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 2025-01-22.

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% 10% 4 8% 5% 5% 5% 4 5% 7% 32%	105316
	Night	15% 11% 4 8% 5% 4 4 4 5% 6% 33%	103928
Transparency	Day	51% 4 11% 21% 12% 1	108974
	Night	50% 4 11% 22% 12% 2	108409
Seeing	Day	18% 11% 28% 24% 14% 6%	15472
	Night	19% 10% 28% 29% 13% 1	25337

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	17% 20% 8% 16% 6% 5% 4 3 5% 4 11%	2674
	11th to 20th	Day	14% 21% 7% 15% 6% 6% 9% 4 3 4 12%	2930
	21st to end	Day	25% 19% 11% 12% 7% 6% 3 2 3 3 9%	3133
February	1st to 10th	Day	17% 17% 5% 12% 7% 4 5% 4 4 5% 21%	1710
	11th to 20th	Day	14% 13% 6% 13% 8% 5% 5% 4 4 6% 22%	1792
	21st to end	Day	17% 14% 5% 10% 6% 5% 4 3 5% 7% 25%	1570
March	1st to 10th	Day	21% 16% 5% 9% 6% 4 3 3 4 6% 24%	3264
	11th to 20th	Day	12% 14% 4 9% 5% 5% 4 3 5% 5% 33%	3480
	21st to end	Day	20% 13% 5% 10% 6% 4 4 2 4 5% 27%	3815
April	1st to 10th	Day	14% 12% 3 9% 5% 5% 5% 4 7% 7% 29%	2147
	11th to 20th	Day	17% 10% 3 6% 4 5% 4 3 6% 7% 34%	2418
	21st to end	Day	19% 9% 3 7% 4 4 4 3 5% 7% 34%	2470
May	1st to 10th	Day	18% 10% 3 8% 5% 5% 5% 4 5% 7% 30%	4082
	11th to 20th	Day	19% 7% 2 7% 5% 5% 4 4 5% 7% 35%	4081
	21st to end	Day	10% 5% 2 7% 5% 6% 5% 5% 6% 8% 41%	4476
June	1st to 10th	Day	13% 7% 2 6% 6% 4 5% 4 6% 9% 37%	2470
	11th to 20th	Day	11% 6% 2 6% 5% 5% 5% 5% 6% 9% 39%	2637
	21st to end	Day	11% 6% 2 5% 5% 5% 6% 4 7% 9% 39%	2660
July	1st to 10th	Day	10% 5% 2 7% 5% 5% 5% 4 7% 9% 39%	4440
	11th to 20th	Day	8% 4 2 6% 4 5% 5% 4 7% 10% 45%	4222
	21st to end	Day	9% 6% 2 7% 5% 5% 6% 4 6% 8% 41%	4466
August	1st to 10th	Day	12% 6% 2 6% 5% 5% 5% 4 7% 9% 40%	4104
	11th to 20th	Day	9% 5% 2 7% 5% 5% 7% 6% 8% 11% 37%	4044
	21st to end	Day	9% 5% 2 6% 5% 5% 5% 4 6% 10% 43%	4510
September	1st to 10th	Day	14% 5% 2 5% 4 4 5% 3 5% 7% 45%	2104
	11th to 20th	Day	9% 7% 2 6% 4 4 5% 4 6% 8% 46%	2090
	21st to end	Day	17% 7% 3 7% 4 4 4 3 5% 6% 39%	2090
October	1st to 10th	Day	13% 7% 3 7% 4 4 4 3 7% 6% 41%	2023
	11th to 20th	Day	17% 6% 2 7% 5% 5% 4 4 6% 7% 37%	1900
	21st to end	Day	18% 11% 3 7% 5% 5% 5% 4 6% 7% 30%	2008
November	1st to 10th	Day	11% 10% 3 7% 5% 4 4 4 6% 7% 39%	1762
	11th to 20th	Day	17% 14% 4 7% 5% 5% 4 3 4 6% 32%	1800
	21st to end	Day	17% 15% 4 10% 5% 5% 4 4 4 6% 25%	1775
December	1st to 10th	Day	16% 13% 6% 13% 7% 5% 5% 3 4 7% 22%	2600
	11th to 20th	Day	19% 18% 8% 11% 5% 5% 3 3 5% 5% 19%	3169
	21st to end	Day	23% 21% 7% 12% 6% 5% 4 3 4 3 14%	4400
January	1st to 10th	Night	16% 19% 7% 13% 6% 5% 4 3 4 4 18%	4468
	11th to 20th	Night	12% 20% 8% 17% 7% 5% 7% 5% 4 4 12%	4250
	21st to end	Night	26% 18% 8% 13% 4 4 3 2 3 3 14%	4546
February	1st to 10th	Night	19% 14% 4 12% 5% 5% 4 4 5% 5% 23%	2470
	11th to 20th	Night	14% 14% 5% 12% 6% 4 5% 4 4 5% 26%	2271
	21st to end	Night	19% 14% 4 11% 7% 4 4 3 4 5% 26%	1884
March	1st to 10th	Night	19% 14% 4 7% 4 4 4 2 3 4 34%	3587
	11th to 20th	Night	13% 9% 2 6% 5% 4 4 4 6% 7% 40%	3480
	21st to end	Night	17% 10% 4 7% 5% 4 3 3 5% 6% 35%	3817
April	1st to 10th	Night	14% 12% 4 7% 5% 5% 5% 4 5% 6% 33%	2047
	11th to 20th	Night	15% 9% 2 7% 5% 5% 4 5% 5% 7% 36%	1711
	21st to end	Night	16% 9% 2 7% 5% 4 4 4 4 7% 37%	1710
May	1st to 10th	Night	21% 9% 3 8% 6% 5% 4 4 5% 7% 28%	2813
	11th to 20th	Night	17% 7% 3 6% 4 4 4 4 5% 8% 38%	2812
	21st to end	Night	9% 6% 2 5% 3 4 5% 4 6% 9% 48%	3079
June	1st to 10th	Night	10% 6% 3 5% 5% 4 5% 3 6% 8% 44%	1710
	11th to 20th	Night	8% 4 2 6% 4 4 6% 4 8% 8% 44%	1536
	21st to end	Night	10% 5% 2 5% 4 5% 5% 4 7% 8% 45%	1520
July	1st to 10th	Night	11% 4 2 5% 4 4 5% 4 6% 8% 46%	2530
	11th to 20th	Night	8% 3 2 4 4 3 4 4 6% 10% 52%	2737
	21st to end	Night	7% 5% 2 6% 5% 5% 5% 4 6% 10% 46%	3087
August	1st to 10th	Night	11% 6% 3 6% 5% 4 4 5% 6% 8% 41%	2825
	11th to 20th	Night	10% 6% 3 7% 4 4 4 3 6% 7% 46%	2785
	21st to end	Night	6% 4 2 6% 5% 5% 5% 5% 7% 8% 48%	3142
September	1st to 10th	Night	10% 6% 2 5% 5% 4 3 3 5% 7% 50%	2055
	11th to 20th	Night	9% 4 2 5% 3 3 4 3 4 7% 54%	2090
	21st to end	Night	14% 6% 3 7% 4 4 4 3 6% 6% 43%	2090
October	1st to 10th	Night	13% 6% 2 7% 4 4 4 3 5% 6% 46%	2156
	11th to 20th	Night	17% 9% 3 7% 4 4 4 3 4 6% 39%	2280
	21st to end	Night	21% 8% 3 7% 4 4 4 3 5% 7% 34%	2589
November	1st to 10th	Night	14% 8% 2 6% 5% 4 4 3 5% 6% 42%	2536
	11th to 20th	Night	15% 13% 4 8% 5% 4 4 4 5% 6% 34%	2600
	21st to end	Night	19% 14% 4 9% 5% 4 4 3 6% 6% 27%	2617
December	1st to 10th	Night	13% 15% 5% 12% 6% 5% 5% 3 5% 6% 24%	4580
	11th to 20th	Night	18% 17% 6% 10% 5% 4 4 4 5% 5% 21%	5003
	21st to end	Night	22% 19% 6% 10% 5% 5% 4 3 5% 6% 14%	6515

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	77% 3 8% 9% 3	2675
	11th to 20th	Day	78% 3 7% 8% 4	2930
	21st to end	Day	83% 2 5% 6% 3	3133
February	1st to 10th	Day	66% 5% 9% 14% 6% 1	1710
	11th to 20th	Day	63% 5% 8% 16% 7% 1	1802
	21st to end	Day	61% 3 12% 15% 7% 1	1570
March	1st to 10th	Day	65% 3 9% 19% 5%	3264
	11th to 20th	Day	53% 4 12% 22% 7% 1	3480
	21st to end	Day	61% 3 12% 16% 7%	3815
April	1st to 10th	Day	53% 5% 11% 18% 11% 1	2147
	11th to 20th	Day	50% 5% 12% 19% 13% 2	2418
	21st to end	Day	50% 4 11% 21% 11% 2	2470
May	1st to 10th	Day	53% 5% 10% 22% 9% 1	4120
	11th to 20th	Day	49% 5% 11% 25% 9% 1	4085
	21st to end	Day	40% 5% 11% 22% 17% 4	4489
June	1st to 10th	Day	43% 6% 10% 27% 12% 2	2470
	11th to 20th	Day	40% 7% 14% 22% 16% 2	2637
	21st to end	Day	40% 7% 14% 21% 15% 4	2660
July	1st to 10th	Day	41% 4 11% 24% 18% 3	4371
	11th to 20th	Day	33% 4 12% 30% 19% 2	4149
	21st to end	Day	40% 4 14% 19% 20% 3	4324
August	1st to 10th	Day	39% 5% 14% 27% 14% 1	4091
	11th to 20th	Day	38% 5% 12% 32% 11% 1	4083
	21st to end	Day	37% 4 14% 30% 13% 2	4509
September	1st to 10th	Day	37% 5% 14% 23% 17% 4	2104
	11th to 20th	Day	36% 5% 12% 26% 19% 2	2090
	21st to end	Day	46% 4 10% 22% 18%	2090
October	1st to 10th	Day	30% 4 13% 32% 21% 1	3361
	11th to 20th	Day	42% 3 9% 25% 20% 1	3140
	21st to end	Day	43% 4 11% 24% 18% 1	3284
November	1st to 10th	Day	44% 5% 11% 24% 15% 1	1762
	11th to 20th	Day	54% 3 10% 20% 11% 1	1800
	21st to end	Day	60% 4 11% 18% 7%	1775
December	1st to 10th	Day	65% 2 14% 15% 3	2600
	11th to 20th	Day	69% 3 9% 16% 4	3166
	21st to end	Day	78% 2 7% 9% 4	4400
January	1st to 10th	Night	70% 3 7% 15% 4	4468
	11th to 20th	Night	77% 3 7% 10% 3	4250
	21st to end	Night	77% 2 7% 10% 3	4546
February	1st to 10th	Night	64% 5% 9% 15% 6% 1	2470
	11th to 20th	Night	60% 4 9% 19% 7% 1	2272
	21st to end	Night	62% 3 9% 16% 8% 2	1884
March	1st to 10th	Night	55% 3 10% 24% 8% 1	3587
	11th to 20th	Night	43% 5% 14% 24% 13% 1	3480
	21st to end	Night	50% 4 9% 28% 9% 1	3817
April	1st to 10th	Night	50% 5% 11% 18% 14% 2	2047
	11th to 20th	Night	47% 5% 10% 18% 17% 3	1711
	21st to end	Night	47% 5% 10% 22% 14% 2	1710
May	1st to 10th	Night	56% 5% 9% 19% 10% 2	2840
	11th to 20th	Night	45% 6% 12% 23% 13% 1	2813
	21st to end	Night	32% 5% 12% 30% 19% 2	3087
June	1st to 10th	Night	38% 6% 10% 26% 16% 3	1710
	11th to 20th	Night	34% 6% 15% 25% 17% 3	1536
	21st to end	Night	36% 5% 14% 27% 16% 3	1520
July	1st to 10th	Night	36% 4 11% 27% 16% 6%	2490
	11th to 20th	Night	29% 4 15% 32% 17% 3	2687
	21st to end	Night	35% 5% 16% 21% 20% 3	2988
August	1st to 10th	Night	40% 5% 12% 26% 15% 2	2814
	11th to 20th	Night	38% 3 11% 30% 16% 1	2812
	21st to end	Night	33% 4 14% 30% 16% 3	3142
September	1st to 10th	Night	34% 5% 13% 26% 17% 5%	2055
	11th to 20th	Night	30% 5% 11% 28% 24% 2	2090
	21st to end	Night	41% 4 11% 23% 19% 2	2090
October	1st to 10th	Night	28% 3 8% 31% 29% 1	3598
	11th to 20th	Night	40% 2 9% 27% 21% 1	3779
	21st to end	Night	38% 3 9% 29% 17% 3	4263
November	1st to 10th	Night	43% 3 11% 24% 16% 2	2536
	11th to 20th	Night	52% 3 10% 21% 12% 2	2600
	21st to end	Night	58% 4 12% 19% 7%	2617
December	1st to 10th	Night	63% 3 11% 18% 6%	4580
	11th to 20th	Night	65% 3 11% 16% 4	5005
	21st to end	Night	72% 3 10% 11% 3	6515

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% 19% 4 1	300
	11th to 20th	Day	25% 19% 39% 12% 4	300
	21st to end	Day	28% 17% 32% 18% 5%	300
February	1st to 10th	Day	32% 16% 36% 14% 2	270
	11th to 20th	Day	24% 18% 34% 20% 4	270
	21st to end	Day	23% 25% 40% 11% 1	225
March	1st to 10th	Day	23% 16% 36% 20% 5%	349
	11th to 20th	Day	24% 15% 36% 20% 4 2	460
	21st to end	Day	28% 17% 29% 20% 5% 1	506
April	1st to 10th	Day	19% 16% 32% 23% 9% 1	460
	11th to 20th	Day	21% 18% 28% 19% 9% 4	452
	21st to end	Day	24% 12% 31% 23% 8% 2	460
May	1st to 10th	Day	27% 10% 31% 21% 8% 3	463
	11th to 20th	Day	21% 8% 27% 25% 13% 6%	487
	21st to end	Day	13% 7% 23% 29% 19% 9%	529
June	1st to 10th	Day	15% 7% 21% 36% 16% 5%	490
	11th to 20th	Day	12% 7% 28% 28% 21% 5%	657
	21st to end	Day	14% 7% 29% 28% 18% 5%	680
July	1st to 10th	Day	10% 5% 19% 31% 22% 13%	671
	11th to 20th	Day	10% 4 22% 30% 22% 12%	543
	21st to end	Day	11% 4 18% 29% 27% 11%	532
August	1st to 10th	Day	12% 3 17% 28% 26% 14%	486
	11th to 20th	Day	12% 2 20% 30% 24% 11%	479
	21st to end	Day	9% 5% 18% 28% 27% 14%	539
September	1st to 10th	Day	14% 4 19% 25% 24% 13%	490
	11th to 20th	Day	9% 3 17% 23% 31% 17%	490
	21st to end	Day	20% 9% 22% 22% 18% 8%	490
October	1st to 10th	Day	13% 8% 26% 24% 22% 8%	490
	11th to 20th	Day	16% 15% 32% 24% 10% 3	490
	21st to end	Day	23% 17% 35% 19% 5% 1	457
November	1st to 10th	Day	16% 14% 37% 19% 12% 2	300
	11th to 20th	Day	27% 14% 33% 17% 7% 1	300
	21st to end	Day	25% 17% 37% 18% 2	287
December	1st to 10th	Day	21% 17% 38% 16% 7% 2	200
	11th to 20th	Day	25% 19% 35% 18% 3	240
	21st to end	Day	31% 16% 35% 15% 3	330
January	1st to 10th	Night	25% 17% 35% 18% 5%	939
	11th to 20th	Night	27% 16% 36% 17% 3 1	800
	21st to end	Night	23% 15% 37% 22% 3 1	841
February	1st to 10th	Night	26% 14% 34% 23% 3	760
	11th to 20th	Night	24% 13% 38% 23% 3	743
	21st to end	Night	27% 16% 37% 18% 3	628
March	1st to 10th	Night	22% 12% 34% 25% 7%	760
	11th to 20th	Night	19% 16% 34% 25% 5% 1	760
	21st to end	Night	23% 12% 30% 27% 7%	836
April	1st to 10th	Night	21% 14% 35% 24% 6%	717
	11th to 20th	Night	19% 13% 34% 23% 9% 2	563
	21st to end	Night	21% 7% 36% 27% 8% 1	570
May	1st to 10th	Night	21% 9% 29% 31% 8% 1	570
	11th to 20th	Night	21% 6% 28% 32% 13% 1	561
	21st to end	Night	12% 3 22% 39% 20% 4	617
June	1st to 10th	Night	12% 4 25% 41% 18%	570
	11th to 20th	Night	10% 3 23% 45% 19% 1	570
	21st to end	Night	11% 4 23% 40% 20% 1	570
July	1st to 10th	Night	11% 3 14% 39% 31% 3	555
	11th to 20th	Night	9% 2 18% 41% 27% 3	552
	21st to end	Night	9% 2 15% 42% 30% 2	624
August	1st to 10th	Night	9% 2 12% 44% 28% 4	567
	11th to 20th	Night	11% 2 13% 40% 30% 5%	564
	21st to end	Night	8% 2 13% 38% 35% 4	627
September	1st to 10th	Night	12% 5% 16% 35% 27% 5%	725
	11th to 20th	Night	10% 2 14% 36% 33% 5%	760
	21st to end	Night	16% 6% 21% 34% 22% 3	760
October	1st to 10th	Night	15% 6% 24% 34% 19% 2	760
	11th to 20th	Night	21% 11% 30% 28% 9% 2	760
	21st to end	Night	23% 14% 30% 26% 6%	836
November	1st to 10th	Night	18% 11% 32% 27% 10% 1	780
	11th to 20th	Night	22% 15% 34% 21% 7% 1	800
	21st to end	Night	26% 13% 33% 22% 6%	800
December	1st to 10th	Night	24% 17% 33% 21% 5%	800
	11th to 20th	Night	26% 15% 35% 21% 3	800
	21st to end	Night	28% 16% 32% 21% 3	892

Page generated at 2025-01-19 03:06:43. Version ac07

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