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 2024-01-16.

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	13% 8% 4 6% 5% 3 5% 5% 6% 8% 38%	74828
	Night	14% 8% 3 6% 5% 3 5% 5% 5% 7% 39%	74998
Transparency	Day	44% 7% 13% 22% 12% 1	74529
	Night	44% 6% 12% 22% 13% 2	74818
Seeing	Day	15% 11% 30% 27% 13% 4	14738
	Night	17% 10% 31% 28% 12% 1	24734

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	11% 11% 6% 7% 6% 3 5% 5% 5% 7% 34%	1517
	11th to 20th	Day	12% 16% 7% 10% 8% 3 5% 5% 5% 6% 23%	1480
	21st to end	Day	11% 14% 8% 10% 6% 3 5% 5% 5% 7% 26%	1584
February	1st to 10th	Day	11% 12% 7% 9% 5% 3 4 5% 5% 7% 33%	1616
	11th to 20th	Day	13% 12% 4 6% 5% 3 5% 5% 5% 5% 36%	1744
	21st to end	Day	12% 13% 5% 9% 6% 3 5% 5% 5% 6% 30%	1480
March	1st to 10th	Day	14% 11% 4 7% 5% 3 5% 5% 5% 7% 35%	1800
	11th to 20th	Day	11% 10% 4 7% 6% 3 5% 5% 4 7% 37%	1853
	21st to end	Day	18% 10% 4 7% 6% 3 5% 4 5% 7% 30%	2376
April	1st to 10th	Day	17% 11% 4 7% 6% 3 4 5% 5% 6% 31%	2160
	11th to 20th	Day	16% 10% 4 7% 7% 3 5% 4 5% 6% 34%	2134
	21st to end	Day	19% 10% 3 7% 4 3 5% 5% 5% 7% 32%	2290
May	1st to 10th	Day	16% 8% 3 7% 5% 4 5% 5% 6% 9% 32%	2347
	11th to 20th	Day	16% 6% 3 5% 6% 4 5% 5% 5% 7% 38%	2479
	21st to end	Day	13% 7% 3 6% 4 3 5% 5% 6% 9% 40%	2725
June	1st to 10th	Day	9% 5% 2 5% 6% 3 5% 4 6% 8% 46%	2520
	11th to 20th	Day	11% 6% 2 6% 5% 3 4 5% 7% 9% 43%	2520
	21st to end	Day	9% 5% 2 5% 5% 3 5% 5% 7% 10% 43%	2520
July	1st to 10th	Day	7% 4 2 4 4 3 6% 6% 7% 10% 48%	2520
	11th to 20th	Day	8% 4 2 5% 5% 3 5% 6% 6% 9% 47%	2520
	21st to end	Day	7% 4 2 5% 5% 3 5% 6% 7% 10% 48%	2743
August	1st to 10th	Day	7% 3 2 6% 6% 4 6% 8% 7% 9% 43%	2505
	11th to 20th	Day	11% 5% 2 5% 5% 3 5% 5% 7% 10% 43%	2189
	21st to end	Day	11% 6% 2 4 5% 3 5% 5% 6% 8% 45%	2376
September	1st to 10th	Day	10% 6% 3 6% 6% 3 5% 5% 6% 7% 43%	2160
	11th to 20th	Day	12% 4 2 5% 4 3 5% 5% 6% 8% 47%	2052
	21st to end	Day	12% 7% 3 5% 5% 3 5% 5% 6% 8% 43%	1980
October	1st to 10th	Day	15% 7% 2 6% 5% 3 4 5% 5% 7% 43%	1916
	11th to 20th	Day	21% 9% 3 6% 5% 3 5% 5% 5% 8% 30%	1764
	21st to end	Day	17% 8% 3 8% 6% 3 4 5% 5% 6% 35%	1782
November	1st to 10th	Day	11% 9% 3 6% 6% 2 4 4 5% 7% 43%	1672
	11th to 20th	Day	11% 10% 4 8% 8% 4 5% 4 5% 8% 32%	1710
	21st to end	Day	16% 10% 3 6% 5% 4 4 4 4 6% 38%	1573
December	1st to 10th	Day	15% 10% 4 8% 7% 3 5% 4 6% 8% 30%	1520
	11th to 20th	Day	12% 13% 4 7% 6% 3 5% 5% 6% 7% 31%	1918
	21st to end	Day	19% 18% 9% 12% 5% 3 4 4 4 5% 19%	2783
January	1st to 10th	Night	13% 12% 6% 7% 5% 3 4 4 4 4 37%	2648
	11th to 20th	Night	15% 12% 5% 10% 7% 3 5% 5% 4 6% 28%	2591
	21st to end	Night	13% 11% 5% 9% 6% 3 5% 5% 6% 8% 29%	2772
February	1st to 10th	Night	13% 12% 5% 8% 6% 3 5% 5% 4 6% 34%	2343
	11th to 20th	Night	12% 9% 3 7% 6% 3 5% 5% 5% 5% 39%	2101
	21st to end	Night	18% 12% 3 6% 4 3 3 4 4 6% 35%	1776
March	1st to 10th	Night	15% 9% 4 6% 5% 3 4 6% 5% 7% 37%	2160
	11th to 20th	Night	12% 6% 3 6% 5% 3 5% 5% 6% 8% 42%	2122
	21st to end	Night	18% 9% 4 6% 5% 3 4 6% 5% 5% 34%	1980
April	1st to 10th	Night	16% 10% 3 8% 5% 3 4 4 5% 6% 37%	1800
	11th to 20th	Night	20% 8% 3 5% 5% 2 4 5% 4 6% 37%	1775
	21st to end	Night	17% 8% 3 5% 4 2 4 5% 5% 7% 39%	1670
May	1st to 10th	Night	16% 8% 3 8% 6% 3 5% 5% 5% 9% 34%	1611
	11th to 20th	Night	16% 7% 2 6% 5% 3 5% 6% 6% 8% 37%	1416
	21st to end	Night	12% 6% 3 5% 5% 3 5% 6% 5% 10% 41%	1551
June	1st to 10th	Night	10% 4 2 4 4 3 5% 5% 5% 9% 47%	1440
	11th to 20th	Night	13% 4 3 5% 4 3 4 4 6% 8% 45%	1440
	21st to end	Night	8% 5% 3 6% 5% 2 5% 4 5% 8% 49%	1440
July	1st to 10th	Night	7% 3 2 4 5% 2 3 4 5% 10% 53%	1440
	11th to 20th	Night	6% 3 2 4 4 3 5% 6% 6% 8% 53%	1440
	21st to end	Night	6% 3 2 3 4 3 6% 6% 7% 9% 52%	1575
August	1st to 10th	Night	6% 4 3 5% 5% 3 5% 5% 7% 9% 50%	1432
	11th to 20th	Night	8% 3 2 4 5% 3 4 5% 4 9% 54%	1710
	21st to end	Night	8% 4 2 5% 4 3 4 5% 5% 7% 53%	1980
September	1st to 10th	Night	10% 5% 2 4 5% 3 3 4 4 6% 54%	1800
	11th to 20th	Night	11% 4 1 4 4 3 3 4 5% 6% 55%	1890
	21st to end	Night	13% 6% 2 5% 5% 2 4 4 5% 7% 47%	1980
October	1st to 10th	Night	14% 6% 2 5% 4 2 4 4 3 7% 48%	2042
	11th to 20th	Night	17% 7% 3 5% 5% 3 5% 4 5% 7% 41%	2196
	21st to end	Night	19% 8% 3 6% 5% 3 5% 4 6% 7% 36%	2574
November	1st to 10th	Night	12% 7% 3 5% 4 2 4 5% 5% 7% 46%	2406
	11th to 20th	Night	14% 9% 3 7% 6% 4 5% 5% 6% 7% 35%	2470
	21st to end	Night	16% 9% 3 5% 5% 3 5% 5% 5% 7% 38%	2604
December	1st to 10th	Night	14% 11% 4 7% 6% 4 4 4 6% 7% 32%	2660
	11th to 20th	Night	13% 12% 5% 7% 7% 4 5% 5% 5% 6% 31%	3279
	21st to end	Night	20% 17% 5% 9% 6% 3 4 4 4 6% 22%	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	49% 7% 14% 18% 11%	1518
	11th to 20th	Day	60% 7% 8% 18% 7%	1480
	21st to end	Day	58% 7% 11% 15% 8% 1	1584
February	1st to 10th	Day	51% 6% 13% 21% 8% 1	1616
	11th to 20th	Day	49% 5% 10% 22% 11% 2	1754
	21st to end	Day	53% 7% 9% 18% 11% 2	1480
March	1st to 10th	Day	49% 8% 12% 22% 7% 2	1800
	11th to 20th	Day	46% 6% 12% 20% 14% 2	1853
	21st to end	Day	55% 6% 13% 19% 7% 1	2376
April	1st to 10th	Day	53% 7% 11% 18% 10% 1	2160
	11th to 20th	Day	50% 6% 10% 19% 12% 3	2134
	21st to end	Day	50% 7% 13% 18% 11% 2	2290
May	1st to 10th	Day	48% 7% 12% 22% 9% 1	2347
	11th to 20th	Day	46% 7% 12% 22% 11% 2	2483
	21st to end	Day	41% 7% 14% 23% 14% 2	2725
June	1st to 10th	Day	35% 7% 14% 27% 15% 2	2520
	11th to 20th	Day	37% 7% 15% 24% 17% 1	2520
	21st to end	Day	35% 9% 15% 23% 16% 2	2520
July	1st to 10th	Day	29% 9% 15% 31% 14% 3	2451
	11th to 20th	Day	31% 8% 16% 27% 16% 2	2445
	21st to end	Day	28% 9% 17% 26% 16% 3	2591
August	1st to 10th	Day	33% 9% 17% 27% 12% 2	2490
	11th to 20th	Day	35% 9% 16% 26% 13% 1	2189
	21st to end	Day	35% 8% 13% 25% 17% 2	2376
September	1st to 10th	Day	38% 8% 11% 26% 15% 2	2160
	11th to 20th	Day	35% 7% 13% 30% 15% 1	2052
	21st to end	Day	40% 6% 12% 30% 12%	1980
October	1st to 10th	Day	41% 6% 10% 28% 15% 1	1916
	11th to 20th	Day	51% 6% 12% 19% 10% 1	1764
	21st to end	Day	49% 6% 13% 20% 11% 1	1782
November	1st to 10th	Day	41% 5% 13% 25% 14% 1	1672
	11th to 20th	Day	50% 6% 14% 21% 8% 1	1710
	21st to end	Day	48% 5% 13% 25% 8%	1573
December	1st to 10th	Day	53% 6% 16% 18% 7% 1	1520
	11th to 20th	Day	51% 6% 16% 18% 7% 2	1915
	21st to end	Day	69% 5% 8% 12% 5%	2783
January	1st to 10th	Night	52% 5% 10% 20% 12% 1	2648
	11th to 20th	Night	58% 5% 12% 17% 7%	2591
	21st to end	Night	54% 6% 13% 17% 9% 1	2772
February	1st to 10th	Night	51% 5% 11% 19% 12% 2	2343
	11th to 20th	Night	46% 6% 11% 21% 15% 2	2102
	21st to end	Night	50% 5% 12% 18% 13% 3	1776
March	1st to 10th	Night	48% 6% 13% 21% 10% 2	2160
	11th to 20th	Night	39% 6% 14% 23% 16% 3	2122
	21st to end	Night	50% 6% 11% 22% 9% 2	1980
April	1st to 10th	Night	49% 5% 9% 19% 17% 1	1800
	11th to 20th	Night	48% 4 8% 19% 16% 3	1775
	21st to end	Night	44% 7% 13% 21% 14% 2	1670
May	1st to 10th	Night	47% 6% 13% 22% 11% 1	1611
	11th to 20th	Night	43% 8% 12% 22% 13% 2	1417
	21st to end	Night	38% 9% 13% 23% 15% 2	1552
June	1st to 10th	Night	33% 6% 14% 27% 18% 1	1440
	11th to 20th	Night	35% 6% 12% 25% 20% 2	1440
	21st to end	Night	35% 7% 16% 24% 17% 2	1440
July	1st to 10th	Night	27% 6% 16% 30% 18% 4	1400
	11th to 20th	Night	26% 7% 15% 28% 19% 4	1392
	21st to end	Night	25% 9% 17% 25% 18% 5%	1487
August	1st to 10th	Night	29% 7% 16% 29% 15% 3	1423
	11th to 20th	Night	28% 6% 19% 30% 16% 1	1710
	21st to end	Night	31% 6% 12% 29% 20% 3	1980
September	1st to 10th	Night	30% 7% 12% 26% 22% 2	1800
	11th to 20th	Night	31% 6% 10% 36% 16% 2	1890
	21st to end	Night	38% 4 11% 32% 15% 1	1980
October	1st to 10th	Night	37% 6% 10% 29% 16% 2	2042
	11th to 20th	Night	43% 6% 14% 21% 15% 1	2196
	21st to end	Night	48% 6% 13% 22% 11%	2574
November	1st to 10th	Night	38% 5% 12% 26% 17% 3	2406
	11th to 20th	Night	47% 7% 14% 20% 11% 1	2470
	21st to end	Night	46% 7% 15% 23% 9% 1	2604
December	1st to 10th	Night	51% 6% 13% 21% 8% 1	2660
	11th to 20th	Night	54% 7% 12% 17% 9% 1	3281
	21st to end	Night	65% 6% 10% 14% 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	17% 16% 39% 23% 6% 1	270
	11th to 20th	Day	16% 20% 32% 25% 7%	255
	21st to end	Day	21% 13% 39% 20% 6% 1	264
February	1st to 10th	Day	15% 18% 47% 15% 5%	240
	11th to 20th	Day	20% 26% 33% 17% 4	240
	21st to end	Day	19% 24% 44% 12% 1	198
March	1st to 10th	Day	16% 23% 45% 14% 3	240
	11th to 20th	Day	21% 18% 31% 22% 6% 2	262
	21st to end	Day	27% 12% 31% 22% 6% 2	462
April	1st to 10th	Day	25% 13% 35% 21% 6%	420
	11th to 20th	Day	21% 19% 26% 22% 10% 2	412
	21st to end	Day	22% 12% 30% 23% 12% 1	420
May	1st to 10th	Day	22% 11% 35% 23% 7% 2	430
	11th to 20th	Day	20% 9% 33% 26% 10% 3	625
	21st to end	Day	15% 9% 28% 29% 14% 5%	679
June	1st to 10th	Day	8% 6% 31% 36% 13% 4	630
	11th to 20th	Day	13% 7% 29% 33% 14% 4	630
	21st to end	Day	10% 6% 31% 32% 16% 4	630
July	1st to 10th	Day	8% 2 20% 34% 26% 10%	621
	11th to 20th	Day	9% 6% 24% 35% 20% 6%	618
	21st to end	Day	6% 2 29% 36% 21% 6%	684
August	1st to 10th	Day	8% 3 21% 40% 19% 9%	624
	11th to 20th	Day	10% 4 19% 28% 26% 13%	439
	21st to end	Day	11% 6% 20% 33% 20% 9%	495
September	1st to 10th	Day	12% 7% 24% 29% 20% 7%	450
	11th to 20th	Day	11% 5% 20% 32% 22% 10%	450
	21st to end	Day	15% 11% 26% 24% 18% 5%	450
October	1st to 10th	Day	20% 7% 25% 29% 14% 4	386
	11th to 20th	Day	22% 18% 33% 19% 8%	270
	21st to end	Day	23% 16% 39% 16% 4 1	297
November	1st to 10th	Day	15% 19% 31% 24% 10% 1	270
	11th to 20th	Day	14% 21% 36% 21% 7%	270
	21st to end	Day	22% 14% 39% 20% 6%	270
December	1st to 10th	Day	19% 19% 41% 16% 5% 1	270
	11th to 20th	Day	22% 19% 36% 15% 7% 1	270
	21st to end	Day	24% 21% 36% 16% 2 1	297
January	1st to 10th	Night	18% 17% 38% 21% 5%	950
	11th to 20th	Night	21% 15% 38% 20% 6% 1	926
	21st to end	Night	19% 13% 38% 24% 6%	990
February	1st to 10th	Night	20% 15% 38% 23% 4	900
	11th to 20th	Night	18% 16% 37% 25% 5%	706
	21st to end	Night	25% 15% 38% 17% 5%	592
March	1st to 10th	Night	19% 13% 36% 23% 9% 1	720
	11th to 20th	Night	14% 12% 38% 27% 8% 1	704
	21st to end	Night	21% 7% 28% 34% 9% 2	594
April	1st to 10th	Night	21% 11% 35% 26% 7% 1	540
	11th to 20th	Night	24% 10% 32% 26% 7% 2	533
	21st to end	Night	21% 7% 29% 30% 11% 1	540
May	1st to 10th	Night	18% 8% 30% 36% 7% 1	540
	11th to 20th	Night	20% 5% 29% 32% 13% 1	531
	21st to end	Night	13% 4 22% 36% 22% 2	584
June	1st to 10th	Night	11% 4 24% 40% 20% 1	540
	11th to 20th	Night	13% 3 30% 35% 18% 1	540
	21st to end	Night	10% 2 24% 44% 19% 1	540
July	1st to 10th	Night	7% 2 15% 40% 32% 5%	525
	11th to 20th	Night	6% 2 21% 42% 27% 3	522
	21st to end	Night	7% 2 20% 44% 26% 1	591
August	1st to 10th	Night	7% 1 17% 44% 28% 4	537
	11th to 20th	Night	9% 2 16% 37% 29% 6%	534
	21st to end	Night	9% 2 20% 38% 27% 4	594
September	1st to 10th	Night	10% 4 21% 35% 25% 6%	540
	11th to 20th	Night	11% 5% 22% 30% 25% 6%	630
	21st to end	Night	15% 9% 23% 26% 23% 5%	720
October	1st to 10th	Night	17% 7% 27% 29% 18% 2	720
	11th to 20th	Night	21% 12% 32% 27% 8% 1	720
	21st to end	Night	22% 10% 34% 26% 8% 1	792
November	1st to 10th	Night	15% 10% 39% 25% 10% 1	740
	11th to 20th	Night	19% 17% 35% 22% 6%	760
	21st to end	Night	21% 13% 37% 22% 7%	894
December	1st to 10th	Night	22% 17% 36% 21% 5%	950
	11th to 20th	Night	22% 14% 37% 20% 6% 1	950
	21st to end	Night	27% 15% 36% 19% 3	1045

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