Mayo
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mayo clear sky chart from 2005-11-06 to 2024-12-09.

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	9% 11% 4 11% 8% 7% 6% 5% 7% 8% 23%	107563
	Night	7% 14% 5% 13% 9% 7% 6% 5% 7% 8% 18%	100749
Transparency	Day	54% 10% 16% 16% 5%	107238
	Night	60% 8% 12% 13% 6% 1	100722
Seeing	Day	13% 6% 17% 27% 25% 12%	17886
	Night	13% 3 13% 33% 29% 9%	23321

By Month

Percentage Cloud Cover NW (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	4 16% 5% 14% 16% 10% 7% 3 6% 7% 11%	1259
	11th to 20th	Day	4 13% 5% 16% 12% 10% 6% 3 4 9% 17%	1353
	21st to end	Day	5% 15% 6% 13% 8% 8% 9% 7% 8% 9% 12%	1868
February	1st to 10th	Day	3 10% 5% 14% 10% 8% 8% 7% 8% 10% 17%	1236
	11th to 20th	Day	3 10% 6% 17% 9% 6% 7% 7% 8% 12% 13%	1388
	21st to end	Day	2 9% 4 18% 12% 11% 10% 6% 11% 7% 11%	1342
March	1st to 10th	Day	1 15% 6% 18% 12% 7% 5% 4 6% 7% 20%	2990
	11th to 20th	Day	4 15% 6% 14% 9% 8% 7% 4 6% 7% 20%	3315
	21st to end	Day	1 10% 6% 15% 9% 7% 7% 4 7% 7% 27%	4101
April	1st to 10th	Day	3 12% 5% 12% 8% 6% 6% 6% 7% 8% 26%	2402
	11th to 20th	Day	4 15% 4 8% 6% 5% 5% 5% 7% 8% 32%	2626
	21st to end	Day	5% 14% 4 9% 6% 6% 6% 5% 7% 8% 32%	2819
May	1st to 10th	Day	10% 12% 4 11% 8% 7% 7% 6% 7% 8% 21%	5060
	11th to 20th	Day	7% 11% 4 9% 7% 7% 6% 5% 7% 8% 30%	5317
	21st to end	Day	12% 11% 4 10% 7% 6% 7% 5% 7% 8% 23%	6205
June	1st to 10th	Day	10% 9% 3 9% 7% 7% 7% 7% 9% 10% 23%	3462
	11th to 20th	Day	10% 9% 3 11% 8% 7% 7% 5% 8% 8% 23%	3762
	21st to end	Day	15% 8% 3 8% 8% 7% 6% 6% 7% 9% 22%	3717
July	1st to 10th	Day	10% 8% 3 10% 8% 8% 7% 6% 9% 10% 21%	5905
	11th to 20th	Day	14% 8% 4 9% 7% 7% 7% 6% 8% 9% 21%	5700
	21st to end	Day	8% 6% 3 8% 6% 7% 7% 6% 9% 11% 30%	5911
August	1st to 10th	Day	10% 7% 3 8% 5% 5% 5% 4 6% 7% 41%	5037
	11th to 20th	Day	13% 8% 3 9% 6% 6% 7% 6% 7% 8% 28%	4661
	21st to end	Day	13% 11% 4 11% 8% 7% 6% 5% 7% 9% 19%	4873
September	1st to 10th	Day	14% 11% 4 10% 7% 6% 6% 4 6% 8% 24%	2417
	11th to 20th	Day	13% 9% 4 10% 7% 7% 5% 4 7% 7% 28%	2280
	21st to end	Day	14% 12% 3 11% 7% 6% 6% 5% 6% 7% 23%	2015
October	1st to 10th	Day	9% 12% 4 9% 5% 6% 6% 4 5% 9% 30%	3144
	11th to 20th	Day	9% 14% 5% 11% 6% 6% 5% 3 5% 7% 28%	2685
	21st to end	Day	8% 15% 8% 21% 11% 6% 6% 4 4 5% 12%	2630
November	1st to 10th	Day	7% 18% 6% 16% 9% 6% 8% 5% 9% 6% 11%	1240
	11th to 20th	Day	6% 17% 8% 17% 11% 10% 8% 4 6% 6% 8%	1088
	21st to end	Day	6% 17% 8% 16% 10% 9% 8% 10% 8% 5% 5%	841
December	1st to 10th	Day	8% 16% 8% 16% 9% 5% 6% 7% 8% 9% 8%	792
	11th to 20th	Day	6% 17% 6% 13% 12% 9% 7% 7% 9% 10% 5%	962
	21st to end	Day	8% 14% 6% 15% 10% 6% 6% 6% 8% 11% 9%	1160
January	1st to 10th	Night	5% 15% 6% 18% 13% 8% 6% 5% 7% 8% 10%	5686
	11th to 20th	Night	5% 14% 5% 14% 9% 9% 6% 4 5% 8% 21%	5575
	21st to end	Night	7% 16% 6% 15% 10% 9% 7% 5% 6% 6% 12%	5787
February	1st to 10th	Night	3 11% 6% 12% 10% 9% 6% 7% 7% 10% 20%	2941
	11th to 20th	Night	4 13% 6% 13% 8% 6% 6% 6% 10% 11% 17%	2679
	21st to end	Night	2 10% 5% 12% 10% 9% 8% 7% 11% 9% 17%	2109
March	1st to 10th	Night	1 13% 4 17% 10% 8% 6% 5% 7% 8% 20%	3874
	11th to 20th	Night	4 14% 7% 15% 9% 7% 7% 5% 6% 7% 18%	3647
	21st to end	Night	4 16% 7% 17% 7% 6% 5% 4 4 5% 25%	3539
April	1st to 10th	Night	2 12% 6% 11% 8% 6% 7% 5% 8% 7% 27%	1777
	11th to 20th	Night	4 13% 4 10% 6% 6% 6% 6% 7% 9% 28%	1503
	21st to end	Night	5% 11% 4 8% 8% 7% 6% 6% 7% 7% 30%	1359
May	1st to 10th	Night	10% 9% 3 11% 7% 6% 7% 5% 8% 9% 24%	1900
	11th to 20th	Night	9% 12% 5% 12% 6% 6% 5% 4 5% 6% 30%	1577
	21st to end	Night	12% 11% 3 9% 7% 5% 7% 6% 7% 8% 25%	1370
June	1st to 10th	Night	12% 9% 3 9% 5% 6% 5% 5% 7% 11% 27%	717
	11th to 20th	Night	8% 7% 2 10% 7% 10% 7% 6% 9% 8% 25%	418
	21st to end	Night	14% 8% 3 9% 7% 5% 7% 4 6% 9% 26%	459
July	1st to 10th	Night	12% 9% 2 8% 6% 8% 7% 6% 8% 10% 24%	1060
	11th to 20th	Night	14% 10% 3 11% 5% 8% 7% 5% 8% 7% 21%	1260
	21st to end	Night	10% 9% 4 9% 6% 5% 7% 4 6% 8% 33%	1639
August	1st to 10th	Night	9% 5% 2 5% 5% 5% 6% 5% 8% 8% 43%	1893
	11th to 20th	Night	14% 7% 4 9% 6% 6% 6% 4 6% 8% 30%	2174
	21st to end	Night	14% 10% 4 11% 7% 7% 7% 6% 8% 8% 18%	2794
September	1st to 10th	Night	13% 11% 4 8% 7% 6% 6% 5% 7% 7% 27%	1760
	11th to 20th	Night	12% 8% 3 11% 7% 6% 7% 4 6% 8% 28%	1900
	21st to end	Night	16% 11% 4 8% 6% 7% 7% 5% 6% 6% 24%	2163
October	1st to 10th	Night	11% 13% 4 8% 6% 5% 5% 4 6% 6% 32%	3826
	11th to 20th	Night	10% 13% 5% 11% 7% 5% 5% 4 7% 8% 24%	4242
	21st to end	Night	7% 18% 8% 17% 9% 7% 6% 4 6% 7% 11%	4925
November	1st to 10th	Night	10% 20% 6% 16% 7% 6% 5% 5% 7% 6% 11%	3055
	11th to 20th	Night	6% 16% 7% 17% 11% 9% 8% 5% 7% 6% 8%	3291
	21st to end	Night	7% 17% 7% 15% 10% 8% 8% 8% 8% 6% 6%	3556
December	1st to 10th	Night	7% 19% 7% 16% 10% 7% 6% 6% 7% 7% 8%	3571
	11th to 20th	Night	6% 17% 7% 16% 11% 9% 8% 6% 8% 7% 6%	4230
	21st to end	Night	7% 19% 6% 13% 9% 8% 7% 5% 7% 9% 11%	6493

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	71% 7% 5% 9% 7% 2	1259
	11th to 20th	Day	65% 3 6% 10% 12% 3	1365
	21st to end	Day	62% 6% 10% 9% 12% 1	1868
February	1st to 10th	Day	58% 5% 10% 14% 12% 2	1236
	11th to 20th	Day	59% 9% 11% 13% 8%	1395
	21st to end	Day	62% 10% 11% 11% 5%	1342
March	1st to 10th	Day	63% 4 7% 16% 10%	2990
	11th to 20th	Day	61% 7% 10% 15% 7%	3315
	21st to end	Day	49% 13% 18% 14% 6%	4101
April	1st to 10th	Day	53% 9% 16% 15% 6% 1	2402
	11th to 20th	Day	46% 8% 18% 20% 7%	2626
	21st to end	Day	47% 9% 17% 21% 6%	2819
May	1st to 10th	Day	54% 10% 15% 16% 3 1	5060
	11th to 20th	Day	45% 10% 14% 23% 9%	5321
	21st to end	Day	53% 11% 14% 18% 5%	6206
June	1st to 10th	Day	50% 12% 15% 17% 5%	3462
	11th to 20th	Day	55% 10% 13% 17% 5%	3762
	21st to end	Day	54% 11% 15% 16% 4	3717
July	1st to 10th	Day	52% 15% 19% 11% 2	5814
	11th to 20th	Day	55% 11% 17% 15% 1	5601
	21st to end	Day	43% 12% 24% 21% 2	5723
August	1st to 10th	Day	41% 9% 21% 17% 11% 1	5018
	11th to 20th	Day	51% 11% 19% 16% 3	4708
	21st to end	Day	58% 10% 21% 10% 1	4872
September	1st to 10th	Day	56% 10% 18% 14% 1	2417
	11th to 20th	Day	52% 10% 21% 14% 2	2280
	21st to end	Day	57% 10% 16% 15% 2	2015
October	1st to 10th	Day	50% 9% 18% 20% 3	3144
	11th to 20th	Day	54% 9% 11% 25% 1	2685
	21st to end	Day	73% 9% 9% 10%	2630
November	1st to 10th	Day	67% 10% 10% 10% 3	1240
	11th to 20th	Day	75% 6% 8% 9% 1	1088
	21st to end	Day	71% 10% 10% 8% 2	841
December	1st to 10th	Day	68% 9% 10% 7% 6%	792
	11th to 20th	Day	68% 7% 7% 9% 9%	964
	21st to end	Day	64% 7% 8% 14% 6%	1160
January	1st to 10th	Night	68% 7% 9% 8% 6% 1	5686
	11th to 20th	Night	61% 5% 6% 8% 15% 6%	5625
	21st to end	Night	69% 5% 7% 9% 8% 2	5787
February	1st to 10th	Night	57% 6% 9% 15% 12% 1	2941
	11th to 20th	Night	55% 9% 9% 16% 10%	2683
	21st to end	Night	54% 9% 14% 14% 8%	2109
March	1st to 10th	Night	59% 5% 9% 15% 11%	3874
	11th to 20th	Night	62% 7% 10% 12% 9%	3649
	21st to end	Night	55% 13% 13% 12% 7%	3539
April	1st to 10th	Night	51% 10% 18% 14% 6% 1	1777
	11th to 20th	Night	49% 10% 14% 19% 8%	1503
	21st to end	Night	47% 10% 16% 20% 6% 1	1359
May	1st to 10th	Night	49% 11% 19% 18% 4	1900
	11th to 20th	Night	51% 8% 11% 26% 4	1577
	21st to end	Night	51% 12% 16% 15% 6%	1370
June	1st to 10th	Night	49% 12% 16% 18% 6%	717
	11th to 20th	Night	50% 14% 11% 20% 5%	418
	21st to end	Night	51% 12% 18% 16% 3	459
July	1st to 10th	Night	52% 15% 20% 9% 3	1042
	11th to 20th	Night	57% 11% 17% 13% 2	1236
	21st to end	Night	46% 9% 21% 22% 1	1588
August	1st to 10th	Night	36% 10% 23% 17% 13% 1	1887
	11th to 20th	Night	50% 9% 20% 20% 2	2193
	21st to end	Night	58% 11% 18% 12%	2794
September	1st to 10th	Night	54% 10% 19% 15% 2	1760
	11th to 20th	Night	52% 10% 19% 17% 3	1900
	21st to end	Night	58% 8% 11% 19% 3	2163
October	1st to 10th	Night	50% 8% 13% 26% 3	3826
	11th to 20th	Night	53% 10% 13% 20% 4	4242
	21st to end	Night	69% 8% 11% 11% 1	4925
November	1st to 10th	Night	68% 8% 12% 9% 3	3055
	11th to 20th	Night	73% 7% 11% 8% 1	3291
	21st to end	Night	69% 8% 10% 11% 2	3556
December	1st to 10th	Night	72% 7% 9% 9% 4	3571
	11th to 20th	Night	71% 7% 9% 8% 5%	4227
	21st to end	Night	66% 6% 8% 12% 6% 2	6493

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	7% 3 9% 28% 41% 12%	90
	11th to 20th	Day	10% 1 9% 37% 27% 17%	90
	21st to end	Day	15% 3 11% 29% 27% 15%	137
February	1st to 10th	Day	5% 4 9% 34% 32% 17%	276
	11th to 20th	Day	6% 3 16% 34% 24% 18%	365
	21st to end	Day	5% 4 12% 35% 28% 17%	307
March	1st to 10th	Day	5% 5% 15% 26% 26% 23%	370
	11th to 20th	Day	7% 4 17% 30% 24% 18%	370
	21st to end	Day	4 6% 15% 33% 27% 14%	488
April	1st to 10th	Day	10% 5% 19% 29% 28% 9%	550
	11th to 20th	Day	8% 5% 18% 32% 27% 10%	640
	21st to end	Day	10% 8% 22% 30% 21% 8%	650
May	1st to 10th	Day	12% 14% 26% 26% 16% 7%	653
	11th to 20th	Day	14% 8% 26% 26% 19% 8%	766
	21st to end	Day	15% 7% 21% 29% 23% 5%	940
June	1st to 10th	Day	13% 6% 17% 27% 27% 10%	912
	11th to 20th	Day	12% 4 15% 27% 30% 12%	1060
	21st to end	Day	15% 4 13% 25% 28% 15%	1060
July	1st to 10th	Day	12% 4 15% 25% 31% 13%	981
	11th to 20th	Day	16% 4 12% 24% 27% 17%	852
	21st to end	Day	14% 3 13% 21% 30% 19%	800
August	1st to 10th	Day	15% 6% 15% 24% 25% 15%	676
	11th to 20th	Day	18% 7% 18% 30% 19% 7%	665
	21st to end	Day	18% 5% 15% 25% 28% 9%	748
September	1st to 10th	Day	16% 8% 21% 19% 23% 14%	579
	11th to 20th	Day	13% 8% 18% 24% 25% 12%	490
	21st to end	Day	20% 9% 18% 24% 18% 11%	430
October	1st to 10th	Day	18% 7% 23% 26% 14% 10%	390
	11th to 20th	Day	21% 7% 16% 23% 20% 13%	390
	21st to end	Day	20% 3 13% 31% 20% 13%	354
November	1st to 10th	Day	14% 5% 16% 32% 25% 9%	200
	11th to 20th	Day	12% 2 9% 33% 23% 22%	200
	21st to end	Day	13% 3 11% 38% 21% 15%	120
December	1st to 10th	Day	15% 3 12% 40% 21% 8%	98
	11th to 20th	Day	12% 3 19% 26% 30% 10%	90
	21st to end	Day	8% 2 11% 35% 28% 15%	99
January	1st to 10th	Night	11% 2 10% 35% 29% 13%	1040
	11th to 20th	Night	15% 3 12% 41% 22% 8%	991
	21st to end	Night	12% 3 15% 37% 26% 7%	935
February	1st to 10th	Night	8% 2 14% 37% 31% 9%	850
	11th to 20th	Night	9% 2 16% 39% 26% 8%	834
	21st to end	Night	6% 2 12% 41% 30% 10%	703
March	1st to 10th	Night	6% 2 13% 36% 32% 12%	800
	11th to 20th	Night	7% 3 12% 35% 36% 8%	674
	21st to end	Night	7% 6% 11% 35% 32% 9%	627
April	1st to 10th	Night	6% 4 12% 35% 35% 8%	570
	11th to 20th	Night	9% 1 16% 32% 34% 8%	563
	21st to end	Night	8% 5% 13% 31% 36% 6%	494
May	1st to 10th	Night	8% 8% 16% 36% 28% 4	380
	11th to 20th	Night	16% 5% 19% 35% 24% 2	290
	21st to end	Night	12% 3 12% 45% 27% 2	206
June	1st to 10th	Night	16% 4 11% 24% 37% 7%	190
	11th to 20th	Night	8% 3 12% 30% 43% 4	190
	21st to end	Night	17% 4 7% 26% 38% 7%	190
July	1st to 10th	Night	16% 1 9% 32% 35% 8%	185
	11th to 20th	Night	19% 4 9% 20% 41% 7%	184
	21st to end	Night	11% 1 5% 22% 48% 12%	219
August	1st to 10th	Night	14% 3 13% 22% 42% 6%	378
	11th to 20th	Night	18% 4 11% 29% 29% 9%	514
	21st to end	Night	19% 3 11% 24% 34% 10%	627
September	1st to 10th	Night	19% 3 12% 26% 31% 8%	570
	11th to 20th	Night	16% 4 10% 29% 32% 8%	570
	21st to end	Night	22% 4 12% 29% 23% 10%	723
October	1st to 10th	Night	22% 4 14% 32% 22% 6%	760
	11th to 20th	Night	20% 3 14% 29% 27% 7%	810
	21st to end	Night	19% 3 12% 32% 26% 7%	946
November	1st to 10th	Night	18% 3 14% 33% 23% 9%	880
	11th to 20th	Night	12% 3 9% 32% 29% 15%	991
	21st to end	Night	14% 4 14% 30% 26% 12%	1100
December	1st to 10th	Night	14% 4 14% 36% 23% 9%	1091
	11th to 20th	Night	13% 4 16% 33% 25% 10%	1040
	21st to end	Night	11% 4 12% 33% 25% 15%	1206

Page generated at 2024-12-06 00:54:50. Version ac07

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