Fred G. Dale Planetarium
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fred G. Dale Planetarium clear sky chart from 2005-11-06 to 2024-03-08.

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	11% 7% 3 6% 5% 3 4 4 5% 7% 43%	78885
	Night	10% 7% 3 6% 5% 3 4 4 5% 7% 46%	80658
Transparency	Day	39% 7% 14% 25% 13% 2	78599
	Night	38% 6% 13% 25% 15% 2	80464
Seeing	Day	14% 10% 32% 29% 13% 2	14850
	Night	13% 10% 36% 31% 10% 1	24964

By Month

Percentage Cloud Cover SE (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	8% 13% 5% 11% 10% 4 4 5% 5% 6% 28%	2576
	11th to 20th	Day	6% 12% 6% 9% 7% 3 9% 4 6% 7% 31%	2850
	21st to end	Day	7% 10% 5% 14% 7% 3 4 4 5% 7% 34%	3135
February	1st to 10th	Day	11% 10% 5% 8% 9% 5% 5% 6% 4 6% 31%	1710
	11th to 20th	Day	9% 9% 4 7% 6% 3 4 5% 4 6% 42%	1725
	21st to end	Day	11% 9% 5% 8% 5% 4 5% 5% 5% 7% 38%	1570
March	1st to 10th	Day	10% 9% 4 7% 5% 2 3 3 6% 7% 43%	1975
	11th to 20th	Day	14% 7% 4 7% 5% 3 4 3 5% 8% 39%	1980
	21st to end	Day	18% 13% 4 7% 5% 3 5% 5% 5% 7% 29%	2178
April	1st to 10th	Day	13% 10% 3 6% 5% 2 4 3 6% 8% 39%	2008
	11th to 20th	Day	19% 8% 3 6% 4 3 3 4 4 7% 38%	2312
	21st to end	Day	20% 8% 2 5% 5% 3 4 4 4 6% 38%	2340
May	1st to 10th	Day	15% 8% 3 6% 5% 3 5% 5% 6% 7% 37%	2340
	11th to 20th	Day	14% 8% 3 5% 5% 3 5% 4 6% 8% 39%	2302
	21st to end	Day	16% 8% 3 5% 6% 3 4 5% 5% 7% 37%	2593
June	1st to 10th	Day	8% 5% 2 5% 5% 3 4 5% 6% 9% 50%	2520
	11th to 20th	Day	11% 5% 2 5% 5% 3 4 6% 6% 8% 46%	2693
	21st to end	Day	7% 5% 2 4 5% 2 5% 5% 6% 9% 50%	2700
July	1st to 10th	Day	6% 3 2 4 5% 3 4 5% 6% 11% 52%	2555
	11th to 20th	Day	6% 3 2 3 4 2 4 5% 5% 8% 58%	2404
	21st to end	Day	6% 4 2 4 4 2 4 5% 6% 10% 53%	2546
August	1st to 10th	Day	9% 5% 3 7% 6% 4 6% 5% 7% 7% 42%	2328
	11th to 20th	Day	10% 5% 2 4 4 3 4 5% 5% 8% 50%	2301
	21st to end	Day	8% 5% 2 4 4 3 4 4 5% 8% 54%	2574
September	1st to 10th	Day	13% 5% 2 5% 4 3 4 3 5% 6% 49%	2057
	11th to 20th	Day	9% 5% 2 4 5% 2 4 4 5% 6% 55%	1980
	21st to end	Day	11% 3 2 3 4 3 3 4 5% 7% 55%	1980
October	1st to 10th	Day	15% 6% 2 4 5% 3 3 4 5% 5% 48%	1872
	11th to 20th	Day	11% 7% 2 4 4 2 2 4 4 5% 56%	1800
	21st to end	Day	15% 7% 3 5% 4 3 3 2 4 6% 49%	1922
November	1st to 10th	Day	8% 6% 2 4 5% 2 4 5% 5% 7% 51%	1673
	11th to 20th	Day	9% 6% 2 5% 7% 3 4 4 4 8% 47%	1667
	21st to end	Day	11% 9% 4 6% 3 3 3 4 4 7% 46%	1520
December	1st to 10th	Day	8% 7% 3 8% 5% 3 4 4 5% 8% 43%	1520
	11th to 20th	Day	6% 9% 4 7% 7% 4 7% 5% 7% 9% 36%	1918
	21st to end	Day	15% 9% 4 12% 8% 3 4 5% 5% 7% 28%	2761
January	1st to 10th	Night	8% 12% 4 9% 12% 5% 7% 5% 5% 6% 27%	4354
	11th to 20th	Night	4 11% 4 8% 6% 4 9% 6% 9% 6% 33%	4120
	21st to end	Night	7% 11% 7% 11% 5% 3 4 4 4 7% 38%	4532
February	1st to 10th	Night	12% 9% 4 8% 6% 3 4 4 4 5% 39%	2470
	11th to 20th	Night	8% 9% 5% 7% 5% 3 5% 5% 5% 7% 42%	2361
	21st to end	Night	9% 7% 4 6% 4 3 6% 4 5% 6% 46%	1884
March	1st to 10th	Night	11% 7% 3 6% 5% 3 4 4 4 6% 46%	2144
	11th to 20th	Night	13% 8% 4 5% 5% 3 3 3 4 6% 45%	1980
	21st to end	Night	16% 10% 3 6% 7% 3 4 5% 5% 7% 35%	2178
April	1st to 10th	Night	14% 8% 2 6% 5% 3 4 3 6% 6% 43%	1950
	11th to 20th	Night	13% 8% 4 5% 5% 3 4 5% 4 6% 44%	1599
	21st to end	Night	16% 7% 2 5% 4 3 4 4 5% 6% 43%	1620
May	1st to 10th	Night	14% 6% 3 4 5% 2 4 5% 5% 8% 44%	1620
	11th to 20th	Night	12% 6% 2 5% 4 3 4 4 6% 8% 46%	1593
	21st to end	Night	15% 6% 2 5% 5% 2 4 5% 6% 9% 40%	1678
June	1st to 10th	Night	7% 3 1 3 5% 2 3 4 6% 9% 55%	1440
	11th to 20th	Night	8% 4 2 4 3 3 3 4 5% 8% 56%	1260
	21st to end	Night	4 3 1 4 4 3 4 4 6% 8% 59%	1260
July	1st to 10th	Night	5% 4 3 4 4 3 3 4 5% 9% 57%	1400
	11th to 20th	Night	3 2 1 3 4 3 4 5% 6% 8% 62%	1552
	21st to end	Night	3 3 1 4 4 3 4 5% 6% 9% 58%	1772
August	1st to 10th	Night	6% 4 2 5% 5% 3 5% 6% 6% 9% 49%	1611
	11th to 20th	Night	7% 4 1 4 3 1 3 4 6% 9% 58%	1600
	21st to end	Night	5% 3 2 3 4 3 4 4 5% 8% 58%	1782
September	1st to 10th	Night	8% 4 1 3 4 3 4 4 4 7% 57%	1900
	11th to 20th	Night	8% 4 2 4 3 2 4 4 4 7% 58%	1980
	21st to end	Night	9% 4 2 4 3 2 3 4 3 6% 61%	1980
October	1st to 10th	Night	15% 5% 2 4 4 2 4 4 4 5% 50%	2068
	11th to 20th	Night	12% 6% 2 3 4 2 3 3 4 4 55%	2160
	21st to end	Night	15% 5% 2 4 3 3 3 3 4 5% 54%	2431
November	1st to 10th	Night	7% 5% 2 4 3 3 3 5% 5% 7% 57%	2405
	11th to 20th	Night	9% 5% 3 6% 6% 2 3 4 6% 6% 50%	2512
	21st to end	Night	9% 7% 3 5% 4 2 4 4 5% 8% 50%	2660
December	1st to 10th	Night	7% 8% 3 8% 5% 3 4 5% 5% 8% 45%	2660
	11th to 20th	Night	8% 7% 4 6% 6% 3 4 4 5% 7% 46%	3279
	21st to end	Night	15% 11% 4 12% 7% 3 4 4 4 5% 31%	4863

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	55% 7% 13% 18% 7% 1	2577
	11th to 20th	Day	52% 5% 13% 22% 7% 1	2850
	21st to end	Day	48% 8% 16% 17% 11%	3135
February	1st to 10th	Day	53% 7% 13% 16% 10% 1	1710
	11th to 20th	Day	43% 5% 13% 23% 13% 3	1734
	21st to end	Day	45% 6% 11% 23% 12% 3	1570
March	1st to 10th	Day	41% 6% 13% 26% 11% 2	1975
	11th to 20th	Day	45% 6% 12% 24% 11% 2	1980
	21st to end	Day	53% 8% 15% 17% 6% 1	2178
April	1st to 10th	Day	43% 7% 14% 24% 11% 1	2008
	11th to 20th	Day	46% 7% 12% 21% 13% 2	2312
	21st to end	Day	46% 6% 12% 25% 11%	2340
May	1st to 10th	Day	45% 8% 13% 20% 13% 1	2340
	11th to 20th	Day	42% 8% 15% 24% 10%	2306
	21st to end	Day	45% 8% 13% 21% 12% 1	2593
June	1st to 10th	Day	30% 8% 18% 30% 13% 1	2520
	11th to 20th	Day	34% 8% 14% 25% 17% 3	2693
	21st to end	Day	28% 9% 16% 32% 12% 4	2700
July	1st to 10th	Day	27% 8% 17% 30% 17% 1	2486
	11th to 20th	Day	25% 8% 14% 29% 19% 6%	2331
	21st to end	Day	24% 8% 16% 30% 19% 2	2405
August	1st to 10th	Day	38% 10% 15% 23% 12% 1	2314
	11th to 20th	Day	31% 7% 14% 32% 14% 1	2301
	21st to end	Day	28% 8% 12% 26% 21% 5%	2574
September	1st to 10th	Day	35% 6% 11% 25% 19% 3	2057
	11th to 20th	Day	30% 7% 12% 33% 18% 2	1980
	21st to end	Day	30% 6% 10% 31% 22% 1	1980
October	1st to 10th	Day	38% 5% 10% 26% 20% 2	1872
	11th to 20th	Day	30% 5% 12% 29% 18% 6%	1800
	21st to end	Day	39% 5% 11% 23% 18% 4	1922
November	1st to 10th	Day	32% 6% 15% 24% 20% 2	1673
	11th to 20th	Day	37% 6% 15% 25% 16% 2	1667
	21st to end	Day	39% 4 13% 26% 15% 2	1520
December	1st to 10th	Day	40% 6% 17% 24% 10% 3	1520
	11th to 20th	Day	43% 7% 18% 27% 5%	1915
	21st to end	Day	54% 8% 11% 19% 8% 1	2761
January	1st to 10th	Night	54% 8% 11% 17% 9% 1	4354
	11th to 20th	Night	45% 6% 15% 23% 9% 2	4120
	21st to end	Night	47% 6% 14% 20% 12% 1	4532
February	1st to 10th	Night	48% 5% 13% 21% 12% 2	2470
	11th to 20th	Night	40% 6% 14% 22% 15% 3	2362
	21st to end	Night	38% 5% 13% 25% 16% 3	1884
March	1st to 10th	Night	39% 5% 13% 29% 12% 2	2144
	11th to 20th	Night	42% 5% 10% 25% 15% 3	1980
	21st to end	Night	48% 7% 14% 21% 8% 1	2178
April	1st to 10th	Night	41% 7% 11% 24% 15% 1	1950
	11th to 20th	Night	42% 5% 9% 26% 16% 2	1599
	21st to end	Night	40% 8% 12% 23% 15% 1	1620
May	1st to 10th	Night	38% 7% 13% 25% 16% 1	1620
	11th to 20th	Night	36% 8% 14% 25% 17%	1594
	21st to end	Night	40% 8% 16% 21% 13% 3	1679
June	1st to 10th	Night	25% 8% 14% 35% 16% 2	1440
	11th to 20th	Night	27% 6% 15% 26% 21% 5%	1260
	21st to end	Night	22% 7% 16% 33% 18% 3	1260
July	1st to 10th	Night	24% 6% 17% 30% 19% 4	1360
	11th to 20th	Night	19% 7% 15% 31% 21% 6%	1502
	21st to end	Night	20% 8% 17% 29% 23% 3	1673
August	1st to 10th	Night	29% 10% 15% 28% 16% 2	1601
	11th to 20th	Night	23% 7% 14% 33% 20% 4	1600
	21st to end	Night	24% 6% 14% 27% 22% 7%	1782
September	1st to 10th	Night	26% 6% 11% 29% 23% 6%	1900
	11th to 20th	Night	25% 7% 12% 33% 21% 3	1980
	21st to end	Night	26% 5% 9% 31% 25% 3	1980
October	1st to 10th	Night	36% 5% 10% 23% 23% 2	2068
	11th to 20th	Night	33% 4 8% 26% 25% 4	2160
	21st to end	Night	34% 4 14% 24% 23% 2	2431
November	1st to 10th	Night	27% 6% 15% 26% 22% 4	2405
	11th to 20th	Night	34% 5% 13% 26% 18% 3	2512
	21st to end	Night	34% 6% 12% 28% 19% 2	2660
December	1st to 10th	Night	37% 6% 16% 27% 12% 1	2660
	11th to 20th	Night	38% 6% 16% 32% 8% 1	3281
	21st to end	Night	55% 5% 10% 21% 8% 1	4863

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	17% 14% 36% 24% 8% 1	270
	11th to 20th	Day	18% 16% 34% 25% 7%	270
	21st to end	Day	13% 11% 44% 25% 6% 1	297
February	1st to 10th	Day	17% 14% 44% 23% 2	270
	11th to 20th	Day	14% 14% 41% 24% 6% 1	270
	21st to end	Day	17% 20% 42% 16% 5%	225
March	1st to 10th	Day	15% 19% 43% 17% 5% 2	261
	11th to 20th	Day	24% 11% 39% 18% 9%	240
	21st to end	Day	29% 13% 36% 14% 7% 1	264
April	1st to 10th	Day	21% 16% 42% 16% 4	268
	11th to 20th	Day	22% 18% 32% 22% 6%	590
	21st to end	Day	24% 15% 29% 22% 9% 2	600
May	1st to 10th	Day	20% 13% 35% 22% 9% 1	603
	11th to 20th	Day	18% 12% 31% 23% 12% 3	625
	21st to end	Day	18% 10% 31% 28% 11% 3	679
June	1st to 10th	Day	7% 7% 26% 36% 20% 4	630
	11th to 20th	Day	11% 6% 35% 32% 13% 3	630
	21st to end	Day	9% 9% 31% 31% 18% 3	630
July	1st to 10th	Day	6% 4 19% 41% 24% 6%	621
	11th to 20th	Day	7% 4 25% 40% 19% 5%	618
	21st to end	Day	5% 4 24% 43% 21% 2	684
August	1st to 10th	Day	9% 4 21% 42% 21% 3	626
	11th to 20th	Day	11% 4 24% 35% 22% 4	615
	21st to end	Day	9% 3 27% 38% 20% 3	693
September	1st to 10th	Day	16% 4 28% 35% 14% 3	347
	11th to 20th	Day	7% 5% 39% 31% 16% 3	270
	21st to end	Day	16% 11% 34% 27% 10% 3	270
October	1st to 10th	Day	21% 11% 27% 24% 13% 4	270
	11th to 20th	Day	18% 14% 39% 19% 7% 3	270
	21st to end	Day	19% 16% 36% 21% 6% 1	297
November	1st to 10th	Day	17% 14% 34% 24% 8% 4	270
	11th to 20th	Day	12% 17% 44% 23% 4	270
	21st to end	Day	23% 16% 27% 25% 9% 1	270
December	1st to 10th	Day	11% 15% 41% 26% 6% 1	270
	11th to 20th	Day	13% 17% 38% 26% 6%	270
	21st to end	Day	21% 17% 41% 16% 4	297
January	1st to 10th	Night	13% 15% 39% 27% 6% 1	950
	11th to 20th	Night	11% 17% 38% 28% 5% 1	950
	21st to end	Night	15% 12% 42% 25% 7%	1045
February	1st to 10th	Night	16% 12% 42% 26% 4	950
	11th to 20th	Night	13% 14% 42% 26% 5%	887
	21st to end	Night	13% 11% 44% 26% 6% 1	628
March	1st to 10th	Night	14% 12% 43% 26% 5%	644
	11th to 20th	Night	17% 10% 40% 26% 6%	540
	21st to end	Night	20% 12% 38% 24% 6%	594
April	1st to 10th	Night	19% 13% 40% 25% 3	540
	11th to 20th	Night	17% 14% 38% 26% 5%	533
	21st to end	Night	20% 12% 34% 26% 9% 1	540
May	1st to 10th	Night	16% 9% 35% 31% 8%	540
	11th to 20th	Night	14% 10% 33% 32% 11% 1	531
	21st to end	Night	17% 8% 32% 31% 11% 1	584
June	1st to 10th	Night	8% 6% 27% 43% 16% 1	540
	11th to 20th	Night	9% 6% 34% 39% 12%	540
	21st to end	Night	4 5% 29% 46% 16%	540
July	1st to 10th	Night	5% 3 22% 41% 28%	525
	11th to 20th	Night	3 2 26% 48% 20%	522
	21st to end	Night	3 2 20% 54% 20%	591
August	1st to 10th	Night	5% 4 24% 45% 22%	537
	11th to 20th	Night	7% 4 25% 43% 20% 1	534
	21st to end	Night	6% 4 29% 41% 19% 2	594
September	1st to 10th	Night	9% 4 29% 41% 15% 1	540
	11th to 20th	Night	10% 5% 32% 37% 14% 2	540
	21st to end	Night	11% 8% 35% 32% 14%	540
October	1st to 10th	Night	18% 8% 33% 31% 9% 1	628
	11th to 20th	Night	16% 14% 36% 28% 6% 1	720
	21st to end	Night	18% 12% 33% 27% 10%	847
November	1st to 10th	Night	9% 11% 41% 31% 7% 1	925
	11th to 20th	Night	12% 12% 43% 27% 6%	950
	21st to end	Night	12% 13% 40% 25% 9%	950
December	1st to 10th	Night	12% 13% 43% 26% 5%	950
	11th to 20th	Night	15% 11% 38% 29% 6% 1	950
	21st to end	Night	18% 14% 38% 25% 5%	1045

Page generated at 2024-03-05 06:23:58. Version ac07

Copyright © 2024 Attilla Danko.