Grieser Field
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Grieser Field clear sky chart from 2005-11-06 to 2025-08-05.

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	15% 10% 4 8% 5% 5% 5% 4 5% 7% 33%	125279
	Night	15% 10% 4 8% 5% 4 4 3 5% 6% 34%	122774
Transparency	Day	49% 4 10% 23% 13% 2	128937
	Night	50% 3 10% 22% 13% 2	127185
Seeing	Day	22% 12% 28% 21% 12% 5%	15795
	Night	22% 10% 25% 28% 14% 2	26022

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	16% 21% 7% 15% 6% 4 3 2 4 5% 18%	4056
	11th to 20th	Day	14% 21% 9% 11% 8% 5% 4 3 3 4 19%	4060
	21st to end	Day	21% 18% 6% 10% 7% 6% 4 3 4 5% 18%	4466
February	1st to 10th	Day	22% 14% 4 9% 5% 4 3 3 4 5% 25%	1800
	11th to 20th	Day	18% 15% 5% 12% 4 3 4 3 4 7% 25%	1862
	21st to end	Day	18% 14% 4 10% 4 4 3 2 4 5% 31%	1650
March	1st to 10th	Day	17% 15% 5% 9% 5% 4 4 3 4 5% 30%	4835
	11th to 20th	Day	12% 8% 3 7% 4 5% 4 4 5% 6% 42%	4980
	21st to end	Day	18% 9% 3 8% 6% 5% 4 3 5% 6% 32%	5465
April	1st to 10th	Day	15% 13% 3 8% 6% 5% 5% 3 6% 5% 31%	2208
	11th to 20th	Day	16% 9% 3 7% 5% 4 5% 4 5% 6% 37%	2525
	21st to end	Day	17% 8% 3 7% 4 5% 5% 4 5% 7% 34%	2600
May	1st to 10th	Day	19% 9% 3 9% 6% 5% 5% 4 6% 7% 26%	5862
	11th to 20th	Day	19% 10% 3 8% 5% 5% 5% 4 6% 8% 29%	5861
	21st to end	Day	16% 7% 3 6% 4 5% 5% 5% 7% 8% 33%	6433
June	1st to 10th	Day	12% 7% 2 7% 5% 5% 5% 5% 7% 9% 36%	2600
	11th to 20th	Day	11% 6% 3 7% 7% 5% 4 5% 7% 10% 35%	2600
	21st to end	Day	11% 6% 2 6% 5% 5% 5% 5% 8% 11% 36%	2600
July	1st to 10th	Day	9% 6% 2 7% 4 6% 5% 4 5% 9% 42%	5900
	11th to 20th	Day	11% 7% 3 7% 5% 5% 6% 5% 7% 10% 34%	5900
	21st to end	Day	11% 8% 3 7% 6% 5% 6% 5% 7% 9% 34%	6424
August	1st to 10th	Day	9% 6% 3 8% 5% 6% 5% 5% 7% 10% 36%	4156
	11th to 20th	Day	9% 6% 3 7% 5% 5% 5% 5% 8% 10% 38%	4044
	21st to end	Day	6% 4 2 6% 4 5% 6% 4 6% 10% 48%	4441
September	1st to 10th	Day	15% 5% 2 5% 4 4 3 3 6% 8% 47%	2133
	11th to 20th	Day	9% 6% 2 6% 4 3 5% 4 6% 8% 48%	2090
	21st to end	Day	19% 8% 3 7% 4 3 3 4 4 6% 41%	2090
October	1st to 10th	Day	13% 6% 2 7% 4 3 5% 3 6% 8% 43%	1986
	11th to 20th	Day	15% 6% 3 6% 5% 4 4 4 4 7% 41%	1900
	21st to end	Day	21% 10% 2 6% 4 4 4 3 4 6% 37%	2090
November	1st to 10th	Day	11% 7% 3 6% 4 4 3 4 4 6% 48%	1786
	11th to 20th	Day	16% 14% 3 7% 4 4 4 3 5% 6% 34%	1800
	21st to end	Day	17% 13% 5% 8% 6% 4 4 3 4 6% 31%	1780
December	1st to 10th	Day	20% 13% 4 15% 5% 4 4 3 3 4 26%	2600
	11th to 20th	Day	25% 16% 5% 10% 4 3 3 2 4 5% 22%	3230
	21st to end	Day	21% 20% 4 11% 5% 5% 5% 3 5% 5% 16%	4466
January	1st to 10th	Night	15% 17% 8% 19% 6% 5% 3 3 4 4 17%	5889
	11th to 20th	Night	16% 16% 6% 13% 9% 6% 6% 3 4 4 17%	5900
	21st to end	Night	21% 13% 6% 11% 5% 3 3 2 3 5% 27%	6490
February	1st to 10th	Night	21% 13% 4 9% 5% 5% 4 3 4 6% 27%	2600
	11th to 20th	Night	20% 13% 4 10% 6% 4 4 3 5% 5% 26%	2420
	21st to end	Night	19% 15% 5% 10% 5% 4 4 3 4 4 28%	1980
March	1st to 10th	Night	19% 13% 4 6% 4 4 4 3 4 5% 35%	5016
	11th to 20th	Night	12% 8% 3 7% 4 4 4 4 6% 7% 40%	4980
	21st to end	Night	18% 9% 3 8% 4 4 4 4 5% 6% 35%	5467
April	1st to 10th	Night	17% 11% 2 6% 5% 4 4 3 5% 6% 35%	2191
	11th to 20th	Night	15% 8% 2 6% 5% 4 4 5% 6% 8% 37%	1841
	21st to end	Night	14% 10% 3 6% 4 4 4 4 7% 8% 37%	1800
May	1st to 10th	Night	24% 11% 3 8% 5% 4 5% 3 5% 5% 26%	4033
	11th to 20th	Night	16% 8% 3 6% 4 4 4 3 6% 9% 36%	4032
	21st to end	Night	14% 8% 3 7% 5% 4 5% 3 6% 9% 36%	4421
June	1st to 10th	Night	9% 7% 2 6% 4 4 5% 4 6% 7% 46%	1800
	11th to 20th	Night	10% 6% 3 5% 4 5% 5% 4 7% 10% 42%	1800
	21st to end	Night	11% 5% 2 5% 4 4 5% 5% 6% 10% 44%	1800
July	1st to 10th	Night	10% 7% 3 7% 4 4 4 4 6% 8% 44%	4058
	11th to 20th	Night	9% 7% 3 6% 5% 5% 6% 5% 7% 9% 38%	4057
	21st to end	Night	8% 7% 2 8% 6% 5% 5% 4 7% 8% 40%	4427
August	1st to 10th	Night	8% 7% 3 8% 5% 5% 5% 4 7% 11% 38%	2861
	11th to 20th	Night	9% 9% 3 8% 5% 4 4 3 5% 6% 43%	2785
	21st to end	Night	5% 4 1 6% 4 4 5% 5% 8% 10% 48%	3181
September	1st to 10th	Night	12% 5% 1 5% 4 4 4 3 5% 7% 52%	2043
	11th to 20th	Night	9% 4 1 5% 4 3 4 4 6% 7% 54%	2090
	21st to end	Night	16% 7% 2 7% 3 3 4 2 5% 6% 43%	2090
October	1st to 10th	Night	11% 6% 2 5% 3 4 4 4 5% 7% 48%	2194
	11th to 20th	Night	15% 7% 2 6% 4 4 4 4 5% 7% 43%	2280
	21st to end	Night	20% 8% 2 5% 4 4 3 3 5% 6% 40%	2508
November	1st to 10th	Night	14% 7% 2 6% 4 3 3 3 3 7% 49%	2507
	11th to 20th	Night	17% 10% 2 7% 5% 6% 4 4 5% 6% 34%	2600
	21st to end	Night	20% 12% 4 8% 5% 4 4 3 5% 5% 31%	2609
December	1st to 10th	Night	18% 13% 6% 12% 5% 3 4 3 5% 5% 25%	4580
	11th to 20th	Night	19% 17% 7% 10% 5% 4 4 3 4 5% 23%	4954
	21st to end	Night	21% 18% 5% 10% 6% 5% 4 3 4 6% 18%	6490

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	71% 2 10% 12% 5%	4057
	11th to 20th	Day	71% 2 7% 11% 8% 1	4060
	21st to end	Day	71% 2 8% 12% 7%	4466
February	1st to 10th	Day	63% 2 10% 16% 9% 1	1800
	11th to 20th	Day	61% 2 8% 18% 10%	1871
	21st to end	Day	57% 2 11% 19% 9% 2	1650
March	1st to 10th	Day	58% 2 7% 23% 9% 2	4835
	11th to 20th	Day	43% 2 9% 32% 12% 2	4980
	21st to end	Day	53% 3 7% 22% 13% 2	5465
April	1st to 10th	Day	54% 2 9% 20% 13% 3	2208
	11th to 20th	Day	48% 3 11% 18% 17% 3	2525
	21st to end	Day	49% 3 9% 24% 13% 2	2600
May	1st to 10th	Day	56% 4 9% 18% 10% 3	5897
	11th to 20th	Day	53% 4 9% 22% 12% 1	5865
	21st to end	Day	46% 4 12% 22% 12% 3	6447
June	1st to 10th	Day	42% 4 11% 25% 16% 2	2600
	11th to 20th	Day	44% 4 14% 23% 14% 1	2600
	21st to end	Day	40% 5% 15% 23% 15% 2	2600
July	1st to 10th	Day	39% 4 12% 26% 17% 2	5835
	11th to 20th	Day	43% 7% 11% 26% 12% 1	5831
	21st to end	Day	44% 5% 11% 20% 18% 2	6240
August	1st to 10th	Day	41% 6% 14% 28% 12%	4143
	11th to 20th	Day	38% 5% 11% 32% 14%	4083
	21st to end	Day	31% 6% 14% 32% 15% 3	4441
September	1st to 10th	Day	36% 3 10% 24% 22% 5%	2133
	11th to 20th	Day	34% 3 11% 28% 21% 3	2090
	21st to end	Day	46% 3 8% 23% 19% 1	2090
October	1st to 10th	Day	26% 3 9% 33% 27% 1	3298
	11th to 20th	Day	35% 5% 11% 26% 19% 4	3140
	21st to end	Day	36% 3 11% 28% 20% 2	3428
November	1st to 10th	Day	38% 3 9% 30% 17% 3	1786
	11th to 20th	Day	52% 2 8% 22% 14% 2	1800
	21st to end	Day	56% 3 8% 21% 11% 1	1780
December	1st to 10th	Day	64% 2 12% 18% 4	2600
	11th to 20th	Day	66% 1 9% 18% 5%	3227
	21st to end	Day	71% 2 9% 13% 5%	4466
January	1st to 10th	Night	72% 2 8% 14% 4	5889
	11th to 20th	Night	73% 2 8% 11% 5% 1	5900
	21st to end	Night	62% 2 10% 16% 7% 2	6490
February	1st to 10th	Night	60% 3 10% 19% 9% 1	2600
	11th to 20th	Night	62% 2 7% 18% 10% 1	2422
	21st to end	Night	61% 2 8% 17% 9% 2	1980
March	1st to 10th	Night	52% 2 6% 27% 11% 2	5016
	11th to 20th	Night	43% 2 9% 32% 12% 2	4980
	21st to end	Night	50% 3 7% 24% 13% 2	5467
April	1st to 10th	Night	49% 3 9% 21% 15% 3	2191
	11th to 20th	Night	44% 3 10% 20% 18% 4	1841
	21st to end	Night	44% 3 10% 24% 17% 2	1800
May	1st to 10th	Night	60% 4 10% 15% 7% 4	4060
	11th to 20th	Night	45% 5% 10% 25% 13% 1	4033
	21st to end	Night	45% 4 12% 26% 10% 3	4429
June	1st to 10th	Night	38% 4 11% 26% 20% 2	1800
	11th to 20th	Night	37% 4 14% 25% 17% 3	1800
	21st to end	Night	35% 6% 13% 26% 18% 3	1800
July	1st to 10th	Night	37% 5% 10% 26% 18% 4	4015
	11th to 20th	Night	40% 8% 16% 25% 11% 1	4006
	21st to end	Night	39% 7% 12% 20% 18% 3	4297
August	1st to 10th	Night	40% 6% 14% 27% 12% 1	2850
	11th to 20th	Night	41% 4 9% 24% 21% 1	2812
	21st to end	Night	29% 5% 14% 31% 18% 3	3181
September	1st to 10th	Night	33% 3 10% 23% 23% 7%	2043
	11th to 20th	Night	29% 3 11% 28% 26% 3	2090
	21st to end	Night	43% 3 8% 22% 22% 2	2090
October	1st to 10th	Night	30% 3 7% 30% 28% 3	3662
	11th to 20th	Night	32% 3 11% 26% 21% 7%	3779
	21st to end	Night	33% 3 7% 28% 26% 3	4120
November	1st to 10th	Night	39% 2 10% 26% 20% 4	2507
	11th to 20th	Night	51% 2 7% 22% 15% 3	2600
	21st to end	Night	55% 2 11% 21% 10% 1	2609
December	1st to 10th	Night	61% 3 11% 20% 4	4580
	11th to 20th	Night	64% 3 12% 17% 4	4956
	21st to end	Night	68% 3 9% 15% 5%	6490

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	33% 21% 32% 10% 4	300
	11th to 20th	Day	35% 25% 32% 7% 1	300
	21st to end	Day	34% 24% 31% 10% 1	330
February	1st to 10th	Day	34% 22% 31% 9% 4	300
	11th to 20th	Day	42% 21% 31% 4 2	300
	21st to end	Day	33% 22% 37% 8%	249
March	1st to 10th	Day	30% 19% 30% 17% 4	448
	11th to 20th	Day	30% 19% 32% 13% 5% 1	500
	21st to end	Day	33% 16% 32% 15% 4	550
April	1st to 10th	Day	28% 17% 33% 13% 7% 2	500
	11th to 20th	Day	30% 15% 29% 16% 7% 3	492
	21st to end	Day	22% 19% 33% 19% 6% 2	500
May	1st to 10th	Day	28% 16% 29% 18% 7% 2	503
	11th to 20th	Day	24% 12% 29% 20% 11% 5%	527
	21st to end	Day	17% 9% 27% 25% 15% 6%	573
June	1st to 10th	Day	16% 7% 30% 27% 15% 5%	530
	11th to 20th	Day	17% 9% 22% 32% 14% 6%	530
	21st to end	Day	13% 8% 28% 28% 16% 7%	530
July	1st to 10th	Day	14% 3 20% 25% 23% 15%	525
	11th to 20th	Day	14% 4 23% 28% 21% 10%	524
	21st to end	Day	15% 5% 19% 30% 21% 11%	576
August	1st to 10th	Day	11% 6% 19% 32% 22% 11%	502
	11th to 20th	Day	14% 4 22% 32% 17% 11%	479
	21st to end	Day	11% 3 20% 28% 24% 13%	539
September	1st to 10th	Day	15% 4 19% 28% 23% 11%	490
	11th to 20th	Day	10% 3 16% 27% 29% 14%	490
	21st to end	Day	26% 8% 22% 23% 17% 4	490
October	1st to 10th	Day	14% 8% 28% 28% 18% 6%	490
	11th to 20th	Day	19% 11% 31% 24% 12% 3	490
	21st to end	Day	27% 12% 31% 20% 8% 1	539
November	1st to 10th	Day	18% 15% 37% 19% 7% 3	324
	11th to 20th	Day	31% 13% 31% 17% 5% 2	300
	21st to end	Day	25% 21% 35% 16% 3	290
December	1st to 10th	Day	32% 15% 37% 11% 5% 2	200
	11th to 20th	Day	29% 21% 36% 10% 3	255
	21st to end	Day	35% 19% 28% 14% 4	330
January	1st to 10th	Night	29% 18% 31% 19% 3	800
	11th to 20th	Night	32% 17% 28% 20% 3	800
	21st to end	Night	28% 19% 32% 19% 2	880
February	1st to 10th	Night	32% 15% 29% 23% 2	800
	11th to 20th	Night	33% 18% 31% 17% 1	783
	21st to end	Night	29% 17% 33% 19% 2	660
March	1st to 10th	Night	26% 15% 31% 23% 4	800
	11th to 20th	Night	27% 17% 27% 22% 6% 1	800
	21st to end	Night	27% 15% 31% 20% 6%	880
April	1st to 10th	Night	26% 14% 33% 21% 6%	800
	11th to 20th	Night	20% 12% 35% 22% 9% 1	657
	21st to end	Night	20% 10% 36% 27% 7% 1	600
May	1st to 10th	Night	23% 9% 27% 29% 12% 1	600
	11th to 20th	Night	20% 7% 24% 32% 15% 1	591
	21st to end	Night	12% 4 22% 33% 25% 3	650
June	1st to 10th	Night	11% 4 23% 39% 22% 1	600
	11th to 20th	Night	13% 4 20% 37% 25% 2	600
	21st to end	Night	13% 3 18% 38% 26% 2	600
July	1st to 10th	Night	11% 2 15% 36% 29% 6%	585
	11th to 20th	Night	8% 2 15% 38% 31% 5%	582
	21st to end	Night	11% 2 16% 33% 34% 3	657
August	1st to 10th	Night	8% 3 12% 39% 34% 4	579
	11th to 20th	Night	12% 3 14% 35% 30% 6%	564
	21st to end	Night	10% 2 17% 31% 34% 7%	658
September	1st to 10th	Night	14% 2 17% 32% 30% 5%	760
	11th to 20th	Night	12% 3 13% 34% 34% 5%	760
	21st to end	Night	20% 5% 20% 31% 21% 4	760
October	1st to 10th	Night	15% 4 22% 32% 24% 3	760
	11th to 20th	Night	19% 9% 27% 29% 14% 2	760
	21st to end	Night	25% 10% 25% 29% 10% 1	836
November	1st to 10th	Night	19% 9% 27% 29% 15% 1	780
	11th to 20th	Night	25% 13% 28% 26% 7% 1	800
	21st to end	Night	27% 12% 27% 29% 6% 1	800
December	1st to 10th	Night	32% 14% 29% 20% 5%	800
	11th to 20th	Night	29% 15% 27% 25% 5%	800
	21st to end	Night	31% 14% 26% 26% 2	880

Page generated at 2025-08-02 01:32:23. Version ac07

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