Fleischmann Planetarium and Science Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fleischmann Planetarium and Science Center clear sky chart from 2005-11-06 to 2024-11-08.

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	2 4 1 4 3 3 3 3 5% 6% 65%	105151
	Night	2 4 2 4 3 3 3 3 5% 7% 63%	102635
Transparency	Day	20% 4 8% 21% 25% 23%	104895
	Night	22% 5% 10% 24% 23% 17%	102481
Seeing	Day	7% 15% 27% 28% 18% 6%	15027
	Night	4 7% 24% 37% 23% 4	24345

By Month

Percentage Cloud Cover SW (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	1 5% 3 6% 5% 6% 6% 6% 8% 10% 45%	2539
	11th to 20th	Day	2 7% 3 8% 5% 5% 6% 5% 6% 9% 44%	2572
	21st to end	Day	5% 9% 3 9% 5% 6% 6% 6% 7% 10% 35%	3146
February	1st to 10th	Day	3 5% 2 5% 4 4 5% 5% 6% 11% 49%	1710
	11th to 20th	Day	2 5% 2 6% 4 4 4 5% 7% 10% 52%	1850
	21st to end	Day	2 5% 2 4 3 4 4 4 8% 10% 55%	1570
March	1st to 10th	Day	2 7% 4 8% 5% 6% 7% 5% 9% 10% 37%	3138
	11th to 20th	Day	1 3 1 4 3 3 3 3 4 6% 68%	3421
	21st to end	Day	2 8% 2 6% 4 4 4 4 7% 8% 52%	4086
April	1st to 10th	Day	2 5% 3 5% 5% 4 4 3 6% 8% 55%	2280
	11th to 20th	Day	2 4 2 5% 4 4 4 4 5% 7% 59%	2249
	21st to end	Day	2 5% 2 3 3 3 3 3 5% 6% 63%	2280
May	1st to 10th	Day	2 3 1 4 3 3 3 3 4 6% 68%	4012
	11th to 20th	Day	3 3 1 3 2 2 3 3 3 6% 72%	4315
	21st to end	Day	3 3 1 4 3 4 4 3 5% 5% 65%	4813
June	1st to 10th	Day	3 3 1 4 4 4 3 4 6% 7% 61%	2660
	11th to 20th	Day	1 2 1 2 2 2 3 2 4 5% 76%	2660
	21st to end	Day	2 2 1 3 2 2 2 2 3 4 76%	2660
July	1st to 10th	Day	1 1 1 1 2 2 2 2 88%	4420
	11th to 20th	Day	2 2 1 3 2 3 3 2 3 5% 73%	4420
	21st to end	Day	1 1 1 2 2 2 3 2 3 5% 77%	4730
August	1st to 10th	Day	2 2 1 2 2 2 2 2 4 5% 75%	4046
	11th to 20th	Day	1 1 1 1 1 2 2 2 2 85%	3724
	21st to end	Day	1 1 1 1 1 2 1 2 2 86%	4180
September	1st to 10th	Day	1 1 2 1 1 1 1 3 4 83%	2280
	11th to 20th	Day	2 2 1 2 2 3 2 3 3 4 75%	2246
	21st to end	Day	2 2 1 3 1 1 2 2 3 5% 77%	2090
October	1st to 10th	Day	2 2 1 3 2 2 2 3 4 7% 73%	3229
	11th to 20th	Day	3 3 1 3 2 2 2 2 3 5% 76%	3161
	21st to end	Day	1 2 1 3 2 2 3 3 5% 8% 70%	3336
November	1st to 10th	Day	3 5% 1 4 3 2 4 4 6% 8% 61%	1737
	11th to 20th	Day	3 3 1 3 2 3 4 5% 6% 10% 59%	1710
	21st to end	Day	1 4 2 5% 3 4 5% 4 5% 9% 58%	1639
December	1st to 10th	Day	2 5% 3 5% 3 4 4 4 6% 10% 52%	1520
	11th to 20th	Day	5% 9% 4 8% 5% 5% 6% 5% 9% 10% 35%	1928
	21st to end	Day	2 8% 3 6% 5% 5% 6% 5% 8% 12% 39%	2794
January	1st to 10th	Night	2 4 2 7% 5% 4 5% 5% 7% 10% 48%	4406
	11th to 20th	Night	2 7% 3 10% 5% 6% 6% 5% 8% 8% 40%	4385
	21st to end	Night	5% 8% 4 9% 6% 6% 6% 4 6% 9% 37%	4521
February	1st to 10th	Night	2 5% 2 5% 4 4 5% 4 7% 9% 53%	2470
	11th to 20th	Night	2 5% 2 5% 3 4 4 4 8% 11% 53%	2218
	21st to end	Night	2 4 2 5% 4 3 4 4 6% 9% 57%	1884
March	1st to 10th	Night	1 7% 3 6% 5% 5% 5% 4 8% 11% 45%	3736
	11th to 20th	Night	1 4 2 4 3 3 4 3 5% 7% 64%	3557
	21st to end	Night	4 7% 3 6% 5% 5% 5% 4 7% 10% 45%	3566
April	1st to 10th	Night	2 3 2 4 4 3 5% 4 6% 10% 57%	1900
	11th to 20th	Night	2 4 2 5% 3 3 4 4 4 7% 63%	1879
	21st to end	Night	4 4 1 4 2 4 4 3 4 7% 64%	1900
May	1st to 10th	Night	3 3 1 3 2 3 3 2 4 5% 73%	2958
	11th to 20th	Night	2 2 1 2 2 2 2 3 4 6% 74%	2562
	21st to end	Night	3 3 1 3 2 3 3 3 5% 6% 68%	2762
June	1st to 10th	Night	4 4 1 4 3 3 4 3 4 7% 64%	1520
	11th to 20th	Night	1 1 1 3 2 2 1 2 4 5% 78%	1520
	21st to end	Night	2 2 2 2 2 2 2 4 4 79%	1520
July	1st to 10th	Night	1 1 1 1 1 2 4 88%	2540
	11th to 20th	Night	3 2 1 3 2 2 3 3 2 3 76%	2540
	21st to end	Night	3 2 2 1 2 1 2 3 5% 78%	2819
August	1st to 10th	Night	3 2 1 3 2 2 2 3 4 5% 73%	2879
	11th to 20th	Night	1 1 1 1 1 1 2 2 2 87%	3126
	21st to end	Night	3 3 2 1 1 1 1 1 2 86%	3498
September	1st to 10th	Night	1 1 2 1 2 1 1 2 4 84%	1900
	11th to 20th	Night	2 2 1 3 2 2 2 2 3 5% 77%	1933
	21st to end	Night	2 1 1 2 2 3 2 2 3 5% 78%	2090
October	1st to 10th	Night	2 2 1 2 2 2 2 2 3 4 79%	3735
	11th to 20th	Night	2 1 2 2 2 2 2 3 5% 80%	3777
	21st to end	Night	3 2 1 4 2 2 2 3 4 7% 69%	4228
November	1st to 10th	Night	2 4 1 4 3 3 2 4 6% 8% 63%	2502
	11th to 20th	Night	1 3 1 4 2 4 3 3 7% 8% 62%	2470
	21st to end	Night	2 4 2 4 4 4 4 4 6% 7% 60%	2536
December	1st to 10th	Night	3 5% 2 6% 4 4 4 4 5% 8% 55%	2660
	11th to 20th	Night	6% 7% 3 7% 5% 4 5% 5% 7% 13% 38%	3276
	21st to end	Night	3 7% 3 8% 5% 6% 6% 5% 8% 10% 39%	4862

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	35% 7% 17% 32% 9%	2539
	11th to 20th	Day	38% 7% 14% 29% 10% 2	2572
	21st to end	Day	44% 8% 13% 25% 10% 1	3146
February	1st to 10th	Day	29% 7% 14% 28% 16% 5%	1710
	11th to 20th	Day	28% 4 14% 32% 18% 4	1860
	21st to end	Day	22% 6% 17% 33% 18% 4	1570
March	1st to 10th	Day	39% 7% 13% 27% 13% 1	3138
	11th to 20th	Day	19% 4 14% 34% 25% 3	3421
	21st to end	Day	30% 7% 14% 27% 18% 3	4086
April	1st to 10th	Day	27% 5% 15% 28% 20% 5%	2280
	11th to 20th	Day	23% 7% 10% 30% 23% 7%	2252
	21st to end	Day	22% 4 11% 32% 26% 5%	2280
May	1st to 10th	Day	18% 5% 6% 29% 35% 7%	4012
	11th to 20th	Day	15% 4 5% 20% 40% 16%	4318
	21st to end	Day	19% 5% 6% 26% 37% 6%	4814
June	1st to 10th	Day	20% 5% 8% 22% 31% 14%	2660
	11th to 20th	Day	12% 3 4 20% 34% 26%	2660
	21st to end	Day	13% 4 1 10% 30% 43%	2660
July	1st to 10th	Day	5% 2 1 4 14% 74%	4351
	11th to 20th	Day	14% 2 2 6% 15% 60%	4345
	21st to end	Day	11% 3 2 7% 24% 54%	4581
August	1st to 10th	Day	13% 3 2 7% 21% 54%	4031
	11th to 20th	Day	7% 2 1 4 21% 64%	3760
	21st to end	Day	8% 2 1 7% 35% 48%	4179
September	1st to 10th	Day	8% 1 1 8% 29% 53%	2280
	11th to 20th	Day	14% 4 3 17% 34% 29%	2246
	21st to end	Day	12% 3 3 18% 35% 29%	2090
October	1st to 10th	Day	13% 2 5% 14% 34% 31%	3229
	11th to 20th	Day	14% 2 5% 22% 43% 14%	3161
	21st to end	Day	13% 3 6% 32% 32% 13%	3336
November	1st to 10th	Day	22% 5% 11% 27% 26% 8%	1737
	11th to 20th	Day	20% 6% 17% 29% 25% 4	1710
	21st to end	Day	24% 5% 11% 29% 26% 4	1639
December	1st to 10th	Day	28% 6% 14% 31% 17% 4	1520
	11th to 20th	Day	42% 10% 11% 25% 11% 2	1928
	21st to end	Day	35% 9% 19% 26% 10% 1	2794
January	1st to 10th	Night	31% 6% 22% 30% 10% 1	4406
	11th to 20th	Night	39% 8% 17% 24% 10% 3	4385
	21st to end	Night	42% 9% 13% 23% 11% 1	4521
February	1st to 10th	Night	28% 6% 14% 29% 18% 5%	2470
	11th to 20th	Night	24% 5% 14% 34% 20% 2	2219
	21st to end	Night	23% 7% 15% 34% 16% 4	1884
March	1st to 10th	Night	33% 7% 14% 29% 14% 2	3736
	11th to 20th	Night	21% 5% 11% 42% 19% 3	3557
	21st to end	Night	33% 6% 18% 28% 13% 2	3566
April	1st to 10th	Night	22% 6% 16% 32% 18% 5%	1900
	11th to 20th	Night	21% 6% 14% 33% 19% 7%	1879
	21st to end	Night	21% 5% 14% 34% 23% 4	1900
May	1st to 10th	Night	15% 4 7% 35% 33% 6%	2958
	11th to 20th	Night	13% 3 8% 22% 39% 15%	2562
	21st to end	Night	18% 4 8% 33% 33% 4	2762
June	1st to 10th	Night	22% 5% 9% 23% 28% 13%	1520
	11th to 20th	Night	11% 2 5% 21% 35% 25%	1520
	21st to end	Night	11% 3 3 14% 31% 39%	1520
July	1st to 10th	Night	5% 2 1 5% 16% 72%	2500
	11th to 20th	Night	15% 2 2 6% 17% 59%	2492
	21st to end	Night	11% 2 3 6% 27% 52%	2731
August	1st to 10th	Night	13% 3 2 9% 26% 47%	2870
	11th to 20th	Night	7% 2 1 6% 26% 59%	3156
	21st to end	Night	9% 1 1 9% 38% 42%	3498
September	1st to 10th	Night	8% 2 2 7% 32% 50%	1900
	11th to 20th	Night	12% 3 4 19% 36% 26%	1933
	21st to end	Night	12% 2 3 20% 34% 29%	2090
October	1st to 10th	Night	11% 2 4 14% 33% 36%	3735
	11th to 20th	Night	9% 3 5% 23% 46% 14%	3777
	21st to end	Night	16% 3 5% 31% 33% 12%	4228
November	1st to 10th	Night	21% 5% 12% 30% 23% 10%	2502
	11th to 20th	Night	19% 5% 13% 32% 26% 5%	2470
	21st to end	Night	23% 5% 11% 30% 25% 6%	2536
December	1st to 10th	Night	28% 8% 14% 27% 20% 4	2660
	11th to 20th	Night	37% 9% 13% 25% 14% 2	3276
	21st to end	Night	39% 8% 16% 24% 12% 2	4862

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	11% 18% 27% 29% 12% 2	180
	11th to 20th	Day	8% 16% 28% 29% 15% 5%	199
	21st to end	Day	7% 11% 31% 31% 15% 4	407
February	1st to 10th	Day	9% 18% 29% 28% 14% 2	370
	11th to 20th	Day	8% 20% 27% 31% 13% 1	455
	21st to end	Day	8% 20% 29% 32% 10% 1	382
March	1st to 10th	Day	11% 21% 35% 22% 9% 2	460
	11th to 20th	Day	9% 22% 31% 22% 15% 2	460
	21st to end	Day	11% 26% 29% 26% 8%	506
April	1st to 10th	Day	10% 22% 29% 22% 12% 3	460
	11th to 20th	Day	12% 25% 27% 22% 11% 3	452
	21st to end	Day	12% 20% 26% 25% 13% 5%	460
May	1st to 10th	Day	11% 20% 29% 25% 10% 4	463
	11th to 20th	Day	14% 19% 24% 21% 14% 8%	488
	21st to end	Day	10% 14% 24% 24% 19% 8%	529
June	1st to 10th	Day	7% 18% 25% 22% 21% 7%	490
	11th to 20th	Day	9% 17% 31% 24% 14% 6%	490
	21st to end	Day	4 12% 25% 31% 21% 7%	490
July	1st to 10th	Day	2 9% 30% 32% 18% 9%	486
	11th to 20th	Day	2 9% 27% 30% 24% 9%	484
	21st to end	Day	2 6% 27% 32% 22% 12%	531
August	1st to 10th	Day	4 8% 25% 30% 22% 11%	487
	11th to 20th	Day	3 9% 27% 29% 21% 11%	477
	21st to end	Day	3 7% 28% 32% 25% 7%	539
September	1st to 10th	Day	3 8% 27% 30% 25% 7%	490
	11th to 20th	Day	7% 12% 25% 29% 22% 4	490
	21st to end	Day	5% 11% 23% 39% 18% 3	490
October	1st to 10th	Day	7% 12% 23% 28% 24% 7%	490
	11th to 20th	Day	8% 11% 22% 28% 26% 6%	490
	21st to end	Day	7% 13% 22% 33% 19% 5%	476
November	1st to 10th	Day	10% 10% 24% 28% 19% 9%	291
	11th to 20th	Day	4 11% 23% 31% 23% 9%	270
	21st to end	Day	5% 11% 25% 30% 23% 6%	237
December	1st to 10th	Day	9% 11% 32% 22% 17% 9%	180
	11th to 20th	Day	6% 12% 34% 24% 16% 7%	180
	21st to end	Day	15% 15% 22% 30% 16% 2	198
January	1st to 10th	Night	5% 10% 28% 32% 19% 6%	760
	11th to 20th	Night	4 9% 24% 39% 20% 4	760
	21st to end	Night	6% 6% 25% 37% 20% 5%	836
February	1st to 10th	Night	4 8% 28% 36% 20% 3	760
	11th to 20th	Night	4 10% 26% 37% 18% 5%	744
	21st to end	Night	4 13% 27% 40% 14% 3	628
March	1st to 10th	Night	6% 13% 31% 31% 15% 3	760
	11th to 20th	Night	4 11% 29% 31% 23% 3	760
	21st to end	Night	4 14% 33% 31% 16% 2	836
April	1st to 10th	Night	5% 11% 30% 35% 19% 1	760
	11th to 20th	Night	5% 15% 26% 32% 19% 4	751
	21st to end	Night	6% 13% 24% 34% 20% 3	760
May	1st to 10th	Night	7% 11% 28% 33% 18% 3	629
	11th to 20th	Night	5% 7% 23% 41% 22% 2	407
	21st to end	Night	7% 5% 19% 39% 27% 3	411
June	1st to 10th	Night	7% 5% 18% 44% 23% 3	380
	11th to 20th	Night	2 4 26% 40% 26% 1	380
	21st to end	Night	2 2 19% 52% 25% 2	380
July	1st to 10th	Night	1 1 16% 54% 26% 2	370
	11th to 20th	Night	1 1 19% 54% 25% 1	368
	21st to end	Night	3 1 9% 50% 33% 3	450
August	1st to 10th	Night	3 1 12% 46% 34% 3	585
	11th to 20th	Night	2 2 18% 43% 31% 4	752
	21st to end	Night	2 3 19% 46% 28% 2	836
September	1st to 10th	Night	1 2 17% 39% 36% 4	760
	11th to 20th	Night	3 5% 18% 34% 34% 7%	760
	21st to end	Night	2 4 19% 38% 28% 9%	760
October	1st to 10th	Night	5% 4 19% 39% 27% 7%	760
	11th to 20th	Night	4 5% 17% 38% 29% 6%	760
	21st to end	Night	6% 4 21% 31% 28% 11%	836
November	1st to 10th	Night	5% 8% 23% 31% 27% 6%	770
	11th to 20th	Night	5% 6% 24% 39% 21% 5%	760
	21st to end	Night	4 7% 25% 33% 25% 6%	760
December	1st to 10th	Night	6% 7% 26% 38% 17% 6%	760
	11th to 20th	Night	6% 9% 28% 33% 18% 5%	760
	21st to end	Night	7% 10% 31% 35% 14% 1	836

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