White Star Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the White Star Park clear sky chart from 2005-11-06 to 2026-06-01.

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	14% 10% 4 9% 5% 5% 5% 4 6% 7% 32%	132085
	Night	14% 11% 4 9% 5% 4 5% 4 5% 7% 33%	131019
Transparency	Day	49% 6% 11% 20% 12% 1	135684
	Night	49% 6% 11% 20% 13% 1	135490
Seeing	Day	17% 11% 29% 24% 14% 6%	17547
	Night	18% 10% 29% 29% 13% 1	27413

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	15% 18% 7% 16% 6% 5% 4 3 5% 6% 15%	4691
	11th to 20th	Day	12% 17% 7% 15% 10% 5% 7% 3 3 4 18%	4968
	21st to end	Day	18% 15% 7% 13% 6% 6% 6% 4 5% 4 15%	5780
February	1st to 10th	Day	15% 16% 5% 12% 7% 5% 5% 3 4 5% 21%	1890
	11th to 20th	Day	15% 11% 6% 12% 7% 6% 5% 4 5% 5% 23%	2013
	21st to end	Day	16% 12% 5% 10% 6% 4 5% 4 6% 6% 26%	1730
March	1st to 10th	Day	17% 13% 6% 11% 5% 4 4 4 4 5% 27%	4717
	11th to 20th	Day	11% 11% 3 8% 5% 4 5% 4 5% 6% 38%	5090
	21st to end	Day	17% 14% 5% 10% 6% 5% 4 4 5% 5% 25%	5586
April	1st to 10th	Day	14% 12% 4 9% 6% 5% 5% 4 6% 7% 28%	2416
	11th to 20th	Day	15% 10% 3 7% 6% 5% 5% 4 5% 7% 33%	2651
	21st to end	Day	19% 8% 3 7% 5% 5% 4 3 5% 7% 34%	2730
May	1st to 10th	Day	21% 9% 3 8% 4 4 4 4 5% 6% 29%	5992
	11th to 20th	Day	16% 8% 3 7% 5% 4 6% 4 6% 7% 33%	5991
	21st to end	Day	16% 6% 2 7% 5% 5% 5% 4 6% 8% 38%	6576
June	1st to 10th	Day	13% 5% 3 7% 5% 5% 5% 5% 6% 8% 38%	2671
	11th to 20th	Day	11% 5% 3 6% 6% 5% 5% 4 6% 8% 42%	2800
	21st to end	Day	10% 6% 2 7% 6% 5% 5% 5% 8% 9% 38%	2800
July	1st to 10th	Day	9% 6% 2 7% 5% 5% 5% 4 7% 10% 39%	6360
	11th to 20th	Day	7% 5% 2 6% 5% 5% 6% 5% 7% 11% 39%	6236
	21st to end	Day	9% 6% 2 7% 5% 5% 5% 5% 7% 9% 39%	6424
August	1st to 10th	Day	10% 5% 2 5% 4 4 5% 4 8% 9% 42%	4234
	11th to 20th	Day	8% 6% 2 6% 5% 5% 6% 5% 10% 12% 37%	4174
	21st to end	Day	8% 5% 2 7% 4 5% 5% 5% 7% 10% 42%	4590
September	1st to 10th	Day	13% 6% 2 5% 4 3 5% 5% 6% 7% 46%	2244
	11th to 20th	Day	8% 5% 2 6% 4 4 5% 5% 6% 8% 47%	2200
	21st to end	Day	16% 8% 2 6% 4 4 4 3 5% 7% 42%	2200
October	1st to 10th	Day	11% 7% 2 7% 4 5% 5% 4 6% 6% 44%	2150
	11th to 20th	Day	16% 8% 2 6% 4 5% 4 3 5% 6% 40%	2000
	21st to end	Day	18% 9% 3 8% 5% 4 5% 5% 6% 8% 31%	2073
November	1st to 10th	Day	12% 9% 3 7% 4 5% 4 3 6% 7% 40%	1852
	11th to 20th	Day	16% 13% 4 8% 5% 4 4 3 5% 5% 34%	1890
	21st to end	Day	18% 15% 4 9% 5% 4 4 4 5% 7% 26%	1890
December	1st to 10th	Day	15% 13% 6% 13% 7% 5% 5% 4 4 6% 22%	2881
	11th to 20th	Day	18% 18% 7% 11% 4 4 4 3 4 5% 21%	3463
	21st to end	Day	24% 20% 7% 13% 5% 4 3 3 3 3 14%	4132
January	1st to 10th	Night	14% 17% 6% 15% 7% 5% 5% 3 4 4 19%	8232
	11th to 20th	Night	9% 17% 8% 14% 7% 5% 5% 5% 5% 5% 19%	8002
	21st to end	Night	17% 14% 6% 10% 4 4 5% 4 5% 6% 23%	8401
February	1st to 10th	Night	17% 13% 5% 11% 6% 5% 4 4 5% 5% 24%	2730
	11th to 20th	Night	14% 13% 4 10% 7% 5% 5% 4 5% 5% 26%	2489
	21st to end	Night	18% 13% 5% 9% 6% 4 4 3 5% 5% 28%	2076
March	1st to 10th	Night	17% 12% 4 8% 4 4 4 3 4 5% 36%	5355
	11th to 20th	Night	10% 7% 2 6% 5% 5% 5% 4 6% 7% 42%	5090
	21st to end	Night	15% 10% 4 8% 5% 4 4 4 5% 6% 35%	5588
April	1st to 10th	Night	16% 11% 4 7% 5% 5% 4 4 6% 7% 32%	2221
	11th to 20th	Night	16% 8% 3 7% 5% 5% 5% 3 6% 6% 37%	1916
	21st to end	Night	16% 8% 2 6% 5% 4 5% 4 5% 6% 37%	1890
May	1st to 10th	Night	19% 12% 4 9% 6% 5% 4 3 5% 6% 28%	4123
	11th to 20th	Night	15% 8% 3 8% 4 4 4 3 5% 7% 38%	4122
	21st to end	Night	13% 6% 3 6% 5% 5% 4 4 6% 8% 41%	4520
June	1st to 10th	Night	11% 7% 2 6% 4 4 5% 3 6% 7% 45%	1723
	11th to 20th	Night	8% 5% 3 6% 4 5% 4 5% 7% 9% 43%	1600
	21st to end	Night	9% 5% 2 5% 4 5% 5% 4 8% 9% 46%	1600
July	1st to 10th	Night	8% 5% 2 7% 4 5% 5% 4 6% 9% 45%	3618
	11th to 20th	Night	8% 5% 2 6% 5% 4 5% 4 8% 10% 42%	3721
	21st to end	Night	8% 5% 2 6% 4 5% 4 4 6% 9% 47%	4427
August	1st to 10th	Night	11% 7% 2 6% 4 4 4 4 7% 8% 43%	2915
	11th to 20th	Night	8% 6% 3 6% 4 4 4 4 6% 9% 46%	2875
	21st to end	Night	7% 5% 2 6% 4 5% 5% 4 6% 8% 46%	3304
September	1st to 10th	Night	10% 5% 2 6% 3 3 5% 3 5% 6% 51%	2135
	11th to 20th	Night	9% 4 2 5% 4 4 3 3 4 8% 56%	2200
	21st to end	Night	13% 7% 2 6% 5% 4 4 3 5% 6% 44%	2200
October	1st to 10th	Night	11% 6% 2 6% 4 4 4 4 5% 7% 48%	2249
	11th to 20th	Night	16% 9% 3 7% 4 4 4 3 4 7% 40%	2400
	21st to end	Night	20% 8% 2 7% 4 4 4 4 5% 7% 36%	2765
November	1st to 10th	Night	12% 9% 3 6% 4 4 5% 3 4 6% 43%	2666
	11th to 20th	Night	15% 11% 4 8% 5% 4 4 3 6% 7% 34%	2730
	21st to end	Night	19% 15% 4 9% 5% 5% 5% 3 4 5% 27%	2730
December	1st to 10th	Night	13% 13% 5% 11% 6% 5% 5% 3 6% 7% 25%	4380
	11th to 20th	Night	16% 17% 6% 11% 5% 5% 4 3 5% 5% 22%	4952
	21st to end	Night	24% 19% 6% 10% 5% 5% 4 3 4 5% 14%	7074

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	69% 6% 11% 11% 2	4692
	11th to 20th	Day	71% 4 7% 7% 10%	4968
	21st to end	Day	71% 4 8% 10% 6%	5780
February	1st to 10th	Day	65% 5% 10% 13% 6%	1890
	11th to 20th	Day	61% 5% 10% 16% 7% 1	2023
	21st to end	Day	57% 6% 14% 15% 7% 2	1730
March	1st to 10th	Day	60% 5% 9% 19% 7%	4717
	11th to 20th	Day	45% 6% 13% 25% 10% 1	5090
	21st to end	Day	59% 6% 10% 16% 8% 1	5586
April	1st to 10th	Day	54% 7% 11% 17% 11% 1	2416
	11th to 20th	Day	49% 6% 12% 18% 12% 2	2651
	21st to end	Day	49% 6% 11% 21% 11% 2	2730
May	1st to 10th	Day	53% 8% 9% 17% 12% 1	6027
	11th to 20th	Day	46% 8% 13% 20% 11% 2	5995
	21st to end	Day	42% 7% 10% 22% 15% 4	6590
June	1st to 10th	Day	41% 8% 10% 25% 13% 3	2671
	11th to 20th	Day	39% 7% 13% 21% 17% 2	2800
	21st to end	Day	39% 8% 14% 20% 15% 4	2800
July	1st to 10th	Day	38% 7% 11% 25% 17% 2	6291
	11th to 20th	Day	34% 9% 14% 25% 17% 1	6161
	21st to end	Day	37% 8% 13% 21% 20% 2	6240
August	1st to 10th	Day	34% 8% 16% 26% 15% 1	4221
	11th to 20th	Day	34% 9% 13% 31% 11% 1	4213
	21st to end	Day	34% 8% 12% 32% 13% 2	4589
September	1st to 10th	Day	36% 7% 13% 25% 17% 3	2244
	11th to 20th	Day	33% 6% 12% 29% 19% 2	2200
	21st to end	Day	42% 6% 11% 23% 18% 1	2200
October	1st to 10th	Day	28% 6% 12% 32% 21% 1	3501
	11th to 20th	Day	38% 5% 9% 27% 19% 1	3240
	21st to end	Day	41% 5% 11% 23% 18% 1	3323
November	1st to 10th	Day	42% 5% 12% 24% 16% 1	1852
	11th to 20th	Day	53% 4 11% 20% 11% 1	1890
	21st to end	Day	58% 5% 11% 18% 7%	1890
December	1st to 10th	Day	62% 6% 15% 14% 4	2881
	11th to 20th	Day	65% 4 9% 17% 5%	3460
	21st to end	Day	76% 4 7% 8% 4	4132
January	1st to 10th	Night	68% 5% 8% 15% 4	8233
	11th to 20th	Night	66% 5% 9% 10% 9% 1	8002
	21st to end	Night	61% 5% 13% 14% 8%	8401
February	1st to 10th	Night	61% 6% 11% 15% 6% 1	2730
	11th to 20th	Night	58% 6% 10% 18% 7% 1	2490
	21st to end	Night	58% 5% 11% 17% 8% 1	2076
March	1st to 10th	Night	51% 4 11% 23% 9% 1	5355
	11th to 20th	Night	38% 7% 14% 26% 13% 1	5090
	21st to end	Night	48% 5% 9% 22% 14% 1	5588
April	1st to 10th	Night	51% 6% 10% 17% 14% 2	2221
	11th to 20th	Night	46% 6% 10% 19% 17% 2	1916
	21st to end	Night	45% 6% 11% 22% 14% 2	1890
May	1st to 10th	Night	56% 7% 8% 14% 13% 2	4150
	11th to 20th	Night	45% 7% 11% 22% 14% 1	4123
	21st to end	Night	39% 7% 12% 25% 16% 2	4528
June	1st to 10th	Night	37% 6% 11% 25% 17% 3	1723
	11th to 20th	Night	35% 8% 12% 25% 17% 3	1600
	21st to end	Night	32% 8% 14% 25% 18% 3	1600
July	1st to 10th	Night	33% 8% 13% 25% 17% 4	3580
	11th to 20th	Night	33% 8% 16% 26% 15% 2	3676
	21st to end	Night	33% 7% 14% 23% 20% 4	4297
August	1st to 10th	Night	37% 8% 12% 26% 15% 2	2904
	11th to 20th	Night	34% 8% 11% 29% 17% 1	2902
	21st to end	Night	32% 8% 12% 29% 17% 2	3304
September	1st to 10th	Night	33% 6% 12% 27% 17% 4	2135
	11th to 20th	Night	27% 7% 10% 28% 26% 2	2200
	21st to end	Night	40% 6% 11% 22% 19% 2	2200
October	1st to 10th	Night	26% 5% 8% 30% 30% 1	3678
	11th to 20th	Night	36% 5% 10% 28% 20% 1	3899
	21st to end	Night	36% 5% 9% 32% 16% 3	4465
November	1st to 10th	Night	41% 5% 12% 24% 17% 2	2666
	11th to 20th	Night	49% 5% 11% 22% 11% 2	2730
	21st to end	Night	59% 5% 11% 18% 6%	2730
December	1st to 10th	Night	58% 6% 12% 18% 6% 1	4380
	11th to 20th	Night	63% 5% 13% 13% 6% 1	4954
	21st to end	Night	72% 6% 10% 9% 4	7074

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	22% 20% 34% 18% 5% 1	330
	11th to 20th	Day	22% 22% 43% 9% 4 1	330
	21st to end	Day	26% 18% 31% 21% 4	363
February	1st to 10th	Day	23% 16% 41% 15% 4 1	330
	11th to 20th	Day	24% 17% 35% 20% 3	330
	21st to end	Day	23% 22% 41% 12% 2	273
March	1st to 10th	Day	24% 15% 39% 17% 5%	389
	11th to 20th	Day	24% 15% 36% 19% 5% 1	540
	21st to end	Day	29% 15% 32% 18% 6% 1	594
April	1st to 10th	Day	21% 16% 32% 21% 9% 1	540
	11th to 20th	Day	22% 17% 31% 18% 8% 3	532
	21st to end	Day	24% 11% 31% 24% 8% 2	540
May	1st to 10th	Day	24% 13% 32% 20% 9% 2	543
	11th to 20th	Day	18% 11% 30% 23% 12% 6%	567
	21st to end	Day	14% 8% 27% 26% 17% 9%	617
June	1st to 10th	Day	12% 7% 29% 31% 16% 4	601
	11th to 20th	Day	13% 6% 30% 28% 19% 4	730
	21st to end	Day	11% 7% 27% 30% 19% 5%	730
July	1st to 10th	Day	9% 4 21% 33% 21% 12%	721
	11th to 20th	Day	8% 4 25% 28% 23% 11%	672
	21st to end	Day	9% 5% 22% 25% 28% 12%	576
August	1st to 10th	Day	10% 5% 15% 29% 26% 15%	526
	11th to 20th	Day	11% 2 17% 34% 23% 12%	519
	21st to end	Day	8% 3 19% 29% 26% 14%	583
September	1st to 10th	Day	14% 5% 16% 28% 22% 15%	530
	11th to 20th	Day	9% 2 15% 24% 31% 19%	530
	21st to end	Day	18% 9% 22% 23% 18% 9%	530
October	1st to 10th	Day	12% 7% 24% 27% 21% 9%	530
	11th to 20th	Day	17% 14% 32% 25% 10% 2	530
	21st to end	Day	20% 15% 37% 21% 6% 1	456
November	1st to 10th	Day	17% 15% 35% 20% 11% 4	330
	11th to 20th	Day	25% 20% 30% 18% 7% 1	330
	21st to end	Day	25% 19% 35% 18% 2	330
December	1st to 10th	Day	19% 20% 36% 17% 7% 1	282
	11th to 20th	Day	21% 21% 37% 17% 3	330
	21st to end	Day	28% 19% 33% 18% 3	363
January	1st to 10th	Night	23% 15% 36% 20% 5%	1050
	11th to 20th	Night	26% 17% 36% 16% 4 1	954
	21st to end	Night	22% 16% 36% 22% 4	924
February	1st to 10th	Night	24% 14% 34% 25% 3	840
	11th to 20th	Night	22% 14% 36% 25% 2	823
	21st to end	Night	24% 17% 38% 18% 2	692
March	1st to 10th	Night	20% 14% 34% 26% 6%	840
	11th to 20th	Night	18% 15% 37% 23% 6% 1	840
	21st to end	Night	22% 14% 31% 26% 7%	924
April	1st to 10th	Night	21% 15% 36% 24% 4	751
	11th to 20th	Night	18% 11% 35% 26% 7% 1	623
	21st to end	Night	20% 8% 34% 29% 8% 1	630
May	1st to 10th	Night	22% 7% 30% 33% 8% 1	630
	11th to 20th	Night	19% 9% 27% 31% 14% 1	621
	21st to end	Night	12% 3 24% 39% 19% 2	683
June	1st to 10th	Night	12% 3 26% 43% 16%	600
	11th to 20th	Night	10% 3 23% 44% 18% 2	600
	21st to end	Night	12% 2 24% 38% 23% 2	600
July	1st to 10th	Night	9% 2 17% 39% 30% 3	585
	11th to 20th	Night	8% 3 19% 40% 25% 4	582
	21st to end	Night	8% 2 14% 43% 31% 2	657
August	1st to 10th	Night	8% 2 14% 43% 30% 3	597
	11th to 20th	Night	9% 2 16% 36% 33% 4	594
	21st to end	Night	8% 2 14% 38% 34% 4	660
September	1st to 10th	Night	13% 4 16% 35% 27% 5%	735
	11th to 20th	Night	10% 2 15% 34% 35% 5%	800
	21st to end	Night	16% 6% 21% 32% 23% 3	800
October	1st to 10th	Night	13% 8% 24% 33% 21% 3	800
	11th to 20th	Night	20% 13% 29% 28% 10% 1	800
	21st to end	Night	23% 12% 30% 27% 7%	880
November	1st to 10th	Night	15% 13% 33% 28% 10% 2	820
	11th to 20th	Night	20% 16% 34% 23% 7% 1	840
	21st to end	Night	27% 11% 34% 23% 5%	840
December	1st to 10th	Night	24% 13% 36% 21% 5%	840
	11th to 20th	Night	26% 13% 37% 21% 4	840
	21st to end	Night	30% 13% 34% 21% 3	1118

Page generated at 2026-05-29 01:53:28. Version ac07

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