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 2024-11-04.

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% 3 8% 5% 4 4 4 6% 7% 34%	100935
	Night	16% 10% 3 8% 5% 4 4 3 5% 6% 35%	98014
Transparency	Day	48% 3 10% 23% 13% 2	104637
	Night	49% 3 10% 23% 14% 2	102451
Seeing	Day	22% 12% 27% 21% 12% 5%	14833
	Night	21% 10% 25% 28% 14% 2	25042

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	19% 20% 6% 10% 5% 4 4 3 4 5% 21%	2836
	11th to 20th	Day	14% 22% 9% 11% 7% 5% 3 3 3 4 19%	2840
	21st to end	Day	26% 22% 7% 9% 5% 4 3 2 3 4 15%	3124
February	1st to 10th	Day	22% 14% 4 9% 6% 4 3 3 4 5% 25%	1710
	11th to 20th	Day	17% 15% 5% 12% 4 3 4 3 4 7% 25%	1766
	21st to end	Day	18% 15% 5% 9% 4 4 3 2 4 5% 31%	1570
March	1st to 10th	Day	21% 16% 5% 9% 5% 3 3 3 4 5% 26%	3363
	11th to 20th	Day	13% 8% 3 8% 5% 6% 4 4 5% 6% 38%	3480
	21st to end	Day	20% 9% 3 7% 5% 4 4 3 6% 7% 33%	3815
April	1st to 10th	Day	14% 13% 3 8% 6% 5% 4 3 6% 6% 32%	2097
	11th to 20th	Day	16% 9% 3 7% 5% 4 4 4 5% 6% 37%	2397
	21st to end	Day	17% 8% 3 7% 4 5% 5% 4 5% 7% 34%	2470
May	1st to 10th	Day	21% 9% 3 9% 6% 5% 5% 3 5% 7% 27%	4082
	11th to 20th	Day	20% 10% 3 7% 4 4 4 3 5% 7% 32%	4081
	21st to end	Day	11% 6% 3 6% 5% 5% 6% 5% 8% 10% 35%	4476
June	1st to 10th	Day	12% 7% 2 7% 5% 5% 5% 5% 7% 9% 36%	2470
	11th to 20th	Day	11% 5% 3 7% 6% 5% 4 5% 7% 10% 36%	2470
	21st to end	Day	12% 6% 2 6% 5% 5% 5% 4 8% 11% 36%	2470
July	1st to 10th	Day	10% 6% 2 7% 5% 6% 5% 5% 6% 10% 39%	4120
	11th to 20th	Day	9% 6% 2 6% 4 4 5% 4 7% 10% 43%	4120
	21st to end	Day	12% 8% 3 7% 6% 5% 5% 5% 6% 9% 34%	4466
August	1st to 10th	Day	9% 6% 3 7% 5% 6% 5% 5% 7% 10% 36%	4104
	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	10% 7% 3 6% 4 4 3 4 4 6% 49%	1723
	11th to 20th	Day	17% 14% 3 7% 4 4 4 2 4 6% 35%	1710
	21st to end	Day	18% 12% 4 7% 6% 4 4 3 4 6% 32%	1691
December	1st to 10th	Day	22% 16% 5% 11% 5% 4 4 3 4 4 21%	1520
	11th to 20th	Day	19% 16% 5% 12% 5% 4 3 3 5% 6% 23%	2066
	21st to end	Day	22% 21% 5% 10% 5% 5% 5% 3 5% 5% 14%	3124
January	1st to 10th	Night	16% 18% 7% 12% 6% 5% 4 4 4 4 20%	4109
	11th to 20th	Night	17% 17% 6% 14% 6% 6% 6% 3 4 4 17%	4120
	21st to end	Night	27% 16% 7% 12% 5% 3 3 2 3 4 18%	4532
February	1st to 10th	Night	22% 13% 3 9% 5% 4 4 3 4 5% 28%	2470
	11th to 20th	Night	20% 13% 4 10% 6% 5% 4 3 5% 5% 26%	2296
	21st to end	Night	20% 15% 5% 9% 5% 4 4 3 4 4 27%	1884
March	1st to 10th	Night	21% 12% 3 6% 4 4 4 3 4 5% 33%	3488
	11th to 20th	Night	14% 8% 4 7% 5% 5% 4 4 5% 6% 37%	3480
	21st to end	Night	19% 9% 2 6% 3 3 3 3 5% 6% 40%	3817
April	1st to 10th	Night	16% 10% 2 6% 5% 4 4 4 5% 7% 37%	2082
	11th to 20th	Night	15% 8% 2 5% 5% 4 4 5% 6% 8% 38%	1748
	21st to end	Night	14% 9% 3 6% 4 5% 4 4 7% 8% 37%	1710
May	1st to 10th	Night	26% 11% 3 7% 5% 4 4 3 5% 5% 26%	2813
	11th to 20th	Night	18% 8% 3 6% 4 4 4 3 4 6% 40%	2812
	21st to end	Night	10% 6% 2 6% 4 4 5% 3 6% 10% 43%	3079
June	1st to 10th	Night	9% 6% 2 5% 5% 4 5% 4 6% 7% 45%	1710
	11th to 20th	Night	10% 6% 2 5% 4 5% 5% 4 7% 11% 42%	1710
	21st to end	Night	11% 5% 2 4 4 4 5% 5% 6% 9% 44%	1710
July	1st to 10th	Night	10% 7% 2 7% 4 4 3 4 6% 9% 44%	2840
	11th to 20th	Night	8% 5% 2 6% 5% 5% 5% 5% 6% 9% 44%	2840
	21st to end	Night	8% 8% 2 8% 6% 6% 5% 4 6% 8% 40%	3087
August	1st to 10th	Night	8% 7% 3 8% 5% 5% 5% 4 7% 11% 37%	2825
	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	13% 8% 2 6% 4 3 3 3 4 6% 49%	2423
	11th to 20th	Night	17% 9% 2 7% 5% 6% 4 4 5% 6% 35%	2470
	21st to end	Night	19% 11% 4 8% 4 5% 4 3 5% 6% 32%	2478
December	1st to 10th	Night	22% 15% 5% 9% 6% 4 4 3 5% 4 24%	2660
	11th to 20th	Night	18% 15% 6% 8% 5% 4 4 3 5% 6% 27%	3118
	21st to end	Night	21% 19% 5% 10% 6% 5% 4 3 4 5% 17%	4532

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	66% 2 11% 14% 6%	2837
	11th to 20th	Day	71% 1 8% 13% 6%	2840
	21st to end	Day	76% 1 6% 14% 3 1	3124
February	1st to 10th	Day	62% 2 10% 16% 9% 1	1710
	11th to 20th	Day	60% 2 8% 19% 10%	1775
	21st to end	Day	57% 1 10% 20% 9% 2	1570
March	1st to 10th	Day	63% 1 8% 21% 7% 1	3363
	11th to 20th	Day	47% 2 8% 30% 12% 1	3480
	21st to end	Day	53% 2 8% 24% 13% 1	3815
April	1st to 10th	Day	53% 2 9% 20% 13% 3	2097
	11th to 20th	Day	48% 3 11% 18% 17% 3	2397
	21st to end	Day	50% 3 9% 23% 13% 2	2470
May	1st to 10th	Day	58% 2 9% 22% 8% 1	4120
	11th to 20th	Day	53% 3 9% 21% 13% 1	4085
	21st to end	Day	43% 4 13% 22% 14% 4	4489
June	1st to 10th	Day	42% 4 11% 26% 15% 2	2470
	11th to 20th	Day	43% 4 15% 23% 14% 1	2470
	21st to end	Day	41% 4 15% 23% 15% 2	2470
July	1st to 10th	Day	41% 4 12% 23% 16% 2	4055
	11th to 20th	Day	34% 5% 10% 33% 16% 1	4051
	21st to end	Day	46% 4 10% 19% 17% 3	4324
August	1st to 10th	Day	41% 6% 14% 28% 12%	4091
	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	37% 3 9% 30% 17% 3	1723
	11th to 20th	Day	52% 2 8% 22% 14% 3	1710
	21st to end	Day	54% 3 8% 22% 12% 1	1691
December	1st to 10th	Day	67% 2 9% 17% 4	1520
	11th to 20th	Day	63% 1 9% 20% 7%	2063
	21st to end	Day	73% 1 11% 11% 4	3124
January	1st to 10th	Night	69% 2 8% 15% 6%	4109
	11th to 20th	Night	72% 1 10% 13% 3	4120
	21st to end	Night	73% 1 6% 15% 4 1	4532
February	1st to 10th	Night	60% 3 9% 19% 9% 1	2470
	11th to 20th	Night	60% 2 7% 19% 10% 1	2298
	21st to end	Night	62% 2 8% 17% 9% 2	1884
March	1st to 10th	Night	55% 2 6% 25% 12% 1	3488
	11th to 20th	Night	48% 2 8% 31% 10% 1	3480
	21st to end	Night	47% 2 6% 30% 13% 2	3817
April	1st to 10th	Night	48% 3 10% 22% 15% 3	2082
	11th to 20th	Night	44% 3 10% 20% 18% 4	1748
	21st to end	Night	44% 4 11% 24% 16% 2	1710
May	1st to 10th	Night	61% 2 8% 18% 8% 2	2840
	11th to 20th	Night	47% 3 9% 25% 13% 2	2813
	21st to end	Night	38% 3 13% 28% 13% 4	3087
June	1st to 10th	Night	38% 4 11% 26% 19% 2	1710
	11th to 20th	Night	36% 5% 14% 25% 18% 3	1710
	21st to end	Night	35% 5% 14% 26% 18% 3	1710
July	1st to 10th	Night	38% 4 11% 24% 18% 5%	2795
	11th to 20th	Night	35% 6% 13% 30% 15% 1	2786
	21st to end	Night	41% 7% 11% 21% 16% 4	2988
August	1st to 10th	Night	40% 6% 15% 26% 12% 1	2814
	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	2423
	11th to 20th	Night	50% 2 7% 22% 16% 2	2470
	21st to end	Night	54% 2 11% 22% 10% 1	2478
December	1st to 10th	Night	64% 2 9% 19% 6% 1	2660
	11th to 20th	Night	59% 2 11% 21% 7%	3120
	21st to end	Night	70% 1 9% 15% 4	4532

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% 20% 33% 10% 4	270
	11th to 20th	Day	35% 23% 33% 7% 1	270
	21st to end	Day	35% 23% 31% 10% 1	297
February	1st to 10th	Day	35% 20% 31% 10% 4	270
	11th to 20th	Day	39% 22% 32% 4 2	270
	21st to end	Day	35% 22% 35% 8%	225
March	1st to 10th	Day	30% 19% 30% 17% 4	410
	11th to 20th	Day	30% 18% 32% 13% 5% 1	460
	21st to end	Day	33% 15% 32% 15% 4	506
April	1st to 10th	Day	27% 16% 35% 13% 7% 2	460
	11th to 20th	Day	31% 14% 29% 17% 7% 3	452
	21st to end	Day	22% 19% 33% 18% 6% 2	460
May	1st to 10th	Day	29% 14% 30% 17% 8% 2	463
	11th to 20th	Day	24% 10% 29% 20% 11% 5%	487
	21st to end	Day	14% 9% 27% 27% 17% 6%	529
June	1st to 10th	Day	17% 6% 29% 27% 16% 5%	490
	11th to 20th	Day	17% 9% 22% 31% 14% 7%	490
	21st to end	Day	14% 8% 29% 28% 14% 7%	490
July	1st to 10th	Day	14% 4 20% 24% 23% 15%	485
	11th to 20th	Day	14% 4 23% 29% 20% 10%	484
	21st to end	Day	14% 5% 20% 29% 21% 11%	532
August	1st to 10th	Day	12% 6% 17% 33% 21% 11%	486
	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	17% 16% 35% 20% 8% 3	303
	11th to 20th	Day	31% 14% 30% 17% 6% 2	270
	21st to end	Day	23% 20% 36% 18% 3	261
December	1st to 10th	Day	32% 14% 37% 11% 5% 2	180
	11th to 20th	Day	27% 23% 37% 10% 3	229
	21st to end	Day	36% 19% 27% 14% 4	297
January	1st to 10th	Night	29% 18% 30% 19% 3	760
	11th to 20th	Night	33% 16% 28% 20% 4	760
	21st to end	Night	28% 18% 32% 20% 2	836
February	1st to 10th	Night	32% 14% 28% 24% 2	760
	11th to 20th	Night	32% 18% 31% 18% 1	743
	21st to end	Night	30% 17% 32% 18% 2	628
March	1st to 10th	Night	26% 15% 31% 24% 4	760
	11th to 20th	Night	27% 17% 27% 22% 6% 1	760
	21st to end	Night	27% 14% 31% 21% 6%	836
April	1st to 10th	Night	24% 14% 33% 22% 7%	760
	11th to 20th	Night	20% 12% 35% 22% 10% 1	624
	21st to end	Night	20% 9% 36% 27% 7% 1	570
May	1st to 10th	Night	23% 8% 27% 29% 12% 1	570
	11th to 20th	Night	20% 6% 24% 33% 15% 1	561
	21st to end	Night	12% 3 22% 34% 26% 4	617
June	1st to 10th	Night	11% 4 24% 38% 22% 1	570
	11th to 20th	Night	12% 3 21% 37% 25% 2	570
	21st to end	Night	14% 3 19% 38% 24% 2	570
July	1st to 10th	Night	12% 2 16% 36% 28% 7%	555
	11th to 20th	Night	8% 2 15% 39% 30% 5%	552
	21st to end	Night	12% 2 16% 33% 34% 3	624
August	1st to 10th	Night	8% 3 11% 39% 34% 4	567
	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% 26% 29% 16% 1	755
	11th to 20th	Night	25% 13% 28% 26% 8% 1	760
	21st to end	Night	26% 10% 27% 29% 6% 1	760
December	1st to 10th	Night	32% 14% 29% 20% 5%	760
	11th to 20th	Night	28% 15% 27% 25% 5%	760
	21st to end	Night	31% 14% 27% 25% 2	836

Page generated at 2024-11-01 22:47:50. Version ac07

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