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 2024-11-05.

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	12% 6% 2 6% 4 4 4 4 6% 8% 42%	101022
	Night	14% 7% 2 6% 4 4 4 3 5% 7% 42%	97965
Transparency	Day	20% 48% 8% 13% 9% 2	104657
	Night	22% 48% 6% 12% 10% 2	102470
Seeing	Day	15% 6% 23% 29% 21% 6%	15262
	Night	16% 7% 25% 32% 18% 3	24809

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% 6% 2 5% 3 3 4 3 4 5% 50%	2645
	11th to 20th	Day	12% 7% 2 6% 5% 3 4 3 4 6% 47%	2840
	21st to end	Day	12% 9% 3 8% 4 4 4 4 5% 6% 40%	3124
February	1st to 10th	Day	12% 9% 3 6% 5% 5% 5% 4 6% 7% 40%	1710
	11th to 20th	Day	20% 7% 2 4 3 3 3 4 5% 6% 44%	1812
	21st to end	Day	17% 8% 2 5% 4 4 5% 3 7% 8% 38%	1570
March	1st to 10th	Day	21% 8% 3 7% 4 3 4 3 4 7% 36%	3304
	11th to 20th	Day	10% 5% 2 4 3 4 3 3 4 7% 55%	3480
	21st to end	Day	17% 8% 2 5% 3 3 4 3 5% 7% 43%	3937
April	1st to 10th	Day	12% 5% 2 5% 4 3 4 3 5% 7% 50%	2280
	11th to 20th	Day	9% 6% 2 6% 4 4 4 4 6% 6% 50%	2254
	21st to end	Day	13% 5% 2 6% 5% 3 4 4 6% 7% 46%	2280
May	1st to 10th	Day	14% 7% 3 8% 5% 4 5% 4 7% 10% 34%	3765
	11th to 20th	Day	19% 8% 3 7% 5% 4 5% 3 6% 8% 34%	4247
	21st to end	Day	8% 5% 2 5% 3 4 4 4 6% 11% 47%	4823
June	1st to 10th	Day	10% 5% 1 4 4 5% 4 5% 8% 11% 43%	2660
	11th to 20th	Day	10% 5% 2 4 4 4 5% 4 7% 11% 44%	2660
	21st to end	Day	6% 3 2 5% 5% 5% 5% 5% 8% 12% 43%	2660
July	1st to 10th	Day	6% 4 2 6% 4 5% 6% 5% 9% 13% 41%	4440
	11th to 20th	Day	11% 6% 3 8% 5% 5% 5% 4 7% 11% 36%	4231
	21st to end	Day	7% 7% 3 7% 6% 6% 7% 6% 7% 10% 35%	4466
August	1st to 10th	Day	13% 8% 4 7% 5% 6% 6% 5% 8% 11% 27%	4074
	11th to 20th	Day	9% 5% 2 7% 5% 6% 6% 5% 8% 9% 38%	3730
	21st to end	Day	8% 5% 2 4 4 4 5% 4 6% 11% 47%	4180
September	1st to 10th	Day	14% 5% 2 5% 4 4 4 4 6% 9% 43%	2280
	11th to 20th	Day	15% 5% 2 7% 4 4 5% 4 5% 7% 43%	2280
	21st to end	Day	19% 7% 3 7% 4 4 4 3 5% 7% 38%	2036
October	1st to 10th	Day	17% 6% 2 6% 4 3 3 3 5% 5% 47%	1900
	11th to 20th	Day	12% 5% 2 6% 3 3 4 2 4 6% 51%	1900
	21st to end	Day	11% 6% 2 5% 5% 4 4 2 4 6% 51%	2090
November	1st to 10th	Day	14% 5% 2 5% 3 4 3 3 4 7% 49%	1799
	11th to 20th	Day	14% 7% 3 4 4 3 3 2 4 7% 50%	1710
	21st to end	Day	15% 5% 2 4 4 4 3 3 5% 6% 51%	1653
December	1st to 10th	Day	17% 6% 2 5% 4 4 4 4 5% 6% 42%	1520
	11th to 20th	Day	15% 6% 2 4 4 2 3 3 4 4 51%	1910
	21st to end	Day	15% 6% 3 6% 3 4 3 3 6% 7% 43%	2772
January	1st to 10th	Night	12% 7% 3 6% 4 4 4 3 5% 7% 45%	4297
	11th to 20th	Night	15% 8% 3 7% 5% 4 3 3 5% 6% 43%	4120
	21st to end	Night	16% 8% 3 8% 4 4 3 3 5% 5% 42%	4532
February	1st to 10th	Night	16% 6% 2 6% 4 4 4 3 5% 7% 43%	2470
	11th to 20th	Night	20% 8% 2 5% 4 3 4 3 4 7% 40%	2252
	21st to end	Night	16% 8% 2 6% 3 4 3 2 4 5% 46%	1884
March	1st to 10th	Night	23% 8% 3 7% 4 4 4 3 5% 5% 34%	3546
	11th to 20th	Night	14% 6% 2 5% 4 3 3 3 5% 6% 49%	3480
	21st to end	Night	17% 9% 3 6% 3 3 3 2 4 5% 46%	3694
April	1st to 10th	Night	13% 7% 2 5% 5% 4 4 5% 6% 6% 43%	1900
	11th to 20th	Night	11% 6% 2 6% 3 3 5% 2 5% 7% 49%	1875
	21st to end	Night	14% 6% 2 5% 4 4 5% 3 5% 7% 45%	1900
May	1st to 10th	Night	16% 9% 3 8% 4 5% 5% 4 6% 8% 32%	3130
	11th to 20th	Night	22% 8% 3 6% 5% 4 4 3 6% 7% 33%	2675
	21st to end	Night	10% 5% 3 6% 4 4 5% 4 6% 10% 41%	2732
June	1st to 10th	Night	12% 5% 1 5% 5% 4 6% 4 7% 11% 40%	1520
	11th to 20th	Night	8% 5% 2 6% 5% 5% 5% 4 7% 10% 42%	1520
	21st to end	Night	7% 4 2 6% 7% 5% 4 6% 8% 8% 43%	1520
July	1st to 10th	Night	7% 5% 3 7% 5% 5% 7% 5% 7% 12% 38%	2520
	11th to 20th	Night	8% 6% 3 7% 5% 5% 5% 6% 8% 10% 37%	2710
	21st to end	Night	12% 9% 3 9% 6% 5% 6% 5% 7% 8% 30%	3087
August	1st to 10th	Night	15% 8% 3 8% 5% 5% 6% 4 7% 10% 30%	2825
	11th to 20th	Night	9% 7% 3 8% 5% 5% 4 4 5% 9% 40%	3094
	21st to end	Night	9% 5% 2 5% 4 4 4 4 7% 10% 45%	3476
September	1st to 10th	Night	12% 5% 2 6% 4 5% 4 3 6% 8% 45%	1900
	11th to 20th	Night	12% 8% 3 7% 4 4 4 3 5% 6% 44%	1900
	21st to end	Night	18% 8% 3 7% 4 5% 4 3 4 6% 36%	2140
October	1st to 10th	Night	16% 5% 2 6% 3 4 4 3 5% 6% 46%	2280
	11th to 20th	Night	15% 7% 2 5% 3 3 3 3 5% 6% 49%	2280
	21st to end	Night	13% 5% 2 5% 3 4 4 3 4 6% 51%	2508
November	1st to 10th	Night	14% 6% 2 5% 4 3 3 3 5% 7% 47%	2377
	11th to 20th	Night	15% 6% 2 5% 4 3 4 3 5% 6% 47%	2470
	21st to end	Night	12% 4 2 5% 4 4 4 3 6% 6% 50%	2522
December	1st to 10th	Night	17% 7% 3 6% 5% 4 4 4 4 6% 40%	2660
	11th to 20th	Night	17% 7% 2 5% 3 3 3 3 5% 6% 47%	3285
	21st to end	Night	13% 7% 2 6% 4 3 4 4 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	22% 38% 4 21% 13% 2	2646
	11th to 20th	Day	23% 38% 5% 13% 19% 3	2840
	21st to end	Day	28% 42% 7% 13% 9% 1	3124
February	1st to 10th	Day	15% 65% 5% 10% 4 1	1710
	11th to 20th	Day	16% 65% 4 7% 6% 3	1821
	21st to end	Day	15% 66% 5% 6% 5% 2	1570
March	1st to 10th	Day	35% 44% 7% 6% 7% 3	3304
	11th to 20th	Day	13% 42% 6% 15% 19% 6%	3480
	21st to end	Day	25% 42% 7% 10% 13% 2	3937
April	1st to 10th	Day	13% 66% 4 8% 8% 1	2280
	11th to 20th	Day	12% 66% 4 9% 7% 1	2254
	21st to end	Day	13% 66% 5% 9% 5% 2	2280
May	1st to 10th	Day	28% 47% 10% 11% 3 1	3800
	11th to 20th	Day	28% 46% 10% 14% 3	4251
	21st to end	Day	15% 44% 11% 17% 10% 2	4837
June	1st to 10th	Day	12% 67% 6% 9% 5% 1	2660
	11th to 20th	Day	9% 67% 7% 9% 7%	2660
	21st to end	Day	10% 66% 7% 11% 6%	2660
July	1st to 10th	Day	21% 41% 19% 11% 6% 2	4370
	11th to 20th	Day	30% 38% 17% 12% 2	4158
	21st to end	Day	31% 40% 8% 12% 9% 1	4324
August	1st to 10th	Day	36% 38% 12% 13% 2	4061
	11th to 20th	Day	25% 39% 10% 18% 9%	3766
	21st to end	Day	17% 38% 9% 22% 13%	4180
September	1st to 10th	Day	16% 63% 7% 8% 5% 2	2280
	11th to 20th	Day	17% 62% 6% 8% 6% 2	2280
	21st to end	Day	23% 61% 4 9% 3	2036
October	1st to 10th	Day	18% 37% 6% 20% 17% 2	3160
	11th to 20th	Day	12% 36% 4 12% 30% 6%	3140
	21st to end	Day	9% 36% 6% 21% 18% 9%	3428
November	1st to 10th	Day	17% 58% 5% 12% 7% 2	1799
	11th to 20th	Day	15% 60% 5% 7% 10% 3	1710
	21st to end	Day	15% 60% 3 11% 9% 1	1653
December	1st to 10th	Day	21% 61% 4 7% 5% 2	1520
	11th to 20th	Day	17% 48% 4 15% 11% 5%	1906
	21st to end	Day	25% 39% 8% 19% 9%	2772
January	1st to 10th	Night	24% 39% 6% 15% 13% 3	4297
	11th to 20th	Night	27% 38% 3 15% 15% 2	4120
	21st to end	Night	28% 42% 5% 11% 10% 3	4532
February	1st to 10th	Night	14% 66% 5% 9% 5% 1	2470
	11th to 20th	Night	18% 64% 3 7% 6% 2	2254
	21st to end	Night	15% 65% 2 10% 6% 2	1884
March	1st to 10th	Night	37% 43% 6% 8% 5% 1	3546
	11th to 20th	Night	18% 41% 4 14% 17% 6%	3480
	21st to end	Night	26% 40% 4 16% 11% 4	3694
April	1st to 10th	Night	15% 66% 4 6% 8% 1	1900
	11th to 20th	Night	13% 67% 5% 8% 7% 1	1875
	21st to end	Night	14% 66% 5% 7% 6% 1	1900
May	1st to 10th	Night	30% 46% 9% 11% 4	3160
	11th to 20th	Night	29% 46% 8% 15% 2	2676
	21st to end	Night	20% 46% 12% 14% 8%	2739
June	1st to 10th	Night	15% 68% 6% 6% 5% 1	1520
	11th to 20th	Night	11% 66% 7% 9% 6%	1520
	21st to end	Night	12% 65% 6% 10% 7% 1	1520
July	1st to 10th	Night	27% 42% 12% 12% 6% 1	2480
	11th to 20th	Night	29% 39% 16% 14% 2	2661
	21st to end	Night	37% 38% 7% 10% 8%	2988
August	1st to 10th	Night	35% 38% 12% 13% 2	2814
	11th to 20th	Night	25% 38% 11% 19% 7%	3124
	21st to end	Night	19% 37% 5% 19% 19% 1	3476
September	1st to 10th	Night	15% 63% 9% 9% 4 1	1900
	11th to 20th	Night	17% 61% 5% 8% 7% 2	1900
	21st to end	Night	24% 61% 4 8% 3	2140
October	1st to 10th	Night	24% 37% 6% 16% 16% 1	3800
	11th to 20th	Night	15% 36% 3 13% 26% 7%	3779
	21st to end	Night	9% 36% 3 23% 20% 9%	4120
November	1st to 10th	Night	19% 58% 4 10% 7% 1	2377
	11th to 20th	Night	15% 60% 4 7% 9% 5%	2470
	21st to end	Night	12% 61% 4 11% 10% 1	2522
December	1st to 10th	Night	23% 61% 4 8% 3 1	2660
	11th to 20th	Night	19% 49% 4 12% 11% 3	3288
	21st to end	Night	24% 41% 10% 16% 9% 1	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	460
	11th to 20th	Day	10% 8% 31% 36% 12% 4	452
	21st to end	Day	14% 7% 30% 33% 15% 1	460
May	1st to 10th	Day	16% 6% 27% 33% 15% 2	463
	11th to 20th	Day	18% 4 19% 34% 22% 3	487
	21st to end	Day	17% 3 15% 32% 25% 8%	529
June	1st to 10th	Day	11% 3 14% 35% 28% 9%	490
	11th to 20th	Day	12% 3 12% 33% 29% 11%	490
	21st to end	Day	9% 2 12% 36% 33% 8%	490
July	1st to 10th	Day	9% 1 6% 29% 42% 13%	485
	11th to 20th	Day	8% 1 6% 26% 46% 13%	484
	21st to end	Day	9% 1 8% 34% 37% 11%	532
August	1st to 10th	Day	13% 2 9% 31% 34% 10%	486
	11th to 20th	Day	13% 2 8% 30% 34% 12%	479
	21st to end	Day	10% 3 10% 26% 37% 15%	539
September	1st to 10th	Day	14% 2 11% 27% 31% 15%	490
	11th to 20th	Day	15% 2 15% 27% 28% 12%	490
	21st to end	Day	21% 5% 19% 28% 22% 5%	490
October	1st to 10th	Day	19% 3 17% 25% 26% 10%	490
	11th to 20th	Day	12% 9% 20% 33% 22% 4	490
	21st to end	Day	14% 6% 27% 31% 16% 7%	539
November	1st to 10th	Day	16% 6% 26% 29% 17% 6%	425
	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% 31% 36% 13%	751
	21st to end	Night	15% 7% 28% 39% 11% 1	760
May	1st to 10th	Night	14% 8% 28% 37% 11% 1	760
	11th to 20th	Night	14% 4 21% 42% 17% 2	489
	21st to end	Night	13% 3 15% 35% 29% 4	411
June	1st to 10th	Night	12% 1 16% 41% 25% 5%	380
	11th to 20th	Night	9% 2 14% 42% 28% 4	380
	21st to end	Night	9% 2 11% 42% 32% 3	380
July	1st to 10th	Night	8% 1 8% 42% 36% 5%	370
	11th to 20th	Night	8% 1 5% 33% 45% 7%	479
	21st to end	Night	10% 2 8% 43% 33% 4	624
August	1st to 10th	Night	11% 2 10% 38% 34% 5%	567
	11th to 20th	Night	13% 1 8% 36% 36% 6%	747
	21st to end	Night	11% 1 10% 30% 39% 8%	836
September	1st to 10th	Night	14% 1 10% 34% 31% 9%	760
	11th to 20th	Night	14% 2 12% 31% 35% 6%	760
	21st to end	Night	23% 4 15% 31% 25% 3	760
October	1st to 10th	Night	18% 4 15% 29% 28% 7%	760
	11th to 20th	Night	17% 7% 23% 31% 19% 3	760
	21st to end	Night	15% 8% 24% 28% 20% 4	836
November	1st to 10th	Night	18% 7% 22% 30% 18% 4	760
	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 2024-11-03 02:11:25. Version ac07

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