Comprix Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Comprix Observatory clear sky chart from 2005-11-06 to 2026-09-29.

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	15% 9% 3 8% 5% 5% 5% 4 5% 7% 33%	149230
	Night	16% 10% 4 8% 5% 4 4 3 5% 7% 34%	142125
Transparency	Day	50% 3 11% 23% 12% 1	152891
	Night	50% 3 10% 22% 13% 2	146535
Seeing	Day	19% 8% 24% 23% 17% 8%	17520
	Night	19% 7% 25% 32% 15% 2	27390

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% 18% 7% 14% 7% 4 4 3 4 5% 16%	5258
	11th to 20th	Day	13% 18% 6% 15% 8% 7% 5% 3 3 4 19%	5280
	21st to end	Day	19% 14% 6% 10% 9% 7% 5% 4 5% 5% 15%	5780
February	1st to 10th	Day	21% 13% 4 10% 6% 4 4 3 5% 5% 25%	1890
	11th to 20th	Day	18% 12% 6% 13% 6% 4 4 4 5% 5% 24%	2023
	21st to end	Day	18% 13% 5% 9% 4 4 4 2 4 5% 30%	1730
March	1st to 10th	Day	18% 14% 5% 10% 5% 4 4 3 4 6% 27%	4807
	11th to 20th	Day	13% 8% 3 8% 5% 5% 4 4 5% 6% 40%	5090
	21st to end	Day	20% 9% 3 8% 5% 5% 4 3 4 6% 32%	5586
April	1st to 10th	Day	16% 13% 3 7% 5% 4 5% 3 5% 6% 34%	2352
	11th to 20th	Day	17% 9% 3 7% 4 4 4 4 5% 6% 37%	2655
	21st to end	Day	17% 8% 3 7% 5% 5% 5% 4 6% 7% 34%	2730
May	1st to 10th	Day	20% 9% 3 7% 5% 5% 5% 4 5% 6% 29%	7616
	11th to 20th	Day	18% 8% 3 6% 4 4 4 4 6% 9% 34%	7626
	21st to end	Day	20% 7% 2 7% 4 4 5% 4 6% 8% 33%	8391
June	1st to 10th	Day	12% 6% 3 7% 6% 5% 5% 4 6% 9% 38%	2730
	11th to 20th	Day	12% 5% 2 8% 5% 4 4 4 7% 10% 38%	2730
	21st to end	Day	11% 6% 2 6% 6% 5% 5% 5% 6% 11% 37%	2849
July	1st to 10th	Day	10% 6% 2 7% 5% 5% 5% 4 6% 9% 41%	7760
	11th to 20th	Day	11% 6% 2 6% 5% 5% 5% 5% 6% 10% 39%	7680
	21st to end	Day	11% 6% 3 7% 5% 5% 6% 5% 7% 9% 37%	8340
August	1st to 10th	Day	12% 6% 3 7% 5% 5% 5% 5% 7% 9% 36%	6014
	11th to 20th	Day	14% 7% 3 7% 5% 6% 5% 5% 7% 9% 32%	5951
	21st to end	Day	5% 4 1 5% 4 5% 6% 4 7% 10% 49%	6485
September	1st to 10th	Day	13% 5% 2 4 4 3 4 3 5% 7% 50%	2311
	11th to 20th	Day	9% 6% 2 5% 4 5% 5% 3 5% 7% 48%	2310
	21st to end	Day	19% 7% 2 6% 4 3 4 3 5% 5% 42%	2288
October	1st to 10th	Day	13% 6% 2 6% 4 5% 4 3 5% 8% 46%	2140
	11th to 20th	Day	14% 7% 2 6% 4 5% 4 4 5% 6% 44%	2000
	21st to end	Day	20% 9% 2 8% 4 4 3 3 5% 5% 36%	2148
November	1st to 10th	Day	11% 8% 2 6% 4 4 4 3 5% 6% 47%	1852
	11th to 20th	Day	16% 13% 3 6% 6% 5% 4 3 4 6% 34%	1890
	21st to end	Day	19% 13% 5% 8% 5% 4 4 3 4 6% 30%	1890
December	1st to 10th	Day	20% 12% 4 15% 5% 4 4 3 4 5% 24%	3020
	11th to 20th	Day	23% 16% 6% 9% 4 4 4 3 5% 5% 21%	3463
	21st to end	Day	24% 19% 6% 10% 5% 5% 4 4 4 4 15%	4565
January	1st to 10th	Night	16% 16% 7% 15% 6% 5% 4 3 4 5% 18%	7635
	11th to 20th	Night	12% 17% 8% 16% 7% 6% 5% 3 4 4 19%	7680
	21st to end	Night	18% 13% 6% 9% 6% 5% 5% 3 4 5% 27%	8401
February	1st to 10th	Night	20% 12% 4 9% 6% 4 4 3 4 5% 29%	2730
	11th to 20th	Night	19% 12% 4 10% 6% 5% 5% 3 5% 6% 26%	2479
	21st to end	Night	20% 13% 6% 10% 4 4 3 3 4 5% 28%	2076
March	1st to 10th	Night	20% 12% 4 7% 4 3 4 3 4 5% 35%	5265
	11th to 20th	Night	14% 7% 2 5% 4 4 4 4 6% 7% 41%	5090
	21st to end	Night	20% 9% 3 7% 5% 4 5% 3 4 5% 36%	5588
April	1st to 10th	Night	17% 9% 3 6% 5% 4 4 4 5% 6% 37%	2286
	11th to 20th	Night	15% 8% 2 7% 4 4 5% 4 6% 7% 37%	1914
	21st to end	Night	15% 8% 2 7% 5% 4 4 3 6% 8% 37%	1890
May	1st to 10th	Night	25% 7% 3 7% 5% 4 5% 4 5% 7% 29%	5237
	11th to 20th	Night	16% 7% 3 6% 4 4 4 4 6% 9% 38%	5234
	21st to end	Night	18% 7% 2 7% 4 4 4 4 5% 8% 37%	5761
June	1st to 10th	Night	10% 5% 2 5% 4 5% 5% 3 6% 8% 47%	1890
	11th to 20th	Night	9% 5% 2 5% 3 5% 6% 4 8% 10% 43%	1890
	21st to end	Night	10% 5% 3 5% 4 4 5% 3 8% 9% 45%	1746
July	1st to 10th	Night	10% 6% 2 7% 5% 5% 6% 4 6% 8% 42%	5141
	11th to 20th	Night	11% 6% 2 7% 5% 4 4 4 6% 9% 41%	5277
	21st to end	Night	9% 5% 3 6% 5% 5% 5% 4 7% 8% 43%	5736
August	1st to 10th	Night	12% 8% 3 8% 5% 5% 5% 4 6% 8% 34%	4135
	11th to 20th	Night	14% 8% 3 8% 5% 4 4 3 5% 7% 38%	4095
	21st to end	Night	5% 3 2 6% 4 4 5% 5% 7% 9% 52%	4624
September	1st to 10th	Night	13% 4 1 4 3 3 4 3 4 6% 54%	2286
	11th to 20th	Night	9% 4 1 4 3 3 4 4 5% 7% 55%	2310
	21st to end	Night	17% 7% 3 6% 3 3 4 3 4 6% 46%	2289
October	1st to 10th	Night	10% 4 2 5% 4 4 4 4 5% 7% 51%	2259
	11th to 20th	Night	15% 8% 2 5% 3 3 4 3 5% 6% 45%	2400
	21st to end	Night	21% 7% 2 6% 4 3 4 3 5% 5% 39%	2690
November	1st to 10th	Night	14% 6% 2 6% 3 4 3 3 5% 6% 49%	2666
	11th to 20th	Night	17% 10% 3 6% 5% 4 4 4 5% 5% 37%	2730
	21st to end	Night	20% 13% 4 7% 5% 4 4 3 5% 5% 29%	2730
December	1st to 10th	Night	19% 12% 5% 9% 5% 4 4 3 6% 6% 27%	4380
	11th to 20th	Night	19% 16% 7% 10% 5% 4 4 3 4 6% 23%	4952
	21st to end	Night	25% 19% 5% 10% 5% 5% 4 3 4 5% 16%	6633

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	73% 2 11% 12% 3	5259
	11th to 20th	Day	72% 2 8% 9% 9% 1	5280
	21st to end	Day	72% 2 10% 11% 6%	5780
February	1st to 10th	Day	62% 3 10% 17% 8%	1890
	11th to 20th	Day	62% 4 8% 17% 8%	2033
	21st to end	Day	58% 2 12% 19% 7% 1	1730
March	1st to 10th	Day	60% 2 7% 23% 7% 1	4807
	11th to 20th	Day	47% 2 9% 29% 11% 1	5090
	21st to end	Day	55% 2 9% 22% 11% 2	5586
April	1st to 10th	Day	52% 3 11% 21% 12% 1	2352
	11th to 20th	Day	48% 4 11% 21% 14% 3	2655
	21st to end	Day	49% 5% 10% 23% 11% 2	2730
May	1st to 10th	Day	56% 2 10% 21% 9% 1	7651
	11th to 20th	Day	49% 3 12% 24% 13%	7630
	21st to end	Day	49% 3 9% 20% 14% 4	8405
June	1st to 10th	Day	43% 5% 11% 24% 16% 2	2730
	11th to 20th	Day	41% 5% 15% 24% 15% 1	2730
	21st to end	Day	40% 5% 16% 21% 15% 3	2849
July	1st to 10th	Day	41% 3 12% 28% 15% 2	7695
	11th to 20th	Day	41% 3 11% 31% 13%	7611
	21st to end	Day	43% 3 11% 23% 18% 2	8156
August	1st to 10th	Day	44% 4 13% 23% 13% 2	6001
	11th to 20th	Day	48% 3 11% 26% 11% 1	5990
	21st to end	Day	30% 4 15% 34% 14% 2	6484
September	1st to 10th	Day	34% 5% 11% 25% 23% 3	2311
	11th to 20th	Day	35% 4 10% 27% 22% 3	2310
	21st to end	Day	44% 3 8% 22% 21% 2	2288
October	1st to 10th	Day	27% 3 8% 34% 27% 1	3491
	11th to 20th	Day	35% 2 10% 28% 22% 3	3240
	21st to end	Day	40% 2 10% 27% 19% 2	3450
November	1st to 10th	Day	38% 4 9% 28% 18% 3	1852
	11th to 20th	Day	52% 3 8% 22% 11% 3	1890
	21st to end	Day	57% 3 11% 19% 9% 1	1890
December	1st to 10th	Day	64% 2 12% 18% 3	3020
	11th to 20th	Day	67% 2 10% 16% 5%	3460
	21st to end	Day	75% 2 9% 10% 4	4565
January	1st to 10th	Night	70% 1 10% 15% 3	7636
	11th to 20th	Night	71% 1 7% 12% 8% 1	7680
	21st to end	Night	61% 1 12% 18% 6% 1	8401
February	1st to 10th	Night	59% 4 10% 19% 8% 1	2730
	11th to 20th	Night	59% 3 10% 18% 10% 1	2480
	21st to end	Night	60% 2 11% 17% 9% 2	2076
March	1st to 10th	Night	53% 2 6% 27% 10% 2	5265
	11th to 20th	Night	42% 2 10% 33% 11% 1	5090
	21st to end	Night	52% 3 7% 24% 14% 2	5588
April	1st to 10th	Night	47% 4 11% 22% 14% 2	2286
	11th to 20th	Night	45% 3 12% 19% 18% 4	1914
	21st to end	Night	45% 4 10% 24% 15% 2	1890
May	1st to 10th	Night	55% 3 10% 21% 8% 3	5264
	11th to 20th	Night	44% 4 10% 27% 14% 1	5235
	21st to end	Night	46% 3 11% 23% 12% 4	5771
June	1st to 10th	Night	35% 6% 12% 23% 21% 3	1890
	11th to 20th	Night	34% 6% 15% 25% 18% 3	1890
	21st to end	Night	34% 7% 16% 23% 18% 2	1746
July	1st to 10th	Night	42% 3 11% 25% 16% 3	5098
	11th to 20th	Night	41% 4 11% 31% 13% 1	5226
	21st to end	Night	38% 3 13% 23% 20% 3	5606
August	1st to 10th	Night	48% 3 14% 21% 13% 2	4124
	11th to 20th	Night	47% 4 11% 23% 15%	4122
	21st to end	Night	29% 3 15% 33% 18% 2	4624
September	1st to 10th	Night	32% 4 12% 24% 22% 6%	2286
	11th to 20th	Night	29% 4 10% 27% 27% 3	2310
	21st to end	Night	41% 3 9% 20% 26% 1	2289
October	1st to 10th	Night	27% 3 6% 30% 32% 3	3688
	11th to 20th	Night	31% 2 10% 29% 24% 4	3899
	21st to end	Night	34% 3 8% 26% 25% 4	4338
November	1st to 10th	Night	38% 3 11% 27% 19% 3	2666
	11th to 20th	Night	49% 3 8% 23% 14% 2	2730
	21st to end	Night	57% 2 11% 20% 8% 1	2730
December	1st to 10th	Night	59% 2 12% 21% 5%	4380
	11th to 20th	Night	65% 2 12% 16% 5%	4954
	21st to end	Night	72% 2 9% 14% 3	6633

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	28% 15% 33% 18% 5% 2	330
	11th to 20th	Day	25% 21% 38% 12% 4	330
	21st to end	Day	28% 16% 34% 16% 6%	363
February	1st to 10th	Day	28% 13% 35% 17% 7% 1	330
	11th to 20th	Day	29% 18% 35% 14% 3 1	330
	21st to end	Day	23% 18% 41% 17% 1	273
March	1st to 10th	Day	24% 15% 34% 21% 5%	427
	11th to 20th	Day	26% 13% 31% 22% 6% 1	540
	21st to end	Day	27% 12% 34% 21% 6%	594
April	1st to 10th	Day	23% 12% 32% 21% 10% 2	540
	11th to 20th	Day	21% 14% 29% 22% 9% 5%	532
	21st to end	Day	20% 9% 32% 25% 12% 2	540
May	1st to 10th	Day	25% 10% 30% 20% 13% 3	543
	11th to 20th	Day	20% 7% 26% 23% 18% 6%	567
	21st to end	Day	16% 5% 21% 27% 22% 9%	617
June	1st to 10th	Day	14% 4 21% 30% 22% 10%	570
	11th to 20th	Day	14% 5% 19% 27% 25% 9%	570
	21st to end	Day	13% 5% 22% 27% 23% 10%	689
July	1st to 10th	Day	14% 3 9% 22% 27% 24%	593
	11th to 20th	Day	10% 2 14% 25% 30% 18%	564
	21st to end	Day	12% 2 11% 28% 29% 18%	620
August	1st to 10th	Day	10% 3 12% 22% 34% 18%	566
	11th to 20th	Day	14% 3 14% 28% 25% 15%	559
	21st to end	Day	8% 2 11% 28% 32% 21%	627
September	1st to 10th	Day	13% 3 12% 25% 29% 18%	570
	11th to 20th	Day	11% 1 8% 23% 36% 21%	570
	21st to end	Day	22% 6% 13% 28% 21% 11%	562
October	1st to 10th	Day	12% 4 21% 29% 21% 12%	530
	11th to 20th	Day	14% 9% 29% 28% 15% 5%	530
	21st to end	Day	22% 8% 32% 26% 11% 1	531
November	1st to 10th	Day	15% 10% 30% 28% 12% 4	330
	11th to 20th	Day	23% 19% 26% 19% 11% 2	330
	21st to end	Day	27% 12% 34% 22% 4 1	330
December	1st to 10th	Day	26% 13% 35% 19% 6% 2	330
	11th to 20th	Day	25% 15% 38% 17% 5%	330
	21st to end	Day	33% 12% 29% 21% 5%	363
January	1st to 10th	Night	24% 13% 32% 26% 4	840
	11th to 20th	Night	27% 12% 33% 23% 4	840
	21st to end	Night	25% 11% 33% 27% 3	924
February	1st to 10th	Night	27% 9% 30% 32% 3	840
	11th to 20th	Night	25% 10% 36% 26% 3	823
	21st to end	Night	24% 12% 37% 25% 2	692
March	1st to 10th	Night	22% 10% 33% 29% 5%	840
	11th to 20th	Night	20% 12% 35% 26% 7%	840
	21st to end	Night	25% 9% 32% 27% 7% 1	924
April	1st to 10th	Night	21% 10% 35% 27% 7%	816
	11th to 20th	Night	17% 7% 36% 28% 11% 1	623
	21st to end	Night	18% 5% 38% 31% 8% 1	630
May	1st to 10th	Night	20% 7% 29% 31% 13%	630
	11th to 20th	Night	19% 4 22% 37% 16% 1	621
	21st to end	Night	10% 4 17% 39% 27% 3	683
June	1st to 10th	Night	11% 3 19% 43% 23% 1	630
	11th to 20th	Night	12% 2 17% 43% 25% 2	630
	21st to end	Night	10% 3 17% 43% 26% 2	630
July	1st to 10th	Night	11% 2 9% 39% 32% 7%	615
	11th to 20th	Night	8% 2 10% 38% 37% 5%	612
	21st to end	Night	10% 2 10% 40% 36% 3	690
August	1st to 10th	Night	7% 1 10% 43% 36% 4	627
	11th to 20th	Night	11% 2 8% 41% 35% 4	624
	21st to end	Night	8% 1 9% 39% 37% 6%	693
September	1st to 10th	Night	15% 2 12% 35% 31% 5%	816
	11th to 20th	Night	10% 2 10% 37% 35% 5%	840
	21st to end	Night	20% 3 18% 34% 24% 2	833
October	1st to 10th	Night	11% 3 20% 37% 25% 3	800
	11th to 20th	Night	18% 6% 27% 34% 14% 1	800
	21st to end	Night	23% 7% 28% 32% 10%	880
November	1st to 10th	Night	18% 5% 27% 33% 16% 1	820
	11th to 20th	Night	21% 11% 30% 29% 9%	840
	21st to end	Night	26% 9% 27% 30% 7% 1	840
December	1st to 10th	Night	28% 8% 30% 29% 5%	840
	11th to 20th	Night	25% 9% 33% 28% 5% 1	840
	21st to end	Night	31% 10% 28% 28% 3	924

Page generated at 2026-09-26 04:18:39. Version ac07

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