Weis Farm observing site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Weis Farm observing site clear sky chart from 2005-11-06 to 2024-11-25.

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	5% 4 1 4 3 3 3 3 5% 7% 61%	105320
	Night	5% 4 2 4 3 3 4 3 5% 7% 58%	102777
Transparency	Day	23% 4 10% 23% 28% 11%	105073
	Night	25% 5% 10% 23% 26% 12%	102614
Seeing	Day	7% 6% 27% 34% 20% 5%	15522
	Night	7% 7% 36% 38% 11%	25475

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	7% 9% 3 5% 3 4 3 2 4 5% 56%	2538
	11th to 20th	Day	3 4 2 6% 4 4 6% 4 6% 5% 56%	2614
	21st to end	Day	7% 7% 2 5% 3 3 3 3 5% 6% 55%	3331
February	1st to 10th	Day	6% 8% 2 6% 3 3 4 2 4 5% 57%	1900
	11th to 20th	Day	3 7% 3 7% 4 2 4 2 4 6% 57%	1849
	21st to end	Day	5% 5% 2 4 3 2 2 4 3 6% 63%	1570
March	1st to 10th	Day	4 5% 1 4 3 2 2 2 3 6% 67%	3130
	11th to 20th	Day	6% 4 1 4 3 3 3 3 5% 7% 60%	3356
	21st to end	Day	7% 6% 2 5% 4 4 4 4 6% 7% 53%	3959
April	1st to 10th	Day	6% 4 1 3 3 3 3 2 5% 6% 64%	2280
	11th to 20th	Day	10% 4 2 3 3 3 3 3 5% 7% 59%	2251
	21st to end	Day	9% 5% 2 4 3 3 3 3 4 7% 56%	2365
May	1st to 10th	Day	8% 5% 1 5% 3 3 3 3 5% 6% 57%	4120
	11th to 20th	Day	7% 4 2 5% 3 4 4 3 6% 7% 55%	4082
	21st to end	Day	6% 3 1 4 3 3 3 3 5% 7% 62%	4489
June	1st to 10th	Day	4 3 1 5% 4 3 4 4 6% 9% 57%	2506
	11th to 20th	Day	5% 3 1 3 3 3 3 4 5% 8% 62%	2660
	21st to end	Day	3 3 1 4 3 4 4 4 6% 9% 59%	2660
July	1st to 10th	Day	5% 3 1 5% 3 3 4 4 6% 9% 57%	4430
	11th to 20th	Day	3 2 1 2 3 3 3 3 6% 10% 65%	4371
	21st to end	Day	3 2 1 4 3 3 4 4 6% 8% 61%	4466
August	1st to 10th	Day	7% 4 1 5% 3 4 4 4 5% 9% 53%	4022
	11th to 20th	Day	4 3 1 3 3 3 4 3 6% 9% 63%	3726
	21st to end	Day	3 3 1 4 3 3 4 4 6% 9% 59%	4180
September	1st to 10th	Day	8% 4 1 5% 3 3 3 3 4 6% 60%	2256
	11th to 20th	Day	6% 4 1 4 3 3 4 3 5% 6% 62%	2090
	21st to end	Day	5% 2 1 4 2 3 2 3 4 5% 68%	2090
October	1st to 10th	Day	6% 3 1 3 2 2 2 2 3 5% 71%	3480
	11th to 20th	Day	4 3 1 4 3 3 3 3 4 6% 67%	3360
	21st to end	Day	5% 3 1 2 1 1 1 2 3 4 76%	3091
November	1st to 10th	Day	6% 5% 1 3 2 2 3 2 3 5% 69%	1763
	11th to 20th	Day	3 4 1 3 3 2 3 2 4 6% 70%	1800
	21st to end	Day	7% 5% 1 3 3 2 3 3 4 4 65%	1746
December	1st to 10th	Day	2 7% 2 4 3 3 3 3 4 7% 61%	1710
	11th to 20th	Day	7% 5% 1 3 2 2 3 3 5% 6% 62%	2161
	21st to end	Day	5% 7% 3 8% 5% 4 4 3 5% 6% 50%	2918
January	1st to 10th	Night	5% 6% 2 6% 5% 4 4 3 4 6% 56%	4417
	11th to 20th	Night	3 5% 2 5% 3 3 3 3 4 7% 61%	4337
	21st to end	Night	7% 8% 2 5% 4 3 3 2 4 7% 55%	4367
February	1st to 10th	Night	4 7% 3 6% 3 4 3 3 4 5% 58%	2280
	11th to 20th	Night	5% 6% 3 6% 4 4 4 3 5% 6% 53%	2218
	21st to end	Night	5% 5% 2 4 3 2 3 3 4 7% 62%	1884
March	1st to 10th	Night	4 5% 2 4 3 2 3 3 4 5% 67%	3734
	11th to 20th	Night	6% 5% 2 5% 4 3 4 4 5% 7% 56%	3593
	21st to end	Night	5% 5% 2 4 3 3 4 3 6% 7% 58%	3674
April	1st to 10th	Night	6% 4 1 4 3 3 3 3 5% 7% 61%	1900
	11th to 20th	Night	8% 5% 2 4 3 3 4 3 5% 8% 56%	1877
	21st to end	Night	10% 5% 2 4 3 3 4 3 6% 7% 53%	1814
May	1st to 10th	Night	9% 6% 2 5% 4 4 3 3 4 6% 53%	2850
	11th to 20th	Night	9% 4 2 5% 4 4 4 3 5% 7% 51%	2823
	21st to end	Night	8% 5% 2 5% 3 4 4 4 5% 8% 53%	3098
June	1st to 10th	Night	4 3 2 3 3 4 5% 4 8% 10% 55%	1667
	11th to 20th	Night	4 4 1 3 3 4 5% 5% 7% 8% 57%	1520
	21st to end	Night	4 4 2 4 3 3 4 4 8% 10% 54%	1520
July	1st to 10th	Night	5% 3 1 4 4 4 4 4 6% 10% 53%	2540
	11th to 20th	Night	3 3 1 5% 4 4 4 4 8% 12% 51%	2596
	21st to end	Night	3 4 2 5% 4 4 5% 5% 7% 11% 50%	3097
August	1st to 10th	Night	9% 4 2 5% 5% 5% 6% 5% 7% 8% 43%	2899
	11th to 20th	Night	4 3 1 5% 4 4 5% 5% 10% 14% 46%	3113
	21st to end	Night	5% 3 1 4 4 4 6% 6% 9% 13% 46%	3487
September	1st to 10th	Night	7% 3 1 4 3 3 3 2 4 7% 63%	1923
	11th to 20th	Night	6% 4 1 4 3 3 3 3 7% 7% 60%	2090
	21st to end	Night	5% 2 1 3 2 3 3 3 4 6% 67%	2090
October	1st to 10th	Night	6% 2 1 2 1 1 2 2 4 5% 74%	3480
	11th to 20th	Night	6% 3 1 4 3 3 3 3 4 6% 64%	3525
	21st to end	Night	6% 3 1 3 2 2 2 2 4 5% 70%	4467
November	1st to 10th	Night	5% 3 1 3 3 2 2 2 4 7% 68%	2535
	11th to 20th	Night	2 2 1 3 3 3 3 3 3 6% 72%	2600
	21st to end	Night	6% 4 1 3 3 2 2 3 4 6% 65%	2529
December	1st to 10th	Night	4 5% 2 5% 4 3 3 2 5% 8% 61%	2470
	11th to 20th	Night	6% 4 1 4 3 3 3 3 5% 7% 61%	3036
	21st to end	Night	4 5% 2 5% 3 4 4 4 5% 8% 55%	4727

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	30% 4 7% 26% 28% 4	2539
	11th to 20th	Day	26% 5% 13% 22% 24% 10%	2614
	21st to end	Day	29% 4 9% 26% 27% 5%	3331
February	1st to 10th	Day	30% 3 11% 22% 23% 10%	1900
	11th to 20th	Day	29% 4 8% 25% 22% 11%	1859
	21st to end	Day	23% 2 6% 22% 30% 16%	1570
March	1st to 10th	Day	20% 2 6% 19% 28% 25%	3130
	11th to 20th	Day	23% 5% 10% 22% 31% 8%	3356
	21st to end	Day	29% 5% 11% 27% 22% 6%	3959
April	1st to 10th	Day	22% 3 9% 24% 26% 16%	2280
	11th to 20th	Day	26% 4 10% 23% 23% 13%	2254
	21st to end	Day	27% 4 11% 24% 26% 9%	2365
May	1st to 10th	Day	26% 6% 10% 21% 19% 17%	4120
	11th to 20th	Day	26% 7% 14% 24% 24% 7%	4086
	21st to end	Day	22% 7% 12% 17% 25% 17%	4489
June	1st to 10th	Day	22% 7% 15% 27% 20% 8%	2506
	11th to 20th	Day	19% 6% 10% 20% 28% 16%	2660
	21st to end	Day	20% 6% 12% 26% 25% 12%	2660
July	1st to 10th	Day	24% 5% 11% 24% 29% 6%	4361
	11th to 20th	Day	15% 4 14% 26% 32% 8%	4296
	21st to end	Day	20% 5% 12% 27% 27% 9%	4325
August	1st to 10th	Day	28% 6% 15% 25% 23% 4	4009
	11th to 20th	Day	19% 5% 14% 24% 30% 9%	3762
	21st to end	Day	21% 4 11% 30% 26% 7%	4179
September	1st to 10th	Day	26% 5% 8% 22% 25% 14%	2256
	11th to 20th	Day	23% 4 8% 22% 29% 14%	2090
	21st to end	Day	19% 4 8% 24% 29% 15%	2090
October	1st to 10th	Day	18% 3 5% 16% 40% 17%	3480
	11th to 20th	Day	21% 2 7% 23% 33% 13%	3360
	21st to end	Day	14% 2 5% 21% 40% 19%	3091
November	1st to 10th	Day	20% 3 8% 21% 34% 15%	1763
	11th to 20th	Day	18% 2 5% 27% 34% 13%	1800
	21st to end	Day	23% 3 6% 20% 32% 16%	1746
December	1st to 10th	Day	23% 4 10% 30% 25% 8%	1710
	11th to 20th	Day	23% 4 8% 26% 30% 10%	2159
	21st to end	Day	33% 5% 8% 19% 26% 9%	2918
January	1st to 10th	Night	29% 4 9% 29% 24% 5%	4417
	11th to 20th	Night	23% 3 15% 25% 24% 9%	4337
	21st to end	Night	31% 4 11% 21% 28% 6%	4367
February	1st to 10th	Night	28% 4 9% 21% 27% 10%	2280
	11th to 20th	Night	31% 4 9% 21% 24% 10%	2218
	21st to end	Night	22% 3 6% 19% 31% 19%	1884
March	1st to 10th	Night	20% 3 6% 20% 26% 25%	3734
	11th to 20th	Night	25% 6% 11% 20% 25% 14%	3593
	21st to end	Night	22% 7% 11% 31% 20% 9%	3674
April	1st to 10th	Night	23% 3 9% 22% 25% 17%	1900
	11th to 20th	Night	26% 6% 11% 23% 23% 13%	1877
	21st to end	Night	30% 4 13% 23% 21% 8%	1814
May	1st to 10th	Night	29% 7% 13% 16% 15% 19%	2850
	11th to 20th	Night	30% 7% 14% 22% 19% 8%	2824
	21st to end	Night	28% 7% 12% 18% 16% 19%	3099
June	1st to 10th	Night	22% 9% 19% 27% 15% 7%	1667
	11th to 20th	Night	22% 9% 13% 22% 24% 12%	1520
	21st to end	Night	23% 6% 13% 26% 20% 12%	1520
July	1st to 10th	Night	26% 5% 12% 30% 22% 4	2500
	11th to 20th	Night	25% 5% 14% 22% 27% 7%	2548
	21st to end	Night	27% 6% 12% 26% 21% 9%	2999
August	1st to 10th	Night	36% 6% 13% 19% 22% 4	2889
	11th to 20th	Night	26% 5% 13% 28% 22% 7%	3143
	21st to end	Night	28% 4 14% 25% 24% 5%	3487
September	1st to 10th	Night	23% 4 12% 22% 25% 14%	1923
	11th to 20th	Night	22% 6% 11% 21% 27% 14%	2090
	21st to end	Night	19% 5% 7% 24% 29% 17%	2090
October	1st to 10th	Night	15% 3 5% 16% 40% 20%	3480
	11th to 20th	Night	23% 2 7% 24% 27% 16%	3525
	21st to end	Night	19% 2 4 20% 40% 16%	4467
November	1st to 10th	Night	17% 3 9% 21% 30% 20%	2535
	11th to 20th	Night	15% 3 7% 24% 36% 16%	2600
	21st to end	Night	22% 3 6% 21% 29% 19%	2529
December	1st to 10th	Night	23% 4 9% 28% 26% 10%	2470
	11th to 20th	Night	23% 3 7% 26% 32% 9%	3037
	21st to end	Night	26% 5% 10% 25% 25% 8%	4727

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	7% 6% 35% 39% 11% 2	270
	11th to 20th	Day	10% 11% 30% 33% 14% 2	270
	21st to end	Day	4 9% 37% 34% 15% 2	297
February	1st to 10th	Day	9% 11% 41% 33% 6%	270
	11th to 20th	Day	9% 8% 43% 26% 10% 3	270
	21st to end	Day	5% 8% 54% 30% 3	225
March	1st to 10th	Day	7% 8% 42% 30% 13%	270
	11th to 20th	Day	13% 10% 34% 29% 14% 1	270
	21st to end	Day	14% 12% 34% 28% 12% 1	378
April	1st to 10th	Day	9% 13% 41% 26% 10% 2	460
	11th to 20th	Day	12% 14% 39% 29% 6% 1	452
	21st to end	Day	14% 14% 37% 25% 9% 1	545
May	1st to 10th	Day	9% 9% 36% 31% 12% 2	653
	11th to 20th	Day	11% 8% 29% 33% 16% 4	675
	21st to end	Day	7% 8% 34% 32% 17% 1	734
June	1st to 10th	Day	5% 4 23% 37% 23% 7%	680
	11th to 20th	Day	5% 5% 29% 36% 21% 4	680
	21st to end	Day	3 4 23% 44% 22% 4	680
July	1st to 10th	Day	6% 2 15% 37% 32% 8%	671
	11th to 20th	Day	3 1 11% 40% 36% 9%	668
	21st to end	Day	5% 1 11% 38% 36% 9%	739
August	1st to 10th	Day	4 1 12% 38% 36% 8%	634
	11th to 20th	Day	3 1 17% 39% 34% 6%	477
	21st to end	Day	4 1 13% 41% 31% 10%	539
September	1st to 10th	Day	8% 2 16% 38% 29% 8%	466
	11th to 20th	Day	3 3 17% 38% 29% 11%	300
	21st to end	Day	8% 3 21% 34% 25% 8%	300
October	1st to 10th	Day	11% 7% 21% 31% 20% 10%	300
	11th to 20th	Day	5% 4 33% 34% 18% 6%	300
	21st to end	Day	15% 8% 26% 27% 19% 5%	330
November	1st to 10th	Day	9% 7% 31% 32% 17% 4	300
	11th to 20th	Day	7% 10% 33% 32% 17% 1	300
	21st to end	Day	13% 9% 25% 30% 17% 6%	282
December	1st to 10th	Day	4 4 36% 38% 15% 3	270
	11th to 20th	Day	10% 7% 34% 32% 17% 1	270
	21st to end	Day	11% 15% 35% 30% 8%	297
January	1st to 10th	Night	6% 9% 35% 41% 9% 1	950
	11th to 20th	Night	8% 8% 33% 38% 11% 1	950
	21st to end	Night	7% 7% 37% 40% 8% 1	945
February	1st to 10th	Night	7% 10% 39% 37% 7%	760
	11th to 20th	Night	8% 10% 48% 29% 5%	744
	21st to end	Night	10% 9% 50% 27% 4	628
March	1st to 10th	Night	8% 10% 42% 35% 5%	760
	11th to 20th	Night	9% 10% 41% 31% 9%	644
	21st to end	Night	11% 14% 49% 24% 3	627
April	1st to 10th	Night	9% 11% 46% 30% 3	570
	11th to 20th	Night	10% 13% 51% 22% 3	563
	21st to end	Night	11% 11% 45% 25% 7% 1	570
May	1st to 10th	Night	10% 11% 45% 29% 5%	570
	11th to 20th	Night	8% 7% 39% 36% 9% 1	561
	21st to end	Night	8% 10% 45% 30% 7%	617
June	1st to 10th	Night	4 6% 41% 38% 11%	570
	11th to 20th	Night	5% 7% 48% 35% 6%	570
	21st to end	Night	4 5% 37% 45% 9%	570
July	1st to 10th	Night	5% 3 23% 51% 19% 1	555
	11th to 20th	Night	3 2 21% 52% 22%	552
	21st to end	Night	6% 1 18% 52% 22% 1	624
August	1st to 10th	Night	5% 2 18% 50% 24%	567
	11th to 20th	Night	9% 1 21% 51% 18%	564
	21st to end	Night	5% 1 22% 49% 22% 1	627
September	1st to 10th	Night	7% 1 25% 51% 15%	570
	11th to 20th	Night	7% 3 39% 40% 10% 2	570
	21st to end	Night	5% 5% 32% 43% 15%	570
October	1st to 10th	Night	11% 6% 30% 41% 11%	570
	11th to 20th	Night	7% 7% 36% 38% 11% 1	599
	21st to end	Night	9% 8% 32% 34% 15% 1	1045
November	1st to 10th	Night	6% 5% 34% 44% 10% 1	975
	11th to 20th	Night	4 8% 39% 39% 10% 1	1000
	21st to end	Night	8% 10% 29% 39% 14% 1	973
December	1st to 10th	Night	5% 8% 37% 41% 9%	950
	11th to 20th	Night	9% 8% 37% 37% 9%	950
	21st to end	Night	10% 11% 37% 35% 7%	1045

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