Slemon Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Slemon Park clear sky chart from 2005-11-06 to 2024-01-31.

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	18% 10% 4 7% 6% 3 5% 4 5% 7% 31%	74999
	Night	19% 11% 4 8% 6% 3 5% 4 5% 6% 29%	75123
Transparency	Day	53% 6% 12% 20% 9% 1	74692
	Night	56% 5% 11% 18% 8% 1	74965
Seeing	Day	23% 12% 30% 24% 9% 2	15925
	Night	25% 13% 30% 25% 7% 1	23525

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	18% 15% 6% 10% 9% 4 5% 4 3 3 22%	1327
	11th to 20th	Day	17% 16% 6% 11% 9% 4 5% 3 4 5% 20%	1478
	21st to end	Day	12% 10% 5% 8% 8% 4 5% 5% 5% 6% 33%	1852
February	1st to 10th	Day	16% 13% 5% 7% 5% 4 4 5% 4 6% 32%	1620
	11th to 20th	Day	16% 13% 5% 8% 6% 4 6% 4 5% 5% 27%	1573
	21st to end	Day	10% 12% 6% 7% 6% 3 5% 5% 6% 8% 34%	1344
March	1st to 10th	Day	15% 12% 6% 8% 6% 3 4 4 5% 6% 31%	1940
	11th to 20th	Day	13% 10% 5% 10% 8% 4 4 4 4 6% 31%	1980
	21st to end	Day	18% 15% 5% 6% 6% 3 4 3 4 5% 31%	2186
April	1st to 10th	Day	19% 11% 5% 6% 6% 3 5% 4 5% 6% 30%	2160
	11th to 20th	Day	19% 10% 3 5% 5% 2 5% 3 5% 8% 35%	2222
	21st to end	Day	21% 12% 3 6% 5% 3 4 5% 5% 7% 28%	2340
May	1st to 10th	Day	24% 10% 3 6% 5% 3 5% 4 5% 7% 29%	2453
	11th to 20th	Day	21% 8% 3 5% 5% 3 4 4 4 6% 36%	2478
	21st to end	Day	19% 8% 3 6% 5% 3 4 5% 5% 7% 36%	2724
June	1st to 10th	Day	25% 9% 3 5% 6% 2 5% 5% 5% 8% 26%	2605
	11th to 20th	Day	20% 8% 3 6% 5% 3 4 5% 5% 7% 35%	2700
	21st to end	Day	23% 7% 3 6% 5% 3 4 4 5% 6% 32%	2700
July	1st to 10th	Day	15% 7% 3 5% 5% 2 5% 5% 6% 9% 39%	2700
	11th to 20th	Day	13% 5% 2 5% 5% 4 5% 6% 7% 10% 37%	2606
	21st to end	Day	15% 7% 3 7% 6% 3 5% 5% 6% 9% 34%	2745
August	1st to 10th	Day	15% 6% 3 5% 4 3 5% 5% 6% 7% 41%	2332
	11th to 20th	Day	15% 5% 2 6% 6% 4 6% 5% 6% 9% 36%	2304
	21st to end	Day	13% 6% 2 5% 4 3 5% 5% 6% 8% 44%	2494
September	1st to 10th	Day	16% 5% 2 5% 4 2 4 5% 5% 9% 43%	2160
	11th to 20th	Day	18% 8% 3 6% 5% 3 3 4 5% 5% 40%	2109
	21st to end	Day	18% 6% 3 5% 5% 3 4 3 5% 7% 42%	1913
October	1st to 10th	Day	19% 7% 3 6% 6% 3 5% 5% 5% 7% 36%	1800
	11th to 20th	Day	19% 11% 3 8% 6% 4 5% 5% 5% 8% 27%	1800
	21st to end	Day	20% 13% 4 8% 6% 4 5% 4 5% 7% 24%	1949
November	1st to 10th	Day	18% 15% 4 6% 7% 4 5% 4 4 6% 26%	1490
	11th to 20th	Day	19% 15% 5% 8% 7% 4 6% 4 6% 7% 20%	1520
	21st to end	Day	18% 14% 8% 12% 8% 3 5% 5% 5% 6% 17%	1520
December	1st to 10th	Day	24% 14% 6% 11% 8% 3 3 5% 4 6% 16%	1520
	11th to 20th	Day	16% 17% 8% 12% 9% 5% 5% 4 3 4 15%	1906
	21st to end	Day	17% 13% 9% 15% 8% 4 4 4 4 4 18%	2449
January	1st to 10th	Night	18% 14% 5% 9% 8% 3 6% 5% 5% 5% 22%	2838
	11th to 20th	Night	17% 14% 6% 9% 7% 3 6% 4 5% 6% 23%	2698
	21st to end	Night	13% 11% 5% 8% 7% 3 4 4 6% 6% 31%	2730
February	1st to 10th	Night	16% 13% 5% 8% 5% 3 4 5% 5% 6% 30%	2340
	11th to 20th	Night	18% 15% 4 8% 8% 3 5% 4 5% 5% 25%	2273
	21st to end	Night	12% 13% 5% 8% 7% 3 5% 4 5% 6% 32%	1911
March	1st to 10th	Night	18% 13% 5% 8% 7% 3 4 3 5% 5% 29%	2005
	11th to 20th	Night	18% 11% 5% 7% 9% 4 4 4 5% 4 29%	1979
	21st to end	Night	19% 14% 5% 9% 5% 2 4 3 4 4 31%	2170
April	1st to 10th	Night	21% 12% 4 7% 7% 3 5% 4 5% 5% 25%	1800
	11th to 20th	Night	21% 11% 4 6% 5% 4 3 4 6% 5% 32%	1684
	21st to end	Night	21% 14% 4 7% 6% 3 4 4 3 5% 28%	1620
May	1st to 10th	Night	26% 8% 2 5% 5% 3 6% 4 5% 5% 32%	1505
	11th to 20th	Night	21% 9% 3 5% 6% 3 3 4 3 5% 37%	1416
	21st to end	Night	17% 8% 3 5% 5% 3 4 4 6% 9% 35%	1550
June	1st to 10th	Night	26% 8% 3 6% 6% 3 4 4 5% 7% 27%	1368
	11th to 20th	Night	20% 7% 2 6% 5% 4 5% 4 5% 6% 36%	1260
	21st to end	Night	22% 9% 5% 5% 5% 3 5% 4 5% 6% 30%	1260
July	1st to 10th	Night	16% 7% 3 7% 5% 4 5% 5% 5% 8% 36%	1260
	11th to 20th	Night	13% 8% 3 7% 5% 4 7% 7% 7% 8% 33%	1332
	21st to end	Night	15% 8% 3 7% 6% 3 5% 6% 6% 8% 31%	1573
August	1st to 10th	Night	15% 6% 2 5% 6% 4 5% 5% 6% 8% 37%	1603
	11th to 20th	Night	15% 7% 3 8% 6% 3 5% 5% 5% 8% 34%	1596
	21st to end	Night	15% 5% 3 5% 5% 3 5% 5% 5% 10% 40%	1862
September	1st to 10th	Night	16% 6% 3 6% 4 3 4 4 5% 8% 41%	1800
	11th to 20th	Night	17% 8% 3 6% 5% 2 4 3 4 6% 42%	1849
	21st to end	Night	17% 6% 3 5% 4 3 4 4 4 6% 44%	2047
October	1st to 10th	Night	19% 7% 2 6% 5% 4 4 4 5% 7% 38%	2160
	11th to 20th	Night	20% 8% 3 7% 5% 3 4 4 6% 7% 33%	2160
	21st to end	Night	25% 12% 4 6% 6% 3 4 4 4 5% 27%	2406
November	1st to 10th	Night	21% 14% 3 6% 5% 3 4 4 4 6% 28%	2587
	11th to 20th	Night	20% 13% 4 8% 6% 3 5% 5% 5% 7% 24%	2660
	21st to end	Night	23% 14% 5% 8% 6% 3 5% 5% 4 6% 19%	2660
December	1st to 10th	Night	23% 14% 6% 10% 8% 4 5% 5% 4 5% 16%	2660
	11th to 20th	Night	20% 19% 6% 11% 7% 3 4 3 4 4 17%	3293
	21st to end	Night	24% 14% 6% 12% 6% 3 4 4 4 4 20%	5208

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	67% 6% 9% 10% 7%	1328
	11th to 20th	Day	67% 6% 6% 13% 7% 1	1478
	21st to end	Day	52% 6% 10% 18% 14% 1	1852
February	1st to 10th	Day	55% 3 12% 17% 12% 1	1620
	11th to 20th	Day	59% 5% 8% 19% 8% 1	1581
	21st to end	Day	49% 5% 12% 19% 13% 2	1344
March	1st to 10th	Day	55% 4 9% 22% 9% 1	1944
	11th to 20th	Day	56% 6% 9% 18% 10% 2	1980
	21st to end	Day	57% 5% 9% 17% 9% 2	2186
April	1st to 10th	Day	55% 4 9% 18% 12% 3	2160
	11th to 20th	Day	49% 5% 9% 22% 13% 1	2222
	21st to end	Day	55% 5% 12% 16% 11% 2	2340
May	1st to 10th	Day	57% 5% 9% 17% 10% 2	2453
	11th to 20th	Day	50% 5% 9% 24% 11% 1	2482
	21st to end	Day	48% 7% 14% 22% 8% 1	2724
June	1st to 10th	Day	56% 6% 11% 20% 6%	2605
	11th to 20th	Day	49% 5% 12% 24% 9% 1	2700
	21st to end	Day	52% 6% 13% 18% 9% 1	2700
July	1st to 10th	Day	40% 7% 19% 25% 9%	2625
	11th to 20th	Day	41% 7% 18% 25% 9% 1	2525
	21st to end	Day	46% 7% 17% 22% 7%	2592
August	1st to 10th	Day	40% 7% 17% 29% 7%	2318
	11th to 20th	Day	44% 8% 18% 25% 5%	2304
	21st to end	Day	38% 7% 16% 28% 11%	2494
September	1st to 10th	Day	38% 7% 16% 26% 13%	2160
	11th to 20th	Day	46% 5% 12% 24% 13% 1	2109
	21st to end	Day	43% 4 11% 27% 14% 1	1913
October	1st to 10th	Day	47% 5% 13% 25% 10% 1	1800
	11th to 20th	Day	56% 6% 13% 19% 5% 1	1800
	21st to end	Day	59% 6% 11% 18% 7%	1949
November	1st to 10th	Day	59% 5% 11% 17% 8%	1490
	11th to 20th	Day	64% 7% 12% 11% 6%	1520
	21st to end	Day	67% 7% 13% 10% 3	1520
December	1st to 10th	Day	70% 6% 10% 10% 3	1520
	11th to 20th	Day	74% 4 6% 11% 5% 1	1905
	21st to end	Day	71% 5% 11% 9% 4 1	2449
January	1st to 10th	Night	63% 5% 10% 15% 6% 1	2838
	11th to 20th	Night	62% 6% 12% 13% 7% 1	2698
	21st to end	Night	53% 6% 10% 21% 10% 1	2730
February	1st to 10th	Night	56% 4 11% 15% 12% 2	2340
	11th to 20th	Night	62% 3 8% 16% 9% 2	2276
	21st to end	Night	54% 5% 9% 18% 12% 3	1911
March	1st to 10th	Night	58% 4 9% 19% 10% 2	2014
	11th to 20th	Night	58% 4 7% 19% 10% 2	1980
	21st to end	Night	58% 4 7% 17% 12% 2	2170
April	1st to 10th	Night	60% 6% 9% 13% 10% 2	1800
	11th to 20th	Night	53% 4 9% 20% 12% 2	1684
	21st to end	Night	60% 3 9% 14% 13% 1	1620
May	1st to 10th	Night	54% 4 9% 20% 10% 2	1505
	11th to 20th	Night	50% 4 10% 22% 12% 1	1417
	21st to end	Night	46% 6% 16% 23% 9% 1	1551
June	1st to 10th	Night	57% 5% 13% 17% 8%	1368
	11th to 20th	Night	48% 5% 11% 24% 11% 1	1260
	21st to end	Night	56% 5% 13% 15% 10% 1	1260
July	1st to 10th	Night	44% 7% 15% 27% 7%	1225
	11th to 20th	Night	46% 8% 16% 21% 9%	1290
	21st to end	Night	50% 7% 17% 19% 7%	1486
August	1st to 10th	Night	43% 8% 15% 27% 7%	1592
	11th to 20th	Night	47% 7% 19% 21% 6%	1596
	21st to end	Night	40% 6% 18% 26% 9%	1862
September	1st to 10th	Night	40% 6% 14% 29% 11%	1800
	11th to 20th	Night	44% 5% 11% 27% 12% 1	1849
	21st to end	Night	41% 5% 11% 28% 13% 1	2047
October	1st to 10th	Night	46% 5% 13% 25% 12%	2160
	11th to 20th	Night	50% 5% 14% 25% 6%	2160
	21st to end	Night	60% 5% 9% 17% 9%	2406
November	1st to 10th	Night	57% 4 12% 18% 7% 1	2587
	11th to 20th	Night	60% 6% 13% 14% 6%	2660
	21st to end	Night	64% 7% 13% 12% 5%	2660
December	1st to 10th	Night	69% 6% 9% 11% 4	2660
	11th to 20th	Night	70% 5% 7% 13% 4	3295
	21st to end	Night	68% 4 12% 11% 4	5208

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	28% 21% 29% 17% 4 1	180
	11th to 20th	Day	28% 17% 34% 14% 7%	328
	21st to end	Day	17% 15% 36% 27% 4	404
February	1st to 10th	Day	27% 14% 38% 18% 4 1	340
	11th to 20th	Day	26% 18% 33% 20% 4	336
	21st to end	Day	17% 16% 34% 24% 8% 1	280
March	1st to 10th	Day	23% 12% 36% 22% 5% 1	404
	11th to 20th	Day	18% 17% 33% 23% 7% 1	420
	21st to end	Day	27% 13% 31% 20% 7% 2	462
April	1st to 10th	Day	27% 14% 36% 16% 6%	420
	11th to 20th	Day	24% 17% 31% 17% 9% 1	412
	21st to end	Day	26% 13% 28% 20% 12%	420
May	1st to 10th	Day	30% 12% 28% 21% 7% 2	536
	11th to 20th	Day	26% 10% 27% 22% 12% 2	624
	21st to end	Day	25% 11% 33% 24% 7% 1	680
June	1st to 10th	Day	31% 8% 27% 23% 10% 2	630
	11th to 20th	Day	24% 8% 30% 26% 11% 2	630
	21st to end	Day	25% 6% 23% 31% 12% 2	630
July	1st to 10th	Day	18% 5% 34% 27% 14% 2	620
	11th to 20th	Day	17% 5% 30% 31% 15% 3	618
	21st to end	Day	20% 6% 25% 35% 13% 2	685
August	1st to 10th	Day	14% 5% 26% 36% 15% 3	451
	11th to 20th	Day	18% 5% 25% 29% 19% 4	439
	21st to end	Day	15% 8% 27% 29% 15% 5%	495
September	1st to 10th	Day	15% 5% 34% 29% 13% 4	450
	11th to 20th	Day	25% 11% 26% 24% 12% 2	450
	21st to end	Day	21% 9% 32% 24% 10% 4	417
October	1st to 10th	Day	20% 12% 26% 24% 15% 3	360
	11th to 20th	Day	22% 16% 29% 22% 9% 3	360
	21st to end	Day	25% 19% 28% 20% 8% 1	396
November	1st to 10th	Day	23% 19% 34% 18% 6% 1	365
	11th to 20th	Day	29% 18% 29% 16% 7% 1	370
	21st to end	Day	29% 19% 32% 16% 3 1	370
December	1st to 10th	Day	34% 17% 30% 15% 4	370
	11th to 20th	Day	30% 22% 32% 15% 1	370
	21st to end	Day	22% 21% 34% 20% 2	203
January	1st to 10th	Night	25% 17% 32% 21% 5%	850
	11th to 20th	Night	24% 17% 32% 22% 4 1	850
	21st to end	Night	19% 16% 34% 23% 7% 1	844
February	1st to 10th	Night	25% 15% 34% 20% 5% 1	720
	11th to 20th	Night	27% 14% 35% 20% 3 1	703
	21st to end	Night	21% 10% 36% 24% 7% 1	592
March	1st to 10th	Night	24% 10% 36% 25% 4	720
	11th to 20th	Night	23% 13% 29% 25% 9% 1	720
	21st to end	Night	27% 13% 27% 23% 8% 1	784
April	1st to 10th	Night	29% 13% 30% 22% 6%	540
	11th to 20th	Night	27% 11% 29% 25% 8%	534
	21st to end	Night	26% 11% 32% 22% 9%	540
May	1st to 10th	Night	29% 7% 30% 24% 9% 1	540
	11th to 20th	Night	25% 8% 31% 26% 10% 2	532
	21st to end	Night	19% 11% 38% 27% 4	583
June	1st to 10th	Night	29% 6% 29% 29% 6% 1	468
	11th to 20th	Night	23% 6% 29% 33% 8% 1	360
	21st to end	Night	25% 5% 29% 32% 8% 1	360
July	1st to 10th	Night	21% 5% 35% 27% 12%	350
	11th to 20th	Night	15% 8% 31% 38% 8% 1	420
	21st to end	Night	18% 5% 31% 35% 11% 1	590
August	1st to 10th	Night	17% 3 30% 35% 14% 1	538
	11th to 20th	Night	15% 7% 26% 36% 15% 1	532
	21st to end	Night	15% 6% 27% 35% 15% 2	594
September	1st to 10th	Night	19% 7% 35% 30% 9% 1	540
	11th to 20th	Night	20% 9% 23% 35% 12% 1	589
	21st to end	Night	21% 11% 32% 26% 10% 1	720
October	1st to 10th	Night	23% 8% 29% 27% 11% 1	720
	11th to 20th	Night	23% 12% 31% 24% 9% 1	720
	21st to end	Night	32% 16% 27% 19% 5%	807
November	1st to 10th	Night	28% 17% 27% 21% 5% 1	830
	11th to 20th	Night	30% 18% 26% 18% 6% 2	850
	21st to end	Night	31% 19% 26% 20% 4	850
December	1st to 10th	Night	31% 17% 30% 18% 3	850
	11th to 20th	Night	27% 23% 31% 15% 3 1	850
	21st to end	Night	31% 19% 26% 19% 4 1	935

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