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 2024-03-23.

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% 5% 7% 6% 3 5% 4 5% 7% 33%	78632
	Night	16% 12% 5% 8% 6% 3 4 4 5% 6% 30%	81311
Transparency	Day	52% 4 12% 20% 11% 1	78333
	Night	56% 4 10% 18% 10% 1	81131
Seeing	Day	16% 11% 29% 26% 14% 5%	14877
	Night	19% 8% 28% 31% 13% 1	24941

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% 23% 10% 13% 10% 5% 5% 4 3 3 10%	2527
	11th to 20th	Day	13% 16% 11% 15% 17% 8% 3 4 3 4 6%	2530
	21st to end	Day	22% 23% 10% 15% 8% 4 4 3 2 2 8%	2783
February	1st to 10th	Day	12% 15% 8% 13% 13% 5% 5% 4 5% 4 17%	1738
	11th to 20th	Day	12% 13% 7% 13% 11% 4 5% 4 4 5% 21%	1848
	21st to end	Day	14% 14% 7% 12% 7% 3 5% 4 5% 6% 22%	1570
March	1st to 10th	Day	14% 12% 5% 8% 7% 4 5% 5% 5% 7% 28%	1900
	11th to 20th	Day	13% 10% 4 7% 6% 3 5% 5% 5% 7% 36%	2017
	21st to end	Day	18% 10% 4 7% 6% 3 5% 4 5% 6% 32%	2297
April	1st to 10th	Day	19% 11% 5% 7% 5% 3 4 4 5% 7% 30%	2160
	11th to 20th	Day	17% 9% 4 6% 5% 3 4 4 6% 7% 36%	2173
	21st to end	Day	17% 8% 4 6% 5% 3 5% 4 5% 8% 35%	2340
May	1st to 10th	Day	17% 7% 3 6% 6% 3 5% 5% 5% 8% 37%	2340
	11th to 20th	Day	18% 7% 2 6% 4 3 4 4 5% 8% 40%	2323
	21st to end	Day	11% 6% 3 5% 5% 3 5% 4 5% 9% 45%	2725
June	1st to 10th	Day	10% 4 2 4 5% 3 5% 5% 6% 9% 46%	2520
	11th to 20th	Day	11% 4 2 5% 5% 3 5% 3 5% 8% 49%	2520
	21st to end	Day	11% 5% 3 5% 4 3 5% 5% 5% 10% 45%	2520
July	1st to 10th	Day	6% 4 2 3 4 3 5% 5% 5% 9% 54%	2520
	11th to 20th	Day	10% 4 1 4 4 3 5% 5% 6% 9% 48%	2520
	21st to end	Day	8% 4 2 4 5% 3 4 6% 6% 9% 48%	2743
August	1st to 10th	Day	10% 4 2 4 5% 3 4 4 7% 10% 46%	2373
	11th to 20th	Day	10% 4 2 5% 5% 3 5% 4 6% 9% 47%	2303
	21st to end	Day	10% 5% 2 5% 5% 3 4 4 5% 9% 47%	2390
September	1st to 10th	Day	11% 6% 3 5% 5% 4 4 4 6% 8% 44%	2143
	11th to 20th	Day	11% 4 2 4 4 3 5% 4 6% 8% 47%	1980
	21st to end	Day	12% 7% 3 5% 6% 4 5% 4 5% 8% 42%	1980
October	1st to 10th	Day	17% 7% 2 6% 6% 3 5% 3 3 5% 43%	1980
	11th to 20th	Day	23% 10% 3 7% 6% 4 5% 5% 5% 6% 25%	1747
	21st to end	Day	25% 11% 4 7% 7% 5% 5% 4 4 5% 23%	1782
November	1st to 10th	Day	13% 12% 3 6% 5% 3 5% 5% 4 7% 36%	1672
	11th to 20th	Day	17% 19% 6% 9% 6% 3 4 5% 4 5% 22%	1710
	21st to end	Day	21% 17% 6% 7% 7% 3 5% 3 4 6% 22%	1710
December	1st to 10th	Day	14% 22% 12% 13% 7% 3 4 3 4 5% 13%	1547
	11th to 20th	Day	14% 19% 12% 13% 8% 4 5% 4 5% 4 13%	1918
	21st to end	Day	21% 25% 8% 11% 8% 3 4 3 3 4 10%	2783
January	1st to 10th	Night	16% 22% 11% 13% 7% 3 4 3 3 4 13%	4428
	11th to 20th	Night	14% 18% 10% 17% 14% 6% 4 3 3 3 9%	4440
	21st to end	Night	23% 19% 10% 12% 8% 3 4 4 3 4 10%	4884
February	1st to 10th	Night	13% 16% 7% 13% 10% 4 5% 4 4 4 19%	2438
	11th to 20th	Night	14% 13% 7% 12% 9% 3 5% 5% 4 5% 24%	2218
	21st to end	Night	16% 14% 5% 10% 7% 3 5% 4 5% 5% 25%	1884
March	1st to 10th	Night	16% 9% 4 7% 6% 3 5% 5% 5% 7% 34%	2280
	11th to 20th	Night	12% 9% 3 6% 5% 4 4 5% 4 7% 41%	2162
	21st to end	Night	19% 8% 3 6% 6% 3 4 5% 5% 7% 33%	2120
April	1st to 10th	Night	15% 9% 4 6% 6% 4 4 5% 6% 6% 35%	1800
	11th to 20th	Night	20% 8% 2 6% 4 3 4 5% 5% 6% 37%	1736
	21st to end	Night	18% 8% 3 5% 5% 2 4 5% 5% 6% 39%	1620
May	1st to 10th	Night	16% 8% 4 5% 7% 4 4 5% 5% 8% 35%	1620
	11th to 20th	Night	18% 6% 2 5% 5% 3 4 5% 5% 8% 40%	1568
	21st to end	Night	12% 7% 2 6% 6% 3 5% 5% 5% 8% 41%	1551
June	1st to 10th	Night	11% 5% 2 4 5% 3 5% 5% 5% 8% 47%	1440
	11th to 20th	Night	10% 6% 3 5% 6% 2 4 5% 6% 9% 46%	1440
	21st to end	Night	10% 4 2 4 5% 4 5% 5% 7% 9% 45%	1440
July	1st to 10th	Night	6% 3 2 5% 4 2 4 5% 5% 9% 53%	1440
	11th to 20th	Night	7% 4 1 4 4 3 5% 5% 6% 8% 52%	1440
	21st to end	Night	7% 4 2 5% 5% 2 4 5% 6% 7% 53%	1575
August	1st to 10th	Night	9% 4 2 4 4 3 4 4 7% 8% 51%	1565
	11th to 20th	Night	10% 4 2 3 5% 3 4 5% 7% 8% 50%	1598
	21st to end	Night	10% 5% 2 5% 5% 3 4 3 6% 7% 51%	1963
September	1st to 10th	Night	10% 5% 3 5% 4 3 5% 4 5% 8% 49%	1800
	11th to 20th	Night	11% 4 2 4 4 2 4 4 5% 6% 54%	1978
	21st to end	Night	12% 7% 2 5% 6% 3 4 3 5% 8% 44%	1980
October	1st to 10th	Night	19% 5% 2 4 4 2 3 3 4 7% 45%	1980
	11th to 20th	Night	22% 11% 3 7% 6% 2 3 4 4 6% 33%	2209
	21st to end	Night	25% 10% 3 6% 5% 2 4 3 5% 6% 31%	2574
November	1st to 10th	Night	15% 12% 3 6% 5% 3 4 4 5% 6% 37%	2406
	11th to 20th	Night	19% 15% 6% 9% 5% 4 4 5% 5% 6% 22%	2470
	21st to end	Night	19% 16% 7% 8% 5% 3 4 4 4 7% 24%	2470
December	1st to 10th	Night	17% 20% 10% 12% 7% 3 4 4 4 5% 14%	2631
	11th to 20th	Night	16% 19% 11% 11% 7% 3 4 4 4 4 16%	3279
	21st to end	Night	27% 20% 7% 10% 6% 3 3 4 3 5% 12%	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	78% 5% 8% 7% 1	2528
	11th to 20th	Day	83% 4 7% 5% 1	2530
	21st to end	Day	85% 2 6% 5% 2	2783
February	1st to 10th	Day	71% 4 8% 14% 3	1738
	11th to 20th	Day	66% 4 8% 15% 7%	1858
	21st to end	Day	63% 4 12% 15% 6%	1570
March	1st to 10th	Day	55% 4 13% 19% 8% 1	1900
	11th to 20th	Day	48% 4 14% 21% 11% 2	2017
	21st to end	Day	54% 4 12% 20% 8% 1	2297
April	1st to 10th	Day	54% 4 10% 20% 11% 1	2160
	11th to 20th	Day	48% 3 10% 22% 14% 3	2173
	21st to end	Day	49% 4 13% 18% 15% 2	2340
May	1st to 10th	Day	46% 5% 12% 25% 12% 1	2340
	11th to 20th	Day	45% 4 12% 22% 15% 3	2327
	21st to end	Day	38% 5% 14% 26% 15% 1	2725
June	1st to 10th	Day	36% 5% 12% 29% 17% 2	2520
	11th to 20th	Day	35% 4 13% 24% 21% 2	2520
	21st to end	Day	36% 5% 16% 24% 18% 2	2520
July	1st to 10th	Day	28% 4 13% 32% 18% 4	2451
	11th to 20th	Day	32% 6% 12% 28% 19% 3	2445
	21st to end	Day	31% 6% 13% 26% 21% 3	2591
August	1st to 10th	Day	33% 5% 15% 32% 13% 2	2358
	11th to 20th	Day	34% 6% 15% 28% 16% 2	2303
	21st to end	Day	35% 3 14% 26% 18% 3	2390
September	1st to 10th	Day	39% 5% 14% 26% 14% 3	2143
	11th to 20th	Day	35% 4 12% 33% 14% 2	1980
	21st to end	Day	41% 4 12% 25% 17%	1980
October	1st to 10th	Day	46% 4 8% 26% 14% 1	1980
	11th to 20th	Day	59% 4 13% 16% 8%	1747
	21st to end	Day	63% 4 11% 15% 6% 1	1782
November	1st to 10th	Day	49% 5% 13% 20% 12% 1	1672
	11th to 20th	Day	65% 4 10% 15% 5% 1	1710
	21st to end	Day	65% 4 13% 13% 4	1710
December	1st to 10th	Day	76% 4 8% 9% 3	1547
	11th to 20th	Day	76% 3 11% 9% 1	1915
	21st to end	Day	80% 3 8% 8% 2	2783
January	1st to 10th	Night	77% 3 7% 8% 4	4428
	11th to 20th	Night	82% 4 6% 5% 3	4440
	21st to end	Night	81% 3 9% 5% 2	4884
February	1st to 10th	Night	70% 3 9% 12% 6%	2438
	11th to 20th	Night	64% 4 8% 17% 7%	2219
	21st to end	Night	62% 4 11% 15% 7% 1	1884
March	1st to 10th	Night	51% 4 13% 22% 8% 1	2280
	11th to 20th	Night	44% 4 11% 24% 13% 3	2162
	21st to end	Night	52% 3 10% 22% 11% 2	2120
April	1st to 10th	Night	50% 4 10% 22% 14% 1	1800
	11th to 20th	Night	49% 4 7% 18% 19% 3	1736
	21st to end	Night	46% 3 12% 20% 16% 4	1620
May	1st to 10th	Night	50% 3 10% 22% 12% 2	1620
	11th to 20th	Night	43% 4 11% 20% 18% 3	1569
	21st to end	Night	42% 5% 11% 24% 15% 2	1552
June	1st to 10th	Night	36% 4 10% 29% 18% 3	1440
	11th to 20th	Night	35% 5% 13% 25% 19% 2	1440
	21st to end	Night	36% 4 15% 26% 15% 3	1440
July	1st to 10th	Night	28% 5% 14% 29% 20% 5%	1400
	11th to 20th	Night	29% 4 14% 29% 21% 2	1392
	21st to end	Night	31% 5% 12% 26% 21% 4	1487
August	1st to 10th	Night	30% 5% 15% 31% 16% 2	1556
	11th to 20th	Night	31% 5% 13% 32% 17% 2	1598
	21st to end	Night	34% 4 10% 28% 21% 3	1963
September	1st to 10th	Night	34% 6% 11% 28% 18% 3	1800
	11th to 20th	Night	32% 3 10% 34% 18% 2	1978
	21st to end	Night	40% 4 13% 28% 14% 1	1980
October	1st to 10th	Night	41% 4 8% 28% 17% 2	1980
	11th to 20th	Night	54% 4 11% 20% 10% 1	2209
	21st to end	Night	56% 4 12% 18% 10%	2574
November	1st to 10th	Night	49% 5% 8% 24% 13% 1	2406
	11th to 20th	Night	62% 4 11% 16% 6% 1	2470
	21st to end	Night	62% 5% 13% 16% 3	2470
December	1st to 10th	Night	75% 4 8% 10% 4	2631
	11th to 20th	Night	73% 4 10% 9% 3	3281
	21st to end	Night	77% 3 11% 7% 2	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% 16% 32% 26% 5% 2	270
	11th to 20th	Day	23% 13% 39% 19% 6%	270
	21st to end	Day	26% 14% 33% 24% 4	297
February	1st to 10th	Day	16% 24% 31% 22% 5% 2	270
	11th to 20th	Day	19% 19% 40% 16% 7%	270
	21st to end	Day	22% 25% 37% 13% 3	225
March	1st to 10th	Day	19% 23% 41% 12% 5%	270
	11th to 20th	Day	19% 16% 28% 27% 8% 1	387
	21st to end	Day	27% 12% 29% 24% 7% 2	470
April	1st to 10th	Day	23% 12% 33% 24% 7% 1	420
	11th to 20th	Day	22% 20% 26% 23% 5% 4	412
	21st to end	Day	22% 13% 31% 20% 13% 1	420
May	1st to 10th	Day	22% 11% 31% 23% 10% 3	423
	11th to 20th	Day	17% 10% 26% 28% 16% 4	469
	21st to end	Day	14% 8% 27% 29% 16% 6%	679
June	1st to 10th	Day	11% 5% 34% 31% 14% 5%	630
	11th to 20th	Day	14% 5% 26% 35% 14% 5%	630
	21st to end	Day	11% 6% 31% 33% 14% 5%	630
July	1st to 10th	Day	6% 3 26% 31% 23% 11%	621
	11th to 20th	Day	9% 6% 24% 34% 20% 7%	618
	21st to end	Day	9% 3 27% 37% 18% 7%	684
August	1st to 10th	Day	10% 3 19% 27% 27% 13%	492
	11th to 20th	Day	10% 4 18% 30% 26% 12%	439
	21st to end	Day	11% 5% 18% 33% 24% 10%	495
September	1st to 10th	Day	15% 5% 17% 33% 22% 9%	450
	11th to 20th	Day	8% 5% 18% 27% 28% 13%	450
	21st to end	Day	15% 10% 22% 24% 21% 8%	450
October	1st to 10th	Day	16% 10% 27% 25% 17% 5%	450
	11th to 20th	Day	24% 19% 27% 25% 6%	342
	21st to end	Day	32% 10% 37% 14% 5% 2	297
November	1st to 10th	Day	18% 18% 30% 24% 9% 1	270
	11th to 20th	Day	19% 23% 36% 17% 4 1	270
	21st to end	Day	26% 16% 41% 13% 5%	270
December	1st to 10th	Day	24% 20% 34% 14% 8%	270
	11th to 20th	Day	20% 21% 36% 17% 4 1	270
	21st to end	Day	25% 20% 36% 16% 3	297
January	1st to 10th	Night	22% 14% 33% 24% 7%	950
	11th to 20th	Night	24% 13% 33% 24% 6% 1	950
	21st to end	Night	22% 9% 32% 32% 5%	1045
February	1st to 10th	Night	20% 11% 37% 27% 4	808
	11th to 20th	Night	21% 12% 34% 27% 6%	743
	21st to end	Night	24% 12% 39% 22% 3	628
March	1st to 10th	Night	19% 10% 34% 29% 7% 1	760
	11th to 20th	Night	15% 11% 34% 30% 8% 1	760
	21st to end	Night	21% 9% 29% 31% 10% 1	720
April	1st to 10th	Night	18% 9% 33% 32% 7% 1	540
	11th to 20th	Night	25% 7% 31% 29% 9% 1	533
	21st to end	Night	20% 7% 30% 33% 9% 1	540
May	1st to 10th	Night	18% 5% 30% 35% 11% 1	540
	11th to 20th	Night	20% 5% 26% 36% 14%	531
	21st to end	Night	16% 3 22% 36% 22% 2	584
June	1st to 10th	Night	11% 4 23% 42% 19%	540
	11th to 20th	Night	12% 3 25% 41% 19%	540
	21st to end	Night	11% 3 20% 43% 21% 2	540
July	1st to 10th	Night	7% 1 15% 41% 32% 3	525
	11th to 20th	Night	6% 3 18% 42% 28% 3	522
	21st to end	Night	8% 2 15% 45% 29% 1	591
August	1st to 10th	Night	9% 1 14% 44% 28% 3	537
	11th to 20th	Night	11% 2 14% 39% 29% 6%	534
	21st to end	Night	11% 3 15% 39% 28% 4	594
September	1st to 10th	Night	12% 3 16% 41% 24% 4	540
	11th to 20th	Night	12% 5% 16% 35% 26% 5%	718
	21st to end	Night	14% 7% 22% 30% 22% 5%	720
October	1st to 10th	Night	21% 5% 21% 33% 19% 1	720
	11th to 20th	Night	28% 11% 25% 27% 9% 1	720
	21st to end	Night	30% 10% 30% 23% 6% 1	792
November	1st to 10th	Night	21% 11% 30% 27% 10%	740
	11th to 20th	Night	26% 14% 32% 23% 5%	760
	21st to end	Night	26% 12% 31% 27% 4	760
December	1st to 10th	Night	26% 15% 31% 22% 6%	921
	11th to 20th	Night	25% 13% 34% 23% 5%	950
	21st to end	Night	31% 11% 36% 20% 2	1045

Page generated at 2024-03-19 23:31:04. Version ac07

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