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 2024-11-03.

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 8% 5% 5% 4 3 5% 7% 35%	101263
	Night	15% 12% 4 9% 5% 4 4 3 5% 6% 32%	97796
Transparency	Day	49% 4 12% 21% 13% 1	101054
	Night	54% 4 10% 19% 11% 1	97677
Seeing	Day	16% 11% 29% 26% 13% 5%	15833
	Night	19% 8% 28% 31% 13% 1	25673

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% 24% 10% 15% 8% 6% 4 3 4 3 10%	2527
	11th to 20th	Day	13% 17% 10% 17% 14% 9% 3 4 3 4 6%	2530
	21st to end	Day	21% 24% 9% 17% 6% 5% 3 2 2 2 8%	2783
February	1st to 10th	Day	11% 17% 6% 15% 11% 6% 4 3 5% 4 17%	1738
	11th to 20th	Day	12% 15% 6% 16% 9% 5% 4 2 5% 5% 21%	1848
	21st to end	Day	14% 16% 6% 13% 5% 5% 4 3 5% 6% 22%	1570
March	1st to 10th	Day	15% 13% 4 7% 5% 5% 5% 3 5% 7% 30%	3120
	11th to 20th	Day	11% 8% 5% 9% 6% 5% 5% 4 5% 6% 35%	3368
	21st to end	Day	19% 13% 6% 9% 5% 4 3 3 5% 5% 29%	3994
April	1st to 10th	Day	19% 13% 4 8% 4 4 3 3 5% 6% 31%	2280
	11th to 20th	Day	17% 10% 3 6% 4 4 4 3 5% 7% 37%	2296
	21st to end	Day	17% 8% 3 7% 4 4 4 4 5% 8% 35%	2470
May	1st to 10th	Day	16% 7% 2 6% 4 4 4 3 5% 8% 39%	4082
	11th to 20th	Day	14% 7% 2 5% 4 4 4 3 6% 9% 42%	4131
	21st to end	Day	10% 6% 2 5% 4 4 4 4 6% 9% 46%	4824
June	1st to 10th	Day	10% 5% 2 5% 5% 4 5% 4 6% 9% 45%	2660
	11th to 20th	Day	11% 5% 2 5% 4 4 4 3 6% 8% 48%	2660
	21st to end	Day	11% 6% 2 6% 4 4 4 4 6% 9% 44%	2660
July	1st to 10th	Day	12% 7% 3 7% 4 5% 5% 4 6% 8% 40%	4440
	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% 3 7% 4 5% 4 4 5% 7% 36%	1690
	11th to 20th	Day	16% 20% 6% 10% 5% 5% 3 4 4 5% 21%	1710
	21st to end	Day	21% 18% 5% 8% 6% 4 4 3 4 6% 21%	1710
December	1st to 10th	Day	14% 25% 10% 14% 7% 4 3 3 4 4 13%	1547
	11th to 20th	Day	14% 21% 10% 14% 6% 6% 4 3 5% 4 13%	1918
	21st to end	Day	21% 26% 7% 13% 6% 4 3 2 3 4 10%	2783
January	1st to 10th	Night	15% 23% 11% 15% 6% 4 4 2 3 3 13%	4428
	11th to 20th	Night	14% 19% 10% 19% 12% 6% 4 2 3 2 9%	4440
	21st to end	Night	22% 21% 9% 14% 6% 4 4 3 3 4 10%	4884
February	1st to 10th	Night	13% 19% 5% 14% 9% 5% 4 3 4 4 19%	2438
	11th to 20th	Night	13% 15% 6% 13% 8% 4 4 4 4 5% 24%	2218
	21st to end	Night	16% 15% 4 11% 6% 4 4 3 5% 5% 25%	1884
March	1st to 10th	Night	16% 8% 4 8% 5% 4 4 4 4 6% 36%	3733
	11th to 20th	Night	9% 7% 2 7% 4 4 5% 4 6% 8% 44%	3591
	21st to end	Night	17% 11% 5% 9% 6% 5% 4 4 5% 6% 27%	3667
April	1st to 10th	Night	15% 11% 3 7% 5% 5% 4 4 5% 6% 36%	1900
	11th to 20th	Night	21% 9% 2 6% 4 4 4 4 5% 6% 36%	1833
	21st to end	Night	17% 8% 3 6% 5% 4 4 4 5% 6% 39%	1710
May	1st to 10th	Night	15% 8% 3 7% 6% 4 5% 3 6% 7% 36%	2813
	11th to 20th	Night	18% 7% 2 7% 4 4 3 3 5% 7% 40%	2762
	21st to end	Night	15% 8% 3 6% 4 5% 4 3 5% 6% 41%	2743
June	1st to 10th	Night	11% 6% 2 5% 4 4 5% 4 6% 8% 46%	1520
	11th to 20th	Night	9% 6% 2 6% 4 4 4 4 6% 8% 45%	1520
	21st to end	Night	10% 5% 2 5% 5% 5% 5% 5% 7% 8% 44%	1520
July	1st to 10th	Night	9% 6% 3 7% 4 5% 5% 4 6% 9% 41%	2530
	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 6% 5% 4 4 3 5% 6% 37%	2433
	11th to 20th	Night	18% 16% 5% 10% 4 5% 4 4 6% 6% 22%	2470
	21st to end	Night	18% 18% 6% 9% 5% 4 3 3 4 7% 23%	2470
December	1st to 10th	Night	16% 23% 8% 13% 6% 4 4 3 4 5% 14%	2631
	11th to 20th	Night	16% 21% 9% 13% 6% 4 5% 3 4 4 15%	3279
	21st to end	Night	26% 21% 6% 11% 5% 4 4 3 4 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% 3 13% 21% 8%	3120
	11th to 20th	Day	49% 5% 15% 21% 9% 1	3368
	21st to end	Day	59% 4 10% 19% 7% 1	3994
April	1st to 10th	Day	54% 4 10% 20% 11% 1	2280
	11th to 20th	Day	48% 3 10% 22% 14% 3	2296
	21st to end	Day	48% 4 12% 19% 15% 2	2470
May	1st to 10th	Day	44% 4 12% 24% 15% 1	4120
	11th to 20th	Day	40% 3 14% 25% 15% 3	4135
	21st to end	Day	36% 4 13% 22% 23% 2	4837
June	1st to 10th	Day	36% 4 11% 29% 17% 2	2660
	11th to 20th	Day	34% 4 13% 25% 21% 2	2660
	21st to end	Day	36% 5% 15% 24% 18% 2	2660
July	1st to 10th	Day	42% 5% 13% 22% 15% 3	4371
	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	44% 4 8% 28% 14% 1	2090
	11th to 20th	Day	57% 4 13% 17% 9%	1843
	21st to end	Day	61% 4 11% 17% 6% 1	1881
November	1st to 10th	Day	49% 5% 13% 21% 12% 1	1690
	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	50% 3 13% 26% 7% 1	3733
	11th to 20th	Night	38% 5% 14% 26% 15% 3	3591
	21st to end	Night	58% 4 11% 18% 9% 1	3667
April	1st to 10th	Night	50% 4 10% 22% 14% 1	1900
	11th to 20th	Night	49% 4 6% 19% 19% 3	1833
	21st to end	Night	46% 3 12% 20% 16% 4	1710
May	1st to 10th	Night	48% 3 11% 21% 15% 2	2840
	11th to 20th	Night	44% 3 9% 23% 17% 3	2763
	21st to end	Night	45% 3 9% 19% 22% 2	2751
June	1st to 10th	Night	36% 4 11% 29% 17% 3	1520
	11th to 20th	Night	36% 5% 13% 25% 19% 2	1520
	21st to end	Night	37% 5% 15% 25% 16% 3	1520
July	1st to 10th	Night	39% 6% 12% 24% 12% 7%	2490
	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	39% 4 8% 29% 18% 2	2090
	11th to 20th	Night	52% 4 11% 21% 11% 1	2332
	21st to end	Night	55% 4 12% 19% 10%	2717
November	1st to 10th	Night	49% 5% 8% 24% 12% 1	2433
	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	26% 13% 30% 23% 6% 2	506
April	1st to 10th	Day	22% 14% 33% 23% 7% 1	460
	11th to 20th	Day	22% 21% 27% 22% 5% 3	452
	21st to end	Day	22% 13% 31% 21% 12% 1	460
May	1st to 10th	Day	22% 11% 32% 24% 10% 2	463
	11th to 20th	Day	16% 10% 27% 28% 15% 4	511
	21st to end	Day	14% 8% 27% 29% 17% 6%	734
June	1st to 10th	Day	11% 7% 33% 30% 14% 5%	680
	11th to 20th	Day	13% 6% 29% 33% 14% 5%	680
	21st to end	Day	12% 7% 32% 32% 13% 4	680
July	1st to 10th	Day	7% 3 27% 30% 22% 10%	671
	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	30% 12% 36% 16% 4 2	330
November	1st to 10th	Day	18% 18% 30% 24% 9% 1	276
	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% 9% 1	750
April	1st to 10th	Night	18% 9% 34% 32% 7% 1	570
	11th to 20th	Night	25% 8% 31% 28% 8% 1	563
	21st to end	Night	20% 7% 31% 33% 9% 1	570
May	1st to 10th	Night	17% 6% 30% 35% 10% 1	570
	11th to 20th	Night	19% 5% 26% 36% 14%	561
	21st to end	Night	16% 3 22% 36% 21% 2	617
June	1st to 10th	Night	11% 4 24% 41% 19%	570
	11th to 20th	Night	11% 3 27% 40% 18%	570
	21st to end	Night	11% 3 21% 43% 20% 2	570
July	1st to 10th	Night	8% 1 16% 41% 30% 3	555
	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	21% 11% 29% 27% 10%	749
	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 2024-10-31 03:39:26. Version ac07

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