Allenford Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Allenford Observatory clear sky chart from 2005-11-06 to 2024-11-01.

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% 12% 4 8% 5% 4 4 3 5% 7% 32%	101487
	Night	16% 14% 5% 11% 6% 4 4 3 4 5% 27%	97478
Transparency	Day	52% 6% 11% 19% 10% 1	101244
	Night	58% 6% 10% 16% 9% 1	97340
Seeing	Day	21% 12% 29% 23% 11% 4	15162
	Night	22% 11% 27% 28% 11% 1	24354

By Month

Percentage Cloud Cover NE (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	15% 24% 15% 15% 8% 5% 4 3 3 3 7%	2240
	11th to 20th	Day	10% 24% 10% 22% 11% 6% 4 2 3 2 6%	2603
	21st to end	Day	17% 23% 11% 15% 7% 6% 4 2 3 3 8%	3124
February	1st to 10th	Day	13% 22% 7% 18% 9% 6% 5% 3 3 3 11%	1710
	11th to 20th	Day	13% 16% 7% 16% 9% 5% 5% 4 5% 4 15%	1663
	21st to end	Day	14% 20% 6% 13% 8% 5% 4 4 4 4 18%	1532
March	1st to 10th	Day	18% 16% 4 9% 6% 4 3 3 4 5% 28%	3331
	11th to 20th	Day	12% 18% 8% 10% 6% 5% 5% 3 4 5% 24%	3480
	21st to end	Day	15% 13% 5% 9% 5% 5% 4 4 5% 6% 28%	3815
April	1st to 10th	Day	19% 15% 4 8% 4 4 4 3 5% 7% 29%	2185
	11th to 20th	Day	19% 11% 3 7% 4 3 4 2 5% 6% 37%	2442
	21st to end	Day	20% 9% 4 7% 4 3 4 3 5% 6% 35%	2470
May	1st to 10th	Day	17% 9% 2 6% 4 4 4 3 5% 7% 38%	4108
	11th to 20th	Day	15% 8% 2 6% 4 4 4 3 6% 8% 39%	4237
	21st to end	Day	15% 5% 2 5% 4 3 4 3 5% 7% 46%	4837
June	1st to 10th	Day	14% 7% 3 6% 5% 4 4 5% 5% 8% 40%	2789
	11th to 20th	Day	11% 5% 2 7% 4 4 5% 4 7% 8% 44%	2850
	21st to end	Day	16% 7% 2 6% 4 4 4 4 6% 7% 41%	2850
July	1st to 10th	Day	14% 6% 2 6% 4 4 5% 4 7% 8% 39%	4760
	11th to 20th	Day	12% 5% 1 5% 3 3 4 4 6% 9% 48%	4622
	21st to end	Day	10% 5% 2 5% 4 4 5% 3 6% 9% 47%	4466
August	1st to 10th	Day	12% 6% 2 5% 3 5% 5% 4 7% 9% 41%	4104
	11th to 20th	Day	15% 6% 2 6% 4 3 5% 4 6% 9% 40%	4044
	21st to end	Day	11% 5% 2 5% 4 4 5% 4 6% 9% 45%	4505
September	1st to 10th	Day	14% 5% 3 8% 4 4 5% 4 6% 8% 39%	2252
	11th to 20th	Day	12% 7% 2 5% 4 3 4 3 6% 8% 44%	2090
	21st to end	Day	17% 8% 3 7% 4 5% 5% 4 5% 7% 34%	2090
October	1st to 10th	Day	19% 9% 3 8% 5% 5% 4 3 5% 7% 33%	1929
	11th to 20th	Day	25% 13% 5% 9% 6% 5% 4 3 5% 5% 20%	1900
	21st to end	Day	30% 14% 4 9% 5% 4 3 3 4 5% 17%	2018
November	1st to 10th	Day	18% 19% 4 9% 6% 5% 4 3 4 6% 21%	1639
	11th to 20th	Day	16% 22% 5% 10% 6% 5% 5% 4 4 6% 17%	1520
	21st to end	Day	20% 26% 8% 10% 6% 3 4 3 4 5% 10%	1520
December	1st to 10th	Day	16% 31% 9% 16% 6% 4 4 2 2 3 6%	1520
	11th to 20th	Day	18% 26% 7% 16% 6% 4 4 2 4 3 9%	1811
	21st to end	Day	26% 25% 6% 15% 5% 4 3 2 3 3 7%	2431
January	1st to 10th	Night	15% 26% 12% 19% 7% 4 3 2 3 3 6%	4712
	11th to 20th	Night	14% 17% 10% 23% 11% 6% 5% 3 2 3 6%	4348
	21st to end	Night	16% 22% 10% 15% 7% 5% 4 3 4 4 10%	4532
February	1st to 10th	Night	13% 20% 6% 18% 10% 5% 4 3 3 4 12%	2470
	11th to 20th	Night	13% 16% 9% 16% 7% 5% 4 3 4 4 18%	2403
	21st to end	Night	14% 17% 5% 13% 7% 4 5% 4 4 4 22%	1918
March	1st to 10th	Night	13% 13% 4 10% 5% 4 4 3 4 6% 34%	3509
	11th to 20th	Night	11% 16% 6% 10% 5% 4 3 3 5% 6% 32%	3479
	21st to end	Night	14% 11% 7% 11% 7% 5% 4 3 4 5% 30%	3817
April	1st to 10th	Night	20% 13% 3 9% 5% 3 4 3 5% 6% 30%	2001
	11th to 20th	Night	18% 10% 3 7% 4 4 4 3 4 6% 38%	1696
	21st to end	Night	20% 11% 4 8% 4 4 3 4 4 5% 32%	1710
May	1st to 10th	Night	15% 7% 2 7% 4 5% 4 4 4 7% 39%	2833
	11th to 20th	Night	15% 7% 2 6% 5% 4 5% 3 4 7% 40%	2655
	21st to end	Night	12% 5% 2 6% 4 4 4 4 5% 6% 47%	2738
June	1st to 10th	Night	14% 7% 2 8% 5% 4 4 4 5% 7% 40%	1386
	11th to 20th	Night	10% 6% 2 6% 4 3 5% 5% 8% 9% 41%	1330
	21st to end	Night	15% 5% 1 7% 4 4 4 5% 6% 7% 41%	1330
July	1st to 10th	Night	10% 8% 3 7% 4 4 3 3 6% 7% 46%	2210
	11th to 20th	Night	12% 5% 2 5% 3 3 4 3 5% 7% 51%	2326
	21st to end	Night	7% 7% 2 6% 4 4 5% 4 6% 7% 48%	3087
August	1st to 10th	Night	12% 7% 3 6% 4 4 5% 3 5% 8% 43%	2825
	11th to 20th	Night	14% 6% 2 7% 4 3 5% 4 5% 8% 40%	2785
	21st to end	Night	13% 5% 2 6% 4 3 4 4 5% 7% 47%	3124
September	1st to 10th	Night	11% 5% 2 6% 4 4 4 4 6% 8% 46%	1920
	11th to 20th	Night	12% 5% 3 5% 4 4 4 4 5% 7% 48%	2090
	21st to end	Night	16% 8% 2 7% 5% 5% 5% 4 4 7% 36%	2090
October	1st to 10th	Night	19% 8% 3 7% 5% 4 5% 3 5% 6% 35%	2251
	11th to 20th	Night	25% 12% 4 9% 5% 4 4 3 5% 6% 23%	2280
	21st to end	Night	27% 14% 4 9% 6% 4 4 4 4 5% 19%	2579
November	1st to 10th	Night	19% 18% 4 8% 5% 4 4 3 5% 5% 25%	2446
	11th to 20th	Night	17% 19% 6% 10% 7% 5% 5% 4 5% 5% 17%	2660
	21st to end	Night	22% 23% 6% 10% 6% 4 3 3 3 5% 14%	2660
December	1st to 10th	Night	19% 29% 10% 13% 5% 4 4 3 2 3 7%	2660
	11th to 20th	Night	15% 23% 9% 15% 6% 5% 5% 3 4 4 11%	3382
	21st to end	Night	24% 24% 9% 16% 6% 4 3 2 3 3 7%	5236

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	81% 7% 8% 4	2241
	11th to 20th	Day	87% 4 4 3 2	2603
	21st to end	Day	82% 5% 7% 4 2	3124
February	1st to 10th	Day	77% 6% 6% 9% 1	1710
	11th to 20th	Day	71% 5% 9% 10% 4	1672
	21st to end	Day	68% 6% 9% 13% 4	1532
March	1st to 10th	Day	59% 4 13% 16% 8% 1	3334
	11th to 20th	Day	62% 6% 10% 15% 6% 1	3480
	21st to end	Day	54% 6% 14% 16% 10% 1	3815
April	1st to 10th	Day	57% 5% 11% 18% 10%	2185
	11th to 20th	Day	49% 4 9% 21% 15% 1	2442
	21st to end	Day	50% 5% 12% 19% 11% 2	2470
May	1st to 10th	Day	44% 6% 11% 21% 17% 1	4120
	11th to 20th	Day	42% 7% 14% 25% 11% 1	4241
	21st to end	Day	37% 5% 11% 22% 19% 6%	4837
June	1st to 10th	Day	41% 7% 10% 25% 16% 1	2789
	11th to 20th	Day	36% 6% 12% 26% 18% 1	2850
	21st to end	Day	42% 6% 12% 25% 14% 2	2850
July	1st to 10th	Day	41% 6% 16% 20% 15% 2	4686
	11th to 20th	Day	33% 6% 13% 35% 12% 1	4541
	21st to end	Day	33% 7% 11% 30% 18% 2	4324
August	1st to 10th	Day	38% 7% 14% 25% 15% 1	4091
	11th to 20th	Day	41% 7% 16% 25% 10%	4083
	21st to end	Day	35% 6% 15% 32% 12% 1	4505
September	1st to 10th	Day	41% 7% 13% 25% 12% 2	2252
	11th to 20th	Day	38% 5% 14% 29% 14%	2090
	21st to end	Day	47% 8% 11% 25% 9% 1	2090
October	1st to 10th	Day	52% 6% 10% 20% 10% 1	1929
	11th to 20th	Day	64% 5% 11% 13% 6% 1	1900
	21st to end	Day	70% 5% 10% 12% 3	2018
November	1st to 10th	Day	64% 5% 10% 15% 6%	1639
	11th to 20th	Day	67% 7% 13% 8% 5%	1520
	21st to end	Day	75% 6% 10% 7% 1	1520
December	1st to 10th	Day	84% 4 6% 4 1	1520
	11th to 20th	Day	79% 5% 10% 6% 1	1810
	21st to end	Day	83% 5% 8% 4	2431
January	1st to 10th	Night	85% 5% 5% 4 1	4712
	11th to 20th	Night	84% 6% 6% 3 1	4348
	21st to end	Night	78% 6% 10% 4 2	4532
February	1st to 10th	Night	77% 5% 7% 10% 2	2470
	11th to 20th	Night	70% 5% 8% 12% 4	2405
	21st to end	Night	63% 5% 12% 13% 6%	1918
March	1st to 10th	Night	52% 5% 16% 19% 8% 1	3519
	11th to 20th	Night	53% 5% 14% 17% 8% 2	3480
	21st to end	Night	55% 5% 10% 19% 10% 1	3817
April	1st to 10th	Night	56% 4 9% 20% 11% 1	2001
	11th to 20th	Night	49% 3 8% 20% 18% 2	1696
	21st to end	Night	53% 6% 8% 16% 15% 2	1710
May	1st to 10th	Night	44% 6% 11% 20% 16% 3	2840
	11th to 20th	Night	42% 6% 10% 24% 16% 2	2656
	21st to end	Night	35% 7% 10% 24% 20% 3	2739
June	1st to 10th	Night	43% 6% 10% 22% 18% 3	1386
	11th to 20th	Night	36% 7% 13% 25% 18% 1	1330
	21st to end	Night	39% 7% 12% 25% 15% 2	1330
July	1st to 10th	Night	37% 5% 12% 23% 17% 6%	2175
	11th to 20th	Night	32% 5% 11% 36% 14% 1	2284
	21st to end	Night	34% 6% 13% 26% 20% 1	2988
August	1st to 10th	Night	40% 6% 12% 28% 15% 1	2814
	11th to 20th	Night	41% 9% 16% 21% 14% 1	2812
	21st to end	Night	36% 7% 12% 31% 14% 1	3124
September	1st to 10th	Night	34% 8% 12% 30% 14% 2	1920
	11th to 20th	Night	34% 6% 13% 30% 16%	2090
	21st to end	Night	46% 7% 13% 24% 9% 1	2090
October	1st to 10th	Night	50% 6% 10% 20% 13% 1	2251
	11th to 20th	Night	59% 7% 11% 16% 6%	2280
	21st to end	Night	67% 6% 10% 13% 5%	2579
November	1st to 10th	Night	60% 6% 10% 18% 6%	2446
	11th to 20th	Night	67% 6% 12% 10% 4 1	2660
	21st to end	Night	72% 6% 12% 9% 1	2660
December	1st to 10th	Night	82% 5% 7% 4 1	2660
	11th to 20th	Night	77% 5% 12% 6% 1	3382
	21st to end	Night	84% 5% 7% 4	5236

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	24% 19% 33% 17% 4 2	189
	11th to 20th	Day	23% 20% 35% 15% 6% 1	270
	21st to end	Day	27% 16% 30% 20% 7%	297
February	1st to 10th	Day	29% 23% 30% 15% 3	270
	11th to 20th	Day	21% 24% 39% 14% 2	270
	21st to end	Day	30% 24% 34% 9% 2	225
March	1st to 10th	Day	25% 16% 35% 17% 7% 1	393
	11th to 20th	Day	23% 15% 33% 22% 5% 1	460
	21st to end	Day	26% 13% 33% 20% 7% 1	506
April	1st to 10th	Day	26% 17% 29% 20% 8% 1	460
	11th to 20th	Day	31% 14% 27% 14% 9% 6%	452
	21st to end	Day	29% 10% 31% 21% 7% 2	460
May	1st to 10th	Day	25% 9% 30% 23% 9% 4	463
	11th to 20th	Day	20% 9% 28% 25% 14% 5%	487
	21st to end	Day	17% 8% 28% 27% 15% 5%	529
June	1st to 10th	Day	16% 11% 32% 27% 13% 3	619
	11th to 20th	Day	13% 12% 32% 29% 11% 3	680
	21st to end	Day	19% 7% 34% 27% 10% 3	680
July	1st to 10th	Day	12% 7% 28% 31% 16% 4	671
	11th to 20th	Day	15% 7% 30% 28% 13% 7%	655
	21st to end	Day	14% 5% 28% 31% 15% 7%	532
August	1st to 10th	Day	14% 6% 23% 32% 16% 9%	486
	11th to 20th	Day	15% 6% 19% 30% 20% 10%	479
	21st to end	Day	17% 7% 21% 30% 17% 8%	539
September	1st to 10th	Day	16% 9% 24% 28% 16% 8%	490
	11th to 20th	Day	11% 7% 21% 28% 21% 13%	490
	21st to end	Day	18% 10% 25% 26% 16% 6%	490
October	1st to 10th	Day	24% 14% 21% 24% 12% 5%	490
	11th to 20th	Day	26% 17% 30% 20% 5% 1	490
	21st to end	Day	35% 14% 30% 16% 5%	467
November	1st to 10th	Day	32% 16% 29% 16% 6%	255
	11th to 20th	Day	29% 19% 28% 19% 3 2	180
	21st to end	Day	31% 23% 31% 13% 3	180
December	1st to 10th	Day	33% 13% 32% 17% 4	180
	11th to 20th	Day	32% 23% 27% 11% 7% 1	180
	21st to end	Day	40% 14% 32% 11% 2 1	198
January	1st to 10th	Night	24% 18% 30% 22% 6%	950
	11th to 20th	Night	29% 15% 30% 19% 7% 1	897
	21st to end	Night	20% 12% 32% 27% 8% 1	836
February	1st to 10th	Night	23% 17% 34% 22% 4	760
	11th to 20th	Night	21% 15% 32% 26% 6%	743
	21st to end	Night	24% 17% 34% 22% 3	628
March	1st to 10th	Night	20% 14% 35% 24% 6% 1	760
	11th to 20th	Night	21% 14% 33% 24% 6% 1	760
	21st to end	Night	23% 10% 30% 27% 9% 1	836
April	1st to 10th	Night	25% 12% 31% 27% 6%	760
	11th to 20th	Night	24% 11% 28% 26% 10% 2	572
	21st to end	Night	26% 8% 25% 29% 11% 1	570
May	1st to 10th	Night	21% 4 26% 34% 13% 1	570
	11th to 20th	Night	19% 7% 19% 41% 13% 1	469
	21st to end	Night	14% 3 27% 40% 16% 1	411
June	1st to 10th	Night	17% 7% 28% 36% 11% 2	380
	11th to 20th	Night	12% 6% 26% 41% 14% 1	380
	21st to end	Night	17% 5% 23% 37% 18%	380
July	1st to 10th	Night	11% 5% 18% 48% 18% 1	370
	11th to 20th	Night	12% 2 22% 38% 24% 1	424
	21st to end	Night	10% 3 19% 45% 23% 1	624
August	1st to 10th	Night	12% 2 17% 38% 29% 1	567
	11th to 20th	Night	12% 2 14% 38% 29% 4	564
	21st to end	Night	16% 4 18% 35% 25% 3	627
September	1st to 10th	Night	13% 6% 21% 34% 20% 5%	755
	11th to 20th	Night	14% 4 17% 38% 23% 5%	760
	21st to end	Night	20% 7% 22% 29% 19% 4	760
October	1st to 10th	Night	22% 7% 26% 29% 14% 2	760
	11th to 20th	Night	30% 12% 24% 25% 8% 1	760
	21st to end	Night	33% 14% 26% 23% 4	836
November	1st to 10th	Night	30% 12% 27% 23% 7% 1	743
	11th to 20th	Night	26% 18% 29% 18% 8% 1	760
	21st to end	Night	33% 14% 31% 18% 4	760
December	1st to 10th	Night	34% 17% 29% 15% 5%	760
	11th to 20th	Night	24% 17% 38% 17% 4 1	817
	21st to end	Night	34% 13% 31% 17% 3	1045

Page generated at 2024-10-29 11:20:51. Version ac07

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