Modine Benstead Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Modine Benstead Observatory clear sky chart from 2005-11-06 to 2024-12-09.

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	12% 9% 3 8% 5% 4 5% 4 6% 8% 38%	101635
	Night	14% 9% 3 7% 5% 4 4 4 5% 6% 38%	98217
Transparency	Day	42% 7% 13% 23% 13% 1	105192
	Night	44% 7% 11% 23% 14% 2	102801
Seeing	Day	15% 9% 29% 28% 14% 4	15968
	Night	17% 9% 30% 29% 13% 2	25860

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	11% 14% 7% 11% 5% 4 5% 3 4 5% 29%	2527
	11th to 20th	Day	11% 13% 6% 14% 5% 4 5% 7% 7% 7% 22%	2530
	21st to end	Day	17% 19% 9% 11% 5% 4 4 2 5% 5% 21%	2797
February	1st to 10th	Day	11% 14% 6% 10% 5% 4 4 5% 5% 7% 29%	1729
	11th to 20th	Day	12% 11% 4 8% 5% 4 5% 4 5% 6% 36%	1848
	21st to end	Day	12% 13% 5% 11% 5% 4 4 4 5% 7% 29%	1570
March	1st to 10th	Day	13% 10% 4 7% 4 4 4 4 5% 6% 39%	3120
	11th to 20th	Day	11% 7% 3 8% 6% 5% 6% 4 5% 6% 40%	3267
	21st to end	Day	20% 12% 5% 11% 5% 4 5% 4 4 5% 25%	4165
April	1st to 10th	Day	17% 13% 4 8% 5% 5% 4 3 6% 6% 29%	2280
	11th to 20th	Day	16% 9% 3 7% 5% 4 4 4 6% 6% 35%	2254
	21st to end	Day	18% 9% 3 7% 5% 4 5% 3 6% 6% 34%	2406
May	1st to 10th	Day	15% 8% 3 8% 4 4 5% 3 6% 7% 36%	4082
	11th to 20th	Day	14% 6% 2 6% 5% 4 4 4 6% 7% 42%	4357
	21st to end	Day	11% 7% 2 6% 4 4 5% 4 7% 9% 42%	4824
June	1st to 10th	Day	10% 5% 2 6% 5% 5% 4 4 6% 9% 46%	2660
	11th to 20th	Day	10% 5% 2 6% 4 4 4 4 6% 10% 45%	2660
	21st to end	Day	10% 7% 2 5% 5% 4 5% 4 7% 9% 41%	2660
July	1st to 10th	Day	11% 8% 2 7% 5% 5% 5% 4 7% 10% 35%	4440
	11th to 20th	Day	5% 4 2 5% 4 5% 5% 4 7% 11% 49%	4440
	21st to end	Day	7% 6% 3 7% 5% 5% 5% 5% 6% 9% 44%	4813
August	1st to 10th	Day	10% 6% 2 6% 4 4 5% 5% 7% 9% 42%	4369
	11th to 20th	Day	10% 4 2 6% 5% 4 5% 4 7% 8% 45%	3800
	21st to end	Day	8% 6% 3 7% 5% 5% 4 4 6% 8% 46%	4180
September	1st to 10th	Day	11% 5% 2 6% 4 4 4 4 7% 9% 45%	2280
	11th to 20th	Day	11% 4 2 5% 3 4 4 3 6% 8% 50%	2160
	21st to end	Day	11% 5% 2 8% 5% 4 4 4 6% 9% 42%	2090
October	1st to 10th	Day	13% 8% 2 5% 4 3 4 3 5% 7% 46%	2033
	11th to 20th	Day	18% 8% 3 8% 4 5% 5% 3 5% 7% 33%	1871
	21st to end	Day	17% 9% 3 9% 3 4 4 3 4 6% 37%	1881
November	1st to 10th	Day	11% 9% 3 7% 5% 4 4 3 4 8% 42%	1762
	11th to 20th	Day	13% 10% 4 11% 5% 5% 4 4 5% 8% 30%	1800
	21st to end	Day	18% 11% 3 8% 4 3 3 2 4 6% 36%	1695
December	1st to 10th	Day	13% 11% 4 9% 6% 5% 5% 4 6% 7% 30%	1584
	11th to 20th	Day	12% 13% 4 9% 5% 5% 5% 5% 6% 6% 30%	1918
	21st to end	Day	18% 20% 8% 14% 6% 4 3 2 4 4 17%	2783
January	1st to 10th	Night	14% 14% 8% 9% 5% 4 4 2 4 4 33%	4428
	11th to 20th	Night	14% 15% 5% 14% 6% 5% 5% 5% 6% 5% 19%	4440
	21st to end	Night	19% 17% 8% 10% 5% 3 3 3 4 5% 23%	4854
February	1st to 10th	Night	12% 14% 4 9% 6% 5% 4 2 4 5% 33%	2451
	11th to 20th	Night	13% 9% 3 8% 4 4 4 3 6% 6% 40%	2218
	21st to end	Night	19% 11% 3 7% 4 4 4 3 5% 5% 35%	1884
March	1st to 10th	Night	16% 11% 2 7% 4 4 3 3 4 6% 40%	3733
	11th to 20th	Night	9% 7% 2 5% 4 4 4 4 6% 8% 46%	3720
	21st to end	Night	20% 11% 5% 10% 6% 5% 4 3 4 4 28%	3466
April	1st to 10th	Night	15% 8% 3 6% 5% 5% 5% 4 6% 5% 38%	1900
	11th to 20th	Night	19% 9% 3 7% 4 4 4 3 4 5% 38%	1875
	21st to end	Night	18% 8% 2 6% 4 4 3 4 5% 7% 38%	1772
May	1st to 10th	Night	15% 8% 3 6% 5% 5% 5% 4 6% 8% 36%	2813
	11th to 20th	Night	16% 6% 2 5% 4 4 5% 4 6% 9% 39%	2542
	21st to end	Night	11% 8% 3 8% 4 4 4 3 5% 7% 43%	2743
June	1st to 10th	Night	9% 4 2 6% 4 4 6% 3 7% 8% 47%	1520
	11th to 20th	Night	10% 7% 2 5% 5% 4 5% 3 6% 10% 44%	1520
	21st to end	Night	9% 6% 2 7% 5% 5% 4 3 7% 8% 44%	1520
July	1st to 10th	Night	13% 6% 2 8% 5% 4 6% 4 6% 7% 39%	2530
	11th to 20th	Night	5% 4 1 4 4 3 5% 4 7% 9% 55%	2530
	21st to end	Night	5% 5% 2 6% 4 5% 5% 4 8% 8% 48%	2750
August	1st to 10th	Night	9% 5% 2 5% 4 4 4 4 6% 8% 51%	2566
	11th to 20th	Night	8% 5% 2 5% 4 4 4 3 6% 9% 50%	3026
	21st to end	Night	7% 4 2 5% 4 4 4 3 6% 10% 51%	3476
September	1st to 10th	Night	8% 5% 2 6% 4 3 4 3 4 6% 53%	1900
	11th to 20th	Night	10% 4 1 5% 3 3 4 3 6% 7% 54%	2000
	21st to end	Night	13% 6% 2 5% 4 5% 4 3 4 6% 47%	2090
October	1st to 10th	Night	12% 6% 2 5% 4 4 4 4 4 5% 51%	2142
	11th to 20th	Night	16% 9% 2 5% 3 3 5% 3 5% 6% 43%	2308
	21st to end	Night	19% 8% 3 6% 4 4 3 4 6% 7% 37%	2717
November	1st to 10th	Night	12% 8% 3 6% 4 4 3 3 5% 6% 46%	2536
	11th to 20th	Night	14% 11% 3 8% 5% 5% 5% 4 5% 6% 35%	2600
	21st to end	Night	17% 10% 3 8% 5% 4 4 3 5% 5% 36%	2705
December	1st to 10th	Night	14% 11% 3 8% 5% 5% 4 4 4 7% 33%	2779
	11th to 20th	Night	15% 13% 4 8% 5% 4 4 5% 5% 6% 31%	3279
	21st to end	Night	21% 18% 5% 9% 5% 5% 5% 3 5% 5% 19%	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	57% 7% 13% 18% 5%	2528
	11th to 20th	Day	58% 8% 12% 17% 5%	2530
	21st to end	Day	67% 4 8% 17% 5%	2797
February	1st to 10th	Day	53% 6% 14% 16% 9% 1	1729
	11th to 20th	Day	48% 6% 11% 23% 10% 2	1858
	21st to end	Day	53% 7% 10% 18% 10% 2	1570
March	1st to 10th	Day	44% 8% 11% 23% 11% 3	3120
	11th to 20th	Day	41% 7% 11% 27% 11% 1	3267
	21st to end	Day	58% 9% 13% 14% 6% 1	4165
April	1st to 10th	Day	53% 8% 10% 19% 10%	2280
	11th to 20th	Day	47% 7% 10% 20% 12% 3	2254
	21st to end	Day	48% 8% 13% 17% 13% 1	2406
May	1st to 10th	Day	43% 10% 12% 21% 14%	4120
	11th to 20th	Day	38% 9% 14% 25% 14%	4361
	21st to end	Day	35% 10% 14% 21% 17% 3	4837
June	1st to 10th	Day	34% 8% 15% 24% 16% 2	2660
	11th to 20th	Day	34% 8% 14% 23% 20% 2	2660
	21st to end	Day	37% 9% 15% 21% 16% 2	2660
July	1st to 10th	Day	42% 7% 13% 24% 12% 2	4371
	11th to 20th	Day	27% 7% 16% 32% 16% 1	4365
	21st to end	Day	35% 8% 16% 20% 18% 2	4662
August	1st to 10th	Day	36% 7% 15% 29% 12% 1	4354
	11th to 20th	Day	33% 8% 13% 33% 12% 1	3838
	21st to end	Day	34% 6% 14% 24% 21% 1	4179
September	1st to 10th	Day	35% 7% 13% 27% 16% 2	2280
	11th to 20th	Day	30% 6% 13% 31% 17% 2	2160
	21st to end	Day	37% 8% 12% 28% 14% 1	2090
October	1st to 10th	Day	24% 4 7% 42% 22% 1	3384
	11th to 20th	Day	35% 5% 9% 29% 21% 1	3087
	21st to end	Day	43% 4 9% 29% 13% 3	3081
November	1st to 10th	Day	41% 6% 13% 24% 14% 1	1762
	11th to 20th	Day	51% 7% 13% 20% 8% 1	1800
	21st to end	Day	51% 5% 12% 25% 7%	1695
December	1st to 10th	Day	52% 8% 17% 15% 7% 1	1584
	11th to 20th	Day	50% 9% 15% 17% 7% 1	1915
	21st to end	Day	72% 5% 8% 11% 4	2783
January	1st to 10th	Night	55% 6% 10% 19% 9% 1	4428
	11th to 20th	Night	64% 7% 11% 12% 6%	4440
	21st to end	Night	64% 5% 10% 15% 5%	4854
February	1st to 10th	Night	53% 6% 10% 17% 12% 1	2451
	11th to 20th	Night	44% 7% 13% 21% 14% 1	2219
	21st to end	Night	50% 6% 10% 20% 11% 4	1884
March	1st to 10th	Night	46% 7% 11% 24% 9% 3	3733
	11th to 20th	Night	33% 8% 12% 28% 17% 3	3720
	21st to end	Night	59% 7% 7% 16% 10% 1	3466
April	1st to 10th	Night	45% 8% 10% 21% 14% 1	1900
	11th to 20th	Night	49% 5% 7% 19% 17% 4	1875
	21st to end	Night	44% 5% 14% 20% 15% 2	1772
May	1st to 10th	Night	42% 9% 13% 19% 15% 2	2840
	11th to 20th	Night	38% 11% 13% 25% 11% 1	2543
	21st to end	Night	40% 7% 11% 16% 18% 8%	2751
June	1st to 10th	Night	32% 9% 12% 27% 17% 3	1520
	11th to 20th	Night	34% 8% 11% 24% 21% 3	1520
	21st to end	Night	36% 8% 14% 24% 16% 2	1520
July	1st to 10th	Night	42% 7% 13% 21% 12% 4	2490
	11th to 20th	Night	23% 7% 14% 38% 15% 3	2482
	21st to end	Night	31% 7% 15% 21% 23% 3	2662
August	1st to 10th	Night	30% 7% 15% 28% 19% 1	2557
	11th to 20th	Night	31% 7% 11% 34% 16% 1	3054
	21st to end	Night	28% 6% 12% 29% 21% 3	3476
September	1st to 10th	Night	31% 7% 11% 25% 23% 3	1900
	11th to 20th	Night	29% 6% 10% 33% 19% 2	2000
	21st to end	Night	38% 6% 9% 29% 16% 1	2090
October	1st to 10th	Night	24% 4 7% 39% 25% 1	3571
	11th to 20th	Night	35% 6% 10% 25% 23% 2	3831
	21st to end	Night	42% 5% 9% 25% 17% 2	4467
November	1st to 10th	Night	38% 6% 11% 26% 17% 3	2536
	11th to 20th	Night	48% 6% 13% 20% 11% 2	2600
	21st to end	Night	49% 6% 13% 23% 9% 1	2705
December	1st to 10th	Night	51% 7% 13% 20% 8% 1	2779
	11th to 20th	Night	52% 9% 12% 18% 9% 1	3281
	21st to end	Night	66% 6% 10% 13% 4	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	17% 15% 35% 27% 6%	270
	11th to 20th	Day	20% 17% 36% 22% 5% 1	270
	21st to end	Day	22% 11% 38% 20% 8% 1	297
February	1st to 10th	Day	14% 17% 43% 20% 6%	270
	11th to 20th	Day	17% 23% 37% 18% 6%	270
	21st to end	Day	20% 16% 47% 15% 2	225
March	1st to 10th	Day	14% 22% 44% 17% 3	270
	11th to 20th	Day	21% 18% 33% 23% 5% 1	297
	21st to end	Day	25% 12% 32% 22% 7% 2	506
April	1st to 10th	Day	21% 13% 36% 25% 5%	460
	11th to 20th	Day	18% 17% 33% 20% 10% 2	452
	21st to end	Day	20% 12% 31% 23% 12% 2	460
May	1st to 10th	Day	19% 10% 33% 27% 10% 2	463
	11th to 20th	Day	20% 7% 30% 30% 11% 3	646
	21st to end	Day	14% 7% 29% 27% 17% 6%	734
June	1st to 10th	Day	9% 6% 29% 34% 18% 5%	680
	11th to 20th	Day	12% 4 28% 36% 15% 5%	680
	21st to end	Day	11% 6% 29% 35% 16% 4	680
July	1st to 10th	Day	7% 3 19% 35% 25% 11%	671
	11th to 20th	Day	8% 4 25% 35% 20% 8%	668
	21st to end	Day	8% 2 22% 40% 22% 6%	739
August	1st to 10th	Day	7% 4 19% 37% 24% 10%	648
	11th to 20th	Day	10% 4 20% 28% 27% 12%	479
	21st to end	Day	9% 4 18% 35% 27% 9%	539
September	1st to 10th	Day	13% 6% 21% 29% 24% 7%	490
	11th to 20th	Day	10% 2 17% 35% 24% 12%	490
	21st to end	Day	14% 9% 26% 28% 16% 8%	490
October	1st to 10th	Day	16% 9% 26% 28% 16% 5%	433
	11th to 20th	Day	20% 20% 27% 25% 8% 1	300
	21st to end	Day	25% 14% 35% 21% 5% 1	330
November	1st to 10th	Day	15% 15% 34% 25% 10% 1	300
	11th to 20th	Day	19% 17% 40% 16% 8%	300
	21st to end	Day	24% 10% 42% 21% 3	300
December	1st to 10th	Day	15% 17% 43% 18% 6% 1	294
	11th to 20th	Day	19% 14% 40% 21% 6%	270
	21st to end	Day	23% 21% 38% 16% 3	297
January	1st to 10th	Night	19% 15% 38% 23% 5%	950
	11th to 20th	Night	21% 15% 36% 21% 6% 1	950
	21st to end	Night	19% 11% 39% 27% 4	1045
February	1st to 10th	Night	19% 13% 38% 24% 6%	931
	11th to 20th	Night	20% 13% 37% 25% 5%	743
	21st to end	Night	24% 11% 41% 20% 5%	628
March	1st to 10th	Night	19% 11% 37% 24% 8% 1	760
	11th to 20th	Night	15% 11% 37% 28% 8% 1	747
	21st to end	Night	22% 8% 31% 30% 8% 1	627
April	1st to 10th	Night	19% 10% 36% 28% 8%	570
	11th to 20th	Night	22% 11% 31% 26% 9% 2	563
	21st to end	Night	21% 7% 29% 32% 10% 1	570
May	1st to 10th	Night	16% 8% 30% 35% 10% 1	570
	11th to 20th	Night	20% 4 25% 33% 17% 1	561
	21st to end	Night	15% 4 23% 33% 23% 3	617
June	1st to 10th	Night	10% 3 21% 46% 19% 1	570
	11th to 20th	Night	13% 3 29% 35% 19% 1	570
	21st to end	Night	10% 4 23% 40% 22% 2	570
July	1st to 10th	Night	8% 2 16% 39% 31% 5%	555
	11th to 20th	Night	7% 3 17% 42% 26% 5%	552
	21st to end	Night	5% 2 15% 49% 27% 2	624
August	1st to 10th	Night	7% 3 13% 45% 28% 4	567
	11th to 20th	Night	7% 2 15% 36% 33% 6%	564
	21st to end	Night	8% 2 16% 39% 33% 3	627
September	1st to 10th	Night	10% 3 18% 36% 27% 6%	570
	11th to 20th	Night	10% 5% 18% 32% 30% 6%	670
	21st to end	Night	13% 8% 25% 27% 22% 5%	760
October	1st to 10th	Night	14% 6% 26% 31% 21% 2	760
	11th to 20th	Night	21% 9% 33% 26% 11% 1	760
	21st to end	Night	22% 10% 32% 26% 8% 1	836
November	1st to 10th	Night	16% 12% 36% 24% 11% 1	780
	11th to 20th	Night	20% 16% 37% 22% 6%	800
	21st to end	Night	21% 13% 36% 23% 7%	905
December	1st to 10th	Night	20% 14% 39% 21% 5%	993
	11th to 20th	Night	22% 14% 36% 23% 6%	950
	21st to end	Night	29% 13% 38% 19% 2	1045

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