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 2024-11-10.

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%	101463
	Night	17% 9% 3 8% 5% 5% 4 4 6% 7% 34%	97695
Transparency	Day	48% 5% 12% 23% 11% 1	104957
	Night	49% 4 12% 22% 12% 1	102289
Seeing	Day	21% 17% 29% 20% 10% 3	14800
	Night	21% 15% 29% 26% 9% 1	23851

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	13% 11% 4 10% 7% 7% 5% 4 6% 6% 25%	2517
	11th to 20th	Day	16% 13% 5% 12% 7% 6% 5% 4 6% 4 21%	2520
	21st to end	Day	19% 13% 4 11% 6% 5% 5% 4 4 6% 22%	2871
February	1st to 10th	Day	13% 13% 3 8% 8% 7% 6% 5% 5% 6% 25%	1710
	11th to 20th	Day	11% 12% 5% 10% 7% 5% 6% 5% 5% 6% 27%	1800
	21st to end	Day	19% 11% 4 9% 6% 4 4 4 4 5% 30%	1570
March	1st to 10th	Day	22% 14% 4 9% 4 4 3 3 4 5% 27%	3116
	11th to 20th	Day	13% 10% 3 9% 6% 5% 5% 4 7% 7% 32%	3316
	21st to end	Day	19% 9% 3 9% 6% 4 4 2 4 5% 36%	4150
April	1st to 10th	Day	18% 11% 4 7% 5% 3 4 4 4 6% 35%	2280
	11th to 20th	Day	17% 7% 2 7% 5% 5% 5% 4 5% 6% 35%	2254
	21st to end	Day	20% 8% 3 8% 5% 5% 5% 3 6% 5% 33%	2361
May	1st to 10th	Day	24% 9% 3 8% 4 4 4 3 5% 6% 31%	4230
	11th to 20th	Day	18% 7% 2 7% 5% 6% 5% 4 6% 8% 32%	4398
	21st to end	Day	12% 6% 2 6% 4 5% 5% 4 6% 9% 40%	4837
June	1st to 10th	Day	15% 7% 3 7% 5% 5% 6% 4 7% 8% 32%	2660
	11th to 20th	Day	16% 5% 2 6% 5% 5% 5% 6% 7% 9% 33%	2660
	21st to end	Day	16% 7% 2 7% 5% 5% 5% 5% 8% 8% 34%	2660
July	1st to 10th	Day	9% 6% 3 7% 5% 5% 6% 5% 7% 10% 36%	4440
	11th to 20th	Day	9% 5% 2 6% 5% 5% 6% 5% 8% 12% 36%	4440
	21st to end	Day	13% 6% 2 7% 5% 5% 7% 5% 7% 8% 35%	4814
August	1st to 10th	Day	15% 6% 2 7% 5% 5% 5% 4 7% 8% 34%	4401
	11th to 20th	Day	14% 7% 2 7% 5% 5% 6% 4 7% 10% 34%	3747
	21st to end	Day	11% 6% 2 6% 5% 5% 5% 5% 7% 9% 39%	4180
September	1st to 10th	Day	13% 5% 2 5% 4 5% 5% 4 6% 8% 44%	2280
	11th to 20th	Day	14% 5% 1 5% 4 4 3 4 5% 8% 47%	2204
	21st to end	Day	16% 6% 3 6% 3 4 4 3 6% 8% 40%	2090
October	1st to 10th	Day	20% 8% 2 8% 5% 5% 5% 3 4 5% 34%	1967
	11th to 20th	Day	17% 7% 2 7% 4 4 4 4 6% 7% 38%	1900
	21st to end	Day	23% 9% 2 6% 4 4 4 4 6% 7% 30%	1895
November	1st to 10th	Day	14% 8% 3 6% 4 4 4 3 6% 8% 41%	1752
	11th to 20th	Day	16% 8% 3 7% 6% 5% 5% 4 6% 7% 35%	1710
	21st to end	Day	19% 9% 4 6% 6% 5% 5% 4 5% 7% 31%	1535
December	1st to 10th	Day	20% 15% 3 9% 6% 5% 4 4 5% 6% 23%	1520
	11th to 20th	Day	22% 10% 3 8% 5% 4 4 3 5% 6% 30%	1906
	21st to end	Day	25% 14% 7% 11% 5% 4 3 3 3 5% 19%	2772
January	1st to 10th	Night	16% 11% 3 9% 5% 4 5% 4 6% 7% 30%	4429
	11th to 20th	Night	14% 11% 5% 11% 7% 6% 5% 4 7% 7% 24%	4440
	21st to end	Night	21% 13% 4 10% 6% 5% 4 3 5% 5% 24%	4784
February	1st to 10th	Night	13% 12% 4 9% 6% 6% 5% 4 7% 6% 27%	2470
	11th to 20th	Night	11% 11% 4 10% 6% 5% 4 5% 6% 6% 31%	2264
	21st to end	Night	17% 8% 4 8% 5% 5% 4 4 6% 7% 31%	1884
March	1st to 10th	Night	24% 11% 4 9% 4 4 4 4 5% 5% 27%	3724
	11th to 20th	Night	16% 11% 3 7% 5% 5% 5% 4 6% 6% 33%	3639
	21st to end	Night	16% 12% 5% 10% 4 4 5% 3 4 4 34%	3481
April	1st to 10th	Night	21% 7% 2 7% 5% 5% 4 4 5% 7% 33%	1900
	11th to 20th	Night	19% 8% 2 6% 5% 4 4 3 6% 7% 35%	1875
	21st to end	Night	20% 7% 3 6% 5% 4 4 3 5% 5% 38%	1819
May	1st to 10th	Night	25% 8% 3 6% 5% 4 4 3 5% 6% 31%	2738
	11th to 20th	Night	17% 9% 3 10% 5% 5% 5% 3 6% 6% 32%	2495
	21st to end	Night	14% 6% 2 7% 5% 5% 6% 4 6% 8% 38%	2738
June	1st to 10th	Night	17% 6% 2 6% 5% 4 4 3 6% 7% 39%	1520
	11th to 20th	Night	16% 6% 2 6% 5% 4 3 4 7% 8% 40%	1520
	21st to end	Night	15% 4 2 4 4 4 5% 5% 5% 9% 42%	1520
July	1st to 10th	Night	10% 6% 2 8% 7% 6% 5% 4 7% 8% 38%	2520
	11th to 20th	Night	13% 6% 2 6% 5% 5% 4 4 6% 7% 40%	2520
	21st to end	Night	13% 7% 2 6% 4 4 5% 5% 6% 7% 39%	2739
August	1st to 10th	Night	19% 6% 2 6% 4 5% 5% 4 6% 8% 35%	2526
	11th to 20th	Night	18% 7% 2 6% 4 4 4 4 6% 8% 38%	3037
	21st to end	Night	12% 5% 2 5% 4 3 5% 3 6% 10% 45%	3476
September	1st to 10th	Night	13% 5% 2 5% 3 5% 4 3 6% 7% 46%	1900
	11th to 20th	Night	14% 5% 1 6% 3 4 4 2 4 7% 51%	1976
	21st to end	Night	15% 5% 3 5% 3 4 4 3 6% 7% 44%	2090
October	1st to 10th	Night	20% 7% 3 7% 4 4 5% 4 5% 6% 35%	2212
	11th to 20th	Night	16% 6% 2 6% 5% 5% 4 3 5% 7% 41%	2280
	21st to end	Night	22% 8% 3 6% 5% 3 5% 4 5% 7% 32%	2702
November	1st to 10th	Night	14% 7% 3 6% 6% 4 4 4 5% 6% 41%	2531
	11th to 20th	Night	19% 6% 2 7% 6% 5% 4 3 6% 7% 36%	2470
	21st to end	Night	16% 8% 3 7% 5% 5% 4 4 5% 7% 36%	2644
December	1st to 10th	Night	19% 12% 4 8% 5% 5% 4 4 5% 7% 28%	2660
	11th to 20th	Night	21% 10% 3 8% 5% 5% 4 4 6% 6% 28%	3288
	21st to end	Night	27% 12% 4 9% 5% 4 4 3 5% 5% 23%	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	56% 3 11% 23% 7% 1	2518
	11th to 20th	Day	62% 4 11% 16% 5% 1	2520
	21st to end	Day	64% 4 11% 15% 5% 1	2871
February	1st to 10th	Day	58% 5% 11% 18% 7% 1	1710
	11th to 20th	Day	57% 5% 8% 19% 10% 2	1809
	21st to end	Day	56% 4 10% 18% 11% 1	1570
March	1st to 10th	Day	61% 3 10% 16% 8% 1	3119
	11th to 20th	Day	52% 3 16% 17% 10% 2	3316
	21st to end	Day	53% 3 5% 18% 18% 3	4150
April	1st to 10th	Day	52% 4 7% 21% 13% 3	2280
	11th to 20th	Day	48% 4 11% 22% 14% 2	2254
	21st to end	Day	52% 3 8% 20% 13% 3	2361
May	1st to 10th	Day	56% 3 9% 21% 10% 1	4244
	11th to 20th	Day	51% 3 13% 23% 9% 1	4402
	21st to end	Day	40% 5% 13% 28% 13% 1	4837
June	1st to 10th	Day	48% 6% 13% 21% 11% 1	2660
	11th to 20th	Day	45% 5% 15% 22% 13% 1	2660
	21st to end	Day	44% 6% 15% 22% 12% 1	2660
July	1st to 10th	Day	40% 8% 14% 24% 13%	4370
	11th to 20th	Day	37% 7% 15% 30% 10%	4365
	21st to end	Day	44% 5% 15% 24% 11%	4661
August	1st to 10th	Day	45% 6% 15% 22% 11% 1	4387
	11th to 20th	Day	44% 6% 17% 26% 7%	3783
	21st to end	Day	38% 7% 15% 30% 10% 1	4180
September	1st to 10th	Day	37% 6% 12% 31% 13% 1	2280
	11th to 20th	Day	35% 4 12% 29% 18% 1	2204
	21st to end	Day	41% 4 11% 27% 14% 2	2090
October	1st to 10th	Day	45% 5% 9% 25% 15% 1	3266
	11th to 20th	Day	40% 3 14% 27% 16% 1	3140
	21st to end	Day	36% 5% 15% 30% 13% 1	3095
November	1st to 10th	Day	41% 4 15% 25% 13% 1	1752
	11th to 20th	Day	49% 4 10% 21% 14% 2	1710
	21st to end	Day	52% 4 16% 19% 8% 1	1535
December	1st to 10th	Day	61% 4 11% 16% 7% 1	1520
	11th to 20th	Day	56% 4 16% 17% 6% 1	1906
	21st to end	Day	68% 3 8% 14% 6%	2772
January	1st to 10th	Night	55% 3 14% 19% 9% 1	4429
	11th to 20th	Night	58% 4 9% 19% 8% 2	4440
	21st to end	Night	64% 2 10% 16% 7% 1	4784
February	1st to 10th	Night	56% 4 11% 20% 8% 1	2470
	11th to 20th	Night	52% 5% 10% 20% 12% 1	2266
	21st to end	Night	52% 5% 11% 21% 8% 2	1884
March	1st to 10th	Night	59% 3 8% 19% 10% 1	3734
	11th to 20th	Night	52% 3 11% 25% 8% 1	3640
	21st to end	Night	55% 3 5% 17% 16% 3	3481
April	1st to 10th	Night	51% 4 10% 21% 13% 2	1900
	11th to 20th	Night	50% 3 9% 22% 14% 1	1875
	21st to end	Night	47% 4 9% 20% 16% 4	1819
May	1st to 10th	Night	55% 3 11% 17% 12% 2	2744
	11th to 20th	Night	54% 3 12% 21% 9% 1	2496
	21st to end	Night	44% 4 14% 20% 16% 2	2739
June	1st to 10th	Night	44% 4 12% 26% 13% 2	1520
	11th to 20th	Night	40% 5% 16% 25% 13% 1	1520
	21st to end	Night	37% 6% 15% 27% 14%	1520
July	1st to 10th	Night	43% 5% 14% 22% 15% 1	2480
	11th to 20th	Night	40% 6% 14% 24% 16%	2472
	21st to end	Night	42% 6% 11% 28% 11% 1	2651
August	1st to 10th	Night	46% 6% 14% 24% 9%	2516
	11th to 20th	Night	43% 6% 17% 24% 10%	3066
	21st to end	Night	35% 4 15% 34% 10% 1	3476
September	1st to 10th	Night	37% 5% 12% 30% 15% 1	1900
	11th to 20th	Night	35% 3 11% 28% 21% 1	1976
	21st to end	Night	40% 4 11% 27% 17% 2	2090
October	1st to 10th	Night	47% 5% 12% 23% 13% 1	3693
	11th to 20th	Night	34% 3 14% 27% 21% 1	3779
	21st to end	Night	41% 5% 13% 30% 11%	4452
November	1st to 10th	Night	43% 4 11% 24% 16% 2	2531
	11th to 20th	Night	47% 5% 10% 24% 13% 2	2470
	21st to end	Night	47% 4 17% 22% 9% 1	2644
December	1st to 10th	Night	56% 4 12% 19% 8%	2660
	11th to 20th	Night	55% 6% 13% 17% 8% 1	3288
	21st to end	Night	64% 3 11% 18% 5%	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	27% 23% 25% 19% 5% 1	180
	11th to 20th	Day	25% 26% 36% 11% 1 1	180
	21st to end	Day	19% 27% 35% 13% 5%	227
February	1st to 10th	Day	30% 30% 27% 12% 1	270
	11th to 20th	Day	27% 29% 31% 12% 1	408
	21st to end	Day	29% 22% 31% 15% 3	382
March	1st to 10th	Day	27% 22% 34% 14% 3	460
	11th to 20th	Day	28% 25% 30% 13% 4 1	460
	21st to end	Day	32% 22% 25% 14% 5% 1	506
April	1st to 10th	Day	30% 22% 27% 14% 7% 1	460
	11th to 20th	Day	27% 26% 23% 14% 8% 2	452
	21st to end	Day	28% 21% 31% 13% 6% 2	460
May	1st to 10th	Day	31% 16% 28% 15% 7% 2	463
	11th to 20th	Day	20% 16% 33% 23% 8% 1	487
	21st to end	Day	17% 14% 29% 24% 13% 3	529
June	1st to 10th	Day	16% 17% 32% 20% 12% 2	490
	11th to 20th	Day	16% 14% 30% 26% 12% 2	490
	21st to end	Day	17% 16% 31% 23% 11% 2	490
July	1st to 10th	Day	14% 8% 28% 29% 16% 4	485
	11th to 20th	Day	12% 8% 32% 31% 14% 3	484
	21st to end	Day	14% 9% 34% 30% 10% 3	532
August	1st to 10th	Day	11% 9% 29% 27% 19% 5%	486
	11th to 20th	Day	15% 8% 27% 29% 15% 6%	479
	21st to end	Day	12% 11% 27% 27% 18% 4	539
September	1st to 10th	Day	16% 9% 25% 23% 18% 9%	490
	11th to 20th	Day	13% 9% 24% 21% 21% 12%	490
	21st to end	Day	17% 10% 27% 26% 13% 6%	490
October	1st to 10th	Day	26% 14% 25% 18% 13% 4	490
	11th to 20th	Day	20% 18% 26% 22% 12% 2	490
	21st to end	Day	27% 14% 29% 22% 7% 1	436
November	1st to 10th	Day	22% 14% 28% 23% 12% 1	392
	11th to 20th	Day	24% 22% 27% 20% 6% 1	370
	21st to end	Day	26% 23% 26% 23% 3	195
December	1st to 10th	Day	27% 27% 26% 13% 6%	180
	11th to 20th	Day	31% 22% 36% 9% 3	180
	21st to end	Day	29% 23% 32% 13% 3 1	198
January	1st to 10th	Night	22% 22% 31% 23% 2	760
	11th to 20th	Night	26% 20% 30% 21% 3	760
	21st to end	Night	17% 24% 34% 22% 2	836
February	1st to 10th	Night	23% 18% 36% 22% 2	760
	11th to 20th	Night	21% 23% 38% 16% 2	743
	21st to end	Night	28% 20% 31% 20% 2	628
March	1st to 10th	Night	23% 23% 34% 18% 3	760
	11th to 20th	Night	24% 21% 32% 19% 3	760
	21st to end	Night	24% 20% 30% 21% 5%	836
April	1st to 10th	Night	25% 19% 32% 21% 3	760
	11th to 20th	Night	24% 19% 30% 21% 6%	751
	21st to end	Night	24% 18% 29% 23% 6%	679
May	1st to 10th	Night	26% 14% 29% 21% 8% 1	513
	11th to 20th	Night	18% 13% 32% 29% 7% 1	374
	21st to end	Night	16% 7% 27% 36% 13% 1	411
June	1st to 10th	Night	18% 7% 30% 33% 11% 2	380
	11th to 20th	Night	17% 8% 24% 36% 14%	380
	21st to end	Night	16% 6% 27% 38% 13% 1	380
July	1st to 10th	Night	12% 6% 25% 36% 20% 1	370
	11th to 20th	Night	13% 6% 21% 41% 18% 1	368
	21st to end	Night	13% 4 26% 39% 17% 1	416
August	1st to 10th	Night	12% 3 23% 41% 20% 1	385
	11th to 20th	Night	17% 4 22% 35% 18% 4	714
	21st to end	Night	17% 6% 21% 34% 20% 1	836
September	1st to 10th	Night	14% 6% 24% 35% 20% 2	760
	11th to 20th	Night	16% 5% 24% 28% 21% 5%	760
	21st to end	Night	17% 7% 27% 31% 16% 2	760
October	1st to 10th	Night	23% 12% 23% 27% 15% 1	760
	11th to 20th	Night	19% 13% 29% 30% 9%	760
	21st to end	Night	27% 13% 30% 25% 6%	836
November	1st to 10th	Night	18% 15% 31% 28% 9%	779
	11th to 20th	Night	22% 19% 26% 25% 7% 1	760
	21st to end	Night	22% 16% 30% 26% 6%	760
December	1st to 10th	Night	26% 19% 32% 20% 3	760
	11th to 20th	Night	23% 22% 30% 20% 4	760
	21st to end	Night	30% 20% 28% 20% 2	836

Page generated at 2024-11-07 06:55:43. Version ac07

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