Peters Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Peters Observatory clear sky chart from 2005-11-06 to 2024-03-18.

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% 12% 5% 8% 6% 3 4 5% 5% 6% 29%	78543
	Night	19% 13% 5% 9% 6% 3 4 4 4 6% 27%	81237
Transparency	Day	57% 4 11% 18% 8% 1	78248
	Night	59% 4 11% 17% 8% 1	81066
Seeing	Day	27% 17% 28% 18% 8% 2	13785
	Night	26% 17% 27% 22% 8% 1	23107

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% 24% 8% 13% 7% 4 4 3 3 4 18%	2517
	11th to 20th	Day	14% 20% 10% 16% 10% 2 3 3 3 3 14%	2520
	21st to end	Day	19% 23% 8% 9% 10% 4 5% 4 3 4 11%	3000
February	1st to 10th	Day	16% 17% 6% 15% 10% 4 5% 5% 4 4 15%	1710
	11th to 20th	Day	13% 17% 8% 14% 9% 4 4 4 4 4 18%	1731
	21st to end	Day	20% 16% 7% 13% 8% 3 4 4 3 4 19%	1570
March	1st to 10th	Day	18% 15% 6% 12% 6% 2 5% 4 4 4 23%	1897
	11th to 20th	Day	17% 17% 7% 8% 5% 3 4 4 4 4 28%	2048
	21st to end	Day	21% 12% 4 7% 4 3 3 4 3 6% 32%	2304
April	1st to 10th	Day	19% 13% 5% 8% 6% 3 3 4 5% 5% 30%	2160
	11th to 20th	Day	19% 11% 3 6% 5% 3 4 4 6% 5% 35%	2134
	21st to end	Day	23% 12% 4 6% 5% 3 4 3 5% 5% 30%	2168
May	1st to 10th	Day	22% 10% 4 6% 6% 3 4 4 4 6% 32%	2499
	11th to 20th	Day	19% 8% 3 5% 5% 3 5% 4 5% 7% 37%	2478
	21st to end	Day	16% 5% 3 6% 6% 3 5% 5% 6% 8% 37%	2725
June	1st to 10th	Day	19% 7% 3 6% 6% 3 5% 5% 6% 8% 32%	2520
	11th to 20th	Day	20% 5% 3 5% 5% 3 6% 5% 6% 9% 33%	2520
	21st to end	Day	17% 6% 3 6% 6% 4 5% 6% 6% 9% 32%	2520
July	1st to 10th	Day	13% 6% 3 5% 6% 3 6% 6% 7% 8% 36%	2520
	11th to 20th	Day	13% 5% 3 7% 6% 4 6% 6% 6% 9% 35%	2520
	21st to end	Day	14% 6% 3 6% 7% 3 5% 7% 7% 8% 35%	2744
August	1st to 10th	Day	14% 6% 2 5% 6% 3 5% 7% 6% 9% 37%	2406
	11th to 20th	Day	14% 6% 2 7% 7% 4 7% 6% 8% 9% 31%	2210
	21st to end	Day	16% 6% 2 5% 6% 4 5% 5% 6% 7% 38%	2376
September	1st to 10th	Day	16% 6% 2 5% 5% 3 4 6% 6% 8% 39%	2160
	11th to 20th	Day	16% 7% 3 5% 4 3 3 4 4 7% 43%	2142
	21st to end	Day	16% 6% 3 6% 6% 4 5% 5% 6% 7% 36%	1954
October	1st to 10th	Day	21% 8% 3 7% 6% 3 5% 4 4 7% 32%	1800
	11th to 20th	Day	20% 8% 3 5% 6% 3 5% 6% 5% 7% 31%	1800
	21st to end	Day	29% 13% 3 6% 5% 3 4 4 5% 6% 22%	1863
November	1st to 10th	Day	17% 11% 4 7% 5% 4 5% 5% 5% 7% 31%	1671
	11th to 20th	Day	16% 16% 5% 9% 7% 3 4 4 4 4 28%	1638
	21st to end	Day	19% 17% 6% 10% 5% 4 4 4 5% 6% 21%	1520
December	1st to 10th	Day	20% 21% 9% 12% 5% 2 4 4 4 5% 15%	1520
	11th to 20th	Day	22% 17% 10% 10% 6% 3 4 3 3 4 17%	1906
	21st to end	Day	27% 20% 8% 8% 6% 3 3 3 3 4 14%	2772
January	1st to 10th	Night	17% 22% 8% 16% 7% 3 4 3 3 4 12%	4429
	11th to 20th	Night	13% 20% 8% 15% 10% 4 4 3 4 4 14%	4440
	21st to end	Night	21% 19% 8% 14% 11% 3 4 3 3 3 11%	4651
February	1st to 10th	Night	16% 16% 7% 14% 9% 4 5% 4 4 4 17%	2470
	11th to 20th	Night	14% 15% 7% 14% 10% 4 6% 5% 4 5% 17%	2333
	21st to end	Night	17% 14% 7% 14% 9% 4 4 3 3 5% 18%	1884
March	1st to 10th	Night	17% 13% 7% 12% 8% 3 4 4 4 5% 23%	2270
	11th to 20th	Night	18% 15% 5% 9% 8% 2 4 4 4 5% 26%	2076
	21st to end	Night	21% 13% 4 7% 5% 3 4 4 5% 5% 31%	2052
April	1st to 10th	Night	21% 14% 5% 6% 5% 2 4 4 5% 6% 29%	1800
	11th to 20th	Night	21% 10% 3 6% 5% 3 5% 5% 4 6% 32%	1775
	21st to end	Night	21% 10% 3 6% 5% 2 4 4 6% 6% 34%	1792
May	1st to 10th	Night	23% 9% 3 5% 6% 2 4 4 3 6% 33%	1476
	11th to 20th	Night	15% 8% 3 5% 5% 3 5% 5% 6% 8% 38%	1415
	21st to end	Night	14% 5% 2 6% 5% 3 5% 5% 7% 7% 40%	1550
June	1st to 10th	Night	20% 5% 2 6% 5% 4 6% 4 5% 8% 37%	1440
	11th to 20th	Night	20% 5% 2 4 5% 3 5% 4 5% 8% 40%	1440
	21st to end	Night	15% 5% 3 6% 5% 3 5% 6% 6% 7% 40%	1440
July	1st to 10th	Night	11% 4 2 5% 6% 4 5% 5% 7% 7% 43%	1440
	11th to 20th	Night	12% 5% 2 5% 5% 3 5% 5% 6% 8% 44%	1440
	21st to end	Night	14% 5% 2 5% 5% 3 4 4 6% 8% 44%	1574
August	1st to 10th	Night	13% 5% 2 5% 5% 2 4 5% 7% 9% 43%	1529
	11th to 20th	Night	13% 6% 3 6% 7% 4 5% 5% 6% 8% 36%	1671
	21st to end	Night	14% 6% 3 6% 4 3 3 4 6% 7% 44%	1980
September	1st to 10th	Night	15% 6% 2 5% 5% 3 4 5% 5% 8% 42%	1800
	11th to 20th	Night	18% 6% 3 4 4 2 4 4 3 6% 47%	1817
	21st to end	Night	18% 5% 2 5% 5% 3 5% 4 6% 8% 39%	2002
October	1st to 10th	Night	24% 6% 3 6% 6% 3 4 4 5% 6% 33%	2160
	11th to 20th	Night	23% 9% 3 6% 6% 3 6% 5% 4 6% 31%	2160
	21st to end	Night	30% 12% 4 6% 6% 3 4 4 4 5% 23%	2492
November	1st to 10th	Night	18% 11% 4 8% 6% 4 5% 4 5% 5% 32%	2407
	11th to 20th	Night	20% 14% 5% 7% 5% 3 5% 4 5% 6% 27%	2540
	21st to end	Night	18% 17% 7% 9% 6% 3 5% 4 5% 6% 22%	2660
December	1st to 10th	Night	22% 21% 8% 10% 6% 3 5% 4 4 4 15%	2660
	11th to 20th	Night	22% 16% 8% 12% 6% 3 4 4 4 5% 16%	3288
	21st to end	Night	28% 17% 9% 8% 6% 3 4 3 3 5% 14%	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	71% 3 10% 12% 3	2518
	11th to 20th	Day	77% 3 8% 9% 3 1	2520
	21st to end	Day	78% 2 10% 6% 3 1	3000
February	1st to 10th	Day	74% 4 7% 11% 3	1710
	11th to 20th	Day	70% 5% 7% 13% 4	1740
	21st to end	Day	71% 3 8% 11% 6%	1570
March	1st to 10th	Day	65% 3 11% 15% 5% 1	1900
	11th to 20th	Day	61% 3 9% 14% 11% 2	2048
	21st to end	Day	57% 3 8% 16% 15% 2	2304
April	1st to 10th	Day	58% 3 7% 21% 9% 2	2160
	11th to 20th	Day	52% 3 10% 21% 12% 1	2134
	21st to end	Day	56% 3 8% 20% 11% 2	2168
May	1st to 10th	Day	55% 4 9% 19% 12% 2	2499
	11th to 20th	Day	47% 4 10% 25% 12% 2	2482
	21st to end	Day	44% 6% 17% 22% 10% 1	2725
June	1st to 10th	Day	50% 6% 12% 19% 12% 1	2520
	11th to 20th	Day	48% 4 14% 24% 10% 1	2520
	21st to end	Day	49% 6% 14% 21% 10%	2520
July	1st to 10th	Day	44% 6% 13% 25% 12% 1	2450
	11th to 20th	Day	44% 6% 16% 27% 7%	2445
	21st to end	Day	47% 6% 13% 23% 11% 1	2591
August	1st to 10th	Day	43% 7% 16% 24% 10% 1	2392
	11th to 20th	Day	48% 6% 16% 23% 7%	2210
	21st to end	Day	44% 6% 13% 26% 9% 1	2376
September	1st to 10th	Day	42% 6% 12% 28% 10% 1	2160
	11th to 20th	Day	43% 3 11% 26% 16% 1	2142
	21st to end	Day	47% 6% 10% 25% 12% 1	1954
October	1st to 10th	Day	54% 4 10% 21% 11% 1	1800
	11th to 20th	Day	52% 6% 14% 22% 6% 1	1800
	21st to end	Day	65% 4 11% 12% 7% 1	1863
November	1st to 10th	Day	53% 5% 11% 19% 11% 1	1671
	11th to 20th	Day	60% 4 11% 16% 7% 2	1638
	21st to end	Day	65% 5% 14% 12% 4	1520
December	1st to 10th	Day	74% 3 9% 11% 3	1520
	11th to 20th	Day	71% 4 13% 8% 4	1906
	21st to end	Day	76% 3 7% 10% 3	2772
January	1st to 10th	Night	77% 4 9% 7% 3	4429
	11th to 20th	Night	74% 3 7% 10% 5%	4440
	21st to end	Night	80% 3 7% 7% 2 1	4651
February	1st to 10th	Night	71% 4 8% 12% 5%	2470
	11th to 20th	Night	71% 4 7% 12% 5%	2335
	21st to end	Night	70% 3 10% 11% 6%	1884
March	1st to 10th	Night	65% 3 10% 15% 6%	2280
	11th to 20th	Night	61% 4 10% 17% 7% 1	2077
	21st to end	Night	57% 4 7% 18% 12% 2	2052
April	1st to 10th	Night	58% 5% 10% 18% 8% 1	1800
	11th to 20th	Night	53% 5% 10% 19% 13% 1	1775
	21st to end	Night	52% 4 10% 19% 12% 3	1792
May	1st to 10th	Night	53% 3 11% 16% 14% 3	1476
	11th to 20th	Night	43% 7% 11% 24% 13% 2	1416
	21st to end	Night	42% 6% 16% 22% 12% 2	1551
June	1st to 10th	Night	47% 5% 11% 24% 12% 1	1440
	11th to 20th	Night	42% 6% 15% 23% 13% 1	1440
	21st to end	Night	43% 6% 12% 28% 11% 1	1440
July	1st to 10th	Night	38% 6% 14% 26% 15% 2	1400
	11th to 20th	Night	37% 5% 17% 28% 13% 1	1392
	21st to end	Night	38% 5% 15% 26% 14% 2	1486
August	1st to 10th	Night	36% 6% 16% 30% 10% 1	1519
	11th to 20th	Night	44% 6% 18% 23% 10%	1671
	21st to end	Night	39% 6% 14% 28% 12% 1	1980
September	1st to 10th	Night	41% 5% 14% 28% 11% 1	1800
	11th to 20th	Night	39% 4 12% 27% 17% 1	1817
	21st to end	Night	43% 5% 11% 28% 12% 1	2002
October	1st to 10th	Night	52% 5% 13% 19% 11%	2160
	11th to 20th	Night	53% 5% 15% 18% 9% 1	2160
	21st to end	Night	65% 4 10% 13% 8% 1	2492
November	1st to 10th	Night	54% 5% 10% 17% 11% 2	2407
	11th to 20th	Night	58% 5% 10% 19% 7% 2	2540
	21st to end	Night	64% 4 13% 15% 4	2660
December	1st to 10th	Night	73% 5% 10% 10% 2	2660
	11th to 20th	Night	71% 4 9% 11% 4	3288
	21st to end	Night	75% 3 9% 11% 2	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	33% 23% 26% 13% 5%	180
	11th to 20th	Day	41% 24% 27% 6% 2 1	180
	21st to end	Day	28% 27% 33% 10% 2	263
February	1st to 10th	Day	42% 27% 24% 7%	270
	11th to 20th	Day	35% 32% 27% 6%	338
	21st to end	Day	39% 24% 25% 9% 2	382
March	1st to 10th	Day	32% 25% 27% 13% 2	460
	11th to 20th	Day	36% 23% 26% 12% 3	449
	21st to end	Day	37% 22% 22% 14% 4 1	462
April	1st to 10th	Day	34% 24% 25% 11% 5%	420
	11th to 20th	Day	32% 22% 23% 13% 7% 3	412
	21st to end	Day	38% 15% 26% 13% 6% 2	420
May	1st to 10th	Day	32% 17% 28% 13% 8% 2	423
	11th to 20th	Day	26% 13% 34% 18% 8% 2	447
	21st to end	Day	18% 15% 31% 22% 11% 3	485
June	1st to 10th	Day	23% 14% 30% 24% 7% 2	450
	11th to 20th	Day	22% 12% 31% 21% 12% 2	450
	21st to end	Day	19% 16% 35% 21% 6% 2	450
July	1st to 10th	Day	15% 9% 30% 28% 14% 4	445
	11th to 20th	Day	14% 8% 30% 32% 12% 3	444
	21st to end	Day	15% 9% 37% 26% 10% 3	488
August	1st to 10th	Day	15% 11% 27% 26% 16% 6%	446
	11th to 20th	Day	18% 8% 28% 28% 13% 6%	439
	21st to end	Day	16% 12% 28% 26% 12% 6%	495
September	1st to 10th	Day	18% 11% 26% 23% 17% 5%	450
	11th to 20th	Day	16% 11% 26% 21% 16% 9%	450
	21st to end	Day	20% 13% 29% 20% 13% 4	450
October	1st to 10th	Day	27% 12% 27% 16% 12% 5%	450
	11th to 20th	Day	25% 20% 30% 15% 8% 1	450
	21st to end	Day	39% 18% 25% 14% 4	436
November	1st to 10th	Day	31% 19% 23% 19% 8%	365
	11th to 20th	Day	31% 28% 24% 14% 3	298
	21st to end	Day	39% 19% 32% 9%	180
December	1st to 10th	Day	37% 23% 28% 10% 1 1	180
	11th to 20th	Day	37% 26% 30% 7%	180
	21st to end	Day	38% 24% 32% 5% 1	198
January	1st to 10th	Night	30% 26% 30% 12% 1	760
	11th to 20th	Night	31% 25% 27% 15% 2 1	760
	21st to end	Night	24% 25% 32% 17% 2	836
February	1st to 10th	Night	31% 23% 30% 16% 1	760
	11th to 20th	Night	29% 26% 30% 13% 2	743
	21st to end	Night	31% 24% 28% 15% 2	628
March	1st to 10th	Night	28% 22% 30% 18% 2	760
	11th to 20th	Night	31% 22% 27% 18% 2	752
	21st to end	Night	30% 21% 23% 19% 6% 1	792
April	1st to 10th	Night	28% 19% 31% 20% 2	720
	11th to 20th	Night	28% 18% 28% 18% 8% 1	711
	21st to end	Night	30% 14% 27% 23% 6%	712
May	1st to 10th	Night	29% 10% 25% 29% 7%	396
	11th to 20th	Night	20% 8% 36% 29% 6% 1	354
	21st to end	Night	16% 6% 34% 32% 11% 1	389
June	1st to 10th	Night	18% 8% 25% 36% 12% 1	360
	11th to 20th	Night	19% 9% 23% 37% 11%	360
	21st to end	Night	14% 7% 28% 41% 9%	360
July	1st to 10th	Night	11% 5% 24% 44% 16% 1	350
	11th to 20th	Night	13% 3 24% 43% 15% 1	348
	21st to end	Night	16% 4 22% 43% 14% 1	394
August	1st to 10th	Night	14% 4 26% 35% 20% 1	455
	11th to 20th	Night	15% 5% 21% 33% 22% 3	607
	21st to end	Night	15% 7% 24% 35% 19% 1	792
September	1st to 10th	Night	17% 8% 25% 31% 18% 2	720
	11th to 20th	Night	20% 7% 21% 29% 19% 3	720
	21st to end	Night	19% 11% 25% 29% 15% 1	720
October	1st to 10th	Night	27% 11% 23% 22% 16% 2	720
	11th to 20th	Night	27% 16% 28% 23% 6%	720
	21st to end	Night	37% 15% 27% 19% 2	792
November	1st to 10th	Night	26% 18% 30% 19% 7%	740
	11th to 20th	Night	29% 21% 27% 15% 6% 1	760
	21st to end	Night	28% 23% 28% 16% 4	760
December	1st to 10th	Night	35% 24% 25% 13% 3	760
	11th to 20th	Night	35% 22% 27% 13% 3	760
	21st to end	Night	34% 26% 27% 11% 1	836

Page generated at 2024-03-15 14:01:45. Version ac07

Copyright © 2024 Attilla Danko.