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 2024-09-14.

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	17% 11% 4 8% 5% 4 5% 4 5% 7% 31%	101332
	Night	18% 12% 4 9% 5% 4 4 3 5% 6% 29%	96635
Transparency	Day	52% 6% 12% 20% 9% 1	101079
	Night	55% 6% 12% 18% 8% 1	96508
Seeing	Day	23% 12% 30% 24% 9% 2	16891
	Night	24% 13% 30% 25% 7% 1	24227

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% 13% 6% 16% 11% 6% 5% 3 4 4 18%	2207
	11th to 20th	Day	11% 13% 5% 12% 7% 5% 5% 3 4 6% 29%	2462
	21st to end	Day	11% 9% 4 13% 6% 5% 4 3 5% 6% 32%	3092
February	1st to 10th	Day	16% 14% 4 8% 5% 4 4 4 5% 5% 31%	1710
	11th to 20th	Day	15% 14% 4 10% 5% 6% 4 3 6% 5% 27%	1663
	21st to end	Day	10% 12% 5% 8% 6% 5% 5% 4 5% 7% 33%	1426
March	1st to 10th	Day	21% 13% 4 8% 5% 5% 4 3 4 6% 29%	3369
	11th to 20th	Day	12% 17% 6% 13% 8% 5% 4 3 5% 5% 21%	3480
	21st to end	Day	23% 17% 4 7% 5% 4 5% 4 6% 6% 21%	3837
April	1st to 10th	Day	18% 13% 4 7% 5% 4 4 3 5% 6% 30%	2280
	11th to 20th	Day	18% 11% 3 7% 4 4 4 3 5% 7% 34%	2347
	21st to end	Day	19% 12% 3 7% 4 4 4 4 5% 7% 30%	2470
May	1st to 10th	Day	22% 14% 3 5% 4 4 4 3 5% 7% 28%	4316
	11th to 20th	Day	16% 8% 3 7% 5% 5% 5% 3 5% 6% 38%	4398
	21st to end	Day	15% 9% 3 8% 5% 5% 5% 5% 6% 7% 31%	4836
June	1st to 10th	Day	25% 11% 2 6% 5% 4 4 4 5% 8% 26%	2750
	11th to 20th	Day	19% 8% 2 7% 5% 4 4 4 5% 7% 35%	2850
	21st to end	Day	24% 8% 3 7% 4 4 4 3 5% 6% 32%	2850
July	1st to 10th	Day	14% 8% 3 8% 5% 5% 5% 4 7% 8% 33%	4760
	11th to 20th	Day	15% 6% 3 6% 4 4 5% 4 6% 8% 38%	4582
	21st to end	Day	12% 7% 2 7% 4 4 5% 4 6% 9% 40%	4815
August	1st to 10th	Day	15% 9% 4 8% 5% 4 4 4 5% 7% 34%	4110
	11th to 20th	Day	12% 6% 2 7% 5% 5% 5% 4 6% 9% 39%	4045
	21st to end	Day	13% 5% 2 5% 4 4 4 3 6% 9% 45%	4382
September	1st to 10th	Day	16% 6% 2 5% 4 3 4 4 5% 9% 43%	2280
	11th to 20th	Day	18% 8% 3 7% 4 4 3 3 5% 5% 40%	2148
	21st to end	Day	18% 6% 3 6% 4 4 4 2 5% 7% 42%	1913
October	1st to 10th	Day	19% 7% 3 7% 5% 4 5% 4 5% 7% 35%	1800
	11th to 20th	Day	19% 11% 3 10% 4 6% 5% 3 5% 8% 26%	1800
	21st to end	Day	19% 14% 4 9% 5% 5% 5% 3 5% 7% 24%	1949
November	1st to 10th	Day	18% 16% 4 8% 6% 6% 5% 3 4 6% 26%	1490
	11th to 20th	Day	18% 16% 5% 10% 6% 5% 6% 3 6% 6% 19%	1520
	21st to end	Day	18% 16% 6% 13% 7% 5% 4 5% 5% 6% 16%	1520
December	1st to 10th	Day	24% 15% 6% 12% 7% 3 4 4 4 5% 16%	1520
	11th to 20th	Day	16% 19% 7% 14% 8% 5% 5% 3 4 3 15%	1906
	21st to end	Day	17% 14% 8% 16% 7% 6% 3 3 4 4 18%	2449
January	1st to 10th	Night	13% 13% 4 12% 7% 6% 6% 4 6% 6% 23%	4748
	11th to 20th	Night	15% 14% 4 10% 6% 4 5% 4 4 5% 28%	4504
	21st to end	Night	11% 14% 5% 14% 7% 4 4 3 6% 6% 27%	4564
February	1st to 10th	Night	16% 14% 4 10% 4 4 4 4 5% 5% 29%	2470
	11th to 20th	Night	17% 16% 4 9% 7% 4 4 3 5% 5% 25%	2403
	21st to end	Night	12% 14% 4 9% 6% 4 4 4 5% 6% 32%	2027
March	1st to 10th	Night	22% 12% 4 11% 5% 4 4 3 4 4 25%	3456
	11th to 20th	Night	20% 18% 5% 10% 6% 5% 4 3 4 4 20%	3479
	21st to end	Night	26% 13% 5% 10% 5% 4 4 4 5% 3 22%	3795
April	1st to 10th	Night	21% 13% 4 8% 6% 4 4 3 5% 5% 27%	1900
	11th to 20th	Night	20% 11% 3 7% 5% 4 4 3 6% 5% 32%	1778
	21st to end	Night	21% 14% 4 7% 5% 4 3 3 4 5% 29%	1710
May	1st to 10th	Night	26% 14% 3 7% 5% 4 5% 3 5% 5% 24%	2629
	11th to 20th	Night	15% 8% 3 7% 5% 4 4 3 5% 6% 40%	2506
	21st to end	Night	15% 9% 4 8% 6% 5% 5% 4 6% 9% 28%	2749
June	1st to 10th	Night	26% 10% 3 7% 5% 4 4 4 5% 7% 27%	1444
	11th to 20th	Night	19% 7% 2 6% 4 5% 5% 3 5% 7% 36%	1330
	21st to end	Night	22% 11% 5% 6% 5% 4 5% 3 5% 6% 29%	1330
July	1st to 10th	Night	13% 8% 3 9% 5% 7% 5% 5% 7% 6% 32%	2210
	11th to 20th	Night	12% 8% 3 8% 5% 5% 7% 6% 8% 8% 31%	2352
	21st to end	Night	12% 7% 3 6% 5% 3 4 4 6% 7% 43%	2750
August	1st to 10th	Night	17% 8% 3 9% 6% 6% 6% 4 6% 7% 28%	2816
	11th to 20th	Night	10% 6% 3 9% 6% 5% 5% 4 6% 8% 39%	2782
	21st to end	Night	12% 6% 2 6% 4 5% 4 4 5% 8% 43%	3274
September	1st to 10th	Night	15% 7% 2 7% 3 4 4 3 5% 8% 42%	1900
	11th to 20th	Night	17% 8% 3 7% 4 3 4 3 4 6% 42%	1888
	21st to end	Night	17% 6% 3 6% 4 4 4 3 4 6% 44%	2047
October	1st to 10th	Night	19% 7% 2 7% 4 5% 3 3 5% 7% 38%	2160
	11th to 20th	Night	20% 8% 2 8% 4 4 5% 3 6% 6% 33%	2160
	21st to end	Night	25% 13% 3 7% 5% 3 4 3 4 5% 27%	2406
November	1st to 10th	Night	21% 14% 2 7% 4 4 4 4 5% 6% 28%	2587
	11th to 20th	Night	20% 15% 3 8% 5% 4 5% 4 5% 7% 24%	2660
	21st to end	Night	23% 16% 5% 9% 5% 5% 4 4 5% 6% 19%	2660
December	1st to 10th	Night	23% 15% 5% 11% 7% 5% 5% 3 4 5% 16%	2660
	11th to 20th	Night	19% 20% 6% 13% 6% 5% 4 3 4 4 17%	3293
	21st to end	Night	24% 15% 6% 13% 5% 3 3 3 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	68% 7% 10% 10% 5%	2208
	11th to 20th	Day	56% 7% 6% 19% 12% 1	2462
	21st to end	Day	52% 6% 14% 16% 12% 1	3092
February	1st to 10th	Day	55% 4 11% 17% 12% 1	1710
	11th to 20th	Day	58% 5% 8% 19% 9% 1	1671
	21st to end	Day	49% 5% 12% 19% 13% 2	1426
March	1st to 10th	Day	58% 4 9% 22% 6% 1	3373
	11th to 20th	Day	65% 5% 8% 14% 7% 1	3480
	21st to end	Day	62% 6% 7% 15% 8% 2	3837
April	1st to 10th	Day	55% 4 9% 18% 12% 3	2280
	11th to 20th	Day	50% 5% 10% 22% 12% 1	2347
	21st to end	Day	53% 5% 11% 16% 12% 3	2470
May	1st to 10th	Day	56% 6% 12% 19% 7% 1	4331
	11th to 20th	Day	46% 7% 14% 26% 7%	4402
	21st to end	Day	49% 9% 13% 20% 8%	4836
June	1st to 10th	Day	56% 6% 11% 20% 6%	2750
	11th to 20th	Day	48% 5% 13% 23% 9% 1	2850
	21st to end	Day	53% 6% 13% 18% 9% 1	2850
July	1st to 10th	Day	46% 6% 18% 19% 11% 1	4685
	11th to 20th	Day	44% 6% 16% 26% 7%	4501
	21st to end	Day	40% 8% 20% 25% 7%	4662
August	1st to 10th	Day	49% 7% 13% 25% 5%	4096
	11th to 20th	Day	41% 7% 15% 25% 12% 1	4084
	21st to end	Day	35% 5% 16% 29% 14%	4382
September	1st to 10th	Day	38% 7% 15% 26% 13%	2280
	11th to 20th	Day	45% 6% 12% 24% 12% 1	2148
	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	57% 8% 14% 17% 4 1	4748
	11th to 20th	Night	56% 7% 9% 19% 9%	4504
	21st to end	Night	55% 7% 10% 19% 8% 1	4564
February	1st to 10th	Night	57% 4 10% 15% 12% 2	2470
	11th to 20th	Night	61% 3 8% 16% 10% 2	2406
	21st to end	Night	53% 5% 9% 19% 12% 3	2027
March	1st to 10th	Night	63% 4 7% 16% 8% 2	3465
	11th to 20th	Night	67% 5% 7% 13% 6% 1	3480
	21st to end	Night	65% 5% 5% 15% 9% 1	3795
April	1st to 10th	Night	59% 6% 9% 13% 11% 2	1900
	11th to 20th	Night	53% 4 9% 21% 11% 2	1778
	21st to end	Night	58% 3 9% 14% 14% 2	1710
May	1st to 10th	Night	60% 5% 10% 16% 7% 1	2634
	11th to 20th	Night	43% 6% 16% 25% 9% 1	2507
	21st to end	Night	51% 8% 17% 17% 7%	2750
June	1st to 10th	Night	57% 5% 13% 16% 8%	1444
	11th to 20th	Night	47% 5% 12% 24% 10% 1	1330
	21st to end	Night	57% 5% 13% 15% 9% 1	1330
July	1st to 10th	Night	50% 7% 13% 20% 10%	2175
	11th to 20th	Night	46% 8% 19% 20% 6%	2310
	21st to end	Night	39% 8% 21% 22% 11%	2663
August	1st to 10th	Night	54% 7% 13% 20% 5%	2805
	11th to 20th	Night	41% 7% 18% 22% 11% 1	2809
	21st to end	Night	38% 5% 18% 25% 14%	3273
September	1st to 10th	Night	39% 6% 13% 30% 12%	1900
	11th to 20th	Night	43% 5% 11% 27% 12% 1	1888
	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% 5%	407
February	1st to 10th	Day	28% 13% 35% 18% 5% 2	370
	11th to 20th	Day	24% 18% 34% 20% 4	366
	21st to end	Day	18% 16% 33% 25% 7% 1	307
March	1st to 10th	Day	24% 13% 36% 21% 5% 1	442
	11th to 20th	Day	18% 17% 33% 24% 8% 1	460
	21st to end	Day	29% 13% 31% 19% 6% 2	506
April	1st to 10th	Day	27% 14% 35% 17% 6%	460
	11th to 20th	Day	23% 17% 32% 17% 9% 1	452
	21st to end	Day	25% 15% 28% 20% 12%	460
May	1st to 10th	Day	30% 11% 30% 21% 7% 2	583
	11th to 20th	Day	24% 10% 27% 23% 13% 2	674
	21st to end	Day	24% 11% 33% 25% 7% 1	735
June	1st to 10th	Day	30% 8% 27% 24% 10% 1	680
	11th to 20th	Day	23% 8% 31% 27% 10% 1	680
	21st to end	Day	26% 6% 24% 30% 11% 2	680
July	1st to 10th	Day	18% 4 34% 28% 14% 2	670
	11th to 20th	Day	17% 5% 30% 30% 15% 2	668
	21st to end	Day	19% 6% 25% 35% 13% 2	740
August	1st to 10th	Day	15% 5% 27% 35% 14% 3	491
	11th to 20th	Day	17% 5% 26% 28% 20% 5%	479
	21st to end	Day	15% 7% 27% 29% 14% 6%	539
September	1st to 10th	Day	16% 5% 34% 29% 12% 3	490
	11th to 20th	Day	24% 11% 25% 24% 14% 2	463
	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	845
February	1st to 10th	Night	26% 15% 33% 20% 5% 1	760
	11th to 20th	Night	26% 15% 35% 20% 3 1	743
	21st to end	Night	21% 11% 36% 25% 7% 1	628
March	1st to 10th	Night	24% 11% 37% 24% 4	760
	11th to 20th	Night	23% 14% 29% 24% 8% 1	760
	21st to end	Night	28% 14% 27% 22% 8% 1	827
April	1st to 10th	Night	29% 14% 29% 23% 5%	570
	11th to 20th	Night	26% 11% 30% 25% 8%	564
	21st to end	Night	26% 11% 32% 22% 9%	570
May	1st to 10th	Night	30% 7% 30% 24% 9% 1	570
	11th to 20th	Night	24% 7% 30% 27% 11% 1	562
	21st to end	Night	18% 11% 39% 27% 4	616
June	1st to 10th	Night	29% 6% 28% 30% 6% 1	494
	11th to 20th	Night	22% 5% 30% 33% 9% 1	380
	21st to end	Night	25% 5% 29% 32% 8% 1	380
July	1st to 10th	Night	20% 5% 35% 27% 12%	370
	11th to 20th	Night	14% 7% 32% 38% 8% 1	445
	21st to end	Night	17% 5% 31% 35% 11% 1	623
August	1st to 10th	Night	16% 4 30% 36% 14% 1	568
	11th to 20th	Night	15% 7% 27% 36% 15% 1	562
	21st to end	Night	15% 6% 27% 34% 15% 2	627
September	1st to 10th	Night	19% 7% 35% 30% 8% 1	570
	11th to 20th	Night	20% 9% 23% 35% 12%	601
	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

Page generated at 2024-09-11 11:00:02. Version ac07

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