DSO - Upham
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the DSO - Upham clear sky chart from 2005-11-06 to 2026-05-02.

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	3 2 1 3 2 3 3 3 5% 7% 68%	139743
	Night	3 3 1 4 3 3 4 3 5% 7% 64%	140278
Transparency	Day	16% 3 6% 16% 29% 30%	134773
	Night	19% 3 6% 15% 29% 28%	136253
Seeing	Day	5% 8% 17% 26% 26% 17%	16221
	Night	4 4 21% 43% 26% 2	26681

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	3 5% 2 5% 2 3 3 3 5% 5% 65%	5318
	11th to 20th	Day	1 1 1 1 1 2 1 4 6% 81%	5340
	21st to end	Day	6% 3 1 4 2 3 3 3 5% 5% 64%	5844
February	1st to 10th	Day	2 3 1 3 2 2 3 4 4 6% 71%	1937
	11th to 20th	Day	4 4 1 4 3 2 3 3 4 5% 67%	2049
	21st to end	Day	2 2 1 2 3 2 2 3 5% 5% 72%	1761
March	1st to 10th	Day	2 2 1 3 2 3 3 3 5% 6% 70%	5064
	11th to 20th	Day	4 3 1 4 3 3 3 3 5% 5% 66%	5110
	21st to end	Day	1 3 2 4 3 3 3 4 5% 7% 65%	5643
April	1st to 10th	Day	2 2 2 2 2 3 3 4 7% 72%	2520
	11th to 20th	Day	3 2 1 3 2 2 2 2 3 4 76%	2491
	21st to end	Day	1 2 1 2 1 2 2 2 3 4 80%	2520
May	1st to 10th	Day	1 1 1 1 1 1 2 2 3 5% 82%	5453
	11th to 20th	Day	1 1 1 2 1 2 2 2 4 6% 78%	5405
	21st to end	Day	1 1 1 1 1 2 2 3 5% 84%	6417
June	1st to 10th	Day	2 2 1 3 3 2 3 3 5% 8% 70%	2600
	11th to 20th	Day	2 1 1 2 1 1 2 2 4 5% 78%	2600
	21st to end	Day	5% 3 1 4 4 4 5% 4 7% 7% 58%	2600
July	1st to 10th	Day	3 2 1 3 3 4 4 4 7% 8% 59%	5879
	11th to 20th	Day	2 1 1 3 3 3 5% 4 8% 12% 59%	5880
	21st to end	Day	3 4 2 5% 5% 5% 6% 6% 9% 12% 42%	6401
August	1st to 10th	Day	2 1 1 3 3 3 4 4 8% 11% 60%	5552
	11th to 20th	Day	2 2 1 3 3 4 5% 4 8% 11% 58%	5366
	21st to end	Day	2 2 1 4 3 4 5% 5% 7% 10% 57%	5984
September	1st to 10th	Day	6% 4 2 5% 4 4 4 4 6% 8% 54%	2400
	11th to 20th	Day	6% 3 1 3 3 3 4 3 6% 7% 60%	2400
	21st to end	Day	2 3 1 3 2 1 2 3 5% 5% 72%	2134
October	1st to 10th	Day	2 2 1 2 2 1 2 2 3 4 79%	3270
	11th to 20th	Day	3 2 1 2 2 3 2 2 4 4 74%	3250
	21st to end	Day	1 1 1 1 1 1 1 1 2 3 86%	3548
November	1st to 10th	Day	2 2 1 2 2 2 2 2 3 6% 76%	2059
	11th to 20th	Day	2 3 1 3 2 2 3 3 4 6% 70%	2100
	21st to end	Day	6% 4 1 3 4 2 3 3 5% 6% 63%	1949
December	1st to 10th	Day	5% 3 1 4 3 2 3 3 4 6% 66%	2903
	11th to 20th	Day	3 3 3 4 3 3 2 2 4 6% 67%	3387
	21st to end	Day	2 2 1 2 2 3 3 2 5% 6% 72%	4609
January	1st to 10th	Night	4 6% 2 5% 4 3 4 3 5% 6% 59%	7605
	11th to 20th	Night	1 1 1 1 1 2 2 2 4 5% 79%	7650
	21st to end	Night	5% 4 2 5% 3 3 4 3 6% 6% 59%	8370
February	1st to 10th	Night	2 3 1 3 2 2 4 3 4 6% 69%	2681
	11th to 20th	Night	5% 4 2 4 3 2 3 3 5% 5% 66%	2458
	21st to end	Night	2 3 1 3 3 2 4 3 5% 6% 69%	2039
March	1st to 10th	Night	2 3 1 2 2 2 3 3 4 6% 70%	5050
	11th to 20th	Night	5% 3 1 3 3 3 3 3 5% 6% 65%	5110
	21st to end	Night	2 3 2 4 3 3 3 3 5% 7% 66%	5570
April	1st to 10th	Night	1 2 1 2 3 3 4 3 5% 7% 68%	2100
	11th to 20th	Night	3 3 1 3 2 3 3 3 4 6% 69%	2077
	21st to end	Night	1 1 1 2 2 2 2 4 4 5% 76%	2100
May	1st to 10th	Night	2 2 1 3 2 2 2 2 4 4 76%	4550
	11th to 20th	Night	2 2 1 4 3 3 4 3 5% 6% 67%	4510
	21st to end	Night	1 1 1 1 2 2 2 2 3 4 81%	4475
June	1st to 10th	Night	2 2 1 3 3 4 4 4 7% 7% 64%	1800
	11th to 20th	Night	2 2 1 2 2 3 5% 3 5% 5% 70%	1800
	21st to end	Night	4 3 1 5% 5% 5% 7% 6% 8% 9% 47%	1800
July	1st to 10th	Night	3 3 2 5% 5% 5% 6% 5% 9% 10% 48%	4100
	11th to 20th	Night	2 3 2 6% 5% 7% 6% 6% 8% 11% 44%	4100
	21st to end	Night	4 5% 2 8% 6% 8% 7% 6% 10% 11% 33%	4472
August	1st to 10th	Night	2 3 1 5% 5% 5% 6% 6% 10% 13% 45%	4247
	11th to 20th	Night	3 3 2 5% 5% 6% 7% 6% 10% 13% 40%	4483
	21st to end	Night	3 4 2 7% 6% 6% 7% 5% 9% 10% 40%	4993
September	1st to 10th	Night	5% 4 2 6% 4 4 5% 6% 7% 9% 47%	2000
	11th to 20th	Night	6% 4 1 5% 4 4 4 4 6% 8% 55%	2000
	21st to end	Night	4 3 1 3 3 4 3 3 5% 6% 65%	2257
October	1st to 10th	Night	2 2 1 3 2 2 2 3 4 4 74%	3920
	11th to 20th	Night	4 2 2 3 2 2 3 2 3 4 72%	3898
	21st to end	Night	1 1 1 1 1 1 2 1 3 5% 82%	4252
November	1st to 10th	Night	3 1 1 1 1 2 3 2 4 5% 77%	2460
	11th to 20th	Night	2 3 1 2 2 2 3 3 4 5% 73%	2520
	21st to end	Night	6% 4 1 3 2 3 2 2 5% 6% 65%	2641
December	1st to 10th	Night	4 3 1 3 2 2 2 3 4 5% 71%	4502
	11th to 20th	Night	2 2 1 4 3 3 4 3 5% 7% 67%	5077
	21st to end	Night	3 2 1 3 2 2 2 2 4 6% 72%	6611

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	22% 2 3 17% 38% 18%	5321
	11th to 20th	Day	8% 1 3 14% 48% 26%	5340
	21st to end	Day	22% 2 4 15% 31% 25%	5844
February	1st to 10th	Day	15% 2 5% 16% 29% 33%	1937
	11th to 20th	Day	20% 3 4 16% 31% 26%	2059
	21st to end	Day	16% 2 2 10% 31% 39%	1761
March	1st to 10th	Day	15% 2 2 6% 32% 43%	5064
	11th to 20th	Day	19% 4 3 13% 28% 33%	5110
	21st to end	Day	18% 3 3 11% 31% 34%	5643
April	1st to 10th	Day	12% 2 3 11% 32% 40%	2520
	11th to 20th	Day	14% 2 2 7% 26% 50%	2494
	21st to end	Day	10% 2 2 9% 28% 49%	2520
May	1st to 10th	Day	8% 1 3 10% 29% 50%	5453
	11th to 20th	Day	8% 3 4 10% 25% 51%	5408
	21st to end	Day	6% 1 3 8% 13% 68%	6418
June	1st to 10th	Day	14% 3 4 13% 26% 40%	2600
	11th to 20th	Day	10% 2 2 7% 21% 57%	2600
	21st to end	Day	23% 5% 7% 15% 20% 30%	2600
July	1st to 10th	Day	19% 6% 12% 18% 23% 21%	5816
	11th to 20th	Day	15% 6% 16% 30% 26% 7%	5811
	21st to end	Day	29% 8% 16% 24% 18% 6%	6217
August	1st to 10th	Day	18% 7% 11% 32% 26% 5%	4036
	11th to 20th	Day	17% 5% 11% 20% 36% 11%	3882
	21st to end	Day	24% 6% 14% 28% 22% 7%	4311
September	1st to 10th	Day	27% 5% 8% 20% 22% 18%	2400
	11th to 20th	Day	22% 5% 6% 18% 28% 21%	2400
	21st to end	Day	15% 3 5% 19% 33% 26%	2134
October	1st to 10th	Day	11% 2 5% 9% 26% 47%	3270
	11th to 20th	Day	15% 2 4 13% 30% 36%	3250
	21st to end	Day	7% 1 1 12% 34% 45%	3548
November	1st to 10th	Day	12% 2 3 16% 37% 29%	2059
	11th to 20th	Day	16% 3 3 18% 29% 31%	2100
	21st to end	Day	22% 3 4 17% 33% 21%	1949
December	1st to 10th	Day	20% 3 4 20% 33% 19%	2903
	11th to 20th	Day	21% 2 3 15% 41% 18%	3386
	21st to end	Day	14% 2 4 20% 40% 20%	4609
January	1st to 10th	Night	27% 2 3 17% 39% 12%	7605
	11th to 20th	Night	9% 2 3 13% 49% 25%	7650
	21st to end	Night	25% 2 5% 15% 29% 24%	8370
February	1st to 10th	Night	17% 2 4 17% 27% 33%	2681
	11th to 20th	Night	21% 3 4 14% 31% 27%	2458
	21st to end	Night	16% 3 3 10% 29% 38%	2039
March	1st to 10th	Night	15% 2 2 7% 33% 40%	5050
	11th to 20th	Night	19% 3 4 13% 32% 30%	5110
	21st to end	Night	19% 2 3 12% 33% 32%	5570
April	1st to 10th	Night	16% 3 3 10% 32% 36%	2100
	11th to 20th	Night	16% 4 2 11% 23% 44%	2077
	21st to end	Night	11% 4 2 11% 29% 44%	2100
May	1st to 10th	Night	13% 2 3 14% 19% 50%	4547
	11th to 20th	Night	16% 4 5% 9% 22% 44%	4511
	21st to end	Night	9% 2 4 7% 11% 68%	4475
June	1st to 10th	Night	17% 4 5% 14% 22% 37%	1800
	11th to 20th	Night	14% 3 4 9% 17% 52%	1800
	21st to end	Night	27% 7% 9% 15% 16% 25%	1800
July	1st to 10th	Night	26% 7% 15% 18% 20% 14%	4055
	11th to 20th	Night	29% 8% 15% 21% 21% 7%	4046
	21st to end	Night	38% 8% 17% 21% 10% 7%	4344
August	1st to 10th	Night	26% 8% 13% 30% 17% 5%	3087
	11th to 20th	Night	24% 6% 13% 15% 31% 11%	3243
	21st to end	Night	38% 8% 13% 20% 16% 5%	3597
September	1st to 10th	Night	29% 7% 11% 17% 19% 17%	2000
	11th to 20th	Night	25% 5% 8% 18% 21% 23%	2000
	21st to end	Night	20% 3 6% 16% 31% 24%	2257
October	1st to 10th	Night	13% 3 5% 9% 24% 46%	3920
	11th to 20th	Night	18% 2 4 12% 24% 41%	3898
	21st to end	Night	9% 1 2 9% 31% 48%	4252
November	1st to 10th	Night	12% 2 3 16% 34% 34%	2460
	11th to 20th	Night	14% 3 2 17% 33% 32%	2520
	21st to end	Night	20% 2 5% 18% 32% 23%	2641
December	1st to 10th	Night	17% 2 4 22% 36% 19%	4502
	11th to 20th	Night	19% 2 5% 14% 39% 22%	5077
	21st to end	Night	16% 2 3 18% 41% 20%	6611

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	8% 8% 18% 40% 21% 5%	330
	11th to 20th	Day	6% 4 17% 39% 24% 9%	330
	21st to end	Day	5% 7% 21% 35% 24% 8%	363
February	1st to 10th	Day	5% 9% 18% 35% 23% 9%	330
	11th to 20th	Day	15% 8% 23% 34% 18% 3	330
	21st to end	Day	8% 17% 22% 31% 16% 6%	304
March	1st to 10th	Day	8% 16% 32% 29% 12% 3	540
	11th to 20th	Day	10% 18% 22% 25% 19% 6%	540
	21st to end	Day	5% 21% 30% 25% 14% 5%	594
April	1st to 10th	Day	8% 15% 28% 24% 16% 9%	540
	11th to 20th	Day	6% 21% 31% 24% 15% 3	532
	21st to end	Day	6% 18% 31% 26% 15% 5%	540
May	1st to 10th	Day	3 12% 33% 27% 18% 6%	508
	11th to 20th	Day	3 11% 27% 28% 23% 8%	528
	21st to end	Day	2 9% 28% 34% 21% 6%	573
June	1st to 10th	Day	3 5% 19% 31% 26% 16%	530
	11th to 20th	Day	4 4 18% 29% 29% 16%	530
	21st to end	Day	4 3 11% 26% 30% 26%	530
July	1st to 10th	Day	4 1 4 20% 37% 33%	526
	11th to 20th	Day	2 1 2 17% 38% 40%	524
	21st to end	Day	4 2 2 13% 33% 45%	575
August	1st to 10th	Day	4 1 2 12% 33% 49%	527
	11th to 20th	Day	4 2 5% 16% 37% 37%	517
	21st to end	Day	5% 1 2 16% 33% 43%	583
September	1st to 10th	Day	8% 1 5% 22% 37% 26%	530
	11th to 20th	Day	4 2 8% 26% 39% 22%	530
	21st to end	Day	3 3 8% 25% 40% 20%	401
October	1st to 10th	Day	4 3 12% 24% 34% 23%	330
	11th to 20th	Day	10% 5% 11% 22% 32% 20%	330
	21st to end	Day	5% 6% 10% 25% 32% 21%	363
November	1st to 10th	Day	6% 3 16% 32% 29% 13%	330
	11th to 20th	Day	2 5% 14% 28% 38% 14%	330
	21st to end	Day	8% 9% 18% 35% 23% 7%	330
December	1st to 10th	Day	9% 3 17% 36% 27% 8%	330
	11th to 20th	Day	5% 6% 20% 38% 22% 10%	330
	21st to end	Day	8% 7% 23% 36% 20% 6%	363
January	1st to 10th	Night	6% 5% 22% 48% 17% 2	840
	11th to 20th	Night	4 4 25% 50% 17% 1	840
	21st to end	Night	6% 6% 25% 47% 15% 1	924
February	1st to 10th	Night	4 4 26% 47% 18% 1	840
	11th to 20th	Night	7% 6% 32% 44% 11%	824
	21st to end	Night	3 8% 41% 39% 9%	692
March	1st to 10th	Night	6% 8% 31% 45% 10%	840
	11th to 20th	Night	4 9% 29% 41% 16% 1	840
	21st to end	Night	3 9% 34% 40% 14%	909
April	1st to 10th	Night	2 9% 40% 40% 10%	630
	11th to 20th	Night	5% 9% 40% 37% 9%	623
	21st to end	Night	2 10% 38% 42% 8% 1	630
May	1st to 10th	Night	3 6% 35% 47% 9%	603
	11th to 20th	Night	2 4 28% 50% 15% 1	591
	21st to end	Night	2 5% 30% 50% 13%	650
June	1st to 10th	Night	3 3 21% 50% 23% 1	600
	11th to 20th	Night	2 1 19% 55% 23%	600
	21st to end	Night	4 2 9% 44% 39% 3	600
July	1st to 10th	Night	5% 2 4 36% 48% 5%	585
	11th to 20th	Night	4 1 3 27% 57% 8%	582
	21st to end	Night	5% 3 2 23% 57% 9%	657
August	1st to 10th	Night	4 1 3 23% 56% 13%	597
	11th to 20th	Night	5% 1 3 24% 56% 10%	594
	21st to end	Night	3 2 4 25% 58% 8%	660
September	1st to 10th	Night	6% 2 4 33% 51% 4	600
	11th to 20th	Night	6% 1 5% 42% 45% 1	600
	21st to end	Night	5% 1 8% 45% 38% 2	731
October	1st to 10th	Night	5% 3 13% 46% 31% 2	800
	11th to 20th	Night	6% 1 16% 47% 29% 1	800
	21st to end	Night	3 3 15% 41% 34% 4	880
November	1st to 10th	Night	4 2 16% 45% 31% 2	820
	11th to 20th	Night	3 2 17% 46% 29% 3	840
	21st to end	Night	8% 4 22% 44% 21% 1	961
December	1st to 10th	Night	7% 4 20% 49% 18% 1	1050
	11th to 20th	Night	5% 4 22% 49% 19% 1	924
	21st to end	Night	4 5% 25% 48% 17% 1	924

Page generated at 2026-04-29 00:21:47. Version ac07

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