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 2026-10-29.

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% 10% 4 9% 5% 5% 4 3 5% 7% 35%	149365
	Night	14% 12% 5% 10% 5% 5% 4 3 5% 6% 32%	143020
Transparency	Day	48% 5% 11% 22% 13% 1	152891
	Night	52% 5% 10% 19% 12% 1	147558
Seeing	Day	17% 12% 29% 25% 13% 4	18587
	Night	19% 9% 28% 31% 12% 1	28363

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	14% 22% 11% 21% 6% 5% 4 3 3 3 9%	4691
	11th to 20th	Day	9% 15% 10% 24% 15% 10% 4 3 3 3 6%	4710
	21st to end	Day	13% 18% 8% 18% 10% 7% 7% 2 2 2 13%	5156
February	1st to 10th	Day	11% 17% 6% 15% 11% 6% 4 4 5% 4 17%	1923
	11th to 20th	Day	12% 15% 6% 16% 9% 5% 4 2 5% 5% 21%	2048
	21st to end	Day	14% 16% 6% 13% 5% 5% 5% 3 5% 6% 22%	1730
March	1st to 10th	Day	14% 11% 4 10% 5% 5% 4 3 4 7% 32%	4580
	11th to 20th	Day	11% 8% 4 8% 5% 5% 5% 4 6% 7% 37%	4918
	21st to end	Day	19% 14% 6% 9% 4 4 3 3 4 5% 28%	5852
April	1st to 10th	Day	19% 13% 4 8% 4 4 4 3 5% 6% 30%	2520
	11th to 20th	Day	17% 10% 3 7% 4 4 4 3 5% 7% 36%	2540
	21st to end	Day	17% 8% 3 7% 4 4 4 4 5% 8% 35%	2730
May	1st to 10th	Day	15% 6% 2 6% 4 4 4 3 5% 8% 41%	7616
	11th to 20th	Day	14% 7% 3 7% 4 4 4 4 6% 8% 40%	7704
	21st to end	Day	14% 6% 2 5% 4 4 4 3 5% 7% 47%	9047
June	1st to 10th	Day	10% 5% 2 5% 5% 4 5% 4 6% 9% 45%	2940
	11th to 20th	Day	11% 5% 2 5% 4 4 4 3 6% 8% 47%	2940
	21st to end	Day	11% 6% 2 6% 4 4 4 4 6% 9% 45%	2940
July	1st to 10th	Day	11% 6% 2 7% 4 4 4 4 6% 9% 44%	8280
	11th to 20th	Day	7% 4 2 5% 3 3 4 4 5% 9% 53%	8280
	21st to end	Day	9% 5% 2 5% 4 4 4 4 6% 9% 49%	8990
August	1st to 10th	Day	15% 6% 2 6% 4 4 5% 4 6% 9% 41%	6131
	11th to 20th	Day	13% 5% 3 6% 4 4 4 3 6% 7% 43%	5951
	21st to end	Day	8% 5% 2 7% 4 4 5% 4 6% 8% 46%	6108
September	1st to 10th	Day	10% 5% 3 6% 4 5% 4 3 5% 8% 45%	2500
	11th to 20th	Day	12% 5% 2 5% 3 4 5% 3 6% 8% 48%	2310
	21st to end	Day	12% 7% 3 7% 5% 5% 4 3 5% 8% 42%	2310
October	1st to 10th	Day	15% 6% 2 7% 5% 4 4 3 4 5% 46%	2310
	11th to 20th	Day	21% 10% 3 8% 5% 6% 5% 4 5% 6% 28%	2037
	21st to end	Day	22% 10% 3 8% 6% 6% 5% 4 5% 6% 26%	2052
November	1st to 10th	Day	13% 13% 4 7% 4 5% 4 4 5% 7% 35%	1852
	11th to 20th	Day	16% 19% 6% 10% 5% 5% 3 4 4 5% 22%	1890
	21st to end	Day	20% 18% 6% 8% 6% 4 4 3 4 6% 20%	1890
December	1st to 10th	Day	11% 25% 11% 15% 6% 4 3 3 4 4 14%	2731
	11th to 20th	Day	16% 24% 13% 14% 8% 4 3 2 3 3 10%	3088
	21st to end	Day	23% 24% 6% 13% 6% 4 3 2 3 4 13%	4070
January	1st to 10th	Night	12% 21% 10% 21% 5% 4 3 2 3 4 14%	8232
	11th to 20th	Night	10% 18% 10% 24% 12% 8% 3 2 2 2 7%	8280
	21st to end	Night	13% 17% 8% 17% 10% 7% 6% 3 4 4 12%	9058
February	1st to 10th	Night	12% 18% 6% 15% 9% 5% 4 3 4 4 20%	2693
	11th to 20th	Night	13% 14% 6% 13% 8% 4 4 4 4 5% 24%	2458
	21st to end	Night	15% 15% 5% 11% 6% 4 4 3 5% 5% 25%	2076
March	1st to 10th	Night	16% 8% 3 9% 5% 4 4 4 5% 7% 36%	5493
	11th to 20th	Night	11% 7% 3 7% 4 4 5% 3 6% 9% 42%	5261
	21st to end	Night	18% 11% 5% 8% 5% 5% 4 4 5% 5% 30%	5363
April	1st to 10th	Night	16% 10% 3 7% 5% 5% 4 4 5% 6% 34%	2100
	11th to 20th	Night	20% 9% 2 6% 4 4 4 4 5% 6% 36%	2028
	21st to end	Night	17% 7% 3 6% 4 4 4 4 5% 7% 39%	1890
May	1st to 10th	Night	14% 7% 3 7% 5% 5% 5% 3 5% 6% 39%	5237
	11th to 20th	Night	13% 6% 2 7% 4 4 4 3 6% 8% 44%	5145
	21st to end	Night	15% 6% 2 6% 4 4 4 3 5% 6% 44%	5139
June	1st to 10th	Night	11% 6% 2 5% 5% 4 5% 4 5% 8% 46%	1680
	11th to 20th	Night	10% 6% 2 6% 4 4 4 4 7% 8% 43%	1680
	21st to end	Night	10% 5% 2 5% 5% 5% 5% 5% 7% 8% 45%	1680
July	1st to 10th	Night	10% 6% 2 6% 4 5% 5% 4 6% 9% 44%	4708
	11th to 20th	Night	6% 4 2 4 3 4 4 3 6% 8% 56%	4707
	21st to end	Night	10% 6% 2 6% 4 4 3 4 5% 7% 51%	5117
August	1st to 10th	Night	14% 6% 2 6% 4 3 4 3 5% 7% 46%	4023
	11th to 20th	Night	12% 6% 3 7% 4 4 5% 4 6% 7% 43%	4095
	21st to end	Night	8% 6% 2 7% 5% 4 4 3 6% 8% 47%	5015
September	1st to 10th	Night	9% 5% 3 5% 4 4 5% 3 5% 7% 50%	2100
	11th to 20th	Night	10% 4 2 5% 3 3 4 3 5% 6% 54%	2308
	21st to end	Night	12% 8% 2 6% 5% 5% 4 2 5% 7% 44%	2310
October	1st to 10th	Night	18% 5% 2 4 3 3 3 2 4 7% 48%	2310
	11th to 20th	Night	20% 11% 2 8% 5% 3 3 3 5% 6% 35%	2578
	21st to end	Night	23% 10% 3 6% 4 3 3 3 5% 6% 33%	2965
November	1st to 10th	Night	15% 12% 3 7% 5% 4 4 3 5% 6% 36%	2666
	11th to 20th	Night	18% 16% 5% 10% 4 5% 4 4 5% 6% 23%	2730
	21st to end	Night	18% 18% 7% 9% 5% 4 3 3 4 6% 22%	2730
December	1st to 10th	Night	11% 23% 9% 14% 5% 4 4 4 4 5% 16%	4676
	11th to 20th	Night	17% 23% 10% 15% 7% 4 3 3 3 4 11%	5339
	21st to end	Night	25% 21% 6% 11% 5% 4 3 3 4 5% 13%	7150

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	80% 5% 7% 7% 1	4692
	11th to 20th	Day	84% 4 6% 4 2	4710
	21st to end	Day	78% 3 8% 8% 3	5156
February	1st to 10th	Day	69% 5% 8% 14% 4	1923
	11th to 20th	Day	66% 4 9% 14% 7% 1	2058
	21st to end	Day	63% 4 12% 15% 6%	1730
March	1st to 10th	Day	53% 4 15% 19% 9% 1	4580
	11th to 20th	Day	45% 5% 17% 23% 9% 1	4918
	21st to end	Day	60% 3 10% 16% 10% 1	5854
April	1st to 10th	Day	55% 4 10% 20% 11% 1	2520
	11th to 20th	Day	48% 4 10% 23% 14% 2	2540
	21st to end	Day	47% 4 13% 20% 14% 2	2730
May	1st to 10th	Day	42% 5% 11% 25% 16% 1	7651
	11th to 20th	Day	42% 5% 12% 21% 17% 2	7708
	21st to end	Day	37% 4 10% 24% 22% 4	9061
June	1st to 10th	Day	36% 4 11% 28% 19% 2	2940
	11th to 20th	Day	35% 5% 14% 25% 20% 2	2940
	21st to end	Day	35% 5% 16% 24% 17% 2	2940
July	1st to 10th	Day	36% 6% 13% 25% 17% 2	8211
	11th to 20th	Day	27% 6% 12% 30% 24% 1	8205
	21st to end	Day	31% 6% 13% 26% 22% 1	8794
August	1st to 10th	Day	39% 6% 13% 26% 16% 1	6116
	11th to 20th	Day	38% 7% 14% 28% 13% 1	5990
	21st to end	Day	34% 6% 15% 30% 14% 1	6107
September	1st to 10th	Day	37% 5% 14% 27% 14% 2	2500
	11th to 20th	Day	34% 4 12% 31% 18% 2	2310
	21st to end	Day	41% 4 11% 25% 17% 1	2310
October	1st to 10th	Day	29% 3 8% 39% 19% 1	3700
	11th to 20th	Day	42% 5% 13% 24% 16%	3227
	21st to end	Day	50% 5% 12% 23% 10% 1	3252
November	1st to 10th	Day	49% 5% 13% 20% 12%	1852
	11th to 20th	Day	65% 4 10% 15% 5% 1	1890
	21st to end	Day	66% 4 13% 13% 4	1890
December	1st to 10th	Day	73% 7% 10% 8% 2	2731
	11th to 20th	Day	81% 3 8% 7% 1	3085
	21st to end	Day	77% 3 7% 10% 3	4070
January	1st to 10th	Night	74% 4 7% 10% 4	8233
	11th to 20th	Night	85% 4 5% 4 3	8280
	21st to end	Night	76% 4 10% 7% 2	9058
February	1st to 10th	Night	69% 3 9% 13% 6%	2693
	11th to 20th	Night	64% 5% 8% 17% 7% 1	2459
	21st to end	Night	61% 4 12% 16% 7% 1	2076
March	1st to 10th	Night	48% 4 14% 25% 8% 1	5493
	11th to 20th	Night	39% 4 14% 28% 12% 2	5261
	21st to end	Night	55% 4 10% 18% 12% 1	5363
April	1st to 10th	Night	51% 4 10% 21% 14% 1	2100
	11th to 20th	Night	49% 4 6% 19% 18% 3	2028
	21st to end	Night	45% 3 12% 21% 15% 3	1890
May	1st to 10th	Night	45% 5% 11% 21% 16% 2	5264
	11th to 20th	Night	39% 5% 11% 24% 18% 3	5146
	21st to end	Night	41% 4 8% 21% 22% 4	5149
June	1st to 10th	Night	36% 5% 10% 28% 18% 3	1680
	11th to 20th	Night	37% 6% 13% 24% 19% 2	1680
	21st to end	Night	36% 5% 15% 26% 16% 2	1680
July	1st to 10th	Night	36% 6% 13% 26% 15% 4	4670
	11th to 20th	Night	25% 5% 12% 29% 26% 2	4662
	21st to end	Night	34% 5% 11% 24% 24% 3	5002
August	1st to 10th	Night	37% 5% 12% 27% 18% 1	4014
	11th to 20th	Night	38% 7% 13% 29% 13% 1	4122
	21st to end	Night	34% 7% 11% 30% 16% 1	5015
September	1st to 10th	Night	33% 6% 12% 28% 18% 2	2100
	11th to 20th	Night	31% 3 10% 32% 21% 2	2308
	21st to end	Night	41% 4 12% 27% 15% 2	2310
October	1st to 10th	Night	28% 4 8% 36% 22% 2	3700
	11th to 20th	Night	41% 4 12% 24% 19% 1	4114
	21st to end	Night	44% 4 10% 27% 16% 1	4715
November	1st to 10th	Night	50% 5% 8% 23% 12% 1	2666
	11th to 20th	Night	61% 4 11% 17% 6% 1	2730
	21st to end	Night	63% 5% 13% 16% 3	2730
December	1st to 10th	Night	69% 6% 13% 9% 2	4676
	11th to 20th	Night	79% 4 8% 7% 2	5341
	21st to end	Night	74% 4 9% 9% 3	7150

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	20% 16% 35% 23% 5% 2	330
	11th to 20th	Day	21% 19% 40% 16% 5%	330
	21st to end	Day	26% 17% 31% 22% 3	363
February	1st to 10th	Day	17% 25% 33% 19% 5% 2	330
	11th to 20th	Day	21% 19% 39% 16% 6%	330
	21st to end	Day	23% 26% 37% 11% 2 1	273
March	1st to 10th	Day	22% 21% 41% 12% 4	330
	11th to 20th	Day	22% 17% 28% 25% 7% 1	459
	21st to end	Day	25% 15% 32% 21% 5% 1	594
April	1st to 10th	Day	24% 16% 32% 22% 6% 1	540
	11th to 20th	Day	23% 21% 28% 21% 5% 3	532
	21st to end	Day	22% 13% 30% 22% 11% 1	540
May	1st to 10th	Day	20% 13% 33% 22% 10% 2	543
	11th to 20th	Day	17% 12% 28% 26% 14% 3	593
	21st to end	Day	14% 8% 29% 27% 15% 5%	844
June	1st to 10th	Day	11% 7% 34% 30% 13% 4	780
	11th to 20th	Day	14% 8% 30% 31% 13% 4	780
	21st to end	Day	11% 8% 33% 31% 13% 4	780
July	1st to 10th	Day	8% 3 28% 31% 21% 9%	771
	11th to 20th	Day	9% 6% 25% 34% 19% 7%	768
	21st to end	Day	9% 4 28% 35% 17% 7%	849
August	1st to 10th	Day	11% 4 20% 28% 25% 12%	619
	11th to 20th	Day	10% 5% 20% 31% 24% 10%	559
	21st to end	Day	10% 5% 20% 31% 24% 10%	627
September	1st to 10th	Day	14% 5% 19% 31% 21% 9%	570
	11th to 20th	Day	10% 5% 18% 25% 27% 14%	570
	21st to end	Day	16% 9% 23% 25% 19% 8%	570
October	1st to 10th	Day	15% 10% 28% 27% 16% 4	570
	11th to 20th	Day	21% 17% 28% 26% 7% 1	443
	21st to end	Day	27% 12% 34% 21% 4 2	387
November	1st to 10th	Day	20% 17% 32% 23% 8% 1	330
	11th to 20th	Day	22% 22% 34% 17% 4 1	330
	21st to end	Day	25% 19% 40% 11% 5%	330
December	1st to 10th	Day	23% 22% 32% 14% 8% 1	330
	11th to 20th	Day	21% 24% 35% 16% 4 1	330
	21st to end	Day	27% 19% 35% 14% 3 1	363
January	1st to 10th	Night	21% 15% 34% 24% 7%	1050
	11th to 20th	Night	23% 15% 33% 23% 5%	1050
	21st to end	Night	22% 11% 33% 30% 5%	1155
February	1st to 10th	Night	20% 11% 37% 27% 4	892
	11th to 20th	Night	21% 13% 34% 26% 6%	823
	21st to end	Night	23% 13% 39% 22% 3	692
March	1st to 10th	Night	19% 11% 34% 27% 7%	840
	11th to 20th	Night	17% 12% 34% 29% 8% 1	840
	21st to end	Night	21% 11% 29% 30% 9%	828
April	1st to 10th	Night	20% 10% 33% 30% 7%	630
	11th to 20th	Night	25% 9% 30% 26% 9% 1	623
	21st to end	Night	19% 7% 31% 33% 8% 1	630
May	1st to 10th	Night	17% 6% 32% 35% 10% 1	630
	11th to 20th	Night	18% 5% 28% 35% 13%	621
	21st to end	Night	16% 3 23% 37% 19% 2	683
June	1st to 10th	Night	11% 4 25% 41% 18%	630
	11th to 20th	Night	11% 4 27% 40% 17%	630
	21st to end	Night	11% 3 22% 44% 19% 1	630
July	1st to 10th	Night	8% 2 16% 41% 30% 3	615
	11th to 20th	Night	7% 3 18% 41% 27% 3	612
	21st to end	Night	8% 2 16% 45% 28% 1	690
August	1st to 10th	Night	9% 2 14% 44% 27% 3	627
	11th to 20th	Night	11% 2 14% 41% 27% 5%	624
	21st to end	Night	11% 3 15% 39% 29% 3	693
September	1st to 10th	Night	11% 3 16% 40% 25% 4	630
	11th to 20th	Night	11% 5% 16% 35% 28% 5%	838
	21st to end	Night	14% 7% 22% 32% 22% 4	840
October	1st to 10th	Night	19% 5% 22% 35% 18% 1	840
	11th to 20th	Night	25% 10% 25% 28% 10% 1	840
	21st to end	Night	28% 10% 29% 25% 7% 1	913
November	1st to 10th	Night	22% 11% 31% 26% 10%	820
	11th to 20th	Night	25% 15% 32% 23% 5%	840
	21st to end	Night	27% 12% 31% 26% 4	840
December	1st to 10th	Night	25% 15% 31% 22% 6%	1019
	11th to 20th	Night	27% 13% 34% 22% 4	1050
	21st to end	Night	31% 11% 36% 20% 2	1155

Page generated at 2026-10-26 04:37:49. Version ac07

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