Monkton Observing Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Monkton Observing Site clear sky chart from 2005-11-06 to 2025-04-26.

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% 12% 4 10% 6% 5% 5% 4 5% 7% 28%	113929
	Night	14% 13% 5% 11% 6% 5% 5% 3 5% 6% 28%	114649
Transparency	Day	55% 3 11% 20% 10% 1	117551
	Night	57% 2 10% 19% 11% 1	119192
Seeing	Day	20% 10% 28% 24% 13% 5%	15559
	Night	20% 10% 30% 28% 11% 1	24875

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	11% 16% 8% 19% 8% 5% 5% 4 4 4 16%	3338
	11th to 20th	Day	10% 20% 10% 26% 9% 9% 6% 2 2 2 5%	4026
	21st to end	Day	15% 19% 7% 21% 8% 6% 5% 3 4 4 8%	4466
February	1st to 10th	Day	14% 18% 7% 17% 10% 6% 4 3 4 4 13%	1800
	11th to 20th	Day	12% 14% 8% 15% 10% 6% 6% 4 5% 5% 15%	1753
	21st to end	Day	14% 17% 6% 14% 7% 6% 4 4 5% 5% 20%	1622
March	1st to 10th	Day	16% 12% 5% 15% 8% 4 4 3 3 5% 26%	4832
	11th to 20th	Day	10% 14% 6% 10% 5% 5% 4 4 6% 8% 28%	4980
	21st to end	Day	17% 13% 6% 12% 6% 4 4 3 4 5% 26%	5465
April	1st to 10th	Day	16% 16% 5% 8% 4 4 4 4 5% 6% 27%	2290
	11th to 20th	Day	17% 11% 4 7% 4 4 4 3 5% 7% 34%	2551
	21st to end	Day	20% 11% 4 7% 4 4 4 3 5% 7% 32%	2535
May	1st to 10th	Day	17% 9% 3 7% 4 5% 5% 4 5% 8% 33%	4108
	11th to 20th	Day	17% 9% 3 8% 5% 4 5% 4 6% 8% 31%	4171
	21st to end	Day	14% 5% 2 5% 4 4 4 4 5% 8% 45%	4837
June	1st to 10th	Day	14% 7% 3 6% 6% 5% 4 4 6% 8% 36%	2674
	11th to 20th	Day	11% 6% 3 6% 4 5% 5% 5% 7% 9% 40%	2850
	21st to end	Day	14% 8% 2 6% 5% 5% 5% 4 7% 8% 38%	2850
July	1st to 10th	Day	11% 5% 3 6% 5% 4 5% 5% 8% 9% 39%	4760
	11th to 20th	Day	11% 5% 2 5% 4 5% 5% 5% 7% 8% 42%	4363
	21st to end	Day	9% 6% 2 6% 4 4 6% 5% 7% 10% 41%	4466
August	1st to 10th	Day	14% 7% 2 6% 5% 5% 5% 5% 7% 9% 36%	4104
	11th to 20th	Day	11% 8% 3 7% 5% 5% 6% 5% 8% 10% 33%	4044
	21st to end	Day	9% 6% 2 7% 4 5% 6% 5% 7% 9% 40%	4472
September	1st to 10th	Day	12% 6% 3 8% 5% 5% 4 4 5% 10% 38%	2251
	11th to 20th	Day	11% 6% 2 5% 4 5% 5% 4 7% 7% 43%	2090
	21st to end	Day	16% 8% 2 7% 5% 4 5% 4 7% 7% 33%	2090
October	1st to 10th	Day	18% 9% 3 8% 5% 5% 4 3 6% 5% 34%	1928
	11th to 20th	Day	21% 11% 4 8% 6% 4 5% 4 5% 7% 25%	1900
	21st to end	Day	24% 14% 4 9% 5% 5% 5% 3 6% 6% 18%	2052
November	1st to 10th	Day	14% 16% 4 9% 6% 4 4 3 6% 6% 28%	1757
	11th to 20th	Day	14% 16% 5% 9% 6% 5% 6% 4 6% 6% 21%	1600
	21st to end	Day	17% 19% 9% 11% 6% 5% 4 3 6% 6% 13%	1600
December	1st to 10th	Day	17% 24% 11% 15% 6% 5% 5% 3 5% 4 7%	2600
	11th to 20th	Day	21% 20% 6% 14% 8% 4 3 2 4 4 13%	2986
	21st to end	Day	25% 22% 7% 13% 5% 4 4 3 3 4 10%	3718
January	1st to 10th	Night	12% 16% 7% 22% 7% 6% 4 3 5% 5% 12%	6600
	11th to 20th	Night	11% 15% 9% 22% 12% 8% 6% 5% 4 3 6%	5859
	21st to end	Night	14% 16% 9% 18% 7% 6% 6% 3 4 5% 12%	6490
February	1st to 10th	Night	14% 19% 6% 13% 10% 6% 5% 4 4 4 16%	2600
	11th to 20th	Night	13% 15% 6% 13% 8% 6% 5% 4 6% 6% 18%	2533
	21st to end	Night	15% 13% 6% 13% 7% 4 5% 4 5% 5% 22%	2005
March	1st to 10th	Night	13% 11% 5% 10% 7% 5% 5% 3 5% 6% 29%	5007
	11th to 20th	Night	9% 10% 5% 11% 5% 5% 5% 4 7% 8% 32%	4979
	21st to end	Night	17% 11% 5% 9% 5% 4 4 3 4 4 34%	5467
April	1st to 10th	Night	18% 12% 4 9% 5% 4 4 3 5% 5% 30%	2110
	11th to 20th	Night	17% 12% 3 6% 5% 4 4 3 5% 7% 34%	1815
	21st to end	Night	16% 11% 4 8% 5% 4 4 3 5% 6% 34%	1761
May	1st to 10th	Night	16% 8% 3 6% 4 4 4 3 5% 7% 41%	2833
	11th to 20th	Night	14% 9% 3 8% 6% 5% 4 4 6% 6% 36%	2721
	21st to end	Night	10% 4 2 5% 3 4 4 4 6% 9% 49%	2738
June	1st to 10th	Night	13% 6% 2 7% 5% 4 5% 4 6% 8% 42%	1500
	11th to 20th	Night	9% 7% 2 5% 5% 5% 5% 4 6% 10% 42%	1330
	21st to end	Night	11% 6% 2 5% 4 6% 4 3 5% 8% 45%	1330
July	1st to 10th	Night	6% 5% 2 5% 4 4 5% 4 6% 9% 50%	2210
	11th to 20th	Night	10% 6% 2 5% 3 3 3 3 4 8% 53%	2580
	21st to end	Night	6% 5% 2 6% 5% 5% 6% 4 6% 7% 48%	3087
August	1st to 10th	Night	11% 6% 2 7% 4 4 4 4 5% 7% 45%	2825
	11th to 20th	Night	12% 9% 3 6% 4 4 4 3 6% 8% 42%	2785
	21st to end	Night	10% 6% 2 6% 4 4 5% 3 5% 7% 47%	3151
September	1st to 10th	Night	11% 6% 2 7% 5% 4 4 4 6% 7% 45%	1927
	11th to 20th	Night	10% 5% 2 5% 4 3 3 4 4 7% 53%	2090
	21st to end	Night	16% 8% 2 7% 5% 4 4 4 6% 7% 39%	2090
October	1st to 10th	Night	14% 8% 3 7% 5% 5% 5% 4 5% 7% 38%	2251
	11th to 20th	Night	20% 11% 4 7% 6% 4 5% 3 5% 6% 30%	2280
	21st to end	Night	21% 12% 3 9% 6% 4 4 4 6% 6% 24%	2542
November	1st to 10th	Night	14% 12% 4 8% 6% 4 5% 3 5% 7% 32%	2539
	11th to 20th	Night	14% 16% 5% 10% 6% 5% 4 4 6% 7% 21%	2800
	21st to end	Night	19% 17% 6% 11% 6% 5% 4 3 5% 6% 18%	2800
December	1st to 10th	Night	13% 22% 10% 17% 7% 6% 5% 4 4 4 9%	4580
	11th to 20th	Night	13% 23% 8% 16% 7% 4 4 3 4 4 14%	5208
	21st to end	Night	21% 21% 9% 12% 6% 4 4 3 4 4 12%	7226

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	72% 2 8% 11% 8%	3339
	11th to 20th	Day	88% 2 4 4 2	4060
	21st to end	Day	81% 1 7% 6% 4	4466
February	1st to 10th	Day	75% 3 6% 13% 3	1800
	11th to 20th	Day	70% 4 6% 14% 6% 1	1762
	21st to end	Day	68% 3 10% 14% 5% 1	1622
March	1st to 10th	Day	64% 1 13% 15% 6% 1	4835
	11th to 20th	Day	56% 1 15% 19% 7% 2	4980
	21st to end	Day	63% 1 9% 17% 9% 1	5465
April	1st to 10th	Day	57% 4 10% 19% 10%	2290
	11th to 20th	Day	51% 3 11% 22% 12% 1	2551
	21st to end	Day	54% 3 12% 19% 11% 2	2535
May	1st to 10th	Day	51% 2 10% 22% 13% 2	4120
	11th to 20th	Day	52% 2 13% 24% 7% 1	4175
	21st to end	Day	39% 2 12% 22% 19% 5%	4837
June	1st to 10th	Day	45% 4 12% 25% 14% 1	2674
	11th to 20th	Day	41% 4 12% 26% 16% 1	2850
	21st to end	Day	44% 4 12% 26% 14%	2850
July	1st to 10th	Day	41% 2 15% 25% 16% 2	4686
	11th to 20th	Day	38% 2 10% 36% 12% 1	4285
	21st to end	Day	39% 3 14% 25% 18% 2	4324
August	1st to 10th	Day	45% 3 12% 26% 13% 1	4091
	11th to 20th	Day	46% 3 16% 27% 9%	4083
	21st to end	Day	40% 3 13% 33% 12% 1	4472
September	1st to 10th	Day	42% 5% 13% 27% 11% 2	2251
	11th to 20th	Day	39% 4 12% 30% 15% 1	2090
	21st to end	Day	49% 4 13% 25% 9% 1	2090
October	1st to 10th	Day	46% 2 11% 24% 16% 1	3201
	11th to 20th	Day	45% 2 12% 24% 16%	3140
	21st to end	Day	57% 2 15% 20% 6%	3366
November	1st to 10th	Day	57% 4 10% 20% 8% 1	1757
	11th to 20th	Day	61% 4 12% 15% 7% 1	1600
	21st to end	Day	71% 4 10% 12% 4	1600
December	1st to 10th	Day	81% 3 6% 7% 2	2600
	11th to 20th	Day	77% 2 7% 11% 4	2986
	21st to end	Day	80% 2 6% 8% 4	3718
January	1st to 10th	Night	74% 2 5% 14% 5%	6600
	11th to 20th	Night	84% 1 6% 7% 2	5900
	21st to end	Night	76% 2 8% 9% 5%	6490
February	1st to 10th	Night	72% 3 7% 14% 4	2600
	11th to 20th	Night	66% 3 9% 14% 7%	2535
	21st to end	Night	63% 3 10% 16% 8%	2005
March	1st to 10th	Night	58% 2 12% 19% 9% 1	5017
	11th to 20th	Night	49% 2 16% 22% 11% 1	4980
	21st to end	Night	55% 2 7% 19% 15% 2	5467
April	1st to 10th	Night	56% 3 8% 18% 13% 1	2110
	11th to 20th	Night	50% 4 7% 20% 16% 2	1815
	21st to end	Night	52% 2 9% 19% 15% 3	1761
May	1st to 10th	Night	45% 2 11% 21% 16% 5%	2840
	11th to 20th	Night	50% 2 12% 23% 11% 2	2722
	21st to end	Night	33% 2 14% 25% 22% 4	2739
June	1st to 10th	Night	40% 4 9% 28% 17% 2	1500
	11th to 20th	Night	37% 4 13% 27% 17% 3	1330
	21st to end	Night	38% 4 13% 27% 17% 1	1330
July	1st to 10th	Night	32% 3 14% 27% 20% 6%	2175
	11th to 20th	Night	32% 3 12% 33% 19% 1	2536
	21st to end	Night	36% 4 13% 27% 19% 2	2988
August	1st to 10th	Night	40% 3 12% 28% 16% 1	2814
	11th to 20th	Night	41% 3 15% 27% 13% 1	2812
	21st to end	Night	37% 3 10% 34% 15% 1	3151
September	1st to 10th	Night	39% 4 11% 29% 15% 2	1927
	11th to 20th	Night	32% 4 11% 31% 21% 1	2090
	21st to end	Night	45% 4 14% 26% 12%	2090
October	1st to 10th	Night	37% 3 8% 28% 24% 1	3758
	11th to 20th	Night	48% 2 13% 22% 15%	3779
	21st to end	Night	48% 3 14% 25% 10%	4178
November	1st to 10th	Night	52% 4 11% 22% 10% 1	2539
	11th to 20th	Night	62% 3 11% 16% 6% 1	2800
	21st to end	Night	67% 3 13% 12% 4	2800
December	1st to 10th	Night	79% 3 9% 8% 2	4580
	11th to 20th	Night	75% 2 7% 11% 5%	5208
	21st to end	Night	77% 2 8% 9% 5%	7226

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% 18% 37% 17% 7% 1	235
	11th to 20th	Day	19% 16% 46% 14% 4 1	300
	21st to end	Day	26% 14% 34% 22% 3 1	330
February	1st to 10th	Day	21% 19% 41% 14% 4	300
	11th to 20th	Day	23% 21% 38% 16% 2	300
	21st to end	Day	27% 24% 31% 17% 1	249
March	1st to 10th	Day	25% 12% 38% 19% 6% 1	448
	11th to 20th	Day	21% 14% 34% 23% 7% 1	500
	21st to end	Day	27% 11% 33% 23% 5% 1	550
April	1st to 10th	Day	23% 15% 32% 21% 6% 1	500
	11th to 20th	Day	25% 15% 28% 17% 11% 4	492
	21st to end	Day	26% 10% 31% 23% 8% 2	480
May	1st to 10th	Day	24% 9% 26% 26% 11% 4	463
	11th to 20th	Day	21% 7% 26% 22% 18% 5%	487
	21st to end	Day	16% 5% 27% 26% 19% 7%	529
June	1st to 10th	Day	16% 10% 27% 30% 14% 3	504
	11th to 20th	Day	14% 8% 27% 32% 15% 3	680
	21st to end	Day	16% 8% 27% 34% 11% 5%	680
July	1st to 10th	Day	11% 5% 22% 31% 22% 10%	671
	11th to 20th	Day	16% 4 24% 28% 20% 9%	557
	21st to end	Day	12% 2 23% 34% 21% 8%	532
August	1st to 10th	Day	12% 4 20% 27% 25% 13%	486
	11th to 20th	Day	14% 3 17% 29% 21% 16%	479
	21st to end	Day	17% 5% 18% 29% 20% 11%	539
September	1st to 10th	Day	14% 6% 20% 28% 19% 13%	490
	11th to 20th	Day	9% 5% 18% 28% 27% 14%	490
	21st to end	Day	16% 10% 24% 27% 15% 9%	490
October	1st to 10th	Day	22% 8% 26% 22% 16% 6%	490
	11th to 20th	Day	22% 13% 31% 25% 7% 1	490
	21st to end	Day	30% 12% 32% 20% 5% 1	501
November	1st to 10th	Day	24% 19% 31% 16% 9% 1	297
	11th to 20th	Day	24% 17% 34% 19% 6% 2	200
	21st to end	Day	22% 18% 40% 17% 4	200
December	1st to 10th	Day	28% 23% 29% 16% 5%	200
	11th to 20th	Day	31% 22% 30% 17% 2	200
	21st to end	Day	35% 16% 35% 12% 3	220
January	1st to 10th	Night	22% 16% 35% 20% 5% 1	984
	11th to 20th	Night	26% 16% 33% 21% 4	800
	21st to end	Night	20% 13% 38% 23% 6%	880
February	1st to 10th	Night	25% 14% 37% 21% 2	800
	11th to 20th	Night	21% 15% 35% 23% 6%	783
	21st to end	Night	23% 15% 37% 22% 3	660
March	1st to 10th	Night	20% 13% 37% 24% 6%	800
	11th to 20th	Night	18% 16% 39% 21% 6%	800
	21st to end	Night	23% 11% 32% 25% 9% 1	880
April	1st to 10th	Night	24% 13% 32% 27% 4	800
	11th to 20th	Night	24% 10% 32% 24% 10% 1	631
	21st to end	Night	21% 9% 31% 32% 7%	587
May	1st to 10th	Night	19% 6% 31% 30% 14% 1	570
	11th to 20th	Night	20% 5% 25% 35% 14% 1	509
	21st to end	Night	13% 3 28% 39% 18%	411
June	1st to 10th	Night	14% 3 28% 39% 14% 1	380
	11th to 20th	Night	12% 6% 28% 41% 14%	380
	21st to end	Night	15% 3 26% 40% 14% 1	380
July	1st to 10th	Night	7% 1 19% 48% 24% 1	370
	11th to 20th	Night	10% 2 21% 42% 24% 2	478
	21st to end	Night	10% 1 18% 48% 22% 1	624
August	1st to 10th	Night	11% 2 13% 45% 27% 3	567
	11th to 20th	Night	9% 2 16% 40% 28% 5%	564
	21st to end	Night	15% 2 19% 34% 26% 3	641
September	1st to 10th	Night	13% 4 23% 34% 21% 5%	760
	11th to 20th	Night	12% 3 18% 35% 26% 5%	760
	21st to end	Night	19% 6% 20% 34% 17% 5%	760
October	1st to 10th	Night	19% 5% 28% 29% 16% 2	760
	11th to 20th	Night	25% 10% 27% 28% 10% 1	760
	21st to end	Night	28% 10% 32% 25% 5%	836
November	1st to 10th	Night	22% 11% 28% 29% 8% 1	780
	11th to 20th	Night	22% 15% 33% 22% 7% 1	800
	21st to end	Night	27% 13% 33% 23% 4	800
December	1st to 10th	Night	27% 18% 30% 19% 6%	800
	11th to 20th	Night	23% 18% 36% 19% 3 1	800
	21st to end	Night	29% 14% 35% 20% 3	980

Page generated at 2025-04-23 09:25:02. Version ac07

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