Viking Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Viking Observatory clear sky chart from 2005-11-06 to 2024-11-05.

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	12% 8% 3 7% 5% 4 4 4 6% 7% 39%	101420
	Night	13% 9% 3 7% 4 4 4 3 5% 6% 41%	97687
Transparency	Day	42% 6% 12% 23% 15% 2	104986
	Night	42% 5% 12% 23% 16% 2	102261
Seeing	Day	15% 10% 29% 26% 15% 5%	15794
	Night	16% 10% 31% 30% 12% 1	25616

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	10% 12% 6% 16% 6% 6% 4 3 5% 5% 26%	2527
	11th to 20th	Day	12% 12% 4 13% 9% 6% 7% 4 7% 6% 20%	2544
	21st to end	Day	16% 19% 9% 14% 6% 4 4 2 3 4 18%	3135
February	1st to 10th	Day	16% 11% 5% 10% 6% 5% 5% 3 3 5% 29%	1710
	11th to 20th	Day	15% 9% 3 8% 7% 4 4 3 4 7% 35%	1772
	21st to end	Day	14% 13% 5% 9% 6% 4 2 3 4 6% 33%	1570
March	1st to 10th	Day	15% 13% 4 7% 4 3 4 2 4 6% 38%	3140
	11th to 20th	Day	9% 7% 2 6% 4 4 5% 4 6% 7% 46%	3480
	21st to end	Day	20% 12% 4 11% 5% 4 4 3 5% 6% 27%	4031
April	1st to 10th	Day	16% 12% 3 7% 4 4 5% 2 5% 6% 36%	2280
	11th to 20th	Day	16% 10% 3 7% 5% 4 4 4 4 6% 38%	2254
	21st to end	Day	20% 8% 3 8% 6% 4 4 3 4 5% 35%	2280
May	1st to 10th	Day	15% 7% 3 6% 5% 5% 4 4 6% 9% 35%	4132
	11th to 20th	Day	17% 8% 3 6% 4 4 4 4 5% 7% 39%	4399
	21st to end	Day	12% 6% 2 6% 4 4 4 4 6% 7% 45%	4824
June	1st to 10th	Day	9% 6% 2 7% 4 3 4 4 7% 8% 46%	2660
	11th to 20th	Day	9% 5% 2 6% 4 4 4 5% 5% 8% 47%	2660
	21st to end	Day	11% 6% 2 5% 5% 5% 5% 4 6% 9% 41%	2660
July	1st to 10th	Day	9% 7% 3 7% 6% 6% 5% 5% 8% 9% 35%	4440
	11th to 20th	Day	6% 4 2 5% 4 4 5% 4 6% 9% 51%	4440
	21st to end	Day	8% 5% 2 6% 5% 5% 6% 5% 7% 11% 41%	4788
August	1st to 10th	Day	7% 4 2 6% 4 4 5% 4 8% 11% 44%	4104
	11th to 20th	Day	11% 6% 2 6% 4 4 5% 4 6% 9% 42%	3823
	21st to end	Day	6% 4 2 7% 4 4 4 4 6% 9% 49%	4180
September	1st to 10th	Day	11% 5% 2 5% 4 4 4 4 5% 7% 49%	2280
	11th to 20th	Day	11% 4 1 5% 3 3 4 4 5% 8% 52%	2259
	21st to end	Day	10% 5% 2 5% 4 5% 4 4 6% 7% 48%	2070
October	1st to 10th	Day	13% 6% 2 6% 3 4 4 3 4 6% 50%	1900
	11th to 20th	Day	15% 8% 3 6% 4 3 4 3 4 6% 45%	1900
	21st to end	Day	19% 8% 3 6% 3 3 4 4 4 6% 40%	2009
November	1st to 10th	Day	12% 7% 2 6% 5% 3 4 3 5% 7% 47%	1708
	11th to 20th	Day	16% 11% 3 6% 5% 4 4 4 5% 7% 36%	1710
	21st to end	Day	16% 11% 3 8% 4 3 4 2 5% 5% 38%	1530
December	1st to 10th	Day	13% 13% 4 10% 5% 4 4 3 5% 5% 33%	1520
	11th to 20th	Day	14% 12% 4 8% 5% 5% 4 5% 6% 6% 32%	1918
	21st to end	Day	21% 18% 10% 12% 6% 3 3 2 4 4 16%	2783
January	1st to 10th	Night	13% 12% 6% 13% 5% 4 4 4 4 5% 30%	4428
	11th to 20th	Night	12% 16% 7% 12% 6% 5% 5% 3 8% 4 23%	4409
	21st to end	Night	18% 15% 7% 13% 5% 4 4 2 3 5% 23%	4532
February	1st to 10th	Night	16% 11% 4 8% 6% 3 5% 3 5% 6% 33%	2470
	11th to 20th	Night	13% 10% 3 7% 5% 5% 4 3 6% 6% 38%	2293
	21st to end	Night	15% 11% 3 8% 4 4 3 3 4 5% 40%	1884
March	1st to 10th	Night	18% 11% 3 6% 4 4 3 3 4 5% 40%	3733
	11th to 20th	Night	12% 7% 3 5% 3 3 3 3 4 7% 50%	3490
	21st to end	Night	20% 12% 5% 11% 5% 5% 4 2 5% 5% 25%	3599
April	1st to 10th	Night	14% 10% 3 6% 4 4 3 3 5% 7% 40%	1900
	11th to 20th	Night	16% 9% 3 5% 4 4 3 3 4 5% 43%	1875
	21st to end	Night	17% 6% 2 9% 5% 3 4 3 5% 7% 39%	1900
May	1st to 10th	Night	18% 8% 3 7% 6% 4 5% 4 5% 7% 33%	2751
	11th to 20th	Night	13% 7% 3 6% 4 4 4 3 7% 8% 41%	2506
	21st to end	Night	8% 6% 2 5% 4 4 4 4 6% 8% 49%	2743
June	1st to 10th	Night	9% 4 2 5% 4 3 4 4 6% 9% 50%	1520
	11th to 20th	Night	7% 5% 2 6% 5% 4 4 4 6% 9% 48%	1520
	21st to end	Night	10% 5% 2 5% 4 4 4 4 6% 8% 47%	1520
July	1st to 10th	Night	13% 6% 2 6% 5% 4 5% 4 6% 8% 40%	2530
	11th to 20th	Night	5% 3 1 4 2 4 4 4 5% 8% 61%	2530
	21st to end	Night	6% 4 2 6% 4 5% 5% 5% 7% 8% 47%	2771
August	1st to 10th	Night	5% 3 2 4 3 4 4 3 6% 10% 56%	2836
	11th to 20th	Night	7% 5% 1 5% 4 4 4 4 5% 7% 55%	3008
	21st to end	Night	6% 3 1 5% 4 4 4 4 5% 8% 54%	3476
September	1st to 10th	Night	11% 5% 2 4 3 3 4 2 4 5% 58%	1900
	11th to 20th	Night	10% 5% 1 5% 3 3 3 3 6% 7% 53%	1900
	21st to end	Night	9% 4 2 6% 4 4 4 4 6% 7% 50%	2106
October	1st to 10th	Night	9% 6% 2 5% 3 4 3 3 4 6% 54%	2280
	11th to 20th	Night	14% 6% 2 5% 4 3 3 3 4 6% 50%	2280
	21st to end	Night	17% 8% 2 6% 4 4 4 3 5% 5% 40%	2587
November	1st to 10th	Night	12% 6% 2 5% 3 3 3 3 5% 7% 52%	2470
	11th to 20th	Night	14% 9% 3 6% 4 4 4 3 5% 7% 41%	2470
	21st to end	Night	16% 10% 3 7% 5% 3 4 3 5% 5% 39%	2647
December	1st to 10th	Night	14% 11% 4 8% 5% 4 4 3 6% 5% 36%	2660
	11th to 20th	Night	14% 12% 4 9% 4 4 4 3 4 5% 36%	3279
	21st to end	Night	22% 17% 7% 11% 6% 5% 4 3 4 4 18%	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	59% 5% 10% 18% 6%	2528
	11th to 20th	Day	63% 5% 10% 15% 8%	2544
	21st to end	Day	70% 4 9% 11% 6%	3135
February	1st to 10th	Day	57% 4 14% 16% 7% 2	1710
	11th to 20th	Day	49% 6% 12% 22% 11% 1	1781
	21st to end	Day	53% 4 11% 22% 9% 2	1570
March	1st to 10th	Day	48% 5% 11% 20% 14% 2	3140
	11th to 20th	Day	36% 6% 13% 27% 17% 1	3480
	21st to end	Day	57% 6% 14% 19% 3 1	4031
April	1st to 10th	Day	49% 6% 11% 22% 12%	2280
	11th to 20th	Day	47% 5% 9% 23% 14% 2	2254
	21st to end	Day	50% 6% 10% 19% 13% 2	2280
May	1st to 10th	Day	44% 8% 12% 21% 14% 1	4169
	11th to 20th	Day	43% 6% 10% 29% 11%	4403
	21st to end	Day	37% 7% 11% 22% 22% 2	4837
June	1st to 10th	Day	33% 9% 14% 26% 16% 2	2660
	11th to 20th	Day	34% 8% 10% 24% 22% 2	2660
	21st to end	Day	38% 8% 16% 21% 15% 3	2660
July	1st to 10th	Day	42% 7% 13% 24% 12% 2	4371
	11th to 20th	Day	29% 7% 16% 29% 17% 2	4365
	21st to end	Day	34% 9% 20% 19% 17% 1	4637
August	1st to 10th	Day	31% 8% 18% 30% 12% 1	4090
	11th to 20th	Day	38% 7% 14% 26% 15% 1	3861
	21st to end	Day	31% 6% 14% 31% 16% 3	4179
September	1st to 10th	Day	33% 6% 11% 25% 20% 5%	2280
	11th to 20th	Day	29% 5% 11% 27% 23% 4	2259
	21st to end	Day	33% 6% 10% 27% 21% 2	2070
October	1st to 10th	Day	24% 3 6% 26% 40% 2	3160
	11th to 20th	Day	28% 3 10% 23% 32% 5%	3140
	21st to end	Day	41% 3 9% 26% 17% 3	3286
November	1st to 10th	Day	37% 5% 15% 25% 15% 3	1708
	11th to 20th	Day	47% 5% 12% 23% 12% 1	1710
	21st to end	Day	50% 5% 14% 22% 10% 1	1530
December	1st to 10th	Day	53% 5% 12% 20% 9% 1	1520
	11th to 20th	Day	50% 5% 12% 24% 7% 3	1915
	21st to end	Day	72% 5% 8% 10% 5%	2783
January	1st to 10th	Night	55% 5% 13% 18% 8%	4428
	11th to 20th	Night	62% 3 11% 14% 9% 1	4409
	21st to end	Night	65% 5% 9% 16% 6% 1	4532
February	1st to 10th	Night	52% 5% 12% 19% 12% 1	2470
	11th to 20th	Night	46% 5% 12% 24% 12% 2	2294
	21st to end	Night	46% 4 8% 24% 14% 3	1884
March	1st to 10th	Night	47% 6% 10% 24% 13% 1	3733
	11th to 20th	Night	35% 4 11% 30% 16% 4	3490
	21st to end	Night	59% 6% 13% 16% 5% 1	3599
April	1st to 10th	Night	44% 5% 10% 25% 14% 2	1900
	11th to 20th	Night	43% 5% 8% 23% 17% 4	1875
	21st to end	Night	45% 6% 12% 20% 14% 3	1900
May	1st to 10th	Night	48% 7% 13% 19% 13% 1	2779
	11th to 20th	Night	38% 8% 16% 26% 11% 1	2507
	21st to end	Night	31% 7% 13% 24% 23% 2	2751
June	1st to 10th	Night	30% 8% 15% 24% 19% 4	1520
	11th to 20th	Night	30% 7% 12% 24% 23% 4	1520
	21st to end	Night	34% 7% 15% 20% 20% 3	1520
July	1st to 10th	Night	41% 6% 15% 21% 14% 2	2490
	11th to 20th	Night	23% 5% 14% 33% 24% 1	2482
	21st to end	Night	31% 8% 17% 21% 19% 4	2683
August	1st to 10th	Night	23% 7% 19% 32% 17% 2	2826
	11th to 20th	Night	29% 7% 15% 30% 17% 1	3036
	21st to end	Night	27% 6% 15% 31% 17% 4	3476
September	1st to 10th	Night	29% 3 12% 26% 26% 5%	1900
	11th to 20th	Night	30% 5% 12% 27% 21% 6%	1900
	21st to end	Night	32% 6% 11% 26% 23% 3	2106
October	1st to 10th	Night	22% 4 7% 27% 36% 4	3800
	11th to 20th	Night	26% 3 9% 22% 34% 5%	3779
	21st to end	Night	41% 4 9% 21% 21% 4	4260
November	1st to 10th	Night	33% 5% 12% 26% 19% 4	2470
	11th to 20th	Night	42% 4 13% 24% 16% 2	2470
	21st to end	Night	47% 4 11% 24% 13% 1	2647
December	1st to 10th	Night	49% 5% 13% 22% 10% 1	2660
	11th to 20th	Night	50% 5% 12% 25% 8% 1	3281
	21st to end	Night	70% 5% 8% 12% 5%	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	20% 18% 32% 22% 7% 1	270
	11th to 20th	Day	23% 21% 39% 14% 4	270
	21st to end	Day	20% 18% 36% 21% 5%	297
February	1st to 10th	Day	21% 16% 44% 14% 5%	270
	11th to 20th	Day	23% 16% 33% 21% 5% 1	270
	21st to end	Day	21% 16% 44% 16% 2	225
March	1st to 10th	Day	19% 22% 37% 18% 4	270
	11th to 20th	Day	22% 18% 34% 19% 7%	270
	21st to end	Day	27% 18% 33% 16% 4 1	424
April	1st to 10th	Day	22% 14% 35% 23% 5% 1	460
	11th to 20th	Day	20% 15% 33% 19% 11% 2	452
	21st to end	Day	23% 13% 33% 22% 7% 2	460
May	1st to 10th	Day	18% 11% 35% 26% 8% 2	538
	11th to 20th	Day	19% 12% 29% 23% 14% 3	675
	21st to end	Day	14% 9% 29% 27% 15% 7%	734
June	1st to 10th	Day	8% 7% 27% 31% 21% 7%	680
	11th to 20th	Day	8% 5% 30% 33% 20% 5%	680
	21st to end	Day	11% 8% 33% 29% 15% 5%	680
July	1st to 10th	Day	10% 4 18% 30% 25% 13%	671
	11th to 20th	Day	10% 3 22% 34% 22% 8%	668
	21st to end	Day	8% 2 19% 36% 28% 7%	739
August	1st to 10th	Day	6% 3 22% 35% 26% 8%	676
	11th to 20th	Day	10% 5% 19% 31% 23% 11%	537
	21st to end	Day	6% 3 17% 33% 29% 10%	539
September	1st to 10th	Day	12% 6% 17% 34% 25% 7%	490
	11th to 20th	Day	8% 3 19% 31% 28% 11%	490
	21st to end	Day	10% 10% 26% 24% 23% 7%	470
October	1st to 10th	Day	16% 6% 29% 29% 16% 4	300
	11th to 20th	Day	16% 20% 32% 20% 11%	300
	21st to end	Day	27% 16% 32% 19% 5% 1	330
November	1st to 10th	Day	11% 10% 44% 22% 10% 3	282
	11th to 20th	Day	22% 18% 30% 21% 6% 2	270
	21st to end	Day	26% 11% 34% 27% 3	270
December	1st to 10th	Day	14% 16% 41% 22% 4 4	270
	11th to 20th	Day	19% 13% 38% 23% 8%	270
	21st to end	Day	24% 25% 35% 15% 2	297
January	1st to 10th	Night	17% 15% 40% 21% 6%	950
	11th to 20th	Night	18% 15% 40% 21% 6%	950
	21st to end	Night	18% 13% 37% 28% 3	1045
February	1st to 10th	Night	23% 11% 39% 23% 4	950
	11th to 20th	Night	17% 15% 38% 26% 3	818
	21st to end	Night	21% 14% 42% 20% 3 1	628
March	1st to 10th	Night	20% 14% 39% 22% 5%	760
	11th to 20th	Night	18% 13% 34% 28% 7%	580
	21st to end	Night	25% 13% 33% 23% 5%	627
April	1st to 10th	Night	18% 15% 36% 26% 4	570
	11th to 20th	Night	21% 13% 31% 27% 7% 1	563
	21st to end	Night	18% 11% 35% 30% 5%	570
May	1st to 10th	Night	17% 9% 36% 31% 6% 1	570
	11th to 20th	Night	17% 8% 27% 36% 11%	561
	21st to end	Night	12% 6% 30% 34% 17% 1	617
June	1st to 10th	Night	9% 5% 24% 44% 16% 1	570
	11th to 20th	Night	9% 5% 28% 41% 18%	570
	21st to end	Night	10% 4 29% 38% 17% 1	570
July	1st to 10th	Night	9% 3 12% 41% 29% 5%	555
	11th to 20th	Night	5% 3 21% 42% 27% 2	552
	21st to end	Night	7% 1 14% 46% 30% 2	624
August	1st to 10th	Night	6% 2 15% 44% 28% 4	567
	11th to 20th	Night	6% 2 15% 43% 29% 5%	564
	21st to end	Night	7% 1 15% 44% 31% 2	627
September	1st to 10th	Night	12% 4 17% 38% 25% 4	570
	11th to 20th	Night	10% 4 19% 35% 28% 4	570
	21st to end	Night	11% 7% 24% 34% 22% 2	760
October	1st to 10th	Night	12% 6% 30% 32% 19% 2	760
	11th to 20th	Night	17% 13% 29% 30% 11%	760
	21st to end	Night	22% 13% 33% 25% 8%	836
November	1st to 10th	Night	16% 10% 39% 26% 9% 1	760
	11th to 20th	Night	18% 15% 36% 25% 6%	760
	21st to end	Night	20% 12% 37% 24% 6%	937
December	1st to 10th	Night	19% 13% 39% 24% 5%	950
	11th to 20th	Night	22% 11% 35% 26% 6%	950
	21st to end	Night	25% 17% 33% 22% 3	1045

Page generated at 2024-11-03 01:11:10. Version ac07

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