Appold Planetarium
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Appold Planetarium clear sky chart from 2005-11-06 to 2026-09-14.

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	14% 9% 3 8% 5% 5% 5% 4 6% 7% 34%	148794
	Night	15% 10% 4 8% 5% 4 4 3 5% 6% 35%	142445
Transparency	Day	47% 6% 12% 21% 13% 1	152379
	Night	48% 5% 11% 21% 13% 1	146920
Seeing	Day	20% 13% 30% 22% 11% 4	18153
	Night	20% 11% 28% 27% 12% 1	27879

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	14% 17% 7% 17% 5% 4 4 4 5% 5% 17%	4691
	11th to 20th	Day	12% 16% 6% 14% 9% 6% 7% 4 4 4 17%	4710
	21st to end	Day	18% 16% 7% 13% 7% 5% 6% 4 5% 4 16%	5778
February	1st to 10th	Day	14% 16% 4 11% 7% 6% 5% 4 5% 6% 22%	1890
	11th to 20th	Day	14% 12% 5% 12% 8% 6% 5% 3 5% 6% 25%	2030
	21st to end	Day	16% 14% 5% 9% 4 5% 4 3 5% 7% 27%	1730
March	1st to 10th	Day	18% 12% 5% 10% 5% 4 5% 4 4 5% 29%	4669
	11th to 20th	Day	12% 13% 3 8% 4 4 4 3 5% 6% 37%	5090
	21st to end	Day	18% 14% 5% 10% 5% 5% 5% 3 4 5% 26%	5586
April	1st to 10th	Day	17% 12% 3 7% 5% 5% 5% 4 5% 7% 29%	2452
	11th to 20th	Day	17% 9% 3 7% 5% 4 4 4 5% 7% 34%	2636
	21st to end	Day	19% 10% 3 7% 4 4 4 4 5% 7% 35%	2730
May	1st to 10th	Day	20% 9% 3 7% 4 4 5% 3 6% 7% 32%	7616
	11th to 20th	Day	15% 7% 3 8% 4 5% 5% 4 6% 8% 34%	7626
	21st to end	Day	16% 6% 3 6% 4 4 4 4 6% 7% 42%	8391
June	1st to 10th	Day	12% 6% 2 6% 4 5% 5% 5% 6% 8% 41%	2888
	11th to 20th	Day	10% 6% 2 6% 4 5% 5% 4 7% 7% 43%	2940
	21st to end	Day	10% 5% 2 6% 5% 5% 6% 5% 7% 10% 40%	2940
July	1st to 10th	Day	11% 5% 2 5% 5% 5% 5% 4 6% 9% 43%	8280
	11th to 20th	Day	7% 4 2 5% 4 5% 5% 4 7% 12% 45%	8280
	21st to end	Day	9% 5% 2 7% 5% 5% 5% 5% 7% 10% 42%	8402
August	1st to 10th	Day	15% 6% 2 6% 4 4 4 4 5% 7% 43%	6014
	11th to 20th	Day	12% 7% 3 7% 6% 6% 6% 5% 8% 9% 33%	5951
	21st to end	Day	7% 4 2 7% 5% 5% 6% 5% 6% 10% 44%	6431
September	1st to 10th	Day	12% 5% 2 6% 4 4 4 5% 5% 8% 44%	2378
	11th to 20th	Day	8% 5% 2 6% 4 5% 5% 4 6% 8% 48%	2233
	21st to end	Day	16% 7% 2 5% 4 4 5% 4 5% 7% 41%	2200
October	1st to 10th	Day	12% 5% 3 6% 4 4 4 4 6% 7% 45%	2167
	11th to 20th	Day	19% 9% 2 7% 4 4 4 3 5% 6% 37%	2000
	21st to end	Day	19% 9% 3 8% 5% 5% 5% 3 6% 6% 32%	2037
November	1st to 10th	Day	12% 8% 2 7% 4 4 4 3 6% 7% 41%	1852
	11th to 20th	Day	17% 15% 3 8% 5% 4 4 3 4 5% 32%	1890
	21st to end	Day	19% 14% 4 8% 5% 4 4 4 4 7% 27%	1890
December	1st to 10th	Day	14% 14% 8% 13% 6% 5% 4 4 4 6% 22%	3020
	11th to 20th	Day	20% 19% 7% 8% 7% 4 4 3 4 5% 18%	3306
	21st to end	Day	27% 20% 6% 12% 4 4 3 2 4 4 14%	4070
January	1st to 10th	Night	15% 16% 6% 15% 6% 5% 4 3 4 4 22%	8232
	11th to 20th	Night	10% 17% 7% 14% 7% 5% 5% 4 5% 5% 20%	8266
	21st to end	Night	16% 14% 6% 10% 5% 5% 5% 3 5% 6% 25%	8401
February	1st to 10th	Night	16% 16% 4 10% 6% 5% 4 4 4 5% 25%	2730
	11th to 20th	Night	14% 13% 5% 10% 5% 5% 5% 3 5% 6% 28%	2474
	21st to end	Night	19% 13% 4 9% 4 4 4 3 4 6% 29%	2076
March	1st to 10th	Night	17% 13% 4 7% 4 3 4 3 4 6% 37%	5404
	11th to 20th	Night	12% 8% 2 6% 5% 4 4 4 5% 7% 44%	5090
	21st to end	Night	16% 10% 4 8% 4 4 4 3 4 6% 36%	5588
April	1st to 10th	Night	18% 10% 3 7% 4 4 4 3 5% 6% 35%	2184
	11th to 20th	Night	17% 8% 2 8% 5% 5% 5% 3 4 7% 37%	1931
	21st to end	Night	16% 10% 2 6% 5% 4 4 4 5% 6% 39%	1890
May	1st to 10th	Night	21% 9% 3 8% 6% 4 5% 3 5% 6% 31%	5237
	11th to 20th	Night	17% 7% 3 7% 4 4 4 3 5% 7% 40%	5234
	21st to end	Night	14% 5% 2 6% 4 4 4 4 5% 7% 43%	5761
June	1st to 10th	Night	10% 5% 2 5% 4 4 5% 5% 7% 7% 45%	1727
	11th to 20th	Night	11% 5% 2 7% 5% 4 4 4 7% 7% 44%	1680
	21st to end	Night	10% 4 2 4 4 4 4 5% 7% 11% 45%	1680
July	1st to 10th	Night	9% 4 2 6% 4 4 4 4 6% 9% 49%	4708
	11th to 20th	Night	7% 4 2 5% 5% 4 5% 4 7% 9% 48%	4707
	21st to end	Night	9% 4 2 5% 4 4 4 4 6% 8% 49%	5674
August	1st to 10th	Night	16% 7% 2 6% 3 3 4 2 5% 7% 44%	4135
	11th to 20th	Night	12% 6% 2 6% 5% 4 4 4 5% 8% 43%	4095
	21st to end	Night	7% 5% 2 6% 4 5% 5% 4 5% 7% 50%	4691
September	1st to 10th	Night	10% 5% 2 5% 4 5% 4 3 4 8% 50%	2219
	11th to 20th	Night	8% 5% 1 5% 4 4 3 3 4 7% 56%	2234
	21st to end	Night	15% 6% 3 7% 4 4 4 3 5% 6% 45%	2200
October	1st to 10th	Night	13% 5% 2 6% 5% 4 3 3 5% 7% 47%	2232
	11th to 20th	Night	17% 9% 2 7% 4 4 4 4 4 6% 39%	2400
	21st to end	Night	20% 8% 3 6% 5% 4 4 3 5% 6% 37%	2800
November	1st to 10th	Night	14% 8% 3 6% 4 4 3 3 5% 6% 44%	2666
	11th to 20th	Night	16% 10% 4 8% 4 4 4 4 6% 6% 34%	2730
	21st to end	Night	20% 14% 3 9% 5% 4 3 4 5% 5% 27%	2730
December	1st to 10th	Night	13% 14% 7% 11% 6% 5% 4 3 4 6% 26%	4380
	11th to 20th	Night	16% 19% 6% 11% 5% 4 4 3 5% 5% 22%	5109
	21st to end	Night	28% 19% 6% 9% 4 4 3 3 4 5% 15%	7150

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	68% 5% 11% 12% 3	4692
	11th to 20th	Day	71% 4 8% 8% 9%	4710
	21st to end	Day	71% 4 8% 10% 6%	5778
February	1st to 10th	Day	63% 5% 11% 14% 6%	1890
	11th to 20th	Day	61% 5% 10% 16% 8%	2040
	21st to end	Day	57% 5% 13% 17% 7% 2	1730
March	1st to 10th	Day	59% 4 11% 18% 8% 1	4669
	11th to 20th	Day	46% 5% 16% 23% 9% 1	5090
	21st to end	Day	59% 6% 11% 15% 9% 1	5586
April	1st to 10th	Day	53% 6% 12% 16% 12%	2452
	11th to 20th	Day	49% 6% 11% 21% 12% 2	2636
	21st to end	Day	48% 5% 12% 22% 11% 2	2730
May	1st to 10th	Day	50% 6% 10% 20% 13% 1	7651
	11th to 20th	Day	46% 7% 13% 21% 12% 1	7630
	21st to end	Day	41% 5% 9% 19% 20% 5%	8405
June	1st to 10th	Day	38% 7% 12% 25% 15% 3	2888
	11th to 20th	Day	38% 6% 13% 23% 16% 3	2940
	21st to end	Day	38% 7% 14% 22% 15% 3	2940
July	1st to 10th	Day	36% 6% 11% 28% 17% 2	8211
	11th to 20th	Day	29% 6% 13% 33% 17% 1	8205
	21st to end	Day	36% 6% 12% 23% 21% 2	8217
August	1st to 10th	Day	39% 6% 12% 22% 18% 2	6001
	11th to 20th	Day	44% 8% 13% 25% 10% 1	5990
	21st to end	Day	33% 7% 14% 34% 11% 1	6430
September	1st to 10th	Day	37% 6% 15% 23% 17% 2	2378
	11th to 20th	Day	32% 6% 11% 32% 18% 1	2233
	21st to end	Day	41% 6% 12% 25% 16% 1	2200
October	1st to 10th	Day	28% 4 12% 31% 22% 1	3531
	11th to 20th	Day	40% 4 9% 27% 19% 1	3240
	21st to end	Day	43% 4 12% 25% 16% 1	3261
November	1st to 10th	Day	42% 5% 12% 25% 15% 1	1852
	11th to 20th	Day	54% 4 11% 18% 11% 2	1890
	21st to end	Day	58% 5% 12% 18% 7%	1890
December	1st to 10th	Day	63% 5% 15% 13% 4	3020
	11th to 20th	Day	67% 5% 10% 14% 3	3303
	21st to end	Day	75% 5% 7% 9% 4	4070
January	1st to 10th	Night	66% 4 9% 15% 5%	8233
	11th to 20th	Night	67% 4 10% 12% 8%	8266
	21st to end	Night	61% 4 13% 14% 8%	8401
February	1st to 10th	Night	60% 6% 11% 16% 6% 1	2730
	11th to 20th	Night	56% 5% 10% 20% 8% 1	2475
	21st to end	Night	57% 5% 11% 17% 8% 1	2076
March	1st to 10th	Night	49% 4 12% 24% 10% 1	5404
	11th to 20th	Night	39% 5% 14% 27% 14% 1	5090
	21st to end	Night	49% 5% 11% 20% 14% 1	5588
April	1st to 10th	Night	49% 6% 10% 20% 13% 2	2184
	11th to 20th	Night	47% 5% 11% 19% 17% 2	1931
	21st to end	Night	45% 5% 11% 22% 15% 2	1890
May	1st to 10th	Night	54% 5% 9% 15% 14% 2	5264
	11th to 20th	Night	44% 6% 11% 25% 13% 1	5235
	21st to end	Night	39% 6% 11% 22% 19% 4	5771
June	1st to 10th	Night	35% 6% 11% 26% 20% 2	1727
	11th to 20th	Night	36% 7% 12% 25% 16% 3	1680
	21st to end	Night	33% 7% 15% 25% 19% 1	1680
July	1st to 10th	Night	32% 6% 11% 29% 18% 4	4670
	11th to 20th	Night	32% 6% 13% 28% 19% 2	4662
	21st to end	Night	32% 6% 12% 22% 25% 3	5546
August	1st to 10th	Night	40% 6% 11% 20% 21% 2	4124
	11th to 20th	Night	39% 7% 15% 25% 13% 1	4122
	21st to end	Night	32% 6% 13% 31% 15% 1	4691
September	1st to 10th	Night	34% 5% 12% 28% 18% 3	2219
	11th to 20th	Night	29% 5% 10% 30% 24% 2	2234
	21st to end	Night	40% 6% 12% 24% 17% 2	2200
October	1st to 10th	Night	25% 4 9% 32% 30% 1	3648
	11th to 20th	Night	38% 4 10% 26% 22%	3899
	21st to end	Night	37% 4 7% 34% 17% 1	4513
November	1st to 10th	Night	41% 5% 11% 25% 17% 1	2666
	11th to 20th	Night	48% 6% 12% 21% 11% 2	2730
	21st to end	Night	58% 5% 11% 19% 6%	2730
December	1st to 10th	Night	59% 5% 13% 18% 5%	4380
	11th to 20th	Night	64% 5% 12% 13% 5% 1	5111
	21st to end	Night	72% 4 10% 8% 5%	7150

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	27% 19% 34% 17% 2 1	330
	11th to 20th	Day	32% 21% 36% 8% 3 1	330
	21st to end	Day	31% 19% 28% 20% 3	363
February	1st to 10th	Day	28% 21% 36% 12% 3 1	330
	11th to 20th	Day	28% 20% 37% 13% 2	330
	21st to end	Day	27% 28% 34% 9% 1	273
March	1st to 10th	Day	28% 23% 35% 11% 3	367
	11th to 20th	Day	30% 14% 35% 16% 5% 1	540
	21st to end	Day	31% 17% 32% 14% 6%	594
April	1st to 10th	Day	28% 17% 30% 18% 6% 1	540
	11th to 20th	Day	29% 19% 29% 15% 7% 2	532
	21st to end	Day	27% 14% 33% 16% 8% 2	540
May	1st to 10th	Day	25% 16% 30% 18% 8% 3	543
	11th to 20th	Day	22% 12% 34% 17% 12% 4	567
	21st to end	Day	16% 10% 29% 22% 16% 6%	617
June	1st to 10th	Day	15% 9% 33% 29% 11% 4	728
	11th to 20th	Day	15% 11% 32% 29% 10% 3	780
	21st to end	Day	12% 9% 31% 31% 12% 4	780
July	1st to 10th	Day	12% 5% 25% 29% 18% 10%	771
	11th to 20th	Day	11% 6% 29% 28% 18% 8%	768
	21st to end	Day	10% 5% 27% 30% 20% 8%	643
August	1st to 10th	Day	11% 2 23% 30% 23% 11%	566
	11th to 20th	Day	14% 4 25% 31% 17% 9%	559
	21st to end	Day	11% 5% 23% 32% 20% 9%	627
September	1st to 10th	Day	15% 6% 22% 27% 19% 10%	570
	11th to 20th	Day	10% 4 19% 28% 26% 12%	542
	21st to end	Day	22% 8% 24% 22% 16% 7%	530
October	1st to 10th	Day	15% 8% 26% 26% 17% 7%	530
	11th to 20th	Day	21% 17% 32% 22% 7% 2	530
	21st to end	Day	27% 19% 30% 17% 5% 1	420
November	1st to 10th	Day	19% 19% 35% 18% 7% 2	330
	11th to 20th	Day	32% 21% 27% 15% 4 1	330
	21st to end	Day	32% 21% 32% 14% 2	330
December	1st to 10th	Day	28% 25% 28% 13% 6%	330
	11th to 20th	Day	27% 25% 33% 12% 3	330
	21st to end	Day	33% 18% 36% 9% 3	363
January	1st to 10th	Night	25% 17% 32% 20% 5%	1050
	11th to 20th	Night	27% 18% 33% 16% 5% 1	1049
	21st to end	Night	24% 17% 32% 22% 4	924
February	1st to 10th	Night	25% 15% 33% 23% 4	840
	11th to 20th	Night	24% 15% 35% 24% 3	823
	21st to end	Night	28% 15% 37% 17% 2	692
March	1st to 10th	Night	23% 14% 31% 25% 6% 1	840
	11th to 20th	Night	21% 17% 34% 21% 6%	840
	21st to end	Night	25% 13% 31% 24% 7%	924
April	1st to 10th	Night	24% 15% 33% 24% 4	714
	11th to 20th	Night	23% 13% 31% 24% 7% 1	623
	21st to end	Night	22% 10% 35% 25% 9%	630
May	1st to 10th	Night	22% 10% 29% 28% 9% 1	630
	11th to 20th	Night	22% 6% 30% 28% 13% 1	621
	21st to end	Night	12% 4 29% 34% 18% 2	683
June	1st to 10th	Night	13% 4 28% 39% 16%	630
	11th to 20th	Night	13% 4 27% 38% 16% 1	630
	21st to end	Night	11% 4 26% 36% 20% 2	630
July	1st to 10th	Night	10% 2 20% 39% 26% 3	615
	11th to 20th	Night	11% 3 21% 40% 22% 4	612
	21st to end	Night	9% 1 17% 43% 27% 2	690
August	1st to 10th	Night	10% 1 19% 40% 27% 3	627
	11th to 20th	Night	13% 2 17% 35% 29% 4	624
	21st to end	Night	9% 3 17% 37% 30% 4	693
September	1st to 10th	Night	12% 5% 21% 33% 26% 4	749
	11th to 20th	Night	10% 4 17% 35% 31% 3	813
	21st to end	Night	17% 6% 20% 30% 24% 3	800
October	1st to 10th	Night	16% 8% 24% 30% 19% 3	800
	11th to 20th	Night	21% 14% 30% 24% 10% 2	800
	21st to end	Night	25% 12% 31% 25% 7%	880
November	1st to 10th	Night	19% 15% 30% 25% 10% 1	820
	11th to 20th	Night	23% 16% 32% 22% 7% 1	840
	21st to end	Night	30% 12% 33% 20% 5% 1	840
December	1st to 10th	Night	26% 16% 31% 21% 5%	840
	11th to 20th	Night	26% 16% 32% 21% 4	908
	21st to end	Night	33% 13% 33% 19% 3	1155

Page generated at 2026-09-11 04:11:52. Version ac07

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