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 2025-02-21.

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	16% 11% 4 9% 5% 5% 5% 4 5% 7% 31%	108781
	Night	17% 13% 4 9% 5% 4 4 3 5% 6% 28%	109894
Transparency	Day	53% 6% 12% 20% 9% 1	112373
	Night	55% 5% 12% 18% 8% 1	114468
Seeing	Day	23% 12% 30% 24% 9% 2	17360
	Night	25% 13% 30% 25% 7% 1	24945

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% 23% 7% 16% 9% 5% 4 3 3 3 12%	3157
	11th to 20th	Day	11% 16% 9% 13% 7% 5% 5% 3 4 5% 22%	3495
	21st to end	Day	8% 9% 4 11% 5% 5% 6% 4 6% 7% 35%	4421
February	1st to 10th	Day	15% 14% 4 8% 5% 5% 4 4 5% 6% 31%	1800
	11th to 20th	Day	15% 14% 4 10% 5% 6% 4 3 6% 5% 28%	1753
	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	17% 8% 3 6% 4 4 3 3 5% 5% 41%	2226
	21st to end	Day	18% 7% 3 6% 4 4 4 2 5% 7% 40%	2019
October	1st to 10th	Day	19% 7% 3 7% 5% 4 5% 4 6% 7% 35%	1900
	11th to 20th	Day	19% 11% 3 10% 4 5% 5% 3 5% 7% 27%	1900
	21st to end	Day	19% 13% 4 9% 5% 5% 5% 3 5% 7% 25%	2057
November	1st to 10th	Day	18% 16% 4 8% 6% 6% 5% 3 4 6% 26%	1570
	11th to 20th	Day	20% 17% 5% 9% 5% 5% 5% 3 6% 6% 19%	1600
	21st to end	Day	19% 16% 6% 13% 7% 4 4 5% 5% 6% 16%	1600
December	1st to 10th	Day	18% 13% 6% 18% 7% 5% 4 3 3 5% 19%	2610
	11th to 20th	Day	17% 15% 6% 13% 7% 6% 4 3 3 3 23%	2996
	21st to end	Day	15% 13% 8% 17% 7% 6% 5% 3 4 4 17%	3494
January	1st to 10th	Night	15% 20% 5% 13% 6% 5% 5% 3 5% 5% 19%	6808
	11th to 20th	Night	13% 17% 7% 13% 6% 4 4 3 4 5% 23%	6392
	21st to end	Night	8% 13% 5% 11% 6% 5% 4 3 5% 6% 33%	6536
February	1st to 10th	Night	16% 14% 4 9% 5% 4 4 4 5% 5% 29%	2600
	11th to 20th	Night	17% 17% 4 9% 6% 4 4 3 5% 5% 25%	2533
	21st to end	Night	12% 14% 4 9% 6% 4 4 4 5% 6% 32%	2028
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	16% 8% 3 6% 4 3 4 3 4 6% 42%	1952
	21st to end	Night	17% 6% 3 6% 4 4 4 3 5% 6% 43%	2161
October	1st to 10th	Night	19% 7% 2 7% 4 5% 3 3 5% 6% 37%	2280
	11th to 20th	Night	19% 8% 3 8% 4 4 5% 3 6% 6% 34%	2280
	21st to end	Night	24% 13% 3 7% 5% 3 4 3 4 5% 28%	2540
November	1st to 10th	Night	21% 14% 2 7% 5% 5% 4 4 5% 6% 28%	2727
	11th to 20th	Night	21% 15% 3 8% 5% 4 5% 3 5% 7% 23%	2800
	21st to end	Night	24% 16% 5% 9% 5% 4 4 4 5% 6% 19%	2800
December	1st to 10th	Night	15% 12% 5% 12% 7% 6% 5% 3 5% 6% 24%	4580
	11th to 20th	Night	18% 16% 5% 10% 5% 4 4 3 5% 5% 25%	5213
	21st to end	Night	21% 14% 6% 14% 5% 4 4 4 4 5% 18%	7474

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% 6% 8% 7% 3	3158
	11th to 20th	Day	64% 7% 6% 13% 8% 1	3524
	21st to end	Day	48% 4 12% 22% 14% 1	4421
February	1st to 10th	Day	55% 4 11% 17% 13% 1	1800
	11th to 20th	Day	58% 5% 8% 19% 9% 1	1761
	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	44% 5% 13% 25% 12% 1	2226
	21st to end	Day	44% 5% 11% 26% 13% 1	2019
October	1st to 10th	Day	47% 5% 13% 26% 8%	3160
	11th to 20th	Day	55% 5% 10% 24% 7%	3140
	21st to end	Day	50% 5% 17% 19% 9%	3373
November	1st to 10th	Day	59% 5% 11% 17% 7%	1570
	11th to 20th	Day	65% 6% 11% 11% 6%	1600
	21st to end	Day	68% 6% 13% 10% 3	1600
December	1st to 10th	Day	69% 5% 9% 15% 2	2610
	11th to 20th	Day	67% 4 9% 12% 8% 1	2995
	21st to end	Day	69% 5% 9% 13% 3	3494
January	1st to 10th	Night	66% 6% 11% 14% 2	6808
	11th to 20th	Night	63% 6% 9% 15% 7%	6438
	21st to end	Night	51% 5% 10% 20% 13% 2	6536
February	1st to 10th	Night	56% 4 10% 15% 13% 2	2600
	11th to 20th	Night	61% 3 8% 16% 10% 1	2536
	21st to end	Night	53% 5% 9% 19% 12% 3	2028
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	42% 5% 12% 28% 12% 1	1952
	21st to end	Night	41% 6% 11% 29% 12% 1	2161
October	1st to 10th	Night	50% 5% 12% 25% 8%	3800
	11th to 20th	Night	46% 4 13% 28% 9%	3779
	21st to end	Night	50% 4 14% 21% 10%	4176
November	1st to 10th	Night	57% 5% 12% 18% 7% 1	2727
	11th to 20th	Night	61% 6% 12% 14% 6%	2800
	21st to end	Night	65% 6% 12% 12% 5%	2800
December	1st to 10th	Night	60% 6% 11% 18% 4	4580
	11th to 20th	Night	60% 5% 9% 18% 7% 1	5215
	21st to end	Night	67% 5% 11% 13% 5%	7474

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	31% 20% 29% 16% 4 1	200
	11th to 20th	Day	27% 16% 33% 15% 9% 1	356
	21st to end	Day	16% 15% 38% 26% 4	440
February	1st to 10th	Day	26% 13% 36% 18% 5% 2	400
	11th to 20th	Day	25% 18% 34% 19% 4	396
	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	23% 10% 25% 25% 13% 3	490
	21st to end	Day	21% 9% 31% 24% 11% 4	453
October	1st to 10th	Day	20% 12% 26% 25% 15% 3	390
	11th to 20th	Day	22% 17% 28% 22% 8% 2	390
	21st to end	Day	24% 18% 29% 20% 8% 1	429
November	1st to 10th	Day	23% 19% 34% 17% 5% 1	395
	11th to 20th	Day	32% 18% 27% 16% 7% 1	400
	21st to end	Day	31% 18% 31% 16% 3 1	400
December	1st to 10th	Day	32% 17% 32% 15% 4	400
	11th to 20th	Day	30% 22% 32% 15% 2	400
	21st to end	Day	21% 20% 33% 21% 4	225
January	1st to 10th	Night	26% 16% 32% 20% 5%	900
	11th to 20th	Night	24% 17% 31% 22% 5% 1	900
	21st to end	Night	18% 17% 35% 22% 7% 1	890
February	1st to 10th	Night	25% 15% 33% 21% 5% 1	800
	11th to 20th	Night	27% 15% 34% 20% 3 1	783
	21st to end	Night	21% 11% 36% 25% 7% 1	629
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	19% 9% 22% 37% 12% 1	622
	21st to end	Night	20% 11% 30% 26% 12% 1	760
October	1st to 10th	Night	23% 8% 29% 28% 11% 1	760
	11th to 20th	Night	23% 12% 31% 24% 9% 1	760
	21st to end	Night	31% 17% 28% 19% 5%	853
November	1st to 10th	Night	28% 18% 28% 21% 5% 1	880
	11th to 20th	Night	33% 18% 25% 18% 5% 2	900
	21st to end	Night	33% 19% 25% 19% 4	900
December	1st to 10th	Night	30% 17% 30% 19% 4	900
	11th to 20th	Night	27% 24% 30% 16% 3 1	900
	21st to end	Night	31% 18% 26% 20% 4 1	990

Page generated at 2025-02-18 04:26:27. Version ac07

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