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 2024-02-20.

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	13% 7% 3 5% 5% 3 4 4 5% 7% 43%	78502
	Night	13% 8% 3 5% 4 3 4 4 5% 6% 45%	80730
Transparency	Day	41% 6% 11% 24% 16% 3	78220
	Night	41% 5% 10% 24% 17% 3	80532
Seeing	Day	18% 12% 28% 25% 13% 3	14546
	Night	18% 12% 31% 27% 11% 1	24574

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	13% 13% 3 7% 5% 2 4 4 4 6% 39%	2753
	11th to 20th	Day	13% 12% 4 7% 5% 4 5% 4 3 5% 39%	2850
	21st to end	Day	19% 12% 4 7% 4 2 3 4 4 5% 36%	3135
February	1st to 10th	Day	14% 11% 5% 9% 6% 3 4 4 4 5% 35%	1710
	11th to 20th	Day	15% 9% 4 5% 6% 3 4 5% 5% 5% 39%	1704
	21st to end	Day	16% 11% 4 6% 4 3 5% 4 4 6% 38%	1484
March	1st to 10th	Day	14% 9% 5% 6% 5% 3 3 3 4 6% 41%	1980
	11th to 20th	Day	22% 11% 3 5% 4 2 3 4 4 5% 36%	1980
	21st to end	Day	22% 11% 4 6% 5% 3 4 4 4 5% 30%	2188
April	1st to 10th	Day	12% 7% 3 5% 6% 3 4 4 4 8% 44%	2160
	11th to 20th	Day	18% 9% 2 5% 4 3 5% 4 5% 6% 39%	2134
	21st to end	Day	21% 8% 4 6% 5% 2 3 5% 5% 6% 35%	2160
May	1st to 10th	Day	19% 6% 3 6% 5% 3 5% 5% 5% 7% 36%	2272
	11th to 20th	Day	17% 5% 2 5% 4 3 5% 5% 6% 7% 40%	2327
	21st to end	Day	13% 6% 3 6% 7% 4 7% 6% 6% 9% 34%	2725
June	1st to 10th	Day	8% 6% 2 5% 5% 3 6% 6% 6% 9% 45%	2520
	11th to 20th	Day	9% 4 2 5% 6% 3 6% 4 6% 9% 47%	2520
	21st to end	Day	6% 2 2 3 5% 3 5% 5% 6% 9% 53%	2520
July	1st to 10th	Day	10% 5% 2 5% 5% 3 6% 6% 7% 10% 41%	2515
	11th to 20th	Day	4 3 2 5% 4 4 6% 6% 7% 10% 50%	2340
	21st to end	Day	9% 4 3 5% 7% 3 5% 6% 7% 8% 42%	2546
August	1st to 10th	Day	7% 4 2 6% 5% 4 6% 7% 7% 9% 43%	2328
	11th to 20th	Day	9% 4 2 5% 5% 4 5% 5% 6% 10% 43%	2223
	21st to end	Day	8% 5% 2 4 4 3 4 5% 6% 8% 51%	2376
September	1st to 10th	Day	12% 5% 2 4 5% 3 4 5% 5% 7% 48%	2160
	11th to 20th	Day	11% 5% 1 4 5% 3 4 5% 5% 6% 50%	2160
	21st to end	Day	8% 3 2 4 5% 3 5% 4 5% 7% 54%	1877
October	1st to 10th	Day	13% 4 2 5% 4 2 3 3 4 6% 54%	1800
	11th to 20th	Day	16% 6% 2 4 3 1 2 3 3 5% 55%	1800
	21st to end	Day	19% 9% 2 4 3 2 3 3 4 5% 46%	1980
November	1st to 10th	Day	12% 6% 1 4 4 2 3 4 3 5% 55%	1828
	11th to 20th	Day	14% 7% 3 5% 4 2 3 3 4 6% 48%	1706
	21st to end	Day	17% 8% 4 5% 2 2 3 4 4 6% 46%	1520
December	1st to 10th	Day	14% 10% 4 6% 3 3 3 5% 4 5% 43%	1520
	11th to 20th	Day	13% 11% 5% 6% 5% 3 3 3 3 5% 43%	1918
	21st to end	Day	16% 17% 5% 9% 5% 3 5% 4 4 5% 28%	2783
January	1st to 10th	Night	12% 11% 5% 10% 7% 3 4 3 3 5% 37%	4199
	11th to 20th	Night	13% 8% 4 10% 7% 5% 7% 5% 4 4 33%	4120
	21st to end	Night	22% 14% 6% 6% 3 2 3 3 4 4 35%	4532
February	1st to 10th	Night	14% 11% 4 7% 5% 3 3 4 5% 6% 38%	2470
	11th to 20th	Night	15% 8% 4 6% 4 2 3 4 4 6% 43%	2346
	21st to end	Night	15% 11% 4 6% 6% 3 3 4 4 6% 39%	1776
March	1st to 10th	Night	15% 9% 3 4 4 3 3 4 4 5% 45%	1990
	11th to 20th	Night	20% 8% 4 6% 5% 2 4 3 4 6% 38%	1980
	21st to end	Night	22% 10% 3 5% 5% 4 5% 4 5% 6% 31%	2167
April	1st to 10th	Night	9% 6% 3 4 4 3 4 3 5% 7% 51%	1800
	11th to 20th	Night	14% 9% 3 4 4 2 3 4 4 7% 47%	1775
	21st to end	Night	19% 6% 3 5% 5% 3 4 4 5% 7% 39%	1800
May	1st to 10th	Night	15% 5% 2 5% 4 3 4 4 6% 7% 43%	1684
	11th to 20th	Night	17% 6% 2 3 3 3 3 4 6% 7% 47%	1563
	21st to end	Night	12% 6% 4 4 6% 3 6% 5% 6% 7% 41%	1551
June	1st to 10th	Night	6% 4 2 4 4 3 6% 5% 7% 9% 50%	1440
	11th to 20th	Night	6% 4 2 3 3 3 4 6% 7% 11% 52%	1440
	21st to end	Night	3 2 1 2 2 3 4 4 6% 10% 61%	1440
July	1st to 10th	Night	9% 4 1 3 5% 3 5% 6% 6% 9% 50%	1441
	11th to 20th	Night	5% 3 1 3 4 3 3 5% 6% 10% 58%	1620
	21st to end	Night	6% 4 2 4 5% 3 5% 5% 6% 9% 51%	1772
August	1st to 10th	Night	5% 3 2 4 4 3 4 5% 6% 9% 52%	1611
	11th to 20th	Night	7% 4 2 4 4 2 4 4 6% 7% 57%	1675
	21st to end	Night	5% 3 2 4 3 2 4 4 5% 8% 58%	1980
September	1st to 10th	Night	13% 5% 2 4 3 2 3 3 4 7% 56%	1800
	11th to 20th	Night	10% 4 2 4 4 3 3 5% 5% 8% 54%	1800
	21st to end	Night	9% 4 1 4 4 2 3 3 5% 7% 57%	2059
October	1st to 10th	Night	8% 4 2 4 3 2 3 4 4 7% 59%	2160
	11th to 20th	Night	16% 5% 1 4 4 3 4 3 4 5% 52%	2160
	21st to end	Night	19% 6% 2 3 4 2 2 3 4 4 51%	2376
November	1st to 10th	Night	11% 5% 2 3 3 2 3 3 4 5% 58%	2248
	11th to 20th	Night	14% 7% 2 5% 4 2 3 3 3 6% 50%	2472
	21st to end	Night	16% 9% 3 5% 4 2 2 3 4 4 47%	2660
December	1st to 10th	Night	14% 11% 4 6% 5% 3 4 3 5% 6% 40%	2660
	11th to 20th	Night	16% 10% 4 6% 4 2 3 3 3 5% 42%	3279
	21st to end	Night	17% 18% 6% 8% 5% 3 4 4 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	1713
	21st to end	Day	48% 4 7% 23% 14% 4	1484
March	1st to 10th	Day	45% 4 9% 20% 16% 5%	1980
	11th to 20th	Day	52% 4 9% 20% 13% 3	1980
	21st to end	Day	57% 5% 11% 16% 9% 1	2188
April	1st to 10th	Day	39% 6% 11% 25% 18% 2	2160
	11th to 20th	Day	46% 5% 12% 21% 14% 3	2134
	21st to end	Day	50% 5% 11% 21% 11% 1	2160
May	1st to 10th	Day	47% 8% 11% 22% 12% 1	2272
	11th to 20th	Day	43% 8% 11% 22% 15% 2	2331
	21st to end	Day	45% 9% 12% 21% 11% 1	2725
June	1st to 10th	Day	34% 9% 15% 26% 15% 2	2520
	11th to 20th	Day	33% 8% 13% 27% 17% 3	2520
	21st to end	Day	25% 8% 16% 30% 17% 4	2520
July	1st to 10th	Day	36% 10% 15% 24% 13% 3	2446
	11th to 20th	Day	28% 9% 15% 24% 20% 4	2271
	21st to end	Day	37% 8% 13% 29% 11% 2	2405
August	1st to 10th	Day	35% 9% 18% 23% 14% 1	2314
	11th to 20th	Day	35% 7% 12% 30% 15% 1	2223
	21st to end	Day	30% 8% 12% 23% 21% 6%	2376
September	1st to 10th	Day	34% 8% 11% 26% 16% 5%	2160
	11th to 20th	Day	34% 5% 9% 24% 26% 2	2160
	21st to end	Day	29% 7% 11% 26% 23% 4	1877
October	1st to 10th	Day	32% 5% 9% 24% 25% 4	1800
	11th to 20th	Day	35% 3 6% 28% 21% 6%	1800
	21st to end	Day	42% 4 8% 24% 18% 4	1980
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	2347
	21st to end	Night	48% 4 8% 21% 14% 5%	1776
March	1st to 10th	Night	42% 4 8% 21% 19% 5%	1990
	11th to 20th	Night	48% 5% 8% 22% 14% 3	1980
	21st to end	Night	54% 6% 11% 19% 10% 1	2167
April	1st to 10th	Night	33% 5% 12% 27% 20% 4	1800
	11th to 20th	Night	38% 5% 11% 25% 16% 5%	1775
	21st to end	Night	45% 5% 10% 24% 15% 1	1800
May	1st to 10th	Night	40% 7% 11% 23% 17% 1	1684
	11th to 20th	Night	37% 8% 13% 23% 16% 3	1564
	21st to end	Night	41% 7% 13% 25% 13% 1	1552
June	1st to 10th	Night	29% 8% 15% 27% 18% 3	1440
	11th to 20th	Night	25% 7% 14% 28% 21% 5%	1440
	21st to end	Night	19% 6% 18% 32% 20% 6%	1440
July	1st to 10th	Night	29% 8% 14% 28% 16% 4	1401
	11th to 20th	Night	22% 6% 16% 29% 24% 4	1566
	21st to end	Night	27% 8% 10% 38% 15% 1	1673
August	1st to 10th	Night	25% 8% 17% 33% 15% 2	1601
	11th to 20th	Night	27% 6% 12% 35% 19% 2	1675
	21st to end	Night	23% 7% 14% 28% 22% 6%	1980
September	1st to 10th	Night	30% 5% 9% 27% 21% 7%	1800
	11th to 20th	Night	30% 5% 10% 23% 28% 4	1800
	21st to end	Night	27% 4 10% 25% 31% 3	2059
October	1st to 10th	Night	26% 5% 9% 28% 27% 5%	2160
	11th to 20th	Night	36% 4 8% 25% 23% 6%	2160
	21st to end	Night	39% 3 8% 22% 23% 5%	2376
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% 30% 11% 3	267
	21st to end	Day	39% 18% 34% 8% 1	198
March	1st to 10th	Day	23% 25% 43% 9% 1	240
	11th to 20th	Day	39% 15% 29% 15% 1 1	240
	21st to end	Day	35% 27% 29% 8%	274
April	1st to 10th	Day	21% 19% 38% 17% 4 1	420
	11th to 20th	Day	29% 17% 30% 18% 5%	412
	21st to end	Day	26% 17% 33% 19% 5%	420
May	1st to 10th	Day	22% 16% 36% 20% 5% 1	535
	11th to 20th	Day	21% 15% 28% 24% 11% 1	625
	21st to end	Day	14% 10% 35% 23% 13% 5%	679
June	1st to 10th	Day	10% 5% 24% 33% 22% 5%	630
	11th to 20th	Day	9% 4 26% 40% 17% 3	630
	21st to end	Day	8% 8% 32% 35% 14% 4	630
July	1st to 10th	Day	14% 2 17% 29% 31% 7%	621
	11th to 20th	Day	4 4 23% 39% 25% 5%	618
	21st to end	Day	10% 3 21% 33% 28% 5%	684
August	1st to 10th	Day	10% 3 18% 41% 24% 4	626
	11th to 20th	Day	10% 4 20% 34% 26% 6%	537
	21st to end	Day	12% 2 17% 31% 28% 10%	495
September	1st to 10th	Day	14% 3 15% 36% 25% 6%	450
	11th to 20th	Day	8% 4 20% 37% 22% 9%	450
	21st to end	Day	8% 9% 26% 36% 16% 3	274
October	1st to 10th	Day	17% 10% 33% 26% 12% 1	270
	11th to 20th	Day	21% 20% 36% 19% 4	270
	21st to end	Day	34% 18% 31% 15% 2	297
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% 37% 19% 2	876
	21st to end	Night	29% 19% 33% 17% 3	592
March	1st to 10th	Night	22% 17% 37% 21% 2	550
	11th to 20th	Night	26% 14% 35% 21% 4	540
	21st to end	Night	29% 14% 34% 19% 4	594
April	1st to 10th	Night	15% 18% 40% 23% 4	540
	11th to 20th	Night	21% 13% 37% 23% 6%	533
	21st to end	Night	22% 12% 37% 22% 6%	540
May	1st to 10th	Night	16% 8% 36% 32% 6% 1	540
	11th to 20th	Night	20% 8% 28% 29% 14% 1	531
	21st to end	Night	14% 7% 28% 30% 19% 2	584
June	1st to 10th	Night	8% 4 20% 40% 26% 2	540
	11th to 20th	Night	7% 2 29% 40% 21% 1	540
	21st to end	Night	4 2 29% 46% 18% 2	540
July	1st to 10th	Night	12% 2 12% 37% 32% 5%	525
	11th to 20th	Night	5% 1 19% 43% 29% 4	522
	21st to end	Night	8% 1 16% 40% 32% 2	591
August	1st to 10th	Night	7% 2 18% 43% 29% 2	537
	11th to 20th	Night	9% 2 16% 43% 28% 2	534
	21st to end	Night	8% 1 15% 39% 32% 5%	594
September	1st to 10th	Night	14% 3 15% 39% 26% 3	540
	11th to 20th	Night	11% 2 19% 34% 28% 5%	540
	21st to end	Night	10% 4 26% 37% 20% 3	627
October	1st to 10th	Night	11% 6% 28% 31% 21% 3	720
	11th to 20th	Night	19% 12% 34% 28% 7%	720
	21st to end	Night	24% 12% 33% 25% 7%	792
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 2024-02-17 05:28:38. Version ac07

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