Joseph P. Strogen Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Joseph P. Strogen Observatory clear sky chart from 2005-11-06 to 2024-10-24.

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	12% 8% 3 6% 4 4 4 4 5% 7% 44%	101026
	Night	13% 8% 3 6% 4 4 3 3 5% 6% 46%	97818
Transparency	Day	39% 6% 11% 25% 16% 3	100832
	Night	39% 5% 11% 25% 17% 3	97683
Seeing	Day	18% 12% 29% 25% 13% 3	15565
	Night	18% 12% 31% 27% 11% 1	25351

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	12% 13% 3 8% 4 4 4 3 4 6% 39%	2753
	11th to 20th	Day	13% 12% 4 8% 4 5% 4 3 3 5% 38%	2850
	21st to end	Day	19% 12% 4 8% 3 3 3 3 4 5% 36%	3135
February	1st to 10th	Day	14% 12% 5% 11% 5% 4 4 3 5% 5% 35%	1710
	11th to 20th	Day	14% 11% 3 6% 5% 3 4 4 5% 5% 40%	1714
	21st to end	Day	16% 11% 3 6% 4 4 4 4 5% 6% 39%	1575
March	1st to 10th	Day	17% 10% 3 5% 3 3 2 2 4 5% 44%	3436
	11th to 20th	Day	14% 8% 2 4 3 3 3 3 4 6% 51%	3480
	21st to end	Day	16% 12% 3 7% 5% 5% 5% 3 5% 5% 34%	3837
April	1st to 10th	Day	12% 8% 2 6% 4 4 4 3 5% 8% 44%	2280
	11th to 20th	Day	17% 9% 2 6% 3 4 5% 3 5% 6% 40%	2254
	21st to end	Day	21% 9% 3 7% 4 3 3 4 5% 6% 35%	2280
May	1st to 10th	Day	16% 8% 3 7% 5% 5% 5% 4 6% 7% 34%	3974
	11th to 20th	Day	16% 7% 2 6% 4 4 5% 4 5% 7% 39%	4135
	21st to end	Day	12% 6% 2 6% 5% 5% 5% 4 5% 8% 42%	4824
June	1st to 10th	Day	8% 6% 2 5% 4 5% 5% 5% 6% 9% 45%	2660
	11th to 20th	Day	8% 4 2 5% 5% 4 5% 4 6% 9% 48%	2660
	21st to end	Day	6% 3 2 4 4 4 5% 4 7% 9% 52%	2660
July	1st to 10th	Day	13% 6% 2 6% 4 4 5% 4 6% 8% 40%	4421
	11th to 20th	Day	5% 4 2 6% 4 5% 5% 5% 6% 10% 48%	4120
	21st to end	Day	7% 4 2 6% 5% 4 6% 5% 9% 11% 40%	4465
August	1st to 10th	Day	5% 3 1 5% 4 4 5% 4 6% 9% 53%	4104
	11th to 20th	Day	10% 5% 2 6% 5% 5% 4 4 5% 9% 45%	3893
	21st to end	Day	7% 5% 2 4 3 4 4 4 6% 8% 53%	4180
September	1st to 10th	Day	11% 6% 1 4 5% 4 4 3 5% 7% 50%	2280
	11th to 20th	Day	11% 5% 2 5% 4 4 4 4 5% 6% 50%	2280
	21st to end	Day	8% 4 2 5% 4 4 4 3 5% 7% 53%	1981
October	1st to 10th	Day	12% 4 2 6% 3 2 3 3 4 5% 57%	1900
	11th to 20th	Day	15% 6% 2 4 2 2 2 3 3 4 56%	1900
	21st to end	Day	18% 9% 2 5% 3 2 3 2 4 5% 47%	2010
November	1st to 10th	Day	12% 6% 1 4 4 3 3 3 4 5% 55%	1828
	11th to 20th	Day	14% 8% 2 5% 4 2 4 2 4 6% 48%	1706
	21st to end	Day	16% 9% 3 5% 2 3 3 4 4 6% 45%	1520
December	1st to 10th	Day	14% 11% 3 6% 3 3 4 4 5% 5% 43%	1520
	11th to 20th	Day	13% 11% 4 7% 4 4 3 2 4 5% 43%	1918
	21st to end	Day	15% 18% 5% 9% 4 4 5% 3 4 5% 28%	2783
January	1st to 10th	Night	12% 11% 4 12% 6% 5% 3 2 3 4 37%	4199
	11th to 20th	Night	13% 9% 3 12% 6% 7% 6% 4 4 4 33%	4120
	21st to end	Night	22% 14% 6% 6% 3 3 3 2 4 4 35%	4532
February	1st to 10th	Night	14% 12% 4 8% 4 3 3 3 5% 6% 37%	2470
	11th to 20th	Night	15% 9% 3 7% 4 3 4 3 4 6% 42%	2351
	21st to end	Night	15% 10% 3 7% 5% 4 3 2 4 5% 40%	1884
March	1st to 10th	Night	19% 11% 2 5% 3 3 3 2 4 4 45%	3429
	11th to 20th	Night	14% 6% 2 4 4 3 3 3 5% 6% 50%	3480
	21st to end	Night	17% 11% 3 8% 5% 5% 4 3 4 5% 34%	3793
April	1st to 10th	Night	9% 7% 3 5% 4 3 4 3 5% 7% 51%	1900
	11th to 20th	Night	14% 9% 2 5% 3 3 3 3 3 7% 47%	1875
	21st to end	Night	18% 7% 2 6% 4 4 4 3 5% 7% 39%	1900
May	1st to 10th	Night	16% 7% 2 6% 4 4 4 3 5% 7% 41%	2924
	11th to 20th	Night	14% 8% 3 6% 4 4 3 3 5% 7% 43%	2765
	21st to end	Night	12% 6% 2 5% 5% 5% 4 4 6% 8% 43%	2743
June	1st to 10th	Night	7% 4 1 5% 3 4 6% 4 7% 8% 49%	1520
	11th to 20th	Night	6% 4 1 3 3 4 4 5% 7% 11% 52%	1520
	21st to end	Night	4 3 1 2 2 4 4 3 7% 10% 60%	1520
July	1st to 10th	Night	12% 6% 2 5% 4 4 4 4 5% 7% 46%	2545
	11th to 20th	Night	5% 3 1 5% 3 3 3 4 5% 10% 57%	2850
	21st to end	Night	6% 4 2 5% 4 4 4 4 7% 11% 50%	3098
August	1st to 10th	Night	4 3 1 4 3 3 3 3 5% 8% 62%	2836
	11th to 20th	Night	10% 5% 2 6% 4 4 4 3 6% 6% 50%	2938
	21st to end	Night	5% 3 2 3 3 3 4 3 5% 9% 62%	3476
September	1st to 10th	Night	12% 5% 1 4 2 2 3 2 4 7% 56%	1900
	11th to 20th	Night	10% 4 2 4 3 3 4 4 5% 8% 53%	1900
	21st to end	Night	10% 5% 1 5% 3 3 3 3 5% 7% 56%	2174
October	1st to 10th	Night	8% 4 2 4 2 3 3 3 4 7% 61%	2280
	11th to 20th	Night	15% 5% 1 4 3 3 3 2 4 5% 53%	2280
	21st to end	Night	19% 6% 1 4 3 3 2 3 4 4 51%	2413
November	1st to 10th	Night	11% 5% 2 4 3 3 3 2 4 5% 58%	2248
	11th to 20th	Night	14% 7% 2 6% 4 3 3 3 4 6% 50%	2472
	21st to end	Night	16% 10% 3 5% 4 3 2 2 4 4 47%	2660
December	1st to 10th	Night	14% 11% 3 6% 4 4 4 3 5% 6% 40%	2660
	11th to 20th	Night	15% 11% 4 7% 4 3 4 3 3 5% 42%	3279
	21st to end	Night	17% 19% 6% 9% 5% 4 4 3 4 4 27%	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	47% 3 8% 26% 15% 1	2754
	11th to 20th	Day	49% 3 10% 24% 13% 1	2850
	21st to end	Day	52% 4 8% 17% 16% 4	3135
February	1st to 10th	Day	52% 4 10% 20% 12% 1	1710
	11th to 20th	Day	47% 4 12% 19% 14% 4	1723
	21st to end	Day	47% 4 7% 23% 14% 5%	1575
March	1st to 10th	Day	44% 4 7% 21% 18% 6%	3436
	11th to 20th	Day	35% 4 10% 30% 15% 6%	3480
	21st to end	Day	51% 6% 14% 20% 8% 1	3837
April	1st to 10th	Day	39% 6% 11% 23% 19% 2	2280
	11th to 20th	Day	44% 5% 12% 21% 15% 3	2254
	21st to end	Day	50% 5% 10% 22% 12% 1	2280
May	1st to 10th	Day	46% 9% 11% 20% 13% 1	4010
	11th to 20th	Day	42% 9% 11% 23% 14% 1	4139
	21st to end	Day	39% 8% 9% 26% 17% 1	4837
June	1st to 10th	Day	34% 9% 15% 25% 15% 2	2660
	11th to 20th	Day	31% 8% 12% 28% 17% 3	2660
	21st to end	Day	26% 8% 16% 29% 17% 4	2660
July	1st to 10th	Day	40% 7% 12% 24% 14% 2	4352
	11th to 20th	Day	30% 7% 13% 30% 17% 2	4051
	21st to end	Day	34% 9% 21% 26% 9% 1	4325
August	1st to 10th	Day	26% 7% 18% 27% 21% 1	4090
	11th to 20th	Day	37% 6% 12% 29% 15% 1	3932
	21st to end	Day	28% 6% 13% 35% 14% 4	4179
September	1st to 10th	Day	33% 7% 10% 25% 18% 6%	2280
	11th to 20th	Day	34% 5% 10% 24% 25% 2	2280
	21st to end	Day	31% 6% 10% 26% 23% 4	1981
October	1st to 10th	Day	31% 5% 9% 24% 28% 5%	1900
	11th to 20th	Day	34% 3 6% 28% 23% 6%	1900
	21st to end	Day	41% 4 7% 24% 19% 4	2010
November	1st to 10th	Day	34% 4 10% 25% 22% 5%	1828
	11th to 20th	Day	38% 4 7% 24% 22% 5%	1706
	21st to end	Day	41% 4 8% 28% 17% 1	1520
December	1st to 10th	Day	43% 6% 10% 28% 12% 2	1520
	11th to 20th	Day	45% 4 8% 23% 18% 2	1915
	21st to end	Day	59% 5% 9% 16% 10% 1	2783
January	1st to 10th	Night	52% 3 10% 21% 13% 1	4199
	11th to 20th	Night	55% 4 9% 21% 10% 1	4120
	21st to end	Night	54% 3 9% 20% 12% 1	4532
February	1st to 10th	Night	48% 5% 10% 21% 14% 2	2470
	11th to 20th	Night	44% 4 10% 22% 17% 3	2352
	21st to end	Night	47% 4 8% 21% 15% 5%	1884
March	1st to 10th	Night	44% 5% 7% 21% 18% 5%	3429
	11th to 20th	Night	35% 5% 10% 25% 21% 3	3480
	21st to end	Night	51% 6% 12% 22% 9%	3793
April	1st to 10th	Night	33% 5% 11% 26% 20% 4	1900
	11th to 20th	Night	38% 5% 11% 24% 17% 6%	1875
	21st to end	Night	45% 5% 10% 24% 15% 1	1900
May	1st to 10th	Night	41% 7% 13% 21% 15% 2	2953
	11th to 20th	Night	40% 8% 12% 27% 12% 2	2766
	21st to end	Night	37% 8% 12% 27% 15% 1	2751
June	1st to 10th	Night	30% 8% 15% 26% 18% 3	1520
	11th to 20th	Night	24% 7% 13% 29% 22% 5%	1520
	21st to end	Night	19% 6% 18% 31% 20% 7%	1520
July	1st to 10th	Night	37% 7% 11% 25% 17% 3	2505
	11th to 20th	Night	23% 5% 11% 38% 20% 2	2796
	21st to end	Night	27% 8% 19% 34% 12% 1	2999
August	1st to 10th	Night	19% 6% 19% 31% 23% 1	2826
	11th to 20th	Night	33% 6% 14% 28% 17% 2	2965
	21st to end	Night	20% 5% 15% 39% 17% 4	3476
September	1st to 10th	Night	30% 5% 9% 26% 23% 7%	1900
	11th to 20th	Night	30% 5% 10% 23% 28% 4	1900
	21st to end	Night	28% 4 10% 25% 30% 3	2174
October	1st to 10th	Night	25% 4 9% 27% 30% 6%	2280
	11th to 20th	Night	34% 4 8% 24% 24% 7%	2280
	21st to end	Night	39% 3 8% 22% 24% 4	2413
November	1st to 10th	Night	30% 4 11% 28% 21% 6%	2248
	11th to 20th	Night	37% 4 6% 25% 24% 5%	2472
	21st to end	Night	42% 4 8% 25% 18% 3	2660
December	1st to 10th	Night	45% 5% 10% 23% 15% 2	2660
	11th to 20th	Night	47% 3 8% 25% 15% 1	3281
	21st to end	Night	61% 5% 10% 14% 8% 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	24% 26% 35% 13% 1	270
	11th to 20th	Day	34% 22% 36% 7% 1	270
	21st to end	Day	23% 27% 37% 12% 2	297
February	1st to 10th	Day	25% 26% 35% 12% 1	270
	11th to 20th	Day	29% 27% 31% 11% 3	270
	21st to end	Day	38% 19% 35% 7% 1	225
March	1st to 10th	Day	24% 24% 41% 10% 1	270
	11th to 20th	Day	36% 17% 31% 14% 1 1	270
	21st to end	Day	34% 27% 30% 8%	308
April	1st to 10th	Day	23% 19% 37% 16% 4 1	460
	11th to 20th	Day	29% 19% 29% 17% 4	452
	21st to end	Day	26% 17% 34% 18% 5%	460
May	1st to 10th	Day	22% 16% 36% 20% 5% 1	582
	11th to 20th	Day	20% 15% 28% 24% 12% 1	675
	21st to end	Day	14% 10% 37% 23% 12% 4	734
June	1st to 10th	Day	10% 5% 26% 33% 20% 5%	680
	11th to 20th	Day	9% 4 27% 41% 17% 3	680
	21st to end	Day	8% 8% 32% 35% 13% 4	680
July	1st to 10th	Day	14% 3 18% 29% 29% 7%	671
	11th to 20th	Day	4 4 24% 39% 24% 5%	668
	21st to end	Day	10% 3 22% 32% 28% 6%	739
August	1st to 10th	Day	9% 3 20% 39% 24% 4	676
	11th to 20th	Day	11% 4 22% 34% 24% 5%	582
	21st to end	Day	12% 2 16% 32% 28% 10%	539
September	1st to 10th	Day	13% 3 15% 37% 26% 6%	490
	11th to 20th	Day	8% 4 21% 38% 21% 8%	490
	21st to end	Day	10% 11% 26% 35% 15% 4	304
October	1st to 10th	Day	15% 9% 33% 28% 12% 3	300
	11th to 20th	Day	20% 18% 36% 20% 6%	300
	21st to end	Day	33% 18% 32% 16% 2	306
November	1st to 10th	Day	18% 14% 40% 21% 6% 1	270
	11th to 20th	Day	26% 17% 33% 17% 6% 1	270
	21st to end	Day	33% 16% 30% 17% 4	270
December	1st to 10th	Day	20% 22% 35% 16% 5% 2	270
	11th to 20th	Day	24% 22% 36% 14% 4	270
	21st to end	Day	26% 28% 34% 11% 1	297
January	1st to 10th	Night	21% 17% 38% 19% 4	950
	11th to 20th	Night	23% 22% 35% 17% 4	950
	21st to end	Night	21% 19% 37% 21% 1	1045
February	1st to 10th	Night	24% 17% 40% 17% 3	950
	11th to 20th	Night	24% 18% 38% 19% 1	877
	21st to end	Night	28% 20% 33% 16% 2	628
March	1st to 10th	Night	22% 17% 37% 21% 2	580
	11th to 20th	Night	25% 15% 34% 22% 4	570
	21st to end	Night	29% 15% 34% 18% 4	627
April	1st to 10th	Night	16% 19% 39% 22% 4	570
	11th to 20th	Night	22% 13% 36% 23% 6%	563
	21st to end	Night	22% 13% 37% 22% 6%	570
May	1st to 10th	Night	16% 9% 36% 32% 6% 1	570
	11th to 20th	Night	19% 8% 28% 29% 14% 1	561
	21st to end	Night	14% 7% 29% 30% 18% 2	617
June	1st to 10th	Night	9% 5% 20% 40% 24% 2	570
	11th to 20th	Night	6% 2 29% 40% 21% 1	570
	21st to end	Night	4 2 29% 46% 17% 2	570
July	1st to 10th	Night	12% 2 13% 37% 30% 5%	555
	11th to 20th	Night	5% 1 18% 44% 28% 3	552
	21st to end	Night	8% 1 16% 40% 32% 2	624
August	1st to 10th	Night	7% 2 18% 43% 29% 2	567
	11th to 20th	Night	9% 2 17% 43% 27% 2	564
	21st to end	Night	7% 1 16% 39% 31% 5%	627
September	1st to 10th	Night	14% 2 15% 40% 26% 3	570
	11th to 20th	Night	11% 2 19% 35% 28% 5%	570
	21st to end	Night	11% 5% 26% 36% 19% 3	662
October	1st to 10th	Night	10% 6% 28% 32% 21% 3	760
	11th to 20th	Night	18% 12% 34% 29% 7%	760
	21st to end	Night	24% 12% 33% 25% 7%	805
November	1st to 10th	Night	14% 14% 38% 26% 8%	740
	11th to 20th	Night	21% 16% 33% 23% 7%	762
	21st to end	Night	24% 16% 33% 22% 5%	950
December	1st to 10th	Night	23% 16% 36% 20% 5%	950
	11th to 20th	Night	25% 14% 36% 22% 3	950
	21st to end	Night	24% 19% 35% 19% 2	1045

Page generated at 2024-10-21 01:20:03. Version ac07

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