Stigler
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stigler clear sky chart from 2005-11-06 to 2024-01-15.

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% 6% 2 5% 5% 3 4 4 5% 7% 48%	74984
	Night	11% 5% 2 4 4 2 3 4 4 7% 53%	74818
Transparency	Day	36% 6% 10% 24% 19% 4	74708
	Night	32% 5% 10% 24% 23% 7%	74614
Seeing	Day	13% 6% 21% 28% 24% 8%	14233
	Night	13% 6% 24% 36% 19% 2	24203

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% 7% 2 5% 4 2 4 3 3 6% 50%	1707
	11th to 20th	Day	12% 7% 3 6% 4 3 4 3 4 5% 48%	1656
	21st to end	Day	15% 8% 2 4 4 2 3 4 4 4 51%	1782
February	1st to 10th	Day	18% 10% 3 5% 5% 2 4 4 3 5% 43%	1620
	11th to 20th	Day	16% 8% 4 6% 4 2 3 4 4 6% 43%	1667
	21st to end	Day	19% 9% 4 5% 4 3 4 4 4 4 42%	1574
March	1st to 10th	Day	14% 7% 2 6% 4 3 3 4 4 6% 48%	1980
	11th to 20th	Day	18% 7% 3 6% 5% 2 5% 4 4 4 43%	1980
	21st to end	Day	17% 9% 3 6% 5% 2 4 3 5% 6% 39%	2178
April	1st to 10th	Day	11% 5% 2 5% 5% 3 4 5% 6% 6% 47%	2020
	11th to 20th	Day	16% 6% 2 5% 5% 3 5% 4 5% 5% 45%	2134
	21st to end	Day	18% 8% 3 6% 5% 3 4 3 4 4 42%	2205
May	1st to 10th	Day	15% 6% 3 6% 5% 3 5% 4 4 6% 43%	2340
	11th to 20th	Day	13% 6% 3 6% 6% 3 4 5% 6% 7% 43%	2302
	21st to end	Day	11% 5% 3 6% 6% 4 5% 5% 6% 9% 40%	2531
June	1st to 10th	Day	9% 5% 2 4 5% 3 5% 5% 7% 9% 46%	2340
	11th to 20th	Day	6% 4 3 5% 5% 3 6% 5% 6% 9% 49%	2340
	21st to end	Day	4 3 2 4 4 3 5% 5% 5% 8% 57%	2340
July	1st to 10th	Day	8% 3 2 5% 5% 4 7% 6% 8% 12% 40%	2340
	11th to 20th	Day	4 2 2 3 5% 3 5% 6% 5% 10% 56%	2340
	21st to end	Day	5% 3 2 5% 6% 4 5% 6% 7% 10% 48%	2546
August	1st to 10th	Day	4 4 2 5% 5% 3 6% 7% 7% 10% 48%	2328
	11th to 20th	Day	8% 5% 2 4 5% 3 5% 5% 6% 8% 48%	2301
	21st to end	Day	5% 3 1 4 5% 4 5% 5% 7% 8% 52%	2386
September	1st to 10th	Day	10% 4 2 4 4 3 4 4 6% 6% 54%	2088
	11th to 20th	Day	11% 5% 2 5% 5% 3 4 4 4 8% 49%	1980
	21st to end	Day	7% 3 2 4 4 3 4 5% 5% 6% 57%	1980
October	1st to 10th	Day	7% 6% 1 4 4 3 4 3 4 6% 57%	1825
	11th to 20th	Day	12% 4 2 4 4 2 3 2 3 4 60%	1800
	21st to end	Day	17% 6% 2 4 4 2 3 3 4 4 52%	1980
November	1st to 10th	Day	10% 4 1 4 3 2 3 4 4 7% 58%	1858
	11th to 20th	Day	11% 5% 2 3 3 2 3 3 4 6% 59%	1820
	21st to end	Day	14% 6% 2 4 3 2 2 4 4 7% 51%	1710
December	1st to 10th	Day	13% 8% 2 4 4 2 4 4 5% 6% 49%	1710
	11th to 20th	Day	15% 9% 3 5% 4 3 4 3 3 5% 45%	2161
	21st to end	Day	17% 12% 4 4 5% 3 4 4 5% 6% 35%	3135
January	1st to 10th	Night	13% 6% 2 4 3 2 3 3 4 5% 54%	2458
	11th to 20th	Night	14% 6% 2 4 4 2 3 3 3 5% 54%	2393
	21st to end	Night	13% 6% 2 3 3 2 2 3 3 5% 57%	2574
February	1st to 10th	Night	16% 9% 3 4 3 2 3 3 5% 6% 46%	2340
	11th to 20th	Night	15% 7% 4 6% 4 2 3 3 4 5% 48%	2196
	21st to end	Night	14% 6% 4 6% 4 2 3 3 5% 5% 47%	1681
March	1st to 10th	Night	14% 6% 3 5% 4 2 4 3 4 5% 48%	1980
	11th to 20th	Night	17% 6% 3 4 4 3 3 3 3 5% 49%	1980
	21st to end	Night	14% 6% 3 5% 5% 2 4 4 4 6% 47%	2178
April	1st to 10th	Night	13% 4 2 4 5% 2 4 5% 5% 6% 51%	1939
	11th to 20th	Night	12% 5% 2 5% 4 2 3 4 4 7% 51%	1775
	21st to end	Night	13% 5% 2 5% 4 3 4 4 5% 7% 49%	1751
May	1st to 10th	Night	11% 4 2 5% 4 3 5% 4 6% 7% 49%	1620
	11th to 20th	Night	11% 4 2 5% 4 2 3 4 6% 10% 47%	1593
	21st to end	Night	10% 4 2 4 5% 3 4 4 6% 12% 47%	1745
June	1st to 10th	Night	4 3 1 4 4 2 4 3 6% 11% 57%	1620
	11th to 20th	Night	5% 3 2 3 3 1 4 5% 5% 10% 60%	1620
	21st to end	Night	3 2 1 3 2 2 3 4 5% 8% 67%	1620
July	1st to 10th	Night	4 2 2 4 4 3 6% 5% 8% 11% 51%	1620
	11th to 20th	Night	2 2 1 2 3 2 3 4 6% 12% 62%	1620
	21st to end	Night	4 2 2 4 4 3 4 5% 6% 12% 56%	1772
August	1st to 10th	Night	3 2 1 5% 5% 3 6% 5% 6% 10% 55%	1611
	11th to 20th	Night	5% 3 2 4 5% 3 4 5% 5% 8% 55%	1600
	21st to end	Night	4 3 1 4 4 3 4 5% 6% 9% 56%	1970
September	1st to 10th	Night	8% 4 2 4 3 2 3 4 5% 7% 57%	1867
	11th to 20th	Night	10% 5% 1 4 4 3 4 5% 5% 6% 52%	1980
	21st to end	Night	7% 3 2 4 4 3 4 4 4 6% 60%	1980
October	1st to 10th	Night	7% 3 1 3 4 2 3 4 5% 6% 61%	2115
	11th to 20th	Night	13% 3 1 3 3 1 3 3 3 4 62%	2160
	21st to end	Night	18% 5% 2 3 2 2 3 3 3 4 56%	2376
November	1st to 10th	Night	10% 4 1 4 3 2 3 3 3 4 61%	2220
	11th to 20th	Night	10% 5% 2 4 3 2 3 4 4 6% 59%	2356
	21st to end	Night	15% 5% 2 3 3 2 3 3 4 6% 53%	2470
December	1st to 10th	Night	14% 6% 2 4 4 2 3 3 4 7% 50%	2470
	11th to 20th	Night	14% 7% 3 5% 4 3 3 3 4 3 51%	3036
	21st to end	Night	15% 9% 4 5% 5% 2 4 4 4 6% 42%	4532

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	37% 5% 7% 25% 23% 4	1708
	11th to 20th	Day	38% 5% 10% 24% 22% 2	1656
	21st to end	Day	37% 4 7% 26% 21% 4	1782
February	1st to 10th	Day	47% 3 10% 18% 17% 4	1620
	11th to 20th	Day	44% 5% 7% 23% 17% 4	1676
	21st to end	Day	47% 4 6% 16% 20% 7%	1574
March	1st to 10th	Day	39% 4 8% 21% 18% 11%	1980
	11th to 20th	Day	46% 5% 7% 22% 14% 6%	1980
	21st to end	Day	46% 6% 8% 24% 13% 3	2178
April	1st to 10th	Day	36% 7% 11% 21% 19% 5%	2020
	11th to 20th	Day	41% 5% 9% 23% 16% 5%	2134
	21st to end	Day	46% 5% 8% 21% 18% 2	2205
May	1st to 10th	Day	43% 6% 9% 22% 18% 2	2340
	11th to 20th	Day	40% 8% 12% 25% 15% 1	2306
	21st to end	Day	38% 10% 14% 25% 14% 1	2531
June	1st to 10th	Day	32% 9% 14% 27% 15% 3	2340
	11th to 20th	Day	31% 8% 14% 26% 19% 2	2340
	21st to end	Day	25% 7% 14% 28% 23% 4	2340
July	1st to 10th	Day	33% 10% 15% 26% 15% 1	2276
	11th to 20th	Day	23% 8% 13% 31% 22% 3	2271
	21st to end	Day	28% 10% 16% 30% 15% 1	2405
August	1st to 10th	Day	28% 10% 15% 28% 17% 2	2314
	11th to 20th	Day	34% 7% 12% 25% 20% 2	2301
	21st to end	Day	28% 8% 15% 28% 18% 3	2386
September	1st to 10th	Day	30% 6% 10% 24% 22% 9%	2088
	11th to 20th	Day	34% 5% 11% 22% 22% 6%	1980
	21st to end	Day	26% 7% 10% 21% 29% 7%	1980
October	1st to 10th	Day	29% 5% 10% 21% 26% 9%	1825
	11th to 20th	Day	30% 4 6% 19% 31% 11%	1800
	21st to end	Day	37% 4 8% 22% 20% 9%	1980
November	1st to 10th	Day	27% 4 9% 26% 27% 7%	1858
	11th to 20th	Day	28% 4 9% 25% 25% 9%	1820
	21st to end	Day	35% 4 9% 20% 27% 6%	1710
December	1st to 10th	Day	37% 5% 10% 25% 20% 4	1710
	11th to 20th	Day	42% 4 6% 20% 22% 5%	2159
	21st to end	Day	49% 6% 9% 19% 15% 4	3135
January	1st to 10th	Night	34% 4 9% 22% 26% 5%	2458
	11th to 20th	Night	35% 3 9% 24% 24% 5%	2393
	21st to end	Night	31% 3 6% 26% 26% 7%	2574
February	1st to 10th	Night	41% 4 9% 24% 17% 5%	2340
	11th to 20th	Night	41% 3 7% 25% 19% 6%	2197
	21st to end	Night	40% 5% 7% 19% 21% 9%	1681
March	1st to 10th	Night	38% 5% 8% 18% 20% 12%	1980
	11th to 20th	Night	39% 5% 10% 21% 18% 7%	1980
	21st to end	Night	38% 6% 9% 24% 18% 4	2178
April	1st to 10th	Night	33% 6% 10% 20% 21% 9%	1939
	11th to 20th	Night	32% 6% 9% 24% 19% 9%	1775
	21st to end	Night	35% 5% 10% 24% 24% 2	1751
May	1st to 10th	Night	33% 8% 11% 24% 19% 5%	1620
	11th to 20th	Night	34% 7% 14% 26% 18% 2	1594
	21st to end	Night	31% 10% 15% 27% 15% 2	1746
June	1st to 10th	Night	21% 7% 14% 32% 22% 3	1620
	11th to 20th	Night	21% 7% 13% 31% 24% 4	1620
	21st to end	Night	16% 5% 14% 30% 30% 6%	1620
July	1st to 10th	Night	24% 10% 16% 26% 22% 1	1575
	11th to 20th	Night	14% 7% 13% 35% 25% 5%	1566
	21st to end	Night	21% 6% 16% 33% 22% 2	1673
August	1st to 10th	Night	23% 9% 15% 29% 22% 3	1601
	11th to 20th	Night	26% 7% 12% 25% 27% 3	1600
	21st to end	Night	23% 7% 13% 27% 24% 5%	1970
September	1st to 10th	Night	26% 6% 9% 25% 23% 11%	1867
	11th to 20th	Night	31% 6% 11% 20% 24% 8%	1980
	21st to end	Night	24% 5% 8% 24% 30% 9%	1980
October	1st to 10th	Night	24% 4 12% 23% 25% 12%	2115
	11th to 20th	Night	28% 4 5% 17% 31% 15%	2160
	21st to end	Night	34% 3 7% 20% 24% 12%	2376
November	1st to 10th	Night	27% 4 9% 23% 27% 10%	2220
	11th to 20th	Night	28% 4 7% 24% 28% 10%	2356
	21st to end	Night	35% 4 7% 20% 28% 7%	2470
December	1st to 10th	Night	36% 5% 10% 21% 23% 6%	2470
	11th to 20th	Night	39% 4 6% 21% 23% 7%	3037
	21st to end	Night	43% 6% 9% 19% 17% 6%	4532

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	20% 9% 36% 26% 7% 2	270
	11th to 20th	Day	18% 16% 38% 23% 5%	252
	21st to end	Day	19% 15% 33% 22% 10%	264
February	1st to 10th	Day	25% 13% 33% 22% 7%	240
	11th to 20th	Day	23% 16% 39% 17% 5%	240
	21st to end	Day	33% 13% 34% 16% 4 1	198
March	1st to 10th	Day	21% 13% 33% 23% 9% 1	240
	11th to 20th	Day	22% 17% 34% 22% 5%	240
	21st to end	Day	24% 14% 41% 15% 5% 1	264
April	1st to 10th	Day	13% 12% 40% 24% 9% 3	280
	11th to 20th	Day	22% 10% 29% 30% 8% 1	412
	21st to end	Day	22% 8% 35% 24% 9% 2	465
May	1st to 10th	Day	16% 6% 33% 33% 12% 1	603
	11th to 20th	Day	15% 5% 25% 33% 18% 4	625
	21st to end	Day	12% 6% 23% 31% 23% 6%	679
June	1st to 10th	Day	10% 3 9% 30% 37% 11%	630
	11th to 20th	Day	8% 3 12% 37% 31% 10%	630
	21st to end	Day	3 1 15% 37% 32% 12%	630
July	1st to 10th	Day	8% 2 8% 28% 36% 19%	621
	11th to 20th	Day	3 1 6% 30% 43% 17%	618
	21st to end	Day	5% 1 4 27% 42% 21%	684
August	1st to 10th	Day	6% 2 7% 32% 44% 10%	626
	11th to 20th	Day	10% 2 7% 28% 40% 13%	615
	21st to end	Day	6% 3 22% 47% 22%	505
September	1st to 10th	Day	8% 2 4 20% 42% 24%	378
	11th to 20th	Day	3 1 7% 31% 36% 22%	270
	21st to end	Day	11% 3 13% 24% 33% 17%	270
October	1st to 10th	Day	4 5% 22% 31% 26% 11%	270
	11th to 20th	Day	13% 7% 27% 36% 15% 3	270
	21st to end	Day	28% 9% 23% 25% 13% 2	297
November	1st to 10th	Day	14% 5% 28% 33% 17% 2	270
	11th to 20th	Day	14% 8% 34% 27% 15% 1	270
	21st to end	Day	19% 13% 31% 24% 11% 2	270
December	1st to 10th	Day	18% 12% 34% 21% 12% 3	270
	11th to 20th	Day	25% 7% 37% 21% 9%	270
	21st to end	Day	19% 16% 37% 23% 5%	297
January	1st to 10th	Night	16% 10% 33% 33% 7% 1	950
	11th to 20th	Night	17% 12% 35% 29% 7%	921
	21st to end	Night	16% 8% 35% 35% 5%	990
February	1st to 10th	Night	20% 11% 32% 30% 6%	900
	11th to 20th	Night	20% 10% 37% 29% 4	802
	21st to end	Night	19% 8% 39% 31% 3	497
March	1st to 10th	Night	18% 8% 33% 36% 5%	540
	11th to 20th	Night	21% 10% 28% 35% 6%	540
	21st to end	Night	15% 7% 40% 29% 8% 1	594
April	1st to 10th	Night	14% 9% 36% 33% 8%	540
	11th to 20th	Night	13% 10% 32% 34% 11%	533
	21st to end	Night	16% 5% 33% 35% 10% 1	540
May	1st to 10th	Night	11% 5% 29% 44% 11%	540
	11th to 20th	Night	13% 5% 21% 42% 17% 2	531
	21st to end	Night	10% 3 20% 40% 24% 2	584
June	1st to 10th	Night	5% 4 9% 39% 39% 4	540
	11th to 20th	Night	6% 2 12% 48% 30% 3	540
	21st to end	Night	2 2 11% 42% 37% 5%	540
July	1st to 10th	Night	4 2 4 38% 46% 7%	525
	11th to 20th	Night	3 1 4 34% 52% 6%	522
	21st to end	Night	4 2 4 33% 50% 7%	591
August	1st to 10th	Night	3 4 41% 47% 5%	537
	11th to 20th	Night	7% 1 5% 35% 47% 4	534
	21st to end	Night	6% 1 3 32% 51% 7%	594
September	1st to 10th	Night	9% 2 5% 34% 45% 4	540
	11th to 20th	Night	13% 6% 36% 40% 5%	540
	21st to end	Night	8% 2 14% 35% 35% 6%	540
October	1st to 10th	Night	8% 2 14% 40% 33% 4	675
	11th to 20th	Night	15% 5% 24% 42% 14% 1	720
	21st to end	Night	19% 6% 25% 34% 16% 1	792
November	1st to 10th	Night	13% 4 25% 41% 15% 1	740
	11th to 20th	Night	11% 10% 28% 37% 13%	836
	21st to end	Night	19% 7% 28% 35% 11%	950
December	1st to 10th	Night	18% 8% 30% 35% 8%	950
	11th to 20th	Night	21% 8% 28% 37% 6%	950
	21st to end	Night	15% 10% 36% 33% 6%	1045

Page generated at 2024-01-11 21:33:49. Version ac07

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