 5% 10% 20% 15% 3	2280
	11th to 20th	Day	43% 6% 11% 20% 18% 3	2254
	21st to end	Day	44% 6% 10% 20% 16% 4	2375
May	1st to 10th	Day	52% 8% 14% 14% 11% 1	4120
	11th to 20th	Day	49% 8% 14% 18% 9% 2	4292
	21st to end	Day	35% 8% 13% 24% 18% 1	4837
June	1st to 10th	Day	43% 8% 12% 24% 12% 1	2660
	11th to 20th	Day	41% 8% 15% 22% 12% 1	2660
	21st to end	Day	40% 8% 14% 23% 13% 1	2660
July	1st to 10th	Day	44% 10% 11% 20% 15% 1	4370
	11th to 20th	Day	40% 8% 16% 22% 13% 1	4365
	21st to end	Day	48% 8% 11% 17% 14% 1	4661
August	1st to 10th	Day	48% 8% 16% 20% 8%	4256
	11th to 20th	Day	38% 7% 16% 28% 11% 1	3766
	21st to end	Day	33% 7% 15% 27% 17% 2	4180
September	1st to 10th	Day	39% 8% 11% 22% 19% 2	2280
	11th to 20th	Day	34% 6% 11% 23% 24% 2	2155
	21st to end	Day	44% 6% 10% 20% 18% 3	2090
October	1st to 10th	Day	44% 7% 9% 20% 17% 3	2052
	11th to 20th	Day	35% 6% 13% 26% 18% 2	1893
	21st to end	Day	43% 6% 10% 21% 17% 3	1881
November	1st to 10th	Day	37% 5% 12% 23% 19% 3	1681
	11th to 20th	Day	39% 4 11% 22% 20% 3	1710
	21st to end	Day	40% 4 14% 26% 12% 3	1677
December	1st to 10th	Day	46% 6% 16% 17% 14% 1	1520
	11th to 20th	Day	42% 3 17% 19% 17% 2	1906
	21st to end	Day	51% 6% 11% 22% 9% 1	2772
January	1st to 10th	Night	39% 4 11% 30% 11% 4	4429
	11th to 20th	Night	44% 5% 12% 24% 13% 3	4440
	21st to end	Night	54% 4 9% 20% 11% 2	4784
February	1st to 10th	Night	45% 5% 12% 23% 13% 2	2412
	11th to 20th	Night	43% 4 11% 20% 18% 4	2220
	21st to end	Night	45% 4 9% 23% 14% 5%	1884
March	1st to 10th	Night	52% 4 10% 19% 12% 2	3734
	11th to 20th	Night	37% 8% 15% 23% 15% 3	3688
	21st to end	Night	45% 4 8% 13% 24% 6%	3466
April	1st to 10th	Night	45% 6% 11% 20% 15% 3	1900
	11th to 20th	Night	44% 5% 11% 19% 20% 1	1875
	21st to end	Night	45% 5% 9% 22% 16% 4	1805
May	1st to 10th	Night	55% 8% 12% 14% 10% 1	2840
	11th to 20th	Night	52% 9% 13% 14% 10% 1	2635
	21st to end	Night	42% 6% 15% 24% 12% 1	2739
June	1st to 10th	Night	45% 7% 11% 19% 17% 2	1520
	11th to 20th	Night	39% 8% 16% 25% 11% 1	1520
	21st to end	Night	39% 8% 13% 25% 15% 1	1520
July	1st to 10th	Night	44% 10% 14% 18% 13% 1	2480
	11th to 20th	Night	43% 8% 16% 22% 10% 1	2472
	21st to end	Night	48% 7% 14% 14% 15% 2	2651
August	1st to 10th	Night	52% 9% 13% 16% 9% 1	2616
	11th to 20th	Night	42% 7% 13% 29% 8% 1	3123
	21st to end	Night	27% 6% 14% 33% 18% 1	3476
September	1st to 10th	Night	40% 6% 10% 25% 18% 2	1900
	11th to 20th	Night	33% 6% 10% 23% 25% 3	2023
	21st to end	Night	43% 7% 8% 20% 20% 2	2090
October	1st to 10th	Night	44% 6% 12% 21% 14% 3	2126
	11th to 20th	Night	36% 6% 12% 28% 17% 2	2285
	21st to end	Night	44% 5% 12% 21% 16% 1	2717
November	1st to 10th	Night	37% 5% 12% 21% 20% 4	2431
	11th to 20th	Night	41% 4 10% 23% 18% 4	2470
	21st to end	Night	39% 4 14% 29% 12% 2	2501
December	1st to 10th	Night	45% 5% 13% 21% 14% 1	2660
	11th to 20th	Night	44% 5% 13% 18% 17% 2	3288
	21st to end	Night	49% 5% 12% 22% 11% 1	4884

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	23% 28% 28% 19% 2	180
	11th to 20th	Day	19% 34% 31% 14% 1 1	180
	21st to end	Day	19% 28% 36% 11% 5% 1	227
February	1st to 10th	Day	26% 25% 35% 13% 1	327
	11th to 20th	Day	22% 28% 37% 12% 1	456
	21st to end	Day	27% 25% 31% 13% 3	382
March	1st to 10th	Day	21% 23% 37% 15% 3	460
	11th to 20th	Day	18% 28% 35% 14% 3 1	460
	21st to end	Day	25% 23% 37% 11% 4 1	506
April	1st to 10th	Day	23% 26% 31% 13% 6% 1	460
	11th to 20th	Day	26% 21% 32% 15% 6% 1	452
	21st to end	Day	26% 18% 34% 15% 5% 1	460
May	1st to 10th	Day	28% 20% 32% 14% 6% 1	463
	11th to 20th	Day	21% 15% 38% 21% 6% 1	487
	21st to end	Day	19% 10% 30% 28% 11% 3	529
June	1st to 10th	Day	18% 12% 30% 26% 11% 2	490
	11th to 20th	Day	15% 11% 32% 28% 12% 1	490
	21st to end	Day	14% 9% 36% 27% 12% 2	490
July	1st to 10th	Day	16% 5% 30% 29% 17% 3	485
	11th to 20th	Day	13% 5% 29% 31% 19% 3	484
	21st to end	Day	14% 8% 32% 34% 11% 1	532
August	1st to 10th	Day	15% 6% 26% 37% 11% 5%	486
	11th to 20th	Day	15% 6% 25% 32% 16% 5%	479
	21st to end	Day	11% 9% 31% 27% 16% 6%	539
September	1st to 10th	Day	16% 11% 28% 23% 19% 4	490
	11th to 20th	Day	15% 7% 29% 27% 13% 8%	490
	21st to end	Day	21% 11% 31% 23% 10% 3	490
October	1st to 10th	Day	25% 10% 26% 21% 13% 4	490
	11th to 20th	Day	15% 20% 30% 24% 10% 2	485
	21st to end	Day	24% 16% 31% 21% 7% 1	429
November	1st to 10th	Day	16% 15% 31% 24% 12% 2	369
	11th to 20th	Day	23% 23% 28% 21% 5%	370
	21st to end	Day	20% 20% 32% 21% 6%	337
December	1st to 10th	Day	24% 18% 36% 17% 5%	180
	11th to 20th	Day	29% 26% 29% 14% 2	180
	21st to end	Day	21% 23% 34% 17% 5% 1	198
January	1st to 10th	Night	21% 20% 37% 19% 3	760
	11th to 20th	Night	26% 19% 33% 19% 3	760
	21st to end	Night	21% 19% 39% 18% 2	836
February	1st to 10th	Night	22% 19% 36% 21% 2	760
	11th to 20th	Night	23% 21% 38% 16% 2	743
	21st to end	Night	24% 20% 35% 17% 3	628
March	1st to 10th	Night	23% 19% 34% 20% 3	760
	11th to 20th	Night	21% 17% 38% 20% 3 1	760
	21st to end	Night	22% 19% 37% 17% 4	836
April	1st to 10th	Night	23% 18% 35% 21% 4	760
	11th to 20th	Night	22% 15% 36% 23% 4	751
	21st to end	Night	21% 15% 36% 21% 5% 1	665
May	1st to 10th	Night	26% 11% 33% 23% 6%	570
	11th to 20th	Night	23% 12% 37% 22% 5%	461
	21st to end	Night	22% 6% 23% 39% 9% 1	411
June	1st to 10th	Night	19% 6% 30% 33% 10% 1	380
	11th to 20th	Night	17% 6% 28% 36% 13%	380
	21st to end	Night	17% 6% 25% 42% 10%	380
July	1st to 10th	Night	14% 4 23% 40% 18% 1	370
	11th to 20th	Night	15% 3 20% 45% 17% 2	368
	21st to end	Night	14% 4 23% 44% 14% 1	416
August	1st to 10th	Night	11% 3 29% 40% 15% 1	446
	11th to 20th	Night	16% 4 21% 38% 19% 2	746
	21st to end	Night	14% 5% 22% 37% 19% 2	836
September	1st to 10th	Night	17% 5% 27% 33% 15% 2	760
	11th to 20th	Night	17% 6% 23% 32% 18% 4	760
	21st to end	Night	21% 7% 27% 30% 15% 1	760
October	1st to 10th	Night	22% 10% 29% 25% 13% 2	760
	11th to 20th	Night	17% 13% 32% 28% 10% 1	760
	21st to end	Night	26% 12% 34% 21% 7%	836
November	1st to 10th	Night	16% 13% 33% 26% 10% 1	748
	11th to 20th	Night	22% 16% 35% 20% 6% 1	760
	21st to end	Night	21% 18% 33% 24% 5% 1	760
December	1st to 10th	Night	26% 16% 33% 19% 5% 1	760
	11th to 20th	Night	23% 19% 33% 21% 3	760
	21st to end	Night	25% 18% 35% 19% 2	836

Page generated at 2024-10-30 13:19:21. Version ac07

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