Gwynedd Mercy College
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Gwynedd Mercy College clear sky chart from 2005-11-06 to 2024-11-05.

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% 7% 2 6% 4 4 4 4 6% 7% 40%	101337
	Night	16% 7% 2 6% 4 4 4 3 5% 7% 42%	97706
Transparency	Day	41% 7% 12% 23% 16% 2	104884
	Night	40% 6% 11% 23% 16% 3	102248
Seeing	Day	21% 15% 28% 22% 11% 3	14987
	Night	19% 12% 31% 28% 9% 1	24235

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	16% 6% 3 5% 4 4 4 3 5% 5% 45%	2517
	11th to 20th	Day	14% 11% 3 9% 6% 5% 4 4 5% 5% 36%	2583
	21st to end	Day	21% 9% 3 7% 4 4 4 3 4 6% 35%	3124
February	1st to 10th	Day	16% 7% 3 6% 5% 3 4 4 6% 7% 39%	1710
	11th to 20th	Day	16% 8% 2 7% 4 4 5% 3 4 6% 40%	1800
	21st to end	Day	18% 9% 3 7% 5% 3 3 4 4 5% 38%	1570
March	1st to 10th	Day	25% 6% 3 6% 5% 3 4 3 4 5% 36%	3116
	11th to 20th	Day	10% 5% 2 5% 5% 5% 5% 4 6% 7% 46%	3478
	21st to end	Day	21% 7% 2 6% 3 3 3 2 4 5% 43%	4038
April	1st to 10th	Day	15% 7% 3 7% 5% 4 4 4 5% 8% 39%	2280
	11th to 20th	Day	15% 7% 2 5% 4 4 4 4 6% 7% 42%	2254
	21st to end	Day	16% 5% 3 7% 5% 4 5% 5% 5% 7% 40%	2280
May	1st to 10th	Day	27% 8% 3 6% 4 4 5% 4 5% 7% 28%	4081
	11th to 20th	Day	24% 8% 3 7% 6% 5% 5% 3 5% 6% 28%	4398
	21st to end	Day	12% 6% 2 5% 4 4 4 4 6% 9% 43%	4837
June	1st to 10th	Day	13% 5% 2 7% 4 5% 5% 5% 7% 8% 39%	2660
	11th to 20th	Day	12% 6% 2 6% 5% 5% 6% 4 7% 9% 37%	2660
	21st to end	Day	11% 5% 2 5% 4 4 5% 5% 7% 11% 41%	2660
July	1st to 10th	Day	7% 6% 2 7% 5% 6% 6% 5% 8% 10% 37%	4440
	11th to 20th	Day	10% 7% 2 5% 4 5% 6% 5% 7% 10% 39%	4440
	21st to end	Day	12% 8% 3 8% 5% 5% 6% 4 7% 8% 34%	4752
August	1st to 10th	Day	19% 6% 2 6% 5% 5% 5% 4 6% 8% 34%	4104
	11th to 20th	Day	13% 5% 2 6% 4 3 4 4 7% 9% 43%	3737
	21st to end	Day	11% 5% 2 5% 4 3 4 3 5% 9% 48%	4180
September	1st to 10th	Day	14% 6% 2 7% 4 4 4 4 5% 6% 45%	2280
	11th to 20th	Day	13% 5% 2 4 3 3 4 3 4 9% 51%	2250
	21st to end	Day	18% 7% 3 7% 4 4 4 3 5% 6% 38%	2090
October	1st to 10th	Day	18% 6% 2 5% 3 4 4 4 5% 7% 42%	1901
	11th to 20th	Day	15% 5% 2 4 4 3 4 3 6% 6% 48%	1900
	21st to end	Day	19% 6% 2 4 3 3 3 3 5% 5% 46%	2019
November	1st to 10th	Day	12% 7% 2 5% 3 3 3 3 4 5% 53%	1708
	11th to 20th	Day	16% 5% 2 5% 4 3 4 3 5% 6% 48%	1710
	21st to end	Day	15% 7% 2 4 4 4 4 4 6% 8% 44%	1582
December	1st to 10th	Day	18% 8% 2 7% 4 3 3 4 5% 7% 38%	1520
	11th to 20th	Day	20% 7% 2 4 4 3 3 3 5% 7% 41%	1906
	21st to end	Day	16% 7% 3 7% 5% 5% 6% 4 6% 7% 35%	2772
January	1st to 10th	Night	16% 7% 2 6% 4 4 4 3 4 6% 45%	4429
	11th to 20th	Night	18% 8% 2 6% 3 3 3 3 4 5% 44%	4376
	21st to end	Night	23% 9% 2 6% 4 3 3 3 4 5% 37%	4532
February	1st to 10th	Night	16% 9% 3 5% 4 4 4 4 4 6% 40%	2470
	11th to 20th	Night	18% 9% 2 7% 4 4 4 3 5% 5% 40%	2264
	21st to end	Night	17% 8% 3 6% 3 4 3 3 4 6% 42%	1884
March	1st to 10th	Night	22% 10% 3 6% 3 4 4 3 5% 5% 37%	3724
	11th to 20th	Night	11% 6% 2 6% 4 4 4 3 4 6% 49%	3479
	21st to end	Night	17% 9% 3 6% 3 3 2 3 4 5% 45%	3580
April	1st to 10th	Night	17% 6% 2 6% 5% 4 4 4 6% 6% 40%	1900
	11th to 20th	Night	15% 6% 3 7% 5% 4 4 3 5% 6% 41%	1875
	21st to end	Night	18% 6% 2 5% 3 4 3 3 6% 8% 42%	1900
May	1st to 10th	Night	23% 9% 2 7% 4 4 4 4 5% 8% 30%	2888
	11th to 20th	Night	23% 9% 3 8% 4 4 4 3 6% 6% 30%	2495
	21st to end	Night	13% 6% 2 6% 4 4 4 4 7% 10% 42%	2738
June	1st to 10th	Night	15% 7% 2 6% 4 4 4 3 6% 7% 43%	1520
	11th to 20th	Night	10% 7% 2 6% 6% 5% 4 4 6% 9% 41%	1520
	21st to end	Night	10% 5% 2 5% 4 4 5% 6% 7% 9% 42%	1520
July	1st to 10th	Night	9% 6% 3 7% 6% 5% 5% 5% 8% 9% 38%	2520
	11th to 20th	Night	12% 6% 2 7% 5% 4 5% 5% 7% 11% 36%	2520
	21st to end	Night	14% 8% 2 7% 4 4 4 5% 7% 8% 36%	2796
August	1st to 10th	Night	22% 7% 3 5% 4 4 4 4 6% 8% 33%	2825
	11th to 20th	Night	13% 7% 3 6% 4 4 4 4 5% 7% 42%	3058
	21st to end	Night	11% 5% 2 5% 3 4 4 4 5% 8% 49%	3476
September	1st to 10th	Night	13% 8% 2 6% 4 3 4 3 4 6% 47%	1900
	11th to 20th	Night	12% 6% 2 5% 3 3 3 3 5% 6% 53%	1929
	21st to end	Night	18% 7% 2 6% 4 4 3 4 5% 7% 40%	2090
October	1st to 10th	Night	18% 7% 2 6% 4 4 3 4 4 5% 43%	2275
	11th to 20th	Night	14% 5% 2 5% 3 3 4 4 4 6% 51%	2280
	21st to end	Night	17% 7% 2 5% 2 3 3 3 4 6% 48%	2577
November	1st to 10th	Night	12% 6% 2 5% 3 3 3 3 4 6% 53%	2470
	11th to 20th	Night	17% 7% 2 5% 4 3 3 2 4 5% 48%	2470
	21st to end	Night	14% 5% 2 5% 4 4 5% 4 6% 7% 45%	2594
December	1st to 10th	Night	20% 8% 2 5% 4 4 4 3 5% 6% 39%	2660
	11th to 20th	Night	18% 6% 2 6% 4 4 4 3 5% 7% 40%	3288
	21st to end	Night	17% 8% 3 6% 4 4 4 4 5% 6% 38%	4884

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	38% 5% 13% 28% 12% 3	2518
	11th to 20th	Day	46% 7% 11% 21% 13% 2	2583
	21st to end	Day	49% 7% 12% 22% 9% 1	3124
February	1st to 10th	Day	43% 7% 15% 24% 11% 2	1710
	11th to 20th	Day	44% 4 10% 24% 15% 2	1809
	21st to end	Day	46% 5% 11% 23% 11% 4	1570
March	1st to 10th	Day	48% 6% 9% 26% 9% 2	3119
	11th to 20th	Day	33% 7% 11% 31% 15% 3	3478
	21st to end	Day	44% 4 8% 18% 21% 3	4038
April	1st to 10th	Day	42% 6% 11% 22% 15% 4	2280
	11th to 20th	Day	40% 6% 12% 23% 16% 4	2254
	21st to end	Day	41% 7% 12% 19% 18% 4	2280
May	1st to 10th	Day	54% 7% 11% 17% 10% 2	4094
	11th to 20th	Day	54% 8% 12% 18% 8% 1	4402
	21st to end	Day	35% 8% 12% 26% 17% 2	4837
June	1st to 10th	Day	39% 8% 14% 23% 14% 1	2660
	11th to 20th	Day	40% 9% 13% 24% 11% 2	2660
	21st to end	Day	36% 9% 14% 24% 16% 1	2660
July	1st to 10th	Day	40% 10% 15% 19% 14% 2	4370
	11th to 20th	Day	38% 8% 17% 23% 14% 1	4365
	21st to end	Day	46% 8% 11% 19% 16% 1	4601
August	1st to 10th	Day	46% 8% 13% 23% 9%	4091
	11th to 20th	Day	36% 7% 11% 31% 14% 1	3773
	21st to end	Day	33% 6% 10% 27% 22% 2	4180
September	1st to 10th	Day	39% 7% 11% 19% 21% 3	2280
	11th to 20th	Day	32% 5% 10% 25% 24% 4	2250
	21st to end	Day	47% 5% 8% 18% 20% 2	2090
October	1st to 10th	Day	36% 5% 9% 18% 27% 5%	3161
	11th to 20th	Day	24% 5% 11% 25% 28% 7%	3140
	21st to end	Day	25% 4 14% 25% 29% 5%	3309
November	1st to 10th	Day	34% 4 12% 25% 21% 3	1708
	11th to 20th	Day	38% 5% 10% 26% 19% 3	1710
	21st to end	Day	37% 5% 14% 31% 11% 2	1582
December	1st to 10th	Day	44% 5% 16% 22% 12%	1520
	11th to 20th	Day	42% 6% 14% 27% 10% 2	1906
	21st to end	Day	45% 8% 13% 22% 11% 1	2772
January	1st to 10th	Night	40% 5% 10% 29% 12% 3	4429
	11th to 20th	Night	43% 5% 11% 26% 12% 2	4376
	21st to end	Night	49% 5% 9% 25% 12% 2	4532
February	1st to 10th	Night	44% 6% 12% 25% 12% 2	2470
	11th to 20th	Night	45% 5% 9% 20% 18% 4	2266
	21st to end	Night	43% 5% 8% 23% 17% 4	1884
March	1st to 10th	Night	49% 5% 9% 23% 12% 2	3734
	11th to 20th	Night	34% 7% 11% 29% 16% 3	3480
	21st to end	Night	43% 4 8% 17% 23% 6%	3580
April	1st to 10th	Night	42% 6% 11% 20% 16% 4	1900
	11th to 20th	Night	42% 6% 10% 21% 19% 3	1875
	21st to end	Night	40% 6% 10% 21% 19% 5%	1900
May	1st to 10th	Night	51% 9% 9% 19% 10% 1	2894
	11th to 20th	Night	53% 8% 14% 14% 10% 2	2496
	21st to end	Night	35% 10% 15% 21% 15% 3	2739
June	1st to 10th	Night	39% 7% 10% 22% 19% 2	1520
	11th to 20th	Night	38% 9% 13% 26% 13% 1	1520
	21st to end	Night	33% 11% 15% 25% 14% 2	1520
July	1st to 10th	Night	40% 10% 19% 16% 13% 2	2480
	11th to 20th	Night	40% 8% 17% 22% 11% 1	2472
	21st to end	Night	43% 8% 15% 18% 15% 1	2707
August	1st to 10th	Night	48% 8% 18% 17% 9% 1	2814
	11th to 20th	Night	40% 7% 12% 26% 14% 1	3088
	21st to end	Night	33% 6% 10% 28% 20% 2	3476
September	1st to 10th	Night	39% 6% 11% 20% 21% 3	1900
	11th to 20th	Night	32% 5% 10% 22% 27% 4	1929
	21st to end	Night	43% 7% 8% 20% 21% 2	2090
October	1st to 10th	Night	42% 4 11% 21% 21% 2	3795
	11th to 20th	Night	24% 4 10% 29% 29% 5%	3779
	21st to end	Night	27% 4 11% 31% 23% 4	4237
November	1st to 10th	Night	33% 5% 13% 25% 20% 5%	2470
	11th to 20th	Night	40% 4 9% 23% 19% 5%	2470
	21st to end	Night	37% 6% 13% 28% 15% 2	2594
December	1st to 10th	Night	45% 6% 12% 23% 13% 1	2660
	11th to 20th	Night	41% 6% 13% 21% 16% 3	3288
	21st to end	Night	44% 7% 13% 25% 11% 1	4884

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	25% 29% 30% 12% 3 2	180
	11th to 20th	Day	36% 26% 26% 10% 2	198
	21st to end	Day	27% 29% 27% 12% 5%	297
February	1st to 10th	Day	30% 24% 32% 9% 4	270
	11th to 20th	Day	30% 23% 35% 11% 1	408
	21st to end	Day	30% 23% 32% 13% 3	382
March	1st to 10th	Day	28% 20% 31% 17% 3	460
	11th to 20th	Day	25% 24% 32% 14% 3 2	460
	21st to end	Day	28% 24% 29% 13% 5% 1	506
April	1st to 10th	Day	28% 22% 30% 14% 5% 1	460
	11th to 20th	Day	22% 24% 30% 15% 7% 2	452
	21st to end	Day	25% 19% 32% 18% 4 2	460
May	1st to 10th	Day	28% 19% 29% 16% 6% 2	463
	11th to 20th	Day	23% 13% 29% 25% 8% 2	487
	21st to end	Day	19% 9% 27% 26% 16% 4	529
June	1st to 10th	Day	16% 12% 30% 27% 12% 3	490
	11th to 20th	Day	16% 12% 28% 29% 13% 3	490
	21st to end	Day	14% 11% 31% 28% 12% 4	490
July	1st to 10th	Day	10% 6% 23% 32% 22% 7%	485
	11th to 20th	Day	9% 3 25% 34% 25% 4	484
	21st to end	Day	13% 6% 28% 32% 16% 4	532
August	1st to 10th	Day	11% 6% 26% 33% 18% 6%	486
	11th to 20th	Day	14% 5% 20% 35% 20% 6%	479
	21st to end	Day	12% 8% 25% 30% 17% 8%	539
September	1st to 10th	Day	18% 11% 22% 27% 16% 7%	490
	11th to 20th	Day	15% 6% 26% 28% 15% 10%	490
	21st to end	Day	26% 13% 21% 23% 11% 5%	490
October	1st to 10th	Day	24% 8% 27% 21% 13% 7%	490
	11th to 20th	Day	17% 16% 29% 24% 10% 3	490
	21st to end	Day	22% 15% 31% 18% 12% 2	502
November	1st to 10th	Day	20% 12% 31% 23% 11% 2	378
	11th to 20th	Day	21% 18% 34% 21% 5% 1	370
	21st to end	Day	21% 19% 36% 19% 4	242
December	1st to 10th	Day	28% 26% 32% 8% 7%	180
	11th to 20th	Day	33% 20% 31% 11% 4	180
	21st to end	Day	28% 20% 32% 12% 7% 1	198
January	1st to 10th	Night	20% 20% 38% 19% 3	760
	11th to 20th	Night	25% 17% 31% 24% 3	760
	21st to end	Night	18% 20% 37% 23% 1	836
February	1st to 10th	Night	21% 16% 38% 23% 1	760
	11th to 20th	Night	25% 22% 35% 17% 1	743
	21st to end	Night	24% 19% 38% 17% 2	628
March	1st to 10th	Night	23% 18% 35% 21% 3	760
	11th to 20th	Night	22% 19% 35% 18% 5%	760
	21st to end	Night	21% 14% 40% 19% 5%	836
April	1st to 10th	Night	21% 19% 38% 16% 5%	760
	11th to 20th	Night	19% 14% 38% 24% 5%	751
	21st to end	Night	21% 11% 34% 28% 5%	760
May	1st to 10th	Night	23% 12% 34% 25% 6%	611
	11th to 20th	Night	21% 9% 37% 27% 6%	374
	21st to end	Night	15% 6% 26% 39% 12% 1	411
June	1st to 10th	Night	17% 5% 29% 38% 11% 1	380
	11th to 20th	Night	10% 6% 31% 41% 12% 1	380
	21st to end	Night	9% 4 28% 47% 11%	380
July	1st to 10th	Night	10% 4 24% 42% 18% 2	370
	11th to 20th	Night	7% 5% 21% 45% 21% 1	368
	21st to end	Night	9% 3 27% 39% 20% 1	449
August	1st to 10th	Night	13% 2 17% 44% 22% 2	567
	11th to 20th	Night	13% 3 19% 37% 25% 2	723
	21st to end	Night	14% 4 19% 38% 22% 2	836
September	1st to 10th	Night	16% 5% 26% 35% 17% 2	760
	11th to 20th	Night	14% 4 22% 35% 21% 4	760
	21st to end	Night	23% 5% 23% 31% 18% 1	760
October	1st to 10th	Night	22% 8% 24% 26% 16% 4	760
	11th to 20th	Night	17% 11% 27% 32% 13%	760
	21st to end	Night	20% 13% 31% 26% 9%	836
November	1st to 10th	Night	16% 9% 36% 27% 12% 1	760
	11th to 20th	Night	21% 16% 29% 26% 8% 1	760
	21st to end	Night	16% 15% 35% 26% 7% 1	760
December	1st to 10th	Night	24% 16% 33% 19% 6% 1	760
	11th to 20th	Night	21% 14% 37% 24% 5%	760
	21st to end	Night	22% 16% 33% 26% 2	836

Page generated at 2024-11-03 02:11:11. Version ac07

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