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 2024-11-02.

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	11% 7% 3 7% 4 4 4 4 5% 7% 43%	101480
	Night	10% 7% 3 7% 4 4 4 3 5% 7% 47%	97507
Transparency	Day	39% 7% 13% 25% 14% 2	101284
	Night	36% 6% 13% 26% 16% 2	97374
Seeing	Day	14% 10% 32% 29% 12% 2	15859
	Night	13% 10% 36% 31% 9% 1	25712

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% 14% 4 13% 8% 5% 4 4 6% 6% 27%	2576
	11th to 20th	Day	6% 12% 5% 11% 5% 5% 8% 3 6% 7% 31%	2850
	21st to end	Day	7% 10% 5% 15% 6% 4 4 3 5% 7% 34%	3135
February	1st to 10th	Day	10% 11% 4 10% 7% 7% 5% 5% 4 5% 31%	1710
	11th to 20th	Day	9% 10% 4 8% 5% 4 5% 3 5% 6% 42%	1725
	21st to end	Day	11% 10% 4 9% 4 4 5% 3 5% 7% 38%	1570
March	1st to 10th	Day	9% 9% 3 8% 4 3 3 3 5% 6% 47%	3310
	11th to 20th	Day	11% 9% 3 6% 4 3 4 2 4 6% 48%	3480
	21st to end	Day	22% 12% 4 13% 5% 4 4 3 5% 6% 22%	3814
April	1st to 10th	Day	13% 10% 3 7% 4 3 3 3 7% 8% 39%	2121
	11th to 20th	Day	18% 9% 3 6% 4 3 3 3 4 7% 39%	2442
	21st to end	Day	20% 9% 2 6% 4 4 4 3 5% 6% 38%	2470
May	1st to 10th	Day	16% 9% 3 7% 5% 5% 4 4 6% 7% 34%	4082
	11th to 20th	Day	11% 7% 2 6% 4 4 4 4 5% 7% 48%	4082
	21st to end	Day	15% 7% 2 6% 4 4 4 4 5% 7% 41%	4594
June	1st to 10th	Day	8% 5% 1 6% 4 4 4 5% 5% 9% 49%	2660
	11th to 20th	Day	11% 6% 2 6% 4 4 4 5% 6% 8% 45%	2843
	21st to end	Day	7% 5% 2 4 5% 3 4 4 6% 9% 50%	2850
July	1st to 10th	Day	12% 5% 2 5% 4 4 4 4 7% 10% 44%	4479
	11th to 20th	Day	7% 4 2 5% 4 4 4 4 5% 7% 54%	4223
	21st to end	Day	4 4 2 4 4 4 4 4 7% 10% 53%	4465
August	1st to 10th	Day	8% 5% 2 6% 4 4 5% 4 7% 7% 47%	4104
	11th to 20th	Day	17% 8% 2 6% 4 3 4 4 5% 7% 40%	4041
	21st to end	Day	7% 5% 2 6% 3 4 4 3 5% 8% 53%	4532
September	1st to 10th	Day	13% 5% 2 5% 3 4 3 3 5% 6% 51%	2170
	11th to 20th	Day	8% 5% 2 4 4 3 4 3 5% 6% 55%	2090
	21st to end	Day	10% 4 2 4 3 3 3 3 5% 7% 57%	2090
October	1st to 10th	Day	14% 6% 2 5% 4 3 3 3 5% 5% 50%	1976
	11th to 20th	Day	10% 7% 2 4 3 2 3 3 5% 5% 56%	1900
	21st to end	Day	15% 7% 3 5% 4 3 3 2 4 6% 49%	2028
November	1st to 10th	Day	8% 7% 2 5% 5% 4 4 4 5% 7% 51%	1682
	11th to 20th	Day	9% 7% 2 7% 6% 5% 3 3 5% 8% 46%	1667
	21st to end	Day	11% 9% 3 6% 3 4 3 3 5% 6% 46%	1520
December	1st to 10th	Day	8% 8% 3 10% 4 5% 4 3 6% 8% 42%	1520
	11th to 20th	Day	6% 9% 4 8% 6% 6% 6% 4 7% 9% 36%	1918
	21st to end	Day	15% 10% 4 14% 6% 4 4 4 5% 6% 28%	2761
January	1st to 10th	Night	8% 13% 4 12% 10% 7% 6% 4 5% 6% 27%	4354
	11th to 20th	Night	4 11% 3 9% 5% 5% 9% 5% 9% 6% 33%	4120
	21st to end	Night	6% 11% 7% 13% 4 4 4 3 4 7% 37%	4532
February	1st to 10th	Night	12% 10% 4 9% 5% 5% 4 3 4 5% 39%	2470
	11th to 20th	Night	8% 11% 4 7% 4 4 5% 4 5% 6% 42%	2361
	21st to end	Night	9% 7% 3 7% 3 5% 5% 3 5% 6% 46%	1884
March	1st to 10th	Night	11% 7% 3 6% 4 3 3 3 4 6% 51%	3547
	11th to 20th	Night	11% 7% 3 5% 3 3 3 3 4 6% 52%	3480
	21st to end	Night	18% 9% 3 9% 5% 4 5% 4 6% 7% 30%	3817
April	1st to 10th	Night	13% 9% 2 7% 4 4 4 3 6% 6% 43%	2057
	11th to 20th	Night	13% 9% 3 6% 4 3 4 4 3 7% 44%	1689
	21st to end	Night	17% 7% 2 6% 3 3 5% 3 5% 6% 43%	1710
May	1st to 10th	Night	16% 6% 2 5% 4 3 4 4 5% 7% 46%	2823
	11th to 20th	Night	9% 5% 2 5% 3 4 4 4 6% 8% 50%	2823
	21st to end	Night	15% 6% 2 5% 3 4 4 3 5% 8% 44%	2968
June	1st to 10th	Night	7% 3 1 4 4 3 3 3 7% 9% 55%	1520
	11th to 20th	Night	8% 5% 2 4 3 3 3 3 5% 8% 55%	1330
	21st to end	Night	4 4 1 5% 3 4 3 3 6% 8% 59%	1330
July	1st to 10th	Night	7% 5% 2 5% 4 4 3 3 5% 7% 55%	2472
	11th to 20th	Night	5% 3 1 4 3 3 4 3 5% 8% 63%	2743
	21st to end	Night	2 3 1 4 3 3 4 4 7% 11% 58%	3098
August	1st to 10th	Night	6% 4 1 4 4 3 5% 4 6% 10% 51%	2836
	11th to 20th	Night	12% 6% 2 5% 3 3 4 3 6% 8% 49%	2798
	21st to end	Night	5% 4 2 5% 4 5% 4 4 5% 8% 55%	3135
September	1st to 10th	Night	8% 4 1 4 3 3 4 3 4 7% 59%	2007
	11th to 20th	Night	7% 4 2 4 2 3 4 3 5% 7% 59%	2090
	21st to end	Night	9% 5% 1 4 3 3 3 3 3 6% 61%	2090
October	1st to 10th	Night	14% 5% 2 4 3 3 4 3 4 5% 52%	2183
	11th to 20th	Night	12% 6% 2 4 3 3 3 2 4 4 56%	2280
	21st to end	Night	14% 6% 2 5% 2 3 3 2 4 6% 53%	2567
November	1st to 10th	Night	7% 5% 2 5% 3 3 3 4 5% 7% 57%	2419
	11th to 20th	Night	9% 6% 2 7% 5% 3 3 4 6% 6% 50%	2512
	21st to end	Night	9% 8% 2 6% 3 3 3 3 5% 7% 50%	2660
December	1st to 10th	Night	7% 8% 3 9% 4 3 4 4 5% 7% 45%	2660
	11th to 20th	Night	8% 8% 3 6% 5% 4 4 3 5% 6% 46%	3279
	21st to end	Night	15% 11% 4 14% 6% 4 3 3 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	37% 6% 11% 29% 16% 2	3310
	11th to 20th	Day	37% 6% 9% 29% 14% 5%	3480
	21st to end	Day	60% 10% 13% 12% 4 1	3814
April	1st to 10th	Day	42% 7% 13% 24% 12% 2	2121
	11th to 20th	Day	44% 7% 12% 21% 14% 3	2442
	21st to end	Day	46% 6% 12% 24% 12%	2470
May	1st to 10th	Day	45% 8% 12% 20% 14% 1	4120
	11th to 20th	Day	34% 8% 13% 27% 16% 2	4086
	21st to end	Day	41% 9% 12% 24% 14% 1	4607
June	1st to 10th	Day	30% 9% 17% 30% 12% 2	2660
	11th to 20th	Day	35% 8% 13% 25% 17% 3	2843
	21st to end	Day	29% 8% 16% 32% 12% 4	2850
July	1st to 10th	Day	36% 7% 15% 29% 13% 1	4410
	11th to 20th	Day	29% 6% 13% 32% 18% 3	4150
	21st to end	Day	24% 7% 17% 26% 22% 3	4325
August	1st to 10th	Day	33% 8% 13% 29% 15% 2	4090
	11th to 20th	Day	44% 5% 12% 27% 12% 1	4080
	21st to end	Day	30% 7% 15% 24% 20% 4	4531
September	1st to 10th	Day	34% 6% 11% 28% 19% 3	2170
	11th to 20th	Day	29% 6% 12% 33% 18% 1	2090
	21st to end	Day	28% 5% 10% 31% 23% 2	2090
October	1st to 10th	Day	36% 5% 9% 26% 22% 2	1976
	11th to 20th	Day	30% 5% 12% 29% 18% 6%	1900
	21st to end	Day	38% 5% 11% 23% 18% 4	2028
November	1st to 10th	Day	32% 6% 16% 24% 19% 2	1682
	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	33% 5% 10% 26% 23% 2	3547
	11th to 20th	Night	34% 5% 8% 29% 19% 4	3480
	21st to end	Night	49% 12% 18% 16% 5% 1	3817
April	1st to 10th	Night	40% 7% 11% 24% 15% 1	2057
	11th to 20th	Night	41% 5% 9% 26% 16% 2	1689
	21st to end	Night	41% 8% 11% 23% 15% 2	1710
May	1st to 10th	Night	36% 7% 13% 22% 20% 2	2850
	11th to 20th	Night	29% 9% 13% 25% 21% 3	2824
	21st to end	Night	37% 8% 13% 24% 16% 3	2976
June	1st to 10th	Night	24% 9% 14% 34% 15% 3	1520
	11th to 20th	Night	28% 6% 15% 26% 21% 4	1330
	21st to end	Night	23% 7% 16% 33% 18% 3	1330
July	1st to 10th	Night	30% 4 17% 34% 13% 3	2432
	11th to 20th	Night	21% 5% 14% 36% 20% 4	2693
	21st to end	Night	19% 8% 18% 30% 22% 3	2999
August	1st to 10th	Night	27% 7% 15% 32% 16% 2	2826
	11th to 20th	Night	34% 6% 15% 27% 17% 2	2825
	21st to end	Night	28% 6% 15% 24% 21% 6%	3135
September	1st to 10th	Night	25% 6% 10% 30% 23% 5%	2007
	11th to 20th	Night	24% 6% 12% 33% 22% 3	2090
	21st to end	Night	26% 5% 9% 31% 26% 4	2090
October	1st to 10th	Night	34% 5% 10% 23% 26% 2	2183
	11th to 20th	Night	32% 4 8% 26% 25% 4	2280
	21st to end	Night	34% 4 13% 25% 22% 2	2567
November	1st to 10th	Night	26% 6% 16% 26% 22% 4	2419
	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	13% 19% 43% 19% 5% 1	270
	11th to 20th	Day	24% 11% 39% 19% 8%	270
	21st to end	Day	29% 12% 37% 15% 6% 1	297
April	1st to 10th	Day	22% 16% 42% 16% 4	301
	11th to 20th	Day	21% 18% 32% 22% 6%	640
	21st to end	Day	24% 16% 29% 22% 9% 1	650
May	1st to 10th	Day	19% 14% 36% 21% 8% 1	653
	11th to 20th	Day	17% 13% 31% 24% 13% 3	675
	21st to end	Day	17% 10% 32% 28% 10% 3	734
June	1st to 10th	Day	7% 8% 27% 35% 19% 4	680
	11th to 20th	Day	12% 6% 36% 31% 12% 3	680
	21st to end	Day	9% 9% 33% 30% 17% 2	680
July	1st to 10th	Day	7% 4 19% 40% 23% 7%	671
	11th to 20th	Day	7% 4 26% 40% 19% 5%	668
	21st to end	Day	5% 4 24% 42% 21% 3	739
August	1st to 10th	Day	8% 4 23% 41% 20% 3	676
	11th to 20th	Day	12% 5% 25% 35% 20% 3	665
	21st to end	Day	8% 3 28% 38% 19% 3	748
September	1st to 10th	Day	15% 4 27% 37% 13% 3	380
	11th to 20th	Day	7% 5% 38% 31% 16% 3	300
	21st to end	Day	14% 12% 32% 28% 11% 3	300
October	1st to 10th	Day	20% 11% 28% 25% 13% 4	300
	11th to 20th	Day	16% 14% 40% 20% 8% 2	300
	21st to end	Day	18% 16% 38% 20% 6% 1	330
November	1st to 10th	Day	16% 14% 34% 24% 8% 4	273
	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% 42% 27% 5%	651
	11th to 20th	Night	17% 11% 41% 26% 6%	570
	21st to end	Night	21% 11% 38% 24% 6%	627
April	1st to 10th	Night	19% 14% 39% 25% 3	570
	11th to 20th	Night	18% 14% 37% 25% 5%	563
	21st to end	Night	20% 12% 34% 25% 8% 1	570
May	1st to 10th	Night	16% 9% 35% 31% 8%	570
	11th to 20th	Night	14% 10% 32% 33% 11% 1	561
	21st to end	Night	17% 8% 33% 31% 11%	617
June	1st to 10th	Night	7% 6% 27% 43% 15% 1	570
	11th to 20th	Night	9% 6% 34% 39% 11%	570
	21st to end	Night	5% 5% 29% 46% 15%	570
July	1st to 10th	Night	5% 3 23% 41% 27%	555
	11th to 20th	Night	3 2 26% 49% 20%	552
	21st to end	Night	3 3 20% 54% 20%	624
August	1st to 10th	Night	5% 4 24% 45% 21%	567
	11th to 20th	Night	9% 5% 24% 43% 19% 1	564
	21st to end	Night	7% 4 29% 41% 18% 2	627
September	1st to 10th	Night	9% 4 28% 41% 16% 2	570
	11th to 20th	Night	9% 5% 33% 38% 13% 2	570
	21st to end	Night	10% 8% 34% 32% 15%	570
October	1st to 10th	Night	17% 8% 32% 32% 9% 1	663
	11th to 20th	Night	15% 14% 37% 29% 6% 1	760
	21st to end	Night	18% 12% 34% 26% 10%	895
November	1st to 10th	Night	9% 11% 41% 32% 7% 1	931
	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 2024-10-30 00:22:56. Version ac07

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