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 2024-08-15.

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%	95415
	Night	15% 11% 4 8% 5% 4 4 4 5% 6% 34%	93193
Transparency	Day	52% 5% 11% 20% 11% 1	95181
	Night	51% 4 11% 21% 11% 2	93032
Seeing	Day	18% 11% 28% 24% 14% 6%	14938
	Night	19% 10% 28% 29% 13% 2	24710

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% 20% 8% 16% 6% 5% 4 3 5% 4 11%	2591
	11th to 20th	Day	15% 21% 7% 15% 6% 6% 9% 4 3 4 11%	2840
	21st to end	Day	25% 19% 11% 12% 7% 6% 3 2 3 3 9%	3124
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	9% 5% 2 6% 5% 5% 6% 5% 8% 9% 42%	2457
	11th to 20th	Day	10% 5% 2 7% 5% 5% 6% 5% 8% 11% 38%	2357
	21st to end	Day	10% 6% 2 6% 5% 5% 4 4 6% 9% 43%	2566
September	1st to 10th	Day	15% 6% 2 5% 5% 4 5% 3 5% 8% 44%	1994
	11th to 20th	Day	10% 7% 2 6% 4 4 5% 4 6% 8% 44%	1980
	21st to end	Day	16% 6% 2 7% 4 4 4 3 5% 6% 41%	1980
October	1st to 10th	Day	14% 8% 3 7% 4 4 4 3 7% 6% 39%	1917
	11th to 20th	Day	18% 7% 3 7% 5% 5% 4 4 5% 7% 36%	1800
	21st to end	Day	19% 11% 3 7% 6% 5% 5% 4 5% 6% 28%	1903
November	1st to 10th	Day	11% 10% 3 7% 4 4 4 3 7% 7% 39%	1672
	11th to 20th	Day	16% 14% 4 7% 5% 5% 4 3 4 6% 33%	1710
	21st to end	Day	17% 14% 4 9% 5% 5% 4 4 4 6% 26%	1687
December	1st to 10th	Day	18% 17% 6% 11% 7% 5% 5% 3 4 5% 19%	1520
	11th to 20th	Day	15% 15% 6% 13% 6% 5% 4 4 6% 6% 20%	2033
	21st to end	Day	22% 22% 8% 12% 5% 5% 5% 3 4 3 11%	3084
January	1st to 10th	Night	16% 19% 7% 13% 6% 5% 4 3 4 4 18%	4332
	11th to 20th	Night	13% 20% 8% 17% 6% 5% 6% 5% 4 4 12%	4120
	21st to end	Night	26% 18% 8% 13% 4 4 3 2 3 3 14%	4532
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	7% 3 2 5% 4 5% 5% 6% 6% 8% 48%	1701
	11th to 20th	Night	8% 5% 2 6% 4 4 4 3 7% 8% 48%	1643
	21st to end	Night	6% 4 2 6% 5% 4 5% 4 7% 8% 49%	1786
September	1st to 10th	Night	10% 6% 2 5% 5% 4 3 3 5% 7% 49%	1946
	11th to 20th	Night	10% 4 2 6% 3 3 4 3 4 7% 53%	1980
	21st to end	Night	13% 5% 3 7% 5% 4 4 3 6% 6% 45%	1980
October	1st to 10th	Night	13% 6% 2 7% 4 4 4 4 5% 6% 44%	2042
	11th to 20th	Night	18% 9% 3 7% 4 4 4 3 4 6% 38%	2160
	21st to end	Night	22% 8% 3 7% 5% 4 3 3 5% 7% 33%	2452
November	1st to 10th	Night	14% 9% 2 6% 5% 4 3 3 5% 6% 41%	2406
	11th to 20th	Night	14% 13% 4 8% 5% 4 4 4 5% 6% 33%	2470
	21st to end	Night	19% 13% 4 8% 5% 4 4 3 6% 6% 27%	2486
December	1st to 10th	Night	17% 18% 5% 11% 5% 4 4 3 5% 6% 22%	2660
	11th to 20th	Night	18% 15% 4 10% 5% 4 4 4 5% 6% 25%	3153
	21st to end	Night	23% 19% 8% 10% 6% 5% 4 3 4 5% 13%	4543

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% 2	2592
	11th to 20th	Day	79% 3 7% 8% 3	2840
	21st to end	Day	84% 2 5% 6% 3	3124
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	36% 7% 14% 28% 14% 1	2444
	11th to 20th	Day	38% 7% 16% 27% 11% 2	2357
	21st to end	Day	37% 6% 12% 23% 18% 3	2566
September	1st to 10th	Day	39% 5% 14% 21% 17% 3	1994
	11th to 20th	Day	38% 5% 12% 26% 17% 2	1980
	21st to end	Day	44% 4 10% 23% 18% 1	1980
October	1st to 10th	Day	43% 6% 10% 23% 16% 1	1917
	11th to 20th	Day	47% 4 12% 23% 13% 2	1800
	21st to end	Day	55% 5% 12% 17% 10% 1	1903
November	1st to 10th	Day	44% 5% 11% 23% 16% 1	1672
	11th to 20th	Day	53% 4 11% 20% 11% 1	1710
	21st to end	Day	59% 4 12% 18% 7%	1687
December	1st to 10th	Day	70% 3 10% 14% 4	1520
	11th to 20th	Day	64% 4 9% 19% 4	2030
	21st to end	Day	79% 3 8% 7% 3	3084
January	1st to 10th	Night	71% 3 7% 14% 4	4332
	11th to 20th	Night	77% 3 7% 10% 3	4120
	21st to end	Night	77% 2 7% 10% 3	4532
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	32% 7% 12% 30% 18% 1	1690
	11th to 20th	Night	34% 5% 15% 31% 14% 2	1643
	21st to end	Night	31% 6% 14% 24% 21% 4	1786
September	1st to 10th	Night	35% 6% 13% 25% 16% 5%	1946
	11th to 20th	Night	31% 5% 11% 28% 23% 2	1980
	21st to end	Night	39% 4 11% 24% 20% 2	1980
October	1st to 10th	Night	39% 4 12% 23% 19% 2	2042
	11th to 20th	Night	48% 3 9% 23% 15% 1	2160
	21st to end	Night	51% 4 10% 22% 11% 2	2452
November	1st to 10th	Night	43% 4 12% 24% 16% 2	2406
	11th to 20th	Night	52% 4 10% 21% 12% 2	2470
	21st to end	Night	58% 4 12% 19% 7%	2486
December	1st to 10th	Night	64% 4 10% 14% 7%	2660
	11th to 20th	Night	60% 4 12% 20% 4	3155
	21st to end	Night	74% 4 11% 9% 2	4543

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	24% 18% 33% 19% 5% 1	270
	11th to 20th	Day	26% 18% 39% 13% 4	270
	21st to end	Day	28% 16% 32% 18% 5%	297
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	13% 2 18% 30% 25% 12%	456
	21st to end	Day	9% 5% 19% 27% 25% 15%	495
September	1st to 10th	Day	15% 5% 19% 25% 24% 13%	450
	11th to 20th	Day	9% 4 17% 23% 30% 17%	450
	21st to end	Day	18% 10% 23% 22% 19% 8%	450
October	1st to 10th	Day	14% 8% 26% 23% 21% 8%	450
	11th to 20th	Day	16% 16% 33% 24% 9% 1	450
	21st to end	Day	25% 17% 35% 19% 4 1	418
November	1st to 10th	Day	16% 13% 37% 19% 12% 3	270
	11th to 20th	Day	26% 16% 32% 17% 8% 1	270
	21st to end	Day	26% 16% 37% 19% 3	259
December	1st to 10th	Day	20% 17% 40% 15% 7% 2	180
	11th to 20th	Day	22% 20% 36% 19% 3	216
	21st to end	Day	31% 17% 35% 14% 3	297
January	1st to 10th	Night	26% 17% 34% 18% 5%	893
	11th to 20th	Night	28% 15% 35% 17% 3 1	760
	21st to end	Night	23% 15% 36% 22% 3 1	836
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 12% 40% 30% 5%	549
	21st to end	Night	8% 2 14% 37% 34% 5%	594
September	1st to 10th	Night	13% 4 15% 35% 28% 5%	686
	11th to 20th	Night	10% 3 14% 36% 32% 5%	720
	21st to end	Night	14% 6% 21% 34% 23% 3	720
October	1st to 10th	Night	15% 6% 24% 33% 19% 3	720
	11th to 20th	Night	22% 11% 30% 27% 8% 2	720
	21st to end	Night	24% 15% 30% 25% 5%	792
November	1st to 10th	Night	19% 11% 32% 26% 11% 1	740
	11th to 20th	Night	22% 15% 34% 21% 7% 1	760
	21st to end	Night	26% 13% 33% 23% 6%	760
December	1st to 10th	Night	24% 18% 33% 20% 5%	760
	11th to 20th	Night	26% 15% 35% 21% 4	760
	21st to end	Night	29% 16% 32% 20% 3	847

Page generated at 2024-08-12 09:52:50. Version ac07

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