Myra
Clear Sky Chart
History

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

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	12% 8% 3 7% 5% 4 5% 4 6% 7% 39%	126836
	Night	12% 9% 3 8% 4 4 4 4 5% 7% 40%	123465
Transparency	Day	42% 6% 12% 24% 13% 1	130336
	Night	43% 5% 12% 23% 15% 2	128039
Seeing	Day	15% 11% 30% 27% 13% 4	17297
	Night	17% 10% 31% 28% 12% 1	27108

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	8% 10% 5% 12% 6% 5% 5% 5% 6% 7% 31%	3617
	11th to 20th	Day	8% 10% 6% 11% 5% 4 5% 5% 6% 7% 33%	3620
	21st to end	Day	13% 15% 6% 8% 4 3 3 3 4 6% 35%	3982
February	1st to 10th	Day	10% 14% 6% 10% 4 3 5% 4 5% 7% 32%	1795
	11th to 20th	Day	12% 13% 4 7% 5% 4 5% 4 5% 5% 36%	1943
	21st to end	Day	11% 13% 5% 9% 5% 4 4 4 5% 6% 32%	1650
March	1st to 10th	Day	13% 8% 2 7% 4 3 4 3 5% 7% 44%	4480
	11th to 20th	Day	10% 7% 3 7% 5% 4 4 3 5% 7% 43%	4671
	21st to end	Day	21% 13% 4 9% 5% 4 4 3 4 5% 28%	5967
April	1st to 10th	Day	17% 13% 2 8% 6% 4 5% 4 5% 5% 32%	2400
	11th to 20th	Day	15% 11% 3 8% 5% 4 5% 3 5% 6% 34%	2374
	21st to end	Day	17% 10% 3 8% 4 5% 5% 4 5% 7% 33%	2545
May	1st to 10th	Day	14% 9% 2 7% 4 4 4 3 5% 7% 41%	5897
	11th to 20th	Day	12% 6% 3 7% 5% 4 4 4 6% 8% 42%	6319
	21st to end	Day	15% 7% 2 6% 4 4 4 4 6% 9% 40%	6935
June	1st to 10th	Day	9% 5% 2 6% 5% 4 5% 3 7% 8% 45%	2800
	11th to 20th	Day	11% 6% 2 7% 4 4 4 4 7% 8% 42%	2800
	21st to end	Day	9% 6% 2 6% 4 4 5% 4 8% 9% 42%	2800
July	1st to 10th	Day	11% 6% 3 7% 4 4 5% 5% 7% 10% 39%	6360
	11th to 20th	Day	6% 4 2 5% 4 5% 5% 5% 7% 10% 46%	6360
	21st to end	Day	8% 5% 2 6% 4 4 5% 4 6% 9% 45%	6924
August	1st to 10th	Day	9% 5% 2 7% 5% 5% 6% 5% 7% 9% 41%	4547
	11th to 20th	Day	11% 5% 2 6% 5% 4 5% 4 7% 8% 44%	3955
	21st to end	Day	10% 6% 2 6% 5% 4 5% 4 6% 8% 44%	4312
September	1st to 10th	Day	9% 6% 3 6% 5% 4 5% 4 6% 7% 45%	2400
	11th to 20th	Day	11% 4 2 5% 3 4 4 4 6% 8% 49%	2280
	21st to end	Day	12% 7% 2 6% 3 4 5% 4 6% 8% 43%	2200
October	1st to 10th	Day	13% 6% 2 6% 3 4 4 4 5% 7% 45%	2128
	11th to 20th	Day	20% 10% 2 6% 4 5% 5% 3 5% 8% 32%	1960
	21st to end	Day	15% 9% 2 9% 5% 4 5% 4 5% 6% 36%	1980
November	1st to 10th	Day	10% 9% 3 7% 5% 3 4 3 5% 7% 43%	1780
	11th to 20th	Day	11% 11% 3 9% 7% 6% 5% 3 6% 8% 31%	1800
	21st to end	Day	16% 12% 3 7% 4 4 4 3 4 6% 37%	1655
December	1st to 10th	Day	9% 8% 4 8% 5% 4 5% 4 8% 9% 36%	2610
	11th to 20th	Day	12% 16% 4 8% 5% 5% 5% 4 6% 7% 28%	3008
	21st to end	Day	20% 19% 8% 12% 4 3 3 3 4 4 18%	3982
January	1st to 10th	Night	10% 9% 6% 11% 6% 4 4 3 4 5% 37%	6348
	11th to 20th	Night	10% 11% 5% 13% 6% 5% 6% 5% 5% 6% 27%	6360
	21st to end	Night	11% 13% 5% 9% 5% 4 4 3 5% 7% 34%	6996
February	1st to 10th	Night	12% 12% 4 8% 5% 4 5% 4 4 6% 35%	2603
	11th to 20th	Night	11% 10% 3 8% 5% 4 5% 4 5% 5% 40%	2341
	21st to end	Night	16% 13% 3 6% 4 4 4 4 5% 6% 36%	1980
March	1st to 10th	Night	15% 8% 2 6% 4 3 4 3 5% 6% 44%	5373
	11th to 20th	Night	10% 6% 2 6% 4 4 5% 4 6% 9% 45%	5318
	21st to end	Night	18% 12% 4 10% 5% 4 4 3 4 5% 31%	4962
April	1st to 10th	Night	16% 10% 3 8% 4 4 4 3 5% 6% 38%	2000
	11th to 20th	Night	19% 9% 3 6% 4 3 4 4 5% 6% 38%	1975
	21st to end	Night	16% 9% 2 6% 4 3 4 4 5% 7% 40%	1854
May	1st to 10th	Night	15% 8% 2 7% 4 4 4 3 5% 7% 40%	3998
	11th to 20th	Night	9% 7% 4 8% 5% 5% 5% 5% 6% 7% 40%	3596
	21st to end	Night	17% 7% 3 6% 4 4 4 4 4 7% 40%	3942
June	1st to 10th	Night	10% 5% 2 6% 4 5% 4 4 6% 9% 47%	1600
	11th to 20th	Night	13% 5% 3 5% 4 5% 4 4 6% 9% 44%	1600
	21st to end	Night	9% 6% 2 7% 5% 4 4 4 6% 7% 47%	1600
July	1st to 10th	Night	9% 6% 3 6% 4 4 4 4 6% 9% 44%	3618
	11th to 20th	Night	5% 5% 2 5% 4 4 4 4 6% 8% 53%	3617
	21st to end	Night	6% 4 2 5% 4 4 5% 5% 6% 8% 51%	3947
August	1st to 10th	Night	10% 5% 2 6% 4 4 5% 3 6% 8% 48%	2610
	11th to 20th	Night	9% 5% 2 6% 5% 4 4 3 5% 8% 48%	3091
	21st to end	Night	7% 5% 2 6% 4 4 4 4 6% 8% 50%	3586
September	1st to 10th	Night	9% 5% 2 5% 4 4 3 3 4 6% 55%	2000
	11th to 20th	Night	10% 4 1 5% 4 3 4 3 6% 7% 54%	2100
	21st to end	Night	12% 6% 3 6% 4 3 4 3 5% 7% 48%	2200
October	1st to 10th	Night	13% 6% 2 6% 4 3 3 3 3 7% 50%	2270
	11th to 20th	Night	17% 7% 3 6% 4 4 4 3 5% 7% 41%	2440
	21st to end	Night	17% 8% 3 7% 4 5% 4 3 6% 7% 37%	2860
November	1st to 10th	Night	12% 7% 2 6% 3 4 4 4 5% 6% 46%	2563
	11th to 20th	Night	14% 9% 3 8% 5% 5% 5% 4 6% 7% 35%	2600
	21st to end	Night	15% 10% 3 6% 5% 4 5% 3 5% 6% 36%	2742
December	1st to 10th	Night	10% 10% 3 7% 4 3 4 3 5% 8% 44%	4580
	11th to 20th	Night	15% 15% 5% 10% 5% 4 4 3 5% 5% 29%	5199
	21st to end	Night	19% 18% 5% 10% 5% 5% 4 3 4 5% 21%	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	53% 5% 14% 20% 8%	3618
	11th to 20th	Day	50% 6% 10% 16% 17% 2	3620
	21st to end	Day	52% 4 9% 21% 14%	3982
February	1st to 10th	Day	51% 6% 12% 21% 9% 1	1795
	11th to 20th	Day	49% 5% 10% 23% 11% 2	1953
	21st to end	Day	52% 6% 10% 19% 11% 2	1650
March	1st to 10th	Day	41% 5% 11% 25% 12% 6%	4480
	11th to 20th	Day	40% 5% 15% 24% 14% 2	4671
	21st to end	Day	58% 5% 11% 15% 11% 1	5969
April	1st to 10th	Day	52% 7% 11% 19% 10%	2400
	11th to 20th	Day	49% 6% 11% 20% 12% 2	2374
	21st to end	Day	49% 7% 13% 18% 11% 1	2545
May	1st to 10th	Day	42% 6% 11% 24% 16% 1	5932
	11th to 20th	Day	39% 8% 13% 25% 13% 1	6323
	21st to end	Day	40% 7% 11% 27% 13% 2	6949
June	1st to 10th	Day	35% 7% 14% 27% 16% 2	2800
	11th to 20th	Day	38% 7% 15% 23% 16% 1	2800
	21st to end	Day	36% 9% 15% 23% 15% 2	2800
July	1st to 10th	Day	39% 7% 12% 31% 10% 1	6291
	11th to 20th	Day	31% 8% 15% 32% 14% 1	6285
	21st to end	Day	33% 8% 16% 24% 18% 2	6728
August	1st to 10th	Day	37% 7% 15% 29% 11% 1	4532
	11th to 20th	Day	35% 7% 14% 32% 11% 1	3994
	21st to end	Day	36% 7% 14% 24% 18% 1	4311
September	1st to 10th	Day	37% 8% 11% 28% 16% 2	2400
	11th to 20th	Day	33% 7% 13% 31% 16% 1	2280
	21st to end	Day	39% 6% 12% 31% 13%	2200
October	1st to 10th	Day	24% 4 7% 39% 25% 1	3466
	11th to 20th	Day	38% 5% 10% 26% 22% 1	3176
	21st to end	Day	41% 4 11% 28% 13% 2	3180
November	1st to 10th	Day	41% 5% 14% 25% 14% 1	1780
	11th to 20th	Day	51% 6% 13% 20% 9% 1	1800
	21st to end	Day	50% 5% 13% 24% 8%	1655
December	1st to 10th	Day	43% 6% 20% 24% 6% 1	2610
	11th to 20th	Day	53% 5% 13% 17% 10% 1	3005
	21st to end	Day	70% 4 6% 12% 7%	3982
January	1st to 10th	Night	51% 4 8% 23% 14% 1	6348
	11th to 20th	Night	57% 5% 9% 12% 16% 1	6360
	21st to end	Night	51% 5% 13% 18% 12%	6996
February	1st to 10th	Night	50% 5% 11% 19% 13% 2	2603
	11th to 20th	Night	45% 5% 10% 23% 15% 2	2342
	21st to end	Night	48% 5% 13% 20% 12% 3	1980
March	1st to 10th	Night	42% 4 14% 24% 13% 4	5373
	11th to 20th	Night	35% 4 15% 27% 15% 4	5318
	21st to end	Night	56% 5% 9% 16% 12% 2	4962
April	1st to 10th	Night	47% 5% 10% 20% 17% 1	2000
	11th to 20th	Night	47% 4 9% 20% 16% 3	1975
	21st to end	Night	43% 6% 12% 23% 14% 2	1854
May	1st to 10th	Night	42% 5% 12% 19% 18% 2	4025
	11th to 20th	Night	40% 7% 14% 21% 16% 2	3597
	21st to end	Night	44% 6% 9% 24% 13% 5%	3950
June	1st to 10th	Night	34% 6% 13% 28% 18% 1	1600
	11th to 20th	Night	36% 6% 12% 24% 19% 2	1600
	21st to end	Night	36% 6% 15% 23% 17% 2	1600
July	1st to 10th	Night	36% 5% 14% 32% 11% 3	3580
	11th to 20th	Night	27% 6% 15% 31% 19% 2	3572
	21st to end	Night	28% 7% 16% 23% 23% 3	3832
August	1st to 10th	Night	33% 6% 15% 25% 19% 2	2601
	11th to 20th	Night	33% 6% 14% 31% 15% 1	3118
	21st to end	Night	30% 6% 13% 27% 20% 4	3586
September	1st to 10th	Night	29% 7% 12% 28% 22% 2	2000
	11th to 20th	Night	30% 5% 10% 35% 18% 1	2100
	21st to end	Night	37% 4 10% 32% 16% 1	2200
October	1st to 10th	Night	26% 4 7% 39% 23% 1	3712
	11th to 20th	Night	34% 4 13% 26% 20% 3	3963
	21st to end	Night	42% 4 9% 27% 17% 1	4610
November	1st to 10th	Night	38% 5% 12% 26% 16% 2	2563
	11th to 20th	Night	47% 7% 14% 20% 11% 2	2600
	21st to end	Night	48% 6% 14% 22% 9% 1	2742
December	1st to 10th	Night	39% 5% 18% 28% 7% 3	4580
	11th to 20th	Night	58% 6% 9% 14% 12% 1	5201
	21st to end	Night	66% 5% 8% 14% 6%	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	16% 16% 39% 23% 5% 1	300
	11th to 20th	Day	14% 22% 34% 24% 6%	300
	21st to end	Day	21% 15% 38% 20% 5% 1	330
February	1st to 10th	Day	15% 17% 45% 16% 5% 1	300
	11th to 20th	Day	19% 25% 34% 17% 5%	300
	21st to end	Day	20% 23% 43% 13%	249
March	1st to 10th	Day	17% 22% 43% 15% 2	300
	11th to 20th	Day	22% 20% 32% 20% 6% 1	325
	21st to end	Day	27% 13% 31% 21% 5% 1	550
April	1st to 10th	Day	25% 15% 35% 20% 5%	500
	11th to 20th	Day	21% 20% 26% 22% 9% 2	492
	21st to end	Day	22% 12% 31% 24% 10% 1	500
May	1st to 10th	Day	21% 11% 36% 24% 7% 2	512
	11th to 20th	Day	18% 10% 32% 26% 11% 3	725
	21st to end	Day	16% 9% 30% 28% 13% 5%	789
June	1st to 10th	Day	9% 7% 32% 35% 13% 4	730
	11th to 20th	Day	14% 7% 30% 32% 13% 4	730
	21st to end	Day	11% 7% 32% 31% 14% 4	730
July	1st to 10th	Day	9% 2 21% 35% 24% 9%	721
	11th to 20th	Day	9% 6% 25% 34% 19% 8%	718
	21st to end	Day	6% 3 27% 37% 21% 6%	794
August	1st to 10th	Day	7% 4 22% 38% 20% 9%	723
	11th to 20th	Day	11% 4 19% 29% 26% 11%	519
	21st to end	Day	10% 6% 20% 33% 22% 9%	583
September	1st to 10th	Day	11% 8% 24% 28% 20% 9%	530
	11th to 20th	Day	9% 4 19% 34% 23% 11%	530
	21st to end	Day	15% 10% 25% 26% 19% 5%	530
October	1st to 10th	Day	17% 8% 27% 29% 15% 4	458
	11th to 20th	Day	21% 17% 35% 20% 7%	330
	21st to end	Day	21% 16% 39% 20% 4 1	363
November	1st to 10th	Day	16% 18% 33% 24% 9% 1	306
	11th to 20th	Day	16% 21% 35% 21% 6%	300
	21st to end	Day	23% 14% 39% 19% 5%	300
December	1st to 10th	Day	18% 19% 40% 16% 5% 1	300
	11th to 20th	Day	22% 21% 34% 15% 7% 1	300
	21st to end	Day	25% 20% 35% 15% 3 2	330
January	1st to 10th	Night	17% 18% 38% 22% 5%	1000
	11th to 20th	Night	19% 16% 40% 19% 6% 1	1000
	21st to end	Night	19% 13% 39% 24% 5%	1100
February	1st to 10th	Night	19% 15% 38% 23% 5%	1000
	11th to 20th	Night	17% 17% 37% 24% 4	786
	21st to end	Night	24% 14% 40% 17% 4	660
March	1st to 10th	Night	19% 13% 37% 23% 8% 1	800
	11th to 20th	Night	14% 14% 38% 26% 7% 1	782
	21st to end	Night	21% 8% 28% 33% 8% 2	660
April	1st to 10th	Night	21% 12% 36% 25% 7% 1	600
	11th to 20th	Night	23% 10% 33% 25% 7% 1	593
	21st to end	Night	20% 8% 30% 31% 11% 1	600
May	1st to 10th	Night	18% 8% 29% 36% 8% 1	600
	11th to 20th	Night	18% 6% 29% 33% 14% 1	591
	21st to end	Night	14% 5% 22% 36% 20% 2	650
June	1st to 10th	Night	11% 4 26% 39% 19% 1	600
	11th to 20th	Night	14% 3 30% 36% 17% 1	600
	21st to end	Night	11% 3 25% 43% 18% 1	600
July	1st to 10th	Night	8% 2 15% 40% 30% 4	585
	11th to 20th	Night	6% 2 21% 41% 27% 3	582
	21st to end	Night	7% 2 19% 44% 27% 2	657
August	1st to 10th	Night	7% 2 17% 44% 27% 3	597
	11th to 20th	Night	10% 2 15% 39% 28% 6%	594
	21st to end	Night	8% 2 20% 39% 27% 4	660
September	1st to 10th	Night	10% 4 21% 34% 25% 6%	600
	11th to 20th	Night	10% 4 20% 30% 27% 8%	700
	21st to end	Night	14% 9% 23% 28% 22% 5%	800
October	1st to 10th	Night	16% 7% 27% 30% 19% 2	800
	11th to 20th	Night	20% 12% 32% 27% 8% 1	800
	21st to end	Night	21% 10% 33% 26% 9%	880
November	1st to 10th	Night	16% 10% 38% 25% 10% 1	789
	11th to 20th	Night	19% 16% 36% 22% 6%	800
	21st to end	Night	21% 14% 38% 22% 6%	942
December	1st to 10th	Night	21% 17% 37% 21% 5%	1000
	11th to 20th	Night	23% 14% 37% 20% 5% 1	1000
	21st to end	Night	27% 15% 35% 19% 3	1100

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