Leitner Observatory and Planetarium
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Leitner Observatory and Planetarium clear sky chart from 2005-11-06 to 2024-02-15.

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	17% 6% 2 5% 5% 3 4 4 5% 7% 41%	78210
	Night	18% 7% 3 5% 4 3 4 4 5% 6% 42%	80857
Transparency	Day	42% 6% 12% 22% 15% 2	77915
	Night	43% 5% 12% 22% 15% 2	80686
Seeing	Day	20% 16% 31% 22% 9% 2	13995
	Night	21% 13% 32% 26% 8% 1	23202

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	17% 6% 2 6% 4 3 4 4 5% 5% 46%	2517
	11th to 20th	Day	17% 9% 3 6% 6% 3 4 5% 5% 5% 37%	2520
	21st to end	Day	22% 9% 3 6% 5% 3 4 4 4 5% 33%	2868
February	1st to 10th	Day	17% 7% 3 5% 5% 3 5% 4 5% 7% 38%	1776
	11th to 20th	Day	16% 6% 2 4 5% 3 4 4 6% 8% 42%	1788
	21st to end	Day	22% 8% 3 5% 4 3 3 4 5% 6% 37%	1480
March	1st to 10th	Day	15% 7% 3 5% 5% 3 4 4 5% 7% 43%	1797
	11th to 20th	Day	17% 6% 2 4 5% 3 5% 5% 6% 8% 39%	1847
	21st to end	Day	20% 7% 3 6% 5% 3 4 4 3 4 41%	2376
April	1st to 10th	Day	19% 8% 2 4 4 3 4 4 5% 7% 40%	2160
	11th to 20th	Day	19% 5% 2 5% 4 3 4 4 3 7% 43%	2134
	21st to end	Day	21% 5% 2 5% 5% 3 4 4 5% 6% 41%	2254
May	1st to 10th	Day	24% 8% 3 4 4 3 4 4 5% 7% 35%	2340
	11th to 20th	Day	20% 5% 3 4 4 3 4 4 5% 8% 40%	2396
	21st to end	Day	16% 5% 2 5% 4 2 4 5% 5% 8% 44%	2725
June	1st to 10th	Day	19% 5% 2 5% 5% 3 5% 6% 6% 8% 36%	2520
	11th to 20th	Day	17% 6% 2 4 5% 3 4 5% 6% 10% 37%	2520
	21st to end	Day	14% 6% 3 4 5% 3 5% 5% 6% 9% 41%	2520
July	1st to 10th	Day	13% 5% 2 5% 5% 3 5% 5% 7% 8% 42%	2520
	11th to 20th	Day	13% 4 2 5% 4 3 6% 6% 6% 9% 42%	2520
	21st to end	Day	13% 6% 2 5% 5% 3 5% 6% 6% 9% 40%	2744
August	1st to 10th	Day	12% 5% 2 5% 5% 4 5% 5% 6% 10% 41%	2413
	11th to 20th	Day	13% 6% 2 5% 5% 3 5% 5% 6% 9% 43%	2132
	21st to end	Day	12% 5% 2 5% 6% 3 4 5% 6% 9% 43%	2376
September	1st to 10th	Day	14% 5% 2 5% 5% 4 4 5% 5% 6% 45%	2160
	11th to 20th	Day	13% 5% 2 4 3 3 4 4 4 6% 52%	2036
	21st to end	Day	19% 5% 2 4 5% 3 4 4 4 6% 43%	1980
October	1st to 10th	Day	22% 7% 2 4 4 3 3 4 4 6% 41%	1953
	11th to 20th	Day	16% 4 2 4 4 2 3 5% 5% 7% 47%	1790
	21st to end	Day	21% 6% 1 4 5% 3 4 5% 6% 6% 40%	1782
November	1st to 10th	Day	14% 6% 2 5% 5% 3 3 3 4 6% 49%	1671
	11th to 20th	Day	20% 5% 2 3 3 2 3 3 4 7% 47%	1710
	21st to end	Day	17% 6% 2 4 4 2 4 4 5% 7% 45%	1687
December	1st to 10th	Day	19% 6% 3 5% 5% 4 4 5% 5% 7% 38%	1520
	11th to 20th	Day	23% 5% 2 3 4 2 3 3 4 6% 45%	1906
	21st to end	Day	20% 11% 3 6% 5% 3 4 4 4 6% 34%	2772
January	1st to 10th	Night	17% 6% 2 4 4 2 3 4 4 6% 47%	4429
	11th to 20th	Night	18% 8% 3 6% 5% 2 3 3 4 5% 44%	4440
	21st to end	Night	25% 11% 3 6% 4 2 3 4 3 5% 34%	4787
February	1st to 10th	Night	17% 8% 3 5% 4 3 4 4 4 6% 41%	2402
	11th to 20th	Night	18% 8% 3 4 5% 2 4 4 4 7% 41%	2153
	21st to end	Night	21% 7% 3 5% 4 3 4 4 3 5% 41%	1776
March	1st to 10th	Night	18% 6% 2 4 4 2 4 5% 5% 6% 44%	2150
	11th to 20th	Night	17% 7% 2 5% 5% 3 4 5% 5% 6% 42%	2106
	21st to end	Night	18% 8% 3 4 4 3 4 4 5% 6% 42%	1980
April	1st to 10th	Night	19% 7% 3 6% 5% 3 4 4 5% 7% 38%	1800
	11th to 20th	Night	20% 5% 2 5% 4 2 4 4 4 6% 43%	1775
	21st to end	Night	21% 6% 3 6% 5% 2 4 3 4 5% 41%	1706
May	1st to 10th	Night	23% 8% 2 5% 6% 3 4 4 5% 7% 33%	1620
	11th to 20th	Night	21% 7% 3 5% 5% 3 4 4 4 7% 38%	1510
	21st to end	Night	19% 7% 3 5% 4 3 4 4 5% 8% 39%	1550
June	1st to 10th	Night	19% 5% 2 6% 5% 3 5% 5% 5% 7% 39%	1440
	11th to 20th	Night	17% 6% 2 4 4 3 3 6% 5% 9% 40%	1440
	21st to end	Night	14% 6% 2 5% 5% 3 4 3 6% 9% 44%	1440
July	1st to 10th	Night	14% 5% 2 5% 5% 3 5% 5% 7% 9% 40%	1440
	11th to 20th	Night	14% 6% 3 4 5% 4 6% 5% 7% 9% 38%	1440
	21st to end	Night	13% 5% 2 5% 5% 3 5% 6% 7% 8% 41%	1574
August	1st to 10th	Night	8% 5% 2 5% 6% 3 5% 7% 7% 9% 43%	1506
	11th to 20th	Night	13% 5% 4 6% 6% 4 6% 6% 6% 8% 37%	1765
	21st to end	Night	14% 4 2 5% 5% 3 4 5% 5% 8% 45%	1980
September	1st to 10th	Night	15% 5% 3 5% 5% 3 4 4 4 8% 43%	1800
	11th to 20th	Night	16% 4 2 3 4 2 3 3 4 6% 53%	1923
	21st to end	Night	18% 6% 2 4 4 3 4 3 4 6% 44%	1980
October	1st to 10th	Night	21% 7% 3 5% 4 3 3 4 4 5% 41%	2005
	11th to 20th	Night	16% 5% 2 5% 4 2 4 3 5% 6% 48%	2168
	21st to end	Night	23% 7% 2 4 4 2 4 3 5% 5% 41%	2574
November	1st to 10th	Night	13% 6% 3 5% 4 2 4 4 5% 6% 49%	2407
	11th to 20th	Night	20% 6% 3 4 3 2 3 3 3 6% 47%	2470
	21st to end	Night	17% 5% 2 4 4 3 4 3 5% 6% 47%	2489
December	1st to 10th	Night	21% 6% 2 5% 4 3 5% 4 5% 5% 40%	2660
	11th to 20th	Night	21% 6% 2 4 3 2 5% 4 5% 6% 42%	3288
	21st to end	Night	22% 10% 3 5% 4 3 4 3 3 5% 37%	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	39% 4 11% 31% 12% 3	2518
	11th to 20th	Day	48% 5% 12% 23% 11% 1	2520
	21st to end	Day	52% 7% 8% 20% 10% 2	2868
February	1st to 10th	Day	45% 6% 13% 20% 14% 2	1776
	11th to 20th	Day	41% 6% 11% 23% 16% 3	1797
	21st to end	Day	48% 5% 10% 19% 14% 3	1480
March	1st to 10th	Day	43% 4 14% 21% 15% 4	1800
	11th to 20th	Day	44% 5% 13% 22% 15% 2	1847
	21st to end	Day	48% 4 8% 16% 18% 5%	2376
April	1st to 10th	Day	43% 6% 11% 20% 17% 4	2160
	11th to 20th	Day	42% 4 11% 21% 18% 3	2134
	21st to end	Day	45% 6% 9% 20% 16% 4	2254
May	1st to 10th	Day	48% 6% 10% 19% 14% 3	2340
	11th to 20th	Day	42% 6% 12% 21% 17% 3	2400
	21st to end	Day	39% 9% 16% 21% 14% 2	2725
June	1st to 10th	Day	44% 8% 13% 23% 11% 1	2520
	11th to 20th	Day	42% 8% 14% 22% 13% 1	2520
	21st to end	Day	39% 9% 13% 24% 14% 1	2520
July	1st to 10th	Day	38% 9% 12% 22% 17% 2	2450
	11th to 20th	Day	36% 8% 14% 26% 14% 2	2445
	21st to end	Day	38% 8% 14% 21% 17% 2	2591
August	1st to 10th	Day	37% 10% 14% 25% 14% 1	2399
	11th to 20th	Day	37% 8% 14% 25% 14% 1	2132
	21st to end	Day	37% 7% 12% 22% 19% 2	2376
September	1st to 10th	Day	38% 8% 12% 22% 18% 2	2160
	11th to 20th	Day	33% 6% 12% 23% 24% 2	2036
	21st to end	Day	42% 6% 8% 21% 20% 3	1980
October	1st to 10th	Day	45% 5% 9% 21% 17% 3	1953
	11th to 20th	Day	36% 5% 14% 27% 17% 1	1790
	21st to end	Day	43% 7% 10% 21% 16% 3	1782
November	1st to 10th	Day	39% 4 13% 21% 20% 3	1671
	11th to 20th	Day	39% 4 12% 22% 20% 3	1710
	21st to end	Day	40% 5% 13% 26% 13% 3	1687
December	1st to 10th	Day	46% 5% 14% 18% 15% 1	1520
	11th to 20th	Day	42% 3 16% 19% 18% 2	1906
	21st to end	Day	52% 5% 11% 22% 10% 1	2772
January	1st to 10th	Night	39% 4 11% 30% 12% 4	4429
	11th to 20th	Night	45% 4 12% 23% 13% 3	4440
	21st to end	Night	55% 4 8% 20% 11% 2	4787
February	1st to 10th	Night	44% 6% 12% 23% 12% 2	2402
	11th to 20th	Night	44% 5% 10% 20% 16% 5%	2155
	21st to end	Night	47% 4 8% 22% 15% 4	1776
March	1st to 10th	Night	40% 5% 13% 22% 17% 4	2160
	11th to 20th	Night	43% 6% 10% 21% 16% 4	2107
	21st to end	Night	44% 4 10% 18% 20% 5%	1980
April	1st to 10th	Night	46% 5% 10% 20% 16% 3	1800
	11th to 20th	Night	43% 5% 11% 20% 20% 1	1775
	21st to end	Night	47% 4 9% 21% 14% 5%	1706
May	1st to 10th	Night	51% 8% 9% 16% 14% 2	1620
	11th to 20th	Night	46% 6% 11% 18% 16% 3	1511
	21st to end	Night	44% 6% 17% 19% 13% 1	1551
June	1st to 10th	Night	45% 6% 10% 20% 16% 2	1440
	11th to 20th	Night	42% 7% 13% 26% 11% 1	1440
	21st to end	Night	39% 8% 13% 26% 14%	1440
July	1st to 10th	Night	39% 11% 13% 20% 15% 2	1400
	11th to 20th	Night	40% 7% 16% 26% 9% 1	1392
	21st to end	Night	36% 8% 16% 23% 14% 2	1486
August	1st to 10th	Night	36% 9% 17% 22% 15% 2	1496
	11th to 20th	Night	44% 7% 14% 23% 11% 1	1765
	21st to end	Night	36% 7% 13% 23% 19% 1	1980
September	1st to 10th	Night	41% 6% 10% 25% 17% 2	1800
	11th to 20th	Night	34% 5% 10% 23% 26% 3	1923
	21st to end	Night	43% 5% 7% 20% 22% 3	1980
October	1st to 10th	Night	46% 6% 10% 22% 14% 3	2005
	11th to 20th	Night	39% 5% 12% 28% 15% 1	2168
	21st to end	Night	46% 5% 12% 20% 16% 1	2574
November	1st to 10th	Night	37% 5% 12% 22% 20% 4	2407
	11th to 20th	Night	41% 4 10% 24% 18% 4	2470
	21st to end	Night	39% 4 13% 29% 13% 2	2489
December	1st to 10th	Night	47% 5% 12% 20% 15% 1	2660
	11th to 20th	Night	44% 5% 15% 17% 18% 2	3288
	21st to end	Night	50% 4 12% 22% 12% 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% 26% 28% 21% 2	180
	11th to 20th	Day	23% 32% 29% 14% 1 1	180
	21st to end	Day	21% 27% 34% 11% 5% 2	225
February	1st to 10th	Day	25% 25% 34% 15% 1	336
	11th to 20th	Day	22% 28% 35% 13% 1	432
	21st to end	Day	27% 25% 32% 14% 3	346
March	1st to 10th	Day	19% 25% 36% 17% 2	420
	11th to 20th	Day	21% 25% 35% 14% 4 1	420
	21st to end	Day	26% 23% 35% 11% 4 1	462
April	1st to 10th	Day	24% 24% 33% 13% 6% 1	420
	11th to 20th	Day	26% 20% 30% 18% 6% 1	412
	21st to end	Day	26% 18% 34% 16% 4 2	420
May	1st to 10th	Day	28% 21% 31% 14% 6% 1	423
	11th to 20th	Day	21% 15% 36% 21% 5% 1	447
	21st to end	Day	20% 10% 29% 27% 12% 2	485
June	1st to 10th	Day	17% 11% 31% 26% 12% 2	450
	11th to 20th	Day	18% 11% 33% 27% 9% 1	450
	21st to end	Day	15% 9% 32% 28% 13% 2	450
July	1st to 10th	Day	16% 5% 27% 31% 18% 2	445
	11th to 20th	Day	14% 5% 25% 36% 16% 4	444
	21st to end	Day	13% 7% 33% 36% 10% 2	488
August	1st to 10th	Day	11% 7% 28% 35% 14% 5%	446
	11th to 20th	Day	13% 5% 28% 31% 18% 5%	439
	21st to end	Day	12% 8% 31% 29% 14% 6%	495
September	1st to 10th	Day	17% 8% 27% 24% 18% 5%	450
	11th to 20th	Day	16% 7% 32% 25% 13% 7%	450
	21st to end	Day	21% 11% 31% 23% 11% 3	450
October	1st to 10th	Day	28% 10% 24% 21% 12% 4	450
	11th to 20th	Day	16% 17% 28% 28% 8% 2	444
	21st to end	Day	26% 17% 31% 17% 7% 2	396
November	1st to 10th	Day	16% 16% 30% 25% 11% 3	365
	11th to 20th	Day	24% 24% 26% 21% 5%	370
	21st to end	Day	19% 22% 29% 22% 7%	347
December	1st to 10th	Day	21% 20% 36% 17% 6%	180
	11th to 20th	Day	27% 27% 32% 13% 2	180
	21st to end	Day	25% 21% 34% 14% 6% 1	198
January	1st to 10th	Night	21% 20% 37% 19% 3	760
	11th to 20th	Night	28% 19% 32% 19% 3	760
	21st to end	Night	20% 21% 37% 19% 3	836
February	1st to 10th	Night	22% 20% 34% 23% 2	760
	11th to 20th	Night	22% 20% 39% 16% 2	722
	21st to end	Night	26% 19% 36% 17% 2	592
March	1st to 10th	Night	23% 18% 36% 20% 3	720
	11th to 20th	Night	23% 14% 38% 21% 4 1	720
	21st to end	Night	22% 19% 36% 20% 3	792
April	1st to 10th	Night	23% 18% 34% 21% 4	720
	11th to 20th	Night	22% 13% 36% 24% 5%	711
	21st to end	Night	23% 14% 36% 21% 5%	626
May	1st to 10th	Night	26% 11% 33% 22% 7%	540
	11th to 20th	Night	23% 10% 39% 22% 6%	449
	21st to end	Night	20% 5% 23% 40% 11% 1	389
June	1st to 10th	Night	23% 5% 30% 32% 11% 1	360
	11th to 20th	Night	19% 4 29% 35% 12%	360
	21st to end	Night	15% 4 27% 42% 11% 1	360
July	1st to 10th	Night	14% 5% 24% 41% 17% 1	350
	11th to 20th	Night	14% 2 20% 46% 18% 1	348
	21st to end	Night	15% 4 24% 43% 13% 1	394
August	1st to 10th	Night	10% 3 29% 41% 15% 1	432
	11th to 20th	Night	15% 3 19% 43% 18% 2	701
	21st to end	Night	15% 4 23% 37% 18% 3	792
September	1st to 10th	Night	18% 3 28% 33% 15% 3	720
	11th to 20th	Night	18% 5% 25% 31% 18% 3	720
	21st to end	Night	22% 6% 26% 29% 16% 1	720
October	1st to 10th	Night	24% 10% 26% 25% 13% 3	720
	11th to 20th	Night	19% 12% 31% 29% 9% 1	720
	21st to end	Night	27% 11% 35% 20% 7%	792
November	1st to 10th	Night	16% 14% 33% 24% 12% 1	740
	11th to 20th	Night	23% 16% 34% 20% 6% 1	760
	21st to end	Night	22% 17% 32% 24% 5% 1	760
December	1st to 10th	Night	26% 16% 31% 20% 5% 1	760
	11th to 20th	Night	25% 19% 31% 21% 3	760
	21st to end	Night	26% 17% 37% 18% 2	836

Page generated at 2024-02-12 06:35:31. Version ac07

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