YCAS Stewartstown Observing Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the YCAS Stewartstown Observing Site clear sky chart from 2005-11-06 to 2025-03-12.

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% 6% 2 6% 4 4 4 4 6% 7% 40%	108856
	Night	15% 7% 2 6% 4 4 4 3 5% 7% 43%	110156
Transparency	Day	24% 43% 7% 15% 10% 2	112491
	Night	24% 42% 6% 15% 11% 2	114661
Seeing	Day	20% 12% 27% 23% 13% 5%	15294
	Night	18% 10% 30% 29% 11% 1	24841

By Month

Percentage Cloud Cover SE (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% 6% 2 4 3 4 4 3 6% 7% 47%	3597
	11th to 20th	Day	13% 8% 3 9% 5% 4 4 3 5% 5% 41%	3950
	21st to end	Day	15% 8% 2 7% 4 5% 4 3 5% 6% 40%	4466
February	1st to 10th	Day	14% 9% 3 6% 5% 4 4 4 7% 7% 37%	1800
	11th to 20th	Day	16% 9% 2 6% 5% 4 4 4 6% 6% 39%	1828
	21st to end	Day	18% 10% 2 7% 4 4 4 3 5% 5% 39%	1650
March	1st to 10th	Day	22% 7% 2 5% 4 5% 4 3 5% 6% 38%	3402
	11th to 20th	Day	9% 6% 2 6% 5% 5% 5% 4 6% 7% 45%	3491
	21st to end	Day	20% 8% 2 5% 4 4 3 3 4 5% 42%	3933
April	1st to 10th	Day	14% 9% 2 6% 4 5% 5% 5% 6% 7% 38%	2280
	11th to 20th	Day	14% 5% 2 6% 4 4 5% 4 6% 7% 44%	2254
	21st to end	Day	18% 6% 2 6% 4 4 4 3 5% 7% 40%	2280
May	1st to 10th	Day	29% 6% 2 5% 4 3 4 3 6% 7% 29%	4009
	11th to 20th	Day	24% 8% 3 7% 4 4 4 4 5% 8% 28%	4398
	21st to end	Day	12% 5% 2 6% 4 4 5% 4 7% 9% 44%	4823
June	1st to 10th	Day	12% 6% 2 6% 4 5% 5% 5% 7% 9% 38%	2660
	11th to 20th	Day	12% 6% 3 6% 5% 5% 5% 4 7% 9% 39%	2660
	21st to end	Day	10% 3 2 6% 5% 5% 5% 4 7% 10% 43%	2660
July	1st to 10th	Day	6% 4 2 6% 6% 6% 6% 5% 8% 11% 39%	4440
	11th to 20th	Day	9% 5% 2 6% 5% 5% 6% 5% 8% 10% 38%	4440
	21st to end	Day	11% 7% 3 8% 6% 5% 5% 5% 7% 8% 35%	4509
August	1st to 10th	Day	18% 5% 2 7% 5% 5% 5% 5% 6% 8% 33%	4104
	11th to 20th	Day	11% 5% 2 6% 4 5% 5% 5% 7% 8% 40%	3853
	21st to end	Day	12% 5% 2 5% 4 4 4 4 6% 7% 47%	4180
September	1st to 10th	Day	15% 7% 2 5% 4 4 4 3 4 6% 46%	2280
	11th to 20th	Day	12% 5% 2 5% 4 4 4 3 5% 8% 48%	2280
	21st to end	Day	21% 7% 2 6% 4 4 4 4 5% 6% 38%	2018
October	1st to 10th	Day	18% 6% 2 5% 4 3 4 3 5% 7% 45%	1900
	11th to 20th	Day	16% 6% 2 5% 3 3 4 3 5% 6% 48%	1900
	21st to end	Day	15% 6% 2 6% 3 3 4 3 6% 6% 46%	2090
November	1st to 10th	Day	12% 6% 2 5% 3 3 3 2 5% 8% 51%	1786
	11th to 20th	Day	16% 5% 2 4 3 3 4 4 5% 6% 48%	1785
	21st to end	Day	14% 7% 2 4 5% 4 4 3 5% 6% 45%	1600
December	1st to 10th	Day	12% 6% 2 6% 5% 4 5% 4 6% 7% 43%	2600
	11th to 20th	Day	18% 10% 2 5% 3 3 4 4 5% 6% 39%	2990
	21st to end	Day	16% 8% 3 7% 4 4 5% 4 6% 7% 36%	3960
January	1st to 10th	Night	11% 7% 2 6% 4 4 4 3 5% 8% 46%	6349
	11th to 20th	Night	13% 7% 3 6% 4 3 3 3 4 6% 49%	5992
	21st to end	Night	15% 8% 2 6% 3 3 3 3 5% 6% 45%	6490
February	1st to 10th	Night	16% 9% 2 7% 4 4 3 4 5% 6% 40%	2600
	11th to 20th	Night	18% 8% 3 6% 4 3 4 3 5% 6% 41%	2456
	21st to end	Night	16% 7% 2 7% 5% 4 4 3 5% 5% 40%	1980
March	1st to 10th	Night	20% 9% 3 6% 4 3 3 3 4 5% 40%	3668
	11th to 20th	Night	10% 5% 2 5% 4 4 4 4 5% 6% 51%	3498
	21st to end	Night	14% 10% 3 6% 4 3 3 2 4 5% 47%	3698
April	1st to 10th	Night	15% 8% 2 7% 5% 4 4 3 6% 7% 38%	1900
	11th to 20th	Night	14% 6% 2 6% 4 4 4 3 6% 8% 43%	1875
	21st to end	Night	18% 8% 2 5% 3 3 4 4 5% 6% 43%	1900
May	1st to 10th	Night	24% 8% 3 6% 5% 4 4 3 5% 7% 31%	2911
	11th to 20th	Night	24% 10% 4 8% 4 3 4 3 5% 6% 29%	2495
	21st to end	Night	12% 5% 2 5% 4 4 5% 4 7% 10% 42%	2732
June	1st to 10th	Night	13% 4 2 6% 3 4 4 4 7% 8% 46%	1520
	11th to 20th	Night	11% 6% 2 6% 4 5% 5% 5% 7% 9% 41%	1520
	21st to end	Night	9% 5% 3 4 4 5% 5% 5% 7% 10% 43%	1520
July	1st to 10th	Night	6% 5% 2 8% 6% 6% 5% 5% 7% 10% 40%	2520
	11th to 20th	Night	8% 6% 2 8% 5% 5% 5% 5% 8% 9% 39%	2520
	21st to end	Night	13% 7% 3 6% 5% 4 4 4 6% 8% 40%	3042
August	1st to 10th	Night	20% 5% 2 6% 4 4 5% 4 7% 9% 35%	2825
	11th to 20th	Night	11% 7% 3 7% 5% 5% 6% 4 5% 8% 40%	2944
	21st to end	Night	12% 5% 2 5% 3 3 4 4 5% 8% 47%	3476
September	1st to 10th	Night	13% 6% 2 7% 4 3 3 3 6% 7% 47%	1900
	11th to 20th	Night	11% 6% 2 5% 2 3 4 3 4 7% 53%	1900
	21st to end	Night	19% 8% 2 6% 4 4 3 4 4 5% 41%	2157
October	1st to 10th	Night	19% 7% 2 6% 3 3 3 3 5% 5% 44%	2280
	11th to 20th	Night	14% 5% 2 4 3 3 3 3 5% 6% 51%	2280
	21st to end	Night	16% 5% 2 4 3 3 4 3 5% 6% 49%	2508
November	1st to 10th	Night	10% 6% 2 4 4 3 4 3 5% 6% 53%	2509
	11th to 20th	Night	15% 8% 2 5% 4 3 3 3 4 6% 46%	2610
	21st to end	Night	13% 5% 2 5% 5% 4 4 3 6% 7% 46%	2800
December	1st to 10th	Night	10% 7% 2 6% 4 4 4 3 6% 7% 46%	4580
	11th to 20th	Night	21% 7% 2 5% 4 4 4 3 5% 6% 39%	5205
	21st to end	Night	16% 8% 3 7% 5% 5% 5% 4 6% 7% 35%	6996

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	25% 28% 6% 20% 18% 3	3598
	11th to 20th	Day	35% 26% 3 16% 14% 5%	3950
	21st to end	Day	33% 29% 8% 18% 11% 1	4466
February	1st to 10th	Day	18% 62% 7% 9% 3 1	1800
	11th to 20th	Day	18% 61% 3 9% 7% 1	1837
	21st to end	Day	17% 62% 4 10% 6% 1	1650
March	1st to 10th	Day	33% 41% 4 15% 6% 3	3402
	11th to 20th	Day	20% 41% 4 21% 12% 2	3491
	21st to end	Day	27% 40% 6% 13% 12% 2	3933
April	1st to 10th	Day	17% 65% 3 7% 7% 1	2280
	11th to 20th	Day	14% 66% 5% 9% 5% 1	2254
	21st to end	Day	16% 65% 3 8% 7% 1	2280
May	1st to 10th	Day	37% 40% 6% 12% 4	4045
	11th to 20th	Day	35% 41% 10% 11% 2	4402
	21st to end	Day	20% 41% 9% 16% 12% 1	4837
June	1st to 10th	Day	16% 65% 3 9% 6%	2660
	11th to 20th	Day	14% 66% 3 10% 6% 1	2660
	21st to end	Day	13% 64% 5% 11% 7% 1	2660
July	1st to 10th	Day	25% 39% 12% 14% 7% 3	4370
	11th to 20th	Day	27% 38% 11% 17% 7%	4365
	21st to end	Day	31% 36% 7% 13% 12% 1	4365
August	1st to 10th	Day	33% 38% 8% 17% 4	4091
	11th to 20th	Day	24% 38% 7% 22% 9%	3892
	21st to end	Day	20% 37% 7% 21% 15% 1	4180
September	1st to 10th	Day	16% 60% 5% 10% 8% 1	2280
	11th to 20th	Day	15% 60% 3 11% 8% 2	2280
	21st to end	Day	22% 59% 4 9% 6%	2018
October	1st to 10th	Day	24% 36% 3 11% 22% 4	3160
	11th to 20th	Day	12% 37% 6% 20% 16% 9%	3140
	21st to end	Day	10% 36% 7% 21% 22% 3	3428
November	1st to 10th	Day	17% 56% 6% 9% 9% 3	1786
	11th to 20th	Day	13% 57% 3 14% 12% 1	1785
	21st to end	Day	16% 57% 5% 16% 5% 2	1600
December	1st to 10th	Day	26% 36% 11% 18% 7% 2	2600
	11th to 20th	Day	33% 32% 8% 20% 7% 1	2986
	21st to end	Day	36% 28% 10% 14% 11% 1	3960
January	1st to 10th	Night	28% 26% 6% 20% 16% 4	6349
	11th to 20th	Night	26% 26% 8% 19% 15% 6%	5992
	21st to end	Night	31% 28% 6% 19% 14% 2	6490
February	1st to 10th	Night	17% 61% 7% 11% 3 1	2600
	11th to 20th	Night	18% 60% 2 8% 10% 1	2458
	21st to end	Night	17% 62% 4 8% 6% 2	1980
March	1st to 10th	Night	35% 40% 3 15% 6% 1	3668
	11th to 20th	Night	17% 40% 7% 25% 10% 1	3498
	21st to end	Night	25% 40% 4 13% 16% 3	3698
April	1st to 10th	Night	17% 65% 3 9% 6% 1	1900
	11th to 20th	Night	14% 66% 5% 8% 6% 1	1875
	21st to end	Night	16% 65% 3 8% 7% 1	1900
May	1st to 10th	Night	36% 41% 5% 11% 6% 1	2941
	11th to 20th	Night	39% 41% 7% 9% 3	2496
	21st to end	Night	23% 42% 9% 16% 7% 3	2739
June	1st to 10th	Night	14% 66% 3 10% 7%	1520
	11th to 20th	Night	13% 66% 4 10% 7%	1520
	21st to end	Night	13% 65% 5% 11% 5% 1	1520
July	1st to 10th	Night	24% 39% 14% 11% 8% 4	2480
	11th to 20th	Night	28% 38% 11% 17% 7%	2472
	21st to end	Night	32% 36% 8% 13% 11% 1	2945
August	1st to 10th	Night	34% 38% 11% 13% 3	2814
	11th to 20th	Night	25% 39% 5% 22% 8%	2971
	21st to end	Night	20% 37% 6% 25% 11% 1	3476
September	1st to 10th	Night	15% 60% 7% 10% 7% 2	1900
	11th to 20th	Night	15% 59% 4 10% 10% 2	1900
	21st to end	Night	21% 59% 4 8% 7%	2157
October	1st to 10th	Night	28% 37% 7% 11% 15% 2	3800
	11th to 20th	Night	12% 36% 6% 19% 22% 5%	3779
	21st to end	Night	12% 36% 7% 24% 17% 4	4120
November	1st to 10th	Night	15% 56% 6% 12% 9% 2	2509
	11th to 20th	Night	15% 56% 3 11% 12% 2	2610
	21st to end	Night	14% 57% 6% 14% 8% 1	2800
December	1st to 10th	Night	22% 36% 10% 22% 9% 1	4580
	11th to 20th	Night	32% 31% 8% 14% 11% 3	5208
	21st to end	Night	38% 28% 7% 13% 14% 1	6996

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% 26% 30% 14% 3 1	200
	11th to 20th	Day	34% 20% 31% 13% 1	277
	21st to end	Day	22% 24% 39% 9% 6% 1	330
February	1st to 10th	Day	26% 21% 39% 11% 3	300
	11th to 20th	Day	31% 23% 35% 9% 2	375
	21st to end	Day	30% 17% 35% 15% 2	414
March	1st to 10th	Day	25% 20% 31% 20% 3	500
	11th to 20th	Day	22% 22% 34% 18% 4 2	464
	21st to end	Day	25% 17% 33% 18% 6% 1	506
April	1st to 10th	Day	22% 17% 36% 18% 6% 1	460
	11th to 20th	Day	19% 18% 29% 20% 9% 4	452
	21st to end	Day	25% 14% 31% 20% 7% 2	460
May	1st to 10th	Day	26% 16% 26% 19% 9% 3	463
	11th to 20th	Day	21% 11% 29% 23% 12% 4	487
	21st to end	Day	18% 5% 23% 27% 20% 8%	529
June	1st to 10th	Day	15% 10% 29% 25% 16% 6%	490
	11th to 20th	Day	16% 6% 26% 29% 17% 6%	490
	21st to end	Day	14% 4 25% 33% 16% 7%	490
July	1st to 10th	Day	13% 2 16% 31% 25% 12%	485
	11th to 20th	Day	6% 3 20% 33% 29% 10%	484
	21st to end	Day	12% 4 22% 33% 22% 6%	532
August	1st to 10th	Day	13% 3 21% 28% 26% 9%	486
	11th to 20th	Day	13% 3 16% 33% 24% 11%	479
	21st to end	Day	11% 4 19% 30% 22% 14%	539
September	1st to 10th	Day	19% 5% 20% 20% 23% 13%	490
	11th to 20th	Day	14% 4 17% 29% 24% 12%	490
	21st to end	Day	27% 9% 21% 25% 13% 6%	490
October	1st to 10th	Day	21% 8% 24% 22% 18% 7%	490
	11th to 20th	Day	18% 12% 27% 26% 13% 4	490
	21st to end	Day	17% 11% 36% 25% 9% 2	539
November	1st to 10th	Day	17% 12% 31% 27% 11% 2	408
	11th to 20th	Day	18% 17% 32% 22% 10% 1	385
	21st to end	Day	27% 20% 32% 17% 6%	200
December	1st to 10th	Day	23% 18% 41% 14% 3 2	200
	11th to 20th	Day	28% 19% 33% 14% 7%	200
	21st to end	Day	20% 20% 36% 15% 8%	220
January	1st to 10th	Night	19% 16% 42% 19% 3	800
	11th to 20th	Night	23% 17% 33% 24% 3	800
	21st to end	Night	18% 15% 45% 21% 2	880
February	1st to 10th	Night	21% 15% 38% 25% 2	800
	11th to 20th	Night	24% 20% 37% 18% 1	783
	21st to end	Night	23% 18% 38% 18% 3	660
March	1st to 10th	Night	20% 17% 38% 22% 4	800
	11th to 20th	Night	22% 15% 36% 22% 5%	767
	21st to end	Night	21% 12% 39% 22% 5%	836
April	1st to 10th	Night	21% 15% 39% 19% 4	760
	11th to 20th	Night	18% 11% 36% 27% 8%	751
	21st to end	Night	23% 10% 32% 27% 8%	760
May	1st to 10th	Night	21% 8% 29% 31% 9% 1	632
	11th to 20th	Night	20% 7% 31% 33% 10% 1	374
	21st to end	Night	15% 3 20% 41% 20% 1	411
June	1st to 10th	Night	14% 2 24% 39% 20% 1	380
	11th to 20th	Night	12% 3 23% 45% 16% 1	380
	21st to end	Night	11% 2 22% 49% 16%	380
July	1st to 10th	Night	10% 2 18% 41% 26% 3	370
	11th to 20th	Night	7% 1 15% 43% 30% 4	368
	21st to end	Night	12% 2 15% 44% 24% 3	592
August	1st to 10th	Night	12% 2 11% 47% 26% 2	567
	11th to 20th	Night	12% 2 14% 40% 28% 3	658
	21st to end	Night	14% 1 14% 40% 27% 3	836
September	1st to 10th	Night	14% 3 21% 34% 24% 4	760
	11th to 20th	Night	15% 3 13% 37% 28% 5%	760
	21st to end	Night	23% 4 20% 32% 20% 2	760
October	1st to 10th	Night	21% 6% 21% 28% 19% 5%	760
	11th to 20th	Night	17% 9% 28% 33% 13% 1	760
	21st to end	Night	20% 7% 34% 27% 12%	836
November	1st to 10th	Night	13% 6% 35% 34% 10% 1	780
	11th to 20th	Night	19% 13% 33% 27% 8% 1	800
	21st to end	Night	17% 15% 35% 26% 7%	800
December	1st to 10th	Night	22% 14% 36% 21% 6% 1	800
	11th to 20th	Night	19% 14% 39% 24% 5%	800
	21st to end	Night	20% 14% 35% 28% 3	880

Page generated at 2025-03-09 08:08:43. Version ac07

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