Winter Star Party
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Winter Star Party clear sky chart from 2005-11-06 to 2026-03-18.

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	5% 4 2 5% 4 5% 5% 5% 8% 12% 45%	130992
	Night	5% 4 2 6% 4 5% 5% 5% 7% 11% 46%	130507
Transparency	Day	28% 11% 23% 26% 11% 2	134707
	Night	30% 9% 21% 25% 12% 2	134849
Seeing	Day	6% 2 8% 24% 37% 23%	17766
	Night	7% 2 9% 27% 37% 19%	27930

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	6% 4 2 5% 4 4 4 4 6% 13% 48%	5258
	11th to 20th	Day	10% 6% 3 8% 5% 6% 6% 5% 8% 9% 34%	5280
	21st to end	Day	9% 6% 2 7% 5% 5% 5% 4 7% 8% 42%	6376
February	1st to 10th	Day	6% 4 1 3 4 4 5% 4 6% 10% 51%	2100
	11th to 20th	Day	4 4 1 4 3 3 4 3 5% 10% 57%	2111
	21st to end	Day	4 2 1 3 2 3 3 3 6% 11% 61%	1903
March	1st to 10th	Day	2 2 1 4 3 3 5% 4 7% 11% 60%	5045
	11th to 20th	Day	3 2 1 3 3 3 3 3 7% 11% 63%	5057
	21st to end	Day	5% 3 1 5% 4 4 4 4 6% 10% 54%	5465
April	1st to 10th	Day	3 2 1 3 3 4 4 4 7% 13% 57%	2200
	11th to 20th	Day	3 3 1 3 3 3 4 3 7% 11% 59%	2176
	21st to end	Day	4 3 1 4 3 3 3 4 7% 10% 58%	2377
May	1st to 10th	Day	2 1 1 2 2 3 3 3 6% 12% 66%	5405
	11th to 20th	Day	5% 3 1 4 3 3 4 3 6% 9% 60%	5580
	21st to end	Day	3 3 1 3 2 2 4 3 5% 10% 63%	6433
June	1st to 10th	Day	10% 8% 3 8% 6% 6% 7% 6% 8% 12% 26%	2600
	11th to 20th	Day	6% 5% 2 7% 6% 6% 8% 7% 12% 12% 29%	2600
	21st to end	Day	4 4 2 7% 6% 7% 6% 7% 11% 17% 30%	2600
July	1st to 10th	Day	3 3 2 6% 5% 6% 7% 6% 11% 17% 35%	5900
	11th to 20th	Day	2 3 2 6% 5% 6% 7% 6% 11% 17% 35%	5900
	21st to end	Day	2 2 1 4 3 4 6% 6% 10% 18% 44%	6424
August	1st to 10th	Day	2 3 2 7% 6% 7% 8% 7% 12% 17% 29%	4188
	11th to 20th	Day	2 3 2 6% 6% 7% 8% 7% 11% 15% 34%	3526
	21st to end	Day	3 3 2 6% 6% 7% 9% 7% 12% 18% 27%	3949
September	1st to 10th	Day	5% 4 2 7% 6% 7% 9% 8% 12% 16% 26%	2200
	11th to 20th	Day	5% 6% 3 8% 5% 6% 9% 7% 11% 14% 27%	2200
	21st to end	Day	8% 7% 3 8% 6% 7% 7% 6% 10% 12% 27%	2200
October	1st to 10th	Day	6% 5% 3 8% 6% 6% 9% 6% 10% 14% 26%	2196
	11th to 20th	Day	8% 5% 2 7% 5% 6% 6% 6% 9% 12% 34%	2000
	21st to end	Day	8% 5% 2 6% 4 5% 6% 5% 8% 9% 41%	2200
November	1st to 10th	Day	7% 4 2 5% 5% 5% 5% 5% 7% 9% 45%	2057
	11th to 20th	Day	7% 6% 2 7% 5% 5% 6% 5% 7% 8% 45%	2100
	21st to end	Day	6% 5% 2 5% 4 4 5% 4 7% 11% 49%	2100
December	1st to 10th	Day	6% 3 1 4 3 4 3 3 6% 9% 57%	3258
	11th to 20th	Day	7% 6% 2 6% 5% 4 4 5% 7% 12% 42%	3463
	21st to end	Day	10% 7% 3 8% 6% 6% 6% 5% 7% 8% 34%	4565
January	1st to 10th	Night	4 3 1 5% 4 4 5% 4 7% 10% 53%	7635
	11th to 20th	Night	11% 7% 3 8% 5% 6% 6% 6% 8% 9% 32%	7680
	21st to end	Night	10% 6% 3 7% 5% 5% 5% 4 6% 8% 41%	7787
February	1st to 10th	Night	6% 4 2 5% 5% 4 5% 4 6% 8% 50%	2520
	11th to 20th	Night	5% 4 1 4 4 4 4 4 6% 8% 57%	2392
	21st to end	Night	5% 3 1 3 3 4 3 3 5% 9% 61%	1903
March	1st to 10th	Night	3 2 1 5% 4 5% 5% 5% 7% 8% 54%	5028
	11th to 20th	Night	3 2 1 4 3 3 4 3 5% 8% 65%	5058
	21st to end	Night	5% 3 1 5% 4 4 4 5% 6% 10% 54%	5467
April	1st to 10th	Night	4 2 1 3 4 3 4 3 7% 11% 57%	2200
	11th to 20th	Night	5% 3 1 4 4 4 4 4 7% 11% 53%	2173
	21st to end	Night	4 3 2 4 3 3 4 4 6% 10% 56%	2020
May	1st to 10th	Night	2 1 1 2 2 2 3 3 5% 10% 69%	4490
	11th to 20th	Night	6% 4 2 6% 4 5% 4 3 6% 7% 54%	4353
	21st to end	Night	3 3 1 3 2 3 3 2 5% 9% 66%	4421
June	1st to 10th	Night	11% 9% 5% 9% 7% 7% 6% 5% 6% 10% 27%	1800
	11th to 20th	Night	7% 5% 2 6% 6% 6% 6% 6% 10% 14% 33%	1800
	21st to end	Night	3 3 2 5% 7% 7% 7% 6% 10% 12% 36%	1800
July	1st to 10th	Night	2 3 1 4 4 6% 7% 6% 12% 19% 36%	4058
	11th to 20th	Night	1 2 1 6% 4 5% 6% 6% 8% 15% 45%	4057
	21st to end	Night	1 2 1 4 3 3 4 5% 8% 14% 54%	4427
August	1st to 10th	Night	2 4 2 6% 5% 6% 7% 6% 10% 18% 35%	2940
	11th to 20th	Night	2 2 1 5% 4 6% 7% 6% 10% 17% 39%	3486
	21st to end	Night	3 4 1 5% 5% 6% 8% 7% 11% 18% 32%	3949
September	1st to 10th	Night	4 4 2 5% 5% 6% 7% 7% 12% 15% 33%	2200
	11th to 20th	Night	3 5% 3 8% 6% 7% 8% 7% 11% 13% 29%	2200
	21st to end	Night	7% 7% 3 9% 5% 6% 8% 7% 9% 11% 28%	2200
October	1st to 10th	Night	6% 6% 3 8% 7% 6% 8% 6% 9% 13% 30%	2200
	11th to 20th	Night	9% 5% 2 7% 6% 5% 6% 5% 9% 12% 32%	2400
	21st to end	Night	10% 6% 3 7% 6% 6% 6% 5% 7% 10% 36%	2640
November	1st to 10th	Night	8% 5% 2 6% 4 5% 5% 4 8% 11% 43%	2461
	11th to 20th	Night	7% 5% 2 6% 5% 5% 5% 4 7% 10% 44%	2520
	21st to end	Night	6% 4 1 5% 4 5% 4 4 7% 9% 49%	2520
December	1st to 10th	Night	5% 3 1 4 3 3 4 3 7% 9% 57%	4137
	11th to 20th	Night	7% 5% 2 6% 4 4 5% 5% 7% 9% 45%	4952
	21st to end	Night	9% 7% 3 10% 6% 6% 6% 5% 7% 9% 33%	6633

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	25% 8% 14% 35% 16% 2	5259
	11th to 20th	Day	41% 10% 19% 21% 6% 3	5280
	21st to end	Day	38% 7% 11% 27% 16% 2	6376
February	1st to 10th	Day	25% 7% 13% 32% 20% 3	2100
	11th to 20th	Day	21% 6% 14% 30% 23% 6%	2121
	21st to end	Day	16% 5% 13% 32% 28% 7%	1903
March	1st to 10th	Day	16% 7% 19% 32% 23% 3	5045
	11th to 20th	Day	14% 5% 21% 30% 21% 10%	5057
	21st to end	Day	23% 6% 13% 34% 21% 3	5465
April	1st to 10th	Day	17% 7% 17% 40% 17% 3	2200
	11th to 20th	Day	18% 7% 20% 31% 19% 4	2176
	21st to end	Day	18% 7% 17% 33% 22% 3	2377
May	1st to 10th	Day	10% 5% 20% 44% 19% 2	5437
	11th to 20th	Day	20% 6% 15% 50% 9%	5584
	21st to end	Day	16% 6% 19% 51% 8%	6447
June	1st to 10th	Day	45% 11% 25% 16% 3	2600
	11th to 20th	Day	37% 19% 29% 14% 1	2600
	21st to end	Day	34% 18% 35% 12% 1	2600
July	1st to 10th	Day	31% 16% 40% 13%	5835
	11th to 20th	Day	29% 16% 44% 11% 1	5831
	21st to end	Day	20% 13% 43% 21% 2	6240
August	1st to 10th	Day	32% 18% 36% 13% 1	4175
	11th to 20th	Day	30% 16% 39% 13% 1	3559
	21st to end	Day	33% 21% 37% 9% 1	3949
September	1st to 10th	Day	35% 23% 31% 11% 1	2200
	11th to 20th	Day	36% 20% 30% 11% 2	2200
	21st to end	Day	41% 16% 23% 15% 4	2200
October	1st to 10th	Day	38% 14% 25% 17% 4 1	3573
	11th to 20th	Day	44% 15% 18% 14% 8% 1	3240
	21st to end	Day	35% 8% 12% 29% 14% 2	3538
November	1st to 10th	Day	31% 8% 15% 24% 18% 3	2057
	11th to 20th	Day	34% 7% 13% 23% 18% 4	2100
	21st to end	Day	28% 8% 14% 25% 22% 3	2100
December	1st to 10th	Day	24% 6% 12% 36% 20% 3	3258
	11th to 20th	Day	32% 9% 16% 26% 14% 3	3460
	21st to end	Day	44% 10% 14% 17% 14% 1	4565
January	1st to 10th	Night	24% 6% 12% 36% 18% 3	7636
	11th to 20th	Night	44% 9% 18% 20% 7% 1	7680
	21st to end	Night	39% 6% 10% 27% 15% 2	7787
February	1st to 10th	Night	29% 7% 13% 27% 19% 4	2520
	11th to 20th	Night	24% 6% 14% 25% 25% 6%	2393
	21st to end	Night	21% 4 12% 25% 29% 9%	1903
March	1st to 10th	Night	24% 8% 13% 28% 23% 4	5028
	11th to 20th	Night	17% 6% 16% 30% 20% 10%	5058
	21st to end	Night	23% 7% 14% 29% 22% 5%	5467
April	1st to 10th	Night	20% 7% 16% 38% 17% 2	2200
	11th to 20th	Night	24% 8% 17% 28% 18% 4	2173
	21st to end	Night	23% 7% 13% 34% 22% 2	2020
May	1st to 10th	Night	10% 5% 15% 51% 17% 2	4520
	11th to 20th	Night	28% 7% 13% 35% 16% 1	4354
	21st to end	Night	16% 5% 20% 47% 13%	4429
June	1st to 10th	Night	50% 10% 20% 17% 3	1800
	11th to 20th	Night	37% 14% 31% 16% 2	1800
	21st to end	Night	35% 15% 35% 15% 1	1800
July	1st to 10th	Night	28% 16% 43% 13%	4015
	11th to 20th	Night	24% 15% 49% 11%	4006
	21st to end	Night	18% 10% 42% 26% 4	4297
August	1st to 10th	Night	31% 14% 37% 16% 1	2929
	11th to 20th	Night	24% 14% 44% 16% 1	3519
	21st to end	Night	31% 19% 40% 9% 1	3949
September	1st to 10th	Night	31% 20% 35% 13% 1	2200
	11th to 20th	Night	39% 17% 29% 12% 2	2200
	21st to end	Night	43% 16% 23% 14% 4	2200
October	1st to 10th	Night	40% 12% 23% 19% 5% 1	3590
	11th to 20th	Night	48% 13% 18% 13% 6% 1	3899
	21st to end	Night	39% 8% 12% 27% 12% 2	4252
November	1st to 10th	Night	33% 8% 15% 25% 16% 3	2461
	11th to 20th	Night	34% 7% 13% 26% 18% 3	2520
	21st to end	Night	28% 8% 14% 25% 22% 3	2520
December	1st to 10th	Night	23% 6% 12% 40% 16% 4	4137
	11th to 20th	Night	33% 7% 15% 28% 14% 3	4954
	21st to end	Night	45% 9% 15% 17% 13% 1	6633

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	7% 3 18% 37% 32% 3	330
	11th to 20th	Day	12% 5% 18% 41% 22% 2	330
	21st to end	Day	11% 3 21% 41% 21% 1	363
February	1st to 10th	Day	4 4 14% 41% 30% 6%	330
	11th to 20th	Day	5% 2 11% 35% 41% 7%	393
	21st to end	Day	4 2 15% 32% 41% 5%	446
March	1st to 10th	Day	2 2 16% 42% 34% 4	540
	11th to 20th	Day	6% 1 15% 38% 35% 5%	528
	21st to end	Day	5% 2 13% 40% 36% 4	550
April	1st to 10th	Day	3 1 10% 43% 40% 4	500
	11th to 20th	Day	3 2 12% 48% 31% 3	492
	21st to end	Day	3 6% 46% 43% 2	500
May	1st to 10th	Day	3 5% 35% 50% 8%	503
	11th to 20th	Day	9% 1 6% 31% 42% 11%	527
	21st to end	Day	8% 1 5% 15% 49% 22%	573
June	1st to 10th	Day	12% 1 5% 18% 38% 26%	530
	11th to 20th	Day	7% 2 2 10% 39% 40%	530
	21st to end	Day	4 2 1 4 32% 58%	530
July	1st to 10th	Day	3 2 5% 35% 54%	525
	11th to 20th	Day	4 2 4 35% 56%	524
	21st to end	Day	5% 1 1 4 36% 53%	576
August	1st to 10th	Day	4 1 2 3 37% 54%	526
	11th to 20th	Day	3 2 4 36% 55%	519
	21st to end	Day	4 2 4 8% 37% 45%	583
September	1st to 10th	Day	5% 1 2 4 34% 55%	530
	11th to 20th	Day	6% 2 6% 25% 61%	530
	21st to end	Day	9% 2 5% 9% 32% 44%	530
October	1st to 10th	Day	5% 2 5% 19% 46% 22%	530
	11th to 20th	Day	9% 2 6% 21% 41% 22%	530
	21st to end	Day	8% 2 10% 28% 38% 13%	583
November	1st to 10th	Day	7% 4 12% 29% 40% 9%	535
	11th to 20th	Day	9% 4 10% 32% 38% 8%	540
	21st to end	Day	6% 3 13% 34% 36% 9%	540
December	1st to 10th	Day	8% 3 11% 30% 41% 7%	477
	11th to 20th	Day	6% 4 12% 28% 42% 8%	330
	21st to end	Day	9% 4 13% 29% 36% 9%	363
January	1st to 10th	Night	6% 3 14% 36% 36% 5%	840
	11th to 20th	Night	10% 4 20% 35% 28% 3	840
	21st to end	Night	9% 5% 20% 37% 28% 1	924
February	1st to 10th	Night	6% 4 16% 38% 33% 3	840
	11th to 20th	Night	5% 3 17% 35% 37% 3	823
	21st to end	Night	4 3 11% 36% 40% 5%	692
March	1st to 10th	Night	3 2 16% 44% 32% 3	840
	11th to 20th	Night	4 1 13% 41% 37% 3	829
	21st to end	Night	4 2 14% 43% 33% 3	880
April	1st to 10th	Night	4 1 8% 44% 40% 3	800
	11th to 20th	Night	4 2 12% 45% 34% 3	791
	21st to end	Night	6% 2 6% 45% 38% 4	800
May	1st to 10th	Night	3 6% 36% 45% 10%	800
	11th to 20th	Night	11% 2 5% 32% 44% 8%	730
	21st to end	Night	8% 2 6% 22% 47% 16%	650
June	1st to 10th	Night	14% 2 6% 19% 40% 20%	600
	11th to 20th	Night	7% 1 3 11% 43% 36%	600
	21st to end	Night	3 1 1 7% 37% 51%	600
July	1st to 10th	Night	4 2 5% 34% 56%	585
	11th to 20th	Night	2 1 1 6% 38% 53%	582
	21st to end	Night	4 1 5% 34% 56%	657
August	1st to 10th	Night	4 1 2 5% 40% 49%	597
	11th to 20th	Night	3 1 1 5% 36% 55%	766
	21st to end	Night	7% 1 3 9% 34% 46%	880
September	1st to 10th	Night	6% 1 2 6% 35% 51%	800
	11th to 20th	Night	5% 1 2 7% 29% 56%	800
	21st to end	Night	10% 1 4 11% 34% 41%	800
October	1st to 10th	Night	7% 2 7% 19% 45% 20%	800
	11th to 20th	Night	11% 1 7% 18% 44% 19%	800
	21st to end	Night	11% 2 10% 29% 37% 11%	880
November	1st to 10th	Night	10% 3 13% 29% 38% 7%	820
	11th to 20th	Night	8% 2 10% 28% 43% 10%	840
	21st to end	Night	6% 3 13% 35% 37% 7%	840
December	1st to 10th	Night	7% 2 11% 32% 41% 6%	840
	11th to 20th	Night	8% 2 12% 34% 38% 5%	840
	21st to end	Night	9% 3 14% 31% 37% 7%	924

Page generated at 2026-03-15 02:23:55. Version ac07

Copyright © 2026 Attilla Danko.