ARGUS Dark Sky Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the ARGUS Dark Sky Site clear sky chart from 2005-11-06 to 2024-11-04.

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% 9% 4 8% 5% 4 4 4 6% 7% 35%	101092
	Night	15% 10% 4 8% 4 4 4 3 5% 7% 36%	97958
Transparency	Day	46% 6% 12% 22% 13% 1	104719
	Night	46% 5% 11% 22% 14% 2	102471
Seeing	Day	17% 10% 27% 23% 16% 6%	15643
	Night	19% 9% 29% 29% 13% 1	25461

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	16% 14% 9% 14% 5% 4 4 4 5% 5% 20%	2527
	11th to 20th	Day	15% 15% 9% 14% 6% 6% 6% 7% 5% 4 13%	2530
	21st to end	Day	29% 21% 8% 11% 4 3 3 2 3 3 15%	2874
February	1st to 10th	Day	17% 15% 5% 11% 7% 5% 4 3 5% 5% 23%	1855
	11th to 20th	Day	17% 12% 4 12% 6% 5% 4 3 6% 5% 28%	1848
	21st to end	Day	17% 16% 5% 10% 5% 3 4 3 5% 5% 28%	1570
March	1st to 10th	Day	20% 18% 6% 8% 5% 3 3 3 3 5% 26%	3120
	11th to 20th	Day	13% 9% 4 7% 5% 3 4 4 6% 8% 38%	3377
	21st to end	Day	17% 12% 5% 10% 5% 4 4 3 5% 6% 27%	3962
April	1st to 10th	Day	16% 12% 4 8% 5% 4 4 4 5% 6% 32%	2280
	11th to 20th	Day	17% 10% 3 7% 4 4 5% 3 5% 7% 36%	2259
	21st to end	Day	19% 8% 3 7% 5% 4 5% 3 5% 8% 32%	2470
May	1st to 10th	Day	18% 9% 3 8% 5% 5% 5% 4 6% 8% 29%	4082
	11th to 20th	Day	17% 7% 2 6% 4 5% 5% 4 6% 8% 35%	4081
	21st to end	Day	10% 5% 2 6% 5% 5% 5% 5% 7% 9% 41%	4629
June	1st to 10th	Day	10% 5% 3 7% 5% 5% 5% 5% 7% 7% 41%	2660
	11th to 20th	Day	9% 5% 2 6% 5% 4 5% 5% 7% 8% 44%	2660
	21st to end	Day	10% 6% 2 6% 5% 6% 6% 5% 7% 9% 38%	2660
July	1st to 10th	Day	14% 6% 3 7% 5% 5% 5% 4 6% 9% 36%	4440
	11th to 20th	Day	7% 4 2 5% 4 4 5% 5% 7% 11% 46%	4440
	21st to end	Day	8% 7% 2 7% 5% 5% 5% 5% 7% 8% 40%	4704
August	1st to 10th	Day	7% 5% 2 6% 5% 4 5% 5% 7% 10% 44%	4104
	11th to 20th	Day	9% 4 2 6% 5% 4 5% 4 7% 8% 46%	3953
	21st to end	Day	7% 4 2 6% 4 4 4 4 6% 8% 50%	4180
September	1st to 10th	Day	11% 6% 2 6% 5% 5% 5% 3 6% 6% 46%	2242
	11th to 20th	Day	11% 4 2 5% 4 4 5% 4 7% 8% 47%	2090
	21st to end	Day	14% 6% 2 5% 4 4 4 3 6% 8% 44%	2090
October	1st to 10th	Day	12% 6% 2 6% 4 4 4 4 6% 6% 46%	2090
	11th to 20th	Day	15% 6% 3 7% 4 5% 4 4 6% 6% 41%	1918
	21st to end	Day	19% 10% 3 8% 5% 4 4 4 5% 7% 31%	1881
November	1st to 10th	Day	11% 6% 2 5% 4 4 3 3 5% 7% 49%	1699
	11th to 20th	Day	18% 12% 3 8% 5% 4 3 3 5% 6% 33%	1710
	21st to end	Day	19% 12% 3 9% 5% 3 4 3 4 5% 32%	1710
December	1st to 10th	Day	17% 17% 5% 11% 7% 4 3 3 4 4 24%	1696
	11th to 20th	Day	14% 17% 7% 11% 6% 4 4 3 4 6% 24%	1918
	21st to end	Day	24% 22% 9% 11% 5% 3 4 2 3 3 12%	2783
January	1st to 10th	Night	17% 17% 8% 12% 5% 4 3 2 4 4 22%	4428
	11th to 20th	Night	15% 21% 7% 15% 6% 5% 5% 3 4 4 16%	4440
	21st to end	Night	26% 18% 8% 8% 4 3 3 2 3 4 20%	4788
February	1st to 10th	Night	19% 15% 6% 9% 5% 4 3 3 4 5% 27%	2323
	11th to 20th	Night	12% 14% 4 9% 6% 6% 4 3 5% 5% 32%	2218
	21st to end	Night	19% 14% 4 9% 5% 4 3 2 4 5% 30%	1884
March	1st to 10th	Night	18% 13% 3 7% 5% 4 4 2 4 5% 34%	3733
	11th to 20th	Night	11% 7% 3 6% 4 4 5% 4 6% 7% 44%	3581
	21st to end	Night	18% 9% 4 8% 5% 4 4 3 5% 6% 34%	3699
April	1st to 10th	Night	13% 9% 2 8% 5% 5% 4 4 5% 7% 37%	1900
	11th to 20th	Night	18% 8% 2 6% 4 4 5% 3 5% 7% 38%	1870
	21st to end	Night	19% 9% 3 7% 3 4 4 4 6% 6% 35%	1710
May	1st to 10th	Night	18% 8% 3 8% 6% 5% 4 4 7% 8% 29%	2813
	11th to 20th	Night	19% 8% 2 5% 4 3 4 3 5% 8% 38%	2812
	21st to end	Night	10% 5% 2 7% 4 5% 5% 4 6% 8% 44%	2927
June	1st to 10th	Night	7% 5% 3 6% 4 5% 5% 4 6% 7% 48%	1520
	11th to 20th	Night	8% 5% 3 6% 4 4 4 4 6% 9% 47%	1520
	21st to end	Night	9% 5% 1 7% 5% 4 4 4 6% 10% 45%	1520
July	1st to 10th	Night	9% 5% 1 6% 5% 4 5% 5% 6% 10% 44%	2530
	11th to 20th	Night	5% 4 2 4 3 4 3 4 6% 9% 56%	2530
	21st to end	Night	9% 7% 3 7% 4 5% 5% 4 6% 9% 41%	2841
August	1st to 10th	Night	11% 5% 2 6% 3 4 5% 4 6% 9% 46%	2825
	11th to 20th	Night	7% 7% 2 5% 3 4 5% 4 6% 8% 48%	2871
	21st to end	Night	8% 5% 2 6% 4 4 4 4 5% 8% 52%	3476
September	1st to 10th	Night	11% 4 2 6% 4 3 4 3 5% 7% 49%	1918
	11th to 20th	Night	9% 3 2 4 3 3 4 4 5% 7% 58%	2090
	21st to end	Night	12% 6% 2 5% 4 4 4 3 5% 6% 48%	2090
October	1st to 10th	Night	10% 5% 2 6% 3 5% 4 3 5% 7% 51%	2090
	11th to 20th	Night	17% 8% 2 7% 4 3 3 3 4 5% 45%	2260
	21st to end	Night	20% 8% 2 6% 5% 4 4 4 5% 6% 38%	2717
November	1st to 10th	Night	12% 9% 3 6% 4 3 3 4 5% 6% 46%	2452
	11th to 20th	Night	14% 10% 3 8% 5% 3 4 3 6% 7% 37%	2470
	21st to end	Night	19% 11% 4 8% 5% 5% 4 4 3 7% 30%	2470
December	1st to 10th	Night	18% 13% 5% 9% 6% 3 4 3 5% 6% 28%	2479
	11th to 20th	Night	17% 15% 6% 11% 5% 4 4 4 4 5% 25%	3279
	21st to end	Night	24% 19% 7% 11% 5% 4 4 3 4 4 15%	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	67% 4 8% 16% 5%	2528
	11th to 20th	Day	73% 4 10% 8% 5%	2530
	21st to end	Day	77% 3 6% 11% 3	2874
February	1st to 10th	Day	64% 4 9% 13% 8% 1	1855
	11th to 20th	Day	58% 4 10% 21% 7% 1	1858
	21st to end	Day	58% 5% 11% 18% 7% 2	1570
March	1st to 10th	Day	63% 4 7% 18% 8%	3120
	11th to 20th	Day	44% 5% 11% 30% 10% 1	3377
	21st to end	Day	56% 6% 16% 19% 3 1	3962
April	1st to 10th	Day	51% 7% 11% 19% 12%	2280
	11th to 20th	Day	48% 6% 9% 22% 11% 3	2259
	21st to end	Day	50% 6% 11% 20% 10% 3	2470
May	1st to 10th	Day	51% 7% 13% 21% 8%	4120
	11th to 20th	Day	44% 8% 14% 24% 9% 1	4085
	21st to end	Day	36% 7% 12% 24% 19% 2	4642
June	1st to 10th	Day	39% 8% 11% 24% 16% 3	2660
	11th to 20th	Day	35% 7% 11% 24% 20% 3	2660
	21st to end	Day	39% 9% 15% 19% 15% 3	2660
July	1st to 10th	Day	44% 7% 11% 21% 15% 2	4371
	11th to 20th	Day	29% 7% 15% 29% 19% 1	4365
	21st to end	Day	39% 8% 15% 17% 18% 3	4555
August	1st to 10th	Day	32% 8% 18% 26% 15% 1	4091
	11th to 20th	Day	32% 8% 12% 31% 16% 1	3992
	21st to end	Day	30% 6% 14% 27% 19% 3	4179
September	1st to 10th	Day	36% 7% 12% 23% 18% 4	2242
	11th to 20th	Day	32% 8% 10% 26% 22% 2	2090
	21st to end	Day	38% 6% 10% 23% 20% 2	2090
October	1st to 10th	Day	26% 5% 11% 32% 25% 1	3480
	11th to 20th	Day	35% 5% 10% 24% 26% 1	3160
	21st to end	Day	44% 3 9% 26% 16% 1	3081
November	1st to 10th	Day	35% 6% 14% 27% 17% 2	1699
	11th to 20th	Day	53% 4 11% 19% 11% 2	1710
	21st to end	Day	55% 4 11% 21% 8% 1	1710
December	1st to 10th	Day	64% 4 11% 15% 6%	1696
	11th to 20th	Day	63% 4 9% 21% 3	1915
	21st to end	Day	79% 4 7% 7% 4	2783
January	1st to 10th	Night	65% 4 10% 14% 7%	4428
	11th to 20th	Night	73% 3 8% 12% 4	4440
	21st to end	Night	70% 3 9% 13% 5%	4788
February	1st to 10th	Night	60% 4 12% 15% 8% 1	2323
	11th to 20th	Night	55% 4 11% 19% 11% 1	2219
	21st to end	Night	57% 5% 10% 17% 9% 2	1884
March	1st to 10th	Night	52% 4 10% 23% 9% 1	3733
	11th to 20th	Night	38% 6% 11% 27% 15% 2	3581
	21st to end	Night	50% 6% 13% 25% 6% 1	3699
April	1st to 10th	Night	46% 7% 11% 22% 14% 1	1900
	11th to 20th	Night	45% 5% 10% 21% 15% 4	1870
	21st to end	Night	47% 7% 10% 22% 12% 3	1710
May	1st to 10th	Night	51% 8% 10% 20% 10% 1	2840
	11th to 20th	Night	43% 9% 12% 25% 10% 1	2813
	21st to end	Night	34% 9% 13% 21% 19% 4	2935
June	1st to 10th	Night	33% 7% 10% 27% 20% 3	1520
	11th to 20th	Night	32% 7% 12% 24% 21% 4	1520
	21st to end	Night	34% 8% 16% 22% 15% 5%	1520
July	1st to 10th	Night	35% 8% 12% 25% 15% 6%	2490
	11th to 20th	Night	24% 6% 15% 28% 25% 2	2482
	21st to end	Night	38% 6% 16% 18% 18% 5%	2750
August	1st to 10th	Night	33% 8% 15% 28% 15% 1	2814
	11th to 20th	Night	32% 8% 12% 30% 16% 1	2898
	21st to end	Night	31% 6% 12% 28% 21% 3	3476
September	1st to 10th	Night	33% 7% 12% 22% 20% 6%	1918
	11th to 20th	Night	26% 5% 10% 29% 27% 3	2090
	21st to end	Night	36% 7% 10% 23% 22% 3	2090
October	1st to 10th	Night	23% 3 7% 32% 33% 1	3480
	11th to 20th	Night	32% 4 9% 23% 30% 1	3757
	21st to end	Night	35% 5% 8% 29% 22% 2	4467
November	1st to 10th	Night	38% 5% 10% 25% 20% 2	2452
	11th to 20th	Night	47% 5% 11% 21% 14% 2	2470
	21st to end	Night	56% 5% 10% 21% 8%	2470
December	1st to 10th	Night	57% 6% 11% 17% 8% 1	2479
	11th to 20th	Night	61% 4 11% 17% 6% 1	3281
	21st to end	Night	73% 4 10% 8% 4	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	23% 18% 36% 16% 6% 1	270
	11th to 20th	Day	26% 17% 38% 13% 5%	270
	21st to end	Day	31% 15% 31% 18% 5%	297
February	1st to 10th	Day	25% 19% 36% 15% 5%	270
	11th to 20th	Day	26% 19% 34% 16% 4 1	270
	21st to end	Day	27% 20% 38% 12% 3	225
March	1st to 10th	Day	22% 21% 37% 16% 4	270
	11th to 20th	Day	24% 13% 35% 20% 6% 1	396
	21st to end	Day	30% 15% 29% 18% 6% 1	506
April	1st to 10th	Day	22% 14% 35% 18% 9% 2	460
	11th to 20th	Day	20% 19% 28% 20% 9% 3	452
	21st to end	Day	24% 16% 31% 19% 9% 2	460
May	1st to 10th	Day	23% 12% 33% 21% 8% 3	463
	11th to 20th	Day	21% 7% 29% 23% 14% 6%	487
	21st to end	Day	12% 6% 30% 26% 18% 9%	617
June	1st to 10th	Day	10% 9% 29% 26% 21% 5%	680
	11th to 20th	Day	11% 6% 27% 29% 21% 6%	680
	21st to end	Day	13% 6% 29% 27% 18% 7%	680
July	1st to 10th	Day	12% 3 18% 27% 24% 15%	671
	11th to 20th	Day	7% 3 23% 30% 25% 13%	668
	21st to end	Day	10% 3 18% 31% 28% 10%	679
August	1st to 10th	Day	7% 3 14% 30% 31% 14%	486
	11th to 20th	Day	10% 3 20% 29% 23% 14%	479
	21st to end	Day	8% 4 14% 28% 34% 13%	539
September	1st to 10th	Day	13% 5% 17% 28% 27% 10%	490
	11th to 20th	Day	10% 2 16% 24% 31% 17%	490
	21st to end	Day	17% 9% 20% 24% 22% 7%	490
October	1st to 10th	Day	12% 6% 24% 32% 18% 8%	490
	11th to 20th	Day	16% 19% 29% 24% 10% 2	422
	21st to end	Day	25% 15% 37% 19% 3 1	330
November	1st to 10th	Day	11% 15% 33% 26% 13% 3	279
	11th to 20th	Day	25% 17% 31% 17% 9% 1	270
	21st to end	Day	28% 14% 37% 18% 4	270
December	1st to 10th	Day	23% 21% 35% 13% 8%	270
	11th to 20th	Day	21% 16% 40% 17% 6%	270
	21st to end	Day	30% 19% 33% 16% 2	297
January	1st to 10th	Night	23% 16% 34% 21% 5%	950
	11th to 20th	Night	26% 14% 36% 20% 4	950
	21st to end	Night	23% 15% 35% 23% 4	988
February	1st to 10th	Night	28% 10% 35% 25% 3	760
	11th to 20th	Night	20% 13% 38% 26% 3	743
	21st to end	Night	27% 15% 37% 18% 3	628
March	1st to 10th	Night	20% 15% 34% 26% 6%	760
	11th to 20th	Night	19% 12% 37% 26% 6% 1	760
	21st to end	Night	25% 11% 33% 26% 5%	769
April	1st to 10th	Night	18% 12% 36% 27% 6% 1	570
	11th to 20th	Night	22% 10% 34% 25% 8% 1	563
	21st to end	Night	22% 9% 36% 23% 9% 1	570
May	1st to 10th	Night	22% 7% 32% 31% 8%	570
	11th to 20th	Night	20% 4 25% 32% 16% 1	561
	21st to end	Night	10% 3 24% 43% 19% 1	617
June	1st to 10th	Night	8% 4 26% 44% 18% 1	570
	11th to 20th	Night	10% 4 25% 40% 20% 1	570
	21st to end	Night	10% 3 22% 39% 25% 1	570
July	1st to 10th	Night	10% 2 16% 37% 30% 5%	555
	11th to 20th	Night	7% 3 16% 40% 31% 4	552
	21st to end	Night	8% 2 14% 43% 31% 2	624
August	1st to 10th	Night	7% 2 13% 42% 31% 4	567
	11th to 20th	Night	8% 2 16% 38% 31% 4	564
	21st to end	Night	8% 2 17% 33% 37% 5%	627
September	1st to 10th	Night	13% 3 15% 37% 29% 4	588
	11th to 20th	Night	11% 3 14% 36% 33% 4	760
	21st to end	Night	14% 5% 22% 34% 22% 2	760
October	1st to 10th	Night	12% 6% 24% 35% 20% 4	760
	11th to 20th	Night	21% 12% 28% 28% 11% 1	760
	21st to end	Night	24% 11% 32% 25% 7%	836
November	1st to 10th	Night	16% 10% 35% 26% 11% 1	755
	11th to 20th	Night	20% 15% 33% 25% 7%	760
	21st to end	Night	25% 13% 31% 23% 8%	760
December	1st to 10th	Night	25% 13% 35% 21% 5%	769
	11th to 20th	Night	25% 13% 31% 24% 6%	950
	21st to end	Night	31% 13% 33% 20% 2	1045

Page generated at 2024-11-01 22:47:37. Version ac07

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