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 2026-08-30.

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% 11% 4 10% 6% 5% 5% 4 5% 7% 30%	144465
	Night	13% 12% 5% 11% 6% 5% 5% 3 5% 6% 29%	137756
Transparency	Day	54% 2 11% 21% 11% 1	148044
	Night	57% 2 10% 19% 11% 1	142267
Seeing	Day	20% 10% 28% 24% 13% 5%	17411
	Night	20% 10% 30% 28% 11% 1	26469

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	13% 17% 9% 19% 9% 5% 5% 3 4 4 13%	4343
	11th to 20th	Day	9% 21% 11% 26% 10% 10% 4 1 2 2 4	5246
	21st to end	Day	12% 17% 7% 20% 10% 9% 7% 3 5% 3 7%	5780
February	1st to 10th	Day	14% 17% 7% 17% 10% 6% 4 3 4 4 14%	1890
	11th to 20th	Day	12% 14% 8% 15% 10% 6% 6% 4 5% 6% 15%	1843
	21st to end	Day	13% 17% 6% 14% 7% 6% 4 4 5% 5% 20%	1701
March	1st to 10th	Day	16% 12% 5% 15% 8% 4 4 3 3 5% 26%	4939
	11th to 20th	Day	11% 14% 6% 10% 5% 5% 4 4 5% 7% 27%	5090
	21st to end	Day	17% 13% 6% 13% 6% 5% 4 3 4 5% 26%	5586
April	1st to 10th	Day	16% 16% 5% 9% 4 4 4 4 5% 6% 27%	2404
	11th to 20th	Day	18% 12% 4 6% 4 4 4 3 5% 7% 34%	2680
	21st to end	Day	19% 11% 4 8% 4 4 4 3 5% 7% 32%	2730
May	1st to 10th	Day	15% 9% 3 7% 4 5% 5% 4 5% 8% 35%	7642
	11th to 20th	Day	14% 10% 3 8% 5% 4 5% 4 6% 8% 33%	7800
	21st to end	Day	17% 8% 2 6% 4 3 4 3 5% 7% 42%	9060
June	1st to 10th	Day	13% 7% 3 6% 6% 5% 5% 4 6% 8% 38%	2956
	11th to 20th	Day	11% 6% 3 6% 5% 5% 5% 5% 7% 9% 39%	3150
	21st to end	Day	14% 8% 2 6% 4 5% 5% 4 7% 8% 38%	3150
July	1st to 10th	Day	11% 6% 3 7% 5% 4 5% 4 7% 9% 40%	8879
	11th to 20th	Day	8% 5% 2 5% 4 5% 5% 5% 7% 9% 46%	8147
	21st to end	Day	8% 6% 2 6% 4 4 5% 4 7% 9% 45%	8340
August	1st to 10th	Day	13% 6% 2 6% 5% 5% 5% 5% 7% 9% 36%	4364
	11th to 20th	Day	11% 7% 3 7% 5% 5% 6% 5% 8% 10% 33%	4304
	21st to end	Day	9% 6% 2 7% 4 5% 6% 5% 7% 10% 40%	4730
September	1st to 10th	Day	11% 6% 3 8% 4 5% 4 4 5% 10% 39%	2369
	11th to 20th	Day	11% 6% 2 5% 4 5% 5% 4 7% 7% 45%	2200
	21st to end	Day	16% 8% 2 7% 5% 4 5% 4 7% 7% 34%	2200
October	1st to 10th	Day	18% 8% 3 8% 5% 4 4 3 6% 6% 36%	2029
	11th to 20th	Day	20% 11% 4 8% 6% 4 5% 4 5% 7% 26%	2000
	21st to end	Day	23% 14% 4 9% 5% 5% 5% 3 6% 6% 19%	2160
November	1st to 10th	Day	15% 16% 4 9% 5% 4 4 3 6% 6% 28%	1847
	11th to 20th	Day	14% 16% 5% 9% 6% 5% 6% 4 6% 6% 21%	1680
	21st to end	Day	16% 20% 9% 12% 6% 5% 4 3 6% 6% 13%	1680
December	1st to 10th	Day	17% 24% 11% 14% 6% 5% 4 3 5% 4 7%	2680
	11th to 20th	Day	20% 20% 6% 15% 8% 4 3 2 4 4 13%	3066
	21st to end	Day	25% 22% 7% 13% 5% 4 4 3 3 4 10%	3800
January	1st to 10th	Night	12% 16% 8% 23% 8% 6% 5% 3 4 5% 10%	8553
	11th to 20th	Night	9% 18% 10% 23% 12% 7% 6% 4 3 2 5%	7639
	21st to end	Night	11% 14% 8% 17% 10% 9% 7% 4 5% 5% 11%	8401
February	1st to 10th	Night	14% 18% 6% 13% 10% 6% 5% 4 4 4 16%	2730
	11th to 20th	Night	13% 15% 6% 13% 8% 6% 5% 4 6% 6% 18%	2663
	21st to end	Night	15% 13% 6% 13% 7% 4 5% 4 5% 5% 22%	2102
March	1st to 10th	Night	13% 11% 5% 10% 7% 5% 5% 3 5% 6% 29%	5120
	11th to 20th	Night	9% 10% 5% 11% 5% 5% 5% 4 7% 8% 32%	5089
	21st to end	Night	17% 11% 5% 9% 5% 4 4 3 4 4 34%	5588
April	1st to 10th	Night	18% 12% 4 9% 5% 4 4 3 5% 5% 30%	2216
	11th to 20th	Night	16% 12% 3 7% 5% 4 4 3 5% 7% 34%	1907
	21st to end	Night	15% 10% 4 8% 5% 4 5% 3 5% 6% 35%	1890
May	1st to 10th	Night	17% 8% 3 7% 4 4 4 3 5% 7% 38%	5257
	11th to 20th	Night	15% 10% 3 8% 5% 4 4 3 5% 6% 37%	5059
	21st to end	Night	18% 6% 2 5% 3 3 3 3 5% 7% 46%	5114
June	1st to 10th	Night	12% 6% 2 6% 5% 4 5% 4 6% 7% 43%	1658
	11th to 20th	Night	9% 7% 2 5% 5% 5% 5% 4 6% 10% 40%	1470
	21st to end	Night	11% 6% 2 5% 4 5% 5% 3 5% 9% 45%	1470
July	1st to 10th	Night	7% 6% 2 6% 4 5% 4 4 6% 9% 47%	4110
	11th to 20th	Night	9% 6% 2 5% 4 4 4 3 5% 9% 50%	4804
	21st to end	Night	9% 6% 2 6% 4 4 4 3 5% 7% 49%	5737
August	1st to 10th	Night	11% 7% 2 6% 5% 4 4 3 5% 7% 45%	3005
	11th to 20th	Night	11% 9% 3 6% 4 4 4 3 6% 8% 43%	2965
	21st to end	Night	10% 6% 2 6% 4 4 5% 3 5% 7% 47%	3332
September	1st to 10th	Night	10% 6% 2 7% 5% 4 4 4 6% 7% 45%	2029
	11th to 20th	Night	10% 4 2 5% 4 3 3 4 4 7% 54%	2200
	21st to end	Night	16% 8% 2 7% 5% 4 4 4 5% 7% 39%	2200
October	1st to 10th	Night	13% 8% 3 7% 5% 4 5% 4 5% 7% 39%	2370
	11th to 20th	Night	20% 11% 4 7% 6% 4 5% 3 5% 6% 31%	2400
	21st to end	Night	21% 12% 3 9% 6% 4 4 4 6% 5% 25%	2676
November	1st to 10th	Night	14% 12% 4 8% 6% 4 5% 3 5% 6% 32%	2669
	11th to 20th	Night	14% 16% 6% 11% 6% 5% 4 4 6% 7% 21%	2940
	21st to end	Night	19% 17% 6% 11% 6% 5% 4 3 5% 6% 17%	2940
December	1st to 10th	Night	12% 22% 10% 17% 7% 6% 5% 4 4 4 9%	4720
	11th to 20th	Night	13% 23% 8% 16% 7% 5% 4 3 4 4 14%	5348
	21st to end	Night	21% 21% 8% 13% 6% 4 4 3 4 4 12%	7385

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	76% 1 7% 10% 6%	4344
	11th to 20th	Day	90% 1 3 3 2	5280
	21st to end	Day	82% 1 7% 5% 4	5780
February	1st to 10th	Day	75% 3 6% 13% 4	1890
	11th to 20th	Day	70% 4 6% 14% 5% 1	1852
	21st to end	Day	67% 3 10% 14% 5% 1	1701
March	1st to 10th	Day	64% 1 13% 15% 6% 1	4942
	11th to 20th	Day	57% 1 14% 19% 7% 2	5090
	21st to end	Day	63% 1 9% 17% 9% 1	5586
April	1st to 10th	Day	57% 3 10% 19% 10%	2404
	11th to 20th	Day	51% 3 11% 22% 12% 1	2680
	21st to end	Day	53% 3 11% 21% 11% 2	2730
May	1st to 10th	Day	50% 1 10% 22% 12% 4	7651
	11th to 20th	Day	51% 2 10% 22% 14% 1	7804
	21st to end	Day	44% 1 8% 26% 17% 3	9061
June	1st to 10th	Day	44% 3 11% 25% 16% 1	2956
	11th to 20th	Day	42% 4 12% 26% 15% 1	3150
	21st to end	Day	43% 3 13% 26% 14%	3150
July	1st to 10th	Day	42% 2 13% 26% 16% 1	8806
	11th to 20th	Day	34% 1 11% 37% 16% 1	8069
	21st to end	Day	36% 2 14% 29% 18% 1	8156
August	1st to 10th	Day	44% 3 12% 26% 14% 1	4351
	11th to 20th	Day	45% 3 16% 28% 9%	4343
	21st to end	Day	40% 3 13% 33% 11% 1	4730
September	1st to 10th	Day	41% 5% 13% 28% 11% 1	2369
	11th to 20th	Day	37% 4 12% 32% 15% 1	2200
	21st to end	Day	48% 3 13% 25% 10% 1	2200
October	1st to 10th	Day	45% 2 10% 25% 16% 1	3302
	11th to 20th	Day	45% 2 12% 25% 16%	3240
	21st to end	Day	57% 2 15% 19% 7%	3474
November	1st to 10th	Day	57% 4 10% 21% 8% 1	1847
	11th to 20th	Day	61% 4 11% 15% 8% 1	1680
	21st to end	Day	71% 4 10% 11% 3	1680
December	1st to 10th	Day	80% 3 6% 8% 2	2680
	11th to 20th	Day	77% 2 7% 11% 4	3066
	21st to end	Day	80% 2 6% 8% 4	3800
January	1st to 10th	Night	77% 1 5% 12% 4	8553
	11th to 20th	Night	85% 1 5% 6% 2	7680
	21st to end	Night	77% 1 7% 9% 5%	8401
February	1st to 10th	Night	71% 3 6% 15% 4 1	2730
	11th to 20th	Night	66% 3 9% 15% 7%	2665
	21st to end	Night	64% 3 10% 16% 7%	2102
March	1st to 10th	Night	58% 2 12% 19% 9% 1	5130
	11th to 20th	Night	50% 2 16% 21% 10% 1	5090
	21st to end	Night	56% 2 8% 19% 15% 2	5588
April	1st to 10th	Night	56% 3 9% 18% 13% 1	2216
	11th to 20th	Night	50% 4 8% 21% 16% 2	1907
	21st to end	Night	52% 2 9% 20% 15% 3	1890
May	1st to 10th	Night	48% 1 10% 18% 16% 6%	5264
	11th to 20th	Night	50% 2 9% 23% 14% 2	5060
	21st to end	Night	41% 1 10% 26% 19% 3	5115
June	1st to 10th	Night	39% 3 9% 27% 19% 3	1658
	11th to 20th	Night	38% 3 13% 27% 16% 2	1470
	21st to end	Night	38% 3 13% 27% 18% 1	1470
July	1st to 10th	Night	35% 2 16% 28% 16% 3	4075
	11th to 20th	Night	35% 2 9% 31% 21% 2	4760
	21st to end	Night	36% 2 10% 27% 23% 2	5606
August	1st to 10th	Night	40% 2 12% 28% 16% 2	2994
	11th to 20th	Night	40% 3 15% 28% 13% 1	2992
	21st to end	Night	37% 3 10% 34% 15% 1	3332
September	1st to 10th	Night	39% 4 11% 30% 14% 2	2029
	11th to 20th	Night	31% 4 11% 32% 21% 1	2200
	21st to end	Night	45% 4 13% 26% 12% 1	2200
October	1st to 10th	Night	36% 2 7% 29% 24% 1	3877
	11th to 20th	Night	48% 2 13% 22% 15%	3899
	21st to end	Night	48% 2 14% 25% 10%	4312
November	1st to 10th	Night	52% 4 10% 23% 10% 1	2669
	11th to 20th	Night	62% 3 11% 17% 6% 1	2940
	21st to end	Night	68% 3 13% 12% 4	2940
December	1st to 10th	Night	78% 2 9% 8% 2	4720
	11th to 20th	Night	74% 2 7% 11% 5%	5348
	21st to end	Night	77% 2 8% 9% 5%	7385

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	21% 19% 37% 15% 7% 1	259
	11th to 20th	Day	20% 18% 45% 13% 4 1	330
	21st to end	Day	25% 15% 34% 21% 3 1	363
February	1st to 10th	Day	21% 19% 39% 15% 5%	330
	11th to 20th	Day	21% 20% 39% 17% 2	330
	21st to end	Day	26% 24% 32% 17% 1	273
March	1st to 10th	Day	25% 12% 38% 18% 6% 1	485
	11th to 20th	Day	23% 15% 32% 22% 7% 1	540
	21st to end	Day	27% 11% 34% 22% 4 1	594
April	1st to 10th	Day	24% 16% 32% 20% 6% 1	540
	11th to 20th	Day	26% 15% 27% 17% 11% 4	532
	21st to end	Day	25% 10% 32% 24% 7% 2	540
May	1st to 10th	Day	23% 9% 29% 25% 10% 3	543
	11th to 20th	Day	21% 8% 27% 24% 16% 5%	567
	21st to end	Day	18% 5% 29% 25% 17% 6%	617
June	1st to 10th	Day	16% 10% 28% 30% 14% 3	586
	11th to 20th	Day	15% 9% 29% 31% 14% 3	780
	21st to end	Day	16% 7% 27% 34% 11% 4	780
July	1st to 10th	Day	11% 5% 22% 32% 21% 9%	771
	11th to 20th	Day	15% 4 25% 29% 19% 8%	645
	21st to end	Day	11% 2 24% 35% 21% 7%	620
August	1st to 10th	Day	12% 4 19% 28% 25% 12%	566
	11th to 20th	Day	14% 2 18% 31% 21% 14%	559
	21st to end	Day	16% 5% 19% 29% 21% 11%	619
September	1st to 10th	Day	13% 6% 21% 26% 19% 14%	530
	11th to 20th	Day	9% 4 17% 27% 28% 15%	530
	21st to end	Day	16% 10% 23% 27% 16% 8%	530
October	1st to 10th	Day	21% 7% 25% 23% 18% 6%	530
	11th to 20th	Day	22% 13% 33% 25% 7% 1	530
	21st to end	Day	29% 12% 32% 21% 5% 1	543
November	1st to 10th	Day	25% 18% 31% 17% 8% 1	327
	11th to 20th	Day	24% 18% 32% 19% 6% 2	220
	21st to end	Day	23% 19% 38% 16% 4	220
December	1st to 10th	Day	27% 22% 29% 16% 5%	220
	11th to 20th	Day	30% 22% 30% 15% 2	220
	21st to end	Day	36% 16% 33% 12% 3	242
January	1st to 10th	Night	22% 17% 35% 20% 5% 1	1033
	11th to 20th	Night	26% 17% 33% 20% 4	840
	21st to end	Night	19% 13% 38% 23% 6%	924
February	1st to 10th	Night	24% 14% 37% 22% 3	840
	11th to 20th	Night	21% 15% 36% 23% 5%	823
	21st to end	Night	23% 15% 36% 22% 3	692
March	1st to 10th	Night	20% 13% 37% 24% 6%	840
	11th to 20th	Night	19% 15% 38% 21% 6%	840
	21st to end	Night	23% 11% 33% 24% 8% 1	924
April	1st to 10th	Night	24% 13% 33% 26% 4	840
	11th to 20th	Night	24% 10% 32% 24% 9% 1	663
	21st to end	Night	20% 10% 30% 33% 7%	630
May	1st to 10th	Night	19% 6% 32% 30% 13% 1	630
	11th to 20th	Night	20% 4 27% 34% 13% 1	563
	21st to end	Night	15% 3 28% 38% 16%	455
June	1st to 10th	Night	14% 3 30% 39% 14% 1	420
	11th to 20th	Night	13% 6% 29% 40% 12%	420
	21st to end	Night	15% 3 25% 41% 14% 1	420
July	1st to 10th	Night	8% 1 17% 50% 22% 1	410
	11th to 20th	Night	10% 2 20% 43% 24% 2	530
	21st to end	Night	10% 1 18% 48% 22% 1	690
August	1st to 10th	Night	11% 2 12% 44% 27% 3	627
	11th to 20th	Night	9% 2 15% 41% 28% 5%	624
	21st to end	Night	15% 2 18% 35% 26% 3	702
September	1st to 10th	Night	13% 4 23% 33% 22% 4	800
	11th to 20th	Night	12% 3 18% 35% 28% 5%	800
	21st to end	Night	19% 5% 20% 35% 17% 4	800
October	1st to 10th	Night	19% 5% 27% 30% 17% 2	800
	11th to 20th	Night	25% 9% 28% 28% 9% 1	800
	21st to end	Night	28% 9% 32% 25% 5%	880
November	1st to 10th	Night	22% 11% 28% 29% 8% 1	820
	11th to 20th	Night	22% 14% 33% 22% 6% 1	840
	21st to end	Night	27% 13% 33% 22% 4	840
December	1st to 10th	Night	26% 18% 31% 20% 5%	840
	11th to 20th	Night	23% 18% 37% 18% 3 1	840
	21st to end	Night	29% 14% 35% 19% 2	1029

Page generated at 2026-08-27 04:07:16. Version ac07

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