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 2024-02-25.

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% 11% 5% 8% 7% 4 5% 5% 5% 7% 28%	78586
	Night	15% 12% 6% 9% 7% 4 5% 4 5% 6% 27%	80679
Transparency	Day	56% 3 11% 20% 10% 1	78296
	Night	58% 3 10% 18% 9% 1	80505
Seeing	Day	20% 10% 28% 25% 13% 5%	14009
	Night	20% 10% 29% 28% 11% 1	23370

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% 18% 10% 13% 8% 3 4 3 3 4 18%	2319
	11th to 20th	Day	11% 18% 10% 21% 10% 6% 8% 3 3 3 6%	2840
	21st to end	Day	19% 21% 9% 15% 9% 4 4 4 4 3 8%	3124
February	1st to 10th	Day	14% 17% 8% 14% 12% 5% 5% 4 4 5% 13%	1710
	11th to 20th	Day	12% 13% 9% 13% 10% 5% 6% 5% 5% 6% 16%	1663
	21st to end	Day	15% 16% 7% 12% 8% 3 5% 4 4 5% 21%	1493
March	1st to 10th	Day	14% 12% 6% 10% 9% 4 5% 4 4 5% 26%	1929
	11th to 20th	Day	11% 13% 7% 9% 7% 4 6% 4 4 5% 29%	1980
	21st to end	Day	17% 11% 6% 9% 6% 3 5% 4 4 6% 29%	2178
April	1st to 10th	Day	17% 14% 6% 7% 5% 3 4 5% 6% 7% 26%	2060
	11th to 20th	Day	18% 10% 4 6% 5% 3 4 4 5% 7% 34%	2293
	21st to end	Day	21% 10% 5% 6% 5% 3 4 4 5% 7% 31%	2340
May	1st to 10th	Day	17% 10% 3 6% 5% 4 5% 4 5% 8% 33%	2340
	11th to 20th	Day	18% 8% 3 6% 5% 3 4 4 5% 6% 38%	2349
	21st to end	Day	13% 6% 2 5% 5% 3 5% 6% 6% 9% 40%	2725
June	1st to 10th	Day	14% 7% 3 5% 6% 4 5% 4 6% 9% 38%	2533
	11th to 20th	Day	12% 6% 3 5% 5% 4 5% 5% 6% 8% 41%	2700
	21st to end	Day	14% 7% 2 5% 5% 3 5% 5% 6% 8% 39%	2700
July	1st to 10th	Day	9% 5% 2 5% 5% 2 5% 5% 7% 8% 47%	2700
	11th to 20th	Day	11% 6% 3 5% 5% 4 5% 7% 7% 8% 39%	2485
	21st to end	Day	11% 6% 3 5% 5% 3 6% 5% 7% 10% 40%	2547
August	1st to 10th	Day	9% 6% 3 4 7% 4 6% 6% 8% 10% 37%	2327
	11th to 20th	Day	10% 6% 3 6% 7% 4 6% 6% 8% 10% 34%	2303
	21st to end	Day	13% 6% 2 6% 5% 4 6% 5% 6% 9% 39%	2542
September	1st to 10th	Day	12% 6% 3 7% 6% 4 5% 5% 5% 10% 37%	2133
	11th to 20th	Day	12% 6% 3 4 5% 4 5% 5% 7% 8% 41%	1980
	21st to end	Day	17% 7% 3 6% 6% 3 5% 5% 6% 7% 34%	1980
October	1st to 10th	Day	19% 8% 3 7% 6% 3 4 4 5% 5% 33%	1827
	11th to 20th	Day	22% 11% 4 8% 6% 3 5% 5% 5% 7% 23%	1800
	21st to end	Day	25% 14% 4 8% 7% 4 5% 4 6% 6% 18%	1944
November	1st to 10th	Day	15% 15% 4 8% 6% 3 4 5% 5% 7% 28%	1668
	11th to 20th	Day	15% 15% 6% 8% 8% 4 6% 5% 6% 6% 21%	1520
	21st to end	Day	18% 17% 10% 10% 7% 4 4 4 6% 6% 15%	1520
December	1st to 10th	Day	14% 21% 12% 14% 8% 4 5% 4 4 5% 10%	1520
	11th to 20th	Day	18% 17% 8% 14% 8% 4 4 4 4 5% 13%	1906
	21st to end	Day	27% 21% 8% 12% 7% 4 4 4 3 4 7%	2608
January	1st to 10th	Night	15% 20% 8% 18% 9% 4 4 4 4 4 10%	4610
	11th to 20th	Night	14% 14% 10% 16% 12% 6% 6% 7% 5% 3 7%	4120
	21st to end	Night	19% 16% 10% 15% 9% 4 5% 3 3 4 12%	4532
February	1st to 10th	Night	15% 17% 7% 11% 11% 4 5% 4 4 5% 16%	2470
	11th to 20th	Night	13% 14% 7% 12% 9% 4 6% 5% 5% 7% 18%	2403
	21st to end	Night	17% 12% 6% 12% 8% 3 5% 5% 5% 5% 23%	1855
March	1st to 10th	Night	14% 9% 4 11% 7% 4 5% 4 6% 7% 29%	2017
	11th to 20th	Night	13% 12% 5% 9% 6% 4 4 4 5% 6% 32%	1979
	21st to end	Night	15% 12% 5% 7% 6% 4 4 4 4 5% 34%	2178
April	1st to 10th	Night	19% 10% 5% 7% 6% 4 5% 4 5% 5% 31%	1900
	11th to 20th	Night	16% 10% 4 5% 5% 3 5% 4 5% 7% 36%	1632
	21st to end	Night	16% 11% 5% 7% 6% 3 4 4 4 7% 34%	1620
May	1st to 10th	Night	17% 8% 3 6% 4 3 5% 5% 5% 7% 37%	1620
	11th to 20th	Night	16% 7% 2 6% 6% 3 4 4 5% 6% 41%	1543
	21st to end	Night	8% 4 2 4 4 3 5% 5% 6% 9% 49%	1550
June	1st to 10th	Night	13% 5% 2 6% 5% 2 5% 5% 6% 8% 43%	1422
	11th to 20th	Night	10% 7% 2 4 5% 3 5% 5% 6% 9% 43%	1260
	21st to end	Night	11% 6% 2 4 4 4 4 5% 4 9% 46%	1260
July	1st to 10th	Night	6% 4 2 4 4 2 5% 4 6% 9% 56%	1260
	11th to 20th	Night	8% 5% 2 5% 5% 2 3 4 6% 9% 50%	1468
	21st to end	Night	8% 4 3 5% 6% 3 5% 5% 6% 8% 46%	1771
August	1st to 10th	Night	8% 6% 1 5% 6% 3 5% 5% 6% 8% 48%	1611
	11th to 20th	Night	6% 6% 3 5% 4 3 3 5% 7% 9% 48%	1598
	21st to end	Night	10% 6% 2 5% 5% 3 5% 3 6% 7% 46%	1795
September	1st to 10th	Night	12% 6% 2 6% 5% 4 4 5% 5% 7% 44%	1825
	11th to 20th	Night	11% 4 2 4 5% 2 3 5% 4 7% 51%	1980
	21st to end	Night	15% 8% 2 6% 6% 3 4 5% 6% 7% 40%	1980
October	1st to 10th	Night	14% 8% 4 7% 6% 3 5% 5% 5% 7% 36%	2132
	11th to 20th	Night	21% 11% 4 6% 7% 3 4 4 5% 6% 29%	2160
	21st to end	Night	23% 12% 4 8% 7% 3 4 4 6% 5% 23%	2408
November	1st to 10th	Night	15% 11% 4 7% 7% 3 5% 4 5% 6% 32%	2408
	11th to 20th	Night	15% 15% 6% 9% 7% 4 4 5% 5% 7% 22%	2660
	21st to end	Night	19% 15% 7% 10% 8% 4 5% 4 5% 6% 18%	2660
December	1st to 10th	Night	18% 21% 10% 12% 7% 3 5% 4 4 4 12%	2660
	11th to 20th	Night	14% 19% 8% 14% 8% 3 5% 4 4 5% 14%	3288
	21st to end	Night	25% 22% 10% 12% 6% 3 4 4 4 4 8%	5044

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	73% 2 9% 10% 6%	2320
	11th to 20th	Day	85% 2 4 6% 3	2840
	21st to end	Day	82% 2 6% 7% 3	3124
February	1st to 10th	Day	75% 3 6% 12% 3	1710
	11th to 20th	Day	68% 4 7% 14% 6% 1	1672
	21st to end	Day	67% 3 9% 14% 6% 1	1493
March	1st to 10th	Day	61% 3 11% 16% 8% 1	1932
	11th to 20th	Day	59% 3 9% 17% 10% 2	1980
	21st to end	Day	57% 3 9% 19% 11% 2	2178
April	1st to 10th	Day	57% 4 11% 18% 10%	2060
	11th to 20th	Day	50% 3 12% 21% 13% 1	2293
	21st to end	Day	54% 3 11% 19% 11% 2	2340
May	1st to 10th	Day	51% 2 10% 24% 12% 1	2340
	11th to 20th	Day	49% 3 10% 25% 11% 2	2353
	21st to end	Day	41% 4 15% 24% 14% 2	2725
June	1st to 10th	Day	44% 4 12% 25% 14% 1	2533
	11th to 20th	Day	41% 4 12% 26% 15% 1	2700
	21st to end	Day	43% 4 12% 26% 15%	2700
July	1st to 10th	Day	35% 4 12% 28% 19% 2	2626
	11th to 20th	Day	40% 4 12% 30% 13% 1	2407
	21st to end	Day	40% 4 13% 27% 15% 2	2405
August	1st to 10th	Day	41% 4 15% 28% 10% 2	2314
	11th to 20th	Day	43% 4 17% 25% 11% 1	2303
	21st to end	Day	42% 4 14% 27% 13% 1	2542
September	1st to 10th	Day	43% 5% 14% 26% 11% 2	2133
	11th to 20th	Day	40% 4 12% 30% 13% 1	1980
	21st to end	Day	48% 4 14% 25% 9% 1	1980
October	1st to 10th	Day	53% 3 11% 19% 12% 1	1827
	11th to 20th	Day	60% 4 11% 18% 7% 1	1800
	21st to end	Day	66% 3 11% 13% 6%	1944
November	1st to 10th	Day	57% 4 10% 21% 8% 1	1668
	11th to 20th	Day	61% 4 12% 15% 7% 1	1520
	21st to end	Day	70% 4 11% 12% 4	1520
December	1st to 10th	Day	76% 5% 7% 10% 2	1520
	11th to 20th	Day	75% 3 9% 10% 3	1906
	21st to end	Day	83% 2 8% 6% 1	2608
January	1st to 10th	Night	79% 2 6% 9% 3	4610
	11th to 20th	Night	81% 2 8% 7% 2	4120
	21st to end	Night	78% 2 7% 9% 4 1	4532
February	1st to 10th	Night	72% 4 6% 14% 3	2470
	11th to 20th	Night	65% 3 9% 14% 7%	2405
	21st to end	Night	63% 3 10% 15% 8%	1855
March	1st to 10th	Night	54% 4 11% 21% 9% 1	2027
	11th to 20th	Night	53% 3 9% 22% 11% 2	1980
	21st to end	Night	55% 3 7% 20% 13% 3	2178
April	1st to 10th	Night	54% 3 8% 19% 14% 1	1900
	11th to 20th	Night	48% 4 8% 20% 17% 2	1632
	21st to end	Night	53% 2 8% 19% 15% 3	1620
May	1st to 10th	Night	47% 3 9% 23% 16% 2	1620
	11th to 20th	Night	44% 3 10% 23% 16% 4	1544
	21st to end	Night	32% 4 15% 28% 17% 4	1551
June	1st to 10th	Night	39% 4 10% 28% 17% 2	1422
	11th to 20th	Night	37% 4 13% 27% 17% 3	1260
	21st to end	Night	37% 3 14% 27% 18% 1	1260
July	1st to 10th	Night	26% 4 12% 30% 24% 3	1225
	11th to 20th	Night	32% 3 13% 31% 19% 1	1424
	21st to end	Night	35% 4 13% 28% 17% 2	1672
August	1st to 10th	Night	34% 4 15% 32% 13% 1	1600
	11th to 20th	Night	32% 5% 16% 31% 15% 1	1598
	21st to end	Night	37% 5% 12% 30% 15% 2	1795
September	1st to 10th	Night	40% 5% 11% 28% 14% 2	1825
	11th to 20th	Night	33% 4 11% 32% 19% 1	1980
	21st to end	Night	43% 4 14% 27% 12%	1980
October	1st to 10th	Night	48% 4 9% 23% 15% 1	2132
	11th to 20th	Night	56% 3 10% 22% 8% 1	2160
	21st to end	Night	61% 4 10% 16% 9%	2408
November	1st to 10th	Night	52% 4 11% 23% 10% 1	2408
	11th to 20th	Night	62% 3 11% 17% 6% 1	2660
	21st to end	Night	66% 4 13% 12% 4	2660
December	1st to 10th	Night	76% 4 8% 10% 3	2660
	11th to 20th	Night	72% 3 11% 11% 2	3288
	21st to end	Night	82% 2 8% 6% 1	5044

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% 18% 34% 18% 8% 1	211
	11th to 20th	Day	21% 14% 46% 13% 4 1	270
	21st to end	Day	27% 12% 32% 24% 3 1	297
February	1st to 10th	Day	21% 17% 42% 14% 5%	270
	11th to 20th	Day	21% 20% 39% 17% 2	270
	21st to end	Day	27% 26% 30% 15% 2	210
March	1st to 10th	Day	25% 12% 38% 18% 7% 1	372
	11th to 20th	Day	21% 12% 34% 24% 8% 1	420
	21st to end	Day	27% 10% 32% 25% 5% 1	462
April	1st to 10th	Day	21% 15% 33% 22% 7% 1	420
	11th to 20th	Day	25% 12% 29% 18% 11% 5%	412
	21st to end	Day	27% 9% 30% 23% 9% 2	420
May	1st to 10th	Day	25% 8% 26% 26% 11% 4	423
	11th to 20th	Day	22% 8% 26% 23% 16% 5%	447
	21st to end	Day	16% 5% 26% 26% 20% 7%	485
June	1st to 10th	Day	16% 10% 27% 31% 14% 4	463
	11th to 20th	Day	15% 9% 26% 31% 15% 3	630
	21st to end	Day	16% 7% 26% 35% 11% 5%	630
July	1st to 10th	Day	10% 5% 21% 31% 23% 10%	621
	11th to 20th	Day	17% 4 24% 28% 19% 9%	513
	21st to end	Day	12% 2 25% 35% 18% 7%	488
August	1st to 10th	Day	11% 4 19% 27% 25% 14%	446
	11th to 20th	Day	13% 3 16% 30% 22% 16%	439
	21st to end	Day	17% 5% 18% 28% 20% 12%	495
September	1st to 10th	Day	14% 5% 20% 29% 19% 13%	450
	11th to 20th	Day	10% 5% 20% 29% 26% 11%	450
	21st to end	Day	16% 11% 25% 25% 14% 9%	450
October	1st to 10th	Day	23% 8% 26% 21% 17% 6%	450
	11th to 20th	Day	24% 13% 32% 24% 5% 1	450
	21st to end	Day	32% 12% 32% 19% 5% 1	459
November	1st to 10th	Day	24% 18% 30% 18% 9% 1	268
	11th to 20th	Day	24% 17% 32% 18% 6% 2	180
	21st to end	Day	23% 18% 38% 18% 3	180
December	1st to 10th	Day	26% 23% 29% 17% 4	180
	11th to 20th	Day	30% 22% 31% 16% 2	180
	21st to end	Day	33% 18% 36% 12% 2	198
January	1st to 10th	Night	23% 16% 35% 20% 6% 1	935
	11th to 20th	Night	27% 15% 32% 21% 4	760
	21st to end	Night	20% 12% 37% 24% 6%	836
February	1st to 10th	Night	25% 15% 36% 22% 2	760
	11th to 20th	Night	21% 14% 36% 23% 6%	743
	21st to end	Night	24% 15% 35% 22% 4	611
March	1st to 10th	Night	20% 12% 37% 24% 7%	720
	11th to 20th	Night	19% 14% 38% 22% 7%	720
	21st to end	Night	23% 10% 32% 26% 9% 1	792
April	1st to 10th	Night	24% 13% 31% 28% 5%	720
	11th to 20th	Night	24% 10% 32% 24% 10% 1	568
	21st to end	Night	21% 9% 30% 32% 7%	540
May	1st to 10th	Night	19% 6% 30% 30% 14% 1	540
	11th to 20th	Night	20% 5% 26% 34% 13% 1	482
	21st to end	Night	12% 3 29% 39% 18%	389
June	1st to 10th	Night	14% 3 28% 39% 14% 1	360
	11th to 20th	Night	13% 6% 28% 40% 14%	360
	21st to end	Night	15% 3 26% 40% 14% 1	360
July	1st to 10th	Night	8% 1 17% 47% 25% 1	350
	11th to 20th	Night	10% 2 21% 42% 24% 2	452
	21st to end	Night	10% 2 18% 48% 21% 1	591
August	1st to 10th	Night	11% 2 12% 45% 27% 3	537
	11th to 20th	Night	8% 2 16% 40% 28% 5%	534
	21st to end	Night	14% 3 19% 35% 25% 3	607
September	1st to 10th	Night	13% 4 22% 34% 21% 5%	720
	11th to 20th	Night	13% 3 19% 36% 24% 5%	720
	21st to end	Night	18% 6% 20% 33% 17% 5%	720
October	1st to 10th	Night	20% 5% 28% 28% 17% 2	720
	11th to 20th	Night	26% 10% 27% 28% 8% 1	720
	21st to end	Night	30% 10% 31% 25% 4	792
November	1st to 10th	Night	22% 10% 28% 30% 9% 1	740
	11th to 20th	Night	22% 14% 34% 21% 7% 1	760
	21st to end	Night	26% 12% 33% 24% 5%	760
December	1st to 10th	Night	27% 18% 30% 19% 5%	760
	11th to 20th	Night	23% 18% 36% 18% 4 1	760
	21st to end	Night	29% 14% 35% 19% 2	931

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