Allendale
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Allendale clear sky chart from 2005-11-06 to 2025-07-06.

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% 4 3 5% 7% 34%	119643
	Night	15% 12% 5% 10% 5% 4 4 3 5% 6% 31%	119348
Transparency	Day	49% 5% 12% 21% 12% 1	123214
	Night	54% 4 10% 19% 11% 1	123905
Seeing	Day	17% 11% 29% 25% 13% 4	16729
	Night	19% 9% 28% 31% 12% 1	26614

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	12% 21% 10% 21% 6% 6% 4 3 4 3 11%	3617
	11th to 20th	Day	11% 15% 8% 22% 15% 10% 4 3 3 3 5%	3620
	21st to end	Day	16% 20% 9% 20% 6% 5% 6% 2 2 2 12%	3982
February	1st to 10th	Day	12% 17% 6% 15% 11% 6% 4 4 5% 4 17%	1831
	11th to 20th	Day	12% 15% 6% 16% 9% 5% 4 2 5% 5% 20%	1948
	21st to end	Day	14% 16% 6% 13% 5% 5% 5% 3 5% 6% 22%	1650
March	1st to 10th	Day	13% 11% 4 11% 5% 5% 5% 3 4 7% 32%	4480
	11th to 20th	Day	11% 8% 4 8% 5% 5% 5% 4 6% 7% 37%	4812
	21st to end	Day	20% 14% 6% 9% 4 4 3 3 4 5% 28%	5726
April	1st to 10th	Day	19% 12% 4 8% 4 4 3 3 5% 6% 31%	2400
	11th to 20th	Day	17% 10% 3 6% 4 4 4 3 5% 7% 37%	2418
	21st to end	Day	17% 8% 3 7% 4 5% 4 4 5% 8% 35%	2600
May	1st to 10th	Day	18% 7% 2 6% 4 4 4 3 5% 8% 40%	5862
	11th to 20th	Day	14% 7% 2 6% 4 4 4 3 6% 9% 41%	5925
	21st to end	Day	14% 6% 2 5% 4 4 4 3 5% 8% 45%	6935
June	1st to 10th	Day	10% 5% 2 5% 5% 4 5% 4 6% 9% 46%	2800
	11th to 20th	Day	11% 5% 2 5% 4 4 4 3 6% 8% 48%	2800
	21st to end	Day	11% 6% 2 6% 4 4 4 4 6% 9% 45%	2800
July	1st to 10th	Day	12% 7% 3 7% 4 5% 5% 4 6% 8% 40%	4511
	11th to 20th	Day	7% 3 1 5% 4 4 5% 4 6% 9% 53%	4440
	21st to end	Day	8% 5% 2 5% 4 4 4 4 6% 9% 47%	4813
August	1st to 10th	Day	12% 5% 2 6% 4 4 5% 4 7% 9% 43%	4177
	11th to 20th	Day	11% 4 2 5% 4 4 4 3 6% 7% 49%	4044
	21st to end	Day	8% 5% 2 7% 4 4 5% 4 5% 8% 47%	4194
September	1st to 10th	Day	11% 6% 3 6% 4 4 4 3 6% 8% 45%	2262
	11th to 20th	Day	11% 5% 2 5% 3 4 5% 3 6% 8% 49%	2090
	21st to end	Day	12% 7% 3 7% 5% 5% 4 3 5% 8% 42%	2090
October	1st to 10th	Day	16% 6% 2 7% 5% 4 4 2 4 5% 44%	2090
	11th to 20th	Day	22% 10% 3 8% 5% 6% 5% 4 5% 7% 26%	1843
	21st to end	Day	23% 11% 4 8% 6% 5% 5% 4 5% 6% 24%	1881
November	1st to 10th	Day	13% 13% 4 7% 4 5% 4 4 5% 7% 35%	1762
	11th to 20th	Day	16% 20% 6% 10% 5% 5% 3 4 4 5% 21%	1800
	21st to end	Day	21% 18% 6% 8% 6% 5% 4 3 4 6% 20%	1800
December	1st to 10th	Day	11% 25% 11% 15% 6% 4 3 3 4 4 14%	2650
	11th to 20th	Day	16% 24% 13% 13% 8% 4 3 2 3 3 10%	3008
	21st to end	Day	23% 24% 6% 13% 5% 4 3 2 3 4 12%	3982
January	1st to 10th	Night	11% 21% 11% 21% 5% 4 3 2 3 3 14%	6348
	11th to 20th	Night	12% 18% 10% 23% 12% 8% 4 2 2 2 7%	6360
	21st to end	Night	16% 19% 9% 16% 6% 7% 5% 3 3 3 13%	6996
February	1st to 10th	Night	13% 18% 6% 15% 9% 5% 4 3 4 4 19%	2565
	11th to 20th	Night	13% 15% 6% 13% 8% 4 4 4 4 5% 23%	2338
	21st to end	Night	15% 15% 4 11% 6% 4 4 3 6% 5% 25%	1980
March	1st to 10th	Night	16% 8% 3 9% 5% 4 4 4 5% 7% 36%	5373
	11th to 20th	Night	11% 7% 3 6% 4 4 5% 4 6% 9% 43%	5147
	21st to end	Night	18% 11% 5% 8% 5% 5% 4 3 5% 5% 30%	5247
April	1st to 10th	Night	16% 10% 3 7% 5% 5% 4 4 5% 6% 35%	2000
	11th to 20th	Night	20% 9% 2 6% 4 4 4 4 5% 6% 37%	1930
	21st to end	Night	17% 8% 3 6% 4 4 4 4 5% 6% 39%	1800
May	1st to 10th	Night	17% 8% 3 7% 5% 4 5% 3 5% 6% 35%	4033
	11th to 20th	Night	15% 7% 2 7% 4 4 4 3 5% 7% 41%	3956
	21st to end	Night	18% 7% 2 6% 4 4 4 3 4 6% 42%	3942
June	1st to 10th	Night	11% 6% 2 5% 5% 4 5% 4 6% 8% 46%	1600
	11th to 20th	Night	10% 7% 2 6% 4 4 4 4 7% 8% 44%	1600
	21st to end	Night	10% 5% 2 5% 5% 5% 5% 5% 7% 8% 44%	1600
July	1st to 10th	Night	9% 6% 2 7% 4 4 6% 4 6% 9% 41%	2570
	11th to 20th	Night	7% 4 2 4 4 4 4 4 6% 7% 56%	2530
	21st to end	Night	7% 5% 3 6% 4 4 4 4 5% 7% 50%	2750
August	1st to 10th	Night	10% 5% 2 5% 4 3 4 4 6% 8% 50%	2754
	11th to 20th	Night	12% 5% 2 5% 4 4 4 3 5% 7% 50%	2785
	21st to end	Night	8% 6% 2 7% 5% 5% 4 3 6% 7% 46%	3459
September	1st to 10th	Night	9% 5% 3 5% 3 4 5% 3 5% 7% 51%	1900
	11th to 20th	Night	11% 4 1 5% 3 3 4 3 5% 6% 55%	2088
	21st to end	Night	12% 8% 2 6% 5% 4 4 2 5% 8% 43%	2090
October	1st to 10th	Night	18% 5% 2 5% 3 3 3 2 4 7% 46%	2090
	11th to 20th	Night	21% 11% 3 8% 4 3 3 3 4 6% 34%	2332
	21st to end	Night	24% 10% 3 7% 4 3 3 3 5% 6% 31%	2717
November	1st to 10th	Night	15% 12% 2 7% 5% 4 4 3 5% 6% 37%	2536
	11th to 20th	Night	18% 16% 5% 10% 4 5% 4 4 5% 6% 22%	2600
	21st to end	Night	18% 18% 6% 9% 5% 4 3 3 4 6% 22%	2600
December	1st to 10th	Night	11% 23% 9% 14% 5% 4 4 3 4 5% 16%	4537
	11th to 20th	Night	18% 24% 10% 15% 7% 4 3 2 3 4 11%	5199
	21st to end	Night	25% 21% 6% 11% 5% 4 3 3 4 5% 13%	6996

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	76% 6% 8% 9% 1	3618
	11th to 20th	Day	83% 5% 7% 4 1	3620
	21st to end	Day	80% 2 9% 7% 2	3982
February	1st to 10th	Day	71% 5% 8% 13% 3	1831
	11th to 20th	Day	67% 4 8% 14% 7%	1958
	21st to end	Day	63% 4 12% 15% 6%	1650
March	1st to 10th	Day	53% 4 15% 19% 9% 1	4480
	11th to 20th	Day	45% 5% 17% 24% 9% 1	4812
	21st to end	Day	60% 3 10% 16% 10% 1	5728
April	1st to 10th	Day	54% 4 10% 20% 11% 1	2400
	11th to 20th	Day	48% 4 10% 23% 14% 2	2418
	21st to end	Day	47% 4 13% 20% 15% 2	2600
May	1st to 10th	Day	44% 5% 12% 22% 16% 1	5897
	11th to 20th	Day	41% 4 13% 22% 17% 2	5929
	21st to end	Day	38% 4 11% 26% 19% 1	6949
June	1st to 10th	Day	36% 4 11% 29% 17% 2	2800
	11th to 20th	Day	35% 4 14% 25% 20% 2	2800
	21st to end	Day	35% 5% 16% 24% 18% 2	2800
July	1st to 10th	Day	41% 5% 13% 22% 15% 3	4442
	11th to 20th	Day	27% 6% 15% 31% 20% 2	4365
	21st to end	Day	33% 7% 14% 22% 22% 2	4662
August	1st to 10th	Day	36% 6% 13% 30% 15% 1	4162
	11th to 20th	Day	34% 6% 12% 29% 18% 1	4083
	21st to end	Day	35% 5% 14% 27% 18% 2	4193
September	1st to 10th	Day	37% 5% 14% 27% 15% 3	2262
	11th to 20th	Day	33% 4 11% 32% 17% 2	2090
	21st to end	Day	41% 4 12% 25% 17%	2090
October	1st to 10th	Day	30% 3 8% 39% 19% 1	3480
	11th to 20th	Day	42% 5% 13% 24% 16%	3033
	21st to end	Day	51% 4 13% 23% 8% 1	3081
November	1st to 10th	Day	50% 5% 13% 20% 12% 1	1762
	11th to 20th	Day	66% 4 10% 15% 5% 1	1800
	21st to end	Day	66% 4 13% 12% 4	1800
December	1st to 10th	Day	73% 7% 10% 7% 2	2650
	11th to 20th	Day	81% 3 8% 7% 1	3005
	21st to end	Day	77% 3 7% 10% 3	3982
January	1st to 10th	Night	75% 4 6% 10% 4 1	6348
	11th to 20th	Night	84% 4 5% 4 2	6360
	21st to end	Night	77% 4 10% 7% 2	6996
February	1st to 10th	Night	70% 3 9% 12% 6%	2565
	11th to 20th	Night	65% 5% 8% 16% 7%	2339
	21st to end	Night	61% 4 12% 15% 7% 1	1980
March	1st to 10th	Night	48% 4 14% 25% 8% 1	5373
	11th to 20th	Night	38% 5% 14% 28% 12% 2	5147
	21st to end	Night	55% 4 10% 18% 13% 1	5247
April	1st to 10th	Night	50% 4 10% 21% 14% 1	2000
	11th to 20th	Night	49% 4 7% 20% 18% 3	1930
	21st to end	Night	46% 3 12% 20% 16% 4	1800
May	1st to 10th	Night	50% 4 12% 17% 15% 3	4060
	11th to 20th	Night	43% 5% 10% 22% 16% 4	3957
	21st to end	Night	44% 3 8% 22% 20% 2	3950
June	1st to 10th	Night	36% 4 10% 29% 17% 3	1600
	11th to 20th	Night	36% 6% 13% 25% 19% 2	1600
	21st to end	Night	36% 5% 15% 26% 16% 2	1600
July	1st to 10th	Night	38% 6% 12% 24% 12% 7%	2530
	11th to 20th	Night	27% 5% 13% 28% 25% 2	2482
	21st to end	Night	34% 5% 12% 20% 25% 3	2662
August	1st to 10th	Night	33% 5% 13% 30% 18% 1	2745
	11th to 20th	Night	33% 6% 10% 33% 17% 1	2812
	21st to end	Night	36% 6% 10% 27% 19% 2	3459
September	1st to 10th	Night	33% 6% 11% 28% 19% 3	1900
	11th to 20th	Night	31% 3 10% 33% 21% 2	2088
	21st to end	Night	41% 4 12% 27% 14% 1	2090
October	1st to 10th	Night	29% 4 9% 36% 22% 2	3480
	11th to 20th	Night	41% 4 12% 24% 18%	3868
	21st to end	Night	45% 4 10% 27% 15%	4467
November	1st to 10th	Night	50% 5% 8% 24% 12% 1	2536
	11th to 20th	Night	62% 4 11% 15% 6% 1	2600
	21st to end	Night	63% 5% 13% 16% 3	2600
December	1st to 10th	Night	69% 6% 14% 9% 2	4537
	11th to 20th	Night	79% 4 8% 7% 2	5201
	21st to end	Night	74% 4 9% 9% 3	6996

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	18% 16% 35% 25% 5% 2	300
	11th to 20th	Day	22% 17% 39% 18% 5%	300
	21st to end	Day	25% 17% 32% 22% 3	330
February	1st to 10th	Day	17% 25% 31% 20% 4 2	300
	11th to 20th	Day	22% 18% 39% 15% 6%	300
	21st to end	Day	24% 25% 36% 12% 2 1	249
March	1st to 10th	Day	20% 23% 41% 12% 5%	300
	11th to 20th	Day	21% 16% 30% 26% 8% 1	423
	21st to end	Day	26% 13% 31% 22% 6% 1	550
April	1st to 10th	Day	24% 15% 32% 23% 6% 1	500
	11th to 20th	Day	22% 22% 27% 22% 4 3	492
	21st to end	Day	22% 13% 31% 22% 11% 1	500
May	1st to 10th	Day	21% 12% 32% 22% 10% 2	503
	11th to 20th	Day	17% 10% 27% 27% 15% 3	552
	21st to end	Day	14% 8% 28% 28% 16% 5%	789
June	1st to 10th	Day	11% 7% 35% 29% 13% 4	730
	11th to 20th	Day	13% 6% 29% 33% 14% 5%	730
	21st to end	Day	12% 7% 32% 32% 14% 4	730
July	1st to 10th	Day	7% 4 28% 30% 22% 10%	697
	11th to 20th	Day	9% 6% 24% 35% 19% 7%	668
	21st to end	Day	9% 3 27% 37% 18% 7%	739
August	1st to 10th	Day	11% 4 20% 27% 25% 13%	534
	11th to 20th	Day	10% 4 20% 30% 25% 11%	479
	21st to end	Day	11% 5% 18% 32% 25% 10%	539
September	1st to 10th	Day	14% 5% 19% 31% 22% 9%	490
	11th to 20th	Day	8% 5% 18% 26% 29% 13%	490
	21st to end	Day	16% 10% 22% 24% 20% 8%	490
October	1st to 10th	Day	16% 10% 27% 26% 16% 4	490
	11th to 20th	Day	22% 18% 28% 26% 6% 1	375
	21st to end	Day	31% 12% 36% 16% 4 2	330
November	1st to 10th	Day	20% 18% 30% 23% 8% 1	300
	11th to 20th	Day	21% 22% 35% 17% 4 1	300
	21st to end	Day	26% 16% 41% 12% 5%	300
December	1st to 10th	Day	24% 21% 32% 14% 8% 1	300
	11th to 20th	Day	21% 23% 35% 17% 4 1	300
	21st to end	Day	26% 20% 34% 15% 3 1	330
January	1st to 10th	Night	21% 15% 33% 24% 7%	1000
	11th to 20th	Night	23% 14% 33% 24% 6% 1	1000
	21st to end	Night	22% 10% 32% 31% 5%	1100
February	1st to 10th	Night	20% 11% 37% 27% 4	850
	11th to 20th	Night	21% 13% 34% 26% 6% 1	783
	21st to end	Night	23% 12% 39% 22% 3	660
March	1st to 10th	Night	19% 10% 35% 28% 7% 1	800
	11th to 20th	Night	15% 12% 34% 30% 8% 1	800
	21st to end	Night	21% 10% 29% 31% 9% 1	789
April	1st to 10th	Night	19% 10% 33% 31% 7% 1	600
	11th to 20th	Night	25% 8% 31% 27% 9% 1	593
	21st to end	Night	20% 7% 31% 33% 8% 1	600
May	1st to 10th	Night	17% 6% 31% 35% 10% 1	600
	11th to 20th	Night	19% 5% 27% 35% 14% 1	591
	21st to end	Night	16% 3 23% 37% 20% 2	650
June	1st to 10th	Night	11% 4 26% 41% 18%	600
	11th to 20th	Night	11% 4 27% 41% 18%	600
	21st to end	Night	10% 3 22% 43% 20% 2	600
July	1st to 10th	Night	8% 1 16% 41% 31% 3	570
	11th to 20th	Night	7% 3 18% 41% 28% 4	552
	21st to end	Night	8% 2 15% 44% 29% 1	624
August	1st to 10th	Night	9% 2 14% 43% 28% 3	567
	11th to 20th	Night	11% 2 14% 40% 28% 5%	564
	21st to end	Night	11% 3 15% 39% 28% 4	627
September	1st to 10th	Night	12% 3 16% 41% 24% 4	570
	11th to 20th	Night	11% 5% 16% 36% 27% 5%	758
	21st to end	Night	14% 7% 22% 31% 21% 4	760
October	1st to 10th	Night	20% 5% 22% 34% 18% 1	760
	11th to 20th	Night	27% 11% 24% 27% 10% 1	760
	21st to end	Night	29% 11% 30% 23% 6% 1	836
November	1st to 10th	Night	22% 11% 30% 27% 10%	780
	11th to 20th	Night	26% 14% 32% 23% 5%	800
	21st to end	Night	27% 12% 31% 26% 4	800
December	1st to 10th	Night	25% 15% 31% 22% 6%	970
	11th to 20th	Night	27% 13% 34% 22% 4	1000
	21st to end	Night	31% 11% 36% 20% 2	1100

Page generated at 2025-07-03 01:30:12. Version ac07

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