Grundland Astronomy Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Grundland Astronomy Park clear sky chart from 2005-11-06 to 2024-04-10.

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	13% 6% 2 5% 5% 3 4 5% 6% 8% 44%	83255
	Night	14% 6% 2 5% 5% 3 4 4 5% 7% 43%	85525
Transparency	Day	36% 8% 13% 23% 16% 3	82967
	Night	39% 7% 12% 22% 17% 3	85333
Seeing	Day	15% 6% 23% 29% 20% 6%	14426
	Night	16% 7% 26% 31% 17% 3	24125

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% 5% 2 4 4 2 4 4 4 5% 50%	2645
	11th to 20th	Day	12% 7% 3 5% 6% 2 3 4 4 6% 47%	2840
	21st to end	Day	12% 8% 3 7% 6% 3 4 5% 5% 6% 40%	3124
February	1st to 10th	Day	12% 8% 3 4 6% 3 5% 5% 6% 7% 40%	1710
	11th to 20th	Day	20% 6% 2 4 3 2 3 4 5% 6% 44%	1812
	21st to end	Day	17% 8% 2 4 4 3 6% 4 7% 8% 38%	1570
March	1st to 10th	Day	21% 8% 3 6% 5% 3 3 4 4 7% 37%	3304
	11th to 20th	Day	10% 5% 2 4 4 3 3 4 4 7% 55%	3480
	21st to end	Day	17% 8% 2 4 4 2 4 4 5% 7% 43%	3937
April	1st to 10th	Day	12% 5% 2 4 4 3 3 4 4 7% 51%	2270
	11th to 20th	Day	9% 5% 2 5% 4 3 4 5% 6% 7% 49%	2134
	21st to end	Day	13% 4 3 5% 5% 2 4 5% 6% 7% 46%	2160
May	1st to 10th	Day	14% 6% 3 4 4 2 3 5% 6% 9% 44%	2160
	11th to 20th	Day	14% 6% 2 5% 5% 3 4 4 6% 9% 41%	2383
	21st to end	Day	12% 6% 2 4 4 3 5% 5% 6% 9% 44%	2725
June	1st to 10th	Day	10% 4 2 3 5% 3 4 6% 7% 11% 43%	2520
	11th to 20th	Day	10% 5% 2 4 5% 3 5% 4 7% 11% 43%	2520
	21st to end	Day	7% 3 2 4 6% 4 6% 6% 8% 13% 42%	2520
July	1st to 10th	Day	8% 3 1 5% 5% 4 5% 6% 8% 12% 43%	2520
	11th to 20th	Day	7% 4 2 5% 5% 4 5% 6% 7% 13% 42%	2409
	21st to end	Day	6% 3 2 4 5% 5% 7% 8% 9% 12% 40%	2547
August	1st to 10th	Day	9% 4 3 5% 6% 4 6% 7% 8% 11% 37%	2310
	11th to 20th	Day	10% 6% 2 6% 6% 5% 6% 5% 8% 9% 37%	2126
	21st to end	Day	10% 7% 2 5% 5% 3 6% 5% 6% 10% 41%	2376
September	1st to 10th	Day	14% 5% 2 4 5% 3 5% 4 6% 9% 43%	2160
	11th to 20th	Day	14% 5% 3 6% 5% 3 4 5% 5% 7% 44%	2160
	21st to end	Day	18% 6% 3 6% 5% 3 4 4 5% 7% 39%	1930
October	1st to 10th	Day	18% 6% 2 5% 4 2 3 4 5% 5% 47%	1800
	11th to 20th	Day	13% 6% 2 5% 5% 2 4 3 3 7% 50%	1800
	21st to end	Day	12% 6% 2 5% 6% 3 4 3 4 6% 50%	1980
November	1st to 10th	Day	14% 5% 3 4 4 3 3 4 4 7% 49%	1758
	11th to 20th	Day	14% 6% 3 4 4 2 4 3 4 7% 50%	1710
	21st to end	Day	15% 4 2 4 4 3 3 4 5% 6% 51%	1653
December	1st to 10th	Day	17% 6% 2 5% 4 3 4 5% 5% 7% 42%	1520
	11th to 20th	Day	15% 6% 2 3 5% 1 3 3 5% 5% 52%	1910
	21st to end	Day	15% 6% 3 5% 4 3 4 4 5% 7% 43%	2772
January	1st to 10th	Night	12% 7% 3 5% 5% 3 4 4 5% 7% 45%	4297
	11th to 20th	Night	15% 7% 3 6% 6% 3 4 4 4 6% 43%	4120
	21st to end	Night	16% 7% 3 7% 5% 3 4 3 4 6% 42%	4532
February	1st to 10th	Night	16% 6% 3 5% 5% 3 4 4 4 7% 43%	2470
	11th to 20th	Night	20% 8% 2 4 5% 2 4 4 4 7% 41%	2252
	21st to end	Night	17% 7% 2 5% 4 3 4 3 3 6% 46%	1884
March	1st to 10th	Night	23% 8% 3 6% 5% 3 4 4 5% 5% 34%	3546
	11th to 20th	Night	14% 6% 2 4 4 3 3 4 5% 6% 49%	3480
	21st to end	Night	18% 9% 3 5% 4 2 3 3 4 5% 47%	3694
April	1st to 10th	Night	13% 7% 2 5% 5% 3 4 5% 6% 6% 44%	1900
	11th to 20th	Night	12% 5% 3 5% 4 2 3 4 5% 7% 50%	1775
	21st to end	Night	14% 6% 2 4 4 4 5% 5% 4 7% 45%	1800
May	1st to 10th	Night	14% 6% 2 5% 6% 3 5% 6% 6% 9% 38%	1800
	11th to 20th	Night	13% 5% 2 5% 5% 4 5% 5% 7% 9% 40%	1525
	21st to end	Night	12% 5% 3 5% 5% 3 5% 4 5% 9% 42%	1550
June	1st to 10th	Night	12% 5% 2 4 5% 3 5% 5% 7% 11% 42%	1440
	11th to 20th	Night	9% 4 3 6% 5% 4 5% 4 7% 10% 41%	1440
	21st to end	Night	7% 4 3 6% 7% 4 5% 7% 8% 9% 42%	1440
July	1st to 10th	Night	8% 5% 3 6% 6% 3 6% 6% 6% 11% 43%	1440
	11th to 20th	Night	7% 4 2 4 5% 3 7% 7% 8% 10% 43%	1546
	21st to end	Night	8% 6% 2 6% 5% 3 7% 6% 9% 11% 37%	1771
August	1st to 10th	Night	7% 5% 3 6% 6% 4 6% 7% 8% 11% 38%	1611
	11th to 20th	Night	10% 6% 3 7% 7% 4 5% 6% 5% 10% 38%	1771
	21st to end	Night	10% 5% 3 6% 6% 4 5% 5% 8% 10% 38%	1980
September	1st to 10th	Night	12% 5% 2 5% 5% 3 5% 4 7% 8% 44%	1800
	11th to 20th	Night	11% 7% 3 6% 5% 3 5% 3 5% 6% 45%	1800
	21st to end	Night	18% 7% 3 6% 5% 4 5% 4 4 7% 37%	2026
October	1st to 10th	Night	16% 5% 2 5% 4 3 4 4 5% 6% 46%	2160
	11th to 20th	Night	15% 7% 2 4 4 2 3 3 5% 7% 48%	2160
	21st to end	Night	14% 5% 2 4 5% 3 4 3 4 6% 49%	2376
November	1st to 10th	Night	15% 6% 2 5% 4 2 3 4 5% 7% 47%	2318
	11th to 20th	Night	15% 5% 2 4 4 2 4 4 4 6% 47%	2470
	21st to end	Night	12% 4 2 5% 4 3 5% 4 5% 6% 50%	2522
December	1st to 10th	Night	17% 7% 3 6% 5% 3 5% 5% 4 6% 40%	2660
	11th to 20th	Night	17% 6% 2 4 4 3 3 4 5% 6% 47%	3285
	21st to end	Night	13% 7% 3 5% 5% 3 4 5% 6% 7% 44%	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	35% 5% 9% 31% 18% 2	2646
	11th to 20th	Day	37% 5% 9% 21% 24% 4	2840
	21st to end	Day	43% 7% 11% 21% 16% 2	3124
February	1st to 10th	Day	42% 6% 12% 24% 13% 3	1710
	11th to 20th	Day	40% 5% 10% 21% 19% 5%	1821
	21st to end	Day	43% 7% 13% 17% 15% 5%	1570
March	1st to 10th	Day	47% 6% 11% 17% 14% 4	3304
	11th to 20th	Day	27% 7% 11% 23% 25% 8%	3480
	21st to end	Day	41% 8% 13% 18% 18% 3	3937
April	1st to 10th	Day	32% 6% 12% 23% 21% 5%	2270
	11th to 20th	Day	32% 7% 13% 23% 20% 5%	2134
	21st to end	Day	36% 7% 12% 24% 16% 5%	2160
May	1st to 10th	Day	36% 8% 16% 22% 15% 3	2160
	11th to 20th	Day	39% 9% 16% 24% 10% 2	2387
	21st to end	Day	34% 10% 16% 26% 13% 1	2725
June	1st to 10th	Day	31% 10% 18% 26% 13% 1	2520
	11th to 20th	Day	33% 10% 17% 23% 14% 2	2520
	21st to end	Day	32% 12% 18% 23% 14% 1	2520
July	1st to 10th	Day	31% 12% 19% 23% 14% 2	2450
	11th to 20th	Day	29% 13% 23% 24% 10% 1	2336
	21st to end	Day	30% 14% 19% 21% 14% 1	2405
August	1st to 10th	Day	35% 12% 19% 26% 8% 1	2297
	11th to 20th	Day	39% 11% 16% 23% 11% 1	2126
	21st to end	Day	35% 11% 17% 20% 14% 3	2376
September	1st to 10th	Day	36% 11% 16% 18% 16% 4	2160
	11th to 20th	Day	38% 7% 12% 22% 19% 2	2160
	21st to end	Day	45% 8% 10% 20% 15% 2	1930
October	1st to 10th	Day	39% 6% 11% 23% 19% 3	1800
	11th to 20th	Day	35% 5% 9% 27% 20% 4	1800
	21st to end	Day	37% 4 8% 23% 22% 5%	1980
November	1st to 10th	Day	36% 6% 11% 25% 19% 3	1758
	11th to 20th	Day	35% 5% 13% 20% 21% 5%	1710
	21st to end	Day	35% 5% 10% 26% 21% 3	1653
December	1st to 10th	Day	41% 6% 13% 22% 15% 3	1520
	11th to 20th	Day	36% 6% 8% 26% 17% 6%	1906
	21st to end	Day	39% 6% 12% 28% 15% 1	2772
January	1st to 10th	Night	37% 6% 10% 24% 19% 4	4297
	11th to 20th	Night	42% 5% 8% 22% 20% 3	4120
	21st to end	Night	43% 7% 9% 19% 17% 4	4532
February	1st to 10th	Night	42% 5% 11% 24% 16% 3	2470
	11th to 20th	Night	45% 5% 8% 22% 17% 5%	2254
	21st to end	Night	41% 5% 8% 22% 18% 6%	1884
March	1st to 10th	Night	50% 7% 10% 17% 14% 2	3546
	11th to 20th	Night	35% 6% 8% 21% 23% 7%	3480
	21st to end	Night	42% 5% 8% 24% 16% 5%	3694
April	1st to 10th	Night	39% 7% 11% 17% 22% 4	1900
	11th to 20th	Night	33% 6% 12% 23% 20% 6%	1775
	21st to end	Night	39% 6% 12% 23% 17% 4	1800
May	1st to 10th	Night	39% 10% 14% 22% 13% 3	1800
	11th to 20th	Night	39% 11% 16% 21% 12% 2	1526
	21st to end	Night	39% 9% 17% 23% 13% 1	1551
June	1st to 10th	Night	36% 10% 17% 22% 14% 1	1440
	11th to 20th	Night	36% 12% 18% 20% 13% 1	1440
	21st to end	Night	35% 11% 16% 22% 14% 2	1440
July	1st to 10th	Night	35% 11% 18% 22% 12% 3	1400
	11th to 20th	Night	29% 13% 20% 28% 10% 1	1497
	21st to end	Night	34% 13% 17% 24% 12%	1672
August	1st to 10th	Night	37% 14% 20% 21% 8%	1600
	11th to 20th	Night	39% 11% 18% 20% 12%	1771
	21st to end	Night	37% 12% 18% 21% 11% 2	1980
September	1st to 10th	Night	36% 10% 16% 21% 15% 3	1800
	11th to 20th	Night	39% 6% 10% 23% 20% 2	1800
	21st to end	Night	46% 8% 11% 18% 15% 2	2026
October	1st to 10th	Night	38% 6% 10% 24% 19% 3	2160
	11th to 20th	Night	37% 5% 10% 24% 21% 4	2160
	21st to end	Night	37% 6% 8% 24% 21% 6%	2376
November	1st to 10th	Night	38% 6% 11% 22% 20% 3	2318
	11th to 20th	Night	38% 5% 10% 20% 19% 8%	2470
	21st to end	Night	33% 6% 10% 26% 22% 3	2522
December	1st to 10th	Night	45% 7% 11% 20% 15% 3	2660
	11th to 20th	Night	38% 6% 11% 22% 19% 5%	3288
	21st to end	Night	36% 7% 14% 25% 15% 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	19% 13% 36% 25% 7%	216
	11th to 20th	Day	17% 15% 41% 24% 3	270
	21st to end	Day	19% 8% 37% 30% 6%	297
February	1st to 10th	Day	16% 13% 31% 31% 7% 1	270
	11th to 20th	Day	25% 10% 40% 20% 3	420
	21st to end	Day	20% 10% 39% 26% 4 1	382
March	1st to 10th	Day	13% 14% 38% 28% 7%	460
	11th to 20th	Day	17% 13% 36% 27% 7% 2	460
	21st to end	Day	16% 10% 35% 31% 8%	506
April	1st to 10th	Day	13% 13% 37% 27% 9% 1	457
	11th to 20th	Day	10% 7% 32% 35% 11% 4	412
	21st to end	Day	14% 7% 31% 32% 15% 1	420
May	1st to 10th	Day	16% 6% 29% 33% 14% 2	423
	11th to 20th	Day	18% 4 19% 34% 23% 4	447
	21st to end	Day	19% 3 14% 31% 26% 8%	485
June	1st to 10th	Day	12% 3 14% 33% 29% 9%	450
	11th to 20th	Day	13% 4 13% 34% 28% 9%	450
	21st to end	Day	8% 2 13% 38% 31% 8%	450
July	1st to 10th	Day	10% 1 6% 30% 41% 12%	445
	11th to 20th	Day	6% 1 7% 27% 45% 14%	444
	21st to end	Day	9% 1 9% 34% 37% 10%	488
August	1st to 10th	Day	11% 3 8% 33% 34% 11%	446
	11th to 20th	Day	13% 2 9% 29% 34% 13%	439
	21st to end	Day	11% 3 11% 27% 36% 14%	495
September	1st to 10th	Day	14% 2 11% 27% 31% 15%	450
	11th to 20th	Day	14% 3 14% 28% 30% 11%	450
	21st to end	Day	21% 5% 20% 27% 22% 5%	450
October	1st to 10th	Day	20% 4 17% 25% 25% 9%	450
	11th to 20th	Day	14% 8% 20% 33% 21% 4	450
	21st to end	Day	15% 6% 28% 32% 14% 5%	495
November	1st to 10th	Day	16% 6% 26% 29% 16% 6%	408
	11th to 20th	Day	17% 11% 31% 26% 12% 3	370
	21st to end	Day	17% 13% 24% 27% 16% 3	313
December	1st to 10th	Day	23% 3 43% 21% 8% 2	180
	11th to 20th	Day	18% 7% 37% 26% 13%	180
	21st to end	Day	20% 8% 33% 24% 15% 1	198
January	1st to 10th	Night	16% 15% 36% 26% 7%	760
	11th to 20th	Night	19% 12% 34% 28% 7%	760
	21st to end	Night	21% 11% 36% 30% 3	836
February	1st to 10th	Night	20% 6% 40% 29% 5%	760
	11th to 20th	Night	23% 12% 41% 20% 3	743
	21st to end	Night	20% 11% 35% 28% 5%	628
March	1st to 10th	Night	16% 9% 37% 30% 8%	760
	11th to 20th	Night	21% 9% 38% 25% 7% 1	760
	21st to end	Night	18% 8% 36% 31% 6%	836
April	1st to 10th	Night	17% 9% 38% 28% 7% 1	760
	11th to 20th	Night	13% 7% 30% 37% 13%	711
	21st to end	Night	16% 7% 28% 38% 11% 1	720
May	1st to 10th	Night	14% 9% 28% 37% 11% 1	720
	11th to 20th	Night	14% 4 21% 43% 17% 2	464
	21st to end	Night	14% 3 15% 34% 30% 4	389
June	1st to 10th	Night	12% 1 16% 40% 26% 5%	360
	11th to 20th	Night	10% 2 15% 42% 27% 4	360
	21st to end	Night	9% 2 12% 43% 31% 3	360
July	1st to 10th	Night	8% 1 8% 43% 35% 4	350
	11th to 20th	Night	8% 1 6% 34% 44% 7%	453
	21st to end	Night	9% 2 8% 42% 34% 4	591
August	1st to 10th	Night	10% 2 10% 39% 34% 5%	537
	11th to 20th	Night	13% 1 8% 35% 36% 6%	707
	21st to end	Night	12% 1 11% 30% 38% 8%	792
September	1st to 10th	Night	15% 1 10% 33% 32% 10%	720
	11th to 20th	Night	13% 2 13% 31% 35% 6%	720
	21st to end	Night	23% 4 15% 32% 24% 2	720
October	1st to 10th	Night	17% 4 16% 28% 27% 7%	720
	11th to 20th	Night	18% 7% 22% 32% 19% 2	720
	21st to end	Night	16% 9% 25% 27% 19% 3	792
November	1st to 10th	Night	19% 7% 23% 29% 17% 5%	740
	11th to 20th	Night	17% 9% 30% 28% 14% 1	760
	21st to end	Night	14% 10% 28% 31% 14% 2	760
December	1st to 10th	Night	21% 8% 36% 23% 11% 1	760
	11th to 20th	Night	19% 8% 36% 28% 9%	760
	21st to end	Night	19% 9% 31% 32% 9%	836

Page generated at 2024-04-07 09:28:13. Version ac07

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