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 2024-11-02.

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% 10% 3 8% 5% 5% 5% 4 6% 7% 34%	101220
	Night	16% 10% 4 7% 5% 4 4 3 5% 6% 35%	97756
Transparency	Day	48% 6% 12% 21% 12% 1	101021
	Night	48% 6% 12% 21% 12% 1	97626
Seeing	Day	20% 12% 29% 22% 12% 5%	15594
	Night	20% 10% 28% 27% 12% 1	25393

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	18% 19% 7% 11% 6% 4 4 4 4 5% 19%	2527
	11th to 20th	Day	16% 19% 6% 11% 6% 6% 9% 4 4 5% 12%	2530
	21st to end	Day	27% 21% 9% 11% 4 3 3 3 3 4 12%	3122
February	1st to 10th	Day	14% 16% 5% 11% 7% 6% 5% 4 5% 5% 21%	1710
	11th to 20th	Day	14% 12% 4 12% 8% 6% 5% 3 5% 5% 26%	1831
	21st to end	Day	17% 14% 4 9% 4 5% 4 3 5% 7% 27%	1570
March	1st to 10th	Day	21% 15% 4 9% 5% 4 4 3 4 5% 26%	3179
	11th to 20th	Day	13% 13% 4 8% 5% 4 4 4 5% 6% 34%	3480
	21st to end	Day	20% 12% 5% 9% 5% 5% 4 3 4 5% 27%	3815
April	1st to 10th	Day	16% 12% 3 7% 5% 5% 5% 4 5% 7% 30%	2218
	11th to 20th	Day	18% 9% 3 7% 5% 4 4 4 5% 8% 34%	2382
	21st to end	Day	19% 9% 3 7% 4 4 4 4 5% 7% 35%	2470
May	1st to 10th	Day	18% 9% 2 7% 5% 4 5% 3 6% 7% 33%	4082
	11th to 20th	Day	18% 8% 3 7% 4 5% 5% 4 6% 8% 34%	4081
	21st to end	Day	11% 6% 3 6% 4 5% 5% 4 6% 7% 44%	4476
June	1st to 10th	Day	12% 6% 2 6% 5% 5% 5% 5% 7% 8% 41%	2612
	11th to 20th	Day	10% 6% 2 6% 5% 5% 5% 4 7% 7% 43%	2660
	21st to end	Day	10% 6% 2 6% 5% 5% 6% 5% 7% 10% 39%	2660
July	1st to 10th	Day	11% 6% 2 6% 5% 5% 5% 4 6% 9% 40%	4440
	11th to 20th	Day	7% 3 2 5% 4 5% 5% 4 7% 11% 45%	4440
	21st to end	Day	7% 5% 2 7% 5% 6% 6% 5% 7% 9% 41%	4500
August	1st to 10th	Day	12% 4 2 6% 4 4 5% 4 7% 8% 44%	4104
	11th to 20th	Day	9% 6% 2 6% 5% 5% 6% 5% 8% 10% 37%	4044
	21st to end	Day	9% 5% 2 7% 5% 5% 5% 5% 6% 10% 41%	4415
September	1st to 10th	Day	13% 6% 2 5% 4 4 4 4 6% 7% 44%	2152
	11th to 20th	Day	8% 5% 2 6% 4 5% 5% 4 6% 9% 46%	2090
	21st to end	Day	16% 7% 2 5% 4 3 5% 4 5% 7% 40%	2090
October	1st to 10th	Day	12% 5% 3 6% 4 4 4 4 6% 7% 44%	2059
	11th to 20th	Day	19% 9% 2 7% 4 4 4 3 5% 6% 37%	1900
	21st to end	Day	19% 9% 3 8% 4 5% 5% 4 6% 6% 32%	1935
November	1st to 10th	Day	11% 8% 2 7% 4 4 4 4 6% 7% 41%	1681
	11th to 20th	Day	17% 15% 3 8% 5% 4 4 3 4 5% 33%	1710
	21st to end	Day	20% 13% 4 7% 5% 4 4 4 4 7% 28%	1710
December	1st to 10th	Day	16% 17% 7% 11% 6% 4 4 3 4 5% 21%	1710
	11th to 20th	Day	15% 16% 6% 9% 6% 5% 5% 4 5% 6% 23%	2052
	21st to end	Day	25% 21% 7% 13% 4 4 4 2 4 5% 12%	2783
January	1st to 10th	Night	17% 18% 7% 9% 6% 5% 4 3 5% 5% 23%	4428
	11th to 20th	Night	16% 19% 7% 14% 6% 4 5% 5% 4 5% 15%	4440
	21st to end	Night	26% 19% 7% 11% 4 4 3 2 3 4 16%	4532
February	1st to 10th	Night	17% 17% 4 10% 6% 5% 4 4 4 5% 25%	2470
	11th to 20th	Night	14% 14% 5% 9% 6% 5% 4 3 5% 6% 28%	2233
	21st to end	Night	20% 13% 4 9% 5% 4 4 3 4 6% 28%	1884
March	1st to 10th	Night	18% 14% 4 7% 4 3 3 2 4 5% 36%	3674
	11th to 20th	Night	12% 8% 2 6% 5% 4 4 4 5% 6% 45%	3480
	21st to end	Night	17% 10% 4 8% 4 4 4 3 5% 6% 34%	3817
April	1st to 10th	Night	16% 10% 3 7% 5% 4 4 3 5% 7% 36%	1976
	11th to 20th	Night	18% 8% 2 7% 4 4 5% 3 4 7% 37%	1745
	21st to end	Night	17% 9% 2 6% 5% 4 4 4 5% 6% 38%	1710
May	1st to 10th	Night	19% 8% 3 7% 5% 5% 5% 4 6% 7% 32%	2813
	11th to 20th	Night	18% 7% 2 6% 4 4 4 3 5% 7% 39%	2812
	21st to end	Night	11% 5% 2 6% 4 4 4 4 6% 8% 48%	3079
June	1st to 10th	Night	10% 5% 2 5% 4 5% 5% 5% 7% 7% 44%	1563
	11th to 20th	Night	11% 5% 2 7% 5% 4 4 4 7% 7% 45%	1520
	21st to end	Night	10% 5% 2 4 4 4 4 6% 7% 10% 44%	1520
July	1st to 10th	Night	10% 3 1 5% 4 3 4 4 6% 10% 50%	2530
	11th to 20th	Night	9% 3 2 4 4 3 4 4 6% 8% 52%	2530
	21st to end	Night	7% 4 2 6% 5% 5% 5% 5% 8% 9% 46%	3051
August	1st to 10th	Night	13% 7% 2 7% 4 3 4 2 5% 8% 44%	2825
	11th to 20th	Night	9% 5% 2 5% 4 4 5% 4 6% 8% 50%	2785
	21st to end	Night	9% 4 2 6% 5% 5% 4 4 5% 7% 50%	3238
September	1st to 10th	Night	10% 5% 2 5% 4 5% 4 3 4 8% 50%	2007
	11th to 20th	Night	9% 5% 1 5% 4 4 3 3 4 7% 55%	2090
	21st to end	Night	15% 6% 3 7% 4 3 4 3 5% 6% 44%	2090
October	1st to 10th	Night	13% 5% 2 6% 5% 4 3 3 5% 7% 46%	2120
	11th to 20th	Night	17% 9% 2 7% 4 4 4 4 4 6% 38%	2280
	21st to end	Night	21% 8% 3 6% 5% 4 4 3 5% 6% 36%	2660
November	1st to 10th	Night	14% 8% 3 6% 4 4 4 3 5% 6% 44%	2420
	11th to 20th	Night	16% 10% 4 8% 5% 4 4 3 6% 7% 33%	2470
	21st to end	Night	20% 13% 4 9% 5% 4 3 3 5% 6% 28%	2470
December	1st to 10th	Night	17% 16% 6% 9% 6% 5% 4 3 4 6% 24%	2470
	11th to 20th	Night	17% 16% 4 10% 4 4 4 3 5% 5% 26%	3140
	21st to end	Night	28% 20% 6% 9% 4 4 4 3 4 5% 13%	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	68% 5% 10% 12% 5%	2528
	11th to 20th	Day	74% 5% 10% 7% 3	2530
	21st to end	Day	78% 4 7% 8% 3	3122
February	1st to 10th	Day	63% 6% 11% 14% 6%	1710
	11th to 20th	Day	60% 5% 10% 17% 8%	1841
	21st to end	Day	57% 5% 14% 17% 6% 2	1570
March	1st to 10th	Day	61% 5% 11% 17% 5%	3179
	11th to 20th	Day	49% 7% 15% 20% 8% 1	3480
	21st to end	Day	57% 7% 13% 16% 7%	3815
April	1st to 10th	Day	52% 6% 12% 17% 13%	2218
	11th to 20th	Day	48% 6% 11% 21% 12% 2	2382
	21st to end	Day	48% 5% 12% 21% 11% 2	2470
May	1st to 10th	Day	48% 7% 12% 22% 11% 1	4120
	11th to 20th	Day	45% 8% 13% 23% 10% 1	4085
	21st to end	Day	38% 7% 11% 19% 20% 5%	4489
June	1st to 10th	Day	38% 7% 12% 26% 13% 3	2612
	11th to 20th	Day	37% 6% 14% 23% 16% 3	2660
	21st to end	Day	39% 7% 15% 21% 15% 4	2660
July	1st to 10th	Day	40% 6% 12% 23% 17% 2	4371
	11th to 20th	Day	29% 7% 13% 32% 17% 1	4365
	21st to end	Day	36% 8% 14% 19% 21% 2	4357
August	1st to 10th	Day	35% 8% 14% 27% 15% 1	4091
	11th to 20th	Day	38% 8% 12% 29% 13% 1	4083
	21st to end	Day	35% 7% 12% 32% 12% 2	4414
September	1st to 10th	Day	38% 6% 15% 22% 17% 3	2152
	11th to 20th	Day	33% 7% 10% 30% 18% 1	2090
	21st to end	Day	41% 6% 12% 25% 15% 1	2090
October	1st to 10th	Day	38% 6% 11% 27% 16% 2	2059
	11th to 20th	Day	47% 5% 10% 23% 14% 1	1900
	21st to end	Day	51% 5% 14% 19% 10% 1	1935
November	1st to 10th	Day	41% 5% 13% 24% 16% 1	1681
	11th to 20th	Day	54% 5% 11% 18% 11% 1	1710
	21st to end	Day	56% 5% 13% 18% 7%	1710
December	1st to 10th	Day	67% 5% 10% 14% 4	1710
	11th to 20th	Day	60% 6% 13% 17% 4	2049
	21st to end	Day	76% 6% 8% 7% 3	2783
January	1st to 10th	Night	63% 5% 10% 15% 6%	4428
	11th to 20th	Night	71% 4 11% 10% 4	4440
	21st to end	Night	73% 4 10% 9% 3	4532
February	1st to 10th	Night	61% 6% 11% 15% 6% 1	2470
	11th to 20th	Night	56% 5% 10% 20% 8% 1	2234
	21st to end	Night	58% 5% 10% 17% 8% 1	1884
March	1st to 10th	Night	52% 4 11% 25% 8% 1	3674
	11th to 20th	Night	38% 7% 15% 22% 17% 2	3480
	21st to end	Night	49% 6% 13% 24% 8% 1	3817
April	1st to 10th	Night	47% 6% 11% 20% 14% 2	1976
	11th to 20th	Night	47% 5% 10% 19% 17% 2	1745
	21st to end	Night	46% 5% 11% 21% 15% 2	1710
May	1st to 10th	Night	50% 6% 11% 18% 13% 1	2840
	11th to 20th	Night	44% 7% 11% 25% 12% 1	2813
	21st to end	Night	32% 7% 12% 25% 20% 3	3087
June	1st to 10th	Night	35% 6% 12% 27% 18% 2	1563
	11th to 20th	Night	35% 8% 12% 26% 16% 3	1520
	21st to end	Night	33% 8% 14% 25% 19% 1	1520
July	1st to 10th	Night	30% 6% 12% 29% 17% 6%	2490
	11th to 20th	Night	29% 6% 16% 28% 19% 2	2482
	21st to end	Night	31% 8% 17% 19% 21% 3	2954
August	1st to 10th	Night	38% 7% 13% 25% 16% 2	2814
	11th to 20th	Night	31% 7% 13% 31% 18% 1	2812
	21st to end	Night	33% 7% 12% 30% 17% 2	3238
September	1st to 10th	Night	34% 6% 12% 26% 19% 4	2007
	11th to 20th	Night	30% 5% 10% 29% 24% 2	2090
	21st to end	Night	40% 6% 12% 25% 16% 2	2090
October	1st to 10th	Night	37% 6% 11% 25% 20% 1	2120
	11th to 20th	Night	46% 6% 10% 21% 16% 1	2280
	21st to end	Night	49% 5% 9% 25% 11% 1	2660
November	1st to 10th	Night	41% 5% 12% 24% 17% 1	2420
	11th to 20th	Night	48% 6% 13% 21% 11% 1	2470
	21st to end	Night	57% 5% 12% 20% 6%	2470
December	1st to 10th	Night	61% 5% 11% 16% 7%	2470
	11th to 20th	Night	59% 6% 14% 14% 7% 1	3142
	21st to end	Night	74% 5% 11% 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	27% 21% 30% 18% 2 1	270
	11th to 20th	Day	31% 18% 38% 9% 3 1	270
	21st to end	Day	32% 17% 28% 20% 3	297
February	1st to 10th	Day	29% 20% 36% 11% 3	270
	11th to 20th	Day	28% 20% 38% 11% 2	270
	21st to end	Day	28% 28% 32% 10% 1	225
March	1st to 10th	Day	26% 23% 34% 13% 3	303
	11th to 20th	Day	27% 13% 37% 17% 5% 1	460
	21st to end	Day	32% 15% 30% 16% 7%	506
April	1st to 10th	Day	24% 16% 32% 20% 7% 1	460
	11th to 20th	Day	28% 19% 28% 15% 8% 2	452
	21st to end	Day	27% 15% 33% 15% 8% 2	460
May	1st to 10th	Day	24% 16% 30% 18% 9% 4	463
	11th to 20th	Day	21% 12% 32% 17% 13% 4	487
	21st to end	Day	13% 9% 29% 23% 18% 7%	529
June	1st to 10th	Day	14% 8% 32% 30% 12% 3	632
	11th to 20th	Day	14% 9% 31% 32% 11% 3	680
	21st to end	Day	13% 9% 31% 29% 12% 5%	680
July	1st to 10th	Day	11% 6% 24% 29% 18% 11%	671
	11th to 20th	Day	11% 6% 29% 27% 19% 9%	668
	21st to end	Day	10% 4 27% 31% 19% 9%	553
August	1st to 10th	Day	11% 2 23% 29% 22% 12%	486
	11th to 20th	Day	13% 4 25% 29% 19% 9%	479
	21st to end	Day	11% 4 22% 32% 21% 10%	539
September	1st to 10th	Day	15% 6% 22% 27% 19% 10%	490
	11th to 20th	Day	10% 4 20% 29% 26% 11%	490
	21st to end	Day	22% 9% 25% 22% 16% 7%	490
October	1st to 10th	Day	15% 9% 27% 27% 16% 7%	490
	11th to 20th	Day	21% 18% 30% 21% 8% 2	490
	21st to end	Day	26% 18% 31% 18% 6% 1	384
November	1st to 10th	Day	16% 19% 36% 19% 8% 3	273
	11th to 20th	Day	29% 21% 26% 18% 4 1	270
	21st to end	Day	29% 20% 33% 16% 2	270
December	1st to 10th	Day	28% 27% 27% 11% 7%	270
	11th to 20th	Day	25% 24% 36% 11% 3	270
	21st to end	Day	31% 19% 35% 11% 3	297
January	1st to 10th	Night	25% 17% 32% 20% 5% 1	950
	11th to 20th	Night	28% 16% 33% 17% 5% 1	950
	21st to end	Night	24% 16% 33% 23% 5%	836
February	1st to 10th	Night	26% 14% 33% 23% 4	760
	11th to 20th	Night	24% 14% 35% 24% 3	743
	21st to end	Night	29% 15% 35% 18% 2	628
March	1st to 10th	Night	23% 13% 30% 27% 6% 1	760
	11th to 20th	Night	20% 17% 34% 23% 6%	760
	21st to end	Night	25% 12% 31% 25% 7%	836
April	1st to 10th	Night	22% 14% 34% 25% 5%	646
	11th to 20th	Night	24% 12% 31% 25% 8% 1	563
	21st to end	Night	21% 9% 35% 25% 9%	570
May	1st to 10th	Night	21% 10% 28% 30% 10% 2	570
	11th to 20th	Night	21% 5% 29% 29% 14% 1	561
	21st to end	Night	12% 4 27% 35% 20% 3	617
June	1st to 10th	Night	13% 4 29% 38% 16%	570
	11th to 20th	Night	12% 4 26% 40% 17% 1	570
	21st to end	Night	12% 4 26% 35% 21% 2	570
July	1st to 10th	Night	10% 2 20% 37% 28% 3	555
	11th to 20th	Night	11% 3 22% 39% 22% 4	552
	21st to end	Night	8% 1 17% 43% 28% 2	624
August	1st to 10th	Night	9% 1 19% 40% 27% 3	567
	11th to 20th	Night	12% 2 16% 35% 30% 5%	564
	21st to end	Night	10% 3 16% 36% 31% 4	627
September	1st to 10th	Night	12% 5% 19% 33% 26% 4	677
	11th to 20th	Night	10% 4 18% 35% 30% 3	760
	21st to end	Night	17% 7% 21% 29% 23% 3	760
October	1st to 10th	Night	16% 9% 25% 29% 18% 3	760
	11th to 20th	Night	22% 14% 30% 23% 10% 2	760
	21st to end	Night	26% 12% 30% 25% 7%	836
November	1st to 10th	Night	19% 15% 28% 25% 11% 1	745
	11th to 20th	Night	23% 15% 32% 22% 7% 1	760
	21st to end	Night	28% 12% 32% 22% 5% 1	760
December	1st to 10th	Night	27% 16% 31% 20% 6%	760
	11th to 20th	Night	26% 16% 32% 21% 5%	821
	21st to end	Night	32% 13% 33% 19% 3	1045

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