Walter E. Schuele Planetarium
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Walter E. Schuele Planetarium clear sky chart from 2005-11-06 to 2026-06-16.

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	15% 11% 4 9% 5% 5% 4 4 5% 7% 31%	137649
	Night	16% 13% 5% 10% 5% 4 4 3 5% 6% 29%	134341
Transparency	Day	50% 6% 12% 19% 11% 1	141280
	Night	54% 6% 11% 17% 11% 1	138784
Seeing	Day	19% 12% 27% 26% 13% 4	17028
	Night	22% 11% 26% 26% 13% 2	26542

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	16% 21% 6% 23% 6% 4 3 2 3 4 11%	5258
	11th to 20th	Day	12% 21% 8% 19% 10% 5% 4 3 3 4 12%	5280
	21st to end	Day	18% 18% 8% 15% 7% 6% 5% 3 3 4 11%	5780
February	1st to 10th	Day	16% 18% 6% 12% 7% 5% 3 3 5% 4 21%	1890
	11th to 20th	Day	14% 15% 7% 16% 8% 4 4 3 4 5% 20%	1922
	21st to end	Day	18% 13% 5% 12% 6% 5% 5% 4 6% 6% 22%	1730
March	1st to 10th	Day	17% 14% 6% 11% 5% 4 3 3 4 5% 28%	4879
	11th to 20th	Day	12% 12% 5% 11% 5% 4 4 3 4 5% 35%	5090
	21st to end	Day	18% 15% 5% 10% 5% 4 4 3 4 5% 28%	5586
April	1st to 10th	Day	15% 14% 3 8% 5% 4 4 4 6% 7% 31%	2335
	11th to 20th	Day	17% 11% 4 6% 5% 4 4 4 5% 6% 35%	2702
	21st to end	Day	19% 11% 3 7% 5% 4 4 3 4 7% 34%	2730
May	1st to 10th	Day	19% 10% 3 8% 5% 5% 5% 3 5% 6% 31%	7616
	11th to 20th	Day	15% 8% 3 7% 5% 5% 5% 4 6% 8% 35%	7626
	21st to end	Day	16% 8% 3 6% 4 4 4 3 6% 7% 38%	8391
June	1st to 10th	Day	12% 7% 2 6% 4 5% 5% 4 6% 8% 40%	2934
	11th to 20th	Day	12% 6% 2 7% 5% 5% 4 4 7% 8% 40%	2932
	21st to end	Day	10% 6% 2 6% 4 5% 5% 5% 7% 11% 41%	2948
July	1st to 10th	Day	9% 6% 2 6% 4 5% 4 4 6% 10% 44%	6250
	11th to 20th	Day	10% 5% 2 6% 5% 4 5% 4 7% 11% 41%	5900
	21st to end	Day	11% 5% 2 6% 4 4 5% 4 6% 9% 43%	6424
August	1st to 10th	Day	12% 6% 2 7% 4 5% 4 4 6% 9% 40%	4234
	11th to 20th	Day	11% 6% 3 7% 5% 5% 5% 5% 7% 9% 38%	4174
	21st to end	Day	9% 5% 2 6% 4 5% 5% 5% 7% 9% 42%	4627
September	1st to 10th	Day	13% 5% 2 5% 5% 4 5% 5% 5% 8% 43%	2267
	11th to 20th	Day	10% 6% 2 6% 5% 4 4 4 6% 8% 47%	2200
	21st to end	Day	18% 9% 3 6% 4 4 3 4 5% 6% 37%	2200
October	1st to 10th	Day	14% 6% 3 7% 4 3 4 3 7% 8% 40%	2084
	11th to 20th	Day	19% 9% 3 7% 4 5% 4 3 5% 6% 35%	2000
	21st to end	Day	22% 10% 3 8% 5% 5% 4 3 6% 6% 27%	2162
November	1st to 10th	Day	15% 12% 3 8% 4 5% 3 3 6% 6% 34%	1852
	11th to 20th	Day	17% 19% 4 8% 5% 4 4 3 5% 6% 26%	1890
	21st to end	Day	19% 19% 6% 10% 6% 5% 5% 3 6% 6% 16%	1680
December	1st to 10th	Day	17% 18% 7% 13% 7% 5% 4 3 5% 5% 16%	2680
	11th to 20th	Day	21% 21% 6% 13% 6% 4 4 4 5% 6% 12%	3070
	21st to end	Day	23% 22% 7% 15% 6% 5% 3 3 4 4 9%	4326
January	1st to 10th	Night	17% 19% 9% 23% 6% 4 3 2 3 4 11%	7635
	11th to 20th	Night	10% 20% 10% 19% 8% 5% 5% 3 4 4 12%	7680
	21st to end	Night	18% 18% 6% 13% 6% 4 4 3 4 5% 19%	8401
February	1st to 10th	Night	19% 16% 5% 13% 7% 4 4 4 4 4 21%	2730
	11th to 20th	Night	17% 16% 5% 12% 6% 6% 5% 3 5% 5% 20%	2579
	21st to end	Night	19% 15% 6% 12% 5% 5% 4 3 5% 4 22%	2076
March	1st to 10th	Night	20% 15% 4 9% 4 4 3 3 4 5% 31%	5193
	11th to 20th	Night	13% 11% 4 6% 4 4 4 3 6% 6% 38%	5090
	21st to end	Night	16% 12% 5% 9% 5% 4 4 3 5% 5% 32%	5588
April	1st to 10th	Night	17% 14% 3 8% 5% 4 4 4 6% 6% 29%	2285
	11th to 20th	Night	16% 10% 3 7% 6% 5% 5% 4 6% 6% 33%	1883
	21st to end	Night	16% 9% 3 6% 5% 4 4 4 6% 7% 37%	1890
May	1st to 10th	Night	22% 10% 4 8% 5% 5% 5% 4 5% 7% 26%	5237
	11th to 20th	Night	15% 8% 3 6% 5% 4 5% 4 5% 8% 38%	5234
	21st to end	Night	18% 7% 2 6% 4 4 5% 4 5% 6% 38%	5761
June	1st to 10th	Night	10% 7% 3 7% 4 5% 5% 3 6% 6% 44%	1680
	11th to 20th	Night	10% 4 2 8% 5% 5% 5% 5% 7% 9% 40%	1569
	21st to end	Night	9% 5% 3 6% 5% 5% 4 4 7% 11% 42%	1446
July	1st to 10th	Night	9% 5% 2 6% 4 5% 5% 5% 7% 10% 43%	3704
	11th to 20th	Night	9% 5% 3 6% 4 5% 5% 4 7% 9% 44%	4057
	21st to end	Night	7% 6% 3 6% 4 4 5% 4 6% 9% 46%	4427
August	1st to 10th	Night	11% 6% 3 7% 4 5% 5% 4 5% 10% 41%	2915
	11th to 20th	Night	13% 8% 3 7% 4 4 4 3 5% 6% 43%	2875
	21st to end	Night	8% 5% 3 7% 5% 6% 6% 4 6% 8% 43%	3237
September	1st to 10th	Night	11% 6% 3 6% 4 4 5% 4 5% 7% 45%	2130
	11th to 20th	Night	10% 5% 2 5% 4 4 4 3 6% 8% 50%	2200
	21st to end	Night	17% 7% 3 6% 6% 4 5% 3 5% 6% 38%	2200
October	1st to 10th	Night	14% 6% 3 6% 4 5% 4 4 5% 7% 43%	2315
	11th to 20th	Night	20% 10% 3 7% 4 3 4 3 5% 6% 34%	2400
	21st to end	Night	26% 10% 3 7% 4 3 4 3 5% 6% 28%	2675
November	1st to 10th	Night	15% 12% 3 7% 5% 4 4 3 6% 5% 35%	2666
	11th to 20th	Night	18% 16% 4 10% 5% 4 4 3 4 5% 26%	2730
	21st to end	Night	23% 18% 5% 8% 5% 5% 4 3 4 6% 20%	2935
December	1st to 10th	Night	16% 18% 7% 12% 6% 5% 5% 4 4 6% 17%	4720
	11th to 20th	Night	19% 22% 7% 11% 5% 4 4 3 4 5% 17%	5345
	21st to end	Night	22% 21% 6% 12% 6% 5% 4 3 4 5% 12%	6853

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	79% 4 8% 6% 2 1	5259
	11th to 20th	Day	77% 6% 9% 5% 4	5280
	21st to end	Day	76% 5% 6% 10% 3	5780
February	1st to 10th	Day	64% 6% 12% 13% 5%	1890
	11th to 20th	Day	64% 8% 10% 14% 5% 1	1931
	21st to end	Day	59% 7% 14% 12% 6% 1	1730
March	1st to 10th	Day	54% 7% 11% 20% 8%	4879
	11th to 20th	Day	46% 8% 16% 22% 7% 1	5090
	21st to end	Day	54% 8% 10% 17% 10% 1	5586
April	1st to 10th	Day	49% 7% 13% 17% 13% 1	2335
	11th to 20th	Day	48% 7% 12% 18% 13% 2	2702
	21st to end	Day	48% 7% 12% 21% 10% 2	2730
May	1st to 10th	Day	51% 6% 10% 20% 11% 2	7651
	11th to 20th	Day	45% 7% 14% 21% 11% 2	7630
	21st to end	Day	42% 7% 11% 19% 17% 5%	8405
June	1st to 10th	Day	40% 8% 11% 25% 15% 1	2934
	11th to 20th	Day	38% 9% 15% 21% 14% 2	2932
	21st to end	Day	35% 8% 15% 23% 17% 3	2948
July	1st to 10th	Day	34% 5% 11% 30% 17% 2	6183
	11th to 20th	Day	35% 5% 15% 27% 16% 1	5831
	21st to end	Day	36% 5% 15% 23% 20% 1	6240
August	1st to 10th	Day	39% 7% 15% 26% 13%	4221
	11th to 20th	Day	38% 6% 13% 32% 9% 1	4213
	21st to end	Day	35% 7% 15% 30% 12% 1	4627
September	1st to 10th	Day	37% 8% 16% 22% 15% 3	2267
	11th to 20th	Day	34% 8% 14% 26% 17% 1	2200
	21st to end	Day	45% 7% 11% 19% 17%	2200
October	1st to 10th	Day	33% 5% 14% 27% 19% 1	3396
	11th to 20th	Day	46% 6% 11% 19% 17% 1	3240
	21st to end	Day	44% 5% 13% 22% 16%	3476
November	1st to 10th	Day	49% 7% 13% 20% 12% 1	1852
	11th to 20th	Day	59% 6% 11% 14% 8% 1	1890
	21st to end	Day	67% 9% 8% 12% 5%	1680
December	1st to 10th	Day	71% 5% 16% 7% 2	2680
	11th to 20th	Day	77% 5% 9% 8% 2	3066
	21st to end	Day	80% 5% 8% 6% 2	4326
January	1st to 10th	Night	78% 5% 7% 8% 2	7636
	11th to 20th	Night	75% 6% 7% 7% 4 1	7680
	21st to end	Night	67% 4 10% 13% 5%	8401
February	1st to 10th	Night	66% 7% 10% 13% 4	2730
	11th to 20th	Night	63% 7% 10% 14% 6%	2581
	21st to end	Night	63% 7% 10% 13% 7% 1	2076
March	1st to 10th	Night	55% 4 14% 18% 8%	5193
	11th to 20th	Night	42% 7% 15% 25% 10% 1	5090
	21st to end	Night	51% 7% 10% 18% 12% 1	5588
April	1st to 10th	Night	54% 6% 12% 15% 11% 2	2285
	11th to 20th	Night	48% 7% 12% 17% 14% 2	1883
	21st to end	Night	44% 6% 13% 20% 14% 3	1890
May	1st to 10th	Night	56% 7% 10% 15% 10% 3	5264
	11th to 20th	Night	44% 6% 12% 22% 14% 1	5235
	21st to end	Night	44% 6% 12% 20% 15% 2	5771
June	1st to 10th	Night	39% 8% 10% 23% 16% 4	1680
	11th to 20th	Night	37% 8% 15% 21% 16% 2	1569
	21st to end	Night	35% 9% 13% 25% 17% 1	1446
July	1st to 10th	Night	35% 5% 14% 24% 18% 5%	3665
	11th to 20th	Night	36% 6% 13% 26% 17% 3	4006
	21st to end	Night	34% 6% 12% 21% 25% 2	4297
August	1st to 10th	Night	39% 7% 13% 26% 14% 1	2904
	11th to 20th	Night	40% 6% 10% 30% 12% 1	2902
	21st to end	Night	37% 6% 12% 28% 14% 2	3237
September	1st to 10th	Night	37% 7% 13% 25% 15% 3	2130
	11th to 20th	Night	31% 7% 13% 26% 20% 2	2200
	21st to end	Night	46% 7% 11% 19% 17% 1	2200
October	1st to 10th	Night	32% 6% 8% 28% 25% 1	3783
	11th to 20th	Night	48% 5% 9% 20% 18%	3899
	21st to end	Night	44% 5% 10% 25% 15% 1	4311
November	1st to 10th	Night	49% 6% 12% 18% 12% 2	2666
	11th to 20th	Night	61% 6% 10% 14% 7% 2	2730
	21st to end	Night	67% 6% 10% 13% 4	2935
December	1st to 10th	Night	71% 5% 14% 8% 3	4720
	11th to 20th	Night	71% 5% 11% 11% 2	5348
	21st to end	Night	74% 7% 10% 8% 1	6853

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	25% 19% 38% 12% 6% 1	330
	11th to 20th	Day	27% 25% 35% 9% 4	330
	21st to end	Day	28% 21% 33% 16% 2 1	363
February	1st to 10th	Day	22% 19% 40% 16% 2	330
	11th to 20th	Day	27% 20% 35% 17% 1	330
	21st to end	Day	23% 27% 36% 12% 1	273
March	1st to 10th	Day	22% 21% 32% 22% 3	460
	11th to 20th	Day	22% 19% 33% 20% 6% 1	540
	21st to end	Day	28% 15% 32% 21% 4	594
April	1st to 10th	Day	21% 16% 34% 21% 6% 1	540
	11th to 20th	Day	20% 18% 29% 22% 8% 3	532
	21st to end	Day	24% 11% 32% 23% 8% 1	540
May	1st to 10th	Day	25% 11% 29% 25% 8% 2	543
	11th to 20th	Day	19% 8% 29% 29% 14% 2	567
	21st to end	Day	15% 8% 24% 32% 17% 5%	617
June	1st to 10th	Day	14% 5% 29% 36% 14% 3	570
	11th to 20th	Day	13% 7% 25% 34% 18% 3	612
	21st to end	Day	12% 6% 24% 36% 19% 3	730
July	1st to 10th	Day	9% 4 21% 32% 25% 8%	678
	11th to 20th	Day	13% 5% 18% 34% 23% 7%	524
	21st to end	Day	9% 4 21% 35% 24% 6%	576
August	1st to 10th	Day	10% 4 19% 32% 28% 8%	526
	11th to 20th	Day	12% 3 20% 34% 24% 7%	519
	21st to end	Day	11% 5% 21% 32% 24% 7%	583
September	1st to 10th	Day	15% 5% 20% 26% 25% 8%	530
	11th to 20th	Day	11% 3 15% 33% 25% 13%	530
	21st to end	Day	22% 9% 22% 26% 14% 8%	530
October	1st to 10th	Day	13% 8% 24% 27% 20% 8%	530
	11th to 20th	Day	21% 14% 30% 24% 8% 3	530
	21st to end	Day	26% 17% 30% 20% 6%	545
November	1st to 10th	Day	20% 20% 26% 22% 9% 2	330
	11th to 20th	Day	28% 22% 30% 13% 7%	330
	21st to end	Day	31% 19% 32% 16% 1	220
December	1st to 10th	Day	25% 24% 29% 17% 5%	220
	11th to 20th	Day	27% 25% 29% 16% 3	220
	21st to end	Day	31% 20% 32% 16% 1	306
January	1st to 10th	Night	29% 20% 32% 15% 4	840
	11th to 20th	Night	31% 19% 31% 16% 3	840
	21st to end	Night	27% 17% 30% 22% 4	924
February	1st to 10th	Night	29% 13% 32% 22% 4	840
	11th to 20th	Night	25% 16% 34% 23% 3	823
	21st to end	Night	26% 15% 37% 19% 2	692
March	1st to 10th	Night	24% 12% 33% 25% 6%	840
	11th to 20th	Night	22% 14% 33% 24% 7% 1	840
	21st to end	Night	25% 10% 30% 26% 9% 1	924
April	1st to 10th	Night	23% 13% 30% 27% 7%	840
	11th to 20th	Night	20% 10% 34% 25% 9% 2	639
	21st to end	Night	19% 8% 32% 32% 8% 1	630
May	1st to 10th	Night	22% 8% 24% 33% 12% 1	630
	11th to 20th	Night	19% 7% 26% 30% 15% 2	621
	21st to end	Night	14% 3 18% 37% 25% 4	683
June	1st to 10th	Night	12% 5% 24% 39% 19% 1	420
	11th to 20th	Night	10% 4 23% 39% 22% 1	410
	21st to end	Night	10% 3 21% 39% 26% 1	446
July	1st to 10th	Night	10% 4 12% 39% 31% 4	585
	11th to 20th	Night	12% 3 17% 35% 28% 5%	582
	21st to end	Night	10% 3 16% 39% 30% 2	657
August	1st to 10th	Night	10% 3 14% 39% 29% 5%	597
	11th to 20th	Night	13% 4 13% 36% 30% 4	594
	21st to end	Night	13% 3 16% 33% 29% 5%	661
September	1st to 10th	Night	13% 5% 17% 33% 27% 6%	800
	11th to 20th	Night	12% 3 14% 31% 34% 6%	800
	21st to end	Night	20% 7% 20% 28% 20% 5%	800
October	1st to 10th	Night	17% 9% 21% 28% 21% 4	800
	11th to 20th	Night	25% 13% 28% 24% 9% 1	800
	21st to end	Night	31% 15% 26% 24% 4	880
November	1st to 10th	Night	24% 14% 28% 25% 9% 1	820
	11th to 20th	Night	30% 18% 29% 17% 5% 1	840
	21st to end	Night	34% 17% 30% 15% 5%	840
December	1st to 10th	Night	31% 18% 31% 16% 4	840
	11th to 20th	Night	29% 20% 31% 16% 3	840
	21st to end	Night	31% 16% 31% 19% 3	924

Page generated at 2026-06-13 02:31:41. Version ac07

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