HVAG SkyTour
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the HVAG SkyTour clear sky chart from 2005-11-06 to 2026-05-17.

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% 10% 4 9% 5% 5% 5% 4 5% 7% 32%	132059
	Night	14% 11% 4 9% 5% 5% 4 4 5% 6% 33%	130710
Transparency	Day	52% 4 11% 21% 12% 1	135673
	Night	51% 3 10% 21% 12% 1	135166
Seeing	Day	18% 11% 28% 23% 14% 6%	17232
	Night	19% 10% 28% 29% 13% 1	27079

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	15% 18% 8% 19% 6% 5% 4 3 5% 5% 12%	4833
	11th to 20th	Day	11% 18% 7% 16% 9% 6% 6% 3 3 4 16%	5280
	21st to end	Day	18% 15% 8% 13% 8% 7% 6% 4 4 5% 14%	5780
February	1st to 10th	Day	16% 16% 6% 13% 7% 4 5% 4 4 5% 20%	1890
	11th to 20th	Day	14% 13% 6% 13% 8% 5% 5% 4 4 6% 22%	1986
	21st to end	Day	16% 13% 6% 11% 6% 5% 4 4 4 7% 25%	1730
March	1st to 10th	Day	17% 13% 6% 12% 6% 4 4 3 4 5% 26%	4784
	11th to 20th	Day	11% 12% 3 9% 5% 4 4 4 5% 6% 36%	5090
	21st to end	Day	18% 14% 4 10% 6% 5% 5% 3 5% 6% 25%	5586
April	1st to 10th	Day	15% 12% 3 9% 5% 5% 5% 4 7% 7% 28%	2373
	11th to 20th	Day	16% 10% 3 7% 5% 5% 5% 4 6% 7% 34%	2676
	21st to end	Day	19% 10% 3 7% 4 5% 4 3 5% 7% 34%	2730
May	1st to 10th	Day	21% 10% 3 8% 5% 5% 4 4 5% 6% 29%	5992
	11th to 20th	Day	17% 7% 2 7% 5% 5% 5% 4 5% 8% 34%	5939
	21st to end	Day	16% 5% 2 7% 5% 5% 5% 4 6% 8% 38%	6433
June	1st to 10th	Day	14% 7% 2 6% 6% 4 5% 4 6% 9% 38%	2600
	11th to 20th	Day	12% 6% 2 6% 5% 5% 5% 5% 6% 9% 38%	2776
	21st to end	Day	11% 6% 2 5% 5% 5% 6% 4 7% 9% 40%	2800
July	1st to 10th	Day	9% 5% 2 7% 5% 5% 5% 4 7% 10% 42%	6360
	11th to 20th	Day	9% 5% 2 6% 5% 5% 5% 5% 7% 10% 40%	6044
	21st to end	Day	11% 6% 2 7% 5% 5% 5% 4 6% 9% 40%	6424
August	1st to 10th	Day	11% 6% 2 6% 4 5% 5% 5% 7% 9% 41%	4234
	11th to 20th	Day	9% 5% 2 7% 5% 5% 7% 6% 8% 11% 38%	4174
	21st to end	Day	9% 5% 2 6% 5% 5% 5% 4 6% 10% 43%	4652
September	1st to 10th	Day	14% 5% 2 4 4 4 5% 3 6% 7% 47%	2215
	11th to 20th	Day	9% 6% 2 6% 4 4 4 3 6% 8% 47%	2200
	21st to end	Day	17% 7% 3 7% 4 5% 4 3 5% 6% 40%	2200
October	1st to 10th	Day	13% 7% 3 7% 4 4 4 3 7% 7% 42%	2129
	11th to 20th	Day	17% 6% 2 7% 5% 5% 4 4 6% 7% 38%	2000
	21st to end	Day	18% 11% 3 7% 5% 5% 5% 4 6% 7% 30%	2113
November	1st to 10th	Day	12% 10% 3 7% 5% 4 4 4 6% 7% 39%	1852
	11th to 20th	Day	16% 14% 4 7% 5% 4 4 3 4 6% 32%	1890
	21st to end	Day	17% 15% 5% 10% 5% 5% 4 4 4 6% 25%	1864
December	1st to 10th	Day	15% 14% 6% 13% 7% 5% 5% 3 4 7% 22%	2680
	11th to 20th	Day	19% 18% 8% 11% 5% 5% 3 3 5% 5% 19%	3253
	21st to end	Day	23% 20% 7% 12% 6% 5% 4 3 4 3 14%	4497
January	1st to 10th	Night	15% 18% 7% 18% 6% 5% 4 3 4 4 16%	8038
	11th to 20th	Night	8% 16% 8% 17% 8% 6% 6% 5% 5% 5% 16%	7680
	21st to end	Night	17% 15% 6% 12% 5% 5% 5% 3 5% 6% 22%	8401
February	1st to 10th	Night	18% 14% 4 12% 6% 5% 4 4 5% 5% 23%	2730
	11th to 20th	Night	14% 14% 5% 12% 6% 4 5% 4 5% 6% 24%	2516
	21st to end	Night	18% 14% 4 11% 7% 4 3 3 4 5% 27%	2076
March	1st to 10th	Night	18% 12% 4 8% 4 3 4 2 4 5% 35%	5287
	11th to 20th	Night	11% 8% 2 6% 5% 4 5% 4 7% 8% 41%	5090
	21st to end	Night	15% 10% 4 8% 5% 4 4 3 5% 6% 36%	5588
April	1st to 10th	Night	15% 12% 4 8% 5% 5% 5% 4 5% 6% 32%	2263
	11th to 20th	Night	14% 9% 3 8% 5% 5% 4 5% 5% 6% 36%	1893
	21st to end	Night	16% 9% 3 7% 5% 4 5% 4 4 7% 37%	1890
May	1st to 10th	Night	21% 11% 3 9% 5% 5% 5% 4 5% 6% 27%	4123
	11th to 20th	Night	15% 7% 3 6% 5% 4 4 4 5% 8% 38%	4086
	21st to end	Night	14% 7% 2 6% 4 4 4 4 5% 8% 41%	4421
June	1st to 10th	Night	11% 6% 3 6% 5% 4 5% 3 6% 8% 44%	1800
	11th to 20th	Night	8% 4 2 7% 4 5% 6% 4 8% 9% 44%	1617
	21st to end	Night	10% 5% 2 5% 4 5% 5% 4 7% 8% 45%	1600
July	1st to 10th	Night	9% 4 2 6% 4 5% 5% 4 6% 9% 45%	3618
	11th to 20th	Night	9% 4 2 5% 5% 4 5% 4 6% 10% 45%	3915
	21st to end	Night	9% 5% 2 6% 4 4 4 4 5% 9% 47%	4427
August	1st to 10th	Night	11% 6% 3 6% 4 4 4 5% 6% 9% 42%	2915
	11th to 20th	Night	10% 6% 3 7% 4 4 4 3 6% 7% 46%	2875
	21st to end	Night	6% 4 2 6% 5% 5% 5% 5% 7% 8% 48%	3242
September	1st to 10th	Night	9% 6% 2 5% 5% 4 3 3 5% 7% 51%	2163
	11th to 20th	Night	9% 4 2 5% 3 3 4 3 4 7% 56%	2200
	21st to end	Night	14% 6% 3 7% 5% 4 4 3 6% 6% 44%	2200
October	1st to 10th	Night	13% 5% 2 7% 4 4 4 3 5% 6% 47%	2270
	11th to 20th	Night	17% 8% 3 7% 4 4 4 3 4 6% 40%	2400
	21st to end	Night	20% 8% 3 7% 4 4 3 3 5% 7% 35%	2725
November	1st to 10th	Night	14% 8% 2 6% 5% 4 4 3 6% 6% 42%	2666
	11th to 20th	Night	15% 13% 3 8% 5% 4 4 4 5% 6% 34%	2730
	21st to end	Night	19% 14% 5% 9% 5% 4 4 3 5% 6% 26%	2748
December	1st to 10th	Night	13% 15% 5% 12% 7% 5% 5% 3 5% 6% 24%	4720
	11th to 20th	Night	18% 17% 6% 11% 5% 4 4 4 5% 5% 22%	5138
	21st to end	Night	22% 19% 7% 10% 5% 5% 4 3 5% 6% 14%	6659

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	75% 2 10% 10% 2	4834
	11th to 20th	Day	74% 2 7% 8% 9%	5280
	21st to end	Day	75% 2 6% 11% 5%	5780
February	1st to 10th	Day	66% 4 9% 14% 6%	1890
	11th to 20th	Day	64% 5% 8% 16% 7% 1	1996
	21st to end	Day	61% 3 13% 16% 7% 1	1730
March	1st to 10th	Day	62% 3 8% 20% 6%	4784
	11th to 20th	Day	50% 3 13% 25% 8% 1	5090
	21st to end	Day	62% 3 10% 17% 9%	5586
April	1st to 10th	Day	55% 5% 11% 18% 11% 1	2373
	11th to 20th	Day	50% 5% 12% 18% 12% 2	2676
	21st to end	Day	50% 4 11% 22% 11% 2	2730
May	1st to 10th	Day	56% 4 9% 18% 12% 1	6027
	11th to 20th	Day	49% 5% 13% 22% 10% 1	5943
	21st to end	Day	45% 4 10% 24% 14% 3	6447
June	1st to 10th	Day	43% 5% 10% 26% 13% 2	2600
	11th to 20th	Day	41% 6% 14% 22% 15% 2	2776
	21st to end	Day	39% 7% 14% 22% 15% 4	2800
July	1st to 10th	Day	39% 4 10% 29% 17% 2	6291
	11th to 20th	Day	39% 3 14% 27% 16% 1	5971
	21st to end	Day	41% 3 12% 22% 20% 3	6240
August	1st to 10th	Day	39% 5% 14% 27% 14% 1	4221
	11th to 20th	Day	38% 5% 12% 32% 11% 1	4213
	21st to end	Day	37% 4 14% 30% 13% 2	4651
September	1st to 10th	Day	36% 5% 13% 25% 17% 4	2215
	11th to 20th	Day	35% 4 12% 28% 18% 2	2200
	21st to end	Day	46% 4 10% 22% 19%	2200
October	1st to 10th	Day	30% 4 12% 32% 22% 1	3467
	11th to 20th	Day	41% 3 9% 25% 20% 1	3240
	21st to end	Day	43% 3 11% 23% 18% 1	3389
November	1st to 10th	Day	44% 4 11% 24% 15% 1	1852
	11th to 20th	Day	54% 3 10% 20% 10% 2	1890
	21st to end	Day	60% 4 11% 18% 7%	1864
December	1st to 10th	Day	65% 2 14% 15% 3	2680
	11th to 20th	Day	68% 3 9% 16% 4	3250
	21st to end	Day	78% 2 7% 9% 4	4497
January	1st to 10th	Night	74% 2 7% 14% 3	8039
	11th to 20th	Night	71% 2 7% 11% 8% 1	7680
	21st to end	Night	65% 2 11% 15% 7%	8401
February	1st to 10th	Night	64% 5% 9% 15% 7% 1	2730
	11th to 20th	Night	61% 4 9% 18% 7% 1	2517
	21st to end	Night	61% 3 10% 17% 8% 1	2076
March	1st to 10th	Night	53% 2 9% 25% 9% 1	5287
	11th to 20th	Night	41% 3 13% 29% 12% 1	5090
	21st to end	Night	51% 3 8% 23% 14% 1	5588
April	1st to 10th	Night	52% 5% 11% 17% 14% 2	2263
	11th to 20th	Night	48% 5% 11% 18% 16% 2	1893
	21st to end	Night	48% 4 10% 23% 13% 2	1890
May	1st to 10th	Night	59% 4 8% 15% 12% 2	4150
	11th to 20th	Night	44% 5% 12% 23% 15% 1	4087
	21st to end	Night	41% 4 11% 27% 15% 2	4429
June	1st to 10th	Night	38% 5% 10% 26% 17% 3	1800
	11th to 20th	Night	35% 6% 14% 25% 17% 3	1617
	21st to end	Night	35% 5% 15% 26% 16% 3	1600
July	1st to 10th	Night	36% 4 13% 27% 17% 4	3580
	11th to 20th	Night	35% 4 16% 29% 15% 2	3868
	21st to end	Night	35% 4 13% 23% 23% 2	4297
August	1st to 10th	Night	39% 5% 12% 27% 15% 2	2904
	11th to 20th	Night	37% 3 11% 31% 16% 1	2902
	21st to end	Night	33% 4 13% 31% 16% 3	3242
September	1st to 10th	Night	33% 5% 12% 28% 17% 5%	2163
	11th to 20th	Night	29% 5% 10% 29% 25% 2	2200
	21st to end	Night	41% 4 11% 23% 19% 2	2200
October	1st to 10th	Night	28% 3 8% 30% 30% 1	3712
	11th to 20th	Night	39% 2 9% 27% 21% 1	3899
	21st to end	Night	38% 2 9% 30% 18% 3	4399
November	1st to 10th	Night	42% 3 11% 25% 16% 2	2666
	11th to 20th	Night	52% 3 10% 22% 11% 2	2730
	21st to end	Night	59% 3 12% 19% 6%	2748
December	1st to 10th	Night	63% 2 11% 18% 6%	4720
	11th to 20th	Night	65% 3 11% 16% 5%	5140
	21st to end	Night	72% 3 10% 11% 3	6659

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% 35% 18% 4 1	330
	11th to 20th	Day	25% 22% 38% 11% 3	330
	21st to end	Day	25% 20% 32% 18% 5%	363
February	1st to 10th	Day	28% 16% 37% 15% 3 1	330
	11th to 20th	Day	25% 18% 34% 19% 3	330
	21st to end	Day	21% 25% 41% 12% 1	273
March	1st to 10th	Day	23% 16% 37% 19% 4	417
	11th to 20th	Day	25% 14% 36% 19% 4 1	540
	21st to end	Day	27% 17% 31% 20% 4 1	594
April	1st to 10th	Day	21% 16% 33% 21% 8% 1	540
	11th to 20th	Day	21% 18% 30% 19% 9% 3	532
	21st to end	Day	24% 12% 30% 23% 9% 1	540
May	1st to 10th	Day	27% 10% 32% 20% 8% 3	543
	11th to 20th	Day	21% 9% 28% 25% 12% 5%	551
	21st to end	Day	14% 8% 24% 28% 17% 8%	573
June	1st to 10th	Day	15% 7% 22% 36% 15% 4	530
	11th to 20th	Day	13% 6% 28% 28% 20% 5%	706
	21st to end	Day	14% 7% 27% 28% 19% 5%	730
July	1st to 10th	Day	9% 5% 19% 32% 22% 12%	721
	11th to 20th	Day	11% 4 22% 30% 22% 12%	586
	21st to end	Day	11% 4 18% 28% 27% 11%	576
August	1st to 10th	Day	11% 3 16% 28% 27% 15%	526
	11th to 20th	Day	12% 2 19% 30% 26% 12%	519
	21st to end	Day	9% 5% 18% 29% 26% 14%	583
September	1st to 10th	Day	13% 5% 19% 25% 24% 15%	530
	11th to 20th	Day	8% 3 16% 23% 32% 18%	530
	21st to end	Day	20% 8% 22% 23% 19% 8%	530
October	1st to 10th	Day	12% 8% 24% 25% 22% 8%	530
	11th to 20th	Day	15% 14% 33% 25% 10% 3	530
	21st to end	Day	23% 16% 36% 19% 5% 1	496
November	1st to 10th	Day	17% 15% 37% 19% 11% 2	330
	11th to 20th	Day	28% 16% 33% 15% 7% 1	330
	21st to end	Day	27% 16% 36% 18% 2	316
December	1st to 10th	Day	21% 16% 39% 16% 6% 1	220
	11th to 20th	Day	26% 20% 34% 17% 3	264
	21st to end	Day	33% 16% 34% 14% 3	363
January	1st to 10th	Night	26% 16% 35% 19% 5%	986
	11th to 20th	Night	26% 17% 37% 17% 3 1	840
	21st to end	Night	23% 16% 37% 21% 3 1	924
February	1st to 10th	Night	25% 14% 35% 23% 4	840
	11th to 20th	Night	23% 13% 38% 23% 3	823
	21st to end	Night	27% 16% 38% 17% 2	692
March	1st to 10th	Night	22% 13% 36% 24% 6%	840
	11th to 20th	Night	19% 16% 35% 24% 5% 1	840
	21st to end	Night	23% 13% 32% 26% 7%	924
April	1st to 10th	Night	23% 14% 34% 23% 5%	793
	11th to 20th	Night	18% 14% 34% 24% 9% 2	623
	21st to end	Night	21% 7% 36% 28% 8% 1	630
May	1st to 10th	Night	22% 9% 30% 31% 8% 1	630
	11th to 20th	Night	20% 6% 28% 32% 12% 1	609
	21st to end	Night	13% 3 22% 39% 19% 4	650
June	1st to 10th	Night	12% 4 26% 40% 18%	600
	11th to 20th	Night	10% 3 23% 45% 18% 2	600
	21st to end	Night	11% 4 22% 40% 22% 1	600
July	1st to 10th	Night	11% 3 14% 39% 31% 3	585
	11th to 20th	Night	10% 2 18% 41% 26% 3	582
	21st to end	Night	10% 2 15% 42% 30% 2	657
August	1st to 10th	Night	8% 2 12% 45% 29% 4	597
	11th to 20th	Night	11% 2 13% 39% 30% 5%	594
	21st to end	Night	8% 2 13% 38% 35% 4	660
September	1st to 10th	Night	12% 4 16% 35% 28% 5%	763
	11th to 20th	Night	10% 2 13% 36% 34% 6%	800
	21st to end	Night	16% 5% 21% 34% 22% 3	800
October	1st to 10th	Night	14% 5% 23% 34% 20% 3	800
	11th to 20th	Night	20% 11% 30% 29% 8% 2	800
	21st to end	Night	23% 14% 30% 27% 6%	880
November	1st to 10th	Night	18% 11% 33% 27% 10% 1	820
	11th to 20th	Night	22% 15% 34% 21% 6% 1	840
	21st to end	Night	27% 12% 34% 22% 6%	840
December	1st to 10th	Night	24% 17% 33% 21% 5%	840
	11th to 20th	Night	25% 15% 36% 20% 3	840
	21st to end	Night	28% 16% 33% 21% 3	937

Page generated at 2026-05-14 01:58:58. Version ac07

Copyright © 2026 Attilla Danko.