Annual International Video Astronomy Star Party
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Annual International Video Astronomy Star Party 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	17% 10% 3 8% 5% 4 4 3 5% 7% 32%	105296
	Night	19% 12% 4 9% 5% 4 4 3 5% 6% 30%	104058
Transparency	Day	51% 7% 11% 21% 9% 1	108779
	Night	55% 6% 11% 18% 9% 1	108664
Seeing	Day	25% 16% 29% 20% 8% 2	14714
	Night	26% 14% 28% 24% 8% 1	23931

By Month

Percentage Cloud Cover NE (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% 18% 5% 12% 7% 6% 4 4 3 5% 19%	2597
	11th to 20th	Day	14% 17% 7% 14% 8% 7% 5% 3 4 4 18%	2600
	21st to end	Day	17% 20% 7% 12% 7% 7% 4 3 5% 5% 15%	2909
February	1st to 10th	Day	17% 16% 5% 12% 6% 5% 4 4 5% 5% 22%	1710
	11th to 20th	Day	16% 15% 6% 10% 7% 5% 4 4 4 5% 25%	1695
	21st to end	Day	20% 16% 5% 9% 6% 5% 4 4 5% 5% 21%	1570
March	1st to 10th	Day	22% 13% 4 10% 4 4 3 3 4 5% 28%	3116
	11th to 20th	Day	14% 17% 5% 10% 6% 5% 4 2 4 5% 29%	3448
	21st to end	Day	15% 8% 3 8% 5% 4 4 2 4 6% 40%	4053
April	1st to 10th	Day	21% 13% 3 6% 5% 4 4 3 4 5% 32%	2280
	11th to 20th	Day	22% 11% 2 6% 5% 3 3 3 4 5% 36%	2254
	21st to end	Day	23% 10% 3 7% 4 4 4 3 5% 5% 32%	2373
May	1st to 10th	Day	21% 9% 3 8% 5% 4 5% 3 5% 6% 31%	4426
	11th to 20th	Day	18% 9% 4 8% 5% 4 5% 3 5% 6% 33%	4398
	21st to end	Day	14% 7% 2 6% 4 5% 5% 4 6% 9% 39%	4837
June	1st to 10th	Day	21% 8% 3 7% 4 4 4 4 6% 7% 31%	2660
	11th to 20th	Day	15% 6% 2 6% 5% 5% 5% 4 6% 8% 37%	2660
	21st to end	Day	20% 7% 3 7% 5% 4 5% 4 6% 7% 33%	2660
July	1st to 10th	Day	13% 6% 3 6% 4 5% 5% 4 7% 9% 38%	4440
	11th to 20th	Day	13% 6% 3 6% 5% 4 5% 4 7% 8% 39%	4440
	21st to end	Day	11% 5% 2 6% 5% 5% 5% 4 7% 10% 41%	4814
August	1st to 10th	Day	16% 8% 3 7% 4 4 5% 4 6% 9% 34%	4342
	11th to 20th	Day	17% 6% 2 7% 4 4 5% 4 6% 8% 38%	3948
	21st to end	Day	17% 6% 2 5% 4 4 4 4 6% 9% 39%	4180
September	1st to 10th	Day	15% 5% 2 6% 5% 5% 4 4 6% 6% 43%	2280
	11th to 20th	Day	15% 5% 2 5% 4 3 4 3 5% 7% 47%	2267
	21st to end	Day	19% 6% 2 6% 4 4 4 3 5% 7% 39%	2049
October	1st to 10th	Day	21% 8% 3 6% 5% 4 5% 3 5% 7% 34%	1900
	11th to 20th	Day	21% 10% 3 9% 4 4 4 4 5% 6% 28%	1900
	21st to end	Day	26% 11% 3 7% 5% 3 5% 3 5% 5% 27%	1933
November	1st to 10th	Day	16% 9% 3 8% 6% 5% 5% 4 6% 7% 31%	1761
	11th to 20th	Day	16% 12% 4 8% 5% 6% 5% 4 5% 6% 29%	1650
	21st to end	Day	21% 15% 4 10% 7% 4 5% 3 5% 7% 20%	1600
December	1st to 10th	Day	22% 21% 5% 11% 5% 5% 4 3 4 5% 15%	2600
	11th to 20th	Day	19% 17% 6% 11% 5% 5% 4 3 3 4 22%	2986
	21st to end	Day	21% 16% 4 12% 5% 4 4 3 3 3 22%	3960
January	1st to 10th	Night	19% 19% 7% 11% 5% 4 4 3 4 4 20%	4569
	11th to 20th	Night	14% 18% 7% 15% 8% 5% 6% 3 4 4 16%	4580
	21st to end	Night	20% 18% 6% 11% 7% 5% 4 2 4 4 19%	4767
February	1st to 10th	Night	19% 15% 6% 13% 6% 5% 4 4 4 5% 19%	2470
	11th to 20th	Night	15% 14% 6% 12% 6% 5% 4 3 4 4 27%	2370
	21st to end	Night	18% 15% 5% 10% 6% 4 4 3 3 5% 27%	1884
March	1st to 10th	Night	20% 12% 4 7% 5% 4 3 3 4 5% 32%	3724
	11th to 20th	Night	21% 17% 5% 8% 4 3 3 3 4 5% 27%	3493
	21st to end	Night	17% 11% 4 8% 4 4 4 3 4 4 37%	3578
April	1st to 10th	Night	21% 11% 4 8% 4 4 4 3 4 5% 32%	1900
	11th to 20th	Night	21% 10% 3 6% 5% 4 4 3 4 5% 35%	1875
	21st to end	Night	22% 10% 2 7% 4 5% 3 3 4 6% 33%	1824
May	1st to 10th	Night	23% 10% 3 7% 5% 4 4 4 6% 7% 28%	2514
	11th to 20th	Night	20% 9% 3 7% 4 4 4 3 4 6% 36%	2495
	21st to end	Night	16% 6% 2 6% 4 4 4 3 7% 8% 40%	2738
June	1st to 10th	Night	18% 7% 3 7% 5% 5% 5% 4 6% 9% 32%	1520
	11th to 20th	Night	16% 6% 2 6% 5% 4 4 3 6% 9% 40%	1520
	21st to end	Night	19% 8% 2 6% 5% 5% 4 4 6% 8% 33%	1520
July	1st to 10th	Night	14% 7% 3 7% 5% 5% 5% 4 6% 7% 37%	2520
	11th to 20th	Night	14% 7% 2 5% 3 4 4 4 6% 8% 43%	2520
	21st to end	Night	11% 6% 2 7% 5% 5% 5% 4 6% 8% 40%	2739
August	1st to 10th	Night	14% 8% 3 8% 4 4 4 4 5% 8% 38%	2583
	11th to 20th	Night	15% 8% 3 7% 4 4 4 3 4 7% 40%	2848
	21st to end	Night	10% 6% 3 7% 5% 4 5% 5% 6% 8% 41%	3476
September	1st to 10th	Night	15% 7% 2 6% 5% 4 3 2 5% 6% 45%	1900
	11th to 20th	Night	14% 5% 2 5% 4 3 3 3 5% 7% 49%	1912
	21st to end	Night	16% 6% 3 6% 5% 4 4 3 6% 6% 41%	2128
October	1st to 10th	Night	19% 9% 3 7% 4 3 4 3 5% 7% 35%	2280
	11th to 20th	Night	20% 9% 3 7% 4 5% 4 4 5% 7% 33%	2280
	21st to end	Night	26% 10% 3 7% 5% 4 4 3 5% 6% 28%	2665
November	1st to 10th	Night	19% 11% 3 7% 4 4 4 3 4 6% 35%	2537
	11th to 20th	Night	18% 12% 4 8% 5% 4 4 3 4 6% 32%	2745
	21st to end	Night	22% 15% 4 9% 5% 4 4 3 5% 6% 23%	2800
December	1st to 10th	Night	21% 19% 6% 13% 7% 5% 4 3 4 4 14%	4580
	11th to 20th	Night	24% 15% 4 9% 5% 4 3 3 3 4 25%	5208
	21st to end	Night	26% 15% 4 12% 5% 4 4 3 5% 4 18%	6996

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	66% 10% 9% 10% 4 1	2598
	11th to 20th	Day	68% 9% 9% 8% 6%	2600
	21st to end	Day	73% 6% 9% 7% 3 1	2909
February	1st to 10th	Day	65% 6% 7% 17% 4 1	1710
	11th to 20th	Day	62% 6% 8% 15% 8% 1	1704
	21st to end	Day	65% 6% 9% 11% 8% 1	1570
March	1st to 10th	Day	59% 6% 9% 18% 7% 1	3119
	11th to 20th	Day	58% 6% 12% 13% 9% 2	3448
	21st to end	Day	46% 6% 7% 21% 17% 3	4053
April	1st to 10th	Day	55% 5% 6% 20% 12% 3	2280
	11th to 20th	Day	51% 4 8% 18% 16% 3	2254
	21st to end	Day	54% 5% 8% 16% 15% 3	2373
May	1st to 10th	Day	53% 7% 9% 20% 10% 1	4440
	11th to 20th	Day	49% 9% 10% 21% 9% 1	4402
	21st to end	Day	41% 8% 11% 26% 13% 1	4837
June	1st to 10th	Day	51% 7% 10% 20% 12% 1	2660
	11th to 20th	Day	44% 7% 10% 25% 12% 2	2660
	21st to end	Day	50% 8% 11% 20% 11% 1	2660
July	1st to 10th	Day	41% 6% 13% 29% 11% 1	4370
	11th to 20th	Day	40% 7% 14% 30% 8%	4365
	21st to end	Day	38% 8% 13% 31% 9%	4661
August	1st to 10th	Day	47% 7% 15% 22% 9%	4328
	11th to 20th	Day	44% 6% 14% 27% 8%	3987
	21st to end	Day	41% 6% 16% 26% 11%	4180
September	1st to 10th	Day	40% 8% 13% 26% 13%	2280
	11th to 20th	Day	37% 6% 11% 32% 14% 1	2267
	21st to end	Day	44% 7% 12% 27% 10%	2049
October	1st to 10th	Day	47% 5% 11% 27% 9%	3160
	11th to 20th	Day	49% 7% 14% 23% 6%	3140
	21st to end	Day	47% 5% 17% 24% 7%	3158
November	1st to 10th	Day	50% 8% 12% 22% 7% 1	1761
	11th to 20th	Day	56% 6% 12% 15% 10% 1	1650
	21st to end	Day	66% 6% 11% 12% 5%	1600
December	1st to 10th	Day	73% 5% 10% 10% 1	2600
	11th to 20th	Day	68% 5% 8% 14% 6%	2986
	21st to end	Day	68% 4 8% 15% 4	3960
January	1st to 10th	Night	66% 8% 13% 9% 4	4569
	11th to 20th	Night	71% 8% 8% 9% 4	4580
	21st to end	Night	72% 6% 8% 9% 5% 1	4767
February	1st to 10th	Night	68% 5% 8% 12% 6%	2470
	11th to 20th	Night	60% 6% 8% 19% 7%	2372
	21st to end	Night	62% 5% 7% 17% 9% 1	1884
March	1st to 10th	Night	55% 4 10% 21% 9% 1	3734
	11th to 20th	Night	60% 6% 13% 12% 7% 1	3494
	21st to end	Night	50% 6% 4 22% 15% 3	3578
April	1st to 10th	Night	54% 5% 8% 19% 12% 1	1900
	11th to 20th	Night	52% 5% 8% 18% 15% 1	1875
	21st to end	Night	53% 5% 8% 17% 13% 4	1824
May	1st to 10th	Night	54% 8% 9% 17% 10% 2	2520
	11th to 20th	Night	48% 9% 10% 22% 10% 2	2496
	21st to end	Night	40% 8% 11% 21% 18% 2	2739
June	1st to 10th	Night	49% 7% 13% 18% 11% 1	1520
	11th to 20th	Night	43% 5% 13% 21% 16% 2	1520
	21st to end	Night	48% 8% 12% 19% 12% 1	1520
July	1st to 10th	Night	45% 6% 12% 22% 14% 1	2480
	11th to 20th	Night	39% 7% 14% 33% 8%	2472
	21st to end	Night	41% 8% 13% 24% 13%	2651
August	1st to 10th	Night	45% 7% 14% 25% 10%	2573
	11th to 20th	Night	44% 6% 13% 28% 8% 1	2875
	21st to end	Night	39% 7% 14% 27% 12% 1	3476
September	1st to 10th	Night	40% 5% 12% 28% 13% 1	1900
	11th to 20th	Night	34% 7% 13% 31% 14% 1	1912
	21st to end	Night	42% 7% 11% 27% 12% 1	2128
October	1st to 10th	Night	44% 6% 12% 28% 10%	3800
	11th to 20th	Night	45% 5% 15% 25% 10%	3779
	21st to end	Night	50% 5% 16% 20% 8%	4390
November	1st to 10th	Night	51% 6% 12% 20% 10% 1	2537
	11th to 20th	Night	53% 7% 11% 17% 9% 2	2745
	21st to end	Night	62% 7% 12% 14% 5%	2800
December	1st to 10th	Night	74% 6% 9% 9% 2	4580
	11th to 20th	Night	65% 6% 8% 13% 8%	5208
	21st to end	Night	69% 5% 7% 11% 8%	6996

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	29% 22% 31% 13% 6%	200
	11th to 20th	Day	30% 21% 32% 13% 4 1	200
	21st to end	Day	26% 23% 28% 19% 5%	237
February	1st to 10th	Day	35% 28% 26% 10% 1	270
	11th to 20th	Day	28% 30% 32% 9% 1	302
	21st to end	Day	35% 20% 29% 14% 2	382
March	1st to 10th	Day	28% 19% 32% 17% 4	460
	11th to 20th	Day	31% 21% 32% 13% 3 1	460
	21st to end	Day	33% 19% 26% 14% 6% 2	506
April	1st to 10th	Day	34% 19% 28% 13% 5%	460
	11th to 20th	Day	34% 20% 22% 16% 5% 3	452
	21st to end	Day	34% 17% 27% 13% 6% 2	460
May	1st to 10th	Day	26% 19% 27% 20% 8% 1	463
	11th to 20th	Day	22% 17% 33% 18% 8% 2	487
	21st to end	Day	19% 16% 30% 25% 9% 1	529
June	1st to 10th	Day	29% 14% 27% 22% 7% 1	490
	11th to 20th	Day	17% 15% 35% 23% 8% 2	490
	21st to end	Day	26% 14% 32% 16% 10% 2	490
July	1st to 10th	Day	15% 11% 29% 31% 11% 2	485
	11th to 20th	Day	15% 13% 28% 27% 13% 3	484
	21st to end	Day	16% 9% 32% 32% 10% 2	532
August	1st to 10th	Day	18% 8% 24% 33% 14% 3	486
	11th to 20th	Day	16% 7% 26% 29% 16% 6%	479
	21st to end	Day	16% 10% 32% 24% 11% 7%	539
September	1st to 10th	Day	18% 9% 29% 24% 12% 7%	490
	11th to 20th	Day	14% 7% 22% 26% 19% 11%	490
	21st to end	Day	19% 13% 26% 24% 14% 3	490
October	1st to 10th	Day	26% 16% 24% 16% 12% 5%	490
	11th to 20th	Day	29% 18% 29% 17% 6% 1	490
	21st to end	Day	34% 13% 28% 20% 5%	456
November	1st to 10th	Day	27% 19% 28% 18% 7% 1	395
	11th to 20th	Day	28% 18% 32% 14% 6% 1	250
	21st to end	Day	33% 21% 34% 7% 6%	200
December	1st to 10th	Day	38% 19% 25% 14% 5% 1	200
	11th to 20th	Day	34% 28% 25% 11% 2	200
	21st to end	Day	37% 17% 27% 13% 5% 1	220
January	1st to 10th	Night	32% 19% 28% 18% 4	800
	11th to 20th	Night	32% 21% 25% 19% 4	800
	21st to end	Night	24% 17% 33% 20% 6%	841
February	1st to 10th	Night	28% 21% 30% 19% 2	760
	11th to 20th	Night	26% 18% 36% 17% 3	743
	21st to end	Night	28% 19% 31% 19% 3	628
March	1st to 10th	Night	29% 16% 29% 23% 4	760
	11th to 20th	Night	30% 19% 30% 17% 4 1	760
	21st to end	Night	27% 14% 31% 20% 7%	836
April	1st to 10th	Night	29% 15% 31% 22% 3	760
	11th to 20th	Night	30% 17% 27% 18% 7%	751
	21st to end	Night	30% 12% 29% 21% 7% 1	684
May	1st to 10th	Night	28% 8% 28% 26% 9% 1	380
	11th to 20th	Night	20% 11% 33% 29% 7%	374
	21st to end	Night	17% 9% 36% 28% 10%	411
June	1st to 10th	Night	19% 10% 28% 35% 7%	380
	11th to 20th	Night	17% 9% 29% 31% 12% 1	380
	21st to end	Night	22% 8% 29% 29% 11% 1	380
July	1st to 10th	Night	11% 7% 29% 41% 11% 1	370
	11th to 20th	Night	14% 5% 28% 37% 15% 1	368
	21st to end	Night	14% 5% 28% 42% 10% 1	416
August	1st to 10th	Night	16% 5% 23% 39% 16%	416
	11th to 20th	Night	16% 5% 22% 36% 20% 1	601
	21st to end	Night	14% 5% 31% 33% 15% 2	836
September	1st to 10th	Night	19% 7% 27% 31% 15% 1	760
	11th to 20th	Night	17% 7% 20% 32% 20% 5%	760
	21st to end	Night	18% 11% 24% 27% 18% 1	760
October	1st to 10th	Night	24% 13% 29% 19% 14% 1	760
	11th to 20th	Night	26% 14% 27% 24% 8%	760
	21st to end	Night	32% 14% 26% 22% 5%	836
November	1st to 10th	Night	28% 14% 29% 21% 7% 1	780
	11th to 20th	Night	26% 17% 30% 18% 9% 1	800
	21st to end	Night	33% 19% 24% 18% 5%	800
December	1st to 10th	Night	36% 18% 25% 18% 4	800
	11th to 20th	Night	31% 20% 30% 15% 4 1	800
	21st to end	Night	36% 16% 27% 18% 3	880

Page generated at 2025-01-19 03:06:48. Version ac07

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