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 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	17% 10% 3 8% 5% 4 4 3 5% 6% 32%	95694
	Night	19% 12% 4 8% 5% 4 4 3 5% 6% 30%	93010
Transparency	Day	52% 7% 11% 20% 9% 1	95413
	Night	55% 7% 10% 18% 9% 1	92845
Seeing	Day	25% 16% 29% 20% 8% 2	14236
	Night	26% 14% 28% 24% 8% 1	23297

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% 5% 4 4 3 5% 19%	2517
	11th to 20th	Day	14% 17% 7% 13% 8% 6% 4 3 4 4 18%	2520
	21st to end	Day	17% 20% 7% 12% 7% 7% 4 3 5% 5% 15%	2901
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	13% 7% 3 7% 5% 5% 5% 4 5% 8% 38%	2604
	11th to 20th	Day	13% 5% 2 7% 4 5% 6% 4 6% 8% 40%	2303
	21st to end	Day	15% 5% 2 6% 5% 4 5% 4 6% 8% 40%	2376
September	1st to 10th	Day	15% 5% 2 6% 4 5% 4 4 6% 6% 42%	2160
	11th to 20th	Day	15% 5% 2 6% 4 3 4 3 4 7% 46%	2148
	21st to end	Day	19% 6% 2 6% 4 4 4 3 5% 8% 39%	1942
October	1st to 10th	Day	22% 8% 3 6% 5% 4 5% 3 5% 6% 33%	1800
	11th to 20th	Day	22% 10% 3 10% 4 4 4 4 5% 6% 27%	1800
	21st to end	Day	27% 11% 3 7% 5% 3 5% 3 5% 5% 26%	1832
November	1st to 10th	Day	17% 9% 3 8% 6% 5% 5% 4 6% 7% 32%	1671
	11th to 20th	Day	17% 13% 4 8% 5% 6% 4 4 4 5% 29%	1568
	21st to end	Day	21% 15% 3 10% 7% 4 5% 3 5% 7% 20%	1520
December	1st to 10th	Day	24% 20% 5% 9% 5% 5% 4 3 4 6% 15%	1520
	11th to 20th	Day	22% 18% 5% 9% 5% 5% 3 3 3 5% 22%	1906
	21st to end	Day	27% 18% 5% 11% 5% 4 4 2 2 2 20%	2772
January	1st to 10th	Night	19% 19% 6% 11% 5% 4 4 3 4 4 21%	4429
	11th to 20th	Night	14% 18% 7% 14% 8% 6% 6% 3 4 4 16%	4440
	21st to end	Night	20% 18% 6% 11% 7% 5% 4 2 4 4 19%	4752
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	12% 6% 2 7% 5% 4 5% 4 6% 7% 41%	1550
	11th to 20th	Night	13% 7% 3 6% 5% 4 4 4 4 7% 43%	1678
	21st to end	Night	12% 6% 3 7% 4 3 4 4 5% 7% 44%	1980
September	1st to 10th	Night	15% 7% 2 6% 5% 4 3 3 5% 6% 45%	1800
	11th to 20th	Night	15% 5% 2 5% 4 3 2 3 5% 8% 48%	1811
	21st to end	Night	16% 6% 3 6% 5% 4 4 3 6% 6% 42%	2016
October	1st to 10th	Night	20% 9% 3 7% 5% 3 4 3 5% 6% 35%	2160
	11th to 20th	Night	20% 9% 3 7% 4 5% 4 4 5% 7% 32%	2160
	21st to end	Night	26% 10% 3 8% 6% 4 3 3 5% 6% 27%	2524
November	1st to 10th	Night	19% 11% 3 6% 4 4 4 3 4 6% 35%	2407
	11th to 20th	Night	18% 12% 3 8% 5% 4 4 3 4 6% 32%	2607
	21st to end	Night	22% 14% 4 9% 5% 4 4 3 5% 6% 23%	2660
December	1st to 10th	Night	23% 18% 5% 11% 6% 4 4 3 4 4 16%	2660
	11th to 20th	Night	23% 17% 4 9% 6% 4 3 2 3 4 26%	3288
	21st to end	Night	31% 15% 5% 11% 4 4 3 3 3 4 17%	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	66% 10% 9% 10% 4 1	2518
	11th to 20th	Day	68% 10% 9% 8% 6%	2520
	21st to end	Day	74% 6% 9% 7% 3 1	2901
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	43% 8% 15% 24% 10%	2590
	11th to 20th	Day	41% 8% 15% 26% 10%	2303
	21st to end	Day	41% 7% 13% 27% 12%	2376
September	1st to 10th	Day	40% 8% 13% 25% 13%	2160
	11th to 20th	Day	38% 6% 11% 31% 13% 1	2148
	21st to end	Day	44% 7% 12% 27% 9%	1942
October	1st to 10th	Day	51% 6% 11% 21% 11% 1	1800
	11th to 20th	Day	56% 9% 13% 16% 6% 1	1800
	21st to end	Day	60% 6% 11% 15% 8% 1	1832
November	1st to 10th	Day	50% 8% 13% 22% 7% 1	1671
	11th to 20th	Day	57% 6% 12% 15% 9% 1	1568
	21st to end	Day	66% 7% 11% 11% 5%	1520
December	1st to 10th	Day	72% 7% 10% 9% 2	1520
	11th to 20th	Day	68% 5% 11% 13% 3	1906
	21st to end	Day	72% 5% 6% 13% 3	2772
January	1st to 10th	Night	66% 9% 13% 9% 4	4429
	11th to 20th	Night	71% 8% 9% 8% 4	4440
	21st to end	Night	72% 6% 8% 9% 4 1	4752
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	40% 9% 16% 23% 12%	1540
	11th to 20th	Night	42% 7% 13% 24% 13% 1	1678
	21st to end	Night	39% 8% 13% 27% 12%	1980
September	1st to 10th	Night	41% 6% 12% 28% 13% 1	1800
	11th to 20th	Night	35% 7% 13% 31% 13% 1	1811
	21st to end	Night	42% 8% 10% 28% 11% 1	2016
October	1st to 10th	Night	49% 7% 10% 21% 12% 1	2160
	11th to 20th	Night	52% 6% 14% 19% 9%	2160
	21st to end	Night	59% 7% 12% 13% 8% 1	2524
November	1st to 10th	Night	51% 6% 13% 19% 10% 1	2407
	11th to 20th	Night	54% 7% 12% 17% 9% 2	2607
	21st to end	Night	62% 7% 12% 14% 5%	2660
December	1st to 10th	Night	72% 6% 8% 11% 2	2660
	11th to 20th	Night	65% 6% 9% 14% 6%	3288
	21st to end	Night	73% 6% 8% 12% 2	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	29% 22% 28% 14% 6%	180
	11th to 20th	Day	31% 19% 32% 13% 4 1	180
	21st to end	Day	26% 23% 28% 18% 5%	235
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	14% 7% 27% 28% 17% 7%	456
	21st to end	Day	16% 11% 33% 22% 11% 7%	495
September	1st to 10th	Day	17% 10% 29% 24% 12% 8%	450
	11th to 20th	Day	16% 8% 24% 27% 15% 10%	450
	21st to end	Day	19% 14% 26% 23% 14% 3	450
October	1st to 10th	Day	27% 17% 23% 16% 13% 5%	450
	11th to 20th	Day	29% 18% 29% 18% 5% 1	450
	21st to end	Day	35% 13% 27% 20% 5%	421
November	1st to 10th	Day	26% 19% 28% 18% 8% 1	365
	11th to 20th	Day	29% 18% 32% 14% 6% 1	228
	21st to end	Day	31% 21% 34% 7% 7%	180
December	1st to 10th	Day	37% 19% 26% 13% 5% 1	180
	11th to 20th	Day	33% 28% 26% 12% 1	180
	21st to end	Day	39% 19% 26% 12% 3 1	198
January	1st to 10th	Night	32% 18% 27% 18% 4	760
	11th to 20th	Night	32% 21% 25% 18% 4	760
	21st to end	Night	24% 17% 33% 20% 6%	836
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% 21% 35% 21% 1	584
	21st to end	Night	14% 6% 31% 32% 16% 2	792
September	1st to 10th	Night	19% 7% 25% 31% 16% 1	720
	11th to 20th	Night	18% 7% 21% 32% 18% 4	720
	21st to end	Night	18% 12% 25% 26% 18% 2	720
October	1st to 10th	Night	24% 13% 29% 19% 14% 1	720
	11th to 20th	Night	26% 14% 28% 24% 8%	720
	21st to end	Night	33% 14% 27% 22% 5%	792
November	1st to 10th	Night	28% 14% 30% 21% 7% 1	740
	11th to 20th	Night	26% 17% 30% 17% 9% 1	760
	21st to end	Night	33% 19% 25% 18% 5%	760
December	1st to 10th	Night	36% 18% 24% 18% 3	760
	11th to 20th	Night	31% 20% 30% 15% 4 1	760
	21st to end	Night	36% 16% 26% 18% 3	836

Page generated at 2024-08-12 09:52:49. Version ac07

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