AAAA Galway
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the AAAA Galway clear sky chart from 2005-11-06 to 2025-12-03.

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% 8% 3 8% 5% 5% 5% 4 6% 7% 33%	127134
	Night	17% 9% 3 8% 5% 5% 5% 4 6% 7% 33%	123580
Transparency	Day	48% 5% 12% 22% 11% 1	130610
	Night	49% 4 12% 21% 12% 1	128190
Seeing	Day	22% 17% 29% 20% 10% 3	16136
	Night	21% 15% 29% 26% 9% 1	25198

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	11% 9% 4 13% 9% 9% 7% 4 5% 5% 23%	3597
	11th to 20th	Day	13% 13% 4 11% 7% 6% 6% 5% 6% 5% 23%	3570
	21st to end	Day	15% 10% 3 9% 6% 6% 6% 4 5% 6% 29%	4115
February	1st to 10th	Day	13% 13% 3 9% 8% 7% 7% 5% 5% 6% 25%	1800
	11th to 20th	Day	12% 12% 5% 10% 7% 5% 6% 5% 5% 6% 27%	1898
	21st to end	Day	19% 11% 4 10% 6% 4 4 4 4 5% 29%	1650
March	1st to 10th	Day	19% 11% 4 10% 5% 5% 4 4 4 5% 29%	4476
	11th to 20th	Day	16% 9% 3 8% 5% 4 4 3 6% 6% 36%	4746
	21st to end	Day	19% 10% 2 8% 6% 5% 4 3 4 5% 34%	5940
April	1st to 10th	Day	19% 10% 4 7% 5% 3 5% 4 4 6% 34%	2400
	11th to 20th	Day	17% 7% 2 8% 5% 5% 5% 4 5% 6% 35%	2374
	21st to end	Day	19% 8% 3 8% 5% 5% 5% 4 5% 5% 33%	2485
May	1st to 10th	Day	31% 9% 3 7% 4 4 4 3 5% 5% 24%	6066
	11th to 20th	Day	16% 9% 3 9% 6% 5% 6% 4 6% 7% 30%	6318
	21st to end	Day	19% 7% 3 7% 5% 5% 5% 4 6% 9% 31%	6949
June	1st to 10th	Day	16% 7% 3 7% 5% 5% 6% 4 7% 8% 32%	2800
	11th to 20th	Day	17% 5% 2 6% 5% 5% 5% 6% 7% 9% 33%	2800
	21st to end	Day	16% 7% 2 6% 5% 4 5% 5% 8% 8% 35%	2800
July	1st to 10th	Day	9% 6% 3 8% 5% 5% 6% 5% 7% 10% 36%	6360
	11th to 20th	Day	9% 5% 2 6% 5% 5% 6% 5% 8% 11% 36%	6360
	21st to end	Day	13% 5% 2 6% 4 5% 6% 4 6% 8% 42%	6926
August	1st to 10th	Day	15% 6% 2 7% 4 5% 5% 4 6% 8% 36%	4540
	11th to 20th	Day	14% 7% 2 7% 5% 5% 6% 4 7% 10% 34%	3868
	21st to end	Day	11% 6% 2 6% 5% 5% 5% 5% 7% 9% 39%	4312
September	1st to 10th	Day	12% 5% 2 5% 4 5% 4 4 6% 8% 45%	2400
	11th to 20th	Day	13% 5% 1 5% 4 4 3 4 5% 8% 48%	2320
	21st to end	Day	16% 6% 3 6% 3 4 4 3 6% 8% 40%	2200
October	1st to 10th	Day	19% 7% 2 8% 5% 5% 4 3 4 6% 36%	2070
	11th to 20th	Day	17% 7% 2 7% 4 4 4 4 6% 7% 38%	2000
	21st to end	Day	22% 9% 2 6% 4 4 5% 4 6% 7% 31%	1995
November	1st to 10th	Day	14% 8% 3 7% 4 3 4 3 6% 8% 40%	1851
	11th to 20th	Day	14% 8% 3 7% 6% 5% 5% 4 6% 7% 35%	1890
	21st to end	Day	19% 10% 4 7% 5% 5% 4 3 5% 7% 30%	1696
December	1st to 10th	Day	18% 15% 3 10% 6% 5% 5% 4 5% 7% 21%	2616
	11th to 20th	Day	22% 10% 3 8% 5% 4 4 4 5% 6% 29%	2986
	21st to end	Day	22% 12% 6% 10% 5% 4 4 3 4 7% 23%	3960
January	1st to 10th	Night	12% 10% 4 11% 7% 6% 6% 5% 6% 7% 26%	6349
	11th to 20th	Night	10% 12% 5% 12% 8% 6% 6% 4 7% 7% 22%	6315
	21st to end	Night	15% 10% 4 10% 6% 6% 5% 4 6% 7% 28%	6840
February	1st to 10th	Night	13% 13% 4 9% 6% 6% 5% 4 7% 6% 27%	2600
	11th to 20th	Night	12% 10% 4 11% 6% 5% 5% 5% 7% 7% 30%	2386
	21st to end	Night	17% 9% 4 9% 5% 5% 5% 4 6% 7% 30%	1980
March	1st to 10th	Night	20% 9% 3 8% 5% 5% 5% 5% 6% 6% 28%	5364
	11th to 20th	Night	16% 10% 3 7% 4 4 4 4 6% 7% 36%	5209
	21st to end	Night	20% 10% 4 9% 4 4 5% 4 4 5% 31%	4991
April	1st to 10th	Night	21% 7% 3 7% 5% 5% 4 4 5% 7% 32%	2000
	11th to 20th	Night	19% 9% 2 7% 5% 5% 4 4 6% 7% 34%	1975
	21st to end	Night	20% 7% 3 6% 4 4 4 3 6% 6% 38%	1914
May	1st to 10th	Night	31% 8% 3 7% 4 4 4 3 5% 6% 24%	3916
	11th to 20th	Night	16% 9% 4 11% 5% 5% 4 3 6% 6% 31%	3575
	21st to end	Night	18% 9% 3 7% 5% 5% 6% 4 6% 7% 31%	3926
June	1st to 10th	Night	18% 7% 2 6% 5% 4 4 3 6% 7% 39%	1600
	11th to 20th	Night	16% 7% 2 6% 5% 4 3 4 6% 8% 39%	1600
	21st to end	Night	15% 4 2 4 4 4 6% 5% 5% 8% 43%	1600
July	1st to 10th	Night	10% 6% 3 8% 6% 5% 5% 4 7% 9% 39%	3600
	11th to 20th	Night	13% 7% 3 8% 5% 5% 5% 5% 6% 7% 36%	3600
	21st to end	Night	10% 6% 2 5% 4 4 4 4 6% 7% 47%	3926
August	1st to 10th	Night	19% 6% 2 6% 4 5% 5% 4 6% 8% 35%	2607
	11th to 20th	Night	17% 7% 2 6% 4 4 4 3 6% 8% 38%	3135
	21st to end	Night	12% 5% 2 5% 4 3 5% 3 6% 10% 45%	3586
September	1st to 10th	Night	13% 5% 3 5% 3 5% 4 3 6% 7% 46%	2000
	11th to 20th	Night	13% 5% 1 6% 3 4 4 2 4 7% 51%	2080
	21st to end	Night	15% 5% 2 6% 3 4 4 3 5% 7% 44%	2200
October	1st to 10th	Night	20% 6% 3 7% 4 4 5% 4 5% 6% 37%	2329
	11th to 20th	Night	16% 6% 2 6% 5% 5% 4 3 5% 7% 40%	2400
	21st to end	Night	21% 8% 3 6% 5% 3 5% 4 5% 7% 33%	2844
November	1st to 10th	Night	14% 7% 3 7% 5% 4 4 4 5% 6% 40%	2667
	11th to 20th	Night	18% 6% 3 7% 6% 5% 4 3 5% 7% 36%	2730
	21st to end	Night	15% 9% 3 7% 5% 6% 4 4 6% 7% 35%	2923
December	1st to 10th	Night	17% 12% 4 8% 6% 5% 6% 5% 6% 7% 24%	4609
	11th to 20th	Night	24% 9% 3 7% 5% 4 4 3 5% 5% 30%	5208
	21st to end	Night	25% 13% 4 8% 4 4 4 3 4 4 27%	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	59% 3 10% 21% 6% 1	3598
	11th to 20th	Day	57% 5% 11% 15% 11% 2	3600
	21st to end	Day	54% 4 11% 19% 11% 1	4115
February	1st to 10th	Day	58% 5% 11% 18% 8% 1	1800
	11th to 20th	Day	57% 5% 9% 19% 9% 2	1907
	21st to end	Day	56% 5% 10% 18% 11% 1	1650
March	1st to 10th	Day	56% 4 10% 16% 10% 4	4479
	11th to 20th	Day	49% 3 18% 19% 9% 4	4746
	21st to end	Day	53% 3 6% 16% 19% 3	5940
April	1st to 10th	Day	53% 4 7% 21% 13% 3	2400
	11th to 20th	Day	48% 4 10% 22% 14% 2	2374
	21st to end	Day	52% 3 9% 20% 13% 3	2485
May	1st to 10th	Day	63% 4 8% 17% 8% 1	6077
	11th to 20th	Day	53% 4 13% 21% 9% 1	6322
	21st to end	Day	50% 5% 12% 23% 9% 1	6949
June	1st to 10th	Day	47% 6% 13% 22% 12% 1	2800
	11th to 20th	Day	45% 5% 15% 21% 12% 1	2800
	21st to end	Day	44% 6% 15% 23% 12% 1	2800
July	1st to 10th	Day	41% 7% 15% 23% 13%	6290
	11th to 20th	Day	38% 8% 15% 26% 13% 1	6285
	21st to end	Day	39% 5% 13% 30% 12%	6728
August	1st to 10th	Day	44% 6% 15% 22% 12%	4526
	11th to 20th	Day	43% 6% 17% 27% 7%	3904
	21st to end	Day	37% 7% 15% 31% 10% 1	4312
September	1st to 10th	Day	37% 6% 12% 32% 13% 1	2400
	11th to 20th	Day	34% 4 12% 29% 19% 1	2320
	21st to end	Day	41% 4 12% 27% 14% 2	2200
October	1st to 10th	Day	44% 5% 9% 26% 16% 1	3369
	11th to 20th	Day	40% 3 13% 27% 16% 1	3240
	21st to end	Day	36% 5% 15% 30% 13% 1	3195
November	1st to 10th	Day	42% 4 15% 25% 13% 1	1851
	11th to 20th	Day	47% 4 11% 22% 15% 2	1890
	21st to end	Day	53% 4 15% 19% 8% 1	1696
December	1st to 10th	Day	60% 6% 13% 17% 4	2616
	11th to 20th	Day	54% 5% 13% 18% 9% 1	2986
	21st to end	Day	61% 3 10% 15% 10% 1	3960
January	1st to 10th	Night	56% 4 13% 17% 9% 1	6349
	11th to 20th	Night	58% 5% 10% 15% 10% 2	6360
	21st to end	Night	56% 3 11% 14% 14% 3	6840
February	1st to 10th	Night	56% 4 11% 20% 8% 1	2600
	11th to 20th	Night	52% 5% 11% 20% 11% 1	2388
	21st to end	Night	53% 5% 12% 21% 8% 2	1980
March	1st to 10th	Night	53% 5% 11% 16% 13% 2	5374
	11th to 20th	Night	47% 4 17% 21% 9% 2	5210
	21st to end	Night	55% 3 6% 18% 16% 2	4991
April	1st to 10th	Night	52% 4 9% 20% 13% 1	2000
	11th to 20th	Night	51% 4 9% 22% 14% 1	1975
	21st to end	Night	47% 4 10% 20% 17% 3	1914
May	1st to 10th	Night	61% 4 10% 14% 9% 1	3922
	11th to 20th	Night	54% 5% 11% 21% 9% 1	3576
	21st to end	Night	53% 5% 12% 18% 11% 1	3927
June	1st to 10th	Night	45% 4 11% 25% 13% 2	1600
	11th to 20th	Night	42% 5% 16% 24% 13% 1	1600
	21st to end	Night	37% 6% 15% 27% 14%	1600
July	1st to 10th	Night	41% 6% 15% 23% 15% 1	3560
	11th to 20th	Night	44% 7% 13% 20% 16%	3552
	21st to end	Night	35% 5% 12% 33% 13% 1	3809
August	1st to 10th	Night	45% 7% 15% 24% 9%	2597
	11th to 20th	Night	43% 6% 17% 24% 10%	3164
	21st to end	Night	35% 5% 15% 35% 10% 1	3586
September	1st to 10th	Night	37% 5% 12% 30% 15% 1	2000
	11th to 20th	Night	35% 4 11% 28% 21% 1	2080
	21st to end	Night	40% 4 11% 26% 17% 2	2200
October	1st to 10th	Night	46% 5% 12% 23% 14% 1	3810
	11th to 20th	Night	34% 3 14% 27% 21% 1	3899
	21st to end	Night	41% 5% 13% 30% 11%	4594
November	1st to 10th	Night	43% 4 11% 25% 15% 2	2667
	11th to 20th	Night	46% 5% 10% 23% 14% 2	2730
	21st to end	Night	47% 4 17% 22% 9% 1	2923
December	1st to 10th	Night	54% 6% 15% 20% 5%	4609
	11th to 20th	Night	55% 5% 12% 16% 12% 1	5208
	21st to end	Night	61% 3 9% 15% 10% 2	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	27% 25% 25% 19% 5% 1	200
	11th to 20th	Day	25% 26% 36% 12% 1 1	200
	21st to end	Day	22% 27% 34% 12% 4	253
February	1st to 10th	Day	30% 30% 28% 11% 1	300
	11th to 20th	Day	30% 27% 30% 11% 1	446
	21st to end	Day	29% 23% 32% 14% 3	414
March	1st to 10th	Day	29% 22% 33% 13% 3	500
	11th to 20th	Day	28% 25% 30% 12% 4 1	500
	21st to end	Day	33% 24% 24% 14% 5% 1	550
April	1st to 10th	Day	33% 22% 26% 13% 6% 1	500
	11th to 20th	Day	28% 26% 23% 13% 7% 2	492
	21st to end	Day	29% 21% 30% 13% 6% 1	500
May	1st to 10th	Day	34% 16% 27% 15% 7% 2	503
	11th to 20th	Day	20% 17% 32% 22% 8% 1	527
	21st to end	Day	19% 13% 28% 24% 12% 3	573
June	1st to 10th	Day	18% 17% 31% 21% 12% 2	530
	11th to 20th	Day	17% 14% 30% 25% 11% 2	530
	21st to end	Day	17% 15% 32% 23% 10% 2	530
July	1st to 10th	Day	13% 9% 29% 30% 16% 4	525
	11th to 20th	Day	12% 8% 32% 31% 15% 3	524
	21st to end	Day	14% 10% 33% 28% 11% 3	576
August	1st to 10th	Day	10% 8% 29% 28% 20% 5%	526
	11th to 20th	Day	15% 8% 26% 29% 16% 6%	519
	21st to end	Day	12% 11% 29% 26% 18% 4	583
September	1st to 10th	Day	15% 9% 25% 24% 18% 9%	530
	11th to 20th	Day	12% 8% 24% 22% 22% 12%	530
	21st to end	Day	18% 10% 27% 27% 13% 6%	530
October	1st to 10th	Day	24% 14% 25% 18% 14% 5%	530
	11th to 20th	Day	20% 19% 27% 21% 11% 2	530
	21st to end	Day	26% 14% 30% 22% 7% 1	470
November	1st to 10th	Day	23% 16% 27% 22% 11% 1	425
	11th to 20th	Day	23% 23% 27% 20% 6% 1	430
	21st to end	Day	29% 25% 25% 19% 3	236
December	1st to 10th	Day	28% 26% 27% 13% 5%	204
	11th to 20th	Day	33% 23% 32% 11% 3	200
	21st to end	Day	27% 22% 31% 15% 5% 1	220
January	1st to 10th	Night	23% 23% 31% 22% 2	800
	11th to 20th	Night	26% 20% 29% 21% 3	800
	21st to end	Night	17% 24% 35% 22% 2	880
February	1st to 10th	Night	23% 19% 35% 21% 2	800
	11th to 20th	Night	23% 23% 37% 16% 2	783
	21st to end	Night	27% 20% 31% 20% 2	660
March	1st to 10th	Night	24% 23% 33% 18% 3	800
	11th to 20th	Night	24% 21% 32% 19% 3	800
	21st to end	Night	24% 20% 31% 20% 5%	880
April	1st to 10th	Night	27% 18% 32% 20% 3	800
	11th to 20th	Night	24% 19% 30% 21% 6%	791
	21st to end	Night	23% 18% 30% 23% 6%	714
May	1st to 10th	Night	27% 14% 29% 20% 8% 1	540
	11th to 20th	Night	18% 14% 31% 28% 7% 1	394
	21st to end	Night	17% 8% 27% 35% 12% 1	433
June	1st to 10th	Night	19% 7% 30% 33% 11% 2	400
	11th to 20th	Night	18% 9% 25% 35% 14%	400
	21st to end	Night	16% 6% 28% 37% 13% 1	400
July	1st to 10th	Night	12% 6% 25% 37% 19% 1	390
	11th to 20th	Night	13% 6% 22% 40% 18% 1	388
	21st to end	Night	13% 4 27% 39% 16% 1	438
August	1st to 10th	Night	12% 3 22% 41% 21% 1	406
	11th to 20th	Night	16% 4 22% 34% 19% 4	752
	21st to end	Night	17% 7% 21% 34% 20% 1	880
September	1st to 10th	Night	14% 6% 23% 35% 20% 2	800
	11th to 20th	Night	16% 5% 23% 29% 22% 5%	800
	21st to end	Night	17% 7% 28% 31% 16% 2	800
October	1st to 10th	Night	22% 11% 22% 27% 16% 1	800
	11th to 20th	Night	19% 13% 29% 30% 9%	800
	21st to end	Night	27% 12% 30% 25% 6%	880
November	1st to 10th	Night	19% 14% 30% 27% 8%	820
	11th to 20th	Night	22% 20% 26% 25% 7% 1	840
	21st to end	Night	23% 16% 30% 25% 5%	840
December	1st to 10th	Night	25% 19% 33% 20% 3	809
	11th to 20th	Night	24% 22% 30% 20% 4	800
	21st to end	Night	29% 19% 27% 20% 3	880

Page generated at 2025-11-30 01:00:52. Version ac07

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